Change of amorphous state of poly(ethylene terephthalate) by heat treatment below the glass transition temperature

Several papers have demonstrated that structural changes in the amorphous regions of semicrystalline polymers can be produced by heat treatment below the glass transition temperature (T_g). In this paper, we report structural change in the amorphous phase of poly(ethylene terephthalate), heat-treated below and above T_g. The density, the T_g, the endothermic peak at T_g and the relative spectral intensity in the 973 cm^?1 band (due to the CO stretching vibration), all increased with heat treatment below T_g, but the specific heat decreased. The stability of the amorphous state was examined by further heat treatment at temperatures above T_g and sufficiently high for crystallization, and it was verified that structural changes in the amorphous regions do not result in acceleration of the rate of crystallization. We therefore suggest that the amorphous region is one phase, rather than two phases consisting of random and regular regions.     

Rigid amorphous phase and low temperature melting endotherm of poly(ethylene terephthalate) studied by modulated differential scanning calorimetry

The rigid amorphous phase, the low temperature melting endotherm, and their development with thermal treatment in poly(ethylene terephthalate) (PET) were investigated by means of modulated differential scanning calorimetry. The differential of the reversing heat capacity and nonreversing heat flow signals were used to analyze the behavior of the glass transition and the low temperature melting endotherm. With increasing annealing time, the increment of the heat capacity at the glass‐transition temperature decreased and the increment of heat capacity at the annealing temperature increased. It was suggested that the origin of the low temperature melting endotherm mainly resulted from the transition of the rigid amorphous fraction for the PET used. The glasslike transition of the rigid amorphous fraction occurred between the glass transition and melting. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2779–2785, 2001     

Mechanical properties developing at the interface of amorphous miscible polymers,below the glass transition temperature: Time–temperature superposition

The bonding of amorphous polystyrene (PS) and poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) was conducted over a broad range of time and temperatures, but always below the (bulk) glass transition temperature (T_g). Stress–strain properties developing at the symmetric (PS/PS and PPO/PPO) and asymmetric interfaces (PS/PPO), in a lap–shear joint geometry, were measured at room temperature as a function of contact time and bonding temperature. Master curves of shear strength and modulus, obtained by time–temperature superposition, were constructed over several decades of time. Arrhenius apparent activation energies calculated for shear strength are 99, 81, and 144 kcal/mol for, respectively, PS/PS, PPO/PPO, and PS/PPO interfaces. A higher value of 191 kcal/mol was calculated for the shear modulus at the PS/PS interface, suggesting that the development of the strength and modulus is controlled by different molecular factors, that is, the modulus is controlled by the number of chains across the interface and the strength by the depth of penetration. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 825–830, 1999     

Poly(ethylene terephthalate), modified with bisphenol S units,with increased glass transition temperature

Novel copolyesters have been prepared by melt mixing poly(ethylene terephthalate) (PET) with an ethoxylated bisphenol S, with the aim to prepare new polyesters with increased T_g, to be used in a wider range of temperatures with respect to neat PET. No side reactions occur during the synthesis of the samples, as proved by NMR analysis. The insertion of the bisphenol S (sulfonyldiphenol) groups does not significantly alter the thermal stability of PET. The thermal analysis showed that T_m and crystallization rate of the copolymers decreased with incasing co‐unit content. The T_g of the copolyesters can be increased by bisphenol S insertion, up to 40°C higher with respect to neat PET, that allows the use of amorphous PET in a wider range of applications. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Glass transition and structural relaxation in semi-crystalline poly(ethylene terephthalate): a DSC study

The aim of this work is to determine the relaxation times of the cooperative conformational rearrangements of the amorphous phase in semi-crystalline poly(ethylene terephthalate) (PET) and compare them with those calculated in amorphous PET. Samples of nearly amorphous polymer were prepared by quenching and samples with different crystallinity fractions were prepared from the amorphous one using cold crystallisation to different temperatures. The differential scanning calorimetry (DSC) thermograms measured on samples rapidly cooled from temperatures immediately above the glass transition show a single glass transition which is much broader in the case of high-crystallinity samples than in the amorphous or low-crystallinity PET. To clarify this behaviour, the samples were subjected to annealing at different temperatures and for different periods prior to the DSC measuring heating scan. The thermograms measured in samples with low crystallinity clearly show the existence of two amorphous phases with different conformational mobility, these are called Phases I and II. Phase I contains polymer chains with a mobility similar to that in the purely amorphous polymer, while Phase II shows a much more restricted mobility, probably corresponding to conformational changes within the intraspherulitic regions. The model simulation allows to determine the temperature dependence of Phase II relaxation times, which are independent from the crystallinity fraction in the sample and around two decades longer than those of the amorphous polymer at the same temperature.     

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.     

Studies of temperature influence on volatile thermal degradation products of poly(ethylene terephthalate)

The temperature influence on the thermal degradation products evolved from poly(ethylene terephthalate) (PET) was investigated. The experiments were carried out within the temperature range of 200–700°C in air. The main volatile toxic products and weight losses during thermal degradation of PET were determined. The results are presented on plots as a function of the degradation temperature. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2377–2381, 1998     

Dye diffusion studies in PET fibres by confocal laser scanning microscopy and the interrelation with the glass transition

Confocal laser scanning microscopy (CLSM) is used to monitor the dye penetration in poly(ethylene terephthalate) fibres during a common commercial dyeing process. The study of optical sections of fibres dyed for prolonged times in the dyeing process allows for a qualitative interpretation of the dye diffusion process, which is not possible by other techniques. A major dissimilarity was revealed between the diffusional behaviours of the two dye classes studied. The anthraquinone dyes showed a much lower temperature onset of dye penetration during the dyeing process than the benzodifuranone dyes (approximately 110 °C vs. 130 °C). Modulated differential scanning calorimetry was used to permit an understanding for this lower temperature onset and thus for the distinction in the driving forces of the dyeing mechanism between both dye classes. These driving forces were further shown to be similar for both the conventional textile fibres and the microfibres studied.     

Influence of diamine structure on the low temperature dielectric relaxation of some poly(ether imide)s

Broadband dielectric relaxation spectra are reported on a range of poly(ether imide) polymers in which the chemical structure of the diamine used to create the polymer is systematically varied with the anhydride structure based on 2,2‐bis‐[4‐(3′,4′‐dicarboxyphenoxy)phenyl]hexafluoroisopropylidine dianhydride. In all the polymers examined, a dipole relaxation was observed below room temperature. The magnitude and activation energy associated with the relaxation process varied with the chemical structure reflecting the effects of steric hindrance on the conformational change associated with the N? C and C? O? C linkages. Values of the activation energies varied between 29 and 34 kJ/mol^?1, and are consistent with the observed relaxation being associated with constrained local oscillatory motions of small elements of the polymer backbone. The glass transition temperatures of these polymers are in the range 195–243°C and are associated with the large scale motion of the polymer backbone. Changes in the backbone structure influence the extent of inter chain–chain interaction and are reflected in the amplitude of the relaxation process and the high frequency limiting dielectric permittivity ε_∞ values which are important when these polymers are used in thin film electronic applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41684.     

Activity of substrates in the catalyzed nucleation of poly(ethylene terephthalate) melts

The activity, Φ of AgBr, AgI, PbF₂, Ag₂S, LiF, and CaF₂ in the catalyzed nucleation of poly(ethylene terephthalate) (PET) melts was determined using a nonisothermal differential scanning calorimetry (DSC) technique. A comparison with existing experimental data was made. It is established that the higher the melting temperature of the substrate the lower its activity as a crystallization core in the heterogeneous nucleation of PET. The lateral surface energy, σ, the end surface energy, σ_e, the adhesion energy, β, and the difference between the surface energies at the substrate/melt, σ_sf, substrate/deposit, σ^*, and the total energy of misfit dislocations, E_d [i.e., σ_sf - (σ^* - E_d)] were calculated. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 349–353, 1997     

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     

Aspects of the chemistry of poly(ethylene terephthalate): 5. Polymerization of bis(hydroxyethyl)terephthalate by various metallic catalysts

Bis(hydroxyethyl)terephthalate (BHET) was polymerized to poly(ethylene terephthalate) (PET) in the presence of various metallic catalysts. The influence of the nature and concentration of these catalysts on the rate of polymerization has been investigated. The effect of the reaction temperature has also been studied. The order of decreasing catalytic influence of various metal ions, on the polymerization of BHET was found to be: Ti>Sn>Mn>Zn>Pb>No.     

Modeling of solid-state polymerization of poly(ethylene terephthalate)

A mathematical model for solid-state polymerization of poly(ethylene terephthalate) was developed. The effects of temperature and chain entanglement on chain mobility were considered to estimate the rate constants of chemical reactions. The diffusivities of volatile byproducts could be determined using the free volume theory.^13,14 The model predictions were validated with experimental data reported in the literature. In addition, assuming that the concentration profiles of volatile byproducts in spherical particles are described by a sinusoidal function, the mass transfer rate of the byproducts at a given time could be derived as an ordinary differential equation that can be easily treated. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:837–846, 1998     

Dielectric relaxation spectroscopy of poly(ethylene terephthalate)

Contour maps of dielectric loss tangent within the ranges 0.1 Hz to 3 MHz and ?175 °C to +190 °C are presented for a commercial poly(ethylene terephthalate) (PET) in two initial states of crystallinity. Individual absorption regions resemble those for poly(butylene terephthalate) and are attributed to carbonyl‐driven α‐ and β‐relaxation processes and to Maxwell–Wagner–Sillars polarizations. Possible causes are considered for the asymmetry and structure apparent in the α‐peak of partially crystalline PET. © 2001 Society of Chemical Industry     

Dielectric properties of polyarylate (PAr) around the glass transition

Dielectric characterization of the α-relaxation in polyarylate (PAr) has been carried out by means of a dielectric spectroscopy technique in a frequency range of 10–30 kHz. Complementary thermally stimulated depolarization currents (TSDC) and differential scanning calorimetry d.s.c.) measurements have also been performed. The results are interpreted in terms of the standard Cole-Cole plot and Havriliak-Negami distribution for the dielectric relaxation times. Information about the temperature and frequency dependence of a.c. conductivity is also obtained from the experimental curves. However, the behaviour of the main dielectric relaxation time is deduced from the experimental data in a wide range of temperature around the glass transition. This behaviour results in close agreement with the theoretical predictions of a free-volume approach for the dielectric α-relaxation recently proposed by the authors.     

Improved adhesion property and electromagnetic interference shielding effectiveness of electroless Cu‐plated layer on poly(ethylene terephthalate) by plasma treatment

To develop high‐quality electromagnetic interference (EMI) shielding materials, the effect of plasma pretreatment with various gases prior to Cu plating was investigated. Plasma treatment increased the surface roughness in the decreasing order of Ar > O₂ > NH₃, but adhesion of the Cu layer on poly(ethylene terephthalate) (PET) film increased in the following order of O₂ < Ar < NH₃, indicating that the appropriate surface roughness and introduction of an affinitive functional group to Pd on the surface of the PET film were key factors for improving adhesion of the Cu layer. As investigated by XPS analysis, plasma treatment with NH₃ produced N atoms on the PET film, which enhances the chemisorption of Pd²⁺ on PET film, resulting in improved adhesion and shielding effectiveness of the Cu layer deposited on the Pd‐catalyzed surface, because of the high affinity of Pd²⁺ for nitrogen. Comparatively, O₂ plasma treatment allowed the chemisorption of more Sn²⁺ than of Pd²⁺ due to a lack in the affinity of Pd²⁺ for oxygen, resulting in the lowest Pd_3d/Sn_3d ratio; thereby, the lowest EMI–shielding effectiveness (SE) value was obtained. In addition, fairly low adhesion was obtained with Ar plasma‐treated PET, even though the PET surface was significantly etched with Ar plasma, due to introduced oxygen groups on the PET surface. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1369–1379, 2002; DOI 10.1002/app.10272     

Improvement of compatibility of poly(ethylene terephthalate) and poly(ethylene octene) blends by γ‐irradiation

Blends of poly(ethylene terephthalate) (PET) and poly(ethylene octene) (POE) were prepared by melt blending with various amounts of trimethylolpropane triacylate (TMPTA). The mechanical properties, phase morphologies, and gel fractions at various absorbed doses of γ‐irradiation have been investigated. It was found that the toughness of blends was enhanced effectively after irradiation as well as the tensile properties. The elongation at break for all studied PET/POE blends (POE being up to 15 wt %) with 2 wt % TMPTA reached 250–400% at most absorbed doses of γ‐irradiation, approximately 50–80 times of those of untreated PET/POE blends. The impact strength of PET/POE (85/15 wt/wt) blends with 2 wt % TMPTA irradiated with as little as 30 kGy absorbed dose exceeded 17 kJ/m², being approximately 3.4 times of those of untreated blends. The improvement of the mechanical properties was supported by the morphology changes. Scanning electron microscope images of fracture surfaces showed a smaller dispersed phase and more indistinct inter‐phase boundaries in the irradiated blends. This indicates increased compatibility of PET and POE in the PET/POE blends. The changes of the morphologies and the enhancement of the mechanical properties were ascribed to the enhanced inter‐phase boundaries by the formation of complex graft structures confirmed by the results of the gelation extraction and Fourier Transform Infrared analyses. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Dielectric Properties of Thermotropic Polymer Liquid Crystals

Abstract

Dielectric relaxation spectrometry is a useful tool to study molecular dynamics of macromolecular systems. Theoretical principles as well as experimental techniques are analyzed from the point of view of their capabilities. Results are reported for PET/xPHB, where PET = poly(ethylene terephthalate), PHB = p-bydroxybenzoic acid (the liquid crystalline component) and x is the mole fraction of PHB in the copolymers.     

PET钛系催化剂的应用进展

聚酯钛系催化剂催化活性高,对环境友好,能够使PET具有更高亮度和透明性,但也具有催化稳定性差、加剧副反应,使合成的PET色相变差、性能指标下降等缺点。通过对国外的一些钛系催化剂产品和对国内学者的钛系催化剂应用研究的简要说明,介绍了PET钛系催化剂应用发展的现状。随着聚酯工业的发展以及人们的环保意识的提高,具有高反应活性的不含重金属的钛系催化剂的开发应用,目前已经成为聚酯缩聚催化剂发展的趋势,有着光明的应用前景。