Polyethylene Samples Research Articles

Formation and reinforcing effect of epitaxial oriented crystallization of polyethylene induced by self‐assembly nucleating agent under stress

AbstractA rare earth nucleating agent (RENA) was introduced to fabricate polyethylene (PE) pipe resin, which self‐assembled into various structures in PE melt during processing and further induced PE molecules to epitaxially crystallize on its surface to form, among others, a hybrid shish‐kebab crystalline structure due to good crystallographic matching between RENA and PE. Under stress, the shish structure formed by needle‐like RENA assembly arranged preferentially along the drawing direction, which was beneficial for an orderly arrangement of PE chains epitaxially crystallizing on its surface in the process of stress‐induced recrystallization and thus promoted the formation of a dense oriented crystalline structure with a large number of shish structures, resulting in higher degree of crystallinity and orientation, and lower long period and lateral size of lamellae than those of PE sample. By orientation, compared with PE sample at the same draw ratio, PE‐RENA samples showed much higher tensile strength and modulus. Especially, the oriented PE‐RENA pipes showed an approximately 96% and 100% increase in tensile strength along the hoop direction and internal pressure resistance, respectively, compared with unoriented pipe sample. This work provides a facile method for fabricating highly enhanced PE pipes with wide application prospects. © 2021 Society of Industrial Chemistry.

Composite Micro-Nanoarchitectonics of MMT-SiO2: Space Charge Characteristics under Tensile State.

Low density polyethylene (LDPE) is a good insulating material which is widely used in cable materials due to its excellent insulation and processability. However, in the DC high voltage environment, pure polyethylene materials still face many problems, the most serious of which is space charge accumulation. The cable will inevitably be subjected to tensile stress during production, installation and operation. Therefore, it is of great significance to study the effect of stretching on the microstructure and space charge characteristics for polymers and their composites. In this paper, MMT/LDPE micro-composites, SiO2/LDPE nano-composites and MMT-SiO2/LDPE micro-nano-composites were prepared by melt blending. Mechanical stretching was carried out on pure LDPE materials and the above three kinds of composite materials. Each material was stretched according to four stretching ratios, which are 0%, 5%, 10% and 20%. The crystal morphology was observed by polarizing microscope (PLM), the crystallization perfection was tested by differential scanning calorimetry (DSC), and the space charge distribution inside each sample was measured by pulsed electro-acoustic (PEA) method. At the same time, the average charge density and apparent charge mobility for samples during depolarization were calculated and analyzed. The experimental results show that when the pure low density polyethylene sample is not stretched, its crystal structure is loose. Tensile stress can make the loose molecular chains align in LDPE and improve its crystalline structure, which is helpful to restrain the accumulation of space charge inside the sample. For MMT/LDPE, SiO2/LDPE and MMT-SiO2/LDPE composites, their internal crystal structure is compact. Stretching will destroy their original crystal structure at first, and then disorder molecular chains inside the three composite materials. With the increase of stretching ratio, the molecular chains begin to orient along the direction of force, the crystallization tends to be perfect gradually, and the space charge accumulation in samples also decreases. From the calculation results of apparent charge mobility for each sample, with the increase of stretching ratio, the trap depth and trap density inside samples firstly increased and then decreased.

Utility of benzothiazoles as markers of tire-derived inputs to estuarine waters assessed by polyethylene sheets

Tire-derived particles and polyethylene (PE) debris co-exist in estuaries and potentially deteriorate water quality. Chemicals can be emitted from tire-derived particles and resorb to PE debris. However, there was lack of information about the interaction (e.g., sorption and desorption) between tire-derived chemicals and PE debris. By combining batch sorption and desorption experiments along with in situ field deployment of PE sheets, we examined the utility of benzothiazoles (BTZs) sorbed in PE as suitable markers of tire-derived inputs. The sorptive characteristics and PE-water partition coefficients (often designated as Kpew) of selected tire-derived marker candidates, i.e., polycyclic aromatic hydrocarbons (PAHs), benzothiophenes (BTPs) and BTZs, were measured. Moderately polar BTPs and BTZs (except for 2-(4-morpholinyl) benzothiazole) reached equilibrium within 2–8 days, compared to 20 days for nonpolar PAHs. The measure Kpew values and octanol-water partition coefficients of PAHs and BTZs were linearly correlated with each other (r2 > 0.80; p < 0.05). The desorption potentiality of PAHs and BTZs from tire particles is consistent with the hydrophilic properties of the target chemicals, while desorption ratios of BTZs and PAHs are 25–87% and <20%, respectively. Samplers with PE sheets as the sorbent phase were deployed in Hailing Bay, an urbanized estuary in South China, to measure concentrations of PAHs, BTPs and BTZs. Benzothiazoles sorbed in PE samples were associated with the massive utilization of automobile tires, while PAHs were linked to the boat maintenance facilities and BTPs were not detected in any tire particle and field PE samples. Therefore sorbed BTZs in PE can potentially serve as chemical markers of tire-derived inputs to estuaries.

Processing of polyethylene in the beam-plasma generated by a ribbon electron beam at forevacuum pressure range

We present research results of the surface modification of polyethylene film by plasma produced by the ribbon electron beam formed by a forevacuum-pressure plasma-cathode electron source. The electron beam was of energy 3 keV and current 150 mA. The gaseous environment was argon at a pressure of 10 Pa. The argon plasma so formed in the electron beam vicinity and at the location of the polyethylene samples was of density about 3 x 1015 m−3. Both direct plasma bombardment, and also energetic ion bombardment with ions accelerated to the sample from the e-beam produced plasma, were investigated. We show that this plasma or ion treatment imparts improved hydrophilic properties to the film and decreased light transmittance in the ultraviolet region.

Ion bombardment technique induced alterations in the surface chemical composition and shielding parameters of polymeric material

At present, ion beam technology is one powerful technique to improve the physico-chemical properties of polymeric material. In this work, ultra high molecular weight polyethylene samples were bombarded with 1 MeV He-ion beam at fluences ranging from 1×1013 to 5×1014 ions/cm2. The changes in the chemical composition of the treated layer caused by the ion beam were investigated. The hydrogen escapes due to the ion beam irradiations were measured by the nuclear reaction analysis (NRA) technique using the 1H(15N, αγ)12C reaction. The oxygen uptake has been studied by the Rutherford backscattering spectrometry (RBS) and Fourier transform infrared spectrometer (FTIR) techniques. The partial and total mass attenuation coefficients of photons at energies 81, 356, 511 and 1332 keV were estimated using the XCOM program (version 3.1). The obtained results showed that the hydrogen release was increasing with an increase in ion fluence. Moreover, important oxygen uptake of bombarded samples was also observed. These effects led to significant improvements in the surface characteristics of the treated materials such as changes in the shielding parameters. The changes in the mass attenuation coefficients (μ/ρ) were calculated relying on the incoming photon energies and the atomic concentrations of the elements that are present in the target material. The total atomic cross-sections and effective atomic numbers were calculated by using the data of the total mass attenuation coefficients. A decrease in both the total atomic cross-section and effective atomic numbers was noticed with an increase in the ion beam fluence.

Fluorescent Polyethylene by In Situ Facile Synthesis of Carbon Quantum Dots Facilitated by Silica Nanoparticle Agglomerates

We describe an in situ facile synthetic approach to prepare carbon quantum dot (CQD) fluorescent markers (FMs) for polyethylene (PE) in the presence of agglomerated silica nanoparticles (SiO2 NPs) under mild reaction conditions. First SiO2 NPs, prepared by the Stöber method, were dispersed in toluene. This dispersion was added to a PE solution in toluene. After heating (either in air or under Ar) a fluorescent mixture was obtained. After drying, PE films were obtained by compression molding, which showed strong blue fluorescence, attributed to CQDs. SiO2 NPs loading values varied between 0.5 and 4 wt %. Subsequent to isolation, the fluorescent CQDs were characterized by TEM, UV–vis, and fluorescence spectroscopy. TEM imaging unveiled a lattice spacing value of 0.21 nm of the isolated fluorescent particles which is typical for (100) graphite plane lattice spacing in CQDs. UV spectroscopy and fluorescence measurements show characteristic absorption and excitation spectra for the aromatic core and oxidized surface defects typically observed for CQDs. The emission maximum for PE/CQD samples increased from 394 to 408 nm when the reaction temperature was decreased from 110 to 90 °C, which is attributed to increasing oxygen content in the reaction mixture upon decreasing the reaction temperature. When the reaction was performed under Ar, the PE/CQD samples emitted in the ultraviolet region (286 nm). Finally, we demonstrated that PE samples marked with CQDs can be easily visually identified upon irradiating with 367 nm light. Thus, the marked PE can be used, for example, as a labeling ingredient in master batches for component identification and in recycling.

Investigating Branched Polyethylene Sensors for Applications in Prosthetics

AbstractThere is a need for new conductive, scalable sensors with piezoresistive and thermoresistive properties for applications in bioengineering. For example, the demand for real‐time sensory feedback in upper‐limb prosthetics requires sensors that are low‐cost, scalable, and sensitive to temperature, pressure, and movement. It is possible to manufacture low‐cost conductive sensors by directly mixing a low‐cost filler such as graphite into fillers such as polyorganosiloxane, although they can have poor electrical and mechanical homogeneity. In this paper, an alternative approach is outlined to form these sensors: ethylene was polymerized using a nickel catalyst to form a polymer with up to 93 branches per 1000 carbon atoms. This branched polyethylene was fibrous and had a greater volume than high‐density polyethylene. After hot pressing with a graphite filler to form a conductive, flexible sensor, the polyethylene samples had electrical resistivity down to 0.067 m, a thermal coefficient of resistance −7.5 at 27 , and a electrical resistance sensitive to forces down to 0.1 N. The process is scalable, and provides a route to homogeneous, low‐cost sensors for future prosthetics applications.

Influence of Tire Rubber Particles Addition in Different Branching Degrees Polyethylene Matrix Composites on Physical and Structural Behavior.

Waste from pneumatic wheels is one of the major environmental problems, and the scientific community is looking for methods to recycle this type of waste. In this paper, ground tire rubber particles (GTR) from disused tires have been mixed with samples of low-density polyethylene (LDPE) and high-density polyethylene (HDPE), and morphological tests have been performed using scanning electron microscopy (SEM), as well as the dynamic electric analysis (DEA) dielectric characterization technique using impedance spectroscopy. From this experience, how GTR reinforcement influences polyethylene and what influence GTR particles have on the branched polyethylene has been detected. For pure LDPE samples, a Debye-type dielectric behavior is observed with an imperfect semicircle, which depends on the temperature, as it shows differences for the samples at 30 °C and 120 °C, unlike the HDPE samples, which do not show such a trend. The behavior in samples with Debye behavior is like an almost perfect dipole and is due to the crystalline behavior of polyethylene at high temperature and without any reinforcement. These have been obtained evidence that for branched PE (LPDE) the Maxwell Wagner Sillars (MWS) effect is highly remarkable and that this happens due to the intrachain polarization effect combined with MWS. This means that the permittivity and conductivity at LDPE/50%GTR are high than LDPE/70%GTR. However, it does not always occur that way with HDPE composites in which HDPE/70%GTR has the highest values of permittivity and conductivity, due to the presence of conductive fraction (Carbon Black-30%) in the GTR particles and their dielectric behavior.

Correction to: Structural health monitoring of irradiated high-density polyethylene samples with electrical resistance tomography

Correction to: Structural health monitoring of irradiated high-density polyethylene samples with electrical resistance tomography

Temperature gradient interaction chromatography of linear polyethylene and isotactic polypropylene

Samples of linear polyethylene and isotactic polypropylene were separated according to their average molar mass using temperature gradient interaction chromatography (TGIC) with mobile phases at near critical composition. It is known that at the critical mobile phase composition, the adsorption of polymers is very sensitive to variations of the temperature. This effect was utilized here. The temperature of the column (Hypercarb™) was changed from 80 °C to 170 °C according to a programmed temperature gradient. Polymers were first adsorbed in the column at 80 °C and desorbed by the temperature increase. In effect, the polymers eluted at different temperatures. The higher the molar mass, the higher both the elution temperature and the elution volume. This suggests that TGIC has the potential to improve separations of polyolefins according to their molar mass and will allow to separate polyolefins according to their long-chain branching content.

Structural health monitoring of irradiated high-density polyethylene samples with electrical resistance tomography

Structural health monitoring of irradiated high-density polyethylene samples with electrical resistance tomography

Analysis of heat transfer during flame spread over energized-wire under high currents

Electrical wire is one of the primary causes of electrical fires because of short circuiting or overload current. Experiments were carried out to characterize the influence of high currents on flame spread and dripping behaviors over wires. Two samples of polyethylene (PE)-insulated copper wires with different sizes (dc/do = 0.9 mm/3.0 mm for wire #1 and 1.3 mm/4.2 mm for wire #2) were electrified with current, ranging from 10 A to 50 A, to conduct experimental study. Results show that the dripping becomes faster as the current increases and the continuous dripping occurs under high current (I > 40 A for wire #1 and I > 30 A for wire #2), causing the flame to be narrower and shorter. The heat transfer by different passages (radiation, convection, conduction through core and the joule heat) were quantitatively analyzed. The heat feedback from core to the insulation (q˙cp) were the dominant heat transfer mode during flame spread over energized wire. Heat required for flame spread (q˙req) is mainly supplied from the core, nearly 80%, including the joule heat (q˙joule) and the heat conduction through the core from the burning zone (q˙cc). The proportions q˙cp/q˙req decreased with the increasing current, and has a sharp decent to 70% or 50% at I = 50 A or 35 A for wire #1 or wire #2, respectively. In addition, the proportion of q˙cp to the sum of q˙joule and q˙cc drops obviously under high current, which means the dominated role of core heat feedback in heat transfer mode is weakened under high current. A flame spread model for energized wire based on the quantitative analysis of controlling heat transfer mechanism was proposed, and it predicted the flame spread rate well within error of ±20%. The findings of the presented study will be essential for simulation study of flame spread behavior over energized wires with high current and may guide the design of future electric fire safety.

Investigations on the influence of multiple extrusion on the degradation of polyolefins

The importance of mechanical recycling of polymers has increased within the last decades, especially due to numerous regulations of governments all over the world. Hereby recycling quotas are enforced to pave the way towards a closed loop recycling. During its lifetime, polymers are exposed to multiple environmental factors, which can already induce degradation. However, a major factor that needs to be taken into account is the increased thermo-mechanical stress during the recycling process, which may have significant impact on the quality of recyclates as well. In the present work, polyolefins (high-density polyethylene and polypropylene) were artificially exposed to stress by continuous extrusion at varying speeds and absence or presence of stabilizers to analyze the extent to which the recycling contributes to degradation processes. These samples were analyzed for low-molecular-weight stress markers by thermodesorption gas chromatography and by high-performance liquid chromatography (both coupled to mass spectrometric detection). Depending on the extent of stress, the occurrence of odd-numbered linear alkane chains was revealed in polyethylene samples, and of oxidized branched alkanes in polypropylene samples. Correlations with molecular weight (determined by high temperature gel permeation chromatography) and with decreasing concentrations of stabilizers could be demonstrated.

FTIR study of gamma and electron irradiated high-density polyethylene for high dose measurements

A reliable and well-characterized dosimetry system which is traceable to the international measurement system, is the key element to quality assurance in radiation processing with cobalt-60 gamma rays, X-rays, and electron beam. This is specifically the case for health-regulated processes, such as the radiation sterilization of single use medical devices and food irradiation for preservation and disinfestation. Polyethylene is considered to possess a lot of interesting dosimetric characteristics. In this work, a detailed study has been performed to determine the dosimetric characteristics of a commercialized high-density polyethylene (HDPE) film using Fourier transformed infrared spectrometry (FTIR). Correlations have been established between the absorbed dose and radiation induced infrared absorption in polyethylene having a maximum at 965 cm−1 (transvinylene band) and 1716 cm −1 (ketone-carbonyl band). We have found that polyethylene dose-response is linear with dose for both bands up to1000 kGy. For transvinylene band, the dose-response is more sensitive if irradiations are made in helium. While, for ketone-carbonyl band, the dose-response is more sensitive when irradiations are carried out in air. The dose-rate effect has been found to be negligible when polyethylene samples are irradiated with electron beam high dose rates. The irradiated polyethylene is relatively stable for several weeks after irradiation.

Benchmarking GEANT4 and PHITS for 14.8-MeV neutron transport in polyethylene and graphite materials

The feasibility of GEANT4 and PHITS with ENDF/B-VIII.0, JEFF-3.3 and JENDL-4.0 evaluated nuclear data libraries in 14.8-MeV neutron transport simulation are verified by comparing with the MCNP calculations and the experimental data. The measured data are from neutron integral experiments including graphite and polyethylene samples. For 6 cm-thick polyethylene and 20 cm-thick graphite samples, the results from GEANT4 and PHITS with three evaluated nuclear data libraries agree well with the MCNP calculations. For a 2 cm-thick graphite sample, the simulated results from GEANT4 and PHITS agree with the MCNP calculations, and they all underestimate the experiment data in below 3 MeV and overestimate them in the energy range of 5–7 MeV. The difference between the simulation results and the experimental data depends on the evaluated nuclear data libraries. In overall, GEANT4 and PHITS are performing reasonable jobs for 14.8-MeV neutron transport simulations.

Ethylene Polymerization Kinetics and Microstructure of Polyethylenes Made with Supported Metallocene Catalysts

The microstructure of polyolefins made with a metallocene supported on a porous carrier is generally less homogeneous than when the polyolefin is made with the same unsupported metallocene. For instance, the molecular weight and chemical composition distributions of ethylene/1-olefin copolymers are often broader when they are made with a supported metallocene. In this article, a mathematical model is used to quantify this phenomenon. The polymerization of ethylene was investigated in parallel semi-batch reactors using a metallocene catalyst supported on an inorganic porous carrier. Ethylene pressure, polymerization temperature, and H2 concentration were the factors changed to study ethylene polymerization kinetics with this catalyst system. Modeling results showed that a three-site model was needed to describe the molecular weight distributions of the polyethylene samples made with this catalyst.

Detection of suspected carcinogen azo dyes in textiles using thermogravimetric analysis

Textiles that are in direct contact with human skin are problematic due to the possibility of transferring the dyes or their aromatic amine metabolites through direct contact. 18 samples of women underwear panties of different colors and fabrics materials were examined for their content of azo dyes using thermogravimetric-gas chromatography-mass spectrometry (TGA-GCMS) technique. The nature of fabrics (cotton, nylon, and polyesters) was identified based on their unique thermogravimetric analyses (TGA) pattern. Aromatic amines produced from thermal degradation of the samples were identified using NIST mass spectra data base. Aniline was found in all samples regardless of their color or fabric composition. Black cotton textiles were characterized by the presence of diaminobenzene, red cotton sample showed the presence of 4-amino-3-nitrobenzene-1-sulfonic acid, blue cotton sample showed the presence of chlorobenzenediamine and chloroaniline, and purple cotton textiles showed the presence of 4-nitroaniline. All four purple nylon samples contained nitroaniline and biphenylamine, the three red nylon samples contained nitroaniline and methyldihydro-thiadiazole, the two pink samples showed the presence of chloro-2-(trifluoromethyl) anilinechloro- benzenediamine, the purple polyethylene sample show the presence of diphenyldiazene, and the brown polyester sample showed the presence of 2-amino-1,4-phenylene) dimethanol.

Attenuated Total Reflection-Far-Ultraviolet Spectroscopy and Quantum Chemical Calculations of the Electronic Structure of the Top Surface and Bulk of Polyethylenes with Different Crystallinities.

In this study, we explored the electronic structure of the surfaces of polyethylene samples having different crystallinities using attenuated total reflection (ATR) far-ultraviolet (FUV) spectroscopy and quantum chemical calculations. Specifically, the ATR-FUV spectra of five types of high-density polyethylene (HDPE), six types of linear low-density PE (LLDPE), and seven types of low-density PE (LDPE) were obtained. All the spectra contained an intense band near 156 nm and a broad band between 180 and 190 nm. Transmission spectra were obtained for the thin-film (30 µm) PE samples between 165 and 250 nm. In this region, the HDPE films show very low-intensity bands. In contrast, the transmission spectra of the LLDPE and LDPE samples yielded weak-to-medium and medium-intensity bands around 180-190 nm, respectively. In addition, to understand the differences in the absorption spectra among the PEs observed, we simulated the spectra of n-pentane as a PE crystal model using time-dependent density functional theory and found that the common intense band at 156 nm is due to the σ (C(2p)-H)→Rydberg 3s, 3p transition. The absorption bands near 180-190 nm may correspond to aggregates of numerous molecular chains in the amorphous parts of the LLDPE and LDPE samples.

Evaluation of the persistence of SARS-CoV-2 (ATCC® VR-1986HK™) on two different food contact materials: flow pack polyethylene and polystyrene food trays

Even though SARS-CoV-2's primary transmission pathway is person-to-person, the role played by surfaces and food contact materials in carrying viral RNA should be further explored. For this purpose, the study aimed to investigate the persistence of SARS-CoV-2 using the strain ATCC® VR-1986HK™ on flow pack polyethylene (FPP) and polystyrene food trays (PFT). Samples of FPP and PFT were contaminated with heat-inactivated SARS-CoV-2 and were incubated at a temperature of 24 ± 1 °C and at controlled relative humidity (RH 65%). The experimental design included analyses at the time 0, 3, 6, 12, 24, 36, 48 and after every 24 h until the viral RNA was no longer detectable. The results showed a significant decrease (P < 0.001) in viral copy numbers on PFT within 3 h (24% reduction) and, at 72 h, the viral RNA had fallen below the limit of detection. Regarding the FPP, it was necessary to wait 24 h for a significant decrease (P = 0.015) in the viral load (14% reduction), while the detection threshold was reached at 96 h. These findings showed that the viral RNA persists longer on flow pack polyethylene samples than on polystyrene food trays, thus highlighting the importance of material characteristics in the persistence of SARS-CoV-2.

Simultaneous determination of eight additives in polyethylene food contact materials by ultrahigh-performance liquid chromatography

食品接触材料中添加剂残留量的测定为食品接触材料从源头进行安全监管具有重要意义。然而目前的大多数研究只针对食品接触材料中有害物迁移量的测定,对于食品接触材料中有害物含量的测定方法仅局限于残留单体、低聚体、重金属,以及邻苯二甲酸酯类、双酚类化合物等环境污染物,对食品接触材料中添加剂残留量的测定较少。该研究系统地优化了样品前处理过程及仪器分析中影响8种添加剂分析准确度与响应灵敏度的各主要因素,建立了超高效液相色谱同时测定聚乙烯材料中8种添加剂的定量分析方法。聚乙烯样品冷冻研磨后,取2.0 g样品采用甲苯作为萃取溶剂,80 ℃, 10.34~11.72 MPa (1500~1700 psi)下对其进行加速溶剂萃取,取10 mL上清液,氮气吹干后用10 mL初始流动相(甲醇-水,7∶3, v/v)定容。采用ACQUITY UPLC BEH C8色谱柱(100 mm×2.1 mm, 1.7 μm)进行分离,柱温30 ℃,进样量5 μL,以乙腈和水作为流动相进行梯度洗脱,流速0.3 mL/min,二极管阵列检测器(DAD)在210~400 nm范围内扫描,230、250、280、330 nm监测,外标法定量。8种目标物在0.2~10 μg/mL质量浓度范围内线性关系良好,相关系数(R 2)>0.999。空白聚乙烯样品添加含量为0.05%时,加标回收率在83.8%~103.4%之间,RSD在0.14%~7.86%之间。对于含量为0.2%~0.9%之间的质控样品,8种目标物的平均回收率在63.5%~118.5%之间,RSD在4.61%~15.6%之间。8种目标物的定量限为0.02%。应用该方法测定10份市售聚乙烯食品包装袋和手套,其中6份样品均检测出含有亚磷酸三(2,4-二叔丁苯基)酯(抗氧剂168),含量为0.02%~0.07%,均小于GB 9685-2016规定的聚乙烯类食品接触材料中抗氧剂168的最大使用量(0.2%)。该方法能够满足聚乙烯类产品中8种添加剂的分析要求,可用于食品接触材料风险监测。