Influence of fibre length and concentration on the properties of glass fibre-reinforced polypropylene .1. Tensile and flexural modulus

In this report we present the results from the first part of a study on the influence of fibre length (0.1-50 mm) and concentration (3-60% w/w) on the properties of glass-reinforced polypropylene laminates. These laminates were prepared in the laboratory using a wet deposition method, and are compared with samples prepared on a commercial melt-impregnation GMT line. We found that laminate stiffness increased linearly with fibre concentration up to 40% w/w. However, stiffness was virtually independent of fibre length above 0.5 mm. Predictions of tensile modulus using the Cox model correlated well with the experimental data. High concentrations of long fibres (>40% w/w) resulted in fibre packing problems and an increase in void content which lead to a reduction in modulus. The matrix molecular weight and the fibre-sizing compatibility had little effect on the laminate stiffness.