Influence of temperature on weldline strength of injection moulded short glass fibre styrene maleic anhydride polymer composites

The effect of weldlines on the tensile strength of injection moulded styrene maleic anhydride (SMA) reinforced with 20, 30, and 40% weight fractions φ_f of short glass fibres was investigated between 25 and 120°C. The weldline was formed in the moulded specimens by direct impingement of two opposing melt fronts. In the absence of weldlines, the tensile strength increased linearly with φ_f and decreased linearly with temperature. In the presence of weldlines, the tensile strength of the matrix and its composites was greatly reduced. Weldline strength had a maximum at φ_f≈10%, beyond which it decreased with further increase in φ_f. A significant drop in weldline strength was noted with increase in temperature. The loss in matrix strength was attributed to the orientation of the polymer chains perpendicular to flow in the weldline region, while the loss in composite strength was attributed to the orientation of the fibres perpendicular to flow in the weldline region. The weldline integrity factor increased with increasing temperature but decreased with increasing φ_f.