Polyolefin degradation
Abdelhay Smaida; Yacine Mecheri; Larbi Boukezzi; Slimane Bouazabia
Abstract
This study focuses on the study of long-term electrical aging effects on dielectric behavior of cross-linked polyethylene (XLPE) used as insulation in high voltage cables. For this reason, we have performed long-term electrical aging tests on full size of HV 36/60 kV XLPE cable samples at three voltage ...
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This study focuses on the study of long-term electrical aging effects on dielectric behavior of cross-linked polyethylene (XLPE) used as insulation in high voltage cables. For this reason, we have performed long-term electrical aging tests on full size of HV 36/60 kV XLPE cable samples at three voltage levels (U0 = 36 kV, 2U0 = 72 kV and 3U0 = 108 kV) during 680 hours. The studied properties are partial discharge threshold, dielectric loss factor, relative permittivity and transverse resistivity. Besides, physico-chemical changes were assessed using Fourier Transform Infrared Spectroscopy (FTIR) and X-ray diffraction (XRD). In the end of paper, the evolution of mechanical properties and hot set test with aging time and voltage levels have been presented and analyzed as additional diagnostic precursors. The obtained results illustrate that examined properties are widely affected by long-term electrical aging. The increase in partial discharges and dissipation factor depending to the voltage level and the aging time and the decrease in partial discharge threshold voltage and transverse resistivity are the mostly marked degradation precursors. These degradation precursors are supported by the increase of carbonyl groups and reduction in the crystallinity degree of the polymer under long-term electrical aging. These parameters are useful parameters for evaluating the quality of underground XLPE cable insulator.
Polyolefins Industry
Derradji Dadache; Farid Rouabah; Zahir Rahem
Abstract
This study demonstrates that quenching and annealing significantly influence the mechanical and thermophysical behavior of low density polyethylene (LDPE). Rapid quenching at temperature of –25 °C enhances ductility by increasing elongation at break, despite reducing thermophysical properties, ...
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This study demonstrates that quenching and annealing significantly influence the mechanical and thermophysical behavior of low density polyethylene (LDPE). Rapid quenching at temperature of –25 °C enhances ductility by increasing elongation at break, despite reducing thermophysical properties, likely due to microstructural refinement. In contrast, post-quenching annealing especially at 100 °C improves thermal conductivity and crystallinity but reduces ductility. The results underscore a tunable balance between thermal and mechanical performance, governed by the interplay of beta (β-) and alpha (α-) relaxation modes during heat treatment. Post-quenching annealing of low density polyethylene LDPE, particularly at 100 °C, significantly enhanced thermal conductivity, diffusivity, and crystallinity, albeit with a trade-off in ductility and increased brittleness. Quenching within the beta (β-) relaxation range promoted maximum ductility, while annealing in the alpha (α-) relaxation range improved thermophysical properties. These findings reveal that precise control of heat treatment conditions enables a tunable balance between mechanical flexibility and thermophysical performance in LDPE
Composites and nanocomposites
Negin Sadat Jalili; Bahereh T. Marouf; Ali Bakhshi-Zadeh; Reza Bagheri
Abstract
The aim of the current study was to first make two compatibilizers, i.e., maleic anhydride grafted polypropylene (PP-g-MA), based on a homo-and a block copolymer. Then, these custom made compatibilizers were incorporated in PP/nanoclay composites made via direct and two-step masterbatch techniques. The ...
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The aim of the current study was to first make two compatibilizers, i.e., maleic anhydride grafted polypropylene (PP-g-MA), based on a homo-and a block copolymer. Then, these custom made compatibilizers were incorporated in PP/nanoclay composites made via direct and two-step masterbatch techniques. The influence of compatibilizer/nanoclay ratio was examined in the direct method. In the two-step processing technique, the compatibilizer content was divided to two parts such that the first part was used when making the masterbatch and the second part was incorporated in the second step when the masterbatch was diluted by the polymer matrix. The characterizations via titration test and Fourier-transform infrared (FTIR) spectroscopy revealed a higher degree of grafting reaction when homo-polymer was used for synthesizing PP-g-MA. In the next step, nanocomposites containing 3 wt.% nanoclay with three different PP-g-MA (both types)/nanoclay ratios of 1:1, 2:1, and 3:1 were made using a co-rotating twin screw extruder. X-ray diffraction (XRD) analysis was done to evaluate morphology and tensile and impact, and tests were performed to evaluate the mechanical properties of the PP samples. Based on the results, maleic anhydride grafted homo-polypropylene (HPP-g-MA) and the composition containing HPP-g-MA/nanoclay ratio of 2:1 with 7.69% improvement in Young’s modulus was reported as the recommended compatibilizer and ratio for applications. Finally, five nanocomposite samples with identical composition were made in two steps. A masterbatch containing 15 wt.% nanoclay was made first and then, it was diluted with PP to reduce the nanoclay content to 3 wt.%. All samples containing 6 wt.% PP-g-MA, but the method of addition of compatibilizer was different. In one sample, the whole compatibilizer was added into the masterbatch. In another sample, the entire PP-g-MA was added in the second stage of compounding. In the other three samples, the addition of compatibilizer was divided between the two stages of the process. The results of the study showed that the highest improvement of elastic modulus (24.26%) was obtained when the majority of the compatibilizer was added in the second step of production. This was associated with the best dispersion of nanoclay platelets in the PP matrix.
Polymer processing
Luisiana Morales-Zamudio; Francisco Rodriguez-Gonzalez; Minerva A.M Zamudio; Tomas Lozano; Juan Guillermo Martinez-Colunga; Saul Sanchez-Valdes; Luciano Da Silva; Erika Lopez-Martinez; Sergio Flores-Gallardo
Abstract
In this research we provide a practical guide to achieve the successful extrusion of LDPE tapes commercially used in mesh fences, with controlled dimensions, good mechanical properties and weather resistance. Here we share: 1) The die design dimensions and its specialized slotted manufacture to get the ...
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In this research we provide a practical guide to achieve the successful extrusion of LDPE tapes commercially used in mesh fences, with controlled dimensions, good mechanical properties and weather resistance. Here we share: 1) The die design dimensions and its specialized slotted manufacture to get the veins of tape, 2) Processing temperatures profile, 3) Cooling method, 4) Hot stretch ratio (HSR), and 5) The effect of colorant and ultraviolet rays’ protector, due to the outdoor use of polymer privacy tape. The formulated tape (0.8 wt. % UV protector and 5 wt. % colorant) showed the best performance under accelerated aging and reached good mechanical properties up to a time of 2000 hours compared to its initial values. The dye and the UV additive improved the mechanical properties. All these, led to obtain a LDPE tape to fulfill the expectative and characteristic of a commercial tape used for mesh fences.
Characterization
Ivan Kuryndin; Sergei Kostromin; Rustam Mamalimov; Anton Chervov; Andrei Grebennikov; Sergei Bronnikov
Abstract
Swelling of high-density polyethylene (PE) in organic solvents, orthodichlorobenzene and orthoxylene, was investigated. The swelling kinetics of the PE specimen was described by the first-order equation. For the first time, the PE specimen swelling rate constant was shown to decrease with increasing ...
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Swelling of high-density polyethylene (PE) in organic solvents, orthodichlorobenzene and orthoxylene, was investigated. The swelling kinetics of the PE specimen was described by the first-order equation. For the first time, the PE specimen swelling rate constant was shown to decrease with increasing thickness of the specimens. The equilibrium swelling of the PE specimen was evaluated. It was found that equilibrium swelling is independent of the thickness of specimens. It was shown that storage of polyethylene specimens in organic solvents changes its mechanical properties (tensile strength, Young’s modulus, and elongation-at-break) due to polymer plasticization. We have shown that the increase in flexibility and elongation-at-break after relatively short-term immersion of PE samples in these organic solvents is significant. However, the tensile strength of swollen specimens remains high enough. The interaction between polymer chains and solvent molecules was not detected. The results obtained are important for the design and operation of PE coatings and PE products, such as pipes, tanks, and other accessories exposed to oil products.
Polymer processing
Fatemeh Hassan; Mehdi Entezam
Abstract
Irradiation of polymers is one of the most effective and economical methods for modifying their properties and for changing their applications. In this study, an extrusion grade polypropylene (PP) was treated by electron beam irradiation to produce a PP suitable for injection molding. Irradiation was ...
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Irradiation of polymers is one of the most effective and economical methods for modifying their properties and for changing their applications. In this study, an extrusion grade polypropylene (PP) was treated by electron beam irradiation to produce a PP suitable for injection molding. Irradiation was carried out at different doses (0-80 kGy) under atmosphere air and at ambient temperature. Melt flow index (MFI) measurements showed PP samples irradiated in the range of 10 to 40 kGy are suitable to use in injection molding. Electron beam irradiation decreased the viscosity and the shear thinning rheological behavior of PP. The differential scanning calorimetry (DSC) analysis revealed that electron beam irradiation increased the crystallinity percentage and temperature of PP, but decreased the melting temperature. Among all treated samples, the PP20, irradiated at the dose of 20 kGy, showed the highest impact resistance. It had higher Young’s modulus and tensile strength, but lower elongation-at-break in comparison with untreated PP.
Structure and property relationship
Fateme Khademeh Molavi; Sedigheh Soltani; Ghasem Naderi; Rohollah Bagheri
Abstract
A novel mixing approach for achieving a good dispersion of multi-walled carbon nanotubes (MWCNTs) in ethylene- propylene diene monomer (EPDM) matrix has been investigated. In this approach EPDM was modified with vinyltrimethoxysilane (VTMS) during melt mixing. In addition the effect of MWCNT concentration ...
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A novel mixing approach for achieving a good dispersion of multi-walled carbon nanotubes (MWCNTs) in ethylene- propylene diene monomer (EPDM) matrix has been investigated. In this approach EPDM was modified with vinyltrimethoxysilane (VTMS) during melt mixing. In addition the effect of MWCNT concentration on mechanical and rheological properties of modified EPDM has been studied. The formulated composites by this method exhibited significantly enhanced physical properties even at very low nanotube concentration. The grafting reaction was confirmed by Fourier transform infrared spectroscopy (FT-IR) peak at 1070 and 1250 cm-1according to Si-O and Si-C vibration. The state of dispersion of the fillers in the polymer matrix was evaluated through transmission electron microscopy (TEM) and scanning electron microscopy (SEM), In addition surface topology was studied with atomic force microscopy (AFM). The results showed that VTMS-grafted on the EPDM surface improved the dispersion of MWCNTs in the matrix. The rheological characteristics have been studied by rubber process analyzer (RPA). Some properties such as storage modulus (Ǵ) and complex viscosity (η^*) increased with increasing MWCNT content. It was found that at concentration of 2 wt.% MWCNT, the nanocomposites exhibited notably enhanced mechanical properties such as modulus and tensile strength.
