Effect of cyclophosphazene nucleated hyperbranched polyester on flame retardancy and mechanical properties of epoxy resins

Abstract

Hexakis(4-hydroxyphenoxy) cyclotriphosphazene (PN-OH) was synthesized by a nucleophilic substitution and aldehyde reduction reaction of hexachlorocyclotriphosphazene with p-hydroxybenzaldehyde, and then cyclophosphazene nucleated hyperbranched polyesters (HBP) were prepared via a one-pot esterification reaction of PN-OH and dimethylolpropionic acid. The chemical structure and molecular weight distribution of HBP were confirmed by 1 H-NMR, FTIR, and GPC. The HBP was applied to epoxy resin (EP) to improve its mechanical properties and flame retardancy. The cone calorimeter test revealed that the maximum heat release rate, total heat release and total smoke release of HBP/EP composites were reduced by 35.9%, 21.6%, and 27.3%, respectively, when 7 wt% HBP was added to the EP matrix compared with pure EP. Meanwhile, when 7 wt% HBP was added to EP composites, the limiting oxygen index value was increased from 24.6% to 27.7% and the UL-94 test reached a V-1 rating. More importantly, the thermal stability and mechanical properties of the HBP/EP composites were enhanced. The flame retardant mechanism analysis showed that HBP primarily acted as a flame retardant in the condensed phase. These results indicate that the HBP/EP composites have exceptional overall performance and a broad range of applications in critical fields.

Solvent-Free Synthesis of a Hyperbranched Polyphosphoramide Cocuring Agent and Its Application in Fire-Safe, Mechanically Strong, and Tough Epoxy Resin

“…DMP, as a cocuring agent, endowed the modified EP composite with better fire safety performance and well-preserved mechanical properties than pure EP. In addition, Figure d and Table S6 exhibited the THR and TSP decline ratios of EP/8DMP and previous EP with P-containing HBPs (EP/P-containing HBPs). ,,,,− It could be found that EP/8DMP showed the highest THR and TSP decline ratios of 51.9 and 53.4%, respectively. Therefore, the as-designed EP/8DMP possessed the best fire safety performance among all EP/P-containing HBP composites listed in Table S6.…”