Preparation Of Phosphorus Phenanthrene Flame Retardant And Its Application In Polylactic Acid

Polylactic acid(PLA)is a renewable,environmentally friendly material with excellent mechanical properties and biodegradability.Since PLA is a highly flammable material,it is of great theoretical and practical value to study the flame retardant modification of PLA.Phosphaphenanthrene flame retardants have the characteristics of low smoke,non-toxicity and high flame retardant efficiency,and they are widely used for flame retardant modification of polymer materials.Two different structures of phosphaphenanthrene flame retardants were synthesized and their chemical structures were characterized.Two kinds of different PLA flame retardant composites were prepared by adding two kinds of synthetic phosphaphenanthrene flame retardants and epoxy chain extenders to PLA.The effects of two different structures of phosphaphenanthrene flame retardants on the properties of PLA flame retardant composites and the flame retardant mechanism were discussed in detail.The influences of epoxy chain extenders on the properties of PLA flame retardant composites were further studied.The main tasks as follows:1.Two kinds of phosphaphenanthrene flame retardants were synthesized,which were 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-yl-hydroxy-phenol(DOPO-PHBA)and 4,4'-{1'',4''-phenylene-bis[amino-(10'''-oxy-10'''-hydrogen-9'''-oxa-10'''?~5-phosphaphenanthrene-10'''-yl)-methyl]}-diphenol(P-PPD-Ph),their structures and thermal properties were characterized by Fourier transform infrared(FT-IR),nuclear magnetic resonance(NMR)and thermogravimetric analyzer(TGA).The testing results showed that DOPO-PHBA and P-PPD-Ph were successfully synthesized,and the thermal stabilities of these two flame retardants were good,the residual carbon rates of DOPO-PHBA and P-PPD-Ph were 18.5%and 25.8%at 800°C,respectively.2.PLA/ECE/DOPO-PHBA and PLA/ECE/P-PPD-Ph flame retardant composites were prepared by adding DOPO-PHBA and P-PPD-Ph with different addition amounts(0wt%,5wt%,10wt%,15wt%)and quantitative(4wt‰)epoxy chain extender(ECE)to PLA.The structures,thermal properties,flame retardant properties and mechanical properties of flame retardant composites were analyzed by FT-IR,TGA,vertical combustion(UL-94),limiting oxygen index(LOI),cone calorimetry(CONE),scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),thermogravimetric-infrared(TG-IR)and mechanical properties test,and the flame retardant mechanism was further discussed.The testing results showed that the addition of DOPO-PHBA and P-PPD-Ph reduced the maximum degradation rate of PLA flame retardant composites and increased the carbon residue rate at 700°C.DOPO-PHBA and P-PPD-Ph had good flame retardant effect.When the added amount was 5wt%,the PLA flame retardant composites could reach UL-94 V-0 grade.And at this time,the LOI values of the PLA/ECE/DOPO-PHBA and PLA/ECE/P-PPD-Ph flame retardant composites were30.0%and 31.4%,respectively.The CONE results showed that the addition of DOPO-PHBA and P-PPD-Ph reduced the peak heat release rate(PHRR),total heat release(THR)and effective heat of combustion(EHC)of the PLA flame retardant composites.Observing the microstructure of the carbon layer by SEM,DOPO-PHBA and P-PPD-Ph could make the carbon layer more dense and complete.The mechanical properties results showed that DOPO-PHBA and P-PPD-Ph could reduce the tensile strength and bending strength of PLA flame retardant composites.The analysis of CONE testing,carbon residue and TG-IR testing showed that DOPO-PHBA and P-PPD-Ph decomposed and released phosphorus-containing substances,which mainly exhibited the gas phase flame retardant mechanism and had a certain condensed phase flame retardant mechanism.3.PLA/DOPO-PHBA/ECE and PLA/P-PPD-Ph/ECE flame retardant composites were prepared by adding quantitative(5wt%)of two kinds of phosphaphenanthrene flame retardants and ECE with different addition amounts(0wt‰,2wt‰,4wt‰,6wt‰,8wt‰)into PLA.The thermal properties,flame retardant properties,and mechanical properties were characterized by TGA,UL-94,LOI,CONE,SEM,EDS and mechanical properties test.The testing results showed that the addition of ECE could make the thermal stabilities of the flame retardant composites slightly improved,and when the amount of ECE was 4wt‰and 2wt‰,the PLA/DOPO-PHBA/ECE and PLA/P-PPD-Ph/ECE flame retardant composites respectively reached UL-94 V-0,and the corresponding LOI values were 30.0%and 30.8%,respectively.The CONE results showed that the addition of ECE reduced the values of PHRR,THR and EHC of PLA flame retardant composites.Observing the microstructure of the carbon layer by SEM,the addition of ECE could make the carbon layer more dense and complete.The mechanical properties results showed that ECE could improve the mechanical properties of PLA flame retardant composites.The results of CONE and carbon residue analysis showed that ECE could make DOPO-PHBA and P-PPD-Ph better to play a synergistic two-phase flame retardant effect in the gas phase and condensed phase in the PLA flame retardant composites.