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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