One of the more unusual chapters in the development of sustainable composites is the Arboskin Pavilion made in 2013. It was created by a team of students and faculty of ITKE (Institute of Building Structures and Structural Design) at the University of Stuttgart, Germany, (several of whose projects have been featured here before). The Façade Mockup, as it is officially called, was the culmination of a two-year research project into architectural use of bioplastics that was funded by the European Fund for Regional Development (EFRE). The facade was constructed of 388 pyramids made of Arboblend, a bio-based composite that was developed for this project by the German firm Tecnaro. The composite pyramids were mounted to a support structure of bracing rings and joists (of an unnamed material). The pyramid panels were >90% made from renewable resources.
Arboblend is made in granules. For the Arboskin pavilion, the granules were extruded into flat sheets and thermoformed as pyramids. The triangular apertures were cut into the skin after molding using CNC Milling techniques. Waste plastic from cutting and milling was re-granulated and returned directly into the extruding process.
Arboblend is a combination of Mirel plastic (see below) with lignin, starch, cellulose, organic additives, natural resins or waxes, and natural reinforcing fibers. The material is 100% biodegradable in certain environments such as industrial composting and anaerobic digestion systems. The blend used in the façade mockup included flame retardants.
The use of a biodegradable material – employed specifically for its biodegradability – is an unusual choice in construction. Wood is, of course, biodegradable, but in most construction applications, great effort is expended to work around that property either by sequestering the wood from exposure to moisture that could enable degradation, or by the use of preservatives or coatings to stabilize and protect it. In general, the idea of the built environment, and the basic function of most architecture, is to separate the building interior from the natural elements of the exterior, and during the history of buildings, that has increasingly been achieved through the use of materials that are immune from degradation by the elements. The notion of biodegradability as a feature (rather than a bug) is uncommon in construction, to say the least. ITKE’s press release about the project mentions that the material was developed specifically for building exteriors. That, in concert with other statements about the suitable environment for biodegradation, suggest that the material is composed in a way that degradation can be avoided under normal conditions of exposure, but easily accomplished when desired.
According to ITKE:
“This research project marks the first occasion for development of bioplastic sheets that are made primarily of renewable resources, can be freely formed, and are furthermore designed for application in the building sector and specifically for building exteriors. At the beginning of this project, such a product was not available on the market. The conception of this material as flame‐ retardant sheet material also aims at applications for building interiors (spek DESIGN).
The future availability of this product is somewhat hazy. Tecnaro continues to feature the material on their website. Their primary marketing target seems to be short-term uses such as packaging – think containers for take-out – where biodegradability is a welcome alternative to an eternal afterlife in a landfill.
However, it is difficult to say if there is still a source for one of the major components, Mirel plastic. Mirel was manufactured by Telles, a joint venture of Metabolix Inc. and agriculture giant Archer Daniels Midland Company (ADM). Mirel was primarily PHA (Polyhydroxyalkanoate), a linear polyester produced by bacterial fermentation of sugar or lipids. Mirel was produced in ADM’s integrated corn processing complex facility in Clinton, Iowa.
ADM ended its relationship with Metabolix in 2012, although it agreed to continue to provide corn fermentation services to Metabolix for up to three years. Metabolix was still advertising Mirel products as of 2015. Metabolix has since changed its named to Yield10 Bioscience, changed the focus of its business, and says it has sold its Mirel plastic business. When we inquired, they did not tell us who they sold it too, and Mirel does not currently appear to be available.
The use of biodegradable plastics does have a certain attraction for large-scale composite structures (such as architectural elements) if the fiber reinforcement is a high-value material such as carbon fiber. Biodegradation of the matrix would make the composite partially recyclable by allowing the reinforcing fiber to be harvested and reused. It’s a significantly different objective than the one announced by ITKE, but one of considerable interest to a number of the researchers currently working on recyclable composites.