Design\nof Intrinsically Flame-Retardant Vanillin-Based\nEpoxy Resin for Thermal-Conductive Epoxy/Graphene Aerogel Composites

Abstract

Vanillin,\nas a lignin-derived mono-aromatic compound, has attracted\nincreasing attention due to its special role as an intermediate for\nthe synthesis of different biobased polymers. Herein, intrinsically\nflame-retardant and thermal-conductive vanillin-based epoxy/graphene\naerogel (GA) composites were designed. First, a bifunctional phenol\nintermediate (DN-bp) was synthesized by coupling vanillin with 4,\n4′-diaminodiphenylmethane and DOPO, and the epoxy monomer (MEP)\nwas obtained by the epoxidation reaction with DN-bp and epichlorohydrin.\nThen, various amounts of MEP and diglycidyl ether of bisphenol A (DER)\nwere mixed and cured. Interestingly, the flexural strength and modulus\nwere greatly enhanced from 72.8 MPa and 1.3 GPa to 90.3 MPa and 2.8\nGPa, respectively, at 30 wt % MEP, due to the rigidity of MEP and\nstrong intermolecular N–H hydrogen bonding interactions. Meanwhile,\nthe cured epoxy achieved a UL-94 V0 rating with a low P content of\n1.06%. The flame-retardant vanillin-based epoxy was then impregnated\ninto the thermal conductive 3D GA networks. The obtained epoxy/graphene\ncomposite showed excellent flame retardancy and thermal conductivity\n[λ = 0.592 W/(m·K)] with only 0.5 wt % graphene in the\nsystem. Based on these results, we believe that this work would represent\na novel solution for the preparation of high-performance biobased\nflame-retardant multipurpose epoxies.