Structure Design Of Layered Double Hydroxides And Study On Smoke Suppression Performance Of EVA

Polymer materials have become an important part of people's daily life,but the smoke generated by their combustion is the primary cause of death in fires.Ethylene-vinyl acetate copolymer(EVA)has excellent properties and is widely used in industrial fields such as wire and cable.However,the large amount of smoke generated by EVA combustion limits its development and application.Layered double hydroxides(LDHs)as two-dimensional nano flame retardants have few studies on the smoke suppression properties of EVA.Carrying out the research on the smoke suppression performance and mechanism of LDHs on EVA is of great significance for the development of high-efficiency EVA smoke suppressants and the expansion of the practical application of LDHs smoke suppression materials.In this thesis,using the controllability of the layer metal of LDHs,LDHs smoke suppression materials with different layer compositions were prepared,and the smoke suppression properties of EVA were studied.The smoke suppression mechanism based on the absorption of acetic acid and condensed phase char formation was proposed.details as follows:1.A series of magnesium-based LDHs were prepared,and the effect of the change in the composition of the layers on the smoke suppression performance of EVA was studied.With the increase of the Mg element content in the LDHs layer,the smoke suppression performance of LDHs gradually increases.When the addition amount is 5 phr,Mg₃Al-LDH can reduce the maximum smoke density of the EVA/LDHs composite from 252.85 to 77.61,with a decrease of 69.3%.The smoke suppression effect of Zn and Mg elements was comparatively studied.At the addition of 5 phr,the smoke suppression performance was Mg2Al-LDH>MgZnAl-LDH>Zn2Al-LDH,and the smoke suppression effect of Mg element was stronger than that of Zn element.TG-IR test results show that the addition of LDHs can effectively reduce the release of acetic acid and enhance the thermal stability of the EVA molecular backbone.The IR,Raman,SEM and other characterizations of the residue show that LDHs can promote the formation of dense and continuous char residue and fix more aliphatic substances in the condensed phase.The smoke suppression mechanism of magnesium-based LDHs on EVA under flameless combustion is proposed:LDHs absorb the acetic acid released by the thermal degradation of EVA,reduce the generation of acid smoke,and enhance the thermal stability of the EVA backbone to delay degradation and make aliphatic hydrocarbons are fixed in the condensed phase to form a dense char layer,thereby inhibiting the generation of smoke.2.Ca₂Al-LDH,Ca₂Fe-LDH,Mg₂Fe-LDH and Ni₂Al-LDH were prepared by introducing Ca,Fe and Ni elements into LDHs layer,and their smoke suppression effects on EVA are researched.TG-IR and char residue characterization showed that Ca₂Al-LDH can absorb the acetic acid produced by the degradation of EVA at the addition of 5 phr,but it promotes the oxidative degradation of the char residue and does not have the effect of suppressing smoke,and CaCO₃ is generated in the residue.Ni₂Al-LDH has a poor ability to absorb acetic acid and has a strong effect of promoting the oxidative degradation of char residual,which increases the amount of smoke produced by EVA,and finally produces NiO.Ca₂Fe-LDH and Mg₂Fe-LDH have a better absorption effect on acetic acid,but promote the oxidative degradation of the residue shows smoke suppression effect in the early stage of the smoke density test,and promotes the generation of smoke in the later stage,and FeO appears in the residue.The investigation of the mechanism of LDHs shows that char formation in the condensed phase plays a dominant role in the smoke suppression effect of LDHs on EVA.