Effect of aramid pulp on low temperature flexural properties of carbon fibre reinforced plastics

Flexural properties of carbon fibre reinforced plastics (CFRPs) with multi-layer interfacial reinforcement of hierarchically structured aramid pulp (AP) fibres were measured at −40 and −100 °C under three-point bending (3 PB) together with unreinforced CFRPs. After curing, the ‘interleaf’ thicknesses were 3.3, 5.6 and 12.2 μm for three different AP areal densities of 0.8, 1.6 and 3.2 g/m², respectively. 3 PB tests of control and AP reinforced CFRPs were also performed at 20 °C to compare the AP strengthening effects and their variations from ambient temperature to −100 °C. The flexural strength increased up to 30.6% at −100 °C for specimens with 1.6 g/m² AP in comparison to 24.5% enhancement at room temperature. This finding proves that a proper composite design, i.e. adding tough and flexible short fibres into the brittle-fibre and brittle-matrix system, can indeed enhance the structural performance of CFRPs. The small-scale in-house ‘pre-preg’ fabrication adopted in this study shows that the ultra-thin layers of AP fibres can be potentially incorporated into a large-scale pre-preg production so that the extra step of inserting the interleaving layers can be removed from the composite forming process. In other words, end users can use the AP toughened pre-pregs just like any carbon fibre pre-pregs currently in use without the trouble of interleaving.