Enhancement of tensile strength, impact strength, and flexural strength of polypropylene/short glass fiber composites by treating the glass fibers with coupling agent, mixing with maleated polypropylene (MPP) for compatibilization and adhesion, and with nucleating agent for improvement of polypropylene crystallization was studied. The results showed that both the silane coupling agent and MPP enhance tensile strength, impact strength, and flexural strength. In the absence of MPP, the effect of silane coupling agent on the mechanical properties of the composites decreases in the following order: alkyl trimethoxy silane (WD-10) > γ-methacryloxypropyl trimethoxysilane (WD-70) > N-(β-aminoethyl)-γ-aminopropyl trimethoxysilane (WD-52), whereas in the presence of MPP, the order changes as follows: WD-70 > WD-10 > WD-52. When the glass fibers were treated with WD-52, 4,4-diamino-diphenylmethane bismaleimide (BMI) can further enhance the mechanical properties of the composite. The three kinds of strengths increase with MPP amount to maximum values at 5% MPP. As a nucleating agent, adipic acid is better than disodium phthalate in improving the mechanical properties, except for the notched impact strength. Wide-angle X-ray diffraction showed that the adipic acid is an α-type nucleating agent, whereas disodium phthalate is a β-type nucleating agent. Blending with styrene–butadiene rubber can somewhat improve the notched impact strength of the composites, but severely lowers the tensile strength and bending strength. Scanning electron micrographs of the broken surface of the composite showed greater interfacial adhesion between the glass fibers and polypropylene in the modified composite than that without modification. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1414–1420, 2005
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