Study On Preparation And Properties Of MOFs/TPU Halogen-free Flame Retaedant Composites

Thermoplastic polyurethane（TPU）is a kind of polymer material with excellent mechanical properties,which is widely used in production and daily life.However,TPU is easy to be ignited in the process of use and will release a large amount of toxic smoke in the process of combustion,which is a threat to human life.This nature hinders its further development to a certain extent.At present,halogen-free flame retardant TPU composites are mainly prepared by adding flame retardants to improve its fire safety.Mainly through the metal elements in the flame retardant in the condensed phase to play the role of flame retardant and smoke suppression.Due to the metal ions and organic ligands of MOFs（Metal Organic Frameworks）materials and the structure of MOFs have certain controllability,it can be used as flame retardants.And silicon dioxide（Si O₂）,multi-walled carbon nanotubes（MWCNT）and graphene oxide（GO）can enhance the properties of MOFs materials.Therefore,the materials,MOFs can be used as an additive flame retardant to add into the TPU matrix to prepare a series of halogen-free flame retardant TPU composites.In this paper,（NH₂-）/MIL-53（Fe）and（NH₂-）/UIO-66（Zr）were prepared by hydrothermal synthesis.NH₂-MIL-53（Fe）and NH₂-UIO-66（Zr）materials were modified by Si O₂,MWCNT and GO.Two kinds of heterojunction materials,MIL-53/UIO-66 and NH₂-MIL-53/NH₂-UIO-66,were prepared by mechanical and thermal action.Using the X-ray diffraction（XRD）,the scanning electron microscope（SEM）and the Fourier transform infrared spectroscopy（FTIR）to characterize the above prepared materials.It was determined that the synthesized materials had complete crystal appearance.The above synthesized materials were used as flame retardants to prepare a series of TPU composites by melt blending with the addition of 2 wt%.The flame retardant,smoke suppression,thermal stability and mechanical properties of TPU composites were investigated by cone calorimeter（CCT）,char analysis,thermogravimetric analysis（TGA）and mechanical properties test.The results of CCT and TGA show that the flame retardant effect of the two heterojunction materials was better than that of the single MOFs material by comparison,in which the peak heat release rate（PHRR）of the NH₂-MIL-53/NH₂-UIO-66heterojunction material decreased by 59.72%compared with the pure TPU material,and the peak smoke produce rate（PSPR）decreased by 70.53%.The flame retardant and smoke suppression effects of modified materials on MOFs materials from low to high are Si O₂,MWCNT and GO.Compared with pure TPU materials,the PSPR of TPU composites with GO modified NH₂-MIL-53（Fe）decreased by 76.30%,while the PHRR of TPU composites with GO modified NH₂-UIO-66（Zr）decreased by 74.62%.Through the mechanical properties test,it was found that the mechanical properties of TPU with GO modified NH₂-MIL-53（Fe）was better,in which the tensile strength and elongation at break decreased by only 18.5%and 19.7%,respectively.The char was analyzed by digital photos,SEM-EDS and XRD.By comparing the digital photos of char,it shows that the char of TPU composites are more dense.MOFs can form metal oxides during combustion and promote the formation of dense high graphitized char in TPU composites.NH₄⁺in organic ligands can form N₂ during combustion,which can dilute the combustible gases in the environment,such as the oxygen.And it also can slow down the combustion of TPU composites.The modified materials Si O₂,MWCNT and GO can further catalyze carbonization and make TPU composites form a more solid and dense carbon layer,which can isolate the contact between oxygen in the air and the matrix,prevent heat transfer in the combustion process and smoke overflow,so as to achieve the role of flame retardant and smoke suppression.