Structure Of High-density Polyethylene Research Articles

Structural Characteristics and Improved Thermal Stability of HDPE/Calcium Pimelate Nanocomposites

In the present research work, calcium pimelate (CaPim) was synthesized and investigated as an additive for high-density polyethylene (HDPE). HDPE/CaPim nanocomposites were prepared by melt-mixing, with CaPim content ranging from 0.1% to 1%, affording white homogeneous materials. The chemical structure of the nanocomposites and the incorporation of CaPim was confirmed by infrared spectroscopy. The surficial morphology and the additive distribution were examined by scanning electron microscopy. Differential scanning calorimetry and X-ray diffraction measurements showed that the thermal transitions and crystal structure of HDPE are not affected by the incorporation of CaPim, while the mechanical properties are retained overall. This study focuses on the thermal degradation of HDPE nanocomposites, investigating the degradation mechanism and kinetic parameters through various analytical methods. Isoconversional techniques, including the Friedman method, Vyazovkin analysis, and Ozawa Flynn Wall analysis, were employed to calculate activation energies (Eα). The degradation mechanism and kinetic triplet were determined based on a multivariate non-linear regression method (model-fitting). Finally, the presence of a CaPim additive was shown to increase the Eα of thermal degradation, consistent with the calculated dependence of Eα on the degree of conversion and the improved thermal stability of the HDPE matrix.

Numerical and experimental analysis of inelastic and rate-dependent buckling of thin injection-moulded high-density polyethylene structure

Semi-crystalline polymers is an important group of materials that is used in a vast array of products. In this study, the rate-dependent properties of high-density polyethylene (HDPE) are investigated, both experimentally and theoretically. Experimental compression testing of a three-dimensional HDPE structure is performed and analysed numerically by use of the finite element method. In addition, an Eulerian constitutive material model for isotropic, semi-crystalline polymers is proposed. The model is able to account for such essential phenomena as strain-rate dependence, work hardening, pressure-dependence of inelastic deformations, and damage. The proposed material model was implemented in Abaqus as a VUMAT, which is an explicit implementation. The material model was calibrated by use of uniaxial tensile tests performed on HDPE dog-bone shaped samples, and the model was further explored by applying the VUMAT implementation to the compression tests of the HDPE structure. The simulation model was able to reproduce the experimental results well, both the uniaxial tests and the compression tests. In particular, the friction present in the compression tests seems to play an important role in determining the buckling mode of the structure.

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.

Optimization of the Physical Properties of HDPE/PU Blends through Improved Compatibility and Electron Beam Crosslinking.

Polymer blending is a method in which polymers with different properties are mixed so that each advantage appears in one polymer blend. Improved thermal and mechanical properties of blends can be prepared by blending with high-density polyethylene (HDPE) of a non-polar polymer and polyurethane (PU) of a polar polymer. However, a compatibilizer is required because it has the disadvantage that blending has low miscibility due to the different phases. In this study, HDPE/PU blends with new and excellent physical properties were developed through optimal composition with improved compatibility between the HDPE and PU. In addition, the effects of improving the physical properties through electron-beam crosslinking were confirmed. In general, a crosslinking structure of HDPE is formed by electron beam irradiation to increase its thermal stability and strength, but its elongation is rapidly decreased. In particular, the elongation of HDPE irradiated at 100 kGy was about 110%, which was decreased about five times compared to unirradiated HDPE (510%). However, the HDPE/PU blend with improved compatibility (PU 30) showed an elongation of about 450% while maintaining excellent strength (22.5 MPa), which was increased by about four times compared to the HDPE irradiated at 100 kGy. In particular, the thermal stability of PU 30 irradiated at 100 kGy at a high temperature (180 °C) was improved more than six times compared to the HDPE. Therefore, it is possible to develop HDPE/PU blends with new and excellent physical properties by improving compatibility and using electron beam crosslinking technology.

Influence of grape marc extract on tuning the intermolecular interactions in the high‐density polyethylene

AbstractIntermolecular interactions and molecular dynamics in thin films of high‐density polyethylene (HDPE) containing a high loading of Grape Marc Extract (GME) were analyzed by solid‐state NMR. Optical microscopy (OM), Scanning Electron Microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) studies were used to corroborate the findings. The OM and SEM images and 1H‐13C RAMP CP/MAS (ramped amplitude cross‐polarization/magic‐angle spinning) spectra of HDPE, HDPE‐GME, and GME confirmed the incorporation of the GME into the HDPE structure. The results were compared to those for an unfilled HDPE film. The influence of GME on enhancing the amorphous nature of HDPE, altering the crystalline melting behavior and possible intermolecular interactions were evident from the DSC and FTIR. The NMR spin‐diffusion and T1(1H), T2(1H), T1ρ*(13C), T1ρ(1H) relaxation and variable contact time experiments revealed the interactions and dynamics at the sub‐micron level.

Investigation of Thermal and Mechanical Behavior of HDPE/ZnFe2O4 Composite

The effect of adding zinc ferrite (ZnFe2O4) nanoparticles (2.5, 5, 10, 15, and 20 wt %) as fillers to high density polyethylene (HDPE) was investigated. HDPE/ZnFe2O4 composite was characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray (EDX). The thermal and mechanical properties of the synthesized composite were studied using thermal gravimetric analysis (TGA) and mechanical tensile tester, respectively. XRD results confirm the cubic spinel structure of ZnFe2O4 nanoparticles with average crystallite size of 25 nm, and hexagonal orthorhombic crystal structure of HDPE. SEM photographs prevail the dispersion of ZnFe2O4 nanoparticles within the polymer matrix and EDX proves the consistency of stoichiometry of compositions. The addition of ZnFe2O4 nanoparticles enhances the thermal stability and shifts Tin from 400.33 °C to 431.68 °C which was more apparent for samples of high filler loading. The mechanical tensile test of HDPE/ZnFe2O4 composite studied at strain rate (7 mm/min), confirming that the values of stiffness, ultimate tensile strength, and yield stress increased by increasing the filler loading due to the stiffness of added ZnFe2O4 nanoparticles. The highest values of Young’s modulus, ultimate tensile strength, and yield stress were 1148.38 MPa, 40.73 MPa, and 38.15 MPa, respectively, achieved by the sample containing 20 wt % of ZnFe2O4 nanoparticles. Whereas, the values of ultimate tensile strain and ductility declined by increasing filler loading. A new combination between thermoplastic polymer (HDPE) which can be easily recycled and ZnFe2O4 nanoparticles introducing a promising combination between both properties towards many future applications in civil infrastructure, industry, coating and barriers.

Biofilms of Pseudomonas and Lysinibacillus Marine Strains on High-Density Polyethylene.

Environmental pollution by plastic debris is estimated on a scale of 100 million metric tons, a portion of which is fragmented into micro- and nanoplastics. These fragments are often colonized by bacterial species in marine environments, possibly contributing to the biodegradation of such materials. However, further investigations are necessary to determine the impact of abiotic polymer weathering on biofilm adhesion, as well as the specific biofilm formation strategies employed by marine isolates. Here, we evaluate deep-sea sediment bacterial isolates for biofilm adhesion, extracellular matrix production, and polymer degradation ability. Our study focuses on high-density polyethylene (HDPE) fragments for their high durability and environmental persistence, subjecting fragments to abiotic weathering prior to bacterial colonization. Marine isolates identified as Pseudomonas sp. and Lysinibacillus sp. exhibited decreasing biofilm formation on weathered HDPE, especially over the first 24h of incubation. This effect was countered by increased extracellular matrix production, likely improving cell adhesion to surfaces roughened by abiotic degradation. These adhesion strategies were contrasted with a reference Pseudomonas aeruginosa strain, which displayed high levels of biofilm formation on non-weathered HDPE and lower extracellular matrix production over the first 24h of incubation. Furthermore, our results suggest that an increase in biofilm biomass correlated with changes to HDPE structure, indicating that these strains have a potential for biodegradation of plastic fragments. Therefore, this work provides a detailed account of biofilm formation strategies and bacteria-plastic interactions that represent crucial steps in the biodegradation of plastic fragments in marine environments.

Investigating the effect of adding CdO nano particles on neutron shielding efficacy of HDPE

Novel neutron shielding material based on borated high-density polyethylene (HDPE) was prepared in this study. In order to enhance the shielding efficacy of borated HDPE, nano particles of high neutron capture cross section material i.e. of cadmium oxide (CdO) were used as neutron absorber. The CdO nano particles were prepared with composite hydroxide mediated (CHM) method and tested with X-ray diffraction to ensure their structural parameters. The grain sizes of CdO sample obtained from reflection peaks at 2θ = 30.39° and 23.52° were 24.9 nm and 36.1 nm, respectively. The corresponding hkl values and lattice spacing for above-mentioned reflection peaks were found (111) & (110) and 0.29 & 0.38, respectively. These nano scale CdO particles were then mixed in HDPE/B4C composite (containing 10% by wt. of B4C) in predetermining concentrations (i.e. 1%, 2%, and 4% by wt.). The admixture were then pressed in sheets and tested for structural stability and neutron shielding efficacy. The structural stability analysis with FTIR revealed the fact there was no significant alteration in HDPE structure on addition of CdO. The values of effective mass removal cross sections from neutron shielding measurements were 0.1567cm2g-1, 0.1906cm2g-1, and 0.1634cm2g-1 for composites containing 1%, 2%, and 4% CdO, respectively. Furthermore, among all, composite with 2% CdO has been observed of having best shielding properties as it contained the appropriate amount of all the constituents. The higher neutron capture cross section of CdO nano particles was attributed for this significant increase in shielding efficacy of HDPE/B4C/CdO nano composites as compared to pure HDPE and HDPE/B4C composites.

Role of percent grafting and chain length of fully fluorinated pendant units in the grafted acrylic compound on crucial characteristic properties of high density polyethylene

This comprehensive study paves way to investigate the effects of not only the extent of grafting but also the chain length of the perfluorinated pendant tail presenting in the three different fluoroalkyl acrylate monomers on the significant characteristic properties; namely the thermal behavior, crystal structure quality, mechanical performance and morphological structure of high density polyethylene (HDPE). The individual graft copolymerizations of the monomer onto HDPE were conducted at the content level from 5 % to 30 % via bulk-melt polymerization. The characterizations of copolymers were performed with differential scanning calorimeter (DSC), powder X-ray diffractometer, universal testing machine and scanning electron microscope (SEM) techniques. As for the results deduced from DSC analysis, both the melting temperatures of HDPE and degree of crystallinity were found to increase systematically with the enhancement in the percent grafting level up to 10 % beyond which the parameters were noted to decrease drastically and reach towards globally minimum values. According to the XRD results, as the percentage of grafting enhanced, the remarkable expansions were observed in unit cell parameters of HDPE crystallized in the orthorhombic symmetry. Moreover, the presence of relatively higher amount of -CF2 groups in the perfluorinated pendant tail caused the formation of three-dimensional lateral repulsions due to its helix structure. Furthermore, there seemed to remarkably improve in the mechanical performance features in case of percent grafting level of 70.6 % where the tensile strength, Modulus and impact strength parameters were measured to be about 42.51 MPa, 539.90 MPa and 41.11 kj/m2, respectively. These reinforcements were found to be explained by the improvement in the regulation, orientations, alignments of HDPE chains. Furthermore, the formation of thick, bulky and long-fibrils were observed at high percent grafting.

Accelerating the Biodegradation of High-Density Polyethylene (HDPE) Using Bjerkandera adusta TBB-03 and Lignocellulose Substrates.

High-density polyethylene (HDPE) is a widely used organic polymer and an emerging pollutant, because it is very stable and nonbiodegradable. Several fungal species that produce delignifying enzymes are known to be promising degraders of recalcitrant polymers, but research on the decomposition of plastics is scarce. In this study, white rot fungus, Bjerkandera adusta TBB-03, was isolated and characterized for its ability to degrade HDPE under lignocellulose substrate treatment. Ash (Fraxinus rhynchophylla) wood chips were found to stimulate laccase production (activity was > 210 U/L after 10 days of cultivation), and subsequently used for HDPE degradation assay. After 90 days, cracks formed on the surface of HDPE samples treated with TBB-03 and ash wood chips in both liquid and solid states. Raman analysis showed that the amorphous structure of HDPE was degraded by enzymes produced by TBB-03. Overall, TBB-03 is a promising resource for the biodegradation of HDPE, and this work sheds light on further applications for fungus-based plastic degradation systems.

Which way do fibrils disappear?

The shrinkage process that results from the reversible deformation of high-density polyethylene (HDPE) via the crazing mechanism has been investigated by atomic force microscopy (AFM) and X-ray scattering. It has been shown that the fibrillar-porous structure resulting from HDPE crazing in a physically active liquid medium (ethanol) undergoes substantial changes during the shrinkage: in the AFM images, separate lamellae and fibrils are replaced by new structural formations, which seem to consist of lamellae and fibrils. A procedure has been developed that implies creating a lithographic label on the surface of a deformed polymer to navigate over the sample surface with a high accuracy (down to a few nanometers and individual lamellae) and in situ observe the structural transformations accompanying the shrinkage of HDPE. The study has shown that the transformation of the structure upon the shrinkage is associated with different factors, including the «attraction» of fibril material to lamellae after load elimination similarly to that taking place in an elastic band. X-ray scattering data have shown that deformation along the extrusion direction leads to molecular orientation of HDPE by orienting lamellae and fibrils in the stretching direction, with this orientation remaining partly preserved after HDPE shrinkage. The SAXS data have confirmed the conclusions inferred from the AFM studies that fibrils are formed in the HDPE structure upon crazing and disappear upon shrinkage.

Tribo-mechanical behavior of HDPE/Natural fibers filler composite materials

ABSTRACTOver the last decade, polymer composites reinforced with natural fibers gained interest, both from the academic world and from various industries. Due to the demanding needs for environmentally friendly composites, the automotive industry is now searching for biodegradable and renewable composite materials and products. There are a wide variety of different natural fibers which can be applied as reinforcement or fillers, showing potential as a replacement for inorganic fibers in automotive components. The fact that plastics are often economical to produce implies an advantage especially in very complex shapes, make them promising for obtaining composite materials, achieving short demolding times, as no chemical reaction is required. Moreover, polymers are used increasingly for stressed tribological components, whereby plastic parts replace metallic bearings, gear wheels or sliding elements. In this regard, the objective of this work was to produce composite materials based on natural fibers and to characterize the influence of the addition of different amounts of filler. To do so, composites of high-density polyethylene (HDPE) and peanut shells (PS), at different proportions (2, 4 6, 8 and 10% wt.), were prepared. The composites were produced by injection molding and molded into a particular tension test simple mold. Although the FTIR presented an increment on the O-H vibration and a band around 1600 cm-1, the HDPE structure did not present modification. The mechanical properties of the HDPE were affected with the inclusion of the fibers. The tensile performance of the HDPE decrease with the increment of the fibers inclusion whiles the elastic modulus increases. The sample with 2% of natural fibers presented the lowest wear rate (k) and coefficient of friction (µ).

Effect of Selected Injection Conditions on the Mechanical Properties and Structure of HDPE

This paper is devoted to research of high-density polyethylene (HDPE), which belongs to one of three main biomaterial groups, i.e. polymeric materials. Hence, due to its unique properties, it still plays an important role in biomedical applications – especially in the production of medical equipment, implants and parts of prostheses. This publication deals with the effect of selected conditions of processing which involved injection moulding on the mechanical properties and structure of HDPE mouldings. Samples for tests were produced on a Krauss  Maffei injection moulder on the basis of a research plan prepared using the STATISTICA program. According to this schedule, the following variable parameters of the injection process were selected: injection temperature Tw [C], mould temperature Tf [C] and injection velocity vw [mm/s]. In addition, a part of the moldings was subjected to a few processings. Then the samples obtained were subjected to different tests: tensile, impact and hardness tests, Differential Scanning Calorimetry (DSC) and the melt flow rate (MFR) test in order to determine the influence of selected injection conditions and the multiplicity of processing on the mechanical, rheological and structural properties of HDPE.

A calorimetric study of the process of formation of a supramolecular high-density polyethylene structure in mixtures with different oxides after plastic deformation under high pressure

Mixtures of ultrahigh-molecular-weight polyethylene with 95 wt % oxides of different elements were subjected to plastic deformation under the pressure of 1 GPa at a high pressure device of the Bridgman anvil type and thermal effects were studied using the DSC technique. Thermograms contained exothermic peaks with a maximum at 50–90°C related to cold crystallization of the polymer. The process of polymer fusion was described by two peaks with the maximums at T 1 = 125–128°C and T 2 = 136–139°C. The low-temperature peak was related to fusion of a structure with high amounts of defects formed on the oxide surface.

Erratum to: Achromobacter xylosoxidans as a new microorganism strain colonizing high-density polyethylene as a key step to its biodegradation.

This study presents results of research on isolation new bacteria strain Achromobacter xylosoxidans able to effect on the structure of high-density polyethylene (HDPE), polymer resistant to degradation in environment. New strain of A. xylosoxidans PE-1 was isolated from the soil and identified by analysis of the 16S ribosome subunit coding sequences. The substance to be degraded was HDPE in the form of thin foil films. The foil samples were analyzed with Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) as well as scanning electron microscope (SEM), and the results revealed degradation of chemical structure of HDPE. About 9 % loss of weight was also detected as a result of A. xylosoxidans PE-1 effect on HDPE foil. On the basis of comparative spectral analysis of the raw material before the bacteria treatment and the spectrum from a spectra database, it was assumed that the HDPE was the only source of carbon and energy for the microorganisms. No fillers or other additives used in the plastic processing were observed in HDPE before experiments. This is the first communication showing that A. xylosoxidans is able to modify chemical structure of HDPE, what was observed both on FTIR, in mass reduction of HDPE and SEM analysis. We also observed quite good growth of the bacteria also when the HDPE was the sole carbon source in the medium. These results prove that A. xylosoxidans is an organism worth applying in future HDPE biodegradation studies.

Effect of electron-induced reactive processing on morphology and structural properties of high-density polyethylene

High-density polyethylene (HD-PE) irradiated in the solid state is compared with HD-PE modified by electron-induced reactive processing (EIReP) which combines in a unique set-up the modification of polymers with high energy electrons and melt mixing processes. The effect of these different processes on the morphology and structural properties of HD-PE was investigated with X-ray analysis, differential scanning calorimetry, optical light microscopy combined with a hot stage and transmission electron microscopy as function of applied dose. The increased molecular mass was measured by using gel permeation chromatography and confirmed with rheological measurements. Even though the crystallinity and melting temperatures are constant within the studied range of dose significant differences have been observed in the morphology as well as in the crystallization behaviour. Electron treatment in the solid state causes a shift of crystallization temperature to lower temperatures due to branching and degradation whereas the irradiation under the dynamic conditions of melt mixing leads to higher crystallization temperatures with increased doses due to in-situ self-nucleation. The morphology and crystalline structure of HD-PE is not influenced by an electron treatment in the solid state, but by EIReP. Spatial and thermal stable heterogeneities have been generated only in HD-PE modified with high energy electrons under the dynamic conditions of melt mixing.

Achromobacter xylosoxidans as a new microorganism strain colonizing high-density polyethylene as a key step to its biodegradation.

This study presents results of research on isolation new bacteria strain Achromobacter xylosoxidans able to effect on the structure of high-density polyethylene (HDPE), polymer resistant to degradation in environment. New strain of A. xylosoxidans PE-1 was isolated from the soil and identified by analysis of the 16S ribosome subunit coding sequences. The substance to be degraded was HDPE in the form of thin foil films. The foil samples were analyzed with Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) as well as scanning electron microscope (SEM), and the results revealed degradation of chemical structure of HDPE. About 9 % loss of weight was also detected as a result of A. xylosoxidans PE-1 effect on HDPE foil. On the basis of comparative spectral analysis of the raw material before the bacteria treatment and the spectrum from a spectra database, it was assumed that the HDPE was the only source of carbon and energy for the microorganisms. No fillers or other additives used in the plastic processing were observed in HDPE before experiments. This is the first communication showing that A. xylosoxidans is able to modify chemical structure of HDPE, what was observed both on FTIR, in mass reduction of HDPE and SEM analysis. We also observed quite good growth of the bacteria also when the HDPE was the sole carbon source in the medium. These results prove that A. xylosoxidans is an organism worth applying in future HDPE biodegradation studies.

Study of cathodic protection shielding under coating disbondment on pipelines

In this work, the cathodic protection (CP) shielding behavior of pipeline coatings, i.e., high density polyethylene (HDPE) and fusion bonded epoxy (FBE), was investigated. While the HDPE is a CP-shielding coating, the FBE is permeable to CP. The structure of HDPE does not change upon CP permeating test, and water molecules are not absorbed into the coating. Conversely, there are obvious changes of the functional groups in FBE. Water uptakes into the coating occur continuously with time. The CP permeation through FBE coating is time dependent. A more negative CP potential level enhances the CP permeation.

The structural evolution of high-density polyethylene during crazing in liquid medium

Atomic force microscopy (AFM) was employed to study structural transformations occurring in high-density polyethylene (HDPE) during deformation in a liquid medium by crazing mechanism. Processing of the obtained images yielded the parameters of HDPE structure at different tensile strains. It was shown that crazing causes the development of a fibrillar–porous structure in the interlamellar space, the fragmentation of lamellae, and the displacement of lamella fragments relative to each other. Moreover, the deformation is accompanied by the separation of lamellae and the long period increases in the proportion to the tensile strain. The scheme of HDPE deformation upon crazing in liquid medium was constructed based on the AFM images.

Expanded graphite (EG) as a potential filler in the reduction of percolation threshold of multiwall carbon nanotubes (MWCNT) in the PMMA/HDPE/EG/MWCNT nanocomposites

A facile route for the development of a conducting hybrid polymer nanocomposites composed of poly(methyl methacrylate) (PMMA)/high density polyethylene (HDPE) filled with multiwall carbon nanotube (MWCNT) and expanded graphite (EG) has been described. The EG used in this study was prepared by simple chemical exfoliation of graphite flakes and characterized by spectroscopic as well as morphological analysis. An industrially feasible melt mixing process was used for the preparation of the nanocomposites through sequential heating protocol. The judicious control of temperature during mixing revealed a highly co‐continuous structure of HDPE throughout the PMMA matrix and thus the percolation of the (75/25, w/w) PMMA/HDPE/bi‐filler nanocomposites was achieved at 0.07 wt% loading of MWCNT. An extensive analysis revealed that the selective dispersion of the conductive bi‐filler in the minor HDPE phase helped in the reduction of the percolation threshold through MWCNT–EG–MWCNT networking. The morphology, electrical conductivity, and their interrelation of the prepared nanocomposites can be found in detail in the manuscript. POLYM. COMPOS., 37:2070–2082, 2016. © 2015 Society of Plastics Engineers