Study on curing characteristics and mechanical properties of the mid-temperature epoxy prepreg regulated by accelerator

To address the high energy consumption and cost of conventional autoclave curing, this study develops a mid-temperature (100-130°C) curing epoxy prepreg system for vacuum bag molding. The effects of two curing accelerators (UR300 organic urea and 2,4-EMI imidazole) on the curing characteristics, reaction kinetics, and room-temperature storage stability of dicyandiamide/epoxy (DICY/EP) systems were systematically compared. Unidirectional [0°] laminates were prepared using Toray T700 carbon fibre (12K) and an optimized resin formulation. The curing process was carried out under a vacuum pressure of 0.098 MPa. The results showed that UR300 achieved a better balance between curing reactivity and room-temperature latency than 2,4-EMI. UR300 lowered the peak curing temperature from 189.5°C to 128.8°C, satisfying mid-temperature curing requirements. After 30 days of room-temperature storage, the curing degree was only 9.7% (calculated via DSC residual enthalpy), and the mechanical properties of the castings decreased by less than 10%. The optimized composite laminates achieved a fibre volume fraction of 63.8%, a porosity of 1.29%, a tensile strength of 1.70 GPa, a bending strength of 1.11 GPa, and an interlaminar shear strength (ILSS) of 63.4 MPa. This study offers theoretical and experimental insights for developing mid-temperature curing epoxy prepreg systems tailored to low-altitude aircraft applications.