Lamellar structure and properties in poly(ethylene terephthalate) fibers

The fibrillar and the lamellar structures in a range of poly(ethylene terephthalate) fibers were studied by small-angle X-ray scattering. The intensity maxima in the lamellar peaks lie on a curve that can be described as an ellipse. Therefore, the two-dimensional images were analyzed in elliptical coordinates. The dimensions of the coherently diffracting lamellar stack, the dimensions of the fibrils, the interfibrillar spacing, and the orientation of the lamellar surfaces were measured in addition to the lamellar spacing. The orientation of the lamellar planes and the size of the lamellar stacks had a better correlation with mechanical properties of the fibers than did the lamellar spacing. In particular, longer and wider lamellar stacks reduced fiber shrinkage, as did the closer alignment of the lamellar normal to the fiber axis. These structural features were also associated with lower tenacity. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2527–2538, 1998     

Effects of hydrolysis on the physical properties of short glass-fibre reinforced poly(ethylene terephthalate)

The mechanical fracture strength and toughness of short-fibre composites, injection moulded from compounds of poly(ethylene terephthalate) (PET) containing 10 and 30% (by weight) (w/o) glass, have been investigated and the dependence upon matrix hydrolytic stability determined. Mouldings have been characterised by several physical techniques to evaluate molecular weight, degradation rates, crystallinity and morphology, whilst time-dependent gravimetric data were derived to quantify sorption kinetics and allow comparisons with theoretical reaction rates to be made. During melt processing, PET is hydrolysed extremely rapidly by traces of moisture (<0.02w/o). yet the inherent strength of moulded composites declines significantly only below an apparently critical molecular weight. However, on long-term humid ageing in hot water, impact behaviour especially is rendered more complex by simultaneous crystallisation, molecular reorder and losses of interfacial bond strength.     

Structure–properties relations of the drawn poly(ethylene terephthalate) filament sewing thread

This article presents research into draw ratio influence on the structure–properties relationship of drawn PET filament threads. Structural modification influence due to the drawing conditions, i.e., the birefringence and filament crystallinity, on the mechanical properties was investigated, as well as the shrinkage and dynamic mechanical properties of the drawn threads. Increasing draw ratio causes a linear increase in the birefringence, degree of crystallinity, filament shrinkage, and a decrease in the loss modulus. In addition, loss tangent and glass transition temperature, determined at the loss modulus peak, were increased by drawing. The observed structural changes influence the thread's mechanical properties, i.e., the breaking tenacity, elasticity modulus, and tension at the yield point increase, while breaking extension decreases by a higher draw ratio. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Linear thermoelastic characterization of anisotropic poly(ethylene terephthalate) films

All nine independent elastic constants have been determined for a biaxially stretched poly(ethylene terephthalate) (PET) film using novel mechanical methods. The orthotropic directions and the in‐plane Poisson's ratios were first characterized using vibrational holographic interferometry of tensioned membrane samples. The out‐of‐plane Poisson's ratio was obtained by measuring the change in tension with the change in pressure for constant strain conditions. Pressure–volume–temperature (PVT) equipment was used to measure the bulk compressibility as well as the volumetric thermal expansion coefficient (TEC). The in‐plane Young's moduli were obtained by tensile tests, while the out‐of‐plane modulus was calculated from the compressibility and other elastic constants that describe the in‐plane behavior. The in‐plane TECs in the machine and transverse directions were determined using a thermal mechanical analyzer (TMA). The out‐of‐plane TEC was determined using these values and the volumetric TEC determined via PVT. The resulting compliance matrix satisfies all of the requirements of a positive‐definite energy criterion. The procedure of characterization utilized in this article can be applied to any orthotropic film. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2937–2947, 2002     

Structural formation of amorphous poly(ethylene terephthalate) during uniaxial deformation above glass temperature

An in situ study of structural formation of amorphous poly(ethylene terephthalate) (PET) during uniaxial deformation above its T_g (at 90 °C) was carried out by wide-angle X-ray diffraction (WAXD) with synchrotron radiations. Results indicate that the relationships between structure and mechanical property can be divided into three zones: I, II and III. In Zone I, oriented mesophase is induced by strain, where the applied load remains about constant but the amount of mesophase increases with strain. In Zone II, crystallization is initiated from the mesophase through nucleation and growth, where the load starts to increase marking the beginning of the strain-hardening region. The initial crystallites are defective but they form an effective three-dimensional network to enhance the mechanical property. The perfection of the crystal structure and the orientation of the crystals all increase with strain in this zone. In Zone III, the ratio between load and strain is about constant, while the stable crystal growth process takes place until the breaking of the sample. The sample damage is probably dominated by the chain pull-out mechanism from the crystal amorphous interface. The increase in molecular weight was found to enhance the overall mechanical properties such as the load to induce the mesophase and the ultimate tensile strength before breakage.     

Effect of glass fibres and fire retardant on the combustion behaviour of composites,glass fibres–poly(butylene terephthalate)

The oxygen index (OI) of poly(butylene terephthalate) (PBT) tends to decrease when it is combined with milled-glass fibres either with or without the sizing treatment. This shows that the previously found apparent increase of flammability of PBT glass fibre composites (GFPBT) as compared to PBT is not due to the introduction of the flammable sizing together with the glass fibres in the polymer which was one suggested explanation in the literature, but rather to the wick and anti-dripping effects of glass fibres. The effectiveness of a typical brominated organic compound-antimony trioxide fire retardant system (FR), as measured by OI, is found to be larger in GFPBT as compared to PBT. A linear increase of the temperature index (TI) of PBT and of GFPBT is observed with increasing concentration of the FR. The fire retardant increases the time to ignite while it decreases the maximum rate of heat release and increases the smoke optical density and CO evolution on burning in the cone calorimeter. The dependence of fire risk and hazard assessement on the combustion model of the combustion test method is discussed for OI and cone calorimeter in the case of PBT, GFPBT and FR corresponding materials. © 1998 John Wiley & Sons, Ltd.     

Effects of physical aging on thermomechanical behaviors of poly(ethylene terephthalate)-glycol (PETG)

ABSTRACT

A series of experiments are performed to investigate the effects of physical aging on thermomechanical properties of poly(ethylene terephthalate)-glycol (PETG). The DMA, DSC and XRD tests are used to characterize the change of dynamic property, heat capacity and microstructure with annealing treatments. The uniaxial tension tests together with the DIC technique are employed to describe the failure behaviors of PETG. The results show that the annealed polymers exhibit a larger maximum local strain and fail at a smaller displacement. The type and size of the geometry defects can also affect the strain localization and final failure behaviors of PETG.     

Structure‐mechanical properties relationship of poly(ethylene terephthalate) fibers

The correlation between the fiber structure and mechanical properties of two different poly(ethylene terephthalate) fiber types, that is, wool and cotton types produced by three producers, was studied. Fiber structure was determined using different analytical methods. Significant differences in the suprastructure of both types of conventional textile fibers were observed, although some slight variations in the structure existed between those fibers of the same type provided by different producers. A better‐developed crystalline structure composed of bigger, more perfect, and more axially oriented crystallites was characterized for the cotton types of PET fibers. Crystallinity is higher, long periods are longer, and amorphous domains inside the long period cover bigger parts in this fiber type in comparison with the wool types of fibers. In addition, amorphous and average molecular orientation is higher. The better mechanical properties of cotton PET fiber types, as demonstrated by a higher breaking tenacity and modulus accompanied by a lower breaking elongation, are due to the observed structural characteristics. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3383–3389, 2003     

Thermal deformations of oriented noncrystalline poly (ethylene terephthalate) fibers in the presence of mesophase structure

Thermally induced dimensional changes, thermal shrinkage and elongation, in oriented noncrystalline PET fibers were investigated. The fibers exhibited two very distinct thermal responses depending on the fiber orientation. The local structure of the oriented noncrystalline PET chains as studied by the X-ray diffraction and FTIR spectroscopy revealed the mesophase structure with the well extended chain conformation in some fibers of high orientation. It was suggested that the oriented noncrystalline structure of PET consists of partially oriented noncrystalline phase and chain-extended noncrystalline phase. Our results demonstrated that the evolution of mesophase structure, i.e. chain-extended noncrystalline phase in the spin line not only led the drastic increase of packing density but also had a strong effect on thermal deformations upon post heat treatment. The amount of thermal shrinkage or the elongation reduced drastically in the fibers containing the mesophase. The high population of trans conformer and the strong inter-chain interactions of the extended chains provided the dimensional stability of the fibers during the thermal treatment.     

Microstructure of amorphous and crystalline poly(ethylene terephthalate)

The microstructures of amorphous and crystalline poly(ethylene terephthalate) (PET) homopolymers have been determined in terms of their trans and gauche conformational isomer contents by using a combination of infrared and density characterization techniques. The effects of isothermal crystallization (from the glassy state between 105–150°C), as well as the effects of different monomer units in the polymerization process, have been investigated. Results indicate that samples, polymerized from different monomer and catalyst systems, show different microstructures in terms of trans and gauche isomers.These variations result in significant differences in PET optical properties. Further investigations find that these dissimilar behaviors accompany conformational isomer variations in the amorphous phase, suggesting different transformation mechanisms of trans and gauche isomers at early stages of crystallization. These unlike microstructural transformation processes give rise to further changes, which are evident in terms of the intensity of Vv light scattering, haze values, thermal properties, and FTIR spectral results. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1965–1976, 1998     

Recycled poly(ethylene terephthalate) reinforced with basalt fibres: Rheology,structure, and utility properties

Utilization of recycled poly(ethylene terephthalate) (PET) as a matrix for composite materials prepared by continuous compounding is challenging from the environmental as well as industrial point of view. In our work, cut basalt fibers and talc powder of various compositions were used and their reinforcing effect on recycled PET was tested by rheology (Advanced Rheometric Expansion System), differential scanning calorimetry, and tensile experiments. The quality of filler dispersion in recycled PET matrix was investigated by scanning electron microscopy (SEM) and melt rheology. Processing and utility properties of composites were enhanced as compared with those of unfilled matrix. Higher melt elasticity, interfacial adhesion, and better mechanical performance of the composites were in a good agreement with the structure observed from SEM micrographs. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

X-ray and neutron scattering studies of poly(ester carbonate)/poly(ethylene terephthalate) alloys

Quenched blends of poly(ester carbonate) (PEC) and poly(ethylene terephthalate) (PET) have a single T_g and behave as single-phase amorphous alloys up to 67% PET. However, small-angle neutron scattering (SANS) data show that the PET molecules are not statistically distributed as classical Gaussian coils in the PEC matrix. In quenched amorphous PEC-rich films (a single phase), PET-rich domains of varying PET concentration appear to be randomly distributed in the PEC matrix, and the excess SANS intensity is attributable to fluctuations in PET concentrations. Wide- and small-angle X-ray scattering data and SANS results show incomplete phase separation of PET and PEC molecules upon annealing. A possible model for annealed blends (two phases) might be domains of folded-chain, crystalline PET with interlamellar amorphous regions composed of a mixture of PET and PEC molecules. These domains are dispersed in the amorphous PEC matrix.     

Effects of curing temperature on poly(ethylene terephthalate)

The effect on poly(ethylene terephthalate) (PET) of thermal curing in a particular temperature range (T max =280-350C) in air have been studied. The changes in the structure were monitored using various characterization techniques such as differential scanning calorimetry, thermogravimetric analysis, optical microscopy equiped with hot-stage, and scanning electron microscopy. It was observed that when (PET) is cured at very high temperature above its original melting point, cross-linking of the (PET) samples occurs. The cross-linking takes place in the melt in this case. With increasing the curing temperature, the area of the higher melting peak temperature decreases due to the increase in cross-linking of (PET). In terms of spherulitic texture, it was found that with increasing the curing temperature more inter-lamellar intra-spherulitic inclusions are observed in the material.     

聚酯(PET)的混料和共混改性

就聚酯加工应用中混料和共混改性一些基本的技术原理进行讨论 ,如间歇法生产中不同批次的混料方法 ,新料与回收料的共混 ,白料与色母料的共混 ,还有PET改性共混涉及到的相容、结晶相分离等问题     

Time-resolved X-ray scattering and calorimetric studies on the crystallization behaviors of poly(ethylene terephthalate) (PET) and its copolymers containing isophthalate units

Time-resolved small-angle X-ray scattering (SAXS) measurements were carried out for PET and its copolymers undergoing isothermal crystallization. Wide-angle X-ray diffraction and differential scanning calorimetric measurements were also performed. Our data analysis of the SAXS results for PET and the copolymers clearly demonstrate that the one layer thickness l₁ (derived directly from the correlation functions of the measured SAXS profiles) is the lamellar crystal thickness d_c, not the amorphous layer thickness d_a. The observed d_c values are found to be always smaller than d_a, regardless of polymer composition. d_c is highly dependent on the crystallization temperature, showing that the degree of supercooling is the major factor determining the thickness of lamellar crystals. No thickening, however, occurs in isothermal crystallizations. The kinked isophthalate units in the copolymer are found to be mostly excluded from the lamellar crystals during the crystallization process, leading to an increase of the amorphous layer thickness. Moreover, the kinked, rigid nature of the isophthalate unit was found to restrict crystal growth along the chain axis of the copolymers and also to lower their crystallinity. Unlike d_c, d_a decreases with crystallization time, causing a reduction of the long period in the lamellar stack. This drop in d_a is interpreted in this paper by taking into account several factors that could influence crystallization behavior: the d_a distribution in the lamellar stacks and its variation with time, the number of lamellae in the lamellar stacks and their effect on the SAXS profile, and the relaxation of polymer chains in the amorphous layers.     

Roll-drawing and die-drawing of toughened poly(ethylene terephthalate). Part 2. Fracture behaviour

Orientation of polymers in the solid-state has been used for a long time in enhancing the properties of the products and the die-drawing process at Leeds University (UK) and the roll-drawing process at IMI (Canada) have been used to produce oriented polymer products in a wide variety of shape and sizes. In this work, we explore the fracture behaviour of isotropic and oriented toughened poly(ethylene terephthalate) (PET) in order to improve the toughness of the oriented products in a direction other than the principal draw direction.The fracture behaviour of isotropic and oriented PET homopolymer and the two PET blends (containing 10% polyethylene elastomer and 10% compatibilized elastomer) was studied using the multi-specimen J-integral approach. In the isotropic case, the compatibilized blend had higher toughness than the homopolymer and the non-compatibilized blend. The oriented sheets from the die-drawing and roll-drawing process, drawn to a draw ratio of 3.2 at 170 °C were tested with the initial notch both parallel and perpendicular to the draw direction. For the former case, the compatibilized blend was tougher and in the other direction the drawn homopolymer was tougher than the blends. At similar draw ratios, the fracture behaviour and the toughness of the oriented sheets from the die-drawing and roll-drawing processes were identical.     

Mechanism and kinetics of transesterification in poly(ethylene terephthalate) and poly(ethylene 2,6-naphthalene dicarboxylate) polymer blends

In a previous work [L. Alexandrova, A. Cabrera, M.A. Hernández, M.J. Cruz, M.J.M. Abadie, O. Manero, D. Likhatchev, Polymer 43 (2002) 5397. [1]], a model compounds study on the kinetics of a transesterification reaction in poly(ethylene terphthalate)-poly(ethylene naphthalene 2,6-dicarboxylate), PET-PEN blends, resulting from melt processing, was simulated using model compounds of ethylene dibenzoate (BEB) and ethylene dinaphthoate (NEN). A first-order kinetics was established under pseudo first-order conditions for both reactants, and thus the overall transesterification reaction was second-order reversible. Direct ester-ester exchange was deduced as a prevailing mechanism for the transesterification reaction under the conditions studied.In this work, the actual PET-PEN system was melt processed by mixing the polymers below the critical reaction temperature in a twin-screw extruder. Thereafter, the reaction was induced by temperature in open glass ampoules. A second order reversible kinetics was measured, in agreement with the kinetics established in the previous model compounds study. The equilibrium constant value corresponds to a forward rate constant which is four times larger than the reverse rate constant. The activation thermodynamic parameters confirmed the direct ester-ester exchange mechanism for the reaction.     

Blends of poly(ethylene terephthalate) and epoxy as matrix material for continuous fibre reinforced composites

Abstract

The morphology and mechanical properties of poly(ethylene terephthalate) (PET)–epoxy blends and the application of these blends in continuous glass fibre reinforced composites have been investigated. Epoxy resin was applied as a reactive solvent for PET to obtain homogeneous solutions with a substantially decreased melt viscosity. The epoxy resin in these solutions was cured using an amine hardener according to two different schedules. In the first, high temperature curing at 260°C preceded low temperature crystallisation of the PET at 180°C. In the second, the PET was allowed to crystallise prior to low temperature curing at 180°C. After cure, all blends revealed a phase separated morphology of dispersed epoxy in a continuous PET matrix. The flexural strength and failure strain of all cured blends showed an increase with increasing epoxy content, whereas the high temperature cured blends exhibited overall lower flexural properties than those cured at the lower temperature. Microstructural analysis and flexural properties of continuous glass fibre reinforced PET–epoxy laminates showed that the composites obtained had a low void content. These PET–epoxy laminates had increased inplane shear strength in comparison with unmodified PET based laminates, indicating considerably increased fibre–matrix adhesion.     

Effect of macromolecular orientation on the structural relaxation mechanisms of poly(ethylene terephthalate)

In this work we used Dielectric Spectroscopy (DS) and Thermally Stimulated Depolarisation Currents (TSDC) analysis to obtain values of fragility indexes as defined in the ‘Strong-fragile’ glass former liquid concept. DS and TSDC measurements have been performed on a series of polyethylene terephthalate (PET) samples with various degrees of macromolecular orientations. These orientations have been obtained by means of uniaxial drawing performed above the glass transition temperature. Samples with draw ratios λ=1, λ=2 and λ=5 have been obtained. From TSDC measurements, the fragility index of the glassy state (m_g) can be obtained, while DS measurements allow to reach the fragility index value of the liquid-like state (m). Furthermore, for low draw ratio, the material is practically wholly amorphous and its liquid state can be classified as ‘fragile’ glass forming liquid while for semi-crystalline PET (draw ratio λ=5), it is shown the remaining amorphous phase becomes stronger (m varies from 170 to 60 and m_g varies from 81 to 21).     

The effect of physical ageing on the properties of poly(ethylene terephthalate)

Physical ageing rates of poly(ethylene terephthalate) have been measured, and ageing is interpreted to be associated with the conventional glass formation process, which occurs at a more rapid rate at higher temperatures. Ageing is accompanied by a marked change in mechanical properties, increased tensile yield stress and drawing stress, more localized yielding of the polymer and a marked decrease in impact strength. The fracture results have been attributed to the increased yield stress and a change in contribution of plane stress and plane strain conditions in the samples. Fracture surfaces show evidence of mixed modes of fracture.