Degradation evolution and mechanism of sheet molding compound with variable composition exposed to acid solution environment

Abstract In the present work, the sheet molding compound (SMC) composites with variable filler, resin and fiber composition were prepared to investigate the effects of composition on acid resistance of SMC composites. The water absorption of SMC composites with various compositions was measured to estimate the influence of water on mechanical properties deterioration. Hardness and flexural properties tests were performed to investigate the degradation evolution. The degradation mechanism was revealed by analyzing the change of molecule configuration and evaluating the thermal stability. A minimum reduction of the flexural strength (3.21%) was observed on the SMC composites with 11.3 wt% hollow glass microspheres (HGMs). The chemical resistance and addition amount of the fillers had significant impacts on the acid resistance of SMC composites. A great flexural property and a minor degradation of flexural strength (6.29%) and modulus (7.86%) was obtained in SMC composites with the mixed resin. The resin characteristics, molecules weight, free volume size and polar groups number, had an important impact on the water absorption and acid resistance of SMC composites. A high flexural property and minor degradation of flexural strength (5.12%) and modulus (7.66%) was observed in SMC composites with 55 wt% glass fibers (GFs). Exposed to 25 ℃, 20 wt% sulfuric acid solution for 28 days, the SMC composites exhibited a minor degradation of HGMs and GFs. In this condition, the deterioration of mechanical properties was dominated by the resin matrix plasticization and decomposition, along with the interface degradation. It can be concluded that the original defects and weak interacted regions in the composites system initiated the degradation of SMC composites, while the microstructure and composition of SMC composites dominated the degradation progress.