Single Polyethylene Research Articles

Capillary Extrusion Studies of LLDPE/LDPE Blends: Effects of Manufacturing Technology of LLDPE and Long Chain Branching

Abstract The processing behavior of a number of LLDPE/LDPE blends with emphasis on the effects of manufacturing technology of LLDPE and long chain branching is presented. A single low-density polyethylene was blended with two Ziegler-Natta linear-low-density polyethylenes LLDPE's and two metallocene-LLDPE's having distinctly different molecular structures. The weight fractions of the LDPEs used in the blends were 1 wt.%, 5 wt.%, 10 wt.%, 20 wt.%, 50 wt.% and 75 wt.%. Capillary extrusion reveals that the onset of sharkskin and gross melt fracture are slightly influenced with the addition of LDPE into LLDPE. However, the amplitude of the oscillations in the stick-slip flow regime was found to scale well with the weight fraction of LDPE even at amounts as low as 1 wt.%. Furthermore, it was observed that the onset of this flow regime was shifted to higher shear rates with increase of LDPE content. Shear rheology was found to be insensitive to detect small levels of LDPE. On the other hand, extensional rheology was found to be capable of detecting levels of LDPE as low as 1 wt.% at high Hencky strain rates (typically greater than 5 s−1) although only for certain blends.

Molecular dynamics simulation of a single polymer in hydrophilic nano-slits

The behavior of a single polyethylene polymer in aqueous solution confined between two hydrophilic walls is studied with molecular dynamics (MD) simulations. The thickness of the nano-slit ranges from 1.26 to 3.15 nm, which is comparative to the polymer dimension. A monotonic transition from 3D-to 2D-like configurations is observed as the distance between the two walls narrows. Monomers are compressed into several layers and the preferred bond orientations alternate between parallel and normal to the walls accordingly. The diffusivity in the direction parallel to the wall is always larger than the one perpendicular to it. Calculation of the entropy and enthalpy changes during the folding of the polymer chain alone cannot explain the spontaneous process. The corresponding increase in water entropy due to volume expansion may be large enough to result in the overall free energy decrease.

The phase behaviour of single polyethylene chains with and without fixing one end

The phase behaviour of a single polyethylene chain is studied by using molecular dynamics simulations. A free chain and a chain with fixing one end are considered here, since the atomic force microscope (AFM) tip can play a significant role in polymer crystallization in experiment. For a free chain, it is confirmed in our calculation that the polymer chain exhibits an extended coil state at high temperatures, collapses into a condensed state at low temperatures, i.e. the coil-to-globule transition that is determined by a high temperature shoulder of the heat capacity curve, and an additional liquid-to-solid transition that is described by a low temperature peak of the same heat curve. These results accord with previous studies of square-well chains and Lennard–Jones homopolymers. However, when one of the end monomers of the same chain is fixed the results become very direrent, and the chain cannot reach an extended coil-like state as a free chain does at high temperatures, i.e. there exists no coil-to-globule-like transition. These results may provide some insights into the influence of AFM tip when it is used to study the phase behaviour of polymer chains. If the interaction force between AFM tip and polymer monomers is strong, some monomers or one of them can be seen as being fixed by the tip, which is similar to our simulation model, and it is also found that AFM tip could induce polymer crystallization.

Shielding experiments with high-energy heavy ions for spaceflight applications

Mitigation of radiation exposures received by astronauts on deep-space missions must be considered in the design of future spacecraft. The galactic cosmic rays (GCR) include high-energy heavy ions, many of which have ranges that exceed the depth of shielding that can be launched in realistic scenarios. Some of these ions are highly ionizing (producing a high dose per particle) and for some biological endpoints are more damaging per unit dose than sparsely ionizing radiation. The principal physical mechanism by which the dose and dose equivalent delivered by these particles can be reduced is nuclear fragmentation, the result of inelastic collisions between nuclei in the hull of the spacecraft and/or other materials. These interactions break the incident ions into lighter, less ionizing and less biologically effective particles. We have previously reported the tests of shielding effectiveness using many materials in a 1 GeV nucleon−1 56Fe beam, and also reported results using a single polyethylene (CH2) target in a variety of beam ions and energies up to 1 GeV nucleon−1. An important, but tentative, conclusion of those studies was that the average behavior of heavy ions in the GCR would be better simulated by heavy beams at energies above 1 GeV nucleon−1. Following up on that work, we report new results using beams of 12C, 28Si and 56Fe, each at three energies, 3, 5 and 10 GeV nucleon−1, on carbon, polyethylene, aluminium and iron targets.

Phase behavior of a single polyethylene chain confined between two adsorption walls

AbstractThe phase behavior of a single polyethylene chain confined between two adsorption walls is investigated by using molecular dynamics simulations. In the free space, it is confirmed in our calculation that the isolated polymer chain exhibits a disordered coil state at high temperatures, and collapses into a condensed state at low temperatures, that is, the coil‐to‐globule transition, and the finite chain length effects are considered since the critical region depends on chain lengths. When the chain is confined between two attractive walls, however, the equilibrium properties not only depend on the chain length but also depend on the adsorption energy and the confinement. Mainly, we focus on the influence of polymer chain length, confinement, and adsorption interaction on the equilibrium thermodynamic properties of the polyethylene chains. Chain lengths of N = 40, 80, and 120 beads, distances between the two walls of D = 10, 20, 30, 50, and 90 Å, and adsorption energies of w = 1.5, 2.5, 3.5, 6.5, and 8.5 kcal/mol are considered here. By considering the confinement–adsorption interactions, some new folding structures are found, that is, the hairpin structure for short chain of N = 40 beads, and the enhanced hairpin or crystal like structures for long chains of N = 80 and 120 beads. The results obtained in our simulations may provide some insights into the phase behaviors of confined polymers, which can not be obtained by previous studies without considering confinement–adsorption interactions. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 370–387, 2008

Efficacious syntheses of alkylphenol ethoxylates and ethoxycarboxylates with long and single length PEG chain and their application to environmental fate study

The Williamson alkylation of a phenolic hydroxyl group of a 4-tert-octylphenol by 2-[2-(2-chloroethoxy)ethoxy]ethanol in the presence of potassium carbonate afforded the corresponding 9-(4-tertoctylphenyl)-3,6,9-trioxanonan-l-ol (OP3EO) quantitatively. Using powdered sodium hydroxide in place of potassium carbonate in the presence of phase transfer catalyst, alkylation of the terminal hydroxyl group occurred to give a mixture of OP3EO, 18-(4-tert-octylpheny)-3,6,9,12,15,18-hexaoxaoctadodecan-l-ol (OP6EO), 27-(4-alkylphenyl)-3,6,9,12,15,18,21,24,27-nonaoxaheptacosan-1-ol (OP9EO) and so on. Many types of OPkEO (k=4, 5, 6···) could be obtained by using OP1EO and OP2EO as starting materials. The use of OPkEO with a long and single length polyethylene glycol (PEG) chain was effective for studying the environmental fate of APEOs.

Steered molecular dynamics investigation of force-induced detachment of adsorbed single polymer chains

The dynamics of the detachment of single polyethylene (PE) chain from a strongly adsorbing surface in vacuum is investigated by steered molecular dynamics method. When the chain is pulled from the monomer of N/3 (here N is the chain length), there are two force plateaus for the curve of the average force 〈f〉 probed by the ideal spring as a function of pulling distance Z，which agrees well with the experimental results. There are four different stages during the detachment of single polyethylene (PE) chains. As the chains are pulled in an inclined direction from one end, there exist always a linear relationship for average force probed by the ideal spring vs inclination angle θ for θ>20 degrees Furthermore, the slope of the line increases with the pulling velocity. However, for θ<20 degrees, the average force probed by the ideal spring tends to a fixed value of 780pN.

Molecular dynamics simulation of interfacial thermal conductance between silicon and amorphous polyethylene

Using nonequilibrium molecular dynamics simulations, we study the interfacial thermal conductance between single crystal silicon and amorphous polyethylene (PE). We estimate that the silicon-PE interfacial thermal conductance is about 20MW∕m2K at room temperature, which is equivalent to the resistance of 16nm thick layer of bulk amorphous polyethylene. We also study the role of solid stiffness and the bonding strength across the interface on the interfacial thermal resistance. With strong interfacial bonding, our results are in agreement with the diffuse mismatch model and phonon radiation limit predictions, suggesting that in this case, heat carrying acoustic phonons in solids have transmission coefficients to polymer equal almost to unity.

Preliminary design of a single sphere multidetector directional neutron spectrometer using TLD-600

This communication summarizes the preliminary results obtained for the design of a neutron spectrometer based on thermoluminiscent 6LiF:Ti,Mg (TLD-600) dosimeters located along three perpendicular axis within a single polyethylene sphere. The neutron response functions have been calculated using the Monte Carlo (MC) code MCNPX 2.5 for different incidence directions. The applicability of the device has been investigated, relying on simulated exposures to reference fields of 241Am-Be and bare 252Cf, using the MAXED, GRAVEL and FRUIT unfolding codes. Moreover, a sensitivity analysis with FRUIT has been performed to evaluate the influence of the TL readout uncertainties on the results of the unfolding process.

Design and feasibility of a multi-detector neutron spectrometer for radiation protection applications based on thermoluminescent 6LiF:Ti,Mg (TLD-600) detectors

The design of a neutron detector with spectrometric capability based on thermoluminescent (TL) 6LiF:Ti,Mg (TLD-600) dosimeters located along three perpendicular axis within a single polyethylene (PE) sphere has been analyzed. The neutron response functions have been calculated in the energy range from 10 −8 to 100 MeV with the Monte Carlo (MC) code MCNPX 2.5 and their shape and behaviour have been used to discuss a suitable configuration for an actual instrument. The feasibility of such a device has been preliminary evaluated by the simulation of exposure to 241Am–Be, bare 252Cf and Fe–PE moderated 252Cf sources. The expected accuracy in the evaluation of energy quantities has been evaluated using the unfolding code FRUIT. The obtained results together with additional calculations performed using MAXED and GRAVEL codes show the spectrometric capability of the proposed design for radiation protection applications, especially in the range 1 keV–20 MeV.

Molecular dynamics simulation of polyethylene on single wall carbon nanotube

Molecular dynamics simulations are carried out on the isothermal crystallization process of single polyethylene chains with different chain lengths on the single wall carbon nanotube. This process is summarized as two steps, i.e., adsorption and orientation, and the bond-orientational order parameter is used to show the details of this process. The results show that the attractive van der Waals interactions control the adsorption and orientation of polyethylene on single wall carbon nanotube, and as the chain length increases, more microstructures appear in the last ordered structure. The stems of the ordered structure align parallel to the single wall carbon nanotube axis.

Effect of soil solarization and biocontrol agents on plant stand and yield on table beet in Córdoba (Argentina)

Field trials were conducted in commercial plots over a 3-year period to determine the effect of soil solarization and biocontrol agents, alone or combined, on plant stand and table beet yield. Single transparent polyethylene sheets were extended along the rows during summer periods. Table beet seeds were coated with biological control agents including strains of: Bacillus subtilis (B-96, B-238 and B-235), Trichoderma harzianum (Th-1) and a combination of B-235 and Th-1. Solarization increased plant stand by 25–95% in Rhizoctonia solani-infested soils and fresh weight by 32–41%, and in certain cases the combination of solarization with the biocontrol agents further improved the results.

Metal-free phthalocyanine and palladium sensor structure with a polyethylene membrane for hydrogen detection in SAW systems

Abstract The results concerning bilayer sensor structures (metal-free phthalocyanine (H2Pc) + palladium (Pd)) with various thicknesses of metal-free phthalocyanine (∼120 nm, ∼160 nm and ∼200 nm), but the same thickness of palladium (∼20 nm), have been studied with respect to the application of hydrogen gas-sensing at a relatively low interaction temperature ∼30–38 °C, employing a method based on the surface acoustic wave (SAW) system. All the films are produced by physical vapour deposition (PVD) in a SAW gas sensor system with a dual-delay line configuration. In the case of the best structure, H2Pc ∼ 160 nm and Pd ∼ 20 nm (the greatest change in frequency due to hydrogen gas interaction at the same temperature), single and double novel polyethylene (PE) membranes are placed on the top of the bilayer structure to reduce the influence of humidity. These PE membranes are made in a special way also by means of the PVD technology (at a temperature of ∼190–250 °C). The thickness of a single PE film amounts to about several score nanometers (60–80 nm). These membranes can also reduce the influence of other gases, like CO, NO2 and ammonia.

Steered molecular dynamics simulation of elastic behavior of adsorbed single polyethylene chains

AbstractWe investigate the dynamics of the detachment of single polyethylene (PE) chains from a strongly adsorbing surface in vacuum using a united atom model. Various statistical properties, including the mean‐square end‐to‐end distance 〈R2〉, the mean‐square radii of gyration $ \langle S^2\rangle_{xy} $, $ \langle S^2\rangle_z $, the shape factor $ \langle\delta \rangle $, the torsion angle distribution, the average surface adsorption energy $ \langle E_{\rm surface}\rangle $, the average total energy $ \langle U\rangle $, and the average force $ \langle f\rangle $, are analyzed. The relationship between the average force $ \langle f\rangle $ and the pulling velocity v shows two distinctive regions: a weakly dependence region at $ v\ <\ 10^{-2} $ Å/ps and a strongly dependence region at $ v\ >\ 10^{-2} $ Å/ps. Remarkably, the PE chain manifests force hysteresis under sequential stretching and releasing. These investigations may provide some insights into the elastic behavior of adsorbed polymer chains. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2322–2332, 2007

Single Wall Carbon Nanotube/Polyethylene Nanocomposites: Thermal and Electrical Conductivity

The thermal and electrical conductivities in nanocomposites of single walled carbon nanotubes (SWNT) and polyethylene (PE) are investigated in terms of SWNT loading, the degree of PE crystallinity, and the PE alignment. Isotropic SWNT/PE nanocomposites show a significant increase in thermal conductivity with increasing SWNT loading, having 1.8 and 3.5 W/mK at a SWNT volume fraction of φ ∼ 0.2 in low-density PE (LDPE) and high-density PE (HDPE), respectively. This increase in SWNT/HDPE is more than additive and suggests a reduction of the interfacial thermal resistance. Fitting the thermal conductivity data of the SWNT/HDPE nanocomposites with two models indicates that the thermal conductivity relies on a percolating SWNT network. Oriented SWNT/HDPE nanocomposites exhibit higher thermal conductivities, which are attributed primarily to the aligned PE matrix.

The free-energy landscape of single-molecule polymer crystals

By using extensive MD simulations the free-energy landscape of the crystallization process of a single polyethylene chain with N = 500 monomers is determined and the roles of both the potential energy and the entropy in shaping its gross features are discussed.

Coprocessing of heavy shale oil with polyethylene waste

Copyrolysis of heavy shale oil with polyethylene (PE) waste in autoclaves at various temperatures and times has been studied. It is shown that the copyrolysis improves the quality of the oil obtained and gives possibility to transform the wastes into liquid fuels. The copyrolysis of heavy oil and PE in the ratio 1:1 increases the percentage of aliphatic hydrocarbons in the oil more than six times, decreases the percentage of heteroatomic compounds more than twice, and decreases substantially viscosity of the oil. The copyrolysis oil of heavy shale oil with PE has a good compatibility at any ratios of the components. It is revealed that the Estonian Dictyonema shale (D) acts as commercial Al-Co-Mo and Akzo Nobel (Mo + S) catalysts, prevailing the latter by cracking ability accompanied by a higher unsaturation degree (iodine number) of the oil. So, the copyrolysis oil requires hydrogenation. As the pyrolysis of heavy oil yields much coke and gas under the optimum temperature for PE destruction (450 °C), a two-stage pyrolysis is proposed. In the first stage the destruction of single PE is carried out at 450 °C. In the second stage the PE oil obtained is added to the heavy oil, and their copyrolysis is carried out with 5% of D as catalyst under the hydrogen atmosphere.

Randomized clinical trial of bowel preparation with a single phosphate enema or polyethylene glycol before elective colorectal surgery (Br J Surg 2006; 93: 427–433)

Randomized clinical trial of bowel preparation with a single phosphate enema or polyethylene glycol before elective colorectal surgery (<i>Br J Surg</i> 2006; 93: 427–433)

Total Skeletal Reconstruction of the Nasal Dorsum

To review the outcomes of rhinoplasty in patients who underwent full-length dorsal reconstruction. Retrospective review. Private-practice facial plastic surgery clinic. Patients Thirty-seven patients in a consecutive series of 1273 rhinoplasty cases. In all patients, a single high-density porous polyethylene implant was used to span the full length of the nasal bridge as part of their rhinoplasty reconstruction. Retrospective review of medical charts and preoperative and postoperative photographs to identify any complications, including infection, extrusion, movement, or displacement, and examination of the aesthetic outcome. A telephone survey was performed to assess patient satisfaction regarding the appearance and sensation of the nose. In all cases, the full-length dorsal implant provided a smooth bridge contour without leaving an inverted V deformity or focal irregularities. There were no cases of infection or extrusion. In 2 cases, revision surgery was required to enhance cosmetic outcome. The high rate of patient acceptance, safety, and success of full-length dorsal reconstruction in providing a natural frontal contour challenges the minimal indications for using this type of reconstruction as opposed to using smaller grafts. As with all alloplasts, long-term follow-up is required.

DYNAMIC MODELING OF MICROCLIMATE AND ENVIRONMENTAL CONTROL STRATEGIES IN A GREENHOUSE COUPLED WITH A HEAT PUMP SYSTEM

ISHS III International Symposium on Models for Plant Growth, Environmental Control and Farm Management in Protected Cultivation (HortiModel 2006) DYNAMIC MODELING OF MICROCLIMATE AND ENVIRONMENTAL CONTROL STRATEGIES IN A GREENHOUSE COUPLED WITH A HEAT PUMP SYSTEM