Automotive Fig. 1:
Automotive Fig. 1: Components made from renewable resources by Daimler (GLK/X204) (Source: Daimler AG) Natural fibre composites Environmental awareness as a key driver for lightweight solutions In 2009 the European Union adopted new legislation that forces the automotive industry to reduce the CO 2 emissions from new cars [1]. In fact the new car fleets are not allowed to emit more than 130 g CO 2 /km by 2015 and 95 g CO 2 /km by 2020. Since the automotive industry is making a big effort to meet these targets the average emissions are falling each year and by 2011 the average emissions were already reduced to about 137.7 g CO 2 /km. In this context the application of natural fibre as a reinforcement in composite materials in the automotive industry plays a crucial role, since the use of renewable or bio-based materials can not only reduce the CO 2 emissions by reducing the component weight, but can also build up the positive image of a company by promoting sustainability and environmental awareness, as well as preserving the limited resources on earth. Fig. 3: Door panel of Mercedes S-Class (W221), made with Lignoflex (Source: Faurecia) Natural fibres as a reinforcement in composite materials The use of natural fibres such as wood, flax, hemp, kenaf or sisal as a reinforcement in composite materials has been well established in the automotive industry for several years. Natural fibre reinforced composites are mainly used in semi-structural automotive interior parts such as door panels, instrument panels, package trays, trunk liners or seats [2]. For these applications the natural fibres (fractions between 50% and 90%) are processed to non-woven mats, where the fibres are distributed almost randomly within the mat, and used as reinforcement in both thermoplastic, mainly polypropylene, and thermoset resins such as acrylic, polyurethane or epoxy resin. Here, the technological advantage of the natural fibres is, due to their low density (approx. 1.45-1.55 g/cm³), a large weight reduction potential at a high level of functionality in the composite. But also such benefits as good crash performance, good energy absorption, fracture resistance (splinter-free failure) or price stability of natural fibres (independent of oil price) play a very important role for the use of natural fibres in automotive applications. 18 bioplastics MAGAZINE [01/13] Vol. 8
Automotive by Luisa Medina Senior Research Manager Institut für Verbundwerkstoffe IVW Kaiserslautern, Germany compression injection material thickness density area weight potential [mm] [g/cm 3 ] [g/m 2 ] [%] LignoLight 1,6 0,90 1450 -44 LignoFlex 2,0 0,95 1900 -26 LignoProp 2,0 0,95 1900 -26 NF PP 2,0 0,95 1900 -26 NF PP 2,4 0,85 2000 -22 NAFI - PP NF20 2,0 0,95 1900 -26 PP LRF 25 2,2 1,00 2200 -15 PP LGF 20 2,2 1,04 2288 -11 ABS 2,2 1,05 2310 -10 ABS+PC 2,2 1,13 2486 -3 PP/PE TD14 2,5 1,03 2575 Reference PP/EPDM T20 2,5 1,04 2600 1 PP T20 2,5 1,05 2625 2 SMA GF15 2,5 1,18 2950 15 Fig. 2: Material analysis showing the lightweight potential of NF materials, done by Faurecia Interior Systems In this respect the company Faurecia Interior System shows, in a material study [3], the lightweight potential of natural fibre reinforced composites compared to standard plastics such as talc-filled polypropylene or PC-ABS (Fig. 2). This study shows a weight saving potential in a door panel of around 25 % compared to the conventional material, (14% filled polypropylene), by the use of commercially available NFPP mats. This potential can be increased up to about 40 % by using the newly-developed wood mat material LignoLight. These new wood-based mats, with an optimized area weight of around 1400 g/m², also show a weight saving of some 25 % compared to the conventional mats with an area weight of around 1900 g/m² (Fig. 3). Not only Faurecia but also all other suppliers are strongly working on material development to improve the material performance despite weight reduction, and to meet the continually increasing demands in the automotive industry. But material development is not the only factor in the forefront of industrial investigations. Process development and optimization is also very much a key factor for increasing the application fields of bio-composites, since optimized processes, including for example functional integration or combining processes, also means cost reduction of the component, which is, another factor contributing to a spread of applications for these kinds of materials. In this context one can point to the new process of Johnson Controls Interior for using natural fibres with epoxy resin (EP) to produce semifinished materials [4]. The production-ready process is already being applied for the production of the door panel of the BMW 5 Series with 2 colour PVC foil (Fig. 4 and 5). Ramstein, Germany) where a natural fibre pre-impregnated mat with about 70% natural fibre content and an acrylic matrix [5] is used. For the manufacturing of these semifinished materials the NF mats are impregnated with the acrylic resin using foulard rollers. After the impregnation the mats must be dried to a certain residual humidity level and can be processed in hot compression moulding (Fig. 6). The BMW door panel with the newly-developed NF material in 2009 won the Automotive Innovation award from the Society of Plastics Engineers. Research and development areas for biopolymers Since the market is asking for more eco-friendly materials with similar properties to the petrochemical-based ones, at competitive prices, science and industry are working together to develop new materials based on renewable resources. This is appreciated in some research projects such as “FENAFA” (founded by the Agency for Renewable Resources / FNR Fachagentur Nachwachsende Rohstoffe in Germany) where a total of 16 partners from agriculture, industry and research are cooperating to develop new products based on renewable materials [6]. FENAFA stands for ‘integrated handling, processing and manufacturing strategies of natural fibre materials’. Within the project small and medium companies in particular are supported in the development of equipment, production lines and systems for the processing of natural fibres in technical areas. Also the automotive industry is strongly involved in the project with JCI as Tier 1 and with Isowood, a natural fibre materials supplier for the automotive industry. This process is not far removed from the manufacturing process of Nafacryl ® (from Dittrich & Söhne Vliesstoffwerk in bioplastics MAGAZINE [01/13] Vol. 8 19
