Effect of fibre concentration, temperature and mould thickness on weldline integrity of short glass-fibre-reinforced polypropylene copolymer composites

Abstract

The effect of fibre concentration, temperature and mould thickness on tensile strength of single- and double-gated injection-moulded polypropylene copolymer reinforced with 0, 10, 20, 30 and 40 wt% short glass fibre was studied at a fixed strain-rate of 7.58 × 10−3 s−1 between 23 and 100 °C. It was found that tensile strength of single-gated mouldings, σc, increased with increasing volume fraction of fibres, ϕf in a nonlinear manner and decreased with increasing temperature in a linear manner. However, for ϕf values in the range 0–10% a simple additive rule-of-mixtures adequately described the variation of σc with ϕf over the entire temperature range 23–100 °C studied here. Tensile strength of double-gated mouldings like their single-gated counterparts decreased linearly with increasing temperature. The presence of weldlines significantly reduced tensile strength of double-gated composite mouldings but had little effect on tensile strength of the matrix. Weldline integrity factor, Fσ, defined as weldline strength divided by unweld strength, decreased with increasing ϕf but increased with increasing temperature. A linear dependence was found between Fσ and temperature. Mould thickness had no significant effect upon weld and unweld tensile strengths and consequently had no significant effect upon weldline integrity factor.