The influence of fibre length and concentration on the properties of glass fibre reinforced polypropylene: 5. Injection moulded long and short fibre PP

We present results of a step by step comparison of the mechanical performance of injection moulded ‘long’ (LF-PP) and ‘short’ (SF-PP) glass fibre-polypropylene compounds. The study allows direct comparison of the mechanical performance of long and short fibre systems in the same resin at the same fibre diameter, and the effect of fibre diameter in short fibre compounds. Furthermore, the comparison of these three systems has been made over the 0–40 wt% fibre content range. At the same fibre diameter and fibre content LF-PP gives significant improvements in room temperature tensile and flexural strength, notched and unnotched impact resistance. The improvement in impact resistance is higher still at lower test temperature. LF-PP also gives increasingly higher modulus over SF-PP as the strain is increased. The effect of lowering the fibre diameter in SF-PP has been shown to increase both strength and unnotched impact, but not to the levels obtained with LF-PP at higher fibre diameter. Notched impact and modulus of SF-PP were relatively unaffected by reduction of the fibre diameter. The relative mechanical data are shown to conform well to available models. The results are discussed in terms of the relevant micro-mechanical parameters of these materials.