Moisture Absorption and Tensile Behaviour of Hybrid Carbon/Flax Composites

Due to environmental concerns, natural fibres are getting their importance as reinforcement in polymer composites. Nevertheless, their hydrophilic nature makes natural fibre composites susceptible to moisture attack. In this regard, one possible solution is to utilise hybrid synthetic/natural fibre composites. This paper aims to characterise the moisture absorption behaviour of carbon, flax, and hybrid carbon/flax composites. The composites were submerged in distilled water at 60 °C until saturation. Subsequently, tensile tests were conducted on dry and wet specimens. Results revealed that the moisture absorption with flax as the outer layers had attained a maximum moisture content of at least 470% higher than carbon as the outer layers. In addition, moisture absorption significantly influences the flax fibre composite, where only 27% of the specific tensile modulus was retained while the specific failure strain was doubled. The modified Halpin–Tsai equation also suggests that carbon fibre has a minimum of 5- and 3-fold larger stress transfer efficiency over the flax fibre with respect to the specific tensile modulus and strength, respectively. Through the modified Chokshi-Chaudhary-Gohil equation, the interphase volume fraction was estimated to be 8–11% for the hybrid composites. The results from this study suggest that it is better to place carbon fibre as the outer layer for hybrid carbon/flax composites to be used in outdoor applications.