The Fabrication And Properties Of Polylactide/Halloysite Nanotubes Composites

Polylactide,as a fully degradable plastic made from biomass materials,can solve the resource shortage and serious plastic pollution caused by traditional plastic products.But its poor toughness,heat resistance and low crystallization rate seriously restrict its wide utilization.In order to maintain the biocompatibility and pollution-free properties of PLA,natural halloysite nanotubes was used to modify it.The purification process was studied firstly to obtain high purity HNTs.The influences of solid content,stirring time and static time were investigated and the suitable conditions were obtained.To solve the problems of HNTs agglomerations and improve its adhesion with PLA matrix,silane coupling agent was used to modify HNTs.The effects of different silane coupling agents,feeding sequence,water-alcohol ratio,reaction temperature and pH value on the modification of HNTs were studied.The halloysite grafted by silane coupling agents were obtained(KH560-HNTs)and PLA/KH560-HNTs composites with different weight ratios were prepared by melting process.The tensile test results showed that the tensile strength of the composites increased obviously and the elongation at break did not decrease when HNTs composition was 2-4wt%.When the weight content of modified halloysite increased to above 4%,the both tensile strength and elongation at break decreased significantly.In order to make full utilization of quality and cheap HNTs and improve the contents of HNTs in the composites,the dimethyl sulfoxide(DMSO)and methyl methacrylate(MMA)were utilized to modifying HNTs.By virture of the multilayer structure of HNTs,DMSO was used as intercalation agent.And MMA monomer was dissolved in DMSO to intercalates into HNTs.After that,PMMA was polymerized in situ in HNTs interlayers and HNTs modified by PMMA(PMMA-HNTs)was obtained.PLA/PMMA-HNTs composites with above 2%weight ratios were prepared by solution blending.The crystallization behaviors,mechanical properties and thermal stabilities of the modified HNTs and PLA composites were studied.The results of isothermal crystallization kinetics showed that PMMA-HNTs could improve PLA crystallization rate obviously.However,PLA/PMMA-HNTs crystallization rate decreases with increasing the ratios of PMMA-HNTs.Besides that,the crystallization rate of PLA/PMMA-HNTs is slower than PLA/HNTs with same weight ratios.Through observing the crystallization morphologies by optical microscop,it was found that in contrast with HNTs,PMMA-HNTs decreased the nucleation rate and the spherulites grew rate.The crystal structures of PLA/PMMA-HNTs formed at 11 0℃ were further studied by wide-angle X-ray diffraction.The result showed that the crystal structure of both PLA/HNTs and PLA/PMMA-HNTs composites formed a crystal structure of PLA.The tensile properties of PLA/PMMA-HNTs were investigated by electronic universal tensile strength testing equipment.It was found that PMMA-HNTs improved the tensile strength of composites,especially for composites with PMMA-HNTs contents above 30%,the tensile strength of PLA/PMMA-HNTs was still higher than that of pure PLA.However,the elongation at break was lower 50%than that of neat PLA.Scanning electron microscopy(SEM)was used to observe the microstructure of PLA/PMMA-HNTs and PLA/HNTs.The SEM images indicated that PMMA-HNTs disperse more uniformly than HNTs in PLA matrix.The results of thermal stabilities demonstrated that a slight decreased in initial degradation temperature and maximum weightlessness temperature when the HNTs and PMMA-HNTs contents were increased.When the weight ratio of PMMA-HNTs was same as HNTs,the thermal stabilities of PLA/PMMA-HNTs was better than that of PLA/HNTs.