Electron beam induced modification of poly(ethylene terephthalate) films

Electron beam processing of poly(ethylene terephthalate) (PET) films is found to promote significant changes in the melting heat, intrinsic viscosity and polymer film-liquid (water, isooctane and toluene) boundary surface tension. These properties are featured with several maximums depending on the absorbed dose and correlating with the modification of PET surface functionality. Studies using adsorption of acid-base indicators and IR-spectroscopy revealed that the increase of PET surface hydrophilicity is determined by the oxidation of methylene and methyne groups. Electron beam treatment of PET films on the surface of N-vinylpyrrolidone aqueous solution provided graft copolymerization with this comonomer at optimum process parameters (energy 700 keV, current 1 mA, absorbed dose 50 kGy).     

Investigation of structural relaxation and surface modification of ultrathin films of poly(ethylene terephthalate)

We studied dynamic properties of ultrathin films of poly(ethylene terephthalate) spincoated on different substrates, by means of dielectric spectroscopy and surface patterning experiments. We did not observe any variations of structural dielectric relaxation dynamics for films spincoated on aluminium substrate having thicknesses down to 40 nm. On the same substrate, 13 nm thick films are instead characterized by a reduction of the chains mobility. Surprisingly the chains dynamics as probed by a surface nanopatterning experiment evidenced a strong dependence on the substrate interaction even for 50 nm thick films, where dielectric relaxation dynamics is unaffected. It can be deduced that different length scales characterise dielectric relaxation dynamics and the processes related to the surface patterning, even if both are related to the chain mobility. Further experiments are wished to better understand this intriguing scenario.     

Investigation of the surface of poly(ethylene terephthalate) films modified by vacuum ultraviolet irradiation in air

This paper reports on the results of measuring the changes in the characteristics of the surface of poly(ethylene terephthalate) films upon radiation-induced oxidation of the polymer under vacuum ultraviolet irradiation in an oxygen-containing medium. The films were irradiated by light from a sealed-off deuterium lamp with the maximum photon energy within the band (10 ±1 eV) in air under conditions where thermal destruction of poly(ethylene terephthalate) could be ignored. The functional relationship between the decrease in the film thickness and the growth of surface irregularities in the course of photoetching was established from measurements of the optical transmission spectra T (γ) of the films and investigations of the surface microrelief by atomic-force microscopy. The hydrophilic properties of the surface of the sample regions irradiated with different doses were examined by measuring the contact angle.     

Glass transition of poly(ethylene terephthalate)

It has been found that commercial poly(ethylene terephthalate) film exhibits current glow curves which have maxima at 73.5 ± 3.4°C and at 105.3 ± 3.4°C. These current glow curves were obtained by measuring the current flowing under zero bias as the temperature was raised 1°C/min. A typical curve, for untreated 1-mil du Pont Mylar A, is seen in Fig. 1. Although a paper on this study will shortly be submitted for publication, some conclusions of that paper may be stated here.     

Direct-current conductivity of poly(ethylene terephthalate)

There have been several previous studies of the dc conductivity of poly(ethylene terephthalate). Disagreement among the various authors indicates the difficulties inherent in this measurement: several authors [1,2] found evidence for ionic conduction through a hopping process; others [3,4] proposed conduction by electrons injected through a barrier.     

Electroless plating of nickel–phosphorous on surface-modified poly(ethylene terephthalate) films

Chemical surface preparation for Ni–P electroless metallization of poly(ethylene terephthalate) (PET) films without using Chromium-based chemicals, was studied. The applicability of this method was verified by a subsequent metallization process. Thermal analysis was conducted to observe the main thermal transitions and stability of the polymer and metallized films. Contact angle analysis was performed to assess the surface hydrophilicity so as to optimize the substrate preparation process. X-ray diffraction, EDAX and SEM analysis were used to understand the composition and morphology of the polymeric substrate and Ni–P coat growing process. Adherence strength, contact sheet resistivity and optical diffuse reflection were measured on the metallized films. The time of chemical etching affects the polymer surface hydrophilicity, polymer/metal adherence strength, surface resistance and optical diffuse reflection, while Ni coating morphology is controlled by the pH of the electroless bath. High wettability of the polymer surface, adherence strength of 800 N cm⁻², high optical diffuse reflection and low surface resistivity of the Ni coating, were found for films etched for 60 min. Metallizations performed at pH 7.5 produce Ni–P coatings with 12.0 wt.% phosphorous content, which were amorphous and flexible. The contact sheet resistivity of the plated films is sensitive to roughness variations of the substrate. The method proposed in this work allows the production of metallized films appropriate for the fabrication of flexible circuits.     

Electron induced modification in poly(ethylene terephthalate)

Abstract

The effect of 100 kGy dose of 2 MeV electron irradiation on Poly(ethylene terepthalate) (PET) has been studied by different characterisation techniques such as the Fourier transformed IR spectroscopy, electron spin resonance spectroscopy, thermogravimetric analysis, differential scanning calorimetry and X-ray diffraction analysis. Oxidative degradation leading to amorphisation of the polymer has been observed from spectral analysis. The thermal stability of the polymer was found to decrease due to electron irradiation. The thermal decomposition temperature as well as the melting temperature in case of irradiated PET was found to be decreased due to electron bombardment. A decrease in crystallinity of the polymer has also been observed after irradiation.     

Superstructure in chemically etched poly(ethylene terephthalate)

The new technique of contact etching has been utilized to study the bulk morphology of polyethylene terephthalate by the echant, n-propylamine. A variety of films and fibers with different mechanical and thermal histories have been subjected to contact etching. The sample surfaces have been studied principally by scanning electron microscopy. A network superstructure with its characteristic dimension (thickness) of from 700 to 3000 Å, depending on sample history, has been observed. In the oriented samples the network superstructure aligns perpendicular to the direction of sample orientation. A simple model is proposed to describe the network superstructure which is believed to be moderately crystalline.     

Persistent internal polarizations in poly(ethylene terephthalate) films. III. Cold crystallization

A polarization process, which may be induced in commercial poly(ethylene terephthalate) films by annealing, has been found to exhibit a current peak under zero bias near 120[ddot]C. This process is identified as the “cold crystallization” phenomenon, and involves the simultaneous gauche-to-trans isomerization and paracrystalline ordering of the glycol linkages.     

Persistent internal polarizations in poly(ethylene terephthalate) films. I. stress-induced polarizations

When heated under zero voltage, commercial polyester film exhibits current peaks manifesting glass transition and glycol linkage motions, as well as a broad, low background. The peaks are due to the depolarization of dipoles oriented by local stresses during manufacture. Their variations with sample thickness and heating rate permit the calculation of “thermodynamically reversible” values of T_g (58.7[ddot] ± 0.5[ddot] C) and T_glycol (87.3[ddot] ± 0.2[ddot]C). The broad background current is a manifestation of the alignment of paracrystalline order in a thermal gradient.     

Structural changes in glassy poly(ethylene terephthalate)

Structural changes in glassy poly(ethylene terephtbalate) and their effects on its crystallization, melting, and various properties were studied. Quenched, annealed below T_g, crystallized, and drawn samples were studied using calorimetry, wide-and small-angle X-ray diffraction, mechanical spectroscopy, and stress-strain analysis. All results indicate some level of order in the glassy polymer which can be increased by annealing below T_g. This order still exists at tempertures above T_g and affects the properties of the polymer.     

Basic aspects of microindentation in multilayered poly(ethylene terephthalate)/polycarbonate films

The microhardness H of multilayered poly(ethylene terephthalate) (PET)/polycarbonate (PC) films, produced by continuous layer multiplying coextrusion has been determined. These materials present rather uniform laminates up to thousands of layers in the micrometre and submicrometre range. The micromechanical properties have been investigated as a function of layer thickness of the single polymer components, the total number of layers, the film thickness and the influence of heat treatment. The microhardness of the microlayered structure has also been determined across the profile in the parallel direction to the packing of the layers. The hardness in the vicinity of the PET/PC phases has been examined. Results reveal that the influence of the interphase on the H values for the samples with a large number of layers is rather small. The most important parameter in determining the final hardness of the multilayered films is the ratio of the penetration depth to the thickness of the layer. Upon heating, a microhardness increase is observed as a consequence of a double contribution: the crystallization of the PET layers, on the one hand, and the physical ageing of the PC zones on the other.     

Synthesis of ultrahigh molecular weight poly(ethylene terephthalate)

Poly(ethylene terephthalate) of number-average molecular weight of the order of 120,000 was prepared from commercial-grade material in the solid state with a gas chromatograph apparatus. Parameters studied were the catalyst, particle size, the molecular weight of the starting material, the reaction temperature and time, and the nature and flow rate of the carrier gas.     

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.     

Angle dependent laser nanopatterning of poly(ethylene terephthalate) surfaces

Interference effects can lead to the formation of ripple structures at laser-irradiated poly(ethylene terephthalate) surfaces. Poly(ethylene terephthalate) surface was irradiated with linearly polarized light of a pulsed 157 nm laser. In a certain range of irradiation parameters, the irradiation resulted in the formation of coherent ripples patterns. The dimension of the pattern depends on the angle of the laser beam incidence. The surface morphology of the nano-patterned poly(ethylene terephthalate) was analyzed by atomic force microscopy and focused ion beam-scanning electron microscopy. Oxygen concentration in the modified polymer surface was studied by angular resolved X-ray induced photo-electron spectroscopy. Gold nano-layers were consecutively sputtered onto the laser irradiated poly(ethylene terephthalate) surfaces. The morphology of the sputtered gold nano-layers was investigated with atomic force microscopy too. We found that the morphology of the gold nano-layers changes and depends on the surface pattern of the laser irradiated poly(ethylene terephthalate). Formation of gold “nano-hills” is observed at the ridges of the ripple structures. The amount of oxygen together with the morphology of prepared polymer pattern may be the dominant factors controlling the gold layer growth. The present results are compared with those obtained earlier on PET irradiated with krypton fluoride laser.     

Aromatic poly(ester carbonate)/poly-(ethylene terephthalate) alloys

When mixtures of poly(ester carbonate) (PEC) and poly(ethylene terephthalate) (PET) containing up to two-thirds of the latter are melt extruded, they produce a single-phase amorphous “alloy.” This alloy is characterized by a sharp, single, composition-dependent glass transition temperature, T_g. When annealed below T_g, the alloy remains unaltered, but when annealed above its T_g, the alloy separates into minute pure-PET crystallites and an amorphous PEC/PET phase. The thermal and dynamic mechanical behavior, crystallization kinetics, and SAXS patterns all strongly suggest the PEC-rich alloys to be solid solutions in which the PET molecules are dispersed individually or in small aggregates containing only a few PET molecules each. Calculations of the interaction parameter and assumed interfacial layer thickness tend to support this suggestion. Use of appropriate solvents allows one to selectively dissolve the PEC and recover from the alloys both PET and PEC in the original purity and molecular weights. Diffusion constants of PET molecules through the amorphous alloys were obtained from studies of PET crystallization above T_g of the alloys. The magnitude of the constants are in the range of expectation. The mechanical properties of the amorphous alloys in the glassy state do not deviate greatly from simple additivity of the respective properties of the parent polymers. However, the melt viscosity of the PEC-rich alloys and their plateau modulus above T show drastic decreases from straight additivity. A qualitative, but not quantitative, explanation of these observations is offered.     

Rheological,thermal, and mechanical properties of poly(ethylene naphthalate)/poly(ethylene terephthalate) blends

Structural, Theological, thermal, and mechanical properties of blends of poly(ethylene naphthalate) (PEN) and poly(ethylene terephthalate) (PET) obtained by melt blending were investigated using capillary rheometry, differential scanning calorimetry (DSC), scanning electron microscopic (SEM) observation, tensile testing. X-ray diffraction, and ¹H nuclear magnetic resonance (NMR) measurements. The melt Theological behavior of the PEN/PET blends was very similar to that of the two parent polymers. The melt viscosity of the blends was between that of PEN and that of PET. Thermal properties and NMR measurement of the blends revealed that PEN is partially miscible with PET in the as molded blends, indicating that an interchange reaction occurs to some extent on melt processing. The blend of 50/50 PEN/PET was more difficult to crystallize compared with blends of other PEN/PET ratios. The blends, once melted during DSC measurements, almost never showed cold crystallization and subsequent melting and definitely exhibited a single glass transition temperature between those of PEN and PET during a reheating run. Improvement of the miscibility between PEN and PET with melting is mostly due to an increase in transesterification. The tensile modulus of the PEN/PET blend strands had a low value, reflecting amorphous structures of the blends, while tensile strength at the yield point increased linearly with increasing PEN content.     

Radiothermoluminescence of poly(tetra fluoroethylene) and poly(ethylene terephthalate) pretreated by xenon ions

Low-temperature (77–300 K) RadioThermoLuminescence (RTL) investigations of Poly(Tetra FluoroEthylene) (PTFE) and Poly(Ethylene TerePhthalate) (PET) foils previously treated by different flux (Φ = 10⁶–10¹¹ cm⁻²) of Xenon ions with energy 1.1 MeV/nucleon have been showed an essential ion-induced changes in RTL of the both polymers under study. In PET as well as in PTFE significant changes of RTL light yield observed at the ion flux more than 10⁹ cm⁻². Variation of RTL light yield in PTFE accompanied by appearance of new TL temperature maxima on the glow curve. An existence of correlation between observed changes of molecular mobility in ion-irradiated polymer and optical (PET) and strength (PTFE) properties have been found.     

On the aging characterization of poly(ethylene terephthalate) by positron spectroscopy

Positron spectroscopy was used to study the free volume properties of glassy poly(ethylene terephthalate) as a function of temperature and aging time. The experimental results indicate that the glass transition temperature increases with increasing aging time. This is confirmed by differential scanning calorimetry measurements. From the aging time dependence of the intensity of the ortho-positronium (o-Ps) component I₃ and the fractional free volume, we observe that the concentration of free volume holes and the fractional free volume show a continuous decrease at a fixed aging temperature, which suggests that structural relaxation and segmental rearrangement occur during physical aging.     

Asymmetric surface modification of poly(ethylene terephthalate) film by CF4 plasma immersion

Poly(ethylene terephthalate) (PET) films were treated with CF₄ plasma immersion. The samples were processed at different RF powers and treatment time. The surface modification of PET films was evaluated by water contact angle (CA), X-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM). Decrease in contact angle of both sides of PET films was observed under mild treatment conditions. However, as raising treatment power and/or time, the change in contact angle between the two sides of PET films was different. The relatively hydrophobic and hydrophilic surfaces were being in situ formed on the two sides of PET films, respectively. And the extreme values of water contact angle reached 108.63 and 7.56°, respectively. XPS analyses revealed that there was a substantial incorporation of fluorine and/or oxygen atoms in both side surfaces. The relative chemical composition of the C (ls) spectra's showed the incorporation of non-polar fluorine-based functionalities (i.e. CFCF_n, CF₂ or CF₃ groups) and polar oxygen-based functionalities (i.e. COOH or OH groups) in the surfaces. Correlation between the plasma parameters and the surface modification of PET films is also discussed.