Effects Of DOPO-phosphoramide Derivatives On The Flame-retardant Properties Of Polylactic Acid

With the depletion of petroleum resources and the difficulty of degradation of most petroleum-based macromolecule materials,the development of bio-based macromolecule materials have become an important research direction.Polylactic acid（PLA）,as a kind of non-petroleum polymer material,has been developed rapidly due to its good tensile strength,gloss,processability and biodegradability.However,PLA is easy to burn and accompanied by severe melting droplets in the combustion process,which limits its application in many fields.Therefore,it is of great practical significance to study the flame retardant of PLA.9,10-dihydro-9-oxa-10-phosphorus heterophenanthrene-10-oxide（DOPO）and its derivatives have the advantages of high flame retardant efficiency,good compatibility with the matrix,and low environmental pollution caused by degradation products,thus attracting extensive attention of researchers.In this paper,DOPO-phosphoramide derivatives with double P-N bonds with different alkyl structure were designed and synthesized,and effects of different structures on the flame retardancy,mechanical properties and thermal degradation properties of PLA composites were investigated in detail.The main contents and conclusions of this paper are as follows:1.Four DOPO-phosphoramide derivatives containing two P-N bonds were synthesized,which is 6H-dibenzo[c,e][1,2]glycerol phosphate-6,6’-（1,2-ethylenediamine）bis-6,6’-dioxide（EDAB-DOPO）,6H-dibenzo[c,e][1,2]glycerol phosphate-6,6’-（1,2-propanediamine）bis-6,6’-dioxide（12AP-DOPO）,6H-dibenzo[c,e][1,2]glycerol phosphate-6,6’-（1,3-propanediamine）bis-6,6’-dioxide（13DAP-DOPO）,6H-dibenzo[c,e][1,2]glycerol phosphate-6,6’-（1,4-butanediamine）bis-6,6’-dioxide（14DAB-DOPO）,respectively.The target products were successfully prepared after characterized by Fourier transform infrared spectroscopy（FT-IR）,nuclear magnetic resonance spectroscopy（NMR）and liquid chromatography-gas chromatography-mass spectrometry（ESI）.The thermal properties of the product were tested by differential scanning calorimeter（DSC）and thermogravimetric analyzer（TGA）.The results of DSC showed that 13DAP-DOPO had the lowest melting point of199℃.The results of TGA showed that EDAB-DOPO had the highest initial decomposition temperature(T_-5%)at 388℃in N₂ atmosphere.The T_-5%of four DPOPO-phosphoramide derivatives displayed little difference in air atmosphere,about340℃.And the residual rate at 600℃decreased with the increase of alkyl chain length.The results of thermal degradation kinetics calculation showed that all the four DPOPO-phosphoramide derivatives have high activation energies.2.DOPO-phosphoramide derivatives（EDAB-DOPO,13DAP-DOPO,14DAB-DOPO）with alkyl groups increased were added to PLA,and their flame retardancy and thermal properties were characterized by TGA,conical calorimetry（CCT）,vertical combustion（UL-94）and limiting oxygen index（LOI）.The results showed that PLA composites can reach UL-94 V-0 grade when EDAB-DOPO content is 10wt%,while the related rating achieved just adding 5wt%13DAP-DOPO and 14DAB-DOPO.In addition,the LOI value of PLA/EDAB-DOPO increased significantly,and the highest LOI value of PLA/10wt%EDAB-DOPO（37.6%）was obtained.The LOI value decreased with the increase of carbon chain.The results of cone calorimetry and residual carbon layer analysis showed that all three DOPO-phosphoramide derivatives play a certain condensed phase in flame-rataading PLA.The condensed phase interaction decreased with the increase of alkyl chain.3.The comparison of flame retardant and thermal properties between DOPO-phosphoramide derivation containing branched methyl group（12DAP-DOPO）and13DAP-DOPO with linear alkyl chain structure in PLA were studied.The results showed that both PLA composites can reach UL-94 V-0 grade at 5 wt%concentration,and the LOI values were significantly improved by the two DOPO-phosphoramide derivatives.The LOI value of PLA/10wt%12AP-DOPO increased to 39.4%,which is slight higher than that of PLA/10wt%13DAP-DOPO.However,the tensile strength of PLA/10wt%13DAP-DOPO（65.1MPa）is better than that of PLA/10 wt%12AP-DOPO（61.3MPa）.As a result,13DAP-DOPO with lower melting point showed good comprehensive performances as a flame retardant for PLA.