No abstract

Epoxy and epoxide composites have a wide range of outdoor applications wherein they are affected by ageing. In this study, epoxy casting plates and epoxy-based composite rods for use in overhead conductors were prepared. A concurrent investigation concerning the ageing of epoxy resins and their carbon fibre composites was carried out via artificially accelerated experiments under hygrothermal and salt mist conditions. The moisture penetration along the depth, water absorption, appearance, hardness, density of the epoxy resins, and variation patterns of the impact strength and tensile strength of the epoxy-based composites were investigated. The ageing mechanisms were explored using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Both ageing modes had essentially similar influences on the properties of the resins and their composites; moreover, they did not significantly affect the chemical structure and microstructure of the epoxy resin, with the physical adsorption of water primarily observed during the ageing process. The moisture absorption behaviour of the epoxy obeyed Fick’s law. Although the water penetration rate in the salt mist ageing mode was slightly higher than that in the hygrothermal ageing mode during the early ageing stage, it was essentially the same during the later stage. The final moisture absorption rate at saturation was approximately 1.1% under both modes. The flexural strengths and impact strengths of the composites in both ageing modes followed a similar trend. They decreased gradually with the ageing time and then stabilized at almost the same value. The flexural strength was reduced from 803 MPa to 760 MPa and the impact strength from 383 J/m2 to 310 J/m2, indicating a decrease of approximately 5.4% and 19%, respectively. The absorbed water during the ageing process caused micro-cracks at the interface between the fibres and resin, weakening the interfacial strength and reducing the mechanical properties of the composites.

Introducing the isocyanate group on the carbon fibre (CF) to improve surface activity is an effective modification method. Still, its application in the industrial field is restricted because the modification process is harmful to the environment and isocyanate is easy to fail. In this paper, 3-isocyanopropyltriethoxysilane (IPTS) has been blocked with caprolactam (CPL) have been prepared. By adjusting the hydrolysis conditions and concentration of the modified coupling agent solution, the CPL-blocked IPTS was grafted to the surface oxidized CF, and the CF-reinforced polyamide 6 (PA6) composites were prepared. After treating CF with 1.0wt% coupling agent solution, the composites’ interlaminar shear strength (ILSS) reached 52.53 MPa, which was 23.83% greater than that of the desized CF/PA6 composites. High-temperature composite molding caused CPL-blocked IPTS to unblock, and the isocyanate that was released thermally intereacted with the terminal amino group of PA6 to establish a high strength interface through covalent grafting, which was the main reason for improving ILSS. This study indicates that this method is safe and simple and can effectively improve the interface properties of CF/PA6 composites.