Synthesis Of A Novel Phosphorus-nitrogen Containing Flame Retardant And Its Application In Intumsecent Flame Retardant LDPE And EVA

Low density polyethylene (LDPE) and ethylene-vinyl acetate (EVA), polymer materials, have good properties and widely uses. But the polymers are easily flammable and subjected to controls in various fields. A widely known method to impart flame retardancy is to add a halogen-containing compound to the polymers. Although halogenated compounds show good flame retardancy, their use has been curtailed in many countries because of toxic and corrosive fumes released during combustion. As an alternative the intumescent flame retardant system possess the properties of enveriment-friendly, halogen-free and high efficient. In recent years, the intumescent flame retardant system has become a hot topic of the flame retardants developed field.In the paper, a novel flame retardant (THPSU) containing phosphorus and nitrogen was synthesized through the reaction of tetrakis hydroxymetyl phosphonium sulfuric (THPS) and urea. The P content of THPSU is14.28%by quinoline phosphomlybdate gravimetric method. The structure of THPSU was characterized by FTIR,13C-NMR,31P-NMR and XPS. The thermal stability and char-forming ability of THPSU were studied by TGA. The results showed that in nitrogen, its initial decomposition temperature was178℃based on1wt%mass loss and char residue was28.0wt%at700℃. THPSU showed a good thermal stability and char-forming ability and met the common plastic (such as EVA, LDPE) processing requirements.The intumescent flame retardant system (IFR) consisting THPSU, ammonium polyphosphate (APP) and other additives were blended with LDPE. The limiting oxygen index (LOI) and UL-94test were used to research the flame retardant properties. The results showed the loading of IFR was32wt%, the sample with the thickness of3.2mm passed UL-94V-0rating without dripping and the LOI value achieved29.0%. The cone calorimeter test (CONE) was used to research the combustion of flame retardant LDPE. The results showed that the time to ignition (TTI), heat release rate (HRR), total heat release (THR) and mass loss rate (MLR) of flame retardant LDPE added IFR decreased obviously. The char residue after CONE test was characterized by scanning electron microscopy (SEM). After combustion the surface of the material formed a uniform and dense char layer and then a protective layer formed to improve the flame retardant properties of the material. The thermal degradation of flame retardant material was studied by TGA. The IFR added to LDPE improved the initial thermal decomposition temperature and char-forming ability. The mechanical properties of flame retardant LDPE were studied by tensile strength and bending strength. Compared to pure LDPE, the loading of IFR was32wt%, the tensile strength fell by3.2MPa while bending strength increased by1.5MPa. The water resistance was studied by boiled in water at70℃/168h. The extraction rate of the flame retardant LDPE was just0.2wt%which showed a good water resistance.Meanwhile, the intumescent flame retardant system (IFR) consisting THPSU, ammonium polyphosphate (APP) and other additives were blended with EVA. The mass ratio of APP and THPSU was2:1, EVA showed the best flame retardant properties. The loading of IFR was28wt%, the sample with the thickness of3.2mm passed UL-94V-0rating without dripping and the LOI value achieved29.0%. The CONE test results showed that TTI, HRR, THR, SPR and MLR of flame retardant EVA added IFR decreased obviously. TGA showed that IFR added to EVA improved the thermal stability and char-forming ability. The analysis of SEM of char residue after CONE test showed after combustion the material formed a uniform and dense char layer and it protected the interior layer of matrix material. The analysis of component of char residue showed it mainly made up of polyaromatic and phosphoric and polyphosphoric acids. Compared to pure EVA, the mechanical properties of flame retardant EVA added IFR decreased. Water resistance test showed the extraction rate of flame retardant EVA added IFR was4.53wt%. Compared to flame retardant LDPE added IFR, the extraction rate of flame retardant EVA added IFR was higher because of the bad water resistance structure of EVA itself.