Preparation Of Chitosan Regulated Inorganic Flame Retardant And Its Application In Poly (Vinyl Chloride) Composites

Polyvinyl chloride(PVC)is one of the most widely used universal plastics in the world due to its good chemical resistance,high mechanical strength and outstanding electrical insulation.Due to the addition of plasticizers in soft PVC,the flammability of the material will increase and a large amount of dense smoke will be generated during combustion,which greatly increases potential fire risk of the materials.The traditional inorganic flame retardants have the disadvantage of low efficiency which makes the more addition.For this reason,the mechanical and processing properties of PVC materials will be greatly affected.Chitosan(CS)is a polysaccharide containing lots of hydroxyls and aminos that can easily react with other compounds.Based on this structure,CS can be used to modify inorganic flame retardants to improve the compatibility between inorganic flame retardants and PVC composites.In this article,CS-based flame retardants such as stannate-chitosan(Sn-CS),molybdate-chitosan(Mo-CS),silicate-chitosan(Si-CS)and tungstate-chitosan(W-CS)were prepared.Then,the traditional zinc stannate flame retardant(Sn-Zn)was modified with different amounts of CS and loaded it with rGO to further improve the overall performance of the material.Afterwards,the flame retardants were applied to PVC to study the flame retardant and mechanical properties of PVC composites.The details research content is as follows:Part one:CS-based inorganic flame retardants Sn-CS,Mo-CS,Si-CS and W-CS were prepared by one-step precipitation by reacting CS with sodium stannate,sodium molybdate,sodium silicate and sodium tungstate respectively.The test results on flame retardants showed that the four flame retardants all have good dispersibility and no agglomeration.Thermogravimetric analysis(TG)test results showed that the decomposition temperature of the flame retardants matches the PVC matrix.The four flame retardants were applied to PVC composites,it can be found that the limiting oxygen index(LOI)value of pure PVC is 26.6%.While the LOI value of PVC/Sn-CS reaches 30.5%,which is significantly improved compared to pure PVC of promotion.The char residual of LOI showed that the char of PVC/Sn-CS is tightly without dripping.Cone calorimetry test(CCT)results showed that the peak of heat release rate(PHRR),total heat release(THR),the peak of smoke release rate(PSPR)and total smoke release(TSP)of PVC/Sn-CS have decreased by 30.5%,18.2%,48.9%,and 52.6%respectively,which is significantly reduced compared to pure PVC.The scanning electron microscope(SEM)image of the char residual of the LOI test showed that the char of the PVC materials added with the flame retardants were denser and can effectively exert physical barrier effects.Mechanical tests showed that compared with pure PVC,the elongation at break of PVC/Sn-CS,which has the best flame retardancy,can reach 88.2%of pure PVC,while the impact toughness increased by 48.62%,which indicating that CS plays a role in the compatibility of the material and the matrix.Part two:The zinc stannate flame retardant(Sn-Zn)and CS-based zinc stannate flame retardant(Sn-Zn-CS)were prepared by one-step precipitation.Then,the reduced graphene oxide(rGO)was dispersed into Sn-Zn-CS to prepare Sn-Zn-CS/rGO hybrid material.The experimental results showed that rGO was uniformly dispersed in Sn-Zn-CS/rGO without agglomeration.Fourier Transform infrared spectroscopy(FT-IR)results showed that rGO was fully reduced.TG test results showed that the addition of flame retardants reduces the initial decomposition temperature of PVC materials,and the char residual of PVC/Sn-4Zn-1CS/rGO is increased by 12.4%compared to pure PVC.The CCT test results showed that the PHRR,THR,PSPR and TSP values of PVC/Sn-4Zn-1CS/rGO are significantly lower than other samples,indicating that rGO can play a good synergistic effect with Sn-4Zn-1CS to improve the flame retardant properties of PVC composites.The results of the mechanical property test showed that the elongation at break of Sn-4Zn-1CS/rGO was 514%,which is comparable to that of pure PVC and has a greater improvement than Sn-Zn.It is worth noting that the impact toughness of PVC/Sn-4Zn-1CS/rGO is 10.51 kJ/m~2,which is 37.7%higher than pure PVC.The results showed that CS played a bridging role between the flame retardant and the PVC matrix.At the same time,rGO further improved the toughness of the PVC composites.