Preparation And Flame Retardancy Of EG And LDH Complex Flame Retardants With Layer Structures

Due to the good mechanism and physical property, poly(ethylene-co-vinyl acetate)copolymer (EVA) was widely applied as insulating material in electric wire and cableindustry. However, EVA would release toxic gas when combustible, which limited itsapplication, therefore, it is important to improve EVA’s flame resistance.Compared with conventional flame retardants, layer-structured expandable graphite andhydrotalcite, as environmentally friendly retardants, had advantages of free-halogen, efficientflame resistance and smoke suppression. In allusion to the special layer structure, herein, weselected silicate as inserting agent induced into layer structure of expandable graphite andhydrotalcite, forming coupling flame retardants, and theirs flame resistance for EVA wereinvestigated respectively.This work includes three parts:1. Using KMnO4, H2SO4, Na2SiO39H2O as oxidant, inserting agent and assistant agent,respectively, silicate coupled expandable graphite (EG) was prepared by two-stepintercalation. The prepared EG possessed initial expansion temperature of202oC, andexpansion volume of517mL g-1. The assistant intercalation from Na2SiO3could sharplyimprove the expansion volume and adjust the initial expansion temperature of EG. Throughcharacterization of SEM, XRD, EDS and FIR, it could be conformed that H2SO4and Na2SiO3had been inserted into layer structure of EG. The limiting oxygen index (LOI) of EG/EVAand vertical-combustion test showed that: compared with single H2SO4-inserted expandablegraphite and expandable graphite mechanically mixed with Na2SiO3·9H2O, EG had a muchbetter flame resistance for EVA. Moreover, EG/APP at various ratios also had a better flameresistance than single EG and APP, and the LOI of70EVA/10APP/20EG even reached30.7%.The EVA/EG system all reached the UL-94level of V-0.2. Using Mg(NO3)26H2O and Al(NO3)39H2O as raw materials, Mg-Al-CO3and Mg-Al-SiO3LDHs were prepared via co-precipitation hydrothermal method and applied inEVA anti-flaming. The LOI test showed that these two LDHs were both play an effective rolein EVA anti-flaming, and the LOI values of Mg-Al-CO3and Mg-Al-SiO3were27.0%and25.8%, respectively. Besides, the TGA and DTG test indicated that the addition of LDHs ledto a higher amount of carbon residue and a better thermal stability. The TGA and DTG testindicated that the addition of flame retardant led to a low thermostability of EVA andaccelerated the decomposition of EVA, however, which also helpful to previously form astable carbon layer, finally increased the amount of carbon residue and delayed thecombustion process. Additionally, the flame resistance mechanism of EVA/Mg-Al-CO3andEVA/Mg-Al-SiO3system were the gas-phase and condensed-phase flame resistance,respectively.3. The flame-resistance effect of EG and Mg-Al-CO3for EVA and their synergisticefficiency were investigated. The experiment results indicated that, the same amount EGexhibited a better flame resistance for EVA than LDH, and an obvious molten-dropphenomenon could be observed in the combustion of EVA/LDH system. However, thevertical combustion level of EG-added system all could reach V-0level. And it is conformedthat there existed no synergistic effect between EG and EVA.Comparing LOI and vertical combustion level of the prepared EG and Mg-Al-CO3LDH,it was indicated that EG/APP system had the best flame resistance. The LOI of70EVA/20LDH/10EG could reach29.7%and the EG-added systems could all reach theUL-94level of V-0.