福 井 大 学 工 学 審 査

学位論文［博士（工学）］

A Dissertation Submitted to the University of Fukui

for the Degree of Doctor of Engineering

Immobilization of Natural Macromolecules onto the

Surface of Synthetic Fabrics Impregnated with

Cross-linking Agents Using Supercritical Carbon Dioxide

(超臨界二酸化炭素を用いる合成繊維布への

架橋剤の注入と天然高分子の固定化)

2010 年 9 月

麻 文 效

Contents Chapter 1. General introduction 1 1.1. Surface modification on polymer material 1 1.1.1. Background of polymer material 1

1.1.2. Conventional techniques in surface modification 2 1.1.2.1. Wet chemical 3

1.1.2.2. Ionized gas treatments 4 1.1.2.2.1. Plasma 4 1.1.2.2.2. Corona discharge 5 1.1.2.2.3. Flame treatment 5

1.1.2.3. Electron beam irradiation 6 1.1.2.4. UV irradiation 6 1.1.2.5. Ozone oxidation 7 1.1.2.6. γ-ray irradiation 7 1.1.2.7. Physical curing or coating method 8

1.1.3. Problems and shortages of conventional techniques 8 1.2. Supercritical fluid techniques in the processing of polymer 8 1.2.1. Supercritical fluid 8 1.2.2. Supercritical carbon dioxide 11 1.2.3. Polymer modification in scCO2 12 1.2.3.1. Foaming 12

1.2.3.2. Impregnation 13 1.2.3.2.1. Fiber dyeing 13 1.2.3.2.2. Drugs loading 14 1.2.3.2.3. Monomer impregnation and polymerization 15 1.2.3.2.4. Other applications by impregnation 16

1.3. Synthetic fiber 17 1.3.1. PET fiber 17 1.3.2. PP fiber 18 1.4. Natural macromolecules 19 1.4.1. Sericin 19 1.4.2. Chitosan 19 1.4.3. Polylysine 20 1.4.4. Collagen 20 1.5. Objective of this research 21 1.6. Outline of the thesis 22

References 24

i

Chapter 2. Coating of natural proteins onto synthetic fabric crosslinked with diisocyanate by supercritical dioxide carbon 35

2.1. Introduction 35 2.2. Experimental procedures 36 2.2.1. Reagents and materials 36 2.2.2. Treatment 37 2.2.2.1. Impregnation of TDI into PET and PP fabrics by scCO2 38 2.2.2.2. Immobilization of natural proteins onto TDI-PET and TDI-PP

fabrics by the pad-dry-cure method 39 2.2.3. Analysis 40 2.3. Results and discussion 40 2.3.1. Supercritical impregnating PET and PP fabrics with TDI 40 2.3.2. Immobilization of natural proteins (sericin and polylysine) onto the

surface of TDI-PET and TDI-PP fabrics 43 2.3.3. FT-IR analysis 44 2.3.4. Staining by methylene blue 48 2.3.5. Hydrophilicity effect 49 2.4. Summary 51 References 52

Chapter 3. Impregnation of cyanuric chloride into PET and PP fabrics with the aid of supercritical carbon dioxide, and its application in immobilizing natural biomacromolecules 54

3.1. Introduction 54 3.2. Experimental procedures 57 3.2.1. Materials and reagents 57 3.2.2. Treatment 57

3.2.2.1. Impregnation of CC into PP and PET fabrics by scCO2 57 3.2.2.2. Immobilization of biomacromolecules (sericin or chitosan) onto

CC-PET and CC-PP fabrics 58 3.2.3. Analysis method 59 3.3. Results and discussion 60 3.3.1. Supercritical impregnation with cyanuric chloride 60 3.3.1.1. Impregnation in pure scCO2 60 3.3.1.2. Impregnation in scCO2 with co-solvents 63 3.3.2. Biomacromolecules immobilization 66 3.3.3. XPS spectra analysis 67 3.3.4. FT-IR spectra analysis 69 3.3.5. Surface morphology 72

ii

iii

3.3.6. Hydrophilicity characterization 75 3.3.6.1. Water contact angles 75 3.3.6.2. Wicking properties 76 3.4. Summary 77 References 78

Chapter 4. Modifying poly(ethylene terephthalate) fabric by supercritical carbon dioxide 81 4.1. Introduction 81

4.2. Experimental procedures 83 4.2.1. Materials and reagents 83 4.2.2. Methods 84 4.2.2.1. Impregnation of GPE into PET by scCO2 84 4.2.2.2. Immobilization of functional agents onto PET fabrics 85 4.2.2.2.1. Processing in an aqueous solution 86 4.2.2.2.2. The pad-dry-cure treatment 86 4.2.3. Characterizations 86 4.3. Results and discussion 89 4.3.1. Supercritical treatment of PET fabric 89 4.3.2. Immobilization of functional agents (sericin, collagen, or chitosan) onto

GPE-PET and original PET fabrics 96 4.3.3. Surface wettability and moisture regain of the original and the modified

PET fabrics 100 4.3.4. Antibacterial efficiency of the untreated and the modified PET fabrics 104 4.4. Summary 106 References 107

Chapter 5. General conclusion 111

List of publication 114

Presentations 115 Acknowledgements 116

Chapter 1. General introduction 1.1. Surface modification on polymer material

1.1.1. Background of polymer material

Now, in the 21st century, it is difficult to find an aspect of our lives that is not affected by

polymers. Polymer, in the form of plastics, rubbers and fibers, have for many years played

essential but varied roles in everyday life: as electrical insulation, as tyres, and as packaging

for food, to mention but three. 1 They have been employed in a variety of biomedical

applications ranging from implantable devices to controlled drug delivery. Polymers such as

poly(methyl methacrylate) find application as photoresist materials used in semiconductor

manufacturing and low-k dielectrics for use in high-performance microprocessors. Recently,

polymers have also been employed as flexible substrates in the development of organic

light-emitting diodes for electronic display. One trend in modern civilization is that the

polymer materials are gradual replacing more traditional materials such as metals, ceramics,

and natural polymers such as wood, cotton, natural rubber ect. In general, successful

applications of polymer materials require special properties such as flame retardancy, ageing

resistance, surface affinity, conductivity, lubricity/roughness, and others. However, ordinary

polymers usually do not present the properties needed for special applications. It is essential

to modify the properties of a polymer according to tailor-made specifications designed for

target applications.

Polymer surfaces are the phase boundaries that reside between the bulk polymer and the

outer environment. The performance of polymeric materials relies largely upon the properties

of the boundaries in many applications.2 For instance, the surface of a fabric used in an

underclothing is often the interface between the body and the underclothing. By controlling

the surface properties of the fabric, the underclothing designer can enhance or inhibit various

reaction of body to the clothing. The interaction between the polymer and its environment

depends in large part on surface composition and structure. As most polymeric materials,

however, have a hydrophobic, chemically inert surface, untreated non-polar polymer surfaces

often have adverse problems in adhesion, coating, painting, coloring, lamination, packaging,

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colloid stabilization, etc. Biomedical applications of polymeric materials have also faced

many critical obstacles such as undesirable protein adsorption and cell adhesion, due to the

poor biocompatibility of conventional polymer surfaces. Since surface composition and

topography play such a large role in the performance of the polymer, precise surface

characterization can be an important part in the rapid deployment of new materials or

understanding of problems and behavior in existing materials. To solve these problems, an

enormous number of basic and applied research has been devoted to the surface modifications

of polymeric materials.3-6

1.1.2. Conventional techniques in surface modification

Surface modification techniques, which can transform inexpensive natural or synthetic

polymers into highly valuable end products, have become important to the polymer industries.

A polymer surface can be modified by means of various chemical and/or physical processes,

even the so-called non-reactive polymers. The most common techniques include plasma-ion

beam treatment, electric discharge, UV-irradiation, γ-ray irradiation, chemical reaction,

surface coating etc. The schematic presentation of the surface modification is presented in

Figure 1.

PolymerFunctionalized Polymer

Grafted/Coated Polymer

Functional agents

Chemical reaction

Coating/Curing

EB, UV, γ-ray, etc

Plasma treatmentFunctional agents or monomer

Grafting

Wet chemical

Ozone oxidization

Figure 1. Schematic representation of the conventional methods of surface modification

on polymer materials.

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1.1.2.1. Wet chemical

In wet chemical surface modification, a material is treated with liquid reagents to generate

reactive functional groups on the surface. The generated functional groups not only improve

the surface properties of materials but can react with new functional molecules for

modification farther. This classical approach to surface modification does not require

specialized equipment and thus can be conducted in most laboratories. It is also more capable

of penetrating porous three-dimensional substrates than plasma and other energy source

surface modification techniques,7 and allows for in situ surface functionalization of

microfluidic devices.

Chromic acid and potassium permanganate in sulfuric acid have been used to introduce

reactive oxygen-containing moieties to PE and PP.8–12 For example, submersion in a 29:42:29

weight ratio solution of chromium trioxide, water, and sulfuric acid at 72°C for 1 min resulted

in 3.3 nmol/cm2 carboxylic acid functionalities on PE.9 Concentrated sodium hydroxide and

sulfuric acid have been used to generate carboxylic acid groups by base and acid hydrolysis of

PMMA.13-15 Specifically, a 16 h treatment in 10M sodium hydroxide at 40°C was reported to

produce 0.66 nmol/cm2 carboxylic acids on PMMA.13 Methyl ester side chains of PMMA also

have been reduced to hydroxyls by treatment in lithium aluminum hydride in ether.16 Primary

amines have been introduced to PMMA, poly(urethane) (PU), PLA, and PLGA by aminolysis

using various diamines including hydrazine hydrate, 1,6-hexanediamine, ethylenediamine,

and N-aminoethyl-1,3-propanediamine, as well as lithiated diamines.14, 17-24 Lastly, PTFE

surfaces have been modified by refluxing with elementary sodium in toluene to generate

double bonds, followed by an 8 h oxidation at 120°C in a 1:1 mixture of trifluoroacetic acid

and hydrogen peroxide (38%) which improved membrane wetting and allowed

immobilization of the enzyme alliinase.25

Unfortunately, these wet chemical methods generate hazardous chemical waste and can

lead to irregular surface etching.26 Many of these techniques require extended treatment in

concentrated corrosive solutions. In addition, those which target modification of polymer side

chains (as in PMMA ester modification) depend on side chain surface orientation. The degree

of surface functionalization may therefore not be repeatable between polymers of different

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molecular weight, crystallinity, or tacticity. For these reasons, while useful in the laboratory

environment, these wet chemical processes may not be suitable for larger scale, industrial

applications.

1.1.2.2. Ionized gas treatments

1.1.2.2.1. Plasma

Plasma is a high energy state of matter, in which a gas is partially ionized into charged

particles, electrons, and neutral molecules.27 Plasma can provide modification of the top

nanometer of a polymer surface without using solvents or generating chemical waste and with

less degradation and roughening of the material than many wet chemical treatments.28, 29 The

type of functionalization imparted can be varied by selection of plasma gas (Ar, N2, O2, H2O,

CO2, NH3) and operating parameters (pressure, power, time, gas flow rate).28

Oxygen plasma is often used to impart oxygen containing functional groups to polymer

surfaces such as PCL,30 PE,31 and PET.32 In addition to oxygen, carbon dioxide plasma has

been used to introduce carboxyl groups on PP,33 PS,34 and PE,35 and air plasma has been used

to oxidize PMMA.14 Ammonia and nitrogen plasmas have been used to impart amine groups

to the surface of PTFE36 and PS,34 respectively. Inert gases can be used to introduce radical

sites on the polymer surface for subsequent graft copolymerization. For instance, Kang et al.

pretreated PTFE with Ar plasma in order to graft polymerize acrylic acid,37 as did Ademovic

et al. on PVDF38 and Cheng et al. on PCL.39 Similarly, PE, PET, and PVDF have been

pretreated with Ar plasma in order to graft polymerize poly(ethylene glycol)

monomethacrylate and 4-vinylpyridine.40 In a process called radio frequency glow discharge

(RFGD), plasma can be used to initiate surface graft polymerization of vaporized

monomers.41 Plasma can be used as a precursor to other surface modification techniques, for

example, plasma activation followed by ultraviolet (UV) graft polymerization42 or plasma

activation followed by silanization.43 However, with the exception of a recent development of

an atmospheric plasma system,44 plasma generation requires a vacuum to empty the chamber

of latent gases, which presents complications for continuous operation in a large scale

industrial setting.45 Also, results are difficult to repeat between laboratories as there are many

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parameters involved to optimize conditions, including time, temperature, power, gas

composition/flow/pressure, orientation of reactor and distance of substrate from plasma

source.29 It should be noted that in addition to the monomers and gases intentionally

introduced to the plasma chamber, latent chemicals from prior users may be present thus

posing a risk of contamination. The plasma chamber should therefore be adequately cleaned,

for example by oxygen plasma, before introducing polymers for surface modification.

1.1.2.2.2. Corona discharge

Corona discharge is a simple, low cost, continuous process in which an electrically

induced stream of ionized air bombards the polymer surface. It is commercially used to

improve printability and adhesion to inert polymers28 by introducing surface oxidation

products.26, 46 However, these results in a broad range of oxygenated groups and therefore may

be less useful as a technique to introduce specific functionalities for bioconjugation. Because

it does not operate under a vacuum, contamination may also be an issue, and variations in

local temperature and humidity can affect consistency of treatment.26 Finally, it has been

reported that surface polar groups on corona treated polyolefins are particularly unstable.

Materials should therefore be used shortly after treatment.29

1.1.2.2.3. Flame treatment

Like corona discharge, flame treatment is a non-specific surface functionalization method

that bombards the polymer surface with ionized air, generating a broad spectrum of surface

oxidation products to the top several monolayers.26, 28 In this method, the reactive oxygen is

generated by burning an oxygen rich gas mixture. Flame treatment has been shown to impart

hydroxyl, aldehyde, and carboxylic acid functionalities to poly(ethylene) and is utilized to

enhance printability, wettability, and adhesion.46 Although fundamentally simple and

inexpensive, flame treatment can reduce optical clarity to polymers, and there are many

parameters (including flame temperature, contact time and composition) that must be

accurately controlled to maintain consistent treatment and to avoid burning.29

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1.1.2.3. Electron beam irradiation

E-beam radiation is a form of ionizing energy that is generally characterized by its low

penetration and high dosage rates. The beam, a concentrated, highly charged stream of

electrons, is generated by the acceleration and conversion of electricity. The electrons are

generated by equipment referred to as accelerators which are capable of producing beams that

are either pulsed or continuous. As the material being sterilized passes beneath or in front of

the electron beam, energy from the electrons is absorbed. This absorption of energy alters

various chemical and biological bonds within the material. Several applications in polymer

industry are well known, as radiation induced degradation, crosslinking, grafting, curing and

polymerization.47-50 For example, functional vinylic monomers along with functional

cross-linkers were spin coated onto the surface of the silicon and exposed to the keV electron

irradiations to obtain long-term hydrophilic surfaces with a cross-linked network of grafted

monomers by Mahapatra et al.51 It was also reported that some synthetic fibers could be easily

grafted with some vinyl monomers by electron beam (EB) irradiation method.52 There are

some limitations or areas of concern associated with electron beam technology, it included

that discoloration may occur on some materials, and short penetration depending on material

density etc.

1.1.2.4. UV irradiation

Ultraviolet (UV) light is electromagnetic radiation with a wavelength shorter than that of

visible light, but longer than X-rays. As an ionizing radiation it can cause chemical reactions,

and causes many substances to glow or fluoresce. When exposed to UV light, polymer

surfaces generate reactive sites which can become functional groups upon exposure to gas or

can be used to initiate UV-induced graft polymerization. This technique differs from ionized

gas treatments by the ability to tailor the depth of surface reactivity by varying wavelength

and thus absorption coefficient.5 UV irradiation has been used to introduce carboxylic acid

functionality to PMMA,53 as well as to activate PS surfaces for enzyme immobilization54 and

tissue engineering55 applications. UV irradiation has also been used to initiate radical graft

polymerization of bioactive compounds. For instance, N-vinylpyrrolidone has been

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photografted to the surface of PP films to generate antimicrobial materials.56 UV treatment

can affect the optical properties of the polymer, and UV light can also be blocked by particles,

which may affect treatment consistency.

1.1.2.5. Ozone oxidation

Mathieson and Bradley57 modified the surface of PE and a polyetheretherkotone (PEEK),

oxidizing the surface with ozone in addition to UV radiation, namely an ultraviolet–ozone

oxidation process. The pretreated polymer surfaces exhibited significant improvement in

adhesion when tested using an epoxy adhesive. The combination of UV and ozone treatment

was also utilized by Walzak et al.58 to improve surface properties of PP and PET. They also

compared the effect between UV/ozone and ozone alone. Reactions of PET with ozone alone

typically needed longer times to show the same contact angle and O/C atomic ratio as those

obtained by the UV/air and UV/ozone treatments. They demonstrated that the treatment with

ozone alone (without UV light) followed a different reaction pathway, resulting in a slower

treatment with less chain scission. Exposure of isotactic PP to ozone resulted in surface

oxidation and formation of peroxides and hydroperoxides.59 The molecular weight of PP was

dramatically reduced after times as short as 5 min of ozonation. It was possible to graft

copolymerization of 2-hydroxyethyl methacrylate to the ozonated samples, and the graft

copolymer acted as a continuous matrix consequently linked to and reinforced by the PP

crystals.

1.1.2.6. γ-ray irradiation

γ-rays are electromagnetic waves, which are shorter in length than UV waves and higher

in energy. γ-rays do not have any mass or charge but interact with the material by colliding

with the electrons in the shells of the atoms. The rays slowly lose energy in the material while

generally travelling significant distances before being stopped. Irradiation by γ-ray produces

radical sites on the polymer backbone. This is usually achieved by the abstraction of hydrogen

atoms.60 Gamma radiation has been used for many years to alter the molecular structure and

microscopic properties of polymers as well as initiating polymerization.61-63 Irradiating

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polymers with γ-ray can lead to a decrease in the molecular weight of the polymer caused by

the breaking of the C–C bond. The molecular weight has also been found to increase where

two radical species on the polymer backbone recombine to form a new bond. γ-radiation can

also lead to the decomposition of polymers resulting in gas evolution or the creation of double

bonds.

1.1.2.7. Physical curing or coating method

Perhaps the easiest and the most strait forward way to modify polymer surface is by

blending functional molecules into the bulk polymer or just coating it on the polymer surface.

Recently, physical blending/curing functional molecules into/onto polymer surface was

significantly developed by appearance of some new techniques, among which includes self

migration,64 self assembly,65, 66 and layer by layer method.67, 68

1.1.3. Problems and shortages of conventional techniques

Although these techniques mentioned can modify polymer materials in varying degrees,

some shortages are always existent and limited in the manufacture scale. Physical coated

product often exhibit peeling problems during the service performance regardless of how mild

or severe the abrasive condition is, because the abrupt interface that frequently formed in the

coating products generates residual stresses in the coated layer, which cause the detachment of

the coated layer from the substrate with a slight application of load.69 Chemical methods, on

the other hand, can permanently modify polymer materials, however, will generate hazardous

chemical waste and can lead to irregular surface etching. Irradiation techniques are also

limited in laboratory scale because they require complicated production equipment, strict

operation requirements and are expensive, while also having a degradation effect on the

substrate polymer. Accordingly, easy-operate, low-cost, environmentally friendly processes

for modifying the polymer surface are always required currently.

1.2. Supercritical fluid techniques in the processing of polymer

1.2.1. Supercritical fluid

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A supercritical fluid (SCF) may be defined as a substance for which both temperature and

pressure are above the critical values (Figure 270, Table 171, 72). However, this definition is of

limited use since it gives no information about the density of the substance. Darr and

Poliakoff offer a more practical definition,72 where a supercritical fluid is described as ``any

substance, the temperature and pressure of which are higher than their critical values, and

which has a density close to or higher than its critical density''. With some exceptions, most

applications reported involve CO2 under conditions of temperature and pressure such that the

density frequently exceeds the critical density (0.47 g cm-3). Indeed, many techniques require

densities that are in the range expected for conventional liquid solvents (0.8-1.0 g cm-3). Close

to the critical density, SCFs display properties that are to some extent intermediate between

those of a liquid and a gas.71, 73, 74 For example, a SCF may be relatively dense and dissolve

certain solids while being miscible with permanent gases and exhibiting high diffusivity and

low viscosity. In addition, supercritical fluids are highly compressible and the density (and

therefore solvent properties) can be ``tuned'' over a wide range by varying pressure [Figure.

3(a)].

Figure 2. Schematic pressure-temperature phase diagram for a pure component showing the

supercritical fluid (SCF) region.

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Table 1. Critical parameters for selected substances (Tc=critical temperature, Pc=critical

pressure, ρc=critical density).

Substrance Tc/°C Pc/bar ρc/g cm-3

CH4 -82.5 46.4 0.16

C2H4 10 51.2 0.22

C2F6 19.9 30.6 0.62

CHF3 26.2 48.5 0.62

CClF3 28.9 38.6 0.58

CO2 31.1 73.8 0.47

C2H6 32.4 48.8 0.2

SF6 45.6 37.2 0.73

Propylene 91.9 46.1 0.24

Propane 97.2 42.5 0.22

NH3 132.5 112.8 0.24

Pentane 187.1 33.7 0.23

iPrOH 235.4 47.6 0.27

MeOH 240.6 79.9 0.27

EtOH 243.5 63.8 0.28

iBuOH 275.1 43 0.27

Benzene 289 48.9 0.3

Pyridine 347.1 56.3 0.31

H2O 374.2 220.5 0.32

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Figure 3. (a) Graph showing the variation in density for pure CO2 at 35°C. At this

temperature (i.e., close to Tc for CO2) there is a rapid but continuous increase in density near

the critical pressure (Pc). (b) Schematic representation of the change from liquid-gas

equilibrium (T<Tc) to supercritical fluid (T>Tc) conditions as a substance is heated above its

critical temperature at a pressure in excess of Pc.

1.2.2. Supercritical carbon dioxide

Carbon dioxide is the most widely used supercritical fluid because it is readily available,

inexpensive, nontoxic, and nonflammable, and it has a relatively low critical temperature

(31.1 °C) and pressure (73.8 bar). It does not threaten the ozone layer as do

chlorofluorocarbons which are used extensively in polymer manufacturing. Moreover, many

polymers become highly swollen and plasticized in the presence of CO2, allowing processing

at low temperatures. The use of supercritical CO2 does not create a problem with respect to

the greenhouse effect as it is recovered during processing. When the process finished, CO2

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can also be separated from a system by simple depressurization. Due to these unique

characteristics, scCO2 has been successfully utilized in separation (extraction),75-77 particle

generatation,78 chemical reaction79 and polymer modification.80

1.2.3. Polymer modification in scCO2

1.2.3.1. Foaming

Microcellular polymers (i.e., polymers with cell sizes less than or equal to 10 mm) are

used as separation media, adsorbents, controlled release devices, biomedical devices, and as

lightweight structural materials. Traditional methods for the formation of these materials are

based on a temperature quench (or, less commonly, the addition of an antisolvent) to induce

phase separation of a homogeneous polymer solution.81 Thermal induced phase separation

involves dissolving the polymer in an appropriate hydrocarbon solvent and quenching the

temperature to induce phase separation. This is followed by solvent removal, either by

freeze-drying or by supercritical fluid extraction. Beckman82 has developed an alternative

``solvent free'' approach, whereby a polymer is saturated with scCO2 at moderately elevated

temperatures followed by rapid depressurisation at constant temperature (i.e., a pressure

quench as opposed to a temperature quench). This method takes advantage of the large

depression in Tg found for many polymers in the presence of CO2,83 which means that the

polymer may be kept in the liquid state at relatively low temperatures. By lowering the

pressure at a fixed temperature the amount of diluent absorbed by the polymer is decreased.

Thus, Tg begins to rise, eventually to the point where Tg for the polymer is higher than the

foaming temperature: at this point the cellular structure can grow no further and is locked in.

The sudden reduction in pressure leads to the generation of nuclei due to supersaturation, and

these nuclei grow to form the cellular structure until vitrification occurs. This method has

been used for the generation of PMMA foams consisting of a microcellular core surrounded

by a relatively non-porous skin. More later, the method by utilizing scCO2 have extended to

the generation of microcellular polystyrene,84 polypropylene,85 polycarbonate,86 and PET

foam so on.87 In some cases, the method was also applied for the foaming of biodegradable

polymers such as poly(lactic-co-glycolic acid),88 poly(3-caprolactone)89 and polylactic acid.90

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1.2.3.2. Impregnation

The impregnation process with the aid of scCO2 is the base of many applications in

polymer modification. Supercritical impregnation here can be described as the delivery of

solutes to the desired sites inside the polymer matrix (Figure 4). The process is feasible when

the active substance (the solute) is soluble in the scCO2, the polymer is swollen by the

supercritical solution and the partition coefficient is favourable enough to allow the matrix to

be charged with enough solute. Of course the degree of impregnation can be controlled by

adjusting the solubility of the additive with temperature and pressure. Most of these were

done by direct contact of impregnating materials and substrates with or without a liquid

carrier present. In addition, some researchers have pointed out that the insoluble solute in

scCO2 can also be incorporated into a polymer matrix because of the high partition

coefficients between polymer and scCO2 phase.91

Solutes

scCO2 Polymer

dissolving loading

swelling

plasticizing

Figure 4. Interactions between the scCO2-assisted impregnation system.

1.2.3.2.1. Fiber dyeing

Dyeing using scCO2, in which the solutes transported are organic dyes, is perhaps the

most common application of impregnation to date. The conventional fiber dyeing process

discharges much wastewater that is contaminated by various kinds of dispersing agents,

surfactants and unused dye. It is very difficult to design a conventional biological process that

treats the wastewater discharged from a conventional dyeing process. The environmentally

friendly supercritical CO2 process does not require any water, dispersing agents or surfactants

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and also does not involve any drying stage after dyeing. This technique is an alternative one

which has been developed widely since early 1990s.

Saus et al.92 reported on dyeing of synthetic fibers by disperse dyes. Gebert et al.93

extended the supercritical dyeing to natural fibers such as cotton and wool. Knittel and

Schollmeyer94 reported on dyeing of PET and polypropylene with different dyes. Shim et al.95

investigated sorption of some disperse dyes (C. I. Disperse Blue 60 (B60), C.I. Disperse Red

60 (R60), C.I. Disperse Yellow 54 (Y54), and C.I. Disperse Orange 30 (O30)) in PET and

PTT fibers as well as difficult-to-dye fibers such as aramid and polypropylene using

supercritical carbon dioxide at pressures between 10 and 33 MPa and temperatures between

35 and 150°C. For dyeing in a co-solvent laden supercritical fluid, ethanol, acetone, or

N-methyl pyrrolidone was also introduced in the dyeing vessel.

Dye molecules are generally large and their diffusion rate is very small. They may

penetrate only into the glassy part and not in the crystalline part of a polymeric matrix. Dye

sorption increased with pressure at the same temperature and increased with temperature at

the same pressure, but this increasing rate was reduced with increasing pressure.

1.2.3.2.2. Drugs loading

In recent years, considerable attention has been focused on the development of drug

delivery systems, which attempt to increase bio-availability, sustain, localize or target drug

action in the body. Polymer microparticles are often employed as supports to deliver drugs,

either as microspheres (monolithic devices) or microcapsules (reservoir devices). In the

preparation of controlled-release drugs, a liquid solvent swelling the polymer matrix and

serving as a carrier for the drug component is used. Because of cost and environmental

regulations associated to the use of organic solvents, the pharmaceutical industry has been

moving away from the use of these solvents, and alternative technologies have been

developed, such as the supercritical fluid technology.96

Polymeric materials have a very limited solubility in scCO2, and this is an interesting

feature for producing monolithic loaded microspheres, obtained by an impregnation process.97

Also, polymer separation using scCO2 is enabling the selection of a pure fraction of a polymer,

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thereby allowing a more precise control of drug release from polymeric delivery systems.

Kazarian and Martirosyan investigated the formation of ibuprofen/PVP composites via in situ

ATR-IR and Raman spectroscopy,98 and the impregnation of 5-fluorouracil and β-estradiol

into PLGA has also been reported.99 PMMA, PCL, and PMMA/Poly(q-caprolactone),

microspheres can also be loaded successfully with different amounts of cholesterol by using

scCO2 impregnation.100

1.2.3.2.3. Monomer impregnation and polymerization

Dissolution of CO2 in a polymer facilitates diffusion of monomers and catalysts/initiators

within the polymer matrix. In this case, CO2 is the carrier of active chemical species101 as well

as the swelling agent. Accordingly, chemical modification of polymers can be carried out in

milder conditions than with standard methods of melt modification in extruders or batch

mixers. This is extremely important for polymers, such as poly(tetrafluoroethylene) (PTFE)102

and PP103 for which modification in the melt is always accompanied by degradation.

The polymeric substrates bisphenol A poly(carbonate) (PC), poly(vinyl chloride) (PVC)

and poly(tetrafluoro ethylene) (PTFE) were modified by the impregnation of vinylic

monomers styrene (S), methyl methacrylate (MMA) and methacrylic acid (MAA) under

supercritical conditions.104 The impregnation of styrene and acrylic acid into a series of

polyamide products (nylon1212, nylon1010, nylon66, nylon6) using supercritical CO2 as

additive carrier and substrate-swelling agent was performed by Xu and Chang.105 It was found

that the relative solubility of the additive in the polymer substrate and CO2 is a major factor

governing the incorporated amount; however swelling of the substrate and CO2-induced

crystallization also contribute to the value. Methyl acrylate,106 2-hydroxyethyl

methacrylate,107 methyl methacrylate,108 styrene109 and maleic anhydride110 are reported to be

successfully grafted onto PP film in CO2 assisted processes. In all these cases the presence of

CO2 does not modify the radical grafting mechanism111 but it provides better dispersion of the

reactive species in the PP matrix at low processing temperature. In the studies, a modification

in the thermal properties of PP was observed and attributed not only to the grafting of polar

groups but to the plasticizing action of CO2.112

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Addition reactions have also been carried out on polymeric substrates in order to graft

active chemical groups onto the backbone. Friedmann et al.113 studied the grafting of

isopropyl isocyanate onto ethylene-vinyl alcohol copolymers (EVOH) concluding that the

major advantage of CO2 consists in the selective dispersion and consequent reaction of the

monomer in the amorphous phase of EVOH. A study about to selectively modify the end

groups of polyamide-6 (PA) in supercritical CO2 was also reported.114 Depending on the

reagent used (e.g. diketene or its adduct with acetone), it is possible to selectively modify acid

or basic end groups of a fiber.

1.2.3.2.4. Other applications by impregnation

Besides organic materials, inorganic metal complexes have also been incorporated into

polymers to fulfill specific functions. For instance, the infusion of silver-containing additives

leads to the formation of metalized polymer film with high reflectivity.115, 116 Polymer/metal

composites, even at a nanoscale level, can be produced by infusing proper metal complexes

into a polymer matrix, such as nanoscale platinum clusters into PTFE,117 copper nanoparticles

in polyacrylate,118 and chelate complexes of copper and iron into polyacrylate.119 Zhao et

al.120 recently proposed a pretreatment method whereby palladium

(II)-hexafluoroacetylacetoneate (Pd(hfa)2) was impregnated into Kevlar○R fiber with scCO2

for producing conductive aramid fibers by subsequent electroless copper plating. The research

is further expanded by Adachi et al.121 in the electroless plating on thermoplastic polymer of

polyamide 6.

In addition, surface modification of some polymers by impregnated with surfactant has

been investigated. Xun Ma and David L. Tomasko122 finished a coating study by the

impregnation of N,N-Dimethyldodecylamine N-oxide into a fibrous PE material. The wetting

properties of this highly hydrophobic material are changed dramatically and permanently

compared to dip coating in an aqueous solution. Generally, utilizing the unique properties of

scCO2, impregnating polymer materials with different additives in scCO2 for new frontiers

and designs is an environmentally friendly, challenging, promising direction of polymer

research. There is expansive space and imagination for researchers to explore.

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1.3. Synthetic fiber

Fiber, one of the three types of polymers, is a class of carbohydrate materials that are

continuous filaments or are in discrete elongated pieces, similar to lengths of thread. They can

be spun into filaments, string or rope, used as a component of composite materials, or matted

into sheets to make products such as paper or felt. Fibers are often used in the manufacture of

textile materials such as fabric or other materials. It is divided mainly into three species:

natural fiber, cellulose fiber, and synthetic fiber. Natural fiber is from plant, animal and

mineral sources, such as cotton, silk, and wool etc. Cellulose fibers are regenerated cellulose

used as textile fibers such as rayon, modal, and the more recently developed Lyocell.

Cellulose fibers are manufactured from dissolving pulp. Cellulose-based fibers are of two

types, regenerated or pure cellulose such as from the cupro-ammonium process and modified

cellulose such as the cellulose acetates. Synthetic fibers are the result of extensive research by

scientists to improve upon naturally occurring animal and plant fibers. In general, synthetic

fibers are created by forcing, usually through extrusion, fiber forming materials through holes

(called spinnerets) into the air, forming a thread. Synthetic fibers account for about half of all

fiber usage, with applications in every field of fiber and textile technology. Four of them -

nylon, polyester, acrylic and polyolefin - account for approximately 98 percent by volume of

synthetic fiber production.123 PET and PP are the important synthetic fibers, which have been

expanding from ordinary cloth, covering to high performance application in hygiene and

medical species.124

1.3.1. PET fiber

Poly(ethylene terephthalate) (PET) was invented in the 1940s by Winfield and Dickson,125,

126 and commercialized in the 1950s as DacronTM (EI DuPont de Nemours) and TeryleneTM

(ICI)127 fibers. Of all man-made fibers, PET has become the most dominant, with worldwide

usage exceeding 20 million tons in 2002,128 thus replacing cotton fiber as the number one in

terms of output. The growing production of polyester fibers is projected to reach 33 million

tons by this year.129 The emergence of PET as the most successful man-made fibers is due to

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its useful properties, such as, durability, strength, stability during heat setting, abrasion

resistance, and resistance to sunlight, acids, alkalis, and bleaches. These fibers also have very

good crease recovery and are durable to washing. Along with these characteristics, PET fiber

has many important uses. Fabrics woven from PET thread or yarn are used extensively in

apparel and home furnishings, from shirts and pants to jackets and hats, bed sheets, blankets

and upholstered furniture. Industrial PET fibers, yarns and ropes are used in tyre

reinforcements, fabrics for conveyor belts, safety belts, coated fabrics and plastic

reinforcements with high-energy absorption. PET fiber is used as cushioning and insulating

material in pillows, comforters and upholstery padding. While synthetic clothing in general is

perceived by some as having a less-natural feel compared to fabrics woven from natural fibres

(such as cotton and wool), polyester fabrics can provide specific advantages over natural

fabrics, such as improved wrinkle resistance.

1.3.2. PP fiber

The synthesis of highly crystalline isotactic polypropylene using stereospecific catalysts

was patented in 1954 by Natta.130 Commercial polypropylene production was initially

undertaken by Montecatini and subsequently expanded by ICI Fibers who introduced their

‘Ulstron’ product in late 1950s.131 However, because of patent restrictions associated with

fiber production, fibrous polypropylene often appeared in the market in the form of tapes and

filaments rather than fibers; it was not until the early 1960s that staple fibers started to be seen

on the market.132 Polypropylene was the first synthetic stereo-regular polymer to achieve

industrial importance133 and it is presently the fastest growing fiber for technical end-uses

where high tensile strength coupled with low-cost are essential feature. In addition, PP fiber

has some characteristics including quick drying, abrasion resistant, stain and soil resistant,

comfortable and lightweight, resistant to deterioration from chemicals, mildew, perspiration,

rot and weather so on. As the materials of apparel, PP fiber can be made of sportswear, socks,

thermal underwear, lining fabrics etc. In industries and home furnishings, it works well as

indoor-outdoor carpeting for its hydrophobicity, as filter fabric or bagging because of the

durable ability and corrosion stability, as fishing rope utilizing its lightweight as well as

- 18 -

waterproof. PP fiber can also be used in automotive components, for instances, interior fabrics

used in or on kick panel, package shelf, seat construction, truck liners, load decks, etc.

Nowadays, PP fibers are being extended widely in new fields, such as hygiene, medicine,

electronics, even aeronautics.134

1.4. Natural macromolecules

Natural macromolecules belong to biomolecules with high relative molecular mass, and

derived from living organisms. These macromolecules have some form of biological activity

which is always drawing the attention from human. Many natural macromolecules including

peptides, proteins and carbohydrates have been used in the surface modification of polymer

because of a broad range of application such as specific protein recognition, hydrophilicity,

antimicrobial activity and others, depending on the kind of grafted molecules.135

1.4.1. Sericin

Sericin is a high molecular weight, water-soluble glycoprotein isolated from silk. It is

made of 18 amino acids most of which have strongly polar side groups such as hydroxyl,

carboxyl, and amino groups.136 The high hydroxyl amino acid content of sericin (approx.

46%) is of particular importance for the water-binding capacity which regulates the skin‘s

moisture content. On the other hand, it has a unique carbohydrate moiety and a unique

repetitive amino acid sequence which give it high affinity for proteins resulting in a tightening,

anti-wrinkle effect. Sericin is therefore the ideal multifunctional ingredient for cosmetic skin

care product lines for dry, sensitive and stressed skin and also for sun protective and after-sun

products. In addition, sericin was found to be a strong antioxidant and antibacterial which can

inhibit tyrosinase activity,137 and can kill micrococcus successfully,136 these promote its

applications in modification of biomaterials.138

1.4.2. Chitosan

Chitosan is a polycationic polymer with a specific structure and properties.139 It contains

more than 5000 glucosamine units and is obtained commercially from shrimp and crab shell

- 19 -

chitin (a N-acetylglucosamine polymer) by alkaline deacetylation (NaOH, 40-50%). Chitosan

is insoluble in most solvents including water, but is soluble after the amino groups participate

in reaction in dilute organic acids such as acetic acid. This is due to the main body containing

a mass of hydroxyl groups. Chitosan is inexpensive and nontoxic and possesses reactive

amino groups. It has been shown to be useful in many different areas,140 as an antimicrobial

compound in agriculture, as a potential elicitor of plant defense responses, as a flocculating

agent in wastewater treatment, as an additive in the food industry, as a hydrating agent in

cosmetics, and more recently as a finishing agent in textiles. Chitosan has been covalently

linked to carboxylic acid functionalized PP using water soluble carbodiimide chemistry. The

resulting material showed enhanced wettability and antimicrobial activity against

Pseudomonas aeruginosa.141

1.4.3. Polylysine

Polylysine (ε-poly-L-lysine) is a small polypeptide of the essential amino acid L-lysine

that is produced by bacterial fermentation. ε-Polylysine belongs to the group of cationic

surfactants. In water, ε-polylysine contains a positively charged hydrophilic amino group and

a hydrophobic methylene group. Cationic surface-active compounds have the ability to inhibit

the growth of microorganisms. According to research, ε-polylysine is absorbed

electrostatically to the cell surface of the bacteria, followed by a stripping of the outer

membrane. This eventually leads to the abnormal distribution of the cytoplasm causing

damage to the bacterial cell.142 Literature studies have reported an antimicrobial effect of

ε-polylysine against yeast, fungi, gram-positive bacteria and gram-negative bacteria.143

Polylysine is commercially used as a food preservative,144 is also used a delivery vehicle for

small drugs in chemotherapy.145 Recently, along with the development technology of

bioelectronics, polycationic compounds including polylysine have been used to construct

biochip and integrated circuit.146 Generally, the utilization of this biopolymer is both

economical and environmental, it is valuable to explore new applicable field.

1.4.4. Collagen

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Collagen is a triple helical coil of amino acid sequences comprised mainly of repeating

residues of glycine, proline, and hydroxyproline.147 It is the most abundant and ubiquitous

protein in the body of animals, making up about 25% to 35% of the whole-body protein

content. Collagen has good biological compatibility and well characterized low antigenicity. It

can be degraded into physiologically well tolerated compounds. Also, it can also be processed

in aqueous base for enhanced cellular penetration and wound repair. Therefore, collagen has

attracted great interest as a biomaterial for medical use, such as drug delivery,148 and tissue

engineering.149 Collagen possesses characteristics as a biomaterial distinct from those of

synthetic polymers. The most distinct is its mode of interaction with the body. It has be

pointed out that collagen minimizes contractions of facial muscles and can encourage skin

renewal as a cosmetic cream.150 Hydrolyzed collagen has an affinity to water because many

hydrophilic groups will occur, such as hydroxyl, amine.

1.5. Objective of this research

As described in the first section, current techniques on surface modification of polymer

still existed in shortcoming in the limited yield scale or environmental issues. It is always

required that new, easy-operation, low-cost, environmentally friendly processes for modifying

the polymer surface can occur. Supercritical technology, where not only there is no pollution

effect but the operation and treatment are very simple, has received wide attentions. The

impregnation process in scCO2 is particularly valuable for us to consider. Synthetic fabrics

(PET or PP) are necessary in our daily life, are important components in textile industry,

which possess superior strength and resilence. For the application of PET and PP fabrics in

health and comfort related respects, these fabrics have to be modified to improve the surface

wettability and biocompatibility. Some natural macromolecules are nontoxic, inexpensive,

hydrophilic and pharmic functional agents. If these functional agents can be grafted onto the

surface of synthetic fabric, there will be a useful application in textile finishing.

Thus, we proposed the new coating technology where the scCO2 impregnation technology

is to be combined with the regular method. In our research, some active cross-linking agents

will be impregnated into synthetic fabrics by using scCO2, and then the impregnated fabrics

- 21 -

will be treated to attach natural macromolecules by aqueous system or pad-dry-cure method.

In addition, the immobilization of natural macromolecules onto the fabric surface without

impregnation pretreatment in scCO2 will also be done only for a comparison.

For the fabrics impregnated with cross-linking agents in scCO2, the cross-linking agents

will penetrate the surface of fabrics, and active functional groups of cross-linking agents will

present on the surface of fabrics. The results will be investigated by FT-IR or XPS spectra.

After the immobilization of natural macromolecules on the surface of functionalized fabrics,

the surface hydrophilicity of fabrics will be improved, the effects will be investigated by

measurements of water contact angle, moisture regain, as well as the wicking height. The

antibacterial properties of some modified fabrics against S. aureus will also be tested for

investigating the biocompatibility. Finally, the feasibility of this research will be given in a

conclusion.

1.6. Outline of the thesis

In chapter one, the surface modification technologies conventionally used in the polymer

processing were reviewed, as well as the application of supercritical technology in polymer

processing. In addition, synthetic fibers (PET and PP) and some natural macromolecules were

also made an introduction in nature and application. The objection of this research was drawn

out finally.

In chapter two, the coating of natural proteins (sericin or polylysine) onto the surface of

synthetic fabrics (PET and PP) functionalized by the diisocyanate crosslink with scCO2 was

reported. Firstly, the experimental background was introduced, and the coating mechanism

between biopolymers and isocyanate was also presented. Secondly, the analysis methods and

concrete experimental operate were described distinctly. Thirdly, the impregnation results and

the coating results were discussed mainly. Finally, a conclusion was obtained from these

results.

In chapter three, the modification of the synthetic fabrics (PET and PP) was reported by

the method of impregnating PET and PP with cyanuric chloride in scCO2 prior to immobilize

sericin or chitosan. The experimental process and the analysis method were described in detail

- 22 -

in the preceding parts. The rest parts discussed mainly the experimental results and analyzed

the experimental phenomena. During the section of results, the modified PET and PP fabrics

were compared in water contact angle and wicking property.

In chapter four, the immobilization of three functional agents to the surface of PET fabric

impregnated with epoxy compounds in scCO2 were reported. The impregnation process and

the immobilization method was definitely made an introduction, three results on the

immobilization of three functional agents were also compared accordingly. The

hydrophilicities of these modified fabrics were investigated in water contact angle and

moisture regain. The antibacterial effects of these fabrics were given in the results section.

In chapter five, the research results in this study were summarized, and some suggestions

were proposed about the research and the developing direction in new projects.

- 23 -

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Chapter 2. Coating of natural proteins onto synthetic fabrics crosslinked with diisocyanate by supercritical dioxide carbon

2.1. Introduction

Natural proteins derived from living organisms, which is known as polypeptides made of

amino acids arranged in the main chain. Some natural proteins including sericin1 and

polylysine2 showed excellent functional characteristics, such as, hydrophilicity, oxidation

resistance and antimicrobial effect etc. Silk sericin is obtained from silkworm Bombyx mori.

During the various stages of producing raw silk and textile, sericin can be recovered for other

uses. Sericin protein can be cross-linked, copolymerized, and blended with other

macromolecular materials, especially artificial polymers, to produce materials with improved

properties. The protein is also used as an improving reagent or a coating material for natural

and artificial fibers, fabrics, and articles. The materials modified with sericin and sericin

composites are useful as degradable biomaterials, biomedical materials or polymers for

forming articles, functional membranes, fibers, and fabrics. Polylysine is produced by

bacterial fermentation, which is a small polypeptide of the essential amino acid L-lysine.

Polylysine is commercially used as a food preservative,3 is also used a delivery vehicle for

small drugs in chemotherapy.4 Recently, along with the development technology of

bioelectronics, polycationic compounds including polylysine have been used to construct

biochip and integrated circuit.5 Generally, natural macromolecules used to modify the fabrics

by impregnation or coating of them onto the substrate materials have got considerable

progress in textiles industry.6-10 Synthetic fabrics of Poly(ethylene terephthalate) (PET) and

polypropylene (PP) possess good mechanical and low producing cost, thus making them

attractive as substrate for natural proteins to cover.11

With the development of supercritical fluid technology, supercritical carbon dioxide

(scCO2) in impregnation aspects is drawing much attentions in research or application.12

Recently, Free-radical grafting of glycidyl methacrylate (GMA) onto PP films has been

studied using scCO2 as a solvent and a swelling agent.13 Making the introduced regents in

polymer to participate in a chemical reaction is a good elicitation for surface modification of a

- 35 -

fiber. It is well known that the impregnated organic regents can remain on the surface of

polymer after the impregnation in scCO2,14 especially for the fiber materials.15 Thus, once

some active molecules was impregnated into the fiber by scCO2, an immobilization of sericin

or polylysine onto the surface of synthetic fabric can be designed by the reaction of sericin or

polylysine with these active molecules embedded on the fiber surface.

Toluene 2,4-diisocyanate (TDI) is a major isocyanate compound used commercially in

surface coating, adhesives, resins, elastomers (especially in polyurethane foams), binders and

sealants.16 The compound has two isocyanate functional groups attached to a parent toluene.

The functional groups of isocyanate have agility properties to be rapid reaction to alcohol,

water, amine, etc., in the ambient temperature,17 in which a reaction between isocyanate

compound and amine occur, an urea compound will be produced. In addition, TDI is the

compound that is hydrophobic and affinitive to CO2. Some reactions about TDI where the

scCO2 is utilized as a medium system have been reported,18, 19 these applications indicated

that TDI has good solubility in scCO2.

Accordingly, to bridge the synthetic fabrics and natural proteins (sericin or polylysine),

TDI is selected as the cross-linking agents in the design. In this study, the impregnation of

TDI into PET and PP fabrics will be investigated by the scCO2 method, and the

immobilization of sericin or polylysine will also be described. The fabrics of TDI-PET,

TDI-PP, TDI-PET and TDI-PP finished by natural proteins will be analyzed by ATR-IR

measurement. The hydrophilicity of these fabrics will be investigated and discussed. The

proteins immobilization results of fabrics will also be evaluated by the staining test using

methylene blue.

2.2. Experimental procedures

2.2.1. Reagents and materials

The cross-linking agents of toluene 2,4-diisocyanate (TDI, Mw: 174.2, d: 1.214g/ml) used

in the impregnation to synthetic fabrics by supercritical CO2 was purchased from

Sigma-Aldrich Inc. The natural functional agents of sericin (Powder, Mw: ca. 30,000) and

polylysine (Mw: ca. 5000, 25% in water) were supplied by Seiren Co., Ltd. and Chisso Co.,

- 36 -

Ltd., respectively. Figure 1 showed the structural formulas of TDI and polylysine. Sericin is

made of 18 amino acids and is dominated by the presence of hydroxyl (Ser, Thr, and Tyr),

acidic (Asp and Glu), and basic (Lys, His, and Arg) amino acid residues.20 PET fabric (90

g/m2) and PP fabric (224 g/m2) used as synthetic fabric substrates for modification were

supplied by Toyobo Co., Ltd. and Asahi Kasei Ind. Co. Ltd. respectively. Previously, the PET

fabric was washed and stabilised by immersing in acetone at 35°C for 30 min, the PP fabric

was rinsed with tetrahydrofuran (THF) for 30 min at 35°C followed by a rinse with acetone,

both of them was dried in vacuum at 70°C. Dimethylformamide (DMF) used as a component

of dipping solution was purchased from Wako Pure Chemical Industries, Ltd. The water in

polylysine solution was distilled deionized water. The carbon dioxide used in all of the

experiments was purchased from Uno Sanso Co., Ltd. (99.5% pure).

CH3

N=C=O

N=C=O

2,4-TDI

CNH

**

O

NH2 n

ε-poly-L-lysine

Figure 1. Structural formulas of Toluene 2,4-diisocyanate and polylysine.

2.2.2. Treatment

The whole process of treating synthetic fabrics (PET and PP) including impregnation of

diisocyanate and surface immobilization of natural proteins were shown schematically in

Figure 2. The details for each process are described below.

- 37 -

In scCO2

ImmobilizationSynthetic fabric TDI-impregnated fabric

Natural protein-TDI-fabric

Natural protein

TDI

Figure 2. Processing flow on immobilization of natural proteins onto the synthetic fabrics.

2.2.2.1. Impregnation of TDI into PET and PP fabrics by scCO2

A size of cleaned synthetic fabrics (10 cm×16 cm), TDI and corresponding glassy filter

paper used as an insulation layer between the fabric and TDI were set into the scCO2

apparatus. The apparatus is schematically illustrated in Figure 3. The impregnation was

conducted in a 50 ml-vessel equipped with a high-pressure needle valve at the export. The

vessel was heated to the preset temperature, carbon dioxide was then introduced, and the

desired pressure was maintained. The system was treated under agitation for detecting time.

After the impregnation, the system was cooled and depressurized slowly (ca. 0.5 MPa/min)

till the temperature close to ambient condition. The treated fabrics were washed by acetone at

room temperature to remove the cross-linking agents which are cohesive on the surface of

fabrics. The impregnation amounts of TDI to PET and PP fabric using supercritical CO2 was

determined gravimetrically and expressed as a percentage of impregnation by the equation 1

and 2:

G (PET) impregnation (%) = [W (PET) 1 – W (PET) 0] / W (PET) 0 × 100 (1)

G (PP) impregnation (%) = [W (PP) 1 – W (PP) 0] / W (PP) 0 × 100 (2)

where W1 and W0 are the weight (g) of TDI-impregnated PET/PP and untreated PET/PP

fabric, correspondingly.

- 38 -

1：CO2 cylinder 2：cooling pump 3：syringe pump 4,9：pressure gauges

5：thermometer 6：heater 7：high pressure stainless vessel 8：magnetic stirrer

10：manual valve 11：needle valve

Figure 3. Illustration of the supercritical impregnation apparatus.

2.2.2.2. Immobilization of natural proteins onto TDI-PET and TDI-PP fabrics by the

pad-dry-cure method

It has been known that toluene diisocyanate react easily with H2O, but the selected natural

proteins (sericin and polylysine) are water-soluble reagents, in order to avoid much of

diisocyanate react with the medium of H2O, a method of pad-dry-cure was adopted for the

immobilization of the two proteins (sericin and polylysine). In the experiment, to immerse the

hydrophobic fabrics (especially for PP) quite in the dipping solution, the dipping solvent is

made up of H2O and DMF, sericin and polylysine finishing solutions were diluted to 1wt%,

3wt% and 5 wt% respectively in relation to the mass of mixed solvent. The fabric samples

were padded twice to about 110% wet pickup with freshly prepared aqueous solutions of

polylysine. Padded fabrics were dried at 60°C for 90 minutes, cured at 120°C for 20 minutes,

washed, and dried. The immobilization ratio of sericin or polylysine onto TDI-PET and

TDI-PP fabrics are defined by equation (3) and (4):

- 39 -

G (PET) immobilization (%) = [W (PET) 2 – W (PET) 1] / W (PET) 1 × 100 (3)

G (PP) immobilization (%) = [W (PP) 2 – W (PP) 1] / W (PP) 1 × 100 (4)

where W2 represent the weights of the natural proteins-finished TDI-PET and TDI-PP fabrics.

2.2.3. Analysis

Infrared absorption spectra of the samples of PET and PP fabrics (untreated, treated in

each step), sericin, polylysine and TDI were obtained from a Fourier-Transform Infrared

Spectroscopy (FT-IR). The fabrics were executed by the method of attenuated total reflection

(ATR) where a total of 200 scans were accumulated at a resolution of 4 cm-1, and reagents of

TDI, sericin and polylysine were performed with usual method of making pellets (ca.0.5%

w/w) with potassium bromide (KBr) where a total of 16 scans were accumulated at a

resolution of 8 cm-1.

Static water contact angles of the original and modified PET and PP fabrics were

measured with a contact angle measurement apparatus (KRÜSS, DSA20) which is a suitable

instrument for the automatic recording of the surface force tension of liquids. For this

measurement, a droplet of distilled water (5 μl) was placed onto the PET fabric surface from a

fixed height (1cm). Before measurement, the samples were dried at 60°C under vacuum.

More than five measurements were carried out and the resulting values were averaged.

Staining test is often used to temporarily stain bacterial in biology technique. The amine

groups in natural proteins are electron-rich, this made it can be stained by methylene blue. For

the staining test, 0.1wt% of methylene blue solution is prepared with deionized water. The

synthetic fabrics were dipped into the solution for 10 minutes with a shake at room

temperature. Then, the fabrics were taken out, dried for 30 minutes, rinsed with deionized

water.

2.3. Results and discussion

2.3.1. Supercritical impregnating PET and PP fabrics with TDI

The impregnation of dyes into synthetic fibers utilizing scCO2 has been investigated by

- 40 -

many studies.21-23 It was pointed out that 120 -130°C is suitable to the PET dyeing and

100-110°C is suitable to the PP dyeing. Thus, the conditions of impregnating synthetic fabrics

with TDI in scCO2 were selected at 120°C, 25MPa for PET, at 100°C, 25MPa for PP. Because

TDI has good solubility in scCO2, the filling amounts of TDI in vessel need to solve here. In

order to investigate the relation of the filling amounts in vessel and the uptakes in the

synthetic fabrics, a 2-hours impregnation was performed for PET and PP, respectively. The

results were shown in Figure 4. From the curve trend, the uptakes of TDI in synthetic fabrics

is increased with the increase of filling amounts initially, when the filling amount is close to

0.66 ml in 50 ml (0.09 mol/L), the uptake in either fabric of PET and PP nearly attained the

maximal value. This indicated that the filling amount of TDI was sufficient in excess of the

amount required to saturate the CO2 during the entire course of impregnation. The uptake of

TDI in PET is more than it in PP, this result is attributed to the affinity of PET to TDI, which

is higher than the affinity of PP to TDI because PET includes some hydroxyl side chains.

Another reason maybe has a relation with the swelling extent of PET and PP fiber in scCO2.

0.05 0.10 0.15 0.20

1.6

2.0

2.4

2.8

TDI u

ptak

e [w

t%]

C [mol/L]

PET (120oC, 25MPa)

PP (100oC, 25MPa)

Figure 4. Uptake of TDI into PET and PP fabric as a function of the filling concentration of

the cross-linking agent in scCO2 for 2 hours.

- 41 -

The impregnation is later than the swelling of substrate in supercritical phase. The

swelling process usually influences the impregnation amount of an additive into the substrate.

After the filling amount of TDI was confirmed, the relation of impregnation uptake and the

time was investigated. The results of impregnation uptakes for TDI into the PET and PP

fabrics were shown in Figure 5. It can be noted, the impregnation equilibrium on PET fabric

was obtained after 4 hours, and the impregnation equilibrium on PP fabric was faster than that

in PET, the time was about 2 hours. The different equilibrium time is considered for the

materials are not same. This can be explained by the cause that the swelling time on PET and

PP fabrics is different. Besides, the uptake of TDI in PP fabric presented a downward trend

after a treatment over 3 hours. The phenomenon maybe account for the cause that microcells

of crystallization appeared in the amorphous domains which pushed the TDI out of the

substrate of PP when the structure of crystal is destroyed next to melting point after long time.

0 60 120 180 240 300 3600

1

2

3

4

TDI u

ptak

e [w

t%]

Impregnation time [minute]

PET (120oC, 25MPa)

PP (100oC, 25MPa)

Figure 5. Uptake of TDI into PET and PP fabrics as a function of impregnation time in

scCO2.

- 42 -

2.3.2. Immobilization of natural proteins (sericin and polylysine) onto the surface of

TDI-PET and TDI-PP fabrics

The investigation above suggested that the upmost uptakes of TDI in synthetic fabrics

were, 3.54wt% for PET treated in scCO2 for 4h at 120°C and 25MPa, and 2.48wt% for PP

treated in scCO2 for 2h at 100°C and 25MPa. The fabric samples impregnated with the

upmost uptake of TDI were used to immobilize natural proteins. The immobilization results

are shown in Table 1. From the data, it can find that, the immobilization amount to TDI-PET

is always more than the value to TDI-PP in the same concentration of finishing solution. This

is mainly understood as the impregnation amount of TDI in PET fabric is higher than it in PP

fabric. The higher the impregnation amount, the more the functional groups of isocyanate will

bare on the surface of the fabric, which can react with more natural proteins. For the TDI-PET

fabric, either protein immobilization attained maximal value after the treatment in 3wt%

solution, even treating it in the case of 5wt%. This result indicated that a concentration of

3wt% protein solution is adequate to react with those isocyanate groups on the surface of

TDI-PET fabric. Comparatively, the protein immobilization amount to TDI-PP has no biggish

change with its concentration, this can be considered that 1wt% of protein solution has been

ample for the required amount to participate in the reaction with isocyanate because the less

uptake of TDI in PP fabric. Obviously, the whole immobilization results of sericin is higher

than of polylysine to TDI-PET or TDI-PP, this can be explained for the more amino groups of

sericin relating to polylysine facilitated the reaction with isocyanate moieties on the fabric

surfaces.

Table 1. Immobilization amount of natural proteins onto the TDI-PET and TDI-PP fabrics.

Fabric samples Sericin finishing solution Polylysine finishing solution

1wt% 3wt% 5wt% 1wt% 3wt% 5wt%

TDI-PET 0.95 1.22 1.19 0.73 1.07 1.02

TDI-PP 0.78 0.84 0.81 0.63 0.65 0.67

- 43 -

2.3.3. FT-IR analysis

To easily compare the results of impregnation and immobilization, the IR spectra of the

cross-linking agent of TDI, of immobilization protein of sericin and polylysine were

investigated and analyzed in Figure 6, Figure 7 and Figure 8, respectively. The typical bands

of several reagents have been indicated in each spectrum.

3500 3000 2500 2000 1500 10000

1

2

3

4

Abs

orba

nce

Wavenumber [cm-1]

N=C=O STRBenzene ring STR

Out-of-plane CH BEND

In plane CH BEND

CH STR (Methyl and Benzene ring)

Methyl CH BEND

Figure 6. IR spectrum of the cross-linking agent TDI.

- 44 -

3500 3000 2500 2000 1500 1000 5000.0

0.4

0.8

1.2

1.6A

bsor

banc

e

Wavenumber [cm-1]

OH and NH STR

CH STR

AmideⅠ

Amide Ⅱ

Amide Ⅲ

N-CH STR

C-OH

Out-of-plane NH2 BEND

Figure 7. IR spectrum of the immobilization agent sericin.

3500 3000 2500 2000 1500 1000 5000.0

0.5

1.0

1.5

2.0

Out-of-plane NH2 BEND

N-C(=O)-N STR

Amide Ⅲ

Amide Ⅱ

AmideⅠ

Abs

orba

nce

Wavenumber [cm-1]

NH STR

CH2 STR

Figure 8. IR spectrum of the immobilization agent polylysine.

- 45 -

After the whole treatment was finished, the ATR-IR spectra of the untreated,

TDI-impregnated and polylysine-immobilized fabrics of PET and PP were measured, as

shown in Figure 9 and Figure 10, respectively. Compared with the spectra of original fabric,

it is obvious that a new peak appeared at 2260 cm-1 in either fabric impregnated with TDI.

This is a convincing poof that TDI was impregnated into the fabrics of PET and PP,

meanwhile, it also suggested the impregnated agent can penetrate the surface of the fibers.

Having immobilized sericin or polylysine onto the TDI-impregnated PET and PP fabrics, the

functional group of –N=C=O disappeared. Instead of it, a broad band about 3300-3500cm-1

was found, this is a character of amine or hydroxyl absorption in IR spectra. From this result,

it is be deduced that the isocyanate group of TDI bared on the surface of fabrics have

participate in reaction in the main. The spectra of sericin-immobilized TDI-PET and TDI-PP

did not shown because it is similar to the spectra of polylysine-immobilized fabrics. For the

proteins-finished TDI-PET and TDI-PP fabrics, some flaxen stains may be noted. This is

accordant with the result on which the samples of TDI-PET or TDI-PP are laid in air or H2O

for a long time. Accordingly, the reaction of TDI with H2O existed affirmatively in the

pad-dry-cure treatment.

- 46 -

3500 3000 2500 2000 1500 10000.00

0.05

0.10

0.15

0.20

0.25A

bsor

banc

e

Wavenumber [cm-1]

Polylysine-TDI-PET TDI-PET Untreated PET

Figure 9. ATR-IR spectra of PET, TDI-impregnated PET and Polylysine-TDI-PET fabrics.

3500 3000 2500 2000 1500 10000.00

0.05

0.10

0.15

0.20

Abs

orba

nce

Wavenumber [cm-1]

Polylysine-TDI-PP TDI-PP Untreated PP

Figure 10. ATR-IR spectra of PP, TDI-impregnated PP and Polylysine-TDI-PP fabrics.

- 47 -

2.3.4. Staining by methylene blue

Although TDI on the surface of fabrics have participated in chemical reaction during the

course of immobilizing natural proteins, the reaction with proteins is still a suspectable matter

for the isocyanate groups were also easily substituted by water. Once the active groups have

reacted with water, the staining effect will not occur. Thus, the investigation of staining by

methylene blue as a detective means is implemented. The TDI-samples treated in 3wt%

finishing solution were stained here and the images of the stained fabrics are shown in Figure

11. Contrastively, the untreated and the TDI-impregnated fabrics of PET and PP can not be

stained by methylene blue essentially, but, the TDI-PET and TDI-PP fabrics finished by

natural proteins captured the methylene blue successfully, even though the color deeper or

lighter. On the whole, the staining on PET is uniform, the uneven color on PP is possible due

to the immobilization of proteins is non-uniform. In addition, the sericin-TDI-fabrics are

stronger than the polylysine-TDI-fabrics in chroma, there may be two reasons for this, firstly,

the electron-rich groups of sericin is more than that in polylysine; secondly, the

immobilization amount of sericin is higher than the polylysine amount on TDI-PET or

TDI-PP fabrics.

Untreated PET TDI-PET Sericin-TDI-PET Polylysine-TDI-PET

Untreated PP TDI-PP Sericin-TDI-PP Polylysine-TDI-PP

Figure 11. Staining of diverse fabrics of PET and PP by mehtylene blue.

- 48 -

2.3.5. Hydrophilicity effect

The static water contact angle on the untreated and modified fabrics of PET and PP was

measured to evaluate the hydrophilicity of these fabrics. Table 2 gave the data of them. The

natural proteins-immobilized samples were the TDI-PET and TDI-PP fabrics treated in 3wt%

finishing solution. It is evident that all modified fabrics of PET and PP have a decrease in

water contact angle. This means the hydrophilicity of the modified fabrics was improved even

after the impregnation of TDI. Compared with the untreated fabric, PET fabric in the aspect of

hydrophilicity was improved consumedly, and PP fabric also gained some progress from 132

to 107 o. The relevant images of water contact angles on these fabrics were shown in Figure

12. From all results, it indicated that sericin has better hydrophilicity than polylysine, this owe

to that much hydroxyl groups also existed in sericin, but there is only amine groups for

polylysine.

Table 2. Static water contact angle of diverse fabrics of PET and PP.

PET samples Static water contact angle (o) PP samples

Untreated PET 102.6 132.2 Untreated PP

TDI-PET 97.4 118.5 TDI-PP

Sericin-TDI-PET 66 107.7 Sericin-TDI-PP

Polylysine-TDI-PET 85 115 Polylysine-TDI-PP

- 49 -

Figure 12. Images of water contact angle on diverse fabrics of PET and PP.

- 50 -

2.4. Summary

An attempt to coat the synthetic fabrics (PET or PP) with natural proteins (sericin or

polylysine) was designed. The study made a success by impregnating the fabric substrate with

a functional reactive agent of TDI prior to attach the natural proteins.

The impregnation of TDI into synthetic fabrics of PET and PP was performed in scCO2.

During the course of impregnation, to reach an optimal impregnation effect, the filling amount

of TDI in scCO2 vessel was investigated firstly, and then, the equilibrium time of

impregnating PET and PP fabric with TDI were also obtained under the experimental

temperature and pressure, respectively. After the optimization treatment, the impregnation

uptakes of TDI attained 3.54wt% for PET, and 2.48wt% for PP fabric.

The coating of sericin or polylysine onto the TDI-PET and TDI-PP fabrics was treated by

the pad-dry-cure method. It is approved that a concentration of 3wt% protein solution was

adequate to react with those isocyanate groups on the surface of TDI-PET and TDI-PP fabrics.

The coating results got recognitions on the IR spectra of the modified samples and the

staining effects of these fabrics. The water contact angle measurement revealed the

hydrophilicity of the modified fabrics of PET and PP was improved to a certain extent,

especially for the sericin-immobilized fabrics.

- 51 -

References

1. Yu-Qing Zhang, Applications of natural silk protein sericin in biomaterials, Biotechnol. Adv. 20 (2002)

91.

2. S. Shima, Antimicrobial action of ε-poly-L-lysine, J. Antibiot. 37 (1984) 1449.

3. J. Hiraki, ε-polylysine: Its development and utilization, Fine Chem. 29 (2000) 25.

4. R. Duncan, Drug–polymer conjugates: potential for improved chemotherapy, Anti-Cancer Drugs 3

(1992) 175.

5. L. Cai, H. Tabata, T. Kawai, Probing electrical properties of oriented DNA by conducting atomic force

microscopy. Nanotechnology 12 (2002) 211.

6. A. Kongdee, S. Okubayashi, I. Tabata, T.Hori, Impregnation of silk sericin into polyester fibers using

supercritical carbon dioxide, J. Appl. Polym. Sci. 105 (2007) 2091.

7. K. F. El-tahlawy, M. A. El-bendary, A. G. Elhendawy, S. M. Hudson, The antimicrobial activity of

cotton fabrics treated with different crosslinking agents and chitosan, Carbohyd. Polym. 60 (2005) 421.

8. A. Hebeish, M.G. Fouda, I.A. Hamdy, S.M. EL-Sawy, F.A. Abdel-Mohdy, Preparation of durable insect

repellent cotton fabric: Limonene as insecticide, Carbohyd. Polym. 74 (2008) 268.

9. N. Blanchemain, S. Haulon, B. Martel, M. Traisnel, M. Morcellet, H. F. Hildebrand. Vascular PET

rostheses Surface Modification with Cyclodextrin Coating: Development of a New Drug Delivery

System, Eur. J. Vasc. Endovasc. Surg. 29 (2005) 628.

10. Y.-C. Tyan, J.-D. Liao, R. Klauser, I.-D. Wu, C.-C. Weng, Assessment and characterization of

degradation effect for the varied degrees of ultra-violet radiation onto the collagen-bonded

polypropylene non-woven fabric surfaces, Biomaterials 23 (2002) 65.

11. M. J. Shenton, M. C. Lovell-Hoare, G. C. Stevens, Adhesion enhancement of polymer surface by

atmospheric plasma treatment, J. Phys. D: Appl. Phys. 34 (2001) 2754.

12. I. Kikic, F. Vecchione, Supercritical impregnation of polymers, Curr. Opin. Solid State Mater. Sci. 7

(2003) 399.

13. M. H. Kunita, A. W. Rinaldi, E. M. Girotto, E. Radovanovic, E. C. Muniz, A. F. Rubira, Grafting of

glycidyl methacrylate onto polypropylene using supercritical carbon dioxide, Eur. Polym. J. 41 (2005)

2176.

14. X. Ma, D. L. Tomasko, Coating and Impregnation of a Nonwoven Fibrous Polyethylene Material with a

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Nonionic Surfactant Using Supercritical Carbon Dioxide, Ind. Eng. Chem. Res. 36 (1997) 1586-1597.

15. Andrew I. Cooper, Polymer synthesis and processing using supercritical carbon dioxide, J. Mater. Chem.

10 (2000) 207.

16. National Institute for Occupational Safety and Health (NIOSH): Determination of Airborne Isocyanate

Exposure, in: M.E. Cassinelli, P.F. O’Connor (Eds.), NIOSH Manual of Analytical Methods (DHHS

[NIOSH] Publication no. 98-119), 4th ed., 2nd suppl., U.S. Department of Health and Human Services,

Public Health Service, Centers for Disease Control and Prevention, NIOSH, Cincinnati, OH, 1998, pp.

115.

17. Y. Shang, Y. Peng, UF membrane of PVA modified with TDI, Desalination 221 (2008) 324.

18. F. Montilla, E. Clara, T. Avile´s, T. Casimiro, A. A. Ricardo, M. N. da Ponte, Transition-metal-mediated

activation of arylisocyanates in supercritical carbon dioxide, J. Organomet. Chem. 626 (2001) 227.

19. P. Chambona, E. Clouteta, H. Cramaila, T. Tassaingb, M. Besnard, Synthesis of core-shell

polyurethane–polydimethylsiloxane particles in cyclohexane and in supercritical carbon dioxide used as

dispersant media: a comparative investigation, Polymer 46 (2005) 1057.

20. J. Huang, R. Valluzzi, E. Bini, B. Vernaglia, D. L. Kaplan, Cloning, expression, and assembly of sericin

-like protein, J. Biol. Chem. 278 (2003) 46117.

21. A. Ehrhardt, I. Tabata, K. Hisada, T. Hori, Imoregnation of Hydroxy-Anthraquinone Compounds into

Polypropylene Fabrics by scCO2 and the Sorption Ability for Metal Ions, Sen’I Gakkaishi 61 (2005)

201.

22. M. Banchero, A. Ferri, Simulation of aqueous and supercritical fluid dyeing of a spool of yarn, J.

Supercrit. Fluids 35 (2005) 157.

23. G. A. Montero, C. B. Smith, W. A. Hendrix, D. L. Butcher, Supercritical Fluid Technology in Textile

Processing: An Overview, Ind. Eng. Chem. Res. 39 (2000) 4806.

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Chapter 3. Impregnation of cyanuric chloride into PET and PP fabrics with the aid of supercritical carbon dioxide, and its application in immobilizing

natural biomacromolecules

3.1. Introduction

Multifunctional polymers have seen rapid growth in the past decade in such industries as

biomedicine, microelectronics, food packaging, wastewater treatment and textiles. The

surface modification of low-cost, commodity-shaped polymer materials – by the addition of

functional molecules – is of great interest since it offers an effective method for pre-existing

polymer materials to gain higher added value in application.1-3 PET and PP are by far the most

widely used commercial pre-existing polymers – in the form of film, plastic, fiber and fabric –

due to their excellent physical and mechanical properties, together with their low cost.

The finishing of PET or PP fiber by immobilizing functional molecules onto their

substrates without losing their inherent special effects (fire retarding,

hydrophilicity/hydrophobicity, antibacterial or even medical properties) has been studied,

including physical padding or coating4, 5 and grafting induced by chemical treatment, such as

wet chemical,6 plasma,7 UV irradiation,8 electron beam irradiation9 and γ-ray radiation.10

Physical immobilization techniques do not have a long-term effect on the fiber because the

agents used are only physically adsorbed on the fiber surfaces, yielding a poor washing

fastness. Chemical methods, on the other hand, can permanently immobilize functional

molecules onto the fiber surfaces. Wet chemical methods, however, will generate hazardous

chemical waste and can lead to irregular surface etching. Irradiation techniques are also

limited in laboratory scale because they require complicated production equipment, strict

operation requirements and are expensive, while also having a degradation effect on the

substrate fiber. In addition, during the process of immobilization the functional molecules,

especially bioactive compounds, sometimes lose activity when linked directly to the

hydrophobic polymer surface and so it may be necessary to graft an intermediate

cross-linking agent between the surface and the bioactive compound.1 Considering the inert

nature of PP and PET with no active side chain, a better cross-linking method is required to

- 54 -

introduce intermediate active-linker agents to the surface of PET and PP fibers prior to

coupling a functional molecule.

Recently, supercritical fluids – especially supercritical carbon dioxide (scCO2) – with their

unique mass transport properties, have had a marked effect on polymer processing,11

including impregnation. Basically, the impregnation process consists of three steps: (i)

exposure of the polymer to scCO2 for a period of time; (ii) introduction of the scCO2

containing solutes to the polymer and conducting the subsequent solute transfer from scCO2

to polymer phase; and (iii) the release of the CO2 in a controlled manner, trapping the solutes

in the polymer. Many researchers have demonstrated that small molecule additives can be

impregnated into fiber using scCO2 as a solvent and swelling agent. Knittel et al. 12 showed

that synthetic fibers like PET can be dyed via a dye impregnation in scCO2, avoiding water

pollution and the need for drying, with excellent firmness levels. Tabata et al.13 investigated

the relationship between the solubility of disperse dyes and the equilibrium dye adsorption in

supercritical fluid dyeing. Xun Ma and Tomasko14 reported the impregnation of a non-ionic

surfactant (N,N-dimethyl-dodecylamine N-oxide) into non-woven fibrous samples of

high-density polyethylene (HDPE) using scCO2 as the only solvent. Zhao et al.15 proposed a

pretreatment method whereby palladium (II)-hexafluoroacetylacetoneate (Pd(hfa)2) was

impregnated into KevlarR fiber with scCO2 for producing conductive aramid fibers by

subsequent electroless copper plating. Based on these uses of scCO2 in fiber finishing, a

cross-linking method of using scCO2 is examined in the present study in order to introduce

intermediate active-linker agents into PET and PP fibers for coupling a functional molecule.

Sericin and chitosan are well known as functional biomolecules to modify polymers for

good hydrophilicity and biocompatibility.16, 17 For example, Kamitani et al.18 investigated a

physical method of modifying polyester fabric with sericin, with data on the moisture regain

and washing fastness of the finished fabric. Hudson et al.19 used two different cross-linking

agents – butanetetracarboxylic acid, BTCA) and Arcofix NEC (low formaldehyde content) –

in the presence of chitosan to provide cotton fabrics with a durable press finishing and

antimicrobial properties by chemical linking of chitosan to the cellulose structure. In the

present study, in order to anchor biomolecules (sericin/chitosan) onto the PET and PP fabric

- 55 -

surfaces, cyanuric chloride (CC), an active-linker agent that is not reactive to CO2, was

chosen to impregnate the fabric substrate with the help of scCO2 for attaching sericin or

chitosan. Cyanuric chloride is a heterocyclic molecule, which allows the subsequent

substitution of its three chlorine atoms by nucleophiles as amine, alcohol or thiols. According

to the literature,20 the substitution of chlorine can be controlled by temperature to run in a

stepwise manner. An empirical rule, based on observation, is that mono-substitution of

chlorine occurs below or at 0°C, di-substitution occurs at room temperature and

tri-substitution occurs above 60°C. The application of cyanuric chloride to serve as a linker

agent can easily react with biomolecules, such as enzymes, antibody protein, silk fibroin and

chitosan. 21-23

With the purpose of giving hydrophilicity as well as biocompatibility to a synthetic fabric

(PET/PP) for some useful application, the present research reports a 2-step process as

described in Scheme 1, i.e. (i) impregnation of cyanuric chloride into PET/PP fabric substrate

and (ii) immobilization of sericin or chitosan onto the CC-PET and CC-PP fabrics via reacting

with cyanuric chloride implanted on the surfaces of PET and PP fabrics. The treated fabrics

are characterized in spectrometrical and morphological analyses. The hygroscopic properties

of the treated fabrics are also evaluated.

Supercritical CO2

N

N

N

Cl

ClCl

Cyanuric chloride

NN

NCl

Cl

Cl

N

NN

Cl

Cl

Cl

NN

N

Aqueous solution

Biomacromolecules(Sericin/Chitosan)

NH

Cl

Cl

N

NN

Cl

Macromolecule

Cl

HN Macromolecule

PP/PET fabric CC-impregnated PP/PET fabric

Biomacromolecule-immobilized PP/PET fabric

Scheme 1. Schematic representation of the immobilization of biomacromolecules (sericin or

chitosan) onto PET (or PP) fabric surface by reacting with cross-linking agent of CC

impregnated into PET (or PP) substrate using scCO2.

- 56 -

3.2. Experimental procedures

3.2.1. Materials and Reagents

The poly(ethylene terephthalate) (PET) fabric (90 g/m2) and the polypropylene (PP) fabric

(224 g/m2) used as base polymer for modification was supplied by Toyobo Co. Ltd. and Asahi

Kasei Ind. Co. Ltd., respectively. First, the PET fabric was washed and was stabilized by

immersing in acetone at 35°C for 30 minutes, while the PP fabric was rinsed with

tetrahydrofuran (THF) for 30 minutes at 35°C, followed by a rinse with acetone. Both fabrics

were then dried in a vacuum at 60°C. The cross-linking agent of cyanuric chloride used in the

scCO2 impregnation to PET and PP fabrics was purchased from Tokyo Chemical Industry Co.

Ltd. Two types of biomolecules – sericin (Mw: ca. 17,000) and chitosan (Mw:

50,000~100,000) – were used as hydrophilic, together with antimicrobial material for the

immobilization onto the surface of PP and PET fabrics. The sericin was supplied by Seiren

Co., Ltd. and the chitosan was purchased from Sigma-Aldrich Inc. All solutions of functional

reagents were prepared with distilled water. The carbon dioxide used in all the experiments

was purchased from Uno Sanso Co. Ltd. (99.5% pure). Several organic solvents and inorganic

salts were purchased as guaranteed-grade reagents from Wako Pure Chemical Industries Ltd.

3.2.2. Treatment

3.2.2.1. Impregnation of CC into PP and PET fabrics by means of scCO2

The high pressure equipment (Model SCF-Sro, JASCO Co., Tokyo) used to impregnate

PP and PET fabric with CC consisted of a 50 ml stainless steel autoclave (Pmax = 30 MPa), a

magnetic stirrer, a constant temperature air bath, a thermocouple and a pressure gauge. The

CO2 was stored in a cylinder and pressurized to the above system by a syringe pump. The

PET (10 cm×12 cm, ca. 1.10 g) or PP (5 cm×5 cm, ca. 1.20 g) fabric substrate was suspended

on a stainless steel net inside the vessel and cyanuric chloride was placed on the bottom of the

vessel. When the autoclave reached the desired temperature, CO2 was let in slowly and

isothermally compressed to working pressure; then, the system was agitated for a certain

period of time to impregnate the substrate fabric with CC. After impregnation, CO2 of the

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system was released at ca. 0.5 MPa min-1 to ambient pressure. The same experiment was

performed with a help of a 3% modifier (acetone, dichloromethane or ethyl acetate) to CO2.

Later, the sample was shaken off and was flushed with air to remove the cross-linking agent

adhering to the surface. The absorption of the cross-linking agents into the PET and PP

fabrics using scCO2 were determined gravimetrically and are expressed as a percentage of

impregnation according to Equations (1) and (2), respectively:

G (PET) impregnation (%) = [W (PET) 1 – W (PET) 0] / W (PET) 0 × 100 (1)

G (PP) impregnation (%) = [W (PP) 1 – W (PP) 0] / W (PP) 0 × 100 (2)

where W1 and W0 correspond to the weight (g) of CC-impregnated and untreated fabrics.

3.2.2.2. Immobilization of biomacromolecules (sericin or chitosan) onto CC-PET and

CC-PP fabrics

The immobilization of biomacromolecules (sericin or chitosan) onto CC-PET and CC-PP

fabric was performed in aqueous solution. The mechanism of immobilization relies on the

reaction of the CC moieties penetrated on the surface of fabric with the active groups (amino

or hydroxyl) of biomacromolecules by the nucleophilic substitution of the chlorine atom.

For the immobilization of sericin, 3wt% finishing solution was prepared and its pH

adjusted to ca. 10 with K2CO3 to trap the HCl formed during the substitution reaction.21, 22

Subsequently, the CC-PET or CC-PP sample was immersed in the sericin solution and was

shaken for 6 hours at 30°C. Then, the solution temperature was raised to 70°C and the

reaction was continued for another 6 hours. Although an alkaline chitosan solution can be

obtained according to the literature,24 the solution was prepared with acetic acid in order to

prevent the reaction of CC with alcohol used in the aqueous solution. The CC-PET or CC-PP

sample was placed in 0.2wt% chitosan water solution containing acetic acid (5vol%) for

reaction at 30°C. After one day, the solution temperature was raised to 70°C and the solution

was maintained for another day. At the end of the immobilization, the samples were removed

from solution, were squeezed and were air-dried. The finished fabric samples were then rinsed

with water, were dried again at 60°C in a vacuum and were conditioned prior to testing. The

- 58 -

immobilization ratio of functional molecules (sericin or chitosan) onto CC-PET and CC-PP

fabrics are defined by Equations (3) and (4), respectively:

G (PET) immobilization (%) = [W (PET) 2 – W (PET) 1] / W (PET) 1 × 100 (3)

G (PP) immobilization (%) = [W (PP) 2 – W (PP) 1] / W (PP) 1 × 100 (4)

where W2 represents the weight (g) of the functional macromolecules-finished CC-PET and

CC-PP fabrics.

3.2.3. Analysis method

Attenuated total reflection-infrared spectra were collected using a Fourier-Transform

Infrared Spectrometer (FT-IR-4100, JASCO), equipped with an ATR accessory (ZnSe crystal,

45°). 200 scans were accumulated for each spectrum at a nominal resolution of 4 cm-1. The

FT-IR spectrum of the CC was also recorded in the apparatus with the method of detecting the

KBr pellets (ca. 0.5% w/w), where a total of 16 scans were accumulated at a resolution of 4

cm-1.

X-ray photoelectron spectroscopy (XPS) measurements were performed on a

photoelectron spectrometer (JPS-9010MCY) with Mg Kα excitation radiation (1253.6 eV).

The X-ray source was run at a potential of 10 kV, a current of 10 mA and an incident angle of

45○. The pressure within the XPS chamber was maintained at 10-7 Pa during the

measurements. Binding energies were calibrated using the containment of carbon (C1s = 285

eV).

Scanning electron microscopy (SEM) images were obtained from detection of the

secondary electron images on a scanning electron microscope (Hitachi S-2600 HS), operating

at 15 kV. Before the SEM observation, the samples were fixed onto a double-faced carbon

tape adhered to a gold support and sputter-coated in an ion sputter (E-1030 Hitachi).

Static water contact angle (SWCA) was determined by the sessile drop method of placing a

5-μL distilled water droplet on the untreated and the modified PET fabrics via a microsyringe.

The drop images were taken after 20 seconds by a monochrome video camera, using

PC-based control acquisition and data processing. All measurements were carried out at room

- 59 -

temperature and the average of at least 5 readings was taken at different positions across the

surface.

The wicking property was estimated by measuring the height of H2O rise through a strip

sample of 5 cm×2 cm fabric which was suspended vertically above the colored distilled water

surface in a glass beaker, such that the horizontal bottom edge just touched the colored water.

The height was recorded after 8 minutes and was repeated twice.

3.3. Results and discussion

3.3.1. Supercritical impregnation with cyanuric chloride

3.3.1.1. Impregnation in pure scCO2

It is well known that impregnation of organic solute into polymer with scCO2 is mainly

dependent on two factors: solubility of the solute and swellability of the polymer. The scCO2

treatment of PET and PP fibers (fabrics) in dye impregnation have been reported in many

studies,13, 25, 26 where the relations between dye uptake and temperature are stated as

120-130°C for PET dyeing and 100-110°C for PP dyeing.

Before the impregnation of CC into PET and PP fabrics, the solubility of CC in scCO2

was investigated by a supercritical apparatus with optical windows. Unfortunately, CC was

found difficult to be dissolved in scCO2 deriving from a turbidity state of the supercritical

fluid viewed with the optical windows. Some researchers have pointed out that the insoluble

dyes in scCO2 can also be incorporated into a polymer matrix because of the high partition

coefficients between polymer and scCO2 phase.27 Thus, the attempt of impregnating PET and

PP fabrics with CC were carried out in pure scCO2 at 120°C for PET and 100°C for PP. The

amount of solute (CC) loaded in the vessel was 0.20 g (ca. 20% of fabric weight), which

guaranteed a saturated bath during the whole impregnation. Figure 1 shows the CC uptake

curves for PET and PP fabrics as a function of time at a variety of pressures in pure scCO2.

It can be noted that the adsorption equilibrium on the PET fabric was obtained within 4

hours at 25 or 30 MPa, and at about 5 hours at 20 MPa, but the equilibrium was not reached

after 6 hours at 15 MPa. The results obtained at 120°C show that pressure influences the

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impregnation rate of CC into the PET fabric. The solute uptake by PET increased with a rise

in pressure from 15 to 25 MPa, and then decreased at 30 MPa. This may be due to fluid

density and solute solubility. When the pressure rose to 25 MPa, scCO2 density was increased

and it facilitated the penetration of CC to the matrix region of PET. Once the pressure

exceeded 25 MPa, the solubility of CC in scCO2 phase became stronger than the polymer

phase, resulting in a CC desorption from polymer phase.

The equilibrium time of CC adsorption by the PP fabric at 100°C was relatively short –

about 2 hours at 20 or 25 MPa. Although the impregnation of CC into PP at 30 MPa was

conducted, data are not shown because the treated sample had a severe shape distortion which

is likely due to a change in the molecular chain. CO2 swelled the PP fabric more at higher

pressure when the temperature was far above its Tg, thus the molecular chain might suffer

distortion in the decompression process.

- 61 -

0 60 120 180 240 300 3600.0

0.2

0.4

0.6

0.8

1.0C

ross

-link

ing

agen

t upt

ake

[wt%

]

Impregnation time [minute]

120°C, 15MPa 120°C, 20MPa 120°C, 25MPa 120°C, 30MPa

(a)

0 30 60 90 120 150 1800.0

0.2

0.4

0.6

Cro

ss-li

nkin

g ag

ent u

ptak

e [w

t%]

Impregnation time [minute]

100°C, 15MPa 100°C, 20MPa 100°C, 25MPa

(b)

Figure 1. Impregnation of CC into a) PET and b) PP fabrics with pure scCO2.

- 62 -

3.3.1.2. Impregnation in scCO2 with co-solvents

In order to improve the solubility of CC in scCO2, and in turn to increase the impregnation

amount of CC into PET and PP fabrics, three co-solvents (3mol% of CO2) – acetone,

dichloromethane and ethyl acetate – were added separately into the supercritical vessel used

in the impregnation experiments. It has been reported that polar solvent participating in scCO2

can enhance the affinity of the fluid by selective interaction with the solute or simply by

changing the polarity of the fluid.28 Three co-solvents chosen here can dissolve CC in ambient

state. Moreover, it was found that CC was also soluble in scCO2 with each co-solvent and

these fluids were clear when they were viewed through the optical windows of the

supercritical vessel. The impregnation of CC into the PET by scCO2 with co-solvent was

performed for 4 hours at 120°C and 25 MPa, while the PP was impregnated with CC for 2

hours at 100°C and 25 MPa. The loading amount of CC was maintained as in the pure scCO2

treatment.

Table 1 shows the CC uptake by the PET and PP fabrics in a variety of fluids. Compared

with the value obtained in pure CO2 treatment, the mass uptakes by PET and PP were

increased in the scCO2-CH2Cl2 and the scCO2-AcOEt fluids. The scCO2-CH2Cl2 treatment

seemed to be more effective, resulting in higher solute adsorption of 1.48wt% in PET and

0.86wt% in PP. It is thought that CH2Cl2 possessed good affinity to CC and CO2, so that much

CC can be carried into the polymer matrix; another possibility is that the presence of CH2Cl2

may increase the swelling of the PET or PP substrate. For the impregnation experiment using

CO2-Acetone, the PET sample was distorted, which is considered as the result of CC reacted

with few -OH of the PET side chain because acetone promoted the activity of the side chain in

scCO2. Thus, CH2Cl2 was judged to be a good modifier to join in the supercritical

impregnation in this study.

- 63 -

Table 1. Solute (CC) uptake by PET (120°C, 25 MPa, 4 hr) and PP (100°C, 25 MPa, 2 hr)

fabrics.

Solvent Pure CO2 CO2-Acetone CO2-Dichloromethane CO2-Ethyl acetate

Mass uptake by PET (wt%) at 120°C

0.85 distorted 1.48 1.03

Mass uptake by PP (wt%) at 100°C

0.54 0.61 0.86 0.69

After the co-solvent was confirmed, the optimization of impregnation on the influence of

temperature in scCO2-CH2Cl2 was investigated at three levels of pressure (15, 20 and 25

MPa). It is known that the temperature needs to exceed the Tg of the material29, 30 for fiber

swelling in scCO2. In the present study, the two initial temperatures (80 and 60°C) used for

treating PET and PP fabrics were sufficiently higher than their glass transition temperatures,

respectively.

Figure 2 shows CC uptake by PET and PP fabrics as a function of temperature. The

impregnation amount of CC into PET displays a groove at ca. 120°C in the top graph (a). A

possible explanation is that is favorable to swell the polymer matrix and to increase the chain

mobility at higher temperature, but a decrease of fluid density will be combined with solute

solubility. This circumstance may result in a stripping effect, whereby the solute actually

desorbs from the fiber into the solution. As regards the result of the CC-impregnated PP by

scCO2-CH2Cl2, it was found that the sample can be partially molten at 110°C, although some

studies of PP fabric dyeing were performed at this temperature. The effect on the PP fabric at

110°C may be that the modifier CH2Cl2 lowers the melting point of the PP fabric. However,

the value of CC uptake by PP increased with temperature up to ca. 100°C without distortion.

Therefore, 100°C was confirmed as the maximum temperature to impregnate PP in

scCO2-CH2Cl2. Furthermore, the CC absorption by PET or PP is increased from 15 to 25 MPa

at either constant temperature, which is consistent with the case in pure scCO2. Thus, the

optimal conditions for impregnating fabrics with CC by scCO2-CH2Cl2 are 120°C, 25 MPa, 4

hr for PET, and 100°C, 25 MPa, 2 hr for PP.

- 64 -

80 90 100 110 120 1300.3

0.6

0.9

1.2

1.5C

ross

-link

ing

agen

t upt

ake

[wt%

]

Impregnation temperature [°C]

15MPa, 4 hr 20MPa, 4 hr 25MPa, 4 hr

(a)

60 70 80 90 100

0.2

0.4

0.6

0.8

1.0

Cro

ss-li

nkin

g ag

ent u

ptak

e [w

t%]

Impregnation temperature [°C]

15MPa, 2 hr 20MPa, 2 hr 25MPa, 2 hr

(b)

Figure 2. Impregnation of CC into a) PET and b) PP fabrics by scCO2-CH2Cl2.

- 65 -

3.3.2. Biomacromolecules immobilization

The samples obtained by the impregnation treatment in optimal conditions were used to

immobilize biomacromolecules. In order to investigate the reaction of CC situated on the

surface of samples under different stages, some samples were deliberately washed to weigh

after treatment at 30°C for 6 hours. Table 2 shows the immobilization of biomacromolecules

(sericin and chitosan) onto the surface of CC-PET and CC-PP fabrics after different

treatments.

For the CC-PET sample, the immobilization amount increased after the whole treatment

when it was compared with treatment at 30°C, and the values of sericin immobilization are

always higher than those of chitosan immobilization. However, for the CC-PP sample, there

was a decrease in the immobilization amount after the whole treatment when it was compared

with treatment at 30°C. This decrease of immobilization amount after treatment at 70°C could

be due to some CC penetrated on the PP surface generating a desorb phenomenon due to the

medium's temperature being excessively over the Tg of the PP fabric. In addition, the reaction

at 70°C did not geminate the immobilization amount on CC-PET. This may be due to the H2O

in the finishing solution which participated in the tri-substitution reaction with CC at high

temperature. The reaction of CC with H2O should also be included in the second step of the

process in immobilizing biomacromolecules onto the CC-PP sample. The immobilization of

sericin onto CC-PET or CC-PP is higher than the value of chitosan immobilization onto these

CC-fabircs. This is accounted for by the reaction of CC with chitosan in which amine groups

are fewer than those in sericin. Another explanation may be that an alkaline system is more

suitable than an acidic system during the process of nucleophilic substitution (deacidification

reaction). The biomacromolecules-immobilized CC-PET and CC-PP fabrics after the whole

finishing treatment were then characterized.

- 66 -

Table 2. Immobilization amount of biomacromolecules (sericin or chitosan) onto CC-PET

and CC-PP fabrics.

Samples

Immobilization amount after the

treatment at 30°C

Immobilization amount after the

whole treatment

Sericin solution Chitosan solution Sericin solution Chitosan solution

CC-PET 0.47 0.38 0.58 0.46

CC-PP 0.38 0.30 0.24 0.19

3.3.3. XPS spectra analysis

Surface chemical characterization of the untreated and modified fabrics (PET and PP) was

investigated by XPS measurement. The wide scan spectra of XPS are shown in Figure 3 for

the PET fabric and in Figure 4 for the PP fabric. After the impregnation of CC into PET and

PP fabrics in scCO2-CH2Cl2 fluid, new peaks appeared at 197.2, 268.2 and 399.2 eV, and

were assigned to Cl2p, Cl2s and N1s. This is confirmed that the CC impregnated can be bared

on the surfaces of the PET and PP fabrics. From the disappearance of Cl2p and Cl2s in the

CC-PP or CC-PET samples finished by sericin or chitosan solution, it is indicated that CC

bared onto the surface of fabric has taken part in some reactions. For the CC-PET samples

finished by macromolecules (sericin or chitosan), the increase in N1s shows that CC

impregnated on the surface of PET engaged in the reaction with sericin and chitosan,

respectively. Correspondingly, an increase of N1s in spectra of sericin-CC-PP is also an

evidence of the reaction of sericin with CC settleed on the surface of the PP sample. The

intensity of N1s in chitosan-CC-PET showed no obvious change, which was due to the result

of CC desorption from the CC-PP sample in the higher temperature aqueous system (as

mentioned in Section 3.3.2), even though some chitosan is linked on the PP surface. The

intensity of O1s in spectra of sericin-CC-PP and chitosan-CC-PP clearly increased, but this

result may be include the instance that H2O participating in the reaction with CC penetrated

on the surface of the PP sample. Aside, the O1s peak in the untreated PP spectrum was

accounted for by the influence of surface contamination.

- 67 -

500 400 300 2000

5000

10000

15000

20000

25000

Cl2p

O1s

Inte

nsity

[a. u

.]

Binding energy [eV]

Sericin-CC-PET Chitosan-CC-PET CC-PET Original PET

N1s

C1s

Cl2s

Figure 3. XPS spectra of untreated and finished PET fabrics.

500 400 300 2000

5000

10000

15000

Inte

nsity

[a. u

.]

Binding energy [eV]

Cl2s

Sericin-CC-PP Chitosan-CC-PP CC-PP Original PP

O1sN1s

C1s

Cl2p

Figure 4. XPS spectra of untreated and finished PP fabrics.

- 68 -

3.3.4. FT-IR spectra analysis

To analyze the impregnation CC into fabrics, the infrared spectrum of the cross-linking

agent was measured and is shown in Figure 5. Three clear groups of absorption peaks,

centered at 1497, 1270 and 850 cm-1, were assigned to the C=N, C-N and C-Cl stretching

vibration modes in heterocyclic rings, respectively. Here, the C=N stretching is shifted to

lower frequency from common region (1500-1600 cm-1) and was explained by a resonance

phenomenon occurring at the bond of C=N and C-N within the ring benzenoid-like

structure.31

2400 2000 1600 1200 8000.0

0.5

1.0

1.5

N

N

N

Cl

ClCl

Abs

orba

nce

Wavenumber [cm-1]

Cyanuric chloride

1497.45

1270.86 850.45

Figure 5. FT-IR spectrum of cyanuric chloride.

ATR-IR spectra of several PET fabrics are shown in Figure 6. After the impregnation of

CC into PET with scCO2, the characteristic peaks of CC at 870 cm-1 and 1500 cm-1 can be

noted; simultaneously, a shoulder appeared at the left side of -C(=O)-O band (1245 cm-1),

which was attributed to the effect of C-N stretching vibration of CC in the surface of PET.

When the immobilization of biomolecules onto CC-PET finished, the broad heave of

chitosan-CC-PET and sericin-CC-PET at 3300-3500 cm-1 was considered as the hydrogen

bonding of hydroxyl and amine groups. Some weak peaks at ca. 1640 cm-1 might be the

amide groups of biomacromolecules. For the spectra of chitosan-CC-PET, a protrudent

shoulder at the right of 1090 cm-1 should be the -C-O-C- peak of chitosan. Furthermore, a

- 69 -

decrease of C-Cl intensity at 850 cm-1 was very clear in the spectra of chitosan-CC-PET and

sericin-CC-PET. These changes suggest that CC was impregnated into PET successfully and

the Cl atoms of CC impregnated onto the PET surface were substituted by biomacromolecules

in aqueous processing.

3500 30000.0

0.1

0.2

0.3

0.4

Abs

orba

nce

Wavenumber [cm-1]

Sericin-CC-PET Chitosan-CC-PET CC-PET Original PET

a)1800 1600 1400 1200 1000 800

0.0

0.1

0.2

0.3

0.4

0.5

Abso

rban

ce

Wavenumber [cm-1]

Sericin-CC-PET Chitosan-CC-PET CC-PET Original PET

b)

Figure 6. Comparison of ATR-IR spectra of various PET fabrics.

Figure 7 shows the spectra of untreated and modified PP fabrics. Compared with the

spectrum of original PP, the CC-PP sample displayed absorption bands at around 1500, 1272

and 850 cm-1, corresponding to the characteristic peaks of CC, whereas these characteristic

peaks decreased greatly in the spectra of chitosan-CC-PP and sericin-CC-PP fabrics. This

decrease of peaks may imply that some CC was disengaged after the process of

biomacromolecules immobilization in the hot aqueous system. Furthermore, there are no

obvious changes observable in the hydroxyl and amine stretching regions around 3300-3500

cm-1 in the spectra of CC-PP fabrics finished by sericin or chitosan. From these effects, one

can conclude that although PP fabric can be impregnated with CC by scCO2, the

immobilization of sericin or chitosan onto CC-PP in an aqueous medium (temperature over

the Tg of PP) is much smaller than is the case with the CC-PET fabric.

- 70 -

1600 1400 1200 1000 8000.00

0.02

0.04

0.06

0.08A

bsor

banc

e

Wavenumber [cm-1]

Sericin-CC-PP Chitosan-CC-PP CC-PP Original PP

a)

3500 3250 3000 27500.00

0.03

0.06

0.09

0.12

Abs

orba

nce

Wavenumber [cm-1]

Sericin-CC-PP Chitosan-CC-PP CC-PP Original PP

b)

Figure 7. Comparison of ATR-IR spectra of various PP fabrics.

- 71 -

3.3.5. Surface morphology

SEM images were examined in order to understand the alteration of the untreated,

CC-impregnated and functional macromolecules-immobilized fabrics of PET and PP. The

results are shown in Figure 8 and Figure 9. As can be seen in Figure 8(a) and Figure 9(a),

the untreated PET and PP fabrics had smooth surfaces, which generally had a poor ability to

attach biomolecules or to capture water. The CC-impregnated PET and PP samples exhibited

micro-roughness on their surfaces. After immobilization treatment, some particles were

distributed on the surface of the PET and PP fabrics, indicating that the rough surface

endowed by sericin or chitosan may provide more capacities for the fabrics to capture water

and also to facilitate the penetration of water into these fabrics. The fact that the

micro-roughness of the biomolecule-CC-PP was smaller than that of the

biomolecule-CC-PET can be attributed to the lower immobilization amount. In addition, no

change in the appearance of the SEM images was observed in PET or PP fabrics before and

after treatment in scCO2-CH2Cl2 without the cross-linking agent of CC (Figure 10).

- 72 -

Figure 8. SEM images of a) untreated PET, b) CC-PET, c) Sericin-CC-PET and d)

Chitosan-CC-PET fabrics.

- 73 -

Figure 9. SEM images of a) untreated PP, b) CC-PP, c) Sericin-CC-PP and d)

Chitosan-CC-PP fabrics

- 74 -

Figure 10. Comparison of SEM images of PET and PP fabrics before and after treatment

in scCO2-CH2Cl2 without the cross-linking agent of CC.

3.3.6. Hydrophilicity characterization

3.3.6.1. Water contact angles

The surface wettability of several PET and PP samples was evaluated by measuring the

static contact angle of water droplet on each fabric's surface. Table 3 gives the contact angles

recorded. Compared with the original fabric, several of the modified fabrics showed an

evident decrease in contact angle, which means that the surface wettability of the PET fabric

has improved to a certain extent. Although CC is insoluble in water at low temperatures, the

CC-impregnated PET and PP samples also displayed a decrease in contact angle, which may

be caused by the increase in surface roughness of those finished fabrics. Sericin-treated

CC-PET and CC-PP fabrics showed smaller contact angles than chitosan-treated samples,

which is due to the immobilization amount of sericin being more than that of chitosan.

- 75 -

Another explanation might be that the hydrophilicity of sericin is inherently stronger than that

of chitosan. Generally, the water contact angles of PET fabrics are smaller than those of PP

fabrics because small hydrophile groups such as hydroxyl existed in PET fabric.

Table 3. Static water contact angles of untreated and modified PET and PP fabrics.

PET samples Static water contact angle, θ (o) PP samples

Untreated PET 102.6 132.2 Untreated PP

CC-PET 94.5 121.4 CC-PP

Sericin-CC-PET 78 112.7 Sericin-CC-PP

Chitosan-CC-PET 82.4 117.8 Chitosan-CC-PP

3.3.6.2. Wicking properties

Testing wicking properties is a conventional method to evaluate the water imbibition

ability of a fabric. The higher the height of the water climbed, the better the wickability of the

fabric. The wicking heights on the PET samples are shown in Table 4. It can be seen that the

wicking heights of untreated and CC-impregnated PET were very low because of their

hydrophobicity, but the value greatly increased after the CC-PET sample was finished by

sericin or chitosan. This behavior is consistent with the results obtained for the static water

contact angles on these PET fabrics (see Section 3.3.6.1). A conclusion that sericin and

chitosan linked on a CC-PET surface has improved the hydrophilicity of the PET fabric can

be obtained.

For the PP samples, the water boundary did not rise, with the slight exception of the

sericin-CC-PP which had a small change (less than 2mm/8min). Thus, the improvement of

hydrophilicity in the PP fabric was not as successful as in the PET fabric.

- 76 -

Table 4. Wicking heights of untreated and modified PET fabrics.

Samples Untreated PET CC-PET Sericin-CC-PET Chitosan-CC-PET

Wicking height (mm) 10 13 42 28

3.4. Summary

The active-linker agent of CC can be introduced into PET and PP fabrics by the

impregnation method in scCO2 to couple biomacromolecules (sericin or chitosan).

Dichloromethane is recognized as an effective co-solvent that boosts the solubility of CC in

scCO2 and further increases the impregnation amount of CC into fabrics of PET and PP. The

optimal conditions for impregnation are localized at 120°C, 25 MPa, 4 hr for PET, and 100°C,

25 MPa, 2 hr for PP. During the process of immobilizing sericin or chitosan onto CC-PET and

CC-PP, the tri-substitution reaction at 70°C is not favorable to the CC-PP sample because of

the decrease of immobilization amount.

Chemical analysis reveals that sericin or chitosan can react with CC impregnated on the

surface of PET and PP fabrics more or less. The SEM images of modified samples show an

increase in the micro-roughness of the fabric surface. Water contact angles and wicking

heights conclude that the hydrophilic properties of PET fabrics are improved effectively after

the whole treatment described in this study.

- 77 -

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Chapter 4. Modifying poly(ethylene terephthalate) fabric by supercritical carbon dioxide

4.1. Introduction

In the textile industry, poly(ethylene terephthalate) (PET), has been an important class of

fibers ever since it was first created in 1946.1 Its basic properties satisfy the highest

requirements, such as excellent mechanical properties, weather resistance, and so on;

moreover, its production cost is low. But then, the PET fabric has also some drawbacks

including weak hydrophilicity and poor biocompatibility, due to the lack of active side chain

as well as rare active binding on organic backbone. In order to create cloth in conformity with

the health safety requirements of the living human body, such as somewhat complicated

processes are conventionally adopted to add value to PET in textile finishing, involving

co-spinning,2 physical coating,3, 4 plasma discharge,5, 6 alkaline treatment,7, 8 graft

polymerization,9, 10 etc. Nevertheless, some of these methods have limited practical use, and

frequently lead to the hardening of the PET material, elevated production costs and

complicated work procedures. Accordingly, there is a demand for a finishing technology that

can be applied to PET fabric more easily and efficiently.

Recently, the use of scCO2 fluid in polymer processing has had a marked effect on

dyeing,11-13 expanding foam,14 plating,15 impregnation,16-18 etc. ScCO2 (Tc = 31°C, Pc = 73.8

bar) is one of the most commonly used supercritical fluids. It is naturally abundant,

chemically inert, non-flammable, essentially non-toxic, easy to handle, and the least

expensive solvent after water.19 Moreover, scCO2 is a good solvent for many non-polar (and

some polar) low-molecular-weight compounds,20, 21 and a few polymers are also known to

have good solubility in scCO2;22 however, it is generally a very poor solvent for

high-molecular-weight polymers under readily achievable conditions, because of its very low

dielectric constant, ε, its low polarizability per volume, α/ν, and its reluctance to engage in

van der Waals interactions. Although scCO2 is a poor solvent for most polymers, it does have

the capability to swell polymers up to several mass percentages;23, 24 thus, a

low-molecular-weight agent dissolved in scCO2 can diffuse into the polymer phase, achieving

- 81 -

the modification of that polymer.25 The swelling of a polymer occurs only in its amorphous

phase, and depends on the interaction of the supercritical fluid with the polymer and on the

crystallinity of the polymer. The higher the crystallinity, the more difficult it is to swell the

polymer.26 The degree of swelling of the polymeric matrix can be modulated by adjusting the

pressure and temperature, and the mass transfer of agents within the polymer can also be

controlled in the same way.27 In addition, a co-solvent participating in scCO2-polymer

processing can also increase the solute uptake in polymer, which attributed mainly to the

solubility improvement of solute in scCO2.28

In the field of polymer fabric modification, sericin,4 , 29, 30 collagen,31, 32 and chitosan33, 34

are known as top natural functional agents; they have been applied widely to improve the

hydrophilicity and biocompatibility of polymer fabric. If these agents can be impregnated into

PET fabric, they can impart desirable properties to the PET. However, this is conventionally

impossible due to the higher molecular weight of these functional agents. In order to modify

PET fabric with these natural macromolecules, on the basis of use of scCO2 fluid in polymer

processing, a type of epoxy compound, GPE35, 36 is chosen in our present study as a

cross-linking agent which will be impregnated into PET fabric with the help of scCO2 to

attach functional macromolecules. As far as we know, there are not other conventional

techniques which can achieve the same result in impregnation of cross-linking agents into

pre-existing polymer without changing their inherent properties but the method of solid-state

foaming or swelling with CO2 as a gas blowing agent.37, 14 This project will be a simple, low

cost and environmentally benign process together with a firm penetration of GPE into

amorphous region of PET fabric. This epoxy compound is chosen here, because the epoxy

group existing at the end of the chain is bared on the surface of the PET fabric and acts as a

reactive site for functional nucleophilic reagents, including proteins, polysaccharides, nucleic

acids, and various small molecules.38

Based on the above considerations, we tried to modify the surface of PET fabric with

natural functional agents (sericin, collagen or chitosan). In this study, the impregnation of

GPE into PET fabric was investigated under various supercritical conditions, in pure CO2 as

well as in CO2 with a co-solvent, by measuring the mass uptake. The surface immobilization

- 82 -

sericin, collagen or chitosan on GPE-PET fabric was conducted by the solution method and

by the Pad-Dry-Cure method.

4.2. Experimental procedures

4.2.1. Materials and reagents

The fully oriented yarn poly(ethylene terephthalate) (PET) fabric (warp/weft, 78T/216; 90

g/m2) used as the substrate for modification in this study was supplied by Toyobo Co., Ltd.

First, the PET fabric was washed and stabilized by immersing it in acetone at 30°C for 30

minutes. The epoxy compound used as a cross-linking agent and impregnated to the PET

fabric with the help of scCO2 was glycerol polyglycidyl ether (GPE, Denacol EX-313, Mw:

ca. 250), which was supplied by Nagase Chemtex Co. without further purification; its main

components have the structural formulas shown in Figure 1. Three natural functional regents,

sericin (SERICIN POWDER, Mw: ca. 17,000), collagen (MARINE COLLAGEN CF, Mw:

ca. 1,000) and chitosan (low-molecular-weight) were used as hydrophilic agents together with

antimicrobial material for immobilization onto the surface of the PET fabric; the former two

were supplied by Seiren Co., Ltd. and Chisso Co., Ltd., respectively, and the third was

purchased from Sigma-Aldrich, Inc. Sodium hydroxide (NaOH) and sodium tetraborate

decahydrate (Na2B4O7･10H2O), used for modulating the pH of the functional solutions, were

purchased from Nacalai Tesque, Inc. All the functional reagent solutions were prepared with

distilled water. The carbon dioxide used in all of the experiments was purchased from Uno

Sanso Co., Ltd. (99.5% pure). Several organic solvents (acetone, ethyl acetate, chloroform

and isopropyl alcohol) were guaranteed-grade reagents obtained from Wako Pure Chemical

Industries, Ltd.

- 83 -

OH2CH2C

HC

HC

CH2

OH

H2C

O

OH2C

HC O

H2C

HC CH2

OCl

OH2CH2C

HC

HC

CH2

O

H2C

O

OH2C

H2C

HC CH2

OHC O

H2C

HC CH2

OCl

OH2CH2C

HC

HC

CH2

OH

H2C

O

OH2CH2C

HC

HC

CH2

O

H2C

O

OH2C

HC CH2

O

H2C

HC CH2

O

(ca. 42mol%) (ca. 14mol%)

(ca. 4mol%)(ca. 39mol%)

OH2C

HC CH2

O

Figure 1. Structural formulas of glycerol polyglycidyl ether (GPE, Denacol EX-313).

4.2.2. Methods

The whole process of PET fabric treatment, including the impregnation of the crosslinking

agents and surface immobilization of the functional agents, is shown schematically in Figure

2. The details of each sub-process are described below.

4.2.2.1. Impregnation of GPE into PET by scCO2

The apparatus for the preparation of the GPE-PET composite consisted of a 50-mL

stainless steel vessel (Tmax=200°C, Pmax=30 MPa), a magnetic stirrer, a constant-temperature

air bath (Model SCF-Sro, JASCO Co., Tokyo), a thermocouple and a pressure gauge. It is a

batch system operating in three main steps: charge, impregnation and discharge. CO2 is stored

in a cylinder and pressurized to working pressure by a pump. The PET fabric substrate (10

cm×12 cm, ca. 1.10 g) was suspended on a stainless steel net inside the vessel, and the

cross-linking agent (0.20 g) was placed on the bottom of the vessel. The quantity of

cross-linking agent was in large excess of the amount required to saturate the CO2 during the

entire course of impregnation into the PET fabric. When the autoclave reached the desired

temperature, CO2 was let in slowly (ca. 5 mL/min) and isothermally compressed to working

- 84 -

pressure; then, the system was agitated for a certain period of time to impregnate the GPE into

the PET fabric. After the impregnation, the system was depressurized at 0.5 MPa/min and

allowed to cool to room temperature in air. The same experiment was performed using a batch

program with the addition to CO2 of 4% modifier (acetone, ethyl acetate or chloroform).

Afterward, the sample was flushed with air and washed with distilled water at room

temperature in order to remove the cross-linking agent adhered on the surface. Finally, the

impregnated sample was dried in an oven at 50°C.

Cross-linking Agents (GPE)

Supercritical CO2

O

O

H2C

OH

H2C

OH

HN MacromoleculeH2N Macromolecule

(Sericin, Collagen, Chitosan) HN Macromolecule

Aqueous solution/Pad-Dry-Cure

PET Fabric GPE-impregnated PET Fabric

Functional Agents-immobilized PET Fabricl

Figure 2. Schematic illustration of the entire process of PET fabric modification.

4.2.2.2. Immobilization of functional agents onto PET fabrics

The immobilization of natural functional agents onto GPE-PET fabric was performed in

two ways: processing in an aqueous solution, and processing by the Pad-Dry-Cure method.

The mechanism of immobilization relies on the GPE epoxy compound impregnated on the

surface of fabric, which can graft the functional agents by the ring-opening reaction of the

epoxy groups. In addition, the original PET fabric was also treated with the two methods to

- 85 -

anchor functional agents.

4.2.2.2.1. Processing in an aqueous solution

For the immobilization of sericin or collagen, 3wt% finishing solutions were prepared and

the pH of the solutions was adjusted to 10~11 with Na2B4O7･10H2O so that the amines

became unprotonated.35, 38 Then, the sample was immersed in sericin or collagen solution and

shaken for 1 week at room temperature. It has been reported that dermal sheep collagen can

be cross-linked by epoxy compound at mild condition for a long time.39 In the case of

chitosan, it was first added to a 30wt% NaOH aqueous solution, stirred for 2 h and placed in a

refrigerator; the lyophilized mixture was then thawed and filtered with isopropyl alcohol to

prepare the chitosan solution.40 Then, the fabric was immersed in the solution under stirring

for 16 h at 50°C. At the end of the immobilization, the fabrics were taken out, squeezed and

air-dried. The finished fabric samples were then rinsed with water and finally dried again at

50°C in vacuum and conditioned prior to testing.

4.2.2.2.2. The pad-dry-cure treatment

Padding is a well-known technique for treating textile materials. The textile is padded into

a chemical solution, followed by a squeezing using two pad rolls to remove the excess liquid

trapped in the textile. The finishing solutions were prepared as mentioned above in Section of

processing in an aqueous solution. The amount of functional agent (sericin, collagen or

chitosan) in the solution was in large excess of the cross-linking agent on the surface of the

PET fabric. The fabric samples were padded by the two-dip-two-nip process to about 90%

wet pickup with freshly prepared aqueous solutions of each of these functional agents. After

treatment, the padded fabrics were dried at 85°C for 3 min, cured at 150°C for 3 min, washed

thoroughly, and finally dried.

4.2.3. Characterizations

The absorption of the cross-linking agent into the PET fabric using supercritical CO2 was

determined gravimetrically and is expressed as a percentage of impregnation, according to

- 86 -

equation (1):

G impregnation (%) = (P1 – P0) / P0 × 100 (1)

where P0 and P1 are the weight (g) of untreated PET fabric and impregnated PET fabric,

respectively. The immobilization ratio of functional agents onto GPE-PET fabric is defined

by equation (2):

G immobilization (%) = (P2 – P1) / P1 × 100 (2)

where P2 represents the weight of the GPE-PET fabric finished with the functional agent.

Analysis was performed using a photoelectron spectrometer (JPS-9010MCY) with Mg Kα

excitation radiation (1,253.6 eV). The X-ray source was run at a potential of 10 kV, a current

of 10 mA and an incident angle of 45°. The pressure within the XPS chamber was maintained

at 10-7 Pa during the measurement. The binding energy of carbon 1s was fixed to 285 eV and

was used as the internal reference for the binding energy scale. The depth profiling of the

samples was performed with argon ion sputtering (1kV, 8 mA) at an incident angle of 90° for

15 second. Deconvolution analysis of the peaks was carried out using the

Gaussian-Lorentzian component profile in the Peakfit○R software.

The FT-IR spectrum of the cross-linking agents (GPE) was obtained using a

Fourier-Transform Infrared Spectroscope (FT/IR-4100, JASCO), by the usual method of

making pellets (ca. 0.5% w/w) with potassium bromide (KBr), where a total of 32 scans were

accumulated at a resolution of 4 cm-1. All spectra of the fabrics were collected at a resolution

of 4 cm-1 and 200 scans using the same instrument with a 45° ZnSe prism (n = 5) as the

internal reflection element wafer set in a single ATR accessory.

Elemental analysis of the functional agents (sericin, collagen or chitosan) and several

types of PET fabrics was carried out to precisely determine the amount of nitrogen, the

analysis was carried out on an elemental analyzer (EA 1110-W) using the classical technique

of combustion analysis. In this technique, the sample is burned in an excess of oxygen, and

various traps collect the combustion products — carbon dioxide, water and nitric oxide. The

weights of these combustion products can be used to calculate the composition of the sample.

Before measurement, each sample was ground to crumb and dried at 100°C for 24 h, after

which it was analyzed to measure the organic content.

- 87 -

Dynamic water contact angle used to evaluate surface wettability of the PET fabric was

measured in a room condition (20°C) by the sessile droplet method using a Contact Angle

Measuring Instrument EasyDrop (RÜSS DSA20). A distilled water droplet of 3-μL was

placed on the sample surface and a picture of the droplet was taken within 5 s. A new water

droplet of 3-μL was added to the sample surface every 15 s and the procedure was repeated 5

times (total 18μL) for each advancing step. Then 3-μL water was retracted every 15 s for each

receding step. The receding procedure was stopped until the surface water droplet disappeared

in camera image.

The moisturization of the PET fabric was measured in a humidity chamber (IH400,

Yamato) in which a weight meter was installed. For the measurement of the isothermal

hygroscopicity, the samples were weighed after the given environmental condition was

maintained for 2 hours. In the experiment for the hygroscopicity/dehygroscopicity, the sample

was weighed for a random period of time under two environmental conditions (25°C, 65%

RH; 30°C, 95% RH). Moisture regain is defined by equation (3), in which Wm is the weight

(g) of the moisturized sample, and Wd is the weight (g) of the sample dried in an oven (100°C,

2 h):

Moisture regain (%) = (Wm – Wd) / Wd ×100 (3)

The antimicrobial assessment of the PET fabric was made through the quantitative method

of microbe absorption proposed by the Japan Spinners Inspection Foundation. The microbe

used here was Staphylococcus aureus (S. aureus), a Gram-positive bacterium, which usually

exists in human nose or skin and often causes an infection on the skin as lesions, pimples or

boils, even brings pneumonia if the infection got worse. All of the samples were incubated for

18 h at 37°C before the bacterial colonies were counted. The antimicrobial effects of the

specimens are evaluated, as a rule, based on the bacteriostatic and bactericidal activities. The

bacteriostatic and bactericidal activities were calculated as follows:

Bactericidal activity = log A – log C

Bacteriostatic activity = log B – log C

where A, B, and C are the number of bacteria in the initial inoculation, the number of colonies

on an incubated piece of control calico, and the number of survivors on the untreated and the

- 88 -

modified PET fabrics after incubation, respectively.

4.3. Results and discussion

4.3.1. Supercritical treatment of PET fabric

ScCO2 can swell PET fiber, and the temperature usually has to reach 80°C in order to

exceed the Tg of PET.23 ScCO2 can also dissolve a wide range of compounds, including epoxy

compounds.41 Here, the solubility of the cross-linking agent GPE in scCO2 was evaluated by

using a stainless steel vessel with transparent windows. In the experimental conditions of the

present study, the fluid had optical uniformity in pure scCO2, but it became clearer in the

presence of a co-solvent such as acetone, ethyl acetate or chloroform. This indicates that these

co-solvents can enhance the solubility of GPE in scCO2. The reason why small amounts

(typically < 5%) of a polar co-solvent as a modifier added to scCO2 increases the solvating

power of CO2 is that the affinity between the solute and fluid is improved.41, 42

To optimize the process of impregnation in the case of pure scCO2, a study on the

absorption of the cross-linking agent by the PET fabric at different temperatures (80, 100 and

120°C) and pressures (10~30 MPa) was carried out. It has been reported that the conventional

dyeing time for PET fiber in scCO2 is 30-120 min.11, 12 With regard to the swelling of PET

fiber in CO2, K. Hirogaki et al. have described that the swelling behavior reached a maximum

after 2 h.24 Therewith, a time period of 2 h was adopted here to impregnate the PET fabric

with cross-linking agents in scCO2. Figure 3 shows the influence of pressure on the uptake of

the cross-linking agent by the fabric at the three temperatures.

- 89 -

10 15 20 25 300.0

0.5

1.0

1.5

2.0

Cro

ss-li

nkin

g ag

ents

Upt

ake

[wt%

]

Pressure [MPa]

120 ° C 100 ° C 80 ° C

Figure 3. Impregnation of GPE into PET fabric for 2 h in pure scCO2.

The results show that the uptake of the cross-linking agent by the PET fabric increased

initially as the pressure increased up to 25 MPa, but fell at pressures higher than 25 MPa,

particularly at higher temperatures. Similar results were obtained when using scCO2 modified

with chloroform. The main reason may be for this explanation that partitioning of GPE in the

fluid phase is enhanced. First, CO2 readily swells PET at higher pressures; however, it is also

a much better solvent for cross-linking agents, and this tendency was reinforced at higher

temperatures considered as the cause of the decreased fluid density.

In addition, we found that the equilibrium concentration in the fabric is much more

sensitive to temperature than to pressure, and that is more profitable to implement the process

at a higher temperature. The temperature influences the uptake of the cross-linking agent

because it affects the polymer matrix. Above the temperature of the glass transition, the free

volume of the polymeric matrix and the chain mobility is increased, and this results in a

higher PET infiltration concentration. Nevertheless, at higher temperatures, certain addition

reactions, including the self-polymerization of the epoxy groups,43 the formation of vinylene

carbonate44 and the carboxylic-acid end-group modification of PET with the epoxy groups

- 90 -

may occur.26 Thus, the maximum temperature for controlled scCO2 treatment was set at

120°C in this study.

To increase the content of the cross-linking agent absorbed by the PET fabric in scCO2,

three co-solvents (4% mol/mol), acetone, ethyl acetate and chloroform, were added to CO2 for

impregnation, respectively, at 120°C and 25 MPa for 2 h. Although alcohols are good

modifiers which can enhance the swelling of PET fiber in scCO2,24 they cannot be used

because epoxy compounds react with alcohols. The results for the uptake of the cross-linking

agent in supercritical CO2 with a co-solvent are shown in Table 1.

Table 1. Mass uptake of the cross-linking agent by the PET fabric in supercritical fluid

at 120°C, 25 MPa for 2h.

Solvent Pure CO2 CO2-Acetone CO2-Ethyl acetate CO2-Chloroform

Mass uptake (wt%) 1.62 2.14 2.47 3.26

In contrast with the sorption of the cross-linking agent into PET fabric treated with pure

scCO2, the sorption increased when the co-solvent entered the supercritical fluid. Chloroform

was more effective than the other two co-solvents examined, owing to its lower dielectric

constant. The uptake of the cross-linking agent by PET as a function of pressure was also

compared in scCO2 with and without CHCl3 at 120°C. The data are shown in Figure 4; the

results were similar, but the uptake tended to decline more strongly in the presence of

chloroform than in pure CO2 over 25 MPa. This is considered that chloroform enhanced the

solubility of GPE in fluid phase more significantly with pressure at the higher pressure.

Another reason may be based on H-bonding interactions between the cross-linking agents and

the polymer matrix.45 While more cross-linking agents penetrated into PET with

scCO2-CHCl3 at higher pressure, H-bonding may form by the OH-functional group of GPE

with the carbonyl group in PET matrix, this bond will introduce more hindrance in polymer

matrix, and thus slow down any further diffusion of GPE into PET fabric. Although the

- 91 -

uptake of GPE into PET decreased at higher pressure, the incorporation of GPE into the PET

fabric was almost twice the value in pure scCO2 for the solubility improvement of GPE or the

enhancement on swelling ability of PET in scCO2-CHCl3.

10 15 20 25 300.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Cro

ss-li

nkin

g ag

ents

Upt

ake

[wt%

]

Pressure [MPa]

scCO2 - CHCl3

Pure scCO2

Figure 4. Comparison of the uptake of the cross-linking agents by the PET fabric in pure

scCO2 and scCO2-CHCl3 (4% mol/mol) at 120°C for 2 h.

Information concerning the manner in which the cross-linking agent was impregnated into

the PET with the scCO2-CHCl3 treatment can be obtained from the XPS signals shown in

Figure 5. It can be seen that the XPS spectrum of original PET mainly contains carbon (C) 1s

and oxygen (O) 1s peaks. After the scCO2-CHCl3 treatment of PET fabric with GPE, new

peaks appeared at 199.8 eV and 269 eV, which were attributed to chlorine (Cl) (2p and 2s)

electrons, regardless of the implementation of argon (Ar) ion etching. These results suggest

that the cross-linking agent (at least the chlorine-containing compounds) was impregnated

into the PET fabric by scCO2. After Ar ion etching of GPE-impregnated PET, the content of

C1s increased markedly and the peak of O1s decreased in height, indicating that the depth

profiling of PET removed its surface contaminants (hydrocarbon) and oxides at the same time.

It was also noted that the surface N1s peak disappeared completely.

- 92 -

500 400 300 2000

10000

20000

30000 GPE-PET with Ar ion etching

GPE-PET without Ar ion etching

Original PET without Ar ion etching

Inte

nsity

(a. u

.)

Binding energy (eV)

O1s

N1s

C1s

Cl 2pCl 2s

Figure 5. Changes in the surface elements on the PET substrate and the GPE-PET fabric

obtained in scCO2-CHCl3 with/without argon ion sputtering.

In order to analyze the surface of original PET and GPE-PET fabric, deconvolution

analysis of the C1s peak in the XPS spectra was carried out, as shown in Figure 6. The C1s

signal of original PET contained three separate peaks at 284.9 eV, 286.6 eV and 288.7 eV,

which were assigned to the functional groups of C-C, C-O and O-C=O, respectively. In the

XPS signal of GPE-PET (Figure 6b), a fourth peak appeared around 286.3 eV, attributable to

the epoxy carbon atoms. Moreover, an increase of the C-O band peaking at 286.6 eV was

observed relative to the spectra for the original PET fabric. These data further confirm that the

cross-linking agent was impregnated into the PET fabric by means of scCO2.

- 93 -

290 288 286 284 282

n* OCH2CH2OC

OCO

*

-C(=O)−C-

-C−O-

-C−C-

Binding energy [eV]

a)

Original PET

290 288 286 284 282

GPE-PET

-C(=O)−C-

-C−O-

-C−C-

Binding energy [eV]

-C−C-O

b)

Figure 6. Deconvolution of the C1s peak in the XPS spectra of PET recorded for a) original

PET fabric and b) GPE-PET fabric obtained in scCO2-CHCl3.

- 94 -

FT-IR spectra were subsequently used to characterize the chemical structure of the

cross-linking agent. Figure 7 shows the spectrum for GPE: 3416 cm-1 (O-H stretching and

O-H…O-H hydrogen bonding); 3050 and 2990 cm-1 (CH2 of the epoxy ring); 2920-2880 cm-1

(CH3, CH2); 1465 cm-1 (CH2 bending); 1342 cm-1 (O-H bending); 1256 cm-1 (symmetrical

stretching of the epoxy ring); 1080-1125 cm-1 (C-O stretching); 950-810 cm-1 (asymmetrical

stretching of the epoxy ring); 754 cm-1 (C-Cl stretching).

3500 3000 2500 2000 1500 10000.0

0.5

1.0

1.5

2.0

2.5

3.0

Abs

orba

nce

Wavenumber [cm-1]

GPE (Cross-linking agents)

Figure 7. FT-IR spectrum of the cross-linking agents (GPE).

The FTIR-ATR spectra of original PET fabric and GPE-PET fabric are shown in Figure 8.

Compared with the original PET spectrum, in the GPE-PET spectrum, a prominent epoxy ring

signal occurred at 847 cm-1, and the absorbance of 2900 cm-1 was attributed to the C-H

stretching which increased with the amount of GPE; furthermore, a new band at a higher

frequency (~3400 cm-1) was discernable, which suggests that a weaker hydrogen-bonding

interaction occurred in O-H…O-H due to the increase in the number of hydroxyl groups in

GPE. Also, the area ratio of C=O band to C-C-O band in GPE-PET spectrum was observed

- 95 -

decreasing versus the ratio of same bands in original PET. This change is due to the influence

of C-O band of GPE impregnated in the fabric.

It was found that the FTIR-ATR spectra of the PET fabric GPE-impregnated with pure

scCO2 was analogous with the spectrum of PET fabric GPE-impregnated with scCO2-CHCl3,

except that the absorbance of some bands decreased markedly. This implies that few GPE

molecules penetrated on the surface of the PET fabric, leading to the small impregnated

amount.

3500 3000 2500 2000 1500 10000.0

0.2

0.4

0.6 OH STR (Alcohol and H-bonding, broad)

C-H STR(Aliphatic groupand epoxy ring)

C-H DEF(Epoxy ring)

Abs

orba

nce

Wavenumber [ cm-1]

PET treated with GPE in scCO2-CHCl3 PET treated with GPE in pure scCO2 Original PET

Figure 8. FTIR/ATR spectra of PET substrate and GPE-PET fabric.

4.3.2. Immobilization of functional agents (sericin, collagen, or chitosan) onto GPE-PET

and original PET fabrics

Samples of GPE-impregnated PET fabric in pure scCO2 and in scCO2-CHCl3 were treated

for the immobilization of functional agents. The results of the immobilization of the three

functional agents onto GPE-PET fabric obtained in scCO2-CHCl3 are shown in Table 2. From

- 96 -

the data, it was concluded that the Pad-Dry-Cure method gives a higher yield than treatment

in an aqueous solution. This indicates that at high temperatures, nucleophilic reagents can

induce the ring-opening of the epoxy groups. Moreover, the low amount of immobilization in

the aqueous solutions might be due to the unstable contact of the functional agents with the

GPE-PET fabric. Collagen was immobilized onto GPE-PET fabric to a higher degree than the

cases of sericin and chitosan, which can be explained for the high-molecular-weight reactant

such as chitosan or sericin, the low-molecular-weight collagen had predominance to access

the epoxy ring bared on the surface of the PET fabric. Regardless of the immobilization

method, i.e., aqueous solution versus pad-dry-cure, there was a small increase of weight, less

than 0.30%, in the GPE-PET fabric obtained in pure scCO2. About the immobilization of

functional agents to the original PET fabric, it was unsuccessful in either immobilization

method, owing to the changeless weight of fabric once the treated sample was washed by

water. Thus, the GPE-PET fabric obtained in scCO2-CHCl3 fluids was elected as the optimal

object for immobilizing functional agents, the pad-dry-cure treatment was also considered as

a better immobilization method to finish GPE-PET fabric with functional agents.

Table 2. Amounts of functional agent immobilized onto GPE-PET fabric and nitrogen

contents of GPE-PET fabric finished with functional agents.

Functional agent Fishing processes Immobilization amount (wt%) Nitrogen content (%)

Sericin

N(%) : 21.1997

Aqueous solution 0.18 0.0365

Pad-Dry-Cure 0.83 0.1739

Collagen

N(%) : 22.7477

Aqueous solution 0.22 0.0474

Pad-Dry-Cure 1.24 0.2791

Chitosan

N(%) : 10.7254

Aqueous solution 0.15 0

Pad-Dry-Cure 0.78 0.0818

- 97 -

GPE-PET fabrics modified with the three functional agents by the Pad-Dry-Cure method

were further investigated by XPS analysis, and wide scan spectra for the identification of the

elements on the PET surface are presented in Figure 9. In contrast with the spectra of

GPE-PET and original PET, there is an obvious N1s peak at 399.5 eV in the spectrum of

GPE-PET fabric modified with each functional agent. This is a convincing qualitative

argument that the functional agents were immobilized on the surface of the GPE-PET fabric.

The order of intensity of the N1s signal was as follows: collagen-GPE-PET >

sericin-GPE-PET > chitosan-GPE-PET; however, the element content obtained from the peak

ratio did not mean the essential value of nitrogen in the fabric because the measurement

belongs to surface analysis. In order to precisely calculate the value, the nitrogen contents of

all the materials were measured by combustion analysis instead of XPS analysis. The values

of N (%) are shown in Table 2; the quantitative order of nitrogen in the PET fabrics modified

with the three functional agents by the combustion method accorded with the intensity order

of N1s in the XPS spectra. The three measured values were almost consistent with the values

calculated from the immobilization amounts and nitrogen contents of the functional agents

(sericin, collagen and chitosan), except when chitosan solution was used for finishing the

GPE-PET fabric. In Figure 9, corresponding to the spectra of GPE-impregnated PET, we also

found that the peak area of Cl2p and Cl2s decreased in the spectra of the three functional PET

fabrics. This was probably due to the fact that the chloride on the GPE-PET surface

participated in the reaction with the functional agents.

- 98 -

600 500 400 300 2000

5000

10000

15000

20000

25000 Original PET GPE-PET Chitosan-GPE-PET Sericin-GPE-PET Collagen-GPE-PET

Inte

nsity

[a. u

.]

Binding energy [eV]

Cl2p

Cl2s

C1s

N1s

O1s

Figure 9. Comparison of the surface chemical elements based on the XPS spectra of the

PET.

The same kinds of samples were also evaluated by FTIR/ATR spectral analysis to

investigate the reaction circumstances of the epoxy groups; unfortunately, the three spectra for

sericin-GPE-PET, collagen-GPE-PET and chitosan-GPE-PET were indiscernible in this

respect, despite these functional agents (sericin, collagen and chitosan) have different

structures and discernible bands of IR spectra. This is due to the case that those discernible

bands are weak usually, and that some discernable bands of the functional agent overlapped

with the band of the PET substrate because of the small immobilization amounts. Figure 10

shows, for comparison, the FT-IR/ATR spectra of GPE-PET and sericin-immobilized

GPE-PET treated by the pad-dry-cure method. A shoulder band occurred at 3300 cm-1 in the

sericin-GPE-PET spectrum, which is characteristic of the amide unit, despite the fact that the

deformation of amide did not appear clearly at 1654 and 1544 cm-1. At the same time, a

remarkable decrease of the bands at 845 cm-1 was observed, indicating that the epoxy groups

bared on the surface of the PET fabric were ring-opened mostly by sericin.

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3500 3000 2500 2000 1500 10000.0

0.1

0.2

0.3

0.4

0.5

0.6A

bsor

banc

e

Wavenumber [cm-1]

Sericin-GPE-PETGPE-PET

Amine absorption

Figure 10. Comparison of the FTIR/ATR spectra of GPE-PET and sericin-immobilized

GPE-PET fabric.

4.3.3. Surface wettability and moisture regain of the original and the modified PET

fabrics

The surface wettability of diversified PET fabrics was evaluated by the contact angle of

water on the fabric surface. For a sample of non-ideal surface such as a tissue or fabric, static

water contact angle always change with the contact time, which is accounted for surface

roughness, surface heterogeneity, penetration of liquid into the surface region etc. Dynamic

contact angle describe the processes at the liquid/solid boundary during the increase in

volume (advancing angle) or decrease in volume (receding angle) of the drop, i.e. during the

wetting and dewetting processes. Thus, dynamic water contact angle was tested as a replace

of static measurement for the advancing contact angle can average negative effect of static

contact angle on the surface heterogeneity and the receding angle can make statements about

the penetration of water or the roughness of solid sample.

The mean values of water contact angles and the retracted volume of water obtained for

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several modified PET fabrics and original PET fabric are presented in Table 3. The samples

of functional agent immobilized GPE-PET fabrics for measurement here were the GPE-PET

fabrics processed with the pad-dry-cure method. It can be seen that, compared with the

original PET fabric, both of the θA and θR of the modified PET fabrics were decreased, and

the decrease of θR was greater than that of θA. Therefore, modification degree impacted θA

slightly, and impacted θR greatly. The decrease in both of θA and θR of the modified PET

fabrics disclosed the improvement in hydrophilicity of these fabrics, which is mainly deduced

that polar functional groups (O-C-O and OH) of cross-linking agents and functional agents

interact with water and the interaction contributes to the decrease of the interfacial free energy

of the fabric surface. The value of receding contact angle basically reflected surface

characterization of polymer reconstruction in water. While the droplet was retracted in the

receding step, surface restructuring minimize the interfacial free energy in water,46 polar

groups of modifiers can be isolated on the surface and θR is decreased greatly resulting in a

greater improvement of surface wettability. Moreover, the decrease of θR here is also affected

by the water imbibition mostly. The water imbibition effect is educed by the retracted volume

of water as the value (18μL-Retracted volume). It can be noted that the GPE-PET fabric held

the strongest water imbibition abilities owing to the least volume of retractile water. The

desirable effects were not achieved because GPE-PET fabric on which functional agents were

immobilized showed some hydrophobicity, unlike simple GPE-PET fabric. This might be due

to hardening caused by the reaction between the epoxy groups of GPE and the amine groups

of the functional agents. The wettability of the PET fabrics increased in the following order:

Original PET < collagen-GPE-PET < sericin-GPE-PET < chitosan-GPE-PET < GPE-PET

Chitosan-GPE-PET showed better wettability than sericin-GPE-PET and

collagen-GPE-PET may be the reason fewer amine groups participated in the reaction with

the epoxide in chitosan, as compared with sericin or collagen. The fact that sericin-GPE-PET

gave better wettability than collagen-GPE-PET was attributed to the higher molecular weight

of sericin than that of collagen, which lessened the reaction opportunity of the amine with

epoxide. Another possible explanation of these results may be functional agents immobilized

into the PET mesh restrained the penetration of water. The more immobilization quantity, the

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more difficult is the water penetration.

Table 3. Water dynamic contact angle and retracted volume of water obtained for original and

several modified PET fabrics.

Samples Advancing angle (o) θA Receding angle(o) θR Retracted volume (μL)

Original PET 92.9±1 62.8±0.5 16.2

GPE-PET 73.7±2 31.7±1 13.2

Chitosan-GPE-PET 76.9±3 37.0±1 13.8

Sericin-GPE-PET 80.5±3 41.5±1 14.2

Collagen-GPE-PET 84.3±4 47.2±2 15.0

The isothermal moisture regain of all the PET fabrics was investigated at 30°C, and the

results are plotted in Figure 11. All of the curves show a reversed S shape, and the moisture

regain increased markedly in the region of high humidity. Clearly, the GPE-PET fabrics on

which functional agents were immobilized were capable of higher water sorption than the

original PET, but could not absorb as much as simple GPE-impregnated PET fabric.

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0 20 40 60 80 1000.0

0.1

0.2

0.3

0.4

0.5

0.6M

oist

ure

rega

in [w

t%]

Relative humidity [%]

Original PET Collagen-GPE-PET Sericin-GPE-PET Chitosan-GPE-PET GPE-PET

Figure 11. Isothermal sorption diagrams for PET fabrics at 30°C.

The moisture-retaining property is another important issue in the study of hydrophilicity of

a fabric. A hygroscopicity/dehygroscopicity experiment was performed to evaluate the

moisture-retaining property of the same kinds of PET samples measured on wettability.

Figure 12 shows the changes in moisture regain of the PET fabrics from the hygroscopicity to

dehygroscopicity phase. During the entire course of the experiment, hygroscopic equilibrium

was reached after 40 min without reference to any phase at (25°C, 65%RH) or (30°C,

95%RH), but, the dehygroscopic behavior went on for close to 2 h. By contrast with the

original PET fabric, the modified PET fabric became hygroscopic quickly and dehygroscopic

slowly. Furthermore, the moisture regains of these PET samples maintained the same order as

the water contact angles in wettability measurement with sessile droplet method.

The samples of functional agents immobilized onto GPE-PET fabrics in aqueous solution

were also measured on water contact angle and moisture-retaining properties. Although the

samples exhibited goodish hydrophilicities in two aspects, the effect is not appreciated

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because these data were almost similar with that of GPE-PET. As viewed from lesser

immobilization quantities by this method, this came down to the cause that GPE bared on the

surface of PET fabric only a little participated in reaction with functional agents in solution.

0 100 200 300 400

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.825°C, 65%RH30°C, 95%RH25°C, 65%RHDry

Moi

stur

e re

gain

[wt%

]

Treating time [min]

Original PET Collagen-GPE-PET Sericin-GPE-PET Chitosan-GPE-PET GPE-PET

Figure 12. Changes in hygroscopicity and dehygroscopicity with the change in the

environmental conditions.

4.3.4. Antibacterial efficiency of the untreated and the modified PET fabrics

In the experiment for microbial absorption, a log (B/A) value of ≧ 1.5 was considered

necessary to claim antibacterial activity due to the intrinsic variability of the antibacterial test

results. In order for a sample to be considered to have antibacterial activity, the value of the

bacteriostatic activity should be over 2.0, and the value of the bactericidal activity should over

0.0. Here, the number of Staphylococcus aureus bacteria at the initial inoculation was A = 2.1

× 104, and the number of colonies of S. aureus on an inoculated piece of control calico was B

= 8.3 × 106. Table 4 lists the data for the antibacterial effect of the PET fabrics against S.

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aureus. The results show that the original PET fabric had no effect against S. aureus, which is

in agreement with the current literature. The GPE-impregnated PET fabric showed some

inhibition of the growth of S. aureus, although it could not kill the bacterial cells. The number

of viable cells decreased after they were inoculated on GPE-PET fabrics on which sericin,

collagen or chitosan had been immobilized, which indicates that these functional modified

PET fabrics killed bacterial cells at a high rate and had a high antibacterial activity.

According to the immobilization amounts of sericin, collagen or chitosan on GPE-PET

fabric listed in Table 2, collagen-GPE-PET containing higher immobilization amounts of

collagen did not show higher antibacterial values than the other two fabrics. This implies that

the antibacterial efficiency of collagen is naturally lower than that of sericin or chitosan.

The antibacterial test was also performed with GPE-PET fabrics on which functional

agents were immobilized in an aqueous solution, but no antibacterial effects against S. aureus

were found. It was considered that the immobilization amounts of functional agents onto

GPE-PET fabric were too little to kill the bacterial cell. This demonstrates that the

pad-dry-cure method is more effective than the solution method for the immobilization of the

functional agent (sericin, collagen or chitosan) onto the surface of GPE-impregnated PET

fabric again.

Table 4. Antibacterial activities of the original and the modified PET fabrics against

Staphylococcus aureus.

Samples Cell number [C] log C Bactericidal activity Bacteriostatic activity

Original PET 7.9×106 6.9 -2.6 0

GPE-PET 4.8×104 4.7 -0.4 2.2

Sericin-GPE-PET 1.0×103 3 1.3 3.9

Collagen-GPE-PET 1.6×103 3.2 1.1 3.7

Chitosan-GPE-PET 2.5×103 3.4 0.9 3.5

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4.4. Summary

The results obtained show that the method of impregnating a cross-linking agent by means

of scCO2 can be used to prepare intermediate PET fabric on which various functional agents

can be immobilized. The scCO2 technique is a powerful method of modifying fibers. The

scCO2 process can not only swell the polymer but also impregnate finishing agents or

cross-linking agents into the polymer under controlled temperature and pressure conditions

and in the presence of co-solvents. In the process of impregnation of an epoxy cross-linking

agent into PET fabric, a good co-solvent proved to be chloroform, which greatly boosted the

uptake of GPE into the PET fabric in scCO2.

Two methods of immobilizing functional agents onto GPE-impregnated PET fabrics were

compared, the pad-dry-cure method and the solution method; the former was found to be

more effective in terms of the immobilized amounts of functional agent and the antibacterial

efficacy. The surface hydrophilicity of the PET fabric can be improved to a certain extent by

immobilizing of a functional agent such as sericin, collagen or chitosan.

Conventional methods of modification of polymer fiber using scCO2 rely on changes in

the fiber structure which lead to the improvement of the physical and mechanical properties of

the fiber. However, cross-linked intermediate fibers can also participate in the reaction with

functional agents for further, surface modification. Generally, this scCO2 pretreatment is

expected to represent a new approach as simplifying the process, lowering the cost of surface

modification of polymer fabrics; also, the subsequent chemical immobilization of functional

agents onto the fiber surface is stronger and more stable when scCO2 pretreatment is carried

out.

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Chapter 5. General conclusion

Generally, synthetic fabrics (PET and PP), onto which the surface immobilization of

natural macromolecules can not be achieved by immersing them directly to the

macromolecules solution even followed by the cure process. Besides, the impregnation of

natural macromolecules into PET or PP fabrics is also impossible due to the higher molecule

weight of these macromolecules, even though supercritical impregnation technology can dye

the synthetic fiber successfully with or without any co-solvents. In order to immobilize

functional macromolecules effectively, it is necessary to introduce some functional molecules

or active cross-linking agents to the inert surface of PET and PP fabrics. Considering the

points of no-pollution, low-cost and easy-operation in current industry manufacture, the

introduction of cross-linking agents to synthetic fabrics by using the supercritical carbon

dioxide was designed. A research on surface immobilization of natural macromolecules onto

PET and PP fabrics functionalized by the impregnation of cross-linking agents with the scCO2

was investigated here.

The surface modification design come down to these explanations. Synthetic fibers can be

penetrated by scCO2 resulting in plasticization and dramatically swelling. Meanwhile, the

cross-linking agents as solute of scCO2 will be diffused to fibrous region with the distribution

of scCO2. After depressurization, CO2 desorbed from fiber quickly, and the cross-linking

agents remain in the inner or surface of fibers. Because the cross-linking agents were active

functional molecules, the reaction of natural macromolecules and the cross-linking agents

remained on the fiber surface will lead to the immobilization of natural macromolecules.

In this research, three types of active organic agents, cyanuric chloride (CC), epoxy

compounds and Tolylene 2,4-Diisocyanate (TDI), as intermediate cross-linking agents, were

selected and used in impregnation into PET or PP fabrics with the aid of scCO2. By viewing

the states of cross-linking agents in pure supercritical dioxide, cyanuric chloride is found to be

difficult to dissolve, Tolylene 2,4-Diisocyanate has good solubility, and epoxy derivative can

dissolve by and large. After several co-solvents were added to scCO2, the CC fluid presented

good optical uniformity, and epoxy derivatives fluid became also clearer than that in pure

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scCO2.

About the impregnation of CC into synthetic fabrics in scCO2, CH2Cl2 was judged to be a

better modifier for increasing the uptake of CC than others greatly, although the uptake in PP

is always less than it in PET. The impregnation of TDI into PET or PP with scCO2 need not

add any co-solvents because TDI can dissolve in scCO2 well. The impregnation of epoxy

compound into PET attained an optimization with the presentation of chloroform. Relatively,

the impregnation effects of these cross-linking agents into synthetic fabric behaved in this

order: TDI > Epoxy derivatives > CC. In addition, the impregnation of these cross-linking

agents into PET is easier than the operation to PP fabrics. Generally, the impregnation

conditions were optimized at 120°C, 25MPa for PET, and 100°C, 25MPa for PP.

The impregnated synthetic fabrics were investigated by the ATR-IR and XPS

measurement. The spectra showed that these cross-linking agents can be introduced into PET

or PP fabrics more or less. For example, a peak of typical epoxy ring was found at 847 cm-1

after epoxy compounds was impregnated into PET fabric. Another example, in the XPS

spectra of the CC-impregnated PET and PP fabrics, new peaks appeared at 197.2 eV, 268.2 eV

and 399.2 eV were assigned to Cl2p, Cl2s, N1s respectively.

After natural macromolecules immobilization finished, chemical analysis revealed that

these macromolecules can react with cross-linking agents in the immobilization process. The

increase of element content on the modified fabrics also indicated that macromolecules were

attached on the surface of cross-linking agents-impregnated fabrics. The SEM images of

modified samples showed changes on the micro-roughness of these fabric surfaces. Surface

wettability and moisturization efficiency of the modified fabrics got improved at different

levels. The modified PET fabric which was cross-linked by epoxy compounds displayed

outstanding antibacterial characteristics against S. aureus. The protein-immobilized fabrics

can also be stained by methylene blue readily. These measurements and analyses

demonstrated that functional macromolecules had been immobilized onto the surface of

synthetic fabrics.

The surface modification of synthetic fabrics were achieved first by the cross-linking

agent impregnation in scCO2, followed by a substitute reaction of impregnated cross-linking

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agents with natural functional molecules for the immobilization of natural macromolecules on

the surface of synthetic fabrics. Generally, this study represented a new approach as

simplifying the process; lowering the cost of surface modification of polymer fabrics. We

expect that the method here help to expand the field of application for modifying polymeric

materials.

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Publication list (1) Wen-Xiao Ma, Chuan Zhao, Satoko Okubayashi, Isao Tabata, Kenji Hisada, Teruo Hori.

『A novel method of modifying poly(ethylene terephthalate) fabric using supercritical

carbon dioxide』

Journal of Applied Polymer Science, 117 (4), p1897 (2010)

(2) Wen-Xiao Ma, Satoko Okubayashi, Kazumasa Hirogaki, Isao Tabata, Kenji Hisada, and

Teruo Hori

『Impregnation of Cyanuric Chloride into Synthetic Fabrics (PET and PP) by

Supercritical Carbon Dioxide and its Application in Immobilizing Natural

Biomacromolecules』

Journal of the Society of Fiber Science and Technology, 66(10), p243 (2010)

(3) Chuan Zhao, Wen-Xiao Ma, Satoko Okubayashi, Isao Tabata, Kenji Hisada, and Teruo

Hori.

『Impregnation of fluorescence dyes into polymer optical fiber with carbon dioxide

fluid』

Coloration Technology (submitted)

(4) 奥林里子， 麻文效， 星野芳哲，岡田睦馬，趙川，堀照夫

『趙臨界流体を用いる革新的加工方法の開発』

福井大学ベンチャービジネスラボラトリー年報，2，p28 (2006)

- 114 -

Presentations

(1) Wenxiao Ma, Satoko Okubayashi, Isao Tabata, Teruo Hori. Modification of polyester

fabric using supercritical carbon dioxide, The 16th Fiber Union Research Symposium, Ueda

of Japan (2005), p207.

(2) Wenxiao Ma, Satoko Okubayashi, Isao Tabata, Teruo Hori. Chemical modification of

polyester fabric using supercritical carbon dioxide, Fifth International Fiber Symposium in

Fukui, January 17-18, 2006.

(3) Wenxiao Ma, Satoko Okubayashi, Isao Tabata, Teruo Hori. Impregnation of the

crosslinking agent using supercritical carbon dioxide into polyester fabric and fixation of

some medicine in polyester cloth, Annual Meeting of The Society of Fiber Science and

Technology, Tokyo (2006), p260.

(4) Wenxiao Ma, Satoko Okubayashi, Isao Tabata, Kenji Hisada, Teruo Hori. Modification of

polyester fabric by impregnation of diisocyanate using supercritical carbon dioxide, Autumn

Meeting of The Society of Fiber Science and Technology, Kanazawa (2006), p79.

(5) Wenxiao Ma, Satoko Okubayashi, Isao Tabata, Kenji Hisada, Teruo Hori. Chemical

modification of polyester fabric by the impregnation of epoxy compound using supercritical

carbon dioxide, Proceedings of International Symposium on Dyeing and Finishing of Textiles,

Kyoto, Japan, December 17-19, 2006, p189.

(6) Wenxiao Ma, Satoko Okubayashi, Isao Tabata, Kenji Hisada, Teruo Hori. Fixation of

functional medicaments and impregnation of epoxy compounds using supercritical carbon

dioxide on polyester fabric, Annual Meeting of The Society of Fiber Science and Technology,

Tokyo (2007), p218.

- 115 -

- 116 -

Acknowledgements

This research is possible based on the support and encouragement of many people. In this occasion,

the author wish to express his gratitude for those contributions and concern during the period of his

doctoral course.

The works presented in this thesis where carried out at Fiber Amenity Course, Graduate School of

Engineering, University of Fukui. Grateful acknowledgement is given to Professor Teruo Hori for his

kind help, encouragement and guidance.

The author would like to express his sincere thanks to Associate Professor Kenji Hisada and

Technician Isao Tabata, for their instruction and assistance and support during these years. The

thankfulness will also be given to Assistant Professor Kazumasa Hirogaki for his generous help.

The author would like to express sincere thanks to Associate Professor Satoko Okubayashi, from

Division of Advanced Fibro Science, Graduate School of Science and Technology, Kyoto Institute of

Technology, for her guidance and advices on the experiment of this research.

The author is extremely thankful to Associate Professor Yuji Tokunaga, from Dept. of Materials

Science & Engineering, University of Fukui, for his guidance and training in the field of organic

synthesis, which were indispensable for this research.

The author do not have enough words to express his gratitude to all members of Hori’s Laboratory,

with a special thanks to Nora Martinez engaged in the supercritical group for her assistance with the

XPS measurements.

Finally, the author would like to express his full gratitude, to his mother and his father for their

love and understanding, to his sister and her family for the support in economy and the encouragement

in mentality.

Wen-Xiao Ma

Intelligent Fiber Engineering

Fiber Amenity Engineering Course

Graduate School of Engineering

University of Fukui