Continuous glass fibre-polypropylene composites made by melt impregnation

Abstract

In order to obtain best possible continuous glass fibre – polypropylene composites the following requisites should be fulfilled; wetting of the fibres by the melt, good adhesive strength between the fibres and the solid polypropylene, a void free pre impregnated lamina and finally good consolidation between plies in the final product.

In this work the wetting kinetics between polypropylenes and different treated fibres was studied by the Wilhelmy principle. It was shown that reactions taking place influenced the advancing polymer front on the fibre surface.

It was shown that it is necessary to apply a coupling system in order to enhance the bond strength between the PP matrix and the glass fibre. Different coupling systems were used, and it was shown that both physical molecular entanglement and direct chemical bonding increases the bond strength significantly.

To study and compare the influence of impregnation degree and bond strength between matrix and fibres, 9 mechanical test methods ranging from the single fibre pull-out test to various laminate tests were selected, and it was possible to distinguish between interface relevant and impregnation relevant test methods. In that context opacity measurements was found to be an effective way to determine the degree of impregnation.

In the investigation of different melt impregnation methods the selected methods were the common pin assisted method, a crosshead impregnation die including different vibration techniques and a slit die. The degree of melt impregnation was studied qualitatively with optical microscopy and determined quantitatively by opacity measurements.

Excellent impregnation efficiency was obtained using the radial slit die, followed by the pin chamber impregnation method.