Thermo-Responsive Shape Memory Self-Healing Polyurethanes and Composites With Continuous Carbon Fiber Reinforcement

Thermally responsive self-healing polyurethanes (1DA1T, 1.5DA1T, and 2DA1H) with shape memory property were developed and the fully reversible Diels-Alder (DA) and retro Diels-Alder (rDA) reactions were employed for the healing mechanism. The transition temperatures of the DA and rDA reactions were confirmed through a differential scanning calorimetry and the molecular level of analysis on the reversibility and the repeatability between the DA and rDA reactions were completed though a variable temperature proton nuclear magnetic resonance at the reaction temperatures. Also, compact tension specimens were made to observe the healing efficiencies. These specimens were healed without the use of external forces to close the crack surfaces after testing for the repeatable healing ability with three cycles. As a result, the average first healing cycle efficiencies of 80%, 84%, and 96% for 1DA1T, 1.5DA1T and 2DA1H, respectively, were achieved and small drops for the second and third healing cycles were observed. Then, using two of the self-healing polyurethanes as resins, continuous carbon fiber fabric reinforced polymer matrix composites (C1.5DA1T and C2DA1H) were fabricated and short beam shear testing was conducted to determine the healing capability on the delamination. Accordingly, the first healing efficiencies of 88% and 85% were measured without any additional treatments on the fibers; however, an external pressure was applied during the composite healing process.