Properties Of Polyolefins Research Articles

Assessment of UV-Aging of Crosslinked Polyethylene Cable Insulation by Electrical Measurements, FTIR and DSC Analyses

Abstract In this study, the effect of UV-radiation on the structural properties of crosslinked polyethylene (XLPE) power cable insulating material was investigated as a function of aging time. XLPE specimens were exposed to UV-radiation for 200 hours using low-pressure vapor fluorescent lamps. Electrical resistivity values, influence and leakage currents, and charging and discharging currents of specimens were measured and quantified. In addition, structural changes in polyethylene chains were also evaluated with Fourier transform infrared (FTIR) analyses and high-temperature oxidation stability was correlated with the level of structural deterioration as a result of UV-aging through determination of oxidation induction time and oxidation onset temperature in differential scanning calorimetry (DSC). Experimental results showed that the electrical properties of XLPE materials were significantly affected by UV radiation and resulting structural changes can be successfully assessed with electrical measurements as a rapid, easy, and reliable tool. It was also confirmed that FTIR and DSC analyses can be used to evaluate oxidative aging level of XLPE and olefinic polymers such as polyethylene and polypropylene, polyolefin-based elastomers. This study also suggests an analytical methodology to constitute the relationship between the thermal and physical properties of polyolefins and their service life.

Effects of addition of clay and alumina nanoparticles on flame-retardant, thermal, and mechanical properties of polyolefin elastomer/magnesium hydroxide composite

This study aims to develop extreme cold temperature resistance and non-halogenated flame retardant sheathing material for Arctic shipboard cables. A series of polyolefin elastomer (POE)/magnesium hydroxide (MHO)-nanosized clay (CL) and POE/MHO-nanosized alumina (AL) composites were prepared by melt-blending and their flame-retardant, thermal and mechanical properties were evaluated. The results reveal that the AL showed a synergistic effect in improving flame-retardant and tensile properties, oil resistance, and thermal stability of the POE/MHO. Notably, the tensile strength, elongation at break, and limit oxygen index of the POE/MHO composite with 1.2 phr AL increased by 54.9%, 39.5%, and 5.2%, respectively. Crucially, except for POE/MHO-CL1.2 phr, the glass transition temperature of all composites remained below −66 °C. Overall, 1.2 phr AL content is deemed optimal for the desired properties.

A Review of Polyolefin-Insulation Materials in High Voltage Transmission; From Electronic Structures to Final Products.

This review focuses on the use of polyolefins in high-voltage direct-current (HVDC) cables and capacitors. A short description of the latest evolution and current use of HVDC cables and capacitors is first provided, followed by the basics of electric insulation and capacitor functions. Methods to determine dielectric properties are described, including charge transport, space charges, resistivity, dielectric loss, and breakdown strength. The semicrystalline structure of polyethylene and isotactic polypropylene is described, and the way it relates to the dielectric properties is discussed. A significant part of the review is devoted to describing the state of art of the modeling and prediction of electric or dielectric properties of polyolefins with consideration of both atomistic and continuum approaches. Furthermore, the effects of the purity of the materials and the presence of nanoparticles are presented, and the review ends with the sustainability aspects of these materials. In summary, the effective use of modeling in combination with experimental work is described as an important route toward understanding and designing the next generations of materials for electrical insulation in high-voltage transmission.

Preparation of polyethylene/Siloxene nanocomposites through siloxene‐MgCl supported Ziegler‐Natta catalyst

AbstractThe two‐dimensional (2D) inorganic fillers could significantly improve the properties of polyolefin, thereby satisfying a wider range of applications. Herein, in this research, high‐performance polyethylene (PE)/siloxene nanocomposites were prepared through an in‐situ polymerization with layered siloxene‐supported Ti‐based catalyst. The catalytic ethylene polymerization activity of the siloxene‐supported Ziegler‐Natta catalyst was almost twice that of the MgCl2/TiCl4 catalyst when equal weights of catalysts were used. During the in‐situ polymerization, the layered siloxene fillers exhibited uniform dispersion within the PE matrix. The incorporation of a minimal amount of siloxene filler resulted in a notable enhancement in the thermal stability and mechanical properties of PE. The breaking strength, modulus, elongation at break, and Td5% of PE/siloxene nanocomposites with only 0.71 wt% siloxene were increased by 115.7%, 45.6%, 50.6%, and 58.2°C, respectively. Therefore, this research presents a straightforward method for manufacturing PE with outstanding performance.Highlights PE/siloxene nanocomposites were prepared through in‐situ polymerization. Siloxene is uniformly scattered in the PE matrix. The siloxene and matrix exhibit excellent interfacial adhesion. PE/siloxene nanocomposites with excellent properties were obtained.

Comparison of the Influence of Carbon Obtained from Kitchen Waste and Synthetic Carbon on the Tensile Properties of Polyolefins

Comparison of the Influence of Carbon Obtained from Kitchen Waste and Synthetic Carbon on the Tensile Properties of Polyolefins

Mechanical properties of polyolefin and polypropylene fibers-reinforced concrete–An experimental study

Mechanical properties of polyolefin and polypropylene fibers-reinforced concrete–An experimental study

Graphene assisted enhancement in the cyclic electromechanical properties of polyolefin based multiphasic conducting nano carbon black nanocomposites

Graphene assisted enhancement in the cyclic electromechanical properties of polyolefin based multiphasic conducting nano carbon black nanocomposites

Combination of titanium dioxide and polyhedral oligomeric silsesquioxane nanofillers to boost mechanical and rheological properties of polyolefins: Recycling possibility

Recycling of polyolefins has become a on-demand route to avoid its environmental threats. Nevertheless, drop of properties after re-extrusion necessitates use of reinforcing agents to compensate for poor mechanical properties. The incorporation of nanoparticles into plastics can boost their mechanical and rheological properties due to the hard nanocrystalline phases. This study aims to promote and identify a polyolefin-based nanocomposite by combination of TiO2 and polyhedral oligomeric silsesquioxane (POSS) at concentration of 1, 3, and 6 wt% in a twin-screw extruder. The nanocomposites were characterized for mechanical and rheological properties. Overall, the results showed that the mechanical properties were improved by adding particles up to 6 wt% loadings. The magnitude of this effect was dependent on the nanofiller weight fraction and particle size. Well-dispersion and, as a result, enhancing the viscosity, modulus, and hardness in the sample containing 3 wt% TiO2 and 3 wt%. POSS was due to the presence of hydroxyl functional groups on its surface. Glass transition temperature and crystallinity of the samples did not show a significant change due to the neutral role of nanoparticle nucleation in the matrix.

Metallocene Polyolefins Reinforced by Low-Entanglement UHMWPE through Interfacial Entanglements

By introducing low-entanglement UHMWPE, the mechanical properties of polyolefins are improved to varying degrees. For polypropylene, the lack of interaction between UHMWPE and polypropylene results in an unsatisfactory reinforcement effect, and the disentangled state makes it easier for the particles to form defects driven by a chain explosion. In contrast, regarding polyethylene and elastomer containing ethylene segments, low-entanglement UHMWPE plays a better role in reinforcement. A series of measurements including scanning electron microscopy (SEM), rheological measurements, differential scanning calorimetry (DSC), and mechanical measurement were used to investigate the mechanisms for the different enhancement effects. It originates from interdiffusion and entanglement forming of polyethylene segments across the interface, endowing the material with different aggregated and defect structures. For instance, EPDM possesses a higher optimal dosage of UHMWPE particles reflected in good interfacial interdiffusion with UHMWPE particles, leading to significant optimized mechanical performance.

Perspectives on Polyolefin Catalysis in Microfluidics for High-Throughput Screening: A Minireview

Polyolefins are the largest produced plastics in the world, wherein continuous stirred tank reactors and fluidized bed reactors are traditionally employed for commercial production. The operating condition, reaction kinetics, and molecular interactions inside the reactor strongly affect the polyolefin properties, which require a stringent process control in conventional procedures. Understanding the catalytic pathway, behavior of polymer particles, and effect of reactor conditions is essential for designing specific polymer properties, namely, the molecular weight, chain length, polydispersity, etc. Microfluidics can play a significant role in designing polymers tailored to the user needs. Smaller channel dimensions help obtain uniform reaction conditions over the length of the microfluidic reactor in a controlled environment. With real-time monitoring techniques in microfluidics, even single-particle growth of polymer can be studied to understand the parameters affecting the polymer properties. High-throughput microfluidics can help catalyst screening in a short duration with less consumption of reagents, generating less waste. When supplemented with efficient machine-learning algorithms, automated high-throughput microfluidics has the potential to rapidly optimize the process and facilitate the development of new knowledge even with a limited data set. When trained on data sets generated using microfluidic experiments that are designed efficiently with working knowledge of the process, machine-learning algorithms can provide the relationship between the multivariable parameters space and polymer properties, which is not possible with the traditional statistical methods and interpolation techniques. The rise in the utilization of microfluidics, with the advancement of machine-learning algorithms, for polyolefin catalysis, highlights the importance of microfluidics for catalyst discovery, parameter optimization, and understanding the reaction pathway for producing polymers with specific properties for specialized applications.

Determination of Short Chain Branching in LLDPE by Rheology

AbstractThe relationship between the structure and the final properties of materials is an important issue in polymer science. In particular, the properties of polyolefins are impacted by their branching contents. A simple rheological method is presented to estimate the degree of short chain branching (SCB) in linear low‐density polyethylene (LLDPE). A range of ethylene‐1‐hexene copolymers is synthetized using a metallocene catalyst to obtain homogenous LLDPE models with various comonomer contents. The polymers are analyzed by size exclusion chromatography, 13C NMR, and crystallization elution fractionation to determine both their molar masses and their chemical composition distributions. Subsequently, they are measured by rheology to assess the impact of SCB. This work provides calibration curves for rheology and proves that it is possible to predict the SCB content in LLDPE from the melt viscosity analysis.

One‐For‐All Polyolefin Functionalization: Active Ester as Gateway to Combine Insertion Polymerization with ROP, NMP, and RAFT

AbstractThis work develops the Polyolefin Active‐Ester Exchange (PACE) process to afford well‐defined polyolefin–polyvinyl block copolymers. α‐Diimine PdII‐catalyzed olefin polymerizations were investigated through in‐depth kinetic studies in comparison to an analog to establish the critical design that facilitates catalyst activation. Simple transformations lead to a diversity of functional groups forming polyolefin macroinitiators or macro‐mediators for various subsequent controlled polymerization techniques. Preparation of block copolymers with different architectures, molecular weights, and compositions was demonstrated with ring‐opening polymerization (ROP), nitroxide‐mediated polymerization (NMP), and photoiniferter reversible addition–fragmentation chain transfer (PI‐RAFT). The significant difference in the properties of polyolefin–polyacrylamide block copolymers was harnessed to carry out polymerization‐induced self‐assembly (PISA) and study the nanostructure behaviors.

One-For-All Polyolefin Functionalization: Active Ester as Gateway to Combine Insertion Polymerization with ROP, NMP, and RAFT.

This work develops the Polyolefin Active-Ester Exchange (PACE) process to afford well-defined polyolefin-polyvinyl block copolymers. α-Diimine PdII -catalyzed olefin polymerizations were investigated through in-depth kinetic studies in comparison to an analog to establish the critical design that facilitates catalyst activation. Simple transformations lead to a diversity of functional groups forming polyolefin macroinitiators or macro-mediators for various subsequent controlled polymerization techniques. Preparation of block copolymers with different architectures, molecular weights, and compositions was demonstrated with ring-opening polymerization (ROP), nitroxide-mediated polymerization (NMP), and photoiniferter reversible addition-fragmentation chain transfer (PI-RAFT). The significant difference in the properties of polyolefin-polyacrylamide block copolymers was harnessed to carry out polymerization-induced self-assembly (PISA) and study the nanostructure behaviors.

Analytical characterization of erucamide degradants by mass spectrometry

• Thermal oxidation of erucamide occurs in polyolefins during processing and improper storage. • The oxidation of erucamide results in several primary and secondary degradation products including off-flavor compounds. • About 16 primary and secondary oxidation products of erucamide were identified and characterized by HRMS. • This research paper describes plausible mechanisms for erucamide degradation compounds formation. Polyolefins use erucamide as one of their primary slip agents. The degradation of erucamide can occur during polymer processing and long-term storage, leading to the formation of numerous oxidation products. Erucamide degradation produces compounds that adversely affect the odor and color properties of polyolefins. The article describes the comprehensive characterization of erucamide degradation products formed in three different lots of low-density polyethylene (LDPE) using thermal desorption-gas chromatography mass spectrometry (TD-GC/MS) and liquid chromatography-high resolution mass spectrometry (LC HRMS) techniques. More than 20 volatile and non-volatile degradation compounds of erucamide were identified in LDPE. The structures of non-volatile degradants were predicted using both the molecular formula generated and MS/MS fragmentation data obtained by LC HRMS. The non-volatile and volatile degradation compounds formed in odorous LDPE resins were compared with that of the reference sample of LDPE having no odor. Further, the plausible mechanism of formation of volatile and non-volatile degradation compounds of erucamide is proposed.

Time-domain NMR relaxometery – a green analytical tool for estimating physico-mechanical properties of polyolefins

Physical and mechanical properties of PE and PP are traditionally determined in the laboratory with methods as specified in ASTM/ISO standards. This is a time-consuming activity in any QC laboratory. In this paper, low-field (20 MHz) NMR has been used to quickly determine properties like density of HDPE, Xylene Solubles (XS) in homo-polymer PP & impact copolymer polypropylene (ICP), ethylene content (C2), flexural modulus (FM) and Izod impact strength of ICP, within a short span of time (∼1/4 h), allowing the plant to get expeditious feedback about the manufactured polymer grade enabling monitoring the manufacturing process more efficiently. The novelty in this work is that even calibration and predictive models for determining mechanical properties of polyolefins like FM and Izod impact strength have been successfully developed. Calibration models were built using known samples and validated using the validated sample set. For HDPE samples, a calibration model for determining the density could be prepared with R 2 of 0.867 and RMSEC of 0.0006 gcm−3. For homo PP samples, a predictive model for determining XS could be prepared with R 2 of 0.934 and RMSEC of 0.20 wt%. In case of calibration models for XS and C2 of ICP samples, R 2 = 0.924 each and RMSEC of 0.54 wt% & 0.45 wt%, respectively was obtained. A model for flexural modulus could be prepared with an R 2 and RMSEC of 0.935 & 28 MPa, respectively. Reasonable model could be developed for Izod impact strength (R 2 = 0.947 & 0.982 for low & high impact respectively). The properties of validation sample set were predicted based on the calibration models and good correlation was obtained between the lab data (QC data) and the predicted data.

Mechanistic study of vanadium-modified and sulfation-modified Phillips catalyst

• Differed from “naked” chromium center, two reduction routes with methyl formate derivant attaching on chromium center are put forward. • Compared with traditional Phillips catalyst, vanadium-modified Phillips catalyst is more exergonic during reduction process. • Alkylation with assistance of cocatalyst is meaningful to Phillips catalyst and assistance of TiBA with larger steric hindrance shows lower Gibbs free energy than dimeric TMA, which is in accordance with experimental evidences. • The addition of sulfur atom directly bonding with chromium center reduces energy barrier of chain propagation significantly. Phillips catalyst is one of the most significant industrial catalyst for polyolefin. Various modified methods have been developed to promote the polymerization activity and regulate properties of polyolefin, including vanadium-modification, sulfation-modification, etc. Vanadium-modified Phillips catalyst can produce bimodal polyethylene with sectional ultra-high molecular weight polyethylene to improve the mechanical property. Compared with traditional Phillips catalyst, sulfation-modified Phillips catalyst exhibits higher polymerization activity and wider molecular weight distribution. However, lack of knowledge still puzzles researchers in reduction, alkylation and modification for Phillips catalyst. In addition, complex chemical surrounding for heterogeneous catalyst is still a big challenge to carry out explicit analysis of this catalyst. In this work, fundamental insight into two modified methods towards Phillips catalyst has been garnered. The possible active metal centers existing on the surface of silica support and feasible precursors with reductant attaching on the chromium center were investigated. Moreover, based on two alkylation precursors with assistance of different alkyl aluminum, we proposed a probable six-membered ring mechanism through the Tischenko reaction with formation of methyl formate derivant. Interestingly, the addition of sulfur atom reduces energy barrier of chain propagation significantly. These results account for the advantages of vanadium-modification, sulfation-modification and cocatalyst for traditional Phillips catalyst.

Preparation of novel thick sheet graphene and its effect on the properties of polyolefins with different crystallinities

Preparation of novel thick sheet graphene and its effect on the properties of polyolefins with different crystallinities

Influence of the amphiphilic molecule on high-density polyethylene crystallization

The influence of organic additives on crystallization of polyolefins has not been paid enough attention due to the low dosage, but it may have a significant impact on the properties of polyolefins. In the paper, the organic amphiphilic molecules were introduced into high-density polyethylene (HDPE) through melt blending, and compared with neat HDPE. It is mainly discussed for the following aspects including analysis of crystal structure and morphology using wide-angle X-ray diffraction (WAXD) and polarized optical microscopy (POM), respectively; analysis of crystallinity, crystal rate, crystal growth and crystallization enthalpy, using the differential scanning calorimetry (DSC). The research indicates that the organic amphiphilic molecules may act as an internal lubricant. On the one hand, HDPE molecular chains are easy to fall off from crystal lattices, resulting in lagging crystallization peak, simultaneously reducing the interaction between HDPE molecules should induce the lower activation energy (ΔEm) to increase the crystallinity of HDPE. On the other hand, the amphiphilic molecules should be exclude from HDPE crystal to the amorphous area due to poor compatibility; thus, the HDPE/amphiphilic molecules blends, similar to neat HDPE, conduct homogeneous nucleation, and the growth of monocrystal performs the tendency of the zero-dimension to the two-dimension with increase in temperature of isothermal crystallization and decreasing cooling rate of non-isothermal crystallization. It is hoped that through these studies, people will pay more attention to the impact of organic additives on the performance of HDPE.

Improved dielectric and mechanical properties of polyolefin based laminates via surface modification silicon dioxide

The rapid development of 5G technique needs higher requirements for laminate under high-frequency condition. In this work, silicon dioxide (SiO2) surface modified by y- aminopropyl triethoxysilane (KH-550) was used as fillers to improve the dielectric and mechanical properties of polyolefin-based laminates. A relative low dielectric constant of 3.61 and dielectric loss of 3.69 × 10−3 at 10 GHz is observed for the laminate with 55 wt% K-SiO2. Moreover, the as-obtained laminate exhibits optimum mechanical properties. These results indicated that the K-SiO2 (surface modified by KH-550)/polyolefin laminate is an ideal candidate for high-frequency substrate.

On the necessity of determining the dynamics of development of deformation during mechanical tests under conditions of cable production

The analysis of results of comparison of mechanical properties of polyolefin filled with fire retardants is carried out. Experimental data for evaluating the dynamics of the development of uniaxial tensile deformation during standard tests of cable polymer compositions under production conditions are presented. The organization of technological control of ensuring the mechanical strength of structural elements made of halogen-free plastics in a specific production environment is one of the urgent tasks in the manufacture of fire-safe cables. To analyze the dynamics of the development of deformation of halogen-free cable plastics and to determine a practically important quantitative characteristic, it is necessary to study the initial section of the relationship between deformation and time, at which the deformation of the polymer is limited by elastic and viscoelastic deformation. The characteristic dependences of the elongation deformation of the samples on the time of uniaxial tension at a constant rate of separation of the clamps are presented in the process of the standard procedure for determining the mechanical characteristics for halogen-free cable plastics. For all samples, an initial (up to 10 – 15 seconds) linear section is observed with a different growth rate of the total tensile strain.