| Polylactic acid(PLA)as a kind of biodegradable polymer,it has good biodegradable compatibility,mechanical properties and machinability,etc.Due to its excellent biodegradable and renewable,it is one of the ideal materials which will be replaced petroleum base non-biodegradable.However,the inherent brittleness,slow crystallization rate and low thermal deformation temperature at room temperature of PLA severely limitedits application.Therefore,we need to modification of PLA by toughening.This paper selected the biological based plasticizer of polyethylene glycol(PEG)on toughening of poly(lactic acid)(PLA).Using multivariate epoxied ADR as a chain extension agent to increase the viscosity of PLA,and the mechanical properties of PLA/PEG blend system,the influence of the microstructure,rheological properties and crystal properties were studied systematically.Eventually,the PLA/PEG blend materials had improved by toughness and processing rheological property and heat resistance.(1)Study plasticizer PEG on the plasticizing and toughening effect of the PLA matrix.The effects of plasticizing and toughening were judged by the tensile properties of blends,melt fluidity,the thermal properties and the microstructure of the composites.The results showed that the addition of PEG significantly improved the toughness of PLA.Meanwhile,the incorporation of PEG made the PLA melt viscosity decreased and MFR value increased.The Tg of the blendwas observed by DSC,it was found that the content of PEG increased,the Tg gradually moved to low temperature.The dispersed phase of PEG could not be observed clearly by SEM.So TEM was selected to observe the PEG dispersion phase,and the diameter was less than 100 nm.It was showed that the PEG had good effect on plasticizing of PLA matrix.ADR chain extender was added to enhance the melt strength on the basis of the optimum ratio of toughening effect.The effects of ADR on mechanical properties,processing torque,melt fluidity,thermal properties and microtopography of PLA/PEG blends were studied.The processing torque value of the PLA/PEG blend was significantly improved by the loading of ADR,and the torque value gradually increased with the loading of ADR.Meanwhile,it was found that adding ADR could significantly improve the melt viscosity of the PLA/PEG blend and increased the melt strength of the blends.ADR extender was added to the PLA/PEG blend system,and the test results showed that ADR did not signigicantly impact on the tensile properties of the blends.There was also no observious influence on the glass transition temperature of the blends and the morphology of PEG dispersed phase.(2)The non-isothermal crystallization and isothermal crystallization of the PLA/PEG blends were studied by DSC,and the crystallization kinetics of the blends was analyzed using Avrami equation.According to the results of non-isothermal melt crystallization behavior,the PLA had almost no crystallization during the melt cooling process of 5 ?/min,and the crystallization peak was obvious after adding PEG plasticizer.With the increase of ADR loads,the position of melt crystallization peak was gradually moved from low temperature to high temperature,and the peak shape of the crystal peak was gradually narrowed.According to the results of the non-isothermal crystallization behavior,the temperature Tcc of the cold crystal peak of pure PLA was 124.6 ? at the heating rate of 30?/min,while the Tcc of the PLA/PEG(88/12)blend was 91.5 ?.After adding ADR,Tcc further increased as the loading of ADR increased.The cold crystallization peak of the PLA matrix was moved to high temperature after adding ADR.The effect of ADR chain extender on the kinetics behavior of isothermal crystallization of PLA/PEG blends was studied by DSC.The results showed that the cooling crystallization capacity increased with the increase of Tc,when the temperature cooled crystallization occurred between 65 ? and 70 ?.At the same temperature,PEG increased the crystallization capacity of the PLA,and the t1/2 decreased.After adding ADR,the cooling crystallization ability of the blend was reduced,and t1/2 increased,and the induced crystallization time was prolonged.With the increase of ADR loads,both t1/2 and tintroduce had increased correspondingly.(3)The effect of ADR on rheological properties of PLA/PEG system was studied by capillary rheology.The test found the n value of the melt blend of PLA/PEG(88/12)was shear thinning fluid.With the increase of ADR loads,the melt pseudoplasticity increased.The K value of the melting blend of PLA/PEG(88/12)was 4.1430,and the K value increased with the loading of ADR.The K value was larger,the melt viscosity was higher.The loading of ADR increased the melt viscosity and melt strength of PLA/PEG blends,which was conducive to improvement of the blown filming performance.Through the extrusion blown film of PLA/PEG/ADR(88/12/0,0.3,0.5,1.0),it was found that the PLA/PEG(88/12)blend was unstable in the film blowing process,and after adding 0.3 phr ADR,the bubble was relatively stable.But the bubble of the blend could not be completely stable.When ADR reached 0.5 phr,the bubble of the blend was basically stable.In addition,the heat resistance of the film could be improved by means of isothermal crystallization heat treatment.At the same time,the tensile properties of heat treatment film was studied,the elongation rate of the films was found to be higher than that of the blends after heat treatment,and then the phenomenon was studied and discussed.The PLA/PEG(88/12)and PLA/PEG/ADR(88/12/0.5)blends were isothermal cold crystallization,it was found that the tensile strength and elongation of film were decreased after the heat treatment,and the elongation of the film after crystallization was much higher than of the corresponding plate. |
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