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Plastics as Heat Managers for High-Tech Products

From laptops to generators: plastics are an integral part of every electronic and electrical device.

In the research project “PolyTherm” experts from chemistry, materials science, plastics and high-voltage engineering pool their expertise. They’re developing and testing novel polymers to facilitate the manufacture of more powerful and compact high-tech products in the future.

Not only our everyday electronics, but also highvoltage generators and transformers need to become more efficient, smarter and at the same time more compact. Because the rising worldwide demand for electrical energy requires an increase in efficiency in order to achieve highest possible effectiveness. But the increasingly powerful devices – from smartphones and laptops to electric vehicles and generators – with their high-efficiency compact parts are placing developers before a key challenge. The smaller the surface area of the components and devices, the more problematic is heat dissipation into the environment. Heat build-up is the most common cause of system outages in electrical devices.

During the development of new working materials for electronic and electrical devices, much effort is made to ensure that all the used materials work together in such a way as to keep the resulting temperatures in check. The role of polymers and polymer-based composites has meanwhile become indispensable to this. Polymers and polymer-based composites are chemical compounds characterised by long chains of more or less regularly structured organic molecules which, in the case of composites, are mixed with inorganic materials. They insulate high-capacity components and go to form protective layers on circuits. And if it goes the way Frank Wiesbrock says it will, plastics will play a key role in heat management in the future.

Aggregation of non-functionalised alumina nanoparticles (left) and statistical distribution of surfacefunctionalised alumina nanoparticles (right) embedded in epoxy resin.

High-perfomance plastics in heat management

The chemist at the Polymer Competence Center Leoben (PCCL) and the Institute for Chemistry and Technology of Materials at TU Graz heads the interdisciplinary K-project “PolyTherm – Polymer Composites for Thermally Demanding Applications”. Together with researchers from chemistry, materials science, plastics and high-voltage engineering as well as industry partners, several objectives are being pursued in the project. “On the one hand, we want to analyse temperature developments and their associated burden on the materials in power electronics systems in simulations. These findings will help us to accurately assess the service life and reliability of electronic components. On the other hand, on the basis of these analyses we will be developing suitable polymers and polymer composites with improved thermo-mechanical properties which show the best performance in use,” says Frank Wiesbrock.

Building a large-scale generator.

Polymers from renewable raw materials 

Special attention will be given to environmental sustainability through the innovative material concepts developed in PolyTherm. “We are developing and testing environmentally friendly polymers with their origin in nature as an alternative to mineral oil synthetic resins. We have already been able to show that rapeseed oil is suitable as a good basis for producing innovative insulating plastics,” says Frank Wiesbrock. The developments are also important with regard to employee protection. This is due to the fact that some of the classical, mineral oil based epoxy resins contain components which may pose health risks in high concentrations. For this reason development from alternative materials is also a long-term aim. 

Industrial manufacture of transformers.

Interdisciplinary research alliance 

In the framework of the COMET programme of the Austrian Research Promotion Agency using funds from the Ministry for Science, Research and Economy and the State of Styria, a budget of six million euros is available for the four-year PolyTherm project which started at the beginning of 2017. On board the project are institutes of five universities among which are TU Graz’s Institute for Chemistry and Technology of Materials, the Institute of High-Voltage Engineering and System Management which among other things will carry out load tests and dielectric characterisations, and the Institute of Inorganic Chemistry. Six partner companies from the microelectronics and high-voltage engineering sector will augment the competence network.

Curing of epoxy-based nanocomposites using UV radiation.

Polymere mit nanoskalierten FüllstoffenPolymers with nanoscale fillers 

Plastics by definition are not good heat conductors and, in general, only have moderate temperature stability. The results which will be obtained from PolyTherm should change all that. A temperature stability up to 180 degrees Celsius is being sought in the new polymers (insulation class H). In comparison, the polymers currently being used have a general temperature stability up to 155 degrees Celsius (insulation class F). The researchers want to achieve this by attaching inorganic, nanoscale fillers onto the polymers. “By combining the nanoparticles with the polymers in a controlled way, we can create new composite materials with certain properties that we can ‘fine tune’,” explains Frank Wiesbrock.

Representation of epoxy-based nanocomposites.

Nanoscale fillers can be mixed with the polymers to alter the physical and chemical properties. The smaller the nanoparticles are, the larger their surface area. In this way interaction with other particles in the polymer base is enhanced, thus increasing strength, thermal stability and thermal conductivity. Currently, the focus of the research project is on investigating surface-functionalised nanofillers. “Metal and semi-metal oxides such as silica or alumina occur naturally in large quantities throughout the world and have been used as fillers for insulators in the plastics industry for a long time. In the last few decades, progress in the field of nanotechnology has opened up new application possibilities for these fillers, particularly with respect to their heat conductivity,” explains Frank Wiesbrock.

What makes the use of nanofillers, such as boron nitride, so special for materials science and chemistry is their chemical structure. Hexagonal boron nitride has a comparable structure to graphite. The individual structural units of the high polymer boron nitride only have very weak bonds. They ensure a better attachment between the matrix – in other words, the polymer, and the nanoscale filler. The researchers are in the process of finding ways of dispersing the nanoscale filler in the plastic matrix equally.

Set-up for testing the tensile strength of nanocomposites.

Preventing tears during expansion and hardening 

Another challenge to the researchers is thermal expansion during heat build-up: this can become a problem when layers of different materials are joined. “On the one hand, the bond between metals and polymers becomes worse when they expand differently due to increasing temperature. On the other hand, polymers can develop tears or hardening, something which has a negative effect on the insulation properties,” explains Frank Wiesbrock. For this reason, the researchers are trying to design the polymers in such a way that a part of the molecular chain increases its volume, while the other part shrinks. In this way the volume of the plastic can remain largely constant even during hardening.

Tailor-made plastic building blocks

The evaluation of alternative production technologies has been planned in the PolyTherm project. “Polymers and polymer composites have outstanding material properties for high-voltage engineering. But because each part has to be adapted to the available environment, even these smallest elements are subject to highly specialised tailor-made solutions. Polymer components are still manufactured according to conventional methods which are generally cost intensive,” says Frank Wiesbrock. But in the future, cheaper and faster processes could be relied on, though currently only a small number of polymers are suitable. “We want to change this by evaluating the uses of certain additives,” continues Frank Wiesbrock.

From a regional point of view, PolyTherm enhances the visibility of the newly established Silicon Alps Cluster, which combines Austrian players from science, economy and the public sector and should open up unique potentials in microelectronics and electrical engineering

This research project is attributed to the Fields of Expertise „Advanced Materials Science“ , one of TU Graz' five strategic areas of research. 

Contact

Frank WIESBROCK
Priv.-Doz. Dipl.-Chem.Univ. Dr.rer.nat.
Institut of Chemistry and Technology os Materials
Stremayrgasse 9
8010 Graz
Phone: +43 316 32283
f.wiesbrocknoSpam@tugraz.at
ictm.tugraz.at