Solvent-Free Synthesis of a Hyperbranched Polyphosphoramide Cocuring Agent and Its Application in Fire-Safe, Mechanically Strong, and Tough Epoxy Resin
Mingyu Ou, Richeng Lian, Rongjia Li, Jiahui Cui, Haocun Guan, Lei Liu, Chuanmei Jiao, Xilei Chen
Abstract
The synthesis procedures of the majority of hyperbranched flame retardants (FRs) involve numerous toxic organic solvents, resulting in severe environmental and human health hazards. Herein, a hyperbranched polyphosphoramide FR (DMP) was synthesized by a one-pot, catalyst-free, and solvent-free strategy, which was utilized as a cocuring agent to fabricate high-performance epoxy resin (EP) composites with excellent fire safety performance, enhanced mechanical strength, and toughness. EP with a loading of 8 wt % of DMP (EP/8DMP) exhibited a UL-94 V-0 rating and a limiting oxygen index of 28.0%. Meanwhile, DMP endowed EP/8DMP with 51.9, 53.4, and 57.6% reductions in total heat release, total smoke production, and total CO production, respectively, compared with those of unmodified EP at a phosphorus content of only 1.12 wt %. The flame-retardant mechanism of DMP in EP composites was attributed to flame inhibition in the gas phase and charring performance in the condensed phase. Additionally, both the flexural property and impact strength of EP/DMP composites were well-preserved. Therefore, this work presents a green and economic approach for developing a highly efficient hyperbranched FR for the fabrication of fire-safe, mechanically strong, and tough EP composites.