Terminally functionalized polyethylenes as compatibilizers for wood-polyethylene composites

Isocyanate-terminated polyethylenes (PE), PE-MDI and PE-PMDI, were synthesized by reacting polyethylene monoalcohol (PEA) with 4,4′-methylenediphenyl diisocyanate (MDI) and polymeric methylene diphenyl diisocyanate (PMDI), respectively. Effects of PEA, PE–MDI, and PE–PMDI on the mechanical properties and water resistance of wood–PE composites were investigated. All three compatibilizers increased the strength of the wood–PE composites. Composites containing PE–MDI or PE–PMDI exhibited a higher modulus of rupture (MOR) than those with PEA. The addition of PE–MDI and PE–PMDI decreased the water uptake rate of the composites while PEA increased this rate. The superior compatibilization effects of PE–MDI and PE–PMDI were attributed to the formation of covalent bonding between isocyanate and wood. This covalent bonding was demonstrated by the FTIR spectra of the wood residues after a p-xylene extraction. Scanning electron microscope (SEM) images revealed that isocyanate-terminated PE samples improved the interfacial adhesion between wood and PE. POLYM. ENG. SCI., 46:108–113, 2006. © 2005 Society of Plastics Engineers