Modification Of Poly(Butylene Adipate-co-terephthalate) And Its Crystallization Properties

Poly（butylene adipate-co-terephthalate）（PBAT）is a new type of biodegradable copolyester that has limited applications in other fields due to its inherently poor thermal properties,expensive price,and other drawbacks.To solve the problem of poor thermal properties of PBAT,small molecule nucleating agents and modifiers were added to PBAT for crystallization modification to improve its crystallization properties and thus the thermal performance of the material.In this paper,four different representative nucleating agents,SiO₂,MMT,TMC-306,NaA,and modifier PBT,were selected for the modification of PBAT by melt blending method through a torque rheometer.Firstly,PBAT composites with different nucleation systems were prepared by selecting inorganic small molecule nucleating agents SiO₂ and MMT and organic small molecule nucleating agents TMC-306 and NaA,respectively,and analyzed by FTIR,DSC,WAXD,POM,and Vicat softening temperature tester.The crystalline properties,crystalline morphology,mechanical properties,and thermal properties of PBAT composites were investigated by characterization means.The results of mechanical property tests and Vicat softening temperature tests showed that the addition of nucleating agent improved the mechanical and thermal properties of PBAT,and the tensile strength of PBAT reached 23.46 MPa,elongation at break increased to 1618.89%,and Vicat softening temperature increased to 94.3°C when the addition of nucleating agent NaA was 3 wt%.The results of DSC tests showed that the nucleating agent could effectively increase the crystallization temperature,exothermic enthalpy of crystallization,and melting temperature of PBAT.When NaA was added at 3 wt%,the crystallization temperature of the sample was 96.84℃,exothermic enthalpy of crystallization was 19.26 J/g and the melting temperature was 130.88℃.The crystallization process of PBAT was further analyzed by Avrami’s equation,WAXD,and POM,and the results showed that the addition of nucleating agent did not affect the crystallization of PBAT,but only shortened the semi-crystallization time of PBAT and effectively refined the grains.In contrast,NaA has a better nucleation effect and the PBAT/NaA system has the best overall performance.Secondly,PBAT/PBT composites were prepared by melt blending with PBT as a modifier,and the effects of PBT content on the mechanical,thermal,crystallization,and processing properties were investigated by FTIR,DSC,DMA,TGA,and rheological analysis.The experimental results showed that the addition of PBT could significantly improve the mechanical properties and increase the Vicat softening temperature of PBAT.With the increase of PBT content,the crystallization and melting temperatures of the composites were more inclined to those of PBT due to the formation of eutectic structure between PBT and PBAT,which were 182.15℃and 222.35℃,respectively.The results of crystallization kinetic analysis showed that PBT dominated the crystallization process of the composites and could effectively increase the crystallization rate of PBAT,shorten the crystallization time and improve the crystallinity.the results of DMA and TGA tests showed that PBT had better compatibility with PBAT and the thermal stability of the composites became better;the results of WAXD and POM tests showed that the diffraction peaks,crystalline The results of WAXD and POM tests show that the diffraction peak and crystalline structure of the composites do not change,the density of spherical crystals becomes larger,the grain refinement,the average grain size decreases from6.98 to 5.85,and the crystalline perfection increases;the results of rheological performance tests show that the values of G’,G’’andη*of the composites increase,the tanδdecreases and shifts to the low-frequency direction,the relaxation time of molecular chains becomes longer,The molecular chain relaxation time becomes longer,the molecular chain movement becomes difficult,and the processing performance becomes worse.This shows that when PBT is added at 30wt%,the composite has the fastest crystallization speed,the smallest grain size,the best nucleation efficiency,and the best overall performance.