Effect of diethylene glycol (DEG) on the crystallization behavior of poly(ethylene terephthalate) (PET)

The effect of diethylene glycol (DEG) on the crystallization of poly(ethylene terephthalate) (PET) was studied under isothermal and dynamic conditions. The strain-induced crystallization of PET and its relationship to DEG content was also studied. The samples were isothermally and dynamically crystallized in the differential scanning calorimeter (DSC). The thermograms were then analyzed to determine the kinetic parameters. Strain-induced crystallization was studied by stretching samples at different strain rates. These samples were then annealed for various periods of time and quenched to room temperature. Birefringence and density were measured on the annealed samples. Results indicate that the DEG content reduces the rate of crystallization of PET when crystallizing from the melt, isothermally and dynamically. When crystallizing from the glassy state, the effects of DEG are not prominent. The mechanism of crystallization is not affected by the amount of DEG, within the range of DEG contents evaluated. In the case of strain-induced crystallization, increased DEG content reduces the crystallinity of PET at intermediate strain rates, but at higher strain rates, the crystallinity is not affected by the DEG content. © 1993 John Wiley & Sons, Inc.     

Effect of diethylene glycol content and annealing temperature on the structure and properties of poly(ethylene terephthalate)

The effect of 2,2′-oxydiethanol (diethylene glycol, DEG) content (ranging from 2 to 15 mol %) and of the annealing temperature (in the range from 100 to 260°C) on the density, calorimetric, dynamic- and static-mechanical and small angle X-ray scattering (SAXS) behavior of undrawn and drawn samples (granules, films, and bristles) of poly(ethylene terephthalate) (PET) has been studied. The known dependences on the annealing temperature are confirmed. Some discrepancies with earlier investigations of the dependences on the DEG content are established: constant values for the SAXS intensity and long spacing, for the lamellar thickness and for the volume fraction crystallinity a_c. These discrepancies are explained by the variation of the glass transition temperature (T_g) and melting temperature (T_m) of the materials with different DEG contents. The previous hypothesis of the segregation of the comonomer (DEG) units into the amorphous regions is confirmed.     

Influence of fine structure on the torsional fatigue behavior of poly(ethylene terephthalate) fibers

Three experimental poly(ethylene terephthalate) fibers have been spun and then drawn at three different temperatures(70°C, 90°C, and 110°C) in such a way that the drawn fibers possess different orientations and crystallinities but retain the same diameters. Wide angle X-ray diffraction and birefringence measurements have been used to characterize orientation and crystallinities of the fibers. The influence of fine structure on the torsional fatigue behavior of the melt spun and drawn PET fibers has been studied by subjecting them to 1.7 Hz torsional cyclic deformation at various amplitudes. Fracture morphology was found to be strongly influenced by the degree of orientation and crystallinity. Highly oriented and crystalline structures tended to separate into a highly fibrillated structure. Fibers of low draw ratio exhibited initial deterioration of the surface structure with the generation of transverse cracks (perpendicular to the fiber axis). Subsequent torsional loading of the structure generated an increase in longitudinal cracks which finally resulted in the catastrophic failure of the fiber. The extent of fibrillation was found to be a function of draw ratio (orientation) and crystallinity. The amplitude of torsional strain was also found to have an effect on the intensity of fibrillation and the number of cycles to fiber failure.     

Biodegradability of diethylene glycol terephthalate and poly(ethylene terephthalate) fiber by crude enzymes extracted from activated sludge

In this study, diethylene glycol terephthalate (DTP) and poly(ethylene terephthalate) (PET) fiber were degraded by crude enzymes extracted from a strain that was isolated from activated sludge obtained from factories. The feasibility of the biodegradation of the PET fiber is discussed through the rule of the biodegradation of DTP, which was used as the simulacrum of the biodegradation of the PET fiber. We concluded that the proper conditions for the degradation of DTP with the crude enzyme were 30°C and a medium pH. Through the degradation kinetics, we determined that the crude enzyme was more capable of degrading DTP than was lipase. In addition, the crude enzyme also degraded the PET fibers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3855–3859, 2006     

Aspects of the yield behavior in poly(ethylene terephthalate) fibers

The yield behavior during cold drawing of commercially spun poly(ethylene terephthalate) (PET) filament yarn was investigated. Microscopic examination revealed the presence of inherent flaws within the spun filaments; these act as points for localized stress concentration. These inhomogeneities appear to be either internal cracks or crazes developed during the fiber melt spinning process. During elongation, stress magnification at these flaws results in shear band formation, indicating the onset of inhomogeneous yielding. At the yield bend in the load-elongation curve a circumferential crack propagates within these shear band regions. This yield crack develops into the classical neck geometry which further localizes additional plastic deformation within the sample at the neck.     

Kinetics of diethylene glycol formation from bishydroxyethyl terephthalate with proton catalyst in the preparation of poly(ethylene terephthalate)

This research focused on the kinetics of diethylene glycol (DEG) formation from the bishydroxyethyl terephthalate (BHET) monomer with a proton catalyst. In this study, the effect of proton concentration and of reaction temperature on DEG formation are discussed. Also, the rate equation of DEG formation from the BHET monomer with a proton catalyst is described. It was found that, as far as kinetics is concerned, the reactivity of the hydroxyl end groups of BHET with protons is greater than that of ethylene glycol (EG) with protons in DEG formation. In addition, the activation energy of BHET with protons is much lower than that of BHET with itself, that is, as protons emerge during the process of PET synthesis from BHET, they catalyze DEG formation. This study provides additional kinetics data to that described in our studies previously published (J Polym Sci Polym Chem Ed 1998, 36, 3073; 1998, 36, 3081). © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1221–1228, 2000     

Influence of branching on the properties of poly(ethylene terephthalate) fibers

A series of branched poly(ethylene terephthalate) samples was prepared by employing 0.07–0.42 mol % trimethylolpropane (TMP) for melt polycondensation. These polymers were characterized with respect to molar mass, intrinsic viscosity, and melt viscosity. Spinning into fibers took place at spinning speeds ranging from 2500 to 4500 m/min. The molecular orientation of the fibers as measured by birefringence and polarized fluorescence decreases with growing amounts of TMP, as does crystallinity. Thus with slightly branched polymers, higher spinning speeds than with a linear polymer can be used to achieve a certain property profile. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 728–734, 1999     

Biodegradability of poly(ethylene terephthalate) copolymers with poly(ethylene glycol)s and poly(tetramethylene glycol)

Poly(ethylene terephthalate) copolymers were prepared by melt polycondensation of dimethyl terephthalate and excess ethylene glycol with 10–40mol% (in feed) of poly(ethylene glycol) (E) and poly(tetramethylene glycol) (B), with molecular weight (MW) of E and B 200–7500 and 1000, respectively. The reduced specific viscosity of copolymers increased with increasing MW and content of polyglycol comonomer. The temperature of melting (T_m), cold crystallization and glass transition (T_g) decreased with the copolymerization. T_m depression of copolymers suggested that the E series copolymers are the block type at higher content of the comonomer. T_g was decreased below room temperature by the copolymerization, which affected the crystallinity and the density of copolymer films. Water absorption increased with increasing content of comonomer, and the increase was much higher for E1000 series films than B1000 series films. The biodegradability was estimated by weight loss of copolymer films in buffer solution with and without a lipase at 37°C. The weight loss was enhanced a little by the presence of a lipase, and increased abruptly at higher comonomer content, which was correlated to the water absorption and the concentration of ester linkages between PET and PEG segments. The weight loss of B series films was much lower than that of E series films. The abrupt increase of the weight loss by alkaline hydrolysis is almost consistent with that by biodegradation.     

Crystallization behavior of poly(ethylene terephthalate)

The crystallization behavior of poly(ethylene terephthalate) (PET) was studied by the methods of small angle light scattering, depolarized light intensity and density measurements. Spherulite growth rates and the overall rates of crystallization were determined at various temperatures. A detailed analysis of the crystallization course has been made with special emphasis on the early stages of crystallization. The results indicate that a significant amount of crystallization takes place in the extraspherulitie material during isothermal crystallization.     

Effects of a small amount of poly(ethylene glycol) on the non-isothermal cold crystallization of uniaxially oriented poly(ethylene terephthalate) fibers

The kinetics of non-isothermal crystallization of uniaxially oriented poly(ethylene terephthalate) fibers modified by poly(ethylene glycol)(PET-co-PEG) was investigated by using a DSC heating scanning method and analyzed by using a new non-isothermal equation. Two crystallization peaks appeared for PET and PET-co-PEG fibers. The kinetics parameters, such as the Avrami exponent, the activation energies of diffusion, and the weight fractions per sub-process, were obtained. Based on the Avrami exponent, peak position, and crystallization rate, the crystallization mechanism was proposed.     

Finite strain behavior of poly(ethylene terephthalate) (PET) and poly(ethylene terephthalate)-glycol (PETG)

Uniaxial and plane strain compression experiments are conducted on amorphous poly(ethylene terephthalate) (PET) and poly(ethylene terephthalate)-glycol (PETG) over a wide range of temperatures (25-110 °C) and strain rates (.005-1.0 s⁻¹). The stress-strain behavior of each material is presented and the results for the two materials are found to be remarkably similar over the investigated range of rates, temperatures, and strain levels. Below the glass transition temperature (θ_g=80 °C), the materials exhibit a distinct yield stress, followed by strain softening then moderate strain hardening at moderate strain levels and dramatic strain hardening at large strains. Above the glass transition temperature, the stress-strain curves exhibit the classic trends of a rubbery material during loading, albeit with a strong temperature and time dependence. Instead of a distinct yield stress, the curve transitions gradually, or rolls over, to flow. As in the sub-θ_g range, this is followed by moderate strain hardening and stiffening, and subsequent dramatic hardening. The exhibition of dramatic hardening in PETG, a copolymer of PET which does not undergo strain-induced crystallization, indicates that crystallization may not be the source of the dramatic hardening and stiffening in PET and, instead molecular orientation is the primary hardening and stiffening mechanism in both PET and PETG. Indeed, it is only in cases of deformation which result in highly uniaxial network orientation that the stress-strain behavior of PET differs significantly from that of PETG, suggesting the influence of a meso-ordered structure or crystallization in these instances. During unloading, PETG exhibits extensive elastic recovery, whereas PET exhibits relatively little recovery, suggesting that crystallization occurs (or continues to develop) after active loading ceases and unloading has commenced, locking in much of the deformation in PET.     

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     

Poly(ethylene terephthalate)/polyarylate blends: Influence of interchange reactions on the melting behavior of poly(ethylene terephthalate)

The influence of the interchange reactions of poly(ethylene terephthalate) (PET)/polyarylate (PAr) blends on the melting behavior of isothermally crystallized PET has been studied. PET shows three melting endotherms in the pure state and also when mixed with PAr. These endotherms are explained in terms of primary and secondary crystallization processes as well as recrystallization during the calorimetric scan. It is also shown that interchange reactions hinder the crystallization processes of PET.     

Improved mechanical properties of poly(ethylene terephthalate) nanocomposite fibers

Improvements in Young's modulus and strength (tenacity) of poly(ethylene terephthalate) (PET) fibers were obtained by drawing unoriented nanocomposite filaments containing low concentrations (<3 wt%) of various organically modified montmorillonites (MMTs) in a second step at temperatures above the glass transition. Prior to melt spinning, solid‐state polymerization was used to rebuild lost molecular weight, due to MMT‐induced degradation, to a level suitable for producing high strength fibers. Greater improvements in mechanical properties occurred when the MMT stacks were intercalated with PET. A nominal 1 wt% loading of dimethyl‐dehydrogenated tallow quaternary ammonium surface modified MMT in drawn PET fiber showed a 28% and 63% increase in Young's modulus and strength, respectively. Relative to an unfilled PET fiber, these results surpassed the upper bound of the rule of mixtures estimate and suggested that both the type of surface modification and concentration of MMT affect the degree of PET orientation and crystallinity. Furthermore, drawability above T_g and elongation at break increased upon the addition of organically modified MMT to unoriented PET fibers, which was a key distinction of this work from others examining similar systems. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

Composition depth profiles of plasma-fluorinated poly(ethylene terephthalate) fibers

Composition depth profiles of the outer 50 Å of plasma-fluorinated poly(ethylene terephthalate) fibers were obtained by angle-dependent X-ray photoelectron spectroscopy (XPS). The effect of sample geometry on XPS sampling depth and the depth distribution function (DDF) was determined theoretically for cylindrical and hemispherical surfaces. The theoretical DDFs are nonexponential. For cylindrical surfaces, the effect is small, a 22% increase in surface sensitivity. The average XPS sampling depth for smooth, properly oriented fibers is shown to vary, as it does for a planar surface, as the sine of the nominal takeoff angle. The DDF appropriate for cylindrical surfaces was incorporated into a computer program for inversion of angle-dependent XPS data to obtain composition depth profiles of the fibers. Plasma-fluorinated PET fibers were used to demonstrate the use of angle-dependent XPS on fibers. XPS results indicate that most fluorination occurs within the top few “monolayers,” attack is preferentially at the phenyl ring, both ? CHF? and ? CF₂ ? moieties are formed, and fluorination causes partial loss of aromaticity. © 1994 John Wiley & Sons, Inc.     

Miscibility and melting behavior of poly(ethylene terephthalate)/poly(trimethylene terephthalate) blends

The miscibility and melting behavior of binary crystalline blends of poly(ethylene terephthalate) (PET)/poly(trimethylene terephthalate) (PTT) have been investigated with differential scanning calorimetry and scanning electron microscope. The blends exhibit a single composition‐dependent glass transition temperature (T_g) and the measured T_g fit well with the predicted T_g value by the Fox equation and Gordon‐Taylor equation. In addition to that, a single composition‐dependent cold crystallization temperature (T_cc) value can be observed and it decreases nearly linearly with the low T_g component, PTT, which can also be taken as a valid supportive evidence for miscibility. The SEM graphs showed complete homogeneity in the fractured surfaces of the quenched PET/PTT blends, which provided morphology evidence of a total miscibility of PET/PTT blend in amorphous state at all compositions. The polymer–polymer interaction parameter, χ₁₂, calculated from equilibrium melting temperature depression of the PET component was ?0.1634, revealing miscibility of PET/PTT blends in the melting state. The melting crystallization temperature (T_mc) of the blends decreased with an increase of the minor component and the 50/50 sample showed the lowest T_mc value, which is also related to its miscible nature in the melting state. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

PEN/PET共混物结晶行为研究

用差示扫描量热法(DSC)研究了不同共混比例PEN/PET共混物的熔体结晶行为,并进行了等温结晶动力学测定。结果表明:随着两种组分向中间比例(50/50)靠近,共混物的熔融温度越低,结晶速率也越慢。