Toughened and self-healing carbon nanotube/epoxy resin composites modified with polycaprolactone filler for coatings, adhesives and FRP

Aiming at the durability problem caused by micro-crack damage in polymer under complex load and hygrothermal conditions, an epoxy resin matrix composite with self-repair function was developed. The multi-damage self-healing function of epoxy resin can be realized by carbon nanotubes (CNTs) reinforcement and polycaprolactone (PCL) toughening. Based on 0.5 wt% CNTs addition, epoxy resin systems with different PCL fillers (1/5/10/15 wt%) were successfully prepared. Through the comparison of thermal and mechanical properties, the optimum formula was obtained as the epoxy resin with CNTs and 5 wt% PCL composite (EPCP5). Furthermore, the tensile strength and elongation at break of EPCP5 increased by 25.4 % and 42.3 %, respectively, compared to the control sample. This improvement was attributed to the formation of hydrogen bonds between PCL and the epoxy resin, enhancing intermolecular forces. The difference in glass transition temperature for samples with varying PCL content was minimal (less than 3.8 %), indicating excellent thermal compatibility between the PCL/CNTs fillers and the resin matrix. Before damage, the tensile and flexural strengths of EPCP5 were 47.28 MPa and 116.35 MPa, respectively. Compared with one cycle for 40 % prefabricated damage, the tensile and flexural strengths of EPCP5 increased by 15.8 % and 25.1 %, 17.4 % and 25.3 % after second and three repair cycles, demonstrating the significant self-healing effect. Under 40 % and 60 % prefabrication loads, the self-healing efficiency of EPCP5 for tensile and flexural strengths reached up to 116.1 % after the third repair cycle. This was because the PCL melt filled and bridged the damaged area, effectively healing and reinforcing the micro-cracks. Noticed, after damage repairing, the micro-morphology showed that the 2–4 μm through cracks in the resin matrix were well healed. Furthermore, the infrared spectrum of EPCP5 showed a combination of the individual spectra of CNTs, PCL, and the resin, which indicated that physical interactions played a major role between the components. Therefore, the low-melting-point PCL effectively filled and bridged the damaged areas during the self-healing process, providing rapid and efficient repair with high responsiveness.