Wood-adhesive interactions in a PVAc latex

Abstract

Static rheological analysis based on time/temperature equivalence was applied to freestanding poly(vinyl acetate-co-N-methylolacrylamide) (PVAc-co-NMA) adhesive films and to wood-bonded films (composites) containing two types of crosslinking: 1) AlCl₃ catalysis of NMA comonomer, and 2) the same AlCl₃ catalysis plus additional crosslinking using a phenolic resol additive, PF. The glass/rubber relaxations for bulk poly(vinyl acetate), PVAc, and in some cases for the poly(vinyl alcohol) interfacial agent (PVOH) also, were evaluated by the empirical Kohlrausch-Williams-Watts (KWW) coupling model. The KWW coupling analysis revealed that accelerated weathering dramatically decreased PVAc segmental coupling in neat films; the PF additive slightly mitigated this weathering effect. In comparison to neat films, composite specimens exhibited increased PVAc coupling for all sample types, demonstrating a significant wood-adhesive interaction. In contrast to neat films, the PF additive completely negated the effects of accelerated weathering in composite specimens. Since PF prevented weathering-induced changes to the PVAc relaxation (in composites), the phenolic additive influenced the bulk adhesive and its effects were not restricted to PVOH crosslinking at the interparticle boundaries. The wood-adhesive interaction was not only detected through the PVAc relaxation but also in the PVOH glass transition. Furthermore, the PF borne weather resistance was dependent upon the presence or absence of wood, suggesting a PF/wood interaction. It is unknown if the putative PF/wood interaction is direct or possibly indirect through wood alteration of PVAc and PVOH.