Sorption and transport of CO2 in poly(ethylene terephthalate) crystallized by sorption of high-pressure CO2

Sorption and permeation of CO₂ in poly(ethylene terephthalate) crystallized by sorption of high-pressure CO₂ were examined below 1 atm at temperatures from 15 to 65°C. A large solubility and a high permeability of CO₂ in this specimen were observed compared to poly(ethylene terephthalate) crystallized by thermal annealing to a similar degree. A large unrelaxed volume is expected to be left in the specimen after removal of high-pressure CO₂ compared to the data of other PET samples. The thermal history during the measurements up to 65°C, which causes relaxation of the specimen, was shown to decrease CO₂ solubility. On the other hand, permeation data after annealing show not only decreased permeability but also increased apparent diffusivity. The results mean a lower mobility of gases sorbed in the unrelaxed volume than that of ordinarily dissolved gases, which corresponds to the partial immobilization model.     

Glass transition and cold crystallization in carbon dioxide treated poly(ethylene terephthalate)

An amorphous poly(ethylene terephthalate) (aPET) and a semicrystalline poly(ethylene terephthalate) obtained through the annealing of aPET at 110°C for 40 min (aPET‐110‐40) were treated in carbon dioxide (CO₂) at 1500 psi and 35°C for 1 h followed by treatment in a vacuum for various times to make samples containing various amount of CO₂ residues in these two CO₂‐treated samples. Glass transition and cold crystallization as a function of the amount of CO₂ residues in these two CO₂‐treated samples were investigated by temperature‐modulated differential scanning calorimetry (TMDSC) and dynamic mechanical analysis (DMA). The CO₂ residues were found to not only depress the glass‐transition temperature (T_g) but also facilitate cold crystallization in both samples. The depressed T_g in both CO₂‐treated poly(ethylene terephthalate) samples was roughly inversely proportional to amount of CO₂ residues and was independent of the crystallinity of the poly(ethylene terephthalate) sample. The nonreversing curves of TMDSC data clearly indicated that both samples exhibited a big overshoot peak around the glass transition. This overshoot peak occurred at lower temperatures and was smaller in magnitude for samples containing more CO₂ residues. The TMDSC nonreversing curves also indicated that aPET exhibited a clear cold‐crystallization exotherm at 120.0°C, but aPET‐110‐40 exhibited two cold‐crystallization exotherms at 109.2 and 127.4°C. The two cold crystallizations in the CO₂‐treated aPET‐110‐40 became one after vacuum treatment. The DMA data exhibited multiple tan δ peaks in both CO₂‐treated poly(ethylene terephthalate) samples. These multiple tan δ peaks, attributed to multiple amorphous phases, tended to shift to higher temperatures for longer vacuum times. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of poly(ethylene glycol) on the solid‐state polymerization of poly(ethylene terephthalate)

Poly(ethylene glycol) (PEG) and end‐capped poly(ethylene glycol) (poly(ethylene glycol) dimethyl ether (PEGDME)) of number average molecular weight 1000 g mol^?1 was melt blended with poly(ethylene terephthalate) (PET) oligomer. NMR, DSC and WAXS techniques characterized the structure and morphology of the blends. Both these samples show reduction in T_g and similar crystallization behavior. Solid‐state polymerization (SSP) was performed on these blend samples using Sb₂O₃ as catalyst under reduced pressure at temperatures below the melting point of the samples. Inherent viscosity data indicate that for the blend sample with PEG there is enhancement of SSP rate, while for the sample with PEGDME the SSP rate is suppressed. NMR data showed that PEG is incorporated into the PET chain, while PEGDME does not react with PET. Copyright © 2005 Society of Chemical Industry     

Effects of pH and Neutral Salts on the Adsorption of the Poly(ethylene glycol terephthalate) Condensates Toward Poly(ethylene terephthalate) Fiber

This study deals with the effects of pH and neutral salts on the adsorption of PET fiber with four kinds of poly(ethylene glycol terephthalate) condensated from dimethyl terephthalate (DMT) and poly(ethylene glycol) (PEG). The surface properties of the aqueous solution, the contact angle of polyol‐treated PET fabrics, and its parameters were also discussed. The pH of the solution or the adding of neutral salt in the polyol solution largely affected the contact angle of polyol‐treated PET fabrics as well as the surface tension of the solution. A lower pH of the polyol solution or adding neutral salts in the solution showed a lower surface tension and a lower contact angle that resulted in a better adsorption between polyol and poly(ethylene terephthalate) fibers. The lower pH of the solutions and a higher valence of the added neutral salt in the solution showed a largely positive effect on the adsorption parameters, and the order of effectiveness is Al₂(SO₄)₃ > MgSO₄ > Na₂SO₄.     

Crystallization kinetics of poly(1,4‐butylene‐co‐ethylene terephthalate)

The crystallization kinetics of poly(butylene terephthalate) (PBT), poly(ethylene terephthalate) (PET), and their copolymers poly(1,4‐butylene‐co‐ethylene terephthalate) (PBET) containing 70/30, 65/35 and 60/40 molar ratios of 1,4‐butanediol/ethylene glycol were investigated using differential scanning calorimetry (DSC) at crystallization temperatures (T_c) which were 35–90 °C below equilibrium melting temperature . Although these copolymers contain both monomers in high proportion, DSC data revealed for copolymer crystallization behaviour. The reason for such copolymers being able to crystallize could be due to the similar chemical structures of 1,4‐butanediol and ethylene glycol. DSC results for isothermal crystallization revealed that random copolymers had a lower degree of crystallinity and lower crystallite growth rate than those of homopolymers. DSC heating scans, after completion of isothermal crystallization, showed triple melting endotherms for all these polyesters, similar to those of other polymers as reported in the literature. The crystallization isotherms followed the Avrami equation with an exponent n of 2–2.5 for PET and 2.5–3.0 for PBT and PBETs. Analyses of the Lauritzen–Hoffman equation for DSC isothermal crystallization data revealed that PBT and PET had higher growth rate constant G_o, and nucleation constant K_g than those of PBET copolymers. © 2001 Society of Chemical Industry     

Controlling sandwich‐structure of PET microcellular foams using coupling of CO2 diffusion and induced crystallization

Controlling sandwich‐structure of poly(ethylene terephthalate) (PET) microcellular foams using coupling of CO₂ diffusion and CO₂‐induced crystallization is presented in this article. The intrinsic kinetics of CO₂‐induced crystallization of amorphous PET at 25°C and different CO₂ pressures were detected using in situ high‐pressure Fourier transform infrared spectroscopy and correlated by Avrami equation. Sorption of CO₂ in PET was measured using magnetic suspension balance and the diffusivity determined by Fick's second law. A model coupling CO₂ diffusion in and CO₂‐induced crystallization of PET was proposed to calculate the CO₂ concentration as well as crystallinity distributions in PET sheet at different saturation times. It was revealed that a sandwich crystallization structure could be built in PET sheet, based on which a solid‐state foaming process was used to manipulate the sandwich‐structure of PET microcellular foams with two microcellular or even ultra‐microcellular foamed crystalline layers outside and a microcellular foamed amorphous layer inside. © 2011 American Institute of Chemical Engineers AIChE J, 58: 2512–2523, 2012     

Study on the alcoholysis of aromatic polyesters and related esters using a high-pressure calorimeter

Summary The heat of base-catalyzed alcoholysis of poly(ethylene terephthalate) (PET) and poly(ethylene 2,6-naphthalenedicarboxylate) (PEN) as well as several related aromatic and aliphatic esters has been measured using a high-pressure calorimeter. The process is essentially thermoneutral, and heats of CH₃ONa-catalyzed methanolysis of PET and PEN are +1.8±0.6 and +9.3±0.2 kJ/mol-carboxyl group, respectively. Furthermore, the heats of Zn(OCOCH₃)₂-catalyzed alcoholysis of PET with ethylene glycol and benzyl alcohol are also calculated as +5.8±0.2 and +6.6±0.8 kJ/mol-carboxyl group, respectively. These values are comparable to those for ethyl esters of p-substituted benzoic acids and propionic acid. Received: 15 December 1998/Revised version: 22 January 1999/Accepted: 29 January 1999     

Glycolysis of poly(ethylene terephthalate) wastes in xylene

To reclaim the monomers or prepare intermediates suitable for other polymers zinc acetate catalayzed glycolysis of waste poly(ethylene terephthalate) (PET) was carried out with ethylene or propylene glycol, with PET/glycol molar ratios of1 : 0.5–1 : 3, in xylene at 170–245°C. During the multiphase reaction, depolymerization products transferred to the xylene medium from the dispersed PET/glycol droplets, shifting the equilibrium to glycolysis. Best results were obtained from the ethylene glycol (EG) reaction at 220°C, which yielded 80 mol % bis-2-hydroxyethyl terephthalate monomer and 20 mol % dimer fractions in quite pure crystalline form. Other advantages of employment of xylene in glycolysis of PET were improvement of mixing at high PET/EG ratios and recycling possibility of excess glycol, which separates from the xylene phase at low temperatures. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2311–2319, 1998     

Effect of alkali on filaments of poly(ethylene terephthalate) and its copolyesters. II. Presence of quaternary ammonium salt in the alkali-bath

Influence of alkyl (C₁₂–C₁₄)-dimethyl-benzyl ammonium chloride in the solution of sodium hydroxide on the hydrolysis of poly(ethylene terephthalate) (PET), anionically modified poly(ethylene terephthalate) copolyster (CDP), and block polymer of poly(ethylene terephthalate)-poly(ethylene glycol) (EDP), has been studied under a variety of proportions, concentrations, time and temperature of reaction, M : L ratio, etc. Mechanical properties of treated polymeric materials are evaluated. Hydrolysis of two polymers in the same bath is compared with that in separate baths.     

Melt polymerization of copoly(ethylene terephthalate–imide)s and thermal properties

Copoly(ethylene terephthalate–imide)s (PETI) were prepared by melt polycondensation of bis(2-hydroxyethyl)terephthalate (BHET) and imide containing oligomer, i.e., 4,4′-bis[(4-carbo-2-hydroxyethoxy)phthalimido]diphenylmethane(BHEI). The apparent rate of poly-condensation reaction was faster than that of homo poly(ethylene terephthalate) (PET) due to the presence of imide units. The PETI copolymers with up to 10 mol % of BHEI unit in the copolymer showed about the same molecular weight and carboxyl end group content as homo PET prepared under similar reaction conditions. The increase in T_g of copolymer was more dependent on molar substitution of BHEI than on substitution of BHEN, reaching 91°C with 8 mol % BHEI units in the copolymer from T_g = 78.9°C of homo PET. In the case of PETN copolymer, 32 mol % of bis(2-Hydroxyethyl)naphthalate (BHEN) units gave T_g of 90°C. The maximum decomposition temperature of PETI copolymer was about the same as that of homo PET by TGA analysis. The char yield at 800°C was higher than that of homo PET. © 1996 John Wiley & Sons, Inc.     

Alkali decomposition of poly(ethylene terephthalate) with sodium hydroxide in nonaqueous ethylene glycol: A study on recycling of terephthalic acid and ethylene glycol

Pellets of poly(ethylene terephthalate) (PET; 0.48–1.92 g) were heated in anhydrous ethylene glycol (EG; 5 mL) with 2-equivs of NaOH at 150°C for 80 min or 180°C for 15 min to convert them quantitatively to disodium terephthalate (Na₂-TPA) and EG. The disodium salt was precipitated quantitatively in pure state from the EG solution and separated readily. The other product EG, being the same component to the solvent, remains in the solution and can be obtained after distillation as a part of the solvent. The rate of decomposition was significantly accelerated by the addition of ethereal solvents to EG, such as dioxane, tetrahydrofuran, and dimethoxyethane. The reaction system is simple; no water and no extra reagent other than NaOH and EG are used. A few recycling systems of PET can be designed on the basis of the present alkali decomposition reaction. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 595–601, 1997     

Relationship between the chain fold period in poly(ethylene terephthalate) and the crystallization temperature

The dependence of the fold period in poly(ethylene terephthalate) (PET) crystals on overcooling was investigated by the small-angle x-ray diffraction method, for samples crystallized at 150°C to 260°C. The equilibrium melting point T_m, determined simultaneously, was 278°C ± 2°C. Using these results, the surface free energy σ_e was calculated.     

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     

Thermal properties of poly(ethylene terephthalate) recovered from municipal solid waste by steam autoclaving

The steam autoclaving of municipal solid waste followed by size separation was shown to be a way to recover virtually 100% of recyclable poly(ethylene terephthalate) (PET); this is a yield not attainable by a typical material recovery facility. The polymer properties of the recovered PET, which had undergone various degrees of thermal processing, were evaluated by thermogravimetric analysis, differential scanning calorimetry, gel permeation chromatography, viscometry, and solid‐state NMR to assess the commercial viability of polymer reuse. The weight‐average molecular weight (M_w) decreased as a result of autoclaving from 61,700 g/mol for postconsumer poly(ethylene terephthalate) (pcPET) to 59,700 g/mol for autoclaved postconsumer poly(ethylene terephthalate) [(apcPET)]. M_w for the reclaimed poly(ethylene terephthalate) (rPET) was slightly lower, at 57,400 g/mol. The melting temperature increased with two heat cycles from 236°C for the heat‐crystallized virgin poly(ethylene terephthalate) (vPET) pellets to 248°C for apcPET and up to 253°C for rPET. Correspondingly, the cold crystallization temperature decreased with increased processing from 134°C for vPET to 120°C for apcPET. The intrinsic viscosity varied from 0.773 dL/g for the vPET to 0.709 dL/g for rPET. Extruded samples were created to assess the potential commercial applications of the recovered rPET samples. The M_w values of the extruded apcPET and rPET samples dropped to 37,000 and 34,000 g/mol, respectively, after extrusion (three heat cycles); this indicated that exposure to heat dictated that these materials would be better suited for downcycled products, such as fibers and injected‐molded products. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2012     

Low temperature melting behavior of CO2 crystallized modified PETs

Differential scanning calorimetry (DSC) analysis has been performed on modified and commericial amorphous samples of poly(ethylene terephthalate) (PET) crystallized by high pressure carbon dioxide (CO²). Two endothermic peaks are present in the DSC scans of all the carbon dioxide-treated samples. A qualitatively analogous behavior has been detected in the case of amorphous samples heat treated at temperatures slightly exceeding the glass transition temperature of virgin material. Wide angle X-ray scattering analysis has confirmed the structural analogies between samples CO₂ crystallized at 50°C and thermally crystallized slightly above T_g. A differential scanning calorimeter capable of working at high pressure of CO₂ has been adopted in order to examine the effect of carbon dioxide on the crystallization temperature range.     

Polysulfone membranes containing ethylene glycol monomers: synthesis,characterization, and CO<Subscript>2</Subscript>/CH<Subscript>4</Subscript> separation

Copolymers based on glassy and rubbery units have been developed to take advantage of both domains to enhance solubility and diffusivity. In this study, a series of gas separation membranes from polysulfone (PSF) containing ethylene glycol were synthesized via nucleophilic substitution polycondensation. The structures of copolymers were characterized by nuclear magnetic resonance spectra, Fourier transform infrared spectra, and thermal gravity analysis. The permeability and selectivity of the membranes were studied at different temperatures of 25–55 °C and pressures of 0.5–1.5 atm using single gases CO₂ and CH₄. Gas permeation measurements showed that copolymers with different contents of poly(ethylene glycol) exhibited different separation performances. For example, the membrane from PSF-PEG2000-20 containing 20 wt% poly(ethylene glycol) showed better performance in terms of ideal selectivity over the other seven copolymer membranes. The highest ideal CO₂/CH₄ selectivity was 43.0 with CO₂ permeability of 6.4 Barrer at 1.5 atm and 25 °C.     

Microwave irradiation as an energy source in poly(ethylene terephthalate) solvolysis

Solvolysis by glycols and alcohols is an established method for the chemical recycling of poly(ethylene terephthalate) (PET). In our work, we investigated the use of microwave radiation as the energy source in PET solvolysis reactions, and the conditions that govern its effectiveness. The main advantage of microwave use are short reaction times, between 4 and 10 min, in which complete PET degradation is achieved. Solvolysis reagents used were methanol, propylene glycol, and polyethylene glycol 400. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1115–1118, 1998     

CO2在PET熔体中的溶解度

通过高温高压磁悬浮天平(MSB)测定表观溶解度、高温高压视窗釜进行溶胀度校正的方法研究了CO₂在PET熔体中的溶解度,考察了温度、压力对改性前后PET在CO₂环境中的溶胀度和CO₂溶解度的影响。结果表明,PET在CO₂环境中的溶胀度和CO₂溶解度均随温度的增加而减小,随压力增加而增加,但高压下溶胀度的增加趋势减缓并趋于某定值;与常规线性PET相比,改性PET具有较小的溶胀度和溶解度。在250~280℃,4~6 MPa下,CO₂在PET熔体中的溶解度具有10^-2 g CO₂·(g PET melt)^-1的量级。1~6 MPa下CO₂在PET熔体中的溶解行为符合亨利定律,利用最小二乘法拟合得到了CO₂在PET熔体中的溶解热。     

Kinetics of glycolysis of poly(ethylene terephthalate) melts

The reaction of poly(ethylene terephthalate) (PET) melts with ethylene glycol was examined in a pressure reactor at temperatures above 245°C. The reaction rate was found to depend on temperature and on the concentrations of liquid ethylene glycol and of ethylene diester groups in the polymer. A kinetic model proposed for the initial period of the reaction was found to be consistent with experimental data. It was found that internal catalysis by ethylene glycol does not play an important role in the glycolytic depolymerization of PET. The rate constants for glycolysis were calculated for three different temperatures, yielding an activation energy of 92 kJ/mol. Zinc salts, which have a catalytic effect on glycolysis of PET below 245°C, do not appear to influence glycolysis rates above that temperature. © 1994 John Wiley & Sons, Inc.     

Synthesis of poly(ethylene terephthalate) in benzyl imidazolium ionic liquids

In order to improve the method of synthesis of poly(ethylene terephthalate) (PET), a series of ionic liquids (ILs) based on benzyl imidazolium ([YBMIM][X], Y = NO₂, CH₃, F; B = benzyl; X = Tf₂N) were used to investigate the formation of PET at low temperature and pressure. High molecular weight PET (M_w up to 2.6 × 10⁴ g mol^?1) was obtained by two‐step polycondensation in these ILs at lower temperature (230–240 °C) than with traditional melt polycondensation (270–290 °C). Moreover, the molecular weight of the resulting PET was found to depend on the activities of the catalysts used in the ILs. The catalysts (Sb₂(OCH₂CH₂O)₃, Sb(OAc)₃, Sb₂O₃) used in the preparation of PET have little effect on the thermostability of the ILs. The ILs can decrease the viscosity of the reaction system, and thus small molecules can be easily removed. Copyright © 2012 Society of Chemical Industry