Study on synthesis of novel phosphorus-containing flame retardant epoxy curing agents from renewable resources and the comprehensive properties of their combined cured products

Two bio-based organophosphorus-containing epoxy curing agents (MMDOPO and MAPDGR) with different rigid or flexible characteristics were synthesized from myrcene and castor oil, respectively. Their molecular structures were characterized by Fourier transform infrared spectroscopy (FTIR), 1H and 31P nuclear magnetic resonance (1HNMR). Then they were mixed at different weight ratios to form new curing agents for epoxy resin (E-51). Results show the tensile and flexural strength of the cured epoxy materials first increase and then decrease with the increase of MMDOPO content. Dynamic mechanical analysis (DMA) shows the glass transition temperature (Tg) rises significantly with the increase of MMDOPO content. The material's thermal stability and flame retardant properties were also investigated. The initial decomposition temperature (Ti) and limiting oxygen index (LOI) both are elevated while the residue decreases with the increase of MMDOPO content. When the MMDOPO/MAPDGR weight ratio is 25/75, the mechanical properties are relatively balanced with a high elongation at break of 160.8% and a moderate tensile strength of 9.95 MPa, and bending test indicates that the sample exhibits a flexible failure behavior with a yielding point.