http://poj.ippi.ac.ir/ Polyolefins Journal en daily 1 Mon, 01 Dec 2025 00:00:00 +0330 Mon, 01 Dec 2025 00:00:00 +0330 http://poj.ippi.ac.ir/article_2128.html 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. http://poj.ippi.ac.ir/article_2127.html 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 http://poj.ippi.ac.ir/article_2129.html In this study, well-defined α-methyl styrene – olefin triblock copolymers were synthesized via living anionic polymerization using alkyl lithium as an initiator and 1,12-dibromododecane as a coupling agent. The polymerization was conducted in cyclohexane under an inert atmosphere at moderate temperature, allowing for precise control over the molecular architecture and narrow molecular weight distribution. Gel permeation chromatography (GPC) revealed monomodal elution curves with dispersity values close to unity, confirming the living nature of the polymerization process and the high structural homogeneity of the resulting copolymers. Structural characterization was performed using 1H and 13C nuclear magnetic resonance (NMR) spectroscopy. The 1H NMR spectra confirmed the successful formation of block copolymers through the identification of characteristic chemical shifts corresponding to the initiator, αMS blocks, and central dodecane units. Notably, the absence of brominated end-groups in the spectrum supports complete coupling and high end-group fidelity. Furthermore, 13C NMR analysis revealed well-defined chemical shifts associated with aromatic, methine, and methylene carbons. The disappearance of signals corresponding to bromine-bound methylene carbons confirmed the full consumption of the coupling agent and the effective formation of the triblock structure. These findings validate the successful synthesis of αMS-based triblock copolymers with a high degree of control over molecular parameters, establishing a robust foundation for tailoring thermomechanical and morphological properties for advanced material applications. http://poj.ippi.ac.ir/article_2141.html The widespread consumption of disposable plastics as food contact articles (FCAs) in the Philippines has raised concerns on food safety due to the potential chemical migration of contaminants. In this study, validation of modified 21 Code of Federal Regulations (CFR) Part 177 method was performed through preliminary screening, determination of validation parameters, and profiling. 18 randomly screened low-density polyethylene (LDPE) bags from 16 brands across Philippine markets were analyzed to identify low and high absorbance levels of total UV-absorbing contaminants (TACs) to be considered for method validation. Validation parameters demonstrated limit of detection (LOD) and quantification (LOQ) of 0.013 AU and 0.033 AU per 50 cm2, ensuring reliable detection at low levels. Results from profiling 47 samples presented variability in migration of TACs across brands and locations, however, all samples were within the maximum allowable limit (MAL) of 0.300 AU set by the Food and Drug Administration (FDA) Philippines for aqueous foods. These findings account for the potential migration of contaminants throughout production, transportation, environmental conditions, and storage processes. Comparison between food simulants, n-Heptane to mimic fatty and oily foods and water for aqueous foods, was conducted through statistical analysis using previously reported same-laboratory data for n-Heptane. An independent nonparametric Mann–Whitney U test indicated a statistically significant difference between TACs levels of the two simulants. Comprehensive research on yet to be specified contaminants is proposed to further explore probable adverse health effects associated with their toxicokinetics and toxicodynamics. http://poj.ippi.ac.ir/article_2142.html The aim of this study is to encourage a shift in industry towards using natural, biodegradable materials with antimicrobial properties to produce polymeric materials that can be used effectively in areas such as food and pharmaceutical packaging. In this study, polymeric films based on low-density polyethylene (LDPE) were produced using extrusion technology with the addition of marjoram powder at concentrations of 1%, 3% and 5%. The second phase of the study involved determining the technological properties of the obtained films, including their antimicrobial, barrier, physical, and mechanical properties. The results of the research showed that polyethylene samples supplemented with marjoram powder exhibited antimicrobial properties against Bacillus subtilis and Candida albicans at concentrations of 3% and 5%. However, the same samples did not exhibit any antimicrobial properties against Escherichia coli and Aspergillus niger at any concentration. Polyethylene samples with a 3% concentration demonstrated the greatest tensile strength in both the longitudinal and transverse directions. However, as the marjoram concentration increased, the elongation-at-break of the samples declined. Polyethylene films recorded the lowest elongation-at-break values at a 5% concentration in both directions. Water vapor permeability of the films also increased with marjoram powder concentration; it increased by 2.8 times at 3% compared to the control sample. http://poj.ippi.ac.ir/article_2147.html Polypropylene (PP), a widely used polyolefin, suffers from poor electrical conductivity, which limits its use in electronic packaging and electromagnetic interference (EMI) shielding. In this study, conductive and EMI-shielding PP nanocomposites were fabricated using dual-functionalized carbon nanotubes (CNTs) via a solvent-free melt-blending route. Sequential acid and silane treatments improved CNT dispersion and interfacial compatibility, yielding a low percolation threshold of ~0.3 wt.% and an electrical conductivity of 1.2 × 10⁻² S/m at 3 wt.% CNT. At 5 wt.%, the EMI shielding effectiveness exceeded 41.5 dB, with more than 80% of the attenuation arising from absorption, as confirmed by S-parameter analysis. AI-assisted image segmentation (U-Net architecture) quantified an ~80% reduction in CNT agglomeration and increased interparticle spacing, correlating with the enhanced electrical, dielectric, and thermal properties. The dielectric constant increased from ~2.3 in neat PP to ~6.0 at 5 wt.% CNT with low dielectric loss (tan δ < 0.02), while thermal conductivity improved by ~75%. Tensile strength and modulus increased up to 3 wt.% CNT with a moderate loss in ductility. The combination of dual CNT functionalization, scalable melt processing, and AI-based dispersion quantification provides a reproducible approach for designing lightweight, conductive, and EMI-shielding polyolefin nanocomposites for electronic, automotive, and aerospace applications. http://poj.ippi.ac.ir/article_2150.html MAO-free supported catalysts for ethylene polymerization were prepared by sequentially treating montmorillonites (MMTs) with R₃Al and then with zirconocene. MMTs possessing different physicochemical properties—such as surface area, acidity, and crystallinity—were employed for catalyst preparation. Three zirconocenes, Cp₂ZrCl₂, (1,3-Me₂Cp)₂ZrCl₂, and Me₂Si(Cp)₂ZrCl₂, were used. Acid treatment of raw MMT (Na⁺-montmorillonite) increased the surface area while decreasing both the Al content and crystallinity. The maximum surface area (316 m² g⁻¹) was obtained when the residual Al content was 18%. The effects of triethylaluminum (TEA) and triisobutylaluminum (TIBA) on catalyst performance were investigated. Although treatment of surface OH groups was necessary to obtain the zirconocene-supported catalysts with high activity, no significant difference in catalytic activity was observed between TEA- and TIBA-treated MMTs. In contrast, the type of R₃Al used as a scavenger during polymerization strongly influenced catalytic activity: catalysts employing TEA exhibited much lower activity than those using TIBA. Since TEA is a stronger Lewis acid than TIBA, it likely coordinates more strongly to the active sites, thereby acting as an inhibitor. Therefore, TIBA was employed in all subsequent experiments. The catalytic activity, based on catalyst weight, increased with both surface area and the amount of supported zirconocene, reaching a maximum when the residual Al content was 54%. A linear correlation between the activity (per catalyst weight) and the amount of supported zirconocene was observed for two zirconocenes, Cp₂ZrCl₂ and (1,3-Me₂Cp)₂ZrCl₂, indicating that the supported zirconocenes functioned uniformly as active species for ethylene polymerization. However, 5–7 μmol g⁻¹-cat of zirconocene formed inactive species in both catalysts. Unusual behavior was observed for the supported Me₂Si(Cp)₂ZrCl₂ catalysts: at higher residual Al content, the correlation was similar to that of the other two catalysts, whereas at lower residual Al content, most of the supported zirconocene formed inactive species, and only a small fraction acted as active sites. We speculate that Me₂Si(Cp)₂ZrCl₂ is difficult to activate, and that only the species formed by reaction of strong acid sites with R₃Al can specifically activate this complex. http://poj.ippi.ac.ir/article_2154.html Understanding the yielding of semicrystalline polymers such as isotactic polypropylene (iPP) remains challenging due to morphology-dependent deformation mechanisms and the sensitivity of yield stress to temperature, strain rate, and loading mode. Here, yield stress is measured across macro- (tensile, compression) and micro-scales (nanoindentation) over a range of temperatures and strain rates. Nanoindentation-derived yield stresses obtained using the expanding cavity model agree closely with compression measurements, confirming the dominance of compressive fields, while Tabor-derived values correlate with tensile maximum stress. To rationalize the observed temperature and rate dependences, three theoretical frameworks—Eyring’s model, crystal plasticity, and the lamellar cluster model—are comparatively evaluated. The Eyring model captures the logarithmic strain-rate sensitivity and thermal softening but lacks structural specificity; the crystal plasticity model provides a slip-based interpretation with improved agreement at elevated temperatures; and the lamellar cluster model differentiates deformation modes, accounting for the convergence of compression and indentation yields. The combined experimental–modeling analysis demonstrates the utility of nanoindentation for localized yield assessment and highlights the model-dependent nature of structural interpretation in semicrystalline polymers. http://poj.ippi.ac.ir/article_2156.html Bicomponent polyethylene (PE)/polypropylene (PP) non-woven sheets made from sheath-core fibres were modified by radiation-induced grafting (RIG) of vinylbenzyl chloride (VBC) monomer in both emulsion- and solvent-mediated systems under varying conditions. The key grafting parameters, including reaction medium, monomer concentration, absorbed dose, and temperature, were systematically investigated to control the grafting yield (GY%) and its distribution across fibres. The structural, morphological, and chemical properties of the resulting poly(VBC) grafted fibres were evaluated using Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM) coupled with energy-dispersive X-ray spectroscopy (EDX), elemental analysis, X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and contact angle measurements. The results demonstrated that the reaction medium significantly influenced both the grafting yield (GY%) and graft distribution. Diffusion of poly(VBC) occurred similarly across the sheath and core; however, distinct differences in grafting rates and yields were observed between the emulsion and solvent systems. Under emulsion conditions, a higher density of poly(VBC) grafts was incorporated into the PE sheath than into the PP core compared to solvent-mediated grafting, whereas the side-chain grafts exhibited a generally homogeneous distribution throughout the bicomponent fibres in both systems. These findings demonstrate an effective approach for tuning the structure and morphology of PE/PP bicomponent fibres, favouring emulsion system, offering valuable insights for the design of advanced functional materials with promising applications in environmental remediation and electrochemical energy systems. http://poj.ippi.ac.ir/article_2164.html The effect of hydrostatic pressure on the viscosity of polymer melts plays a critical role in injection molding processes, particularly under high-pressure conditions typical of thin-walled and micro-scale components. Despite its importance, pressure-dependent viscosity data are often incomplete or unavailable in commercial simulation software, especially for semi-crystalline polymers such as polyolefins. In this study, the pressure dependence of viscosity for polypropylene (PP) and high-density polyethylene (HDPE) was investigated by analyzing rheological and volumetric parameters retrieved from the Moldflow material database. The coefficient describing the pressure effect on viscosity was evaluated using a thermodynamic approach based on polymer compressibility, thermal expansion, and the temperature dependence of zero-shear viscosity, and was compared with the corresponding parameter obtained from experimental rheological measurements embedded in the Cross–WLF viscosity model. A clear linear correlation was found between the estimated and experimentally derived pressure coefficients, with the former systematically exceeding the latter by a nearly constant proportionality factor. The proposed approach enables a simple determination of material parameters for injection molding simulations and contributes to improved prediction accuracy under high-pressure processing conditions http://poj.ippi.ac.ir/article_2166.html As a novel class of lightweight conductive material, segregated polymer composites are widely regarded as their unique architecture enables the formation of electrical networks at exceptionally low filler loadings. In such configuration, the conductive phase is preferentially localized at the polymer microgranule boundaries, forming continuous channels for electron transport. This promotes superior performance, particularly in electromagnetic interference shielding. The influence of initial polyethylene particle size on electrical conductivity and electromagnetic interference shielding performance of polyethylene/carbon black segregated structured composites was studied in the present research. Composite samples were fabricated using polymer particles with varying size distributions (100–150, 150–250, 250–500, and mixed <500 μm). Characterization Results demonstrated that increase in initial polymer particle size enhances electrical conductivity; as an illustration, conductivity improved from 94.74 S/m at 105-150 μm to 163.31 S/m at 250-500 μm. In terms of shielding behavior, absorption ratio of 69-76%, confirms a dominant absorptive contribution in segregated structure regardless of initial particle size. The mixed-particle sample (<500 μm) exhibited the best overall performance, combining a high conductivity of 158.40 S/m with the highest total and absorption shielding effectiveness of 11.07 and 7.70 dB, respectively. The incorporation of finer particles not only improved interfacial adhesion among larger polymer particles, but also increased the number of “cages” that trap incident waves and prolong multiple scattering pathways.