Flame-retardant glass fiber reinforced polysilsesquioxane epoxy composite with excellent mechanical strength and water resistance

Owing to the high viscosity and poor flame retardancy of epoxy resins, the development of glass fiber reinforced epoxy resin composites (GFREPs) in large-scale application has been limited. It is vital for meeting requirements of vacuum-assisted resin transfer molding (VARTM) process to develop a low-viscosity and flame-retardant epoxy resin. In this work, a polysilsesquioxane epoxy resin with low viscosity was prepared and a glass fiber reinforced polysilsesquioxane epoxy composite (EPHPOSS30/GF) was successfully constructed through VARTM process. Compared with traditional GFREPs (EP-257/GF), the bending strength, interfacial shear strength and interlaminar shear strength of EPHPOSS30/GF reach 604.5 MPa, 38.5 MPa and 26.9 MPa, which are 104%, 63.1% and 28.6% higher than that of the EP-257/GF, respectively. The EPHPOSS30/GF exhibits high water resistance, which can maintain its dielectric properties and mechanical properties after water treatment. The EPHPOSS30/GF demonstrates improved thermal behavior, with significant increments in the thermal initial decomposition temperature and the glass transition temperature. Notably, the EPHPOSS30/GF is a low-heat, low-smoke and low-toxicity composite, the peak heat release rate, carbon monoxide production, and maximum smoke density are 38.9%, 48.2% and 77.8% lower than that of EP-257/GF, respectively. This strategy addresses the key issues of traditional GFREPs in viscosity, mechanical properties, water resistance and flame retardancy, enabling its large-scale application.