Chemistry Reference
In-Depth Information
CH
2
OH
CH
2
OH
O
O
H
H
H
H
H
H
OH
H
OH
H
O
O
O
H
OH
H
OH
(a)
Amylose -
α
-1, 4 linkage
n
CH
2
OH
CH
2
OH
O
O
H
H
H
H
O
O
H
O
OH
OH
H
H
H
H
OH
H
OH
(b)
Cellulose -
β
-1, 4 linkage
n
FIGURE 13.1
Two types of glucose linkages (a)
-1,4 (cellulose). Each star
denotes the anomeric carbon used to determine the position of the ether bond (down
position, α, or up position β).
α
-1,4 (amylose) and (b)
β
differences in solubility
[5,9]
. The ratio of amylopectin to amylose in natural
starch varies based on plant species; however, amylopectin is always more abun-
dant. Amylose is mainly linear in structure which can have a degree of polymeri-
zation as high as 600
[5]
. Amylose resembles cellulose apart from the
α
-1,4
linkage between glucose rings. Amylopectin is a branched polymer with
-1,6
branch points
[5]
. Amylopectin contains 4-6% of branch points which is a signifi-
cant difference from the structure of amylose, a linear chain
[4,9]
. The branches
in amylopectin have been classified into A-, B-, and C-chains, where A-chains do
not carry any other chains, B-chains carry one or more chains, and the C-chain is
the original chain carrying the sole reducing end
[9]
. Starch is used in a wide
range of commercial products from filler in toothpaste to food products as well as
in plastics. The processing and manufacturing of starch plastics will be discussed
along with blending of starch with other polymers in
Section 13.3
.
α
13.2.2.2
Cellulose
Cellulose is the most abundant biopolymer and is the largest organic carbon
source on earth. Cellulose is synthesized by plants and makes up a large portion
of a plant's chemical structure. The content of cellulose in plants varies from
90% in cotton to 40
50% in wood. Cellulose is a hydrophilic linear polymer
