Polyethylene Fractions Research Articles

Characterization, processing, and modeling of industrial recycled polyolefins

AbstractThis study aims to establish a systematic approach for characterizing recycled polyolefins of unknown composition, with a specific focus on predicting their performance in film extrusion. We explore various characterization techniques, including differential scanning calorimetry (DSC), Fourier‐transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and rheometry to assess their effectiveness in identifying the polyethylene (PE) fractions within polypropylene (PP) recyclates. By integrating experimental data with modeling techniques, we aim to provide insights into the predictive capabilities of these techniques in determining processing behaviors. The research highlights the superior fidelity of DSC in predicting the relative fraction and type of PE in a PP recyclate. FTIR is also identified as a high‐fidelity approach, albeit requiring application‐specific calibration. TGA, capillary, and oscillatory rheometry are recognized for their ability to distinguish between grades of recycled polyolefins but provide aggregate behaviors rather than detailed constituent information. 3D flow simulation of the cast film extrusion investigated the effect of the viscosity characterization method, non‐isothermal assumption, and process settings but could not fully replicate the observed variations in the cast film processing of two industrial polyolefins with similar melt flow rates and viscosity behaviors. This underscores the practical challenge of predicting processing issues prior to actual processing, necessitating reliance on reliable instrumentation suites and human expertise for diagnosing and remedying variations.Highlights Two industrial recycled polypropylene materials having similar melt flow rates exhibit drastically different cast film processing behaviors. DSC and FTIR provide reasonable approaches for identifying constituent materials. Modeling of the melt viscosities characterized by capillary and parallel plate rheology suggests that viscosity variations relative to the power‐law behavior assumed in the coat hanger die design is a predominant driver of cast film instabilities.

Hydrothermal Co-Liquefaction of Food and Plastic Waste for Biocrude Production

In this study, hydrothermal co-liquefaction of restaurant waste for biocrude production was conducted. The feedstock was resembled using the organic fraction of restaurant waste and low-density polyethylene, polypropylene, polystyrene, and polyethylene terephthalate, four plastic types commonly present in municipal solid waste. Using design of experiment and a face-centered central composite design, three factors (feedstock plastic fraction, temperature, time) were varied at three levels each: feedstock plastic fraction (0, 0.25, 0.5), temperature (290 °C, 330 °C, 370 °C), and reaction time (0 min, 30 min, 60 min). The literature reports positive synergistic interactions in hydrothermal co-liquefaction of biomass and plastics; however, in this work, only negative synergistic interactions could be observed. A reason could be the high thermal stability of produced fatty acids that give little room for interactions with plastics. At the same time, mass might transfer to other product phases.

The role of recycling in UV and thermal ageing of polypropylene block copolymer

While polypropylene (PP) copolymers containing small amounts of polyethylene are greatly used in automotive, packaging, healthcare and pipe applications an understanding on how their properties are affected with recycling and subsequent ageing is limited. This study involves a characterization of a PP block copolymer that has been recycled three times and has been subjected to thermal and UV ageing. The materials have been characterized by Differential Scanning Calorimetry (DSC), Thermogravimetric analysis (TGA), Fourier Transform Infrared Analysis (FTIR) and micro-indentation. Qualitative differences between the non-recycled, recycled and aged materials are discovered and discussed. The results showed that with recycling only the crystallinity of the polyethylene (PE) fraction is affected. Thermal ageing affected the crystallinity of both PP and PE fractions while UV ageing affected only the crystallinity of the PP fraction. The connection between crystallinity, oxidation and hardness changes with recycling and ageing of the material is discussed.

A study on HyFRCC consisting of PE and carbon fiber: Investigation of electrical and fracture properties based on orthogonal design

AbstractHybrid fiber‐reinforced cementitious composites (HyFRCC) consisting of polyethylene (PE) and carbon fiber (CF) have potential for use in advanced composite materials by integrating high mechanical performance with smart functions based on electrical properties. However, an evaluation of the electrical and fracture properties of HyFRCC has not yet been reported. An orthogonal experimental design was used to investigate the effect of the water‐to‐binder (w/b) ratio and volume fraction of PE and carbon fiber on the electrical properties and fracture behavior of HyFRCC in this paper. The results show that the w/b ratio plays a major role in controlling the electrical resistivity of HyFRCC. The larger the amount of hybrid fibers added, the higher the w/b ratio needed. In particular, the PE fiber must not exceed 1.5 vol% to obtain HyFRCC with low electrical resistivity. Carbon fiber has a significant effect on the initial fracture toughness of HyFRCC, while PE fiber determines its unstable fracture toughness. A hybrid fiber system containing 1.0 vol% PE fiber and 0.5 vol% carbon fiber at a w/b ratio of 0.35 was used to reach a compatible electrical property and fracture behavior of HyFRCC. The results of this work provide a novel approach for designing and developing multifunctional cementitious composites, which would be a promising building material for structural strengthening and protection of steel corrosion as well as structural health monitoring.

Investigation of dust ignition sensitivity and co-pyrolysis properties of biomass and plastic waste during resource utilization

This study investigated the sensitivity of dust to ignition and the co-pyrolysis properties of biomass-plastic composites (BPCs) during resource utilization process. A model of co-pyrolysis process for four BPCs was developed using a BP neural network algorithm. The addition of polyethylene increased the biomass powder's tendency to pyrolyze. In the main pyrolysis stage, the lignin and polyethylene fractions significantly impact the synergistic effect more than the other fractions. Corn stalk/polyethylene and rice husk/polyethylene are synergistic during the pyrolysis process making these BPC products relatively promising for utilization. However, more attention should be paid to the dust explosion hazard posed by the BPCs. PE increases the ignition sensitivity of the biomass powder. Compared to other BPCs, minimum ignition temperature (420 °C) and minimum ignition energy (21 mJ) values for rice husk/polyethylene composites are the lowest. The volatile fraction of biomass content is one of the most influential factors affecting the ignition sensitivity of BPCs.

Modifying Effect of Polyethylene Fractions of Different Molecular Weights on the Morphology and Properties of Reactor Polymer Compositions Based on Ultrahigh Molecular Weight Polyethylene

Reactor polymer compositions (RPCs) based on UHMWPE with Mw = 1000 kg mol–1 and low molecular weight HDPE (LMWPE) were studied. Two series of UHMWPE compositions were used to determine the influence of the molecular weight and properties of the LMWPE fraction on the morpho-logy, mechanical and rheological properties of UHMWPE/LMWPE. Сompositions, including from 10 to 80 wt % UHMWPE with Mw = 160 kg mol–1 (PE-160) were obtained in a two-stage process of ethylene polymerization with a metallocene catalyst. They differed in the order of introduction of PE-160 into UHMWPE (PE-160/UHMWPE and UHMWPE/PE-160). Compositions of UHMWPE and LMWPE with Mw = 48 kg mol–1 (PE-48/UHMWPE) with PE-48 content from 6 to 30 wt % were synthesized in a single-stage polymerization of ethylene in the presence of a tandem catalyst. A comparison of the shape and size of particles of nascent polymer products was made using the SEM method. The morphology, tensile, dynamic mechanical and rheological properties of RPC have been studied depending on the method of their preparation, the content of the low molecular weight fraction, its molecular weight and physical and mechanical properties. An increase in the proportion of PE-160 and PE-48 in PE-160/UHMWPE and PE‑48/UHMWPE leads to an increase in RPC crystallinity, tensile modulus and dynamic mechanical modulus with significant deviations from the additivity rule.

Effect of the cross-linking agent on the cross-linking degree and electrical properties of cross-linked polyethylene

To study the effect of a cross-linking agent on the cross-linking degree and electrical properties of cross-linked polyethylene, different mass fractions of cross-linked polyethylene and their electrical properties were investigated. The cross-linking degree of cross-linked polyethylene with different mass fractions was tested by the extraction method. The breakdown field strength was tested by DC voltage breakdown tester, and the space charge injection of two kinds of cross-linked polyethylene was tested by Pulsed Electro-Acoustic. In addition, the resistivity was measured with conductivity test. The obtained results show that the crossing degree and breakdown field are the highest when the mass fraction of DCP is 2.5 wt% and BIPB is 1.5 wt%, which is 89.39% and approximately 310 kv mm−1, respectively, while the cross-linking degree and breakdown field are 88.28% and approximately 340 kv mm−1, respectively. At the same time, when DCP is used as the cross-linking agent, the amount of the same cross-linking agent is greater, which leads to more impurities contained in the material and increased space charge accumulation in the material; thus, the breakdown strength is lower than that of BIPB, and the conductivity is higher with the cross linking agent of DCP.

Identification of microplastic pathways within a typical European urban wastewater system

AbstractIn recent years, thermoextraction/desorption‐gas chromatography/mass spectrometry (TED‐GC/MS) has been developed as a rapid detection method for the determination of microplastics (MP) mass contents in numerous environmentally relevant matrices and, in particular, for the measurement of polymers in water samples without time‐consuming sample preparation. The TED‐GC/MS method was applied to investigate a typical European municipal wastewater system for possible MP masses. Such investigations are important in view of the recent revision of the Urban Wastewater Treatment Directive. Four different representative sampling sites were selected: greywater (domestic wastewater without toilet), combined sewer, and influent and effluent of a wastewater treatment plant (WWTP). All samples were collected by fractional filtration. Filtration was carried out over mesh sizes of 500, 100, 50, and in some cases, 5 µm. Polyethylene (PE), polypropylene (PP), and polystyrene (PS) were detected in all samples, with the PE fraction dominating in all cases. Styrene‐butadiene rubber which serves as an indication of tire abrasion, was only found in the influent of the WWTP. The highest MP mass contents were found in the combined sewer, so MP can become a source of pollution during heavy rain events when the capacity limits of the effluent are reached, and the polluted effluent is released uncontrolled into the environment. Based on the studies, MP retention from the WWTP could be estimated to be approximately 96%. Few trends in polymer type or mass contents were detected within the different fractions of the samples or when comparing samples to each other.

Finite Element Analysis of Hybrid Fiber Reinforced Engineered Cementitious Composite Link Slabs

Finite element (FE) analysis of hybrid fiber reinforced engineered cementitious composite (hybrid-ECC) link slabs is conducted under static loading. First, the material model of hybrid-ECC is developed and validated with standard material test results. Numerical analyses are then conductedto investigate the materials’ effects on the structural performances of link slabs built by using hybrid-ECCs with different volume fractions of polyethylene (PE) and steel (ST) fibers. The FE model of the link slab is validated against test results. Analysis results suggest the hybrid-ECC with volume fractions of 1.25% PE and 0.75% ST fiber is suitable for link slab applications.

Ethylene Polymerization over Supported Vanadium-Magnesium Catalysts with Different Vanadium Content: The Effect of Hydrogen on Molecular Weight Characteristics of the Produced Bimodal Polyethylene

Data are presented on the activity of supported vanadium-magnesium catalysts (VMCs) with different vanadium content in ethylene polymerization and the molecular weight characteristics of the produced polyethylene. The VC1 catalyst, with a very low vanadium content (0.12 wt.%), showed a sixfold higher activity per unit weight of vanadium than the VC2 catalyst with a high-vanadium content (4.0 wt.%). Additionally, the total activity of VC2 (kg PE/g cat·h) was fivefold higher when compared to VC1. The introduction of hydrogen in polymerization leads to a considerable decrease in the activity of both catalysts. The polyethylene obtained in the presence of hydrogen over both catalysts has a broad bimodal molecular weight distribution (MWD) with a distinct shoulder in the high-molecular region (Mw ≥ 106 g/mol). Decomposition of the MWD curves of bimodal polyethylene into two fractions (high- and low-molecular fractions) made it possible to determine for the first time the ratio of the reaction rate constants of chain transfer with hydrogen (KtrH) and polymer chain propagation (Kp) for two groups of the VMC active sites producing low- and high-molecular fractions of bimodal polyethylene.

A Ziegler-type spherical cap model reveals early stage ethylene polymerization growth versus catalyst fragmentation relationships

Polyolefin catalysts are characterized by their hierarchically complex nature, which complicates studies on the interplay between the catalyst and formed polymer phases. Here, the missing link in the morphology gap between planar model systems and industrially relevant spherical catalyst particles is introduced through the use of a spherical cap Ziegler-type catalyst model system for the polymerization of ethylene. More specifically, a moisture-stable LaOCl framework with enhanced imaging contrast has been designed to support the TiCl4 pre-active site, which could mimic the behaviour of the highly hygroscopic and industrially used MgCl2 framework. As a function of polymerization time, the fragmentation behaviour of the LaOCl framework changed from a mixture of the shrinking core (i.e., peeling off small polyethylene fragments at the surface) and continuous bisection (i.e., internal cleavage of the framework) into dominantly a continuous bisection model, which is linked to the evolution of the estimated polyethylene volume and the fraction of crystalline polyethylene formed. The combination of the spherical cap model system and the used advanced micro-spectroscopy toolbox, opens the route for high-throughput screening of catalyst functions with industrially relevant morphologies on the nano-scale.

Fast successive self‐nucleation and annealing (SSA) thermal fractionation protocol for the characterization of polyolefin blends from mechanical recycling

AbstractThe sorting stage of mechanical recycling of post‐consumer polyolefins has severe challenges. Polypropylene (PP) is often contaminated with polyethylene (PE) and vice versa. To meet quality requirements, characterization of the recycled pellets is needed. To address this problem, fast characterization generating a statistical assessment of the content of the various batches from recycling is required. This investigation shows that the use of fast scanning rates (in a conventional Differential Scanning Calorimeter) in the successive self‐nucleation and annealing (SSA) protocol can reduce the thermal fractionation time, without losing resolution power, as long as the increase in heating/cooling rate is compensated by reducing sample mass. Using a “coupled SSA protocol” for polypropylene and polyethylene fractions at a rate of 10 °C/min, the measurement time is approximately 420 min. Implementing mass compensation, faster heating rates (i.e., 30 °C/min) and using a single‐fraction protocol, sufficient to determine the content of PP and high‐density PE, reduced the time of the measurement to 75 min. Examples of fractionations of commercial post‐consumer and post‐industrial recycled polyolefin blends conducted at a faster rate are provided. The derived polyolefin content is compared with the standard temperature rising elution fractionation analysis to assess the validity of the proposed method.

Synergistic effect of the co-pyrolysis of cardboard and polyethylene: A kinetic and thermodynamic study

Pyrolysis of municipal solid waste (MSW) represents one of the most promising solutions to recycle materials and recover energy. Two of the main components of MSW are waste cardboard and plastic. In this study, the pyrolysis of cardboard and polyethylene (PE) and the co-pyrolysis of their mixtures were conducted to investigate the synergistic effect by using thermogravimetric analysis. The whole reaction process was divided into four pseudoreactions, namely, hemicellulose, lignin, cellulose, and PE, by using the Frazer-Suzuki deconvolution method. It was found that the co-pyrolysis of cardboard and PE could promote the decomposition degrees of cardboard from 70.28% to 75.31%, when the PE fraction increased from 0 to 75%. However, the presence of cardboard can hinder the heat adsorption of PE, which shifts the peak of the PE reaction to a higher temperature. This results in higher Ea and ΔH‡ values for PE pyrolysis with an increasing fraction of cardboard. On the other hand, the Ea and ΔH‡ values of cellulose pyrolysis have their lowest values when the mixing rate is around 50%. This research deepens the understanding of the synergistic effect of co-pyrolysis of cardboard and PE, which supports the potential application of pyrolysis of MSW.

Properties of Starve-Fed Extrusion on a Material Containing a VHMWPE Fraction.

Single-screw extruders are usually operated with the screw fully filled (flood-fed mode) and not partially filled (starve-fed mode). These modes result in completely different processing characteristics, and although starve-fed mode has been shown to have significant advantages, such as improved mixing and melting performance, it is rarely used, and experimental studies are scarce. Here, we present extensive experimental research into starve-fed extrusion at feeding rates as low as 25%. We compared various operating parameters (e.g., residence time, pressure build-up, and melting performance) at various feeding rates and screw speeds. The results show a first insight into the performance of starve-fed extruders compared to flood-fed extruders. We explored starve-fed extrusion of a polyethylene material which contains a Very High Molecular Weight Polyethylene fraction (VHMWPE). VHMWPE offers several advantages in terms of mechanical properties, but its high viscosity renders common continuous melt processes, such as compression molding, ram extrusion and sintering, ineffective. This work shows that operating single-screw extruders in extreme starve-fed mode significantly increases residence time, melt temperature, and improves melting and that-in combination—this results in significant elongation of VHMWPE particles.

Determining the PE fraction in recycled PP

The presence of a polyethylene (PE) fraction in recycled polypropylene (PP) will influence the processing as well as mechanical and thermal properties of recycled polypropylene. The objective of this work has been to compare methods used to determine the fraction of PE in recycled PP, establishing calibration curves for each method. Plastics waste will be a mix of different grades – homopolymers and copolymers. It has therefore been tested how specific material grades affect the results. Characterization methods used were differential scanning calorimetry (DSC), FT-IR spectroscopy, NMR, and gel content measurement after peroxide extrusion. We have applied the derived calibration curves for two different post-consumer, recycled PP (rPP) in addition to a known 50/50 blend of PE and PP. DSC, NMR, FT-IR and gel content give quite consistent estimates of the PE content.

Nanocomposites and polyethylene blends: two potentially synergistic strategies for HVDC insulation materials with ultra-low electrical conductivity

Among the various requirements that high voltage direct current (HVDC) insulation materials need to satisfy, sufficiently low electrical conductivity is one of the most important. The leading commercial HVDC insulation material is currently an exceptionally clean cross-linked low-density polyethylene (XLPE). Previous studies have reported that the DC-conductivity of low-density polyethylene (LDPE) can be markedly reduced either by including a fraction of high-density polyethylene (HDPE) or by adding a small amount of a well dispersed, semiconducting nanofiller such as Al2O3 coated with a silane. This study demonstrates that by combining these two strategies a synergistic effect can be achieved, resulting in an insulation material with an ultra-low electrical conductivity. The addition of both HDPE and C8–Al2O3 nanoparticles to LDPE resulted in ultra-insulating nanocomposites with a conductivity around 500 times lower than of the neat LDPE at an electric field of 32 kV/mm and 60–90 °C. The new nanocomposite is thus a promising material regarding the electrical conductivity and it can be further optimized since the polyethylene blend and the nanoparticles can be improved independently.

Thermochemical interaction of wood and polyethylene during co-oxidation in the conditions of thermogravimetric analysis

In this work, using the methods of thermal analysis, we investigated the features of the oxidative decomposition of mixtures of polyethylene and sawdust (in different mass ratios). The results show that during the mixtures decomposition, the effects of interaction between wood and polyethylene are observed, which, apparently, are associated with the chain nature of the oxidation reactions of both components. It was found that the oxidation of mixtures with a polyethylene fraction of 20% or less proceeds without the formation of a significant amount of products of incomplete decomposition of hydrocarbon chains. Thermogravimetric and calorimetric data are compared with data from mass spectrometric analysis of decomposition products. These data indicate competition between the oxidation and thermal cracking of polyethylene. The presence of biomass due to its high reactivity contributes to an increase in the proportion of oxidation in the total decomposition of polyethylene.

Influence of ethylene-vinyl acetate on the performance improvements of low-density polyethylene-modified bitumen

Due to the low recyclability and slow degradation in nature, waste polyethylene (PE) represents a negative effect on the environment and its disposal is discordant with the idea of sustainable development in general. On the other hand, the application of the polymer-modified bitumen is an economical and efficient alternative for improving the performance of asphalt pavements. However, the thermal storage stability of PE-modified bitumen is the main factor that prevents its wider application. The main objective of this research was to investigate the feasibility and to quantify the effect of the addition of ethylene-vinyl acetate (EVA) on PE-modified bitumen. This was achieved by testing the modified bitumen produced with the single mass fraction of PE of 4% and different mass fractions of EVA in the range from 2 to 8%. The experimental program included penetration, softening, ductility, rheological properties in high-and low-temperature range, thermal storage stability and compatibility of phases, environmental scanning electron microscopy, and Fourier transform infrared spectroscopy. The results indicated that the addition of EVA increased the viscosity, complex shear modulus, as well as the elasticity of bitumen. Although the high-temperature behaviour was improved, the behaviour in the low temperature range was practically unaffected. The storage stability and segregation of phases were positively affected to a remarkable extent. The base bitumen and PE interacted only physically, but some particular chemical interaction took place with the addition of EVA.

Experimental study of the co‐gasification of wood and polyethylene in a two‐stage gasifier

AbstractCo‐gasification of wood mixed with 20% (mass fraction) of polyethylene (PE) in a two‐stage NOTAR® fixed‐bed gasifier was studied in the present paper. The ratio of air flow injected in the pyrolyzer and air flow injected in the oxidation zone is called the air ratio (AR). The AR of 0.35, 0.43, and 0.49 were used for test runs. Mass and energy balances were established. The study showed the feasibility of co‐gasification of wood mixed with 20% of PE in the two‐stage gasifier. However, considerable quantity of residues rich in fixed carbon content (17% of the fuel mass and 69% of fixed carbon content) was produced due to a low reactivity of the charcoal obtained after the pyrolysis. AR increasing reduces the gas CO content due to overconsumption of char at the pyrolysis stage. H2 and CH4 highest values are obtained for the intermediate AR = 0.43 which maximized the LHV, energy efficiency, and carbon conversion with respectively 4674 kJ/Nm3, 64.35%, and 74.52%. Low reactivity and carbon content of the pyrolysis char likely lead to lower performance of co‐gasification of PE mixed with wood compared to wood gasification.

Production of jet fuel from cracked fractions of waste polypropylene and polyethylene

Because of increasing consumption and the environmental impacts, the search for alternatives to fossil-fuel-based kerosene is crucial. Plastic waste cracking and subsequent co‑hydrogenation can be a promising way to produce jet fuels. The aim of this study was to investigate the feasibility of production of standard jet fuel from mixtures of cracked fractions of polyethylene (PE) or polypropylene (PP) and straight-run kerosene on commercial NiMo/Al2O3/P catalyst (10–30% cracked fraction content). The effects of process parameters (T = 200–300 °C, P = 40 bar, Liquid Hourly Space velocity (LHSV) = 1.0–3.0 h−1, H2/hydrocarbon ratio = 400 Nm3/m3) and the feedstock composition on the hydrodesulphurisation and hydrodearomatisation efficiencies and the main product properties were investigated. It was found that, olefins affect the hydrodesulphurisation and the hydrodearomatisation reactions until 220 °C and 240 °C, respectively. At the most favourable process parameters (T = 300 °C, LHSV = 1.0–3.0 h−1) practically sulphur and olefin-free jet products with reduced aromatic contents (7.2–11.2%) were produced. The freezing points of the jet fuel (−60.3 to −56.4 °C) produced from the 10–30% cracked PP fraction containing feedstocks were significantly lower than the required −47 °C, but in the case of the products containing the cracked PE fraction one further step (hydroisomerisation) is needed before the application.