Polyethylene Samples Research Articles

Effect of temperature and crystallinity on the thermal conductivity of semi-crystalline polymers: A case study of polyethylene

In this work, the effect of temperature and crystallinity on the thermal conductivity was investigated in a series of polyethylenes (PEs) with different crystallinities including high-density polyethylene (HDPE), medium-density polyethylene (MDPE), linear low-density polyethylene (LLDPE) and low-density polyethylene (LDPE). It was found that the applied ambient temperature has a significant effect on the thermal conductivity. At −20~100 °C, the thermal conductivity of PE showed a linearly decline with the increase of temperature. The thermal properties of a series of PE samples were also investigated by differential scanning calorimeter. The results showed that the higher the crystallinity, the higher the thermal conductivity of polyethylene. However, above the melting point, thermal conductivity of all PE samples tended to be the same, with a value of about 0.21 W/m·K. Based on the crystallinity and temperature, an empirical formula was proposed to predict the thermal conductivity of PEs with an error within 3%, which was also consistent with the results of other reported thermal conductivity of PEs. This work can guide the design of thermally conductive polymers in the future.

Characterization of Dendritic Defects of Polyethylene Insulation Materials Based on Microstrip Gap Resonator

This article attempts to reveal the detection ability of microstrip slot resonator for water and electrical tree defects in insulating samples. The characteristics of microstrip gap resonator are analyzed in high-frequency electromagnetic simulation software. A gap capacitance extraction method is proposed based on two-port transmission theory, and the gap capacitances under different dielectric constants are analyzed based on this method. The resonant frequency of sensor is found to be negatively correlated with the dielectric constant of the materials. In the experimental part, the sensor made of double-sided copper clad plate with medium FR4 was used to detect the water tree and electrical tree in low-density polyethylene (LDPE) samples, and the experiment results showed good feasibility.

Self-Healing and Shape Memory Behavior of Functionalized Polyethylene Elastomer Modified by Zinc Oxide and Stearic Acid

There is still a great need to develop self-healing polymers (SHPs) using a cost-effective modification approach for commercial polymers. Herein, we describe our preparation of self-healing (SH), acrylic acid-functionalized, metallocene polyethylene elastomer (mPE-g-AA) composites containing ZnO and stearic acid (SA) that feature both supramolecular hydrogen bonding and ionic interactions. Regarding mechanical properties, with the addition of various contents of ZnO/SA in the mPE-g-AA matrix, their tensile strength increased to be higher than that of mPE-g-AA. As for the shape memory properties, with this synergistic effect of zinc oxide (ZnO), SA, and grafting AA, both the shape fixing ratio and shape recovery ratio of those functionalized polyethylene samples modified by ZnO and SA increased up to above 80% as a result of the hydrogen bonding and reversible ionic crosslinked networks acting as physical crosslinks. Among all of the samples, mPE-g-AA/ZnO 4/SA 1 (4 phr of ZnO and 1 phr of SA) exhibited the highest SH efficiency, at 44.6% for half-hour healing and up to 64.4% under 6 h healing, being higher than those related self-healing mPE studies in the literature. These hydrogen bonded reversible networks, along with the enhanced molecular flow at high temperatures in addition to ionic interactions, could also have a great potential in self-healing applications, besides the shape memory performance. So far, to the authors’ best knowledge, there have been no published reports of the design of polyolefin elastomers with thermally-triggered shape memory effect by adding ZnO to assist the self-healing behavior. The current synergistic approach paves the way for preparing various SH commercial polymers where surface scratches and cuts have previously been hard to repair.

Heavy metals, PAHs and POPs in recycled polyethylene samples of agricultural, post-commercial, post-industrial and post-consumer origin

In the present work, recycled polyethylene (LDPE) samples of agricultural, post-commercial, post-industrial and post-consumer origin were selected and analysed. The analysis comprised the determination of different contaminants such as metals, polycyclic aromatic hydrocarbons (PAHs), dioxin-like biphenyl polychlorides (PCBs), and polychlorinated-dibenzo-p-dioxins and furans (PCDD/Fs). A comparison with one sample of virgin plastic (unrecycled) was performed. The study aimed at stressing the importance of this type of analysis in recycled plastics. Indeed, such an examination will determine the material’s final destination, and the possible origin of the pollutants analysed is investigated. Black post-industrial and post-consumer samples presented the highest concentration of PCBs and PCDD/Fs, attaining a maximum value of 2.40 pg WHO-TEQ/g, while the least toxic sample (post-commercial) presented a toxicity of 0.38 pg WHO-TEQ/g. PAHs content was also much higher in black samples, reaching 514.41 ng/g, while the lowest concentrations were obtained for the post-commercial plastic sample, which did not exceed 38.98 ng/g. The higher PAHs concentrations in the black samples were related to the carbon black content of the black samples, which was 2.00% for black post-industrial sample and 1.51% for post-consumer sample. The PCDD/Fs congener profile observed in almost all samples was very similar to the profile found in the literature on urban air samples, indicating that the plastic is mainly influenced by the environment. The presence of some metals (mainly copper) showed a slight correlation with PCDD/Fs content. The pollutants analysed were found to be significantly reduced during the cleaning processes that are generally carried out in recycling companies.

Effects of residual wax content on the thermal, rheological, and mechanical properties of high‐density polyethylene

AbstractThe influence of residual wax content on the thermal, rheological, and mechanical behavior of two high‐density polyethylene (HDPE) samples from different lots of the same supplier was characterized. HDPE with a low wax content presented a higher melting temperature and a wider melting endotherm. A decrease in the degree of crystallinity and thermal stability of HDPE with a higher wax content was observed. Thermograms obtained by DSC indicated a small additional exothermic transition associated with the exclusion of residual wax. A higher wax content in HDPE produces a decrease in its viscosity due to a lubricating effect, which allows the sliding of HDPE chains of high molecular weight. In contrast, HDPE with lower wax content achieves greater elongational viscosity and melt strength. The mechanical testing results show that HDPE with higher wax content presented lower Young's modulus, tensile strength, elongation at break, and Izod impact strength than HDPE with lower wax content. The results obtained show that a relatively slight difference in wax content significantly affects HDPE properties.

Production and mechanical characterization of polyethylene matrix composites with the addition of linen and cotton waste fabric filler materials

In this study, linen and cotton fibers obtained from fabric waste were used as filler materials and polyethylene was used as matrix material to produce fiber reinforced polymer composites using injection molding. Use of fabric waste as filler material enables utilization of linen and cotton wastes while decreasing the amount of polyethylene used in the composites resulting in an environmentally friendly material. Prepared samples with varying content of linen and cotton wastes (5, 10 and 20 vol. %) were compared with each other and with polyethylene samples without any filler, based on their yield, tensile and fracture strengths, percent elongation and hardness values. Samples were also evaluated for their chip formation characteristics based on chip lengths at various machining speeds and examined for their visual appearance. Results indicated that linen waste fibers can be used to improve the strength of polyethylene based composites while cotton waste fibers can be utilized to enhance the elongation characteristics of the samples.

Reactive Extrusion Grafting of Glycidyl Methacrylate onto Low-Density and Recycled Polyethylene Using Supercritical Carbon Dioxide

Glycidyl methacrylate (GMA) was grafted onto (recycled) polyethylene (PE) to design a new adhesive with better mechanical properties compared to non-grafted PE. The effects of the amount of GMA, the amount of dicumyl peroxide (DCP) and the use of supercritical carbon dioxide (scCO2) in a reactive extrusion (REX) were evaluated based on the grafting degree and efficiency of the grafted samples. Generally speaking, higher amounts of GMA led to higher functionalization degrees (FD), whereas higher amounts of DCP resulted in a lower FD due to the occurrence of more unfavorable side reactions. The influence of scCO2 showed different outcomes for the two substrates used. Higher FDs were obtained for the low-density polyethylene (LDPE) samples while, by contrast, lower FDs were obtained for the recycled polyethylene (RPE) samples when using scCO2. Additionally, adjusting the screw speed and the temperature profile of the extruder to the half-life time of the radical initiator appeared to have the highest positive impact on the FD. According to the tensile tests, all the grafted samples can withstand higher stress levels, especially the grafted RPE, compared to the non-grafted samples.

Safety assessment of bleached cellulose pulp for use in plastic food contact materials.

The EFSA Panel on Food Contact Materials, Enzymes and Processing Aids assessed the safety of the substance bleached cellulose pulp, consisting of cellulose fibres (70–92%) and hemicellulose (8–30%) obtained from pine and spruce wood. The substance is intended to be used ■■■■■ in polyethylene and polypropylene food contact materials. The final articles are intended to be used for all food types and for long‐term storage at room temperature, with or without a short time at higher temperature, including hot‐fill. Low‐density polyethylene samples containing ■■■■■ of the substance were subjected to a broad set of migration tests with food simulants and extraction tests with dichloromethane. The limits of detection ranged from ■■■■■ (when specified). The Panel noted that they do not ensure the detection of genotoxic substances at a concentration leading to a human exposure above the Threshold of Toxicological Concern. Moreover, not all possibly migrating substances were identified or amenable to the analytical methods applied. No toxicological data were provided for the substance itself, as its migration into food is not expected. The safety of the potentially migrating substances of low molecular mass detected was addressed individually and was considered adequate. However, the Panel considered this approach insufficient owing to a substantial fraction of unidentified components. The Panel concluded that the information provided by the applicant does not allow the safety assessment of the substances below 1,000 Da from bleached cellulose pulp from pine and spruce wood used in plastic food contact materials potentially migrating into food. Therefore, the Panel could not conclude on the safety of the use of bleached cellulose pulp from pine and spruce wood as a plastic additive.

Efficacy of Cavern Isolates for Biodegradation of Synthetic Plastic

Abstract: Synthetic plastic waste management is a tenacious environmental concern at global level. Although all types of synthetic plastics are a nuisance to the environment, however, versatility and one time use has made polyethylene (PE) a foremost environmental issue. Current study has investigated cavern bacterial strains isolated from PE samples from San Giovanni cave, Sardinia, Italy for their efficacy to biodegrade low density polyethylene (LDPE) film. It was an initial effort to use cavern bacteria in plastic biodegradation studies. Chemical and physical changes in the composition of LDPE were studied by Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) after incubation with the bacterial consortium for two months. Collected cavern PE plastic samples were also studied for biodegradation after incubation in nutrient broth for two months. FTIR revealed obvious signs of degradation with the appearance of two new peaks of functional groups, nitriles (C≡N) and amines (N-H) in LDPE film, which are intermediate metabolites of β-oxidation pathway. An increase in various existing peaks of several intermediate metabolites, including aldehydes, ketones, alcohols, and carboxylic acids, were also observed in experimental LDPE compared to control. Peaks of alkanes decreased significantly owing to cavern bacterial activity. SEM revealed biofilm formation on experimental LDPE surface with substantial mechanical damage. Similar signs of degradation were observed in the cavern PE samples. Four bacterial strains in the current consortium including Bacillus sonorensis, Bacillus subtilis, Aneurinibacillus spp., and Alcaligenes faecalis are first time reported to be linked with biodegradation of plastics. The cavern bacteria under study have the potential to biodegrade LDPE.

An insight into the effect surface morphology, processing, and lubricating conditions on tribological properties of Ti6Al4V and UHMWPE pairs

The effects of surface topography, processing, and environment conditions during tribological contact between Ti6Al4V titanium alloy and UHMWPE friction pairs were systematically evaluated. Hence, in this research the polyethylene samples (blocks) having a constant surface roughness were rubbed against counter-bodies (rollers) made of titanium alloy with different roughness of surfaces. The counter-samples were manufactured using either dry machining and/or minimum quantity lubrication (MQL) conditions. Such cutting conditions are harmless to humans and the environment. Simulated body fluid (SBF) and distilled water was used to simulate the tribological trials. We have noted that the lubricant applied to protect the integrity of machined parts, the rollers, have only minor impact on the tribological features of the friction pairs tested. Further, the samples produced with dry machining demonstrated a slightly lower momentary friction coefficient and temperature. In contrast, the MQL method enable reduced friction surface and significant wear accumulation. Further, it was found that the minimum and maximum values of the Sa texture parameter associated to tribological parameters do not exceed 21% and 4%, when is used dry and MQL methods, respectively. Nevertheless, the distilled water revealed a much better wear resistance when comparing to SBF, and the later one trigger as well as an accentuated wear progress with different patterns. The results of the study are important in the design of new biomedical components produced by finish turning.

Improved line–line method for propagation constant measurement of reflection-asymmetric networks

A new formalism using line–line measurements is proposed to improve the accuracy of propagation constant measurement of reflection-asymmetric networks using non-calibrated scattering (S-) parameters. For this measurement, the method uses a reference network with arbitrary forward and backward impedance, propagation constant, and length, thus giving flexibility in the application of line–line methods. S-parameter measurements were carried out for propagation constant extraction of a reflection-asymmetric waveguide loaded with a bianisotropic metamaterial slab made by C-shaped split-ring-resonators using two different kinds of reference networks (two empty waveguide sections as the first kind and the same sections loaded by polyethylene samples as the second kind). It is observed that the standard deviation in the extracted real part of the propagation constant of this network by our method could be reduced by using the first kind of reference network, indicating that the accuracy of our method could be improved using a suitable reference network.

Circular Economy Assessment in Recycling of LLDPE Bags According to European Resolution, Thermal and Structural Characterization.

According to the Circular Economy Package promoted by the European directive, plastic bags companies must use in their formulations a percentage of polyethylene waste (industrial and/or domestic) greater than 70%. Following that regulation requires an understanding of its consequences in the final product from an industrial point of view. This manuscript analyzes the thermal and morphological changes related to the tear resistance of linear-low density polyethylene (LLDPE) samples from industrial waste generated by the company Sphere Spain subjected to the degradation produced by the recycling cycles. The process is analogue to the industrial, starts from samples in pellets then a film by blow extrusion is obtained (odd steps) and posteriorly this film is recycled to pellets again (even steps). The results obtained show that the LLDPE samples develop two crystalline structures (CS1 and CS2) which evolve differently through the recycling cycles with a tendency to decrease in crystallinity due to degradation that is not the same for the process of obtaining film or recycling to pellet. The molecules with a more linear structure and a longer chain break and branch. The more branched structure increases and tends to crosslinking. This leads to a decrease in tear strength in the longitudinal direction, which is not so evident in the transversal direction. The samples could admit four recycling cycles with and acceptable tear resistance. The longitudinal tear strength value decreases by 40% for each film and 20% in the case of tearing in the transverse direction. The results obtained in this research work show that the regulations included in the cited circular economy package can be applied in the manufacture of consumer bags, helping also to reduce the dependence of manufacturers on fluctuations in delivery by collapses in shipping.

Spectra of Internal Friction in Polyethylene.

The study of spectra of internal friction and temperature dependencies of frequency of freely damped oscillatory process excited in investigated samples of polyethylene with different degree of crystallinity in the temperature range from −150 C to +150 C. It is established that four local dissipative processes of different intensity shown in different temperature intervals are observed on the spectra . These are , , , processes. The theoretical analysis of the relationship between the anomalous changes of the vibrational process frequency and the shift modulus defect and the internal friction mechanisms for each of the dissipative loss processes detected on the spectrum is carried out. The influence of supramolecular structures on local dissipative process in polyethylene is estimated.

Safety assessment of the substance fatty acid-coated nano precipitated calcium carbonate for use in plastic food contact materials.

The EFSA Panel on Food Contact Materials, Enzymes and Processing Aids (CEP) assessed the safety of the substance identified by the applicant as ‘fatty acid‐coated nano precipitated calcium carbonate’. It is intended to be used as a filler in all plastics at up to 5% for contact with acidic food and at up to 40% for contact with all other types of food. Articles made with the substance are intended for long‐term storage over 6 months at room temperature and below. No information was provided on the mechanism of coating as to whether there is chemical modification of the surface and/or physical adsorption. The substance was not properly characterised, either as pristine material or when incorporated into plastic. Contrary to the non‐coated material, data show that the coated material does not dissolve fully and quickly under pH conditions simulating gastrointestinal tract. Surface analysis with electron microscopy of low‐density polyethylene (LDPE) samples before and after migration experiments showed major differences that indicate release of the substance from the surface after the tests with 3% acetic acid and to a lesser extent with 10% ethanol. This is consistent with measurable migrations that were up to 39 mg CaCO3/kg when using an LDPE sample made with 5% of the substance in contact with acetic acid for 64 days at 40°C. The required data on the release of nanoparticles and on the potential toxicity of the substance in nanoform were not provided. Therefore, the Panel could not conclude on the safe use of the substance.

Legacy halogenated organic contaminants in urban-influenced waters using passive polyethylene samplers: Emerging evidence of anthropogenic land-use-based sources and ecological risks

Legacy halogenated organic pollutants, including organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs), remain ubiquitous in the environment and continue to pose potential (eco-)toxicological threats because of their ongoing releases from land-based sources. This study investigated the spatial trends of freely dissolved PCBs and OCPs by polyethylene passive samplers, and provided evidence of their land-use-based sources and ecological risk in an urbanized estuary area of Narragansett Bay. Dissolved Σ29PCB concentrations ranged from 0.01 to 1.37 ng L−1, and exhibited higher concentrations in the upper, more urban/built-up watershed, and in north coastal areas. Major inputs of PCBs were urban stormwater or treated wastewater that might carry past releases of Aroclors, pigment manufacturing byproducts, and volatilization-associated PCBs from ageing buildings from the Narragansett watershed to the bay. The dioxin toxicity equivalent values of Σ5PCBs were 8.6E-03 pg L−1 in water. Dissolved OCP concentrations had similar spatial trends to PCBs and were dominated by DDTs (average 230 pg L−1), followed by chlordanes (average 230 pg L−1), and HCB (average 22 pg L−1). Secondary sources of past usage and historic contamination were expected to re-enter the surface water via atmospheric transport and deposition. The risk quotients of DDE, DDD, DDT and α-Endosulfane showed medium to high ecological risks in the northern area, while chlordane, HCB, oxychlordane, and heptachlor epoxide showed low to negligible risks in all zones. This study presented new insights into the presence, sources and transport of legacy halogenated organic contaminants in an urban estuary's watershed by combining passive samplers and geographic information system (GIS) technology. The approach is promising and could be extended to get better understand of terrestrial pollutant mobilization into estuaries affected by anthropogenic activities.

Determination of error-corrected full scattering parameters of a two-port device from uncalibrated measurements

A methodology relying on relating terms of a two-port error network to the scattering (S-) parameters of a two-port network or device is applied to extract its full S-parameters. The new methodology has only one sign ambiguity problem (two solutions) in evaluation of S11 (and thus S22) while the similar methodology in the literature has two sign ambiguity problems (4 solutions). This ambiguity problem of our method is shown to be eliminated by applying an approach based on continuity of the argument of S11 in the frequency domain. On the other hand, our methodology, as compared with the thru-reflect-line calibration technique, does not necessitate usage of any reflection standard in determining full S-parameters of a two-port network or device. Finally, it gives information about error networks. For its validation, S-parameters of a microwave phase shifter and a polyethylene sample flushed with the left/bottom terminal of the coaxial cell were extracted.

Enhanced peroxidase-mediated biodegradation of polyethylene using the bacterial consortia under H2O2-biostimulation

Biotreatment is an environmentally friendly process for pollution control. A novel biotreatment process was investigated for the degradation of plastic wastes. The biodegradation of low-density polyethylene (LDPE) films using a bacterial consortium capable of peroxidase production in the presence of H2O2 was investigated for a 12-month period. Effective biodegradation was observed using the selected bacterial consortia; a 19.8% weight loss was detected during 12 months of biotreatment of the LDPE films. The daily addition of H2O2 to the bioreactor stimulated the microbial activity resulted in improving the weight loss to 22.5% due to the in-situ production of peroxidase. The number average molecular weight (Mn) decreased by 20.1 and 49.5% when the polyethylene sample was biotreated for 12 months in the absence and presence of H2O2, respectively. The depolymerization of the LDPE films during the biotreatment using the selected bacterial consortia was confirmed by increasing the value of polydispersity index. The morphological and structural analyses confirmed the efficient decomposition of the LDPE films using the selected bacterial species, showing that the selected bacteria could use the LDPE films and/or their degradation intermediates as carbon and energy sources. Overall, using a peroxidase-generating bacterial mixed culture is a promising biotechnique for the efficient biodegradation of the polyethylene wastes.

Experimental Investigation Joining Al 5083 and High-density Polyethylen by Protrusion Friction Stir Spot Welding Containing Nanoparticles using Taguchi Method

One of the most important challenges of the Friction Stir Spot Welding (FSSW) process is the appearance of a void in the welded parts. This causes the stress to be stacked against the created void, and as a result, the mechanical properties would be reduced. To solve this problem in this research, the aluminum and polyethylene sheets are joined by means of H13 steel tools, protruding fixtures, and also three types of nanoparticles. Appending three types of Nano-particles, namely Al2O3, TiO2, SiO2, the constituent materials of Al 5083 and high-density polyethylene sheets have been prepared. To improve the mechanical properties of the welded samples, these three types of Nano-materials are integrated to the Stir Zone (SZ). In order to find the maximum strength of welded composite plates, the Design of Experiment (DOE) is performed using the Taguchi method. The Rotation Speed, Dwell Time, Tool d/ Protrusion d besides the type and percentage of Nano-material are chosen as input parameters. The maximum fracture force and the maximum strength are respectively as 2249 N and 4.13 MPa. Without using nanoparticles, a rupture is occurred in the tensile tests of polyethylene samples. Thus, the polyethylene samples capture more sediment by addition of nanoparticles, and the nanoparticles’ deposition improves the mechanical properties of the Al/PE composite. Compared to the base material of pure aluminum and polyethylene, a nearly eightfold increment of the mechanical properties of the Al/PE composite sample is observed by addition of nanoparticles in the welding nugget. According to the S/N ratio analysis, the rotation speed of 2500 rpm, dwell time of 12 s, tool d/ protrusion d of 3 mm, Nano-material’s type of Sio2 and percentage of 10% are considered as the optimum states.

Quantifying nanoscale forces using machine learning in dynamic atomic force microscopy.

Dynamic atomic force microscopy (AFM) is a key platform that enables topological and nanomechanical characterization of novel materials. This is achieved by linking the nanoscale forces that exist between the AFM tip and the sample to specific mathematical functions through modeling. However, the main challenge in dynamic AFM is to quantify these nanoscale forces without the use of complex models that are routinely used to explain the physics of tip–sample interaction. Here, we make use of machine learning and data science to characterize tip–sample forces purely from experimental data with sub-microsecond resolution. Our machine learning approach is first trained on standard AFM models and then showcased experimentally on a polymer blend of polystyrene (PS) and low density polyethylene (LDPE) sample. Using this algorithm we probe the complex physics of tip–sample contact in polymers, estimate elasticity, and provide insight into energy dissipation during contact. Our study opens a new route in dynamic AFM characterization where machine learning can be combined with experimental methodologies to probe transient processes involved in phase transformation as well as complex chemical and biological phenomena in real-time.

Rheological and morphological analysis of irradiated high and low density polyethylene samples

The influence of intensity of the ?-irradiation on commercial high and low density polyethylene (LDPE and HDPE) granules (Kazanorgsintez PJSC, Kazan, Tatarstan, Russia) on their rheological and morphological properties at irradiation doses of 5 and 10 kGy was studied. Experiments in the oscillation mode revealed an increase in the dynamic moduli values with increasing radiation dose compared to the initial samples. At the same ?-irradiation doses, the HDPE samples compared to the LDPE ones showed the greatest changes in rheological properties, while the zero shear viscosity of HDPE increased by order of magnitude compared to the initial one at the irradiation dose of 10 kGy. Morphology analysis of supramolecular structures revealed an increase in cob-web-type structures for the irradiated sample in comparison with the initial sample, which may indicate the formation of branched structures under ?-irradiation.