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# Attraktiivinen kapillaarivoima - PowerPoint PPT Presentation

Laplacen yhtälöstä voidaan johtaa: Edellyttäen että  < 90 o pintoja vetää kokoon voima. Pintojen välinen etäisyys H. Kontaktikulma . P 1. P 2. r. Nesteen tilavuus V. Attraktiivinen kapillaarivoima. Esim: Voima vetää kuituja yhteen rainan kuivatessa Paperinvalmistajat käyttävät

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Edellyttäen että  < 90o pintoja vetää kokoon voima

Pintojen välinen etäisyys H

Kontaktikulma 

P1

P2

r

Nesteen tilavuus V

Attraktiivinen kapillaarivoima

Esim: Voima vetää kuituja yhteen rainan

kuivatessa

Paperinvalmistajat käyttävät

nimeä ”Campbell-voima”

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

F1

F2

50 kg

50 kg

friction forces

Friction

Amontons law: F (friction force) = µL

µ= friction coefficient, L = load

F1=F2 ie no dependence on contact area!

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?

The real contact area is usually much smaller than the geometrical area

For 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

F geometrical area

static friction Fs

kinetic friction Fk

stick – slip friction

friction forces

Kinetic versus static friction

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

friction forces geometrical area

Stick-slip vs. smooth sliding

Observed for stiff surfaces and or high velocities

Observed for soft systems and/or low velocities

Braum et al Surf Sci Rep60 (2006) 79

SLIP geometrical area

STICK

STICK

solidlike state

liquidlike state

solidlike state

friction forces

Stick-slip phenomenon: different models

the thin film between the surfaces alternately freezes and melts

surface roughness

J. Phys. Chem. 1993, 97, 11300

friction forces geometrical area

Friction forces

• Friction loops at different loads are measured

• Friction as a function of load

• Friction coefficients

Cellulose – xyloglucan – cellulose geometrical area

Friction

xyloglucan

xyloglucan

Stiernstedt et al. Biomacromolecules, 2006

Cellulose – xyloglucan – cellulose geometrical area

• 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

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

Reference

Beatability !!!

Dispersing of surface fibrils

Effect of CMC on coefficient of friction by AFM viscosity at different shear rates

Ref.

CMC

Without polymer

With polymer

Strech at break of paper (60 g/m of paper2) vs. beating degree

Tensile strength of paper (60 g/m of paper2) vs. beating degree

Laimeat vesiliuokset of paper

• Pintajännitys

• A

• Pinta-aktiiviset aineet rikastuvat

• rajapintaan pintajännitystä alentaen

• B

• Kohdassa A pinta-aktiivinen aine

• “kondensoituu” pinnassa,

• tiivistä pintakerrosta muodostaen

• Kohdassa B muodostuu

• misellejä liuoksessa

• log(kons.)

• Pintakonsentraatio

• B

• A

• log(kons.)

Pinta-aktiivinen aine of paper

Hydrofobinen osa (hiilivety-

ketju tai fluorattu ketju)

Liukenee huonosti veteen

Hydrofiilinen (poolinen) osa

Liukenee hyvin veteen

Amfifiilinenrakenne

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

Tensile index vs. surface content of extractives in mechanical pulp fines (Luukko et al., 1997)

COO mechanical pulp fines (Luukko et al., 1997)- R+

Surface modification of fibres with irreversible adsorption of polymers

• 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

Laine et al. 2000

Initial Wet Strength

Different polymers

influence the

development of stregth

during drying

in different ways !!!

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

• Microfibrillar nature, crystallinity and crystal size remain mostly unchanged

• Penetrates fiber  oxidation on the surface and inside fibers

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

Saito et al. Biomacromolecules2007, 8, 2485.

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

Bridging... 2003)

Bridging

Salmi et al, Coll Surf A, 2006

Polyelectrolyte complexes adsorbed on cellulose surfaces

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

Myllytie 2009

Polymer-induced behaviour of wet web during drying cellulose surfaces at pH 7

55 % dryness 92 % dryness

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

Saari 2006

A gel layer model of fibre surfaces cellulose surfaces at pH 7

• 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

1.6 MPa 0.3 MPa

Apparent elastic modulus

Laine et al. 2002

no polymer, 10x obj. cellulose surfaces at pH 7

C-PAM, 10x obj.

CMC 10x obj.

Behaviour of surface fibril aggregates by addition of different polymers

Myllytie et al. 2006

CMC-treatment makes the surface layer looser cellulose surfaces at pH 7

Cell wall

Apparent elastic modulus

1.6 MPa

Surface teated with CMC:

Apparent elastic modulus

0.13 MPa

Fors 2001

Strength development during drying cellulose surfaces at pH 7

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

Drying stress as a function of WRV (Htun et al.) cellulose surfaces at pH 7

Drying stress, kNm/kg

CnH2n-1COONa

• Kons

• Kons

Spreding, reaction

orientation

Size

H2O

H2O

Size

Paper surface

Strength development during drying dewatering

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

A gel layer model of fibre surfaces dewatering

• 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

1.6 MPa 0.3 MPa

Apparent elastic modulus

Laine et al. 2002

After drying

Myllytie 2009

Bridging of single polymer chains dewateringin a polymer melt

Sun and Butt Macromolecules37 (2004) 6086.

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

structure

High Mw

Medium Mw

Low Mw

Dynamic light scattering data

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

0 M NaCl

1 mM NaCl

10 mM NaCl

1 M NaCl