Investigation of new compatibilizer systems for wood-polyethylene composites

Wood-plastic composites (WPCs) are one of the fastest-growing sectors of the wood composites industry. However, the strengths of WPCs are typically low because of the poor interfacial adhesion between hydrophilic wood and hydrophobic thermoplastics. A compatibilizer that can form bridges between wood and plastics is required to give WPCs desirable strength properties. At present, the choice of effective compatibilizers is limited and the compatibilization mechanisms are not fully understood. In this study, three novel compatibilizer systems were investigated for wood-polyethylene composites.; A widely used paper wet-strength agent polyaminoamide-epichlorohydrin (PAE) combined with stearic anhydride was applied as a compatibilizer system for wood-polyethylene composites. It was found that the pH value of the PAE solution had a significant impact on the modulus of rupture (MOR) and the modulus of elasticity (MOE) of the resulting wood-polyethylene composites. The dosages of PAE and stearic anhydride were optimized in terms of the enhancement of MOR and MOE. Under optimal conditions, the PAE-stearic anhydride compatibilizer resulted in a higher MOR and MOE than commercially available maleic anhydride-grafted polyethylene (MAPE). Fourier Transform Infrared Spectroscopy (FTIR) analysis revealed that PAE and stearic anhydride formed covalent bondings with wood flour. Water-resistance tests indicated that PAE-stearic anhydride compatibilizer system increased the water-resistance of the resulting composites.; A combination of poly(diphenylmethane diisocyanate) (PMDI), and stearic anhydride was also studied as a compatibilizer system. PMDI alone increased the MOR and MOE of the resulting WPCs to some extent. Stearic anhydride alone had limited effects on the enhancement of MOR and MOE of the WPCs. A combination of PMDI and stearic anhydride resulted in higher MOR and MOE than PMDI. The PMDI-stearic anhydride compatibilizer system was even superior to commercially available MAPE in terms of increasing strengths (MOR and MOE) and water-resistance. The compatibilization mechanism of the PMDI-stearic anhydride compatibilizer system was investigated and proposed as follows: PMDI bonded wood and stearic anhydride, and the hydrocarbon chain of stearic anhydride bonded polyethylene through secondary bonds, entanglements and/or co-crystallization with the polyethylene matrix. (Abstract shortened by UMI.)...