苯基次磷酸盐离聚物/聚磷酸铵协效阻燃增韧改性聚乳酸

通过将双端羟基的聚己内酯(PCL)、聚乳酸(PLA)预聚物以及苯基次磷酸离子盐扩链得到一种含苯基次磷酸盐的离子共聚物,将其与聚磷酸铵(APP)复合用于协同改性聚乳酸,离聚物中苯基次磷酸盐结构与APP具有优异的协同阻燃PLA的作用,同时该离聚物中PLA与苯基次磷酸盐结构有效提升了APP在PLA中的分散能力,最后该离聚物中PCL柔性链段有效改善了PLA的韧性,最终得到更高效阻燃性能且韧性也较好改善的PLA/PCLA-PIU/APP复合材料.一方面,离聚物中苯基次磷酸盐结构与APP协同有效促进了PLA的成炭,形成更连续致密的炭层从而阻隔可燃气体的释放,达到更好的阻燃效果.锥形量热、残炭的扫描电子显微镜(SEM)、能谱分析(EDS)、拉曼光谱等测试证实了这一结果,与纯PLA以及仅使用APP的PLA/APP相比,PLA/PCLA-PIU/APP的热释放速率与总热释放均降低,同时残炭的石墨化程度更高,形成了更为致密的炭层.另一方面,力学性能测试结果表明,离聚物中PCL柔性链段的存在使得与APP复合改性后的PLA的韧性相比纯PLA和PLA/APP有较大的提升;SEM测试表明,离聚物中PLA与苯基次磷酸盐结构起到增容作用,提升了APP在PLA中的分散性.

Flame Retardant and Toughening Modification of Poly(lactic acid)with Phenylhypophosphate Ionomer/Ammonium Polyphosphate

Poly(lactic acid)(PLA),as a kind of aliphatic polyester derived from biomass with excellent mechanical strength,biocompatibility and biodegradability,is a kind of green polymers with promising potential application.However,the application of PLA as a commodity polyester has been restricted dramatically because of its brittleness and flammability nature.It is still a great challenge to improve flame retardancy and toughness of PLA simultaneously by a simple blending method.In this work,copolymer ionomer(PCLA-PIU)was prepared by chain extension copolymerization of hydroxyl terminated poly(ε-caprolactone)(PCL),PLA prepolymer and phenylhypophosphate,and then incorporated with ammonium polyphosphate(APP)for synergistic modification of PLA.The ionomer can act as a compatibilizer to enhance the dispersion of APP in PLA matrix because of its PLA segments and phenylhypophosphate groups.The SEM observation shows that the APP particles dispersed in PLA/PCLA-PIU/APP composite has significantly smaller size and uniform dispersity,compared to the PLA/APP20.The phenyl hypophosphate groups in the ionomer also has an excellent synergistic effect with APP for improving the flame-retardance of PLA.The flame-retardant properties and mechanism of the PLA and its composites were investigated by LOI,UL-94,Cone calorimeter test,SEM,EDS,Raman spectroscopy,etc.Compared with neat PLA and PLA/APP,the composite PLA/PCLA-PIU10/APP10 containing 10 wt%of PCLAPIU and 10 wt%of APP10 achieves the V-0 rating in UL-94 burning test with limiting oxygen index(LOI)as high as 27.6%.The heat release rate and total heat release of PLA/PCLA-PIU10/APP10 are also reduced significantly to 254.9 kW/m^2 and 55.8 MJ/m^2,respectively.SEM and Raman analysis for char residues after Cone calorimeter test suggest PCLA-PIU and APP had synergistic effect on promoting charring of PLA,which result in compact char residue with high graphitization degree,therefore effectively improving the flame-retardant efficiency.Moreover,the toughness of PLA is improved effectively by the flexible PCL segments of ionomers,resulting in a PLA/PCLA-PIU/APP composite with improved flame retardancy and toughness simultaneously.The mechanical properties test results show that the toughness of the modified PLA(10.3 kJ/m^2 of PLA/PCLA-PIU10/APP10)is significantly improved compared to those of neat PLA(3.7 kJ/m^2)and PLA/APP20(2.5 kJ/m^2).