Study On Reactive Blending In Situ-synthesized Polyestertoughening Polylactic Acid

Polylactic acid(PLA)is bio-based thermoplastic polyester with high-modulus and high-strength.It has good biocompatibility,it is biodegradable and it can not pollute the environment.It is currently one of the most promising environmental protection materials.However,its defects such as poor thermal stability and high brittleness limit its application.Polyethylene glycol(PEG)has the characteristics of a wide range of relative molecular masses,and it is a plasticizer with good biocompatibility and degradability.In this paper,with polylactic acid(PLA),polyethylene glycol(PEG)and citric acid(CA)biodegradable bio-based materials as the core.Through reactive blending,in the process of blending PEG and CA to form branched polyester in situ and react with the hydroxyl end of PLA to form block or graft copolymer at the interface to improve the interfacial compatibility of the material.This article mainly studied the effect of adding CA on the compatibility and mechanical properties of PLA/PEG blend system,and the polylactide blends were prepared by different blending process parameters,the effect of blending temperature on the properties of the blends and the effect of the relative mass of different polyethylene glycols on the properties of the blends were investigated.The mechanical properties,rheological properties,micro-morphology,and thermodynamic properties of the blends were characterized by using a torque rheometer,a differential scanning calorimeter,an electronic tensile tester,and a thermogravimetric analyzer.The results showed that after adding CA,the ratio of PLA:PEGCA=85:15,the elongation at break of the blend was 3 times higher than that of PLA/PEG,the tensile strength changed little,and the compatibility of the blend was improved.Using 180°C as the blending temperature and blending for 13 minutes,the contact probability of the reactive groups in the system is large,and the reaction degree reaches the highest.The toughened polylactic acid with a PEG relative molecular weight of 4000 was selected..The blends exhibited the best combination of elongation at break,impact strength and tensile strength.The phase structures of the blends of PEG,CA and PLA with different ratios were further studied.The interfacial compatibility and interfacial adhesion between the dispersed phase and the matrix were discussed.When the ratio of PLA:PEGCA was85:15,the blend had an impact strength of 5.89 kJ/m~2,an elongation at break of 475.3%and a high degree of reactivity.Through the relationship between microstructure and mechanical properties,the toughening of PEGCA was investigated.At the same time,the mechanical properties and structural changes of the blends over time were studied under acid and alkaline earth conditions.The toughening behavior of the blends of PLA and PEGCA corresponds to the Cavitation Theory,which there is remarkable shear yield in the cavity of polymer matrix.According to the SEM images of fracture surface and fracture side surface,there is substantial deformation and orientation of disperse phase along with direction of impact force.The dispersed particles of PEGCA elastomer play as hard spots which induced in shear yield.Moreover,plenty of microfibers are generated under shear yield which absorb much impact energy to improve impact strength of materials.It was found that the degradation rate of PLA/PEGCA blends was faster than that of pure PLA under different degradation conditions.With the prolongation of the degradation time,the tensile and impact properties of the blends decreased significantly,the degradation of the blends was fastest in alkaline solution,and the slowest degradation occurred in the soil,this may be related to the phase separation.