Tensile strength and fracture mode I toughness of photocurable carbon fiber/polyether-polythioether composites

Abstract

This paper reports the development of a novel photocurable carbon fiber/polyether-polythioether (TF CFEC) composite and the comparison of its mechanical performance with that of a conventional thermally cured carbon fiber-epoxi composite (CTC CFEC). Unidirectional carbon fiber (CF) was used as the reinforcement agent in both composites. In the case of the TF CFEC, the CF employed was surface-functionalized with thiol groups to promote chemical bonding to the polyether-polythioether matrix derived from the epoxy/thiol-ene system. This was achieved by means of a transesterification reaction of (3-mercaptopropyl) trimethoxysilane (MPTS) with the hydroxyl groups produced on the surface of the CF after an oxidative plasma treatment. Mechanical testing revealed that although TF CFEC displayed slightly lower mechanical properties than CTC CFEC, it exhibited 50% higher fracture toughness. This difference in behavior was explained by the difference in the chemical nature of both polymeric matrices, where a highly crosslinked poly(hydroxyl-amine) is produced in the case of CTC CFEC , while a polyether-polythioether matrix with inherent toughness due to the flexibility of polythioethers, is obtained during the photo-thermal treatment to obtain TF CFEC. Considering that TF CFEC was cured in only 1h at 40 mW/cm2 of UV intensity and 85°C, and the CTC CFEC was cured at room temperature for 4h, followed by heating at 100°C for 4h, there is considerable energy savings in the production of the photocurable composite. The result is a cost-effective process that could have potential applications in the automotive and aerospace industries.