Haile et al. Bioresour. Bioprocess.
(2021) 8:35
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materials and production cost is the driving force of finding cheaper and renewable alternatives. A potential and interesting substitute precursor for carbon fiber production is lignin. It can be utilized for the production of a high volume of carbon fibers for a multitude of applications. This is possible, because espe- cially the lignin from kraft pulp consists of high carbon content of around 60–65% and the lignin is available in huge quantity. This also makes lignin a promising alter- native precursor based on high yield after processing into carbon fiber (Olsson et al. 2017; Hubbe et al. 2019). The lignin can be used as a potential precursor for car- bon fiber production by incorporating appropriate spin- ning and carbonization processes. The most common way of manufacturing carbon fibers from lignin involves melt spinning to produce precursor fibers, thermo-stabi- lization (200–350 °C), and carbonization (over 1000 °C under nitrogen atmosphere) to produce carbon fibers (Fig. 9). Wet spinning can also be used when rheological problems are encountered in melt spinning. It is reported that greater than 35% of manufacturing cost is reduced using renewable lignin as a precursor in carbon fiber pro- duction (Bengtsson et al. 2018; Gbenebor and Adeosun 2019). The challenges in regards to lignin to carbon fiber conversion are the availability of fiber spinning technolo- gies (Souto et al. 2018) in some countries which limit the product diversification scheme. Bioplastics from black liquor hemicellulose The hemicellulose from black liquor consists of xylan among other ingredients (Yang et al. 2019a; Liu et al. 2012). The polysaccharide-based xylans are made
Several approaches have been used to purify the spent black liquor for the production of pure lignin (Hubbe et al. 2019; Xinde 1996). Acidification via precipitation is the most prominent. The extraction involved pre- cipitation of the black liquor in acid solution, coagula- tion, and removal of lignin (Norberg 2012; Olsson et al. 2017; Bengtsson et al. 2018). The biomaterial options for lignin are versatile. The modern interest in carbon fibers is very crucial, and lignin is one of the important biomasses for the pro- duction of carbon fibers. Carbon fiber is known for its extremely high strength-to-weight ratio which makes it an ideal engineering material for a load-bearing ele- ment in lightweight high-performance composites. The versatile application of carbon fiber in the modern industry especially in composites is related to its low density and excellent mechanical properties. High-performance carbon fibers are currently pro- duced primarily from polyacrylonitrile (PAN). Carbon- rich precursor fiber with a carbon content of more than 90% is required for the manufacturing of carbon fibers. Once the precursor is availed the transformation is car- ried out in a two-stage thermal process. The delicate and rigorous web spinning process used for polyacry- lonitrile-based precursors is one of the bottlenecks in the cost-effective manufacturing of carbon fiber. Half the cost of manufacturing carbon fiber is spent in mak- ing the PAN precursor (Bengtsson et al. 2019). Another potential limitation of using PAN precursors is the raw materials are fossil-based which entails a high cost. The high price of carbon from the perspective of raw
Fig. 9 Spinning of lignin into carbon fiber (Gbenebor and Adeosun 2019)
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