North Carolina State University

1
Fitting Polymers to the Demands of the Wet End A
subtle Balance of Interactions at the Nanoscale
Orlando J. Rojas, NC State
www4.ncsu.edu/ojrojas

(see abstract t22-0 in page 48)
2007 Nanotechnology for the Forest Products
Industry 13-15, JUNE, 2007 KNOXVILLE Surface
Modification and Characterization Session Chair
Pete Lancaster, Weyerhaeuser
North Carolina State University Raleigh, North
Carolina, USA
2
Fitting polymers to the demands of the wet end A
subtle balance of interactions at the
nanoscale or The Soft Side of Nanotechnology
Outline
3
Fitting polymers to the demands of the wet end A
subtle balance of interactions at the nanoscale
Introduction
4
Papermaking A Colloidal Soup
Pulping Bleaching
Recycling other process streams
Chemical Additives

• promoters
• dyes
• defoamers
• slimicides
• glue

• dry strength resins
• wet strength resins
• release emulsions
• surfactants
• retention aids
• pitch control aids

• salts
• dissolved organic compds
• suspended solids
• carry-over chemicals

monolayer
surfactant molecule
entrained air
polymer
colloidal pitch
size precipitate or emulsion microdroplet
biological organism
micelle
fines
fiber
pigment/filler particle
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Fitting polymers to the demands of the wet end A
subtle balance of interactions at the nanoscale
Simple Polyelectrolytes (PE) (and the Effect of
PE Charge Density)
10
Interaction forces are difficult to measure and
understand
How do surface modifiers affect adhesion and
macroscopic properties of papermaking surfaces?
Complex nature of fiber (and mineral) surfaces
(chemical and morphological) Subtle balance of
interactions at the nanoscale
11
Simple Polyelectrolytes PE ()
3-(2-methylpropionamido)propyl
trimethylammonium chloride (MAPTAC )
t (charge density) 1, 10, 30, 100 (Mw 1M)
Substrates
Silica, glass, mica and cellulose(-)
12
XPS to Quantify Polyelectrolyte Adsorption
C1s
O1s Si2p K2p N1s
Photoelectron
I
I
A
A
Al Ka X-Ray
L
2,3
1486.6
eV
L
1
u
h
Emission
Excitation
polyelectrolyte
q
K
x
mica
N
N
I
mg Polyelectrolyte
N
N
N
I
N
A
A
K
K
Rojas et al., J. Phys. Chem. B, 104(43)
10032-10042 (2000)
13
Bimorph surface force apparatus Measurement and
Analysis of Surface and Interfacial Forces
Piezo tube
LVDT
Motor translation
Teflon seal
Clamps for the bimorph
Teflon diaphragm
To charge amplifier...
Teflon sheath
Surfaces
Bimorph
14
Polyelectrolyte Adsorption
J Colloid Interface Sci. 20577 (1998)
15
XPS N1s
Adsorption Isotherms
3.0
Mica
2.5
2.0
XPS detailed N 1s spectrum for cellulose after
immersion in 0.1 mM KBr solution
Adsorbed Polyelectrolyte, mg/m2
1.5
1.0
LB-Cellulose
0.5
XPS N1s
0.0
0
50
100
150
200
Polyelectrolyte Concentration, mg/mL
XPS detailed N 1s spectrum for cellulose after
immersion in 0.1 mM KBr containing 200 mg/L of
polyelectrolyte
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Interaction Forces
Double-layer repulsion
Total energy
Repulsion ()
DLVO
Interaction Energy
Distance
0
van der Waals attraction
Attraction (-)
Intl J Mineral Process, 56 130 (1999).
18
Cat. PE t 1 Adsorbed Conformation and Adhesion
Alexander-de
Gennes
fit
Steric repulsion
(elastic and osmotic contributions)

é
ù
/
/
æ
ö
æ
ö
9
4
3
4
k
T
L
D
2

ç

-
ç

B
ê
ú
P
D
(
)
è
ø
è
ø
3
s
D
L
2
ë
û
/m
N
m
F/R,
2d
c
0.45
nm
2d
s
AM-MAPTAC-1 copolymer (AM
MAPTAC)
101
122
0
20
40
60
80
100
Distance,
nm
loop
tail
10 of mica charges are compensated
17
nm
(24
nm
from Alexander-de
Gennes
fit)
Loop density 2.02x10
17
loops/m
2
Tail density 3.34x10
15
tails/m
2
JCIS 205 77 (1998)
19
Cat. PE t 10 Adsorbed Conformation and Adhesion
10
Electrosteric repulsion
1
F/R, mN/m
0.1
DLVO fit
adhesion
0.01
0
20
40
60
80
100
Apparent Separation Distance, nm
Adv. Colloid Interface Sci 104 53 (2003)
20
2
1
1.5
1
F/R (mN/m)
0.5
10
0
100
30
-0.5
0
200
400
600
800
Distance (Å)
Force normalized by radius between surfaces
precoated with various polyelectrolytes in
aqueous 0.1 mM KBr solution. The arrow indicates
an inward jump and the vertical lines the layer
thicknesses for adsorbed polyelectrolytes.
Langmuir 18 1604 1612 (2002)
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Flocculation Stabilization
1.5
1.0
Charge Neutralization
0.5
0.0
0
10
20
30
40
50
60
70
80
90
100
Polyelectrolyte Charge Density,
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Fitting polymers to the demands of the wet end A
subtle balance of interactions at the nanoscale
Macroscopic Effects (two cases retention and
adhesion)
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Adsorption of Guar Gums (GG)
high t cationic GG whole pulp
low t cationic GG whole pulp
t charge density
24
Adsorption of Guar Gums (GG)
high t cationic GG whole pulp
low t cationic GG whole pulp
t charge density
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Fines Retention
50
50
low t cationic GG (whole pulp)
40
45
40
30
Dissolved and Colloidal Carbohydrates, mg/g
Fines Retention
35
20
low DS cationic GG whole pulp
30
10
25
0
5
10
15
20
25
0
0
5
10
15
20
25
Dosage, mg/g
Dosage, mg/g
Colloids Surfaces A.155, 419-432 (1999)
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ADHESION Symmetrical Systems Asymmetrica
l Systems
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High charge density polymers
extensive BRIDGING
Surface contact
On separation
r/r0 0.65-0.75 (0.63 JKR)
PE layer thickness increase of 0.5-1 nm
PE stretching
PE collapses in different conformation
() Note Contact area on separation stick-slip
behavior
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Effect of PE Charge Density on Adhesion
3000
2000
layer is disrupted
F/R (mN/m)
Decreasing importance of electrostatic bridging
1st
1000
5th sep.
Interpenetration and entanglement
0
0
20
40
60
80
100
Charge density ()
Langmuir 20(8)3221-3230 (2004)
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• Paper strength
• Fiber intrinsic strength
• Bond strength
• Number of bonds
• Fiber and bond distribution

Charge density of pulp fibers Fibers are dried
in close proximity (surface tension and
capillary effects). Larger chances for polymer
layers to interpenetrate and interlock
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Conclusions I
Polyelectrolyte charge density important effect
on adsorbed state (surface modification)
Interaction forces at the nanoscale shapes up
macroscopic phenomena (e.g., retention and
adhesion) PE charge density key in adhesion
development. Evidence of formation of
electrostatic bridges (for PEs with high charge
density). Entanglement contributes to
adhesion in the case of PEs of low charge
density
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Fitting polymers to the demands of the wet end A
subtle balance of interactions at the nanoscale
Polyampholytes
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Polyampholytes
H
O
Dimethylaminoprolylacrylamide (DMAPAA) monomer
group
O
n
m
100-n-m
O
O
NH
HO
N
H2
Itaconic acid monomer group
Acrylamide monomer group
(H3C)2N
33
Synthesis of acrylamide-based polyampholytes and
copolymers
Sam-ple
Polymer Type
DMAPAA mol
IA (mol )
Mw (106 Daltons)
A
Amphoteric
2.5
1
2.95
B
5
2
2.85
C
10
4
2.90
D
20
8
2.93
F
Cationic
5
0
2.98
G
Anionic
0
2
3.23
Mass-average molecular mass evaluated by
SEC-LALLS-VIS (TDA-302, Viscotek).
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Expected conformational changes following
adsorption of a polyampholyte in which the
distribution of charged groups is segregated
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SP vs pH HW FBG
10
5
Poly-base () F
0
Streaming Potential (mV)
-
5
Poly-ampholyte B
-
10
Blank
Poly-acid (-) G
-
15
Kraft fiber
-
20
2
4
6
8
10
12
pH
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SP vs pH HW Fiber
8
Increasing charge
A
B
4
C
0
D
Blank
-
4
Streaming Potential (mV)
-
8
-
12
Kraft fiber
-
16
2
4
6
8
10
12
pH
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Adsorption vs pH
1.0
0.9
Poly-ampholyte B
0.8
0.7
0.6
Poly-base () F
Adsorbed Amount (g/100g pulp)
0.5
0.4
0.3
0.2
B, 5 cat, 4 an
0.1
F, 5 cationic
0.0
3
4
5
6
7
8
9
10
11
pH
NPPRJ 21(5) 638-645 (2006)
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5.0
pH4
Bleached HW Kraft Fibers
pH5
4.5
pH8.5
4.0
Breaking Length (km)
3.5
3.0
2.5
2.0
Blank
A
B
C
D
F
G
Polymer (1 Treatment Level)
JPPS 32(3) 156-162 (2006)
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Conclusions II
Polyampholytes interesting alternative to
fine-tune (surface) properties of fiber and fiber
networks. Strength is related with the mass of
polymer adsorbed
Broad maximum in polyampholyte adsorption in pH
range 6 to 9, greatly exceeding adsorbed amounts
of corresponding polyelectrolytes
There appears to be an optimum charge density of
polyampholytes to provide strength gains in
paper.
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Fitting polymers to the demands of the wet end A
subtle balance of interactions at the nanoscale
Mixing Effects
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Polymers and surfactants are included in fluid
formulations to achieve independent objectives.
suspensions and slurries pigment, paper,
printing and coating formulations.
The effects of polymer/surfactant interactions on
adsorption and adhesion remain difficult to
predict
Polymers are intended to control rheology
Surfactants are intended to control capillarity
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Polymer-Surfactant-Surface Systems
Surfactant binds to polymer surface is
selective (type I) surface is non-selective
(type II) Surfactant does not bind to
polymer surface is selective (type III) surface
is non-selective (type IV)
Our case Selective Surfaces I
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Polymer () Surfactant (-)
t 10
O
-
S
O
O
CH
O
Na dedecyl sulphate (SDS)
3
(
)
C
CH
(
)
2
n
CH
CH
2
n
CO
CO
NH
NH
CH
2
2
CH
acrylamide (AM )
2
CH
2

N
CH
CH
3
3
-
CH
Cl
3
3-(2-methylpropionamido)propyl
trimethylammonium chloride (MAPTAC )
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(Polymer Surfactant) Coadsorption
One step adsorption
Sequential adsorption
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Mixed (polyelectrolyte/surfactant) coadsorption
How do adsorbed polyelectrolytes respond to
changes in surfactant concentration?
Challenge Understand the origins of the
synergies in polymer systems and rationalize
issues related to processing history.
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Polymer-Surfactant-Surface Systems
(Polymer Surfactant) Coadsorption
One step adsorption
Sequential adsorption
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One-step Coadsorption Case
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Polymer-Surfactant-Surface Systems
(Polymer Surfactant) Coadsorption
One step adsorption
Sequential adsorption
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Sequential Coadsorption Case
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Coadsorption
Sequential adsorption One-step adsorption
0.6
4.2
Layer of aggregates
3.6
0.5
3.0
0.4
2.4
Surface Concentration (mg/m2)
Effective Optical Thickness (nm)
0.3
1.8
0.2
1.2
0.1
0.6
0
0.1
0.5
2
Rinse
SDS Concentration (normalized cmc)
PE t 10 / SDS / silica
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Coadsorption
Sequential adsorption One-step adsorption
0.6
4.2
Layer of aggregates
3.6
0.5
3.0
0.4
Not path dependant!
2.4
Surface Concentration (mg/m2)
Effective Optical Thickness (nm)
0.3
1.8
0.2
1.2
0.1
0.6
0
0.1
0.5
2
Rinse
SDS Concentration (normalized cmc)
PE t 10 / SDS / silica
53


v



















0
0.1
0.5
2
Rinse
SDS Concentration (normalized cmc)
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Interaction forces
0 SDS On approach Electrosteric interaction
forces On separation Adhesion, interpenetration
and bridging 0.1 and 0.5 cmc SDS On approach
compression of thick layer of aggregates On
separation No Adhesion 2 cmc SDS On
approach Electrosteric interaction forces On
separation Reappearance of Adhesion
interpenetration and bridging
Reversibility! (the exception to the rule)
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(Polymer Surfactant) Coadsorption
Type I co-adsorption systems In most cases the
composition and structure of the adsorbed layers
depends on the order in which the surface is
exposed to surfactants and polymers. Not in our
case
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Type I systems (surfactant and polymer associate
in solution and the surface is selective for the
polymer) AM-MAPTAC SDS / SILICA PEO-PPO-PEO
SDS / SILICA
Polymer adsorbs irreversibly. Mixed layers
respond reversible to changes in surfactant
Strong Surfactant-Polymer affinity
cellulose (HPC or hmHEC) SDS / SILICA
Strongly path-dependent coadsorption
Weak Surfactant-Polymer affinity
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Weak Polymer affinity
Activation barrier (against polymer desorption or
rearrangement) is small
No capacity to respond to changes. Path-dependant
coadsorption
SDS stripped off. More train segments
Segments solubilized More loops and tails
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Conclusions III
Mixed adsorbed layers respond reversibly to
changes in the concentration of SDS in a mixed PE
/ SDS solution Most common cases
Path-dependent co-adsorption (hysteretic)
(characterized by persistent non-equilibrium
states at interfaces). Balance of affinities
explains hysteretic effects
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Fitting polymers to the demands of the wet end A
subtle balance of interactions at the nanoscale
Conclusions
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Soft side of Fiber Nanotechnology
Papermaking wet end adsorption from polymer
mixtures to the solid-liquid interface is a
critical aspect of the process. Interaction
forces, balance of charges and adsorbed mass
dominates cause-effect relationships (from the
nano- to the macro-scales!)
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Acknowledgments
Dr. Kim Cellulose Nanorods and Electrospinning
of Cellulose Nanocrystal Composites
Dr. Montero Cellulose Nanocrystals
Electrospinning Lignin Thermal Properties
Hongyi Liu Boundary Layer Lubrication and
Molecular Dynamics Simulation
Kelley Spence Self Assembly Monolayers of
Cellulose
Junlong Song Polyampholyte Adsorption, Boundary
Layer Lubrication and Molecular Dynamics
Simulation
Dr. Xavier Turon Enzyme Activity via
piezoelectric Sensors and Molecular Dynamics
Simulation
Chang Woo Jeong Enzyme Activity via
piezoelectric Sensors, Thin films and Boundary
Layer Lubrication
Wes Crawford Surfactants in Paper Recycling
Special thanks to Prof. Martin Hubbe, Dr. Xingwu
Wang and Yun Wang. Generous support from the
National Research Initiative of the USDA
Cooperative State Research (grant number
2004-35504-14655) Harima Chemical Co., and NCSU
Nanotechnology Seed Grant are acknowledged.
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Thanks for your attention