Study on the Properties of Highly Transparent Thermosetting Glass Fiber Composites Fabricated Using the Transparent Prepreg Process

ABSTRACT The industrial‐scale production of transparent composites faces challenges. Here, we propose a scalable strategy by integrating E‐glass fiber (GF) into a refractive‐index (RI)‐tunable thermosetting epoxy resin (EP). By introducing methylhexahydrophthalic anhydride (MHHPA), we achieved RI matching between GF and matrix, enabling excellent opto‐mechanical properties. The thermosetting glass‐fiber transparent composite (TGFTC) was fabricated using transparent prepreg (TP) combined with a hotpressing process, which effectively minimized surface defects. The 0.16 mm‐thick TGFTC fabricated demonstrated the highest transmittance (90.1%) and the lowest haze (3.6%). The TGFTC samples, containing 20 layers of TPs, maintained exceptional optical transparency (84%) while exhibiting superior mechanical properties (413 MPa tensile strength, 785 MPa flexural strength and 193 KJ/m ² impact strength). Furthermore, after 28 days of hygrothermal aging, the TGFTC demonstrates excellent aging resistance. Specifically, the composite exhibits 84% transmittance, 15% haze, and 206 MPa tensile strength. The aging degradation mechanism is attributed to water‐induced matrix softening, which leads to the propagation of microcracks and fiber/matrix interfacial debonding. Optical uniformity was assessed using a 300 × 300 mm specimen segmented into 20 distinct zones. The results demonstrated excellent consistency in light transmittance, haze, and thickness across all regions. This research provides a novel fabrication method for transparent composites.