Structural Design And Properties Of Layered Structure Pvc Smoke Suppressant

As an important chemical raw material,polyvinyl chloride(PVC)has been widely used in industry and life.However,PVC will release a large amount of aromatic toxic gases and soot particles during the combustion process,which poses a serious hazard to human life and property safety.LDHs as halogen-free flame retardants with smoke suppression,have been widely concerned and applied in industrial production.but mainly for structural design and performance research on their flame retardant properties.Smoke suppression is only an incidental performance of flame retardant,and its smoke suppression mechanism has not been studied,which is not conducive to improving the smoke suppression performance of LDHs on PVC.Therefore,it is of great theoretical significance and practical value to study the smoke suppression performance and mechanism of LDHs on PVC.In this paper,a series of zinc-based smoke suppression materials,such as MgZnAl-LDHs and ZnAl-LDHs,were prepared by nucleation/crystallization isolation method by introducing Zn element into the laminates,using the controllability of the composition and structure of LDHs.It was found that with the increase of Zn content in LDHs laminates,smoke suppression performance gradually improved.When the molar ratio of Zn/Al was 2.5,the smoke suppression effect of ZnAl-LDHs on PVC was the best.When adding 5 phr,the maximum smoke density of PVC decreased from 595.58 to 286.77,with a decrease of 51.8%.When the molar ratio of Zn/Al was 2,the maximum smoke density of PVC decreased to 313.36,with a decrease of 51.8%with the addition of 5 phr ZnAl-LDHs.On this basis,based on the convenience of preparation,ZnAl-LDHs smoke suppressants with different particle sizes of Zn/Al=2 were prepared by urea method and atomic economic reaction method respectively.The smoke density test results show that these samples have similar smoke suppressing properties to PVC,indicating that the grain size of LDHs has no obvious influence on its smoke suppressing properties.In order to study the effects of LDHs laminate-OH,interlayer bound H20 and anionic CO32-on smoke suppression performance,LDO,the calcined product of LDHs,was used as smoke suppressant in this paper.It was found that the smoke suppression efficiency of LDO was better than that of LDHs when the metal content was the same.This indicated that the smoke suppression effect of LDHs was independent of laminate-OH,interlayer bound H2O and anionic CO32-and that the smoke suppression mechanism of LDHs was different from its flame retardant mechanism.In this paper,the smoke suppression mechanism of LDHs was further studied.Through on-line detection of smoke components by TG-MS,it was found that the content of chlorinated compounds and benzene in the gas phase products produced by decomposition of PVC decreased significantly after adding LDHs.Meanwhile,the residual char structure of PVC after NBS was studied by FT-IR LRS and XPS,etc.It was found that the graphitization degree and thermal stability of the residual char of PVC were lower after adding LDHs.Further analysis showed that zinc base structure smoke suppressant could react with HCl produced by decomposition of PVC to produce Lewis acid ZnCl2,which could make the decomposition of PVC proceed towards trans-olefin structure,effectively inhibit the formation of cis-olefins and the conversion to aromatic hydrocarbon precursor of flue gas,and reduce the smoke production of PVC.