Study On Synthesis And Properties Of PBT Copolyester Modified By 1,4-Cyclohexanedimethanol

Polybutylene terephthalate(PBT)is an important type of commercially semi-crystalline thermoplastic polyester materials with a wide range of applications in the fields of automotive,electrical,electronics and textile industries.However,it has shortcomings such as low notched impact strength,low heat distortion temperature and poor toughness,which has limited its applications in the field of membtanes.1,4-cyclohexanedimethanol(CHDM)is a new type of diol.The rigidity of cyclohexyl group in the molecular structure provides a new way to improve the thermal stability and crystallization properties of copolyesters.The CHDM modified polyethylene terephthalate(PET)copolyester(PETG)has been commercialized and successfully used for a highly transparent PETG polyester film up to now.We could not find any reports on the preparation of CHDM modified PBT copolyester by using the direct esterification and melt polycondensation process in the literature.In this paper,different molar ratios of CHDM modified PBT copolyester(PBTG)were prepared by direct esterification melt polycondensation process,and the properties of PBTG copolyester were studied.The suitable process conditions for preparation of PBTG copolyester were obtained and PBTG polyester film was prepared,which provided a new method for preparation PBT film resin.Viscosity method,hydrogn nuclear magnetic resonance spectroscopy(~1H NMR),differential scanning calorimetry(DSC),hot stage orthogonal polarizing microscope(POM),capillary rheometer and rotational rheometer were used to characterize the structure and properties for PBTG.The viscosity average molecular weight,molecular structure,crystallization properties,crystal morphology,rheology and dynamic rheological properties of PETG copolyester samples were determined.Viscosity test results show that the intrinsic viscosity values of PBTG copolyesters have reached the commercial PBT level.The ~1H NMR spectrum test confirmed the presence of CHDM structure unit in PBTG copolyesters,and with the increase of CHDM content,the determined content of CHDM was gradually lower than the actual feed value.DSC results show that the addition of CHDM reduces the melting point and crystallization temperature of PBT,and the crystallization ability decreases.The results of non-isothermal crystallization kinetics showed that the linear relationship of PBT and PBTG samples for non-isothermal crystallization curves was obvious.At the same cooling rate?,the non-isothermal crystallization kinetic rate constant Z_c of PBTG was lower than that of PBT.The results of POM observation show that the diameter of spherulites decreases gradually with the addition of CHDM,the phenomenon of cross extinction is not obvious,and the morphology of spherulites is incomplete.The results of extrusion capillary rheological and dynamic rheological determination show that PBTG copolyester is a pseudoplastic fluid,and the addition of CHDM increases the melt viscosity,strength and fluidity of PBT polyester.The biaxially stretched polyester film experiment shows that the PBT polyester could give a translucent oneven film with a broken edge,while the PBTG polyester could give a transparent uniform film with complete edges.Further tensile and thermal shrinkage tests on the polyester film showed that the addition of CHDM increased the tensile strength of the polyester film,the elongation at break decreased,and the heat shrinkage rate decreased.It this paper rovides a new way to prepare modified polyester films.