Synthesis of Relatively High Molecular Weight Polylactide and Its Blend Modification
|Course||Polymer Chemistry and Physics|
|Keywords||Polylactide poly(lactic acid) synthesis modification blend plasticization compotibility|
Poly（lactic acid）（PLA）is an synthesized aliphatic polyester made up of lactic acid, which is made by fermentation processes of glucose.It is common knowledge that glucose can be derived from the starch of annually renewable resources,such as corn and potatoes etc.PLA is a biodegradable polymer,and can be decomposed to water and carbon dioxide（CO2）in natural condition;this is a perfect ecological circulation and none pollution in the whole process.So among the biodegradable polymers,PLA was studied extensively because of its biodegradability,biocompatibility,and good mechanical properties.PLA has been succeeding in biomedical field and have exhibited great potential in daily market.Although,to replace the common plasctics,there is need for the modification of PLA due to its higher cost,brittleness,rigidity and poor hydrophilicity.Four parts are included in this dissertation as follows:Synthesis process of high molecular weight PLA was studied,the best recrystallization times and concentration of catlyst was confirmed in synthesizing of PDLLA.The flexibility,hydrophilicity,and thermal stability of PLLA were improved through modification with solution blending. All additives are low toxicity for utmost holding the environmental friendliness of PLA.1.The PDLLA with Mv=l25000 was synthesized by ring-opening-polymerization of lactide,and Sn（Oct）2 was used as catlyst.The best recrystallization times of lactide was 4,and the best molar ratio of lactide and Sn（Oct）2 was 3000:1 to 5000:1.2.Di-n-octyl phthalate（DOP）,Diisobutyl phthalate（DIBP）,Tri-n-butyl citrate（TBC）, Polyethylene glycol)s having Mw of 400 and 800 g/mol（PEG400 and PEG800） were used to plasticize PLLA by solvent casting method,and with the mass fraction of plasticizer from 2%to 20%.DSC and TGA results show that all of the plasticizers were compatible with PLLA in the experimental scale.The effects of PEG400 to Tg of PLLA were the most significant,and the Tg of PLLA was reduced to 24℃when the mass fraction of PEG400 was 20%.However,the thermal stability of PLLA plasticized with PEG400 was the worst.The temperature of Onset and mass loss 50%of pure PLLA were 350.5℃and 366℃respectively, when the mass fraction of PEG400 was 20%,them reduced to 268℃and 292℃respectively.Undoubtedly,TBC was the most effect plasticizer for PLLA in our work.When the mass fraction of TBC was 20%,the Tg of PLLA was reduced to 27.5℃,and the temperature of Onset and mass loss 50%of plasticized PLLA with TBC were 350℃and 360℃respectively.3.The hydrophilicity and flexibility of PLLA were enhanced by blending with PEG-b-PPG-b-PEG block copolymer.The blending experiments were carried out with the mass fraction of PEG-PPG-PEG from 2%to 20%.DSC and FTIR show that PEG-PPG-PEG was compatible with PLLA in the experimental scale.There was none obvious effect to the crystallization of PLLA,and none obvious hydrogen bond interaction between PLLA and PEG-PPG-PEG either.The Tg of PLLA was reduced to 52℃when the mass fraction of PEG-PPG-PEG was 20%.At the same time,the temperature of Onset and mass loss 50%of plasticized PLLA with TBC were 340.3℃and 355.5℃respectively.4.The thermal stability of PLLA was improved by blending with 2 kinds of nano SiO2 with-NH2（RNS）and-CH3（DNS）functional group.The blending experiments were carried out with the mass fraction of nano from 0.5%to 5%. DSC and FTIR show that 2 kinds of nano SiO2 were compatible with PLLA in the experimental scale.RNS nano SiO2 with-NH2 functional group can decrease the Tg of PLLA.The Tg of PLLA / RNS nano SiO2 blend was 52℃when the mass fraction of RNS nano SiO2 was 5%.The thermal stability of PLLA / RNS nano SiO2 blends were higher than that of PLLA / DNS nano SiO2 blends at the same mass fraction of nano SiO2.The Onset temperature of PLLA/RNS nano SiO2 blend and PLLA/DNS nano SiO2 which mass fraction of nano SiO2 were 5%were 370℃and 365℃respectively.