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

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, σ_c, increased with increasing volume fraction of fibres, ϕ_f in a nonlinear manner and decreased with increasing temperature in a linear manner. However, for ϕ_f values in the range 0–10% a simple additive rule-of-mixtures adequately described the variation of σ_c with ϕ_f 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, F _σ, defined as weldline strength divided by unweld strength, decreased with increasing ϕ_f but increased with increasing temperature. A linear dependence was found between F _σ and temperature. Mould thickness had no significant effect upon weld and unweld tensile strengths and consequently had no significant effect upon weldline integrity factor.