Secondary and ternary emulsions from vinyl acetate,N-hydroxymethyl acrylamide,and urea for wood bonding

In this study, N-hydroxymethyl acrylamide (NMA) and vinyl acetate (VAc) were used in order to prepare secondary emulsions; additionally urea was then introduced into the polymerization to form ternary emulsions, adjusting different proportions of the three components. Compared to pure polyvinyl acetate, these two emulsion types presented shorter curing time, improved water resistance, and higher bond strength; this is based on the crosslinking ability introduced by the NMA, enabling such a partial crosslinking already during the polymerization process and during storage. The viscosity, solid content, storage stability, curing and drying behavior, water resistance, delamination time, and bond strength were influenced by the proportions of NMA and urea in the two systems. Urea had a positive effect on the wet bond strength, but a negative effect on the dry bond strength. The proportion of NMA and of urea during the polymerization preferably was 1–2 % based on VAc.