Abstract
Parallel-plate rheological analysis was conducted on two types of cross-linking poly(vinyl acetate) latex films: dry freestanding films, and dry films bonded directly to wood (composites). For each sample type, three levels of cross-linking were used: (1) little or no cross-linking of unaltered latex; (2) substantial cross-linking through AlCl3 catalysis of N-methylolacrylamide co-monomer; and (3) greater cross-linking from a phenol-formaldehyde resol additive, in addition to AlCl3 catalysis. Simple thermal scans revealed a strong wood/adhesive interaction; wood increased the base polymer Tg by ∼5°C in all adhesives. Relative to the simple thermal scans, time-temperature master curves provided more insight and information about the wood/adhesive interaction. Storage modulus and tan δ master curves both indicated that wood retarded adhesive cross-linking. Using time-temperature superposition, a segmental coupling analysis demonstrated that wood actually narrowed the breadth of the glass transition, or reduced segmental coupling. Cross-linking influenced segmental coupling, but in a fashion that was dependent on the presence or absence of wood. Wood-induced reductions in cross-linking and in segmental coupling were attributed to the diffusion of water-soluble reactive compounds away from the adhesive layer and into the bulk wood. Time/temperature equivalence provides a sensitive means to detect interactions between wood and viscoelastic adhesives.
References
Armour, W.B. (1962) N-Methylolacrylamide – thermosetting elastomeric polyvinyl acetate adhesives containing trimethylol phenol. US Patent 3041301.Search in Google Scholar
ASTM Standard (1987) D 1489. Standard test method for nonvolatile content of aqueous adhesives.Search in Google Scholar
Bonardi, C., Christou, P., Llauro-Darricades, M.F., Guillot, J., Guyot, A., Pichot, C. (1991) Acrylic latexes functionalized by N-methylolacrylamide and cross-linked films from these latexes. New Polym. Mater.2:295–314.Search in Google Scholar
Ferry, J.D. Viscoelastic Properties of Polymers, 3rd ed. John Wiley & Sons, New York, 1980.Search in Google Scholar
Goldberg, A.I., Jasinski, V. (1967) N-Methylolacrylamide-vinyl acetate copolymer emulsions containing poly(vinyl alcohol) for film manufacture. US Patent 3301809.Search in Google Scholar
Keddie, J.L. (1997) Film formation of latex. Mater. Sci. Eng. R21:101–170.10.1016/S0927-796X(97)00011-9Search in Google Scholar
Lopez-Suevos, F., Frazier, C.E. (2005) Parallel-plate rheology of latex films bonded to wood. Holzforschung, accept for publication.10.1515/HF.2005.071Search in Google Scholar
Plazek, D.J., Ngai, K.L. (1991) Correlation of polymer segmental chain dynamics with temperature-dependent time-scale shifts. Macromolecules24:1222–1224.10.1021/ma00005a044Search in Google Scholar
Steward, P.A., Hearn, J., Wilkinson, M.C. (2000) An overview of polymer latex film formation and properties. Adv. Colloid Interface Sci.86:195–267.10.1016/S0001-8686(99)00037-8Search in Google Scholar
©2006 by Walter de Gruyter Berlin New York