vtt: kristian salminen, janne kataja-aho, elias retulainen

The Effects of Certain Polymers on Tensile Strength and Tension Relaxation of Wet WebStrength and Tension Relaxation of Wet Web

VTT: Kristian Salminen, Janne Kataja-aho, Elias Retulainen & Timo RantanenÅbo Akademi: Hanna Lindqvist & Anna Sundberg

PaperCon 2011 Page 833

Table of contents

BackgroundBackgroundObjectives

Methods

Results & Discussion

Summary & Conclusions


Background (1/3): Wet web strength studies•Lyne & Gallay 1954: The strength of wet web (up to a dryness levelof 25%) originates from surface tension forces and friction betweenfibers. Above this level of dryness, inter-fiber bonding starts to play any g yessential role

•Gierz & Roedland 1979: There is bound water on fiber surfaces.When two fibers with high amount of bound water get close to eachWhen two fibers with high amount of bound water get close to eachother, a high adhesion between these fibers is formed

•Pelton 1993 & 2000 / Hubbe 2006 / Myllytie 2009: Wet fibery ysurface can be considered as a gel-like layer of hydrated cellulosemicrofibrills and polymers. The mixing and orientation of the polymersin the bonding domain affect the strength of dry and wet web

•Tajedo & van de Ven 2008 & 2009: Entanglement friction betweenfibers plays a major role in wet web strength (at dryness 30-55%),whereas surface tension forces have more or less no effect at a givenwhereas surface tension forces have more or less no effect at a givendryness level


Background (2/3): Wet web properties and paper machine runnability

• Paper machines have reachedtheir practical maximum width(~11 m). To increaseproduction, higher speed andless downtime is required

•Increase of production speed isoften limited by mechanicalproperties of wet web

Pakarinen et al 1995

properties of wet web

• The fact remains that paperThe fact remains that papermills do not typically addchemicals to improvemechanical properties of wetp pweb Hokkanen 1996


Background (3/3): What should we measure from wet web?

Modified from Kurki et al 2004 & Kurki et al 2000


Objective of this study…

…was to clarify the effects of some i ll il bl lcommercially available polymers or

combinations of polymers on tensile and relaxation characteristics of wet webrelaxation characteristics of wet web


Methods (1/2): Spraying tests

Preparation of samples Measurements

Wet ipressing

50 kPa 350 kP

CMC, PVA & CHITOSAN

350 kPa

CHITOSAN CMC + CHITOSAN

CMC + C-PAM C-PAM + A-PAM


Methods (2/2): Mode of addition testsSpray applicationSpray application

A-PAMC-PAM

Pulp suspension applicationC-PAM

0%Whole pulp

50%

50%

Handsheets

A-PAM50%

PaperCon 2011 40

Why to add polymers by spraying?

Higher retention of polymers (with no cationic charge)

No effect on formation

To avoid adsorption of polymers mainly to fines fraction


Results: Spraying testsResults: Spraying tests


Reference CMC 1 g/m2

1 2

Reference CMC 1 g/m2CMC 2 g/m2 Chitosan 1 g/m2CMC + Chitosan (1 + 1 g/m2) Pva 1 g/m2CMC + C-PAM (1 + 0.5 g/m2) C-PAM + A-PAM (0.5 + 0.5 g/m2)

1.0

1.2

kN/m

] Dual application trial points

PVA+100%

0.6

0.8

engt

h [ k

ChitosanCMC

+100%

0 2

0.4

nsile

str

e

Reference (Water spray 200 g/m2)

0.0

0.2

45 50 55 60 65

Ten

45 50 55 60 65Dryness [ % ]


Reference CMC 1 g/m2

1 2

Reference CMC 1 g/m2CMC 2 g/m2 Chitosan 1 g/m2CMC + Chitosan (1 + 1 g/m2) Pva 1 g/m2CMC + C-PAM (1 + 0.5 g/m2) C-PAM + A-PAM (0.5 + 0.5 g/m2)

1.0

1.2

kN/m

] Dual application trial points

PVA+100%

0.6

0.8

engt

h [ k

ChitosanCMC

+100%

0 2

0.4

nsile

str

e

Reference (Water spray 200 g/m2)

GGM (1 / 2)

0.0

0.2

45 50 55 60 65

Ten

Cationic starch / Xylan (1 g/m2)GGM (1 g/m2)

45 50 55 60 65Dryness [ % ]


Adding different polymers had no clear effect on elastic modulus(tensile stiffness) and residual tension (the tension remaining(tensile stiffness) and residual tension (the tension remainingafter 0.475 s of relaxation) of wet web

Reference CMC 1 g/m2 Reference CMC 1 g/m2

30

40

s [ k

N/m

]

Reference CMC 1 g/m2CMC 2 g/m2 Chitosan 1 g/m2CMC + Chitosan (1 + 1 g/m2) PVA 1 g/m2CMC + C-PAM (1 + 0.5 g/m2) C-PAM + A-PAM (0.5 + 0.5 g/m2)

506070

n [ N

/m ]

Reference CMC 1 g/m2CMC 2 g/m2 Chitosan 1 g/m2CMC + Chitosan (1 + 1 g/m2) PVA 1 g/m2CMC + C-PAM (1 + 0.5 g/m2) C-PAM + A-PAM (0.5 + 0.5 g/m2)

10

20

last

ic m

odul

us

10203040

esid

ual t

ensi

o

045 50 55 60 65

Drynness [ % ]

El 045 50 55 60 65

Dryness [ % ]

Re

It seems likely that different polymers increasedstrength of fiber-fiber contacts, but had only minor if anyeffect on the readiness of fiber segments to carry load


Adding different polymers by spraying increased drypaper tensile index, but had no effect on density.p p , y

Bond strength increases

50607080

[ Nm

/g ]

400500600700

[kg/

m3 ]

01020304050

e 2 2 2 2) 2 2) 2)

Tens

ile in

dex

0100200300400

rence

g/m2)

g/m2)

g/m2)

g/m2)

g/m2)

g/m2)

g/m2)

Den

sity

[

Referen

ceCMC 1

g/m2

CMC 2 g/m

2Chito

san 1

g/m2

CMC + Chito

san (1

+ 1 g/m

2)PVA 1

g/m2

CMC + C-P

AM (1 +

0.5 g/m

2)

CPAM +

A-PAM (0

.5 + 0

.5 g/m

2)

Refere

CMC (1 g/

CMC (2 g/

Chitosa

n (1 g/

CMC + Chito

san (1

+ 1 g/

PVA (1 g/

CMC + C-P

AM (1 +

0.5 g/

C-PAM +

A-PAM (0

.5 + 0

.5 g/

C-P

Biggest increase in dry paper tensile strength was obtained with sequential addition of CMC and chitosan


Results: Mode of addition testsResults: Mode of addition tests


Sequential addition of oppositely charged polymersimproved dry and wet web strength, while adding of thesame polymers on separately to different part of pulpsuspensions (50/50) only minor effects were seen70

0.8

1.0

h [ k

N/m

]

Reference C-PAM + A-PAM by sprayingC-PAM + A-PAM to pulp

40

50

60

70

ex [

Nm

/g ]

0 0

0.2

0.4

0.6

ensi

le s

tren

gth

0

10

20

30

Tens

ile in

de

0.045 50 55 60 65

Dryness [ % ]

T0Reference C-PAM + A-PAM

by sprayingC-PAM + A-PAM

to pulp

Adding polymers to pulp suspension resulted as loweradsorption of polymers and impaired formation of thep p y psheets (compared to spray application trial point)


• S i f l t b i t ti ibilit t

Summary / Conclusions• Spraying of polymers seems to be an interesting possibility to

improve dry and wet web strength• It could enable higher retention of different polymers and thus

d th t f l ill it ld kreduce the cost of polymers on paper mill or it could makepossible the usage of polymers having no cationic charge

• The effect of polymers on strength of dry and wet web wash t i ti f h lcharacteristic for each polymer

• Polymers improved the strength of the wet web significantlymore (relatively) than dry paper

• Highest increase in wet web strength was obtained withsequential spray addition of oppositely charged polymers andwith a hydrophilic polymer having high molar mass

• Spraying of anionic polymers to the outermost layer of papermight also reduce adhesion problems at (anionic) center roll

• It seems also likely that electrostatic interactions play anIt seems also likely that electrostatic interactions play anessential role in wet web strength


Th kThank you ffor your

attention!!!The support of Kemira, Metso Paper, Stora Enso, UPM and

TEKES to this study is gratefully acknowledged


vtt: kristian salminen, janne kataja-aho, elias retulainen

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