Facile Synthesis of Phosphorus-Free Biobased Epoxy Resin with Exceptional Flame Retardancy, Mechanical Properties, and Heat Resistance

Preparing biobased epoxy resins with intrinsic flame retardancy, excellent mechanical properties, and high heat resistance has the potential to be used in high heat and flame-retardant fields (e.g., aerospace industry, electrical, and electronic areas). However, seeking renewable epoxy resins with those goals is still challenging. In this work, we prepare a biobased epoxy precursor (PGE) derived from phloretin via a one-step epoxidizing reaction and then solidified by 4,4′-diaminodiphenyl sulfone (DDS) to obtain the target epoxy resin (PGE/DDS). The high molecular chain rigidness and char yield by in situ-generated Schiff bases combined with aromatic rings endow the PGE/DDS with high glass transition temperature (Tg up to ∼259.2 °C), excellent mechanical properties (i.e., Young's modulus and hardness up to ∼5.41 and ∼0.35 GPa, respectively), and intrinsic flame retardancy. PGE/DDS resin passed V-0 rating in the underwriters laboratories-94 (UL-94) test with a limiting oxygen index (LOI) of 33.5% and significantly decreased the peak heat release rate (PHRR) and total heat release (THR) by 71.1 and 41.2%, respectively. Furthermore, the PGE/DDS resin exhibits enhanced dimensional stability due to its increased cross-linking density and additional antibacterial characteristics because of the in situ-generated Schiff bases. Our strategy will promote the facile preparation and application of biobased epoxy resins with high performance and versatile properties in high heat and flame-retardant fields.