Nanofibrils of cellulose

Figure 1 Nanofibrils of cellulose from Acetobacterxylinum grown In the presence of CMC. Courtesy of Professor C. H. Haigler, In Biosynthesis and Biodegradation of Cellulose-, C. H. Halgler, P. J. Weimer, Eds. Marcel Dekker New York, 1991 p99.

Recently, a more detailed model of the supermolecular structure of natural cellulose has been developed and proposed (loelovich et al., 2010 loelovich, 2014b Pakzad et al., 2012). According to this model, the elementary nanofibril of cellulose is built from orientated nanocrystaUites and noncrystalline nanodomains (NCD) arranged along the fibril also, a thin paracrystalline layer (PCL) is located on the surface of the crystalline core (CRC), while the crystallites can contain local defects (DEF), for example, vacancies, caused by ends of the chains (Figure 9.6). 

Non-crystalline domains (NCD) are other significant constituents of elementary nanofibrils of cellulose. Content of these domains, i.e., degree of amorphicity, influences expressivety on sorption ability, accessibility, reactivity, deformation and some other properties of cellulose materials. The degree of amorphicity (F) can vary from... 

Abstract Cellulose is the most important biopolymer in Nature and is used in preparation of new compounds. Molecular structure of cellulose is a repeating unit of p-D-glucopyranose molecules forming a linear chain that can have a crystallographic or an amorphous form. Cellulose is insoluble in water, but can dissolve in ionic liquids. Hemicelluloses are the second most abundant polysaccharides in Nature, in which xylan is one of the major constituents of this polymer. There are several sources of cellulose and hemicelluloses, but the most important source is wood. Typical chemical modifications are esterifications and etherifications of hydroxyl groups. TEMPO-mediated oxidation is a good method to promote oxidation of primary hydroxyl groups to aldehyde and carboxylic acids, selectively. Modified cellulose can be used in the pharmaceutical industry as a metal adsorbent. It is used in the preparation of cellulosic fibers and biocomposites such as nanofibrils and as biofuels. 

It is important at this point to address the need for a new paradigm that was not recognized in the early work of Atalla and VanderHart. The title of the early articles was still defined in terms of the classical approach to cellulose structure in that the two forms of cellulose, and 1,3, were referred to as two distinct crystalline forms. Note was not taken at that point of the rapidly developing evidence that the lateral dimensions of most native cellulose fibrils were very limited and that cellulose nanofibrils have an inherent tendency to develop a right-handed twist when cellulose chain molecules aggregate. While this important development had shed some light on the controversies associated with many of the prior interpretations of diffractometric characterizations of native celluloses, it had not yet provided conclusive evidence that the interpretations based on the symmetry of the P2i space group for crystalline cellulose cannot be valid for native celluloses. It was the acquisition of the Raman spectra of Tunicate and Valonia celluloses that provided the conclusive evidence. 

On the basis of the results of electron diffraction studies by Sugiyama, Nishiyama et al undertook their very elaborate analyses of the diffraction patterns of the two forms of cellulose using X-ray, synchrotron, and neutron scattering. They also concluded that the two forms of cellulose have different unit cells, which imply that three different conformations coexist in the algal celluloses that are 60-70% of the Iq, form. This not only contradicts the clear evidence from the Raman spectra shown in Figure 9, but even more importantly is in direct conflict with the results of the lattice image studies reported earlier by Sugiyama et alJ that showed the nanofibrils of... 

Mechanical separation of cellulose fibrils from natural fibre resources may involve the process of grinding to apply shear stress to the longitudinal axis of the fibres, so that the fibrillated fibres will have diameters ranging 20—90 nm (Taniguchi and Okamura, 1998). Ultrasonic extraction is another approach to disrupt the adhesion among the fibrils so as to extract nanofibrils from both cellulosic and protein fibre sources... 

In Suopajarvi s work [38], dicarboxylic acid nanocellulose [DCC] flocculants were produced by nanofibrillation of periodate and chlorite-oxidized celluloses with a homogenizer. The flocculation performance levels of five such anionic nanocelluloses with variable charge densities were examined in the coagulation-flocculation treatment of municipal wastewater and the results compared with the performance of a commercial coagulant and a synthetic... 

Nonwoven mats of cellulose microfibrils were also used to prepare polyurethane composite materials via film stacking method [160], Water-redispersible nanofibrillated cellulose in powder form was recently prepared from refined bleached beech pulp by carboxymethylation and mechanical disintegration [161], However, the carboxymethylated sample displayed a loss of crystallinity and strong decrease in thermal stability limiting its use for nanocomposite processing. 

CNY is manufactured by means of electrospinning technology (Doshi and Reneker, 1995). The natural nanofibrils of bacterial cellulose are produced by several species of bacteria, for example, G. xylinus. The biosynthesized long and thin elementary nanofibrils of bacterial cellulose are aggregated to microfibrils forming a network filled with water. 

The nanofibrillated (microfibrillated) cellulose was first developed by Herrick et al. (1983) and Turbak et al. (1983) via grinding of diluted pulp suspensions in high-pressure mills. Currently, a preliminary mild chemical modification is performed before mechanical disintegration in order to minimize energy consumption. The NFC is composed of nanofibriUar bundles with a lateral size of several tens of nanometers and length of a few microns. 

Several terms are used to denote the nanocellulose obtained by a technique of high-pressure (high-shear) mechanical disintegration of cellulose pulp, namely microfibrillated cellulose, nanofibrillated cellulose, nanofibers, etc. Here we use predominantly the term nanofibrillated cellulose. ... 

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. 

Dong H, Snyder IF, Williams KS, Andzelm JW (2013) Cation-induced hydrogels of cellulose nanofibrils with tunable moduli. Biomacromolecules 14 3338-3345... 

Fall AB, Lindstrom SB, Sprakel J, WagbtTg L (2013) A physical cross-linking process of cellulose nanofibril gels with shear-controlled fibril orientatimi. Soft Matter 9 1852-1863... 

Acciaro R, Aulin C, Waghtig L et al (2011) Investigation of the formation, structure and release characteristics of self-assembled composite films of cellulose nanofibrils and temperature responsive microgels. Soft MattCT 7 1369-1377... 

Spagnol C, Rodrigues FHA, Pereira AGB, Fajardo AR, Rubira AF, Muniz EC (2012) Superabsorbent hydrogel composite made of cellulose nanofibrils and chitosan-grq/if-poly (acrylic acid). Carbohydr Polym 87 2038-2045... 

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