Ethylene Naphthalate Research Articles

Confined crystallization in phase-separated poly(ethylene terephthalate)/poly(ethylene naphthalene 2,6-dicarboxilate) blends

The isothermal cold crystallization of poly(ethylene terephthalate)(PET) in cryogenic mechanical alloyed blends of PET and Poly(ethylene naphthalene 2,6-dicarboxilate)(PEN) 1:1 by weight has been investigated by simultaneous small and wide angle X-ray scattering (SAXS and WAXS) and dielectric spectroscopy (DS). For transesterification levels higher than 23% the blends tend to transform into a one-phase system and the crystallization of PET is strongly inhibited due to the significant reduction of the PET segment length. For lower levels of transesterification the blends are phase separated and the overall crystallization behaviour can be explained considering the confined nature of the PET domains in these blends. The formation of a rigid amorphous phase in the intra-lamellar stack amorphous regions is reduced in the blends due to a lower probability of stack formation in the confined PET-rich domains. The more effective filling of the space by the lamellar crystals in the blends provokes a stronger restriction to the amorphous phase mobility of PET in the blends than in pure PET.

Nonlinear Mechanooptical Behavior of Poly(ethylene naphthalate)/Poly(ether imide) Blends. Dynamic Phase Behavior

The mechanooptical behavior and structural organization processes in melt miscible PEN−PEI blends have been investigated in the rubbery state as influenced by blend composition, stretching temperature, and deformation rate. This was accomplished using a spectral birefringence system integrated in a specially built uniaxial stretching machine1,2 where real-time birefringence, true stress, and true strain are monitored during the course of the deformation. Three distinct stress−optical regimes have been observed with an additional glassy component. The final structure and deformation behavior of the blends have been mapped out in a dynamic phase diagram showing that the material undergoes three critical structural transitions. At low temperatures near Tg the polymer remains in a nematic-like state, and orientation-induced crystallization occurs only above a certain stretching temperature. At intermediate temperatures the liquid−liquid (Tll) transition occurs wherein the material transforms from a “structured liquid” to a “true liquid” state at (1.08Tg (K)) exhibited by the disappearance of the initial glassy component as the material becomes devoid of the segmental correlations. At higher temperatures, where the relaxation process dominates and where the thermal induced crystallization is still suppressed, the material was found to remain in the amorphous state even after being stretched to large deformation levels.

Properties of poly(ethylene terephthalate)–poly(ethylene naphthalene 2,6‐dicarboxylate) blends with montmorillonite clay

AbstractThe production and properties of blends of poly(ethylene terephthalate) (PET) and poly(ethylene naphthalene 2,6‐dicarboxylate) (PEN) with three modified clays are reported. Octadecylammonium chloride and maleic anhydride (MAH) are used to modify the surface of the montmorillonite–Na+ clay particles (clay–Na+) to produce clay–C18 and clay–MAH, respectively, before they are mixed with the PET/PEN system. The transesterification degree, hydrophobicity and the effect of the clays on the mechanical, rheological and thermal properties are analysed. The PET–PEN/clay–C18 system does not show any improvements in the mechanical properties, which is attributed to poor exfoliation. On the other hand, in the PET–PEN/clay–MAH blends, the modified clay restricts crystallization of the matrix, as evidenced in the low value of the crystallization enthalpy. The process‐induced PET–PEN transesterification reaction is affected by the clay particles. Clay–C18 induces the largest proportion of naphthalate–ethylene–terephthalate (NET) blocks, as opposed to clay–Na+ which renders the lowest proportion. The clay readily incorporates in the bulk polymer, but receding contact‐angle measurements reveal a small influence of the particles on the surface properties of the sample. The clay–Na+ blend shows a predominant solid‐like behaviour, as evidenced by the magnitude of the storage modulus in the low‐frequency range, which reflects a high entanglement density and a substantial degree of polymer–particle interactions. Copyright © 2005 Society of Chemical Industry

Rheological properties and interfacial slip of a multilayer structure under dynamic shear

AbstractInterfacial slip between polymer melt under steady shear has been studied using a simplified multilayer structure. In this investigation, interfacial slip under dynamic shear was studied by calculating the angular displacements of the multilayer structure and its component layers. On the basis of the angular displacements, a slip index was defined to quantify the degree of interfacial slip. A relationship governing the rheological behavior of the multilayer structure under slip and nonslip condition was established. These results were correlated with equations derived from consideration of energy equilibrium in the multilayer structure. Polymer multilayer structures of high‐density polyethylene/polystyrene and liquid crystal polymer(LCP)/poly ethylene naphthalate(PEN) were investigated. Of all the polymers investigated, large interfacial slip was found at LCP/PEN interface under dynamic shear. The high rigidity and alignment along the interface of LCP molecules was believed to prevent chain entanglement in the interfacial layer and therefore promote interfacial slip at the interface. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2683–2693, 2005

Short‐term thermal endurance evaluation of thermoplastic polyesters by isothermal and nonisothermal thermogravimetric analysis

AbstractThermogravimetric analysis, carried out in a pure oxygen flow both in isothermal and constant‐rate heating conditions, is proposed as an analytical technique for the estimation of thermal endurance parameters (the temperature index and halving interval) of polymeric materials, according to the short‐term procedure suggested by the IEC 61026 Standard. This technique was applied for the determination of the activation energy of the degradation process of three thermoplastic polyesters used in the electrical and packaging industries: poly(ethylene terephthalate), poly(buthylene terephtalate), and poly(ethylene naphthalate). The results obtained are presented and compared with results previously derived by the long‐term conventional procedure described in IEC 60216; satisfactory agreement of the thermal endurance parameters was generally observed. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 968–973, 2005

Uniaxially stretched poly(ethylene naphthalene 2,6-dicarboxylate) films studied by broadband dielectric spectroscopy

The thermal behaviors of amorphous PEN films uniaxially stretched above and below T g have been characterized by Temperature Modulated DSC. When drawing is performed above T g, the degree of crystallinity and the glass transition temperature T g increase with increasing drawing ratio. PEN samples stretched below T g are more crystalline than when stretched above T g. Moreover the cold crystallization phenomenon disappears with drawing as a result of the mechanically induced crystallization. Broadband dielectric spectroscopy has also been used to study the influence of the orientation on the molecular mobility of PEN to gain insight into the microscopic origin of the relaxation processes in the transverse direction i.e. when the electric field is perpendicular to the stretching direction. Dielectric relaxation phenomena are thus discussed as a function of the microstructure (orientation, crystallinity). The α-relaxation dynamics associated with the glass transition are largely slowed down by the drawing process and the relaxation strength decreases. This can be related to a transformation of the amorphous phase into (i) crystalline, (ii) rigid amorphous fraction (RAF) and/or constrained amorphous phase with lower molecular mobility due to the crystallization induced by the orientation process. In contrast, the dynamics of the β*-relaxation are apparently increased and the activation energy for the uniaxially stretched samples decreases compared to the unstretched isotropic amorphous state. If the β*-relaxation is assigned to the presence of naphthalene aggregates, this leads to the conclusion that stretching is structurally altering the naphthalene aggregates (creation of defective aggregates that induces a higher molecular mobility) or orientation is selecting the faster motions active for β*. The β-relaxation which corresponds to more local motions implying reorientation of the ester groups seems to be broad and composed of two components as in the case of PET: the β 1- and β 2-relaxations. While the high frequency β 1-component relaxation strength is increasing significantly with the deformation below T g, that of the β 2-process is more related to the presence of water.

Application of fractional calculus to the modeling of dielectric relaxation phenomena in polymeric materials

AbstractA model based on the concept of fractional calculus is proposed for the description of the relative complex permittivity (ε*r = ε′r − iε′r, where ε′r and ε″r are the real and imaginary parts of ε*r) in polymeric materials. This model takes into account three dielectric relaxation phenomena. The differential equations obtained for this model have derivatives of fractional order between 0 and 1. Applying the Fourier transform to fractional differential equations and considering that each relaxation mode is associated with cooperative or noncooperative movements, we have calculated ε*r(iω,T) (where ω is the angular frequency and T is the temperature). The isothermal and isochronal diagrams obtained from the proposed model of ε′r and ε″r clearly show three dielectric relaxation phenomena; in the isochronal case, each relaxation mode manifests by an increase in ε′r with increasing temperature, and this behavior is associated with a peak of ε″r(T) in each case. The model is matched with the experimental data on poly(ethylene naphthalene 2,6‐dicarboxylate) (PEN) to justify its validity. Poly(ethylene 2, 6–naphthalene dicarboxylate) (PEN) is a semicrystalline polymer that displays three dielectric relaxation processes: β, β*, and α. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 923–935, 2005

Viscoelastic properties of poly(butylene terephthalate)/poly(ethylene naphthalate) blends

Melt blends of poly(butylene terephalate) (PBT) and poly(ethylene naphthalate) (PEN) with 30 and 60 wt% PEN were prepared using a single screw extruder and an injection moulding machine. Stress relaxation tests for the specimens of PBT/PEN blends and the homopolymers were carried out using an Instron testing machine in an Instron environmental chamber. The Taguchi method of experimental design analysed how different levels of temperature, PEN content and initial stress affected the relaxation behaviour of PBT/PEN blends and homopolymers. From the response tables and analyses of main and interaction effects, it was shown that the most significant factor was temperature, followed by PEN content and then the initial stress. Consequently, high temperature, low PEN content and high initial stress speeded up stress relaxation rate of specimens. Interaction effects between factors were insignificant. To fit the relaxation curves of the PBT/PEN blends and the homopolymers at different temperatures, PEN contents and the initial stresses, four different equations were attempted with Matlab™, which determined the coefficients of these functions using the experimental data of stress change with time. The simulated curves from the most suitable function among them were shown using the calculated coefficients to predict the relaxation behaviour of PBT/PEN blends (50% PEN) at temperatures of 30 and 60°C with an initial stress of 7 MPa.

Thermal and NMR characterization on trans-esterification-induced phase changes in blends of poly(ethylene-2,6-naphthalate) with poly(pentylene terephthalate)

By using thermal and NMR analyses with supporting evidence from X-ray and scanning electron and optical microscopy, this study has attempted to clarify confusing issues of physical miscibility vs. chemical trans-reaction in blends of aryl polyesters upon heating. The study demonstrated that the blends of poly(pentylene terephthalate) (PPT) with poly(ethylene naphthalate) (PEN) were initially immiscible; however, with heating/annealing at high temperatures (300 °C) for long enough times, the original two phases merged into one single phase composed of two polyesters and some minor fractions of copolyesters. Upon extended heating, however, two original polyesters disappeared, and a random copolyester, coded as EN- co-PT, of various sequence lengths was produced as a result of extensive trans-reactions between PEN and PPT. The trans-reacted products from heated PEN/PPT (50/50) blend were characterized using 1H NMR. The sequence structures of the produced co-polyesters and intermediate products were determined by a triad analysis, which showed that the mean sequence lengths became shorter and the randomness increased with time of heating. X-ray analysis confirmed that the PEN/PPT (50/50) blend completely lost its crystallizability only when heated at 300 °C for time of 60 min or longer, indicating formation of fully random copolyesters.

Large Deformation Mechano-Optical and Dynamical Phase Behavior in Uniaxially Stretched Poly(ethylene naphthalate)

Uniaxial deformation behavior of PEN films in the rubbery state is investigated as a function of processing temperature, draw rate, and molecular weight (Mw). Real-time measurement of true stress−true strain and birefringence of the films during the process of stretching is obtained by using a novel instrumented uniaxial stretching machine that couples the spectral birefringence system with the real-time strain detection system. This enables quantitative measurement of true stress−true strain and birefringence, enabling quick and nonstop measurement of stress−optical behavior (SOB) of PEN. A three-regime SOB was obtained for PEN films: (i) regime Istress optical rule applies with a stress optical constant (SOC) of 27.5 GPa-1; following this regime the behavior become nonlinear in (ii) regime II and birefringence rises steeply; finally in (iii) regime III, birefringence reaches a plateau while stress increases. All regimes are affected by the temperature, rate, and Mw. Decreasing temperature and increasing stretching rate and Mw extend the range of regime I over which the material remains amorphous. Regime II and III slopes were found to be dependent on rate and Mw. Measurement of strain rate indicates that affine deformation holds until the end of regime I, rising sharply in regime II, as a result of spontaneous deformation. The strain rate rapidly decreases to zero when regime III starts. The peak in strain rate coincides with the fast increase of birefringence during regime II. According to WAXD and DSC studies, the material remains amorphous in the regime I. Right after the transition to the regime II, the amorphous chains are extremely oriented but possess low translational order, which prevents them from crystallizing. Further stretching the structure evolves very rapidly to a crystalline structure, with approximately 40% crystallinity that is maintained throughout the regime III at the end of which finite chain extensibility prevents further changes in the structure. A model representing the structural mechanisms followed from the amorphous to the crystalline state is suggested. Both rate and temperature have a significant effect on the structural development of PEN: at intermediate to high rates and low temperatures a semicrystalline structure is obtained whereas at very high temperatures and low rates the structure remains completely amorphous despite the large deformation that has been applied. On the basis of the these data, a dynamic phase diagram was constructed.

Thermal and crystallization characteristics of poly(trimethylene terephthalate)/poly(ethylene naphthalate) blends

Poly(trimethylene terephthalate) (PTT)/poly(ethylene naphthalate) (PEN) blends were miscible in the amorphous state in all of the blend compositions studied, as evidenced by a single, composition-dependent glass transition temperature ( T g) observed for each blend composition. The variation in the T g value with the blend composition was well predicted by the Gordon–Taylor equation, with the fitting parameter being 0.57. The cold-crystallization peak temperature decreased with increasing PTT content, while the melt-crystallization peak temperature decreased with increasing amount of the minor component. The subsequent melting behavior after both cold- and melt-crystallization exhibited melting point depression, in which the observed melting temperatures decreased with increasing amount of the minor component. During melt-crystallization, both components in the blends crystallized concurrently just to form their own crystals. The blend with 60% w/w of PTT exhibited the lowest total apparent degree of crystallinity.

Lifetime improvement of poly(ethylene naphthalate) by ZnO adhesive coatings

Zinc oxide (ZnO) coatings were deposited by RF magnetron sputtering on the surface of poly(ethylene naphthalate) (PEN) films to protect the polymer against ultraviolet (UV) radiation. To increase the adhesion of the coating, PEN films were submitted to cold plasma treatments before deposition. Wettability measurements showed that the adhesion strength of the coatings was increased by a CO 2 plasma treatment of PEN and varied with the oxygen partial pressure in the sputtering gas. The photodegradation of the ceramic/polymer assemblies, in conditions of artificial accelerated ageing, was monitored by infra-red and UV-vis spectroscopies. Results showed that photoprotection increases with ZnO thickness up to 200 nm. In addition, the sputtering parameters, which act on the composition, the structure and the optical properties of ZnO, were optimised to obtain the best coating in terms of UV and oxygen barrier.

Moisture barrier of AlxOy coating on poly(ethylene terephthalate), poly(ethylene naphthalate) and poly(carbonate) substrates

The moisture barrier property of AlxOy coated poly(ethylene terephthalate) (PET), poly(ethylene naphthalate) (PEN) and poly(carbonate) (PC), have been investigated. The differences in the morphology of the AlxOy sputtered grown on these substrate were investigated using atomic force microscopy (AFM). The initial growth of the AlxOy followed closely the topology of the substrate and an amplified roughness was observed. In the fully grown AlxOy, the comparative roughness followed that of the substrates. It has been found that a single layer AlxOy improved the moisture barrier of PET by an order of magnitude, PC by two orders of magnitude while no improvement was observed for PEN. UV-ozone treatment on PC further improved the moisture barrier, while no improvement was observed for PET and PEN. The comparative effects of the substrate surface roughness and surface energy on the moisture barrier are discussed.

二段階プラズマプロセスによる超はっ水高分子基板の作製

The wettability of a solid surface is governed by two factors, that is, its surface morphology and composition. Ultra water-repellent polymeric substrates [poly(ethylene naphthalate) and polystyrene] have been fabricated while retaining their transparency by a two-step plasma process combining oxygen plasma etching and plasma-enhanced chemical vapor deposition (PECVD). In order to avoid optical scattering, appropriate nanotextures were prepared on the polymeric substrates through the oxygen plasma etching. Subsequently, a hydrophobic layer was coated on the nanotextured surfaces by PECVD using an organosilane source. The modified surfaces were certainly ultra-water-repellent, showing water contact angles greater than 150°.

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.

Effects of Residual Nuclei on Crystals and Equilibrium Melting Points of Dual Crystals in Poly(ethylene 2,6‐naphthalene‐dicarboxylate)

AbstractSummary: The crystal structures and possible transformations in poly(ethylene naphthalate) (PEN) were examined using differential scanning calorimetry (DSC) and wide‐angle X‐ray diffraction (WAXD). The crystal cells (α‐ and β‐form) were dependent on several factors related to their thermal histories. For PEN subjected to Tmax = 280 °C (where Tmax is the maximum melt temperature at which the samples were treated before crystallization), only the α‐form developed regardless of the temperature of crystallization or cooling rate. However, for PEN subjected to Tmax = 300 °C, PEN developed mixed dual crystals, with greater fractions of the α‐form at low temperatures of crystallization (220 °C or lower) or higher cooling rates, but higher β‐form fractions at higher crystallization temperatures (>230 °C). The difference in the relative stability of these two crystals was utilized to prepare PEN containing only the α‐form or only the β‐form. The equilibrium melting temperatures of these two crystal forms in PEN were then measured separately. For PEN containing only the β‐form, T (289.3 °C) was found by using the Hoffman‐Weeks technique, while for PEN containing only the α‐form, T was determined using the same technique but was found to be lower (282.6 °C).Comparison of Hoffman‐Weeks extrapolations for the α‐crystal and β‐crystal, respectively, in PEN.magnified imageComparison of Hoffman‐Weeks extrapolations for the α‐crystal and β‐crystal, respectively, in PEN.

Permeability of N2, Ar, He, O2, and CO2 through as‐extruded amorphous and biaxially oriented polyester films: Dependence on chain mobility

AbstractFor as‐extruded amorphous and biaxially orientated polyester films based on poly(ethylene terephthalate), poly(ethylene naphthalate), and copolymers containing poly(ethylene terephthalate) and poly(ethylene naphthalate) moieties, permeability, diffusion, and solubility coefficients are interpreted in terms of chain mobility. The influence of polymer morphology is determined by comparison of the data for as‐extruded amorphous sheets and materials produced with different biaxial draw ratios. The crystallinities of the samples were assessed using differential scanning calorimetry and density measurements. Changes in mobility at a molecular level were investigated using dielectric spectroscopy and dynamic mechanical thermal analysis. The study, in conjunction with our earlier work, leads to the conclusion that the key to understanding differences in gas transport is the difference in local chain motions rather than in free volume. This was illustrated by the permeability results for He, Ar, N2, and O2 in the range of polyesters. However, the permeability of CO2 was found to require alternative explanations because of polymer–penetrant interactions. For biaxially oriented samples, the differences in diffusivity are not only due to differences in local chain motions, but also additional constraints resulting from the increased crystallinity and chain rigidity—which also act to hinder segmental mobility. The effectiveness of the reduction in permeability in the biaxially oriented films is consequently determined by the ability of the polymer chains to effectively align and form crystalline structures. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2916–2929, 2004

Synthesis of patterned polymer brushes from flexible polymeric films

Surface-initiated polymerizations were carried out from polymeric surfaces of commercially important polyester films, poly(ethylene terephthalate) (PET) and poly(ethylene naphthalate) (PEN). These plastic films were modified prior to polymerization by plasma oxidation, exposing surface hydroxyl groups, in order to immobilise patterned self assembled monolayers (SAMs) of trichlorosilane initiator, through the soft lithographic method of microcontact printing (μCP). Subsequently, polymerizations were initiated from the surface via controlled atom transfer radical polymerization (ATRP), under aqueous conditions, to create patterned brushes of the thermo-responsive polymer poly( N-isopropyl acrylamide) (PNIPAM). By creating patterned, rather than homogeneous brushes characterization was made possible by atomic force microscopy (AFM).

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

AbstractThe 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

Mechanical, hygroscopic, and thermal properties of metal particle and metal evaporated tapes and their individual layers

AbstractMechanical and thermal properties of magnetic tapes and their individual layers strongly affect the tribology of magnetic head–tape interface and reliability of tape drives. Dynamic mechanical analysis, longitudinal creep, lateral creep, Poisson's ratio, the coefficient of hygroscopic expansion (CHE), and the coefficient of thermal expansion (CTE) tests were performed on magnetic tapes, tapes with front coat or back coat removed, substrates (with front and back coats removed), and never‐coated virgin films of the substrates. Storage modulus and loss tangent values were obtained at a frequency range from 0.016 to 28 Hz, and at a temperature range from −50 to 150 or 210°C. Longitudinal creep tests were performed at 25°C/50% RH, 40°C/25% RH, and 55°C/10% RH for 50 h. The Poisson's ratio and lateral creep were measured at 25°C/50% RH. CHE was measured at 25°C/15–80% RH. CTE values of various samples were measured at a temperature range from 30 to 70°C. The tapes used in this research included two magnetic particle (MP) tapes and two metal evaporated (ME) tapes that were based on poly(ethylene terephthalate) and poly(ethylene naphthalate) substrates. The master curves of storage modulus and creep compliance for these samples were generated for a frequency range from 10−20 to 1015 Hz. The effect of tape manufacturing process on the various mechanical properties of substrates was analyzed by comparing the data for the substrates (with front and back coats removed) and the never‐coated virgin films. A model based on the rule of mixtures was developed to determine the storage modulus, complex modulus, creep compliance, and CTE for the front coat and back coat of MP and ME tapes. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1319–1345, 2004