The Preparation, Properties Of Halogen-free Flame Retardant EVA, POE And Their Cross-linking Modification Composites

Hydrotalcites (LDHs) are a kind of layered double hydroxides. Due to their special structure characteristics, LDHs are very promising for the application as high efficiency, halogen-free, low-smoke flame retardant additives. The research on the use of nano magnesium hydroxide (NMH) and nano hydrotalcite (NLDH) as flame retardant additive in ethylene vinyl acetate copolymer (EVA) was performed. The microcosmic structure, tensile properties, combustion characteristics and thermal behavior affected by NMH and NLDH of the composites were studied. The results indicate that NLDH is better not only in enhancing the flame retardant properties than that of NMH, but also in smoke suppressant aspect. The loading level of NLDH is very high in order to obtain an adequate level of flame retardant property of EVA. The study of the synergistic effect between NLDH and some other halogen-free retardants, such as microencapsulated red phosphorous (MRP) and fumed silica (SiO₂) in EVA was conducted. The results indicate that there is a great synergistic effect between NLDH and MRP in improving flame retardancy of the composites. Compared with EVA/NLDH composite, the addition of MRP into EVA/NLDH composite could improve the LOI and UL-94 test rating, reduce the peak of heat release rate (PHRR) and enhance the thermal stability. But fumed silica only plays a role in the improving the UL-94 testing rating.The effect of NLDH modified by two kinds of surface modifiers on the tensile properties, combustion properties and thermal behavior of EVA/NLDH composites was studied. It has been found that the tensile properties and thermal stability of EVA/NLDH composite with NLDH modified by stearic acid is better than that of EVA/NLDH composite with NLDH modified by titanate coupling agent. The main reason is due to the surface and distribution. Moreover, the effect of VA content on the tensile properties and combustion properties was also studied. The results indicate that VA content affects the flame retardant efficiency.The EVA/NLDH/MRP composites were crosslinked by ⁶⁰Co irradiation. The effects of gamma irradiation on the properties of the irradiated EVA/NLDH/MRP composites were investigated. The results have shown that gamma irradiation is an effective method of crosslinking for EVA/NLDH/MRP composites. The mechanical properties, flame retardant properties and thermal distortion of the EVA/NLDH/MRP composites were all markedly improved by suitable amount of gamma irradiation doses. The maximal value is achieved when the gamma irradiation dose is 100 kGy; The effect of the silane crosslinking on the flame-retarded EVA by MH was studied. The results indicate that the silane crosslinking can improve the flame-retardant properties and the mechanic properties of the composites of EVA/MH. Meanwhile, the addition of silicone can enhance the flame-retardant properties and thermal stabilities of the EVA/MH composites.Mg/Al-CO₃ LDHs and Mg/Al/Fe-CO₃ LDHs are synthesized by a co-precipitation method and characterized using powder X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TG). EVA composites flame retarded by LDHs were prepared in a melt process and characterized by LOI, UL-94 testing, TG and cone calorimeter test (CCT). It has been found that introduction of Fe³⁺ into Mg/Al-CO₃ LDHs can enhance the LOI and UL 94 rating, improve the melt dripping phenomenon, reduce HRR, and prolong the combustion time.The grafting of silane on ethylene-octene copolymer (POE) in presence of DCP in the melt process and the effect of various factors, such as silane content, reaction temperature and time on silane grafting of POE were studied. The TG analysis shows that the thermal stability of the crosslinked POE increases compared to the pure POE resin. The non-isothermal crystallization kinetics of sliane crosslinked POE was studied by differential scanning calorimetry (DSC) at different cooling rate. The results indicate that the crystallization rates decrease with the increase of the crosslinking degree. However, the crosslinked POE is still combustible. Therefore, some research work was done on the halogen-free flame retardation of silane crosslinked POE. The results indicate that fumed silica is not only as the reinforcing filler but also as the synergistic flame retardant additives of MH.