Injection Moulding of Long-glass-fibre-reinforced Poly(ethylene Terephthalate): Influence of Processing Conditions on Flexural and Impact Strengths

This paper aims to identify the main parameters that influence the mechanical properties of long-glass-fibre-reinforced poly(ethylene terephtalate) parts in order to optimise the potential of these composites. A Taguchi design of experiments (DOE) was used for this purpose. The shape of the injection-moulded specimen was representative of the complexity of industrial parts (presence of sharp frontal and tangential steps). The mechanical properties (bending and Charpy impact tests) were measured at different locations in the part in order to highlight anisotropy. Variance analysis has shown that holding pressure, injection speed, and mould temperature are the most effective processing parameters. It has also shown that the optimised parameter sets that lead to the highest flexural strength on the one hand and the highest impact strength on the other hand are different, the polymer melt and mould temperatures being opposite. Finally, microstructure analysis has shown a fibre content gradient along the flow axis, which is greatly amplified by the presence of geometrical accidents (frontal and tangential steps) including the reorientation of fibres in the flow direction at the end of the parts.