Nanofibers microfibrils

The historical term microfibril can be a source of confusion as it has been used by different authors along with closely related terms such as protofibril, elementary fibril, and nanofibers. As pointed out by Nishiyama, the term cellulose microfibril addresses features that are not limited to its size. For this reason, it is used throughout this article. 

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. ... 

M. Henriksson, G. Henriksson, L.A. Berglund, and T. Lindstrom, An environmentcJly friendly method for enzyme-assisted preparation of microfibrillated cellulose (MFC) nanofibers. Eur. Polym. J. 43, 3434-3441 (2007). 

There are basically two families of nanosized cellulosic particles. The first one consists of cellulose nanocrystals and the second one is microfibrillated cellulose (MFC) [17]. However, different terminologies are used to describe these cellulose nanoparticles, leading to some misunderstanding and ambiguities. Currently, the isolation, characterization, and search for applications of novel forms of cellulose, variously termed crystallites, nanocrystals, whiskers, nanofibrils, and nanofibers, is generating... 

Over time, a number of possibilities have been explored to produce cellulose-based nanometric fillers. In particular, microfibrillated cellulose (MFC) (Section 6.2.1) is formed by fibrous cellulose structures with the length of several tens of microns and generally a few tens of nanometers thick, as it consists of aggregates of microfibrils, natmally occurring as an effect of the hierarchical structure of cellulose in plants [3]. In other words, MFC is formed by long, flexible and entangled cellulose nanofibers, where both amorphous and crystalline phases are present [4]. 

Overall, cellulose I is mainly responsible for the mechanical properties of reinforced polymer composites due to its high elastic modulus and crystallinity. The elastic modulus of perfect cellulose crystals has been calculated and estimated between 130 GPa to 250 GPa, whereas the tensile strength is approximately between 0.8 GPa to 10 GPa [28]. In previous studies cellulose has already been processed into films, gels, fibers, microfibers, nanofibers and nanocrystals for different applications [29-32]. Actually, cellulose fiber is the bundle of microfibrils comprising nanocrystalline domains linking through amorphous domains [33]. 

Natural cellulose, a polysaccharide, is a linear natural polymer of fS-(l — 4)-d-glucopyranose possessing abundant surface hydroxyl groups that form abundant inter- and intramolecular hydrogen bonds (Figure 2.16). The polymer chains accumulate into elementary fibrils (diameter 1.5-3.5 nm), and bundle to microfibrils (nanofibers, diameter tens to hundreds of nanometers), further form randomly interconnected hierarchical networks of microfibrillar fibers (microfibers, diameter in the micrometer scale or larger), resrdting in the familiar bulk cellulose... 

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