Preparation Of A Novel Intumescent Flame Retardant Nanosheets And Its Application In Polylactide

Polylactide(PLA)is a non-petroleum-based biological material derived from renewable plant resources and is degradable.Traditional petroleum-based materials are faced with non-degradable environmental pollution problems,so the PLA bio-based materials will be expected to replace the traditional unsustainable petroleum-based materials.However,PLA is highly flammable and accompanied by severe melt dripping,which limits its wider application.Therefore,it is necessary to develop an efficient flame retardant for PLA.Based on sustainable bio-based materials phytic acid and phosphazene with high thermal stability,we obtained mono-component intumescent flame retardant through self-assembly of phytic acid and hexakis(4-aminophenoxy)cyclotriphosphazene(HACP-PA).By adjusting various reaction conditions,a uniform 2D nanosheet layer was obtained.The molecular structure and microstructure of HACP-PA were characterized by FTIR(Fourier infrared),NMR(nuclear magnetic resonance),XPS(photoelectron spectroscopy),EA(elemental analysis),SEM(scanning electron microscopy),TEM(transmission electron microscopy),etc.,which proved that HACP-PA is a kind of nanosheet with microporous structure.Adding 5 wt%of HACP-PA to PLA can reach UL-94 V-0 rating,and the LOI value was increased to 24.2%.Compared with PLA,the addition of 5 wt%HACP-PA reduced the total heat release(THR)and peak heat release(p HRR)of the PLA composite by 21.5%and 15.3%,respectively.In addition,the total smoke production(TSP)was also significantly reduced by 31.0%,indicating that HACP-PA is a good flame retardant and smoke suppressant.Through the analysis of TG-FTIR(Thermogravimetric-Fourier Transform Infrared Spectroscopy),HACP-PA significantly reduced the release of flammable volatile products.In addition,the microstructure of the char residue was observed by SEM,and it was found that the char layer with 5 wt%HACP-PA was dense and continuous on the outside and porous inside,thus greatly reducing the thermal conductivity of the char residue and improving the flame retardancy of the material.In order to further improve the flame retardant performance of HACP-PA in PLA,two synergistic flame retardants,LDH and H₃BO₃,were introduced into PLA/HACP-PA system.The flame retardant properties of the composite were studied by vertical combustion and oxygen index.It was found that when the total amount of flame retardant was kept unchanged at 4 wt%,adding 1 wt%LDH reached UL-94 V0 rating and the LOI was also increased.When 3 wt%of H₃BO₃ was added to PLA/HACP-PA,the UL-94 V0 rating was reached,and the LOI increased from 19.8%of PLA to 33.1%.The char residues of PLA/HACP-PA/LDH and PLA/HACP-PA/H₃BO₃ composites were observed by SEM,and it was found that the composites with 1 wt%LDH and 3 wt%H₃BO₃ had a high-quality char layer.The structure of the char layers was studied by FTIR,and both LDH and H₃BO₃participated in the formation of char residue.This work provides an effective way to improve the flame retardant properties of PLA by introducing sustainable bio-based intumescent flame retardants with unique nanostructures,which will make PLA have greater potential application prospects.