Study On Modification Of PET By Solid-State Polycondensation And Thermal Degradation

Poly(ethylene terephalate)(PET)was widely used,due to its excellent performance.The solid-state polycondensation with the advantages of low energy consumption,less side reaction and good product quality,became the effective method for producing high molecular weight PET.Moreover,solid-state polymerizations can also be applied for the purpose of preparing copolymer materials.This process was called solid-state modification(SSM)of polymeric materials.The reaction conditions were moderate,the SSM method provided the ability to obtain copolyesters with retained crystallinity and enhanced the ductility of copolyester,SSM can as a novel copolymerization concept.The melt delivery process was the key to achieve continuous polymerization and direct spinning.It was critical for viscosity loss and melt degradation to control the factors that melt residence time and melt temperature,which directly related to the melt spinning.In the paper,the kinetics of solid-state polycondensation reaction was studied by different conditions.Copolyesters based on Poly(ethylene terephalate)(PET)and 1,10-decanediol were prepared by solid-state modification(SSM).And the factors that affect melt quality in PET melt delivery process were discussed.The main researches and results were shown as followed:(1)The solid-state polymerization reaction(SSP)of polyethylene terephthalate(PET)was carried out under vacuum or nitrogen conditions.And,based on the changes of intrinsic viscosity and the carboxyl group content of PET,the reaction kinetics of PET were examined.The experiment showed that the intrinsic viscosity of PET chips increased with the increament of the reaction temperature and time,however the carboxyl contents were opposite.In the whole reaction process,intrinsic viscosity increased slowly at the beginning of reaction for the lower temperature.But with the increase of the reaction temperature,by-products were removed from the reaction system timely by nitrogen or vacuum,so the intrinsic viscosity increased rapidly.When the temperature was higher than 230 ?,intrinsic viscosity growth trend got slower,for the diffusion of by-products were easily bound to be limited by the macromolecular PET chains.Besides,this study was also associated with the kinetic model,the results showed that the solid-state polymerization reaction was consistent with second order kinetic model,at the same time,the solid-state polymerization reaction rate constant and the activation energy were calculated in the study according to Arrhenius equation.(2)Copolyesters based on Poly(ethylene terephalate)(PET)and 1,10-decanediol were prepared by solid-state modification(SSM).The chemical incorporation of the 1,10-decanediol into the backbone of the PET was proven using various techniques.The resultant materials were characterized to analyze the structure,intrinsic viscosity,thermal properties and crystallization properties copolyesters.The results that 1,10-decanediol was incorporated into the backbone of an existing polymer by two consecutive trans-reactions,intrinsic viscosity changes from low to high.The glass transition temperature and melting point of the copolymers decreased with the increase of the amount of 1,10-decanediol.1,10-decanediol did not participate in crystallization,PET chain involved in crystallization.(3)In the melt delivery process,the melt viscosity was mainly influenced by the initial melt intrinsic viscosity,temperature and time.The changes of intrinsity viscosity,carboxyl content and hue with reaction conditions were studied for different intrinsic viscosity PET chips in the melt state.The results showed that the intrinsic viscosity of PET chips decreased with the increament of the reaction temperature and time,however the carboxyl contents were opposite.As the degradation was severe,increasing the hue of the value b caused that the samples color were yellow.The lower of the initial melt intrinsic viscosity increased degradation comparing to high intrinsic viscosity,that the intrinsic viscosity fluctuates greatly.Liquid state polycondensation PET with degradation seriously compared to solid-state polycondensation PET.