Crystalline Polyethylene Research Articles

Study on the effects of aging on the pyrolysis of plastic and the synergistic mechanisms of co-pyrolysis with lignite

Co-pyrolysis of waste plastic with low-rank coal explored how photoaging impacts the pyrolysis of plastics and delves into the synergistic mechanisms involved in co-pyrolysis. The results of elemental analysis, X-ray powder diffraction and Fourier transform infrared spectroscopy showed that photoaging primarily involves oxidizing and breaking the aliphatic chains in polyethylene (PE), as well as generating oxygen-containing functional groups like hydroxyl (-OH), carbonyl (-C=O), and ether (-C-O), thereby reducing the crystallinity of PE. The results of individual plastic pyrolysis showed that photoaging is beneficial to the generation of gas and tar. Pyrolysis tar of PE samples contains significant amounts of alcohols, and olefins and alkynes (O&As). The results of co-pyrolysis indicated that photoaging can enhance the yields of gas and oil from the co-pyrolysis between PE and Naomaohu (NMH) coal. Co-pyrolysis effectively reduced the relative content of O&As in the tar from the pyrolysis of PE samples alone by 8.0%–29.0 %. The synergistic mechanism of co-pyrolysis between aged PE and NMH involved supplying a significant quantity of hydrogen and hydroxyl radicals by NMH, which react with alkyl radicals generated from PE pyrolysis, leading to the production of additional alkanes and alcohols. These findings offered new insights for a deeper understanding of the co-pyrolysis behaviors between waste plastic and lignite.

Mechanoenzymatic Depolymerization of Highly Crystalline Polyethylene Naphthalate under Moist-Solid Conditions

Mechanoenzymatic Depolymerization of Highly Crystalline Polyethylene Naphthalate under Moist-Solid Conditions

Molecular dynamics study of axial tensile response of crystalline ultra-high molecular weight polyethylene under different loading conditions

Through molecular dynamics simulations, we investigated the effects of temperature on the axial tensile behavior of ultra-high molecular weight polyethylene (UHMWPE) crystals, considering the combined effects of transverse compression, strain rate, and molecular weight. The effects of temperature over the range of 100 K to 450 K is shown to reduce the mechanical properties. Existing chain end defects facilitate chain sliding and induce stress concentration in adjacent molecules, thereby reducing the strength and modulus of crystals. Lower molecular weight and higher temperatures promote chain sliding, while higher transverse compression and increased strain rates inhibit chain sliding, resulting in higher properties. Additionally, higher temperatures increase stress concentration due to thermal vibrations, which induce localized high stress conditions within polyethylene chains. The transition of the failure mode from chain sliding to bond breakage occurs at strain rates between 1012 s−1 and 1013 s−1, and is found to be independent of temperature, pressure, and molecular weight. The results are compared to the response of crystals without chain end defects. These insights contribute to a deeper understanding of the behavior of UHMWPE crystals under extreme loading conditions.

Effect of deformation ratio of flow-induced crystallization on polyethylene in crystalline behavior, thermal stability, and tensile loading: A molecular dynamics simulation

Since the physical and mechanical properties of semicrystalline polymers strongly depend on crystalline morphology, understanding the correlation between the crystallization kinetics and crystalline structure of polythene is beneficial for their rational processing and applications. In this study, united-atom (UA) molecular dynamics (MD) simulations were employed to elucidate the variations in crystalline structure, phase transition temperatures, and uniaxial tensile deformation among polyethylene (PE) with randomly oriented and flow-induced crystallization (FIC). The results showed that crystallization occurs in areas with low potential energy. For the FIC process, the entanglement parameter and interplanar spacing was less than for randomly oriented crystallization, and the crystallinity was higher. The relationship between the deformation and the crystallinity of PE with randomly oriented crystallization was expressed, which indicates that the crystalline structure promoted elongation at break of PE in tensile deformation. As PE was oriented to crystallize during the FIC process, the polymer stiffness is positively correlated with the deformation ratio of the PE model, so crystal conformation systems with higher deformation ratios produce higher ultimate stresses in tensile loading. From the visualization results, the crystalline phase was stable and does not easily transform into an amorphous phase during tensile loading. Additional results show that the fracture region of PE at tensile fracture tends to develop in the amorphous phase under tensile loading. Energy analysis showed that the elastic and yield regions were mainly dominated by intra-chain bonds, angles, and dihedral motion of PE, whereas interchain nonbonded interactions mainly dominated strain-hardening regions.

Mild Catalytic Degradation of Crystalline Polyethylene Units in a Solid State Assisted by Carboxylic Acid Groups.

Crystalline polyethylenes bearing carboxylic acid groups in the main chain were successfully degraded with a Ce catalyst and visible light. The reaction proceeds in a crystalline solid state without swelling in acetonitrile or water at a reaction temperature as low as 60 or 80 °C, employing dioxygen in air as the only stoichiometric reactant with nearly quantitative recovery of carbon atoms. Heterogeneous features of the reaction allowed us to reveal a dynamic morphological change of polymer crystals during the degradation.

Hydrolase-Catalyzed Depolymerization Mechanism toward Crystalline and Amorphous Polyethylene Terephthalate

Hydrolase-Catalyzed Depolymerization Mechanism toward Crystalline and Amorphous Polyethylene Terephthalate

X-ray Diffraction Study of Metallized Polyethylene for Creating Heat Storage Systems

The paper analyzes the prospects of using a heat-accumulating material consisting of metallized polyethylene granules. X-ray diffraction analysis has been used to study the influence of the number of heating and cooling cycles of the heat-accumulating material on the change in the degree of crystallinity of polyethylene. It was shown that the proposed heat-accumulating material showed a low resistance and a significant decrease in the degree of crystallinity of polyethylene under the experimental conditions. The crystal structure of polyethylene did not change during cyclic heating and cooling. Grounded on the obtained experimental results, it was determined that a high degree of polyethylene crystallinity is being kept for 200–300 heating-cooling cycles.

Molecular-scale mechanics of a crystalline polyethylene interface formed by projection of carbon nanotube structures

The semicrystalline nature of polymer chains induced by the intrusion of carbon nanotubes (CNTs) is a decisive factor in understanding the properties of interfacial regions. Herein, the structural and mechanical behavior of polyethylene (PE) formed around CNT surfaces were determined using a combination of classical molecular dynamics simulations and subcontinuum-scale analysis. The results suggest that inserting CNTs into the polymer domain forces the PE chains to align along the longitudinal axis of the CNTs. The interface functions as a nucleating agent, and the area occupied by the crystalline phase propagates radially as PE chains are stacked over long distances. The crystalline PE, grown with CNT as the central axis, exhibits extreme mechanical anisotropy, particularly for normal and shear deformations in the transverse direction. Therefore, this study provides an important theoretical guideline for understanding polymeric semi-crystals around CNTs.

Strain rate effects on the axial tensile behavior of crystalline polyethylene: Insights from molecular dynamics simulations

During a transverse impact, ultra-high molecular weight polyethylene fibers within the laminates experience axial tension over a range of high strain rate loading. We employed molecular dynamics simulations to explore the influence of strain rate on the axial tensile behavior of polyethylene crystals, both with and without chain end defects. When the strain rate increased from 1010 s−1 to 1013 s−1, polyethylene crystals without chain ends showed an approximate 60% increase in strength. This increase can be attributed to the fact that higher strain rates impede the relaxation of individual polymer chains, compelling them to store more energy. Furthermore, our results revealed that the strength of crystals with short chains improved more than sevenfold when the strain rate increased from 1010 s−1 to 1013 s−1. This substantial strength increase can be mainly attributed to the transition of the failure mode from chain end sliding to chain scission at multiple locations along each chain. This transition occurs when the loading velocity surpasses the maximum speed at which chains can slide. Additionally, our simulations find that the effect of strain rate on the modulus and strength of crystals initiates at relatively lower strain rates as the molecular weight increases.

Infrared spectroscopy as a tool to study the vibrational, mechanical, and structural changes in commercial plastic bags: Physical principles

This paper investigates the application of Fourier-transform infrared (FT-IR) spectroscopy by analyzing a commercially available plastic bag as an example. The study investigates the vibrational modes, mechanical properties, and structural changes of a bare sample during a tensile test. By measuring the absorption bands and their intensities, valuable information about the chemical composition and the concentration of certain components in the plastic bag is obtained. The behavior of vibrational modes in one, two, and three-dimensional systems is studied, with a focus on their representation in the IR spectrum. The concept of the dipolar electric moment and phenomena such as overtone bands and Fermi resonance are also explained. The X-ray patterns of the bag show talc and polyethylene crystalline phases. Scanning electron microscopy (SEM) determines the thickness of the sample. Tensile tests are performed to investigate the mechanical behavior of the plastic bags. This study demonstrates the informative and educational capabilities of FT-IR spectroscopy in studying the vibrational, mechanical, and structural properties of materials, with an emphasis on the correct application of this technique. The study highlights the importance of considering the effects of thickness and absorption coefficient and applying the Beer-Lambert law to understand the changes in vibrational modes during tensile testing. The results contribute to a deeper understanding of the structural behavior of plastic bags and demonstrate the effectiveness of FT-IR spectroscopy in characterizing such materials.

The strength of particulate polymer composite: A new insight on crystallinity and structural morphology

AbstractWe have demonstrated the significant impact of high density polyethylene (HDPE) crystallinity and structural morphology on the tensile strength of 60/40 NR/HDPE polymer blend composites. Introducing nanoscale Boron Carbide (B4C‐type compounds) fillers noticeably changed the crystallinity and morphology of HDPE, leading to the formation of fine spherulites. Conversely, microscale fillers mainly impacted the crystallinity while preserving a coarse architecture. Although both composites experienced a reduction in crystallinity, the nanocomposites outperformed microcomposites and even the pristine polymer blend in terms of strength, implying the effect of a fine structure. The nanocomposite with a filler loading of 2 wt% exhibited the highest strength. This investigation provides novel insights into the interplay between crystallinity, HDPE structure, and the size of fillers, which heavily influence the strength of polymer blend composites.

Effect of oxygen plasma-treatment on surface functional groups, wettability, and nanotopography features of medically relevant polymers with various crystallinities

The surface properties of polymeric biomaterials play a crucial role in their biocompatibility and performance. This study explores the application of cold oxygen plasma treatment as a versatile technique for surface modification of polymeric materials with different degrees of crystallinity: crystalline high-density polyethylene (HDPE), crystalline-amorphous poly(chloro‑paraxylylene) (parylene C), and amorphous aromatic polyether-based polyurethane (PU). The investigations focus on the generation of surface functional groups and hydrophilicity, as well as nanotopography. X-ray photoelectron spectroscopy (XPS) analysis confirmed the generation of oxygen-containing functional groups, resulting in controlled wettability (water contact angle), while atomic force microscopy (AFM) showed topography modifications in the nanoscale. At the same time, it was revealed that oxygen plasma treatment did not affect the bulk properties (confirmed by TG and XRD). The effects of the same plasma treatment conditions varied significantly among the different polymers studied, depending on their crystallinity. This was discussed in terms of the preferential etching of amorphous regions in the polymeric structures. The findings emphasize the advantages of oxygen plasma treatment for tailoring the surface properties of polymeric biomaterials, highlighting its significance for biomedical applications.

Regulating the structure of crosslinked polyethylene and its application in ultra‐high voltage cables

AbstractThe crystallinity of polyethylene has been extensively studied, but in situ experiments designed to investigate the crystallization of PE and XLPE have hardly been discussed. In this work, the crystallization behavior of PE and XLPE was investigated by designing in situ crystallization observation experiments. We have compared the crystallinity, crosslinking, viscosity properties, and gas byproducts of different XLPE insulating materials. COMSOL simulations demonstrate that the DTAP and DTBP crosslinker initiated crosslinks have better insulating properties and cable stability than the DTBC and DTBTMC crosslinkers. The formation of an insulation layer initiated by the DTAP crosslinker is beneficial for improving the breakdown strength, processing performance, and stable operation of cables. Our work is of great significance for understanding the crystallinity of XLPE and determining the correct crosslinker.Highlights In situ crystallization observation of PE and XLPE. Simulation of ultra‐high voltage cables. Finite element analysis. Investigation of gas byproducts in XLPE.

Investigation of the Properties of Polyethylene and Ethylene-Vinyl Acetate Copolymer Blends for 3D Printing Applications.

3D printing of polyolefins, such as polyethylene (PE) and polypropylene (PP), is of great practical interest due to the combination of high properties of these materials. However, the use of these materials in 3D printing is associated with many problems due to their high rate of crystallization, which causes shrinkage and warpage of the printed object. In this regard, blends of PE and ethylene-vinyl acetate copolymer (EVA) of various compositions were investigated for 3D printing. It was found that with an increase in the concentration of EVA, an increase in the pseudoplastic effect and amorphization of PE occurs. It has been shown that with an increase in the EVA content, the degree of crystallinity of PE decreases slightly (by 11% at a content of 80% EVA); however, a significant decrease in the rate of crystallization of PE is observed (by 87.5% at the same EVA concentration). It was found that PE and EVA are completely compatible in the amorphous phase and partially compatible in the crystalline phase, which leads to a slight decrease in the melting point of PE. The introduction of EVA also leads to a significant increase in impact strength: the maximum value is achieved at a 50/50 ratio, which is five times the value of the initial PE and two times the value of the initial EVA. At the same time, it was revealed that EVA leads to a gradual decrease in the elastic modulus and strength of PE, the change of which generally obeys the additivity rule. The resulting printing filaments are characterized by a certain ovality due to their shrinkage, which decreases with increasing EVA content and reaches a minimum value at a PE/EVA ratio of 30/70. This composition also demonstrates the lowest shrinkage of the printed sample and higher processability during printing.

Direct observation of radiation-induced graft polymerization on a polyethylene film

Radiation-induced graft polymerization is widely used in the synthesis of polymeric materials with various functionalities; however, the details of the reaction mechanism are still unresolved. Herein, the initial stage of the graft polymerization reaction was investigated through atomic force microscopy (AFM). We used glycidyl methacrylate (GMA) in methanol (monomer solution) and a high-density polyethylene (HDPE) film with a well-ordered lamellar structure as the substrate. Using polymer film surfaces with a maximum grafting degree of 0.5%, AFM can distinguish between crystalline and amorphous polyethylene (PE) phases as well as a grafted polymer GMA (PGMA) phase. The graft polymerization reaction started from the interface between the crystalline and amorphous PE phases. As the reaction proceeded, the PGMA covered the crystalline PE phase: i.e., the entire surface of the PE film were covered by the PGMA. Further, the crystalline lamellae of the PE film eventually became a scaffold for the formation of aggregates comprising grafted polymer chains alone. The graft polymerization reaction mechanism was explained by comparing the solubility parameters of the monomer solution, substrate, and grafted polymer chains. Understanding the reaction mechanism at a low grafting degree obtained in this study may contribute to enhancing the efficiency of the graft polymerization reaction on any polymeric material.

Transcrystallization, enhanced interface strength and mechanical properties in PE/(PA6 nanofiber)/graphene oxide thermoplastic polymer-polymer nanocomposites via annealing and increased remolding temperature

The importance of polymer-polymer thermoplastic composites is increasing due to ease of recycling. This work investigates the effects of remolding temperature and thermal annealing on the properties of polyethylene (PE) composites containing PA6 and GO/PA6 electrospun nanofibers. Nanocomposite samples were prepared by sandwiching several layers of PA6 or GO/PA6 electrospun mats and PE films in a hot press and subsequently were remolded at varying higher temperatures in a range of 180 to 210°C. Furthermore the remolded samples at 200°C were then annealed at 100°C for 10 h. SEM and DMTA results of the developed samples showed that the application of higher remolding temperatures, close to the melting point of PA6, improves wettability and interfacial strength in the composites. The DSC results of the samples revealed a slight increase in PE crystallinity due to the induced crystallization on the surface of nanofiber mat. It was also observed that an increase in the remolding temperature increases the tensile properties of the composites with the best properties obtained at a remolding temperature of 200°C. Increasing the remolding temperature beyond 200°C decreases the tensile properties of the composites due to melting and geometry degradation of the nanofibers. The results revealed that the annealing of the samples at 100°C for 10 h increases the degree of crystallinity and tensile properties. The highest yield strength, 16.4 MPa, and modulus, 277 MPa, were obtained for the composite containing 10.5 wt% of pure PA6 nanofibers. The elongation and toughness of this composite compared to those of pure matrix were increased by 61% and 83%, respectively. In the remolded and annealed nanocomposites, a crystalline region, as thick as 20 microns, grown on the surface of the nanofiber mat or nanofiber rich region, so called transcrystalline region, was observed by polarized reflected light microscopy.

An intrinsic phase change elastomer with superior stretchability and reparable capabilities for self-thermal managing stretchable electronics

In recent years, phase change materials (PCMs) are gradually developed and utilized for thermal management in wearable electronics due to their autonomous heat absorption ability during the phase change process. However, the high rigidity (elastic modulus ＞ 100 MPa) and stiffness (yield strain ＜ 15%) severely limited the thermal management application of the reported PCMs in stretchable electronics. Herein, we present an intrinsic phase change elastomer (IPCE) combining the function of PCM and elastomer by introducing crystalline polyethylene glycol segments and amorphous polypropylene glycol segments into an elaborately designed chemical cross-linked networks. The fabricated IPCE merges excellent softness (elastic modulus ＜ 20 MPa), stretchability of 900%, elastic mechanical behavior (without yield phenomenon), fantastic thermal management ability, and outstanding thermal repairable capability. Eventually, we fabricated a simple strain sensor with IPCE as substrate by spraying gold nanoparticles on both sides of the IPCE film. The stable sensing ability that repeatedly monitoring the subtle human motion and autonomous thermal management behavior of the strain sensor demonstrated the appealing practicability of our IPCE. This work paved an avenue for fabricating stretchable and self-thermal managing elastomer for stretchable electronics.

A quantum chemical and molecular dynamics simulation study on photo-oxidative aging of polyethylene: Mechanism and differences between crystalline and amorphous phases

It is well known that polyethylene (PE) generates CO2 during photo-oxidative aging; however, there is still some ambiguity in the exact mechanistic steps involved. In this work, the photo-oxidative aging mechanism of PE is considered via quantum chemical (QC) calculations. This demonstrates that it is difficult for some previously proposed Norrish I mechanisms to occur because of the high energy required and forbidden transitions. A synergistic effect between oxygen and ultraviolet (UV) radiation is shown to promote the initiation of photo-oxidative aging, providing a more reasonable description of photo-oxidation than existing mechanisms. The charge differential density (CDD) indicates that UV radiation alters the electron distribution so that the electron transfer from the secondary C–H bond to the H–OO bond promotes the formation of HOO·. As is well established, after the initiation reaction, the formed radical is converted into hydroperoxide. UV radiation promotes the conversion of hydroperoxide into ketones via cleavage of the O–OH bonds and the formation of hydroxyl radicals. The hydroxyl radicals can further react with ketonic carbonyls, resulting in carbonic acid. Finally, the carbonic acid decomposes into CO2. The difference in photo-oxidative aging between the crystalline and amorphous phases of PE was studied by molecular dynamics (MD) simulation. The MD results show that the crystalline phase is more difficult to photo-oxidize than the amorphous phase because of the poorer permeation ability and solubility but not the diffusion ability of O2.

Multiblock Copolymers Based on Highly Crystalline Polyethylene and Soft Poly(ethylene‐co‐butadiene) Segments: Towards Polyolefin Thermoplastic Elastomers

AbstractBlock copolymers based on polyethylene (PE) and ethylene butadiene rubber (EBR) were obtained by successive controlled coordinative chain transfer polymerization (CCTP) of a mixture of ethylene and butadiene (80/20) and pure ethylene. EBR‐b‐PE diblock copolymers were synthesized using the {Me2Si(C13H8)2Nd(BH4)2Li(THF)}2 complex in combination with n‐butyl,n‐octyl magnesium (BOMAG) used as both the alkylating and chain transfer agent (CTA). Triblock and multiblock copolymers featuring highly semi‐crystalline PE hard segments and soft EBR segments were further obtained by the development of a bimetallic CTA, the pentanediyl‐1,5‐di(magnesium bromide) (PDMB). These new block copolymers undergo crystallization‐driven organization into lamellar structures and exhibit a variety of mechanical properties, including excellent extensibility and elastic recovery in the case of triblock and multiblock copolymers.

Multiblock Copolymers Based on Highly Crystalline Polyethylene and Soft Poly(ethylene-co-butadiene) Segments: Towards Polyolefin Thermoplastic Elastomers.

Block copolymers based on polyethylene (PE) and ethylene butadiene rubber (EBR) were obtained by successive controlled coordinative chain transfer polymerization (CCTP) of a mixture of ethylene and butadiene (80/20) and pure ethylene. EBR-b-PE diblock copolymers were synthesized using the {Me2 Si(C13 H8 )2 Nd(BH4 )2 Li(THF)}2 complex in combination with n-butyl,n-octyl magnesium (BOMAG) used as both the alkylating and chain transfer agent (CTA). Triblock and multiblock copolymers featuring highly semi-crystalline PE hard segments and soft EBR segments were further obtained by the development of a bimetallic CTA, the pentanediyl-1,5-di(magnesium bromide) (PDMB). These new block copolymers undergo crystallization-driven organization into lamellar structures and exhibit a variety of mechanical properties, including excellent extensibility and elastic recovery in the case of triblock and multiblock copolymers.