Processing of post-industrial unidirectional prepreg tapes using SMC equipment

Abstract

The aerospace industry has an issue of what to do with waste, unused carbon fiber unidirectional prepreg tapes. One idea is to repurpose unused prepreg tapes for the manufacture of sheet-molding compound (SMC). The resulting material, per Sultana [1], should be stronger due to their carbon fiber and high strength epoxy resin, as compared to traditional SMC, which has lower strength glass fibers and epoxy resin. The cure state of the epoxy resin in the prepreg tapes, which is affected by the amount of time the material has spent at elevated temperatures or room temperature, significantly changes the ability of the material to be chopped into short fiber SMC. In addition, several equipment-related factors impact the material’s ability to be chopped into SMC. This thesis characterized each of the factors impacting the process and used statistical methods to design experiments to investigate the impact each of these material-related and equipment-related factors on the success of the cutting portion of the process. The cure state, as measured by endothermic peak, glass-transition temperature (Tg), or heat of reaction/degree of cure, has the greatest impact on the cutting process. For material with a moderate level of cure, the sharpness of the blades in the cutting roller also has a major impact on the success of the process. The cutting pressure, roller speed, and tape tension also have an impact on the success of the process, but impact of these factors lessens for feedstock prepreg with a sufficient high level of cure. An optimal setup was determined, and general rules of thumb for selecting material and equipment settings were established.