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.
