Construction Of Induced Nucleation System For PET And Its Effect On Crystallization Behavior

Poly（ethylene terephthalate）is a thermoplastic semi-crystalline polymer,which is widely used in industrial fields due to its outstanding physical and chemical properties such as high strength and high thermal stability.However,even though PET molecule exhibits a symmetrical linear structure,the crystallization rate of PET is still very low due to the rigid benzene ring structure in the molecular chain.The slow crystallization rate severely limits the application of PET in the field of engineering plastics.Therefore,improving crystallization rate has always been a research hotspot in the field of PET engineering plastics.This thesis mainly focus on the construction and performance of new polyester nucleation systems.In order to establish the internal relationship between"structure and properties",the influence mechanism of different interactions between different nucleation systems and polyester matrix on the crystallization properties of PET were explored,and the optimal polyester nucleation system was selected.The glycidyl ether functionalized POSS and the synthesized epoxy cyclohexane functionalized POSS were reacted with the PET end groups to construct PET/POSS nucleation system.The reaction mechanism of PET and epoxy functionalized POSS,the mechanism of action of the two POSS on PET crystallization,and the influence mechanism on the thermal and mechanical properties of PET nanocomposites have been fully studied.The results showed that the epoxy groups in the epoxy-functionalized POSS could react with the PET end groups,and the covalent bond enhances the interaction between PET and POSS,and also promotes the dispersion of the nucleating agent in PET matrix.The addition of EPOSS significantly increased the crystallization property of PET,which increased the crystallization temperature of PET from 194.3°C to 205.6°C,the half crystallization time reduced to 56.9%compared with PET.In addition,EPOSS has better thermal stability compared with GPOSS.Therefore,the adoption of EPOSS endowed the PET/POSS nanocomposites with higher thermal stability,which increased the initial decomposition temperature of PET from 404.3°C to 421.3°C.The metal organic framework material UiO-66 was synthesized as the nucleating agent,and the PET/UiO-66 nucleation system was constructed.The results showed that the addition of UiO-66 in the PET/UiO-66 nanocomposites system significantly increased the crystallization temperature of PET.The crystallization temperature of PET-UiO-66-1 reached 211.6℃,while that of PET is only 194.6°C,and the half crystallization time reduced to 41.0%of pure PET.It was indicated that a proper content of UiO-66 could act as nucleating agent to increase the crystallization temperature of PET significantly.Although the initial decomposition temperature of the nanocomposites was slightly lower than PET,the residue at 550°C was significantly improved.The tensile strength of PET nanocomposites with 1.0%UiO-66 was increased by 21.8%,and the elongation at break was consistent with that of pure PET.In the PET nanocomposites with 3.0%UiO-66,the tensile strength even increased to 55.3MPa,which increased 31.0%compared with PET.In addition,it was found that the Zr⁴⁺exposed by the UiO-66 defect could form a coordination effect with the ester bond of PET,which significantly improved the crystallization property of PET.The PET copolyester containing 2,6-pyridinedicarboxylic acid as a coordinating group（PEPT copolyester）was synthesized to explore the mechanism of the effect of coordination on PET crystallization.After Zn²⁺and Zr⁴⁺were adopt to coordinate PEPT copolyester,the effect of different coordination ions on the crystallization properties of the PEPT copolyester was also studied.The results showed that although the introduction of the rigid pyridinedicarboxylic acid as third monomer decreased the crystallization temperature of PEPT copolyester,the crystallization temperature of the copolyester was significantly increased after Zr⁴⁺introduced into PEPT to form a coordination copolyester.The results showed that although the introduction of the rigid pyridinedicarboxylic acid as third monomer decreased the crystallization temperature of PEPT copolyester,the crystallization temperature of the coordinated copolyesters increased significantly after Zr⁴⁺introduced into PEPT polyesters.The crystallization temperature of PEPT-Zr-0.5increased from 194.3℃to 209.3℃,and the half crystallization time reduced to 45.4%of PET.In addition,due to the coordination effect in the coordinated copolyester PEPT-Zr-0.5,the tensile strength was increased by 16%,but the elongation at break was higher than that of pure PET.It was confirmed that the coordination effect between metal ions with PEPT has a significant impact on the crystallization property of PET.The diol monomer SBDO containing sulfonate side chain was synthesized.The PET ionomer was synthesised by esterification-polycondensation method with SBDO as the third monomer.It was showed that SBDO could promote the nucleation of PET and significantly increase the crystallization temperature of PET.The crystallization temperature of PET ionomer containing SBDO was higher than that of PET,the crystallization temperature of PETi1 reaches 210.8℃and the half crystallization time of PETi3 reduced to 39.9%of PET.The thermal stability of PET ionomer was same as that of pure PET,and the residue at 550℃was significantly improved.Compared with pure PET,the tensile strength of PETi3 was increased by 26.7%.In addition,rheological tests showed that the viscosity and modulus of PET ionomers were similar to PET at high shear frequency,indicating that PET ionomers have excellent processability.In this thesis,the polyester nucleation system was constructed from the perspective of nucleating agent structure and polyester structure.The influence mechanism of different nucleation systems on the crystallization and properties of polyester was also explored.The synthesis of PET nucleating agent and the exploration of the interaction between nucleating agent and PET in this thesis provide new ideas for the research of high crystallization rate PET engineering plastics,and help to promote the application of PET in the field of engineering plastics.