1 Green Alternative?

The development of sustainable materials for making new products is a necessary step toward a ready-for-the-future mobility. This is the main incentive for IfBB (Institute for Bioplastics and Biocomposites, University of Hanover, Germany) to engage in a cooperation with the race driver Smudo (a well-known celebrity in Germany as a singer of the German hip-hop group “Die Fantastischen Vier”) and the Four Motors Racing Team. Funded by the Agency for Renewable Resources (FNR Fachagentur Nachwachsende Rohstoffe e.V.) on behalf of the German Federal Ministry of Food, Agriculture and Consumer Protection, this joint endeavour is focused on the development of bio-based materials and sustainable parts for the automotive industry. Bioplastics and biocomposites in this context are defined as fully or partially bio-based materials or as composites with bio-based reinforcement fibers and/or bio-based matrices.

With increasing use of bio-based components in its construction, the Bioconcept Car is well equipped to stand the strain of competitive long-distance races such as the VLN Endurance Championship or the ADAC 24 h races on the famous Nürburgring circuit. So the Bioconcept-Car sets out a path for a change toward sustainable materials not only in racing but also in normal traffic. There is growing evidence that bio-based materials can well be applied in modern technical constructions which are exposed to heavy strains like automotive parts.

2 Materials and Methods

An increasing number of components for the Bioconcept Car are made of resource-saving bio-based materials, which are extremely light-weight and therefore minimize the vehicle’s fuel, or energy, consumption. To achieve the best possible result, different materials and material combinations are tested. On the one hand, thermoplastics which may be bio-based or petro-based (in this case thermoplastics combined with natural fibers to obtain a bio-composite) are used, either reinforced with different fibers or modified without fiber reinforcement; on the other hand, bio-based or petro-based thermosetting materials are combined with various fibers. In any case, the developed materials are fully or partly bio-based—either the fiber and/or the resin. For the light-weight car body resins are used which are reinforced with natural fibers.

Different natural and non-natural fabrics with variable weight and variable weave were produced and tested to achieve the necessary quality/character in terms of stability or processing properties (see Table 1) and to ensure the desired results in combination with the resin. In order to attain the properties of the natural fibers in the composites, they are laminated with a well-known resin (“Epoxidharz L” with “Epoxidhärter GL2” by “R&G Faserverbundwerkstoffe GmbH”, see Table 2).

Table 1 Fabrics overview (based on manufacturer’s data)
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Table 2 Comparison of potential lightweight materials
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The used test samples (Type “1B”l: 115.0 ± 0.2 mm, b: 10.0 ± 0.2 mm h: according to quantity layer) are milled from the composites. They are produced by means of a vacuum bag process on a steel plate (370 × 370 mm) which was coated with a priming wax and a form release agent. The different layers are laminated by hand before they are cured at 70 °C for 24 h under vacuum. The mechanical parameters are determined after DIN EN ISO 527_2 by means of a universal testing machine Zwick/Roell type “Zmart.Pro”.

3 Results of Experiments

A comparison of potential lightweight materials reveals the advantages and disadvantages of the different fibers (see Table 2 and Figs. 1 and 2). On the x-axis the Figs. 1 and 2 show the density and on the y-axis the E-Modulus, or tensile strength, in [MPa], the table gives an overview of the main characteristics of the compared materials for design layout.

Fig. 1
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Composite density versus young modulus

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Fig. 2
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Composite density versus tensile strength

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The advantage of carbon fibers lies in their construction performance, however, this comes at a price—both economically and environmentally. Glass fibers are certainly less costly but more heavy-weight and have some ecological disadvantages similar to those of carbon fibers. Viscose fibers have advantages because of their light weight and better ecological and acoustic properties, but they lack the higher mechanical performance of carbon or glass fibers. Even flax fibers do not reach these levels but come out well in terms of weight, splitting behavior, cost, ecology and acoustics. Considering their very low weight (and price), it is in fact a viable and cost-saving option to increase their use for those parts where they already meet the requirements regarding mechanical performance.

3.1 Next Steps Toward More Sustainability

To increase the proportion of renewable raw materials in the vehicle (see Fig. 3), bio-based resin instead of petro-based resin is used for the components of the Bioconcept car. The raw materials for a bio-based epoxy resin can be different vegetable oils which are suited to achieve the necessary properties, e.g. hardness, viscosity, a quick curing time, or the ability to combine well with natural fibers. A new bio-based resin is currently being used in the tailgate of the Bioconcept Car.

Fig. 3
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Renewable raw materials BCC (Based on: four motors GmbH)

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Furthermore, other parts with more complex shapes—for example components under the hood and the interior part of a car—are designed with injection-moulded bio-based plastics or bio-composites. Different materials, i.e. material components and their configuration, are preselected according to the requirements of the application and the part that is to be realized. The next step is a laboratory-confirmed specific development and optimization of different material concepts of biobased materials. For example, the new fuel filler flap of the Bioconcept Car was produced in a comparable quality on a large-scale production injection-moulding machine with the standard mould.

Especially for this application a commercially available bio-based Polyamid 6.10 from DuPont was modified with talc and different additives.

4 Conclusion/Summary

The Bioconcept Car paves the way for a future sustainable mobility. The project clearly shows the advantages of natural fibers and makes them applicable for future series production in the automobile industry. Using natural fibers as reinforcements for thermoset resins is a sustainable option for light-weight car bodies and is even successful under extreme stress situations during racing. Even though alternative parts are currently being developed specifically for motor sports, these parts are well suited to be included in the series production of standard cars as well.