Civil Engineering Reference
In-Depth Information
16.1
Historical Overview
Cellulose is the most abundant organic polymer on Earth with the formula (C
6
H
10
O
5
)
n, a polysaccharide consisting of a linear chain of several hundred to over ten thousand
β
(1→4)
linked D-glucose units [1]. It is an important structural component of the primary
cell wall of green plants, many forms of algae and the oomycetes. Some species of bac-
teria secrete it to form bioi lms [2]. Many natural materials such as cotton, wood, etc.,
are enriched with cellulose. h e cellulose content of cotton i ber is 90%, that of wood is
40-50% and that of dried hemp is approximately 45%. It was i rst isolated from wood
in 1885 by Charles F. Cross and Edward Bevan at the Jodrell Laboratory of the Royal
Botanic Garden, Kew, London. In 1898, Charles Frederick Cross, Edward John Bevan
and Clayton Beadle discovered the process for manufacturing cellulose i lms from vis-
cose. However the commercial production of cellulose was started in 1913 at the 'La
Cellophane SA factory in Bezons, France, when Dr. Jacques Brandenberger developed
thin transparent cellulose i lm.
Cellulose i lm can be made by dissolving cellulose i bers into a solution and cast-
ing it. Cellophane is a well-known cellulosic i lm made with cellulose xanthate solu-
tion. Scheme 16.1 shows the chemical reaction for cellulose xanthate process. Cotton
pulps are saturated with sodium hydroxide and allowed to steep for enough time for
the caustic solution to penetrate the cellulose and convert into the sodium cellulose.
At er the pressing, shredding and aging process the solution is treated with gaseous
cabon disuli de to form xanthate ester groups. h en the solution is allowed to stand for
a period of time to ripen. At er the solution is made it is extruded through a nozzle into
two sulfuric acid baths, followed by a drying process. Once the solution is coagulated
in the acid bath it is converted back to pure white cellulose. A roller system conveys the
i lm via these baths and washing and drying processes are followed by a reel system.
(C
6
H
10
O
5
)n + nNaOH → (C
6
H
9
O
4
)n + nH
2
O: Sodium cellulose, swelled cellulose
(C
6
H
9
O
4
)n + nCS
2
→ n(SC-OC
6
H
9
O
4
)n: Sodium cellulose xanthate
SNa
n(SC-OC
6
H
9
O
4
)n + H+ → (C
6
H
10
O
5
)n : Redgenerated cellulose
SNa
Scheme 16.1
Chemical reaction for cellulose xanthate process.
h e primary use of cellulose i lm has been for wrapping purposes. h e past years
have witnessed a renewed interest in cellulose research and application sparked mostly
by technological interests in renewable raw materials and more environmentally-
friendly and sustainable recourses. It has been estimated that the yearly biomass pro-
duction of cellulose is 1.5 tons, making it an inexhaustible source of raw material for
environmentally-friendly and biocompatible products [3]. Cellulose derivatives are used
for coatings, laminates, optical i lms, pharmaceuticals, food, and textiles. Numerous
new applications of cellulose take advantage of its biocompatibility and chirality for
the immobilization of proteins and antibodies and for the separation of enantiometric
molecules, as well as the formation of cellulose composite with synthetic polymers and
biopolymers. h is chapter basically discussed on the medical applications of cellulose.
