Study On Preparation And Properties Of Modified Polylactic Acid Composites

Since the beginning of the 21st century,the new biomass material industry represented by polylactic acid has experienced a rapid development,which has greatly reduced human’s dependence on non-renewable resources such as oil.Polylactic acid(PLA)is a polymer material,mainly formed by polymerization of small molecules of lactic acid.Because of its great biocompatibility and degradability,it satisfies people’s pursuit of a green,enviromental nature.However,polylactic acid also has some defects,such as slower crystallization rate,poor thermal deformation resistance,the hard and brittle texture as well as the high cost,which limits its practical application.Therefore,it has become an important research topic to improve the crystallization behavior,heat resistance and mechanical properties of polylactic acid.The study used PLA as the base material,liquid crystal ionomer(LCI)intercalated montmorillonoid nano-hybrid material(LCI-MMT)as reinforcement and toughening agent to prepare LCI-MMT/PLA composites and characterize its performance.Through X-ray diffraction and differential scanning calorimetry analysis,it was found that the crystallization rate and crystallinity of LCI-MMT/PLA increased and the crystal particles became larger.Via the thermogravimetric analysis showed that LCI-MMT improves the thermal stability of the composites.Through mechanical properties test,scanning electron microscopy and hydrophilicity analysis,it was concluded that LCI-MMT was able to improve the mechanical properties and hydrophilicity of the composites.When LCI content in LCI-MMT was 1.96%,the composites had good crystallization behavior,heat resistance and mechanical properties.In this situation,the crystallinity of LCI-MMT/PLA composite was 70.11%,which was 58.12%higher than that of MMT/PLA.Also the initial decomposition temperature was 344℃,which was 51.42℃higher than the MMT/PLA.The elongation at break was 5.8%,which was87.10%higher than the MMT/PLA.The half crystallization time derived from non-isothermal kinetics,the value of reaction activity fitted by Kissinger equation were consistent with the experimental results.To improve the comprehensive performance of PLA,the study used twin-screw melt process to prepare PLA/PP blending materials with the mass ratio of 3/7,also PEG was used as a compatibilizer.The results showed that with PEG content increasing the crystallization and the grain size of PLA/PP blending materials would first decrease and then increase.The elongation at break increased at first and then decreased,the impact and tensile strength decreased gradually.Furthermore,hydrophilicity increased and the compatibility of PP and PLA was improved.When PEG content was 9%,the elongation at break of PLA/PP blending materials was 13.8%,which was 24.32%higher than that without PEG,materials exhibiting a bicontinuous phase.Based on the result of PLA/PP blends system with 9%PEG content,the blending material got better mechanical properties by changing the blend ratio of PP and PLA.The blending material had the best mechanical properties and good compatibility at a 6/4 ratio of PLA/PP.In this condition,the elongation at break was 16.12%,the tensile strength was19.67MPa,and the impact strength was 8.33KJ/m~2.Conclusively,in the LCI-MMT/PLA composite system,LCI-MMT improved compatibility,the crystallinity and the heat resistance of polylactic acid.At the same time,the LCI-MMT microfiber reinforcement enhanced the mechanical properties of polylactic acid.When the LCI content in LCI-MMT was 1.96%,the composite material system displayed the best comprehensive performance.In the PLA/PP blends system,PEG changed the crystallization behavior of the system and effectively improved its mechanical properties and two-phase compatibility.When the PEG content was 9%and the ratio of PLA and PP was 6/4,the blending material system showed the best and optimum comprehensive performance.