Metallocene Polyethylene Research Articles

High wear resistance of metallocene polyethylene with long-chain branch for artificial joints

Ultra-low-wear polyethylene (ULWPE) is a promising material for artificial joint implants, owing to its good biocompatibility and wear resistance. However, its molecular weight is almost an order of magnitude lower than that of Ultrahigh molecular weight polyethylene (UHMWPE). The mechanism between wear resistance and the structure of ULWPE is still unknown. This study analyzed their attributes from microstructure to macroscopic performance and revealed the wear resistance mechanisms of ULWPE by conducting an in-depth investigation of four types of polyethylene, including ULWPE, UHMWPE, and high-density polyethylene. Impact tests showed that ULWPE, with a molecular weight of 282 kg/mol, exhibited an impact energy of 110 kJ/m2, surpassing the 97 kJ/m2 recorded for UHMWPE (molecular weight over 5000 kg/mol). Furthermore, tribology tests indicated that the wear rate of the most anti-wear ULWPE was 4.479 ± 0.040 mm³/Mc, which was significantly lower than the 5.601 ± 0.456 mm³/Mc for UHMWPE. The excellent mechanical properties and wear resistance of ULWPE were derived from its unique structure. Dynamic rheological assessments and thermal classification techniques confirmed that ULWPE had long-branched chains. The long-branched chains markedly increased the proportion of the high entanglement and the tie molecules in the amorphous regions, endowing it with superior toughness. At the same time, the high crystallinity of ULWPE gives it sufficient hardness and strength. The combination of high crystallinity and high entanglement endowed ULWPE with a good balance between strength and toughness, leading to its exceptional mechanical properties and wear resistance. This study provided robust data for ULWPE's clinical use and theoretical insights for designing durable, implantable polymers.

Global metallocene polyethylene market report 2023: Surge in demand for mLLDPE and innovative applications in packaging fuelling growth – Forecasts to 2028

Global metallocene polyethylene market report 2023: Surge in demand for mLLDPE and innovative applications in packaging fuelling growth – Forecasts to 2028

Effect of nucleating agents on the electrical properties of cross‐linked polyethylene under tensile stress

AbstractDuring the operation of high‐voltage cables, external stress and residual stress can affect the aggregated structure of insulating materials and lead to significant deterioration in their electrical performance. To investigate the evolution characteristics of the electrical properties of cross‐linked polyethylene (XLPE) under mechanical stress, this paper explains the relationship between the aggregated structure of XLPE and its electrical properties and proposes a method for improving insulation performance under mechanical stress. The results show that metallocene polyethylene used as a nucleating agent can promote crystallisation through heterogeneous nucleation and increase Young's modulus by non‐uniform nucleation, increasing crystallinity and reducing interplanar spacing, resulting in more complete crystal forms and reduced damage to the aggregated structure during the tensile process. After nucleating agent modification, the XLPE crystallisation becomes more uniform, and interfacial adhesion forces increase. The weakened interface damage process between the amorphous and crystalline regions under tensile stress effectively inhibits the process of molecular chain polarisation turning and reduces trap density. The modified XLPE crystal structure shows a tendency towards densification and enhanced molecular chain interactions, which can reduce the damage to the aggregated structure under tensile stress, while the reduced free volume inside the material and the shortened average free path of carriers can weaken the damage of high‐energy electrons to molecular chains, thereby inhibiting the process of electrical tree degradation. The results show that nucleating agents have great potential for maintaining the stable operation of XLPE cables under mechanical stress.

Metallocene polyethylene (mPE) market worth $10.5 bn by 2028

Metallocene polyethylene (mPE) market worth $10.5 bn by 2028

Surface-enhanced nucleation in immiscible polypropylene and polyethylene blends: The effect of polyethylene chain regularity

In blends where polyethylene (PE) is the minor component dispersed in an isotactic-polypropylene (PP) matrix, an enhancement of the crystallization rate of PE was found when the crystallization temperature of the matrix phase is increased by means of a self-nucleation protocol. Such an effect is interpreted as the result of the epitaxial nucleation of PE droplet domains at the interface with the PP matrix (Macromolecules, 2021, 54, 19, 9100–9112). This study extends the findings on immiscible blends of a PP matrix and various industrially produced PE grades as the dispersed phase. Eight different PEs with varying molecular architecture, and thus density and melting temperatures, were mixed with PP in a 20/80 PE/PP weight ratio. The possible existence of surface nucleation was probed by applying a self-nucleation thermal protocol to the PP matrix and recording the concomitant variation of PE crystallization temperature (Tc). Different behaviours are observed for various PEs. In particular, those with relatively high density display a clear increase in crystallization temperature, over 3.0 °C, when the Tc of the matrix is increased (i.e., as PP lamellar thickness increased), indicating an efficient surface nucleation mechanism. Metallocene-made LLDPE also shows a small increase, about 1.7 °C, while PEs with lower densities, below 927 kg/m3, metallocene PEs or LDPE display no meaningful change in Tc with matrix self-nucleation. It was demonstrated that a threshold value of chain regularity is required to trigger the surface nucleation of PE on PP. Only polymers with a density above approximately 920 kg/m3 and melting temperatures exceeding about 115 °C can efficiently nucleate onto the PP substrate. It is postulated that the presence of a high amount of branches or comonomers along the PE chains hinders the epitaxial matching between PE and PP.

Self-Healing and Shape Memory Behavior of Functionalized Polyethylene Elastomer Modified by Zinc Oxide and Stearic Acid

There is still a great need to develop self-healing polymers (SHPs) using a cost-effective modification approach for commercial polymers. Herein, we describe our preparation of self-healing (SH), acrylic acid-functionalized, metallocene polyethylene elastomer (mPE-g-AA) composites containing ZnO and stearic acid (SA) that feature both supramolecular hydrogen bonding and ionic interactions. Regarding mechanical properties, with the addition of various contents of ZnO/SA in the mPE-g-AA matrix, their tensile strength increased to be higher than that of mPE-g-AA. As for the shape memory properties, with this synergistic effect of zinc oxide (ZnO), SA, and grafting AA, both the shape fixing ratio and shape recovery ratio of those functionalized polyethylene samples modified by ZnO and SA increased up to above 80% as a result of the hydrogen bonding and reversible ionic crosslinked networks acting as physical crosslinks. Among all of the samples, mPE-g-AA/ZnO 4/SA 1 (4 phr of ZnO and 1 phr of SA) exhibited the highest SH efficiency, at 44.6% for half-hour healing and up to 64.4% under 6 h healing, being higher than those related self-healing mPE studies in the literature. These hydrogen bonded reversible networks, along with the enhanced molecular flow at high temperatures in addition to ionic interactions, could also have a great potential in self-healing applications, besides the shape memory performance. So far, to the authors’ best knowledge, there have been no published reports of the design of polyolefin elastomers with thermally-triggered shape memory effect by adding ZnO to assist the self-healing behavior. The current synergistic approach paves the way for preparing various SH commercial polymers where surface scratches and cuts have previously been hard to repair.

Crystallization behavior and structure of metallocene polyethylene with long-chain branch

Crystallization behavior and structure of metallocene polyethylene with long-chain branch

Synergistic Effects of Thermal and Near-Infrared Radiation Heating on the Self-Healing Effect of Shape Memory Polyethylene Elastomer Nanocomposites

The preparation of commodity polymers that can undergo self-healing of scratched surfaces is still quite challenging without involving complicated synthetic processes and high cost of healing agents. In the research described here, we prepared a self-healing acrylic acid-functionalized metallocene polyethylene elastomer (mPE-g-AA) nanocomposite with the addition of arginine to form supramolecular hydrogen bonding. Thermal characterization, mechanical properties, shape memory effect, and self-healing properties were investigated. The addition of mutilwall carbon nanotubes (MWCNTs) effectively increased the tensile properties of the modified mPE. The acrylic acid-modified mPE greatly improved its shape recovery ratio, up to 94.2 ± 4.7%, and maintained a high shape fixing ratio (91.6 ± 1.3%) due to the hydrogen bonding acting as physical crosslinks. Overall, all modified mPE samples showed good shape memory performance. Besides the conventional thermal heating to heal the scratched surface cracks, MWCNTs were incorporated to permit healing the surface cracks through near-infrared radiation (NIR). However, the MWCNTs-filled samples under the thermal healing process unexpectedly resulted in the crack widths increasing, perhaps due to the effect of the MWCNTs with high recovery stress pushing outward on both sides of the crack during heating. Interestingly, the synergistic approach of combining thermal healing and NIR was found to be the most effective in improving the healing efficiency of the mPE-g-AA-Arg/MWCNTs, close to 50% within a short time, in comparison with the existing literature with required healing times of 60 min to have a self-healing efficiency of 45% for mPE modified with maleic anhydride and 3-amino-1,2,4-triazole. To the best of the authors’ knowledge, no work has been reported on the preparation of self-healing thermoplastic elastomer nanocomposites through this approach so far.

Research perspectives on the photocatalytic activity of titanium dioxide: Catalytic assessment methods in solution and solid-state in relation to particle surface activity

A range of prepared titania nanoparticles were characterised by Brunauer-Emmett-Teller (BET) surface area, X-ray Diffraction (XRD), CPS Disc Centrifuge, Transmission Electron Microscope (TEM), Scanning Electron Micrographs (SEM), Thermogravimetric Analysis (TGA) and Fourier Transform Infrared Measurements (DRIFTS). In addition, the activities of the different catalysts were determined via rapid assessment methodologies like Microwave Dielectric Spectroscopy (MDS), Hydroxyl content, Phosphorescence and Chemiluminescence Spectroscopy and Isopropanol Oxidation Test and the data related to actual weathering properties of the pigments doped in metallocene polyethylene under dry and humid conditions. Quantum size effects, which lead to high surface areas and blue shifts and diminish electron–hole recombination, are used to explain the high activities of the nanoparticle products. In situ FTIR data and OH content determination show the presence of high contents of hydroxyl groups and large amounts of adsorbed water on TiO2 nanoparticles. The Disc Centrifuge results and BET surface area combined with the XRD particle size results show that a careful distinction between the crystal and aggregate sizes must be made in order to properly interpret the activity of TiO2 pigments. Aggregation of TiO2 pigments affects not only the surface area offered by the TiO2 but also the type of interaction between the light and the TiO2. The treatment conditions used for the crystallization of the primary material (precursor) in order to prepare the nanoparticle pigments, not only influenced the anatase crystal size but also other anatase properties (such as the surface hydroxylation, adsorbed water, recombination rate, aggregation state and type of structural defects). Chemiluminescence of the titania particles is discussed in light of potential surface active peroxidic species.

Risk Assessment of Agricultural Plastic Films Based on Release Kinetics of Phthalate Acid Esters.

Plastic films have become an integral part of fruit and vegetable production systems, but their release of phthalate acid esters (PAEs) is a threat to human health. The release kinetics of PAEs and measures of risk are still not well understood. We investigated 50 agricultural films, with concentrations ranging from 2.59 to 282,000 mg kg-1. The seven commercially available film types included were polyvinylchloride (PVC), metallocene polyethylene (mPE), ethylene vinyl acetate (EVA), polyolefin (PO), and three mulch films. Bis(2-ethylhexyl) phthalate (DEHP) was detected in most of films, and its release fitted well into the first-order kinetic model. The release rate of DEHP was negatively related to the film thickness. The potential carcinogenic risks of DEHP in the air of six kinds of plastic greenhouses to human health were estimated. We found that the carcinogenic risks associated with PVC and mPE greenhouse films warrant greater attention. Though EVA, PO greenhouse, and mulch films were lower risk, we advise keeping plastic greenhouses well ventilated during the first month of use to reduce direct human exposure to volatile PAEs.

Improved Properties of Metallocene Polyethylene/Poly(ethylene terephthalate) Blends Processed by an Innovative Eccentric Rotor Extruder.

In this investigation, metallocene polyethylene (m-PE) was melt blended with poly(ethylene terephthalate) (PET) with an effort to achieve improved mechanical properties using a novel eccentric rotor extruder (ERE) without the addition of any compatibilizers. The phase morphology, rheological properties, crystallization behavior, and mechanical properties of the fabricated blends were carefully studied to explore the effect of the elongational flow field on the dispersion and mixing of PET in the m-PE matrix and the interface of the two immiscible polymers. For comparison, a conventional twin-screw extruder (TSE) was used to prepare the same blends as references using the same processing condition. It shows that the elongational flow field in ERE is much more effective to disperse the immiscible PET in the m-PE matrix with a smaller particle size and a narrower particle size distribution, compared to the shear flow field in TSE. A compatibilizer, ethylene-co-methyl acrylate-co-glycidyl methacrylate (E-MA-GMA), was added to the m-PE/PET blends during the processing using TSE and ERE. It was observed that the improvement of the tensile property by adding the compatibilizer is marginal for the m-PE/PET blends processed using ERE, which indirectly proves the high effectiveness of the elongational flow field on the enhancement of the dispersion and mixing of PET in the m-PE matrix and the interface interaction.

Non-Newtonian Flow of Structured Systems. XXIX. Viscoelasticity of Metallocene Polyethylene Melt

Non-Newtonian Flow of Structured Systems. XXIX. Viscoelasticity of Metallocene Polyethylene Melt

Melt compatibility between polyolefins: Evaluation and reliability of interfacial/surface tensions obtained by various techniques

Abstract The interfacial tension in the melt state represents a key parameter to quantify the compatibility of polymer blends processed by extrusion techniques. Its evaluation is still challenging for polyolefin-based blends and, here, two complementary techniques (i.e. rheological and optical methods) were tested to evaluate the PP/PE compatibility in the melt state. In particular, interfacial/surface tensions at 200 °C between several types of isotactic polypropylene (iPP) and polyethylene (PE) (i.e. Ziegler Natta- and metallocene-catalyzed grades) are specifically addressed to detect slight modifications of melt compatibility and to potentially highlight the role of polymer structure induced by the used catalyst. Classical dynamic rheology experiments coupled with morphological analyses were first attempted and several trends are clearly observed in term of iPP/PE interfacial tensions. iPP/metallocene PE associations display the lowest interfacial tension (0.9–1.2 mN/m, relative standard deviation ≈ 20%) and as-selected metallocene PE clearly gave rise to an enhanced melt compatibility with iPP matrices. Interfacial tensions could not be directly and precisely evaluated by optical methods using the polymer-in-polymer pendant drop method due a poor precision arising from an ultra-low iPP/PE melt density difference. However, surface tensions in the melt state obtained by the pendant drop method under nitrogen atmosphere represent the most reliable tool with an excellent sensitivity to as-selected polyolefin catalysts. An indirect but precise insight on polyolefin compatibility was found possible using surface tensions with a full discrimination between as-selected polyolefins in agreement with enhanced melt compatibilities in metallocene iPP/metallocene PE blends.

<i>In Situ</i> Reactive Interfacial Compatibilization of Poly(Ethylene Terephthalate)/Metallocene Polyethylene Blends

Poly (ethylene terephthalate) (PET) was melt blended with metallocene polyethylene (m-PE) with an effort to achieve excellent mechanical properties, a terpolymer elastomer, ethylene-methyl acrylate-glycidyl methacrylate (E-MA-GMA), was loaded as compatibilizer through in situ reacting with the end groups of PET to bond two immiscible phases. In order to investigate the in situ effects of the compatibilizer, scanning electron microscopy (SEM) and mechanical analysis was applied to investigate PET/m-PE blends’ properties along with the variation of compatibilizer content. Statistics of particle size were applied to demonstrate the variation of the blends’ properties along with morphology. The results revealed that an appropriate loading of compatibilizer can obtain stiffness-toughness balanced blends.

Erratum: Development and blood compatibility assessment of electrospun polyvinyl alcohol blended with metallocene polyethylene and plectranthus amboinicus (PVA/mPE/PA) for bone tissue engineering [Corrigendum

[This corrects the article on p. 2777 in vol. 13, PMID: 29785105.].

Development and blood compatibility assessment of electrospun polyvinyl alcohol blended with metallocene polyethylene and plectranthus amboinicus (PVA/mPE/PA) for bone tissue engineering.

IntroductionCurrently, the design of extracellular matrix (ECM) with nanoscale properties in bone tissue engineering is challenging. For bone tissue engineering, the ECM must have certain properties such as being nontoxic, highly porous, and should not cause foreign body reactions.Materials and methodsIn this study, the hybrid scaffold based on polyvinyl alcohol (PVA) blended with metallocene polyethylene (mPE) and plectranthus amboinicus (PA) was fabricated for bone tissue engineering via electrospinning. The fabricated hybrid nanocomposites were characterized by scanning electron microscopy (SEM), Fourier transform and infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), contact angle measurement, and atomic force microscopy (AFM). Furthermore, activated partial thromboplastin time (APTT), prothrombin time (PT), and hemolytic assays were used to investigate the blood compatibility of the prepared hybrid nanocomposites.ResultsThe prepared hybrid nanocomposites showed reduced fiber diameter (238±45 nm) and also increased porosity (87%) with decreased pore diameter (340±86 nm) compared with pure PVA. The interactions between PVA, mPE, and PA were identified by the formation of the additional peaks as revealed in FTIR. Furthermore, the prepared hybrid nanocomposites showed a decreased contact angle of 51°±1.32° indicating a hydrophilic nature and exhibited lower thermal stability compared to pristine PVA. Moreover, the mechanical results revealed that the electrospun scaffold showed an improved tensile strength of 3.55±0.29 MPa compared with the pristine PVA (1.8±0.52 MPa). The prepared hybrid nanocomposites showed delayed blood clotting as noted in APTT and PT assays indicating better blood compatibility. Moreover, the hemolysis assay revealed that the hybrid nanocomposites exhibited a low hemolytic index of 0.6% compared with pure PVA, which was 1.6% suggesting the safety of the developed nanocomposite to red blood cells (RBCs).ConclusionThe prepared nanocomposites exhibited better physico-chemical properties, sufficient porosity, mechanical strength, and blood compatibility, which favors it as a valuable candidate in bone tissue engineering for repairing the bone defects.

Role of phenol and phosphite antioxidant combinations in the thermal stabilisation of metallocene LLDPE (mLLDPE): Optimisation and performance and influence of metal stearates on multiple extrusions

This study progresses our earlier studies and takes the performance characteristics of a 1:1 Irganox 1010: Irgafos 168 combination at 1000 ppm each through multiple extrusion processes in a metallocene LLDPE (mLLDPE) investigating for the first time the role of a broad range of calcium and zinc stearates based on animal vs vegetable origins of the stearine function. In this case performance was assessed using Melt Flow Rate (MFR) coupled with HPLC to determine not only the additive depletions after processing but also the rate of production of the phosphite to phosphonate. Comparative control studies were also undertaken on the single use of the separate antioxidants. Both stearates influenced the activity of the antioxidants in particular their consumption. A greater consumption after the third and fifth extrusion was observed with metal stearates produced from the vegetable stearine. Moreover, zinc stearates seemed to provide a greater detrimental effect than calcium stearates. Hydroperoxide analysis on the stearates confirmed the animal stearine to contain higher levels of peroxides which may contribute toward the higher activity. The optimisation of the thermal stabilisation of the metallocene polyethylene (mLLDPE) has also been investigated in this study. Several conditions of stability were determined for the determination of the optimal antioxidant (phenol:phosphite) ratio. The main parameter was high melt stability for a maximum processing stability of the final package via DSC analysis (OIT) coupled with assessments of embrittlement time (oven ageing) and yellowness index. Long-term stability against thermo-oxidation was considered coupled with a consideration of their hydrolytic stability as a complicating factor. In this work the (phenol/phosphite) antioxidant formulations with two different phenolic antioxidants (Irganox 1010, Irganox 1076) and six different phosphite antioxidants (Irgafos 168, Irgafos P-EPQ, Adekastab PEP-8, Adekastab PEP-36, Adekastab PEP-24G, Adekastab HP-10) were assessed at different levels taking into account the various criteria for optimal performance providing hitherto useful information than many prior studies on 1:1% ratios i.e. how much phosphite is required for optimal activity. A question often posed in the field with the results concluding an interesting unified optimum ratio of 4:1 (for most antioxidants studied) taking into account all the critical parameters.

UV induced surface modification on improving the cytocompatibility of metallocene polyethylene.

Demand for medical implants is rising day by day as the world becomes the place for more diseased and older people. Accordingly, in this research, metallocene polyethylene (mPE), a commonly used polymer was treated with UV rays for improving its biocompatibility. Scanning electron microscopy (SEM) images confirmed the formation of crests and troughs, which depicts the improvement of surface roughness of mPE substrates caused by UV etching. Accordingly, the contact angle measurements revealed that the wettability of mPE-2.5 J/cm2 (68.09º) and mPE-5 J/cm2 (57.93º) samples were found to be increased compared to untreated mPE (86.84º) indicating better hydrophilicity. Further, the UV treated surface exhibited enhanced blood compatibility as determined in APTT (untreated mPE- 55.3 ± 2.5 s, mPE-2.5 J/cm2 - 76.7 ± 4.1 s and mPE-5 J/cm2 - 112.3 ± 2 s) and PT (untreated mPE - 24.7 ± 1.5 s, mPE- 2.5 J/cm2 - 34.3 ± 1.1 s and mPE-5 J/cm2 - 43 ± 2 s) assay. Moreover, the treated mPE-2.5 J/cm2 (4.88%) and mPE-5 J/cm2 (1.79%) showed decreased hemolytic percentage compared to untreated mPE (15.40%) indicating better safety to red blood cells. Interestingly, the changes in physicochemical properties of mPE are directly proportional to the dosage of the UV rays. UV modified mPE surfaces were found to be more compatible as identified through MTT assay, photomicrograph and SEM images of the seeded 3T3 cell population. Hence UV-modified surface of mPE may be successfully exploited for medical implants.

Facile preparation and good performance of nano-Ag/metallocene polyethylene antibacterial coatings

Metallocene polyethylene/nano-silver coatings were prepared by a facile air-spray method on polymer films. Different from the prevailing strategy to endow polyethylene with antibacterial performance, we used metallocene polyethylene sol and nano-silver as a precursor to deposit coatings on polymers at a relatively low operating temperature. Antibacterial coatings with excellent mechanical properties, water resistance, and low silver release were achieved. The composite coatings were examined in terms of surface characteristics, mechanical properties, and antibacterial activity against two representative bacterial strains including Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The composite coatings exhibited favorable microstructure, good mechanical properties, and suitable crystallinity. The antimicrobial tests indicated that the fabricated composite coatings showed promising antibacterial activity against E. coli and S. aureus. Furthermore, Ag ions released by the composite coating after 30 days were under 1.2 ppb. These results indicated a promising prospect of the composite coating for wide antibacterial applications.

Microwave-Assisted Dip Coating of Aloe Vera on Metallocene Polyethylene Incorporated with Nano-Rods of Hydroxyapaptite for Bone Tissue Engineering

Bone tissue engineering widely explores the use of ceramic reinforced polymer-matrix composites. Among the various widely-used ceramic reinforcements, hydroxyapatite is an undisputed choice due to its inherent osteoconductive nature. In this study, a novel nanocomposite comprising metallocene polyethylene (mPE) incorporated with nano-hydroxyapaptite nanorods (mPE-nHA) was synthesized and dip coated with Aloe vera after subjecting it to microwave treatment. The samples were characterized using contact angle, Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), atomic force microscopy (AFM) and 3D Hirox microscopy scanning. Contact angle results show that the hydrophilicity of mPE-nHA improved notably with the coating of Aloe vera. The surface topology and increase in surface roughness were observed using the SEM, AFM and 3D Hirox microscopy. Blood compatibility assays of pure mPE and the Aloe vera coated nanocomposite were performed. The prothrombin time (PT) was delayed by 1.06% for 24 h Aloe-vera-treated mPE-nHA compared to the pristine mPE-nHA. Similarly, the 24 h Aloe-vera-coated mPE-nHA nanocomposite prolonged the activated partial thromboplastin time (APTT) by 41 s against the control of pristine mPE-nHA. The hemolysis percentage was also found to be the least for the 24 h Aloe-vera-treated mPE-nHA which was only 0.2449% compared to the pristine mPE-nHA, which was 2.188%. To conclude, this novel hydroxyapatite-reinforced, Aloe-vera-coated mPE with a better mechanical and anti-thrombogenic nature may hold a great potential to be exploited for bone tissue engineering applications.