The Application Of High-efficiency Intumescent Flame Retardant Systems In Polystyrene And Polylactic Acid

Polystyrene（PS）is a widely used polymer,which has the advantages of great processability,transparency and electrical insulation.It is widely used in the fields of automobile shells,packaging materials and electronic industry.However,PS is flammable and a large amount of flue gas and toxic gas produced in the combustion process will seriously endanger people’s life safety.Polylactic acid（PLA）,as a biodegradable polymer material with excellent properties,has attracted extensive attention because of its great transparency and biocompatibility.However,the disadvantages of PLA such as easy combustion and poor thermal stability limit its application in some fields with high safety standards.Therefore,it is of great significance to improve the flame retardant properties of PS and PLA.Based on the different combustion characteristics and flame retardant mechanisms of PS and PLA,zinc borate（ZB）synergistic novel intumescent flame retardant system,single component supramolecular intumescent flame retardant system and metal-organic frameworks（MOFs）synergistic flame retardant system were designed,and then they were introduced into the matrix by melt blending method to prepare PS and PLA flame retardant composites,taking into account other properties while improving the flame retardant properties of the matrix.The corresponding flame retardant mechanism was studied and the important research results are as follows:1.A novel phosphorus-nitrogen-sulfur flame retardant MAP was synthesized based on ion-exchange reaction.PS/N-IFR/ZB composites were prepared by compounding a novel intumescent flame retardant（N-IFR）composed of MAP-ammonium polyphosphate（APP）-pentaerythritol（PER）with ZB.The experimental results showed that the limiting oxygen index（LOI）of PS/22%N-IFR/1%ZB sample was increased to 27.7,and passed V-0 level in verticel burning test（UL-94）,the peak heat release rate（p HRR）,total heat release（THR）and total smoke release（TSP）were reduced by 67.6%,11.8%and 25.9%respectively.ZB and N-IFR promoted the formation of high-quality carbon layers and effectively inhibited the heat and smoke release of PS.2.Based on the structure of MAP in the previous chapter,a single component supramolecular intumescent flame retardant（IFR）was designed.MAP-Fe/MAP-Zn were obtained by chelating Fe³⁺/Zn²⁺in the outer layer of MAP.PLA flame retardant composites were prepared by melt blending MAP/MAP-Fe/MAP-Zn with PLA.The LOI of PLA/3%MAP-Zn increased to 29.2,UL-94 reached V-0 level,and the p HRR and THR decreased by 18.7%and 10.5%respectively.MAP-Zn mainly promoted the formation of graphite carbon in residuals.In addition,MAP-Zn had little negative effect on the mechanical properties of PLA.The tensile strength of PLA-3%MAP-Zn was slightly reduced from 64.9 MPa to 60.1 MPa,which could still meet the requirements of most practical applications.3.A novel organic ligand was synthesized by Schiff base reaction using tris（hydroxymethyl）aminomethane and 1,4-piperazine dialdehyde.Then it was coordinated with Fe³⁺to obtain Fe-MOF flame retardant synergist containing Schiff base and polyhydroxy structure at the same time.Fe-MOF was compounded with IFR for flame retardancy of PS.Adding 20%IFR/2%Fe-MOF made PS pass UL-94 V-0 level and its LOI increased to 28.3.The p HRR,THR and TSP decreased by 77.6%,35.2%and 33.7%respectively.Fe-MOF could synergistically catalyze carbon formation with IFR and played the role of condensed phase flame retardant.In addition,the organic ligand in Fe-MOF had good compatibility with PS matrix,which alleviated the deterioration of mechanical properties caused by the addition of IFR to a certain extent.