Performance Evaluation of Out-of-Spec Carbon Prepregs for Upcycling Purposes

In view of exploring the possibility of upcycling aerospace scrap, cure characteristics of out-of-spec carbon fiber prepregs are investigated in this study. The cure behavior of the prepreg is examined in the form of the mechanical cure conversion state of the material using a Dynamic Mechanical Analyzer (DMA). Cure kinetics is modeled by comparing the storage modulus at the start of the reaction (E'₀) and instantaneously (E'_t) during isothermal experiments with those of the fully cured material (E'_∞) obtained from dynamic scans. The glass transition temperature T_g and the extent of reaction before gelation are modeled using the DiBenedetto model, where the T_g of each laminate is determined in a DMA, per standard ASTM D7028. The mechanical properties, the extent of cure, and the glass transition temperature of the cured laminates were determined according to industry and international standards. The maximum conversion at temperatures between 100 °C and 140 °C is approximately 80% (±5%). The modeled rate of conversion shows a reasonable match with the experimental data, exhibiting a maximum reaction rate at about 30-40% of the cure conversion. The predicted evolution of the T_g as a function of cure conversion using the DiBenedetto model provides a 94% match with the experimental data. The multi-stage cure cycle based on the models offers shorter cycle times and high-quality laminates. The mechanical test results indicate approximately a 13% and 15% decrease in tensile strength and modulus, respectively, compared to pristine ones. The experimental extent of cure of the cured laminates (95.4%) is in close agreement with that predicted by the model (97%). The porosity in the laminates is estimated to be approximately 2.4%, which is acceptable in several industries.