Preparation And Properties Of PLA/PBAT Compatibilized Blends

Polylactic acid（PLA）is a biodegradable polymer with good biocompatibility,but the low toughness of PLA has seriously hindered its development and application in many fields.Poly（butylene adipate-co-terephthalate）（PBAT）is a biodegradable polymer with good flexibility,and its blending with PLA can achieve toughening while ensuring biodegradability of the material.However,the poor compatibility between PLA and PBAT reduces the comprehensive properties of the blends.Therefore,it is important to improve the compatibility between PLA and PBAT in order to obtain PLA/PBAT blends with excellent overall performance and thus broaden their application scope.In this study,we designed and synthesized a series of epoxides and used them as compatibilizers for PLA/PBAT blend system,and explored the compatibilization effect and mechanism of compatibilizers.The details of the study are as follows:Firstly,two epoxy compatibilizers PGMA_L and PGMA_H with different molecular weights were synthesized by free radical polymerization using glycidyl methacrylate（GMA）as raw material.The structures of these two compatibilizers were characterized by infrared spectrometer and nuclear magnetic resonance spectrometer.The compatibility of the compatibilizer with the system was investigated by contact angle test,and the results showed that the compatibilizer had better compatibility with PLA.The relationship between the molecular weight of the compatibilizer and its reactivity was investigated by torque variation and epoxy consumption calculation,and the results showed that the PGMA_L with lower molecular weight had higher reactivity.The PGMA compatibilizer was applied to the compatibilization modification of PLA/PBAT system,and its compatibilization effect on PLA/PBAT system was investigated by micromorphology analysis and mechanical properties testing.The addition of 1 wt%PGMA_L can increase the tensile strength of PLA/PBAT blends from 27.7 MPa to 39.7 MPa,the elongation at break from 225%to 467%and the notched impact strength from 17.4 k J/m² to 34.2 k J/m²,while the particle size of PBAT dispersed phase from 3.7μm to 0.9μm.Finally,the grafting products produced by the reaction were tested by infrared spectroscopy and nuclear magnetic resonance hydrogen spectroscopy,and the compatibilization mechanism was explored.Based on the previous chapter,three epoxy compatibilizers M₃G₁,M₁G₁ and M₁G₃ with similar molecular weights but different molecular chain structures were synthesized by free radical copolymerization of GMA and methyl methacrylate（MMA）.The structures of these three compatibilizers were characterized by infrared spectroscopy,nuclear magnetic resonance and epoxy value titration.The relationship between the molecular chain structure of the compatibilizer and its reactivity was analyzed by the torque curves,and the results showed that M₃G₁ had the highest reactivity due to the lowest density of epoxy groups.MG compatibilizer was applied to the compatibilization modification of PLA/PBAT system,and its compatibilization effect on PLA/PBAT system was investigated by micromorphology analysis and tensile testing.The addition of 1 wt%M₃G₁ could increase the tensile strength of PLA/PBAT blends from 27.7 MPa to 37.1 MPa,the elongation at break from 225%to 417.4%,and the fracture toughness from 64.1 MJ/m³ to 120 MJ/m³,while the particle size of PBAT dispersed phase from 3.7μm to 0.83μm.Finally,the correlation between the linear viscoelasticity of the system and the compatibilization effect was discussed from the rheological point of view by using a rotary rheometer,and the compatibilization mechanism of the compatibilizer was summarized.In order to improve the upper temperature limit of epoxy compatibilizer and give full play to the advantages of complete biodegradability of PLA/PBAT system,a biodegradable monomer MDO was prepared and purified,and it was copolymerized with GMA by free radical copolymerization to synthesize two degradable compatibilizers MDO₁G₃ and MDO₁G₁ with similar molecular weights but different molecular chain structures.The structures of these two compatibilizers were characterized by nuclear magnetic resonance.The thermal properties were characterized by thermogravimetric analyzer,and the results showed that the introduction of MDO structural units substantially improved the thermal stability of the compatibilizers.The degradation testing of the compatibilizer showed that it had good degradation performance.MDO₁G₃ compatibilizer was initially applied to the compatibilization modification of PLA/PBAT system,and its compatibilization effect on PLA/PBAT system was investigated by micromorphology analysis and tensile testing.The addition of 0.5 wt%MDO₁G₃ could increase the tensile strength of PLA/PBAT blends from 27.7 MPa to 34.6 MPa,the elongation at break from 225%to 394.4%,and the fracture toughness from 64.1 MJ/m³ to 115.8 MJ/m³,while the particle size of PBAT dispersed phase decreased from 3.7μm to 1.6μm.Finally,the correlation between the linear viscoelasticity of the system and the compatibilization effect was discussed from the rheological point of view by using a rotary rheometer.In conclusion,under the condition of low addition amount,PGMA_L has a high epoxy content,which can fully react with PLA matrix and PBAT dispersed phase and has the best compatibilization effect.The reaction between M₃G₁ and PBAT is relatively insufficient,so the compatibilization effect is second.MDO₁G₃ has insufficient compatibility with PLA matrix,so the compatibilization effect is general.