| Polyester materials are widely used in textiles,garments,packaging,rope nets,webbing,electronic devices and automobiles due to their excellent physical,chemical properties and mechanical properties.In addition to PET for textile and garments,which can be directly prepared by melt polycondensation,PET materials for other uses usually require further viscosity-increasing reaction.Solid phase polycondensation is commonly used in the industry to prepare polyethylene terephthalate(PET)with high intrinsic viscosity.The temperature of solid phase polycondensation reaction is below the melting point,therefore the PET chain growth rate,reaction efficiency is low.The solid phase polycondensation reaction process is long and high equipment investment cost.Compared with the traditional solid phase polycondensation technology,the melt polycondensation reaction which can make PET reach higher molecular weight in short time,has high efficiency,and the product can be processed directly,so the process flow and production energy consumption reduced.The properties of melt film affect the removal of small molecular substances,especially the thickness and composition of the film seriously affect the polycondensation and product's properties of the melt polycondensation.In this paper,PET film with different thickness was prepared by textile yarn PET,participated polycondensation reaction after static melting.The effect of PET post-polycondensation under different process conditions was investigated.The mechanism of PET melt polycondensation was discussed,the apparent kinetics model of PET melt polycondensation was established combined with end group content and color value analysis,The results show that the post-melting polycondensation efficiency of PET increases with the decrease of system vacuum pressure and melt film thickness,but the effect of temperature is more complicated.When temperature range from 270? to 280?,the intrinsic viscosity of PET increases with increasing temperature,but the intrinsic viscosity increases less during the same time if temperature reaches 290?,because of the degradation reaction is enhanced.At the same time,the lower temperature,pressure and thinner thickness of the melt film,the better performance with low carboxyl content and white color.The experimental values under different polycondensation conditions are consistent with the results of the polycondensation apparent kinetic model.The reaction rate constant further validates the effect of reaction conditions on the polycondensation process.Three kinds of dihydric phenol were mixed with PET slices by dissolution method and the obtained mixture was prepared for post-polycondensation.The effects of addition diphenolic components on the intrinsic viscosity and properties of modified PET were investigated.It shows that the addition of a small amount of diphenolic compounds with different chemical structures could improve the ability of post-polycondensation.The intrinsic viscosity of PET modified by diphenol was decreased if more diphenol added.Therefore,it was speculated that diphenol was involved in the chain growth reaction of PET,so the intrinsic viscosity of PET increased rapidly.However,the degradation reaction was enhanced with the higher content of diphenol,so the intrinsic viscosity increasing was decreased.The results of studying PET modified by 4,4 dihydroxydiphenyl sulfide(TDP)through infrared spectroscopy analysis,show that the conjugated system of benzene ring and ester group in the structure of diphenol makes carbonyl group move in the direction of low wave number.Analysis of the crystallization and thermal properties of products after post-polycondensation,show that small molecules of diphenols could inhibit the crystallization properties of PET,reduce crystallization rate and crystallinity.TDP has the greatest influence on the crystallization performance of PET,and other diphenol has no significant influence on the thermal stability of PET. |
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