Preparation Of Cobalt Hydroxystannate And Its Flame Retardant Application In PVC And EP

Polyvinyl chloride?PVC?and epoxy resin?EP?are the two widely used polymer materials.However,PVC generates a large amount of heat and harmful gases during the combustion process,and EP continues to burn after ignition and generates droplets and a large amount of heat,which restrict their futher application.Therefore,it is of great significance to study the flame retardancy and smoke suppression of PVC and EP.In this paper,cobalt hydroxystannate?CoSn?OH?₆,CHS?flame retardant was prepared and applied to PVC and EP.The flame retardancy,smoke suppression and mechanical properties of PVC and EP composites were investigated by limiting oxygen index?LOI?,cone calorimeter?Cone?and universal tensile tests.The flame retardant mechanism was preliminarily analyzed by thermogravimetric analysis?TGA?,cone and scanning electron microscopy-energy dispersive spectrometer?SEM-EDS?.The specific research contents are as follows:In the first part,amorphous and spherical CoSn?OH?₆ were successfully prepared via co-precipitation method and template method,which were recorded as C-CHS and T-CHS,respectively.The products were characterized by X-ray diffraction?XRD?,fourier transform infrared spectroscopy?FTIR?,SEM,particle size analyzer and TGA.The results showed that the products were pure CoSn?OH?₆,and C-CHS was a particle with serious aggregation,and an average particle size of 143.8 nm;T-CHS was a relatively uniform dispersion microsphere with an average particle size of 438.2 nm.Their initial decomposition temperature(T_5%)were both higher than the processing temperature and sufficient for the processing of PVC.In the second part,the study of CHS flame retardant PVC.The results showed that when the addition amount of C-CHS and T-CHS were 10 phr and 5 phr,respectively,the flame retardant samples met the requirements of flame retardancy?LOI?30%?and mechanical properties?When the tensile rate is 200 mm/min,the tensile strength?15 MPa,and the elongation?150%?of soft PVC cable materials of 70?.Compared with the pure PVC,when the addition amount of CHS was 10 phr,the LOI of the corresponding flame retardant samples PVC/10C-CHS and PVC/10T-CHS increased by 2.3%and 3.8%,respectively;the total heat release?THR?of them were decreased by 10.2%and 18.5%,and their total smoke production?TSP?decreased by 45.5%and 50.3%,separately.These results could be attributed to the following two aspects,the water produced by the dehydration of CHS,has dilution and cooling effects on the PVC matrix;On the other hand,CoCl₂,Co₂O₃ and Co₃O₄ generated during the combustion process can effectively catalyze the early decomposition of PVC and then rapidly form a dense and continuous char layer,which prevents the penetration of oxygen and heat into the PVC matrix,thereby effectively suppresses the combustion of PVC.The third part involves in the study of CHS flame retardant EP.The results showed that compared with the pure EP,when the addition amount of CHS was 7 phr,the LOI of corresponding flame retardant samples EP/7C-CHS and EP/7T-CHS increased by 6%and5.8%,respectively;the peak of heat release rate?PHRR?were reduced by 44.3%and 46.2%,separately;and the peak of smoke production rate?PSPR?decreased by 40.6%and 43.8%,respectively.However,all the samples failed the UL-94 V-0 test.To improve the combustion grade,T-CHS and ammonium polyphosphate?APP?were added to the EP.The results showed that when the total addition amount of flame retardant was 6 phr and the mass ratio of APP and T-CHS was 5.9:0.1 and 5.5:0.5,respectively,synergy effect exists between APP and T-CHS,and the flame retardant EP samples can pass the UL-94 V-0 grade.Cone and XPS results showed that the synergistic system EP/5.9APP/0.1T-CHS has the lowest PHRR,the peak of CO production?PCOP?and the peak of CO₂ production?PCO₂P?,which were 68.7%,61.1%and 70%lower than that of pure EP,respectively.The synergistic system EP/5.5APP/0.5T-CHS has the lowest PSPR,which was 59.5%lower than that of pure EP.The enhancements in flame retardation mainly attributes that the T-CHS can effectively catalyze the early decomposition of APP,and rapidly remove H₂O and NH₃ to dilute the flammable gas in the gas phase.The Co₃O₄,CoO,SnO and SnO₂ generated during the combustion process acts as a physical barrier effect.At the same time,the formation of phosphoric acid-containing substances further promotes the decomposition of EP,and catalyzes the formation of an expanded char layer,which acts as a carbon sequestration.The cross-linking reaction produces a more stable O=P-O-C structure and increases the quality of the polycyclic aromatic hydrocarbons,which makes the char layer has a better thermal oxidation resistant performance and of char layer and increase the flame retardancy.