Fire Safety Performance Of Chitosan And Its Composition For Flame Retardant Thermoplastic Polyurethane Elastomer

Chitosan(CS)is a kind of green natural polymer compound,which is extracted from the shell of shrimp and crab.Every year,a lot of shrimp and crab shells are not used effectively,which causes some problems to the environment.The discovery of CS solved this problem.With the continuous exploration of the nature of CS,its application field is very wide.Thermoplastic polyurethane elastomer(TPU)is widely used in various industries due to its excellent corrosion resistance,wear resistance,aging resistance,oil resistance,water resistance and elasticity.But TPU is inflammable,even in combustion,it will occur melting drop,so the study of flame retardant TPU has become a very important topic.Traditional flame retardants have many disadvantages,such as low flame retardant effect,large amount of additives and environmental damage,so it is the development direction of new flame retardants to find a green,environmental friendly and efficient flame retardant.CS itself contains a lot of carbon,which can be used as a carbon source of flame retardant;CS contains a lot of amino acids,which has a positive effect on TPU flame retardant.Based on the above problems,the flame-retardant TPU systems of CS,CS / PWA,CS / CUSA and CS / PF were constructed respectively.The system was tested by CCT,SDT,MCC,TG,TG-IR,SEM,EDS and GC-MS.In TPU / CS system,CS can effectively reduce the heat and smoke release rate of TPU.The peak values of heat release rate(pHRR)and smoke release rate(pSPR)of TPU / CS2(2.0wt%)were 65.9% and 44.0% lower than those of pure TPU.The SEM results show that the carbon slag is fibrous after the combustion of TPU / CS2.It is speculated that the reason is that the amino group of CS reacts with the thermal decomposition products.The results of GC-MS showed that the amount of isocyanate produced by TPU / CS2 was significantly reduced during the cracking process,while the amount of isocyanate produced by the cracking of chitin(CH)sample containing 2.0wt%(TPU / CH2)was still high.The difference between CS and CH is only whether there is amino group in the chain,so the mechanism of CS flame retardant TPU can be inferred: TPU thermal decomposition products react with CS,thus reducing the release rate of heat and smoke.In TPU / CSPWA system,the research shows that CSPWA composition can effectively reduce the heat and smoke release rate of TPU,and has better effect than CS or PWA alone.The pHRR and pSPR of TPU / CSPWA 1(1.0wt% CSPWA)were 75.0% and 77.8% lower than that of pure TPU,and the pHRR were 41.8% and 44.7% lower than that of TPU / CS1(1.0wt% CS)and TPU / PWA 1.0wt% PWA,respectively.The SEM results show that after the combustion of TPU / CS1,the carbon slag is fibrous,but the carbon layer of TPU / CSPWA1 is compact and continuous.The results of GC-MS showed that the amount of isocyanate produced by TPU / CSPWA1 was much lower than that of TPU / CS1.Therefore,it is concluded that PWA and CS react in the process of TPU combustion,which makes the chain combine with each other and form carbon layer under the action of high temperature,thus further improving the carbon layer formed by TPU flame retardant with CS alone and increasing the flame retardant efficiency.In TPU / CSCuSA system,the heat and smoke release of TPU is inhibited by CSCuSA composition,and the flame retardant effect of CS is improved by adding CuSA.The pHRR of TPU / CSCuSA 0.1(2.9wt% CS / 0.1wt% CuSA)was 69.5% and 11.5% lower than that of pure TPU and CS only TPU(TPU / CS3).The picture of carbon slag can be stuck out,and the carbon layer becomes continuous and dense.TG results show that CSCuSA composition can reduce the fire risk of TPU by improving the thermal stability of the material.The carbon residue of TPU / CSCuSA 0.1 is 10.4% higher than that of pure TPU.It is also found that CuSA can enhance the flame retardant effect of CS in a certain proportion.The optimum addition amount of CS and CuSA in TPU / CSCuSA 0.1 was similar.In TPU / CSPF system,when 2.0wt% of TPU is added and the ratio of CS: PF is close to 4:6,the flame retardant effect of CSPF composition is the best,and it exceeds the sample added 2.0wt% of CS(TPU / CS2).The pHRR of TPU / CS0.8PF1.2(0.8wt% CS / 1.2wt% PF)is 60.7% lower than that of pure TPU,and 4.5% and 42.5% lower than that of TPU / CS2(2.0wt% CS)and TPU / PF2(2.0wt% PF).It shows that the addition of PF improves the flame retardancy of CS.The photos of carbon residue show that CSPF composition can further improve the carbonization of TPU material,promote the formation of carbon layer on the surface of TPU,thus play a role of heat insulation and smoke suppression.