Reaction Kinetics and Simulations for Solid-State Polymerization of Poly(ethylene terephthalate)

Abstract

A comprehensive model for solid-state polymerization of poly(ethylene terephthalate) was developed from analyzing the similarities and the differences between solid-state and melt polymerization. Considering the end groups diffusion limitation and the modification of concentrations of end groups and byproducts in the amorphous phase, a system of mass transfer and balance equations suitable for the solid-state polymerization of PET were obtained, based on simplifying the reaction kinetics of melt polymerization of PET. The degradation and other side reactions neglected in the earlier models for the solid-state polymerization of PET were included in the model. This simulation gave a quantitative prediction in the effect of temperature, particle size, starting molecular weight, and ratio of end groups on the degree of polymerization of products during the solid-state polymerization of poly(ethylene terephthalate). These simulation results were in agreement with experiments.

A Review of Modeling of Diffusion Controlled Polymerization Reactions

“…In contrast, if the amorphous parts of the matrix are distributed in such a way that the reactive end groups are well dispersed, and if the distance they need to diffuse in order to react with neighboring groups is short, then the rate of reaction will be relatively high. In order to describe the effect of the end group diffusion limitation on both esterification and polycondensation reaction, Wu et al [186] used a model similar to that proposed by Chiu et al [51] for free radical polymerization reactions. Both reactions rates were calculated as a function of a diffusion parameter, Q, defined in a similar way to Equation (99), as:…”

Properties of Poly(ethylene terephthalate)/Layered Silicate Nanocomposites Prepared by Two-Step Polymerization Procedure

“…The precursors were heated at 140 • C for 2 h prior to the SSP process for the following purposes. [9][10][11] The water molecule remaining in the sample would cause degradation of PET during the reaction, so the samples must be dried vigorously. Moreover, by the crystallization of PET during the heating process, the reactive chain ends and catalysts are considered to be concentrated into the amorphous region, which is necessary for the progress of SSP.…”

“…A solid-state polymerization (SSP) process can be applied to increase the average molecular weight of PET without being affected by the viscosity of the reactants. [9][10][11] In the SSP process, the crystallized PET prepolymer is heated at a temperature below the crystalline melting point (T m ) but well-above the glass transition temperature (T g ) under a flow of inert gas or under vacuum. The hydroxyethyl end groups of the PET prepolymer are considered to be concentrated into the amorphous region during the crystallization process.…”

Solid‐State Polymerization of Poly(ethylene terephthalate): The Effect of Water Vapor in the Carrier Gas

“…Most published studies regard the modeling and analysis of the diffusion phenomena inside the polymer particles, [7][8][9][10][11][12][13][14][15][16][17][18][19][20] neglecting mass transfer limitations on the particles surface, which can be associated to the properties of the gas phase. [21][22][23] Despite that, although particle models are fundamental to provide understanding about how reaction kinetics interacts with transfer phenomena, external mass transfer resistance can exert enormous influence on the solutions obtained with the help of diffusion-reaction models.…”

“…As already mentioned, the large majority of available PET particle models neglect the existence of mass transfer resistance on the particles surface; however, even when this mass transfer resistance is considered, constitutive equations derived from other particulate systems are used for prediction of mass transfer coefficients without any independent experimental validation. [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] Model fitting is usually attained through re-estimation of diffusion coefficients within the polymer matrix, using experimental data obtained from sorption experiments as initial guesses. [25][26][27][28] In summary, it seems clear that the main focus of the PET SSP literature regarding mass transfer phenomena has been the polymer-side diffusion mechanism, which does not necessarily describe continuous industrial PET processes appropriately.…”