Eco plastic formed with water

Tom Shelley reports on a novel polymer derived from natural fibres that depends on neither resins nor binders

By grinding up natural cellulose-containing materials with water, it is possible to produce a mouldable polymer. It can be made from a wide range of normally waste materials, and spray moulded or formed into commercial products with mechanical properties similar to those of hard wood. The material contains no toxic materials and is completely recyclable, sustainable and biodegradable. The first commercial factory producing the material in bulk goes on stream this month. The Zelfo process was invented in Europe in 1992 and patented in early 2000 by an Austrian team now based in New South Wales in Australia. The principle inventor was Martin Ernegg, now the company’s technical director. It relies on the fact that wet cellulose fibres stick to each other, as in the manufacture of paper and papier maché. “The material is cost effective in some specific applications,” says managing director Paul Benhaim. “Our current business model means Zelfo is best suited for objects with runs of 1 to 10,000 – any more than that, and regular plastics usually beat us.” The material cannot be injection moulded, but can be formed using relatively low cost tooling – hence its suitability for short to medium production runs. The cellulose-containing material is ground up with water and optional natural additives, such as plant-based pigments. The material may then be spray moulded or pressed to shape. Several moulding processes can be used, which may involve pressure and interim drying and reshaping, according to the product being manufactured. A pre-coating may be applied after which the moulding is dried slowly to the required density and stiffness. As feedstock material, the team has used a number of natural substances including hemp fibre, sugar cane and waste paper. The product made from hemp is sold under the name Hempstone. Densities range from 0.5 to 1.5g/cm3, tensile moduli are 1,500-10,000 MPa, while tensile strengths go from 7 to beyond 90MPa. Products can be made thin enough to be translucent, 2mm, or 20mm thick or more, although they then take longer to dry. The final material may be finished, screwed and glued as hard wood. Maximum part size is 2m x 2m x 2.2m. Acoustic properties are good and so one of the favoured applications is as a wood substitute for making musical instruments. The material is completely non flammable – you can hold a lighter to the edge of a piece of sheet until the fuel runs out but it will not ignite. It is also heat resistant to 140ºC (100% hemp) or up to more than 220ºC as a blend. The material is water resistant but not suited for complete immersion in water although technology to enable this is in R&D. Benhaim says: “We have many high-end designers from around the world who are interested in our material.” Applications already successfully trialled or manufactured on a small scale include speaker cabinets, bowls, drums, guitars, translucent lighting, furniture – and “eco coffins”. Zelfo Australia Pointers * Material can be made from any cellulose-containing raw materials such as hemp, sugar cane and waste paper * It is spray moulded or formed to shape using low cost tooling, but is not suitable for injection moulding * It has price advantages over conventional plastics and fibre glass in runs up to about 10,000 off