Wood Adhesive from Crosslinked Poly(Vinyl Alcohol) and Partially Gelatinized Starch: Preparation and Properties

An environmentally friendly wood adhesive was developed by crosslinking cornstarch and poly(vinyl alcohol) (PVOH) with hexamethoxy-methylmelamine (Cymel 323). Citric acid was used as a catalyst and latex (UCar 443) was added to improve moisture resistance. The adhesive was evaluated for its utility in plywood manufacture. It exhibited excellent mechanical properties comparable to many of the commercially available urea-formaldehyde plywood adhesives used for interior applications. The viscosity of the adhesive at 27 % (w/v) was 7000 mPas, allowing easy application to wood surfaces by brush. The minimum concentration of crosslinking agent needed to achieve good mechanical properties in plywood was 15 % (w/w proportion of total solids). Optimum curing temperature and curing time were 175 °C and 15 min, respectively. Addition of latex to the adhesive formulation improved both moisture resistance and physical properties of plywood test samples. Samples prepared with an optimal adhesive formulation, when completely immersed in water for 2 h or exposed at 93 % or 50 % relative humidity (RH) for 30 days, exhibited > 90 % failure in the veneer as opposed to < 10 % failure in the adhesive joints.