Whiskers of celluloses

There are four types of nanocellulose depending on their fabrication method bacterial cellulose, electrospun cellulose, microfibrillated cellulose (MFC) and whiskers of cellulose (nanorods). Bacterial cellulose is a nanomaterial derived from plant material by bacterial action in the presence of oxygen. Various strains of Acetobacter species [82,83] can be used to produce cellulose, although strains of pseudomonas, Achrobacter, Alcaligene, Aerobacter and Azotobacter [84] can also be used. The bacterial cellulose... 

Sustainability of the materials becomes one of the prime concerns in the research development in industries and academic institutions. The search for nonpetroleum-based fillers has accelerated the research into bio-nanofillers from biomass. In some cases, bio-based nanocomposites show unique advantages over traditional inorganic nanoparticles. Commonly used bio-nanofillers in NR are whiskers of cellulose, chitosan, nanocrystals of starch etc. The studies on these fillers are aimed at competitive production cost and equivalent properties as compared to other petroleum-based fillers. In addition, biocompatibility and biodegradability of the bio-based fillers are hoped to be retained after dispersion in the NR matrix. 

Whiskers of cellulose can be obtained from various sources including Syngo-nanthusnitens (Capim Dourado), rachis of palm tree, sisal and bagasse and an animal cellulose called tunicin. Cellulose whiskers are of particular interest... 

Chauve et al. [253] utilized the same technique to examine the reinforcing effects of cellulose whiskers in EVA copolymer nanocomposites. It was shown that larger energy is needed to separate polar EVA copolymers from cellulose than for the nonpolar ethylene homopolymer. The elastomeric properties in the presence of spherical nanoparticles were studied by Sen et al. [254] utilizing Monte Carlo simulations on polypropylene matrix. They found that the presence of the nanofillers, due to their effect on chain conformation, significantly affected the elastomeric properties of nanocomposites. 

The similar term nanosized cellulose is used in case of isolated crystallites and whiskers formed by acid-catalyzed degradation of cellulosics. This field and the application of that nanosized cellulose, e.g. in composites, have been intensively investigated. Typical examples have been presented in current papers [3,4] and at the 231st American Chemical Society (ACS) national meeting in Atlanta. 

Bondeson D, Kvien I, Oksman K (2006) Strategies for preparation of cellulose whiskers from MCC as reinforcement in nanocomposites. ACS Symp Ser 938 10-25... 

In terms of nanocomposite reinforcement of thermoplastic starch polymers there has been many exciting new developments. Dufresne [62] and Angles [63] highlight work on the use of microcrystalline whiskers of starch and cellulose as reinforcement in thermoplastic starch polymer and synthetic polymer nanocomposites. They find excellent enhancement of properties, probably due to transcrystallisation processes at the matrix/fibre interface. McGlashan [64] examine the use of nanoscale montmorillonite into thermoplastic starch/polyester blends and find excellent improvements in film blowability and tensile properties. Perhaps surprisingly McGlashan [64] also found an improvement in the clarity of the thermoplastic starch based blown films with nanocomposite addition which was attributed to disruption of large crystals. 

Surprisingly, the association between TPS and cellulose fibres (polysaccharide-based composites) has been little analysed. In the literature, cellulose fillers used in association with a plasticized starch matrix are commercial paper fibres,10 potato pulp microfibrils,11 12 tunicin whiskers and paper bleached pulp.13-14 The literature reports that these cellulose fillers improve the tensile strength. Besides, the composite water sorption seems to be decreased. This behaviour is related to the well known lower water uptake of cellulose compared to starch.10-14... 

It may be estimated that the surface chains in tunicin microfibrils constitute no more than 5% of the total number of tunicin chains, whereas surface chains may constitute 70% of the total number in parenchyma microfibrils. The result of increasing number of surface chains and decrease in whisker diameter can also be evidenced by infiared spectroscopy, with a broadening of tire absorption bands and loss of resolution. A peak at 1635 cm may be attributed to vibrations arising from water molecules absorbed in the noncrystalline regions of cellulose. 

Y. Habibi, H. Chanzy, and M. Vignon, TEMPO-mediated surface oxidation of cellulose whiskers. Cellulose, 13 (2006) 679-687. 

AZI04] Azizi Samir M.A.S., Alloin F., Sanchez J.Y., et ai, Preparation of cellulose whiskers reinforced nanocomposites from an organic medium suspension . Macromolecules, vol. 37, no. 4, pp. 1386-1393,2004. 

Oksman, K., et al., 2006. Manufacturing process of cellulose whiskers/polylactic acid nanocomposites. Composites Science and Technology 66 (15), 2776—2784. 

Cellulose is insoluble in water and common organic solvents. This leads to the formation of colloidal suspension when cellulose whiskers are suspended in water. The stability of these suspensions depends on the dimensions of the dispersed particles, their size polydispersity and surface charge. Different acids have been used as solvents for dissolution of cellulose. Sulfuric and hydrochloric acids have been extensively used for whisker preparation, but phosphoric [68] and hydro-bromic acids [69] have also been reported for such purposes. When whiskers are... 

Figure 2.2 shows a TEM micrograph of cellulose whiskers prepared from cotton. Geometrical characteristics of cellulose whiskers depend on the origin of cellulose microfibrils and on the conditions of the acid hydrolysis process such as time, temperature, and purity of materials. Samir et al. [75] have reported the dimensions of cotton and tunicin whiskers. The length (L) and lateral dimension (D) of cotton whiskers were around 200 and 5 nm, respectively (ratio L/D = 40). The length and lateral dimension of tunicin whiskers were reported to be around 1,000 and 15 nm, respectively (ratio L/D = 67). De Souza [76] studied cotton and tunicate whiskers in aqueous suspensions as well. The average size whisker dimensions reported were L = 255 nm and D = 15 nm for cotton whiskers (ratio L/D — 17) while the values were L — 1,160 nm and D = 6 nm (ratio L/D = 72.5) for tunicate whiskers. 

In this chapter we have reviewed some of the most important characteristics of cellulose and cellulose based blends, composites and nanocomposites. The intrinsic properties of cellulose such as its remarkable mechanical properties have promoted its use as a reinforcement material for different composites. It has been showed that cellulose is a material with a defined hierarchy that tends to form fibrillar elements such as elementary fibrils, micro fibrils, and macro fibers. Physical and chemical processes allow us to obtain different scale cellulose reinforcements. Macro fibers, such as lignocellulosic fibers of sisal, jute, cabuya, etc. are used for the production of composites, whereas nano-sized fibers, such as whiskers or bacterial cellulose fibers are used to produce nanocomposites. Given that cellulose can be used to obtain macro- and nano-reinforcements, it can be used as raw material for the production of several composites and nanocomposites with many different applications. The understanding of the characteristics and properties of cellulose is important for the development of novel composites and nanocomposites with new applications. 

---