The Application Of High-efficient Phosphorus-containing Flame-retardants For Thermoplastic Polyurethane

Thermoplastic polyurethane(TPU)is flammable and can produce melt droplets,which poses a potential to cause fire hazard.In this work,ammonium polyphosphate(APP)and aluminum hypophosphite(AHP)were respectively introduced into TPU by melt blending to improve the flame retardant retardancy of the composite.And the synergistic effect of bio-based flame retardants and malic anhydride-carbon 9(MAH-C9)copolymer particles for APP flame retardant M-TPU system were investigated.The main outcomes are as follows:1.The structural characteristics and thermal degradation process analysis of polyether TPU(M-TPU)and polyester TPU(Z-TPU)demonstrated that APP had higher flame-retardant efficiency than AHP in M-TPU,while AHP had higher flame-retardant efficiency than APP in Z-TPU.With the addition of 10 wt%APP,the LOI of M-TPU increased from 21.6%to 27.4%,UL-94 vertical burning test reached V-0 rating,and the heat release rate droped significantly.And with the addition of 10 wt%AHP,the LOI of Z-TPU increased from 21.3%to 28.7%,UL-94 vertical burning test reached V-0 rating and heat release rate droped significantly.It is suggested that the different decomposition temperature,carbon forming and the interface barrier for residual carbon of APP and AHP are responsible for the improved flame retardancy.2.Bio-based synergistic flame retardants(chitosan,casein,starch,bamboo powder(BF))were added to the M-TPU/APP composite to further improve the flame-retardancy.The results showed that the optimal ratio of APP/bio-base synergistic flame retardants was 8/2.Compared with the addition of the same amount of pure APP,the addition of the flame-retardant formulation has less mechanical loss to the elastomer blend,the LOI of the M-TPU/APP8/BF2 sample reached 28.5%and was self-extinguished during fire performance test.It was analysised that the phenolic hydroxyl groups in the BF could act as a radical scavenger during combustion.3.Silane coupling agent KH550 modified BF(BF-KH550)and diammonium phosphate(DAP)soaking treatment BF(BF-DAP)were used to further improve the compatibility with M-TPU matrix and flame-retardant properties.The results showed that the LOI of M-TPU/APP8/BF-KH550(2)and M-TPU/APP8/BF-DAP2 composites were increased to 30.3%and 30.5%,both of them could be self-extinguished from fire,and the fire rating(FPI)was further improved.The interfacial adhesion between BF-KH550 or BF-DAP and M-TPU matrix were enhanced.And the tensile strength of them were also increased to 23.9 MPa and 23.0 MPa,respectively.4.MAH-C9 copolymer particles and APP were introduced to M-TPU to prepare flame-retardant composite materials.The optimal ratio of APP/MAH-C9 was 9/1,which could achieve self-extinguishing during UL-94 test,and the FPI from cone test was increased to 0.095 m2/s/kW.It was found that the M-TPU/APP/MAH-C9 formulation has the maximal residual carbon quality.When the total addition amount was 10 wt%with thickness of 1.6 mm or the total addition amount was 5 wt%with thickness of 3.2 mm,UL-94 of·M-TPU/APP/MAH-C9 formulation could still reach V-0.MAH-C9 could also improve the thermal stability of the M-TPU composites.