Liquid Phase Assisted Polyester Solid State Polycondensation

Solid state polycondensation(SSP) is the process taking place among the polymer chain end groups at the temperature between the melting point and glass transition point. According to the expand work of previous documents ,there are four limiting steps during SSP: the intrinsic kinetics of the chemical reaction; the diffusion of the reactive end groups; the interior diffusion and the surface diffusion.Affected by the chemical and physical diffusion,the long production period and annealing are the common problems for polyester SSP.This work was aimed to research the chemical reaction and physcical diffusion during the liquid phase assisted polyester SSP.Intrinsic viscosity measurement was used to study the influence of some parameters upon SSP,such as:reaction temperature, flow rate of inert gas, pellet sizes, porosity and pre-heated time. DSC analysis showed the melting point and cyrstallinity change at various reaction conditions.The mass fraction of small molecular and heat stablility information were reflected by TGA curves.The effect of tetradecane in SSP of PET pellets with temperatures range of 200-240℃was studied. As the intrinsic viscosity curves shown, the optimum reaction temperature was around 230℃. Using the DSC characterization method, the melting point increased along with the reaction temperature accordingly, reflecting the main polymer chains were lengthened effectively. Compared with traditional gas environmental SSP, the intrinsic viscosity curves of postpolymer obtained by dispersed phase SSP were always on the above. Measuring data showed there was no obvious change of the porosity during the dispersed phase SSP process. However, according to the analysis of mercury porosimeter, the porosity of postpolymer pellets after pretreatment with phenol-tetrachloroethane solution boomed from 4.89% to 7.08%, corresponding to the furthermore higher molecular weight PET. Therefore, swollen of polymer particles rather than the increase of porosity maybe the most significant reason of the rate enhancement ,due to the soaking effect of tetradecane.PBT pellets in tetradecane assisted SSP showed the higher reaction velocity. The number average molecular weight after dispersed phase SSP was about 85,000 compared with 70,000 via gas SSP. The melting point of dispersed phase SSP PBT acheived about 235℃, which was much higher than the ralated reports. According to SEM photos , obvious holes appeared after the soaking of tetradecane.PBT pellets in tetradecane assisted SSP showed the higher reaction velocity. The number average molecular weight after dispersed phase SSP was about 85,000 compared with 70,000 via gas SSP. The melting point of dispersed phase SSP PBT acheived about 235℃, which was much higher than the related reports. According to SEM photos , obvious holes appeared after the soaking of tetradecane. However,in the beginning,the crystallization temperature decreased and then increased along with reaction time.Silica oil could enhace the heat diffusion in the reacation system,in case of the annealing and agglomeration. Additionally, in melting phase diphenylketone the polyester would be well swollen ,therefore,the much higher IV polymer could be obtained.Hence,the mixture solvent,with 5g diphenylketone and 20ml silica oil,was choosen for liquid phase assisted SSP. In mixture solvent environment,the IV of PET increased much more rapidly compared to tetradecane.Turning to PBT, the IV curves was a little below the ones of tetradecane.The main reason for reaction acceleration maybe swollen by diphenylketone. In addition, crystallization temperature of PET during mixture solvent assisted SSP disappeared, indicating that the mixture solvent had already destroyed the crystallization configuration,which maybe the another reason.