Cross-linking poly(vinyl acetate-co-N-methylolacrylamide) latex adhesive performance Part II: Fracture mechanics and microscopic durability studies

Fracture mechanics, scanning electron microscopy (SEM), and fluorescence microscopy were used to evaluate the performance and durability of three poly[(vinyl acetate)-co-N-methylolacrylamide] latex adhesives. Results from mode I fracture tests of wood-adhesive double cantilever beam specimens indicated that in the absence of accelerated aging conditions, the three adhesives performed similarly. After the samples were exposed to either boil or vacuum soak accelerated aging, differences among the adhesives emerged. Latex I (N-methylolacrylamide (NMA) injected throughout the polymerization) exhibited enhanced performance after weathering, whereas the performance of latexes DI (delayed injections of NMA) and C (continuous addition of NMA) either remained unchanged or declined after weathering. Fluorescence microscopy of wood-adhesive bond lines and SEM of latex films after accelerated aging exposures both indicated that latex I showed a unique resistance to the aging conditions. Relatively high proportions of water-phase NMA correlate with improved latex durability.