Preparation And Properties Of Flame Retardant Thermoplastic Polyurethane

A step-by-step approach was used to improve the flame retardancy of thermoplastic polyurethane（TPU）.The process was divided into three parts,and two directions of polytetramethylene ether glycol（PTMG）ether-based and polycaprolactone glycol（PCL）ester-based TPU were simultaneously explored.First,hydroxypropyl-terminated polydimethylsiloxane（PDMS）block TPUs were prepared as the raw material Si-TPUs.The thermoplastic vulcanizates（TPV）were prepared by dynamic vulcanization with methyl vinyl silicone rubber（VMQ）.The bonding between silicon-based materials and TPU was realized by two ways of chemical block PDMS and physical blending VMQ.Finally,TPV was used as the matrix,supplemented by the intumescent flame retardant system to obtain the final composite flame retardant TPU.Moreover,the flame retardant mechanism was explored.In this paper,Si-TPUs were obtained from PDMS block TPU.The microstructure of TPU was characterized using FTIR,DSC,DMA and XRD;the changes in its macroscopic properties were explored using mechanical properties,water contact angle,TGA and flame retardancy tests.The results showed that the block of PDMS will increase the microphase separation of TPU and destroy the crystallization,and the system will form a more refined three-phase structure.PDMS blocks had a damaging effect on the mechanical properties of TPU.However,it reduced the decomposition rate and improves flame retardancy.In this paper,the above PDMS block TPU was used as raw material,and TPV was prepared by dynamic vulcanization with VMQ.There was a similar compatible intrinsic compatibilization effect between the PDMS present on the main chain and the dispersed phase VMQ.The microstructure of the two levels in the TPV was explored using FTIR,DSC and SEM.The results showed that for the sea-island phase structure formed in TPV,the compatibility increased with the increase of PDMS,thereby reducing the phase separation of the island phase VMQ and increasing the dispersion.For macroscopic properties,the intrinsic compatibility between PDMS and VMQ would superficially lead to low TPV mechanical properties.However,this effect will increase the retention of mechanical strength and have a stronger toughening effect on ZTPV.For flame retardant performance,the LOI of ZTPV-323 was increased to a flame retardant level of 27.But the UL-94 rating did not improve significantly.VMQ was added to TPU by dynamic vulcanization to prepare TPV,which greatly reduced the heat release of the TPV system,but increased the amount of smoke released.The siloxane layer formed by combustion had an excellent flame retardant structure.In this paper,ZTPV-129 was used as the matrix,and the intumescent flame retardant system was added.The mechanism of synergistic flame retardant for silicon-based and intumescent system was completed while satisfying the flame retardant level of the matrix.The intumescent flame retardant system will have a damaging effect on the tensile strength of ZTPV-129,but basically no damage to the toughness.For the flame retardant performance,EG had a great effect on improving the LOI index of ZTPV.When the filling fraction of ZTPV-8 was 15%,it can reach the V-0 flame retardant level,which was extinguished immediately after fire.The mechanical properties were 5.3 MPa and 610%.The combination of silicon base and TPU matrix had intrinsic compatibilization,which reduced the calorific value of the matrix and maintains or imparts better performance;during the combustion process,the formation of a silicon-oxycarbon layer with EG and a composite carbon layer with EG expanded carbon layer play a role in termination.Flame retardant effect of heat exchange;EG not only played the role of forming a carbon source for a high-expansion carbon layer,but at the same time,the EG in the upper layer will form a fully expanded composite carbon layer structure combined with the silicon oxycarbon layer with the silicon-containing compound migrated on the surface during combustion.The synergy of the two effects was more efficient for flame retardant than the single use,and it also maintained the mechanical properties to the greatest extent.