Cellulose nanocellulose

On the other hand, native cellulose is an abundant and inexpensive macromolecular compound that reinforces most plant cell walls. During recent years, attention has been devoted to the use of cellulose (nanocellulose or nanofibrillated cellulose), and important studies have been published [13-22]. The outstanding mechanical properties of nanocellulose or nanofibrillated cellulose, linked to its wide availability, biodegradability, and extensive number of alternatives for chemical modification, have been the driving force for its utilization as reinforcement in polymers. These cellulosic materials are composed of nanosized cellulose fibrils with a high aspect ratio (length-to-width... 

Because of the extraordinary supramolecular structure and exceptional product characteristics as high-molecular and high-crystalline cellulosics with a water content up to 99%, nanocelluloses require increasing attention. This review assembles the current knowledge in research, development, and application in the field of nanocelluloses through examples. The topics combine selected results on nanocelluloses from bacteria and wood as well as their use as technical membranes and composites with the first longtime study of cellulosics in the animal body for the development of medical devices such as artificial blood vessels, and the application of bacterial nanocellulose as animal wound dressings and cosmetic tissues. 

If cellulosics such as BC are composed of nanosized fibers and the nanofiber structuring determines the product properties, these polymers are described as nanocelluloses. 

Fig. 2 Shape and structure of BC. a molecular cellulose chain, b scanning electron microscopy (SEM) of freeze-dried nanofiber network (magnification 10000), c pellicle of bacterial nanocellulose from common static culture...

It should also be mentioned that the application of wood nanocellulose prepared by the described techniques - where the cell wall is further disintegrated by mechanical treatment - leads to lower-strength cellulose fiber-reinforced composites than in the corresponding BC materials [34]. 

Membranes and composites from cellulose and cellulose esters are important domains in the development and application of these polymer materials. The most important segment by volume in the chemical processing of cellulose contains regenerated cellulose fibers, films, and membranes, hi the case of the cellulose esters mainly cellulose nitrate and cellulose acetate as well as novel high-performance materials created therefrom are widely used as laminates, composites, optical/photographic films and membranes, or other separation media, as reviewed in [1], The previously specified nanocelluloses from bacteria and wood tie in with these important potentials and open novel fields of application. 

Yano and Nakahara [15] used accessory polysaccharides to form composites with wood MFC/nanocelluloses. The disintegrated wood celluloses were mixed with starch as a binder and then hot-pressed between porous metal plates. Using a starch content of 2 wt %, the bending strength reached 310 MPa, compared to 250 MPa for unmodified fibers. Concurrently, the Young s modulus decreased from 16 to 12.5 GPa. When the starch content was 20 wt %, the bending strength decreased to 270 MPa. This indicates that added starch may act not only as a binder but also as a plasticizer. 

To improve the thermal, mechanical, and viscoelastic properties of cellulose acetate butyrate, it was reinforced with nanocellulose crystals prepared from BC by acid hydrolysis. Using this nanosized cellulose (Sect. 1) a significant improvement in the properties of the composites was demonstrated [57]. 

The wall of the BASYC tubes consists of BC loaded with water in the nanofiber network up to 99%. The hollow space of the material transports water, monovalent ions and small molecules, but not biopolymers or corpuscular blood constituents. The stored water not only stabilizes the cellulose network, but also contributes to the tissue- and hemocompatibility of the nanocellulose device. 

Internal medicine, urology, gynecology, otolaryngology, maxillofacial and plastic surgery could be potential users of this designed nanocellulose. For this reason, hollow cellulose tubes with different inside diameter and different wall thickness have been prepared in micro-dimensions. Figure 14 shows a collection of BASYC tubes. Foils, patches, and other shapes are possible, too. 

During the past 5-10 years a considerable increase in knowledge of the structure, chemistry, and processing of cellulose, as well as development of innovative cellulose products, has been observed. New frontiers involve sophisticated methods of structural analysis, environmentally safe cellulose-fiber technologies, as well as progressive work with bacterial nanocellulose, (bio)materials, and a broad spectrum of cellulose composites. 

The second chapter by Dieter Klemm, Dieter Schumann, Hans-Peter Schmauder, and coworkers focuses on the recent knowledge of cellulosics characterized by a property-determining supramolecular nanofiber structure. Topics in this interdisciplinary contribution are the types of nanocelluloses and their use in technical membranes and composites as well as in the development of medical devices, in veterinary medicine, and in cosmetics. 

Moran, J.I. Alvarez, V.A. Cyras, V.P. Vazquez, A. Extraction of cellulose and preparation of nanocellulose from sisal fibers. Cellulose 2008,15 (1), 149-159. 

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... 

Nanocellulose, such as that produced by the bacteria Gluconacetobacter xylinus (bacterial cellulose, BC), is an emerging biomaterial with great potential in several applications. The performance of bacterial cellulose stems from its high purity, ultra-fine network structure and high mechanical properties in the dry state [114]. These features allow its applications in scaffold for tissue regeneration, medical applications and nanocomposites. A few researchers have used bacterial cellulose mats to reinforce polymeric matrices and scaffolds with wound healing properties [115-121]. BC is pure cellulose made by bacterial fabrication via biochemical... 

Fig. 10.7 Examples of biomedical applications of BC are meniscus replacements (pig meniscus on the left, BC meniscus on the right), artificial blood vessels and wound dressing for skin heaiing [76-78], Nanocellulose (bacterial cellulose, BC), such as that produced by Acetobacter xylinum, has shown promising results as a replacement material for small diameter vascular grafts (Fig. 10.8). These BC tubes have been tested in a pig model as an infrarcnal aortic bypass and show promising results for use as vascular grafts in the future...

However, thermal stability and mechanical properties of ANP are poor. Young s modulus and tensile strength of this kind of nanocellulose are 10—20 times lower than those of cellulose nanocrystals (loelovich, 2012a,b). Therefore, ANP of cellulose cannot be suitable as a reinforcing nanofiller. 

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. ... 

Despite the high crystallinity, this kind of nanocellulose exhibits an enhanced enzymatic hydrolyzability, which can be attributed to the high porosity and well-developed surface of the nanostructured bacterial cellulose. Due to these structural features, the BNC sample acquires a high accessibility for molecules of cellulolytic enzymes, which contributes to deep enzymatic hydrolysis of this NC both in never-dried and dry states (loelovich, 2014c). 

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. 

Despite great potential, the widespread use of various kinds of nanocellulose has a limitation due to lack of information on their biological safety. Nevertheless, diverse experiments on animals and human volunteers prove that topical application of nanocellulose is quite safe. For example, testing of experimental peeling cream NAPA containing CNP of cellulose on volunteers showed negative skin reactions. Clinical examinations demonstrated that the cosmetic masks made by BNC do not cause any unwanted skin reactions such as irritation, sensitization, or allergy (Klemm et al., 2006). 

Klemm, D., Schumann, D., Kramer, F., HeBler, N., Koth, D., Sultanova, B., 2009. Nanocellulose materials—different cellulose, different functionality. Macromol. Symp. 280 (1), 60-71. 

Fig. 4 Structure and properties of nanocellulose, (a) Hierarchical assembly of cellulose molecules into cellulosic fibers. Adapted, with permission, from [131]. Copyright 2012 Elsevier, (b) Proposed mechanism of formation of CNF cross-linked with metal cations. Reproduced, with permission, from [132]. Copyright 2013 American Chtanical Society, (c) Effect of the type of metal cation on the frequency-dependent storage modulus of CNF hydrogels, probed by dynamic frequency sweeps (25 °C) at a strain rate of 0.5 %. Adapted, with permission, from [132]. Copyright 2013 American Chemical Society, (d) Polarization optical microscopy photograph of a biphasic 8.78 % (w/w) CNC suspension. Adapted, with permission, from [133]. Copyright 1996 American Chemical Society, (e) Polarization optical microscopy photograph of a CNC suspension. Scale bar. 200 pm. Reproduced, with permission, from [134]. Copyright 2000 Amaiean Chemical Society...

Supramolecular Cellulose Hydrogels Prepared from Nanocellulose. 217... 

---