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ePaper created 2017-03-14, 10:25:37 | version 1.49.03
CHEMISTRY AND PROCESS INDUSTRY 1 2 CARBOPREC – CARBON FIBERS FROM RENEWABLE RESOURCES Morit z Leschinsk y, Christine Roßberg, Maik Tretbar, Daniela Pufk y- Heinrich, Jakob Bar z Background The demand for high-performance composite materials is increasing in a growing number of industrial applications. This requires new, improved possibilities for the production of carbon ibers. At present, more than 80 percent of the carbon ibers are produced based on polyacrylonitrile (PAN) as the precursor due to its outstanding technical properties. However, this polymer is expensive and available only in a limited amount, which currently limits the use of carbon ibers to a few premium sectors, where the considerable cost can be tolerated in favor of high performance. In order to be able to use carbon ibers in other industries such as automotive engineering or the construction of wind power plants, more lower-priced precursor materials have to be developed. Approach The EU project “CARBOPREC” brings together 14 partners from seven countries who are working together to develop two new precursor materials based on renewable raw materi- als, which are readily available in Europe in the form of ligno- cellulose, i.e. cellulose and lignin. Carbon nanotubes (CNT) are used as reinforcements in both cases, and new production methods are being developed. The preparation processes of the precursors are highly depen- dent on the macro-molecular structure of the raw materials used. Cellulose is isolated from commercially available paper grade pulp in pure form and then spun as a multi-ilament in a phosphoric acid-based wet spinning process. Lignin is isolated in pure form from wood by means of organosolv frac- tionation, compounded with CNT and other polymers, and subsequently spun from the melt as a multi-ilament. The various process stages, from the extraction of raw materi- als, iber production, stabilization and carbonization, to the inal application in demonstrator components are the subject of the project. A modiied organosolv method optimizes lignin properties In the project, the Fraunhofer Center for Chemical-Biotech- nological Processes CBP plays a leading role in the isolation and property optimization of the raw materials lignin and cellulose. Using organosolv fractionation on pilot scale, estab- lished at Fraunhofer IGB’s branch in Leuna, optimization of the lignin properties was systematically carried out by varying the process conditions and by selecting various lignocelluloses. Subsequently, more than 150 kilograms of the optimized lignins were produced and handed over to the consortium for the production of demonstrators. The lignins produced in this way display particularly advantageous spinning properties compared with commercially available lignins. In addition, a cellulose extraction process developed by the University of Hamburg was successfully transferred to the pilot scale in Leuna. This resulted in the production of 120 kilograms of dissolving grade cellulose for the project’s wet spinning experiments. Fiber stabilization by plasma technology A crucial aspect in the carbonization of lignin ibers is the stabilization of the initially still thermoplastic precursor. To enable this in plasma, a new lignin derivative was developed at Fraunhofer CBP in Leuna, whose functional groups react and cross-link in the plasma. After extensive plasma testing, 7 8