Strong, transparent composites based on glass-fiber textile and a polycarbonate-polycaprolactone blend with matching refractive indices

Composites are being researched as lightweight, thermal-insulating alternatives to glass; however, composite materials are generally opaque. In this study, a transparent composite is developed based on E-glass fiber and a polymer blend by matching their refractive indices. To avoid the opacity caused by phase separation, a polymer blend featuring highly miscible polycarbonate (PC) and polycaprolactone (PCL) is used as the matrix of the composite. The refractive indices of PC and PCL are higher and lower, respectively, than that of E-glass fiber; thus, the refractive index of a PC-PCL blend can be matched with that of E-glass fiber by optimizing its composition (PC:PCL weight ratio). Moreover, the crystallization of PCL in a PC-PCL blend is inhibited by the incorporation of sufficient PC, eliminating the light scattering associated with crystalline PCL. The transparency of the proposed composite based on E-glass fiber and a PC-PCL blend is optimal at a PC:PCL weight ratio of 65:35. Furthermore, the impregnation of a glass-fiber textile with a PC-PCL blend with a PC:PCL weight ratio of 65:35 under evacuated conditions produces a strong, transparent composite with tensile and impact strengths that exceed those of PC and a corresponding short glass fiber-reinforced composite.