Effect of fibre straightness and sizing in carbon fibre reinforced powder epoxy composites

Carbon fibres with three different sizing agents were used to manufacture unidirectional composites based on powder epoxy resin. A specially designed tensioning apparatus was adopted to apply tension on fibres during the thermal curing cycle, in order to achieve an enhancement of fibre straightness. Chemical composition and surface morphologies of the carbon fibres were extensively characterised. The composites were evaluated using tensile, flexural and interlaminar shear strength tests, and mechanical performance measured based on fibre orientation, fracture modes and interfacial properties. The results demonstrated that composites processed with fibres under tension resulted in an increased unidirectional character in connection with the different amounts of sizing. Flexural and interlaminar testing of the laminates, in addition to Scanning Electron Microscopy and Dynamic Mechanical Thermal Analyses, revealed interfacial adhesion differences, emphasizing the importance of the adequate combination of the polymeric matrix and the type of reinforcement to the structural integrity of composite.