Recyclable high-performance glass-fiber/epoxy composites with UV-shielding and intrinsic damage self-reporting properties

Predicting the barely visible damage on high-performance glass-fiber-reinforced composites (GFRCs) is of vital importance, as it can mitigate catastrophic material failure, and hence, help save costs and lives if GFRCs are used as structural parts. However, the use of current damage self-reporting GFRCs often involves complicated modifications of the matrix or fibers, further, interfacial defect generation and poor resulting mechanical properties may be inevitable when extrinsic mechanochromic additives are employed. In this study, a disulfide bond-tailored epoxy matrix for GFRCs was synthesized from the diglycidyl ester of aliphatic cyclo (DGEAC) and 4,4-dithiodianiline (AFD), which possessed sufficient solvent resistance, good thermal/mechanical performance (Tg ≥ 206 °C, tensile strength ≈ 70 MPa), and UV-shielding properties. Owing to the exchange reaction of disulfide bonds and dynamic transesterification reactions catalyzed by internal tertiary amines, the DGEAC/AFD networks could topologically rearrange, and were easily degraded by dithiothreitol (DTT). More importantly, the DGEAC/AFD networks showed intrinsic mechanochromic properties upon damage due to the formation of sulfenyl radicals. This indicated that the GF/DGEAC/AFD composites were damaged, which was manifested by the appearance of colors visible to the naked eye (a kind of self-reporting mechanism). In this case, the degree of damage could be accurately determined, providing a pre-indication of material failure. In addition, benefiting from the good comprehensive performance of the DGEAC/AFD matrix, the GF/DGEAC/AFD composites exhibited outstanding mechanical properties (tensile strength of approximately 470 MPa and flexural strength of approximately 726 MPa). Meanwhile, the glass fibers (GFs) could be completely recycled in a non-destructive manner by immersing the GF/DGEAC/AFD composites in a solution of DTT. The work presents an interesting example on the synthesis of high-performance, pre-damage-indicative, and recyclable GFRCs.