Civil Engineering Reference
In-Depth Information
to cellulose-Iβ or cellulose-I to cellulose-II. In particular, the processes of regenera-
tion and mercerization with alkali yield cellulose-II. In chemical pulps, the total cel-
lulose-I content, i.e., the crystallinity, is on the order of 55% [10]. Other polymorphs
of cellulose-II, cellulose-III
I
, cellulose-III
II
, cellulose-IV
I
and cellulose-IV
II
, have dif er-
ent hydrogen-bonding networks and molecular orientations. Cellulose-II is the most
extensively studied crystalline structure besides cellulose-I and can be formed from
cellulose-I via treatment with aqueous sodium hydroxide (mercerization) or by the dis-
solution of the cellulose and its subsequent precipitation/regeneration. Cellulose-II has
some improved material properties compared to cellulose-I that make it preferable for
some textiles and pulp-derived materials. Processing cellulose-I and cellulose-II with
ammonia yields cellulose-III
I
and cellulose-III
II
, collectively referred to as cellulose III.
As reviewed by O'Sullivan [11] the structural dif erences between cellulose-I and cellu-
lose-II are commonly studied. It is now accepted that cellulose-I chains are directed in
a parallel up arrangement with all the non-reducing ends on one side and the reducing
(aldehyde) ends on the other. In contrast, the cellulose-II chains have an antiparallel
arrangement. Another dif erence involves the conversion of the
gt
conformation of the
hydroxymethyl groups in cellulose-I to a
gt
conformation in cellulose-II [12] . h e crys-
tal structure of cellulose-I also has a higher elastic modulus than that of cellulose-II,
138 and 88 GPa, respectively [13].
12.3
Applications of Cellulose
Owing to its diverse properties, cellulose and modii ed cellulose i nds widespread
applications. h e chief application of cellulosic i bers is in the textile industry. Both
natural and manufactured i bers are commonly used for nonwoven textiles. Cotton,
rayon, lyocell and linen are commonly used to make fabrics. Regenerated cellulosic
i bers also i nd use in the textile industry. Regenerated cellulose is made by dissolving
pulp in viscose. Because cellulose is a biopolymer, it i nds application in biomedical
applications. Microcrystalline cellulose is used as inactive i ller in drugs. Cellulose also
i nds application in the food and beverage industry. It is a commonly used emulsi-
i er and thickening agent. Cellulose can also be converted into other useful materials
like cellophane, nitrocellulose, celluloid, carboxy methyl cellulose, etc. h ese i nd wide
application in various industries. Nitrocellulose is a main ingredient in smokeless gun
powder. Cellophene is a major constituent in adhesives. Carboxy methyl cellulose and
methyl cellulose are commonly used in the food processing industry as a thickening
agent and an emulsii er. Due to the presence of strong hydrogen bonding in cellulose,
it can be used on the basis of its strength for the building and construction industry.
Cellulose treated with boric acid can be used as a i re retardant material. In recent
times, it has been reported that cellulose can also be converted to biofuels.
12.4
Electrospinning
Electrospinning is a simple and ei cient method to prepare polymer membranes
with fully interconnected pore structure and micron-sized i bers. h e electrospinning
technique has been generally considered as a variant of the electrostatic spraying or
