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In this study, DICY (dicyandiamide)-containing novolac (NN) was first prepared, and then DOPO (9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) was introduced to react with the unsaturated bonds from DICY to obtain a novel phosphorus-nitrogen-containing novolac resin (PNN), which was used as a curing agent for epoxy resins. The curing condition was confirmed by a non-isothermal curing kinetics study. The thermal stability and flame retardancy of the cured epoxy resin system were studied by thermogravimetric analysis (TGA), limited oxygen index (LOI) measurement, UL-94 test and cone calorimeter. The morphology of the burned chard residues was observed by Scanning electron microscopy (SEM). The results show that epoxy resin cured by the prepared PNN curing system presents excellent flame retardancy. The cured resin system, which contains only 1.31wt% phosphorus and 2.48wt% nitrogen, can achieve UL 94 V-0 rating.

A novel high-efficient flame retardant epoxy grafted poly-acrylic resin modified by phosphorus and nitrogen was successfully synthesized by radical grafting polymerization and solution polymerization simultaneously. The flame retardancy of copolymer resin was investigated using thermogravimetric analysis (TGA), cone calorimetric test (CONE), limiting oxygen index (LOI) and so on. The micro-morphology and chemical composition of char formed after a CONE calorimetric test was analyzed using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), respectively. The Kissinger method was used to evaluate the kinetics of thermal decomposition on copolymer resin. The results showed that the flame retardant property of copolymer resin increased with the increase in phosphorus content. With the increase in nitrogen content, however, the flame retardant property first increased and then decreased. The flame retardant property of the resin was the best and the limiting oxygen index could reach 34.3% when the phosphorus content and nitrogen content of the copolymer resin were 6.45 wt% and 2.33 wt%, respectively. Meanwhile, nitrogen-containing compounds will interact with phosphorus-containing compounds to form P-N intermediates during combustion, which have stronger dehydration and carbonization and could further enhance the flame retardant performance of the resin and generate phosphorus-nitrogen synergistic interactions.

Purpose The flammability of poly-acrylate (PA) resin is a major disadvantage in applications that require flame resistance. It has been reported that a flame-retardant PA resin could be prepared by covalent incorporate phosphorous containing monomer with vinyl group via free radical polymerization, and the prepared modified PA resin is expected to exhibit better flame resistance than those by an additive approach. However, the phosphorus-containing monomers reported previously are made from expensive or toxic materials, and the production procedure is tedious and under harsh reaction conditions, which are not feasible for industrial application. Therefore, the purpose of this paper is the preparation of flame-retardant PA resin modified by epoxy resin phosphorous acid (EPPA) and the study of its flame retardancy. Design/methodology/approach EPPA is first prepared by epoxy resin E-51 and phosphorous acid and then used to prepare phosphorous containing PA resin by free radical polymerization. The flame retardancy of the prepared EPPA-modified PA (EPPA-PA) resin is studied. Findings The results show that EPPA can graft onto the PA polymer chain by free radical polymerization, the flame retardancy of the EPPA-PA resin increases as the EPPA content increasing. The flame retardancy of EPPA-PA resin prepared reaches 27.8% and can pass the V-0 rating in the UL-94 test when EPPA content is 30.0%. SEM and EDS results indicate that phosphorous element in the EPPA-PA resin shows a condensed-phase flame retardant effect. Research limitations/implications The grafting degree of EPPA cannot be accurately tested. Practical implications It is expected that the large-scale production of this epoxy resin phosphoric acid modified PA resin will enable practical industrial applications. Originality/value This method for synthesis of epoxy resin phosphoric acid modified PA resin is newfrangled.