Thermoset polymer composites with gradient natural and synthetic fiber reinforcement: Self-healing, shape-memory, and fiber recyclability

Abstract

Natural fibers have high potential as renewable reinforcement for polymers; however, their lower load-carrying capacity compared to synthetic fibers significantly limits the wide application in fiber-reinforced polymer composites. In laminated composite beams under bending load, the normal stress is the highest on the top and bottom layers but is zero at the mid-plane, with almost a linear normal strain distribution. Although the shear stress is the highest at the mid-plane, it may not be a major concern as most polymers can survive the high shear stress. Using this concept, we have designed a hybrid fiber reinforcement in a gradient manner: from the surface to the mid-plane were carbon fiber, glass fiber, and natural jute fiber, respectively. A newly synthesized self-healable shape memory polymer was used for laminating the fibers. Performance characterizations demonstrated that even using a significant amount of natural fibers in the composites, the samples with gradient fiber reinforcement showed competitive mechanical properties to fully carbon or glass fiber reinforced composites and much higher mechanical properties than the composite prepared with entirely natural fibers or glass fibers. For example, the gradient composites show up to 550 % flexural strength of the composites made of fully natural fibers, and around 14 % and 34 % higher flexural strength than that of the composites made of pure glass and pure carbon fibers, respectively. In addition, the composites retain excellent self-healing, shape-recovery, and fiber-recycling properties.