Polyethylene Molecules Research Articles

Thermal and mechanical performance assessment of composite (CPCM) for energy storage

Phase change materials (PCMs) face obstacles in being widely used due to issues with heat transfer and maintaining their shape. In this research, instead of using binders, the Hexadecane (H) is melted in such a way that the capillary forces of the molten wax allow it to be impregnated into the low-density polyethylene (P) molecules and bind it together as a composite. It was found that the hot melt extrusion (HME) combines the two materials at the micro-scale, forming a phase change composite (CPCM) with various geometries that possesses superior latent heat and shape stability during phase transition. The structure can incorporate a higher percentage of PCM (60 %) using this method, which also results in lower costs. According to the thermal analysis, (H60P40) provides great thermal stability and can store a lot of energy per unit of weight. It has a high capacity of storing latent heat at 129.56 J/g and can also prevent Hexadecane leakage. Based on the mechanical properties results, hexadecane acts like plasticizer thus the addition of PCM decreases Young's modulus, stress in break, and stress at yield. This trend is observed as the PCM content increases. The high values of elongation at break also indicates the strong plasticizing properties of PCM. Based on the obtained results, the CPCMs as a potential candidate for an application in buildings for thermal regulation, reducing energy consumption, and reducing indoor temperature swing.

Modification of Petroleum Bitumen with Secondary Polyethylene in the Presence of Vermiculite

This article presents studies on the modification of petroleum bitumen with polymer waste in the presence of vermiculite. An increase in temperature leads to an increase in the interaction of components, partial breakage of polyethylene and bitumen macromolecules, and the formation of radical-free valences. As a result, fragments of polyethylene and bitumen molecules react with each other, and the formation of qualitatively new structural formations occurs via the strong connection of polar and amorphous bitumen with nonpolar structurally viscous polyethylene. Domestically produced Kulantau vermiculite was used to ensure stable adhesion over a wide temperature range and increase the specific surface area, which acquired additional energy, resulting in an increase in the degree of adhesion to bitumen and increased durability of the binder with improved rheological characteristics. Because of the increased service life of road asphalt pavements, the use of the latter results in a considerable decrease in the cost of polymer-bitumen binders. Based on improved binder formulations, asphalt concrete exhibits excellent water resistance and strength at 50 °C (4.7 to 5.0 MPa). In summary, the modification of bitumen with polymer waste and vermiculite offers a promising avenue for improving the performance and longevity of asphalt pavements.

Effect of hexyl‐branched backbone size on the size distribution and coalescence of free volume around an amphiphilic molecule

AbstractWe used molecular dynamics simulation to study the size distribution and coalescence of free volume around an amphiphilic molecule (nonyl ethoxylate (NE)) at a concentration of 0.5 wt% in blends of linear and branched polyethylene that contained a small four‐arm alkane (7,12 hexyl octadecane). The branched polyethylene chains had 10 and 82 hexyl branches/1000 backbone carbons. The coalescence dynamics (fluctuation of free volume in time) was quantified by the number of Fourier frequencies and the corresponding power (amplitude). In our previous work, we hypothesized that cavitation, the first step of environmental stress cracking observed experimentally, starts from the free volume coalescence at the interface between NE and polyethylene molecules and showed that hexyl branches in the branched polyethylene molecules suppress such coalescence, suggesting that cavitation, a much longer time scale process, could also be slowed down. The current work showed that the behavior of hexyl branches in branched polyethylene in a blend with linear polyethylene was similar to that in pure branched polyethylene, but that the hexyl branches in the 7,12 hexyl octadecane exhibited the opposite behavior. In particular, they intensified free volume coalescence, especially around the hydrophilic ethylene oxide segments of NE. The addition of 7,12 hexyl octadecane to branched polyethylene alone or blended with linear polyethylene does not seem to slow down free volume coalescence (cavitation), leading us to conclude that the effect of hexyl branches on the free volume coalescence around NE depends on the size of the backbone to which the branches are attached.Highlights Hexyl branches reduce free volume coalescence activities. The longer the backbone is, the stronger the hexyl branch effect. More coalescence activities occur on the hydrophilic segment of NE.

Improved DC Dielectric Performance of Cross-Linked Polyethylene Modified by Free Radical-Initiated Grafting BMIE.

To enhance the direct current (DC) dielectric properties of cross-linked polyethylene (XLPE) for high-voltage (HV) cable insulation, the polyethylene molecular chain is modified by grafting bismaleimide ethane (BMIE), which creates carrier deep traps within the polymer material. Compared to the traditional modified molecule maleic anhydride (MAH), BMIE has a significantly higher boiling point than the production temperature of XLPE. Additionally, it does not release bubbles during the production process and, thus, preserves the dielectric properties. It was proved by infrared spectroscopy and a gel content test that BMIE was successfully grafted onto the polyethylene molecular chain and had no effect on the crosslinking degree of the polymer while reducing the amount of crosslinker, thereby reducing the influence of the by-products of the decomposition of dicumene peroxide (DCP) on the electrical resistance of polymers. The analysis of DC breakdown field strength, current density, and space charge distribution at various temperatures demonstrates that grafting BMIE can greatly enhance the dielectric properties of insulation. Polar groups in the BMIE molecule create deep trap energy levels in XLPE-g-BMIE, and these trap energy levels contribute to the formation of a charged layer near the electrode, which is shielded by Coulomb potential. As a result, the charge injection barrier increases. Additionally, the presence of these polar groups reduces the mobility of charge carriers through trap-carrier scattering, effectively suppressing the accumulation of space charge within the material. First-principle calculations also confirm that bound states can be introduced as carrier traps by grafting BMIE onto polyethylene molecules. The agreement between experimental results and simulation calculations indicates that grafting BMIE to enhance the dielectric properties of polyethylene is a new and feasible research direction in the exploitation of materials for HVDC cables.

Optimizing the formulation design and investigating the composite modification mechanism of pyrolysis carbon Black/Polyethylene/Synthetic plant ester composite modified asphalt

Pyrolysis carbon black (PCB) is the surplus product of waste tires after pyrolysis. Polyethylene (PE) is the main component of disposable plastic bags, and synthetic plant ester (SPE) is an environmentally friendly plasticizer that has recently emerged. In this study, the aforementioned three materials were used to prepare an environmentally friendly composite-modified asphalt (CM-A). The optimization of the formulation design of the PCB/PE/SPE additive with asphalt was performed using the response surface mixture-design method, with conventional asphalt performance as the control index. The compound modification mechanism was investigated using modern microscopic testing techniques. The recommended formulations for the additives were BA:PCB:PE:SPE = 0.881:0.081:0.022:0.016 by mass. The resulting CM-A exhibited comparable penetration, ductility, and fatigue properties to base asphalt (BA), with higher high-temperature rutting resistance and softening point values. Microscopic test results revealed that the PCB/PE/SPE was physically blended with asphalt. The plasticizing effect of SPE enhanced the plasticity of PE molecules and significantly improved the compatibility properties of PE and BA. The thermal behavior of CM-A was similar to that of BA but with a slightly higher ash content due to the presence of PCB. The results provide a reference for the industrial production of asphalt modifiers, modification mechanism studies, and a new solution to alleviate environmental pollution and resource waste problems from solid waste accumulation.

A novel strategy for construction of multiple dynamic hybrid crosslinking network for polyethylene pipes and self-healing behavior via thermal stimulation

Polyethylene (PE) pipes with excellent comprehensive performances have been most widely applied, while endowing PE pipes with self-healing property was conducive to prolong their service life. Due to nonpolar nature of PE molecules, its self-healing functionalization remains extremely challenging. In this work, by introducing amide and carboxyl groups into PE/natural rubber (NR) chains to construct reactive sites and compositing with zinc acrylate (ZDA)/ferric chloride (FeCl3), the hybrid crosslinking network composed of covalent bonds and multiple dynamic bonds, including hydrogen bonds, Fe3+-carboxyl/amide coordination bonds and Zn2+-carboxylate ionic bonds was successfully constructed in PE/NR blend via reactive processing and in-situ vulcanization crosslinking. Upon stretching, the dynamic crosslinking network was first broken, resulting in large energy dissipation, apparent hysteresis loss and stress relaxation, while when removing stress, its residual strain decreased remarkably with increasing waiting time, displaying reversible dynamic characteristic. As a result, the hybrid crosslinking network was reconstructed via thermal stimulation, facilitating diffusion and entanglement of PE/NR chains across interface, and the width/depth of the scratch obviously decreased. The tensile strength and fracture toughness recovered obviously, and the self-healing efficiency of the blends and pipes reached 65–70 %, showing a significantly enhanced self-healing ability with promising application potential.

Molecular simulation of hydrogen permeation behavior in liner polymer materials of Type Ⅳ hydrogen storage vessels

Compared with Type III hydrogen storage vessels, the great advantages of Type IV hydrogen storage vessels are their large hydrogen storage density, less weight, and not prone to fatigue failure, which extends the service life. However, due to the penetration of hydrogen, buckling of the plastic liner will happen. Therefore hydrogen permeation behavior in the liner polymer materials of Type Ⅳ hydrogen storage vessels is an important problem. In order to investigate the hydrogen permeation in the liner material of type Ⅳ hydrogen storage vessels, the polyethylene and polyamide models were constructed by the Materials Studio (MS) molecular simulation software to simulate the diffusion and adsorption process of hydrogen molecules in polyethylene and polyamide under the temperature of 263–353 K. The influence of solubility coefficient, diffusion coefficient, and Fractional Free Volume on the permeability of gas molecules were also analyzed. The permeation mechanism of hydrogen in polyethylene and polyamide materials was investigated at molecular scale. The results show under the same conditions, solubility coefficient, diffusion coefficient and permeability coefficient of hydrogen in polyethylene are greater than those in polyamide. Under the simulated conditions in the paper, compared with polyethylene, polyamide shows better hydrogen permeability resistance.

CRYSTAF, DSC and SAXS Study of the Co-Crystallization, Phase Separation and Lamellar Packing of the Blends with Different Polyethylenes.

The crystallization of polyethylene (PE) blends is a highly complex process, owing to the significant differences in crystallizability of the various PE components and the varying PE sequence distributions resulting from short- or long-chain branching. In this study, we examined both the resins and their blends through crystallization analysis fractionation (CRYSTAF) to understand the PE sequence distribution and differential scanning calorimetry (DSC) to investigate the non-isothermal crystallization behavior of the bulk materials. Small-angle X-ray scattering (SAXS) was utilized to study the crystal packing structure. The results showed that the PE molecules in the blends crystallize at different rates during cooling, resulting in a complicated crystallization behavior characterized by nucleation, co-crystallization, and fractionation. We compared these behaviors to those of reference immiscible blends and found that the extent of the differences is related to the disparity in crystallizability between components. Furthermore, the lamellar packing of the blends is closely associated with their crystallization behaviors, and the crystalline structure varies significantly depending on the components' compositions. Specifically, the lamellar packing of the HDPE/LLDPE and HDPE/LDPE blends is similar to that of the HDPE component owing to its strong crystallizability, while the lamellar packing of the LLDPE/LDPE blend is approximately an average of the two neat components.

Evolution of light olefins during the pyrolysis of polyethylene in a two-stage process

The accumulation of waste plastics has been one of the most urgent and difficult environmental challenges. In this work, the pyrolysis of polyethylene (PE) has been studied by thermogravimetric analysis (TGA), pyrolysis/gas chromatography/mass spectrometry (PyGC-MS), and a two-stage tube reactor. The pyrolysis behavior of high-density polyethylene (HDPE) and low-density polyethylene (LDPE) is compared, and there are almost no differences in the thermogravimetric curves obtained by TGA and the yield of gaseous products obtained in a two-stage process. The evolution of light olefins (C2–C4) during the pyrolysis of PE is investigated in a two-stage process with a constant condition in the first stage (500 °C) and various conditions in the second stage (700–1000 °C, 0.2–0.4 s). The temperature in the second stage has a more significant effect on the yield and selectivity of light olefins than the residence time, and the ethylene, propylene, and butene yields do not increase monotonously as the temperature rises. The highest yield of light olefins of 76.1 wt% is obtained at 800 °C with a selectivity of 91.7%. The maximum yields of ethylene, propylene, and butene are 45.1 wt%, 17.3 wt%, and 24.3 wt%, respectively. The scission mechanisms are proposed to provide insight into the process during which PE molecules transform into light olefins.

Effective depolymerization of polyethylene plastic wastes under hydrothermal and solvothermal liquefaction conditions

Depolymerization of polyethylene (PE) is one of the most challenging tasks in the chemical upcycling of PE-based plastic wastes because the disassociation of the stable carbon–carbon bonds in PE is only possible at a very high reaction temperature. The thermal liquefaction of PE cable plastic waste in a stainless-steel batch reactor was thoroughly evaluated in this study. The effect of different liquefaction methods (hydrothermal liquefaction (HTL), ionic liquids catalyzed HTL, and solvothermal liquefaction (STL)) on the yields of product fractions (oil products, solid residue, and gas) and the properties of the oil products were examined. At 350 °C and 90 min reaction duration, the conversion (%) of 75.43%, the oil yield of 39.33%, the energy recovery rate of 39.7%, the higher heating values (HHV) of 43.83 MJ/kg for the oil samples, and the lower boiling range molecular distribution were obtained by the solvothermal liquefaction method with acetone as a solvent. The HHV of the oil samples obtained in the STL method (43.28–43.83 MJ/kg) is comparable to that of gasoline (HHV − 43.4 MJ/kg). The contribution of the solvent to the depolymerization reaction was mainly the dissolution and dispersion of feedstock by solvation, therefore reducing thermal cracking temperature through enhanced mass and thermal energy transfer. In thermal liquefaction, solvent and feedstock had a low level of solvolysis reactions, so the depolymerization reaction mainly follows thermal cracking. The main reaction path is the random scission of PE molecules during heat treatment, with a low level of polymerization, cyclization, and radical recombination reactions, which occurred through the free radical mechanisms. This work has demonstrated the feasibility of a very promising technique for effective chemical upcycling of polyethylene-based plastics.

Size Dependency of Super Gecko Structure Consisting of Normal Polyethylenes for Their Formation Process by Coulombic Force and Tensile Strength

Gecko has ability to climb up easily on smooth vertical surface such as window glass. There are thousands of nano size hairs on the Gecko's feet. They cause strong attractive van der Waal’s force. Aihara and Chibana suggested the Super Gecko structure in which the normal polyethylene (PE) molecules are vertically transplanted on a plate. Two of this structure are interlocked like as zip fastener. In present study, self-formation process of the Super Gecko structure is simulated by molecular dynamics (MD) method. The separated Super Gecko structures with distributed electric charge on the PE molecules form the zipped Super Gecko structure on oneself. The opposite electric charges cause attractive force between two separated structures. The size dependency of self-formation of Super Gecko structure is simulated.

Formation and reinforcing effect of epitaxial oriented crystallization of polyethylene induced by self‐assembly nucleating agent under stress

AbstractA rare earth nucleating agent (RENA) was introduced to fabricate polyethylene (PE) pipe resin, which self‐assembled into various structures in PE melt during processing and further induced PE molecules to epitaxially crystallize on its surface to form, among others, a hybrid shish‐kebab crystalline structure due to good crystallographic matching between RENA and PE. Under stress, the shish structure formed by needle‐like RENA assembly arranged preferentially along the drawing direction, which was beneficial for an orderly arrangement of PE chains epitaxially crystallizing on its surface in the process of stress‐induced recrystallization and thus promoted the formation of a dense oriented crystalline structure with a large number of shish structures, resulting in higher degree of crystallinity and orientation, and lower long period and lateral size of lamellae than those of PE sample. By orientation, compared with PE sample at the same draw ratio, PE‐RENA samples showed much higher tensile strength and modulus. Especially, the oriented PE‐RENA pipes showed an approximately 96% and 100% increase in tensile strength along the hoop direction and internal pressure resistance, respectively, compared with unoriented pipe sample. This work provides a facile method for fabricating highly enhanced PE pipes with wide application prospects. © 2021 Society of Industrial Chemistry.

Thermal stability enhancement of oriented polyethylene by formation of epitaxial shish-kebab crystalline structure

Oriented polyethylene (PE) products usually exhibit thermodynamic instability in oriented crystalline structure under high temperature during long term service. In this work, self-assembly rare-earth nucleating agent (RENA) was innovatively introduced to fabricate oriented PE and induced PE molecules to form stable epitaxial oriented crystalline structure. Compared with oriented neat PE, oriented PE-RENA showed much higher dimensional/strength retention during aging, which reached as high as 90.13%/86.46% after aging at 100 °C for 1000 h, exhibiting high dimensional/mechanical stability. At low draw ratio, PE-RENA exhibited hybrid oriented shish-kebab structure, for which oriented RENA assembly acted as shish structure and PE lamellae acted as kebab structure, while, after aging, new stable anisotropic shish-kebab crystalline structure formed and the crystallinity (Xc) changed slightly. At high draw ratio, highly oriented shish-kebab structure formed, most of which was retained after aging and the changes of Xc/orientation degree was insignificant, while the molecular mobility in crystalline phase/intermediate phase was weakened, exhibiting enhanced thermal stability in oriented crystalline structure.

Machine Learning-Assisted Hybrid ReaxFF Simulations.

We have developed a machine learning (ML)-assisted Hybrid ReaxFF simulation method ("Hybrid/Reax"), which alternates reactive and non-reactive molecular dynamics simulations with the assistance of ML models to simulate phenomena that require longer time scales and/or larger systems than are typically accessible to ReaxFF. Hybrid/Reax uses a specialized tracking tool during the reactive simulations to further accelerate chemical reactions. Non-reactive simulations are used to equilibrate the system after the reactive simulation stage. ML models are used between reactive and non-reactive stages to predict non-reactive force field parameters of the system based on the updated bond topology. Hybrid/Reax simulation cycles can be continued until the desired chemical reactions are observed. As a case study, this method was used to study the cross-linking of a polyethylene (PE) matrix analogue (decane) with the cross-linking agent dicumyl peroxide (DCP). We were able to run relatively long simulations [>20 million molecular dynamics (MD) steps] on a small test system (4660 atoms) to simulate cross-linking reactions of PE in the presence of DCP. Starting with 80 PE molecules, more than half of them cross-linked by the end of the Hybrid/Reax cycles on a single Xeon processor in under 48 h. This simulation would take approximately 1 month if run with pure ReaxFF MD on the same machine.

Ameliorated Dielectric Performances of UV-Initiated Auxiliary Crosslinking Polyethylene

In photon-initiated crosslinking reactions of polyethylene molecules, the auxiliary crosslinkers in form of either monomer or homopolymer will cause bridging connections between polymeric molecules by transforming the irradiated photon energy to chemical energy under the assistance of photon-initiators, which can improve photon-initiation quantum efficiency and crosslinking uniformity. In the present study, the auxiliary crosslinkers of TAIC, TAC and TMPTA combining the macromolecular photon-initiator of BPL are employed into the ultraviolet (UV)-initiation technology to develop high-level crosslinked polyethylene (XLPE) insulation materials, whilst elucidating the structural and electrical mechanisms of the dielectric amelioration deriving from auxiliary crosslinking schemes. The specified photosensitive auxiliary crosslinkers can chemically bridge polyethylene molecules in the UV-initiated polyethylene crosslinking process, which can effectively promote polyethylene crosslinking degree but will slightly abate polyethylene crystallinity. Whereas, the orientation polarization and relaxation of molecular electric-dipoles on auxiliary crosslinkers cause additional dielectric permittivity and loss respectively, which will probably reduce insulation performances of XLPE. By contrast to XLPE benchmark, especially for grafting auxiliary crosslinker TAIC with the multiple-coupling carbonyl groups in a ring-conjugation, the preferable deep charge-traps can be introduced into polyethylene matrix to effectively improve electrical conductance and AC dielectric breakdown strength. This study provides experimental basis for developing the photon-initiated XLPE insulation materials with advanced dielectric performances required for manufacturing high-voltage grade cables.

Thermal conductivity and interfacial thermal conductivity of complex graphene nanoribbons without and with polyethylene molecules

We investigate the thermal conductivity (TC) and interfacial TC (ITC) of complex graphene nanoribbons (GNRs) with homojunctions formed by two monolayer GNR regions (MRs) and one central multi-layer GNR region (CR), as well as the influences of the CR layer number and length, the MR length, the GNR width, and the temperature. We show that the ITC is always smaller than the TC, indicating the entire heat transport performance is fundamentally determined by the interfaces. The GNRs with the two-layer CR show the largest ITC, which is much greater than the GNRs with other CR layer numbers. With increasing the temperature and the CR length, the ITC will increase while the TC will decrease for the GNRs with arbitrary CR layer numbers. However, the TC and ITC show the oscillations around certain values with the increase of the GNR width, and the TC will increase with the increase of the length of the MR. In addition, the TC (ITC) in the left part of the complex GNR changes in the same pace as the TC (ITC) in the right counterpart, while the TC always changes in the pace opposite to the ITC in the left or right part of the complex GNR. Finally, we show that the ITC can be increased by placing polyethylene molecules at the interfaces. This research should be an important reference for understanding the heat transport mechanism and designing the thermal functional materials.

Ultra-high gas barrier composites with aligned graphene flakes and polyethylene molecules for high-pressure gas storage tanks

Despite polymers have great advantage in improving the energy density of hydrogen storage containers due to their lightweight characteristic, the production of high gas barrier polymers in a low-cost and high-efficiency manner remains a challenge. Here, polyethylene/graphene flakes (PE/GFs) composite films with ultra-high gas barrier properties were produced by no-boundary constraints hot-pressing method. Theoretical analysis showed that an extensional-shear coupled flow was generated inside the polymer melts and the shear-flow force near the polymer melts surface is always higher than that inside the melts during this process, which is responsible for the alignment of GFs and PE molecules. The DSC results indicated that the crystallinity of the composites after hot-pressing is increased by about 10%. The quantitative results of positron annihilation lifetime spectrum (PALS) showed that the fractional free volume of composites is reduced from 6.52 vol% to 5.43 vol%. As a consequence of the synergistic effect of the above aspects, the barrier performance of the composites has been significantly improved, and the helium leak rate of the composites reached an astonishing 3.92 × 10−9 Pa•m3/s with only 0.5 wt% GFs, outperforming unoriented pure PE with a decrease of 98.6%. Moreover, the tensile strength and Young's modulus of the oriented composites were increased by 31.4% and 21.1%, respectively. The work presented here demonstrates that the simple, fast, and economical preparation method can be readily used to produce composites with superior barrier performance, which will provide great reference for the processing technology of hydrogen storage containers.

Potato Starch Edible Films as Environmentally Friendly Carriers for Model Drug: In vitro Release Study

Starch is a vital plant polymer used in thousands of food and non-food products. Researchers have made great efforts over the past 20 years to develop ingredients based on nature which enhance starch texture and nutritional values. Starch has many non-food applications, ranging from body care to medicinal applications, among its uses in other foodstuffs. Since starch is sustainable and environmentally friendly material, in many chemical applications, including plastics, detergents and glues, it can serve as a good substitute for fossil-fuel components. This work aims to introduce edible starch films-based carriers for supporting the release of fluorescein as a model drug. Physical modification for potato starch carriers (PSS) was done by incorporating glycerol and low-density polyethylene (LDPE) molecules. Fluorescein dye was incorporated in edible films to investigate the amount of release by UV-vis technique. It was found that PSS-LDPE is spread better than LDPE at physiological temperature and PSS dissolution is also appropriate at this temperature. While PSS formed faster edible film than LDPE and PSS-LDPE, it decayed within 3 days. The amounts of dye released from PSS and PSS-LDPE films were higher than that of fluorescein dispersed in starch suspension in buffer solution (pH 7.5) at 37 o C.

Adsorption of three pesticides on polyethylene microplastics in aqueous solutions: Kinetics, isotherms, thermodynamics, and molecular dynamics simulation

Microplastics could act as a carrier for pesticides in the water environment and pose a potential risk. This study mainly investigated the effects of reaction time, microplastics dosages, pH, and NaCl salinity on the adsorption characteristics of three pesticides (Imidacloprid, Buprofezin, Difenoconazole) on polyethylene (PE) microplastics in aqueous solution. The results showed that high pH and low NaCl salinity were conducive to the adsorption. The adsorption data were well fitted by the Freundlich isotherm model and the pseudo-first-order kinetics, indicating that it was mainly controlled by physical function. The adsorption capacity of three pesticides on PE microplastics followed the order of Difenoconazole > Buprofezin > Imidacloprid. The thermodynamic study indicated the adsorption of all pesticides as spontaneous and exothermic processes, and the elevated temperature was favorable to the adsorption. SEM-EDS and FTIR results verified that pesticides were adsorbed on the microplastics but the adsorption process was mainly controlled by intermolecular Van Der Waals Force and the microporous filling mechanism. Grand Canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulation results indicated that surface adsorption was the exclusive mechanism for the adsorption of pesticides on microplastics, and the final adsorption configurations revealed that there were complex interactions between the pesticide molecules and the C, H atoms in PE molecules. The results of this study illustrated that PE microplastics are potential carriers for pesticides in the water environment.

Elevated-Temperature Space Charge Characteristics and Trapping Mechanism of Cross-Linked Polyethylene Modified by UV-Initiated Grafting MAH.

Space charge characteristics of cross-linked polyethylene (XLPE) at elevated temperatures have been evidently improved by the graft modifications with ultraviolet (UV) initiation technique, which can be efficiently utilized in industrial cable manufactures. Maleic anhydride (MAH) of representative cyclic anhydride has been successfully grafted onto polyethylene molecules through UV irradiation process. Thermal stimulation currents and space charge characteristics at the elevated temperatures are coordinately analyzed to elucidate the trapping behavior of blocking charge injection and impeding carrier transport which is caused by grafting MAH. It is also verified from the first-principles calculations that the bound states as charge carrier traps can be introduced by grafting MAH onto polyethylene molecules. Compared with pure XLPE, the remarkably suppressed space charge accumulations at high temperatures have been achieved in XLPE-g-MAH. The polar groups on the grafted MAH can provide deep traps in XLPE-g-MAH, which will increase charge injection barrier by forming a charged layer of Coulomb-potential screening near electrodes and simultaneously reduce the electrical mobility of charge carriers by trap-carrier scattering, resulting in an appreciable suppression of space charge accumulations inside material. The exact consistence of experimental results with the quantum mechanics calculations demonstrates a promising routine for the modification strategy of grafting polar molecules with UV initiation technique in the development of high-voltage DC cable materials.