PEN Films Research Articles

Investigation of the optical anisotropy of PET and PEN films by VIS-FUV to IR spectroscopic ellipsometry

In the last years, a significant amount of research is being performed in the field of polymer research for novel applications, such as flexible electronic devices, photovoltaic cells, high performance optics, data storage, etc. Toward this direction, in this work, the optical anisotropy of biaxially stretched poly(ethylene terephthalate) (PET) and poly(ethylene naphthalate) (PEN) films has been extensively investigated. The optical properties of the films have been studied in terms of their optical, electronic and vibrational response, by Fourier transform IR spectroscopic ellipsometry (FTIRSE) (900–3500 cm −1) and Vis-fUV variable angle SE (1.5–6.5 eV) techniques. The films optical anisotropy is the result of the stretching procedure during their fabrication, which results to the structural rearrangement of the macromolecular chains parallel to the stretching direction and to a higher structural symmetry. During the SE spectra analysis, the films have been approximated as uniaxial materials with their optic axis parallel to the sample/ambient interface leading to the accurate determination of the principal components ɛ ||( ω) and ɛ ⊥( ω) of the dielectric function ɛ( ω). The detailed study of the electronic transitions has been performed in the Vis-fUV region, where the characteristic features corresponding to the n → π* electronic transitions of the carbonyl –C O group and the 1A 1g → 1B 1u transition due to the π → π* excitation of the π-electron structures have been identified and analysed. Furthermore, the FTIRSE spectra allowed the accurate identification and assignment of the features of ɛ( ω) to the vibrational modes of the various bonding structures characteristic of the PET and PEN macromolecular chains.

Morphology and texture development of uniaxially stretched poly(ethylene naphthalene-2,6-dicarboxylate)

The texture development of PEN films with different semicrystalline morphologies have been studied by X-ray diffraction. These different structures have been obtained by uniaxially stretching PEN amorphous films at 100 and 160°C (below and above Tg) at different drawing ratios. Samples have also been characterized by DSC to determine the crystallinity ratios, the crystallization, and melting temperatures. To define the orientation of crystallites in the oriented samples, pole figures have been constructed, as a function of temperature and drawing ratio (DR) in the range 1.5–4. In the range from DR = 2 to 4 the orientation is clearly uniplanar-axial. At Tdraw = 100°C the crystallinity shown by DSC analysis is higher than the sample stretched at 160°C. The orientation is also higher when samples are stretched at 100°C. The naphthalene rings mainly stay in the plane of the film with a lower fraction perpendicular to the plane of the film. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 395–401, 2007

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.

Characterization of Higher-Order Structure of Poly(ethylene-2,6-naphthalate) Treated with Supercritical Carbon Dioxide

We have prepared poly(ethylene-2,6-naphthalate) (PEN) films having higher-order structure with fine crystallites using a supercritical carbon dioxide (scCO2) treatment technique at a relatively low-temperature range, from 110 to 170 °C. After the scCO2 treatment, the glass transition temperature Tg decreased by more than 50 °C, and the PEN films were crystallized. Long-term change in the FT-IR absorbance intensity at 2335 cm-1 (CO) was in good agreement with the change in Tg. The large decrease in Tg was attributed to the sorption of the CO2 molecules into the PEN film. Moreover, the increase in the treatment pressure increased the amount of absorbed CO2 and reduced Tg, which can promote crystallization. The higher-order structure, long period, lamella, and interface thickness of the crystallized PEN films were calculated from the one-dimensional correlation function by SAXS. These parameters were all linearly related to the treatment temperature. The crystallite size obtained from the Scherrer equation d...

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.

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.

Study on impedance transition of PEN thin film

PEN films were prepared by vacuum deposition. Their electrical bistable properties were studied under conditions of various circuit parameters.A decrease of time needed for impedance transition with increasing circuit current was observed. The film impedance showed a nonlinear characteristics and then data fitting was done for the nonlinearity. Furthermore, an energy effect was found during the transition, i.e. when the applied voltage exceeds a threshold, the energy consumption keeps invariable.

Photoprotection of poly(ethylene-naphthalate) by zinc oxide coating

Zinc oxide coatings were deposited by sputtering on poly(ethylene-naphthalate) (PEN) films in order to protect the polymer against photodegradation. The main effects of the sputtering parameters (power, pressure, oxygen concentration) on the composition, structure and optical properties were studied. The adhesion of the ZnO coating on PEN films was evaluated by means of the 180° peeling test. Treatments by cold plasmas (Ar, Ar–O2, CO2) were used to increase the surface energy of PEN. The barrier properties of the ZnO coating to the oxygen diffusion were examined. The photo-protective properties of zinc oxide coatings deposited in various conditions on PEN films were studied by irradiating assemblies in artificial conditions (wavelength >300 nm). The rate of photo-oxidation of PEN was characterized by infrared measurements of the hydroxylated photoproducts (3100–3700 cm−1). The results indicate that the photodegradation of PEN was strongly reduced by the presence of ZnO coatings.

Photoprotection of poly(ethylene-naphthalate) by zinc oxide coating

Zinc oxide coatings were deposited by sputtering on poly(ethylene-naphthalate) (PEN) films in order to protect the polymer against photodegradation. The main effects of the sputtering parameters (power, pressure, oxygen concentration) on the composition, structure and optical properties were studied. The adhesion of the ZnO coating on PEN films was evaluated by means of the 180° peeling test. Treatments by cold plasmas (Ar, Ar–O 2, CO 2) were used to increase the surface energy of PEN. The barrier properties of the ZnO coating to the oxygen diffusion were examined. The photo-protective properties of zinc oxide coatings deposited in various conditions on PEN films were studied by irradiating assemblies in artificial conditions (wavelength >300 nm). The rate of photo-oxidation of PEN was characterized by infrared measurements of the hydroxylated photoproducts (3100–3700 cm −1). The results indicate that the photodegradation of PEN was strongly reduced by the presence of ZnO coatings.

Structural development of poly(ethylene 2,6-naphthalene dicarboxylate) film upon solvent drawing

To investigate the effect of “chemical energy” by solvent on structural development, initially molded amorphous poly(ethylene 2,6-naphthalene dicarboxylate) (PEN) films were drawn in various solvent systems and at the optimum temperatures deliberately determined, and the resulting fine structure and properties were analyzed by using several experimental techniques. Water, 1-butanol, 1,4-dioxane/water (20 : 80 by volume), and 1,4-dioxane/1-butanol (20 : 80 by volume) were chosen for drawing solvent. For this study, in view of chemical structure and solubility parameter, though, these are nearly immiscible or partially miscible liquids against PEN, with just the plasticizing actions more or less the primary concern here. Interesting enough, the temperature range near the main endothermic peak corresponding to the depressed boiling point of liquid caused by unfavorable interaction between PEN and solvent in mixtures of amorphous PEN film with various solvent systems, as determined by the DSC scans, was found to coincide with the optimum drawable range for each solvent system, over which several experiments, including the determination of maximum draw ratio (DRmax) have been carried out throughout the study. The experimental results obtained from this study could be explained, through qualitatively, in terms of the interactions between PEN and solvents. Hence, it is expected to control the fine structure and properties of PEN films resulting from the low-temperature solvent drawing via a suitable choice of liquids and the corresponding draw temperature ranges. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1357–1365, 2003

Shrinkage behavior after the heat setting of biaxially stretched poly(ethylene 2,6‐naphthalate) films and bottles

AbstractAmorphous preforms of poly(ethylene 2,6‐naphthalate) (PEN) were biaxially drawn into bottles up to the desired volume under industrial conditions. These bottles were used to characterize the shrinkage behavior of the drawn bottles with or without heat treatment and to study structural variations during heat setting. During drawing, a rigid phase structure was induced, and the amount of the induced rigid phase structure was linearly related to the square root of the extra first strain invariant under equilibrium conditions. During the production of these bottles, this equilibrium was not attained because of high stretching conditions and rapid cooling after stretching. The structure after orientation contained a rigid amorphous phase and an oriented amorphous phase. The shrinkage behavior was a function of the temperature and time of heat setting. Long heat‐setting times, around 30 min, were used to characterize the possible structural variations of the oriented PEN after heat setting at equilibrium. Under the equilibrium conditions of heat setting, the start temperature of the shrinkage was directly related to the heat‐setting temperature and moved from 60°C without heat treatment up to a temperature of 255°C by a heat‐setting temperature of 255°C; this contrasted with poly(ethylene terephthalate) (PET), for which the start temperature of shrinkage was always around 80°C. For heat‐setting temperatures higher than 220°C, the structural variations changed rapidly as a function of the heat‐setting time, and the corresponding shrinkage of the heat‐set samples sank below 1% in a timescale of 30–60 s for a film thickness of 500 μm. The heat treatment of the oriented films taken out of the bottle walls with fixed ends stabilized the induced structures, and the shrinkage of these heat‐set films was zero for temperatures up to the heat‐setting temperature, between 220 and 265°C, if the heat‐setting time was sufficient. According to the results obtained, a heat‐setting time of 30 s, for a film thickness of 500 μm, was sufficient at a heat‐setting temperature of 255°C to stabilize the produced biaxially oriented PEN bottles and to take them out the mold without further shrinkage. During the drawing of PEN, two different types of rigid amorphous phases seemed to be induced, one with a mean shrinkage temperature of 151°C and another rigid amorphous phase, more temperature‐stable than the first one, that shrank in the temperature range of 200–310°C. During heat setting at high temperatures, a continuous transformation of the less stable phase into the very stable phase took place. The heat‐set method after blow molding is industrially possible with PEN, without the complicated process of subsequent cooling before the molds are opened, in contrast to PET. This constitutes a big advantage for the blow molding of PEN bottles and the production of oriented PEN films. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1462–1473, 2003

Adhesive properties of silanol surface modified poly(ethylene naphthalate) film

Semicrystalline poly(ethylene naphthalate) (PEN) films were modified with 3-aminopropyltriethoxysilane (APS) and subsequently hydrolyzed to give silanol (SiOH) functionality to the PEN surface by means of amide linkages (PEN-CONH(CH2)3Si(OH)3). The modified PEN films were characterized by reflectance FT-IR, contact angle (ca. 80° before modification and ca. 43° after modification) and by fluorescence spectroscopy. The modified films were terminated at 130 °C and 500 psi. The adhesion peel test showed that these modified PEN films form strong adhesive bonds with each other (12.51 kg/m) as well as with glass (6.43 kg/m). SEM analysis showed that failure during the peel strength determination occurred within the film matrix and not at the adhesion interface. Delaminated area of the modified PEN surface after the peel test (film-to-glass; 350 ×).

An X-ray diffraction study of poly(ethylene-2,6-naphthalate), PEN

X-ray diffraction techniques have been applied to study the crystallization of poly(ethylene-2,6-naphthalate), PEN. Uniaxial and biaxial orientation of amorphous cast PEN films resulted in stress-induced crystallization of the triclinic α-PEN polymorph. Annealing of the amorphous PEN samples in the range of 160–240 °C produced thermally induced crystallization of α-PEN. Slow cooling of amorphous PEN from the melt state generated α-PEN as well as the triclinic β-PEN polymorph.

Dielectric relaxation behaviour of poly(ethylene naphthalene 2,6 dicarboxylate) (PEN)

Dielectric spectroscopy has been used to study poly(ethylene naphthalene 2,6 dicarboxylate) (PEN) samples of different morphologies obtained by thermally treating bi-axially stretched PEN films. Neat and thermally treated samples of PEN films have been characterised by differential scanning calorimetry in order to measure the glass transition and melting temperatures as well as the degrees of crystallinity. Dielectric analysis has allowed the observation of the evolution of molecular relaxation phenomena with morphology changes and has revealed three relaxation processes: β-, β *- and α-relaxation (increasing temperature). The β-relaxation is associated with local motions of ester and the β *-relaxation with partially cooperative motions of naphthalene groups. The latter has been shown to be related to the morphology of the materials under study. The α-relaxation associated to the glass transition of PEN corresponds to cooperative motions induced by conformational rearrangements of the main chain and depends also on the morphology of the PEN films. Dielectric relaxation behaviours were compared using the activation energies calculated from Arrhenius equation formalism for the two sub-glass processes. Vogel–Fulcher–Tammann fits were performed on the α-relaxation. Our important contribution for the bi-axially stretched PEN films study is related to the assignment of the β *-relaxation that can be attributed to naphthalene aggregates.

Molecular orientation behaviour of thermally treated biaxially stretched poly(ethylene naphthalene 2,6 dicarboxylate) films studied by polarised infrared spectroscopy

PEN films of different morphologies have been studied by polarised infrared spectroscopy. These different structures have been obtained by thermally treating biaxially stretched PEN films. Calculations of orientation factors from the 767 and 1138 cm −1 bands which are characteristic of naphthalene ring vibrations predominantly in the amorphous phase show that the amorphous phase is significantly disoriented when annealed at a temperature of 260 °C despite the increasing crystallinity.

Tensile and dynamic mechanical properties of improved ultrathin polymeric films

AbstractTensile and dynamic mechanical properties of improved ultrathin polymeric films for magnetic tapes are presented. These films include poly(ethylene terephthalate) or PET, poly(ethylene naphthalate) or PEN, and aromatic polyamide (ARAMID). PET film is currently the standard substrate used for magnetic tapes; thinner tensilized‐type PET, PEN, and ARAMID were recently used as alternate substrates with improved material properties. The thickness of the films ranges from 6.2 to 4.8 μm. Young's modulus of elasticity, F5 value, strain‐at‐yield, breaking strength, and strain‐at‐break were obtained at low strain rates by using a tensile machine. Storage (or elastic) modulus, E′, and the loss tangent, tan δ, which is a measurement of viscous energy dissipation, are measured by using a dynamic mechanical analyzer at temperature ranges of −50 to 150°C (for PET), and −50 to 210°C (for PEN and ARAMID), and at a frequency range of 0.016 to 29 Hz. Frequency–temperature superposition was used to predict the dynamic mechanical behavior of the films over a 28 decade frequency range. Results show that ARAMID and tensilized films tend to have higher strength and moduli than standard PET and PEN. The rates of decrease of storage modulus as a function of temperature are lower for PET films than those for PEN and ARAMID films. Storage modulus for PEN films are higher than that for PET films at high frequencies, but this relationship reverses at low frequencies. ARAMID has the highest modulus and strength among the films in this study. The relationship between polymeric structure and mechanical properties are also discussed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2225–2244, 2002

Combined electroluminescence and charge profile measurements in poly(ethylene-2, 6-naphthalate) under a dc field

The existing interpretation and models of electroluminescence(EL) in poly(ethylene-2, 6-naphthalate) (PEN) suggest a mechanismtriggered by the impact excitation and/or ionization of the luminescentcentres by hot electrons. Excitation by bipolar charge recombination hasnot been considered extensively because of the lack of knowledge of thebehaviour of electrons and holes in insulating films subjected to a dcstress. An investigation of the internal space charge distribution versusfield is believed to constitute a relevant approach to discussing the ELexcitation process. Transient and steady-state EL of PEN films areanalysed with the support of space charge profiles obtained by the laserinduced pressure pulse (LIPP) method for dc fields in the range of25-225 kV mm-1. For field values up to 75 kV mm-1, the internalcharge is dominated by dipolar polarization without any excitation of EL.Space charge polarization is evidenced from 75 kV mm-1 upwards, theLIPP response being a superposition of space charge and dipolarpolarization effects. Space charge polarization dominates in the fieldrange where EL is continuously emitted (E>150 kV mm-1). The ELexcitation mechanism is discussed on the basis of the recorded chargeprofiles.

Role of the structure on the photo and cathodo-luminescence of poly(ethylene naphthalate): PEN

The photoluminescence in the blue emission band at 430 nm of poly(ethylene naphthalate), assigned in literature to the formation of excimers states involving the naphthalene groups, is shown to be very sensitive to the disorder induced by irradiations. The cathodoluminescence, excited by a beam of 4 keV electrons, exhibits two components: a rapidly decreasing fluorescence at 430 nm and a broad and more stable one at 640 nm assigned to short chain segments. The influence of mechanical stretching and temperature on the fluorescence of non-treated PEN films has been investigated. The enhancement of the fluorescence with film elongation is attributed to the increase of the polymer chain ordering along the stretching direction, whereas the decrease of the fluorescence with temperature is correlated to the β ∗ relaxation associated in dielectric spectroscopy to the movements of the naphthalene groups, known to be responsible for the excimer fluorescence. The dependence of the blue and red fluorescence components on the polymer structural organization provides efficient probes to study the local order and degradation stage of PEN and accounts for the results reported in literature according to the different film histories.

Electrostatic Printing of Metal Traces on PET and PEN Films for Flexible Display and Flex Circuit Applications

Electrostatic Printing of Metal Traces on PET and PEN Films for Flexible Display and Flex Circuit Applications

Physical and microstructural effects of heat setting in polyester films

AbstractThe effects of a controlled heat‐setting treatment on the properties and microstructure of biaxially stretched poly(ethylene terephthalate) (PET) and poly(ethylene‐2,6‐naphthalene dicarboxylate) (PEN) films are described. Substantial changes in crystalline fraction, crystallite size, glass transition temperature and significant enhancement in dimensional stability are observed for both film types upon increase in heat‐set temperature. A distinct melting peak in the vicinity of the heatset temperature, observed in differential scanning calorimetry thermograms for both materials, is shown to be an effective marker of the heat‐setting process underlying the dual nature of the morphology of the heat‐treated films. We also observe that the PET films undergo significant molecular realignment on heat setting, while the orientation of the PEN films is only weakly modified by the heat‐set conditions. A morphological transition is detected for both films at high heat‐set temperature (THS*) near the onset of the primary melting range, marking a qualitative change in the physical response of the biaxially oriented films; Measurable drop in planar orientation and glass transition temperature, and a sharp rise in crystallite size are noted for films heat‐treated above THS*. The morphological models of previous workers (Schultz et al. and Fischer and Fakirov), invoking the idea of fibrillar‐to‐lamellar transformation, are used to explain some of our observations.