Phosphorus-free curcumin-derived epoxy resin with exceptional flame retardancy, glass transition temperature and mechanical properties

The fabrication of bio-based epoxy resins having better intrinsic flame retardancy and mechanical performances than petroleum-based epoxy thermosets is important for alleviation of energy and health concerns. In this study, bio-based monomer of diglycidyl ether of curcumin (DGEC) was successfully synthesized from a natural and renewable curcumin through a facile one-step process. The biocompatible epoxy resin obtained was then cured with 4,4′-diaminodiphenyl sulfone (DDS) and compared with petroleum-based diglycidyl ether of bisphenol A (DGEBA). The DGEC/DDS exhibited a higher glass-transition temperature (300 °C) than DGEBA/DDS (215 °C), indicating the outstanding heat resistance. The tensile strength of DGEC/DDS was 65.9 MPa, higher than that of DGEBA/DDS (56.1 MPa). Furthermore, DGEC/DDS showed excellent charring ability with char yield of 50.15% at 800 °C in N2, which was approximatively 3.5 times as much as that of the cured DGEBA/DDS (14.68%). Microscale combustion calorimeter (MCC) test demonstrated that the DGEC/DDS possessed lower heat release capacity (HRC, 130 J/gk), peak heat release rate (PHRR, 115.0 W/g) and total heat release (THR, 9.9 kJ/g), which were reduced by 80.2%, 74.8% and 59.4%, respectively, compared to those of DGEBA/DDS (658 J/gk, 457.3 W/g, 24.4 kJ/g). The DGEC/DDS passed the UL-94 test and attained the V-0 rating, revealing the good flame retardancy. This work provided an opportunity to prepare bio-based epoxy resins with better properties than DGEBA, which exhibited promising applications in high heat and flame retardancy fields.