Isolation of nanocellulose

Nanocellulose in the form of NFC or CNC can be extracted by various methods. Ihis section briefly describes the processes for producing nanocellulose, their advantages and disadvantages, as well as some important issues regarding these methods. 

In 1983, Herrick and Turbak applied this method to isolate NFC from wood fiber for the first time [54,55]. Although homogenization is a very simple process without the need for organic solvents [56],clogging is one of the most important issues 

Apart from the production process of NFC by homogenization, their final application is a critical issue. Because of the hydrophilic nature of cellulose nanofibers, their incorporation and dispersion with common polymers, which are hydrophobic, are very critical issues [38]. Low interfacial adhesion between these two parts in composite leads to reduction in the mechanical and other properties of the final product. Thus, a wide variety of modifications like carboxymethylation [65], 2,2,6,6-tetramethylpiperdine-1-oxyl (TEMPO) oxidation [66, 67], acetylation [68, 69], and silylation [70, 71] have been designed to overcome this problem. The modification strategies of cellulose nanosize materials are discussed in Section 11.6. 

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Cherian BM, Leao AL, Souza SF, Thomas S, Pothan LA, Kottaisamy M (2010) Isolation of nanocellulose from pineapple leaf fibres by steam explosion. Carbohydr Polym 81 720-725... 

Mandal, A., Chakrabarty, D. (2011). Isolation of nanocellulose from waste sugarcane bagasse (SCB) and its characterization. (3), 1291 1299. 

Bibin Mathew Cherian, Alcides Lopes Le3o, Sivoney Ferreira de Souza, Sabu Thomas, Laly A. Pothan, M. Kottaisamy. (2010). Isolation of nanocellulose from pineapple leaf fibers by steam explosion. Carbohydrate Polymers 81, 720725. 

The nanostructured organization of cellulose promotes the isolation of free nanoconstituents such as nanofilaments, nanofibrils, nanocrystals, and ANP. In recent years, extensive investigations have been carried out regarding the obtaining of various kinds of nanocellulose, such as CNP and ANP, NFC, BNC, and CNY. 

For more than 5000 years, cellulose fabrics and fibers have been used in medicine as wound dressings for treatment of wounds and burns. In the twentieth century, along with cellulose dressings, various cellulose derivatives, powdered and microcrystalline cellulose began to be used, and in the twenty-first century nanocellulose joined these products. Among various organic substances, cellulose is the most appropriate for preparation of nanoscale materials, since this most abundant natural polymer has nanostmctured organization, which promotes isolation of free nanoconstituents. 

Zhou et al. [53] studied the effect of nanocellulose isolation techniques on the quality of nanocellulose and its performance in reinforced nanocomposites. They employed three different techniques including acid hydrolysis (AH), TEMPO-mediated oxidation (TMO) and ultrasonica-tion (US) to isolate nanocellulose from microcrystalline cellulose (MCC) and to evaluate the quality of nanocellulose and the reinforcing ability of these nanocelluloses in PVA matrices. The characterization of nanocellulose indicated that nanocellulose with higher aspect ratio, surface charge (-47 mV) and yields (37%) was obtained by TMO treatment, while acid hydrolysis treatment resulted in higher crystallinity index (88.1 %) and better size dispersion. 

In this chapter, different methods of isolation of nanoceUulose from different cellulosic sources and methods to increase the compatibility in nanocomposites were demonstrated. The technology developed in the use of cellulose has shown big advantages in medicine because of their compatibility with the human and animal bodies. The nanocellulose as framework has great potential in some applications like it was demcmstrated for the case of tissues, where the cells grow faster than conventional procedures. 

This chapter has focused on the isolation techniques and fundamental properties of nanocellulose that have been developed so far, and ultimately the application of this nanocellulose in composites. Natural fibers are commonly used to produce nanocelluloses which contain both crystalline and amorphous regions at varying proportions depending on the species. Thus, the characteristics of nanocellulosic materials depend... 

The first step to obtain nanocellulose by acid hydrolysis constitutes a number of processes, known as pulping and bleaching, that involves the isolation of fibers from the breakdown of cellulose-lignin-poUosis complex without the destruction of fibrils [22,23]. 

Zhou YM, Fu SY, Zheng LM, Zhan HY (2012) Effect of nanocellulose isolation techniques on the formation of reinforced poly (vinyl alcohol) nanocomposite films. eXPRESS Polym Lett 6 794-80... 

Nanocelluloses isolated from AH technique have individual crystallites and disperse uniformly showing needle-shaped structures (namely nanocrystals), with diameters of 30-40 nm and lengths of 200-400 nm, while the TMO-derived nanocelluloses are interconnected webs showing nanofibrils with diameters of 40-80 nm and lengths ranging from 200 nm to several micrometers, having a wide range of aspect ratio. 

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