Ageing of poly(ethylene terephthalate) and poly(ethylene naphthalate) under moderately accelerated conditions

PEN is thought to have increased thermal and hydrolytic resistance in comparison to PET. However, due to a lack of research, few studies have been published on the degradation of PEN. In our research, we report on the extent of degradation in PET and PEN after ageing under contrasting environments (dry nitrogen, dry air, wet nitrogen, and wet air) at temperatures between 140°C and 190°C. A combination of analysis techniques were employed in order to characterize and track the physical and chemical changes in the aged polyester samples, enabling the effects of temperature, water, and oxygen to be mapped onto the resultant property changes of PET and PEN. The extent of degradation has been shown to differ between both polymers and the dominant degradation mechanism in PET was shown to differ with ageing temperature. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Sequence distribution and crystal structure of poly(ethylene/trimethylene terephthalate) copolyesters

The sequence distribution and the crystal structure of copolyesters synthesized from ethylene glycol, 1,3-propanediol, and dimethyl terephthalate with different molar volume ratios were investigated in this study. The triad sequence probabilities of ethylene/trimethylene terephthalate were characterized from the aromatic quaternary carbons by ¹³C NMR. The composition of the copolyesters was determined from the aromatic quaternary carbons by ¹³C NMR, and the methylene protons by ¹H NMR. Results show that 1,3-propanediol reacted faster with terephthalic acid in copolyester polymerization than ethylene glycol. The difference in monomer reactivity is significant in the polymerization. Although the constitutional units revealed a random distribution in the molecular chain by ¹³C NMR, crystallites formed across the full range of ethylene glycol/1,3-propanediol composition by use of differential scanning calorimetry, a hot stage polarizing microscope, and a wide angle X-ray diffraction method. The WAXD deconvolution results show that the major constitutional repeating unit in the molecular chain dominates the crystal structure as a host crystal. The crystal structure was examined by a scanning electron microscope after a solvent etching. Photomicrographs show that the random distribution of the third constitutional unit in the molecular chain of copolyester significantly disturbs the host crystal formation and lamellar orientation.     

Dynamic process of cold crystallization of poly(butylene terephthalate) solids revealed by fluorescence spectroscopy

The crystallinity of poly(butylene terephthalate) (PBT) films was investigated by comparing measurements of fluorescence and density. It was found that the ratio of the fluorescence intensity at 320 nm to that at 365 nm can be an effective indicator of crystallinity. The dynamic process of cold crystallization was directly observed for PBT films prepared using a spin-casting method on quartz disks by means of fluorescence measurements at several temperatures between 360 and 400 K. The cold crystallization of such films was found to proceed one-dimensionally under the mechanism of heterogeneous nucleation, since the Avrami exponent, n, was determined to be one. The apparent activation energy of cold crystallization was determined to be 24 kJ/mol, indicating that rotation around carbon-carbon bonds in a butylene unit of PBT participates in reorientation and crystallization. The present work should provide a quick and nondestructive method for determining the crystallinity of PBT factory products.     

Thermodynamic properties of poly(butylene terephthalate)

Specific heat of poly(butylene terephthalate) was measured in a Mettler TC 10 differential thermal analyzer. Its glass transition, melting behaviour, as well as its enthalpy, entropy, Gibbs free energy, and the rigidity of the chains are described.     

Electrical properties of poly(butylene terephthalate)

Direct current (dc) and alternating current (ac) electrical properties of semicrystalline poly(butylene terephthalate) (PBT) are investigated as a function of temperature and frequency. Dc electrical conductivity measurements have been performed over the temperature range ?75°C to 130°C and point out an essentially ionic mechanism of charge transport. Charge carriers are identified in protons supplied by ionization of carboxyl end-groups after dissociation of the existing hydrogen bonds. Dielectric constant and loss factor have been measured over the temperature range ?100°C to 130°C and over the frequency range 10^?6 to 10⁶ Hz. Together with de measurements, they allow the detection of the α glass-rubber and the β subglass relaxation processes, as well as an interfacial polarization of the Maxwell–Wagner–Sillars type. Finally, the contour map of loss factor, summarizing the overall dielectric behavior of the polymer, is reported and discussed for electrical applications of PBT.     

Physical properties of oriented poly(butylene terephthalate)

The effect of orientation on the low-strain mechanical properties, dielectric relaxation, and thermal expansivity of poly(butylene terephthalate) has been studied. The α relaxation at 50°C (1 Hz), which involves large-scale chain motion in the amorphous regions, is reduced in magnitude and shifted to higher temperature after drawing. In contrast, the localized motions of the carbonyl and glycol groups associated with the β process at ?90°C (1 Hz) is not much affected by orientation. At low temperature, a large difference along and normal to the draw direction is observed for both Young's modulus and thermal expansivity. The anisotropy, however, diminishes with increasing temperature and becomes nearly zero above the α relaxation. This feature can be understood on the basis of the Takayanagi model.     

Morphology and physical properties of poly(butylene terephthalate)

Liquid nitrogen-quenched PBT samples produce much larger spherulites of an optic axis orientation different from the of the air-cooled samples. Optical and scanning electron microscopy show that glass fibers in the glass-reinforced PBT sample nucleate the growth of well-defined spherulites along the glass fiber axis. Fracture studies at temperatures below and above the T_g indicate, respectively, brittle and ductile interspherulite boundary fracture. From dynamic mechanical studies, three transitions designated by α (flow transition), β (T_g), and γ (secondary relaxation) are observed. The magnitudes of the β and γ transitions are larger for the more amorphous quenched sample than the air-cooled sample, suggesting their amorphous phase origin. Addition of glass fibers raises the dynamic modulus and flow temperature, but suppresses the γ transition without significantly affecting the melting and glass transition temperatures.     

Degradation of poly(butylene terephthalate) in different supercritical alcohol solvents

Reactions were carried out in a batch autoclave reactor. Poly(butylene terephthalate) (PBT) and different alcohol solvents were used in the vessel. The reaction products were analyzed by infrared spectroscopy and gas chromatography/mass spectrometry. Alcoholysis of PBT occurred in supercritical methanol, ethanol, and propanol, and we obtained dimethyl terephthalate (DMT), diethyl terephthalate (DET), and dipropyl terephthalate (DPT), respectively. The conversion of PBT at different temperatures showed similar trends but different degradation degrees. The reactivity for the alcoholysis of PBT in supercritical methanol was much higher than those in supercritical ethanol and propanol. DMT and 1,4‐butanediol obtained from the depolymerization of PBT in supercritical methanol reached 98.5 and 72.3%, respectively, at 583 K for 75 min. The yield of DET reached 76% for 75 min. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis and characterization of poly(butylene terephthalate)‐co‐poly(butylene succinate)‐block‐poly(ethylene glycol) segmented block copolymers

Poly(butylene terephthalate)‐co‐poly(butylene succinate)‐block‐poly(ethylene glycol) segmented random copolymers, with poly(butylene succinate) (PBS) molar fraction (M_PBS) varying from 10 to 60 %, were synthesized through a melt polycondensation process and characterized by means of GPC, NMR, DSC and mechanical testing. The number‐average relative molecular mass of the copolymers was higher than 4 × 10⁴ g mol^?1 with polydispersity below 1.9. Sequence distribution analysis on the two types of hard segments by means of ¹H NMR revealed that the number‐average sequence length of PBT decreased from 2.80 to 1.23, while that of PBS increased from 1.27 to 4.76 with increasing M_PBS. The random distribution of hard segments was also justified because of the degree of randomness around 1.0. Micro‐phase separation structure was verified for the appearance of two glass transition temperatures and two melting points, respectively, in DSC thermograms of most samples. The crystallinity of hard segments changed with the crystallizability controlled by the average sequence length and reached the minimum value at an M_PBS of about 50–60 mol%. The results can also be ascribed to the co‐crystallization between two structurally analogous hard segments. Mechanical testing results demonstrated that incorporating a certain amount of PBS moieties (less than 30 mol%), at the expense of a minute depression of the elastic modulus, that higher relative elongation and more flexibility of polymer chain could be expected. Maximum equilibrium water absorption and faster degradation rates were observed on samples with higher M_PBS values and lower crystallinity of hard segments were better hydrophilicity of the polymer chain, through in vitro degradation experiments. Copyright © 2003 Society of Chemical Industry     

Dynamic mechanical analysis of poly(trimethylene terephthalate)—A comparison with poly(ethylene terephthalate) and poly(ethylene naphthalate)

The fiber properties of PTT have been the subject of several reports, although very few reports describe the properties of molded specimens. In this work, the dynamic mechanical relaxation behavior of compression‐molded PTT films has been investigated. The added flexibility of the PTT was found to lower the temperature of the β‐ and α‐transitions relative to the PET and PEN. The results suggest that the β‐transition is at least two relaxations for PET and PTT due to the increase in the breadth of the relaxation. The results seem to support the hypothesized mechanism of others, in that the β‐transition involves the relaxation of the carbonyl entity and the aromatic C1–C4 ring flips for PTT and PET, and the relaxation of the carbonyl for PEN. The β*‐ and α‐transitions for all three polymers seem to be cooperative in nature. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2791–2796, 2004     

Fluorinated poly(butylene terephthalate): Preparation and properties

Fluorinated poly(butylene terephthalate) (PBT) can be easily prepared using a telechelic perfluoropolyether (PFPE) as a comonomer. The functional groups of the PFPE react completely with other monomers, but the distribution of the PFPE blocks is not homogeneous and in the final polymeric material there is a significant fraction of PFPE bonded to very short segments of polyester. Due to the very poor miscibility of PFPE and PBT, the PFPE is present as a separate phase dispersed in an almost pure PBT matrix. Accordingly, both thermal and mechanical properties of PBT are little affected by the PFPE. The presence of PFPE induces a slight improvement on the fracture resistance and on surface properties such as wear resistance and coefficient of friction. © 1994 John Wiley & Sons, Inc.     

Blends of poly(ethylene terephthalate) and poly(butylene terephthalate)

Commercial grade poly(ethylene terephthalate), (PET, intrinsic viscosity = 0.80 dL/g) and poly(butylene terephthalate), (PBT, intrinsic viscosity = 1.00 dL/g) were melt blended over the entire composition range using a counterrotating twin‐screw extruder. The mechanical, thermal, electrical, and rheological properties of the blends were studied. All of the blends showed higher impact properties than that of PET or PBT. The 50:50 blend composition exhibited the highest impact value. Other mechanical properties also showed similar trends for blends of this composition. The addition of PBT increased the processability of PET. Differential scanning calorimetry data showed the presence of both phases. For all blends, only a single glass‐transition temperature was observed. The melting characteristics of one phase were influenced by the presence of the other. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 75–82, 2005     

Miscibility of poly (etherimide) and poly (butylene naphthalate) blends

Summary Differential scanning calorimeter (DSC), optical microscopy (OM) and scanning electron microscopy (SEM) were performed to characterize the miscibility of a blend system comprising poly (butylene naphthalate) (PBN) and poly (ether imide) (PEI). DSC scans showed there was only one single Tg for each blend and the glass transitions increase monotonously with the increase of PEI content. The glass transition temperatures of the blends fitted the Fox equation well implying that the blends exhibited fine segmental scale of mixing. No lower critical solution temperature (LCST) was observed by OM for the blends. SEM micrographs showed the fracture surface of quenched sample exhibited a homogeneous structure. No obvious IR peak shift of C=O absorption at 1780 cm⁻¹ was observed suggesting a relatively low level of specific interaction between two molecules. It was concluded that these blends were miscible with non-specific intermolecular interactions. Received: 5 January 2001/Accepted: 27 February 2001     

Sequence analysis of poly(ethylene terephthalate)/poly(butylene terephthalate) copolymer prepared by ester-interchange reactions

The molecular structure of the copolyester formed through the interchange reaction in poly(ethylene terephthalate)/poly(butylene terephthalate) blends was investigated with ¹³C-NMR spectroscopy. The molar fractions of heterolinkage triads in the copolyesters were lower than the values calculated by Bernoullian statistics; this indicates that the sequence of heterolinkages was far from a random distribution at the initial stage of the interchange reaction. However, the randomness increased and the number-average sequence length decreased with reaction time. The solubility of the blend decreased with increasing sequence length, resulting from the formation of block copolymers with long sequence lengths at the initial stage of the interchange reaction. The solubility of the copolyester formed by a dibutyltin dilaurate (DBTDL)-catalyzed reaction was higher than that of the copolyester formed by a titanium tetrabutoxide-catalyzed reaction; this is related to the fact that alcoholysis prevailed in the DBTDL-catalyzed reaction. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 159–168, 2001     

Mechanical properties in torsion for poly(butylene terephthalate) and a poly(ether ester) based on poly(ethylene glycol) and poly(butylene terephthalate)

The torsional behavior of poly(ether ester) (PEE) thermoplastic elastomer, based on poly(ethylene glycol) (PEG) and poly(butylene terephthalate) (PBT) was studied and compared with that of PBT itself. Two types of experiments were performed: (1) stress relaxation in torsion, and (2) measurement of intermittent couple-twist responses. It was shown that the relaxation of the torsional couple M could be represented as a sum of several exponential terms in the time, rather than as a simple exponential function. This sum might be called a Prony series on the analogy of the usual stress relaxation which occurs after stretching a sample to a certain deformation and holding it constant. The intermittent couple-twist experiments were carried out by analogy with similar experiments in elongation. For PEE the couple rises steadily with the twist, whereas for PBT it rises abruptly and remains constant within the experimental error for high twists. The residual twist, however, showed a similar trend for both PEE and PBT. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 495–502, 1998     

Rheological and thermal properties of blends of modified poly(ethylene terephthalate) with p‐acetoxybenzoic acid and poly(butylene terephthalate)

Blending of thermotropic liquid crystalline polyesters (LCPs) with conventional polymers could result in materials that can be used as an alternative for short fiber‐reinforced thermoplastic composites, because of their low melt viscosity as well as their inherent high stiffness and strength, high use temperature, and excellent chemical resistance and low coefficient of expansion. In most of the blends was used LCP of 40 mol % of poly(ethylene terephthalate) (PET) and 60 mol % of p‐acetoxybenzoic acid (PABA). In this work, blends of several copolyesters having various PABA compositions from 10 to 70 mol % and poly(butylene terephthalate) (PBT) were prepared and their rheological and thermal properties were investigated. For convenience, the copolyesters were designated as PETA‐x, where x is the mol % of PABA. It was found that PET‐60 and PET‐70 copolyesters decreased the melt viscosity of PBT in the blends and those PBT/PETA‐60 and PBT/PETA‐70 blends showed different melt viscosity behaviors with the change in shear rate, while blends of PBT and PET‐x having less than 50 mol % of PABA exhibited totally different rheological behaviors. The blends of PBT with PETA‐50, PETA‐60, and PETA‐70 showed the morphology of multiple layers of fibers. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1797–1806, 1999     

Crystallization of poly(butylene terephthalate)

This article provides a thorough analysis of the crystallization process of poly(butylene terephthalate) (PBT). Isothermal crystal growth rates have been experimentally measured between 459 and 491 K, and analyzed according to the Hoffman and Lauritzen theory. A II–III regime transition occurs at 484 K, accompanied by a change in crystal morphology. By means of a non‐linear fitting procedure, precise values of the nucleation constant K_g were obtained. The lateral surface free energy σ was calculated and, from this, the α parameter of the Thomas‐Staveley expression was obtained.     

Hydrolysis of poly(butylene terephthalate)

The hydrolytic stability of poly(butylene terephthalate) (PBT) resins and compounds was studied. Rates of reaction were determined by measuring changes in melt flow rate. Hydrolysis was slightly accelerated by contact of PBT with glass containers and reduced by incorporation of some flame retardant additives. Melt flow rates were related to tensile elongation ofunfilled PBT and tensile strength ofthe glass fiber reinforced polymer and used as failure criteria. Reaction rates were used to predict failure times at various conditions.     

Thermal oxidative degradation kinetics and thermal properties of poly(ethylene terephthalate) modified with poly(lactic acid)

The thermal oxidative degradation kinetics of poly(ethylene terephthalate) (PET) copolymers modified with poly(lactic acid) (PLA) were investigated with thermogravimetric analyzer (TGA). The thermal properties of the modified products were also determined by differential scanning calorimeter (DSC) technique. Waste PET (P100) obtained from postconsumer water bottles was modified with a low‐molecular‐weight PLA. The PET/PLA weight ratio was 90/10 (P90) and 50/50 (P50) in the modified samples. The thermal oxidative degradation kinetics of the modified samples was compared with those of PET (P100). The segmented block and/or random copolymer structure of the modified samples formed by a transesterification reaction between the PLA and PET units in solution and the length of the aliphatic and aromatic blocks were found to have a great effect on the degradation behavior. On the basis of the results of the degradation kinetics determined by Kissinger method, the degradation rate of the samples decreased in the order of P50 > P90 > P100, depending on the amount of PLA in the copolymer structure. However, the degradation activation energies (E_A) of the samples decreased in the order of P100 > P90 > P50. It was concluded that the degradation rate and mechanism were affected significantly by the incorporation of PLA into the copolymer structure. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Crystallization and melting behaviour of poly(butylene terephthalate) in poly(butylene terephthalate)/polyarylate blends

Summary The crystallization and melting behaviour of poly(butylene terephthalate) has been studied in the pure state and in its blends with a polyarylate of bisphenol A and isophthalic/terephthalic acids. Differential scanning calorimetry has been used as experimental technique and the effects of different thermal treatments have been analyzed. Results show the hindrance for the crystallization of poly(butylene terephthalate) imposed by the presence of polyarylate, as well as the existence of multiple melting after isothermal crystallization. Explanations are given for the observed behaviours.