Glass fibre-reinforced plastics have become an integral part of our everyday life: in cars, playground slides, swimming pools or on facades, such composites are used wherever stability is required. Unfortunately, both production and disposal are far from sustainable. Scientists from the German Institutes for Textile and Fiber Research Denkendorf have now developed an innovative material made from pure cellulose, which has practically the same basic mechanical properties as glass fibre-reinforced plastics, but can be produced simply and non-toxically, and is also fully recyclable.
For many decades, glass fibre-reinforced plastics (GRP), also known as fibreglass, have been one of the most widely used composites in many constructions and construction components, especially in areas where stability and strength are required, such as in the car and bridge construction sectors. The demand for such materials is enormous; more than a million tonnes of GRP are produced every year in Europe.* However, GRPs are associated with a number of problems: toxic fumes can occur during production and considerable amounts of problematic fine dust are generated during processing. In addition, the materials cannot be recycled; they are either disposed of on waste dumps or combusted. Since these approaches are no longer in line with the EU directive that stipulates that at least 95% of an end-of-life car is recycled or recovered, alternatives are urgently needed.
Researchers at the German Institutes for Textile and Fiber Research Denkendorf (DITF) are working on finding a substitute for GRPs. They have developed a material called PURCELL, which is a recyclable composite material made of pure cellulose. Cellulose is used both as reinforcing fibre and as a matrix component into which the reinforcing fibres are embedded. “Cellulose is one of the most common biopolymers in the world; it can easily be obtained from wood and is therefore a renewable sustainable raw material that is available in almost unlimited quantities,” explains Dr. Frank Hermanutz who coordinates the research work at the DITF.
Hermanutz and his team of chemists have been working on processes for the environmentally friendly production of cellulose fibres with ionic liquids (IL) for many years. “These ionic liquids can dissolve cellulose and are completely non-toxic, amongst other things because they do not generate vapour pressure, thus avoiding exhaust air problems,” says Hermanutz. “They are also stable in the air at room temperature and ideally suited for embedding fibres into a matrix. The IL solutions are later rinsed out and the material is dried – that’s all.” With the procedure established, the researchers applied for funding under the “Resource Efficiency” project run by the Baden-Württemberg government. They were granted financial support and since 2015 have been working on the development of PURCELL – with successful results. “PURCELL now meets the basic mechanical properties we were aiming to achieve,” says the chemist. “Although the material will not be able to replace all GRP applications, it will be suitable for many of them.”
Another advantage of the material is that it is easy to recycle. “You simply chop the PURCELL plates into small pieces, dissolve them in an IL solution and apply them again as a matrix,” explains Hermanutz. “This can be repeated several times. Our composite plates are now in the fourth generation with no damage to the cellulose or no alteration of the material’s properties. When used in cars, this would mean a lifetime of about 40 years. If not required, PURCELL can also be composted. The water-course contamination problem created by micropolymers is not an issue with PURCELL. On the contrary, it can be crushed and used as fish feed, and therefore does not generate end-of-life waste as GRPs do.” At Techtextil, an international trade fair for technical textiles and nonwovens, the material received the “2017 Innovation Award New Materials” for its excellent properties.
The development of new composite material is in principle already complete. Laboratory samples in the form of small, A4-sized, Z-shaped plates called profiles have already been produced. Common manufacturing equipment available in the industry can be used to produce these profiles; no special machines are required. Commercial tyre cord fibres can be used as reinforcing fibres. However, other fibres, for example those made of hemp, flax and cotton, can also be used. "The fibre used determines the strength of the material,” says the chemist. You can be very flexible – depending on the application for which the material will be used.”
The DITF scientists are now working to find out how PURCELL can be processed. “The material has met our mechanical targets and we are now investigating possible applications,” says Hermanutz. “We will be working on specific problems and components. For example, we are currently investigating how the material can be used for making glove box compartments, as well as ways to coat PURCELL.” In addition, the manufacturing process will be scaled up and automated. However, this will not be done by Hermanutz’s work group, but by researchers from the DITF’s composite materials division who were also involved in the development of the material. A small series will be produced in a pilot factory. Large-scale production of PURCELL will not be done at the DITF,” says Hermanutz. “We are purely focused on research. Large-scale production will be done by our clients.”
There is already quite a bit of interest in the innovative material. Hermanutz comments: “At Techtexil a lot of people showed an interest in PURCELL. We have already established our first contacts, and it remains to be seen how it all pans out. However, technical implementation is definitely on its way. Time will tell what future applications will look like in concrete terms. The cellulose-based material is not as hard as GRPs; therefore, it will not be possible to produce highly robust construction parts such as A and B pillars of cars. However, the material has very high impact strength, which makes it suitable for interior car parts.”
* Source: AVK Industrievereinigung Verstärkte Kunststoffe e.V. Frankfurt: Composites market report 2016.