A novel high phosphorus‐efficiency phosphaphenanthrene curing agent for fabricating flame retardant and toughened epoxy thermoset

Abstract

AbstractA novel high phosphorus‐efficiency phosphaphenanthrene curing agent (VND) was synthesized successfully using bio‐based vanillin, N‐phenyl‐p‐phenylenediamine, and 9,10‐dihydro‐9‐oxa‐10 phosphaphenanthrene‐10‐oxide (DOPO). Then, as co‐curing agent, VND combined with 4, 4′‐diaminodiphenyl methane (DDM) to fabricate flame retardant epoxy thermosets (VND/EP/DDM). The VND/EP/DDM thermosets exhibited excellent flame‐retardant performance and toughness, simultaneously. With only 0.35 wt% phosphorus loading, 6%VND/EP/DDM achieved a LOI value of 39.2%, and passed UL94 V‐0 rating. The three reactive functional groups in VND made itself better interpose in the burning process of thermoset matrix, endowing VND with higher efficiency in facilitating matrix carbonization. Meanwhile, the decomposition volatile tracking disclosed the inhibition effect of VND on oxidative cracking. Through gas‐ and condensed‐phased actions, VND decreased the heat release and smoke production of burning epoxy thermosets, efficiently. In addition, three reactive functional groups in VND also brought itself good toughening effect on thermoset matrix, endowing epoxy thermoset with better anti‐impact performance. The flame retarding and toughening behavior of VND provides a new insight to development advanced flame‐retardant epoxy thermosets.