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Issue 03/2015

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  • Bioplastics
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Biocomposites Figure 1:

Biocomposites Figure 1: Reduction of weight and cost using powerRibs at a constant flexural stiffness Price (EUR/m 2 ) Relative specific flexural stiffness (-) 45 40 35 30 25 Plates for given flexural stiffness (t CFRP = 1 mm) -27 % CFRP -40 % 20 CFRP + powerRibs GFRP -30 % 15 -43 % GFRP + powerRibs 10 -42 % NF Mat + powerRibs NF Mat 5 1.0 1.5 2.0 2.5 3.0 3.5 Weight (kg/m 2 ) Figure 2: Flexural stiffness increase with powerRibs at constant weight 12 Bcomp powerRibs 10 8 6 4 2 0 Aluminium Glass fibre composite Carbon fibre composite Increasing rib thickness Flax fibre composite powerRibs technology Well-known concepts Back in 2010, two PhD students from the Swiss Federal Institute of Technology Lausanne (EPFL) were discussing a technical problem during a run in the forest. They wanted to develop a natural fibre composite tube which was lighter and stiffer than the carbon composite version. The materials engineer Christian Fischer had the idea to reinforce the tube from the inside with a ribbed structure. While the idea sounded interesting, the mechanical engineer Julien Rion demonstrated how this concept would increase the stiffness of the tube’s wall, but not of the overall tube. The intense exchange that followed lead to the invention of the powerRibs technology, and the patent was filed soon after. This technology is based on the concept of the leaf-veins, rigidifying a surface with minimum weight. Instead of the nervures we use so called ribs made with flax fibres to reinforce thin-walled structures, resulting in a pseudo mini sandwich, since no core material is involved. These ribs are easily combined with any type of base fabrics, such as natural fibre- (NF), glass fibre- (GF) or carbon fibre (CF) preforms Natural fibres in space With their high stiffness, low density and limited length, flax fibres are ideal for the use in the powerRibs technology. Their maximum fibre length of 60 cm – looking like a disadvantage at first sight – is a key factor for this technology, since the fibres need to be spun into a continuous yarn for further textile processing. Thanks to the resulting twist, the yarn has a good compression strength perpendicular to its direction, keeping its shape during composite processing, and leading to a 3D surface characteristic to the powerRibs technology. However, the mechanical properties in yarn direction rapidly decrease when the twist is too high. With this in mind, the Bcomp Ltd. engineers have been optimizing the yarn twist angle over several years. The findings have been further developed in the framework of several R&D Potential applications using powerRibs powerRibs with Duroplast powerRibs with Thermoplast Automotive Space Leisure Automotive Luggage Body parts Roof Spoiler Trunk lid Back rest Satelite Canoes & structures kayaks Star tracker Surf & SUP baffles Solid rocket booster top Bike frames cones Maintenance doors Front panel Door interior panels Loading areas Trunk lid Back rest Luggage shell parts Local reinforcement Electro casing 40 bioplastics MAGAZINE [03/15] Vol. 10

Biocomposites By: cYrille Boinay managing director, co-founder Bcomp Ltd. Fribourg, Switzerland Figure 3: Effect of powerRibs on damping properties projects, and have been applied to various customer projects within the mobility-, space- and sports & leisure industries. One example is the European Space Agency which is highly interested in the unique combination of high stiffness and damping properties offered by this technology. High relevance due to less weight and less cost The main effect of the powerRibs is that they triple the flexural stiffness of thin-walled structures without adding weight. Thus, cost and weight can be reduced when making composite parts, and damping properties can be increased by up to 250 %. For any given composite part, a large part of the synthetic fibres – such as glass or carbon – can be replaced with this novel material, increasing the part’s biobased material content. This effect adds up to the powerRibs structure’s lower weight, outperforming any given material in terms of sustainability. The powerRibs fabrics can easily be processed with the common vacuum molding techniques. Furthermore, Bcomp Ltd. has partnered with processing technology partners, to develop concepts for the mass production of powerRibs parts. Depending on the final application, two processing technologies are currently available: a sophisticated thermoplastic version for interior automotive parts and luggage shells on one hand side, and a thermoset-based version for the production of automotive body- and space parts on the other hand side. The powerRibs technology was awarded with the JEC Innovation Award 2015, the Swiss Excellence Award and the Hermes Price. Normalized specific flexural stiffness (-) 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6 Carbon Carbon + powerRibs Flax + powerRibs 0.002 0.004 0.006 0.008 0.010 0.012 0.014 Loss factor, ξ (-) Figure 4: Eco-footprint of flax fibre composites Specific tensile modulus, E/ρ (MPa/(kg/m 3 )) 90 85 30 25 20 Stiffer Flax fiber composites Thermoset Carbon fiber composites Recycled Thermoplastic Glass fiber composites Wood Aluminium Greener Primary Bcomp have compiled a significant amount of data on the material‘s mechanical properties, such as static- and dynamic behaviour, thermo-mechanical characteristics and processing parameters of various production technologies which can be found on the website 15 0 1x10 5 2x10 5 3x10 5 4x10 5 5x10 5 6x10 5 Embodied energy per m 3 , H m *ρ (MJ/m 3 ) Technical data powerRibs: Rib thickness Yarn thickness Grid mesh size Rib stiffness 1 – 2 mm 1,500 – 3,000 tex 15 – 28 mm 20 GPa Fabric Areal Weight (FAW) 200 – 240 g/m 2 Standard width Sales unit 1,150 mm Roll of 50 linear meters Fibre volume ratio (vacuum infusion) 40 % Weight reduction* 25 % Damping properties* +350 % CO 2 reduction* -50 % *Comparison between a 0/90° carbon composite plate of 1 mm thickness, and a plate with half the carbon quantity with powerRibs bioplastics MAGAZINE [03/15] Vol. 10 41

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