In this research, the effects of the materials and the processing conditions on the cell morphology of foamed PVC/wood‐fiber composites were studied with a view to establishing their process‐structure relationships. Each step of microcellular PVC/wood‐fiber composites processing is addressed, including the surface treatment of the wood‐fiber, mixing of polymer and wood‐fiber, manufacture of the composites, the saturation of the composites with gas, microcellular foaming of the composites, and characterization of the cell morphology. The cellular morphologies of the foamed PVC/wood‐fiber composites are a strong function of the content of plasticizer and the surface treatment of wood‐fiber as well as the gas saturation and foaming conditions.

Wood-fiber composites make use of cellulose fibers as a reinforcing filler in the polymer matrix and are known to have a lower material cost and a higher stiffness than neat polymers. However, the lower material cost and enhanced stiffness of wood-fiber composites are achieved at the expense of other properties such as the ductility and impact strength. Since microcellular plastics exhibit a higher impact strength, higher toughness, and increased fatigue life compared to unfoamed plastics, microcellular foaming of wood-fiber composites will improve the mechanical properties of the composites and therefore increase the usefulness of the materials. In this paper, microcellular foamed WC/wood-fiber composites with unique cell morphology and material composition are characterized. Microcellular structures are produced in WC/wood-fiber composites by first saturating the composite samples with CO, under high pressure followed by rapidly decreasing the solubility of gas in the samples. The void fraction of the microcellular foamed WC/wood-fiber composites is controlled by tailoring the composition of materials and the foaming process parameters. The results indicate that tensile and impact properties of microcellular foamed WC/wood-fiber composites are most sensitive to changes in the cell morphology and the surface modification of fibers.

The surface properties at the interface between thermoplastic and cellulosic fibers strongly influence the mechanical properties of plastic/cellulosic fiber composites. This paper examines the role of surface acid‐base properties of plasticized PVC and cellulosic fibers on the mechanical properties of the composites. The acid‐base surface characteristics of cellulosic fibers were modified by treating the fibers with γ‐aminopropyltriethoxysilane (A‐1100), dichlorodiethylsilane, phthalic anhydride, and maleated polypropylene. The empirical acid (KA) and base (KD) characteristics (i.e., electron donor/acceptor abilities) of untreated and treated fibers, as well as plasticized PVC, were determined using inverse gas chromatography (IGC) technique. These parameters were used to yield information on the acid‐base pair interactions that were correlated with the tensile and notched Izod impact properties of the composites. Acid‐base pair interactions have been found to be a valuable parameter in the design of surface modification strategies intended to optimize the tensile strength of the composites. By tailoring the acid‐base characteristics of cellulosic fibers and plasticized PVC, a composite with equal tensile strength and greater modulus than unfilled PVC was developed. However, the acid‐base factors did not correlate with tensile modulus, the elongation at break, and the notched Izod impact property of PVC/newsprint fiber composites. Aminosilane has been observed to be a suitable adhesion promoter for PVC/wood composites improving significantly the tensile strength of the composites. Other treatments (dichlorodiethylsilane, phtalic anhydride, and maleated polypropylene) were found to be ineffective, giving similar strength compared to the composites with untreated cellulosic fibers. FTIR spectroscopy results suggested that aminosilane was effective because treated cellulosic fibers can react with PVC to form chemical bonds. The resulting bond between PVC and cellulosic fibers accounts for the effectiveness of aminosilane, when compared with other coupling agents.

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