Agriculture Reference
In-Depth Information
Table 13.1.
Chemical composition of hemp.
Whole plant (%)
Bast (%)
Softwood (%)
Hardwood (%)
Holocellulose
80-83
81-86
75-85
60-70
Alpha-cellulose
50-55
65-67
58-61
45-55
Lignin
17-20
8-10
23-26
20-25
Ash
2-4
3-5
0.3-0.4
0.2-0.1
Solvent extract
2-3
1-2
0.1-0.5
2-13
Water soluble extract
5-8
9-11
2-3
3-13
Fibre (mm)
0
2
4
6
8
10
Hemp bast
Flax
Abaca
Cotton (linters)
Sisal
Kena
Jute
Softwoo
Reed
Bagasse
Wheat
Hemp core
Hard wood
Bamboo
Fig. 13.2.
Comparison of fibre lengths of annual plants.
Cellulose
elements. They are linked to the lignin and
play an important role in the elimination of
lignin.
Cellulose is a carbohydrate polymer built of
glucose units (Fig. 13.4). It is less sensitive to
cooking conditions compared to lignin.
Cellulose is the most important compo-
nent of the fibre for papermaking. The fibre
structure is built of cellulose chains, constitut-
ing protofibrils made of microfibrils (themselves
made of macrofibrils). The fibre structure is
illustrated in Fig. 13.5.
13.3.2
Structure of a fibre
A fibre is composed of several cylindrical walls,
as described in Fig. 13.6. In the figure: M rep-
resents the middle lamella, composed mainly
of lignin (70%) and hemicelluloses; P repre-
sents the primary wall, which is very thin (0.1
to 0.5
Hemicelluloses
m) and composed of lignin (50%),
pectins and hemicelluloses; and S represents
the secondary walls, which are mainly cellulose
containing and the thickness of the walls are
0.1-0.2
μ
These are sugar chains of low polymerization
degree and different compositions, such as dif-
ferent hexoses and pentoses.
These compounds are easily hydrolysable
by alkali or acid solutions, generating soluble
μ
m, 0.5-8
μ
m and 0.07-0.1
μ
m for
S1, S2 and S3, respectively.
