Models for the formation of poly(butylene terephthalate): effect of water on the kinetics of the titanium tetrabutylate-catalysed reactions: 3

In an effort to investigate the mechanism of catalysis of titanium tetrabutoxide on the polycondensation of poly(butylene terephthalate), alcoholysis and hydrolysis reactions were studied with the aid of model molecules. The retarding effect of water has also been taken into account. Appropriate kinetic equations are derived and discussed and the results compared with experimental data obtained at different molar ratios of reactants.     

Toughening of poly(butylene terephthalate) by AES terpolymer

AES, a terpolymer of acrylonitrile-EPDM(ethylene/propylene/diene elastomer)-styrene, was blended in poly(butylene terephthalate) (PBT). Uniaxial tensile tests were carried out at various strain rates on blends containing 0-50 wt% of AES in order to study the yielding behavior of PBT in these blends by the Eyring equation. It was found that stress concentration factor (γ) increases sharply when a small content of AES is incorporated in the PBT matrix, but further incorporation seems to have small effect and γ levels out, a behavior that can be explained by the blend morphology and AES mechanical characteristics. The effect of AES content on the notched Izod impact strength of PBT blends was also examined in depth. It was found that a supertough blend can be achieved with at least 30 wt% of AES in PBT in appropriate molding temperature. Macroscopic and microscopic observations indicate that dilatational process play an important role on the toughening mechanism in PBT/AES blends at notched Izod impact tests.     

Hydrolytic stability of sulfonated poly(butylene terephthalate)

The hydrolysis of sulfonated poly(butylene terephthalate) copolymers was studied. Sulfonated poly(butylene terephthalate) copolymers, referred to as PBT-ionomers (PBTIs), were shown to hydrolyze faster than poly(butylene terephthalate) (PBT). An experiment designed to isolate the effect of the sulfonated isophthalate (SIP) moieties on hydrolysis rate showed that the SIP moieties were responsible for the faster hydrolysis. Experiments aimed at identifying the mechanism of influence of the SIP moieties on hydrolytic stability indicated that hydrolysis was enhanced by the presence of ionic multiplets which increase amorphous content, imbibe water, and perhaps exert a medium effect on the hydrolysis of esters associated with the ionic groups.     

Synthesis and thermal characterization of poly(butylene terephthalate-co-thiodiethylene terephthalate) copolyesters

Poly(butylene terephthalate-co-thiodiethylene terephthalate) copolymers of various compositions were synthesized and characterized in terms of chemical structure and molecular weight. The thermal behavior was examined by thermogravimetric analysis and differential scanning calorimetry. All the polymers under investigation show a good thermal stability. At room temperature they appear as semicrystalline materials: the main effect of copolymerization was a lowering in the amount of crystallinity and a decrease of melting temperature with respect to homopolymers. A pure crystalline phase has been evidenced at high content of butylene terephthalate or thiodiethylene terephthalate units and Baur's equation was found to describe well the T_m-composition data. Amorphous samples (containing 50-100 mol% of thiodiethylene terephthalate units) showed a monotonic decrease of T_g as the content of sulfur-containing units is increased, due to the presence of flexible C-S-C bonds in the polymeric chain. Finally, the Fox equation described well the T_g-composition data.     

Toughening of poly(butylene terephthalate) with epoxy-functionalized acrylonitrile-butadiene-styrene

Glycidyl methacrylate (GMA) functionalized acrylonitrile-butadiene-styrene (ABS) copolymers have been prepared via an emulsion polymerization process. These functionalized ABS copolymers (ABS-g-GMA) were blended with poly(butylene terephthalate) (PBT). DMA result showed PBT was partially miscible with ABS and ABS-g-GMA, and DSC test further identified the introduction of GMA improved miscibility between PBT and ABS. Scanning electron microscopy (SEM) displayed a very good dispersion of ABS-g-GMA particles in the PBT matrix compared with the PBT/ABS blend when the content of GMA in PBT/ABS-g-GMA blends was relatively low (<8 wt% in ABS-g-GMA). The improvement of the disperse phase morphology was due to interfacial reactions between PBT chains end and epoxy groups of GMA, resulting in the formation of PBT-co-ABS copolymer. However, a coarse, non-spherical phase morphology was obtained when the disperse phase contained a high GMA content (≥8 wt%) because of cross-linking reaction between the functional groups of PBT and GMA. Rheological measurements further identified the reactions between PBT and GMA. Mechanical tests showed the presence of only a small amount of GMA (1 wt%) within the disperse phase was sufficient to induce a pronounced improvement of the impact and tensile properties of PBT blends. SEM results showed shear yielding of PBT matrix and cavitation of rubber particles were the major toughening mechanisms.     

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     

New catalysts for poly(butylene terephthalate) synthesis. Part 3: effect of phosphate co-catalysts

An exhaustive study of the co-catalytic activity of phosphates on titanium and titanium/hafnium based catalytic systems in poly(butylene terephthalate) synthesis was conducted in order to investigate any improvement in the process and/or in the properties of the final polymer with respect to the industrially used titanium based catalyst. Small scale polymerisation and subsequent scale up in higher capacity reactors showed a strong co-catalytic effect of phosphates. A screening on model compounds showed NaH₂PO₄ to be the most active co-catalyst. The co-catalysts had a stronger effect on titanium with respect to hafnium. Decreases in polymerisation time and tetrahydrofuran formation were observed, which in turn can improve the productivity of the whole process. Moreover, the use of phosphate improved the thermal stability of the final polymers.     

Phase separation in poly(butylene terephthalate)-based materials prepared by solid-state modification

The morphology of a series of poly(butylene terephthalate) (PBT)/fatty acid dimer diol (FADD)-based copolyesters prepared by solid-state modification (SSM) was studied. It was shown that in copolyesters containing less than 10 wt% FADD two different phases, i.e. a PBT crystalline phase and a PBT-rich amorphous phase, are present. The FADD residues were more or less homogeneously distributed throughout the interlamellar regions. For copolymers containing more than 10 wt% of FADD, a three-phase morphological model has to be used due to phase separation of a FADD-rich amorphous phase from the PBT-rich matrix, as confirmed by solid-state nuclear magnetic resonance spectroscopy and transmission electron microscopy. The final morphology was dependent on the morphology of the PBT/FADD-based physical mixtures prior to SSM. In addition, it was shown that FADD diffusion during SSM influences the final morphology.     

Strain recovery of post-yield compressed semicrystalline poly(butylene terephthalate)

Cubic specimens of a semicrystalline poly(butylene terephthalate) (PBT) have been compressed up to post-yield deformation levels with a fast (3.0 × 10⁻² s⁻¹) and a slow (1.5 × 10⁻⁴ s⁻¹) strain rate at three different temperatures (25 °C, 45 °C, and 100 °C, i.e. below, close and above the glass transition temperature of the material, T_g, respectively). Differently from literature results reported for amorphous polymers, semicrystalline PBT shows that, after a post-yield deformation, recovery occurs also at temperatures higher than T_g, and that an irreversible deformation, ?_irr, is set in the material. The irreversible strain component has been evaluated as the residual deformation after a thermal treatment of 1 h at 180 °C.After unloading, isothermal strain recovery has been monitored for time periods of 1 h at various temperatures. From the obtained data, strain recovery master curves have been constructed by a time-temperature superposition scheme. The features of the recovery process for the various deformation conditions have been analysed. In particular, it appears that specimens deformed below T_g show a lower irreversible component, whereas, when deformed above T_g, they display a higher irreversible deformation and a slower recovery process. Moreover, the effect of deformation rate appears particularly marked for samples deformed above T_g.     

Stiffer and super-tough poly(butylene terephthalate) based blends by modification with phenoxy and maleated poly(ethylene-octene) copolymers

New super-tough poly(butylene terephthalate) (PBT) materials were obtained by melt blending PBT with both 20 wt% phenoxy (Ph) and 0-30 wt% maleic anhydride grafted poly(ethylene-octene) (mPEO) copolymers with different grafting levels. Ph was completely miscible in the PBT matrix. The presence of mPEO did not influence either the nature of the PBT-Ph matrix or the crystallization of PBT. The overall decrease in particle size and in interfacial tension upon grafting indicated that compatibilization had taken place. Super-tough (impact strength 23-fold that of the PBT) and stiffer PBT based blends were obtained at mPEO contents equal to or higher than 15%. The dependence of the critical inter-particle distance (τ_c), on both adhesion measured by means of the interfacial tension, and on the relation between the modulus of the matrix and that of the rubbery dispersed phase (E_m/E_d), is proposed.     

Morphological study on three kinds of two-dimensional spherulites of poly(butylene terephthalate) (PBT)

Three kinds of thin film specimens, each of which containing one of the three types of two-dimensional poly(butylene terephthalate) (PBT) spherulites (i: usual-positive type, ii: usual-negative type, and iii: unusual type), were prepared and studied mainly by transmission electron microscopy. It was confirmed that all these kinds of spherulites are made up of only the α-modification crystals, and the growth directions for usual-positive type, usual-negative type, and unusual type are the [010]^∗, ^∗, and ^∗ directions in the reciprocal lattice, respectively. Furthermore, the arrangement of unit cell in each type of the spherulites was determined. The relationships between the arrangements of unit cell and the types of each resulting spherulite are discussed.     

Post-yield compressed semicrystalline poly(butylene terephthalate): energy storage and release

Post yield deformation of semicrystalline poly(butylene terephthalate) (PBT) is studied by differential scanning calorimetry (DSC) measurements on compressed specimens after unloading. In particular, the effects of strain level, loading-unloading rate, and deformation temperature are analyzed. DSC traces indicate that a remarkable fraction of the mechanical work of deformation (in the range from 25 up to 62%) is stored in the material after unloading. Final strain dependence of stored energy values for specimens deformed up to 40% follows the general S-shaped trend observed for many amorphous and semicrystalline polymers. The ratio of the stored energy to the mechanical work of deformation (ΔU_ST/W) is decreasing as the final deformation level increases. For a given final strain level, the amount of energy stored in specimens deformed under T_g increases as either loading or unloading rates increase: in particular, both ΔU_ST and ΔU_ST/W values are linearly increasing with the logarithm of loading rate. On the other hand, energy storage for specimens deformed at T_g results to be practically independent from the loading rate. Moreover, as the deformation temperature increases from 25 to 100 °C, ΔU_ST values markedly decrease, while the ratio ΔU_ST/W is almost constant around an average value of about 51%.     

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     

A constitutive law for poly(butylene terephthalate) nanofibers mats

A three‐dimensional structural constitutive equation is proposed to describe the mechanical properties of poly(butylene terephthalate) nanofibers mats. The model is formulated under the assumption that the mechanical response of the fibrous mat is determined by the individual fibers. The inelasticity, which has been observed when subjecting the fibrous mat to tensile tests, is assumed to be due to the gradual breakage of linear elastic fibers. The constitutive relation also takes the material anisotropy associated with the fibers' architecture into account. Uniaxial experimental data were used to assess the proposed model. The results demonstrate that the model is well suited to reproduce the typical tensile behavior of the fibrous mat. In agreement with the empirical observations, the model predicts that almost all the fibers fail when the poly(butylene terephthalate) fibrous mat sample breaks. Nevertheless, multiaxial stress–strain data and quantification of the fibers' orientation are required to completely validate the constitutive law. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5280–5283, 2006     

Investigation of the Reaction Kinetics of Poly(butylene terephthalate) and Epoxide Chain Extender

Polyesters, such as poly (butylene terephthalate) (PBT), owe a rather low melt strength, which is considered as not beneficial for foaming. To overcome this issue, a typical attempt is the incorporation of chemical modifications—so-called chain extenders (CE)—in the reactive extrusion process. In this study, the reaction kinetic variables are investigated depending on the material and process parameters. For this purpose, different series of experiments are performed with varying PBT with different molecular weights and the commonly used CE, Joncryl ADR4468, on a micro compounder. The screw force is recorded and analyzed using an Avrami and an Arrhenius plot. First, the amount of CE is systematically varied. To study the course of the reaction in more detail, the reaction is stopped in a series of measurements (10, 30, 60, and 90 s after complete filling). Gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FT-IR), and Raman spectra are recorded. In the second series, the effect of processing temperatures between 250 and 270 °C is investigated, and finally, in the third series, the average molecular weight of PBT is varied. It could be shown that the activation energy seems to be dependent on the initial molecular weight; lower molecular weights result in lower activation energy.     

聚对苯二甲酸甲二酯的热分解行为及其动力学研究

研究了惰性气氛下聚对苯二甲酸甲二酯(PMT)的非等温热分解行为及其动力学,并与聚对苯二甲酸丁二酯 (PBT)进行了对比。研究发现,PMT的热降解过程包括两个主要失重阶段,其热分解反应不是一级反应。第一阶段的起始分解温度较低是由于产物的分子链末端基中含有Br或Cl能催化聚合物的降解反应;第二阶段为分子链主体的热分解过程,由于分子链中苯环的密度较大,分子链的热稳定性比具有较低苯环密度的PBT要高。而PBT的降解失重过程仅为一个阶段,为一级反应。     

Processing and assessment of poly(butylene terephthalate) nanocomposites reinforced with oxidized single wall carbon nanotubes

Thermoplastic composites with carbon nanotubes (CNT) have a great potential as structural material because of their superior mechanical properties and ease of processing. The objective of this report is to evaluate the effect of oxidized single walled carbon nanotubes (oSWCNT) on the properties of poly(butylene terephthalate) (PBT) thermoplastic polymers, as a function of their weight content. The nanocomposites are obtained by introducing the oSWCNT into the reaction mixture whilst the synthesis of PBT. The polymers without and with carbon nanotubes were synthesised using an in situ polycondensation reaction process. Weight percentages ranging from 0.01 to 0.2 wt% of single walled nanotubes were dispersed in 1,4-butanediol (BD) by ultrasonication and ultrahigh speed stirring. After polycondensation the nanocomposites were extruded followed by injection moulding. The samples were characterised by thermal analysis, electron microscopy, dynamic-mechanical analysis, and tensile testing.The addition of only a small amount of oSWCNT was enough to improve the thermo-mechanical properties of the nanocomposites. The Young's modulus, tensile strength, and strain to failure increased with increasing amount from 0.01 to 0.1 wt% of CNT in the PBT matrix. However, when the content of CNT was increased from 0.1 to 0.2 wt%, the strength and the strain of the nanocomposites decreased slightly.     

Chain extension of poly(butylene terephthalate) by reactive extrusion

The chain extension reaction in poly(butylene terephthalate) (PBT) melt was studied in detail. A high‐reactivity diepoxy, diglycidyl tetrahydrophthalate, was used as a chain extender that can react with the hydroxyl and carboxyl end groups of PBT at a very fast reaction rate and a relatively high temperature. A Haake mixer 600 was used to record the torque during the chain extension reaction. The data show that this chain extension reaction could be completed within 2 to 3 min at temperatures above 250°C, and the reaction time decreased very fast with an increase in the temperature. Shear rate also had some effects on the reaction rate. The effect of the diepoxy chain extender on the flowability, thermal stability, and mechanical properties of PBT were investigated. The melt flow index (MFI) of the chain‐extended PBT dramatically decreased as the diepoxy was added to PBT. In addition, the notched Izod impact strength and elongation‐at‐break of the chain‐extended PBT also increased. The chain‐extended PBT is more stable thermally. Compared with the conventional solid post‐polycondensation method, this approach is simpler and cheaper to obtain high‐molecular‐weight PBT resins. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1827–1834, 1999     

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