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A special issue of Polymers (ISSN 2073-4360).

Deadline for manuscript submissions: closed (31 January 2016) | Viewed by 114194

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Prof. Dr. Frank Wiesbrock

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Institute for Chemistry and Technology of Materials, University of Technology Graz, NAWI Graz, 8010 Graz, Austria
Interests: functional polymers; ring-opening polymerizations; crosslinked polymers; biopolyesters; polymeranalogous modifications
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Special Issue Information

Dear Colleagues,

Polymers aims to compile the current trends and research directions within the preparation, characterization and application of polymer-based composite materials in electrical engineering applications. This type of material has evolved to become one of the most thoroughly investigated materials these days, stimulated by the demand for resource-efficient assembly of generators, transformers, communication devices, etc. Novel composites are to be used as insulating materials with high thermal conductivity and excellent temperature stability, through which premature ageing and degradation of devices shall be avoided or at least reduced.

Aiming at a comprehensive representation of research activities in the field, contributions that describe one or multiple steps of the material research and development are invited to this Special Issue. Material research and development comprises the molecular structure of polymers, adequate processing technologies and the inner material structure, as well as material properties and the functionality of composites. Hence, potential topics for this Special Issue comprise the synthesis of functionalized polymers and/or the surface modification of particles in order to enhance compatibility, the processing of the materials, and the physico-chemical characterization of composite materials, with a special focus on thermal conductivity, ageing and electrical characterization.

Review articles, as well as original papers, will be considered for this Special Issue.

Prof. Dr. Frank Wiesbrock
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Polymers is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

functionalized polymers
surface functionalization of micro- and nanoparticles
curing of composites
composite processing
adhesion in multilayer composites
thermal conductivity
electrical characterization of composite materials
stability/reliability of devices and ageing phenomena

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Published Papers (11 papers)

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Editorial

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149 KiB

Open AccessEditorial

Interdisciplinary Approaches towards Materials with Enhanced Properties for Electrical Engineering

by Frank Wiesbrock

Polymers 2016, 8(8), 307; https://doi.org/10.3390/polym8080307 - 16 Aug 2016

Viewed by 3354

Abstract

The internationally growing demand for electrical energy is one of the most prominent triggers stimulating research these days.[...] Full article

(This article belongs to the Special Issue Nano- and Microcomposites for Electrical Engineering Applications)

Research

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2073 KiB

Open AccessArticle

The Effects of in Situ-Formed Silver Nanoparticles on the Electrical Properties of Epoxy Resin Filled with Silver Nanowires

by Gwang-Seok Song, Dai Soo Lee and Ilho Kang

Polymers 2016, 8(4), 157; https://doi.org/10.3390/polym8040157 - 21 Apr 2016

Cited by 10 | Viewed by 6737

Abstract

A novel method for preparing epoxy/silver nanocomposites was developed via the in situ formation of silver nanoparticles (AgNPs) within the epoxy resin matrix while using silver nanowires (AgNWs) as a conductive filler. The silver–imidazole complex was synthesized from silver acetate (AgAc) and 1-(2-cyanoethyl)-2-ethyl-4-methylimidazole (imidazole). AgNPs were generated in situ during the curing of the epoxy resin through the thermal decomposition of the AgAc–imidazole complex, which was capable of reducing Ag⁺ to Ag by itself. The released imidazole acted as a catalyst to cure the epoxy. Additionally, after the curing process, the in situ-generated AgNPs were stabilized by the formed epoxy network. Therefore, by using the thermal decomposition method, uniformly dispersed AgNPs of approximately 100 nm were formed in situ in the epoxy matrix filled with AgNWs. It was observed that the nanocomposites containing in situ-formed AgNPs exhibited isotropic electrical properties in the epoxy resins in the presence of AgNWs. Full article

(This article belongs to the Special Issue Nano- and Microcomposites for Electrical Engineering Applications)

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3393 KiB

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On the Effect of Nanoparticle Surface Chemistry on the Electrical Characteristics of Epoxy-Based Nanocomposites

by Celia Yeung and Alun S. Vaughan

Polymers 2016, 8(4), 126; https://doi.org/10.3390/polym8040126 - 6 Apr 2016

Cited by 15 | Viewed by 5779

Abstract

The effect of nanosilica surface chemistry on the electrical behavior of epoxy-based nanocomposites is described. The nanosilica was reacted with different volumes of (3-glycidyloxypropyl)trimethoxysilane and the efficacy of the process was demonstrated by infrared spectroscopy and combustion analysis. Nanocomposites containing 2 wt % of nanosilica were prepared and characterized by scanning electron microscopy (SEM), AC ramp electrical breakdown testing, differential scanning calorimetry (DSC) and dielectric spectroscopy. SEM examination indicated that, although the nanoparticle dispersion improved somewhat as the degree of surface functionalization increased, all samples nevertheless contained agglomerates. Despite the non-ideal nature of the samples, major improvements in breakdown strength (from 182 ± 5 kV·mm⁻¹ to 268 ± 12 kV·mm⁻¹) were observed in systems formulated from optimally treated nanosilicas. DSC studies of the glass transition revealed no evidence for any modified interphase regions between the nanosilica and the matrix, but interfacial effects were evident in the dielectric spectra. In particular, changes in the magnitude of the real part of the permittivity and variations in the interfacial α′-relaxation suggest that the observed changes in breakdown performance stem from variations in the polar character of the nanosilica surface, which may affect the local density of trapping states and, thereby, charge transport dynamics. Full article

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2749 KiB

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Charge Transport in LDPE Nanocomposites Part II—Computational Approach

by Anh T. Hoang, Yuriy V. Serdyuk and Stanislaw M. Gubanski

Polymers 2016, 8(4), 103; https://doi.org/10.3390/polym8040103 - 23 Mar 2016

Cited by 54 | Viewed by 6152

Abstract

A bipolar charge transport model is employed to investigate the remarkable reduction in dc conductivity of low-density polyethylene (LDPE) based material filled with uncoated nanofillers (reported in the first part of this work). The effect of temperature on charge transport is considered and the model outcomes are compared with measured conduction currents. The simulations reveal that the contribution of charge carrier recombination to the total transport process becomes more significant at elevated temperatures. Among the effects caused by the presence of nanoparticles, a reduced charge injection at electrodes has been found as the most essential one. Possible mechanisms for charge injection at different temperatures are therefore discussed. Full article

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6132 KiB

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Charge Transport in LDPE Nanocomposites Part I—Experimental Approach

by Anh T. Hoang, Love Pallon, Dongming Liu, Yuriy V. Serdyuk, Stanislaw M. Gubanski and Ulf W. Gedde

Polymers 2016, 8(3), 87; https://doi.org/10.3390/polym8030087 - 16 Mar 2016

Cited by 62 | Viewed by 7386

Abstract

This work presents results of bulk conductivity and surface potential decay measurements on low-density polyethylene and its nanocomposites filled with uncoated MgO and Al₂O₃, with the aim to highlight the effect of the nanofillers on charge transport processes. Material samples at various filler contents, up to 9 wt %, were prepared in the form of thin films. The performed measurements show a significant impact of the nanofillers on reduction of material’s direct current (dc) conductivity. The investigations thus focused on the nanocomposites having the lowest dc conductivity. Various mechanisms of charge generation and transport in solids, including space charge limited current, Poole-Frenkel effect and Schottky injection, were utilized for examining the experimental results. The mobilities of charge carriers were deduced from the measured surface potential decay characteristics and were found to be at least two times lower for the nanocomposites. The temperature dependencies of the mobilities were compared for different materials. Full article

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3017 KiB

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Structural and Spectroscopic Characterization of A Nanosized Sulfated TiO₂ Filler and of Nanocomposite Nafion Membranes

by Valentina Allodi, Sergio Brutti, Marco Giarola, Mirko Sgambetterra, Maria Assunta Navarra, Stefania Panero and Gino Mariotto

Polymers 2016, 8(3), 68; https://doi.org/10.3390/polym8030068 - 1 Mar 2016

Cited by 21 | Viewed by 6451

Abstract

A large number of nano-sized oxides have been studied in the literature as fillers for polymeric membranes, such as Nafion^®. Superacidic sulfated oxides have been proposed and characterized. Once incorporated into polymer matrices, their beneficial effect on peculiar membrane properties has been demonstrated. The alteration of physical-chemical properties of composite membranes has roots in the intermolecular interaction between the inorganic filler surface groups and the polymer chains. In the attempt to tackle this fundamental issue, here we discuss, by a multi-technique approach, the properties of a nanosized sulfated titania material as a candidate filler for Nafion membranes. The results of a systematic study carried out by synchrotron X-ray diffraction, transmission electron microscopy, thermogravimetry, Raman and infrared spectroscopies are presented and discussed to get novel insights about the structural features, molecular properties, and morphological characteristics of sulphated TiO₂ nanopowders and composite Nafion membranes containing different amount of sulfated TiO₂ nanoparticles (2%, 5%, 7% w/w). Full article

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4670 KiB

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Dielectric Properties and Energy Storage Densities of Poly(vinylidenefluoride) Nanocomposite with Surface Hydroxylated Cube Shaped Ba_0.6Sr_0.4TiO₃ Nanoparticles

by Shaohui Liu, Shaomei Xiu, Bo Shen, Jiwei Zhai and Ling Bing Kong

Polymers 2016, 8(2), 45; https://doi.org/10.3390/polym8020045 - 16 Feb 2016

Cited by 58 | Viewed by 7740

Abstract

Ceramic-polymer nanocomposites, consisting of surface hydroxylated cube-shaped Ba_0.6Sr_0.4TiO₃ nanoparticles (BST–NPs) as fillers and poly(vinylidenefluoride) (PVDF) as matrix, have been fabricated by using a solution casting method. The nanocomposites exhibited increased dielectric constant and improved breakdown strength. Dielectric constants of the nanocomposite with surface hydroxylated BST–NPs (BST–NPs–OH) were higher as compared with those of their untreated BST–NPs composites. The sample with 40 vol % BST–NPs–OH had a dielectric constant of 36 (1 kHz). Different theoretical models have been employed to predict the dielectric constants of the nanocomposites, in order to compare with the experimental data. The BST–NPs–OH/PVDF composites also exhibited higher breakdown strength than their BST–NP/PVDF counterparts. A maximal energy density of 3.9 J/cm³ was achieved in the composite with 5 vol % BST–NPs–OH. This hydroxylation strategy could be used as a reference to develop ceramic-polymer composite materials with enhanced dielectric properties and energy storage densities. Full article

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1802 KiB

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Crosslinked Poly(2-oxazoline)s as “Green” Materials for Electronic Applications

by Martin Fimberger, Ioannis-Alexandros Tsekmes, Roman Kochetov, Johan J. Smit and Frank Wiesbrock

Polymers 2016, 8(1), 6; https://doi.org/10.3390/polym8010006 - 30 Dec 2015

Cited by 13 | Viewed by 7762

Abstract

Poly(2-nonyl-2-oxazoline)₈₀-stat-poly(2-dec-9′-enyl-2-oxazoline)₂₀ and poly(2-dec-9′-enyl-2-oxazoline)₁₀₀ can be synthesized from the cationic ring-opening polymerization of monomers that can be derived from fatty acids from renewable resources. These (co)poly(2-oxazoline)s can be crosslinked with di- and trifunctional mercapto compounds using the UV-induced thiol-ene reaction. The complex permittivity of the corresponding networks increases with the temperature and decreases with the network density. In a frequency range from 10⁻² to 10⁶ Hz and at temperatures ranging from −20 to 40 °C, the changes of the real part of the complex permittivity as well as the loss factor can be explained by interfacial polarization within the material. At a temperature of 20 °C and a frequency of 50 Hz, the permittivity of the crosslinked (co)poly(2-oxazoline)s covers a range from 4.29 to 4.97, and the loss factors are in the range from 0.030 to 0.093. The electrical conductivities of these polymer networks span a range from 5 × 10⁻¹² to 8 × 10⁻⁹ S/m, classifying these materials as medium insulators. Notably, the values for the permittivity, loss factor and conductivity of these copoly(2-oxazoline)s are in the same range as for polyamides, and, hence, these copoly(2-oxazoline)-based networks may be referred to as “green” alternatives for polyamides as insulators in electronic applications. Full article

(This article belongs to the Special Issue Nano- and Microcomposites for Electrical Engineering Applications)

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Review

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2168 KiB

Open AccessReview

Mechanical Properties of Composites Used in High-Voltage Applications

by Andreas Moser and Michael Feuchter

Polymers 2016, 8(7), 260; https://doi.org/10.3390/polym8070260 - 14 Jul 2016

Cited by 12 | Viewed by 10106

Abstract

Materials used in high voltage applications have to meet a lot of regulations for their safety and functional usage during their lifetime. For high voltage applications the electrical properties are the most relevant designing criteria. However, the mechanical properties of such materials have rarely been considered for application dimensioning over the last decades. This article gives an overview of composite materials used in high voltage applications and some basic mechanical and thermo-mechanical characterization methods of such materials, including a discussion of influences on practically used epoxy based thermosets. Full article

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5570 KiB

Open AccessReview

Mica/Epoxy-Composites in the Electrical Industry: Applications, Composites for Insulation, and Investigations on Failure Mechanisms for Prospective Optimizations

by Natascha Andraschek, Andrea Johanna Wanner, Catharina Ebner and Gisbert Riess

Polymers 2016, 8(5), 201; https://doi.org/10.3390/polym8050201 - 20 May 2016

Cited by 52 | Viewed by 13012

Abstract

The investigation of mica and mica/epoxy-composites has always been of high importance and has gained increased attention in recent years due to their significant role as insulation material in the electrical industry. Electrical insulation represents a key factor regarding the reliability and lifespan of high voltage rotating machines. As the demand for generating power plants is increasing, rotating machines are of intrinsic importance to the electrical energy supply. Therefore, impeccable functioning is of immense importance for both the producers of high voltage machines as well as the energy suppliers. Thus, cost reduction caused by shorter maintenance times and higher operational lifespan has become the focus of attention. Besides the electrical properties, composites should offer compatible chemical and mechanical, as well as thermal characteristics for their usage in insulating systems. Furthermore, knowledge of several occurring stresses leading to the final breakdown of the whole insulation is required. This review aims to give an overview of the properties of pure components, the composite, and the possible occurring failure mechanisms which can lead to a full understanding of insulation materials for high voltage rotating machines and therefore establish a basis for prospective optimizations. Full article

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11529 KiB

Open AccessReview

Properties of Polymer Composites Used in High-Voltage Applications

by Ilona Pleşa, Petru V. Noţingher, Sandra Schlögl, Christof Sumereder and Michael Muhr

Polymers 2016, 8(5), 173; https://doi.org/10.3390/polym8050173 - 28 Apr 2016

Cited by 302 | Viewed by 37716

Abstract

The present review article represents a comprehensive study on polymer micro/nanocomposites that are used in high-voltage applications. Particular focus is on the structure-property relationship of composite materials used in power engineering, by exploiting fundamental theory as well as numerical/analytical models and the influence of material design on electrical, mechanical and thermal properties. In addition to describing the scientific development of micro/nanocomposites electrical features desired in power engineering, the study is mainly focused on the electrical properties of insulating materials, particularly cross-linked polyethylene (XLPE) and epoxy resins, unfilled and filled with different types of filler. Polymer micro/nanocomposites based on XLPE and epoxy resins are usually used as insulating systems for high-voltage applications, such as: cables, generators, motors, cast resin dry-type transformers, etc. Furthermore, this paper includes ample discussions regarding the advantages and disadvantages resulting in the electrical, mechanical and thermal properties by the addition of micro- and nanofillers into the base polymer. The study goals are to determine the impact of filler size, type and distribution of the particles into the polymer matrix on the electrical, mechanical and thermal properties of the polymer micro/nanocomposites compared to the neat polymer and traditionally materials used as insulation systems in high-voltage engineering. Properties such as electrical conductivity, relative permittivity, dielectric losses, partial discharges, erosion resistance, space charge behavior, electric breakdown, tracking and electrical tree resistance, thermal conductivity, tensile strength and modulus, elongation at break of micro- and nanocomposites based on epoxy resin and XLPE are analyzed. Finally, it was concluded that the use of polymer micro/nanocomposites in electrical engineering is very promising and further research work must be accomplished in order to diversify the polymer composites matrices and to improve their properties. Full article

(This article belongs to the Special Issue Nano- and Microcomposites for Electrical Engineering Applications)

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