144
Chapter 7 · From Wood to Pulp - Cellulose
7
organics, such as carbonates and silicates, as well
as resins, waxes, pigments, pectins and turpentine oils.
The polymer chain of cellulose is shown in
. Fig. 7.1. If the unbranched chain of cellulose
is to be drawn in a “space-saving” manner, a
representation is chosen - as in . Fig. 7.1 - in
which oxygen atoms in the ring of the glucose
units are located alternating in the front and
back of the structure. This results in cellobiose
units consisting of two glucose units linked
by a glycoside bond. Cellulose consists of
500–5000 glucose units and thus has molecular weights between 200,000 and one Mio.
Dalton. Cellulose is insoluble in water as well
as in almost all organic solvents. An “activation” of cellulose is possible by aqueous sodium
hydroxide solution.
The molecular chains of cellulose can
arrange via hydrogen bonding to form crystalline segments. A cellulose chain can therefore
pass through several crystalline and amorphous
regions. Several molecular chains form a microfibril which is up to several micrometers long
and has a cross-section of 10–100 nm. Several
microfibrils bundle to form macrofibrils and
these finally combine to form cellulose fibers.
Chapter Timetable
5 You will learn the composition of wood
and how to extract cellulose from wood.
5 The paper production as the most
important use of cellulose is explained.
5 We discuss the derivatization of cellulose
to fibers, esters and ether.
7.1 Occurrence and Production
of Cellulose
Cellulose is a polysaccharide in which glucose
units are linked together in a β-1,4-glycoside
manner. It is part of the cell wall of many plants,
e.g. jute, flax and hemp. The seed hairs of the
cotton plant consist almost entirely of cellulose;
grasses contain up to 30% of it. However, the
main source of cellulose is wood, which contains
up to 50% cellulose, depending on the type of
wood. This makes cellulose the most abundant
biopolymer in nature (7 Sect. 19.2). The typical composition of the most important cellulose
sources is given in . Table 7.1. The main components of wood are cellulose, hemicelluloses and
lignin; important secondary components are in
. Table 7.1 Composition of important cellulose sources (based on dry matter in % by weight)
Plant
Cotton
Jute
Flax
Hemp
Wood
Cellulose
93
72
72
74
40–50
Hemicellulose
5
14
18
18
10–20
Lignin
0
13
2
4
20–30
Secondary components
2
2
8
4
5–10
Chapter 7 · From Wood to Pulp - Cellulose
7
organics, such as carbonates and silicates, as well
as resins, waxes, pigments, pectins and turpentine oils.
The polymer chain of cellulose is shown in
. Fig. 7.1. If the unbranched chain of cellulose
is to be drawn in a “space-saving” manner, a
representation is chosen - as in . Fig. 7.1 - in
which oxygen atoms in the ring of the glucose
units are located alternating in the front and
back of the structure. This results in cellobiose
units consisting of two glucose units linked
by a glycoside bond. Cellulose consists of
500–5000 glucose units and thus has molecular weights between 200,000 and one Mio.
Dalton. Cellulose is insoluble in water as well
as in almost all organic solvents. An “activation” of cellulose is possible by aqueous sodium
hydroxide solution.
The molecular chains of cellulose can
arrange via hydrogen bonding to form crystalline segments. A cellulose chain can therefore
pass through several crystalline and amorphous
regions. Several molecular chains form a microfibril which is up to several micrometers long
and has a cross-section of 10–100 nm. Several
microfibrils bundle to form macrofibrils and
these finally combine to form cellulose fibers.
Chapter Timetable
5 You will learn the composition of wood
and how to extract cellulose from wood.
5 The paper production as the most
important use of cellulose is explained.
5 We discuss the derivatization of cellulose
to fibers, esters and ether.
7.1 Occurrence and Production
of Cellulose
Cellulose is a polysaccharide in which glucose
units are linked together in a β-1,4-glycoside
manner. It is part of the cell wall of many plants,
e.g. jute, flax and hemp. The seed hairs of the
cotton plant consist almost entirely of cellulose;
grasses contain up to 30% of it. However, the
main source of cellulose is wood, which contains
up to 50% cellulose, depending on the type of
wood. This makes cellulose the most abundant
biopolymer in nature (7 Sect. 19.2). The typical composition of the most important cellulose
sources is given in . Table 7.1. The main components of wood are cellulose, hemicelluloses and
lignin; important secondary components are in
. Table 7.1 Composition of important cellulose sources (based on dry matter in % by weight)
Plant
Cotton
Jute
Flax
Hemp
Wood
Cellulose
93
72
72
74
40–50
Hemicellulose
5
14
18
18
10–20
Lignin
0
13
2
4
20–30
Secondary components
2
2
8
4
5–10