The forced gas sweeping process for semibatch melt polycondensation of poly(ethylene terephthalate)

The experimental and modeling studies are presented on the melt polycondensation of poly(ethylene terephthalate) by a gas sweeping process. In this process, low molecular weight prepolymer is polymerized to a higher molecular weight polymer in a molten state at ambient pressure as ethylene glycol is removed by nitrogen gas bubbles injected directly to the polymer melt through a metal tube. In the temperature range of 260–280°C, the rate of polymerization by the gas sweeping process is quite comparable to that of conventional high vacuum process. The effects of nitrogen gas flow rate and reaction temperature on polymerization rate and polymer molecular weight were investigated. Polymer molecular weight increases with an increase in gas flow rate up to certain limits. A dynamic mass transfer–reaction model has been developed, and the agreement between experimental data and model simulations was quite satisfactory. The effect of ethylene glycol bubble nucleation on the polymerization has also been investigated. It was observed that the presence of nucleated ethylene glycol bubbles induced by the bulk motion of polymer melt has negligible impact on the polymerization rate and polymer molecular weight. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1388–1400, 2001     

Modification of poly(ethylene terephthalate) by combination of reactive extrusion and followed solid‐state polycondensation for melt foaming

A combination of reactive extrusion and followed solid‐state polycondensation (SSP) was applied to modify the virgin fiber grade poly(ethylene terephthalate) (v‐PET) and recycled bottle‐grade PET (r‐PET) for melt foaming. Pyromellitic dianhydride (PMDA) and triglycidyl isocyanurate (TGIC) were chosen as the modifiers for the reactive extrusion performed in a twin‐screw extruder. For comparison, commercially available chain extender ADR JONCRYL ADR‐4370‐S was also used. The characterizations of the intrinsic viscosity, i.e., [η], and rheological properties whose changes were correlated to the long chain branches introduced in the molecular structure were performed on the modified PET to evaluate their chain extension extent. The results revealed that the [η] of 1.37 dL/g was obtained for PMDA modified v‐PET while that of 1.15 dL/g for TGIC modified r‐PET. Such difference was attributed to the different reactivity of the two chain extenders with the two types of PET. Increases in shear viscosity and storage modulus, and the high pronounced shear thinning behavior were also observed in the modified PET. Finally, the foamability of the certain modified PET was verified by the batch melt foaming experiments. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42708.     

Phase equilibrium characteristics of supercritical CO2/poly(ethylene terephthalate) binary system

The solubility of carbon dioxide in poly (ethylene terephthalate) (PET) at high pressure and elevated temperature conditions was investigated for a better understanding of the phase equilibrium characteristics of supercritical CO₂/PET binary system and useful data for the process development of the supercritical fluid dyeing. Based on the principle of pressure decaying, a novel experimental apparatus suitable to high pressure and high temperature measurement was established. The solubilities of CO₂ in PET were measured with the apparatus at temperatures of 110, 120, and 130°C and pressures up to 30.0 MPa. The results show that the solubility of CO₂ in PET increases with the increase of pressure and CO₂ density, respectively, at a constant temperature, whereas it decreases with the increase of temperature at a constant pressure. The Sanchez‐Lacombe equation of state (S‐L EOS) was used to correlate the experimental data. The calculated results are in good agreement with the experimental ones. The average absolute relative derivation (AARD) is less than 3.91%. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Impact modification of poly(ethylene terephthalate)

The tensile and impact resistance of impact‐modified poly(ethylene terephthalate) (PET) is investigated. The impact modifiers are polyolefin‐based elastomers or elastomer blends containing glycidyl methacrylate moieties to improve the adhesion with the polyester. The tensile properties are measured on injection molded specimens at room temperature while the Izod impact strength is measured from ?40 to 20°C. The blend morphology is observed by scanning electron microscopy and the dispersed phase average diameter is determined by image analysis. The relation between the impact resistance and the phase morphology is discussed, and the critical ligament size for PET is determined. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2919–2932, 2003     

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(sc CO2) 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 sc CO_2 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 sc CO_(2-) 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.     

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

A 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(ethylene terephthalate): Kinetics and mechanism

A 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.     

Photochemical surface modification of poly(ethylene terephthalate)

To elucidate the role of chemical interactions in the promotion of metal–polymer adhesion, a poly(ethylene terephalate)/copper system was studied. Surface photografting of unsaturated monomers containing different chemical functional groups onto a three-mil poly(ethylene terephthalate) film provided a means of examining a variety of copper-polymer interfaces. Initial graft verification was accomplished via contact angle measurements. Adhesion strengths to vacuum-deposited copper were determined using 90° peel tests. Graft analysis, as well as investigation of the interfacial interaction between copper and the grafted moieties, was accomplished using X-ray photoelectron spectroscopy.     

Optimization of the polycondensation stage of poly(ethylene terephthalate) reactors

A general kinetic scheme for the polycondensation step of the PET formation has been used to establish the mole balance equations of various functional groups in batch reactors. An objective function has been defined which aims to attain a desired degree of polymerization in the shortest time, has a specified level of diethylene glycol group content, and minimizes the other side products. Using the control vector iteration procedure, an optimum temperature profile has been calculated. The computations suggest that a high temperature should be used initially which must be lowered as the time of reaction increases for limiting the formation of side products.     

Plasma-solution modification of poly(ethylene terephthalate) fibre material

Plasma-chemical modification of polyester thread ensures formation of active hydroxyl and carboxyl groups on its surface, necessary for fixation of functional preparations whose application on the surface of fibre material gives it new properties — water-repellent, antimicrobial, deodorizing, etc. A comparison of the efficacy of plasma-chemical and chemical methods of surface activation of polyester fibre material shows that in the first case, greater losses of strength are observed in the thread. However, in the case of plasma-chemical activation, an additional number of carbonyl/carboxyl groups is formed, which is an important advantage in selecting the method of activating polyester materials.     

聚酯(PET)的混料和共混改性

就聚酯加工应用中混料和共混改性一些基本的技术原理进行讨论 ,如间歇法生产中不同批次的混料方法 ,新料与回收料的共混 ,白料与色母料的共混 ,还有PET改性共混涉及到的相容、结晶相分离等问题     

Effect of antimony catalyst on solid-state polycondensation of poly(ethylene terephthalate)

The effect of antimony trioxide (Sb₂O₃) catalyst on the solid-state polycondensation (SSP) of poly(ethylene terephthalate) (PET) has been rigorously studied. It has been determined that the rate constant increases, while the activation energy decreases, linearly with increasing catalyst concentration within the range of 0-100 ppm Sb. The SSP rate reaches its maximum value at about 150 ppm Sb. The activation energies are 30.7 and 23.3 kcal/mol respectively for the uncatalyzed and fully catalyzed SSP. The frequency factor decreases with increasing catalyst concentration due to the decreased mobility of catalyzed end groups. A mechanism of Sb catalysis has been proposed to explain these observations.     

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

A 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.     

Melt polycondensation of poly(ethylene terephthalate) in a rotating disk reactor

A multicompartment model is proposed for a semibatch melt polycondensation of poly(ethylene terephthalate) in a rotating disk polymerization reactor and compared with laboratory experimental data. The reactor is a horizontal cylindrical vessel with a horizontal shaft on which multiple disks are mounted. The reactor is assumed to comprise N equal sized compartments and each compartment consists of a film phase on the rotating disk and a bulk phase in which disks are partially immersed. The effects of disk rotating speed, number of disks, reaction temperature, and pressure were investigated. It was observed that ethylene glycol is predominantly removed from thin polymer layers on the rotating disks and the enhanced interfacial area exerted by ethylene glycol bubbles accounts for about 30–50% of the total available interfacial mass transfer area. Although the rate of polymerization increases as more disks are used, the maximum number of disks in a reactor must be determined properly in order to prevent the formation of thick polymer films that result in a reduced specific interfacial area and reduced polymerization efficiency. At a fixed reaction pressure, the equilibrium conversion is reached but the rate of reaction can be further increased by increasing the reaction temperature. The results of the proposed multicompartment model are also compared with those predicted by a simple one-parameter model. © 1995 John Wiley & Sons, Inc.     

Incorporation of disperse dye in N,N-dimethylacrylamide modified poly(ethylene terephthalate) fibers with supercritical CO2

The effects of modifying agents and dyeing conditions of dispersed dyes for PET films and fibers has been thoroughly studied. This research reports on the dye incorporation process of non-modified and N,N-dimethylacrylamide modified PET fibers with supercritical CO₂. Spectral analysis in the infrared region to the modified PET fibers showed peaks of the modifier, but the thermal stability of the modified fiber did not show variation when compared with the non-modified. The amount of disperse dye incorporated in the PET fibers was determined by UV–Vis spectroscopy at 579 nm through the dye extraction using N,N-dimethylformamide. A 2⁴ factorial design was realized with the purpose to study the influence of variables in the dye incorporation process as well as their interaction effects. The pre-treatment of the PET fibers with N,N-dimethylacrylamide increases the amount of incorporated dye 3.8 times, in average. The main effect on the dye incorporation was the dyeing time for the modified fibers, but for the non-modified fibers, the pressure and the temperature presented analogous main effect     

酯交换-熔融缩聚法合成PEF工艺及性能研究

以2,5-呋喃二甲酸二甲酯(DMFD)和乙二醇为原料,通过酯交换-熔融缩聚法合成了聚呋喃二甲酸乙二醇酯(PEF),研究了催化剂用量、酯交换温度及缩聚温度对反应速率的影响,利用红外(FTIR)和核磁(NMR)对合成的PEF结构进行了表征,并对合成的PEF进行了差示扫描量热(DSC)和热失重(TGA)测试.研究结果表明,酯...     

Effect of CO2 on crystallization kinetics of poly(ethylene terephthalate)

The effect of CO₂ on the isothermal crystallization kinetics of poly(ethylene terephthalate), PET, was investigated using a high‐pressure differential scanning calorimeter (DSC), which performed calorimetric measurements while keeping the polymer in contact with presurized CO₂. It was found that the crystallization rate followed the Avrami equation with values of the crystallization kinetic constant dependent on the crystallization temperature and concentration of CO₂ in PET. The presence of CO₂ in the PET increased its overall crystallization rate. CO₂ also decreased the glass transition temperature, T_g, and the melting temperature, T_m. As a result, the observed changes in crystallization rate caused by CO₂ can be qualitatively predicted from the magnitude of T_g depression and that of the equilibrium melting temperature, T_m⁰.     

Effect of pressure on CO2 transport in poly(ethylene terephthalate)

The CO₂ solubility, permeability, and diffusion time lag in poly(ethylene terephthalate) are reported at 35° and 65°C for CO₂ pressures ranging from 0.07 to 20 atm. The subatmospheric time lag and permeability measurements were made with a glass system at North Carolina State University, while the measurements between 1 and 20 atmospheres, using an identical polymer sample, were made at The University of Texas with a metal system capable of tolerating gauge pressures up to 30 atm. The measured solubility, permeability, and time lag all show strong deviations from the well-known simple expressions for gases in rubbery polymers. The solubility isotherm is non-linear in pressure, and both θ and P are quite pressure dependent, with each showing tendencies to approach low and high pressure asymptotic limits. These effects decrease as temperature increases and would be expected to disappear at or near the glass transition where the amorphous regions become rubbery. The importance of reporting the pressure levels used in transport measurements is emphasized for gas/glassy polymer systems where transport process do not follow linear laws.     

Film reaction kinetics for melt postpolycondensation of poly(ethylene terephthalate)

Melt polycondensation has recently been reported to prepare high-viscosity poly(ethylene terephthalate) (PET), the reaction efficiency is greatly improved in over 10-folds compared with conventional solid state polycondensation (SSP). Melt postpolycondensation of common PET chips was conducted in specified film thickness to obtain industrial PET. Based on the investigation of reaction conditions, film reaction kinetics were determined in the principle of end groups analysis. It was positively regulated that the intrinsic viscosity of PET could be achieved in condition of high vacuum, thin melt film and proper temperature, degradation reaction would be increased at exorbitant temperature. An apparent reaction kinetic model was proposed and was verified by experiments. Results indicated the activation energy of melt postpolycondensation of PET was 88.22 kJ/mol and the reaction rate constant was significant higher than that of solid state polycondensation.     

Effect of drawing temperature on mesomorphic transitions of oriented poly(ethylene terephthalate) fibers exposed to supercritical CO2

Samples of partially oriented yarn (POY) PET fibers were uniaxially drawn at 23, 68 °C (cold drawing) and 100 °C (hot drawing) and then exposed to the supercritical carbon dioxide (scCO₂) without tension at a temperature of 80 °C and a pressure of 220 bar. The effect of drawing temperature on the evolution of mesomorphic phases and the structural changes under exposure to scCO₂ were investigated by differential scanning calorimetry (DSC), Fourier transform infrared (FTIR), and wide-angle X-ray diffraction. The orientation factor of the samples was measured using a polarizing microscope. A good correlation was obtained between the results of various analyses. The results illustrate that evolution of structure strongly depends on both process temperature and post-treatment by scCO₂ exposure. The latter process leads to plasticization and reduced glass transition temperature of the samples, thus inducing structural changes in the fibers.