Adhesives from Polymeric Methylene Diphenyl Diisocyanate Resin and Recycled Polyols for Plywood

Abstract In this study, polyols recycled from decomposed polyurethane (PU) foam wastes were used in preparing adhesives for plywood manufacturing. A polyol was made from chemically decomposed flexible PU foam wastes separated from automobile shredder residue. The recycled polyol was mixed with a commercial polyol at weight ratios of 100/0, 25/75, 50/50, 25/75, and 0/100, respectively. These polyol mixtures were mixed, respectively, with polymeric methylene diphenyl diisocyanate at isocyanate group–to–hydroxyl group (NCO/OH) molar ratios of 1.0, 1.25, and 1.5 to prepare adhesives. The recycled polyol and adhesives were characterized by Fourier transform infrared spectroscopy. Plywood specimens bonded by the adhesives were fabricated and tested. The effects of NCO/OH molar ratio and recycled polyol–to–commercial polyol weight ratio on adhesive gel time and bonding strength before and after water treatments were evaluated. The adhesives prepared from recycled polyol presented shorter gel time and greater dry bonding strength than those prepared from commercial polyol. The adhesives prepared from the recycled polyol–commercial polyol weight ratio of 50/50 and NCO/OH molar ratio of 1.25 showed the best bonding performance after cyclic boiling water treatment. Multilinear regressions showed that NCO/OH molar ratio was the main factor in developing plywood shear strength.