Effects Of Phosphorus-based Flame Retardants On The Flame Retardancy,Smoke Suppression And Mechanical Properties Of Thermoplastic Polyurethane

Thermoplastic polyurethane（TPU）was a kind of synthetic polymers.It was widely used in many fields due to its excellent properties.However,TPU was flammable,and the combustion of TPU was accompanied by a large number of droplets dripping and smoke production.It was very necessary to carry out research on flame-retardant TPU.In this paper,the flame-retardant modification of TPU was carried out concerning two phosphorus-based flame retardants（FRs）.The flame retardancy and smoke suppression properties of TPU was improved,and the problem of deterioration of mechanical properties caused by FRs was also solved to broadening the application scope of TPU.The research results of this paper mainly included three aspects:（1）Ammonium polyphosphate（APP）was chosen as the acid source and melamine（MEL）was chosen as the gas source.The intumescent flame retardant（IFR）composed of APP/MEL and commercially available ionic liquids[BMIM]PF₆ were applied to TPU.The influence on the combustion and mechanical properties of TPU was discussed.When 1.5 wt.%IFR was replaced by[BMIM]PF₆,the limiting oxygen index（LOI）was increased from 25.9 to27.1 with 10 wt.%addition of the FRs.The vertical combustion（UL-94）grade was improved from V-2 to V-0,demonstrating that there was significant synergy between[BMIM]PF₆ and IFR.However,the mechanical properties of TPU were greatly reduced by IFR.The addition of 1.5 wt.%[BMIM]PF₆ improved the mechanical properties of TPU/IFR composites to a certain extent.（2）In order to further improve the mechanical properties of TPU,aluminum hypophosphite（AHP）as a new high-efficiency phosphorus-based FR was applied to TPU.The AHP was coated with polyurethane to prepare CAHP in order to improve the compatibility between AHP and TPU.After replacing the corresponding AHP with 8 wt.%CAHP,the LOI of the TPU composites increased from 30.4 to 31.5.The UL-94 grade obtained V-0 and the tensile strength increased by 11.1%.The study proved that CAHP was more compatible with TPU,which promoted the improvement of LOI and mechanical properties of TPU composites.（3）The Ni-Fe layered double hydroxide（Ni Fe-LDH）was synthesized and applied to TPU combined with AHP.It was proved that there was significant synergistic effect between Ni Fe-LDH and AHP.With the addition of 6 wt.%AHP and 1 wt.%Ni Fe-LDH,the peak of heat release rate（p HRR）,the peak of smoke production rate（p SPR）and the total smoke production（TSP）of TPU composites decreased by 67.4%,56.5%and 38.8%,respectively.Moreover,the peak of CO and CO₂ yield（p COY and p CO₂Y）decreased by 68.6%and 60.5%,respectively.In addition,the tensile strength and elongation at break were 30.1MPa and 1419.2%,which were only 6.0%and 6.8%lower than those of control TPU.