Amorphous Polyethylene Research Articles

Effect of Nanotube Functionalization on the Elastic Properties of Polyethylene Nanotube Composites

The effects of the chemical functionalization of a single-wall carbon nanotube in nanotube/polyethylene composites on the bulk elastic properties are presented. Constitutive equations are established for composites containing both functionalized and nonfunctionalized nanotubes using an equivalent-continuum modeling technique. The elastic properties of both composite systems are predicted for amorphous and crystalline polyethylene matrices with various nanotube lengths, volume fractions, and orientations. The results indicate that for the specific composite materials considered in this study most of the elastic stiffness constants of the composite with functionalized nanotubes are either less than or equal to those of the composite without functionalized nanotubes.

Amorphous Polyethylene by Tandem Action of Cobalt and Titanium Single‐Site Catalysts

AbstractSummary: A variety of branched polyethylenes, spanning from semicrystalline LLDPE to completely amorphous, rubbery PE, was obtained from ethylene by homogeneous tandem catalysis using combinations of CoCl2(N) (1) (N = [1‐(6‐benzo[b]thiophen‐2‐yl‐pyridin‐2‐yl)‐ethylidlene)‐(2,6‐diisopropyl‐phenyl)‐amine) and [(η5‐C5Me4)SiMe2(tBuN)]TiCl2 (2) in the presence of MAO at 30 °C. The productivity reached a maximum of 4 570 kg PE (mol Ti · h)−1 at χCo = 0.50, yielding a rubbery material with d25 = 0.868 g · cm−3 and Tg = −55 °C.Conversion of ethylene into branched polyethylene using CoII iminopyridyl complex CoCl2(N) (1) and TiCl2[(η5‐C5Me4)SiMe2(tBuN)] (2).magnified imageConversion of ethylene into branched polyethylene using CoII iminopyridyl complex CoCl2(N) (1) and TiCl2[(η5‐C5Me4)SiMe2(tBuN)] (2).

A Novel Approach for Synthesis of a Nanocrystalline Yttria Stabilized Zirconia Powder via Polymeric Precursor Routes

A nanocrystalline powder of 5 mol% yttria stabilized zirconia (YSZ) is prepared by polymeric precursor routes. Three different routes, viz. (i) amorphous citrate process, (ii) Pechini process and (iii) polyethylene glycol (PEG) assisted process are examined. In these processes, parameters such as metal cations to fuel ratio or components of fuel are varied and the effects analyzed. A novel experimental procedure for controlled combustion based on the thermal analysis has been adopted. All the three processes yield nanocrystalline powders with average crystallite size lying in the range of 9 to 18 nm. Densities as high as 99% of theoretical density (TD) could be achieved by sintering the compacts of powders at a relatively low temperature of 1400°C for 2 h.

Polyethylene/keratin fiber composites with varying polyethylene crystallinity

Short-fiber reinforced composites are made from keratin fibers obtained from poultry feathers and polyethylenes of varying crystallinity. The chemical nature of the polymer and fiber is kept constant and the molecular architecture of the polymer is varied. It is found that low crystallinity polyethylenes are reinforced by keratin fibers but high crystallinity polyethylenes are not. The keratin fibers inhibit crystallinity in low crystallinity polyethylenes but enhance crystallinity in high crystallinity polyethylenes. Microscopy shows increased adhesion between the fibers and the polymer for the more amorphous polyethylenes. A model is presented that describes composite properties as a function of fiber properties and matrix crystallinity.

ESR Study on Segmental Motion of Polyethylene in Amorphous Region, Dependent on Crystallinity, Molecular Weight, and Labeled Site

The transition temperature of high-density polyethylene (PE), low-density PE, and hydrogenated poly(butadiene), which was detected by the spin-labeled ESR method, was evaluated. The detected transition corresponded to the β transition of semicrystalline polymer PE. The transition temperature was found to depend on the crystallinity, the molecular weight of the sample, and labeled site. The β relaxation around chain-end segments was observed by the selective spin-labeling method. The mobility of the end segment as well as the inner segments was revealed to depend on the molecular weight (Mn) of the sample. The motional length scale (cooperative segment length) ξ of amorphous PE at Tg was estimated to be around 2 nm, which was the same order as the reported ξ for various polymers and the Kuhn length of PE.

Mechanisms of lithium transport in amorphous polyethylene oxide

We report calculations using a previously reported model of lithium perchlorate in polyethylene oxide in order to understand the mechanism of lithium transport in these systems. Using an algorithm suggested by Voter, we find results for the diffusion rate which are quite close to experimental values. By analysis of the individual events in which large lithium motions occur during short times, we find that no single type of rearrangement of the lithium environment characterizes these events. We estimate the free energies of the lithium ion as a function of position during these events by calculation of potentials of mean force and thus derive an approximate map of the free energy as a function of lithium position during these events. The results are consistent with a Marcus-like picture in which the system slowly climbs a free energy barrier dominated by rearrangement of the polymer around the lithium ions, after which the lithium moves very quickly to a new position. Reducing the torsion forces in the model causes the diffusion rates to increase.

Computational Characterization of Micro- to Macroscopic Deformation Behavior of Amorphous, Crystalline, and Semicrystalline Polyethylene

Computational Characterization of Micro- to Macroscopic Deformation Behavior of Amorphous, Crystalline, and Semicrystalline Polyethylene

Oxidative stability of cream cheese stored in thermoformed trays as affected by packaging material, drawing depth and light

Abstract The oxidative stability of cream cheese stored in thermoformed trays made of amorphous polyethylene terephtalate (A-PET)/polyethylene (PE), polystyrene (PS)/Ethylene-vinylalcohol copolymer (EVOH)/PE and Polypropylene (PP)/PE with different depth (25, 50 and 70 mm) and colour (black, white and transparent) was studied by sensory evaluation and gas chromatographic analysis of volatile compounds. The polymer combination had an important effect on sensory scores of both sunlight and acidulous flavour in cream cheese stored in the dark for 2, 4 and 6 months. Cream cheese stored in trays made of A-PET/PE had higher acidulous flavour and lower content of hexanal and 2-nonanone. Only small differences were observed between PS/EVOH/PE and PP/PE despite the great diversity of oxygen transmission rates. The drawing depth of the packages had no significant effect on oxidative stability of cream cheese, irrespective of storage in the dark or under illumination. The colour of the examined packaging material had a pronounced effect on photoxidative changes in cream cheese.

Ethylene and 1-Hexene Sorption in LLDPE under Typical Gas Phase Reactor Conditions: A Priori Simulation and Modeling for Prediction of Experimental Observations

A detailed study has been conducted of the sorption of ethylene and 1-hexene in linear low density polyethylene (LLDPE) under typical gas phase LLDPE reactor conditions. The recently proposed osmotic ensemble hyperparallel tempering method is used to simulate ethylene and 1-hexene gas sorption in the polymer samples. Simulations are used to parametrize the PC−SAFT equation of state for calculation of gas sorption in amorphous polyethylene. A model for crystallite induced elastic constraints is adopted to modify the equation of state for description of gas sorption in polyethylene below melting point conditions. Single-component ethylene and 1-hexene gas sorption as well as ethylene/1-hexene gas co-sorption are studied in this work. It is observed that simulations provide an effective method to parametrize the PC−SAFT equation of state. In addition, since simulations and PC−SAFT assume a hypothetically amorphous polymer, a quantitative description of elastic effects for gas sorption in semicrystalline poly...

Modeling the Cloud Curves and the Solubility of Gases in Amorphous and Semicrystalline Polyethylene with the SAFT-VR Approach and Flory Theory of Crystallization

The statistical associating fluid theory for potentials of variable range SAFT-VR [Gil-Villegas, A.; et al. J. Chem. Phys. 1997, 106, 4168] is used to examine the fluid-phase behavior of mixtures of n-alkanes, alk-1-enes (R-olefins), and nitrogen with polyethylene. The molecules are modeled as flexible chains of tangent spherical segments, with segment-segment dispersive interactions treated via square-well potentials. The parameters of the polyethylene polymer are determined from those of the n-alkanes by using simple extrapolations with molecular weight. As a test of the extrapolated parameters for polyethylene, the absorption (vapor-liquid equilibria) and cloud curves (liquid-liquid equilibria) of n-pentane-polyethylene systems are predicted without adjustable binary parameters, and the effect of the polymer parameters on the phase behavior of the mixture is discussed. The liquid-liquid immiscibility curve is found to be very sensitive to the intermolecular potential parameters used to describe the polymer. The change in the lower critical solution temperature (LCST) for mixtures of n-alkanes of increasing chain length in polyethylene is also predicted. Good agreement with experimental data is also obtained for the absorption of small gases in amorphous polyethylene. The predictions of the SAFT-VR approach confirm experimental findings that the solubility of nitrogen increases with temperature while the solubility of heavier molecules such as ethene and but-1-ene decreases. Strong synergies can be observed when several gases absorb in the same polyethylene polymer. The co-absorption effects are explained in terms of the interactions between gas and polyethylene molecules. When the temperature of interest is below the melting temperature of polyethylene, the polymer exists in a semicrystalline state. In this case, the crystallinity of polyethylene has to be taken into account in order to predict the solubility of the various gases. We present an accurate theory to predict the crystallinity of polyethylene as a function of temperature. The approach, which is based on Flory’s theory of copolymer crystallinity [Flory, P. J. Trans. Faraday Soc. 1955, 51, 848], is accurate for a large variety of polyethylene samples, and requires only the experimental crystallinity or polymer density at 25 °C as an input parameter. On combining the Flory and SAFT-VR approaches, we can predict the solubility of various gases in semicrystalline polyethylene samples, by assuming that the molecules of gas only absorb in the amorphous regions of the polymer.

Simulation of the effects of chain architecture on the sorption of ethylene in polyethylene

An osmotic ensemble hyperparallel tempering technique has been developed to study the solubility of ethylene in amorphous linear low-density polyethylene of different chain architectures. The NERD united-atom force field (Nath, Escobedo, and de Pablo revised united-atom force field) is used in all simulations. We have investigated the effect of polyethylene chain length and branching on ethylene solubility. In this study, we have considered short-chain branching of amorphous linear low-density ethylene-1-hexene copolymers under typical polymerization reactor conditions. It is observed that, in the polymer, ethylene prefers to reside in the vicinity of polymer chain ends. This clustering causes a decrease in ethylene solubility with polymer chain length. When short-chain branches are introduced to a linear polymer chain, however, the chain-end clustering effect is counteracted by a higher density, thereby leading to an ethylene solubility almost identical to that in the linear polymer.

Monte Carlo simulations on the effects of nanoparticles on chain deformations and reinforcement in amorphous polyethylene networks

Reinforcing effects in an amorphous polyethylene matrix were estimated for spherical filler particles arranged either on a cubic lattice or randomly in space. Attention was first focused on the effects of the type of arrangement of the particles on the microscopic properties of the polymer chains. Specifically, Monte Carlo rotational isomeric state (MC-RIS) simulations were carried out to predict the effects of the volumes excluded by the filler particles on the configurational distribution functions of the chains, and from these distributions the elastomeric properties of the composites. The calculations were carried out for a range of particle sizes and particle volume fractions. As expected, filler inclusions are found to increase the non-Gaussian behavior of the chains. The results were compared with those from small-angle neutron scattering (SANS) experiments. In the case of arrangement on a cubic lattice, chains dimensions were always found to decrease. In the randomly-dispersed filler arrangements, there were significant increases in chain dimensions relative to the unfilled system in some instances, and the changes were in excellent agreement with the SANS results. The present simulations thus give further encouragement to interpretations of chain deformations in filled systems in terms of volume exclusion effects from the nanoparticle inclusions, including their dispersions and arrangements within polymer matrices.

Tearing resistance of some co-polyester sheets

A three-zone model consisting of initial, evolutionary and stabilised plastic zones for tearing resistance was proposed for polymer sheets. An analysis with the model, based on the essential work of fracture (EWF) approach, was demonstrated to be capable for predicting specific total work of fracture along the tear path across all the plastic zones although accuracy of specific essential work of fracture is subject to improvement. Photo-elastic images were used for identification of plastic deformation sizes and profiles. Fracture mode change during loading was described in relation with the three zones. Tearing fracture behaviour of extruded mono- and bi-layer sheets of different types of amorphous co-polyesters and different thicknesses was investigated. Thick material exhibited higher specific total work of tear fracture than thin mono-layer sheet in the case of amorphous polyethylene terephthalate (PET). This finding was explained in terms of plastic zone size formed along the tear path, i.e., thick material underwent larger plastic deformation than thin material. When PET and polyethylene terephthalate glycol (PETG) were laminated with each other, specific total work of fracture of the bi-layer sheets was not noticeably improved over that of the constituent materials.

Computer simulations of localized small polarons in amorphous polyethylene.

We use a simple mean field scheme to compute the polarization energy of an excess electron in amorphous polyethylene that allows us to study dynamical properties. Nonadiabatic simulations of an excess electron in amorphous polyethylene at room temperature show the spontaneous formation of localized small polaron states in which the electron is confined in a spherically shaped region with a typical dimension of 5 A. We compute the self-trapping energy to be -0.06+/-0.03 eV, with a lifetime on the time scale of a few tens of picoseconds.

Microscopic calculation of the energetics of charged states in amorphous polyethylene.

Polarization energies are calculated for a single excess charge on a polyethylene chain in amorphous polyethylene using (i) local segment and nonlocal distributed molecular polarizabilities, (ii) material structures simulated by both general-purpose and specialist Monte Carlo software, and (iii) uniform and Gaussian distributions of charge with different extents of charge delocalization. Local and distributed response lead to results that are essentially the same except that they correspond to different mean polarizabilities. With increasing delocalization of the charge along the chain, the polarization energies shift to higher values and the width of their distribution decreases, the differences being more pronounced for the uniform distribution. The polarization energies for charges delocalized over 10-20 methylene units form a distribution some 14 eV wide centered around 1 eV, narrowing significantly for more homogeneous polymer melts. The calculations are relevant to trapping of charge in polyethylene. They also yield the microscopic variation in the potential along the polymer chain caused by the polarization energy difference, and so may provide useful inputs to theories of electronic conduction in polymer materials.

A test of the method of images at the surface of molecular materials.

The method of images is tested by comparing two ways of calculating the polarization energy in crystalline fullerene C60 and in bulk amorphous polyethylene (PE): (i) treating the whole molecular material microscopically, and (ii) replacing part of the material by a uniform dielectric continuum of the same relative permittivity. The method of images is accurate to within 5% once the distance of the charge from the surface of the dielectric continuum exceeds about twice the average spacing between the polarizable units in the molecular material. For C60 crystals the method of images always overestimates the magnitude of the polarization energy, partly because it ignores the reduction in the relative permittivity of the dielectric continuum near its surface. For amorphous PE the method of images can overestimate or underestimate the true result, depending on the local density around the charge.

Novel approach for the bulk synthesis of nanocrystalline yttria doped thoria powders via polymeric precursor routes

Three different polymeric precursor routes viz., (i) amorphous citrate process, (ii) Pechini process and (iii) polyethylene glycol assisted process were compared for synthesising nanocrystalline powders of 7.5 mol% yttria doped thoria (YDT). In each of the processes, parameters such as metal-to-fuel ratio or composition of fuel were varied and the effects were analysed. TG/DTA studies were conducted to identify the ignition temperatures of the precursors. Also, a novel experimental procedure with controlled combustion was devised for the preparation of powders based on the thermal analysis data. All the processes result in phase pure and nanocrystalline powders. The average crystallite size of the powders ranged between 9 and 18 nm. The powder samples were analysed for their carbon content and studied for their sinterability. Densities as high as 99% th.d. could be achieved by sintering the compacts of powders obtained from (i) amorphous citrate process with CA/M ratios 2.0 and 3.0, (ii) Pechini processes (independent of fuel composition) and (iii) PEG-assisted process using PEG 4000 at a relatively low temperature of 1500 °C for 2 h.

単軸引張下の非晶性ポリマー内部における分子鎖配向とからみ点形成の分子動力学解析

A nanoscopic specimen of amorphous polyethylene, involving 3, 542 random coil molecular chains composed of 500-1500 methylene monomers with about 2 million methylene groups, is subjected to uniaxial tension by means of molecular dynamics simulation. After showing a linear elastic relationship at the initial stage of ezz≤0.03 at ezz=5.0×1011/s, the material “yields” by elongating without stress increase up to the strain of 1.5, where strain hardening appears. Careful investigation on change in dihedral angle and morphology of all molecular chains reveals that the gauche→trans transition takes place during yielding, generating a new network-like structure composed of entangled molecular clusters and oriented chains bridging them. The strain hardening is caused by the directional orientation and stretching of molecular chains between entanglements in the nucleated structure.

Analysis of thermally stimulated current and effect of rubbery annealing around glass-rubber transition temperature in polyethylene terephthalate

Thermally stimulated currents (TSC) in amorphous polyethylene terephthalate films have been investigated in the temperature range of −180 to 140°C. This material shows a very weak intensity peak at approximately −95°C and another around 80°C originated from dipolar process (α-peak), as evidenced from the variation of polarizing conditions such as applied electric field and polarizing time. The effect of isochronal rubbery annealing starts to appear from a temperature of annealing of 90°C, it then appears in a TSC spectrum two components around 88 and 108°C allotted, respectively to the true and rigid amorphous phases. The first component tends to disappear in an irreversible way to the detriment of the second which implies the establishment of an order within material during annealing by the formation and growth of nodules. The thermostimulated currents technique allowed to calculate with good precision the activation parameters of each process as well as the evaluation of the crystallinity rate by an established empirical formula.

Microscopic calculation of the energetics of ions in polyethylene

Polarization energies are calculated for a point charge ion in amorphous polyethylene using local segment and non-local distributed molecular polarizabilities with material structures simulated by both general-purpose and specialist Monte Carlo software. An expression is derived for the polarization energy of a molecular system divided into submolecules that may acquire both induced dipoles and induced charges in the presence of external charges. The two descriptions of the molecular response lead to results that generally differ only because of the polarizability difference, so that less computationally demanding local polarizabilities may suffice, with results for distributed response estimated by suitable scaling. The polarization energy is correlated with the molecular packing around the ion and its position in the polymer material through fluctuations of the polymer density. The polarization energy distribution from the general-purpose software has a range of some ±0.6 eV about a maximum at −1 eV and from the specialist software has a range of some ±0.5 eV centered about a maximum at −1.5 eV, both for a density of 0.8 g cm−3. Relaxation of the sample after inserting the ion lowers the polarization energy by typically 0.5 eV and broadens the distribution. The results for polyethylene as a test system suggest that the methodology may be applied to more complicated systems, such as practical polymer electrolytes.