Thermoplastic materials in sheet molding compound

Sheet Molding Compound (SMC) has proven to be a suitable process for the manufacturing of automotive body parts. Thermosetting matrix materials combined with glass fiber reinforcement deliver a good performance to weight ratio at a competitive cost. The downside of SMC, as with all thermoset-based composites, is the limited recycling potential, especially compared to thermoplastic alternatives. A recently introduced resin system based on acrylates enables, for the first time, the production of a thermoplastic SMC, combining the strengths of the SMC process with the advantages of the thermoplastic resin systems. Replacing conventional glass fibers by synthetic fibers as reinforcement enables the production of a completely thermoplastic material, which is suited for lightweight and eco-friendly design in automotive applications of the future. In the present work, the acrylic resin system Elium, a reactive thermoplastic material with processing characteristics similar to those of polyester resins, was used to produce semi-finished materials and mold parts thereof on industrial-scale production equipment. Aramid fibers were introduced to the SMC material in the form of non-woven fabrics, as, due to the tough nature of those fibers, direct processing on a conventional SMC fiber-cutting unit was not feasible. For reference, an Elium-based SMC with glass fiber reinforcement was also produced, as well as a thermoset epoxy SMC with aramid fiber reinforcement. The material variants were characterized in regard to their tensile and flexural properties, as well as their impact strength. The obtained mechanical characteristics were benchmarked against commercial SMC products. The aramid fiber-based SMC variants exhibited good strength under both tensile and flexural load. Stiffness, in both load cases, ranged in between those of comparable glass and carbon fiber SMCs, which is in line with the modulus of the respective neat fibers. The impact strength of both aramid fiber reinforced materials was also good. Between those two materials, the epoxy variant displayed better mechanical performance. The glass-reinforced Elium SMC performed on a similar level to commercially available vinyl ester SMC. Overall, the achieved material performance was very promising. Paired with the low density of the produced material and its recycling potential this new type of SMC forms a valuable proposition for the composite market.