Composites of high density polyethylene (HDPE) and carbon fibre (C fibre) were compoundedand moulded into tensile test bars in compounding injection moulding (CIM) equipment thatcombines a twin-screw extruder and an injection moulding unit. Two HDPE grades exhibitingdifferent rheological behaviours were used as matrices. The mechanical properties of themoulded parts were assessed by both tensile and impact tests. The respective morphologieswere characterised by scanning electron microscopy (SEM) and the semicrystalline structures ofthe matrices investigated by X-ray diffraction. The final fibre length distribution and fibreorientation profiles along the part thickness were also quantified. The composites with lowerviscosity exhibit higher stiffness, higher strength and superior impact performance. Bothcomposites exhibit a three layer laminated morphology, featuring two shell zones and a coreregion. Interfacial interaction is favoured by a lower melt viscosity that enhances the wetting of thefibre surfaces and promotes mechanical interlocking. The composites display a bimodal fibrelength distribution that accounts for significant fibre length degradation upon processing. Thedimensions of the transversely orientated core differ for the two composites, which is attributed tothe dissimilar pseudoplastic behaviour of the two HDPE grades and the different thermal levels ofthe compounds during injection moulding. Further improvements in mechanical performance areexpected through the optimisation of the processing conditions, tailoring of the rheologicalbehaviour of the compound and the use of more adequate mould designs
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