Rapid-cycle epoxy prepreg for automotive composites: thermal behavior and unconventional cure kinetics

Fast-curing prepregs are increasingly gaining attention for high-throughput composite manufacturing, especially in the automotive industry where cost, cycle time, and scalability are critical. In this work, we investigated the thermal and mechanical behavior of a commercial fast-cure carbon/epoxy prepreg processed via hot compression molding in a 13-min cycle. Thermogravimetric analysis (TGA) showed thermal stability up to 300 °C, while differential scanning calorimetry (DSC) revealed an atypical dual-mechanism curing behavior. Both dynamic and isothermal DSC analyses demonstrated deviations from conventional kinetics, including non-linear Arrhenius behavior and a shift in activation parameters depending on the method employed. The prepreg achieved a glass transition temperature of 153 °C and delivered tensile, compressive, and interlaminar shear strengths of 786 MPa, 276 MPa, and 42 MPa, respectively. With a low void content (2.8 vol%) and full cure completion experimentally confirmed within 13 min, this material demonstrates strong potential for structural automotive applications. The study provides new insights into the kinetic complexity of snap-cure epoxy systems and supports their applicability in fast-cycle composite manufacturing.