Facile method to enhance the optical properties of transparent glass fiber-reinforced epoxy composites by controlling the curing agent content ratio

In this study, the refractive index of epoxy resin was adjusted according to the mixing ratio of two types of curing agents, namely 4,4′-diaminodiphenylmethane and poly(propylene glycol) bis(2-aminopropyl ether). The optical properties of the cured pure polymers and transparent glass fiber-reinforced plastics (GFRP) 1 (analyzed with an ultraviolet–visible spectrophotometer) were compared. Epoxy (EP)/P9D1-F exhibited excellent optical properties (transmittance of 89.54 % and a haze of 9.30 %). The small refractive index difference between EP/P9D1 and glass fiber reduced the phase delay and fabricated high-transmittance, transparent GFRP. In addition, EP/P9D1-F exhibited superior mechanical properties, with enhanced flexural strength and fracture toughness owing to the improved stress distribution between the fiber and matrix. These findings suggest that a transparent GFRP with high transmittance and glass-like optical properties, as well as excellent mechanical performance, can be fabricated by appropriately mixing and adjusting two or more types of curing agents.