Flame Retardancy Of Thermoplastic Polyurethane Elastomer Based On Aramid Fiber And Its Modification

Aramid fiber is a new high-tech synthetic fiber.However,with the application of aramid fiber becoming more and more widely,the increasing waste of aramid fiber has a great impact on the waste of resources and environmental pollution.Recycling and utilization of waste aramid fiber has become a top priority.Thermoplastic polyurethane elastomer is one of the most versatile engineering thermoplastics with properties between plastic and rubber.Because of its excellent properties,TPU has been widely applied in many fields.However,as many other thermoplastics,due to its flammability and smoke generation during combustion,the applications are greatly limited.Hence it is urgent and important to improve the flame retardancy of TPU.The traditional flame retardants often need a large addition and show low efficiency,even toxic,and destructiveness in the mechanical properties of polymers,so it has been a major challenge to find a clean and effective flame retardant of TPU.In this paper,the flame retardant TPU composites were prepared with aramid fiber（AF）,phosphoric acid modified aramid fiber（AF-P）,melamine phosphate modified aramid fiber（AF-MP）and diethyl iron hypophosphite modified aramid fiber（AF-Fe）respectively.The combustion and thermal stability of samples were investigated b y limiting oxygen index（LOI）,cone calorimeter test（CCT）,smoke density test（SDT）,microscale combustion calorimeter test（MCC）and thermogravimetric analysis/infrared spectroscopy（TG-IR）.The results in CCT showed that compared with pure TPU,the peak heat release rate（pHRR）of AF-2（1.0 wt%）decreased by 52%,the peak smoke production rate（pSPR）decreased by 40.5%,smoke factor（SF）decreased by 51.4%.While in the AF-P,AF-MP and AF-Fe systems,the modified AF showed more excellent flame retardancy and smoke suppression property than pure AF.Compared with the pure AF samples（1.0 wt%）:The total heat release rate（THR）of AF-P-3（1.0 wt%）decreased by 28.3%,the total smoke production rate（TSR）decreased by 27.7%,SF decreased by 30%,the residual mass increased by 19.2%.The p HRR of AF-MP-3（1.0 wt%）decreased by 31.8%,the THR decreased by 24.5%,the SF decreased by 26.2%,and the carbon layer became more dense and hard.The pHRR of AF-Fe-3（1.0 wt%）decreased by 27.6%,the THR decreased by 27.3%,the SF decreased by 33.9%.The results in SDT showed that AF and modified AF had played an important role in the smoke suppression of TPU system,especially in the AF-MP and AF-Fe systems under the condition of flameless combustion,the luminous flux increased obviously.TGA results showed that AF and its modification could improve the thermal stability of TPU and promote the crosslinking to form carbon,the decomposition rate of polymer had been decreased and the residual mass had increased.TG-IR results also showed that TPU composites containing AF and its modification release less toxic and harmful gases in the thermal decomposition process,and release H₂O and other nonflammalbe gases at low temperature.