High Molecular Weight Polyethylene Research Articles

Experimental and numerical studies of ballistic resistance of hybrid sandwich composite body armor

Abstract Defense mechanisms remain important and indispensable due to the different types of pistols and ordnance besides many guns. Hybrid composite sandwich panels are an attractive focus because of their ingrained characteristics, such as high stuffiness and high energy absorption. Hybrid composite sandwich panels are among the most important in armoring various structures. Despite the high density of these panels, they have significant qualities that qualify them to be the first selection for use in armored vehicles or body armor. Recently, there have been several types of structures, and selecting the appropriate structure as armor against the projectiles is very important. The study subjected three samples to the ballistic impact test using a 7.62 × 39 mm bullet. The first sample, S1, consists of ultra high molecular weight polyethylene (UHMWPE)/epoxy, unfilled honeycomb core, Kevlar/epoxy, unfilled honeycomb core, Kevlar/epoxy, and UHMWPE/epoxy; the second sample, S2, comprises Kevlar/epoxy, unfilled honeycomb core, Kevlar/epoxy, unfilled honeycomb core, and UHMWPE/epoxy, and the third sample, S3, comprises Al2O3, Kevlar/epoxy, unfilled honeycomb core, carbon/epoxy, unfilled honeycomb core, and carbon/epoxy. ABAQUS software was used to evaluate the ballistic impact numerically, and after that, the study examined the same armor samples experimentally. The results manifested that only the armor S3 succeeded in stopping the bullet. This is attributed to the structure of the cores, which helps compress and accumulate the cells under the projectile. The speeds of the bullet after penetration (residual velocity; VR) were 748.5 and 715.3 m/s for S1 and S2 armors, respectively, where the back face signature for S3 was 1.5 mm, which is optimum and within the allowed range. The total energy absorption of these armors S1, S2, and S3 is 344.65, 539.04, and 2585.66 J. Furthermore, the highest deviation between numerical and experimental approaches is about 2.04% in the VR.

Improving barrier properties of polyethylene/Fe2O3‐modified nanographene nanocomposites in a magnetic field

AbstractThe present work aims at improving the barrier properties of high molecular weight Polyethylene/ graphene nanoplatelets (HMWPE/GnP) nanocomposites by aligning the embedded modified graphene nanoparticles in a magnetic field. Graphene nanoplatelets (GnP) were modified by magnetic Fe2O3 to produce Fe2O3‐modified Graphene, GnP‐mFe2O3. The magnetic properties of Fe2O3 were previously characterized by the vibrating sample magnetometer (VSM) method and resulting GnP‐mFe2O3 nanoparticles were characterized by Fourier transform infrared (FTIR) analysis. HMWPE/GnP nanocomposites were prepared via melt mixing. The prepared nanocomposites were sheeted at high temperatures in a magnetic field using a hot press. The barrier properties of prepared films, HMWPE/GnP and HMWPE/GnP‐mFe2O3 were characterized by carrying out a permeation to oxygen experiment as a function of GnP and GnP‐mFe2O3 contents. A decrease in gas transmission rate (GTR) was observed for the samples after being subjected to the magnetic field compared to the non‐treated sample. The results of differential scanning calorimetry (DSC) and field emission electron microscopy (FESEM) experiments confirmed the orientation of GnP‐mFe2O3 nanoparticles in nanocomposites.

In vitro test methods for evaluating high molecular weight polyethylene oxide polymer induced hemolytic and thrombotic potential

To combat opioid abuse, the U.S. Food and Drug Administration (FDA) released a comprehensive action plan to address opioid addiction, abuse, and overdose that included increasing the prevalence of abuse-deterrent formulations (ADFs) in opioid tablets. Polyethylene oxide (PEO) has been widely used as an excipient to deter abuse via nasal insufflation. However, changes in abuse patterns have led to unexpected shifts in abuse from the nasal route to intravenous injection. Case reports identify adverse effects similar to thrombotic thrombocytopenic purpura (TTP) syndrome following the intravenous (IV) abuse of opioids containing PEO excipient. Increased risk of IV opioid ADF abuse compared to clinical benefit of the drug led to the removal of one opioid product from the market in 2017. Because many generic drugs containing PEO are still in development, there is interest in assessing safety consistent with generic drug regulation and unintended uses. Currently, there are no guidelines or in vitro assessment tools to characterize the safety of PEO excipients taken via intravenous injection. To create a more robust excipient safety evaluation tool and to study the mechanistic basis of HMW PEO-induced TMA, a dynamic in vitro test system involving blood flow through a needle model has been developed.

Unveiling the mutual effects of hydroxyl and dibenzhydryl groups in α‐diimino‐nickel precatalysts for direct synthesis of polyethylene elastomers

The properties and practical applications of polyethylene are closely associated with the polymer molecular weight, polydispersity, degree of branching, and the type of branches and its arrangement within microstructure. In this study, a set of structurally diverse unsymmetrical 1‐(2,6‐dibenzhydryl‐4‐hydroxylphenylimino)‐2‐(2,6‐(R)‐4‐(R1)phenylimino)acenaphthene‐nickel dibromide precatalysts (where Ni2Me [R = Me, R1 = H], Ni2Et [R = Et, R1 = H], Ni2iPr [R = iPr, R1 = H], Ni3Me [R, R1 = Me], Ni2Et,Me [R = Et, R1 = Me]) has been prepared and studied for ethylene polymerization. Molecular structure analysis of Ni2Me and Ni2Et complexes revealed distorted tetrahedral geometries at nickel. The polymerization activities are extremely high for all precatalysts upon activation with either EASC or MMAO aluminum reagents, a trend notably pronounced in the case of the EASC‐activated systems, entering activity in the range of 10 million g mol−1 h−1 at 30°C. The Ni2Me demonstrated exceptional performance at higher temperatures, achieving an activity of 2.4 × 106 g mol−1 h−1 at 100°C and generated high molecular weight polyethylene (Mw = 105 g mol−1) with narrow polymer dispersity across all reaction temperatures (Ð ≈ 1.5). High temperature 13C NMR spectra identified 97–142/1000C branches in resulting polyethylene, a feature significantly dependent on the reaction temperature. In terms of mechanical properties, stress–strain analysis indicated that polyethylene synthesized at lower temperatures displayed superior tensile strength compared with that produced at higher reaction temperatures, while a reverse trend was observed in strain recovery analysis. The high strain recovery (up to 72%) of these polyethylene highlights the characteristic properties of thermoplastic elastomers.

A universal strategy for rapid and scalable surface modification of ultra high molecular weight polyethylene fiber

The high performance UHMWPE fiber usually demonstrates extremely poor surface adhesion with resin matrix. Therefore, improving the interfacial adhesion property becomes one of the toughest challenges faced by UHMWPE fibers. In this study, a simple and universal surface welding strategy is promoted to effectively modifying UHMWPE fiber with improved surface adhesion in a short time. The surface welding manufacturing approach is realized by the controllable Joule heating generated from the high contact resistance and rapid thermal response of the conductive nano-material layer coated on UHMWPE surface, which can locally melt the UHMWPE fiber surface and weld the nano materials on UHMWE with a strong and robust mechanical bonding. Since the whole welding process is simple and lasts only for a few seconds, it can be easily applied to the current industrial UHMWPE fiber and fabric manufacturing, enabling a continuous, fast, efficiency and scalable roll-to-roll UHMWPE surface modification process.

Determination of tribotechnical properties of polymers depending on the test conditions

The paper presents the results of morphological and tribotechnical tests of samples of ultrahigh molecular weight polyethylene (UHMWPE), high molecular weight polyethylene (HMWPE), polyethylene terephthalate (PET), polyoxymethylene (POM). Tribotechnical tests were carried out on a friction machine with a vertical axis of rotation of the spindle according to the scheme: “the end of the annular surface of the counter–flange sleeve (steel 40Kh, 48-52 HRC) is a plane (wide side of the polymer sample).” The moment of friction and the load on the samples were determined using strain gauges placed in the friction machine in continuous mode. The effect of the surface roughness of a 40Kh steel counter-tile on the friction coefficients when tested without lubricant and in the presence of hydraulic oil MGE-10A at a constant sliding speed has been established. The maximum values of the friction coefficients were obtained during friction without lubrication after processing the end face of the counter-tile with sandpaper P180 and P1200. The minimum values of the friction coefficients were obtained by lubricating MGE-10A after processing with sandpaper P1200 of a 40Kh steel counterplate. According to the morphology of the friction surfaces, the main wear mechanisms for UHMWPE, micro-cutting, HWMPE and PET, micro-cutting and plowing and for POM, fatigue wear and plowing are determined.

Static and dynamic behaviour of ultra high molecular weight poly-ethylene (UHMWPE) Tensylon® composite

Static and dynamic behaviour of ultra high molecular weight poly-ethylene (UHMWPE) Tensylon® composite

Impact of o-aryl halogen effects on ethylene polymerization: steric vs. electronic effects.

Ligand steric hindrance and electronic effects play a crucial role in late-transition metal-catalyzed olefin polymerization. In this research, a series of o-aryl halogenated α-diimine ligands bearing bulky dibenzhydryl substituents, along with their corresponding nickel catalysts, have been synthesized and thoroughly characterized. The nickel catalysts demonstrated very high activity in ethylene polymerization, achieving a high rate of up to 107 g mol-1 h-1. The produced polyethylenes displayed a broad spectrum of molecular weights (12.2-871.7 kg mol-1) but maintained consistent branching densities (50-82/1000 C) when polymerized at a fixed temperature with different nickel catalysts. Notably, the polymerization temperature has a significant influence on both the molecular weight and branching density of the resulting polyethylene. Higher temperatures led to the formation of polyethylenes with lower molecular weights and increased branching densities. Interestingly, the o-aryl halogens significantly impact the molecular weight of the polyethylene. The size of the halogen substituents primarily determines the molecular weight of the polyethylene. However, in terms of branching density, the steric and electronic effects of these substituents appear to counteract each other. In addition, the branched high molecular weight polyethylenes from the bromine and chlorine substituted nickel catalysts are excellent polyethylene thermoplastic elastomers with high strain at break values (688-2478%) and high strain recovery values (42-62%).

Model Simulation and Rheological Research on Crosslinking Behavior of Polyethylene Resin.

The crosslinking behavior of polyethylene (PE) determines its exceptional performance and application. In this study, we investigated the crosslinking behaviors of different PE resins through model simulation and rheological methods. Specifically, the mathematical equation of "S" model was established for PE resin. According to this equation, the optimal maximum gel content for high-density polyethylene (HDPE) was found to be around 85%. Moreover, the maximum crosslinking degrees for different PE resins depended largely on their density and molecular weight. The melt viscosities before crosslinking in PE resins were highly influenced by their melt index. The higher melt indexes resulted in the lower storage moduli, improving melt processability during processing. In addition, the crosslinking rates of PE resins were strongly influenced by peroxide concentration, independent of PE resin structures. For high molecular weight and low-density PE resins, they exhibited decreased ti values, increased A0 values, and decreased k6 values. However, there were no noticeable variations in the values of k2 and phi among different PE resins. All simulated modeling outcomes showed remarkable consistency with the experimental rheological data. These findings are of strong significance in the industrial manufacture of PE resin.

PETR: A novel peristaltic mixed tubular bioreactor simulating human colonic conditions.

A novel bioreactor simulating human colonic conditions for in vitro cultivation of intestinal microbiota is presented. The PEristaltic mixed Tubular bioReactor (PETR) is modular designed and periodically kneaded to simulate intestinal peristalsis. The reactor is introduced, characterized from a bioprocess engineer's perspective and discussed in its ability to mimic colon conditions. PETR provides physiological temperature and appropriate anaerobic conditions, simulates intestinal peristalsis, and has a mean residence time of 32.8 ± 0.8 h comparable to the adult human colon. The single-tube design enables a time-constant and longitudinally progressive pH gradient from 5.5 to 7.0. Using a dialysis liquid containing high molecular weight polyethylene glycol, the integrated dialysis system efficiently absorbs short chain fatty acids (up to 60%) and water (on average 850 mL d-1 ). Cultivation of a typical gut bacterium (Bifidobacterium animalis) was performed to demonstrate the applicability for controlled microbiota cultivation. PETR is unique in combining simulation of the entire colon, peristaltic mixing, dialytic water and metabolite absorption, and a progressive pH gradient in a single-tube design. PETR is a further step to precise replication of colonic conditions in vitro for reliable and reproducible microbiota research, such as studying the effect of food compounds, prebiotics or probiotics, or the development and treatment of infections with enteric pathogens, but also for further medical applications such as drug delivery studies or to study the effect of drugs on and their degradation by the microbiota.

Computer-aided ligand screening to develop polymer-free catalyst in Cr-catalyzed ethylene oligomerization

Preventing the formation of undesirable polymer in ethylene oligomerization is a major challenge since the presence of these insoluble materials can cause severe reactor fouling. Based on previous experimental data, the concomitant formation of these solid compounds can be divided in two types. Detailed discussion in combination with mathematical analysis revealed that the low-molecular weight waxes (low-Mw waxes) are most likely the tail products of the Schulz-Flory distribution while high-molecular weight polyethylene (high-Mw PE) may be catalyzed by multiple active sites independent from the oligomerization cycle. Controlling the Schulz-Flory coefficient (K value) to remain in a lower range is crucial in achieving plentiful C4–C8 components and inhibiting polymer formation at the same time. Attempting to predict the K value, the energetic disparities of key transition states which control 1-butene selectivity have been extracted as a chemical descriptor to establish a general model. Promising ligands derived from computer-aided screening are expected to avoid the inherent waxes formation. Plausible strategies for the elimination of external polymerization sites are also suggested. The combination of them may provide a chance to develop more polymer-free catalysts to meet the requirements of industrial manufacturing.

Concerted flexible and steric strategy in α-diimine nickel and palladium mediated insertion (Co-)Polymerization

To address the issues of poor thermostability of catalyst and low polymer molecular weight resulted from chain transfer at high temperature in olefin polymerization, versatile strategies have been utilized in the benchmark α-diimine nickel and palladium catalysts. In this contribution, a concerted flexible and steric strategy was highlighted in the α-diimine nickel and palladium catalysts. Compared to the seminal Brookhart catalyst, these newly generated nickel catalysts exhibited improved thermostability over a wide range of temperature from 30 °C to 130 °C, showed higher catalytic activities, and produced significantly higher (4.7–5.8 times) molecular weight polymers in ethylene polymerization, which are highly branched polyethylenes (76–110/1000C, SR = 72 %). Notably, high molecular weight polyethylene (up to 219 kg mol−1) was even afforded at 130 °C, which is extremely challenging when the flexible substituent is used in α-diimine system. The corresponding palladium analogues by using the same strategy further produced high molecular weight ethylene-methyl acrylate copolymers (up to 137 kg mol−1) at the difficult 70 °C in the copolymerization of ethylene and methyl acrylate. The incorporation of methyl acrylate could be tuned (0.6–2.9 mol%), where methyl acrylate units distribute both in the main chain and at the end of branches (15 %:85 %).

Measurement and control of extensional viscosity in barrier coating dispersions

This study aimed to understand the effect of various rheological additives on the extensional viscosity of barrier coating dispersions, as well as to understand the role extensional viscosity plays in stabilizing a liquid curtain. The apparent extensional viscosity was measured using two devices that create accelerating flows: a capillary viscometer and an orifice rheometer. Additives tested include several polyvinyl alcohols, a high molecular weight polyethylene oxide, and carboxymethylcellulose. Extensional viscosity plays a significant role in stabilizing a liquid curtain, as it slows down hole expansion and prevents impurities and disturbances from causing holes in the first place. Some of the additives could substantially increase the extensional viscosity of the dispersions without increasing the shear viscosity outside the typical range of processability for a curtain coater. Some of the additives exhibited coil-stretch transition, meaning they start increasing extensional viscosity above a certain extension rate. Polymers with low chain lengths exhibited finite extensibility, which indicates the polymer chain has fully extended and cannot provide further extensional viscosity, even though the extending force is increased. Polymeric additives with stiff or branched chains significantly raised shear viscosity without increasing extensional viscosity. Both methods could reliably measure extensional viscosity in curtain coating barrier dispersions.

Crystallization in blend of polycaprolactone and high molecular weight polyethylene oxide

The concentration distribution in blend of polyethylene oxide (PEO)/polycaprolactone (PCL) and subsequent crystallization were investigated with differential scanning calorimetry, in-situ small angle X-ray scattering and wide angle X-ray scattering. By using PEOs with a molecular weight of 1 × 106 g/mol (PEO1M) and 1 × 105 g/mol (PEO100k), respectively, it is revealed that in initial blend the concentration of PEO1M in PEO-rich region is higher than that determined by miscibility. This non-equilibrium distribution induced by crystallization is maintained after melting, since slow relaxation of PEO1M hinders the redistribution process. Crystallization behavior of blend with 25 % of PEO1M at different melting temperatures was further investigated. The crystallinity shows no dependence on melting temperature, while the long period of PEO1M decreases continuously when melting temperature exceeds 140 °C. This decrease indicates more PCL chains diffuse into PEO-rich regions with increasing temperature and molten PCL chains reduce the entanglement number of PEO1M as solvent. Moreover, the periodicity of PEO1M lamellae becomes worse when crystallization proceeds faster, which is related to slower exclusion of PCL chains.

Application of SFEM Method to Analyse Crack Parameters of Ultra High Molecular Weight Polyethylene Material

The application of numerical methods, today occupies a much needed place for modeling, and for finding solutions to any problem related to fatigue and damage to materials. This article deals numerically with the evolution of the stress intensity factor and the integral of the contour J in I mode, of an initial rectilinear crack of languor a=0.7, 1.4, 2.1, 2.8 and 3.5mm, with different ratio, a/w=0.1, 0.2, 0.3, 0.4 and 0.5mm. By the stretching finite element method (SFEM) of the (UHMWPE) Ultra High Molecular Weight Polyethylene material. On the other hand, the creation of the parametric mesh based on the computer language (FORTRAN) and to create a model of the square crack front with 5 contours of size L=1mm. In addition, the simulation was done by Abaqus 16.3.1 code. The maximal circumferential stress criterion MCSC were applied. Other materials like Alu20- 17 and Steel XC65-90 were used to make the comparison. Crack parameters, such as stress intensity factors KI, KII and J-contour integral were evaluated. The results obtained in our work have justified that there is proportionality between the three materials.

Wear Resistance and Microstructure of Ultra High Molecular Weight Polyethylene During Uniaxial Tension

Wear Resistance and Microstructure of Ultra High Molecular Weight Polyethylene During Uniaxial Tension

Degradation of mechanical properties of polyurethane elastomer coatings under different pavement pollution conditions

The purpose is to reveal the property development laws of polyurethane elastomer coatings for pavement in different polluted environments, and further promote their application in the road field. The ultra high molecular weight polyethylene (UHMWPE) micropowder/polyurethane elastomer (PU) composite coatings and the UHMWPE micropowder/polyvinyl alcohol (PVA) fiber/PU composite coatings were prepared. The basic pavement performances of different elastomer composites formulations were evaluated. Four different pavement polluted environments in practical application, including acid, alkali, salt, and gasoline, were simulated. The degradation laws of mechanical properties such as tensile, tearing, impact, and cushion for polyurethane elastomer coatings at different polluted environments and curing times were studied systematically. The durability of polyurethane elastomer coatings was clarified. The results indicate that the optimal formulation of the composites is determined as "PU+ 3 wt% UHMWPE" based on pavement performances and mechanical properties. The retention rates of mechanical properties for UHMWPE/PU composites after continuous exposure to different polluted environments for 7 days are over 90%. After 30 days of exposure, the decay rates of mechanical strength indicators such as tension and tear are relatively high, about 20 %− 25 %. The decay rate of absorbed energy is relatively low, about 10 %− 15 %.

Unraveling the cytotoxicity and cellular uptake of low, medium and high molecular weight polyethylene glycol polymers in MCF-7 cells by green UPLC-MS/MS methods

Unraveling the cytotoxicity and cellular uptake of low, medium and high molecular weight polyethylene glycol (PEG) in cells is important for evaluation of therapeutic efficacy and toxicity of PEGylated drug delivery systems. In this study, cellular uptake of PEG600, PEG2K, PEG4K and PEG10K in MCF-7 cells was first studied by an UPLC-MS/MS assay coupled with collision induced dissociation (CID) in source technique. The CID of PEG in source with high values of declustering potentials generates numerous PEG-related product ions. These PEG-related fragment ions can be further broken into specific product ions in the collision cell as alternative ions for detection of PEG. The quantification of PEG was finally performed with the MRM transition (m/z 221.0 → 89.0). The experimental results indicated that the toxicity of PEG600, PEG2K, PEG4K and PEG10K was not significant at concentrations of 5–1200 μg/mL and the amounts of PEG polymers entry into MCF-7 cells at was small. The greenness of the developed analytical methods was also assessed by Analytical Eco-Scale, Analytical Greenness calculator (AGREE) and Green Analytical Procedure Index (GAPI) in this study.

Direct synthesis of polyethylene thermoplastic elastomers with high molecular weight and excellent elastic recovery via a hybrid steric bulky strategy

Recently, α-diimine nickel-catalyzed ethylene chain walking polymerization has enabled the direct preparation of polyethylene thermoplastic elastomers using ethylene as a single feedstock. In this study, a series of hybrid bulky butyl-based α-diimine nickel complexes constructed with o-aryl and -diarylmethyl anilines were synthesized and employed for the ethylene polymerization. All the nickel complexes showed high activities (level of 106 g mol-1h−1) and high molecular weight (Mn up to 1230.9 kg/mol) polyethylene with high branching density (82–118/1000C) were yielded in ethylene polymerization. The polyethylene obtained by Ni1-3 showed distinguished elastic properties (SR = 72–91 %) and the sample obtained by Ni1 at 50 °C exhibited optimal elastic recovery values (91 %), which is also the best reported so far in polyethylene elastomers. Compared to the corresponding nickel complexes with symmetrical ligand substituents, the complexes with unsymmetrical substituents (hybrid) in this study facilitate the synthesis of significantly higher branched polyethylene with much better elastic recovery. The hybrid cationic nickel catalysts are also capable of catalyzing the copolymerization of ethylene with methyl 10-undecenoate.

Effect of γ irradiation and Vitamin-E on the thermal and mechanical properties of graphene/nanodiamond reinforced hybrid UHMWPE nanocomposites

This work focus on solving the problems of fabricating inadequate prosthetic joint from mechanical perspective in total joint replacement. Ultra high molecular weight polyethylene (UHMWPE) composites with different weight fractions of Graphene (Gr) and Nanodiamond (ND) nanoparticles (0.2–0.5 wt %) were prepared by high pressure compression molding. The effect of vitamin E (vit E) and gamma irradiation at 50 kGy and 100 kGy doses on the structural and thermal properties of UHMWPE composites were investigated through swell ratio test, fourier transformation infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The mechanical properties including tensile, flexural, impact test, nanoindentation and micro scratch were studied and the fractured surfaces were analyzed under scanning electron microscope (SEM). Influence of gamma irradiation on UHMWPE composites shows better crosslinks and crystallinity in the polymer matrix. The nano-composites shows significant improvements in various mechanical properties compared to the 0.5 wt % vitamin-E + UHMWPE composite, with a 23 % increase in Young's modulus, a 21 % increase in flexural strength, a 24 % increase in hardness, and a 17 % increase in impact strength. The results shows that 100 kGy gamma irradiated composites exhibited better results. Composite with 0.5 wt % vit E + 0.3 wt % Gr + 0.5 wt % ND shown significant improvement in structural, thermal and mechanical properties.