High-density Polyethylene Research Articles

Particle-resolved simulation of the pyrolysis process of a single plastic particle

Particle-resolved simulations have been performed to study the pyrolysis process of a high-density polyethylene (HDPE) particle in an inert hot nitrogen flow. The simulations resolve the velocity and temperature boundary layers around the particle, as well as the gradients of temperature and concentration within the particle. The objective of this work is to gain an in-depth understanding of the effect of particle morphology-specifically, the particle size and shape-on the interplay between heat transfer and pyrolysis progress, as well as to assess the applicable particle size when using the Lagrangian concept for simulating plastic pyrolysis. In all simulation cases, the pyrolysis reaction is initiated at the external surface of the particle, where the particle is heated the fastest. The reaction front propagates inward toward the core of the particle until it is fully pyrolyzed. For particle diameters larger than 4 mm, distinct temperature gradients within the particle can be detected, leading to a temperature difference of more than 10 K between the core and the external surface of the plastic particle. In this case, the Lagrangian simulations yield a considerably slower conversion compared with the particle-resolved simulations. Moreover, the cylindrical particle in longitudinal flow has been found to be pyrolyzed more slowly compared with the spherical and shell-shaped particles, which is attributed to the enhanced heat transfer conditions for the cylindrical particle. The results reveal the importance of considering particle morphology when modeling plastic pyrolysis. In addition, the Lagrangian approach, which assumes particle homogeneity, is only applicable for particle diameters smaller than 2 mm when modeling plastic pyrolysis.

The role of habitat preference and feeding strategy on exposure to microplastic pollution in freshwater fish species.

Microplastic (MP) pollution has been observed in a variety of ecosystems, but there is a limited number of studies on reservoir ecosystems. The aim of this study was to determine the levels of MP contamination in sediment, water and commercially important fish species (Cyprinus carpio, Perca fluviatilis, Atherina boyeri and Sander lucioperca) collected from the Yamula Reservoir in Türkiye. Water samples were collected at five stations. Four sediment samples were collected from the lake. As sediments from the lake represent a vital element of the lake ecosystem, they function as a historical archive that reflects alterations in land use and the characteristics of the lake over time. The average amounts of MPs observed in sediment and water samples were 0.12 MP/g and 0.58 MP/m3 respectively. The digestive systems of 30 individuals of each fish species were examined. The highest amount of MP was observed for C. carpio (6 ± 5.9 MP/individual), while the lowest amount of MP was observed for A. boyeri (1.8 ± 1.7 MP/individual). MP abundance in S. lucioperca and P. fluviatilis was 2 ± 2.8 and 4.6 ± 6.3 MP per individual. The most commonly observed polymer types were polypropylene (67%), polyvinyl alcohol (13%), polyethylene resin (13%) and high-density polyethylene (7%). The pollution load indexes determined for each fish species from the highest to the lowest were as follows: 1.83 (C. carpio) 1.6 (S. lucioperca) 1.05 (P. fluviatilis) and, 1 (A. boyeri). The findings of the study indicate that all sampling stations, including both sediment and water, are contaminated with MPs. Furthermore, the results demonstrate that all examined fish species ingest MPs. Additionally, the results indicate that fish inhabiting a wide range of habitats and consuming diverse diets are more susceptible to MP contamination.

Upcycling of Polyethylene Wastes to Valuable Chemicals over Group VIII Metal-decorated WO3 Nanosheets.

Catalytic cracking of polyolefin wastes into valuable chemicals at mild conditions using non-noble metal catalysts is highly attractive yet challenging. Herein it is reported that 2D tungsten trioxide (2D WO3) nanosheets, after decorating with group VIII metal promoters (i.e., Fe, Co, or Ni), convert high-density polyethylene (HDPE) into alkylaromatics and olefins at low temperature and ambient pressure without using any solvent or hydrogen: 2D Ni/WO3 with abundant Brønsted acidic sites initiates HDPE cracking at a low temperature of 240°C; 2D Fe/WO3 with low energy barrier of cyclization achieves a high HDPE conversion to 84.2% liquid hydrocarbons with a selectivity of 30.9% to aromatics at 300°C. In-situ spectroscopic investigations and supplementary theoretical calculations illustrate that these aromatics are formed through the cyclization of alkene intermediates. These 2D catalysts also display high efficiency in the low-temperature cracking of single-use commercial polyethylene wastes such as packaging bags and bottles. This work has demonstrated the high potential of 2D non-noble metal catalysts in the efficient upcycling of waste polyolefin at mild conditions.

Application of MATLAB and SAS Viya AI models towards the elucidation of potential microplastics in the Neuse River Basin

Microplastics (MPLs) are ubiquitous particles derived from degradation from plastic refuse or directly from anthropogenic sources. These particles are present in aquatic environments with potential toxicology across the biosphere. In order to characterize their presence, the Neuse River basin was selected for sampling. However, like many MPLs, spectroscopic characterization can be sullied by weathering processes that obscure the native spectra. Therefore, to enhance MPL identification, Principal Component Analysis (PCA), K-means Clustering (KMC), MATLAB, and SAS Viya’s machine learning (ML) modules were implemented on the Neuse River basin's samples. 18 unknown samples were recorded with attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy against the controls for PCA and KMC: high-density polyethylene (HDPE), low-density polyethylene (LDPE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), polyethylene terephthalate (PET), and nylon-6 (PA6). Later on, these unknowns were tested against a new set of 900 commercial control samples partitioned by 9 classes for MATLAB and SAS Viya: cellulose acetate (CA), HDPE, LDPE, PP, PS, PVC, PET, polymethyl(methacrylate) (PMMA), and PA6 using µ-FTIR (micro-FTIR) for single-particle discrepancy. Application of MATLAB’s Classification Learner and SAS Viya for Learners software helped aggregate multiple machine learning (ML) models to test for corroboration of predictions with datasets derived from Version 1 (V1), Version 2 (V2), and Version 3 (V3) feature extraction algorithms. Novel feature extractions, based on regressions of discrete data from spectral intensities, in V2 and unique probing of the relationships informing the regressions in V3 showed moderate to moderately high predictor strength, contributing to accuracy increase in V3 according to various predictor strength algorithms in MATLAB. In the test scenario of the strongest version, V3, 63.2% (+ 5.3% from V1) of the models performed very strongly (90% cutoff in accuracy), and 89.5% (+ 0% from V1) of the models performed moderately strongly (80% cutoff in accuracy). The models, coupled with the unsupervised PCA and KMC, indicated microparticle (MP) from Stockinghead Creek in Duplin County, NC; SHR-1b(2), as LDPE. However, the change in corroboration across model types was not significant, according to Kruskal-Wallis (H = 0.555, p = .7577). An ANOVA was performed to see if LDPE incidence was similar across all unknowns, indicating a similar ratio of predictions, excluding NRCP-1 (F = 31.479, p < .0001). While it is unclear if this particle is truly LDPE, the results may suggest that LDPE could be of high presence in the river basin (specifically, PE) when taking into account the predictor set across all versions. Lastly, misclassification was further elucidated for samples “CF-3” and “NRCP-1(2)” which are thought to be extensively-degraded PVC MPLs.

The Characteristics of Resin Waste (RW)/Recycled High-Density Polyethylene (R-HDPE) Blends to Enhanced Pavement

Permeable pavement is characterized by open cell structures that enable the drainage of rainfall and snowmelt, as opposed to the runoff observed on impervious pavements. The structural strength of commercial permeable pavement materials is lower than that of conventional pavements due to inherent permeability and structural distinctions. This research focuses on the fabrication of samples using a combination of Resin Waste (RW) and reinforced Recycled High-Density Polyethylene (R-HDPE) in varying ratios of RW (30%, 40%, 50%, 60% and 70% wt/wt). The fabrication process involves a 3-hour heating process at 200°C in a furnace, followed by a 24-hour cure at room temperature. Physical and mechanical properties of the RW/R-HDPE Blends were examined, revealing that the 60% R-HDPE ratio resulted in the lowest density (4.523 g/cm3) and porosity (0.246%). SEM images displayed fewer voids, indicating effective filler dispersion and resin matrix interaction at the 60% resin waste ratio. Tensile strength and stiffness elasticity were maximized at 60% wt/wt of R-HDPE, reaching 3.36 MPa, while the bending strength peaked at 1.1 MPa at the same ratio. The 60% RW/R-HDPE ratio recorded the highest impact strength (26.25 kJ/m2) and energy absorption (1.69 J), showcasing the sample's ability to absorb impact energy through controlled failure mechanisms. In conclusion, the 60% wt/wt RW/R-HDPE Blends exhibit promising potential for enhancing the properties of permeable pavement, particularly in road applications, due to its superior bending and tensile strength.

Application of aluminum diethyl hypophosphite, iron-based metal organic framework-NH2-MIL-53(Fe), and expandable graphite complexes as flame retardants for high-density polyethylene

High-density polyethylene (HDPE) composites are made by melt blending HDPE with MIL-53(Fe), amino-functionalized NH2-MIL-53(Fe), aluminum diethyl hypophosphite (ADP), and expandable graphite (EG). The experimental disclosed showed that the aminated NH2-MIL-53(Fe) could improve residual carbon quality and exert a better flame retardant effect than MIL-53(Fe). When 25 wt% of EG/ADP/NH2-MIL-53(Fe) was added and the ratio of EG to ADP/ NH2-MIL-53(Fe) was 1:1, HDPE/EG/ADP/NH2-MIL-53(Fe) composites could achieve a limiting oxygen index of 31.1 %, which passed UL-94 testing and was rated V-0. This results in a considerable improvement in flame retardant efficiency as the peak heat release rate was lowered by 83.4 % and the total heat release was reduced by 35.8 % when compared to the pure HDPE material. Therefore, NH2-MIL-53(Fe)/ADP/EG synergistic flame retardancy can lead to high flame retardancy efficiency in HDPE. This provided a new potential direction for the preparation of highly efficient flame retardants.

Co-pyrolysis of corn stalk and high-density polyethylene with emphasis on the fibrous tissue difference on thermal behavior and kinetics

The thermal properties of various corn stalk tissues (including stem, husk, ear, cob, and leaf), high-density polyethylene (HDPE), and their blends were investigated using thermogravimetric analysis under a nitrogen atmosphere. The results indicate that the thermal decomposition process of corn stalk tissue/HDPE mixtures is delayed with an increasing heating rate, regardless of the tissue type. Besides, the structural differences among various corn stalk tissues significantly influence their thermal behavior, product distribution, and co-pyrolysis kinetics with HDPE. Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) was conducted to analyze the pyrolytic products of the blends with different corn stalk tissues, revealing that corn cob/HDPE blends produce a higher yield of valuable chemicals, such as the furan derivates and aromatic hydrocarbons. Kinetic analysis was further performed using Kissinger-Akahira-Sunose (KAS) and Flynn-Wall-Ozawa (FWO) methods to determine the activation energy for the reactions occurring during co-pyrolysis. The co-pyrolysis of corn cob/HDPE blend requires the least activation energy (149.3 kJ/mol) among five blends, which was ascribed to the high hemicellulose content in corn cob. Moreover, machine learning algorithms, including random forest (RF) and gradient boost regression tree (GBRT), were applied to predict mass loss in the corn fiber/HDPE blends, which showed RF possessed superior accuracy over GBRT. These findings suggest that isolating plant tissues during the feedstock pre-management could enhance the valorization performance of lignocellulose-waste plastic co-pyrolysis.

Characterization of high-performance composite bricks fabricated from recycled HDPE/PS blends and brick powder

Abstract This study explores the feasibility and benefits of utilizing plastic waste in the production of construction materials, specifically composite bricks. The escalating accumulation of plastic waste poses significant environmental challenges, which necessitates innovative approaches for recycling and re-utilization to mitigate pollution and reduce landfill use. Our research focuses on the synthesis of bricks by incorporating high-density polyethylene (HDPE) and polystyrene (PS) with sand brick powder, utilizing a compatibilizer (SBS-g-MA) to enhance interfacial adhesion and mechanical integrity. The experimental methodology involved the preparation of composite materials through melt mixing, followed by molding to form brick specimens. These were analyzed for their mechanical properties, including tensile strength, Young’s modulus, and elongation at break, as well as thermal properties such as degradation temperature and crystallization behavior. Results showed that the inclusion of sand brick powder significantly enhances the thermal stability of the composites, as evidenced by the higher degradation temperatures observed. Specifically, the degradation temperature increased from 300.59 °C in pure HDPE/PS blends to 420.39 °C in composites with 7% brick powder, suggesting the formation of a protective barrier against thermal decomposition. Moreover, mechanical testing revealed that composites with up to 7% brick powder exhibited improved tensile strength and Young’s modulus compared to pure polymer blends.

Conversion of tomato waste into a poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate) by a mixed microbial community

Tomato waste (TW) originating from tomato processing is produced in large quantities and has a low cost, presenting as an interesting feedstock for biotechnological valorization into value-added bioproducts. This study explored the utilization of TW as feedstock to produce polyhydroxyalkanoates (PHA) by a mixed microbial community. The bioprocess encompassed acidogenic fermentation of TW with a maximum yield of 0.22 ± 0.05 gFP/gVS. A maximum PHA content of 66.8 ± 11.0wt.% was reached in the accumulation assays, with a yield of 0.75 ± 0.10 CmmolPHA/CmmolFP. The biopolymer was composed of 3-hydroxybutyrate (3HB), hydroxyvalerate (3HV) and hydroxyhexanoate (3HHx) with an average composition of 82:11:7 (3HB:3HV:3HHx, molar basis) and similar mechanical and thermal properties to other 3HB:3HV:3HHx terpolymers and comparable to high density polyethylene and polypropylene. These findings demonstrated that TW can be used to efficiently produce a PHA terpolymer with properties that render it suitable for replacing petrochemical-derived plastics.

3D-printed polycaprolactone/collagen/alginate scaffold incorporating phlorotannin for bone tissue regeneration: Assessment of sub-chronic toxicity

The development of effective scaffolds for bone regeneration is crucial given the increasing demand for innovative solutions to address bone defects and enhance healing process. In this study, a polycaprolactone/fish collagen/alginate (P/FC/A) 3D scaffold incorporating phlorotannin was developed to promote bone tissue regeneration. While the efficacy of the P/FC/A scaffold has been demonstrated through in vitro and in vivo experiments, its sub-chronic toxicity in animal models remains understudied, raising concerns regarding its safety in clinical application. Therefore, this study assessed the sub-chronic toxicity of the P/FC/A scaffold over 12 week using a New Zealand White rabbit model. Our results indicate no significant adverse effects in the group exposed to the P/FC/A scaffold compared with the negative control group implanted with a high-density polyethylene scaffold. These findings underscore the non-toxicity and safety profile of the P/FC/A scaffold, further supporting its potential suitability for clinical use in bone regeneration.

Asphalt Binder Modification with High-Density Polyethylene Polymer and Low-Density Polyethylene Polymer – Efficiency of Conducting Semi-Wet Mixing Process

Asphalt Binder Modification with High-Density Polyethylene Polymer and Low-Density Polyethylene Polymer – Efficiency of Conducting Semi-Wet Mixing Process

Enhanced carbon fiber interface with thermoplastics via nanostructure surface modification: failure, morphology and wettability analysis

Improving the fiber-matrix adhesion in thermoplastic composites remains a significant challenge due to the lack of chemical bonding between thermoplastics and common reinforcing fibers. This study investigates the effectiveness of carbon fibers enhanced with nanostructure surface modification for strengthening the interfacial adhesion to thermoplastic matrices. The fiber surface was modified with graphene nanoplatelets (GNP) through the facile coating method, and the apparent interfacial shear strength (IFSS) was determined by the single-fiber pullout test. GNP-coated fiber improved IFSS by 74% with neat high-density polyethylene (HDPE-Neat) and 28% with maleic anhydride-grafted HDPE (HDPE-8MA), while reduced by 27% with polyamide 6 (PA6) due to different failure mechanisms. Morphology, chemical, and wettability analysis were conducted on the nano-enhanced carbon fibers to quantitatively elucidate these findings on micro/nanoscale, combining machine learning-based image segmentation, X-ray photoelectron spectroscopy (XPS), and contact-angle measurements of intermittent beading on fibers.

Optimization in Extrusion Process for Polypropylene and High-Density Polyethylene Pellets in Additive Manufacturing of 3D Printing Filament

The increasing demand for sustainable and cost-effective materials in additive manufacturing has driven research into optimizing the extrusion process for creating 3D printing filament from Polypropylene (PP) and High-Density Polyethylene (HDPE) pellets. This study explores the critical parameters in the extrusion process, including temperature, and screw speed, to enhance the quality and consistency of the resulting filament. Through a series of controlled experiments, we analyze the effects of these parameters on the filament’s diameter, mechanical properties, and printability. Our findings demonstrate that by optimizing these variables, it is possible to produce high-quality 3D printing filament with excellent mechanical strength and dimensional accuracy, meeting industry standards. This research not only contributes to the broader adoption of PP and HDPE in 3D printing but also supports the development of more sustainable manufacturing practices by utilizing recyclable materials.

Experimental Analysis of Dynamic Vibrations in Rails by Using Different Types of Vibration Absorption Pads

Railway pads are a type of component that is used in railway construction and maintenance. They are typically made of rubber or similar material and are placed between the railway sleeper and the rail itself. Railway pads provide a layer of cushioning and insulation between the rail and the sleeper, which helps to reduce noise and vibration from passing trains. Railway pads can also help extend the rail's life by reducing the wear and tear caused by constant friction between the rail and sleeper. They are especially useful in areas where noise pollution is a concern, such as residential areas or near hospitals and schools. Several types of railway pads are available, including continuous, discrete, and ribbed designs. The specific type of pad used will depend on factors such as the type of rail being used, the expected loads and speeds of passing trains, and the requirements of the railway system. Overall, railway pads are an important component in the construction and maintenance of railway systems, helping to reduce noise and vibration while also prolonging the life of the rail and other components. In this paper, we are testing three types of vibration rubber pads i.e., Ethylene Propylene Diene Monomer (EPDM), High-Density Polyethylene (HDPE), nitrile and comparing three vibration frequencies. The dynamic frequency of welded rails with HDPE pads has having 1190 Hz mean value. The dynamic frequency of rail tracks with single- and double-layer EPDM pads their mean values are 499 Hz and 335 Hz respectively. The experimental values clearly show that single- and double-layer EPDM pad dynamic frequencies are reduced by up to 58% and 71%, respectively, over the HDPE pad.

Effects of microplastics on the physiology of living organisms on the example of laboratory reared bloodsucking mosquitoes Aedes aegypti L.

AbstractThe presence of environmental microplastics (MPs) poses a significant threat to terrestrial and aquatic animals, including insects such as blood‐sucking mosquitoes. The paper reports on the laboratory study of the effect of three different types of MPs, including fragmented high‐density polyethylene (HDPE), polypropylene (PP) and polystyrene (PS), on the viability, innate immune responses, activity of detoxifying enzymes and malondialdehyde (MDA) concentration in Aedes aegypti (Linnaeus, 1762). The results showed that dietary administration of microfragments of PP, PS and HDPE at low concentrations (4 mg/L) had no effect on the survival rate of mosquito larvae, but was observed to suppress the larval immune response. The addition of MPs to the diet resulted in a significant suppression of phenoloxidase activity compared to the control. A decrease in the activity of the detoxifying enzymes glutathione‐S‐transferase and non‐specific esterase was observed. Dietary administration of MPs did not cause any significant change in alkaline proteolytic enzyme activity in larvae compared to the control. However, we observed a twofold increase in the activity of acid proteolytic enzymes in all experiments compared to the control (p &lt; 0.05). MDA levels in larval homogenates remained unchanged, while lysozyme‐like activity showed a slight decrease compared to the control. The observed processes may be a consequence of intestinal obstruction by MPs, which may cause microtraumas to intestinal tissues and changes in the structure and composition of the microbiota. These changes may have a profound effect on the resistance of mosquito larvae to insecticides and pathogens.

Microplastics in Morocco's most consumed fisheries: Chemical characterization, ecological traits, and implications for human health

The pervasive presence of microplastics (MPs) in the environment is well established, yet many critical questions remain about their distribution and potential impacts on both ecological and human health. To assess the risks that MPs pose, especially through marine ecosystems and human consumption, monitoring their ingestion by fish in natural environments is essential. This study investigated the contamination of 12 fish species, the most commonly consumed in Morocco, collected from the Atlantic Ocean off the Moroccan coast. Analysis of 240 fish (20 individuals per species) revealed that 100 % of the samples contained microplastics. MPs were detected in the gills, gonads, and gastrointestinal tracts of all 12 species. The average abundance of microplastics per fish ranged from 20.6 to 133.2 MPs, with the forms identified as fragments (60 %), fibers (30 %), films (8 %), and pellets and foams (1 %). Additionally, omnivorous and demersal species presented the highest levels of MP contamination. Infrared spectroscopy (ATR-FTIR) analysis identified seven polymers, with high-density polyethylene (34 %), polyethylene terephthalate (30 %), and polypropylene (17.5 %) being the most prevalent. The microplastics were predominantly dark or light in color, with a notable presence of red and blue particles. Fish ingest various sizes of microplastics, primarily particles smaller than 1 mm. Scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM/EDX) revealed that most MPs exhibited visible signs of weathering and contained inorganic components on their surfaces. The potential risk of MPs to fish, as assessed by the polymer hazard index (PHI), was categorized as level V, indicating that MPs may pose significant risks to human health. The highest estimated daily intake (EDI) of microplastics was found in children (1620 MPs/year), whereas the lowest intake was estimated in women (350 MPs/year) and men (337 MPs/year). Given the widespread presence of microplastics in commonly consumed fish species in Morocco, there is an urgent need for regulatory measures to ensure the safety of fisheries, both for domestic consumption and export. Policymakers should consider the development of guidelines for acceptable levels of microplastic contamination in fish to safeguard public health.

Performance and geocell-soil interaction of sand subgrade reinforced with high-density polyethylene, polyester, and polymer-blend geocells: 3D numerical studies

Geocells are widely used in geotechnical and road applications due to their excellent reinforcing properties. However, variations in materials, joint configurations, pocket shapes, and other factors have led to geocell development in a wide range of types. Given this, the present study compared three typical geocells, polymer-blend geocells (PBGs), high-density polyethylene geocells (HDPEGs), and polyester (PETGs) geocells, in terms of pressure-settlement responses and geocell-soil interactions. A numerical model was firstly validated based on a plate loading test, and subsequently extended to analyze the sand subgrade reinforced with three geocell types. The numerical simulations considered geocells with varying weld distances, heights, and pocket-opening shapes. Numerical results showed that the reinforced performance of PETGs (diamond shape) was less sensitive to changes in wall height compared to PBGs and HDPEGs (honeycomb shape). There was little difference in the capacity to reduce soil bed settlement among the three geocell types, unless significant deformation occurs and the soil enters the plastic state. Furthermore, based on the shape of the opening pockets, the three types of geocells were classified into honeycomb-shaped and diamond-shaped categories to investigate geocell-soil interactions. The results of coupling shear stress, confining stress, and normal deformations demonstrated that diamond shapes may generate unreasonable lateral confining resistance, which was the main factor causing the geocell-soil interaction variation between these geocells.

DESAIN KONTRUKSI KAPAL RISET POLBENG BERBAHAN DASAR PLASTIK HDPE

The Polbeng Research Vessel is a ship owned by the Department of Naval Architecture at the Bengkalis State Polytechnic. This vessel is designed using High-Density Polyethylene (HDPE) plastic material. As this is a new material in shipbuilding, further calculations and construction designs are needed in the development of the ship. The construction calculation method used refers to the regulations of Det Norske Veritas (DNV) and the Indonesian Classification Bureau (BKI). The calculation results show that the hull thickness is 10 mm, and all hull construction also uses 10 mm thick plates. The longitudinal strength of the vessel is designed with two side girders located at the bottom of the ship, and it is not equipped with a center girder.

Spatiotemporal dynamics and tidal transport of microplastics in the tropical waters of the Gulf of Thailand

Microplastics (MPs) contamination was investigated along a freshwater-seawater continuum from Chumphon River to the Gulf of Thailand. The vertical distribution in the water column and contamination in green mussels were also studied. MPs were detected in all water samples and sediment samples. Furthermore, MPs were detected in 75% of the green mussels. A higher abundance of MPs was observed in the river system than in the coastal region, indicating that river runoff associated with inland human activities is the major sources of MPs in the coastal regions and cultured green mussels. In the water column, a polymer gradient varying with depth existed where low-density particles decreased from surface to subsurface and sediment while high-density particles exhibited the opposite pattern. Polymers in surface and subsurface water were predominantly composed of low-density polyethylene, polypropylene, and polystyrene particles. However, sediment samples were equally dominated by those mentioned low-density polymers and high-density polyethylene terephthalate, polyamide, rayon, and cotton particles. Furthermore, fibers were the most common shape found in water, sediment, and mussel samples representing 95% of all particles in river water samples and were evenly distributed throughout the water column regardless of density. However, only shorter fiber (mostly <1 mm) was detected in green mussel samples similar to their living environment. Blue, black and white particles dominated all samples. During the tidal cycle, half of the MPs entering the Gulf of Thailand returned to the river during high tide. This backflow predominantly comprised small fibers and low-density polymer MPs. The average daily load of MPs from Chumphon River to the Gulf of Thailand was 3.33 × 102 million items/day.

Ethylene polymerization catalyzed by salicylaldimine Fe or Cr complexes: A DFT study of the metal effects

Salicylaldimine transition metal catalysts are of great interest in the field of ethylene polymerization. Especially, the late transition metal Fe and the middle transition metal Cr complexes exhibited completely different catalytic behaviors. We carried out systematic DFT studies to understand the catalytic mechanism in detail and revealed the intriguing metal effect on ethylene polymerization in propagation, β-hydride elimination, and termination stages. The metal centers would lead to dissociative or associative insertion mechanisms in the chain propagation stage due to their preference for different coordination features. The metal centers also significantly influence the β-hydride elimination, i.e., the late transition metal Fe center much prefers the β-hydride elimination over the middle transition metal Cr, due to the stronger hydride affinity of the Fe center than that of the Cr center. Therefore, salicylaldimine Fe produces a highly branched product, however, salicylaldimine Cr prevents β-hydride elimination producing linear high-density polyethylene. On the other hand, the higher hydride affinity of the Fe center leads to an easy chain transfer, resulting in only oligomer for salicylaldimine Fe systems. In contrast, the chain transfer step is difficult for the Cr center, leading to a successful ethylene polymerization for the salicylaldimine Cr system. These mechanistic insights into the metal center effects well explain the distinct ethylene polymerization behaviors for salicylaldimine Fe and Cr systems, providing helpful guidelines for the design of structure-controllable polymerization catalysts with different metal centers.