Solid-state Polycondensation Of Poly Research Articles

Kinetics of acetaldehyde removal in solid-state polycondensation of poly(ethylene terephthalate)

Kinetics of acetaldehyde removal in solid-state polycondensation of poly(ethylene terephthalate)

High-efficiency acetaldehyde removal during solid-state polycondensation of poly(ethylene terephthalate) assisted by supercritical carbon dioxide

The concentration of acetaldehyde (AA) is the main quality index of poly(ethylene terephthalate) (PET) used in food and drink packaging. A new method for AA removal has been developed by using supercritical carbon dioxide (scCO2) during the solid-state polycondensation of PET. The influence factors of AA removal including the temperature, pressure, reaction time and the size of pre-polymer particles are systematically studied in this work. The results indicate that it is a highly efficient way to obtain high molecular weight PET with relative low concentration of AA. Correspondingly, the polymerization degree of PET could increase from 27.9 to 85.6 while the concentration of AA reduces from 0.229 × 10−6 to 0.055 × 10−6 under the optimal operation conditions of 230 °C, 8 MPa and size of 0.30–0.45 mm. Thermodynamic performance tests show the increasing extent of PET crystallinity due to the fact that the plasticization of scCO2 is not obvious with extended reaction time, therefore the increasing crystallinity has no significant influence on AA removal. SEM observations reveal that the effects of scCO2-induced plasticization and swelling on PET increase significantly with the decrease of prepolymer size, and the surface of PET becomes more loose and porous in favor of the AA removal.

Effects of molecular weight and catalyst on stereoblock formation via solid state polycondensation of poly(lactic acid)

This work reports the synthesis of stereoblock poly(lactic acid) (sb-PLA) by solid state polymerization (SSP) using a combination of PLA enantiomers with low molecular weight, focusing on effects of catalyst and molecular weight of the enantiomers. It was revealed for the first time that the PLA enantiomers synthesized with a novel methanesulfonic acid (SO) catalyst form sb-PLA with higher molecular weight at a higher yield, whereas the PLA enantiomers synthesized with a widely used tin(II) (Sn) catalyst causes a significant side reaction resulting in a low yield. These phenomena would be characteristic of the sb-PLA synthesized via SSP, since the side reaction of the lactide formation is promoted by vigorous sublimation of the lactide under the conditions of high temperature and a low pressure used for the SSP process. Reaction mechanisms were proposed for the SSP using the two different catalysts, which successfully explained the present results. It was also demonstrated that the molecular weight of the starting PLA enantiomers significantly affects the final molecular weight and sc crystallinity of sb-PLA.

The Effect of Crystallization on the Solid State Polycondensation of Poly(L‐lactic Acid)

Melt solid polycondensation is an approach to increase the molecular weight of poly (L‐lactic acid) (PLLA). For this report, the effect of crystallization time of PLLA prepolymer on the molecular weight of the biomaterial was studied. In this process, PLLA prepolymer with a molecular weight of 18,000 was first prepared by the ordinary melt‐polycondensation process. The prepolymer was crystallized at 105°C for various times, and then heated at 135°C for 15–50 h for further solid state polycondensation (SSP). The differential scanning calorimetry (DSC) and viscosity measurements were used to characterize the crystalline properties and molecular weight of the resulting PLLA polymers, respectively. The results showed that the molecular weight of PLLA reached a maximum value under the condition of a crystallization time of 30 min and SSP of 35 h.

Solid-state polycondensation of poly(ethylene terephthalate) modified with isophthalic acid: kinetics and simulation

The kinetics for the solid-state polycondensation (SSP) of poly(ethylene terephthalate) modified with isophthalic acid at the protection of nitrogen gas was studied in the paper. A kinetic model controlled by the reversible chemical reactions and the three dimension diffusions of small molecule by-products has been established. The kinetic parameters of the SSP of PET at different temperatures, including the forward rate constants of transesterification reaction ( k 1) and esterification reaction ( k 2), the diffusion coefficients of EG ( D 1) and water ( D 2), the concentrations of EG ( g s) and water ( w s) on the surface of PET chips in SSP, and the activation energies of these kinetic parameters were obtained by experiments and solution of the model. Using the model and the kinetic parameters, the SSP of poly(ethylene terephthalate) modified with isophthalic acid can be simulated with good accuracy. In addition, the influences of nitrogen gas flow rate, the chip dimension and the carboxyl end-group concentration of the PET prepolymer on the molecular weight of PET after SSP, and the change of the EG concentration of PET chips with reaction time were also studied by simulation.

Solid‐state polycondensation of poly(ethylene terephthalate): Kinetics and mechanism

AbstractA numerical method to seek a solution for the solid‐state polycondensation (SSP) proces has been proposed to analyze the mechanism of SSP. Results expound that, for the industrial SSP process of PET, the overall reaction rate in a single pellet is appropriately simulated by the diffusion and reaction rate jointly controlling the model. From the core to the surface the SSP rate increase monotonically due to a gradual reduction of the concentration of such by‐products as ethylene glycol and water. However, the SSP rate at any location within the pellet is constrained between two purely reaction rate controlling cases. © 1995 John Wiley & Sons, Inc.

Modeling of poly(ethylene terephthalate) reactors. IX. Solid state polycondensation process

AbstractA mathematical model for simulation of industrial process of solid state polycondensation of poly(ethylene terephthalate) (PET) has been developed. The model eliminates errors evident in the earlier models by proper formulation. The model results have been validated by experimental data in the literature. It enables prediction of the influence of particle shape, size, temperature, etc. on the polycondensation process correctly in all different regimes of operation, apart from bringing out the importance of gas‐side resistance, influence of carrier gas, etc. for the first time.

Solid state polycondensation of poly(1,4-butyleneterephthalate).

The optimum reaction conditions in solid-state polycondensation of poly (1, 4-butylene terephthalate) (PBT) were investigated in order to obtain high molecular weight PBT. It was found that the solid-state polycondensation of PBT proceeds at a temperature in the range of 185 to 200°C under reduced pressure. This is due to the fact that the activation energy of the polycondensation reaction is 29.5kcal/mol and considerably smaller than that of the thermal decomposition reaction of PBT, i.e., ca. 40kcal/mol. To accelerate the reaction rate, it is important to carry out the polycondensation reaction at low humidity using PBT having a low carboxyl end group content and a large specific surface area.

Solid state polycondensation of poly(butylene terephthalate)

Solid state polycondensation of poly(butylene terephthalate) has been studied under vacuum at 200°C for various particle sizes. The effect of the process on intrinsic viscosity and number of end groups has been examined. The results suggest that the increasing of the number average molecular weight can be explained by a mechanism involving hydroxyl groups, which approach each other by diffusion until a limiting value of their concentration is attained.

Kinetics of thermally induced solid state polycondensation of poly(ethylene terephthalate)

AbstractA diffusional model was established to study the kinetics of thermally‐induced solid state polycondensation of poly(ethylene terephthalate). Diffusion through solid polymer is the rate controlling step when temperature is higher than 210°C and particle size is no smaller than 100 mesh. The activation energy is 30 Kcal/g mole. In polymerizing powders (20‐200 mesh), the crystallinity of prepolymer and its changes during the polymerization affect the diffusivity and thus the polymerization rate. The diffusivity was found to be linearly proportional to the mass fraction of the amorphous phase in PET polymer.