Effect of chemical treatment and water absorption on properties of sisal fiber and its interface with resin

Sisal fibers with surface treatments, including potassium permanganate, sodium hydroxide, flame retardant agent, silane, and without treatment were investigated. The tensile properties and interfacial shear strength (IFSS) of sisal fiber with modified acrylate and epoxy resin were tested by using single fiber tensile method and micro-droplet debonding method, respectively. The effect of water absorption on the sisal fiber surface morphologies, the tensile properties and its interfacial adhesion were analyzed, and the corresponding fracture mode as well. The results show that after chemical treatments the tensile strength and modulus of sisal fibers are decreased to varying degrees. Compared with the untreated sisal fiber, the tensile strengths of potassium permanganate and silane treated fibers both decrease by 44%, the strength of sodium hydroxide treated fiber decreases by 27%, while that of flame retardant treated fiber is almost equivalent. The chemical treatments can decrease the IFSS of sisal fiber/modified acrylate and the decreasing degrees are different from those of the fiber tensile properties, in which lowest IFSS is found for flame retardant sisal fiber/modified acrylate with 2.0 MPa, decreasing by 80% in comparison with the untreated fiber system. After silane treatment, the water absorption rate is decreased, and the property retention rate is higher for the sisal fiber than those of the untreated fiber. For the hygrometric state sisal fiber/epoxy, the untreated fiber system shows IFSS of 6.6 MPa, higher than the silane treated fiber system. The fracture morphologies indicate that silane treatment tends to reduce the bonding of the inter-fibrils, thereby decreasing the sisal fiber tensile and interfacial properties with resin.