Weight Polyethylene Research Articles

Dynamic strain rate and relative density effect on compression behavior of PP and PP/PE copolymers foamed by microcellular injection molding

ABSTRACTIsotactic polypropylene–polyethylene copolymer microcellular foams of various relative densities were prepared using nitrogen (N2) in supercritical solid state. Also, series of copolymers with different polyethylene weight percentages were prepared. Mechanical properties (compression and impact conditions) dependence on relative density, PE content, and strain rate was studied. Results showed that yield stress gradually decreased with lower density. The yield stress of PP copolymer foams decreased with the relative densities, and was always smaller than that of the solid PP copolymer. Nevertheless, the sensitivity to strain rate effect decreases at impact velocities. Analytical models were developed including the effects of both relative density and strain rate.

Study on biocompatibility, tribological property and wear debris characterization of ultra-low-wear polyethylene as artificial joint materials.

Ultra-low-wear polyethylene (ULWPE) is a new type polyethylene made by experts who are from China petrochemical research institute, which is easy to process and implant. Preliminary test showed it was more resistant to wear than that of Ultra-high-molecular weight polyethylene (UHMWPE). The purpose of the research is to study biocompatibility, bio-tribological properties and debris characterization of ULWPE. Cytotoxicity test, hemolysis test, acute/chronic toxicity and muscular implantation test were conducted according to national standard GB/T-16886/ISO-10993 for evaluation requirements of medical surgical implants. We obtained that this novel material had good biocompatibility and biological safety. The wear performance of ULWPE and UHMWPE was evaluated in a pin-on-disc (POD) wear tester within two million cycles and a knee wear simulator within six million cycles. We found that the ULWPE was higher abrasion resistance than the UHMWPE, the wear rate of ULWPE by POD test and knee wear simulator was 0.4 mg/106cycles and (16.9 ± 1.8)mg/106cycles respectively, while that of UHMWPE was 1.8 mg/106cycles and (24.6 ± 2.4)mg/106cycles. The morphology of wear debris is also an important factor to evaluate artificial joint materials, this study showed that the ULWPE wear debris gotten from the simulator had various different shapes, including spherical, block, tear, etc. The morphology of worn surface and wear debris analysis showed that wear mechanisms of ULWPE were adhesion wear, abrasive wear and fatigue wear and other wear forms, which were consistent with that of UHMWPE. Thus we conclude that ULWPE is expected to be a lifetime implantation of artificial joint.

Electrical Conductivity and Dielectric Permittivity of γ-Irradiated Nanocomposites Based on Ultrahigh-Molecular-Weight Polyethylene Filled with α-SiO2

UHMWPE/SiO2 composites were obtained from a homogeneous mixture of ultrahigh-molecular- weight polyethylene (UHMWPE) and silicon dioxide (α-SiO2) by hot pressing. The temperature dependence (20–170°C) of their conductivities σdс prior to and after γ irradiation (D = 200 kGy), the effect of absorbed dose on the σdс value (dose dependence), the behavior of the function logσdc = f(T) under heating–cooling conditions, and the frequency dependences (25–106 Hz) of the real (e') and imaginary (e'') parts of the complex dielectric constant were studied. The logσdc = f(T) dependence was shown to have in both cases a complex pattern: “breaks” due to phase transitions were observed. With an increase in the concentration of α-SiO2, the e' and e'' (tanδ) values in the matrix increased and the frequency dependences of these values corresponded to an exponential rule.

Editorial

Editorial

Study of oriented polyethylene structures using a Raman longwave acoustic mode

This paper concerns the basics of using longwave (low-frequency) Raman spectroscopy in the region of a longitudinal acoustic mode for the study of structural features of polymers. Using ultrahighmolecular- weight polyethylene (UHMW PE)-based reactor powders, gels, and oriented fibers obtained by the gel technology, the length distribution of straight-chain segments and its relation to the morphology of the sample were analyzed. An important role of the low-frequency Raman spectroscopy in creating domestic gel technology for preparing ultrahigh-strength threads from polyethylene was demonstrated.

Tricoordinate Organochromium(III) Complexes Supported by a Bulky Silylamido Ligand Produce Ultra‐High‐Molecular Weight Polyethylene in the Absence of Activators

Low‐coordinate organoCr(III) complexes supported by the silylamido ligand –N(SiMe3)DIPP (DIPP = 2,6‐diisopropylphenyl) are ethylene polymerization catalyst precursors without the need of additional cocatalyst. The reaction of CrCl3(THF)3 with 3 or 2 equiv. of LiN(SiMe3)DIPP yields either a four‐membered cyclometalated Cr complex or Cr[N(SiMe3)DIPP]2Cl, respectively, with no trace of Cr[N(SiMe3)DIPP]3. Addition of 1 equiv. of LiN(SiMe3)DIPP to Cr[N(SiMe3)DIPP]2Cl also leads to the four‐membered metallacycle, which upon heating transforms to a new six‐membered Cr metallacycle, likely via a σ‐bond metathesis step. Cr[N(SiMe3)DIPP]2Cl can be readily converted to bis(amido)Cr(III) vinyl and alkyl complexes Cr[N(SiMe3)DIPP]2R (R = vinyl, Bn, and Me). All of these structurally characterized low‐coordinate Cr(III) complexes with a Cr–C bond initiate the polymerization of ethylene in the absence of activators or cocatalysts, producing ultra‐high‐molecular weight polyethylene.

Effect of Modified NanoSiO<sub>2</sub> Agents on the Morphologies and Performances of UHMWPE Microporous Membrane via Thermally Induced Phase Separation

The effects of Modified NanoSiO2 Agents on the morphology and performance of ultra-high-molecular weight polyethylene (UHMWPE) microporous membranes via thermally induced phase separation were investigated in this work. The NanoSiO2 was surface modified by silane coupling agent KH570 (KH570-NanoSiO2). Differential scanning calorimetry (DSC) and X-Ray Diffraction (XRD) were performed to obtain crystallization of UHMWPE/white oil/ KH570-NanoSiO2 doped system. The morphology and performance of the prepared UHMWPE microporous membranes were characterized with scanning electron microscopy (SEM) and microfiltration experiments. The results showed that the morphology of UHMWPE membrane could be disturbed by KH570-NanoSiO2. Porosity and the rejection of Bovine serum albumin (BSA) of the blend membrane increased with increasing concentration of Modified NanoSiO2, while the water flux slightly decreased.

Microbial degradation of low-density polyethylene (LDPE) by Aspergillus clavatus strain JASK1 isolated from landfill soil.

Polythene and plastic waste are found to accumulate in the environment, posing a major ecological threat. They are found to be considered non-degradable, once it enters the environment it has been found to remain there indefinitely. However, significant attention has been placed on biodegradable polymer, identification of microbes with degradative potential on plastic material. The aim of the present investigation was to biodegrade low-density polyethylene (LDPE) using potential fungi isolated from landfill soil. Based on 18S rRNA analyses the isolated strain was identified as Aspergillus clavatus. LDPE degradation by A. clavatus was monitored for 90 days of incubation in aqueous medium. The degradation was confirmed by changes in polyethylene weight, CO2 evolution by Strum test, infrared spectra and morphological changes by SEM and AFM analysis.

Tribological and oxidational properties of porous high-pressure crystallized and vitamin E–incorporated ultra-high-molecular weight polyethylene as an artificial cartilage

The material properties of porous high-pressure crystallized ultra-high-molecular weight polyethylene containing vitamin E as a plasticizing agent and an antioxidant were studied. Two porous ultra-high-molecular weight polyethylene samples, with and without vitamin E, were produced by mixing ultra-high-molecular weight polyethylene powder and sodium chloride micro particles before the high-pressure crystallized process. A solid ultra-high-molecular weight polyethylene without vitamin E additive was made as a benchmark. The porosities of both porous samples were evaluated by energy-dispersive X-ray analysis of cross-sectional areas. The crystallinity of the composites was examined by thermal (differential scanning calorimetry) and spectral (X-ray diffraction) analyses. The short-term and long-term oxidative stabilities of porous ultra-high-molecular weight polyethylenes, with or without incorporated vitamin E, were investigated, respectively, by evaluations of differential scanning calorimetry oxidation induction time and Fourier transform infrared oxidation index. The tribological performance was also studied by a pin-on-disk test under lubrication with normal saline. The particulate size distribution of wear debris demonstrated the better biocompatibility of ultra-high-molecular weight polyethylenes with higher porosity. However, the antiwear capability and the oxidation resistance of the porous ultra-high-molecular weight polyethylene were inferior to those of the solid one. These drawbacks were significantly reduced by the influence of the vitamin E agent.

Rheological characterization of Poly(ethylene oxide) and carboxymethyl cellulose suspensions with added solids

Many foods are suspensions of solid particles randomly distributed in a non-Newtonian polymeric fluid. The rheological properties of high molecular weight poly(ethylene oxide) (PEO) and carboxymethyl cellulose (CMC) suspensions by adding micro-metric solid particles such as fibres or spheres were studied. The particle volume fraction, Φ, was varied between 0 and 0.4. Their rheological properties were obtained after fitting a Cross model. Rheological behaviour of the solutions was compared with rheological behaviour of food reported in the literature. For PEO and CMC solutions with spherical particle, the behaviour of the normalized steady shear viscosity, μ/μ0, as function of the fraction volume was compared with a Thomas model. However, for PEO the multibody interactions were not well represented and for CMC suspensions, μ/μ0 seems to be lineal with Φ. To observe and explain more the influence of the particle concentrations on the rheological behaviour, dynamic rheological measurements (upon verification of the linearity limit) were also performed. A transition from a dominantly viscous fluid to a dominantly elastic material was observed when Φ was increased.

Modeling unidirectional composites by bundling fibers into strips with experimental determination of shear and compression properties at high pressures

Numerical models of unidirectional panels of ultra-high-molecular weight polyethylene (UHMWPE), like Dyneema® HB80 or Spectra®, have been a difficult challenge. The problem arises from the intimate structure of the material. It is a huge collection of fibers loosely held together by a matrix. For example, for HB80 the fibers are very small in diameter (∼17 μm) but extremely strong (∼3.5 GPa). The amount of matrix is small (∼20% in volume) and very weak. The “natural” scale to use in the numerical model for this material is the fiber scale (∼17 μm). This scale would provide the right sound speed, transverse wave speed, failure strain, strength of the laminate, deflection, slippage between the fibers/layers, etc. which are all essential details if we want to have predictive capability. But even with the very powerful computers available nowadays we are still very far from being able to simulate a real-size laminated target (for example 30 cm wide and 1 or 2 cm thick) at the fiber scale. This paper proposes an “intermediate” scale that bundles or consolidates many fibers together so that the numerical problem is solvable in a few hours (or maximum one or two days for thick targets) of computation in a single board (24 processors). The scale is chosen precisely so that the essential physics of the ballistics problem is kept and the material properties used are the ones measured in the lab for the fiber and matrix. A similar approach was presented in a previous paper for fabrics (Kevlar, Dyneema, and PBO) where a yarn-level model was able to reproduce both the wave propagation patterns and the ballistic limits. This paper first describes new material test results (shear and compression at low and high confinement pressures). These were essential in properly capturing the delamination of the material. Then, for completeness, transverse wave propagation and ballistics results in Dyneema published elsewhere are briefly presented. Finally the numerical model in LS-DYNA is developed and comparison with deflection history and ballistic limits is conferred.

Antifriction properties increasing of ceramic MAO-coatings

In the past years, the most promising technology of producing ceramic coatings is a method of microarc oxidation. This method is characterized by universal properties of surface layer, which combines high-wear resistance, corrosion resistance, heat, and erosion resistance. The aim of the present work is to improve the tribological properties of microarc oxidation coatings using additional filling layer of coating as a thin film of polymer material. Ultra-high-molecular weight polyethylene was chosen as a polymer material. This composition material was tested under different friction conditions and showed significant decrease in friction coefficient for many friction pairs in different lubricant environment. The proposed technology of antifriction characteristics improvement of microarc oxidation coatings will significantly expand their application.

Effects of the Residues of Environmental Degradable Polyethylene Film on Soil Phosphatase Activities

Although environmental degradable film has been degraded from block disintegration to “rice water” appearance “dissolved” into soil environment under the natural environmental conditions effects of light, temperature, water, atmosphere and microorganisms, the "dissolved" plastic film still have serious pollution to environment which has become new hotspot of discussion. In this study, the orthogonal test L9(34) methods was applied to investigate the effects of four factors (the molecular weight of polyethylene, the amount of polyethylene residue, soil type and depth) on the soil phosphatase activities. The results indicate that the mean activity of phosphatase is 2135.7 μg /(h＊g),1472.97μg/(h＊g) and 1687.23μg/(h＊g) in the seeding, flowering and mature stage of brasscia juncea in clay soil, respectively, and 2.54, 1.56, 1.22 fold in that of sandy soil and 1.32, 0.87, 0.79 in that of loam, respectively.

The Influence of e-Beam Irradiation on the Morphology and Functional Properties of UHMWPE

The paper presents an analysis of the effectiveness of radiation modification of GUR 1050 and GUR 1020 polymers intended for endoprosthesis bearing components. It has been demonstrated through extraction and expansion that the crosslinking density increases as the applied dose of electron irradiation and the molecular weight of polyethylene grow. The recorded changes were accompanied by an increase in the degree of crystallinity, which was more significant in the case of the more heavy GUR 1050 (compared to GUR 1020). The morphological changes are supported by the results of micromechanical, sclerometric and tribological examinations. Tribological examinations were documented with SEM images of the surface of specimens subjected to oscillatory friction (roll-block tester). Series of crosswise valleys and projections, arranged along the friction direction, were found on the friction surface. The smoothening of the surface and a lack of lamella fragments on the base specimens which were not subjected to e-beam irradiation are observed along with a reduction of wear due to the increasing dose of irradiation.

Microporous Bio-Membrane Materials Based on High Molecular Weight Polylactide and Low Molecular Weight Poly(ethylene glycol)

In this work, microporous membrane biomaterials based on high weight molecular polylactide (PLA) and low molecular weight poly(ethylene glycol) (PEG) using rapid solvent evaporation method were prepared and investigated. The effect of PEG segments added on the thermal and degradation behaviors was studied. According to the results, produced PLA/PEG biomaterial has lower glass transition temperature (Tg)in comparison with neat PLA. It was also found that the degradation rates of the PLA/PEG biomaterials were significantly increased with adding of PEG, which explained by increasing hydrophilic groups. For better porous fixation, CL-blocked polyisocyanate (CL-bp), which was synthesized from reaction of isophorone diisocyanate (IPDI) with dimethylol propionic acid (DMPA) and Trimethylolpropane (TMP) followed by addition of caprolactam (CL), were introduced. The microporous forms were observed by the scanning electron microscope (SEM), which showed the mean diameters of prepared PLA/PEG microporous were around 10μm.

Meniscal Repair

The surgical techniques and associated devices for meniscus repair have improved over time, spurred in part by the clear recognition of the benefits of meniscal preservation and in part by the introduction of ultra-high-molecular weight polyethylene containing sutures. The desires for more minimally invasive techniques that decrease the risks of neurovascular injury and articular cartilage excoriation have seen 1 device generation after another introduced and improved upon. The current generation of meniscal repair all-inside devices are easier to use, limit the presence of material on the meniscal surface, and are self-adjusting and suture based. Although the speed of meniscus fixation device development places increasingly useful devices in surgeons' hands, clinical evidence of their effectiveness lag behind.

Study on molding process of UHMWPE microporous filter materials

AbstractA method called loose sintering was first introduced to prepare ultrahigh‐molecular weight polyethylene (UHMWPE) microporous materials. The pore size was predicted by the face‐centered cubic structure model while considering the particles' arrangement and melt. The results showed that the experimental pore diameter was close to that calculated by the present model. The effects of UHMWPE molecular weight, particle diameter, packing density, sintering temperature, and sintering time on pore size, compressive strength, pore diameter distribution, and density were presented. The morphology of micropore and the uniformity of pore distribution were analyzed by scanning electron microscopy and fractal geometry. The results showed that average pore diameter and porosity both increased with the UHMWPE particle diameter while decreased with compressive strength and bulk density. Sintering temperature and sintering time determined whether the heat was redundant to melt the particles. They also determined the pore size and the uniformity. UHMWPE microporous materials could be successfully prepared with suitable processing conditions. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Preparation and characterization of high molecular weight poly(trimethylene terephthalate) by solid-state polymerization

AbstractSolid-state polymerization has been widely used to prepare high molecular weight poly(ethylene terephthalate). Solid-state polymerization is generally carried out by heating solid, melt-phase-polymerized polymer below its melting temperature but above its glass transition temperature. Solid-state polymerization of poly(trimethylene terephthalate)(PTT) is not an independent process but rather an additional process with respect to melt polymerization that is used when PTT of a higher molecular weight is required. Two kinds of commercial PTT chips were polymerized in the solid state to prepare high molecular weight PTT, which were characterized by end group contents, molecular weight, thermal analysis and X-ray diffraction. In the solid-state polymerization of PTT, the overall reaction rate was governed by the reaction temperature, reaction time and pellet size. The content of carboxyl end groups was decreased during the solid-state polymerization with increasing reaction time and temperature. The melting temperature and crystallinity of solid-state-polymerized PTT were higher at longer times and higher temperatures of polymerization. The activation energy for the solid-state polymerization of PTT was in the range of 24~25 kcal/mol for each chip. Through the solid-state polymerization of commercial PTT chips, we could get high molecular weight polymers up to an intrinsic viscosity value of 1.63 dl/g, which is equivalent to about a 117,000 weight-average molecular weight.

Ultradrawing properties of ultrahigh‐molecular weight polyethylene/functionalized carbon nanotube fibers and transmittance properties of their gel solutions

AbstractThe influences of the dispersion level of carbon nanotubes (CNTs) and functionalized CNTs on the transmittance properties of ultrahigh‐molecular weight polyethylene (UHMWPE) gel solutions and on ultradrawing properties of their as‐prepared fibers are reported. The transmittance properties suggest that the dispersion level of functionalized CNTs in UHMWPE/functionalized CNTs gel solution is significantly better than plain CNTs in UHMWPE/CNTs gel solutions. The orientation factors, achievable draw ratios, tensile strength (σf), and modulus (E) values of UHMWPE/CNTs (FxCy) and UHMWPE/functionalized CNTs (FxCf‐y) as‐prepared fiber specimens reached a maximum value as their CNT and functionalized CNT contents approached optimum contents at 0.00015 and 0.0001 wt%, respectively. The σf and E values of both FxC0.0012 and FxCf‐0.001 series fiber specimens prepared at their optimum CNT and functionalized CNT contents reached another maximum as their UHMWPE approached optimum UHMWPE concentration of 1.7 wt%. Possible reasons accounting for these interesting properties are proposed. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

Cross-linked ultra-high-molecular weight polyethylene liner and ceramic femoral head in total hip arthroplasty: a prospective study at 5 years follow-up

Recent data indicate that enhanced wear resistance can be obtained with new cross-linked ultra-high-molecular weight polyethylene (CL-UHMWPE) liners, in comparison with previous-generation liners. The current prospective, cohort study was undertaken to analyse whether the use of a new CL-UHMWPE (Rexpol) results in a lower wear rate than ultra-high-molecular weight polyethylene (UHMWPE) in a group of similar patients undergoing total hip arthroplasty (THA). This study provides the first clinical data with this particular CL-UHMWPE. Between January 2001 and December 2001, patients underwent THA with biconical threaded cups and ceramic femoral heads using either a CL-UHMWPE liner (n = 50) or a regular UHMWPE liner (n = 57). At the time of the final 5-year evaluation, there were 48 patients available in the CL-UHMWPE and 54 patients available in the UHMWPE group. After a mean 5.6 years follow-up, there were no significant differences between the groups in Harris Hip Score outcomes. However, there was a 69.1% decrease in wear at 5 years for the CL-UHMWPE group in comparison with the UHMWPE group (p < 0.01). The use of CL-UHMWPE significantly reduced the risk of polyethylene wear in patients undergoing THA with biconical threaded cups and ceramic femoral heads. Further follow-up is needed to determine how this will influence long-term outcomes.