Cellulose nanofibers extraction

Cellulose nanofibers from different sources have showed remarkable characteristics as reinforcement material for optically transparent composites [160, 161], Iwamoto et al. [160] prepared optically transparent composites of transparent acrylic resin reinforced with cellulose nanofibers extracted from wood pulp fibers by fibrillation process. They showed that cellulose nanofiber-reinforced composites are able to retain the transparency of the matrix resin even at high fiber content (up to70 % wt). The aggregation of cellulose nanofibers also contributes to a significant improvement in the thermal expansion properties of plastics. 

Fig. 21.12 Suspensions of cellulose nanofibers (on the left) and (a) scanning transmission electron micrographs of nanofibers (at two magnifications), (b) atomic force micrographs of cellulose nanofibers extracted from white and naturally colored cotton fibers by sulfuric acid treatment. Reproduced with permission from Teixeira et al. (2010). Copyright 2010 Springer Science + Business Media B.V.

In some cases the isolation of cellulose micro/nanofibrils involves enzymatic pretreatment followed by mechanical treatments [22,23]. The morphology and aspect ratio of the extracted nanofibers may vary depending upon the raw materials and extraction techniques [24]. Examples of various cellulose nanofiber extraction methods, including microfibrillar cellulose (MFC) are shown in Table 5.1. 

Other biopolymers useful for synthesis of nanocomposites include (i) gelatin—a water-soluble protein obtained by extracting collagen liom animal skin and bones and thermal denaturation. (ii) PHB—a natural product of biosynthesis performed by bacteria in nature, (iii) Chitosan—a natural polymer widely found in exoskeletons of crustaceans and insects, as well as in the cell walls of microorganisms (Maiti et al. 2003 Zheng et al. 2002 Takegawa et al. 2010). Moreover, the mechanical and water vapor barrier properties of chitosan-based nanocomposites with cellulose nanofibers could be enhanced. 

Cellulose EFB could disintegrate in order to produce cellulose nanofiber (CNF). In history, there are various techniques studied in order to obtain pure, new, and improved EFB fiber. The purity and quality of the final product is distinguished from the very beginning of each process integration. There are several processes in nanofiber isolation that include pretreatment, bleaching, and extraction of cellulose nanofiber suspension which can be done through hydrolysis using chemical or mechanical process. 

The source of nanofiber is varied either from animal or plant that contains different amount of chemical composition. Thus, in nanofiber production, different natural fibers need to imdergo several chemical and physical treatments. In addition, every extraction method gave different results in term of quality and yields, hence other techniques of cellulose nanofiber production need to be explored. Furthermore, as found in previous research, combination of chemical, enzymatic, and physical... 

Many studies have been done on isolation and characterization of cellulose nanofibers from various sources. Cellulose nanofibers can be extracted from the cell walls by simple mechanical shearing or by a combination of both chemical and mechanical routes [10]. 

Alemdar and Sain [19] have extracted cellulose nanofibers from wheat straw by a chemical treatment followed by a mechanical treatment (cryocrushing, disintegration, and defibrillation steps) to individuahze the nanofibers from the cell walls. 

Zimmermann et at [20] separated nanofibrillated cellulose (NFC) from different cellulosic precursors by mechanical dispersion and high pressure homogenization processes (up to 1500 bar). The diameter was below 100 nm. Cellulose nanofibers were extracted by Wang and Sain [21] from soybean stock by chemomechanical treatments (Figure 5.2). These were bxmdles of cellulose nanofibers with a diameter ranging between 50 and 100 nm and lengths of thousands of nanometers. 

Table 5.1 Extraction of cellulose nanofibers and their dimensions [25].

An interesting work was carried out by Banerjee et al. [65] in the area of in-situ polymerized cellulose nanocomposites. They surface treated extracted cellulose nanofibers with methyl methacrylate monomer (MCNF) and PMMA/cellulose nanocomposites (MMIPC) were formed by in-situ suspension polymerization process. 

All in all, cellulose nanofiUers offer some attractive properties as potential candidates to substitute conventional synthetic fibers. Nonetheless, some hurdles must still be overcome, the major one being the proper nanofiber extraction. More energy-efficient processes relying on affordable devices are needed for the application of cellulose nanofibers in the manufactore of commodity products. 

Nakagaito, A.N., Nakano, K., Takagi, H., Pandey, J.K., 2012. Extraction of cellulose nanofibers from grass by a domestic blender. In 7th International Workshop on Green Composites. August 28—30, Hamamatsu, Japan. 

Takagi, H., Nakagaito, A.N., Bistamam, M.S.A., 2013. Extraction of cellulose nanofiber from waste papers and application to reinforcement in biodegradable composites. Journal of Reinforced Plastics and Composites 32, 1542—1546. 

Yano HSJ, Nakagaito AN, Nogi M, Matsuura T, Hridta M, Handa K (2005) Optically transparent composites reinforced with networks of bacterial nanofibers. Adv Mater 17 153 Young R (1994) Comparison of the properties of chemical cellulose pulps. Cellulose 1 107-130 Zhao H-P, Feng X-Q,Gao H (2007) Ultrasonic technique for extracting nanofibers from nature materials. Appl Phys Lett 90(7) 073112... 

A chemical method of extraction of nanofibers from never-dried native cellulose was developed by Saito et al. (2006) by oxidizing the surface of the nanofibers by a 2,2,6,6-tetramethylpiperidine-l-oxyl (TEMPO)-radical-catalyzed process, that requires just a posterior mechanical agitation by a Waring blender to individualize the original fibers into nanofibers of 3—5 nm in diameter. Another chemical extraction is acid hydrolysis, which ultimately produces smaller elements called cellulose... 

As already made known in the introductory part, chitin is also an abundant polysaccharide found in the exoskeleton of some arthropods and in the cell walls of many filamentous fungi. Cellulose and chitin differ in molecular structure only for a hydroxyl group at every ring in cellulose being replaced by an acetamido group in chitin (Stevens, 2002). As hard shells intended to support and protect the small bodies of crustaceans, these biocomposites must be subjected to less intense loads than larger trees, therefore the nanofibers become easier to extract. Add to that the possibility to cationize the... 

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