Polyethylene Nanocomposites Research Articles

Wear resistance of graphene reinforced ultra-high molecular weight polyethylene nanocomposites prepared by octa-screw extrusion process

Ultra-high molecular weight polyethylene (UHMWPE) is one of the well-established bio-materials for artificial prostheses. In order to improve its wear resistance, graphene incorporated UHMWPE nanocomposites are synthesized by octa-screw extrusion process. The exceptional compounding ability of the process is confirmed by uniform graphene dispersion in the matrix. An 18% improvement in yield strength, superior anti-wear property, 67% increase in crystallinity, and 4% increase in the decomposition temperature as compared to pure UHMWPE is measured. The nanocomposites are also more hydrophilic and show absence of cytotoxicity. The UHMWPE/graphene nanocomposites prepared by octa-screw extrusion are a potential candidate for joint replacement applications.

Effective Enhancement of a Carbon Nanothread on the Mechanical Properties of the Polyethylene Nanocomposite

The mechanical performance of nanomaterial-reinforced polymer nanocomposites is a prerequisite for their engineering implementations, which is largely determined by the interfacial load transfer efficiency. This work investigates the role of the nanofillers via molecular dynamics simulations under different deformation scenarios, mimicking a maximum and minimum load transfer scenario from the polymer matrix. On the basis of the polyethylene (PE) nanocomposite reinforced by a new nanofiller-carbon nanothread (NTH), we find that the loading conditions dominantly determine its enhancement effect on the mechanical properties of the PE nanocomposite. Under tensile deformation, the ultimate tensile strength of the PE nanocomposite receives around 61 to 211% increment when the filler deforms simultaneously with the PE matrix. However, such enhancement is largely suppressed when the NTH is deforming nonsimultaneously. Similar results are observed from the compressive deformation. Specifically, both morphology and functionalization are found to alter the enhancement effect from the NTH fillers, while also relying on the loading directions. Overall, this work provides an in-depth understanding of the role of the nanofiller. The observations signify the importance of establishing effective load transfer at the interface, which could benefit the design and fabrication of high-performance polymer nanocomposites.

Hybrid Layered Silicate/Calcium Carbonate Reinforced High-density Polyethylene Nanocomposites: Systematic Morphological Evaluation through Rheological Properties and Response Surface Method

High-density polyethylene (HDPE) based hybrid nanocomposites comprising varying concentrations of layered nanoclay (NC) and spherical nano calcium carbonate (nCaCO3) were prepared by a two-step melt compounding process in the presence of polyethylene grafted maleic anhydride (PE-g-MA) as the compatibilizer. Regarding multiple material variables (the NC, nCaCO3 and compatibilizer contents) participated in fabrication of the nanocomposites, response surface methodology (RSM) was utilized to find the correlation between the material variables, morphology and viscoelastic responses in the melt state. Intercalation of the layered silicates was investigated by X-ray diffraction (XRD) technique, and morphological characterization of the nanosized calcium carbonates was carried out by scanning electron microscope (SEM). The findings indicated that higher contents of the PE-g-MA facilitated the intercalation process and increased the interlayer distance. Interestingly, incorporation of the second nanoparticle, nano calcium carbonate, resulted in viscosity increment which is an influential factor on applied stresses during the melt mixing and subsequently, dispersion state of the nanoclay layers. The interplay between the designated material parameters was also discussed by means of interaction plots.

Ultra-high molecular weight polyethylene nanocomposites reinforced with novel surface chemically modified sonic-exfoliated graphene

A sequence of chemical modifications was performed on natural graphite flakes from initial oxidation, producing graphene oxide (GO), followed by thermally-reduced graphene expansion (GE) to a final sonic exfoliation forming nanoparticles (GES). Employing Raman spectroscopy, it is found that the graphite ID/IG intensity ratio of 0.86 was substantially decreased to 0.54 for GES, indicating a smaller number of more ordered graphene sheet layers. The crystalline index (CI) obtained by X-ray diffraction of the final sonic-exfoliated GES (48%) is improved in comparison to the expanded GE (31%), suggesting better-organized sheets. Scanning electron microscopy shows GES with decreasing stacking of almost transparent layers due to increased spacing between graphene sheets. Nanocomposites fabricated with 0.05, 0.1, 1.0, 3.0, and 5.0 wt.% GES incorporated into ultra-high molecular weight polyethylene, lubricated with mineral oil (UHMWPE/OM), disclosed superior CI and higher temperatures for the onset and maximum rate of thermal degradation. Dynamic mechanical analysis reveals improved viscoelastic stiffness from 1 up to 3 wt.% of GES incorporation, indicating that this novel graphene-based GES acts as reinforcement for UHMWPE/OM nanocomposites. In particular, the 3 wt.% GES nanocomposites with the best thermal and mechanical performance as well as enhanced processability might be considered a practical option for replacing structural applied common UHMWPE.

Space–charge electret properties of polypropylene films with transcrystalline or spherulitic structures—A comparison of functionalities at interfaces

Spherulite-related space–charge electret properties of polypropylene (PP) have been widely discussed in the past decades. In the present paper, a less-common crystalline structure in PP—transcrystalline PP—is studied regarding its electret behavior in comparison with the typical spherulitic morphology. Polarized light microscopy and differential scanning calorimetry were employed to characterize the crystallite types and crystallinities of transcrystalline and spherulitic PP. Their electret functionality is investigated by means of thermally stimulated discharge experiments, where the cross-over phenomenon is observed on transcrystalline PP films, whereas surface-potential saturation and undercharging on the surface occur on the spherulitic samples. Besides, an asymmetrical behavior of positive and negative surface-charge stabilities is found on PP with spherulites, the negatively charged spherulitic surfaces show a better charge stability. It is shown that PP electrets are very sensitive to changes in the microscopic crystalline structures and their interfaces as well as in the molecular conformations controlled through adjustments of the respective processing steps. In addition, surface and bulk nanocomposites of PP or low-density polyethylene with inorganic particles are included in the comparison. In view of recent developments in the areas of PP-based electret-fiber filters and cellular-foam ferroelectrets, the observed changes in the charge-storage properties may have particular relevance, as the required film, fiber, or foam processing might significantly modify crystalline morphologies and nano-scale interfaces in PP electrets. Limitations in the charge-storage capabilities of interface structures may also be of interest in the context of high-voltage electrical-insulation materials where reduced space–charge accumulation and slightly increased charge transport can be advantageous.

Ameliorated Electrical-Tree Resistant Characteristics of UV-Initiated Cross-Linked Polyethylene Nanocomposites with Surface-Functionalized Nanosilica

Given the high interest in promoting crosslinking efficiency of ultraviolet-initiated crosslinking technique and ameliorating electrical resistance of crosslinked polyethylene (XLPE) materials, we have developed the funcionalized-SiO2/XLPE nanocomposites by chemically grafting auxiliary crosslinkers onto nanosilica surfaces. Trimethylolpropane triacrylate (TMPTA) as an effective auxiliary crosslinker for polyethylene is grafted successfully on nanosilica surfaces through thiolene-click chemical reactions with coupling agents of sulfur silanes and 3-mercaptopropyl trimethoxy silane (MPTMS), as characterized by nuclear magnetic resonance and Fourier transform infrared spectroscopy. The functionalized SiO2 nanoparticles could be dispersively filled into polyethylene matrix even at a high filling content that would generally produce agglomerations of neat SiO2 nanofillers. Ultraviolet-initiated polyethylene crosslinking reactions are efficiently stimulated by TMPTA grafted onto surfaces of SiO2 nanofillers, averting thermal migrations out of polyethylene matrix. Electrical-tree pathways and growth mechanism are specifically investigated by elucidating the microscopic tree-morphology with fractal dimension and simulating electric field distributions with finite-element method. Near nano-interfaces where the shielded-out electric fluxlines concentrate, the highly enhanced electric fields will stimulate partial discharging and thus lead to the electrical-trees being able to propagate along the routes between nanofillers. Surface-modified SiO2 nanofillers evidently elongate the circuitous routes of electrical-tree growth to be restricted from directly developing toward ground electrode, which accounts for the larger fractal dimension and shorter length of electrical-trees in the functionlized-SiO2/XLPE nanocomposite compared with XLPE and neat-SiO2/XLPE nanocomposite. Polar-groups on the modified nanosilica surfaces inhibit electrical-tree growth and simultaneously introduce deep traps impeding charge injections, accounting for the significant improvements of electrical-tree resistance and dielectric breakdown strength. Combining surface functionalization and nanodielectric technology, we propose a strategy to develop XLPE materials with high electrical resistance.

Experimental and atomistic insight on the thermal transport properties of h-BN/high density polyethylene nanocomposite

The article investigates the effect of hexagonal boron nitride nanosheet (BNNS) on the thermal transport properties of high density polyethylene (PE) based nanocomposites. An experimental approach was adopted to investigate the effect of the concentration of boron nitride nanoplatelets (BNNP) on thermal conductivity, whereas an atomistic approach was utilized to study the governing mechanism for interfacial thermal conductance (ITC) in BNNS/PE nanocomposites. It was reported from experiments performed using a hot disc analyzer that PE's thermal conductivity improves up to 29.6% with 7wt.% of BNNP. Large dimension nanosheet grown using chemical vapor deposition based techniques are polycrystalline. In continuation with experimental characterization, ITC in mono-crystal and bi-crystal BNNS reinforced PE nanocomposites was predicted using atomistic simulations. It was concluded from the reverse non equilibrium molecular dynamics based simulations that bi-crystalline BNNS with higher mis-orientation angle have superior reinforcing capabilities to improve thermal transport properties. Based on structures of dislocations at the grain boundaries (GB), ITC values were predicted. Depending on the two crystals' alignment, GB configurations can be either nitrogen-rich (N-N) or boron-rich (B-B). It was predicted from the simulations that higher energy nitrogen-rich GBs are better aligned with the PE chains that enhance ITC values.

A facile strategy for the construction of TiO2/Ag nanohybrid-based polyethylene nanocomposite for antimicrobial applications

This work aims to explore the antibacterial activity of PE–TiO2/Ag nanocomposites. Rutil-TiO2/Ag hybrid nanoparticles (the content of 0.2–0.6 wt%) were introduced into the PE matrix under melt mixing process. The TEM images for the ultra-thin section (about 80 nm thick) of nanocomposite showed that TiO2/Ag hybrid nanoparticles were well dispersed into the PE matrix. Moreover, mechanical tests indicated that the tensile property of PE was slightly reduced in the presence of hybrid nanoparticles due to the low contents of nanofillers. Besides, the antibacterial tests revealed that the nanocomposites displayed a potent bactericidal efficiency against both E. coli and S. aureus bacteria (i.e. 1.83 log and 1.9 log after 24 h, respectively). The developed fabrication technique and delivered results of the TiO2/Ag nanohybrid-based PE nanocomposite enable a promising avenue to design and construct the advanced nanostructured hybrid materials for potential antimicrobial applications.

Enhanced dielectric, energy storage and tensile properties of BaTiO3–NH2/low-density polyethylene nanocomposites with POE-GMA as interfacial modifier

Dielectric polymer nanocomposites with excellent dielectric performance and high discharge energy storage are important for capacitor applications. In this study, γ-Aminopropyl triethoxysilane (γ-APS) grafted BaTiO3 nanoparticles (BaTiO3–NH2) were used as filler to improve the dielectric and energy storage properties of low-density polyethylene (LDPE). Glycidyl methacrylate grafted ethylene-octene copolymer (POE-GMA) was used as interfacial modifier between LDPE and BaTiO3–NH2 particles. Because of the chemical reaction between the epoxy groups of POE-GMA and the amino groups of BaTiO3–NH2, the soft shell/hard core structure of POE-GMA@BaTiO3–NH2 can be formed during the blending process. The BaTiO3–NH2/POE-GMA/LDPE nanocomposites with superior dielectric properties were obtained. When the contents of POE-GMA and BaTiO3–NH2 were 10 wt%, the favorable breakdown strength of 350 MV/m and fine discharged energy density of 2.46 J/cm3 for BaTiO3–NH2/POE-GMA/LDPE blend were achieved. This work provided a useful and easy way to exploit perspective dielectric candidates for energy-storage applications.

Functional performance evolution of urchin‐like structured SiO2‐carbon nanotube hybrid constructions reinforcing polyethylene‐based composites

AbstractIn order to meet the growing demands for high specific performance in advanced composite system, carbon nanotubes (CNTs) are widely utilized to endow composite with optimized properties. However, the performance improvement is always impeded by CNTs aggregation. Herein, two typical urchin‐liked SiO2‐CNTs hybrid (SCH) and SiO2@SiO2‐CNTs hybrid (SSCH) were synthesized by utilizing chemical vapor deposition. SCH and SSCH filled polyethylene (PE) nanocomposites were fabricated by solution‐blending and hot‐compression. The electrical, dielectric, rheological, and thermal behaviors of the composites were carefully studied. Both composites showed the low percolation threshold that below 0.5 wt%. By adding 1 wt% hybrid, the electrical conductivity of composites were enhanced by 12 orders of magnitude. Moreover, the self‐strengthened SSCH was preferred to form homogeneous dispersion in polymer matrix, leading to a slightly negative influence on processability. All these features provide a reasonable route for designing CNTs‐filled composites with advanced structural or highly conductive properties in future.

Effect of BNNR on mechanical properties of polyethylene nanocomposites

In the present study authors have studies the mechanical behavior of the hexagonal boron nitride nanoribbon (BNNR) filled polyethylene (PE) nanocomposites using classical mechanics based approach. Reaction force field in conjunction with L-J potentials are used to model the bonded and non-bonded interaction between PE and BNNR. In order to calculate the mechanical properties of the polyethylene based nanocomposites uniaxial tensile testing was applied on the PE/BNNR nanocomposites. Maximum stress, elastic modulus and strain at failure were calculated at the strain rate of 109 s−1 and compared with the corresponding pristine PE value. It was predicted that, 4% BNNR in polyethylene significantly enhance the maximum stress and elastic modulus. This study gives deep insight of the load transfer mechanism in case of the nanofiller reinforced polymer nanocomposites.

Heat transport and surface functionalization in nanocomposites of boron nitride nanotubes and polyethylene.

This work explores the possibility for improving heat transport in a polymeric, electrical insulating material, such as polyethylene, by adding boron nitride nanotubes - a heat superdiffusive material. We use molecular dynamics simulations to study the nanocomposites formed by addition of the nanotubes to both amorphous and crystalline polyethylene, and also investigate the effect of surface functionalization using a silane coupling agent, which, being covalently attached to both the nanofiller and the polymer matrix, facilitates the heat transport between them. Even though transport is shown to deteriorate in each simulation when the coupling agents are added, they are expected to favor the nucleation of the crystalline regions about the nanotubes, thus significantly boosting heat conduction in the material along their direction.

Nanoindentation characterization of polymer nanocomposites for elastic and viscoelastic properties: Experimental and mathematical approach

This work aims to determine the elastic and viscoelastic properties of microwave processed nanocomposites. Three different power rating has been used in microwave processing of polymer nanocomposite, i.e., 180 W, 360 W, and 540 W. Nanomechanical elastic properties of nanocomposites have been determined using the conventional nanoindentation method. Viscoelastic properties of nanocomposites have been determined by observing the increase in depth at maximum load (10 mN) during a small holding period (2 s). Polypropylene nanocomposites (PNT), high-density polyethylene nanocomposites (HNT), and low-density polyethylene nanocomposites (LNT) have shown an increase in modulus, hardness, and viscosity term with an increase in microwave power. The plasticity index has been obtained using the area under the loading and unloading curves. HNT and PNT samples have shown a plasticity index of 0.71 ± 0.02 and 0.62 ± 0.05, respectively. However, LNT samples have shown the same plasticity index 0.61 at all three-power ratings.

A Potential Approach to Enhance the Seebeck Coefficient of UHMWPE by Using the Graphene Oxide

Thermoelectric materials have been a competent source for the production of energy in the present decade. The most important and potential parameter required for the material to have better thermoelectric characteristics is the Seebeck coefficient. In this work, ultra high molecular weight polyethylene (UHMWPE) and graphene oxide (GO) nanocomposites were prepared by mechanical mixing by containing 10000ppm, 50000ppm, 70000ppm, 100000ppm, 150000ppm, and 200000ppm loadings of graphene oxide. Due to the intrinsic insulating nature of UHMWPE, the value of Seebeck for pristine UHMWPE and its nanocomposites with 10000ppm & 50000ppm of GO concentration was too low to be detected. However, the Seebeck coefficient for composites with 70000ppm, 100000ppm, 150000ppm, and 200000ppm loadings of GO was found to be 180, 206, 230, and 235 µV/ K, respectively. These higher values of Seebeck coefficients were attributed to the superior thermal insulating nature of UHMWPE and the conductive network induced by the GO within the UHMWPE insulating matrix. Although, the values of the figure of merit and power factor were negligibly small due to the lower concentration of charge carriers in UHMWPE/ GO nanocomposites but still reported, results are extremely hopeful for considering the composite as the potential candidate for thermoelectric applications.

Reliability of Free Inflation and Dynamic Mechanics Tests on the Prediction of the Behavior of the Polymethylsilsesquioxane-High-Density Polyethylene Nanocomposite for Thermoforming Applications.

Numerical modeling of the thermoforming process of polymeric sheets requires precise knowledge of the viscoelastic behavior under conjugate effect pressure and temperature. Using two different experiments, bubble inflation and dynamic mechanical testing on a high-density polyethylene (HDPE) nanocomposite reinforced with polymethylsilsesquioxane HDPE (PMSQ–HDPE) nanoparticles, material constants for Christensen’s model were determined by the least squares optimization. The viscoelastic identification relative to the inflation test seemed to be the most appropriate for the numerical study of thermoforming of a thin PMSQ–HDPE part. For this purpose, the finite element method was considered.

Effects of the Filler Property, Electron–Phonon Coupling on Thermal Conductivity, and Strain Rate on the Mechanical Property of Polyethylene Nanocomposites

Electron–phonon interaction (EPI) plays an important role in the transport property of metals. Nevertheless, EPI in polymer nanocomposites containing metal fillers has not been fully investigated due to the complicated physical mechanisms. In this work, the copper–polyethylene (Cu–PE) nanocomposite is used as a model system, and nonequilibrium molecular dynamics (NEMD) simulation combined with the two-temperature model (TTM) is conducted to reveal the role of EPI in Cu–PE systems. The effects of filler length, filler property, and EPI strength on thermal conductivity are revealed. A dimensionless number (Θ) is defined to characterize the electron–phonon nonequilibrium (EPN) degree. The results show that the EPN degree has a significant impact on thermal conductivity. When the system is in a strong EPN state, the effects of EPI on thermal conductivity can be negligible. However, when the EPN degree gradually decreases, ignoring EPI can severely underestimate the thermal conductivity. Furthermore, the temperature profile of electrons and phonons is extracted and the equivalent thermal circuit is presented. The additional thermal resistances induced by the nonlocal and nonequilibrium effects are revealed. Phonon spectra analysis and heat current decomposition are performed to uncover the underlying mechanisms. In addition, the effects of atomic mass density and filler types on thermal conductivity are revealed. Stress–strain simulation is conducted to unravel the effects of strain rates on the mechanical property. The results are useful for designing polymer nanocomposites with controlled thermal conductivity.

Reactor Blend and Nanocomposite of Polyethylene Using a Binary Catalyst of Metallocene/Nickel

The present study aimed to conduct the ethylene polymerization using two binary catalytic systems to evaluate the resulting reactor blend of polyethylene. Subsequently, the study continued to explore the effects of catalyst to monomer molar ratio, reaction temperature, ethylene pressure and nanofillers on the catalysts activity, molar mass, thermal behavior, structural and morphological properties of the obtained polyethylene. The catalytic system containing α-diimine catalyst based on nickel showed higher activity, higher melting point (75.6 × 104 g polyethylene/(mol catalyst h), 125°C, respectively) and the extent of crystallinity (up to 48.5%) in comparison with the analogous system bearing pyridine-imine catalyst. The augmentation of nanoparticles increased the branching content in the system with α-diimine catalyst based on nickel, while these trends were reverse in pyridine-imine catalyst system, so that the branches were reduced as the nanoparticle concentration was increased. SEM images revealed distinct fibrous phases and the presence of obvious and well dispersed nanoparticles in the prepared nanocomposites. The synthesized polyethylene blend exhibited high thermal stability.

Effect of Graphene Nanoplatelets on the Structure, the Morphology, and the Dielectric Behavior of Low-Density Polyethylene Nanocomposites.

The incorporation of graphene nanoplatelets (GnPs) within a polymer matrix can play an important role in the physical properties and the functionality of the composite material. Composites consisting of low-density polyethylene (LDPE) and GnPs of different concentrations were developed by mixing GnPs with a molten form of the polymeric matrix. The effect of the GnPs content on the morphological, structural, and electrical properties of the composites were investigated. As shown, graphene presence and its concentration significantly modified the polymer matrix properties, a behavior that can be employed for tailoring its applicability in electrical applications. It was found that the increase of the graphene platelets concentration seems to promote the formation of graphene agglomerates, air gaps, and inhomogeneities, while higher dielectric constant/lower dielectric losses can be achieved.

Modeling of Mechanical Properties of Clay-Reinforced Polymer Nanocomposites Using Deep Neural Network.

Due to the non-linear characteristics of the processing parameters, predicting the desired properties of nanocomposites using the conventional regression approach is often unsatisfactory. Thus, it is essential to use a machine learning approach to determine the optimum processing parameters. In this study, a backpropagation deep neural network (DNN) with nanoclay and compatibilizer content, and processing parameters as input, was developed to predict the mechanical properties, including tensile modulus and tensile strength, of clay-reinforced polyethylene nanocomposites. The high accuracy of the developed model proves that DNN can be used as an efficient tool for predicting mechanical properties of the nanocomposites in terms of four independent parameters.

Study on the Structure and Dielectric Properties of Zeolite/LDPE Nanocomposite under Thermal Aging.

Nanodoping is an effective way to improve the dielectric properties and the aging resistance of polyethylene. Nano-zeolite has a nano-level porous structure and larger specific surface area than ordinary nano-inorganic oxide, which can be used to improve dielectric properties of low-density polyethylene (LDPE) nanocomposite. The zeolite/LDPE nanocomposites were prepared and subjected to thermal aging treatment to obtain samples with different aging time. Using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and the differential scanning calorimetry (DSC) test to study the microscopic and structure characteristics, it was found that nano-zeolite doping can effectively reduce the thermal aging damage to the internal structure of the nanocomposite; carbonyl and hydroxyl decreased significantly during the thermal aging time, and the crystallinity effectively improved. Nano-zeolite doping significantly improved the morphology and strengthened the aging resistance of the nanocomposite. In the dielectric strength test, it was found that nanodoping can effectively improve the direct current (DC) and alternating current (AC) breakdown field strength and the stability after the thermal aging. The dielectric constant of nanocomposite can be reduced, and the dielectric loss had no obvious change during the aging process. Moreover, the zeolite/LDPE nanocomposite with the doping concentration of 1 wt % had the best performance, for the nano-zeolite was better dispersed.