Long discontinuous carbon fibre/polypropylene composites for high volume structural applications

A processing route is presented to manufacture discontinuous carbon fibre-reinforced polypropylene composites, using much longer fibre lengths (25？mm) and higher volume fractions (up to 45%) than previously reported in the literature. Carbon fibre tows are coated with different ratios of polypropylene, blended with a maleic anhydride coupling agent, to investigate the influence of the interfacial shear strength at the microscale on the macroscale composite properties. Improvements in the tensile performance at the macroscale (70% increase) are not as high as those reported for the interfacial shear strength at the microscale (300%), following the addition of the coupling agent. Consequently, the tensile strength of the carbon fibre-reinforced polypropylene material is only 45% of values reported for carbon fibre/epoxy systems, however, the tensile stiffness is comparable. This demonstrates the potential for using carbon fibre-reinforced polypropylene for structural applications, following further process optimisation to overcome the current high levels of porosity (3.3% at 0.45Vf) to improve the tensile strength