| High-density polyethylene (HDPE) has been widely applied in many areas such as packing materials, wire and cable, and automobile parts, due to its balanced mechanical properties, chemical resistance, and ease processing advantages; and in order to improve its toughness, flexibility and environmental stress cracking resistance, many attempts, such as blending HDPE with poly(ethylene-co-vinyl acetate)(EVA), have been made. However, the flammability of HDPE/EVA has limited its applications, so flame retardants need be added into HDPE/EVA to improve flame retardant property. Traditional halogen-containing flame retardant materials produce smoke and toxic gases during the combustion. It is therefore worthwhile to investigate halogen-free flame retardant.Expandable graphite (EG) has non-toxic and low smoke characteristics which are both meet the development trend of green environmental protection, so it has become a hot research of intumescents. However, flame retardant efficiency of polyolefin only with EG as a flame retardant is relatively low, so it is necessary to add some other synergistic flame retardants. Ammonium polyphosphate (APP) is one of the most widely used inorganic phosphate flame retardants, and it has low smoke and high flame retardant efficiency characteristics. Red phosphorus (RP) is one of common inorganic flame retardants, which has high flame retardant efficiency characteristic. As far as we are aware, few studies on the synergistic effect between EG and APP, EG and RP on the flame retardancy of HDPE/EVA have so far been reported in the literature. So, the aim of this work is a very worth studying topic.In this paper, flame-retardant HDPE/EVA is the research objective, four flame retardants are choiced which are EG, EG/AP, EG/RP and EG/(APP+RP). The thermal stability, flammability properties and mechanical properties were investigated by thermogravimetric analysis (TGA), UL-94test, limit oxygen index(LOI), cone calorimeter test (CCT), scanning electron microscopy (SEM) and tensile test. Flame retardant mechanism and synergistic effect were also discussed. The main contents are as the follows.The EG flame retardant HDPE/EVA system was studied. The addition of EG with different content, particle size and surface modification improved significantly the thermal stability and flammability properties of flame retardant HDPE/EVA. The residue of HDPE/EVA/EG increased due to increasing EG content, inducing EG particle size and modifying, meanwhile, the peak heat release rate (PHRR), the total heat release (THR) of HDPE/EVA/EG dramatically decreased, but the residual mass increased.The synergistic flame retardant HDPE/EVA system by EG and APP was studied. The results showed that, EG and APP had good synergistic effect. When the mass ratio of them was2:1, flame-retardant effect is best, with26.4%LOI, and the sample reached UL-94V-0rating. The values of the PHRR and THR were lower than these of HDPE/EVA/EG during the combustion, and HDPE/EVA/EG/APP had more char residue and the char layer structure was more compact.The synergistic flame retardant HDPE/EVA system by EG and RP was studied. The results showed that, EG and RP had good synergistic effect. When the mass ratio of them was2:1, flame-retardant effect is best, with28.4%LOI, and all of the samples reached UL-94V-0rating. The values of the PHRR and THR were lower than these of HDPE/EVA/EG during the combustion, and HDPE/EVA/EG/RP had more char residue and the char layer structure was more compact.The synergistic flame retardant HDPE/EVA system by EG and APP+RP was studied. The results showed that, EG and APP+RP had best synergistic effect, so the LOI of the sample was higher than HDPE/EVA/EG/APP and HDPE/EVA/EG/RP, and all of them reached UL-94V-0rating. The values of the PHRR and THR were lower than these of HDPE/EVA/EG, HDPE/EVA/EG/APP and HDPE/EVA/EG/RP during the combustion, and HDPE/EVA/EG/(APP+RP) had more char residue and the char layer structure was more compact. So the HDPE/EVA/EG/(APP+RP) had best flammability property. |
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