Adhesion of Poly(vinylamine) Microgels to Wet Cellulose - Industrial

Aug 22, 2007 - Poly(N-vinylformamide) microgel, crosslinked by 1,3-divinylimidazolid-2-one (BVU), was synthesized via precipitation polymerization in ...
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Adhesion of Poly(vinylamine) Microgels to Wet Cellulose Chuanwei Miao, Xiaonong Chen, and Robert Pelton* McMaster Centre for Pulp and Paper Research, Department of Chemical Engineering, JHE-136, McMaster UniVersity, Hamilton, Ontario, Canada, L8S 4L7

Poly(N-vinylformamide) microgel, crosslinked by 1,3-divinylimidazolid-2-one (BVU), was synthesized via precipitation polymerization in methyl ethyl ketone (MEK), giving aggregated particles with a broad size distribution. Alkaline hydrolysis yielded a series of poly(vinylamine) (PVAm) microgels. The wet adhesion properties of the microgels on a regenerated cellulose membrane were studied by delamination experiments, and the results were compared with that of a linear PVAm. Above the polymer coverage (i.e., the amount of polymer in the adhesive joint) of 15 mg/m2, the linear polymer and the microgel give similar adhesion, and higher polymer coverage does not increase the wet strength any further. However, when the polymers are applied on the wet cellulose membranes by adsorption from solution, the delamination force of the membranes with the microgel was much stronger than those with the linear polymer, because the microgel formed a much thicker polymer layer on membranes. Confocal laser scanning microscopy (CLSM) images of laminates prepared with fluorescently labeled polymers and microgels revealed that the linear polymer gives cohesive failure during peeling test, while adhesive failure is dominant for the microgel. Introduction Water-soluble polymers are used to strengthen wet paper and paper board that is used for filtration, toweling, and packaging, where wet strength is important.1 The wet-strength polymers are usually adsorbed onto fiber surfaces in the papermaking process and the polymers function by increasing fiber-fiber adhesion in the presence of water. Because cellulose fibers are rough on most distance scales, we hypothesized that relatively large microgels might give better wet strength than the corresponding smaller linear polymers. When comparing microgel adhesives to the corresponding linear polymers, it is useful to separate substrate surface roughness effects from intrinsic adhesion. Therefore, in this work, we compare the wet adhesion characteristics of microgels to the corresponding linear polymer on relatively smooth regenerated cellulose films; future publications will describe the corresponding work with rough wood pulp fibers. We choose poly(vinylamine) (PVAm) as the polymer platform for this work, because it has been shown to give strong wet adhesion to cellulose2,3 and because it can be prepared in both linear and microgel forms. Linear PVAm is synthesized from a precursor monomer, N-vinylformamide (NVF) which can be readily polymerized with free-radical initiators, followed by the hydrolysis under either acidic or basic conditions4 (see Figure 1). In water, PVAm is highly positively charged, which leads to applications that inculde papermaking,5-7 wastewater treatment,5 and superabsorbent materials.8 Most linear water-soluble polymers can also be prepared as cross-linked gels, and PVAm is no exception. The synthesis of PVAm macrogels has been describe by Suh et al.,9 who prepared slab PVAm gels by casting the mixture of linear PVAm solution and a bis-epoxide crosslinker in a small mold. They reported swelling behavior with varying pH and ionic strength. Yamamoto et al.10 obtained a PVAm copolymer hydrogel by copolymerizing NVF with N-vinylisobutyramide (NVIBA) and N,N-butylene-bis-N-vinylacetamide (Bis-NVA), followed by hydrolysis. The resultant hydrogel was responsive to both pH * To whom correspondence should be addressed. Tel.: (905) 529 7070,ext.27045.Fax: (905)5285114.E-mailaddress: [email protected].

Figure 1. Synthesis route from N-vinylformamide (NVF) to poly(vinylamine) (PVAm).

and temperature. Finally, we have described the mechanical and swelling properties of macrogels based on complexes between PVAm and carboxymethyl cellulose.11,12 Although the preparation and applications of linear PVAm and PVAm macrogels are well-established, there have been few reports in the literature on the preparation of PVAm microgels. In a Japanese patent application, Itagaki et al.13 reported a method to prepare PVAm spheres by dispersing linear PVAm aqueous solutions in a oil phase, and then crosslinking the amino groups. The only other report comes from our laboratory and describes poly(N-isopropylacrylamide) microgels that contain low concentrations of amine groups.14 We have reported the adhesion properties of linear PVAm to wet cellulose. PVAm gives high and constant adhesion values from pH 3 to pH 9, and the results are not sensitive to PVAm molecular weight or ionic strength.15,16 On the other hand, mild oxidization of the cellulose films with TEMPO/NaBr/NaClO greatly increased adhesion, which we explained by covalent bond formation between primary amine groups on PVAm and hemiacetal groups on cellulose.15,17 The cellulose substrates in this work were regenerated cellulose membranes and adhesion

10.1021/ie0705608 CCC: $37.00 © 2007 American Chemical Society Published on Web 08/22/2007

Ind. Eng. Chem. Res., Vol. 46, No. 20, 2007 6487 Table 1. Polymerization Recipesa polymer

LS

LMb

LLb,c

HS

HMb

HLb,c

NVF BVU VAZO 52 MEK

5g 0.5 g 50 mg 45 (+ 25d) g

5g 0.25 g 50 mg 10 g

5g 0.25 g 50 mg 10 g

5g 1g 50 mg 45 (+ 25d) g

5g 0.75 g 50 mg 10 g

5g 0.75 g 50 mg 10 g

a Sample designations are described as follows. The first letter denotes the crosslinker content (L ) low, H ) high), and the second letter gives the size (S ) small, M ) medium, L ) large). b Samples were milled. c Fines were removed using an 11-µm filter. d The numbers given in parentheses represent the amount of MEK that is added dropwise into the flask 1 h after initiation.

was measured as the force required to peel apart wet cellulose films laminated with a very thin layer of PVAm.15,16 This approach was first reported by McLaren18 and has been used by other researchers.19 We view the cellulose laminates as physical models for fiber-fiber joints in paper. In this paper, we compare linear PVAm to a series of PVAm microgels as wet adhesives for cellulose using smooth regenerated cellulose as the substrates. The goal was to determine the role of microgel size and degree of crosslinking in the absence of substrate roughness effects. Experimental Section Materials. The monomer, N-vinylformamide (NVF, Aldrich Canada), was distilled under low pressure before use. The crosslinking monomer, 1,3-divinylimidazolid-2-one (BVU), and the linear poly(N-vinylformamide) (PNVF; MW ) 950 kDa) were provided by BASF (Ludwigshafen, Germany). 2,2′-Azobis(2,4-dimethylpentane nitrile (VAZO 52), which is a free radical initiator, obtained from DuPont Canada, was recrystallized in methanol. Methyl ethyl ketone (MEK, Caledon Laboratories), acetone (Caledon Laboratories), fluorescein-5-isothiocyanate (FITC, Molecular Probes), rhodamine B isothiocyanate (mixture of isomers, Aldrich), sodium hydroxide (EM Science), and hydrochloric acid (Fisher Scientific) were used as received. The regenerated cellulose membrane was cut from Spectra/Por2 dialysis tubing (MWCO: 12-14,000 kDa, Product No. 132684, Spectrum Laboratories, Inc., Rancho Dominguez, CA). Microgel Synthesis. The PVAm microgel suspensions used in this study were synthesized in our laboratory via precipitation polymerization. The recipes are summarized in Table 1. Using microgel LS as an example, the reaction was performed as follows. A three-neck round-bottom flask was equipped with a mechanical stirrer (200 rpm) with a Teflon blade and a condenser. The crosslinker, 0.5 g of BVU, was dissolved in 5 g of NVF and then the solution was added into the flask containing 45 g of MEK. The system was purged with N2 for 15 min at room temperature and heated to 50 °C with an oil bath. Fifty milligrams of VAZO 52 then was charged into the flask to initiate the polymerization. Approximately 1 h after the initiation, 25 g more MEK was added, using a dropping funnel, to dilute the suspension. After 6 h of reaction, a white PNVF suspension was obtained. These polymer particles were centrifuged to separate them from the suspension, and then they were redispersed in acetone. This process was repeated at least four times to remove unreacted monomers and the initiator. Finally, after the acetone was removed, the dry polymer was dispersed in water at the concentration of 5 wt %. An ultrasonicator was used to hasten the dispersion of microgels in this step. Finally, all PNVF microgels were hydrolyzed in 5 wt % NaOH solutions at 70 °C for 100 h to obtain completely hydrolyzed PVAm microgels.20

The product of the polymerizations, giving medium- and large-sized microgels, were white thick pastes. The pastes were cleaned by acetone and dispersed in water following the same procedures as described previously. After washing, the aqueous suspensions were milled in a CrushMaster blender (Black & Decker). The size of the gel particles was monitored by a Mastersizer (Malvern Corp.) intermittently during the milling process. For medium-sized particles, the milling time was ∼4560 min, whereas the large-sized samples need less time (∼2030 min). Because the gel particles prepared using this method had a wide size distribution, the fine particles fraction were removed from the large microgels (HL and LL; see Table 1) by washing them on an 11-µm nylon filter (Millipore, Catalog No. NY1100010). Microgel Characterization. The volumetric mean size and size distribution of the microgel dispersed in 5 mM NaCl (pH 7) was measured using a Mastersizer 2000 (Malvern Corp.). To determine the degree of swelling (wet mass, relative to dry mass) of the microgels at pH 7 in 5 mM NaCl, microgel suspensions were centrifuged at 14 000 rpm for 15 min, using an Allegra 25R centrifuge (Beckman Coulter). After the supernatant was decanted, the microgel was weighed and lyophilized, and then the dry microgel was weighed again to yield the degree of swelling. The hydrolysis degree of the microgels was measured using nuclear magnetic resonance (1H NMR) (Bruker, 200 MHz). Lyophilized microgels were dispersed in deuterated water (Cambridge Isotope Laboratories) to acquire the spectra. A transmission electron microscopy (TEM) system (JEOL, model JEM-1200EX) was used to produce the images of the microgels. Samples were added dropwise onto a copper grid that had been coated with Formvar and were observed after drying. The PVAm polymers and cellulose membranes labeled by fluorescent probes were examined by a confocal laser scanning microscopy (CLSM) system (Zeiss, model LSM 510). The FITC and rhodamine, which are the labels on the PVAm and cellulose membrane, were excited by lasers with wavelengths of 488 and 543 nm, respectively. Images giving the distribution of PVAm on a cellulose membrane were obtained with a C-Apochromat 63× objective lens, whereas the peeled membrane surface was examined by a Fluar 20× objective lens. Fluorescent Labeling of PVAm and Cellulose Membrane. To label the PVAm polymers, FITC was first dissolved in dimethylsulfoxide (DMSO) to form a 1 mg/mL solution. To 10 mL of 2 mg/mL target PVAm (linear or microgel) in pH 9 borate buffer was added 0.1 mL of the probe solution. The mixtures were then stirred using a magnetic stirring bar for 10 h at 4 °C, followed by quenching with 0.26 mL of 2 M NH4Cl for 2 h. To remove the unreacted FITC, 5 mL of the linear PVAm solution was eluted through a Sephadex G-25 gel filtration column with pH 9 borate buffer. The eluted polymer was dialyzed against deionized water for 3 days and then lyophilized. The PVAm microgel was purified by washing with 5 mM NaCl via centrifugation, decantation, and redispersion cycles. To label the cellulose membranes, 0.4 mL of the 2 mg/ mL rhodamine DMSO solution was mixed with 0.2 g of cellulose membrane in 40 mL of borate buffer at pH 9. The reaction was performed by increasing the temperature to 70 °C for 1 h. The membrane then was rinsed thoroughly with deionized water. All the aforementioned procedures were conducted in darkness. Wet Regenerated Cellulose Membrane Delamination. Spectra/Por regenerated cellulose tubing (diameter of 12 cm) was cut to strips with dimensions of 2 cm × 6 cm (top

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Figure 2. Transmission electron microscopy (TEM) images of PNVF and PVAm microgels prepared by precipitation polymerization, using 1,3-divinylimidazolid-2-one (BVU) as a crosslinker: (a) primary microgel particles, (b) aggregated primary particles, (c) nonhydrolyzed PNVF microgel, and (d) PVAm microgel (hydrolyzed). Table 2. Volume-Weighted Mean Size and the Swelling Ratio of Poly(vinylamine) (PVAm) Microgelsa microgel

mean size (µm)

D90% - D10% D50%

MassWet MassDry

LS LM LL HS HM HL

1.5 10.4 24.2 2.1 8.6 30

3.136 1.484 1.707 7.584 1.429 1.888

27.8 37.6 25.2 16.0 19.7 16.6

a

Figure 3. Volumetric size distribution of non-hydrolyzed (PNVF) and hydrolyzed (PVAm) microgels. Particle sizes were measured using a Mastersizer 2000 in 5 mM NaCl at pH 7.

membrane) and 3 cm × 6 cm (bottom membrane) with the long axis of the test strips parallel to the original long axis of the dialysis tube. Only the interior surfaces of the tubing were used to form the laminated joint. The strips were extracted with boiling Milli-Q water for 1 h to remove all preservatives. PVAm polymers were applied on the membranes via two methods: direct application and adsorption application. In the direct application method, the bottom strip was laid on a stainless steel disk, after the excess water was removed with a lint-free tissue.

The gels were suspended in 5 mM NaCl at pH 7 for the measurements.

A 40 mm × 12.7 mm piece of Teflon tape (G.F. Thompson Co. Ltd., TWB480P) was placed across one end of the bottom strip and a 15 µL drop of PVAm (linear or microgel), in 5 mM NaCl at pH 7, was applied with a 20-µL micropipette (Eppendorf) onto the bottom strip near the Teflon. The top strip was progressively placed over the bottom strip, starting at the end with the Teflon tape. If this was done carefully, the 15 µL polymer solution droplet spread uniformly between the top and bottom strips, with negligible loss of polymer solution. In the adsorption method, the top strip was covered with 0.6 mL of PVAm solution or suspension (0.5 g/L in 5 mM NaCl at pH 7) for 30 min. After rinsing thoroughly with 5 mM NaCl at pH7, the strip then was carefully laid on the bottom strip with one end covered by the Teflon tape. We assumed that there

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Figure 4. Nuclear magnetic resonance (NMR) spectra of microgel LS before and after hydrolysis in D2O; the disappearance of the peak at 7.8 ppm confirms the complete hydrolysis of the microgel.

Figure 5. Wet regenerated cellulose membrane delamination force, as a function of polymer coverage in the joint. The laminates were soaked in 5 mM NaCl at pH 7 for 30 min before testing. The error bars in the figure are the standard deviation of four identical measurements, and the lines in the figure are present only to guide the eye.

was a saturated polymer layer on the membrane after rinsing off the excess polymer solution or suspension. For both application methods, the laminates were pressed between blotting paper with a force of 89 kN at room temperature for 30 min, and were then conditioned overnight at a temperature of 23 °C and 50% relative humidity. The laminates were rewetted for testing by soaking in 5 mM NaCl solution (pH 7) for 30 min. The excess water was removed by uniform pressing (2.4-kg hand roller) between two pieces of blotting paper, and the bottom strip was mounted on a freely rotating aluminum wheel used for 90° peel testing. The tail was lifted from the Teflon tape and clamped in the upper jaw of the Instron testing machine. The crosshead moved at a rate of 20 mm/min, and the delamination force was recorded as a function of peeling length. The average delamination force was derived from the steady-state section of the peel curve. The result was divided by the width of the peel strip to give a width-normalized peeling force. For each sample, four identical specimens were tested and the average value was calculated. More details of the adhesion testing have been published.15,16 Results and Discussion Cross-linked PNVF particles were prepared by precipitation polymerization in MEK. The chemical structures are shown in Figure 1, and the polymerization recipes are summarized in

Figure 6. Comparison of the delamination forces of wet regenerated cellulose membrane with polymer added by direct application and adsorption application. The error bars represent the standard deviation of four identical measurements.

Table 1. The PNVF microgels were converted to the corresponding PVAm microgels by alkaline hydrolysis.20 1,3Divinylimidazolid-2-one (BVU) was used as the cross-linking monomer, because the crosslinks cannot be destroyed under the alkaline conditions used for the hydrolysis of the formamide groups (see Figure 1).21,22 In preliminary work with morecommon cross-linking monomers, we found that (i) the methylene-bisacrylamide linkages hydrolyzed and (ii) divinylbenzene did not copolymerize with NVF; similar results were reported by Pinschmidt et al.23 The TEM images in Figure 2 show samples taken at four stages of particles formation. The initial PNVF sample (Figure 2A) was well-dispersed with uniform particles. However, the microgel particles aggregated in early stages of the NVF polymerization and the aggregates persisted throughout the hydrolysis step. The particle size distributions of the microgel suspensions were measured before and after hydrolysis, and the results are shown in Figure 3 for microgel LS. Both the PNVF and PVAm gels had bimodal particle distributions. As expected, the size distribution of the ionized PVAm gels was shifted to the right, because of increased swelling. Particle size information for all of the gels is given in Table 2. Proton NMR was used to confirm that all of the formamide groups were converted to amines (see Figure 1). Figure 4 compares the spectra before and after hydrolysis. The disappearance of the peak at 7.8 ppm indicates essentially complete hydrolysis.

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Figure 7. Confocal laser scanning microscopy (CLSM) images of unpeeled wet cellulose laminates. The large square images are top views, beneath which are the projections of the z-direction. PVAm polymers were labeled with green fluorescein-5-isothiocyanate (FITC) and the cellulose membranes were labeled with red rhodamine. The experimental conditions correspond to those in Figure 6.

The ability of the microgels to function as a wet adhesive for cellulose was assessed by measuring the force required to delaminate a sandwich that consisted of two cellulose films laminated with a layer of PVAm microgels or linear polymers. The cellulose films have a dried thickness of ∼70 µm and a roughness of ∼60 nm. Roughness is defined as24

Rq )

x

1 n

n

(Zi - Z h )2 ∑ i)1

In water, the cellulose films have a water content of ∼60%. Figure 5 shows the delamination force as a function of polymer coverage, which is the mass of dry polymer per area of joint in the laminates. Note that there was no adhesion whatsoever for the laminates prepared without PVAm. At low adhesive coverages (i.e., 15 mg/m2, the delamination force was not very sensitive to adhesive

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Figure 8. CLSM images of delaminated cellulose membranes. The polymer coverage is 15 mg/m2 in both samples. Polymers were labeled with FITC.

coverage. Only the HS microgel (highly crosslinked, small diameter) gave significantly weaker laminates, perhaps because the HS gels were too rigid to deform completely in the adhesive joint. Note that the results for microgels LL, HL, and HM are not shown in Figure 5, because the delamination forces were too small to measure accurately. The main conclusion from the results shown in Figure 5 is that the best microgels and the linear polymers had the same intrinsic adhesion, when compared at the same adhesive coverage. The results in Figure 5 were obtained by directly applying polymer to the cellulose surfaces, which means that virtually any coverage of microgel or linear polymer could be evaluated. However, in papermaking, the polymer is adsorbed onto cellulose fibers in a dilute aqueous suspension. The driving force for adsorption is the electrostatic attraction between the low concentration of anionic carboxyl groups on the cellulose fibers and the cationic microgels or linear PVAm. Adsorption from the solution limits the amount of adsorbed polymer to a saturated adsorbed monolayer, which is typically 0.1-5 mg/m2 for linear polymers.25 In other words, when applying linear polymer or

microgels to a cellulose surface by adsorption from solution, the maximum coverage of adhesive in the laminate will correspond to two adsorbed monolayers (one on each surface), simply because polymers do not have a tendency to form adsorbed multilayers.25 Figure 6 illustrates the influence of the method used to apply linear polymers or microgels to the cellulose film surfaces. Delamination forces were measured using laminates prepared with linear PVAm and with PVAm microgels for two application methods: direct application and adsorption from solution onto one of the bonding surfaces, giving a saturated adsorbed layer. The following three observations come from the results in Figure 6: (1) The laminates with adsorbed linear PVAm were much weaker than those in which the linear polymer was directly applied. We propose that the explanation involves the amount of adsorbed polymer. Geffroy et al. reported the adsorption maximum for linear PVAm onto cellulose as a function of ionic strength and pH.26 The maximum adsorbed coverages were observed in the range of 0.1-1.2 mg/m2. For conditions of low

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ionic strength and neutral pH, similar to our experiments, the adsorption maximum was ∼0.1 mg/m2. Pefferkorn’s group has published several studies of PVAm adsorption onto cellulose and silica.27,28 For glass surfaces, the maximum coverage was ∼0.6 mg/m2. Therefore, based on published adsorption data for linear PVAm, we propose that the quantity of adsorbed linear PVAm in our experiments was ∼0.6 mg/m2, which is an order of magnitude less than the 7.5 mg/m2 for the directly applied linear PVAm. Thus, the laminates made with adsorbed linear PVAm were much weaker than those made with directly applied linear PVAm, simply because adsorption gave less polymeric adhesive in the joint. (2) The adsorbed LS and LM microgels were almost an order of magnitude stronger than the adsorbed linear polymer. Adsorption gives much greater coverage (mass of dry polymer per joint area) of microgels, compared to adsorbing the linear polymer, simply because the microgels are bigger. The coverage corresponding to a saturated adsorbed monolayer of microgel LS can be estimated as follows. Assuming that a 2-µm-thick PVAm gel with a degree of swelling of 30 forms a uniform 2-µm-thick layer on the smooth cellulose surface, the corresponding coverage of dry polymer is 67 mg/m2. This is 100 times greater than our estimate of the amount of adsorbed linear polymer and 10 times greater than the amount of directly applied linear polymer for the results in Figure 6. (3) The adsorbed LS and LM microgels gaVe stronger laminates than did the directly applied microgels with a coVerage of 7.5 mg/m2. The proposed explanation again involves the quantity of adhesive in the joint. In the previous paragraph, we estimated that the a saturated monolayer of adsorbed LS microgels corresponds to a coverage of 67 mg/m2, which is 10 times greater than 7.5 mg/m2. The distribution of adhesives in the laminates was studied using CLSM. Both the linear PVAm and the PVAm microgels were labeled with the green fluorescent label, FITC, and the cellulose films were labeled with the red fluorescent dye, rhodamine. A series of confocal images were taken through the joint region of the laminates and the results are shown in Figure 7. The directly applied linear PVAm showed a uniform distribution in the x-y plane, whereas the adsorbed linear PVAm was barely visible, reflecting the limited capacity of the cellulose to adsorb linear polymer. The microgels gave intense images, regardless of whether they were applied by coating or adsorption. However, the microgel was much less uniformly distributed in the x-y plane than was the linear PVAm. In previous paragraphs, it was estimated that 7.5 mg/m2 of microgel represented submonolayer coverage; Figure 7 supports this view. The thickness of the joint region was ∼5 µm for both types of adhesives. There was no evidence that the linear PVAm penetrated deeper into the cellulose films than did the microgels. Confocal microscopy was also used to characterize the bonding surfaces after delamination. Figure 8 shows that the microgels cleanly separated from one surface, suggesting adhesive failure at the microgel/cellulose interface. In contrast, the linear PVAm was distributed on both surfaces after peeling, perhaps indicating cohesive failure within the PVAm layer. Conclusions A future publication from our group will show that poly(vinylamine) (PVAm) microgels give stronger wet paper than does linear PVAm. However, paper is a complex material, and it is often difficult to explain physical property changes in fundamental terms. The current adhesion study was performed

with well-defined regenerated cellulose films and gives two important conclusions, which will help us understand the paper data. First, Figure 4 clearly shows that the best microgels are not intrinsically stronger adhesives for wet cellulose than are linear PVAm, when compared at the same coverage. In fact, very large and highly cross-linked microgels give weaker wet adhesion than linear PVAm. Second, when the coverage of adhesive is limited by the adsorption maximum, Figure 6 shows that microgels give much stronger laminates than the linear polymer, because more microgel than linear PVAm is present in the cellulose/PVAm/ cellulose joint. The microgel TEM images shown in Figure 3 and the laminate confocal images shown in Figure 7 underscore the polydisperse nature of the microgels. Our future work will focus on the preparation of more-uniform microgels to explore, in more depth, the role of microgel size and crosslink density. Acknowledgment The authors thank Dr. Marc Leduc and Dr. Simon Champ from BASF for useful discussions. In addition, we acknowledge the financial support from BASF Canada and the Natural Sciences and Engineering Research Council of Canada (NSERC). Literature Cited (1) Espy, H. H. The Mechanism of Wet-Strength Development in Paper: A Review. Tappi J. 1995, 78, 90. (2) Weisgerber, C. A. Wet-Strength Paper. U.S. Patent 2,721,140, October 18, 1955. (3) Pelton, R.; Hong, J. Some Properties of Newsprint Impregnated with Polyvinylamine. Tappi J. 2002, 1, 21. (4) Gu, L.; Zhu, S.; Hrymak, A. N.; Pelton, R. H. Kinetics and Modeling of Free Radical Polymerization of N-Vinylformamide. Polymer 2001, 42, 3077. (5) Brunnmueller, F.; Schneider, R.; Kroener, M.; Mueller, H.; Linhart, F. Linear Basic Polymers, Their Preparation and Their Use. U.S. Patent 4,421,602, December 20, 1983. (6) Lai, T. W.; Vijayendran, B. R. High Molecular Weight Poly(Vinylamines) as Wet-End Additives in Papermaking. Euro. Patent EP 0331047, 19890224, 1989. (7) Wang, F.; Kitaoka, T.; Tanaka, H. Vinylformamide-Based Cationic Polymers as Retention Aids in Alkaline Papermaking. Tappi J. 2003, 2, 21. (8) Mitchell, M. A.; Beihoffer, T. W.; Lobo, L. L.; Darlington, J. W., Jr. Poly(vinylamine)-Based Superabsorbent Gels and Method of Manufacturing the Same. U.S. Patent 6,121,409, September 19, 2000. (9) Suh, K.-D.; Bae, Y.-C.; Kim, J.-W.; Kobayashi, S. Swelling of Poly(Vinyl Amine) Gels: Applicability of the Donnan Theory. J. Macromol. Sci., Chem. 1999, A36, 507. (10) Yamamoto, K.; Serizawa, T.; Muraoka, Y.; Akashi, M. Synthesis and Functionalities of Poly(N-Vinylalkylamide). 13. Synthesis and Properties of Thermal and pH Stimuli-Responsive Poly(Vinylamine) Copolymers. Macromolecules 2001, 34, 8014. (11) Feng, X.; Pelton, R. Carboxymethyl Cellulose:Polyvinylamine Complex Hydrogel Swelling. Macromolecules 2007, 40, 1624. (12) Feng, X. H.; Pelton, R.; Leduc, M. Mechanical Properties of Polyelectrolyte Complex Films Based on Polyvinylamine and Carboxymethyl Cellulose. Ind. Eng. Chem. Res. 2006, 45, 6665. (13) Itagaki, K.; Ito, T.; Ando, K.; Watanabe, S.; Sawayama, S. Crosslinked Polyvinylamine Spheres. Jpn. Patents 61051006 and 19840820, 1986. (14) Xu, J. J.; Timmons, A. B.; Pelton, R. N-Vinylformamide as a Route to Amine-Containing Latexes and Microgels. Colloid Polym. Sci. 2004, 282, 256. (15) DiFlavio, J. L.; Bertoia, R.; Pelton, R.; Leduc, M. The Mechanism of Polyvinylamine Wet Strengthening. In 13th Fundamental Research Symposium, Cambridge, U.K., September 11-16, 2005; FRC: Cambridge, U.K., 2005; pp 1293-1316. (16) Kurosu, K.; Pelton, R. Simple Lysine-Containing Polypeptide and Polyvinylamine Adhesives for Wet Cellulose. J. Pulp Paper Sci. 2004, 30, 228.

Ind. Eng. Chem. Res., Vol. 46, No. 20, 2007 6493 (17) Saito, T.; Isogai, A. Wet Strength Improvement of Tempo-Oxidized Cellulose Sheets Prepared with Cationic Polymers. Ind. Eng. Chem. Res. 2007, 46, 773. (18) McLaren, A. D. Adhesion of High Polymers to Cellulose. Influence of Structure, Polarity, and Tack Temperature. J. Polym. Sci. 1948, 3, 652. (19) Ben-Zion, O.; Nussinovitch, A. Physical Properties of Hydrocolloid Wet Glues. Food Hydrocolloids 1997, 11, 429. (20) Gu, L.; Zhu, S.; Hrymak, A. N. Acidic and Basic Hydrolysis of Poly(N-Vinylformamide). J. Appl. Polym. Sci. 2002, 86, 3412. (21) Meyer, T.; Hellweg, T.; Spange, S.; Hesse, S.; Jager, C.; Bellmann, C. Synthesis and Properties of Crosslinked Polyvinylformamide and Polyvinylamine Hydrogels in Conjunction with Silica Particles. J. Polym. Sci., Part A 2002, 40, 3144. (22) Spange, S.; Meyer, T.; Voigt, I.; Eschner, M.; Estel, K.; Pleul, D.; Simon, F. Poly(Vinylformamide-Co-Vinylamine)/Inorganic Oxide Hybrid Materials. In Polyelectrolytes with Defined Molecular Architecture, Volume 1; Schmidt, M., Ed.; Advances in Polymer Science, 165; Springer: Berlin, London, 2004; pp 43-78. (23) Pinschmidt, R. K.; Wasowski, L. A.; Orphanides, G. G.; Yacoub, K. Amine Functional Polymers Based on N-Ethenylformamide. Prog. Org. Coat. 1996, 27, 209.

(24) DiFlavio, J. L. The Mechanism of Polyvinylamine Adhesion to Cellulose, Ph.D. Thesis, McMaster University, Hamilton, Ontario, Canada, 2007. (25) Fleer, G. J.; Cohen Stuart, M. A.; Scheutjens, J. M. H. M.; Cosgrove, T.; Vincent, B. Polymers at Interfaces; Chapman & Hall: London, 1993. (26) Geffroy, C.; Labeau, M. P.; Wong, K.; Cabane, B.; Stuart, M. A. C. Kinetics of Adsorption of Polyvinylamine onto Cellulose. Colloids Surf. A 2000, 172, 47. (27) Shulga, A.; Widmaier, J.; Pefferkorn, E.; Champ, S.; Auweter, H. Kinetics of Adsorption of Polyvinylamine on Cellulose Fibers. I. Adsorption from Salt-Free Solutions. J. Colloid Interface Sci. 2003, 258, 219. (28) Shulga, A.; Widmaier, J.; Pefferkorn, E.; Champ, S.; Auweter, H. Kinetics of Adsorption of Polyvinylamine on Cellulose Fibers. II. Adsorption from Electrolyte Solutions. J. Colloid Interface Sci. 2003, 258, 228.

ReceiVed for reView April 22, 2007 ReVised manuscript receiVed July 10, 2007 Accepted July 19, 2007 IE0705608