Preparation And Crystallinity Of PET Modified By Epoxy Cyclohexane Diester Diol

Polyethylene terephthalate（PET）is an important semi-crystalline thermoplastic polyester with excellent fatigue resistance,mechanical properties,thermal stability,non-toxic,and it has lower production cost and higher cost performance ratio,so PET is widely used in textile,food,medicine and other fields.At the same time,PET also has problems such as slow crystallization,high mold temperature,long production cycle and low mechanical strength,which restricts its application in other fields such as engineering plastics.In this paper,by means of copolymerization modification,the crystallization capacity of PET is reduced,its melting temperature,crystallization temperature,crystallization rate is changed,so as to expand the application range of PET.In this paper,epoxy cyclohexane diester diol succinate/epoxy cyclohexane diester diol glutarate/epoxy cyclohexane diester diol succinate（SCHD/GCHD/ACHD）was synthesized from epoxy cyclohexane（CHO）and succinic acid/glutarate/adipic acid（SA/GA/AA）as raw materials.Then,using SCHD/GCHD/ACHD as the third monomer,using terephthalic acid（PTA）and ethylene glycol（EG）as raw materials,using direct esterification melt polycondensation method,SCHD modified PET copolyester（PESHT）,GCHD modified PET copolyester（PEGHT）and ACHD modified PET copolyester（PEAHT）were prepared.The chemical structure,intrinsic viscosity,melt crystallization properties and thermal properties of the compound were characterized and analyzed by infrared spectrometer,Ubiscotti viscometer,differential scanning calorimeter,thermogravimetric analyzer and orthogonal polarizing microscope.Infrared spectrum test confirmed that PESHT,PEGHT and PEAHT copolyesters were successfully prepared.Test results showed that the viscosity of modified PET copolyesters sticky molecular weight more than 8000.DSC results show that with the increase of SCHD/GCHD/ACHD content,the melting temperature（T_m）and crystallization temperature（T_c）of the modified PET co-polyester decrease,and the half-crystallization time(t_1/2)decreases.In addition,compared with the addition of GCHD and ACHD,the addition of SCHD has a greater effect on the T_mand T_cof PET,and only when the molar ratio of SCHD to EG reaches 7/93,the crystallization peak disappears completely.Jeziorny method can be used to analyze the non-isothermal crystallization kinetics of PET and its modified copolyester.Compared with the non-isothermal crystallization rate（Z_c）value of PET,the Z_cvalue of the modified PET copolyester increases,indicating that the addition of SCHD/GCHD/ACHD accelerates the crystallization rate of PET.The results of TGA showed that the addition of SCHD/GCHD/ACHD did not change the thermal stability of PET.The observation results of isothermal crystallization morphology showed that the addition of SCHD/GCHD/ACHD makes the PET grain more finely broken,the crystallization state changes,and the crystallization ability weakens.