Attraktiivinen kapillaarivoima

1. Laplacen yhtälöstä voidaan johtaa: 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”

2. Influence of drying strategy on strain at break

3. Influence of drying strategy on shrinkage force

4. Influence of drying strategy on tensile stiffness

5. Influence of drying strategy on tensile strength

6. friction forces 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

7. 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! 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?

8. 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

9. F 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

10. friction forces 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

11. SLIP 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

12. friction forces Friction forces • Friction loops at different loads are measured • Friction as a function of load • Friction coefficients

13. Cellulose – xyloglucan – cellulose Adhesion Friction xyloglucan xyloglucan Stiernstedt et al. Biomacromolecules, 2006

14. Cellulose – xyloglucan – cellulose • 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

15. Effect of CMC adsorption on apparent dispersion (pulp) viscosity at different shear rates Reference Beatability !!! Adsorption of CMC Dispersing of surface fibrils

16. 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

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

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

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

22. Laimeat vesiliuokset • 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.)

23. Pinta-aktiiviset aineet paperinvalmistuksessa

24. Pinta-aktiivinen aine Hydrofobinen osa (hiilivety- ketju tai fluorattu ketju) Liukenee huonosti veteen Hydrofiilinen (poolinen) osa Liukenee hyvin veteen Amfifiilinenrakenne

25. Effect of extractives on the ESCAC 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. COO- 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

28. Certain polysaccharides have a natural affinity to cellulose surfaces Laine et al. 2000

29. Effect of Wet Strengthening Aids on Initial Wet Strength Different polymers influence the development of stregth during drying in different ways !!!

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

31. TEMPO-oxidized cellulose 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.

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... Adhesion between charged surfaces Bridging Salmi et al, Coll Surf A, 2006 Polyelectrolyte complexes adsorbed on cellulose surfaces

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 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

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 1.6 MPa 0.3 MPa Apparent elastic modulus Laine et al. 2002

37. no polymer, 10x obj. C-PAM, 10x obj. CMC 10x obj. Behaviour of surface fibril aggregates by addition of different polymers Myllytie et al. 2006

38. CMC-treatment makes the surface layer looser Cell wall Apparent elastic modulus 1.6 MPa Surface teated with CMC: Apparent elastic modulus 0.13 MPa Fors 2001

39. 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

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

43. Natriumalkanoaattien vesiliuosten pintajännitys CnH2n-1COONa Hilivetykejun kasvaessa cmc laskee ja adsorptio voimistuu

44. Adsorptio hydrofiiliseen ja hydrofobiseen pintaan Adsorptio hydrofobiseen pintaan Adsorptio hydrofiiliseen pintaan •  •  • Kons • Kons

45. Treatment of paper with hydrophobic materials Spreding, reaction orientation Size H2O H2O Size Paper surface

46. 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 1.6 MPa 0.3 MPa Apparent elastic modulus Laine et al. 2002 After drying Myllytie 2009

48. Bridging of single polymer chains in a polymer melt Sun and Butt Macromolecules37 (2004) 6086.

49. Size of complex particlesformed by A-PAM and C-PAM with low charge density and different Mw Tailor-made fine structure High Mw Medium Mw Low Mw Dynamic light scattering data

50. 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