Cellulose Nanoreinforcements

Cellulose nanoreinforcements (CNRs) are gaining interest as reinforcing materials for the preparation of low cost, lightweight, and high-strength nanocomposites [73,74], Cellulose is a material which is widespread in 

There are basically two families of nano-sized cellulosic particles [81]  

Nanofibrillar cellulose which includes mechanically isolated microfibrils, chemically isolated microfibrils (TEMPO-oxidation), bacterial cellulose and can be considered as spaghetti-like  

Cellulose nanocrystals are rods of highly crystalline cellulose which are usually isolated by acid hydrolysis Cellulose nanocrystals are represented in literature by synonyms like cellulose whiskers, cellulose nanowhiskers, cellulose microfibrils. 

These are needle-shaped (100 nm to 200 nm x 10 nm), highly crystalline, strong (E = 150 GPa) forms of liquid crystal 

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Improvement of barrier property due to the presence of cellulose nanoreinforcements in polymer matrix can be well explained by the increase of the tortuosity of the diffusivity path for the permeants, lowering the polymer permeability similarly to nanoclays [101]. The barrier properties are further enhanced if the filler is less permeable, well dispersed in the matrix, and with a high aspect ratio [116], and are strongly related to the dimensions and consequent aspect ratio of the fillers [117], as well as to orientation of the nanostructures [118]. 

There are two main issues with the use of cellulose nanoreinforcement in biopolymer matrices which ultimately affect the mechanical properties of the... 

The most commonly used matrices with cellulose nanoreinforcement are PLA, PVA, PCL, and NR. We shall now discuss the mechanical properties of a selection of such composites. 

It has been shown that if cellulose nanoreinforcement can be made to align in a biopolymer matrix, they exhibit optimum properties in the direction of alignment, just like in synthetic fiber composites. Chitosan is a semicrystalline biopolymer which is used both as a matrix and as nanoreinforcement in composites. The use of chitosan nanoreinforcements in biopolymer matrices results in improvement in properties of composites. However, an optimum loading limit has been observed, depending on the biopolymer matrix, above which the properties of nanocomposites start to decline. A similar optimum loading limit has been found to exist when CNCs are used as reinforcements in chitosan matrix. 

In the present chapter, the modulation of the final properties of a nanocomposite containing cellulosic nanoreinforcement combined with a second filler, will be analyzed and reported. In this way, the properties of the final materials can be adjusted as a function of the particle size and distribution, shape, as well as by their interactions with the cellulose surface. The effect of the second reinforcement will be considered for a wide variety of potential applications, including network structures for tissue engineering, antimicrobial films, electronics, protective coatings, barrier/filter membrane systems. 

In the present chapter, selected approaches for the modulation of the final properties of a polymeric nanocomposite containing cellulosic nanoreinforcement with a second... 

It is finally clear that an extensive and copious literature exists on the use of cellulose nanoreinforcements and metal nanoparticles as hybrid systems and significant interest is devoted to the study of such high performance hybrids and new related applications in the evolving area of nanotechnology. 

The adoption of ternary polymeric systems including cellulosic nanoreinforcements and other nanoparticles leads to considerable assets in terms of multifunctionality, but also of tailored modification of the properties of the selected polymer matrix. A number of issues remain nonetheless open for discussion, particularly linked to the polysaccharides source from which nanocellulose is obtained, the process used to fabricate it and the strength of its interface with the polymer matrix and with the particles. This involves other aspects, such as the degree of hydrophilicity and the improvement of... 

Few examples of nanocomposites in which the cellulosic nanostructure is used in biobased thermosets can be also foimd. Due to the fact that these environment friendly composites suffer from several limitations, such as low mechanical properties due to low strength in reinforcement plus inadequate interfacial strength, and that cellulose nanostructures have been shown to have significant potential as a reinforcement, the possibility of using cellulose nanofibers as reinforcements in a bio-derived resin was revised. In Masoodi et al. [200], cellulose nanofibers were used as reinforcements in the forms of layered films, while in Lee et al. [201] the stability of the gas-soybean oil foam templates and the mechanical properties of the polymer nanocomposite foams are enhanced upon the addition of bacterial cellulose nanofibrils. Other examples of biobased thermosets containing cellulosic nanoreinforcements are the work of Shibata [202] in which the use of a biobased epoxy was revised, and systems in which cellulose nanocrystals are incorporated in biobased polyurethanes [203,204], Few examples exist also in the literature on the polymerization of furfuryl alcohol in presence of CNR [205,206] in these papers, the authors established the feasibility of producing furfuryl... 

The use of cellulose nanowhiskers as nanoreinforcement is a new field in nanotechnology and as a result there are still many obstacles remaining to their use. Namely, cellulose nanowhiskers are not commercially available and their production is time consuming with low yields. In addition, they are difftcult to be deployed in systems that are not water based due to their strong intermolecular hydrogen bonding thus, the CNW have to be transferred from water to an appropriate solvent for this type of PLA. In the past decade, the field of PLA/CNW still remained sow in progress due to these obstacles. 

Petersson, L., Oksman, K. Biopolymer based nanocomposites Comparing layered silicates and microcrystalline cellulose as nanoreinforcement. Compos. Sci. Technol. 66, 2187-2196 (2006)... 

Some NR-based nanocomposites with bio-based nanoreinforcements like chi-tin whiskers, starch nanocrystals, cellulose whiskers. A lot of work on bionanocomposites of NR has been reported by Alain Dufresne and coworkers.But most of these studies use latex blending technique without vulcanization, for the bionanocomposites preparation. There are less reports available on vulcanized rubber-based bionanocomposites prepared by master batch processing and two-roll mill mixing, which have the potential to be adapted for commercial use. ... 

Peresin MS, Habibi Y, Zoppe JO et al (2010) Nanofiber composites of polyvinyl alcohol and cellulose nanocrystals manufacture and characterization. Biomacromolecules 11 674—681 Petersson L, Oksman K (2006) Biopoljoner based nanocomposites comparing layered silicates and microcrystalline cellulose as nanoreinforcement. Compos Sci Technol 66 2187-2196... 

Although effective at improving the barrier properties, layered silicates are not biodegradable. Cellulose can be a biodegradable alternative to the use of sihcates. There are two types of nanoreinforcements that can be obtained firom cellulose fibers microfibrils (cellulose chains synthesized by plants or animals) and nanowhiskers (isolated crystalline... 

The main objective of this chapter is to provide a snapshot of the rapidly developing nanocomposite materials based on PLA. To date, various types of nanoreinforcements such as nanoclay, cellulose nanowhiskers, ultrahne layered titanate, nanoalumina, carbon nanotubes [13-19], and so on have been used for the preparation of PLA nanocomposites. For each particular system, progress is discussed chronologically, beginning with the pioneering work. Various physicochemical characterization and improved mechanical properties are summarized. Ongoing developments and promises are also discussed. Finally, possible suitable applications and future prospect of nanocomposites based on PLA are described. 

Raquez JM, Murena Y, Goffin AL, Habibi Y Ruelle B, DeBuyl F, Dubois P. Surface-modification of cellulose nanowhiskers and their use as nanoreinforcers into polylactide a sustainably-integrated approach. Compos Sci Technol 2012 72 544-549. 

Starting from these considerations, the present chapter summarizes several types of cellulose nanocomposite (including the cellulose acetate-based ones), classified according to nanoreinforcement namre and surface modification processes. These recent scientific information can add to the basic knowledge in the field of polymeric materials, and to the diversification of their applications, especially in the biomedical domain, as due to their antimicrobial properties. 

Starch is another semicrystalline biopolymer which can be used both as nanoreinforcement and as a matrix in composites. When used as a matrix, starch is usually blended with plasticizer to improve its processing and mechanical properties. Studies have shown significant improvements in tensile properties of nanocomposites, whether starch is used as a reinforcement or a matrix. BC-based nanocomposites have been shown to exhibit superior properties than vegetable cellulose-based nanocomposites. 

The hydrophilic surface of the cellulose-based nanoreinforcements leads to poor interaction between matrix and the filler [29]. Furthermore, the chemical compatibility is very important in controlling the dispersion and the adhesion among them. Therefore, it is common to see weak filler-matrix interactions when hydrophilic whiskers were added to hydrophobic matrices [4]. The miscibility of cellulose nanofillers with hydro-phobic matrices can be improved by various surface modifications, for example, esterification and acylation. The increment in the filler/matrlx compatibility produces the enhancement of mechanical and thermal properties but also enhances the barrier properties [30]. 

In this chapter, we will describe the production of cellulose nanocrystals (CNCs) by acid hydrolysis process from different cellulosic resources. Also, the drying process and extensive characterization of CNCs to better understand the inherent and processing properties of this nanomaterial with functionalization is discussed as potential nanoreinforcement. New developments in potential industrial and biomedical areas are also discussed. 

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