Synthesis Of Thermotropic Liquid Crystalline Polyester (PET/PHB) And Study Of The Preparation Of PET/PHB-CNT Composite Via In-Situ Polymerization

PET/60PHB semi-aromatic thermotropic liquid crystal copolyester has advantages of superior mechanical, heat resistant properties and low cost. However, PET/PHB molecular chain has blocky monomer sequence alignment which was generated during the polymerization process. The above chain structure mentioned would damage the properties of PET/PHB. Insoluble and infusible compound were generated when the homopolymerisation conducted seriously. To further improve comprehensive properties of PET/PHB, in our study, polymerization process for PET/PHB was improved to synthetize copolyester with high molecular weight and random chain structure.In addition to those reserch, PET/60PHB-CNT composite material was prepared via in situ polymerization. This work has important significance on expanding PET/PHB application.In this work, PABA and PET were used to synthesize PET/PHB copolyester in the presence of acetic anhydride, and the influence of acetic anhydride on copolymerization process was studied. The addition of acetic anhydride facilitated the mixing of reactant monomer and thus reducing homopolymerisation. And on this basis, PET/60PHB-CNT was prepared via in situ polymerization. Finally, the effects of CNT contents on the structure and properties of composites were studied.The effects of acetic anhydride added in polymerization on copolyester PET/60PHB were studied in this work. The results showed that intrinsic viscosities of PET/60PHB increased and then decreased with increasing the amount of acetic anhydride. When the addition of acetic anhydride was raised to2:1(AC2O:PET unit, mol), intrinsic viscosities of PET/60PHB reached to0.78dl/g which was the highest. Compared to the original PET/60PHB, the strength and modulus of new PET/60PHB was increased by63%and191%respectively. And on this basis, it was found that the nematic liquid crystalline texture appeared clearly when the mole fraction of PABA was among50～70%. While increasing PABA content, nematic liquid crystalline texture of PET/PHB became imperceptible and intrinsic viscosities of PET/PHB decreased. Microstructure characterization of PET/60PHB-CNT found that CNT was dispersed uniformly in the PET/60PHB matrix, especially when CNT content was among01-0.3wt%. Due to the homogeneous dispersion of CNT, the mechanical properties and thermal stability of PET/60PHB-CNT were enhanced with the increase of CNT content, and the overall properties were optimized when the mass ratio was0.3%. Compared to pure PET/60PHB, the strength, modulus and elongation at break of PET/60PHB-CNT increased by38.7%,62.5%,46.4%, and the degradation temperatures increased by8℃.