Synthesis and cryogenic mechanical properties of degradable epoxy resins containing hexahydro-s-triazine structure

Epoxy resins are widely used in cryogenic applications due to their distinguished mechanical and electrical insulation properties. To avoid generating enormous amounts of waste that affect the environment and cause economic losses, covalent adaptable networks can be introduced into the epoxy structure to make the thermosetting network reversible. In this study, ester bond and hexahydro-s-triazine structure were adopted in epoxy structures. Two new degradable epoxy resins (HPBE and HPHE) with variances in the content of benzene rings were synthesized which were confirmed by FTIR and NMR. After curing, the thermal, mechanical, thermal conducting properties of the resulting materials were examined. The products exhibited tensile strength and flexural strength all above 120 MPa at 77 K, with glass transition temperature of 89.1 °C and 86.9 °C, respectively. Meanwhile, HPBE and HPHE demonstrated favorable thermal stability, with thermal conductivity comparable to that of the commonly used epoxy resin DGEBA. These resins could be degraded under mild conditions and demonstrated high hydrolysis efficiency (approximately 90 %). This investigation presented a viable method for the application of degradable thermosetting materials in cryogenic environments and the possibility for repairing of high-value equipment.1