1

Attraktiivinen kapillaarivoima

P1 P2r

Kontaktikulma Pintojen välinen etäisyys H

Nesteen tilavuus V

Laplacen yhtälöstä voidaan johtaa:Edellyttäen että < 90o pintoja vetää kokoon voima

F

2V cos

H2

Esim: Voima vetää kuituja yhteen rainankuivatessa

Paperinvalmistajat käyttävätnimeä ”Campbell-voima”

2

Influence of drying strategy on strain at break

1.5

2.5

3.5

4.5

5.5

-3 -2 -1 0 1 2 3 4

Strain/ %

Strain at break/ %

Chem. Mod.WRV 165 Beating

WRV 145

Stretch Shrink

3

Influence of drying strategy on shrinkage force

0

500

1000

1500

2000

-3 -2 -1 0 1 2 3 4

Strain/ %

Beating, WRV 145

Chem. Mod. WRV 165

Shrinkage force/ Nm

Stretch Shrink

4

Influence of drying strategy on tensile stiffness

2.0

4.0

6.0

8.0

10.0

12.0

-3 -2 -1 0 1 2 3 4

Strain/ %

Tensile stiffness/ Nm/g

Chem. Mod.WRV 165

BeatingWRV 145

Stretch Shrink

5

Influence of drying strategy on tensile strength

60

65

70

75

80

85

90

-3 -2 -1 0 1 2 3 4

Strain (%)

Tensile index (Nm/g)

BeatingWRV 145

Stretch Shrink

Chem. Mod.WRV 165

6

Friction – what is it?

One should distinguish between two different regimes: • hydrodynamic (liquid) friction

– the substrates are separated by a thick (> 0.01 mm) liquid film– friction mainly determined by viscosity of liquid lubricant

• boundary lubrication– the substrates are separated by a thin (a few atomic diameters)

lubricating film– also dry friction

• Friction is the resistance to motion during sliding or rolling of a solid body against another.

• the force acting in the direction opposite to the direction of motion is called friction force

friction forces

7

Friction

Amontons law: F (friction force) = µL

µ= friction coefficient, L = load

F1=F2 ie no dependence on contact area!

F1 F250 kg 50 kg

What about surface roughness??

Since friction usually is affected by roughness we need to seek an explanation which involves adhesion.This requires that surface area is important BUT Amontons law tells us that friction depends only on load

?Is there a load – area relationship?

friction forces

8

The real contact area is usually much smaller than the geometrical areaFor soft samples the real area is dependent on load => Amontons law

A fundamental understanding of adhesion and friction requires an understanding of the mechanisms on the atomic/molecular scale =>Friction force measurements with AFM or SFA

friction forces

9

Kinetic versus static friction

F

kinetic friction Fk

static friction Fs

stick – slip friction

The static friction force is always larger than the kinetic friction force

friction forces

10

Stick-slip vs. smooth sliding

Braum et al Surf Sci Rep 60 (2006) 79

Observed for soft systems and/or low velocities

Observed for stiff surfaces and or high velocities

friction forces

11

Stick-slip phenomenon: different models

the thin film between the surfaces alternately freezes and melts

STICK STICKSLIP

solidlike state liquidlike state solidlike state

friction forces

surface roughness

J. Phys. Chem. 1993, 97, 11300

12

Friction forces

Friction loops at different loads are measured

Friction as a function of load

Friction coefficients

friction forces

13

Cellulose – xyloglucan – cellulose

Stiernstedt et al. Biomacromolecules, 2006

Adhesion Friction

xyloglucan

xyloglucan

14

• Increase in adhesion and decrease in friction with adsorption of xyloglucan

• Bridging adhesion that is dependent on time in contact

• An explanation why it works well as strength additive

Cellulose – xyloglucan – cellulose

15

0

5

10

15

20

25

30

0 100 200 300 400 500 600 700 800Shear rate (1/s)

Dispersion viscosity (m Pa s)

Effect of CMC adsorption on apparent dispersion (pulp) viscosity at different shear rates

Adsorption of CMCDispersing of surface fibrils

Reference

Beatability !!!

16

0,00

0,05

0,10

0,15

0,20

0,25

0 25 50 75 100 125 150Normal Force [nN]

Co

effi

cien

t o

f F

rict

ion

Effect of CMC on coefficient of friction by AFM

Ref.

CMC

17

Modification of stress concentration during drying by using polymers

Without polymer With polymer

18

Shrinkage during drying in CD and MD vs. beating degree of paper

0

2

4

6

8

10

12

10 20 30 40 50 60

SR

Shrinkage (%)

CD

MD

100 g/m2

100 g/m2

60 g/m2

30 g/m2

60 g/m2

30 g/m2

19

Maximum stress during drying in CD and MD vs. beating degree of paper

0

250

500

750

1000

1250

1500

1750

2000

10 20 30 40 50 60

SR

Stress (N/m)

MD

100 g/m2

60 g/m2

30 g/m2

MD

MD

CD

CD

CD

20

Strech at break of paper (60 g/m2) vs. beating degree

0

1

2

3

4

5

6

7

10 20 30 40 50 60

SR

Strech at break (%)

CD, freely dried

MD, freely dried

MD, dried restr.

CD, dried restr.

21

Tensile strength of paper (60 g/m2) vs. beating degree

0

20

40

60

80

100

120

10 20 30 40 50 60SR

Tensile strength (Nm/g)

MD

CD

Freely dried

Freely dried

Dried restraint

Dried restraint

22

Laimeat vesiliuokset

• Pinta-aktiiviset aineet rikastuvat rajapintaan pintajännitystä alentaen

• Kohdassa A pinta-aktiivinen aine“kondensoituu” pinnassa, tiivistä pintakerrosta muodostaen

• Kohdassa B muodostuumisellejä liuoksessa

log(kons.)

B

APintajännitys

B

A

Pintakonsentraatio

log(kons.)

23

Pinta-aktiiviset aineet paperinvalmistuksessa

Pinta-aktiiviset aineet Kemiallinen koostumus Alkuperä

Rasvahappojen suolat Hartsihapot ja niiden suolat Nonioniset pinta-aktiiviset aineet Alkyylisulfaatit, sulfonaatit Rasva-amiinit

Kemiallinen ja mekaaninen massa (uuteaineet) hartsiliimat Dispergointiaineet päällystetystä hylystä, keräyskuitu, pesuaineet päällystetty hylky Vaahdonestoaineet

24

Pinta-aktiivinen aine

Hydrofobinen osa (hiilivety-ketju tai fluorattu ketju)Liukenee huonosti veteen

Hydrofiilinen (poolinen) osaLiukenee hyvin veteen

Amfifiilinenrakenne

25

Effect of extractives on the ESCA C 1s peak of mechanical pulp fines (Luukko et al., 1997)

26

Tensile index vs. surface content of extractives in mechanical pulp fines (Luukko

et al., 1997)

27

Surface modification of fibres with irreversible adsorption of polymers

COO- R+

• It has been found that the adsorption

of certain polymers such as CMC, xyloglucan,

gums can be used to modify cellulose surfaces

•The adsorption mechanism is non-electrostatic

28

Certain polysaccharides have a natural affinity to cellulose surfaces

O

OHOH

OH

O OOH

O

OH

OHO

OHOH

OH

OH

On OH

OH

OH

OH

H

O

0

2

4

6

8

10

12

0 60 120 180 240 300Treatment time (min)

Ca-form

Na-form, 2h

Attached amount of CMC (mg/g)

Laine et al. 2000

29

Effect of Wet Strengthening Aids on Initial Wet Strength

Different polymers influence the development of stregthduring dryingin different ways !!!

30

Surface composition of mechanical pulp fines (Mosbye et al. 2003)

0

1020

30

40

5060

70

flake likefines

first fibrillarfines

secondfibrillar fines

surf

ace

cont

ent (

%)

lignin

extractives

carbohydrates

31

TEMPO-oxidized cellulose

Saito et al. Biomacromolecules 2007, 8, 2485.

O O

CH2OH

OH

OH

O O

OH

OH

CHO

O O

OH

OH

COOH

N OH

N O

N O

TEMPO

NaCl

NaClO

NaBrO

NaBr

+

o Microfibrillar nature, crystallinity and crystal size remain mostly unchanged

o Penetrates fiber oxidation on the surface and inside fibers

o Combined with mechanical treatment, TEMPO-oxidation enables individualization of microfibrils

• 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)

• High selectivity on primary alcohols in alkaline conditions

• Introduces aldehyde and carboxylate groups to the surface of microfibrils

32

Why TEMPO is extremely effective in fibrillation ?

Supramolecular structure of the cellulose I polymorph showing the main intermolecular O6-H → O3 (green) and intramolecular O3-H → O5 (black) hydrogen bonding patterns

33

Bridging...

Salmi et al, Coll Surf A, 2006

Polyelectrolyte complexes adsorbed on cellulose surfaces

Adhesion between charged surfaces Bridging

34

Pull-off force (open symbols) between chitosan coated cellulose surfaces at pH 7

Myllytie 2009

35

Polymer-induced behaviour of wet web during drying

Polymer adsorbed samples vs zero addition on a dry matter content of 55%

0

1

2

3

4

5

6

0 0,02 0,04 0,06

Strain [mm/mm]

Lo

ad

[N

]

Zero addition

C-Starch 5 mg/g

CMC 2,5 mg/g

Chitosan 5 mg/g

Saari 2006

55 % dryness 92 % dryness

• Draw optimization test showed that CMC activates by draws, whereas starch is sensitive to high draws in wet stage

36

A gel layer model of fibre surfaces

• The external surface of wet fiber can be considered as swollen polymer or polyelectrolyte gel

• The gel layer consists mainly of cellulose microfibrils extending out from the fiber surface

• Polymers are mixed with cellulose microfibrils

Apparent elastic modulusLaine et al. 2002

1.6 MPa 0.3 MPa

37

Behaviour of surface fibril aggregates by addition of different polymers

no polymer, 10x obj. CMC 10x obj.

C-PAM, 10x obj.

Myllytie et al. 2006

38

CMC-treatment makes the surface layer looser

Surface teated with CMC:Apparent elastic modulus0.13 MPa

Fors 2001

Cell wallApparent elastic modulus1.6 MPa

39

40 50 60 70 80 90 1000,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

45 50 55 60 650,0

0,1

0,2

0,3

CMC + Chi. CMCTe

nsile

stre

ngth

[kN

/m]

Dry solids [%]

Ref.

Chi. pH1020mg

CMC + Chi.

CMC

Te

nsi

le s

tre

ng

th [

kN/m

]

Dry solids [%]

Ref.

Chi. 20mg pH10

Strength development during drying

CMC + chitosan two-layer adsorption gives superior wet and dry strength properties

40

Drying stress as a function of WRV (Htun et al.)

Drying stress, kNm/kg

41

42

Effect of addition strategy of SDS/C-PAM system on dewatering

0

5

10

15

20

25

0 0,05 0,1 0,15 0,2 0,25 0,3SDS % dry pulp

C-PAM and SDS added insteps

C-PAM and SDS added as amixture

43

Natriumalkanoaattien vesiliuosten pintajännitys

CnH2n-1COONa

Hilivetykejun kasvaessa cmc laskeeja adsorptio voimistuu

44

Adsorptio hydrofiiliseen ja hydrofobiseen pintaan

Adsorptio hydrofiiliseen pintaanAdsorptio hydrofobiseen pintaan

Kons

Kons

45

Treatment of paper with hydrophobic materials

Size

Size

Spreding, reactionorientation

Paper surface

H2O H2O

46

40 50 60 70 80 90 1000,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

45 50 55 60 650,0

0,1

0,2

0,3

CMC + Chi. CMCTe

nsile

stre

ngth

[kN

/m]

Dry solids [%]

Ref.

Chi. pH1020mg

CMC + Chi.

CMC

Te

nsi

le s

tre

ng

th [

kN/m

]

Dry solids [%]

Ref.

Chi. 20mg pH10

Strength development during drying

CMC + chitosan two-layer adsorption gives superior wet and dry strength properties

47

A gel layer model of fibre surfaces

• The external surface of wet fiber can be considered as swollen polymer or polyelectrolyte gel

• The gel layer consists mainly of cellulose microfibrils extending out from the fiber surface

• Papermaking additives are mixed with cellulose microfibrils

Apparent elastic modulusLaine et al. 2002

1.6 MPa 0.3 MPa

After drying

Myllytie 2009

48

Bridging of single polymer chains in a polymer melt

Sun and Butt Macromolecules 37 (2004) 6086.

49

Size of complex particles formed by A-PAM and C-PAM with low charge density and different Mw

0

500

1000

1500

2000

0,00 1,00 2,00 3,00 4,00

Anionic/cationic polymer charge ratio

Par

ticle

siz

e nm

A-PAM I/C-PAM I

A-PAM I/C-PAM II

A-PAM II/C-PAM III

Low Mw

Medium Mw

High Mw

Dynamic light scattering data

Tailor-made finestructure

50

Viscosity as a function of the A-PAM/ C-PAM ratio at different NaCl concentrations

0

5

10

15

20

25

0,04 0,08 0,16 0,24 0,4 1 2

A-PAM /C-PAM

red

uce

d v

isco

sity

1 M NaCl

10 mM NaCl

1 mM NaCl

0 M NaCl

51

Viscosity as a function of polymer concentration

0

2

4

6

8

10

12

0 0,5 1 1,5 2 2,5 3 3,5

Polymer concentration, g/l

Spe

cific

vis

cosi

ty

C-PAM

C-PAM/A-PAM