Synthesis Of Multihydroxymethylaminomethane Phosphate And Its Application In Flame Retardant PLA

PLA derived from renewable resources has attracted more and more attentions for its good biocompatibility and biodegradability.However,PLA is a kind of flammable polymeric material which limits its wide application and development.Hence,it is necessary to reduce the flammability of PLA.Due to halogen-free and low toxicity,organic phosphorus flame retardants are widely used in flame retrdant PLA.However,the high addition of flame retardant will cause the decrease of the mechanical properties and thermal stability of the material.Therefore,the development of ultra-efficient flame retardants is very important and of great significance.DOP derived from the reaction of neopentyl glycol with phosphorus oxychloride plays an important role in the condensed phase,while DOPO-OH is the derivative of DOPO and has a wide application as a gas-phase flame retardant.In this paper,PLA was modified with four as-synthesized multihydroxymethylaminomethane phosphates and the comprehensive properties of FR-PLA were studied.In detail,the content of this work is mainly composed of three parts which are related to the synthesis of flame retardant,and the flame retardancy and mechanism of multihydroxymethylaminomethane phosphate when incorporated into PLA.Firstly,four multihydroxyaminomethane phosphates were obtained by the reaction of DOP or DOPO-OH and TRIS or AMPD,respectively.The structures of DTP,DAP,DOT and DOA were clearly characterized.Afterwards,these flame retardants were separately introduced to PLA so as to prepare four flame-retardant PLA systems,namely PLA/DTP,PLA/DAP,PLA/DOT and PLA/DOA.Secondly,the thermal properties,flame-retardance and flame-retardant mechanism of PLA/DTP and PLA/DAP were all analyzed.The results showed that both DTP and DAP had high flame-retardant efficiency.When the the loading of DTP was 2.5 wt%,the flame-retardant PLA could reach the V-0 level of UL-94,while the DAP with the amount of only 0.5 wt% got the same results.Besides,as the amount of flame retardant increases,the flame retardancy of PLA was significantly enhanced.Moreover,the existence of DTP and DAP could promote the crystallization of PLA.Finally,the study on the flameretardant mechanism shows that the flame-retardant activities of DTP and DAP existed in the gas-phase,and the effect of promoting melt dripping for DTP and DAP was also responsible for the improved flame retardancy.Finally,in order to improve the thermal stabilities of flame-retardant PLA and distinguish the different behavior as compared to DTP and DAP,the flame-retardant properties of PLA/DOT and PLA/DOA were also investigated.The results showed that DOT and DOA had high flame retardant efficiency for PLA.PLA reached a UL-94 V-0level when the addition amount of DOT and DOA increased to 0.75%.At the same time,the addition of DOT and DOA could effectively suppress the heat release peak rate(PHRR),total heat release(THR)and average heat radiation rate(ARHE),and hence reduce the fire risk of the materials.The analysis of TG-IR and Py-GC/MS indicated that the improved flame retardancy of PLA/DOT and PLADOA was due to the effect of promoting melt dripping and gas-phaseactivities.