An Excellent Intrinsic Transparent Epoxy Resin with High Flame Retardancy: Synthesis, Characterization, and Properties

In this paper, a novel multifunctional, liquid, and colorless curing agent, namely DPTA, is prepared through diphenylphosphinic chloride (DPPC) and tetraethylenepentamine (TEPA). Different measurements confirm that the DPTA is prepared successfully and the cured DPTA-EPs simultaneously display excellent flame retardancy and transparency. The resulting DPTA-EP system reaches high optical transmittance up to 90% within the visible region. Meanwhile, the introduction of the flame-retardant groups in DPTA-EP does not deteriorate the mechanical behaviors compared with that of reference sample TEPA-EP. More importantly, with only 15 wt% DPTA addition, the resulting DPTA-EP with 1.6 mm passes UL-94 V-0 rating, and limiting oxygen index reaches 29.0%. Moreover, the peaks of heat release rate and total smoke production of DPTA-EP are largely reduced by 43.1% and 58.8%, respectively, further verifying the excellent smoke-suppression efficiency and flame retardancy. The analyses from both cone calorimeter (CC) and thermogravimetric (TG) results suggest that the satisfactory flame retardancy of cured DPTA-EP dominates in the gaseous phase. The earlier release of large amount of non-combustion gas and phosphorus containing groups improve the flame-retardant efficiency.