Synthesis,Functionalization Of Perovskite-type Nano-micro Scale Calcium Hydroxytinate And Its Application On Flame Retardant Polyvinyl Chloride

Polyvinyl chloride(PVC)has been widely applied in industrial building materials,daily necessities and other fields.However,the flammability of flexible PVC is greatly improved due to the large amount of plasticizers'addition.It generates a large amount of toxic fumes during the combustion process,which greatly affects its application in various fields.Although there have been many research on flame retarded PVC materials,the development of low-toxic and efficient PVC flame-retardant systems is still a hot issue to be solved urgently.In recent years,hydroxystannates containing a variety of metal elements have begun to attract attention in the flame retardant field due to their high efficiency in catalyzing carbon formation and suppressing smoke and toxicity.Therefore,in this article,perovskite calcium hydroxystannate(CaSn(OH)₆)was synthesized.Based on the exploration of its synthesis process,its morphology and chemical composition are adjusted through hybridization and coating modification.The effect on the flame retardant properties of PVC is systematically explored and the flame retardant mechanism is revealed.The specific research content is as follows:Firstly,calcium chloride and sodium stannate are used as raw materials to synthesize the perovskite-type CaSn(OH)₆ by chemical co-precipitation method.And through hybridization and coating modification,the obtained CaSn(OH)₆ above is functionalized to obtain boron-doped calcium hydroxystannate(B@CaSn(OH)₆)and hydroxyapatite(HA)coated calcium hydroxystannate(HA@CaSn(OH)₆)and characterized them by scanning electron microscope(SEM),infrared spectroscopy(FTIR),X-ray photoelectron diffraction(XRD)and thermogravimetric analysis(TGA).The results show that the product have uniform particle size,complete morphology,high crystallinity and thermal stability.The hybridization of boron can precisely control the morphology of CaSn(OH)₆.The coating amount of HA is controllable and can adjust the surface characteristics of CaSn(OH)₆.Then CaSn(OH)₆ and its hybrid functional materials were applied to flame retarded PVC.TGA,limiting oxygen index(LOI),cone calorimetry(CONE)and gas chromatography-mass spectrometry analysis(GC-MS)was performed to characterize the thermal stability,flame retardancy and restraining smoke and poison properties of PVC flame retardant materials.Compared with pure PVC,the results show that with 5 wt%addition of flame retardants(CaSn(OH)₆,B@CaSn(OH)₆ and HA@CaSn(OH)₆),the residual of PVC composite materials increased by 9.2%,11.7%and 10.4%at 800^oC,respectively.The LOI values has been increased by 6.3%,7.4%,and 6.5%,respectively.The total smoke production(TSP)and total heat release(THR)of PVC flame-retardant composites were significantly reduced.Flame retardants can effectively inhibit the formation of toxic polycyclic aromatic compounds in gas phase products,thereby effectively reducing the smoke toxicity.Based on the analysis of the thermal stability,char formation and combustion performance of PVC flame retardant composite materials,the flame retardant mechanism of flame retardants on PVC was revealed through the characterization of the burning carbon residue.During the combustion process,in the solid phase,CaSn(OH)₆ can catalyze the formation of a dense carbon layer from the PVC material which prevent erosion by the outer flame for the matrix.In the gas phase,the water vapor released by the decomposition of CaSn(OH)₆ can dilute the flammable gas.The CaSn O₃ reacts further with the HCl produced by the degradation of PVC,which reduces the toxicity of the smoke,thereby the excellent flame retardant and smoke suppression effect are achieved.The flame retardant elements boron and phosphorus in B@CaSn(OH)₆ and HA@CaSn(OH)₆ can be synergized with CaSn(OH)₆,leading to the further improvement on the flame-retardant efficiency.With comprehensively investigating the flame retardant properties of PVC composites,this paper also characterizes the mechanical properties and microscopic changes of the breakage of the tensile deformation process of PVC flame-retardant composites.The results show that CaSn(OH)₆ can significantly improve the mechanical strength of PVC composites.It is found that B@CaSn(OH)₆ and HA@CaSn(OH)₆ can further improve the elongation at break for PVC composite materials.Thereby achieving the dual improvement of flame-retardant properties and mechanical properties of PVC materials.The research in this thesis provides a reference for the synthesis and application of new flame retardants.