Highly thermo-stable resveratrol-based flame retardant for enhancing mechanical and fire safety properties of epoxy resins

The integration of flame-retardant additive with both excellent thermal stability and remarkable fire-retarded efficiency into epoxy resins (EP) is highly demanded while challenging. Herein, a novel bio-based flame retardant (referred to DPOR) was synthesized via one-step reaction of resveratrol and diphenylphosphonyl chloride. The as-prepared DPOR exhibited outstanding thermal stability, with an initial thermal decomposition temperature of 438.4 °C, contributing from the reduced intermolecular π–π interaction and incremental oligomerization during the heating process. It was further utilized as additive for the manufacture of high-performance EP composites (EP-DPOR). Notably, DPOR can also act as mechanical reinforcer that enhanced the strength and toughness of EP. The EP-DPOR3 (3 wt% DPOR) showed a superior stretchability (15.9 %) and high tensile strength (59.3 MPa) compared to neat EP (12.4 %, 46.7 MPa). Additionally, the burning test results indicated that DPOR endowed the EP with greatly enhanced flame resistance, achieving a UL-94 V-0 rating with an increase of LOI values to 34.5 % at a low loading of 5 wt%. In cone calorimeter tests, it showed that heat and smoke release was effectively inhibited during combustion in comparison with EP, wherein the PHRR value of EP-DPOR was 27.5 % lower than EP. Thus, it is highly anticipated that DPOR, as a new type of bio-based flame retardant with superior thermal stability and efficient flame- retardant properties, holds a great potential for the development of next-generation flame retardant.