Polyethylene Thin Films Research Articles

Plastic balloons with thin polyethylene films for high altitude observations

Balloons made of thin films have been frequently used to observe high altitude winds. Such a balloon is also useful to perform some scientific observations now performed by sounding rockets. Since this balloon is lighter than a normal balloon, it can easily reach an altitude more than 40km with a payload less than 10 kg. A ceiling altitude of 48.7 km was achieved by the new balloon with a volume of 30,000m 3 in a test flight in 1995. We need to reduce mechanical stress by attaching an exhaust duct especially for a thin polyethylene balloon. Three types of exhaust ducts were tested in flights in 1995. We have confirmed good performance of the thin polyethylene balloon. The launching device for the high altitude balloon is also described.

Ion beam effects in polymer films: Structure evolution of the implanted layer

Thin films of polyethylene, polyamide-6 and cellulose implanted with 100 keV B +, N + and Sb + ions to the fluences of 10 13–10 17 cm −2 were investigated using RBS and NDP techniques as well as IR, UV-visible and EPR spectroscopies. The peculiarities of the depth distribution of implanted species and the origin of the processes responsible for modification of the structural, optical and paramagnetic properties of polymers are discussed with consideration for two major reactions occurring in the implanted layer: (i) oxidation of the radiation-damaged polymer that predominates at moderate doses; (ii) clusterization of radiation defects with the formation of carbon-enriched domains (“drops”) which can overlap at high ion fluences yielding the network of conjugated carbon structures.

Greenhouse solar heating in the Argentinian northwest

In the present paper a low cost solar active water heating system is proposed to increase the average night temperature and avoid freezing problems inside greenhouses. The system collects the excess of energy in the greenhouse during the day, and returns it at night. The most important part of the system is a plastic bag made of two thin polyethylene films vertically hung inside the greenhouse, that works as a solar collector during the day and as a heat exchanger at night. The films are soldered in such a way that the water introduced at the top of the bag falls by gravity following a zig-zag path. The warm water is stored in a pond directly built in the ground and waterproofed with a polyethylene film. The system has been designed taking into account the meteorological conditions in Salta where 12 freezing days are expected each year with minimum temperatures down to −8°C. A prototype was built in a 600 m 2 greenhouse covered with a single polyethylene film. It was located in the Province of Salta, Argentina, with a 24.5° South latitude and an altitude of 1200 m. Tests were performed for three years beginning at the 1992 winter, and a satisfactory thermal and operational behavior was obtained. With outside temperatures down to −6°C at the end of the night, the system was able to keep a temperature of 2°C inside the greenhouse.

Design of radial neutron spectrometer array for the International Thermonuclear Experimental Reactor

We designed the radial neutron spectrometer using a new type DT neutron spectrometer base on a recoil proton counter-telescope technique aiming ion temperature measurement for the International Thermonuclear Experimental Reactor (ITER). The neutron spectrometer will be installed on the well collimated neutron beam line. A large area recoil proton emitter is placed parallel to the incident neutron beam and microchannel collimating plates are inserted between the radiator and the recoil proton detectors away from the neutron beam in order to limit the scattering angle of protons to the proton detectors. Here a very thin polyethylene film and a silicon surface barrier detector are employed as the radiator and proton detector, respectively. The energy resolution and detection efficiency are estimated to be 2.5% and 1×10−5 counts neutron−1 m2, respectively, for the DT neutron through Monte Carlo calculations. Five units of the spectrometers will be installed just outside the biological shield, will include a fan array using penetrations inside the bioshield and a precollimator in the horizontal port. The lifetime of the proton detectors is estimated to be about one year in the basic performance phase of ITER by neutron transport calculations using the Monte Carlo neutron and photon transport code (MCNP).

Fully atomistic models of the surface of amorphous polyethylene

Fully atomistic models of very thin films of amorphous polyethylene are studied. The density profile of the thin films shows that the surface layer is thicker than the result obtained previously for thin films of poly(1,4-cis-butadiene), using a similar method. This difference in thickness of the surface layer is attributed to the fact that polyethylene is a stiffer chain than poly(1,4-cis-butadiene), as reflected by the difference in their characteristic ratios. The C-C bonds are randomly oriented in the interior of the film, but in the outer portion of the surface layer they have a slight preference for an orientation in the plane of the film. The contribution of the internal energy to the surface energy of the film is estimated to be 20 erg cm−2, which is lower than the experimental value of 26 erg cm−2 reported in the literature for the surface energy. The roughness of the surface varies from 0 to 6 Å as the radius of the spherical probe used in the measurement becomes smaller.

Deformation of spherulitic polyethylene thin films

Thin spherulitic films of polyethylene (PE), made by casting from xylene solution, were deformed on copper grids and their deformation microstructure studied using optical and transmission electron microscopy. A range of molecular weights, branch amounts and types, and thermal histories was used to study the influence of sample microstructure on the deformation behaviour. The spherulite boundaries were the weakest regions of spherulitic structures in all types of PE. Higher strains were generally required to deform the interiors of spherulites, which deformed by a different mechanism. The toughness of the films was increased by increasing the tie-molecule density and disentanglement resistance, to strengthen spherulite boundaries. Three methods for increasing the toughness were demonstrated and were: (1) decreasing the crystallization time in order to increase the tie-molecule density, (2) increasing the molecular weight in order to increase the tie-molecule density, and (3) incorporating short-chain branches on the main chains in order to increase the tie-molecule density and increase the disentanglement resistance. Incorporation of short-chain branches was shown to be the most effective way of strengthening spherulitic structures, with the toughest films being those made of branched PE that had been crystallized rapidly. The branch length and spherulite size were found to be unimportant.

Optical properties of extruded polyethylene thin films related to anisotropy and inhomogeneous microstructure

AbstractIn this paper a method has been developed to extend the use of the well‐known expression of Clausius‐Mosotti for inhomogeneous materials, considering their anisotropy through a series expansion based on the structural factor of nonsphericity. This is related to experimental results available from the ordinary and extraordinary refractive indices of a set of samples of low‐density polyethylene films, where such phenomena are observed. Here results are obtained which are valid for the microscopic optical response, as it is shown by the linear fitting of these general expressions, with excellent correlation coefficients. Furthermore, if we apply the Bergman‐Milton limits, we can theoretically confirm the existence of two neutral lines experimentally obtained.

Nonlinear behavior of linear low‐density polyethylene

AbstractTo predict the response of polyethylene thin films subjected to stress for a long time, it is necessary to understand the influence of stress on either the relaxation modulus or creep compliance. Extensive testing has been conducted on 20‐micron‐thick samples of a particular linear low‐density polyethylene film at temperatures from 23°C to −50°C. When reduced to creep compliance and compared with results from dynamic mechanical analysis (DMA), the influence of nonlinearities in the response function is apparent. However, the use of a two‐step loading procedure has produced sufficient data to discriminate between the effect of stress on amplitude and time on the creep compliance. It has been found that a master curve of compliance generated by DMA equipment may be used in conjunction with certain nonlinear functions to accurately predict the response of the polyethylene. Perhaps of more importance is the observation that the principles of simple time‐temperature superposition, commonly used with linear viscoelastic characterization, are insufficient for use with polyethylene films at most stress levels of interest.

Infrared spectroscopic characterization of plasma-treated polyethylene

Thin polyethylene films cast on copper or gold were treated with low-pressure oxygen plasma. Changes in the chemical structure of these films were investigated by infrared spectroscopy using a reflection method in combination with chemical derivatization (CD) reactions. The potential of the CD is demonstrated for hydroxyl groups and carbonyl groups by the reaction with trifluoroacetic anhydride and hydrazine. The reaction conditions were varied to check for side reactions. The results of the derivatization are discussed in terms of secondary structures. © 1996 John Wiley & Sons, Inc.

Fundamental Study of Electrorheological Fluids. Similarity of Velocity Profiles.

Hydrous electrorheological (ER) fluid was poured into the annular interstitial space between two coaxial cylinders: the outer cylinder can rotate on its axis and the inner stationary one is connected to a torque meter. Upon application of an electric field and rotation of the outer cylinder, measurements of velocity distributions of ER fluid in the annular space were made using a laser Doppler velocimeter and those of shear stress exerted on the inner cylinder surface were made using the torque meter. When the rotational speed was very low, the flow was observed directly. Since high -water-content ER fluid requires a high electric current, a countermeasure for reducing the current was also examined. It was found that the ratio of electrical force to viscous force (=the inverse of the Mason number) plays an important role in determining the flow pattern of ER fluid and, upon increasing the magnitude of the ratio, the flow pattern varies from Couette flow to plug flow. Insulation of the inner cylinder surface with thin polyethylene films and a rubber membrane reduced the electric current but the magnitude of the generated shear stress decreased to one-tenth of that without insulation films.

Biodegradation of low‐density polyethylene, polystyrene, polyvinyl chloride, and urea formaldehyde resin buried under soil for over 32 years

AbstractThe biodegradation of several polymers that had been buried under soil for over 32 years was examined. No evidence of biodegradation was found for polystyrene, polyvinylchloride, and urea formaldehyde resin. A remarkable degradation was indicated for low density polyethylene thin films which were directly in contact with soil. Severely degraded parts of the film is characterized by whitening. Many small holes were recognized on the surface of the whitened part. The whitened part is specific for the growth of hyphae. FT‐IR spectra of the whitened part showed a characteristic band in the vicinity of 1640 cm−1 which was assigned to the stretching vibration of CC bond. Although the part which was not in contact with soil was clear, it also showed evidence of degradation from the presence of carbonyl band in FT‐IR. It was suggested that the degradation of the clear part is due to the usual thermo‐oxidative process, while the degradation of the whitened part is due to the biotic process. © 1995 John Wiley & Sons, Inc.

Weibull statistics in short-term dielectric breakdown of thin polyethylene films [comments and reply

In the original paper (see ibid., vol. 1, no. 1, p. 153-9, 1994), the authors show that the two-parameter Weibull distribution is satisfactory to represent the results on samples of HV thermally aged EPR cables. This does not exclude, as well as they indicate it, that the three-parameter Weibull distribution is sometimes justified, especially in the case of results of short term dielectric breakdown tests. The quality of test data available and the efficiency of usable methods, result partly from the international standardization and recent statistical work. The difficult problem remains of the choice for the statistical distribution of dielectric test results. It concerns a general enough problem that does not possess a unique solution and must take into account simultaneous physical and statistical considerations. A reply is given. >

In-situ Kinetic Studies on Direct Fluorination of Thin Polyethylene Films with QCM

Abstract Fluorination of polyethylene (PE) films with fluorine gas was studied by using the quartz crystal microbalance technique from the interest for the preparation of wet-proofed carbon black with fluorinated polyethylene (FPE) film for application to gas-diffusion electrodes in fuel cells. The fluorination reaction proceeds clearly in three separated steps, i.e., the first transient step, the 2nd step controlled by the chemical reaction between F2 and PE molecules, and the 3rd step controlled by the diffusion rate of dissolved F2 in FPE. The complete fluorination of PE films of ca. 2—10 μm in thickness can be achieved after sufficient reaction time. It was found that the fluorination at the 2nd step obeys the first order kinetics regarding F2 concentration with the activation energy of only 34.3 kJ mol−1. The fluorination at the 3rd step proceeded linearly with the square-root of the reaction time. Diffusion parameters and apparent activation energies for the fluorination at the 3rd step were determined by solving Fick’s diffusion equation based on those experimental data. Both of them were very large in comparison with that for un-reacting gases, which were ascribed to the fluorination step proceeded by the reactive diffusion process.

Fundamental Study of Electrorheological Fluids. Similarity of the Velocity Profiles.

Hydrous electrorheological (ER) fluid was filled in between two coaxial cylinders : the outer cylinder can rotate on its axis and the inner stationary one is connected to a torquemeter. Upon application of an electric field and rotation, measurements of velocity distributions of ER fluid in the annular region were taken by a laser velocimeter and those of shear stress exerted on the inner cylinder surface were taken by the torquemeter. When the rotational speed was very low, the flow was observed directly. Since high-water-content ER fluid requires high electric current, a counter-plan to reduce the current was also examined. It was found that the ratio of electrical force to viscous force plays an important role in determining the flow pattern of ER fluid and, upon increasing the magnitude of the ratio, the flow pattern varies from couette flow to plug flow. Insulation of the inner cylinder surface with thin polyethylene film could reduce the electric current and the magnitude of the generated shear stress decreased to one-tenth of that without insulation film.

A.c. and d.c. conductivities in a metal/polymer composite/metal sandwich. Case of charge-transfer ‘doped’ polyethylene complex

Low density polyethylene thin films with inclusion of crystalline tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) organic conductors have been investigated. Films are cast onto glass plates or silicon substrates at 80 °C using the reticulate-doping technique, and exhibit conductivities according to the additive ratio and heating treatment. Electrical a.c. and d.c. characteristics are performed to investigate electrical properties of associated metal/polyethylene composite/metal (MPM) sandwich structures for several concentrations of TTF-TCNQ. Measurements on MPM devices reveal the following: (i) d.c. currents can be evaluated with classical models of electronic (space-charge-limited currents); (ii) an obvious interpolation is possible between a.c. and d.c. characteristics; (iii) a specific behaviour of conductivities with frequency characterizes the additive presence in the polyethylene matrix; (iv) a conduction similar to typical hopping conduction modes that can be assigned to the composite characteristics.

Weibull statistics in short-term dielectric breakdown of thin polyethylene films [comment and reply

For original paper see ibid., vol.28, p18-29 (1993).The comments make it clear and underline that a parameter obtained from ramped voltages bears no relationship whatsoever with the life threshold parameter that would be derived from constant stress experiments. A reply is given.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Weibull statistics in short-term dielectric breakdown of thin polyethylene films

Results of electric strength tests performed on specimens cut from aged and unaged EPR-insulated HV cables are processed by the two and three parameter Weibull function. It is shown that the latter often fits the experimental data better than the former, but the difference is not significant, except, in a few cases, for the lowest percentiles. Therefore, the easier distribution parameter estimation and smaller confidence intervals of parameters and percentiles generally support the use of the two-parameter Weibull function. >

Deposition of polymer bilayer configuration by pulsed laser ablation and its use for study of polymer-polymer interface

Thin films of polyphenylene sulphide (PPS) and polyethylene (PE) polymers have been deposited in a bilayer configuration using pulsed excimer laser ablation. Such bilayer specimens have been annealed at different temperatures, up to a maximum of 120°C, and for different time intervals, up to a maximum of 110 min, to investigate the evolution of the interface. By employing the technique of spectroscopic ellipsometry, the nature and the degree of thermally induced polymeric transport across the interface are brought out.

Crystallization of isotactic polypropylene and high‐density polyethylene under negative pressure resulting from uncompensated volume change

AbstractThe melting behavior of spherulites in thin sections of isotactic polypropylene bulk samples and high‐density polyethylene thin films crystallized isothermally at various temperatures has been studied by polarized light microscopy. The regions around cavities and multiple boundary points between spherulites have higher melting temperatures than the other parts of spherulites crystallized in Regime III. The increase in melting temperature is explained as a result of crystallization under negative pressure arising locally in pockets of occluded melt due to density change during spherulitic crystallization. The negative pressure lowers locally the equilibrium melting temperature and therefore decreases the undercooling, which results in an increase in lamellar thickness. Sectioning of bulk samples releases frozen negative pressure and reveals the increase in melting temperature of those parts of spherulites that were crystallized at lower undercooling. © 1993 John Wiley &amp; Sons, Inc.

Study of ultrafine particles-organic polymer thin films

Au ultrafine particles-polyethylene thin films and C 60-polyethylene thin films have been prepared in an ionized-cluster-beam time-of-flight mass spectrometer system and analysed by transmission electron microscopy. We found that the small Au clusters with a size of 2.0–5.0 nm are suspended randomly in the polyethylene thin films, and the C 60-polyethylene thin films are f.c.c. structures with a lattice constant a of 1.454 nm.