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This paper presents an analysis of the stress evolution of high-density polyethylene (HDPE) at loading, relaxation, and recovery stages in a multirelaxation-recovery (RR) test. The analysis is based on a three-branch springdashpot model that uses the Eyring's law to govern the viscous behavior. The spring-dashpot model comprises two viscous branches to represent the shortand long-term time-dependent stress responses to deformation, and a quasistatic branch to represent the time-independent stress response. A fast numerical analysis framework based on genetic algorithms was developed to determine values for the model parameters so that the difference between the simulation and the experimental data could be less than 0.08 MPa. Using this approach, values of the model parameters were determined as functions of deformation and time so that the model can simulate the stress response at loading, relaxation, and recovery stages of the RR test. The simulation also generated 10 sets of model parameter values to examine their consistency. The study concludes that the three-branch model can serve as a suitable tool for analyzing the mechanical properties of HDPE, and values for the model parameters can potentially be used to characterize the difference among PEs for their mechanical performance. Highlights * Developed computer programs to determine parameter values automatically. * Explained the unusual stress drop during stress recovery after unloading. * Evaluated the statistical range of the parameter values for the good fitting. KEYWORDS deformation mechanism, modeling, polyethylene, recovery, relaxation, 1 | INTRODUCTION Semi-crystalline polymers (SCP) such as polyethylene (PE) have long been used in industries due to their advantages in the physical and chemical properties. (1) The microstructure of [...]

Polyethylene (PE) is susceptible to environmental stress cracking (ESC). In the presence of an amphiphilic compound and subjected to stress, ESC starts with cavitation followed by slow crack growth and ends with brittle fracture. In this study, we used molecular dynamics simulation to study how branch ends which were chemically modified with vinyl acetate groups affect free volume coalescence around an amphiphilic compound, nonyl ethoxylate (NE), dispersed in branched PE models. Branch ends modified with vinyl acetate significantly impact the free volume coalescence dynamics around NE. Compared with methyl branch ends, vinyl acetate branch ends show a much higher affinity, as quantified by the corresponding radial distribution functions, for the hydrophilic ethylene oxide-segment of NE. However, this is not the case for the hydrophobic ethylene-segment. Interestingly, vinyl acetate branch ends tend to reduce the power (amplitude) of the free volume size fluctuations around both the ethylene oxide- and ethylene-segments. Indeed, the powers of the fluctuations with different PE branching characteristics decrease with increasing vinyl acetate concentration. We believe that free volume coalescence leads to cavitation and that vinyl acetate branches could inhibit cavitation, thereby crack propagation in PE. The power results seem to be consistent with the experimental observation that the addition of copolymer ethylene vinyl acetate to low-density polyethylene improves the ESC resistance of the blend. Highlights * Vinyl acetate branches reduce free volume coalescence activities. * Vinyl acetate branches are attracted to the hydrophilic segment of NE. * Cavitation likely starts from the free volume coalescence around NE. KEYWORDS coalescence dynamics, environmental stress cracking, free volume, polyethylene, vinyl acetate branch ends, 1 | INTRODUCTION Polyethylene (PE) is a widely used polymer known for its excellent mechanical properties, chemical resistance, and durability. (1,2) However, polyethylene is susceptible to a phenomenon called environmental [...]

This study aims to predict the compression behavior of ultra-high molecular weight polyethylene (UHMWPE) at various temperatures (25, 40, and 55[degrees]C) and strain rates (~[10.sup.-4]/s and ~[10.sup.-2]/s) using a single set of three-network (TN) viscoplastic model parameters. The TN model is made up of three parallel networks: networks A and B use nonlinear springs and dashpots to control the responses of the crystalline phase and confined amorphous phases, respectively, while network C captures the macromolecular amorphous networks using a single nonlinear spring. A single set of TN model parameters captures the yield and post-yield hardening responses of the stress-strain curves at experimental temperatures and strain rates. When these TN model calibrated parameters are used as material property in a commercial finite element tool to simulate UHMWPE compression, the predicted and simulated results match well, showing the model's fidelity. Additionally, the model predicts experiments conducted at 40 and 70[degrees]C with loading rates of ~[10.sup.-3]/s and ~[10.sup.-2]/s, respectively. The study also correlates the deformations of UHMWPE's crystalline structure and macromolecular amorphous networks with its global stress versus strain response by extracting stresses from individual networks of the TN model at different strain rates and temperatures. Highlights * UHMWPE's mechanical behavior predicted by a single set of TN model parameters * TN model predicts mechanical response at various strain rates and temperatures. * TN model explains microstructural crystalline and amorphous phase deformations. KEYWORDS compression properties, numerical simulations, three-network (TN) viscoplastic model, UHMWPE, 1 | INTRODUCTION Ultra-high molecular weight polyethylene (UHMWPE) is one such polymer, which demonstrates an encouraging potential as an impact, chemical, and wear-resistant material. (1) UHMWPE has found diverse applications, [...]

A new, low-cost, and direct green synthesis strategy was developed for the preparation of polymer composites composed of silver nanoparticles (AgNPs) decorated on a shape memory polymer blend using Rubus caesius L. leaves. X-ray powder diffraction, ultraviolet-visible spectroscopy (UV-vis), scanning electron microscopy, and energy dispersive X-ray spectroscopy (EDS) elemental composition were applied to characterize the crystal size, morphology, and elemental composition of Ag-NPs. UV-vis spectra detected the characteristic absorbance signal of AgNPs at about 430 nm, and the average crystal size of nanoparticles was calculated as about 12.60 nm. When nanocomposite films were characterized by attenuated total reflectance infrared spectroscopy, characteristic polylactic acid, and poly ethylene glycol (PEG) signals were determined. From the thermogravimetric analysis curves, it was determined that the amount of residue of nanocomposites increased as the amount of AgNP increased. It was seen that AgNPs did not affect the [T.sub.g] temperature of the nanocomposite films, while it was also a proof that the polymer blend was immiscible. It was observed that the shape recovery properties of nanocomposite films were better with increasing AgNPs content. Finally, both green synthesized AgNPs and nanocomposites prepared with shape memory polymers showed very good antibacterial activity against Gram-positive and Gram- negative bacteria. Highlights * Green synthesis of silver nanoparticles (AgNPs) was carried out with Rubus caesius L. leaves. * The synthesized AgNPs were characterized by ultraviolet visible spectroscopy and x-ray powder diffraction. * Composite films were prepared with poly lactic acid/poly [epsilon]- caprolactone blend by solvent casting method. * The amount of residue of nanocomposites increased with increasing AgNPs percentage. * The nanocomposite film containing 10% AgNPs has good activity. KEYWORDS antibacterial, green synthesis silver nanoparticles, nanocomposite, poly [epsilon]-caprolactone, poly lactic acid, shape memory effect, 1 | INTRODUCTION Nanoscale materials ranging from 1 to 100 nm are thought to provide solutions to environmental and technological challenges in medicine and water treatment. (1,2) This increasing demand [...]

Clariant data highlight advantages of metallocene PE waxes on pearlescent aesthetics Pearlescent pigments are a popular color option. Among the suppliers of process aids for these materials is Clariant Corp., [...]

In our second installment of the infrared (IR) spectra of polymers, we finish the discussion of the spectrum of polyethylene (PE) started last time. We explore how different PE syntheses [...]

Polymers are perhaps the most common type of sample analyzed by infrared spectroscopy. In this first of a series of columns, I will introduce the properties of polymers, discuss what infrared spectroscopy can tell us about polymers, and begin the analysis of the spectra of polymers with a look at the spectrum of polyethylene., I have over 30 years experience as an infrared (IR) spectroscopist, and have written three books on the subject (1-3). I have also taught infrared spectral interpretation to thousands of [...]

The objective of this study was to investigate the wear resistance of ultrahigh-molecular weight polyethylene (UHMWPE) and crosslinked polyethylene (XLPE) against different counterfaces. Friction and wear studies were evaluated under dry reciprocating sliding conditions at room temperature. TI6AI4V discs finished in polished, lapped, and ground conditions were reciprocated against polymer cylinders. In addition, abrasive wear studies were conducted using different abrasive grit sizes. The friction and wear properties of the two polyethylenes were strongly affected by the different counterfaces. XLPE showed important friction and wear sensitivity with the change of surface roughness of the TI6AI4V disc, as well as with the change in abrasive grit size. Scanning electron microscopy and energy-dispersive X-ray (EDX) analysis of the worn disc surfaces and the polymer pins indicated the wear mechanisms affecting the polyethylenes., INTRODUCTION Ultrahigh-molecular weight polyethylene (UHMWPE) and crosslinked polyethylene (XLPE) are extensively used biopolymers as a bearing material in total joint replacements (TJRs) [1], UHMWPE was used as a gold-standard material [...]

We propose a method for the estimation of the stress-strain state of cylindrical large-size structures with hollow (cellular) structures of the wall. Structures of this type are modeled by cylindrical orthotropic shells for which the cylindrical and tensile stiffnesses are theoretically found. The relations for the estimation of the stress state in hollow walls of cellular structures are proposed. We study the stress-strain state of cellular reservoirs vertically placed in soil and develop recommendations for their design., UDC 539.3 Introduction At the present, polymers and, especially, polyethylene prove to the most extensively used materials for the production of industrial low-pressure pipelines (8), (17). Pipelines fabricated of these [...]

This research used laboratory evaluations to study the effect of using low-density polyethylene (LDPE) additive on the fracture toughness of asphalt concrete mixtures. LDPE was mixed with asphalt at 160[degrees]C and incorporated into the mixture. LDPE content of 1.5, 3, and 4.5% by total weight of asphalt was adapted. Fracture toughness evaluation was based on the J-integral concept. Innovative semicircular specimen geometry (76-mm radius and 57-mm thickness) is employed in fracture toughness evaluation. Notches with different depth-to-radius ratios were introduced at the middle of the flat surface of each specimen. Three-point bend loading was used to allow the separation of the two surfaces as a result of tensile stresses at the crack tip. Application of the J- integral concept revealed the fracture toughness superiority of the LDPE-modified asphalt concrete mixtures as compared to the unmodified mixture. The fracture toughness is sensitive to the LDPE concentration. Mixtures modified with 4.5% LDPE experienced the highest fracture toughness. LDPE modification has also enhanced the physical properties of asphalt cement. The LDPE-modified asphalt concrete mix displayed a significant increase in both indirect tensile and compressive strength. DOI: 10.1061/(ASCE)MT.1943-5533.0000106 CE Database subject headings: Asphalts; Concrete; Toughness mixtures; Polyethylene. Author keywords: Asphaltic mixtures; Low-density polyethylene; Physical properties.

Within the framework of a coupled problem of thermoviscoelasticity, using the method of numerical modeling, we have studied the thermal instability of a rectangular prism, composed of copper and polyethylene or polymethylmethacrylate layers, in the course of its dissipative heating. The prism is subjected to high-frequency force or kinematic shear. We have established that, in the case of polyethylene, thermal instability occurs under conditions of force loading and is absent under a kinematic one. However, for polymethylmethacrylate, thermal instability takes place for both cases of loading. This effect is attributable to the existence of temperature intervals where the shear and volume loss compliances for each of the polymers increases with the temperature. We have also revealed that the critical values of thermal instability for a prism with metal layers are substantially higher than those for a homogeneous prism. In addition to thermal instability, thermal resonance instability is also possible. It is caused by the jump of the thermal state from the low- to high-temperature branch of the soft-type resonance characteristic. UDC 539.3, Vibratory heating induced by intense vibrations of viscoelastic solids can lead to a substantial growth of their temperature (8, 11, 14). Upon reaching the temperature of softening or melting of [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.solener.2008.11.008 Byline: Ibrahim M. Al-Helal, Abdullah M. Alhamdan Keywords: Arid environment; Greenhouse polyethylene films; Transmittance; GSR; PAR Abstract: Degradation of the radiative properties of a 200[mu]m-polyethylene film caused by exposure to the harsh environment of Riyadh, Saudi Arabia has been investigated over a period of 13 months. Measurements of global solar radiation (GSR), photosynthetically active radiation (PAR), air temperature and relative humidity were made inside and outside two single-polyethylene-covered model structures. Each model structure was 1m wide, 1m long, and 0.75m high. The east side of each model structure was open for natural ventilation. One of the model structures was exposed to the environment during the 13-month period, while the other was kept indoor in a room to protect the polyethylene film from environment and was used as a control when measurements were carried out. Results showed that exposure to the environment reduced the polyethylene film transmittance to GSR and PAR. The reduction in solar radiation transmitted minimized air temperatures inside the structure. The average summer daytime temperature inside the exposed structure was 45.7[degrees]C, as compared to 46.9[degrees]C inside the control structure, while the average of outside temperature was 38.2[degrees]C. The degradation of the polyethylene transmittance progresses rapidly during the first three months of exposure. The relative losses of GSR and PAR transmittance were 9% and 15.3%, respectively, after three months. However, the losses decreased to 5% and 8%, respectively, after 11 months due to rainfall in the area. Radiation transmittance was found to be dependent on season of the year. The averages (standard deviations) of GSR and PAR transmittance for the control film during winter months were 0.8 (0.01) and 0.75 (0.00), respectively. Whereas, during summer months, the averages (standard deviations) were 0.75 (0.02) and 0.71 (0.02), respectively. The averages (standard deviations) of GSR and PAR transmittance for the exposed film during winter months were 0.77 (0.03) and 0.70 (0.03), respectively, as compared to 0.68 (0.01) and 0.61 (0.02), respectively, during summer months. Author Affiliation: Department of Agricultural Engineering, College of Food and Agricultural Sciences, King Saud University, P.O. Box 2460, Riyadh 11451, Saudi Arabia Article History: Received 30 June 2007; Revised 22 October 2008; Accepted 20 November 2008 Article Note: (miscellaneous) Communicated by: Associate Editor Darren Bagnall

This paper describes important aspects of partial discharge (PD) diagnostics of distribution power cables. PD parameter were discussed under consideration of attenuation and dispersive effects of cable characteristics. Field experiences with PD diagnosis on paper insulated cables (PILC) and cables with cross linked polyethylen insulation (XLPE) by energizing with Damped AC Voltage demonstrate relevant demands and the effective outcome for asset management decision support. The main difficulty is to evaluate the risc of PD occurrences on the reliability of the cable system. If an sufficient amount of PD diagnostic data for the cable components is available statistical methods can be used for determing threshold levels and relevant condition indexes for the asset management. Index Terms--Power cables, partial discharges, PD pulse attenuation, dispersion, knowledge rules, asset management.

A traditional constant voltage conductivity test method was used to measure how the conductivity of highly insulating low-density polyethylene (LDPE) polymer films depends on applied electric field, repeated and prolonged electric field exposure, and sample temperature. The strength of the applied voltage was varied to determine the electric field dependence. At low electric field, the resistivity was measured from cryogenic temperatures to well above the glass transition temperature. Comparisons were made with a variety of models of the conduction mechanisms common in insulators, including transient polarization and diffusion and steady-state thermally activated hopping conductivity and variable range hopping conductivity, to determine which mechanisms were active for LDPE and to provide a better picture of its electrical behavior. Index Terms--Conductivity, dielectric materials, electric field effects, polyethylene.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.forsciint.2008.01.006 Byline: Erica Taylor (a), James F. Carter (b), Jenny C. Hill (b), Carolyn Morton (a), Niamh Nic Daeid (c), Richard Sleeman (b) Keywords: Plastic materials; Polyethylene; Plastic bag examination; Birefringence; Isotope ratio; Isotope ratio mass spectrometry (IRMS) Abstract: Plastic bags are frequently used to package drugs, explosives and other contraband. There exists, therefore, a requirement in forensic casework to compare bags found at different locations. This is currently achieved almost exclusively by the use of physical comparisons such as birefringence patterns. This paper discusses some of the advantages and shortcomings of this approach, and presents stable isotope ratio mass spectrometry (IRMS) as a supplementary tool for effecting comparisons of this nature. Carbon and hydrogen isotopic data are presented for sixteen grip-seal plastic bags from a wide range of sources, in order to demonstrate the range of values which is likely to be encountered. Both isotopic and physical comparison (specifically birefringence) techniques are then applied to the analysis of rolls of bags from different manufacturing lots from a leading manufacturer. Both approaches are able to associate bags from a common production batch. IRMS can be applied to small fragments which are not amenable to physical comparisons, and is able to discriminate bags which could be confused using birefringence patterns alone. Similarly, in certain cases birefringence patterns discriminate bags with similar isotopic compositions. The two approaches are therefore complementary. When more than one isotopically distinct region exists within a bag (e.g. the grip-seal is distinct from the body) the ability to discriminate and associate bags is greatly increased. Author Affiliation: (a) Faculty of Applied Sciences, University of the West of England, Frenchay Campus, Coldharbour Lane, Bristol BS16 1QY, UK (b) Mass Spec Analytical Ltd., Building 20F, Golf Course Lane, Filton, Bristol BS99 7AR, UK (c) Centre for Forensic Science, Department of Pure and Applied Chemistry, University of Strathclyde, Royal College, 204 George Street, Glasgow G1 1XW, UK Article History: Received 22 May 2007; Revised 3 January 2008; Accepted 9 January 2008

This paper describes an experimental method, bio-ferrography, to separate ultrahigh molecular weight polyethylene (UHMWPE) wear debris, generated in hip simulators, from bovine serum lubricating fluid. A total of 54 experiments were performed in which an enzyme digestion 'cocktail' was developed and used to clean the bovine serum samples of extraneous sugars, proteins, and lipids that interfere with the UHMWPE particle separation. Erbium chloride was used to marginally magnetize particles in the fluid prior to passing through the ferrographic device. The particles were captured and separated from the fluid by traversing the treated serum across a magnetic gap of a bio-ferrograph. Morphology of the captured and separated wear debris was compared with particles from samples of fluid filtered through a paper sieve arrangement with pores of 0.05 micrometers in diameter. The UHMWPE wear debris collected using the described experimental method, were found to be between 0.1 and 20 micrometers in diameter with spherical and pill-shaped particles. The filtered UHMWPE particles were in the same size range as the debris separated using bio-ferrography. To show that the experimental method captured UHMWPE particles, the spectra of the chemical composition of UHMWPE from an acetabular cup insert of a hip implant and of UHMWPE particles separated using bio-ferrography were compared and found to be the same. To further demonstrate that polyethylene could be captured and separated through the experimental method, manufactured polyethylene microspheres in the diameter range of 3-45 micrometers, were captured and separated using the bio-ferrographic process. [DOI: 10.1115/1.2162554] Keyword: bio-ferrography, debris, wear particles, polyethylene, prosthesis, UHMWPE, hip simulator