Replacement of volatile styrene by flame retardant crosslinking diluents in unsaturated polyester resins

Abstract

<p indent="0mm">The flammability of unsaturated polyester resins (UPR) and the volatility of their toxic styrene diluents pose serious safety risks. In this paper, three non-volatile flame retardant diluents (PBHA, POHA and PSHA) containing different phosphorus structures were synthesized, which can completely replace styrene and provide excellent flame retardant performance for UPR. Their structures were characterized by FTIR and NMR (¹H, ³¹P). The potential of synthesized reactive diluents as substitutes in UPR and their glass fabric reinforced composites was assessed through volatility, processability, curing kinetics and gel contents. Meanwhile, by comparing the effects of different phosphorous structures, PBHA diluent can bring best flame retardant efficiency. UP/PBHA reached V0 in UL-94 and 28% of LOI. The PHRR and THR of UP/PBHA were decreased by 64.06% and 61.54% compared with neat UP/St. For glass fabric/UPR composites, GF/UP/PBHA also reached V0 rating, and LOI was as high as 38%. Meanwhile, through the study of thermal stability, thermal degradation and combustion process, it was found that PBHA mainly worked in gas phase to capture H<x content-type="symbol">×</x> and HO<x content-type="symbol">×</x>, supplemented by promoting formation of dense carbon layer in condensed phase to isolate oxygen and thermal radiation.