Hydrothermal durability of unidirectional flax/carbon fiber hybrid composite plates

Abstract

Hybrid carbon fiber/flax reinforced polymer composites (HFRPs) meet the requirements of high property to cost ratio for many structural applications. In the present study, HFRP plates produced with filament winding were studied on the property evolution subjected to 40 and 70 °C water immersion for eight-week. Water uptake and flexural properties of the HFRP samples were tested and analyzed in terms of the hybrid modes and fiber contents. The diffusion coefficient and equilibrium water absorption of fiber reinforced polymer composites increase and the performance deterioration intensifies with the increase in temperature. The equilibrium water absorption and the diffusion coefficient of the FFRPs are 7.6 and 3.8 times higher than those of the carbon fiber reinforced polymer composites (CFRPs), respectively. With the increase in the carbon fiber content, the hybrid samples showed a decrease in the water uptake and diffusion coefficient. HFRP with carbon fiber on the surface shows better hydrothermal resistance than other hybrid modes due to the barrier behavior of carbon fibers for water molecules. Fiber contents and hybrid modes also play a crucial role in the degradation of flexural properties. The flexural strength and modulus of HFRPs increase with increasing carbon fiber content but the nonlinear behavior becomes less obvious. The flexural strength and modulus of HFRPs with carbon fibers on the surfaces (CFC) are 3.59 and 7.96 times higher than those of the HFRP plates with flax on the surfaces (FCF) respectively. However, the significant water absorption in the flax layers deteriorates the stress transferring ability of the core flax layer, which causes the aging of CFC seriously.

Keywords

• Flax/carbon hybrid composites
• Hydrothermal environment
• Water absorption
• Degradation of flexural properties