Civil Engineering Reference
In-Depth Information
OH
OH
OH
O
H
O
O
H
H
H
H
H
H
O
OH
H
OH
H
H
OH
O
n
OH
OH
HO
OH
H
OH
H
OH
OH
H
Figure 5.1
Chemical structure of cellulose.
5.2.2
Structure
Cellulose consists of a linear homopolysaccharide composed of β-D-glucopyranose
units linked together by β-1-4-linkages [11]. Each monomer bears three hydroxyl
groups. It is therefore obvious that these hydroxyl groups and their ability to form
hydrogen bonds play a major role in directing the crystalline packing and also gov-
erning the physical properties of cellulose [12]. Solid cellulose has a semicrystalline
structure, i.e., consists of highly crystalline and amorphous regions. Cellulose forms
slender rodlike crystalline microi brils. h e crystal structure (monoclinic sphenodic)
of naturally occurring cellulose is known as cellulose I. Cellulose is resistant to strong
alkali (17.5 wt%) but is easily hydrolyzed to water-soluble sugars by acids. Cellulose is
relatively resistant to oxidizing agents.
5.2.3
Properties
Because of the unique structural hierarchy derived from biological origin, cellulose
i bers exhibit attractive properties like high specii c strength and modulus, low density
[13] . h ey are also inexpensive, biodegradable and renewable in nature. Recently the
demand for environmentally benign materials has increased the use of such natural i ll-
ers in various polymer composites [14, 15]. Lignocellulosic i bers like jute, l ax, hemp,
kenaf, etc., grow abundantly in dif erent parts of the world and are used as the source
for extracting micro/nano crystalline cellulose, which can be further used as reinforce-
ment in polymer matrix composites.
5.2.4
Cellulose Nanoi llers
Cellulosic nanoi llers are composed of nanosized cellulose having high aspect ratio
with typical lateral dimensions of 4 nm to 20 nm and longitudinal dimension ranging
between tens of nm to several microns [16]. Recently cellulose nanoi llers have received
a signii cant attention in materials science and engineering because of its facile and
large scale production possibilities as well as its interesting and applicable rheological
properties [10, 17]. Due to its high mechanical strength, ease of chemical modii ca-
tion and high surface to volume ratio, cellulose nanoi llers have been increasingly used
as reinforcement in various matrix materials with high mechanical ei ciency of stress
transfer in the composites [10, 18]. Moreover, the high surface area and functionality of
cellulose nanoi llers can also be used as template for polymerization, which then could
create the ability of making highly reactive surface for a wide range of applications.
