Electronics Surround
Electronics Surround system of loudspeaker boxes with spherical shape: housing material Arboform of 10 mm wall thickness, lacquer coated Biocomposites obtained exclusively from renewable resources meet the requirements of sustainable processes and eco-innovation, and will expand future material research for engineering applications in industry. The properties, treatment and processing of these materials have to meet industrial standards concerning raw materials from biomass, fibres, wood extraction constituents and biopolymers, to enable their supply to mass consumer goods manufacturers, the construction industry, and the automotive and electronics industries. Thermoplastic matrices of composites include biopolymers such as polylactide (PLA), polyhydroxy-butyrate (PHB) and starch, as well as lignin from the paper industry. Reinforcement is carried out by the use of natural short fibres from hemp, flax and wood 1-4 . The natural polymer lignin is generated as a by-product of the pulp and paper industry, at a rate of approximately 60 million tonnes in chemical pulp mills Lignin Matrix Composites for Loudspeaker Boxes Article contributed by H. Nägele, J. Pfitzer, both of Tecnaro GmbH, Ilsfeld-Auenstein, Germany N. Eisenreich, W. Eckl, E. Inone- Kauffmann, E. Walschburger all Fraunhofer-ICT, Pfinztal,Germany Housing parts of the complex loudspeaker design as obtained directly from the mould every year, worldwide. This biomass extraction can also be carried out in an environmentally friendly way by using only water 5,6 . Thermal use of lignin for the power supply of the chemical pulp mills dominates its current utilisation rather than its use as a material for components. Its integration as a component in engineering materials has proven to be difficult 7,8 . However, recent work has succeeded in establishing lignin as the main component of a new class of engineering materials: Arboform®, based only on renewable resources, applicable for use in industrial equipment parts 9,10 . Technical advantages of these materials over synthetic polymers, such as the acoustic properties of lignin matrix composites (Arboform), could strongly support their application. The material consists of lignin, natural fibres for reinforcement, and natural additives to support processing and performance. It exhibits wood-like properties. Various sources of lignin - from different pulping procedures - and of natural fibres such as wood, hemp, flax, sisal, kenaf etc. - can be used. The choice of the lignin depends on the application field of the product. However, the material can be processed like a thermoplastic material and used for various engineering products. The processing includes: 16 bioplastics MAGAZINE [04/08] Vol. 3
Surround system of loudspeaker boxes, complex shape: housing material Arboform of with 5 mm wall thickness, lacquer coated Electronics • Mixing of the constituents: lignin (40-70%), natural fibres (30-60%) and natural additives (150 MPa) and so is the injection speed. The holding pressure should be about 30% of the machine’s capacity and the related time only 0.5 – 2 seconds. The cooling time must be extended by about 20% compared to that of a synthetic thermoplastic material. The mould tools should be designed for the series production of special materials. Important issues for tool design should take into account: • The shrinkage on injection moulding is very low and does not exceed 0.3% • Core-pullers should be foreseen for de-moulding, which are useful to achieve fast working cycles • Hot runner nozzles work only in limited cases. Depending on the fibre content the Young’s Modulus can vary between 2 and 8 GPa and the Charpy Impact Strength between 2 and 6 kJ/m 2 , but the latter value can be extended to 16 by the use of impact modifiers. The elongation at fracture is between 0.3-0.6%. The thermal expansion coefficient establishes below 5x10 -5 1/K. Nearly no resonance frequencies are found and a strong damping of vibration leads to excellent acoustic properties, which enables the material to be used in loudspeaker applications. Two types of loudspeaker housings were designed and manufactured according to the procedures described above. The material itself exhibits a unique structure which varies from part to part (see fig. 1). Original colours are limited to brown, green and red. Figures 2 and 3 show the completed boxes including a lacquered surface finish. info@tecnaro.de eri@ict.fraunhofer.de Acknowledgements The work was partially supported by the NEDO grant Nr.2002GP008, the EC, General Directorate XII, Biocomp: NMP2-CT-2005-515769 and Deutsche Bundesstiftung Umwelt. 1. Kaplan, D.L. ed., Biopolymers from Renewable Resources, Springer Verlag, Heidelberg, 1998 2. Bledzki, A.K., Gassan, J.: Composites reinforced with cellulose based fibres. Prog. Polym. Sci. 24(1999) 211- 274 3. Bledzki A. K., Sperber V. E., Development in wood fiber composites, Int. Symp. on Wood Based Materials, Vienna, Austria 2002. 4. E. Inone-Kauffmann, N. Eisenreich, Biocomp - composites from renewable resources - a European project, in Polymer Processing Society PPS23 Proceedings, San Salvador, Brazil, May, 2007 5. Bobleter, O. (1998). „Hydrothermal Degradation and Fractionation of Saccharides and Polysaccharides“. Polysaccharides, Structural Diversity and Functional Versatility, Marcel Dekker, Inc. pp. 775-833. 6. Jedicke O., Eisenreich N., „Aquasolv - Hydrothermolyse „The Development of a Process for Completely Use of Biomass“ Proceedings 1st Biomass World Conference, Sevilla, Spain, 2000. 7. Roffael, E., Dix, B. :Lignin and ligninsulfonate in non-conventional bonding systems - an overview. S. 1st European Workshop on Lignocellulosics and Pulp, Utilization and Analysics Of Lignins - Hamburg- Bergedorf, Federal Republic of Germany, Sept. 18.- 20.1991. 8. Glasser, W.W., R.A. Northey, T.P. Schultz, eds., Lignin: Historical, Biological, and Materials Perspectives. American Chemical Society Symposium Series 742. American Chemical Society, Washington, DC, 2000. 9. Eisenreich N., Eckl W., Inone E. R., Nägele H., Pfitzer J., Arboform – a thermoplastic made of renewable resources, Proceedings Electronic Goes Green 2000, Vol. 1, Technical Lectures (Joint International Congress and Exhibition, Berlin, Germany, Sept. 2000). 10. Nägele, H., Pfitzer, J., Nägele, E., Inone, E. R., Eisenreich, N., Eckl, W., Eyerer, P., Arboform - A thermoplastic, processable material from lignin and natural fibers, in: Chemical Modification, Properties, and Usages of Lignin , Th. Q. Hu Ed.; Kluwer Academic / Plenum Publisher, New York, 2002, 101-120. bioplastics MAGAZINE [04/08] Vol. 3 17
