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1.4. CELLULOSE AND
ITS DERIVATIVES
1.4.1. General.
Cellulose is the most abundant biopolymer on the planet since it is the main
constituent of wood (40-45% of the dry weight). It is a major component of the
cell walls of plants, where it forms a composite with lignin and hemicelluloses.
Cellulose is also formed by some bacteria such as
Acetobacter xylinum
.
Cellulose is formed by CO
2
fixation (photosynthesis). Biomass from plants is
thus ‘CO
2
neutral’ since the CO
2
released by conversion of biomass to energy
can be recycled back to biomass (plants). The efficiency of the conversion is
currently a hot topic (for obvious reasons), and research on the biosynthesis,
structure, properties and degradation of cellulose is intense and competitive.
Cellulose degrading enzymes are continuously being tailored to obtain much
faster degradation (which is inherently slow – just think of the low rate of
rotting of wood). Another fascinating aspect is cellulose nanofibers, which
possess promising properties in bionanotechnology.
1.4.2. Chemical
structure
Cellulose has an extremely simple chemical structure, being a linear
(unbranched) polymer of exclusively 1
→
4 linked
β
-D-glucose (strictly
β
-D-
glycopyranose since glucose occurs in the common pyranose form).
Haworth-formula of cellulose:
O
OH
OH
O
CH
2
OH
O
OH
OH
O
CH
2
OH
O
OH
OH
O
CH
2
OH
O
OH
OH
O
CH
2
OH
O
HO
OH
OH
OH
CH
2
OH
H H
H
H
H
O
HO
OH
OH
OH
CH
2
OH
=
β
-D-glucose
C
O H
OH
H
H
OH
H
OH
H
CH
2
OH
HO