Electrical Properties Of Polypropylene Research Articles

Effect of zinc oxide nanoparticle size on the dielectric properties of polypropylene‐based nanocomposites

AbstractTo develop new environmentally friendly and recyclable high‐voltage cable insulation materials, the effects of the particle size of zinc oxide (ZnO) on the mechanical and electrical properties of nanocomposites were investigated based on a feasibility study of polypropylene (PP) as a high‐performance cable insulation material. The small particle size of ZnO can synergistically toughen PP with a polyolefin elastomer (POE), but the large particle size of ZnO leads to lower elongation at break. Adding ZnO nanoparticles can improve the bulk resistivity of the composites and suppress space charge injection. 0.5ZnO200 has the highest direct current and alternating current breakdown field strengths, 36.6% and 14.7% higher than PP/POE, respectively. This improvement may be due to the ability of 200 nm ZnO to introduce more deep traps. However, as the nanoparticle content rises and the particle size decreases, the agglomeration becomes more frequent, leading to the overlap of inter‐nano interfaces and reducing the modification effect of the nanoparticles. This study on the effect law of nano‐ZnO with different particle sizes on the microstructure, mechanical properties, and electrical properties of PP can provide a reference for developing new recyclable high‐voltage insulated cable materials.

Effect of Shear Action on Structural and Electrical Insulation Properties of Polypropylene

Polypropylene undergoes permanent alterations during the processing and manufacture of cables due to shear effects, which in turn affect all of its qualities. There are currently few research papers on the modulation of material structure and many performance parameters by the shear stress field. In this study, we examined the impact of various shear levels on the structural, mechanical, and electrical properties of polypropylene, as well as their relationships. The results indicated that shear strength decreased the material’s viscosity and oxidation resistance. As shear duration increased, crystallinity began to diminish. In the meantime, the crystallinity improved as the shear temperature rose. The thermal elongations of the sheared samples were all about 5%. Short-term shearing boosted the material’s toughness, but as the degree of shear continued to increase, the material’s toughness and rigidity steadily decreased. The storage modulus of the material decreased with increasing shear, the loss peak initially increased and subsequently decreased, the peak position shifted from low to high temperature, and the loss factor was relatively small. In samples sheared for brief periods, an accumulation of space charge and an increase in its nonlinear threshold field strength were observed. With increasing shear time, the material’s space charge accumulation was repressed, the current density initially grew and then reduced, and the nonlinear threshold field strength initially fell and then increased. Under shearing, the electrical strength of the material increased by approximately 2%. In addition, the presence of an antioxidant improved all of the aforementioned features.

Influence of phosphorus-based flame retardants on polypropylene insulation for high-voltage power cable applications

For high voltage (HV) power cable applications, various studies have been performed to improve the mechanical and electrical properties of polypropylene (PP)-based insulation materials to replace crosslinked polyethylene. However, studies on the effect of additives to yield additional PP properties are still lacking. Herein, we prepared PP blends by melt-mixing widely used commercial flame retardants for PP with isotactic PP (iPP) and investigated their electrical breakdown, flame retardancy behaviors, and UV stability. Among the five kinds of flame retardants employed, aluminum hypophosphite (AHP), aluminum diethyl phosphinate, melamine pyrophosphate, ammonium polyphosphate (APP), and APP treated with silane, AHP was very effective in minimizing the decrease of the direct current breakdown strength of iPP at both 25 °C and 110 °C in the range of 5–20 phr. Particularly, only AHP afforded V-2 grade flame retardancy to iPP, and the flame retardancy was maintained even when the content was reduced to 3 phr. Furthermore, upon exposure to ultraviolet (UV) rays for 5 d, the tensile strength of pristine iPP decreased by approximately 44%, while that of a blend with 3 phr AHP decreased by only 10%. The study results will contribute to the optimization of power cable products through the use of appropriate flame retardants in the design of high-performance PP-based HV insulation materials.

Effect of Hydrophilic/Hydrophobic Nanostructured TiO2 on Space Charge and Breakdown Properties of Polypropylene.

Polypropylene (PP) has received more and more attention in the field of insulating materials as a recyclable thermoplastic. To further enhance the applicability of polypropylene in the field of insulation, it needs to be modified to improve its electrical properties. In this paper, the impact mechanism of AEROXIDE® TiO2 P 90 (P90) and AEROXIDE® TiO2 NKT 90 (NKT90) as nanosized hydrophilic and hydrophobic fumed titania from Evonik on the electrical properties of PP was studied mainly through the crystallization behavior and space charge distribution of PP nanocomposites. Two kinds of nanostructured TiO2 were melt-blended with PP according to four types of contents. The results of alternating current (AC)/direct current (DC) breakdown field strength of the two materials were explained by studying the microstructure and space charge characteristics of the nanocomposites. Among them, hydrophilic nanostructured TiO2 are agglomerated when the content is low. The spherulite size of the nanocomposite is large, the space charge suppression ability is poor, the charge is easy to penetrate into the pattern, and the AC/DC breakdown field strength is significantly reduced. However, hydrophobic nanostructured TiO2 has better dispersion in PP, smaller spherulites, more regular arrangement, and less space charge accumulation. The charge penetration occurs only when the nanostructured material content is 2 wt%, and the AC/DC breakdown strength increases by 20.8% at the highest when the nanostructured material content is 1 wt%. It provides the possibility to prepare recyclable high-performance DC PP composite insulating materials.

Dielectric Property Improvement of Polypropylene Films Doped with POSS for HVDC Polymer Film Capacitors

This paper focuses on the effects of the nano Polyhedral oligomericsilsesquioxanes (POSS) with three similar molecular structures on the thermal and electrical properties of polypropylene (PP) films, aiming to propose a comprehensive modification method. After doping with micro amount of nano POSS, the crystallinity and regularity of films are elevated. Correspondingly, PP with optimized microstructure has the lowest conductivity, due to the interaction between the nanoparticles and the matrix, as well as the strong binding force of the crystal region to the carriers. The loss of the sample is restricted, especially in the low frequency region, since the combined effect of polarization and conduction. The DC breakdown strength of the modified PP is higher than that of the PP, with an increase of above 20% at 25-85 °C. Based on quantum chemical calculations, the energy level distributions are analyzed. By selecting appropriate additives, deep trap sites can be introduced to catch carriers, preventing the breaks of polymer molecular chains. This modification of PP films shows huge potential in the improvement of dielectric properties in the field of DC capacitors.

Evaluation flammability, mechanical and electrical properties of polypropylene after using zinc borates and montmorillonite

This manuscript was built on studying the ignition, thermal, mechanical and electrical conductivity properties of the polypropylene by blending with different weight percentages of zinc borate (ZB) and potassium montmorillonite (MM). The tensile strength (TS) and elongation percentage ( E%) of the specimen were investigated. The thermogravimetric analysis (TGA) and differential thermal analysis (differential scanning calorimetry) were examined. LCR Meter instrument (Agilent E4980A, USA) was used to measure the electrical characteristics of the specimens. The heat capacity of the test specimens was determined according to EN ISO 1716:2004 (oxygen bomb calorimeter). By comparing the heat capacity results of the unblended with composite specimens, the difference in values is noticed. The flammability behaviours of the specimen were investigated by Underwriters Laboratories Horizontal Burning (UL-94HB) and limiting oxygen index (LOI) tests. The burning rate decreased by increasing the time of ignition with slightly LOI increased. These prove the main role of the ZB and MM at increasing the mechanical properties and electrical resistivity. The ash residue increased as the percentage of MM increased, while the heat capacity deceased.

Effect of blending and nanoclay on dielectric properties of polypropylene

This paper investigates the effects of organomodified montmorillonite (clay) and styrene-(ethylene-co-butylene)-styrene triblock copolymer (SEBS) on the morphological and electrical properties of polypropylene (PP). A series of binary PP-clay nanocomposites along with nanocomposites having a blend matrix were prepared. The nanofillers were found to be well-embedded into the polymeric matrix with a high degree of dispersion. The microstructure of the blend matrix revealed a co-continuous structure for the equal proportion of the two polymers. This was shown to control the localization of nanofiller by triggering them to migrate into the SEBS phase, mostly accommodating in the interface and creating a strong network which eventually resulted in more exfoliation of clay platelets and comparable/superior electrical properties comparing to binary nanocomposites. The incorporation of clay resulted in a solid-like rheological behavior which was more enhanced in blend nanocomposites due to the stronger network of nanofiller. The dielectric spectra of the nanocomposites revealed two major relaxation processes aroused by the presence of clay. A new relaxation process was observed for the nanocomposites with the blend matrix, related to the SEBS phase. Both blending and nanofiller inclusion resulted in less accumulated space charge. A significant improvement in the AC breakdown strength of PP was witnessed upon addition of clay. Despite the less inherent breakdown strength of SEBS, the blend nanocomposites showed even more enhanced breakdown properties confirming the further improvement of nanofiller network structure.

Melt-Mixed Thermoplastic Nanocomposite Containing Carbon Nanotubes and Titanium Dioxide for Flame Retardancy Applications

The study of polymeric nanocomposites is a possible alternative to conventional flame retardants. The aim of the present work is to investigate the effects of carbon-nanotubes (CNT) and TiO2 nanoparticles (NPs) on the thermo-mechanical, flammability, and electrical properties of polypropylene (PP). In this work, PP-TiO2/CNT nanocomposites were obtained with TiO2/CNT mixtures (ratio 1:2) through the melt extrusion process, with different weight percentage of nanoparticles (1, 5, and 10 wt %). The PP-TiO2/CNT nanocomposites were characterized by DSC, TGA, MFI, FTIR, XRD, and SEM. It was possible to determine that the thermal stability of the PP increases when increasing the content of NPs. A contrary situation is observed in the degree of crystallinity and thermo-oxidative degradation, which decreased with respect to pure PP. The TiO2 NPs undergo coalition and increase their size at a lower viscosity of the nanocomposite (1 and 5 wt %). The mechanical properties decreased slightly, however, the Young’s modulus presented an improvement of 10% as well as electrical conductivity, this behavior was noted in nanocomposites of 10 wt % of NPs. Flammability properties were measured with a cone calorimeter, and a reduction in the peak heat release rate was observed in nanocomposites with contents of nanoparticles of 5 and 10 wt %

Tailoring interfacial compatibility and electrical breakdown properties in polypropylene based composites by surface functionalized POSS

Incorporating polymeric matrix with inorganic fillers is a preferential method to improve electrical properties, while functionalization on filler surface has always been employed. In this study, two interfacial microstructures were constructed by using different functionalized polyhedral oligomeric silsesquioxane (POSS) and electrical properties of polypropylene (PP) based composites were evaluated. It is found that the electrical properties are closely related to interfacial compatibility and trap. The improved electrical breakdown strength corresponds with the composite possessing better intermolecular compatibility and deeper traps. The molecular simulation further reveals that interfacial compatibility and trap energy are affected by interaction energy and electrostatic potential between functionalized groups and PP molecular. The greater interaction energy leads to more compatible interfacial microstructure, and larger electrostatic potential leads to deeper trap energy with enhanced trapping effect, thereby restraining the charge carriers injection and migration, which synergistically leads to improved electrical breakdown strength. Contrastive interfacial traps and electrical properties of PP/POSS composites by different functionalized groups reveal the effect of interfacial compatibility. Thorough understanding of the functionalized groups and interfacial effects are beneficial for tailor-synthesizing composites with expected electrical properties.

Studying the physico-mechanical and electrical properties of polypropylene / nano copper composites for industrial applications

Polypropylene/ nano-copper composites have been prepared with 0.5, 1, 1.5 and 2.5 wt.% nano-copper particles by mixing the nano-copper physically with the polypropylene granules then extruded by a twin screw extruder. A comprehensive study on these composites was conducted by measuring the material relative permittivity, electrical conductivity, thermal properties and tensile strength. The results showed a significant enhancement of the composite behavior up to 1.5 wt.% nano-particles addition. The increase of the nanoparticles up to 1.5 wt.% Cu decreases the relative permittivity and slightly increases the electrical conductivity. Finally, the fabricated composites with different nano-copper contents have large findings within different applications especially in electronics, packaging, and environmental issues.

Recyclable insulation material for HVDC cables in Global Energy Interconnection

With the development of modern power systems, especially that of the global energy internet, high-voltage, direct current (HVDC) cable power transmission will play an important role in the future. The key problem of HVDC cable power transmission is the need for novel cable insulation materials that have high performance, recyclability, and higher working temperature to replace traditional crosslinked polyethylene. This paper investigates the thermal and electrical properties of polypropylene (PP)/Al2O3 nanocomposites as a potential recyclable HVDC cable insulation material. The developed nanocomposites exhibit excellent thermal and electrical properties with the introduction of Al2O3 nanoparticles. Particularly, the space charge accumulation is greatly suppressed.

A study on the effects of graphene nano-platelets (GnPs) sheet sizes from a few to hundred microns on the thermal, mechanical, and electrical properties of polypropylene (PP)/GnPs composites

A study on the effects of graphene nano-platelets (GnPs) sheet sizes from a few to hundred microns on the thermal, mechanical, and electrical properties of polypropylene (PP)/GnPs composites

Conductive network formation and destruction in polypropylene/carbon nanotube composites via crystal control using supercritical carbon dioxide

This study reports on the effects of the matrix's crystal type (α or γ crystal) and chain mobility on the electrical properties of polypropylene (PP)/carbon nanotube (CNT) composites. Isothermal crystallization of the composites was performed at various temperatures and under atmospheric and elevated pressures with supercritical carbon dioxide (scCO2). Remarkably, experimental results indicated that the composites' isothermal annealing at 150 °C under a supercritical carbon dioxide (scCO2) pressure of 31 MPa reduced their percolation threshold by nearly 50%, via the formation of a significant amount of γ crystals. On the other hand, isothermal annealing of PP/CNT at 135 °C under the scCO2 conditions destructed the conductive network via promoting heterogeneous nucleation of α crystals on the CNT surface. Consequently, this led to a desirable combination of a high dielectric permittivity of ε' = 58.0 and a low dielectric loss of tan δ = 0.2 of PP/1.0 wt% CNT composites at a frequency of 100 Hz.

Large impact in electrical properties of polypropylene by improving the filler-matrix interface effect in PP/PS blends

Inorganic nanoparticles are widely used to improve space charge behavior, DC breakdown strength and other electrical properties of polymer insulating materials, but the uniform distribution of inorganic nanofillers in matrix is difficult due to their agglomeration and bad compatibility with the polymeric matrix. In this paper, polypropylene (PP)/polystyrene (PS) blends were prepared to suppress space charge accumulation and improve DC breakdown strength. Polypropylene-g-polystyrene (PP-g-PS) graft copolymer was used as compatibilizer to improve the compatibility of PP matrix and PS filler. The evolution of microstructure of PP/PS blends were investigated by scanning electron microscope (SEM), the space charge distributions were measured by a pulsed electro-acoustic (PEA) system, and DC breakdown strength was also tested. The morphologies show that the size of PS particles reduced to 310 nm when the content of PP-g-PS graft copolymer increased to 24 wt%, and the interaction between PP matrix and PS particles enhanced. The presence of PS particles in all PP/PS blends suppressed the space charge accumulation compared to neat PP, but the DC breakdown strength in uncompatibilized blend was lower than neat PP. The increasing of content of PP-g-PS improved the DC breakdown strength with the maximum value of 408.9 kV/mm was obtained. This may attribute to excellent interface structure formed between PP matrix and PS particles.

Effect of nanoclay concentration level on the electrical properties of polypropylene under electron irradiation in a SEM.

For studying the electrical properties (charge trapping, transport and secondary electron emission) of the polypropylene-based nanocomposites with different contents of natural clay, the specimens were submitted to electron irradiation of a scanning electron microscope. A device, suitably mounted on the sample holder of the scanning electron microscope, was used to measure two currents (i.e. leakage and displacement currents) induced in the polypropylene-based nanocomposites (polymer nanocomposites) under electron irradiation. The evolution of trapped charge during irradiation for each type of studied polymer nanocomposites is deduced. The amount of trapped charge at the steady state is also determined by measuring the change of secondary electron image size associated to the electron trajectory simulation. It is found, surprisingly, that not only the leakage current increases as a function of clay loading level but also trapped charge. However, this could be related to the increase of conductivity in one hand and to proliferation of interfaces between nanoparticles and neighbouring materials on the other hand. These two processes play crucial role in controlling the carrier transport (through polymer nanocomposites or/and along its surface) closely related to the charge storage and leakage current. Additional experiment using dielectric spectroscopy were performed to show the effect of clay concentration in changing the dielectric relaxation behaviour and to evidence the existence of interfaces between nanoparticles and polymer. The secondary electron emission during electron irradiation is also studied through the total electron yield that is deduced by correlating the measured leakage and displacement currents.

Enhancement in Mechanical and Electrical Properties of Polypropylene Using Graphene Oxide Grafted with End-Functionalized Polypropylene.

Terminally hydroxylated polypropylene (PP) synthesized by a chain transfer method was grafted to graphene oxide (GO) at the chain end. Thus obtained PP-modified GO (PP-GO) was melt mixed with PP without the use of a compatibilizer to prepare PP/GO nanocomposites. Mechanical and electrical properties of the resultant nanocomposites and reference samples that contained graphite nanoplatelets, partially reduced GO, or fully reduced GO were examined. The best improvement in the tensile strength was obtained using PP-GO at 1.0 wt %. The inclusion of PP-GO also led to the highest electrical conductivity, in spite of the incomplete reduction. These observations pointed out that terminally hydroxylated PP covalently grafted to GO prevented GO layers from re-stacking and agglomeration during melt mixing, affording improved dispersion as well as stronger interfacial bonding between the matrix and GO.

Electrical properties of modified‐grafted polypropylene

AbstractThe electrical properties of polypropylene (PP), grafted polypropylene (PP‐g‐PVP), and modified‐grafted PVP with α‐cyano‐β‐(2‐thienyl) crotononitrile were investigated. Also, the electrical characteristic of the modified‐grafted PVP subjected to γ‐irradiation (60 kGy) was studied. The results show that the σ of trunk polymer undergoing different degree of grafting generally increases as function of the grafting yield. The grafting yield between 64.1 and 149% resulted in a progressive decrease in ΔEσ value. Inclusion of sulfur‐containing substrate in different films, having various grafting yields, leads to both increase and decrease in σ values. A significant increase in σ values is observed upon inclusion of sulfur‐containing substrate having maximum grafting yield (149%). These changes are accompanied by fluctuation in σ values. The exposure of sulfur‐containing substrate in grafting film to a dose of 60 kGy results in a significant decrease in ΔEσ values for the films undergoing a grafting yield between 64.1 and 149%. The observed changes in ΔEσ of different films investigated could be attributed mainly to corresponding changes in σ values. The observed improvement in electrical properties is mainly because of possible increase in concentration of charge carrier and/or their mobilities. The scanning electron micrographs of some selected films show significant changes in the morphology of the films investigated due to changing the grafting yield, inclusion of sulfur‐containing substrate, and exposure to γ‐irradiation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3797–3803, 2007

Thermal and electrical properties of magnetite filled polymers

By the addition of metal-oxide particles to plastics the electrical and thermal conductivity of polymers can be increased significantly. Such particle filled polymers can substitute metals and metal oxides in applications like radio frequency interference shielding. Furthermore, particle filled polymers with higher thermal conductivity than unfilled ones become more and more important in applications with decreasing geometric dimensions and increasing output of power, like in computer chips. Therefore, thermal and electrical properties of polypropylene and polyamide with metal-oxide particle filler (magnetite, Fe3O4) are investigated. Different particle sizes of magnetite and types of additives were added in various proportions to a standard polypropylene and polyamide in an extrusion process. Samples were prepared by injection molding to investigate thermal and electrical properties systematically. The thermal conductivity increases from 0.22 to 0.93 W/(m K) for a filler content of 44 vol% of magnetite, whereas the electrical resistivity decreases more than seven orders of magnitude from an insulator (0% of magnetite) to 10 kΩ m (47 vol% of magnetite). The experimental results of thermal and electrical conductivity were correlated to the amount and particle sizes of magnetite filler. Electrical resistivity shows a significant drop at the theoretical percolation threshold (∼0.33) and for filler contents exceeding 33 vol% the magnetite particles have point contacts and are surrounded by the polymer matrix.

Effect of surface modification of glass wool on the mechanical and electrical properties of polypropylene/modified glass‐wool composites

AbstractThe surface of glass wool (GW) was modified by two different methods, either by grafting methyl acrylate (MA) onto GW in the presence of potassium persulfate (PPS) as initiator, or by adsorbing stearic acid (AS) as surface active agent onto the GW surface. It was found that conversion and grafting yield of poly(methyl acrylate) (PMA) onto the GW surface increased with increasing initiator concentration, whereas by modifying the GW surface by adsorption of SA, the adsorption of SA was found to be high at small values of equilibrium concentrations and two distinct plateau regions were observed. Mechanical and electrical properties of polypropylene (PP) sheets loaded with modified GW were measured. The obtained data showed that the presence of PMA as grafted polymer onto the GW surface has a plasticizing effect on the prepared PP composites. On the other hand, SA, as a surface modifier for GW, acts as a reinforcing agent for the formed PP composites, which have very good dielectric properties. From the obtained results, one can deduce that the prepared PP/GW composites have promising dielectric properties. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1061–1069, 2002

Microstructures and electrical properties of polypropylene bombarded by pulsed high energy density plasma

Pulsed High Energy Density Plasma (PHEDP) was produced by evaporating and ionizing the surface materials of coaxial metallic electrodes fixed in the plasma gun. The results of the characterization of metallic plasma-bombarded polypropylene (PP) by Fourier infrared-ray spectroscopy (FTIR), scanning electron microscopy (SEM) and surface resistivity measurements were presented. The condensation process of the plasma with single pulse in polymers was investigated. The crystallinity of PP decreased with the applied voltage. The microstructures of PP after plasma bombardment were observed with plan and cross-section view. Metallic particles were deposited on the surface of PP substrates, whereas metallic atoms implanted into PP bulk. The absence of significant decrease of the PP surface resistivity would be discussed.