Topic of the Month March 2009

Photo: A plastic-metal hybrid in the form of granulate or strands. In the next step, the conductive material can be plasticized again and apply as a printed circuit board track. © Fraunhofer IFAM

Intelligent composites: Plastic-metal hybrids

Plastics are usually good electrical insulators – which is frequently a welcome and extensively used property. However, this property prohibits any applications that require the removal of electric charges, such as the grounding of components or uses in constructive discharging structures. Scientists at Fraunhofer Institute for Manufacturing Technology and Applied Materials Research (IFAM) in Bremen, Germany, have recently developed so-called hybrid materials that lend themselves to combinations of the characteristic properties of metals and plastics. The possibility to combine the desired characteristics of both material classes generates multiple synergies for a wide variety of high-tech applications – when combined with metallic components, relatively lightweight and low-cost plastics can gain in mechanical strength and become electrically and thermally conductive. The scientists also provided an innovative process that permits the conversion of the two different material types into a homogeneous mixture of materials and their processing into semifinished goods and components using established forming technologies. These plastic-metal hybrids have a very high substitution potential and will be especially attractive for applications where the integration of functions is important.

Fire protection: Functional nano fillers

In his doctoral thesis, Dr.-Ing. Francis R. Costa, a scientist of TU Dresden, explored a new, environmental-friendly way of fire-proofing plastics. The approach is based on the exploration of nano-scale Layered Double Hydroxides (LDHs) as function-bearing additives for the modification of plastics such as polyethylene. An LDH variant – the so-called hydrotalkites – provide an interesting set of characteristics for this specific application: When heated to temperatures above 320 degrees Celsius, i.e. above the melting point of most thermoplastics, they precipitate water, acting as an integrated fire extinguisher. This behavior virtually predestines this material group for use as an environmental-friendly fire protection in plastics and plastic components. The flame-retardant effect of the water precipitation is additionally intensified by the flaky morphology of the nano fillers, since these flakes result in surface scaling that inhibits the gas exchange. Due to this effect, the flame-retardant effect in plastics can already be achieved with a lower percentage of filler than it is possible with traditional micro-scale flame retardants. Additionally, the nano flakes have a strengthening effect that results in a marked improvement of the mechanical properties of the plastic matrix. Feasibility has already been successfully demonstrated on a small technical scale. Currently, specific projects for industrial implementation are being worked on with several partners from the industry.

Self-healing corrosion protection

Photo: Presented by the inventors: Self-healing coatings as compared to conventional coatings. Photo by L. Brian Stauffer

Recently, scientists of the University of Illinois presented an intelligent polymer coating that is able to provide powerful corrosion protection. The coating works even if its surface is destroyed by scratching and wear mechanisms. This innovation relies on an integrated self-healing effect. Paul Braun and his colleagues realize this material property through the encapsulaton of special catalysts and molecules in hollow spheres with less than 100 micrometers in diameter. These can be homogeneously dispersed in a wide variety of coating materials and paint systems and can be applied by conventional processes. Parts and components that are coated using this technology have demonstrated excellent performance characteristics in different corrosion tests. The effect is easy to explain: If the coating is damaged, some of the filled hollow spheres will also break, and their contents will flow into the damaged surface region. The released substances come into contact and react while forming a new, adhesive and covering coating that protects the damaged part against further corrosive effects.

Optimized plastics – a matter of ingredients …

Plastics have an interesting set of properties – especially in the context of sustainable and resource-friendly product strategies. Their low density, good processability, workability and chemical resistance are only a few characteristics that make this material group an attractive candidate for demanding applications in the field of pipes, hoses and other components that are used to transport fluids. Nevertheless, plastics cannot reliably meet all of the requested criteria; for instance, weak mechanical properties, low resistance to wear and low temperature resistance are typical limiting weaknesses of this material class. However, recent findings from chemical additives research or on the basis of innovative composite concepts have been pointing to exciting approaches to eliminate these disadvantages, thereby transporting plastics into new worlds of application.

Dr.-Ing. Christoph Konetschny
Material- und Nanoexperte

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