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02 | 2008

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Natural Fibres Natural

Natural Fibres Natural Fibre and Biocomposites for Technical Applications Article contributed by: Andrzej K. Bledzki, Adam Jaszkiewicz, Institut für Werkstofftechnik, Kunststoff- und Recyclingtechnik, University of Kassel, Germany Dietrich Scherzer, BASF SE, Global Polymer Research – Biopolymers, Ludwigshafen, Germany Figure 1: Rear cover in the Mercedes A-Class, produced by Rieter Automotive AG, Switzerland Figure 2: Abaca fibre cord as delivered from Rieter Automotive AG, Switzerland. A new group of materials, consisting of bioplastics reinforced with natural fibres, offers a broad and very interesting field of applications because of their highly promising properties. For years fibres, such as jute, hemp, sisal, kenaf or cotton, have continuously gained more and more importance (see article on page 18). In spite of their many advantages, natural fibres also have some drawbacks. Lack of reproduction consistency and insufficient impact strength limit their use. Thus these material properties will have to be further researched and improved. In 2003 Daimler and Rieter Automotive together with the Philippine company Manila Cordage started a project with the aim of developing a natural-fibre-reinforced plastic component for the automobile body and to introduce it into mass production. The motivation for this project was the potential for weight and cost reduction compared with common glass-fibre-reinforced composites (GFC). Parts made of PP/abaca are now installed in Mercedes A-Class automobiles as sub-floor coverings (fig. 1). Abaca (banana fibre, ‘musa textilis’ or Manila hemp, see fig. 2) was chosen as a suitable reinforcement fibre. The reason was the precise growth and preparation control of the fibres (cooperation with fibre manufacturer Manila Cordage) as well as very good mechanical properties when compared with other natural fibres. Cellulose is a base component of plants and thus is an almost inexhaustible source of raw material. The raw material for man-made cellulose fibres (fig. 3) is mainly the cellulose that is obtained from wood. In recent years the possibilities for reinforcing with cellulose spun fibres (man-made cellulose, e.g. Cordenka, Lenzing) have been intensively researched, especially with regard to injection moulding. Produced using a variant of the viscose process in a method geared to technical fibres of cellulose it becomes a filament yarn, similar to glass fibre roving. Also biocomposites, with both biogenous matrix and natural fibres, are slowly establishing themselves in market place. Parts made of biocomposites can be found predominantly on the Japanese market. Companies like 12 bioplastics MAGAZINE [02/08] Vol. 3

Natural Fibres Toyota, Mazda, NEC (Nippon Electric Company), and Sony have already started production of some applications. For example a PLA/Kenaf spare tyre cover (Toyota Raum and Prius, see bM 01/2007), a PLA-based Walkman housing (Sony) and a PLA/Kenaf cell-phone housing (NEC, see bM 01/2006). Other applications are under examination. Research project of Kassel University Biocomposites on a technical scale are mostly thermoplastics, which allows processing methods such as injection moulding or extrusion. For this reason research at the University of Kassel in Germany is focused on thermoplastic biopolymers. They are established on the market, have good mechanical properties and are available with guaranteed reproducibility of properties on a technical scale. Materials chosen for the project described here are PLA (4042D from NatureWorks) and polyhydroxyalkanoates (PHA from Tianan Biologic Material). The composites that were tested consist of a biogenous matrix (70% by weight) and Abaca or man-made cellulose fibres (30% by weight). PHAs were blended with Ecoflex ® (biodegradable synthetic polymer from BASF) and additives. The blend properties were adopted to be similar to common PP. The content of PHAs in the blend is over 65% by weight. Abaca fibres from Manila Cordage (with the kind assistance of Rieter Automotive) were added as continuous fibres (filament yarn). The man-made cellulose fibres used here were made by Cordenka (Cordenka ® 700 Super 3). All compounds were pre-processed by extrusion, using a coating technique. In a first step the polymers, together with the fibres, were extruded via a coating nozzle (like cable-coating), cooled to ambient temperature with water and cut into long pellets. In a second step these pellets were melted and homogenised on a single-screw extruder and then injection-moulded into ‘dog bone’ specimen in line with DIN EN ISO 294-1 (specimen type 1A). Figure 3: Man-made cellulose fibre ‘roving’. [MPa] 10000 8000 6000 4000 2000 0 120 E Modulus PP Composites PHA Composites PLA Composites Figure 4: E-Modulus of tested biocomposites in comparison to PP composites. Tensile Strength The processing temperatures during extrusion were in the range of 150-200°C (depending on the biopolymer); during homogenisation approx. 150-180°C. The temperature profile during injection moulding was about 170- 190°C. Virgin granulate and fibre-filled pellets were dried each time before further processing. The moisture content was about 0.02% for the virgin polymers and about 0.20% for the compounds. All tests were performed according to DIN standards. [MPa] 80 40 0 PP Composites PHA Composites PLA Composites Figure 5: Tensile strength of tested composites. Figures 4 and 5 show the results of tensile tests for biocomposites in comparison with PP composites. PP composites were reinforced with the same fibres and produced by the same processing techniques. The main difference is the use of a coupling agent (maleic anhydride; MAH-PP) for PP/natural fibres; for the biocomposites no coupling agent was used. unreinforced polymer abaca composite cellulose composite bioplastics MAGAZINE [02/08] Vol. 3 13

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