EFFECTS OF PROCESSING CONDITION ONMORPHOLOGY AND MECHANICAL BEHAVIOUR OFPP/PP COMPOSITES

摘要

Composites consisting of the same thermoplastic material for the matrix phase and reinforcement, theso-called ‘polymer unity composites’, are gaining increasing attention. These composites, typicallythose made from polypropylene (PP) and/or polyethylene (PE), possess distinct properties withpotential unique applications. Unlike the conventional composites containing glass or carbon fibresembedded in polymer matrices, they can be easily recycled as they do not require the tedious processto separate the reinforcement fibres from the matrix before individual recycling. These compositescan be called the ‘green composites’ as they are more environment-friendly than other compositematerials in terms of ease of recycling.In the present study, the effects of processing conditions are investigated on the morphology andimportant mechanical properties of all PP composites consisting of homo-PP fibers and propyleneethylenerandom copolymer matrix. Highly oriented PP fibres are spun, and composite laminates ofdifferent cooling rates and thermal treatments are prepared using the filming stacking andcompression molding techniques. The fibre-matrix interfacial bond strengths and the composite bulkmechanical properties are measured, which are in turn correlated to crystallinity and crystallinemorphology affected by the processing condition. The single filament fragmentation test shows thatthe slow cooled samples have higher interfacial shear strengths (IFSS) than the fast cooled ones. Thetensile modulus and strength generally increase with decreasing cooling rate and due to isothermaltreatment. This observation can be attributed to the change in the crystallinity induced by differentthermal processes. A higher crystallinity in the slow cooled samples gives rise to high tensileproperties and a brittle fracture mechanism, and vice versa. There are functionally similar variationsin IFSS and tensile properties with respect to cooling rate. The Charpy impact test results indicate thatthe impact fracture performance of the composites is highly dependent on the testing temperature.There were only marginal differences in impact fracture toughness between the samples processed atdifferent cooling rates when tested at room temperature. The sensitivity of cooling rate on impactfracture energy became significant when tested at sub-zero temperatures. The impact fracturetoughness are generally higher for the samples with slower cooling rates than the fast cooled samples.