Sustainable biobased flame-retardant epoxy thermoset derived from renewable phytic acid and itaconic-acid for high-performance rubber wood coatings

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Developing a green and sustainable bio-based coating is a feasible approach to improve safety and usability of rubber wood. In this study, a phytate-based flame-retardant curing agent, PAIM, was synthesized through neutralization reaction between phytic acid (PA) and imidazole (IM). This curing agent was co-cross-linked with trifunctional biobased epoxy resin (TEIA) derived from itaconic acid. The results showed that the cured PAIM-TEIA composites exhibited outstanding thermal stability, water resistance and solvent resistance. When the PAIM content was 15 wt% (the P content is 1.7 %), the glass transition temperature ( T g ) of PAIM-15-TEIA-W reaches 99.3 °C. Subsequently, a series of PAIM-TEIA resin coatings of rubber wood were prepared. The PAIM-15-TEIA-W coating achieved V-0 rating in UL-94 test and displayed a limiting oxygen index (LOI) value of 30.1 %. Compared to pure rubber wood and IM-6-TEIA-W, the peak heat release rate (PHRR) and total heat release (THR) of PAIM-15-TEIA-W decreased by 16.30 % and 28.27 %, and 42.62 % and 10.6 %, respectively. Furthermore, PAIM exhibited gas and condensed flame-retardant action, forming an intumescent char layer while releasing phosphorus radicals and non-flammable gases to protect the wood. This sustainable strategy enhances rubber wood's flame resistance for diverse applications.