Effects of a new compatibilizer system on the flexural properties of wood-polyethylene composites

A novel wood-plastic compatibilizer system containing a paper wet-strength agent as a wood-binding domain and stearic anhydride as a polyethylene (PE) binding domain was investigated. Treatment of wood flour with a commercial paper wet-strength agent Kymene((R)) 557H (simply called Kymene) before the mixing of PE and the wood flour increased the modulus of rupture (MOR) and the modulus of elasticity (MOE) of the resulting wood-PE composites. Addition of stearic acid in the mixing of PE and the wood-Kymene mixture further increased the MOR and MOE. Stearic anhydride was even more effective than stearic acid in the increase of the MOR and MOE. Compared to wood-PE composites without a compatibilizer, the stearic anhydride-Kymene compatibilizer system increased the MOR by about 33% and the MOE by about 40%. The stearic anhydride-Kymene compatibilizer system gave a slightly lower MOR, but higher MOE than those of the commercially used compatibilizer (maleic anhydride-grafted polypropylene). The compatibilization mechanisms were proposed as follows: Kymene not only bound to wood fibers, but also strengthened and stiffened the wood fibers. Stearic anhydride formed covalent linkages such as ester and amide with the Kymene-consolidated wood fibers and the long hydrocarbon chain of the stearic anhydride bonded to the PE matrix through entanglements and/or cocrystallization. (C) 2004 Wiley Periodicals, Inc.