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.
