Wood fiber/polyvinyl chloride composites and their microcellular foams

grantor: University of TorontoThis thesis presents a fundamental study of the adhesion between chemically modified wood-fibers and PVC to develop PVC/wood-fiber composites with satisfactory performance. Wood-fibers were treated with $\gamma$-aminopropyltriethoxysilane, dichlorodiethylsilane, phthalic anhydride, and maleated polypropylene for surface modifications. The effectiveness of chemical modifications made on the surface of wood-fibers was then characterized using various complementary surface analytical techniques: X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and surface tension measurements. Inverse gas chromatography (IGC) was used to describe the electron acceptor/donor (acid/base) characteristics of the wood-fiber surface and PVC, and also to estimate the specific pair interaction parameters for PVC/wood-fiber systems. Single-lap joint shear test, tensile test, notched Izod impact test, and scanning electron microscopy (SEM) were employed to evaluate the adhesion between the wood-fibers and the PVC matrix. Amino-silane has been identified as a good adhesion promoter for PVC/wood-fiber composites while other coupling agents did not promote adhesion between PVC and wood-fibers. This implied that the well known claim of the interfacial tension matching of the two phases by converting the hydrophilic surface of wood-fiber to hydrophobic one is not sufficient condition for a good adhesion between PVC and wood-fiber. The experimental results revealed that the amino-silane treated wood-fibers react chemically with PVC. The resulting chemical bond between treated-wood-fibers and PVC accounts for the effectiveness of amino-silane when compared with other coupling agents. The concept of creating cellular structures in the composite to reduce its density and to improve the impact property has also been investigated. Microcellular structures were produced in the PVC/wood-fiber composites by first saturating the composites with CO$\sb2$ under high pressure followed by rapidly decreasing the solubility of gas in the composites. The critical processing parameters that affect the cell morphology and mechanical properties of foamed PVC and PVC/wood-fiber composites have been identified. These include the concentration of plasticizer, the surface treatment of wood-fibers, the foaming time, and the foaming temperature. By tailoring these process parameters, the desired cell morphology was achieved. The tensile and impact properties of microcellular foamed PVC/wood-fiber composites have also been characterized in terms of the cell morphology and the surface modification of fibers. The deteriorated impact strength of PVC/wood-fiber composites was improved by microcellular foaming.Ph.D