Study On Preparation And Properties Of Low-melting Point PBT Copolyesters

The low melting point copolyester is an important kind of modified copolyesters.Compared with common polyesters,it has the characteristics of low melting point and good fluidity.Due to its moderate price and good compatibility with common polyesters,its application field is very extensive,including automotive industry,non-woven fabrics,coatings,electronic appliances,construction and others.With the rapid development of the polyester industry,the demand for low melting point copolyesters is increasing and the application prospects are more extensive.Through extensive readings of the literature,it has been found that the research of low melting point copolyesters is mainly focused on the modification of PET and PTT,except PBT;2-methyl-1,3-propanediol?MPO?is a new kind of diol and the unique methyl branched structure exhibiting excellent performance in chemical synthesis,up to now,the use of MPO on modification of PBT has not been reported.Therefore,in this paper.We synthesized PBT copolyester with different molar ratios of isophthalic acid?IPA?and MPO.The purpose is to synthesize copolyesters with low melting point and suitable crystallinity so that they can be used in chemical fiber,no-woven fibers and other industries with better applications.MPO and IPA were added as the third or fourth monomer during the conventional synthesis of polybutylene terephthalate?PBT?.A series of modified PBT copolyesters were synthesized in a 5L magnetic stirring polycondensation reactor by direct esterification melting polycondensation process.The structures of the copolyester samples were characterized by infrared spectroscopy;the viscosity average relative molecular weight of the modified copolyester was determined by viscosity method;differential scanning calorimetry?DSC?and cross-polarization microscopy?POM?were used to characterize the melt crystallization and crystal morphology of the samples,the isothermal crystallization kinetics and non-isothermal crystallization kinetics were studied;the rheological properties of the samples were characterized using a capillary rheometer.In order to obtain a low crystallinity and low melting point PBT copolyester,preliminary research of low melting point PBT copolyester was studied in the field of non-woven fabrics.Viscosity test results show that the as-prepared modified PBT copolyesters have a viscosity average molecular weight in the range of 19000-31000 g?mol^-1,which all reach the level of conventional PBT.DSC results show that both IPA and MPO can decrease the melting point of the modified PBT copolyester,increase the glass transition temperature and the cold crystallization temperature;the crystallization ability of the copolyester decreases with the increase of the addition of IPA and MPO.The observation of POM indicated that the addition of MPO and IPA all resulted in the formation of spherical crystalline morphology of the modified PBT copolyester.With the increase of the amount of addition,the spherulite size decreased;The change in the size of modified PBT simultaneously modified by MPO and IPA of the spherulite crystal structure of polyester is not obvious,further indicating that MPO has a great influence on the crystallization performance of PBT.The results of isothermal crystallization kinetics show that the addition of IPA and MPO can reduce the crystallinity of PBT.As the cooling rate increases,the half-crystallization time of the modified copolyester is larger than that of pure PBT.The non-isothermal crystallization kinetics results show that the Ozawa method shows a non-isothermal crystallization curve,and the Jeziorny method can describe the non-isothermal crystallization process of the modified PBT copolyesters.Capillary rheometer test results show that the as-prepared low melting point copolyester is a pseudoplastic fluid,modified for the copolyester.The non-Newtonian index is less than 1,and the increase in temperature will help improve the of flowability low melting point copolyester.