perkuliahan 7 material polimer dan komposit

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MM091372

POLYMER AND COMPOSITE MATERIALCredit: 3 SKS

Semester: 7

LECTURE 7DEPARTMENT OF MATERIALS AND METALLURGICAL ENGINEERING

FACULTY OF INDUSTRIAL ENGINEERINGINSTITUT TEKNOLOGI SEPULUH NOPEMBER (ITS) SURABAYA

Dr. Eng. Hosta Ardhyananta, S.T., M.Sc.

NIP. 19801207 2005 01 1 004


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MEASUREMENT OFMOLECULAR WEIGHT AND SIZE

Molecular weights of polymers can be determinedby chemical or physical methods of functional-groupanalysis, by measurement of the colligativeproperties, light scattering, or ultracentrifugation, orby measurement of dilute-solution viscosity

Absolute measurement: molecular weights can becalculated without reference to calibration by

another method

Dilute solution viscosity is not a direct measure ofmolecular weight

Require solubility of the polymer


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To understand the size of polymer : explain theschematic illustration below

small ???

BIG ???

light ???

HEAVY ???


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End group analysis

Require known number of determinable groups permolecule

The long chain limits

Count the number of molecules in a given weight

It yield number-average molecular weight

Insensitive at high molecular weight

Condensation polymers: End-group analysisinvolves chemical methods for functional groups.Carboxyl groups titrated with base. Amino groupstitrated with acid. Hydroxyl groups by reagent orinfrared spectroscopy. Limited by insolubility of the

polymer


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Addition polymers: no general procedure becausevariety of type and origin. Analysis may be made for

Initiator containing identifiable functional groups,elements, or radioactive atoms, vinyl group


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Colligative property measurement Activity equal to its mole fraction

Colligative property based on vapor-pressure

lowering, boiling-point elevation (ebulliometry),freezing-point depression (cryoscopy), osmoticpressure (osmometry)

Number-average molecular weight: typical polymersconsist of mixtures of many molecular species,molecular weight yield average values

=

=

=

==~

1

~

1

~

1 i

i

i

ii

i

i

n

N

NM

N

wM


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Concentration dependence of the colligativeproperties is developed in terms of the osmotic

pressure Vapor-phase osmometry: temperature difference

from different rates of solvent evaporation andcondensation

Ebulliometry: boiling point of the polymer solution iscompared with pure solvent

Cryoscopy: freezing-point depression

Membrane osmometry: osmotic pressure


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Light scattering

The scattering of light occurs whenever a beam oflight encounters matter

Determination of polymer molecular weights by lightscattering

Refractive index , n

The amplitude of the scattered light is proportionalto the polarizability and mass of the scatteringparticle

The intensity of scattering is proportional to thesquare of the particle mass

The heavier molecules contribute more to the

scattering than the light ones


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i

i

i

i

ii

i

ii

i

ii

w

MN

MN

Mwc

Mc

M

=

=

=

====

1

1

2

1

1

Weight-average molecular weight

Average-Mw is greater than average-Mn

Average-Mw/Mn is a measure of polydispersity

Average-Mw is sensitive of high-molecular-weight

species

Average-Mn is influenced at the lower end of themolecular weight distribution


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Sample preparation

Calibration

Treatment of data


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Ultracentrifugation

Determining the molecular weight of high polymer

Protein molecule, biological material

Centrifugation by high speed rotation

The concentration of polymer is determined byoptical methods based on measurements of

refractive index or absorption Solvents must be chosen for difference from the

polymer in both density (to ensure sedimentation)

and refractive index (to allow measurement)


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Solution viscosity and molecular size

Measure the size or extension in space of polymermolecules

Molecular weight for linear polymers

Comparing efflux time , t , flow

Viscosity of a polymer is proportional to its molecular

weight Viscosity-average molecular weight


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Gel Permeation Chromatography

Gel permeation chromatography is a powerful new

separation technique Discovery by Moore 1964

The separation takes place in a chromatographic

column filled with beads of a rigid porous gel ; highlycrosslinked porous polystyrene and porous glass ;the pores in gels are the same size as thedimensions of polymer molecules

A sample of a dilute polymer solution is introducedinto a solvent stream flowing through the column


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The dissolved polymer molecules flow past theporous beads, they can diffuse into the internal pore

structure depending on their size and the pore-sizedistribution of the gel

Larger molecules can enter a small fraction of the

internal portion of the gel, or are excluded; smallerpolymer molecules penetrate a larger fraction of theinterior of the gel


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The larger the molecule, the less time it spendsinside the gel and the sooner it flows through thecolumn

The different molecular species are eluted from thecolumn in order of their molecular size asdistinguished from their molecular weight, the

largest emerging first

A specific column or set of column (with gels ofdiffering pore size) is calibrated empirically to give

such a relationship, a plot of amount of soluteversus retention volume (the chromatogram) can beconverted into a molecular-size distribution curve


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Calibration: commercial narrow-distributionpolystyrene

Gel permeation chromatography has valuable forsystem from low to very high molecular weight

Wide variety of solvent and polymer, depending on

the type of gel


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Polyelectrolytes Polymers with ionizable group are termed

polyelectrolytes

Polyacids such as poly(acrylic acid) and hydrolyzedcopolymers of maleic anhydride

Polybases such as poly(vinyl amine) and poly(4-

vinyl pyridine) Polyphosphates, nucleic acids, proteins


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Because of the preponderance of small ions, thecolligative properties of polyelectrolytes in ionizing

solvents measure counterion activities rather thanmolecular weight

In the presence of added salt, correct molecularweights of polyelectrolytes can be measured bymembrane osmometry, since the small ions canequilibrate across the membrane


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ANALYSIS AND TESTING OFPOLYMERS

Methods of physical and chemical analysis ofpolymers


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Chemical analysis of polymers

Spectroscopic methods

X-ray diffraction analysis

Microscopy

Thermal analysis

Physical testing Nuclear magnetic and electron paramagnetic

resonance spectroscopy


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Chemical Analysis of Polymers

The chemical analysis of polymers is not basicallydifferent from the analysis of low-molecular-weight

organic compounds Appropriate modification is made to ensure solubility

or the availability of sites for reaction (e.g., insoluble

specimens should be ground to expose a largesurface area)

Chemical analysis of molecule

Chemical reactions of polymers


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Mass spectrometry: polymer is reacted (as in thermaldegradation) to form low-molecular-weight fragmentswhich are condensed at liquid-air temperature. Then,volatilized, ionized, and separated according to mass

and charge by the action of electric and magnetic fields.From the various ionic species found, the structures ofthe low-molecular-weight species can be inferred

Gas chromatography is a method of separation in which

gaseous or vaporized components are distributedbetween a moving gas phase and a fixed liquid phase orsolid adsorbent. Adsorption or elution steps taking placeat a specific rate for each component, separation isachieved. Chromatographic column. Detector signal isproportional to the concentration of the dilute componentin the gas stream.


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Infrared spectroscopy Emission or absorption spectra arise when

molecules undergo transitions between quantum

states corresponding to two different internalenergies

The energy differenceE between the states isrelated to the frequencyE = hv

Infrared frequencies in the wavelength range 1 50

m are associated with molecular vibration andvibration-rotation spectra

A molecule containing N atoms has 3N normalvibration modes, including rotational andtranslational motions of the entire molecule


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Raman spectrum : frequency of visible light is

altered in the scattering process by the absorptionor emission of energy produced by changes inmolecular vibration and vibration-rotation quantum

states In polymers, the infrared absorption spectrum is

surprisingly simple considering the large number ofatoms involved. This simplicity results first frommany vibration have almost same frequency andappear in the same spectrum; second from the strictselection rules that prevent vibrations from causing

absorptions The approximate wavelengths of some infrared

absorption bands arising from functional group and

atomic vibrations


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Experimental methods Sources : electrically heated silicon carbide or rare

earth oxide rods

Dispersion methods : Both diffraction gratings andprisms of inorganic salts. Prism materials are NaCl

(below 15 m), KBr (below 25 m), CsBr (below 35m), LiF (below 6 m), CaF

2

(below 9 m)

Detectors : sensitive heat detectors such asmultiple-junction thermocouple, pneumatic detector,photocells.

Samples : solid, liquid or gaseous samples. High orlow temperature. Microscope attachments.Transparency to infrared radiation needs special

window materials. Thin samples


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Application to polymers

Detection of chemical groups : C=C at 6.1 m in naturalrubber, carbonyl at 5.8 m and ether at 8.9 m in PMMA,

aromatic structures at 6.2 , 6.7 , 13.3 , 14.4 m inpolystyrene, C-Cl at 14.5 m in PVC , peptide groups at3.0 , 6.1 , 6.5 m in nylon , C-F2 at 8.2 8.3 m in PTFE

Dichroism : molecular vibration leading to infraredabsorption, there is periodic change in electric dipolemoment. The dipole-moment change can be confined tospecific direction. The use of polarized infrared radiation

leads to absorption which is a function of the orientationof the plane of polarization, which is called dichroism asthe dichroic ratio.


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Crystallinity : the infrared absorption spectra ofpolymer in the crystalline and amorphous state can

differ for two reasons. First, Intermolecularinteractions may exist in the crystalline polymerwhich lead to sharpening or splitting bands; Second,conformations may exist leading to band. PET,

Nylon


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Nuclear magnetic and electron paramagneticresonance spectroscopy

Nuclear magnetic resonance (NMR) spectroscopy

detects the motion of nuclei (such as proton) havingnonzero spin

Electron paramagnetic resonance (EPR)

spectroscopy detects free radical species

NMR spectroscopy

To study the chain configuration Developed technique for observing narrow-line or

high-resolution spectra

To study the position of protons


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magnet


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Experimental methods

NMR utilizes the property of spin (angularmomentum and its associated magnetic moment)

possessed by nuclei. Atomic number and mass number are not both even

Nuclei of isotopes H1, C13, O17, and F19

Application of strong magnetic field splits the energylevels into two, representing states with spin paralleland antiparallel

Transition between the states lead to absorption oremission of an energy

00 2 HhvE ==


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Frequency v0 in the microwave region, field ofstrength H0 of the order of 10,000 gauss , is the

magnetic moment of the nucleus The energy change is observed as a resonance

peak or line


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With an assembly of nuclei, the field on any one ismodified by the presence of the others

HL is the local field with a strength of 5 10 gauss

A distribution of local fields usually exist so that theresonance line becomes broadened

Line width and its second moment

)(2 00 LHHhv +=


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If molecular motion is enhanced by working with asolution and by increasing the temperature, narrowline can be observed

Deuterated solvent used, since contribute noresonance

Scale unit : chemical shifts relative to standard

Two scale :scale, zero ; scale, 10.00

Coupling : neighbor, high magnetic field strength

Double resonance or spin decoupling


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A typical NMR spectrum for a simple compound


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NMR spectrum of polycarbonate


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NMR development, double resonance or spin decoupling


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EPR spectroscopy

Detection of free radical

Magnetic moment, arising from the presence ofunpaired electron


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X-ray diffraction analysis

X-ray diffraction method investigate orderarrangement of atom through the interaction ofelectromagnetic radiation to give interference effectwith structure comparable in size to the wavelengthof the radiation.

The wavelengths of x-rays are comparable tointeratomic distances in crystals

Polymer single crystals are too small for x-raydiffraction experiments. The crystal structure isusually determined from a fiber drawn of the

polymer. Because of the alignment of the crystallineregions with the long axes of the molecules parallelto the fiber axis. Rotation pattern from a single

crystal


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Chain conformations : atoms regularly spaced alonghelices. Helical structures

Chain packing : crystallinity

Disorder in the crystal structure : defect, distortion

Orientation


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Microscopy

Light and electron microscopy

Light microscopy

Reflected-light microscopy for examining the textureof solid polymer

Thin film examining by transmitted light

Polarized microscopy : ability of crystalline materialto rotate the plane of polarized light. Spherulitestructure. Crystalline melting point

Phase-contrast microscopy : involving differences inrefractive index

Interference microscopy : low thickness specimen


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Electron microscopy and electron diffraction

Resolution of smaller object Morphology of crystalline polymer

Light


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Scanning electron microscopy

Beam of electron scanning across the surface of

specimen Conducting film

Secondary electrons, backscattered electrons, x-ray

photons


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Thermal analysis

Traditional calorimetric, differential thermal analysis,thermogravimetric analysis, thermomechanicalanalysis, electrical thermal analysis, effluent gasanalysis

Enthalpy changes associated with heating,

annealing, crystallizing,

Thermall treatment of polymer

Response of system to temperature, including

polymerization, degradation, or other chemicalchanges


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Differential thermal analysis curve


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Thermogravimetric analysis


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Physical testing

Physical properties of polymer

Rheology and viscoelasticity

Stress-strain properties in tension

Measuring force developed as the sample iselongated at constant rate of extension

Modulus or stiffness (slope of the curve), yield stress,strength, elongation at break

F


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Polyethylene


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Tensile stress-strain curves for several types of

polymeric material


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Shear, flexure, compression, torsion

Fatigue tests

Cyclic mechanical stress

Various modes of fatigue testing

Alternating tensile and compressive stress

Cyclic flexural stress

Fatigue failure may arise from the absorption ofenergy in a material which is not perfectly elastic.

Manifested as heat, leading to a temperature rise, alower modulus, and rapid failure

Impact tests


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p

Rupture may be divided into two classes: brittle andductile

Brittle rupture occurs if the material behaves elasticallyup to the point of failure , does not yield or draw

In ductile rupture, the specimen is permanently distortednear the point of failure

Brittle failure : lack of distortion of the broken parts

Brittle point or temperature at the onset of brittleness Brittle point is roughly related to the glass transition

temperature

Impact strength : energy required to cause the break.Notched specimen to improve reproducibility

Other forms of impact test : falling objects strike thespecimen


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Tear resistance

Film : packaging application Fatigue tests

Tear strength and tensile strength are closelyrelated

Hardness

Resistance to penetration, scratching, marring

Resistance to penetration by an indentor pressedinto the plastic under a constant load


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Abrasion resistance

Scratch test

Degree of abrasion Friction, hardness and abrasion resistance are

related closely to the viscoelastic properties

Th l ti


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Thermal properties

Softening temperature

Observation of temperature : (a) an indentor underfixed load penetrates into the material (Vicat test) (b)

a bar deforms a specified amount (deflectiontemperature of heat distortion test) (c) samplebecome molten and leaves trail when moved across

a hot metal surface (polymer melt or sticktemperature test) (d) fail in tension under its ownweight (zero strength temperature test)

Flammability

Burning rate

Self-extinguishing : removal of an external flame


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heat

O i l i


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Optical properties

Transmittance and reflectance

Transparent : does not scatter light

Transmittance : ratio of the intensities of lightpassing through and light incident on the specimen

Opaque : reflect light , does not transmit it

Reflectance : ratio of the intensities of the reflected

and the incident light

Translucent substance : transmit and reflects light

Transmittance and reflectance may be measured as

a function of the wavelength of light in aspectrophotometer

Luminous transmittance and luminous reflectance


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light light

light


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Color Subjective sensation in the brain resulting from the

perception of the appearance which result from the

spectral composition of the light reaching the eye

Gloss

Geometrically selective reflectance of a surfaceresponsible for its shiny or lustrous appearance

Surface reflectance : specular direction which is the

direction of mirror would reflect light Photoelectric instrument for measuring gloss at a

variety of angles of incidence and reflection

Haze


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Haze

Percentage of transmitted light which in passing throughthe specimen deviates from the incident beam byforward scattering

Hazemeter : light deviating more than 2.5 o from thetransmitted beam direction

The effect of haze is to impart a cloudy or milkyappearance

Transparency

The state permitting perception of objects through or

beyond the specimen Fraction of the normally incident light which is

transmitted without deviation from the primary beamdirection of more than 0.1 o

Electrical properties

Dielectric constant and loss factor


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Dielectric constant and loss factor

Dielectric constant of an insulating material is the ratio ofthe capacities

The difference is due to the polarization of the dielectric

Loss factor is proportional to the energy absorbed percycle by the dielectric from the field

Resistivity

Resistance to the flow of direct current

Dielectric strength

Insulator will not sustain an indefinitely high voltage

As the applied voltage is increased, a point is reachedwhere a catastrophic decrease in resistance takes place,

accompanied by a physical breakdown of the dielectric


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electric electric

Electron conduction

Arc resistance

The surface of polymer may become carbonized andconduct current readily when exposed to an electricaldischarge


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Chemical properties

Resistance to solvents

Effect of solvent on polymer

Solubility, swelling, environmental stress cracking,crazing

Vapor permeability Permeability to a gas or vapor

Rate of transfer of vapor through unit thickness

Weathering

Exposure to weather


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chemical chemical


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MORPHOLOGY AND ORDER INCRYSTALLINE POLYMERS

RHEOLOGY AND THEMECHANICAL PROPERTIES OF

POLYMERS

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