Effects of molding pressure on mechanical and sound insulation of sisal fiber/carbon fiber hybrid reinforced composites with sandwich structure

Abstract Plant fiber reinforced polymer composites are attracting interest due to their mechanical and sound insulation properties. The role of the inherently hollow morphology of natural fibers in their reinforcing mechanisms is not completely understood. Sisal fiber is an excellent sound proofing material due to its natural hollow structure. For the vacuum assisted resin infusion molding (VARIM) process, the molding pressure will affect the composite impregnation state of resin and fibers, the compaction degree, and physical morphology of plant fibers, and then the mechanical and damping properties of composite materials. This article designed a sandwich structure composites with short sisal fiber as the core layer and continuous carbon fiber as the shell layer. Different molding pressures are used to aim to preserve the hollow structure of sisal fibers. The results show that reducing the vacuum degree during resin infusion within a certain range improved the sound insulation performance. When the molding pressure is 0.065 MPa, the composite laminate reaches a maximum sound absorption of 50.31 dB, an increase of 23.70% compared to the maximum sound absorption of 40.67 dB of the composites fabricated at 0.1 MPa, while the impact and flexural properties remained within an acceptable range, at 63.700 KJ/M² and 285.193 MPa, respectively. Highlights Designed a sandwich composite structure, sisal as core, carbon fiber as shell. The hollow structure of sisal shows obvious sound insulation in the composites. The mechanical performance decreases attributed to lower molding pressure.