IV. Native cellulose can be found in two crystalline phases, known as Iα e Iβ (Atalla
and Vander Hart 1984).
The average molecular mass of celluloses from sugarcane bagasse is around
157.800–168.400 g mol
À1 and the cellulose fibers vary from 1.0 to 1.5 mm in
size. One unit of cellulose, which is called elementary fibril, goes through selfassembly, so as to compose microfibrils that can be englobed by hemicellulose
matrices, in order to produce macrofibrils, becoming resistant to chemical and
enzymatic degradation (Bezerra and Ragauskas 2016). The average polymerization
degree of cellulose from sugarcane bagasse varies from 974 to 1039 glucose
monomers (Bian et al. 2014).
The polymerization degree refers to the amount of glucose monomers present in
the chain, besides being able to influence in how efficient the enzymatic hydrolysis
is. The natural structure of cellulose is firstly resistant to enzymatic hydrolysis, a
condition that is a result of its high crystallinity and polymerization degree; moreover cellulose has the characteristic to be insoluble in water (Sant’anna et al. 2014).
2.6
Hemicelluloses
Hemicellulose compound is the second most abundant renewable polysaccharide in
the planet, only behind cellulose (Sun et al. 2001; Peng 2009). They are classified as
heterogeneous polysaccharides, found in big quantities in wood and perennial plants,
forming the plant cell wall, along with cellulose and lignin (Peng 2009). However,
hemicelluloses are closely associated with celluloses via physical and hydrogen
connections; meanwhile, when it comes to lignin, they are gathered by covalent
connections, which are characterized by sharing of one or more pairs of electrons
between atoms, being them mainly R(radical)-benzyl and ether connections
(Freudenberg 1965; Peng 2009).
In general, hemicelluloses are polysaccharides composed of 80 to 200 units of
low molecular mass sugar residues. The general chemical formula for hemicelluloses
is (C5H8O4) and they are organized into oses and hexoses (Paszner 1988). Among
pentoses, D-xylose, L-arabinose, and L-rhamnose are highlighted, and among
hexoses more common are the following sugars: D-glucose, D-mannose, and
D-galactose. Hemicelluloses may also contain uronic acids, being the most important ones the 4-omethyl-D-glucoronic and the D-galacturonic acids (Timell 1964).
In annual plants, the most abundant hemicellulose kind is arabinoxylan, which
contains D-xylopyranosyl molecules connected by β-(1-4) glycoside bonds. The
hemicellulose from the sugarcane bagasse, for example, is defined as L-arabino(4-O-methyl-D-glucuron)-D xylan (Brienzo et al. 2009). α-L-arabinofuranose and
α-D-glucuronic acid (or its derivative 4-O-methyl) molecules are connected to them,
in positions C-2, C-3, or both, as simple unit chains (Macgregor and Fincher 1993;
Peng 2009). A natural compound, xylan, contains O-acetyl groups in some of the
hydroxyl groups, at carbons 2 or 3, in its main chain (Peng 2009).
2 Biofuels Generation Based on Technical Process and Biomass Quality
45
and Vander Hart 1984).
The average molecular mass of celluloses from sugarcane bagasse is around
157.800–168.400 g mol
À1 and the cellulose fibers vary from 1.0 to 1.5 mm in
size. One unit of cellulose, which is called elementary fibril, goes through selfassembly, so as to compose microfibrils that can be englobed by hemicellulose
matrices, in order to produce macrofibrils, becoming resistant to chemical and
enzymatic degradation (Bezerra and Ragauskas 2016). The average polymerization
degree of cellulose from sugarcane bagasse varies from 974 to 1039 glucose
monomers (Bian et al. 2014).
The polymerization degree refers to the amount of glucose monomers present in
the chain, besides being able to influence in how efficient the enzymatic hydrolysis
is. The natural structure of cellulose is firstly resistant to enzymatic hydrolysis, a
condition that is a result of its high crystallinity and polymerization degree; moreover cellulose has the characteristic to be insoluble in water (Sant’anna et al. 2014).
2.6
Hemicelluloses
Hemicellulose compound is the second most abundant renewable polysaccharide in
the planet, only behind cellulose (Sun et al. 2001; Peng 2009). They are classified as
heterogeneous polysaccharides, found in big quantities in wood and perennial plants,
forming the plant cell wall, along with cellulose and lignin (Peng 2009). However,
hemicelluloses are closely associated with celluloses via physical and hydrogen
connections; meanwhile, when it comes to lignin, they are gathered by covalent
connections, which are characterized by sharing of one or more pairs of electrons
between atoms, being them mainly R(radical)-benzyl and ether connections
(Freudenberg 1965; Peng 2009).
In general, hemicelluloses are polysaccharides composed of 80 to 200 units of
low molecular mass sugar residues. The general chemical formula for hemicelluloses
is (C5H8O4) and they are organized into oses and hexoses (Paszner 1988). Among
pentoses, D-xylose, L-arabinose, and L-rhamnose are highlighted, and among
hexoses more common are the following sugars: D-glucose, D-mannose, and
D-galactose. Hemicelluloses may also contain uronic acids, being the most important ones the 4-omethyl-D-glucoronic and the D-galacturonic acids (Timell 1964).
In annual plants, the most abundant hemicellulose kind is arabinoxylan, which
contains D-xylopyranosyl molecules connected by β-(1-4) glycoside bonds. The
hemicellulose from the sugarcane bagasse, for example, is defined as L-arabino(4-O-methyl-D-glucuron)-D xylan (Brienzo et al. 2009). α-L-arabinofuranose and
α-D-glucuronic acid (or its derivative 4-O-methyl) molecules are connected to them,
in positions C-2, C-3, or both, as simple unit chains (Macgregor and Fincher 1993;
Peng 2009). A natural compound, xylan, contains O-acetyl groups in some of the
hydroxyl groups, at carbons 2 or 3, in its main chain (Peng 2009).
2 Biofuels Generation Based on Technical Process and Biomass Quality
45