Rigid polyvinyl chloride/wood-flour composites and their foams.

摘要

The effects of impact modifier types (crosslinked vs. uncrosslinked) and addition levels on the mechanical properties of rigid PVC/wood-fiber composites were examined. With the proper choice of modifier type and concentration, the impact strength of rigid PVC/wood-fiber composites can be significantly improved without degrading the tensile properties.; Foaming is an effective method for reducing the density and brittleness of polymers. The experimental results indicated that impact modification (crosslinked and uncrosslinked modifiers) accelerated the rate of gas loss during foaming process, which impeded the growth of nucleated cells. Consequently, impact modifiers are an unnecessary ingredient in the formulation of foamed neat rigid PVC and rigid PVC/wood-flour composites.; Since the batch foaming process used to generate cellular foamed structures in the composites is not likely to be implemented in the industrial production of foams because it is not cost-effective, the manufacture of PVC/wood-flour composite foams in an extrusion process needs to be investigated.; The foamability of rigid PVC/wood-flour composites using moisture present in the wood flour as the foaming agent was investigated using a central composite design (CCD) experiment. It was determined that wood flour moisture could be used effectively as the foaming agent in the production of rigid PVC/wood-flour composite foams.; Finally, mechanical property characterizations of extrusion-foamed rigid PVC/wood-flour composites were done. Extrusion foaming reduced the density and the brittleness of the composites, but also caused a reduction in the tensile strength and modulus of the rigid PVC/wood-flour composites.; This study suggested that depending on the application, the problems associated with the rigid PVC/wood-flour composite products; high density, brittleness and low impact resistance can be overcome by adopting impact modification and/or extrusion foaming. Since impact modification improves the impact resistance of the material and extrusion foaming reduces the brittleness and density of the material, a co-extrusion process, which utilizes separate extruders for the outside skin and inside core layer of the material, might be the most viable and cost-effective method for rigid PVC/wood-flour composites. The manufacturing of impact modified skin and foamed core might provide overall low density, low brittleness and high impact resistance for rigid PVC/wood-flour composites. (Abstract shortened by UMI.)