The Research Of Vacuum Solid State Polymerization And Crystallization Behavior Of Hybrid Titanium Catalyst Based Pet

Polyethylene terephthalate（PET）is widely used in industry,among which high molecular weight PET is widely used in plastic bottle packaging,industrial yarn,polyester cord fabric,aerospace and other fields.There are three main methods to increase the molecular weight of PET polyester:melt polycondensation,chemical viscosity increasing and solid phase polycondensation.At present,solid phase polycondensation is widely used because of its mild reaction conditions,simple process,effective inhibition of side reactions and good viscosity increasing effect.At present,most PET is synthesized with antimony based catalysts,and antimony is a heavy metal element,which will endanger human health and cause environmental pollution in the process of PET use.Therefore,environment-friendly titanium based catalysts and PET synthesized by them have become the focus of researchers and industry in recent years.Previous studies have shown that polymerization catalysts play an important role in the rate of solid-state polycondensation and the effect of viscosity enhancement,Therefore,in this paper,the influence and mechanism of antimony and titanium based catalysts on the viscosity enhancement of PET were systematically studied.This research group adopts the DH-Hy Ti-LCEJ titanium based polyester catalyst which has been independently developed and has been large-scale produced,and has prepared a new titanium based polyester（BR-PET）on the continuous production line.Compared with the traditional antimony based polyester（Sb-PET）,it is more green and environmentally friendly and has stable performance.In this paper,titanium based polyester and antimony based polyester were compared.Solid phase viscosity enhancement was carried out in vacuum oven and vacuum drum.The optimal polycondensation conditions were determined by adjusting the process conditions（temperature and time）.The effects of basic properties of raw materials（catalyst type,particle size,carboxyl end group content,initial crystallinity,etc.）on the viscosity enhancement effect of polyester and the structure and performance of the product were studied.A comparative analysis was carried out through a series of characterization,The main research results are as follows:（1）The best temperature for the pre crystallization of polyester was determined by experiments to be 120°C.According to the characteristics of the pilot test process,the heating program for the pre crystallization drying was established:after holding at90°C for 1 h,the temperature was raised to 120°C for 3 h at 1°C min^-1,turned over every 1 h,then the temperature was raised to 160°C for 6-8 h at 1°C min^-1,and finally the temperature was raised to the solid phase polycondensation reaction temperature for tackifying reaction.（2）The influence of the basic properties of raw materials on the viscosity increase of polyester was studied.After 10 hours of polycondensation at 225°C of small/large particle size BR-PET polyester with the same initial viscosity,it was found that the viscosity increase effect of smaller particle size polyester was better;Compared with the viscosity difference of BR-PET polyester with different carboxyl end group content(C_COOH is 7 mol t^-1 and 21.7 mol t^-1 respectively)after viscosity increasing under the same conditions,it was confirmed that the polyester with higher carboxyl end group content had better viscosity increasing effect;Further comparison between Sb-PET(C_COOH=27 mol t^-1)and BR-PET(C_COOH=21.7 mol t^-1)shows that the viscosity of Sb-PET is increased from 0.633 d L g^-1 to 1.039 d L g^-1,and the viscosity of BR-PET is increased from 0.634 d L g^-1 to 1.099 d L g^-1.The viscosity increasing effect of titanium based polyester is better than that of antimony based polyester under the condition of lower end condensation content,which indicates that even under the condition of lower end carboxyl content,Titanium based catalysts can bond with multiple molecular chains of polyester due to their unique lamellar structure and larger specific surface area,effectively enriching active end groups and improving the solid-state polycondensation rate.（3）In order to further explore the mechanism of titanium based polyester catalyst in the process of polyester viscosity increasing,the crystallization behavior of polyester with different catalysts was studied.The main results show that with the increase of molecular weight,the decreasing range of melt crystallization temperature of BR-PET polyester（9.77°C）is smaller than that of Sb-PET polyester（14.36°C）;Through the study of non-isothermal crystallization kinetics,it was found that with the increase of cooling rate,the falling range of melt crystallization temperature of BR-PET polyester（12.4°C）was smaller than that of Sb-PET polyester（31.05°C）,and its melt crystallization temperature was less affected by molecular weight and cooling rate;Through the study of dynamic thermo mechanical analyzer,it was found that the storage modulus of BR-PET polyester was higher than that of Sb-PET polyester under the same molecular weight,and the rigidity was greater.Based on the above results,it can be inferred that the action mechanism of the titanium catalyst system:because the self-made titanium catalyst system is a sheet micro nano structure,which can be uniformly dispersed in the polyester,bonded with multiple molecular chains,and the entanglement ability is increased,it shows a faster solid state polycondensation rate.