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North Carolina State University Raleigh, North Carolina, USA

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 t#22-0 in page 48). 2007 Nanotechnology for the Forest Products Industry 13-15, JUNE, 2007 | KNOXVILLE

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North Carolina State University Raleigh, North Carolina, USA

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  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 t#22-0 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. Polymers are added as surface modifiers (fibers and fines) 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 compd’s • suspended solids • carry-over chemicals monolayer surfactant molecule entrained air polymer colloidal pitch size precipitate or emulsion microdroplet biological organism fines micelle fiber pigment/filler particle

  5. 1 mm Fiber particles Wood fiber Wood fiber

  6. 0.1 mm Fiber Clay agglom- erates PAM PAM Fiber fine

  7. 0.01 mm Kaolin Amylose TiO2 PAM Bentonite Fibrils Amylo- pectin Wood fiber Cat. PAM TiO2 Kaolin

  8. 0.001 mm (1 µm) Amylopectin TiO2 Colloidal silica TiO2 Bentonite TiO2 Kaolin Amylose Fiberwall fibrils PAM

  9. 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. CH 3 ( ) CH C 2 n C=O acrylamide (AM ) NH ( ) CH CH 2 n CH 2 C=O CH 2 NH 2 CH 2 + N + CH CH 3 3 - CH Cl 3 + + + + + + + + + + + + + + + + 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 Bimorph Surfaces

  14. Equilibrium Adsorption Adsorption kinetics 3.5 3.0 3.0 2.5 2.5 2.0 G, mg/m2 G, mg/m2 2.0 1.5 1.5 1.0 1.0 0.5 0.5 Ellipsometry /Silica XPS/Mica 0 0.0 0 1000 2000 3000 4000 5000 6000 0 100 200 300 400 500 Time, s PE (t =1%) Concentration, mg/ml • Polyelectrolyte Adsorption J Colloid Interface Sci. 205:77 (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

  16. Polyelectrolyte Charge Density - Adsorbed Amount and Conformation at the Interface 3.0 2.5 2.0 1.5 Adsorbed Polyelectrolyte, mg/m2 1.0 0.5 0.0 0 10 20 30 40 50 60 70 80 90 100 Polyelectrolyte Charge Density, % Langmuir 18: 1604 (2002)

  17. 10000 Steric forces! F/R, mN/m 0 0 20 20 40 40 60 60 80 80 100 100 Distance, nm 10000 Nanoscale Interaction Forces! What are their implications at the macroscale? 1000 100 10 Interaction Forces Double-layer repulsion Total energy Repulsion (+) DLVO Interaction Energy Distance 0 van der Waals attraction Attraction (-) Intl J Mineral Process, 56: 1–30 (1999).

  18. 10000 1000 100 10 d =50 nm s d =5-8 nm c Cat. PE t= 1% Adsorbed Conformation and Adhesion Alexander-de Gennes fit Steric repulsion (elastic and osmotic contributions) é ù 9 / 4 3 / 4 æ ö æ ö k T 2 L D = - ç ÷ ç ÷ B ê ú P ( D ) è ø è ø 3 s D 2 L 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) 17 2 Loop density= 2.02x10 loops/m 15 2 Tail density= 3.34x10 tails/m JCIS 205: 77 (1998)

  19. Interpenetration & bridging adhesion 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)

  21. + + + + + + + + + + + + + + + Charge reversal re-dispersion + Steric repulsion Bridging flocculation Patch & 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, %

  22. Fitting polymers to the demands of the wet end: A subtle balance of interactions at the nanoscale Macroscopic Effects (two cases: retention and adhesion)

  23. 0.6 1.0 0.5 0.8 0.4 1.0 0.6 0.3 Absorbance Absorbance 0.8 Absorbance 0.4 0.2 0.6 0.2 0.1 0.4 0.0 0.0 0 5 10 15 20 25 0 5 10 15 20 Dosage, mg/g 0.2 Dosage, mg/g Dosage, mg/g 1.4 underivatized GG whole pulp 0.0 1.2 0 5 10 15 20 1.0 0.8 Absorbance 0.6 0.4 anionic GG whole pulp 0.2 0.0 0 5 10 15 20 Dosage, mg/g Adsorption of Guar Gums (GG) high t cationic GG whole pulp low t* cationic GG whole pulp * t = charge density

  24. 0.6 1.0 0.5 0.8 0.4 1.0 0.6 0.3 0.8 0.4 0.2 0.6 0.2 0.1 0.4 0.0 0.0 0 5 10 15 20 25 0 5 10 15 20 Dosage, mg/g 0.2 Dosage, mg/g Dosage, mg/g 1.4 0.0 1.2 0 5 10 15 20 anionic GG whole pulp 1.0 0.8 0.6 0.4 0.2 underivatized GG whole pulp 0.0 0 5 10 15 20 Dosage, mg/g Adsorption of Guar Gums (GG) high t cationic GG whole pulp low t* cationic GG whole pulp * t = charge density

  25. Fines Retention 50 50 low t cationic GG (whole pulp) 40 45 40 30 Dissolved and Colloidal Carbohydrates, mg/g % Fines Retention 35 20 30 low DS cationic GG whole pulp 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)

  26. ADHESION: Symmetrical Systems Asymmetrical Systems

  27. 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

  28. 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)

  29. 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

  30. 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

  31. Fitting polymers to the demands of the wet end: A subtle balance of interactions at the nanoscale Polyampholytes

  32. O 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. Increasing charge 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).

  34. Expected conformational changes following adsorption of a polyampholyte in which the distribution of charged groups is segregated

  35. 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

  36. SP vs pH: HW Fiber Increasing charge 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

  37. 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)

  38. 5.0 pH=4 Bleached HW Kraft Fibers pH=5 4.5 pH=8.5 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)

  39. 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.

  40. Fitting polymers to the demands of the wet end: A subtle balance of interactions at the nanoscale Mixing Effects

  41. 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

  42. 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

  43. + + + + + + + + + + + + + + + + + + + Polymer (+) & Surfactant (-) t= 10% O - S O O CH O Na dedecyl sulphate (SDS) 3 ( ) CH C 2 n ( ) CH CH 2 n C=O C=O 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 )

  44. 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) Polymer-Surfactant-Surface Systems (Polymer + Surfactant) Coadsorption One step adsorption Sequential adsorption

  45. 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.

  46. 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) Polymer-Surfactant-Surface Systems (Polymer + Surfactant) Coadsorption One step adsorption Sequential adsorption

  47. Polyelectrolyte + Surfactant Adsorption 2 Polyelectrolyte + Surfactant Adsorption 1 + + + + + + One-step Coadsorption Case

  48. 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) Polymer-Surfactant-Surface Systems (Polymer + Surfactant) Coadsorption One step adsorption Sequential adsorption

  49. Sequential Coadsorption Case New solution, higher surfactant conc. Polyelectrolyte + Surfactant Adsorption + + + + + + + + + rinsing

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