Rheological Properties of Aminosilane Surface Treated Short Glass Fibre Reinforced Polypropylenes. Part 1: Steady Shear and Oscillatory Flow Properties in Molten State

The effect of surface treatment on the rheological properties of 20 and 40 wt.% short glass fibre reinforced polypropylenes (GF/PP) and of the same composites containing maleic anhydride modified polypropylene (GF/mPP/PP) were investigated. Glass fibres were surface-treated by aminosilane coupling agent (ASC, γ-aminopropyltriethoxysilane). Steady state shear and dynamic properties in the molten state were measured using a cone and plate type rotational viscometer. Surface treatment increased the rheological properties of the molten composites. This trend was more pronounced for composites containing modified PP. In the case of the GF/PP materials the increase was monotonous for all measured functions, while in the case of the GF/mPP/PP ones, the parameters representing elasticity showed peaks at 0.5 wt.% ASC. The Cox-Merz empirical law was found to be applicable to untreated GF/PP and GF/mPP/PP composites at low shear rates (angular frequencies), where the materials showed Newtonian plateaux. As for ASC surface treated materials, GF/mPP/PP followed the same trend. On the other hand, GF/PP exhibited a higher complex viscosity than the steady state shear one over the whole range of angular frequencies (shear rate) covered by the experiments. Surface treatment enhanced apparent yield stress, as did increasing the glass fibre content. The effect of the latter was more pronounced in the case of the GF/mPP/PP series. The viscosities of the re-mixed composites became lower than those of the original ones, and the difference between untreated and ASC treated systems was detectable only in the case of the complex viscosity of the GF/mPP/PP sample.