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ePaper created 2016-03-17, 15:06:18 | version 1.45.01
fiber washing homogenizer nanofibrillar cellulose decomposition 9 0 Biobased raw material for new applications Cellulose is the main component in plants and is of great technological and economic importance. In our latitudes, it is obtained mainly from wood or straw. The largest quantities of cellulose are converted in the paper and textile industries. The current interest focuses on three new forms of cellulose: nanofibrillar cellulose , nanocrystalline cellulose , and bacterial nanocellulose (BNC). These are summarized by the umbrella term nanocellulose. However, nanocellulose is not yet commercially available. It is currently only being pro- duced in pilot plants. Nanocellulose produced from residual biomass from lignocellulose biorefineries Nanocellulose is produced at Fraunhofer IGB using, as yet, unexploited residual biomass from the Fraunhofer CBP ligno- cellulose biorefinery as the raw material This process initially involves breaking down the wood, followed by separation into its chemical constituents for the conversion of wood or lignocellulose into platform chemicals for a chemistry of the future anofibrillar cellulose was successfully produced from the, as yet, unexploited residual biomass containing lignocellulose (Fig. 1). The focus is on the development and optimization of process engineering parameters through ex- posure to shear forces during treatment in the high-pressure homogenizer or the use of ultrasound. Likewise, the relevant purification and bleaching processes are being optimi ed Novel NFC manufacturing procedure through combining different processes The overall process for the manufacture of NFC is divided into three steps purification, bleaching and e traction Purifica- tion (step 1) consists of a swelling process to increase surface area and ethanolic purification of the fibers, with subse uent alkaline treatment. Bleaching (step 2) removes residual lignin and other undesirable components. NFC extraction (step 3) is realized through exposure to high shear forces. In this step, a variety of process steps were investigated under labora- tory conditions at Fraunhofer IGB, such as ultrasonication, rotor-stator homogenization and the use of high-pressure homogenization, and a suitable overall procedure was devel- oped through combining different processes. NFC (Fig. 2) can currently be produced at the institute at the scale of grams and upscaling of the process is viable. Cellulose as the basis for novel materials The demand for fiber-reinforced composites, for e ample fiberglass-reinforced or carbon-fiber-reinforced polymers, is on the rise in a variety of industrial sectors. The use of nano- cellulose would constitute a true biobased alternative to the materials that have been used until now for many of these ap- plications. The advantages of cellulose are its biodegradability, CO2 neutrality, high availability, and low price. Furthermore, cellulose is characterized by high tensile strength and low den- sity In comparison, carbon fibers and carbon nanotubes T have an elastic modulus ranging from 270 GPa to 950 GPa, with a tensile strength of 30 GPa [1]. However, their produc- tion costs are very high. This is where the opportunity lies for nanocellulose, which has the potential for being far cheaper to produce. Given an elastic modulus of 150 GPa and tensile strength of 10 GPa – equating to 8 times that for steel – and the lowest density of the materials used for comparison here, composite materials are possible that could reduce weight and costs many times over, at the same tensile strength and loading [2]. Fraunhofer IGB is currently investigating the incorporation of nanocellulose into polylactide and polyethylene (Fig. 3). The NANOFIBRILLAR CELLULOSE Carmen Gruber-Traub, Achim Weber 1 CHEMISTRY pulping lignin precipation/ solvent recovery lignin washing digester 400 L 200°C tank farm enzymatic hydrolysis concentration lignin drying dewatering dewatering ethanol/water ethanol/ water mother liquor wood chips fiber fraction xylose fraction conc. glucose solution hydrolysis lignin organosolv ligninlignin hydrolysis residue glucose solution 90