2 ABCs of Cellulose and Nanocellulose
Cellulose is the most abundant renewable polymer (Mokhena and John 2020)
produced by several organisms for a variety of functions, including structural
support, source of energy, and cell connection to form tissues. Globally, one billion
tons of cellulose are produced annually, of which 6 Â 10
9 tons are mainly used in the
paper, fiber, and material industry as well as in the chemical industry (Habibi et al.
2010). Plants contribute to the lion’s share of cellulose but can also be extracted from
sea animals, algae, fungi, amoebae, cellular slime molds, and certain bacteria.
Regardless of its origin, cellulose is a high-molecular-weight polysaccharide, composed of β-D-glucopyranose units linked together by β-1, 4 glucosidic bonds. Plant
cellulose is hierarchically assembled from elementary fibrils, which are in turn generally made of 18–24 or more cellulose macromolecules, associated through intraand inter hydrogen bonding and van der Waals forces (Nishiyama 2009; Fernandes
et al. 2011; Oehme et al. 2015; Okita et al. 2010). The elementary fibrils are stacked
together to form nanofibrils, which link together to form cellulosic fibers, typically
observed in the vascular systems of woody plants (Fig. 4.1). Cellulose contains a
highly disordered or amorphous zone and ordered crystalline regions. Cellulose
exists in six types of polymorphs, namely, cellulose I, II, III I , III II , IV I , and IV II , as
confirmed with nuclear magnetic resonance (NMR), infrared, and diffraction studies
(O’Sullivan 1997; Wada et al. 2004). While cellulose I is the native cellulose from
plant or microbial origin (Vander Hart and Atalla 1984; Sugiyama et al. 1991), other
polymorphs are produced either from native or various derivatives by chemical and
thermal treatments (Mahmud et al. 2019).
Nanocellulose, on the other hand, generally refers to nanosized cellulosic fibers
or cellulosic crystallites that could be extracted from multiple sources, such as
plants, bacteria, algae, and some sea animals, following top-down or bottom-up
strategies of nanomaterial synthesis. The nanoscale attributes of high surface area
and aspect ratio, quantum size effects, special morphology, amenability for a
plethora of chemical functionalization, and notable biocompatibility have conferred
a special niche to nanocellulosic materials in a wide gamut of applications. Based on
the recommendations of the Technical Association of the Pulp and Paper Industry
(TAPPI) and the relevant international organizations, nanocellulose has been classified into two categories: crystalline nanocellulose (CNCs) and cellulosic nanofiber
(CNFs) (Carpenter et al. 2015). Multiple nomenclatures exist for both crystalline
nanocellulose (also called nanocrystalline cellulose (NCC) and cellulose
nanowhisker (CNW)) and cellulose nanofiber (also called nanofibrillated cellulose
(NFC), nanofibrillar cellulose, and nanofibrous cellulose). The two types vary based
on the extraction process, cellulose source, and physico-mechanical properties,
especially with regard to dimensions, purity, and crystallinity. In addition,
nanocellulose can also be obtained from bacteria (bottom-up method), in particular
from Komagataeibacter xylinus (previously classified as Acetobacter or
Gluconacetobacter), with the ability to synthesize NC from low-molecular-weight
sugars and alcohols as starting materials (Vigentini et al. 2019; Gopu and Govindan
2018). Although bacterial nanocellulose has a chemical formula similar to plant4 Harnessing the Sustainable Bioresource, Cellulose at the Nanoscale for. . .
67
Cellulose is the most abundant renewable polymer (Mokhena and John 2020)
produced by several organisms for a variety of functions, including structural
support, source of energy, and cell connection to form tissues. Globally, one billion
tons of cellulose are produced annually, of which 6 Â 10
9 tons are mainly used in the
paper, fiber, and material industry as well as in the chemical industry (Habibi et al.
2010). Plants contribute to the lion’s share of cellulose but can also be extracted from
sea animals, algae, fungi, amoebae, cellular slime molds, and certain bacteria.
Regardless of its origin, cellulose is a high-molecular-weight polysaccharide, composed of β-D-glucopyranose units linked together by β-1, 4 glucosidic bonds. Plant
cellulose is hierarchically assembled from elementary fibrils, which are in turn generally made of 18–24 or more cellulose macromolecules, associated through intraand inter hydrogen bonding and van der Waals forces (Nishiyama 2009; Fernandes
et al. 2011; Oehme et al. 2015; Okita et al. 2010). The elementary fibrils are stacked
together to form nanofibrils, which link together to form cellulosic fibers, typically
observed in the vascular systems of woody plants (Fig. 4.1). Cellulose contains a
highly disordered or amorphous zone and ordered crystalline regions. Cellulose
exists in six types of polymorphs, namely, cellulose I, II, III I , III II , IV I , and IV II , as
confirmed with nuclear magnetic resonance (NMR), infrared, and diffraction studies
(O’Sullivan 1997; Wada et al. 2004). While cellulose I is the native cellulose from
plant or microbial origin (Vander Hart and Atalla 1984; Sugiyama et al. 1991), other
polymorphs are produced either from native or various derivatives by chemical and
thermal treatments (Mahmud et al. 2019).
Nanocellulose, on the other hand, generally refers to nanosized cellulosic fibers
or cellulosic crystallites that could be extracted from multiple sources, such as
plants, bacteria, algae, and some sea animals, following top-down or bottom-up
strategies of nanomaterial synthesis. The nanoscale attributes of high surface area
and aspect ratio, quantum size effects, special morphology, amenability for a
plethora of chemical functionalization, and notable biocompatibility have conferred
a special niche to nanocellulosic materials in a wide gamut of applications. Based on
the recommendations of the Technical Association of the Pulp and Paper Industry
(TAPPI) and the relevant international organizations, nanocellulose has been classified into two categories: crystalline nanocellulose (CNCs) and cellulosic nanofiber
(CNFs) (Carpenter et al. 2015). Multiple nomenclatures exist for both crystalline
nanocellulose (also called nanocrystalline cellulose (NCC) and cellulose
nanowhisker (CNW)) and cellulose nanofiber (also called nanofibrillated cellulose
(NFC), nanofibrillar cellulose, and nanofibrous cellulose). The two types vary based
on the extraction process, cellulose source, and physico-mechanical properties,
especially with regard to dimensions, purity, and crystallinity. In addition,
nanocellulose can also be obtained from bacteria (bottom-up method), in particular
from Komagataeibacter xylinus (previously classified as Acetobacter or
Gluconacetobacter), with the ability to synthesize NC from low-molecular-weight
sugars and alcohols as starting materials (Vigentini et al. 2019; Gopu and Govindan
2018). Although bacterial nanocellulose has a chemical formula similar to plant4 Harnessing the Sustainable Bioresource, Cellulose at the Nanoscale for. . .
67