Synthesis of phosphorus-containing modifier based on phenolic epoxy resin and its application in flexible poly(vinyl chloride)/magnesium hydroxide composites

In this study, a phosphorus-containing and polyether structure modifier, phenolic epoxy phosphate ester (PEPE), was prepared by the reaction of phenolic epoxy resin (EPN) and phosphoric acid. It was used to solve the trade-off dilemma of simultaneously improving the mechanical properties and flame resistance of flexible poly (vinyl chloride) (fPVC)/magnesium hydroxide (MH) composites. The peak heat release rate, total heat release, peak smoke production rate, and total smoke production of the fPVC/MHPEPE-5 (PEPE modified MH as filler) composite were decreased by 35.31 %, 49.2 %, 40.42 %, and 27.26 %, respectively, in comparison with the fPVC/MH composite. More importantly, the fPVC/MHPEPE-5 composite passed V-0 rating in the UL-94 test, while the fPVC and fPVC/MH composite passed V-2 and V-1 rating. The presence of phosphorus compounds in the condensed phase promoted the formation of a dense char residue of the fPVC/MHPEPE-5 composite. Therefore, the heat and flammable volatiles cannot migrate between the substrate zone and the combustion zone. In the gas phase, the dilution effect of H₂O reduced the concentration of oxygen and combustible volatiles. The radicals quenching effect of the primary and secondary pyrolysis products of PEPE (such as PO· and PO₂·) with ·H and ·OH^. radicals played a crucial role in flame extinguishing and combustion termination. In addition, the scanning electron microscopy results showed that MHPEPE performed good compatibility with the fPVC matrix. The tensile and impact strength of the fPVC/MHPEPE-5 composite was 12.19 % and 19.26 % higher than that of the fPVC/MH composite, respectively.