Cellulose amorphous nanoparticles

In Section 9.3.2 it was shown that amorphous nanoparticles of cellulose (ANP) have spherical to elliptical shapes with average diameters of 100 nm, high degree of amorphicity and increased content of sulfonic groups (Table 9.16). 

Table 9.16 Main Features of Amorphous Nanoparticles of Cellulose...

Engelhard , J., Fischer, S., Hettrich, K., Kriiger, C., Nachtkamp, K., Pinnow, M., 2011. Nanoparticles made of amorphous cellulose. US Patent Appl. 20110293732. 

As previously mentioned, natural fibres present a multi-level organization and consist of several cells formed out of semi-crystalline oriented cellulose micro fibrils. Each microfibril can be considered as a string of cellulose crystallites, linked along the chain axis by amorphous domains (Fig. 19.10) and having a modulus close to the theoretical limit for cellulose. They are biosynthesized by enzymes and deposited in a continuous fashion. A similar structure is reported for chitin, as discussed in Chapter 25. Nanoscale dimensions and impressive mechanical properties make polysaccharide nanocrystals, particularly when occurring as high aspect ratio rod-like nanoparticles, ideal candidates to improve the mechanical properties of the host material. These properties are profitably exploited by Mother Nature. 

Microcellular foams can be produced by noncontinuous processes such as a batch process [2, 12, 15, 16, 31, 32, 34, 35], continuous processes such as extrusion and injection molding [24,33,36,37], orby asemicontinuousprocess [38]. Since the semicontinuous process is not extensively used in the scientific community or in the industry, it will not be described in this chapter. Readers are encouraged to refer Ref. 38 for detailed information on this process. To date, microcellular foams have been produced in amorphous polymers [12, 31, 32, 34], semicrystalline polymers [35], and in elastomers [16]. Recently, MCF structures have also been produced in plastics filled with inorganic nanoparticles (montmorillonite) [39-43], as well as organic cellulosic fiber filled plastic composites [12, 31, 32, 34]. 

Nonaqueous sol-gel routes are not restricted to the deposition of preformed metal oxide nanoparticles. In feet, chemical principles such as ester elimination have been extended to atomic layer deposition, which enabled the coating of a wide range of materials (carbon nanotubes, wool, cellulose fibers, and single crystals) with a thin layer of amorphous titania or hafnia [115]. Detailed discussion of these procedures is out of the scope of this chapter, and the interested reader is referred to a more detailed review [195]. 

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