Transparent fiber-reinforced composites based on a thermoset resin using liquid composite molding (LCM) techniques

The production of optically transparent glass-fiber-reinforced composites based on a thermoset resin using both vacuum-assisted resin infiltration (L-RTM) and resin transfer molding (RTM) was successfully accomplished. The composites have been characterized in terms of infiltration quality, degree of transparency, mechanical and thermal properties. A good match in the RIs, smooth composite surfaces, and high infiltration quality have been achieved. The key to success was the low viscosity of the resin-hardener mixture. The good surface quality was accomplished via polymerization in a glass cavity of the L-RTM setup. The mechanical properties of the composites containing 5- or 10-layers of the glass fabric correlate with a heterogeneous distribution of these fabrics. By contrast, composites containing 29-layers, corresponding to 44 v. % of fiber, possess strongly enhanced mechanical properties. By matching the RIs of the materials at 589 nm, almost unchanged optical properties were obtained in this wavelength region for the 5- and 10-layer samples. Furthermore, compared to 86% of the pure polymer matrix, up to 75% transmittance was accomplished with the composite containing 29 layers of fabric, both prepared by L-RTM. A tensile strength of 435 MPa and a modulus of 24.3 GPa were achieved for the same composite, compared to 67 MPa strength and 3.6 GPa modulus of the polymer matrix, both prepared by RTM. Manual process control of the presented LCM manufacturing methods is challenging, particularly with regard to controlling sample thickness i.e., fiber v. %. Also, the flow front propagation requires better mold design, resin volume flow, and injection pressure control. For a homogeneous distribution of the textiles within the cavity, a new mold design combining the good surface quality of the L-RTM and the capability of the RTM setups to produce large-sized parts is required. Considering that commercially available resin systems and textiles were used in this study, the major limitation of the technology outlined here is related to upscaling and equipment. To satisfy these needs, a new RTM mold design and development is required that can provide an industry-scale, low porosity, and smooth surface production.