ABSTRACT
Currently, biobased materials are an important global research topic as there is a genuine interest and need to decrease society’s dependency on petroleum-based products. Cellulose as the most abundant natural polymer available in earth is produced in nature at an annual rate of 7.5 × 1010 tons and is present in natural bers such as wood, cotton, or hemp, as well as in a wide variety of living species, such as animals, plants, and bacteria (Habibi et al., 2010). Extensive interest has been recently focused on nding new material applications for this biopolymer. One of these applications has been the development of cellulose nanoparticles. Cellulose is a linear polymer consisting of β-d-glucopyranose units linked together by β-1,4-linkages. Hierarchy levels in wood bers are presented in Figure 23.1 (Rowland and Roberts, 1972). The cellulosic components of a wood ber wall structure are the cellulose molecule, the elementary bril or microbrils, the bril and
23.1 Introduction .......................................................................................................................... 519 23.2 Kinds of Nanocellulose ........................................................................................................ 520
23.2.1 Cellulose Nanowhisker ............................................................................................. 520 23.2.1.1 Cellulose Nanowhiskers Preparation ......................................................... 521
23.2.2 Microbrillated Cellulose ......................................................................................... 522 23.2.2.1 MFC Production Processes ........................................................................ 522
23.2.3 Bacterial Cellulose .................................................................................................... 525 23.3 Chemical Modication of Cellulose Nanoparticles.............................................................. 525
23.3.1 Ring Opening Polymerization Method..................................................................... 526 23.3.2 Grafting of Vinyl Monomers through Free Radical Polymerization ....................... 528 23.3.3 Living Radical Polymerization Method ................................................................... 530 23.3.4 Graft Modication through Coupling Reaction ....................................................... 531 23.3.5 Other Methods .......................................................................................................... 533
23.4 Cellulose Nanoparticle Applications .................................................................................... 535 23.4.1 Nanocomposites ........................................................................................................ 535 23.4.2 Biomedical Application ............................................................................................ 536
23.5 Conclusion ............................................................................................................................ 536 References ...................................................................................................................................... 539
the lamellar membrane. The term “elementary bril” refers to a component with a diameter of 3.5 nm that is composed of about 36 individual cellulose chains (Frey-Wyssling, 1954; Somerville, 2006; Mutwil et al., 2008). It seems that elementary brils are universal structural units of natural cellulose in all kinds of cellulose sources. Elementary brils assembled into larger units known as microbrillated cellulose (MFC) to reduce the free energy of the surface. Therefore, MFC has diameters in multiples of 3.5 nm (30-50 nm). Each microbril can also be considered as a exible semicrystalline strand with cellulose crystals linked along the microbrils axis by disordered amorphous domains. Microbrils then in turn are assembled into bers. Ultimately, ber aggregates form a lamellar structure in wood bers (Meier, 1962; Nj Heyn, 1969; Blackwell and Kolpak, 1975; Chinga-Carrasco, 2011; Chinga-Carrasco et al., 2011).
