A process for coupling wood to thermoplastic using graft copolymers

A chemical modification method has been developed to convert lignin into lignin–styrene graft copolymers. The graft products are macromolecular surface active agents because, within each molecule, a hydrocarbon sidechain has been grown off of a natural oxyphenylpropyl backbone. Surface activity of the graft copolymers was indicated by their capacity to form stable emulsions between incompatible fluid phases and to adhesively bond to wood surfaces. Dynamic contact angle measurement using the Wilhelmy plate technique showed that the graft copolymers changed the contact angle of water on wood from 50° to 110°. Coating birch wood (Betula papyrifera) with lignin–styrene graft copolymerization product increases the water contact angle and the binding strength of polystyrene on the wood. Lap shear strengths increased 56%, from 1826 to 2840 kPa, when the wood was coated with a graft copolymer containing 51.7% lignin. Binding was tested by coating the birch with a solution of graft copolymer, drying the wood, injection molding polystyrene onto the surface of the wood, and pulling the polystyrene off the wood surface in a lap shear brace. These properties of the copolymers were used to design a process for forming wood-thermoplastic composites. © 1995 John Wiley & Sons, Inc.