While aramid fibre composites are generally said to have excellent impact properties, this has not yet been translated to the aerospace sector, where impact prone secondary structures remain to be made from metals or glass fibre reinforced polymer. Aramid fibre reinforced engineering thermoplastics could combine the stiffness of thermoset resins with the ductility of commodity thermoplastics in a novel composite with both high structural and impact properties. In the following thesis work, Twaron and Technora fibres are evaluated for their suitability in such a material.

Processing aramid reinforced materials is a trade-off between the composite consolidation quality and tensile strength retention in the fiber. Good consolidation is required to achieve the required bending properties in structural laminates and requires a low polymer melt viscosity. Strength loss in the yarn is caused by the high temperatures needed to achieve such levels of viscosity, which induce a number of degradation mechanisms if no countermeasures are taken. Oxidation, hydrolysis and a purely thermal component are identified as the main mechanisms causing deterioration. Using a Kapton vacuum bag as well as drying the reinforcement and matrix material greatly improves strength retention during processing. Purely thermal degradation cannot be counteracted and makes Twaron or other para-aramid homopolymers unsuitable for reinforcing polymers with processing temperatures above 250°C. Technora is shown to be more resistant against both hydrolysis and thermal degradation, with only minor strength losses well beyond 320°C. The high toughness of Technora attributes these fibres a high energy absorption potential.

Various Twaron and Technora reinforced engineering thermoplastics are produced to evaluate the influence of the fibre-matrix interface and matrix material on the low-velocity impact response. Higher interfacial adhesion is achieved by using epoxy sizing on Twaron yarn and appears to improve the energy absorbed during perforation through increased fracture toughness. Technora reinforced PPS and PEI appear to have a high energy absorption potential but relatively low out-of plane performance. The eventual feasibility of the novel material will eventually depend on its high impact performance with respect to other, conventional laminates such as aramid-epoxy.