The influence of surface treatment on the mechanical properties of long glass fiber reinforced polypropylenes were investigated. Surface treatment by different kinds of silane coupling agents (aminosilane, diaminosilane, epoxysilane and acrylsilane) with different concentrations was performed on glass fibers. Glass fiber and polypropylene fiber mixed mats were prepared by a mixing machine which is called “Fiber separating/flying machine” and then compression molded. Various mechanical tests were carried out, and the result were compared with those of short glass fiber reinforced polypropylenes. It was found that tensile and flexural properties were improved by surface treatment of fibers, but the influence of concentration of silane coupling agents were complex and varies fiber contents. Impact and fracture properties were significantly improved by surface treatment of fibers. These properties generally improved with increasing concentration of coupling agents. Comparing with those of short fiber filled systems, surface treatment of fibers remarkably affects on long fiber filled systems.

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The influence of surface treatment on the rheological behavior of long glass fiber reinforced polypropylene melts were investigated. Surface treatment by different kinds of silane coupling agents (aminosilane, diaminosilane, epoxysilane and acryl silane) with different concentrations was performed on glass fibers. Glass fiber and polypropylene fiber mixed mats were prepared by a mixing machine which is called “Fiber separating/flying machine” and then compression molded. Rheological behavior on a rotational parallel plate rheometer were evaluated. Dynamic visco-elastic properties are descussed in terms of various factors: angular frequency, concentration of silane coupling agent, various kind of silane coupling agent, volume fraction of fiber, temperature and strain amplitude. Surface treatment was shown to increase storage modulus (G′) and also reduce the peak of loss tangent (tan δ=G″/G′), which means that the adhesion between the polymer matrix and the fibers is improved. Dynamic viscosity (η′), however, was changed by the concentration of silane coupling agent. This is because coupling agents act to couple the fiber to the polymer matrix, as a wetting agent or as an internal lubricant. Diaminosilane coupling agent was the most effective of the various silane systems for enhancement of rheological behavior. The dependence of the visco-elastic properties on the concentration of silane coupling agent showed the existence of an optimum concentration for systems at each volume fraction of fiber. From the results of the measurement at different temperatures and strain amplitude, it was found that surface treatments decrease the temperature dependence of rheological behavior, and that the dependence of visco-elastic properties on strain amplitude (oscillatory angle) was minimal.

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