The influence of matrix crystallinity on the mechanical performance of short-fibre composites – Based on homo-polypropylene and a random polypropylene copolymer reinforced with man-made cellulose and glass fibres

Abstract This research shows the influence of the crystallinity of thermoplastic polymer matrix on the mechanical properties of short-fibre composites. It proves that crystal phase affects not only the properties of matrix but predominantly the transfer of stresses to fibres. The injection moulded composites were based on homo-polypropylene and random polypropylene copolymer matrices with glass and man-made cellulose short fibre reinforcements. They were also subjected to annealing to induce growth of crystal phase in the matrices, which was investigated using XRD, DSC and density measurements. The mechanical performance of applied polypropylenes and their composites was compared with annealed counterparts. This comparison shows that matrix crystallinity is important for the mechanical performance of composite and may cause its inconstancy induced by factors like variation of molecular mass distribution, processing conditions and cold crystallisation happening over time. This effect should be heeded at the production, exploitation and research on composites with semicrystalline matrices.