Agriculture Reference
In-Depth Information
Fig. 13.1.
Hemp fibre before treatment.
cotton, bagasse, wheat straw, sisal, abaca, reed
and other exotic species.
The world hemp paper production was
around 120,000 t/year, which was about
0.05% of the world paper production volume.
Hemp pulps are generally blended with
other (wood) pulps for paper production.
The composition of the woody core is simi-
lar to a hardwood but is generally considered as
waste and is used in other applications.
Compared to all annual plants used in
papermaking, hemp bast fibre is one of the
longest. The woody core fraction generates
one of the shortest fibres (Fig. 13.2).
13.3 Hemp Composition
13.3.1
Raw material structure
The stem of the plant is composed of two
fractions:
30% bast fibres
Hemp is composed mainly of lignin, hemicel-
luloses and cellulose.
The separation of the fibres is carried out
following the paper pulping processes, consisting
of dissolution of the lignin and part of the hemi-
celluloses responsible for the linkages between
fibres (which give the stem its rigid structure).
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•
The chemical composition of the different
fractions of the plant (Table 13.1) indicates
that the entire hemp stalk can be used for
the production of cellulose fibres. The com-
parison with hardwood and softwood shows
similar composition, but the bast fraction
has the higher A-cellulose content available
for papermaking. The low lignin content of
the bast fraction is interesting because of the
lower chemical required in the cooking
processes.
70% woody core.
Lignin
Lignin is a polymer of complex and varied
propylphenol units. Figure 13.3 illustrates the
structure of lignin. Alkali can partially depo-
lymerize this molecule, leading to soluble
compounds.
