Francisco López-Suevos, Charles E. Frazier
Fracture cleavage analysis of PVAc latex adhesives: Influence of phenolic additives
Mode I fracture cleavage testing was conducted on wood bonded with poly(vinyl acetate-co-NMA) latex adhesive containing two types/degrees of cross-linking: (1) cross-linking through AlCl3 catalysis of N-methylolacrylamide (NMA) comonomer; and (2) additional cross-linking using a phenol-formaldehyde resol additive, in addition to AlCl3 catalysis. The formulation lacking the phenolic additive performed well under dry conditions; but it completely failed during testing as a result of accelerated weathering. In contrast, fortification with the phenolic additive provided durability against accelerated weathering. In an effort to understand the effects of accelerated weathering, parallel-plate dynamic mechanical analysis was applied to freestanding neat adhesive films and to wood-bonded films (composites). Accelerated weathering dramatically altered the viscoelastic response of films and composites that lacked the phenolic additive; weathering caused a second, broad and reversible relaxation near 100°C, which might be because of softening of the poly(vinyl alcohol) interfacial agent used during emulsion polymerization. In contrast, samples formulated with the phenolic additive only displayed the typical base-polymer glass transition. Correlation of the fracture testing and the rheological analysis suggests that the phenolic additive promotes adhesive durability by cross-linking the interparticle boundaries, where poly(vinyl alcohol) is believed to reside.
Holzforschung, Walter de Gruyter
Print ISSN: 0018-3830
Volume: 60, 05/2006
Pages: 313 - 317
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