Materials Green
Materials Green biocomposites Green thermoset biocomposites Green biocomposites are composed of natural fibres and biobased matrices. Bio-based matrices and industrial natural fibres composition, including hemp, jute and flax, etc. leads mostly to product price increases, hence generating green thermoset biocomposite market limitations. The option of choosing cheaper available fibres from another natural fibres resource, as in the case of agro-fibres (i.e. agricultural plant fibre residues) is here suggested and applied. The main key that can provide attractive products for architectural applications using available thermoset biocomposites’ production techniques is the innovative product designs that can offer different innovative solutions for modern architectural spaces. Agro-fibre thermoset biocomposites Commercially, thermoset biocomposites are still not widely available. In spite of this, high interest in such composites is pushing up demand due to the known higher material performance of the thermoset composites than that of the thermoplastic ones. Manufacturing techniques as found in the conventional thermoset composite industry, include both open mould (e.g. hand lay-up and spray-up) and closed mould techniques (e.g. resin transfer moulding, vacuum infusion and compression moulding). Limitations in the case of agrofibres are their relative short fibre-lengths, while most of the compounding techniques are directed mainly for the usage of long fibres, fleece and fabrics. In case of bioresins appliance (i.e. biobased thermoset resins), a high curing temperature – one of the most currently available ones in the contemporary market - is another limitation to the whole process. In the following product design case-studies, agro-fibres and bioresins of different types were applied using different thermoset composite techniques. Product designs concepts differed according to the desired architectural outcome, between the form, surface texture, natural fibre’s coloureffect, pigments, glowing additives and others. Green biocomposites for architecture - case studies The following case studies are products designed and manufactured by the author and students of the Faculty of Architecture - University of Stuttgart, Germany within the framework of educational courses. The products are composed up to 70% by weight of agro-fibre contents that were from different origins. The general criteria for designing the green biocomposites here is the appropriate material selection including the agro-fibre and the bioresin as well as the processing techniques. This influenced the designed product outcome as illustrated in Fig. 1. By: Hanaa Dahy ITKE - (Institute for Building Structures and Structural Design) University of Stuttgart, Germany Fig. 1 Materials and processing interaction with the product design concept Composite form: sandwich panel, particle board, …etc Geometry: Freeform, flat, profiled,…etc Color Texture Transparency … Design + Application Concept Inner Cladding Partitions False-ceiling tiles … Natural fibre from Agricultural residues Materials Processes Physical Processing: Fibre chopping Mold manufacturing Press molding techniques with vacuum assistance Fibre-spray techniques Bio-resin Natural Fibre + Matrix Processing Chemical Processing: chemical reaction activities combining resin components within molding with the agro-fibres 28 bioplastics MAGAZINE [03/14] Vol. 9
Materials for architectural applications Case study – 1: TRAshell Case study – 2: BiOrnament Product description Free-form interior and exterior architectural cladding screens made from cereal straw short fibres and plantbased epoxy resin (TRAshell) processed by press-moulding (cold process). Materials, design and production description Cereal straw, coconut of a reddish brown colour and black coal ash were here applied in their original colours. Agrofibres were chopped then combined with a linseed-oil based epoxy resin based on two components that hardened after mixing at room temperature within ~ 24 to 48 hours. The free-form panels were designed in two modules (A) and (B), as illustrated to provide through their combination a desired 3D physical curvature when the patterns are combined as illustrated. The moulds were carved using a robot machine at the faculty of architecture-University of Stuttgart, Germany, and the mixtures were moulded in the forms using different natural fibres and glowing pigments, as illustrated in Fig. 2 and 3. Fig. 2. TRAshell product design and application simulation as architectural cladding panels in an experimental pavilion, Eco- Pavilion in the foyer of the faculty of Architecture-University of Stuttgart Pavilion (Photo: B.Milklautsch) Product description Coloured laser-cut flat panels (BiOrnament), processed by hand using the lay-up open moulding technique (hot process), for interior and exterior architectural cladding screens. Materials, design and production description The design sketch illustrates the idea of the pattern that was applied and repeated depending on using both the positive and negative cutting models that would result from the laser cutting procedures after the flat panels were separately manufactured. The product theme depended on the rhythm and diversity within unity using a repetitive pattern with different colourings whether positive or negative cut modules. Therefore, the mixtures were pigmented according to the most suitable product design. Cereal straw fibres were bonded with a biobased epoxy thermoset polymer, composed of three components. Plant oil based (e.g. linseed) epoxidized triglycerides are combined with polycarboxylic acid anhydrides (based on bio-ethanol) and an initiator. This compound was only activated by heat to polymerize. Therefore, the mould was composed of flat metal plates. Fig. 4. Illustration of the ornamental pattern design according to which the developed biocomposite panels were laser cut. Right (Photo: B.Miklautsch) Fig. 3. TRAshell with glowing glass particles and cereal straw, with coconut fibres, plus raw straw and black coal ash respectively. Photo credit: B.Milklautsch bioplastics MAGAZINE [03/14] Vol. 9 29
