A novel biobased epoxy resin with high mechanical stiffness and low flammability: synthesis, characterization and properties

Exploring renewable biobased epoxy resins possessing intrinsic fire retardancy and high mechanical and thermal properties will greatly advance their potential to satisfy sustainability demands. Herein we develop a biobased route to synthesize a novel eugenol-based difunctional epoxy resin (TPEU-EP) with a full aromatic ester backbone. With 3,3'-diaminodiphenyl sulfone (33DDS) as the curing agent, TPEU-EP is compared with a standard bisphenol A epoxy resin (DGEBA) regarding their cure reactions and ultimate properties. The results show that TPEU-EP/33DDS expresses a higher reaction activation energy and a slower curing rate than DGEBA/33DDS. The isothermal cure reaction of TPEU-EP/33DDS is found to be autocatalytic. We accurately model the curing kinetics and elaborate on the related mechanisms based on the isoconversional analysis. The structure-property study reveals that TPEU-EP/33DDS manifests a 27%, 20% and 17% higher storage modulus (30 degrees C), Young's modulus and hardness than DGEBA/33DDS, respectively. TPEU-EP/33DDS displays a high glass temperature (168.4 degrees C) and thermal stability (up to 300 degrees C), and shows a much higher damping than DGEBA/33DDS in the glassy state. Moreover, compared with DGEBA/33DDS, TPEU-EP/33DDS shows a 130% and 3.3 increase in char yield (in N-2) and limiting oxygen index and a 68% and 40% decrease in the heat release rate and total heat release (microscale combustion test), respectively. Impressively, TPEU-EP/33DDS can self-extinguish in a vertical burning test, and the cone calorimeter test further confirms that TPEU-EP/33DDS has a much improved flame retardancy with a notably lowered smoke production. In brief, TPEU-EP possesses good intrinsic flame retardancy, low smoke production, and excellent mechanical properties, showing high promise for application. Our contribution will open a new avenue to develop sustainable high-performance flame-retardant epoxy resins.