A Study On The Preparation And Properties Of PVC/wood Flour Composites

Wood-plastics composites (WPC) are manufactured by dispersing wood fibers or wood flour into molten plastic matrix to form composites by processing technology such as extrusion, thermoforming, and compression or injection molding. Because of the natural incompatibility between the hydrophilic, polar wood-fibers and hydrophobic, non-polar PVC, PVC/WF composites are more brittle and have lower impact resistance than neat PVC products. In addition, the high density of PVC/wood-fiber composites may hinder their acceptance in the conventional structural lumber market. The purpose of this research is to use some physical and chemical methods to construct the interfacial compatibility between PVC and wood flour.This paper investigated the influence of wood flour content and particle size of wood flour on the mechanical properties of the composites. The results obtained show that the tensile strength and impact strength of the composites decreased sharply with the increase of wood flour content. However, good filler dispersion can not be obtained when the particle size of wood flour is too large or too small. The silane coupling agent (KH550) has a good modification effect on the interfacial interactions. The–OH end group of the silanols can bond to the wood surface through hydrogen bonding. The amino group (Lewis basic side) of the silanols, attacked to PVC matrix (Lewis acidic side) through acid-base interaction and weak Van-der Waals force so that interfacial adhesion can be established between wood flour and PVC.When wood flour was treated by microwave radiation, the izod notched impact strength and tensile strength of the composites made of the Mw-treated WF were significantly improved. Fractured surfaces were examined by scanning electron microscopic (SEM), which indicate that Mw-treated wood flour/PVC composites had a better compatibility between the interfaces than untreated wood flour. Mw radiation method was extended to treat wood flour infiltrated by acryl amide (AM) solution, and FTIR image shows that grafting reaction between wood flour and AM occurred after Mw radiation. SEM examination indicates that Mw-treated wood flour/PVC composites had a better compatibility between the interfaces than untreated wood flour.In addition, foamed rigid PVC/wood flour composites were prepared in supercritical CO₂. The influence of pressure and temperature on density and mechanical properties of the composites was investigated. With the increase of temperature, the cell size of the foamed composites increased, and the density decreased. But the impact strength decreased because the cell size went beyond the limitation of interface defects between wood flour and PVC matrix. Under higher pressure, the matrix absorbed more CO2 and the density of the foamed samples decreased significantly, and the impact strength of the foamed samples increased further.