Grades Of Polyethylene Research Articles

Modification of Рolymer Wastes and Obtaining Com Comрosites Based on Them Annotation

The sources of scientific literature on the research have been investigated, various approaches to the processing and modification of polymers have been analyzed and the main direction of the study have been identified. The changes in the properties of thin layers of industrially produced low-density polyethylene (LDPE) grades 10803-20 and 16603-011 operating under different climatic conditions have been studied. It has been determined that changes with different intensities occur in the structure and in this connection in the physical and mechanical properties of LDPE that was in operation at different time intervals and in different climatic conditions of the Absheron Peninsula and the Aran region: melt flow index of polymer alloy, tensile strength at break, relative extension and values of other indicators are deteriorating. In polymer samples is formed 24,2 – 28,6% of insoluble phase and as a result of oxidation up to  12,3 – 16,8% carbonyl, hydroxyl and other functional groups.

Study of the high-temperature hardening zone in Borealis polyethylene

The temperature dependences of tear strength for the main Borealis polyethylene grades were studied. It is shown that along with the common areas where the strength decreases with temperature, there are temperature, regions where the temperature dependence is weakly expressed or there is a maximum tear resistance associated with orientational hardening, similar to the maximum in materials of PE-RT II type.

Studying the mechanism of biodiesel acting as an environmental stress cracking agent with polyethylenes

This paper focuses on understanding the compatibility of biodiesel with different grades of polyethylene, specifically examining the environmental stress cracking ability of biodiesel. Traditional testing methods were coupled with a nondestructive ultrasonic testing method to investigate the modes of interaction by biodiesel with the polymer. The mechanism of failure was studied by gravimetric analysis and infrared spectroscopy to monitor fluid absorption in the notched and bent specimens while attenuation in the higher harmonics of an emitted acoustic pulse followed internal stresses. The ultrasonic technique offered a unique opportunity to link fuel penetration with microstructural changes prior to visible fracturing. Analysis of the mechanism was aided by the color of the fuel showing that cracking was preceded by highly localized absorption around the notch of the specimen, whereas resin grades with apparent immunity to cracking experienced uniform absorption over the whole body of a specimen.

Evaluation of UV‐induced embrittlement of PE‐HD by Charpy impact test

AbstractThe impact fracture behavior of two common high‐density polyethylene grades for container applications were intensively studied by the instrumented Charpy impact test after well‐defined exposure to UV‐irradiation. Individual stages of the impact event, such as crack initiation and crack propagation energy as well as maximum impact load, were investigated from the recorded load–deflection curves. UV‐induced material property changes were further investigated by infrared spectroscopy, differential scanning calorimetry, and dynamic‐mechanical analysis as well as density measurements. Based on the results of the Charpy impact test, three indicators were identified to describe the extend of photooxidation on high‐density polyethylene: (a) a reduced Charpy impact strength—at least to half of its initial value for a distinctly brittle impact fracture, (b) a marked decrease in the crack propagation contribution to the impact strength, and (c) an increase of the brittle features of the fracture surface.

Click chemistry‐type crosslinking of a low‐conductivity polyethylene copolymer ternary blend for power cable insulation

AbstractHigh‐voltage direct‐current power cables are vital for the efficient transport of electricity derived from renewable sources of energy. The most widely used material for high‐voltage power cable insulation – low‐density polyethylene (LDPE) – is usually crosslinked with peroxides, a process that releases unwanted by‐products. Hence, by‐product‐free crosslinking concepts that mitigate the associated increase in electrical conductivity are in high demand. Click chemistry‐type crosslinking of polyethylene copolymer mixtures that contain glycidyl methacrylate and acrylic acid co‐monomers is a promising alternative, provided that the curing reaction can be controlled. Here, we demonstrate that the rate of the curing reaction can be adjusted by tuning the number of epoxy and carboxyl groups. Both dilution of copolymer mixtures with neat LDPE and the selection of copolymers with a lower co‐monomer content have an equivalent effect on the curing speed. Ternary blends that contain 50 wt% of neat LDPE feature an extended extrusion window of up to 170 °C. Instead, at 200 °C rapid curing is possible, leading to thermosets with a low direct‐current electrical conductivity of about 10−16 S cm−1 at an electric field of 20 kV mm−1 and 70 °C. The conductivity of the blends explored here is comparable to or even lower than values measured for both ultraclean LDPE and a peroxide‐cured commercial crosslinked polyethylene grade. Hence, click chemistry curing represents a promising alternative to radical crosslinking with peroxides. © 2019 Society of Chemical Industry

A robustly model predictive control strategy applied in the control of a simulated industrial polyethylene polymerization process

This work investigates the quality control problem of polyethylene grades produced in an industrial polymerization plant. The plant is represented by a phenomenological model previously validated using industrial data. Three advanced control strategies were developed in order to propose strategies capable of dealing with different grades of products. A stability guaranteed [IHMPC (Infinite Horizon Model Predictive Control)] technique and a robust stabilized [RIHMPC (Robust IHMPC)] technique were designed and compared with a conventional MPC. The results show that RIHMPC outperformed the other techniques, providing smoother and faster grade transitions and setpoint tracking. This result provides a significative contribution, since no report of application of RIHMPC on polymerization plants was found. The RHIMPC controller seems to be a promising option for other polymerization reactor control problems in which the diversity of resins produced, coupled with the nonlinear characteristic of the system, lend themselves to the use of different linear models.

Synthesis of Long-Chain Branched Polyolefins by Coordinative Chain Transfer Polymerization

Synthesis of long-chain branched polymers has been a crucial concern in the polyolefin industry. In this study, a method to produce long-chain branches (LCBs) in coordinative chain transfer copolymerization (CCTcoP) is suggested. A dialkylzinc compound bearing vinyl groups ((9-decenyl)2Zn) is prepared, which works well not only as a chain transfer agent but also as a comonomer in CCTcoP, resulting in the generation of LCBs. The generation of LCBs is confirmed by gel permeation chromatography studies and through the analysis of rheology data. The formation of LCBs by connecting the two growing polyolefin chains can facilitate the generation of polymers with molecular weights higher than that expected. Owing to the presence of LCBs, considerable shear thinning behavior is observed. Ethylene/1-octene copolymers can be prepared facilely to show almost the same shear thinning behavior with the commercial grade of low-density polyethylene, which is known to have a substantial amount of LCBs.

Linking Antioxidant Depletion with Material Properties for Polyethylene Pipes Resins

Plastic pipes used in gas distribution networks are typically made from polyethylene (PE) and are stabilized against degradation by antioxidants. Over time, the antioxidant is consumed and the polymer integrity can become compromised. The rate of antioxidant depletion can be dependent on the specific grade of PE and the surrounding environment. In this research, the crystallinity, tensile strength, Young's modulus, and strain at break were measured for the four most commonly used PE pipe resins in the Australian natural gas distribution network as a function of antioxidant content. A relationship between the changes in material properties with antioxidant consumption was established. By measuring the carbonyl index (CI), which quantifies the amount of degradation products present, and linking this with the oxygen induction time (OIT), it was found that three clear regions exist for all investigated PE resins. These distinct regions of the OIT–CI relationship correlate with regions of substantially different rate of change in material properties, and hence indicate a measure of the integrity of the PE. POLYM. ENG. SCI., 60: 323–329, 2019. © 2019 Society of Plastics Engineers

Rheological quantification of the extent of dissolution of ultrahigh molecular weight polyethylene in melt-compounded blends with high density polyethylene

Melt compounding of ultrahigh molecular weight polyethylene (UHMWPE) with high density polyethylene (HDPE) promises to be an alternative route to prepare bimodal polyethylene grades. However, complete dissolution of UHMWPE in HDPE cannot be guaranteed during melt compounding. Indeed, in an earlier work [K. Chaudhuri et al., Polym. Eng. Sci. 59, 821–829 (2019)], it was shown that a fully entangled UHMWPE did not mix well with commercial HDPE. However, a disentangled UHMWPE (dPE) could be melt-mixed in the same HDPE as evidenced qualitatively by rheological measurements. The present work is focused on quantifying the extent of dissolution of dPE in HDPE. The proposed method involves fitting rheological models for linear viscoelasticity of entangled bimodal blends of polydisperse polymers to dynamic oscillatory shear data and extracting information on the extent of dissolved species. The time-dependent diffusion model of des Cloizeaux is used along with the theory of double reptation (DR) to describe the dynamics of polydisperse homopolymers and also to extract the molecular weight distribution of the UHMWPE sample. A quadratic mixing rule, consistent with the DR model, is used to describe the dynamics of bimodal blends. Melt-mixed dPE/HDPE blends were prepared and characterized for their linear viscoelastic response by frequency sweep tests. The blends showed complex behavior with multiple crossover points, especially for the higher content of dPE. The bimodal model was then fit to the experimental frequency sweep data to determine the only unknown parameter, namely, the extent of dissolved dPE. It was found that a considerable fraction of dPE is dissolved in HDPE during melt compounding.

Rheological behavior of binary polymer compositions

The article presents the results of a study of the rheological behavior of binary composites based on serial polyethylene grade LDPE 15803-020 with different content of microcellulose grade Filtracell, in a wide range of temperatures and shear rates during deformation through a capillary diameter of 1 mm and a length of 5 and 30 mm. Stable flow regime is manifested in the temperature range from 160 to 200°C for composites containing microcellulose in an amount of 30 wt.%, and its partial replacement with spent microcellulose (waste production of vegetable oils) can reduce the effective viscosity to 25%, but the upper limit of the temperature range is limited to the exudation of impurities (190°C). The Bagley correction is carried out, the coefficients of the equations describing the dependences of the true shear stress, regardless of the capillary length, are calculated.

Strain hardening test on the limits of Slow Crack Growth evaluation in high resistance polyethylene resins: Effect of comonomer type

Long term performance assessment of polyethylene pipes is an issue that has greatly increased in importance in recent years due to the incorporation in the market of high resistance to crack polyethylene grades (PE100RC), where established Slow Crack Growth (SCG) evaluation using traditional tests such as Full Notch Creep Test (FNCT) or Pennsylvania Notch Tensile (PENT) Test is insufficient. The development in recent years of fast evaluation techniques such as Strain Hardening (SH) modulus has opened an important alternative for quick SCG evaluation since it correlates well with other conventional tests such as FNCT and PENT. In this work, a large number of commercial and experimental polyethylene pipe resins with different comonomer types were evaluated in order to define their SH values to rank the resins as PE100 or PE100RC. A relationship is proposed that utilizes SH test results to estimate the SCG resistance of PE pipes. 1-Butene copolymer resins display threshold SH values of 38 and 53 MPa that have been assigned to PE100 and 100RC grades, respectively. Moreover, dependence of the SH values on comonomer type used has been demonstrated. The experimental results show that 1-hexene copolymer resins exhibit higher SH values than 1-butene comonomer based resins.

A comparison between $K$ and $G$ approaches for a viscoelastic material: the case of environmental stress cracking of HDPE

According to linear elastic fracture mechanics the stress intensity factor and the energy release rate are two fracture parameters linked by the elastic modulus and Poisson’s ratio of the considered material. This concept has been extended to the analysis of linear viscoelastic materials, by introducing time-dependent quantities; it is also used for nonlinear viscoelastic polymers, even if its accuracy in this case is still an open question. In this work the slow crack growth and the environmental stress cracking resistance of two high-density polyethylene grades were investigated, differing for their molecular weight distribution and fracture resistance. The description of the fracture behavior of the two materials provided by the stress intensity factor or the energy release rate turned out to be equivalent, despite the nonlinear mechanical behavior exhibited by the two polymers. Moreover, a time-dependent effective modulus, related to the two fracture parameters, was evaluated: its value was in good agreement with the modulus experimentally determined from tensile tests. A constant relevant effective strain was found despite the different testing conditions (i.e. applied mechanical loading, temperature and presence of an active environment), its value being equal for the two considered polyethylenes.

Halogen-Free Flame-Retardant Compounds. Thermal Decomposition and Flammability Behavior for Alternative Polyethylene Grades.

The effect of six halogen-free flame retardant (FR) formulations was investigated on the thermal stability of two low-density polyethylenes (LDPE) and one linear low-density polyethylene (LLDPE), by means of thermogravimetric analysis (TGA) under nitrogen and air atmosphere. The relative data were combined with flammability properties and the overall performance of the FRs was correlated with the type of branching in the polyethylene grades and to their processing behavior. The thermal degradation kinetics was further determined based on the Kissinger and Coats-Redfern methods. In terms of flammability, the addition of a triazine derivative and ammonium polyphosphate at a loading of 35 wt. %. was found to be the most efficient, leading to UL 94 V0 ranking in the case of the LDPE grade produced in an autoclave reactor.

Methodology of Accelerated Characterization for long-term creep prediction of polymer structures to ensure their service life

Abstract Predicting long-term creep behaviour (10 or 20 years) is important in the development and design of thermoplastic structures to ensure their service life. But providing robust material data to engineers is not easy, as testing is expensive and time-consuming. The purpose of this paper is to propose a new Methodology of Accelerated Characterization for long-term creep Prediction (MACcreeP) which gives more material information much faster and at a lower cost, than Classical Methodology (CM) used today by engineers. In order to prove the effectiveness of this new method, the material used for the study is a well-known high density polyethylene grade (HDPE). More precisely MACcreeP is a characterization protocol based on creep tests performed in true tensile stress conditions over short time periods (24 h) and at different temperatures combined with the Time-Temperature Superposition Principle to construct master curves. In addition to the material data obtained over a short period of time, the data generated by the behaviour laws and the use of the CREEP law in a FEA software allows a more predictive numerical response than in CM. Finally, this methodology, which implies very few tests, allows to compare and choose the appropriate material properties to design a thermoplastic structure which will comply with end-use product requirements.

Plasticizing effect of oxidized biodiesel on polyethylene observed by nondestructive method

This paper explores the compatibility of biodiesel with different grades of polyethylene, specifically examining the extent of plasticization in order to gain a better understanding of the biofuel’s compatibility with this common polymer. Its bulk influences on polyethylene were investigated by gravimetric and mechanical testing, and by the application of a newly developed nondestructive ultrasonic testing method. Diffusion rates and the extent of plasticization by biodiesel were compared to results obtained with toluene, a known plasticizer for polyethylene. Mechanical and gravimetric analysis showed that biodiesel exhibited bulk attributes of a plasticizer for the tested polyethylenes with reduced moduli proportional to the amount of fuel uptake and that uptake was inversely proportional to crystalline content of the polymer. Based on uptake amounts, the efficiency of biodiesel as a plasticizer towards polyethylene was found to be more than double that of toluene. However, spectral analysis by ultrasonics showed that absorbed toluene and biodiesel influenced the microstructure of polyethylene differently. Notable differences in internal stresses were noted between the two fluids for the same amount absorbed. A subsequent study analyzed the impact that biodiesel degradation had on plasticization. Although the trend showed a slight change in diffusion rate with increasing oxidation of the medium, the mechanical and ultrasonic results did not show significant differences between fresh and degraded biodiesel within the 45 days span of the test. Combining the evidence observed in this study, a mechanism is proposed for biodiesel plasticization that can help with failure prevention and material selection.

Effects of electron beam sterilization on polyethylene terephthalate: Physico-chemical modifications and formation of non-volatile organic extractables

Our investigations hereby involve the effects of ionizing radiation as a sterilization method, and especially electron beams, on a medical grade Polyethylene Terephthalate (PET). Ionizing radiations are known to induce free radicals formation in the polymer that will then either degrade or crosslink, depending on its chemical nature, ionizing type and irradiation atmosphere (Charlesby, 1967; Dole, 1972 and Dole, 1973). The evaluation of packaging material modifications under radiation sterilization is of great interest and the objective of our paper is to focus on both PET volume modifications and extractable analyses after electron beam sterilization. As regards the polymeric matrix and after sterilization, we did not observe by means of spectral analyses, any single chemical modification whatsoever, whereas by thermal techniques we evidenced polymer chain scissions. As for the non-volatile organic extractables, we further substantiate the presence of numerous compounds, namely oligomers and trimers especially, along with benzoic and terephthalic acids in particular. With respect to pharmaceutical stakes however, we claim herein that the 25kGy sterilization dose used, triggers oligomers and extractables formation, a result which is promising for further risk analysis.

Relation between life time, failure stress and craze microstructure in polyethylene as evidenced by fracture surface texture analysis after an accelerated Full-Notch Creep Test

A set of five polyethylenes, of which four have 1-butene as co-monomer and one has 1-hexene as co-monomer was evaluated to determine their respective strain hardening values at 80 °C and to determine their failure times applying an accelerated Full-Notch Creep Test at 90 °C with loads varying between 1 and 6 MPa using Lauramine Oxide as detergent in an aqueous solution. The resulting failure times, fracture surface analysis and strain hardening values were described using the Kramer-Berger theory for craze propagation and the Paris-Erdogan phenomenological description of crack growth. From this exercise it is clearly demonstrated that the experimental findings are in line with the Kramer-Berger model. Hence, the viability and validity of these tests for probing the slow crack growth performance of polyethylene grades was shown.

Development of Composite Materials Based on Ultrahigh-Molecular Weight Polyethylene and Thermally Expanded Graphite

In connection with the huge range of ultra-high molecular weight polyethylene (UHMWPE) grades, the choice of a particular brand is a difficult task. Rational choice of the polymer matrix is a necessary condition for the increase in reliability and service life of products, and consequently, for the efficiency of using these composite materials. The given article presents the results of tests on stress-strain properties of GUR-2122, 4113, 4120, 4130, 4150, 4170 and GHR-8020 ultra-high molecular weight polyethylene grades. GUR-4150 UHMWPE is chosen as the polymer matrix on the base of the test results. It is shown that the friction coefficient of the polymer composite material is reduced even with the modification of UHMWPE with nanodispersed thermally expanded graphite (TEG) in amount of 0.001-0.5 mass%. It is established that the rate of mass wear decreases by 3-4.3 while maintaining the stress-strain properties of the composites at the level of the initial UHMWPE. Polymer composite materials with an improved set of performance indicators are developed.

Physical and chemical effects of biodiesel storage on high-density polyethylene: Evidence of co-oxidation

The physical and chemical effects of diesel and biodiesel fuels on two high-density polyethylene (PE-HD) types were investigated. Both semi-crystalline PE-HD are common thermoplastic materials for container and storage tank applications. Biodiesel, a composition of unsaturated fatty acid esters from renewable resources, was chosen as it is regarded a possible green alternative to fossil fuels. The study aims at identifying significant differences between biodiesel and conventional diesel fuels based on the differences in the chemical nature of the two.The physical effects of the fuels on the polymer at first comprises the sorption behavior, i.e. kinetics and final equilibrium concentration. Not only are both fuels absorbed by the amorphous phase of the semi-crystalline PE-HD, they also induce a plasticization effect that modifies the molecular mobility and therefore also the characteristic yielding properties, manifest in the obtained stress-strain curves.The chemical effects related to degradation phenomena is investigated by a long-term storage scenario using partially immersed tensile test specimens in diesel and biodiesel. We were able to confirm the proposed co-oxidation mechanism by Richaud et al. for polyethylene-unsaturated penetrant systems on a larger scale based on practical tensile tests. One of the investigated polyethylene grades subjected to tensile drawing showed a significant loss of plastic deformation and the onset of premature failure after 150 days of storage in biodiesel. Further biodiesel storage showed a systematically reduced elongation at break before necking. None of these effects were observed in diesel. Oxidation of fuels and polymer after progressing storage times were analyzed by the evolution of carbonyl species in FT-IR/ATR spectroscopy.

Response to fatigue stress of biomedical grade polyethylene joints welded by a diode laser.

Biomedical grade UHMWPE double lap joint, welded by a diode laser, has been mechanically characterized by static and dynamic tests. A nanocomposite sheet (UHMWPE filled with low carbon nanoparticles amount) was interposed between two polymeric sheets in order to absorb the laser light, sealing the sheets by means of a melting process. Fatigue test has been performed in the joint with 0.016 wt% of carbon nanofiller for its best mechanical static resistance among those studied. Its fatigue limits resulted to be equal to 22000 cycles. Breaks occurred at the 2nd welded interface, where a poor melting process weakens the entire joint.