Automotive use of reinforced plastic composites has grown significantly at the same time that environmental pressures have increased demanding responsible recycling of all materials. The suppliers of sheet molding composite (SMC) recognize their responsibility to ensure that viable recycling techniques are developed. To this end, the SMC molders and their raw material suppliers are investigating processes that create the opportunity to produce viable products from recycled SMC.
To fully “close the loop,” the successful recycling of automotive-grade, glass-reinforced, unsaturated-polyester-based composites such as SMC (also included are bulk molding compound [BMC] and thick molding compound [TMC]) must include the reuse of the recycled material in the production of new composite parts. This paper discusses the compounding, molding and testing of automotive parts molded from composites containing recycled SMC. Granulated and milled, as well as pyrolyzed and milled, SMC was studied in new SMC formulations. The formulations containing recycled material were based on both “low-profile” and “general-purpose” unsaturated polyester resins.
For commercial acceptance, parts containing recycled SMC must have structural and aesthetic attributes comparable to existing non-recycled materials. Data on the engineering properties and surface quality of parts made from the recycled materials were generated in this study. Tensile, flexural, impact properties and Loria® surface smoothness were measured.
This paper demonstrates that recycled SMC can be milled to a powder and used as a partial replacement for calcium carbonate in SMC formulations to give molded parts with equivalent properties to control materials.