Effects Of Oxygen Concentration And Material Properties On Fire Smoke Toxicity Of TPU

Polyurethane is widely used in the fields of automobile,architecture,shoes and medicine because of its excellent properties of abrasion resistance and low temperature resistance.Its combustion will release a lot of heat,CO,HCN,HC1 and other toxic and harmful gases.Previous studies on the fire smoke mainly focus on CO and CO2,but there are few studies on HCN and the interaction between toxic gases.At the same time,previous studies on the effect of flame retardants on polyurethane materials were carried out,but the main focus was on the effect of single component flame retardants on the toxic release of fire smoke.In addition,previous studies have found the importance of oxygen for material combustion,but there are few studies on the rule and mechanism of the change of fire smoke toxic gas with oxygen concentration,and the oxygen concentration selected in the experiment is not continuous.In this paper,a series of experiments were carried out to study the influence of oxygen concentration and material properties on the fire smoke toxicity release of thermoplastic polyurethane materials.Firstly,the pyrolysis behavior of thermoplastic polyurethane(TPU)was studied by changing the oxygen concentration.The temperature at which TPU reached the peak of its decomposition rate was advanced by oxygen,indicating that the thermal stability of TPU decreased due to the increase of oxygen.When oxygen concentration exceeds 30%,TPU combustion dominates.Ea value increased as oxygen concentration increased,and decreased as oxygen concentration continued to increase after 15%oxygen concentration.HCN is released continuously in TPU combustion process and is not affected by oxygen concentration.The maximum release value of CO increases with the increase of oxygen concentration,possibly because O2 is used for TPU combustion and CO oxidation simultaneously.With the increase of oxygen concentration,oxygen is continuously used in TPU combustion and becomes the main consumption way,so the release of CO also increases.Secondly,ammonium polyphosphate(APP),aluminum hydroxide(ATH)and nano-montmoronite(MMT)were combined into three groups of flame retardant additives in different proportions,including APP-ATH,APP-MMT,and APP-ATH-MMT.Different additives were added to TPU to reduce their toxicity.Through pyrolysis gas analysis of thermoplastic polyurethane and its composites,APP,ATH and MMT strengthen the conversion process from TPU to isocyanate,so the production of CO and CO2 is reduced,and the O2 used for CO oxidation is also reduced,and the corresponding consumption of O2 is also reduced.FED calculation showed that for each group of toxic gases,the toxicity reduction of APP-ATH group samples was mainly due to the release of CO and HCN,and the addition of MMT could help to reduce the release of CO.More than 50%of FED values were caused by the toxicity of HCN,indicating that the toxicity of HCN plays an important role in TPU fire smoke.Finally,montmorillonite(MMT),aluminum hydroxide(ATH)and ammonium polyphosphate(APP)were added as flame retardants for thermal polyurethane(TPU).Static state tube furnace,steady state tube furnace and cone calorimeter have been used to measure the data.Total HCN concentration was regarded as special toxicity hazard index,CO and CO2 yields were regarded as general toxicity hazard indexes.The heat release rate,average heat release rate and total heat release were regarded as heat hazard indexes.The smoke produce rate was regarded as smoke hazard.Fire hazard of TPU and its nanocomposites were assessed by analytic hierarchy process,which was used to calculate the weights of indexes.APP can strongly reduce heat release,and the reason why APP,ATH and MMT have the lowest fire risk may be that the three strengthen the conversion of TPU to isocyanate,thus reducing the yield of CO and CO2.The experimental results show that it is feasible to reduce the fire risk of polymer materials by integrating heat,smoke and toxicity.