Search Results (858)

The increasing presence of microplastics (MPs) in wastewater sludge raises concerns about their potential interference with anaerobic digestion (AD), a key process for energy recovery and sludge stabilization. This study investigated the impact of three common MPs, polystyrene (PS), polyethylene terephthalate (PET), and high-density polyethylene (HDPE), on the anaerobic degradation of a synthetic, rapidly biodegradable substrate under controlled batch conditions with the biomass from an anaerobic digester as inoculum. Biogas production, intermediate metabolic parameters, and microbial community dynamics were comprehensively assessed. The results showed a moderate inhibition of methane yield in the presence of MPs, with HDPE causing the most significant reduction (up to 24%) in biogas generation. PS exhibited the lowest impact, independent of the concentration added (0.5 and 1.0 g·L⁻¹). The microbial community structure demonstrated robustness, with Firmicutes and Bacteroidota maintaining dominance and methanogenic populations largely unaffected, except in the presence of HDPE. Raman spectroscopy indicated that none of the MPs underwent substantial structural degradation, but the subtle spectral shifts—particularly in PET—suggested the initial stages of physicochemical alteration. These findings offer new insights into the short-term resilience and adaptability of anaerobic microbiomes in the presence of MPs while revealing potential signals of process disruption. Full article

The increasing demand for sustainable materials has driven interest in biocomposites that incorporate low-value agricultural residues to offset the use of virgin plastics. The study investigated the production of blend pellets from raw and torrefied almond shells and post-consumer plastic waste as a potential feedstock for biocomposite and biofuels applications. Almond shells were torrefied in a lab-scale fixed-bed reactor at 300 °C for 30 min prior to the pelleting tests. High-density polyethylene (HDPE) and polypropylene (PP) wastes were size-reduced in a Crumbler (rotary shear grinder) fitted with a 2 mm head and a 2 mm screen to remove the fines. A portion of the crumbled HDPE, and torrefied almond shells were further ground in a Wiley mill fitted with 2 and 1 mm screens for flat die pelleting tests. The flat die pellet mill used for testing had a 6 mm die and a length-to-diameter (L/D) ratio of 2.0. The blend ratio consisted of 30% torrefied almond shells and 70% HDPE, with a 10% starch binder. The measured pellet properties include unit, bulk and tap densities, durability, and expansion ratio. The bulk density of the blend pellets ranged from 360 to 410 kg/m³, and durability ranged from 80% to 88%. The blend pellet unit density ranged from 830 to 880 kg/m³. The blend pellets produced using crumbled HDPE, PP and raw and torrefied almond shells in a ring die pilot-scale pellet mill with an L/D ratio of 6 and steam conditioning exhibit similar densities to those of HDPE pellets produced using a flat die pellet mill, albeit with lower durability. The study indicated that a smaller grind size and preheating the blend before pelleting produce blend pellets with higher density and greater durability. Full article

The accumulation of plastic waste represents a significant environmental challenge worldwide, and its reuse in construction materials offers a sustainable management alternative. This study investigates the use of recycled high-density polyethylene (HDPE) and polypropylene (PP) granules as partial volumetric replacements (10%, 20%, and 30%) for limestone aggregate in mortar mixtures. A total of seven mixtures were produced and evaluated in terms of flow value, unit weight, water absorption, porosity, compressive strength, flexural strength, and capillary water absorption. In comparison to the control mixture, it was found that the use of plastic aggregate improved the workability. It was found that the flexural and compressive strengths of mixtures decrease when plastic aggregate is added. Additionally, it was understood that utilization of plastic aggregate in mixtures caused an increase in water absorption rate and porosity values. HDPE and PP plastic aggregates increased flow by 9% to 13% and reduced unit weight by 15 to 15.3%, while compressive and flexural strengths decreased by 48 to 30% and 46 to 54%, respectively. The optimum replacement level was 10% for both HDPE and PP mixtures. Full article

Protection of water resources is an urgent priority in the context of increasing freshwater scarcity. Sustainable and circular water management focuses on reducing water consumption as well as measures to recover and reuse alternative water sources. This study assesses the life cycle assessment (LCA) of a domestic rainwater harvesting (DRWH) system located in Poland. Moreover, the most significant environmental contributors and the quantification of each component’s role in the system’s overall footprint are assessed. The study used the OpenLCA tool and assumes 1 m³ of treated water as the functional unit. Findings reveal a highly concentrated impact distribution for the components. The high-density polyethylene (HDPE) tank dominates, which represents 78.69% of total environmental impacts and leads in 18 of the 18 categories examined. Its influence is greatest in non-renewable fossil energy use, where it accounts for 92% of the impact, and in photochemical oxidant formation, with contributions exceeding 90%. The data quality assessment (DQA) of the system resulted in uncertain temporal and geographical correlation. Further Monte Carlo simulations confirmed the uncertainties regarding climate change and energy-related impact categories. The methodology aligns with ISO 14044 guidelines, providing a foundation for evidence-based environmental management decisions. Full article

The long-term creep performance of geosynthetics is crucial for the safe design of reinforced-soil structures. Previous studies have not sufficiently clarified the long-term creep behavior of high-density polyethylene (HDPE) geogrids or the influence of different failure criteria. Therefore, further research is needed to validate creep reduction factors’ (RF_CR) estimation and the applicability of the stepped isothermal method (SIM). In this study, the creep behavior of HDPE geogrids was examined using both conventional creep tests and SIM, conducted in accordance with ISO 13431 and ASTM D6992. Master curves were generated under load levels representing 40–60% of the ultimate tensile strength. The SIM results matched with the conventional tests in the early stage but exhibited higher creep strains beyond 1000 h, primarily due to the thermal sensitivity of HDPE. RF_CR values were determined using two design criteria, namely, 20% creep strain and creep rupture. For a 100-year design life, the RF_CR values based on a 20% creep strain were determined to be 3.04 and 2.43 based on the combined data and block-shift analysis, respectively, whereas the rupture criterion yielded a lower value of 2.30. These findings demonstrate that the 20% strain limit provides a more conservative and reliable criterion for estimating the long-term design strength. This study confirms the applicability of SIM for accelerated creep evaluation and provides practical guidance for the selection of RF_CR values in reinforced-soil design. Full article

This study examines the tribological and micro-mechanical behavior of high-density polyethylene (HDPE), which has been advanced to the class of advanced polymers through electron beam irradiation (irradiation dose of 33 kGy to 198 kGy). The tribological and mechanical behaviors were analyzed at the surface and at various depths beneath the surface to verify the extent of radiation effects across the entire cross-section of the specimen. Changes in tribological and mechanical behavior are closely related to changes in the structure of the material, mainly changes in crystallinity. As this study shows, 99 kGy appears to be the ideal radiation dose in terms of the properties examined. An increase in absorbed radiation dose leads to a deterioration of tribological and mechanical performance, which correlates with material degradation and a concomitant reduction in crystallinity. The improvement in the properties examined between unirradiated and irradiated HDPE at a dose of 99 kGy is 18% for mechanical behaviors and 8% for tribological behaviors on the surface of the sample. A maximum deviation of 39% was identified between the surface and the center of the material. There was also a change in crystallinity of up to 12%. These modifications result in enhanced surface wear resistance and increased overall stiffness, effectively shifting commodity-grade HDPE toward the performance domain of advanced polymers with only minimal cost implications. Full article

As the principal load-bearing components of cable-supported bridges, cables are critical to structural safety, and their durability is strongly governed by the integrity of high-density polyethylene (HDPE) sheaths. Prolonged exposure to ultraviolet (UV) radiation and chloride-rich environments can significantly degrade the mechanical performance of HDPE sheaths. To clarify the degradation behavior, HDPE sheaths were pre-exposed to UV alone, chloride alone, or a sequential two-stage UV–chloride protocol (with a single switch). Subsequently, uniaxial tensile tests were performed at different loading temperatures. The yield strength and O–A secant modulus decreased monotonically with increasing pre-exposure duration. A pronounced sequence effect was observed, with UV pre-exposure followed by chloride exposure causing greater deterioration than the reverse order. Under UV alone, the maximum reductions in yield strength and O–A secant modulus were 19.81% and 46.21%, respectively; under chloride alone, they were 10.97% and 22.00%; and under the sequential UV–chloride exposure, they were 31.97% and 26.24%. Moreover, the tensile response showed strong temperature sensitivity: under otherwise identical pre-exposure conditions, the yield strength measured at 60 °C was 64.89% lower than that measured at −10 °C, representing the maximum reduction within the investigated temperature range. Full article

This study investigates the influence of cooling rates on the structural evolution and mechanical properties of ultra-high-molecular-weight polyethylene/high-density polyethylene fibers by systematically varying cooling media from ambient air (f1) to room-temperature water (f5). A significant structural inversion was observed between the as-spun and drawn fiber stages: while slow cooling (f1) promotes thermodynamic crystallization to form large, stable grains and maximum initial crystallinity (54%), rapid quenching (f5) effectively “freezes” the molecular chains in a low-crystallinity, highly orientable precursor state by suppressing thermal relaxation. During subsequent hot-drawing, the quenched samples (f5) exhibited a superior response to tensile stress, achieving the highest maximum draw ratio due to reduced crystalline obstacles and enhanced chain mobility. This enables efficient stress-induced crystallization, leading to near-perfect crystal orientation (f_c > 0.95) and a dense microfibrillar framework. Consequently, the fiber performance trends reversed, with f5 achieving peak tensile strength (1.33 GPa) and modulus, whereas f1 remained limited by its rigid thermal history. These findings highlight that rapid quenching is essential for developing high-performance fibers by preserving a precursor structure that maximizes the potential of stress-induced crystallization. Full article

This study aimed to characterize the impacts of high density polyethylene (HDPE) and polyethylene terephthalate (PET) on the co-pyrolysis mechanisms and products of municipal sludge (MS) by using thermogravimetric analysis. Compared with PET, the addition of 30% HDPE maximized the comprehensive pyrolysis index of MS from 7.68 to 20.37 × 10⁻⁶ %³/(min²·°C³). Between 350 and 500 °C, the facilitatory effect of the MS-PET co-pyrolysis was stronger than that of HDPE-MS. Between 500 and 1000 °C, the addition of PET/HDPE exerted an inhibitory effect on the MS pyrolysis. Prior to adding either plastic, the two main pyrolysis stages of MS followed distinct reaction models: a first-order reaction between 162.6 and 431.5 °C and a sixth-order (F6) reaction between 431.5 and 735.8 °C. However, the addition of HDPE transformed the high-temperature stage kinetics from the F6 model to nucleation growth. Throughout the (co-)pyrolysis process, the decomposition of alcohols, aliphatic hydrocarbons, acids, and aromatic substances occurred, accompanied by the formation of new aromatic compounds. The addition of HDPE further disrupted the char structure, while the addition of PET formed a barrier within the co-pyrolytic char, hindering the release of volatiles. Multi-objective optimization revealed that both HDPE and PET yielded superior energy performance compared with the MS pyrolysis. Increasing HDPE content further enhanced energetic optimization, with temperature and plastic type identified as the primary factors governing energy output at a heating rate of 10 °C/min. This study introduces a novel co-pyrolytic approach for tightening the co-circularity of both MS and PET/HDPE. Full article

Addressing the growing need for sustainable innovation in PVC materials, this study presents an illustrative framework that develops and demonstrates an ontological system that integrates lifecycle simulation using Granta EduPack, systematic literature analysis (including bibliometric, thematic, and content analytics) of peer-reviewed publications, and Protégé-based semantic reasoning, and their combination, in a holistic manner. Material and use-phase data for PVC, HDPE, PP, PET, and FRP cooling-tower components were sourced from ANSYS Granta EduPack Level-3 Polymer Sustainability 2023 R2 Version; 23.2.1, and a systematic analysis of the literature was then encoded as ontology classes, properties, and individuals following the Seven-Step ontology development method. Eco-audit simulations, standardised to a functional unit of 1 kg cooling tower fill material, reveal that the use phase dominates environmental impact (67 MJ primary energy, ~80% of total lifecycle), while material production and end-of-life recycling contribute ~15% and credits of ~900 MJ and 28 kg CO₂ via recycling offsets. Ontology reasoning with corrected SWRL rules and SPARQL queries classifies VirginPVCRef and PVC10ES as strong structural materials (tensile strength ≥ 40 MPa), identifies PVCRH40 as high-moisture-risk (water absorption > 0.10 g/g), and ranks hydro-thermal dechlorination (recyclability 0.90) over mechanical recycling (0.55). A systematic analysis of 40 Scopus-indexed publications (2015–2025) highlighted key themes in recycling technologies, LCA emissions, additive toxicity, ontology frameworks, machine learning integration, circular economy policy, and cooling-tower applications. Demonstrated via a simulation-based cooling-tower case study, hybrid PVC-FRP designs yield the highest justified Material Sustainability Performance Index (MSPI), outperforming PVC-only and FRP-only alternatives. This framework provides a conceptual decision-support tool for exploring PVC material optimisation, illustrating pathways to enhancing circularity and environmental responsibility in industrial applications. The proposed framework is, therefore, not intended as a validated decision-support tool, nor does it claim analytical optimisation or predictive performance but rather serves as a method of illustration that shows how domain knowledge can be formally structured using ontology principles linked to simulation representations, and that was examined for internal logical consistency. Full article

This study investigates the processability and performance limits of high-density polyethylene (HDPE) recovered from mixed polyolefin waste under realistic mechanical recycling conditions. The waste stream was processed by extrusion and injection molding, with parameters actively adapted. ATR-FTIR and DSC analysis confirmed HDPE as the matrix, contaminated with minor fractions of polypropylene (PP), PET, and polyurethane (PU). The reprocessed material exhibited a single melting peak at 132 °C and a melt flow rate (MFR) of 9.9 ± 0.6 g 10 min⁻¹, indicative of moderate degradation. Mechanical testing revealed reduced tensile strength and elongation at break compared to virgin HDPE, indicating compositional heterogeneity and poor interfacial adhesion. Field emission scanning electron microscopy (FESEM) revealed dispersed inclusions and microvoids acting as stress concentrators, consistent with reduced ductility. Crucially, progressive reduction of back pressure during processing optimization was essential for stabilizing melt flow and minimizing shear-induced degradation. This adjustment enabled consistent mold filling despite the material’s variability. The results demonstrate that mixed HDPE waste can be successfully valorized for non-structural applications such as plastic lumber or pallets, providing a sustainable pathway for recycling heterogeneous streams without costly pre-treatment or compatibilization. Full article

To enhance the anti-ultraviolet aging capacity of high-density polyethylene (HDPE) monofilaments for fishery applications, this study prepared pure HDPE and a blend of HDPE/UHMWPE (80/20 wt%) monofilaments via a melt spinning process. Systematic ultraviolet accelerated-aging experiments were conducted on these monofilaments for durations ranging from 0 to 600 h. The evolution of material properties was assessed using various quantitative characterization methods, including scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and mechanical tensile testing. The results indicate that after 600 h of aging, the density and size of surface cracks in the blended monofilament are significantly lower than those observed in pure HDPE. The carbonyl index (CI) and unsaturated index (UI) of the blend are approximately 55% and 40% of those of pure HDPE, respectively. Additionally, the initial thermal decomposition temperature (T_5%), as determined by TGA, decreases by only 13 °C, which is a considerably lower reduction than the 28 °C observed for pure HDPE. Furthermore, the attenuation rates of breaking strength and elongation at break for the blended monofilament are 43.7% and 54.0%, respectively, which are markedly lower than the corresponding rates of 54.5% and 66.0% for pure HDPE. Research indicates that the observed performance improvement is closely linked to the synergistic mechanism of the “physical hindration–structural skeleton” formed by the UHMWPE phase. Furthermore, this mechanism may interact synergistically with the antioxidants present in the system, thereby altering the material’s failure mode from “rapid brittle failure” to “progressive slow deterioration.” This study offers novel modification strategies and experimental references for developing high-performance, UV-resistant polyolefin materials suitable for fishery applications. Full article

This study presents the design and performance evaluation of an advanced inorganic filler system composed of calcite (CaCO₃) and talc (Mg₃Si₄O₁₀(OH)₂), modified with a polyolefin elastomer (POE), and integrated into a high-density polyethylene (HDPE) carrier resin with process additives such as erucamide, montan wax, pe wax, and PIB. The composite was developed to improve the structural integrity and longevity of HDPE double-wall corrugated pipes. Comprehensive characterization of the filler was performed using TGA–DSC, FTIR, SEM–EDX, XRD, and XRF analyses, confirming the presence of every individual component and homogeneous dispersion in the compound. Pilot-scale extrusion pipe trials confirmed uniform filler dispersion when evaluated by SEM-EDX analysis. The filler addition increased both the density and MFI values up to 1.03 g/cm³ and 1.5 g/10 min, respectively, while test results indicated oxidation induction times (OIT) reaching up to 40 min. The developed filler-added pipes demonstrated a significantly higher ring stiffness value of 12.20 kN/m², exceeding the minimum requirement of 8 kN/m² specified for the SN8 class pipes. The POE effectively attenuated rigidity and brittleness typically induced by mineral fillers, yielding this superior stiffness while maintaining adequate ring flexibility. These findings highlight the potential of this tailored filler system to advance the production of lightweight, mechanically robust corrugated piping solutions for demanding infrastructure applications. Full article

Concrete production contributes approximately 4–8% of global cardon dioxide emissions, largely due to Portland cement. Incorporating municipal solid waste (MSW) into concrete offers a pathway to reduce cement demand while supporting circular economy objectives. This study evaluates the mechanical performance, environmental impacts, and optimization potential of concrete incorporating three MSW-derived materials: cardboard kraft fibers (KFs), recycled high-density polyethylene (HDPE), and textile fibers. A maximum 10% cement replacement strategy was adopted. Compressive strength was assessed at 7, 14, and 28 days, and a cradle-to-gate life cycle assessment (LCA) was conducted using OpenLCA to quantify global warming potential (GWP100) and other midpoint impacts. A surrogate-based optimization implemented using Non-dominated Sorting Genetic Algorithm II (NSGA-II) was applied to minimize cost and GWP while enforcing compressive strength as a feasibility constraint. The results show that fiber-based wastes significantly reduce embodied carbon, with KF achieving the largest GWP reduction (19%) and textile waste achieving moderate reductions (10%) relative to the control. HDPE-modified concrete exhibited near-control mechanical performance but increased GWP and fossil depletion due to polymer processing burdens. The optimization results revealed well-defined Pareto trade-offs for KF and textile concretes, identifying clear compromise solutions between cost and emissions, while HDPE was consistently dominated. Overall, textile waste emerged as the most balanced option, offering favorable environmental gains with minimal cost and acceptable mechanical performance. The integrated LCA optimization framework demonstrates a robust approach for evaluating MSW-derived concrete and supports evidence-based decision-making toward low-carbon, circular construction materials. Full article

Wastewater treatment systems retain a significant proportion of microplastics (MPs) derived from domestic and industrial discharges; however, these emerging pollutants are not completely removed and tend to accumulate in the biological sludge generated during the treatment process. In this study, three biological-type wastewater treatment plants (WWTPs) located in Acapulco, Mexico, were analyzed. The concentrations of MPs in the biological sludge ranged from 830 to 9300 particles/L. Using differential scanning calorimetry (DSC), the predominant polymers identified were high-density polyethylene (HDPE), polyethylene terephthalate (PET), and polypropylene (PP). It was estimated that the monthly concentrations of MPs in the sludge could reach up to 5.36 × 10⁹ particles/L, while the annual concentrations could rise to 3.55 × 10¹⁰ particles/L. These findings highlight the urgent need to review and update the regulatory framework related to the use of residual sludge for agricultural purposes, since high loads of MPs and their transfer pose a potential risk to soil quality, ecosystem health, and long-term environmental sustainability. Full article