Preparation and properties of polyurethane elastomers modified by phosphorus-nitrogen organic salts
A novel phosphorus-nitrogen flame retardant(etidronic acid 2-furfurylamine organic salt,EAFOS)was synthesized with etidronic acid and 2-furfurylamine as starting materials,and it was added to thermoplastic polyurethane elastomer(TPU)by melt blending method to fabricate modified TPU(TPU/EAFOS).The chemical structure of EAFOS was characterized by infrared spectroscopy and nuclear magnetic resonance spectroscopy.The flame retardancy,thermal stability and mechanical properties of TPU/EAFOS were investigated by limiting oxygen index(LOI),underwriters laboratory-94(UL-94),thermogravimetric analysis,muffle pyrolysis,Raman and tensile test.The results reveal that the addition of EAFOS significantly improves the flame retardancy of TPU and inhibits the melt-drop phenomenon during the combustion.The sample with only 1％mass fraction of EAFOS shows an increase of 40％in LOI value(30.5％)compared with the pure TPU,and it can pass the V-0 rating for UL-94.The thermal decomposition of EAFOS catalyzes the formation of char during combustion,forming a higher degree of graphitization and denser char layer to inhibit the exchange of heat and oxygen during the combustion of TPU,which improves the flame retardancy of TPU.In addition,the mechanical properties of TPU decrease after the addition of EAFOS.The likely cause of this problem is that the hydrogen bonds between the TPU molecular chains are broken by EAFOS.
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