Methodologies for Development and Characterization of Polymer Nanocomposite Dielectrics with Insulating Properties - PoNaDIP

      Project director: Professor Florin CIUPRINA

Thematic fields S/T:

      Nanosciences & Nanotechnologies and Materials (N&N, M) thematic fields have strong cross-sectorial importance. Novel innovative materials are a prerequisite for new products and developments in many sectors, whereas advances in process design enable energy efficient, resource-saving and competitive production of such materials and give rise to process innovations in other sectors ranging from the electronics industry to energy production. Accordingly, a strong relationship between N&N, M thematic fields and a large number of Technology Platforms exists, clearly illustrating the role of these areas as an engine for major innovation in different industries.

      The present project supports, and it is in line with the orientations proposed in the Materials Technology field by four related Technology Platforms having as common goal to improve the competitiveness of European Industry by using advanced materials and high performance processes and technologies:

      The research activities of the project are focused on:

Project’s abstract:

      The proposed project is highly inter and multi-disciplinary. Polymer nanocomposites are the 21st century engineering materials, with wide range of markets such as transportation, electrical and (nano)electronics, food packaging and building industries. They are particularly promising as near-future advanced dielectrics and electrical insulation from the viewpoint of their excellent properties.

      Polymer nanocomposites are defined as polymers with a small amount of nano-fillers. Usually, the nano-fillers are 1 to 100 nm in size, 1 to 10 wt% in content, and should be homogeneously dispersed in the polymer matrix. Polymers such as polyamide (PA), polyethylene (PE), polypropylene (PP), ethylene vynyl acetate (EVA), epoxy resins and silicone rubbers are combined with nano-fillers such as layered silicate (LS), silica (SiO2), titania (TiO2), and alumina (Al2O3). It was found that nano-filler addition has positive effect on electrical characteristics, resistance to high voltage environment and thermal endurance, but further investigation is required. Nanocomposites are also expected to hold functional performances such as gas barrier effect, flame retardancy, biodegradability, foaming ability, paint performance and the like, depending on their application.

      The activities in the project are not only related to research, but they also include transfer of knowledge and innovation at the highest level. The proposed project is part of a coherent and complementary series of national and European projects related to nanoscale analysis of polymer dielectrics used as electrical insulation. Each project in the series has got a specific role, and moreover, the synergy between them adds extra value, for instance by using the experimental results obtained in one project into the other projects or by blending the research with the PhD training.

      The proposed research project aims to attract and train young PhD Romanian students in the domain of the development of new nanometric dielectrics, considering that other European projects allow the financing of foreign researchers that undergo doctoral studies in Romania. Another expected effect is the structuring at national level by means of support actions for the scientific community interested in the development of polymer nanocomposites, the increase of the competitiveness of the Romanian industry of advanced materials and its access to one or more European technological platforms and to FP7. Without consistent research, training and transfer of knowledge effort, we cannot imagine how else to achieve this goal. The project will enlarge the reservoir of new models, theories, methods and techniques for development and characterization of polymer nanocomposite dielectrics. The project will enlarge the reservoir of studies, models, theories concerning polymer nanodielectrics, and of the new methods and t echniques of manufacturing and characterization of polymer nanocomposites with high performances

      Together with our European partners, the research goal is, first of all, the development of suitable not only laboratory scale but also industrial methods of manufacturing polymer nanocomposites. This will help to create reproducible and reliable data needed for the research development of our field. The samples manufactured in the first stage will be properly characterized by advanced analytical tools and the data obtained from this investigation will be correlated with their properties (electrical, thermal, mechanical, etc). Then, the research will focus on clarifying phenomena at interfaces between nanoparticles and polymer matrices, by combining experimental results with models of interfaces. Such phenomena certainly depend on the kind of nanoparticle materials, physical and chemical conditions of their surfaces, the kind of coupling agents to bridge inorganic and organic substances chemically and physically, the kind and content of compatibiliseres and/or dispersants, and the kind of polymer matrices.

      We also aim to create a forum for research and to promote international cooperation to facilitate and accelerate our research.

      Finally, the materials developed in the project will be classified by indicating their possible applications.

Directions, priorities, objectives, state of the art

      On 6 July 2005 the European Commission adopted the Communication Nanosciences and nanotechnologies: An action plan for Europe 2005-2009 (COM(2005) 243) which defines a series of articulated and interconnected actions for the immediate implementation of a safe, integrated and responsible strategy for N&N. These actions are:

      According to Directorate-General for Research of European Commission [2] the main objective of the thematic field Nanosciences & Nanotechnologies is “Increasing and support the take-up of knowledge generated in this revolutionary field for all industrial sectors”, having as priorities: Expanding knowledge of size, dimension and geometry dependent phenomena; Extending the limits of control and material properties for micro-,macro-applications; Nano- and high-precision technologies for chemistry; Expanding knowledge to support new evolutions in electronics. The main objective of the Materials thematic field is “Generating new knowledge to enable new industrial products and processes to be achieved, exploiting the potential of interdisciplinary approaches in materials research”, with the priorities: Knowledge-based materials with tailored properties and enhanced processibility; Reliable design and simulation for material engineering; Integration at nano-molecular-macro levels in the chemical te chnology and materials processing industries; New nano-,bio-,hybrid-,materials including their process design and control. Starting from these priorities, the four European Technical Platforms the present project is in line with, have in their Strategic Research Agenda (SRA) the following priorities related to Nanosciences & Nanotechnologies and Materials:

      The IEEE Dielectrics and Electrical Insulation Society have been focused on nanocomposite dielectrics in the last 5 years, several issues of its main scientific publication “IEEE Transactions on Dielectrics and Electrical Insulation” have been dedicated to the state of the art of this research area. The last digest papers on this topic [7] present a range of results on dielectric and electric insulation systems. Tanaka et al review the types of nano-composite materials available, processing and fabrication methods, and the work to date on their electrical properties. Their summary is very encouraging: they show improved insulation properties and reliability and that "Polymer nanocomposites will give much innovation in dielectric and insulation technologies". This is borne out by other papers in this digest. For example, the degradation of surfaces by partial discharges is shown to be greatly reduced by the incorporation of discharge-resistant nano-platelets in the paper by Kozako et al. Montanari et al confirms that space charge dispersion, conductivity and breakdown voltages of EVA and PP are improved when filled with synthetic nano-Iayers. Brosseau shows that conventional models for the dielectric response of mixtures, such as the Bruggeman model, cannot be used to predict the behavior of such nano-filled systems, confirming the importance of considering the interface regions (sometimes referred to as "interaction zones"). In some senses mono-layers may be thought of as an archetype for interface regions in a nano-composite. Iwamoto considers this special case and shows, for non-centro-symmetric systems, that the measurement of Maxwell Displacement Current coupled with the optical second harmonic generation (SHG) measurement is effective for the detection of surface polarization and thus helpful for the determination of the orientational order of the layer dipoles The role of the interface has been also emphasized by Lewis and by Roy et al [8]. There is also an industrial view of the subject, very important for all of us, addressing the way in which nano-dielectrics can be used commercially.

      It becomes clear that the progress in nanodielectrics cannot be made only by professionals in chemistry, a coherent multi-disciplinary effort of researchers from chemistry, physics, mathematics, computer science, and electrical engineering must be carried on in this respect. It is exactly the approach of the present proposal.

Significant results obtained and their application

      Polymer nanocomposites could be advantageous over traditional filled polymers in electrical and thermal properties as well as mechanical properties from the standpoint of dielectrics and electrical insulation. This feature will technologically result in compact design of electrical equipments with high reliability and thereby in significant cost reduction for system integration and maintenance. Since this feature is originated from mesoscopic characteristics of interaction zones between polymer matrices and nanofillers, it will open a new academic arena for dielectric and electrical insulation that will need quantum mechanics as well. Such interaction zones might be related to free volume and charge carrier trap distribution shallow and deep traps), which should be further explored. In order to obtain excellent but low-cost polymer nanocomposites, existing material processing technologies should be more advanced so as to match dielectrics and electrical insulation. Results are summarized as follows [9]:

Effects of nanomization

  1. DC conductivity increases and decreases depending on measurement conditions. Introduction of deep traps are suggested.
  2. Interfacial polarization can be reduced compared to microcomposites.
  3. There seems to be a certain reduction of permittivity due to nanomization. But change of permittivity as well as tan d is complicated, and not conclusive. Manufacturing processes should be more investigated for homogenous dispersion of nanofillers.
  4. Space charge, TSC and EL also give complex results in their threshold field and quantity. Introduction of additional levels of shallow and deep traps, as well as increase of trap density, might be involved. These might be deeply related to "interaction zones". It is therefore necessary to characterize the interaction zones between nanofillers and polymer matrices chemically and physically.
  5. Partial Discharge and tracking resistance improve. It is most probable. Role of nanofillers and interaction zones should be more clarified.
  6. Thermal conductivity and glass transition temperature could be increased by proper methods.

Properties of polymer nanocomposites

  1. Electrical and thermal properties as well as mechanical properties could be improved by nanomization of polymers. Polymer nanocomposites are advantageous over conventional filled polymers, because a small amount of nanofillers might not modify the characteristics of base polymers considerably and processing behavior.
  2. Intercalation methods, sol-gel method, molecular composite formation method and nanofiller direct dispersion method are the major processing technologies, and should be more developed for better and cheaper materials with excellent interaction zones.
  3. Polymer matrices, nanofillers, and interaction zones between them are three major parts of nanocomposites. Their respective roles should be investigated based on material characteristics of interest.
  4. Especially interaction zones should be characterized chemically and physically.
  5. Deep and shallow traps should be investigated and correlated with physical and chemical characteristics of interaction zones. Especially a theory for trap level and density modification should be established.
  6. Interaction zones are mesoscopic in nature. This will open a completely new aspect of dielectrics and insulation studies, which need consideration based on quantum and statistical mechanics, too.
  7. Heat resistant thermoplastic nanocomposites are environmentally benign because of their recyclability. These could replace thermoset resins that cannot be recycled.
  8. Biodegradable polymers such as polylactic acid can be filled with nanofillers. PLA nanocomposites are expected to be used for eco-friendly electrical insulation.

Applications

  1. Polymer nanocomposites have been investigated for future use of electrical insulation for power apparatus, power cables, outdoor insulators, and insulated wires for electric power technologies as well as printed circuit boards for electronics.
  2. Insulation could be more compact by using polymer nanocomposites, resulting in overall cost reduction in apparatus and installation.
  3. Reliability could be improved by using polymer nanocomposites, resulting in lower maintenance cost.
  4. Polymer nanocomposites will give much innovation in dielectric and insulation technologies.

R&D units interested in the domain

      At European level, the main R&D units in the domain of nanodielectrics are University of Wales and University of Leicester – UK, High Voltage and Material Engineering Laboratory of the Department of Electrical Engineering, University of Bologna – Italy, Institute of Macromolecular Chemistry of the Albert-Ludwig University from Freiburg – Germany, and Electrical Engineering Laboratory of the Universite Toulouse III – France. All top technical universities from Europe, including Romania, have research teams interested in different types of nanocomposites. The main Romanian R&D institutes with research dedicated to this domain are: National Institute for R&D in Chemistry and petrochemistry ICECHIM Bucharest (one of the partners in the present project), National Institute for R&D in Microtechnologies IMT Bucharest and National Institute for R&D of Materials Physics Magurele. Most Romanian teams are interested mainly in the structures and technology progress, and less in the behavior of the nanodielectrics as electrical insulation which is one important goal of our project.

Potential users

      The national PoNaDIP consortium includes among public institutions, a private company ELJ. This company which will be the main user of the research results, designs and manufactures mostly highly complex power electronics equipment for industrial investments. ELJ’s offer for domains with high quality standards (such as: nuclear, military, energetic and rail-way fields) determined its specialists to focus their efforts on the achievement of a structure of equipment based on a unique hardware and customized software for each application, utilizing components and materials with the best performances and reliability.

      As the 21st century unfolds, it is becoming more apparent that the next technological frontiers will be opened not through a better understanding and application of a particular material, but rather by understanding and optimizing material combinations and their synergistic function, hence blurring the distinction between a material and a functional device comprised of distinct materials. Discovery of new materials with tailored properties and the way to process them are the rate-limiting steps in new business development in many industries. The demands of tomorrow’s technology translate directly into increasingly stringent demands on the materials involved, e.g. their intrinsic properties, costs, processing and fabrication, benign health and environmental attributes and recyclability with focus on eco-efficiency.

Nanodielectric materials science deals with the design and manufacture of nanodielectrics, an area in which obviously chemistry plays the central role but there is also considerable overlap with the ?eld of electrical engineering, biotechnology, computational material science and physics. Nanodielectric materials science has made substantial contributions to many ?elds including: modern plastics, paints, textiles and electronic materials; but there are greater opportunities and challenges for the future. Materials technology is vital for all areas of science and technology as well as for the needs of society in respect of energy, information and communications technology (ICT), healthcare, quality of life, transportation and citizen protection (see figure below). This is the reason why the proposed project aims exactly at the most intimate core of the engine responsible for the knowledge-based society. The social effect of the most insignificant innovation or improvement at the nanostructured material level is amplified thousand of times. Doing complete lifecycle analysis on newly developed products, and considering all the ecological as well as the socio-economic components, will help to ensure growth and employment in the European Economic Area (EEA). Furthermore, material science will play an important role in contributing to the solutions for some emerging societal needs and in increasing the quality of life of European citizens. Converging with the various performance demands are a suite of new technologies and approaches that offer more rapid new materials discovery, better characterization, more direct molecular-level control of their properties and more reliable design and simulation.

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