Environmental durability of carbon/flax fiber hybrid composites

Hybridization of synthetic fibers with natural fibers is receiving more attention in recent years. Experimental study on the durability of carbon/flax fiber reinforced polypropylene composites and single flax fibers was carried out. Three composite lay-ups were designed by altering the position of the carbon fiber ply, i.e., pure flax/polypropylene laminates, laminates with flax ply at the surface and laminates with the carbon ply at the surface. Samples were exposed to water immersion ageing at elevated temperature until saturation. The transport law of moisture in hybrid composites and mechanisms of possible change in microstructures and mechanical properties were particularly explored. Carbon fibers reduced the amount of water absorption in flax/polypropylene composites and improved their mechanical properties. These beneficial effects were optimum when carbon fibers were placed at the outer layers. However, the interface between the carbon ply and flax ply was vulnerable to both hygrothermal attack and delamination. After hygrothermal ageing, the tensile and flexural properties of the laminates decreased while the tensile failure strain increased, primarily due to plasticization and fiber/matrix interface deterioration. Single flax fibers which were exposed to the same ageing condition also experienced decrease in strength and modulus. However, elongation-at-break of single flax fiber decreased after ageing.