Synthesis Of Iron-tin Oxide Hydroxide And Its Coating Kaolin And Their Flame Retardant Application In PVC

Polyvinyl chloride（PVC）is one of the most widely used general-purpose thermoplastic materials,but due to the addition of a large amount of plasticizer during the molding process,the flame retardancy is greatly reduced,and a large amount of toxic and harmful gases are generated during the combustion process,and those products will cause great harm to human lives and the natural environment.Therefore,it is of great significance to study the flame retardancy and smoke suppression of PVC.In this paper,iron-tin oxide hydroxide（FeSnO（OH）₅,ITOH）and its coating calcined kaolin（KLN@ITOH）composites were prepared,and the crystal morphology,morphology and thermal decomposition of the product were characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）and thermogravimetric analysis（TGA）.Then the ITOH and its coating kaolin were used for the flame-retardant PVC research（based on the test of the PVC cable material）,and the flame retardant,thermal degradation and combustion performance of the flame-retardant composite were studied using limiting oxygen index（LOI）,TGA and cone calorimeter（Cone）.The SEM-energy spectrum analysis（EDS）and X-ray photoelectron spectroscopy analysis（XPS）of the char residue of the Cone test were conducted to study the flame-retardant mechanism of FeSnO（OH）₅ and KLN@ITOH on PVC.The main content is divided into the following two parts:In the first part,FeSnO（OH）₅ was successfully prepared by hydrothermal synthesis and co-precipitation method,which were recorded as H-ITOH and C-ITOH,respectively.The results show that H-ITOH is a submicron mesoporous structure with a concave cube,good dispersion,uniform particle size,and an average size of 171.2 nm;C-ITOH is a mesoporous cube that is easily agglomerated and has an average size of 52.8 nm.The thermal stability of both is sufficient for PVC processing conditions.When 5 phr of H-ITOH and 10 phr of C-ITOH are added,the samples meet the flame-retardant application standard of PVC cable materials.From the results of thermal analysis,FeSnO（OH）₅ can improve the thermal stability of PVC samples and has a highly efficient catalytic char formation.Cone data show that FeSnO（OH）₅ can effectively reduce the heat release rate,smoke release rate,the total heat release and the total smoke rate of PVC materials,and has a good flame-retardant effect on PVC.In the second part,KLN@ITOH flame retardants with different coating ratios（the mass ratio of 1:2,1:3,1:5 and 1:10）were obtained by co-precipitation method.After a series of explorations,when the coating ratio is 1:5 and the addition amount is 15 phr,the flame retardant and mechanical properties of the corresponding PVC sample meets the flame-retardant application standard of PVC cable materials,and its mechanical properties are superior to other samples.From the results of Cone,KLN@ITOH can reduce the heat release and smoke release of PVC compared with the compounded sample;the PVC sample with 15 phr ITOH stopped burning within 120³00 s during the cone test,resulting a significant reduction in heat release and smoke release,which facilitates the evacuation of personnel in the event of a fire and prevents the spread of fire,there is a good flame-retardant effect.From XPS analysis results,the flame retardant effect of ITOH on PVC is mainly to produce Lewis acid FeCl₂ and FeOCl,which can effectively catalyze PVC cross-linking into carbon;in the combustion process of PVC/KLN@ITOH,ITOH not only generates FeCl₂ and FeOCl,but also produces strong Lewis acid FeCl₃,which increases the efficiency of catalyzing the cross-linking of PVC into carbon;in the combustion process of PVC/KLN/ITOH,most of Fe is converted to Fe₂O₃,and a small part of Fe is present in the form of FeCl₂ and FeOCl.The ITOH after coating can be better dispersed in the PVC matrix to produce more Lewis acid and improve the flame retardancy and smoke suppression efficiency of ITOH.