Agriculture Reference
In-Depth Information
a)
2000
b)
3500
Hemp
Cotton
3000
1500
2500
2000
1000
1500
1000
500
500
0
0
0
20000
40000
60000
0
100
200
300
400
Cross-sectional area, μm²
Cross-sectional area, μm²
c)
2500
1200
d)
Ramie
Sisal
1000
2000
800
1500
600
1000
400
500
200
0
0
0
20.000
40.000
60.000
80.000
0
500
1000
1500
Cross-sectional area, μm²
Cross-sectional area, μm²
Fig. 10.12.
Young's modulus versus cross-sectional area for (a) cotton, (b) hemp, (c) flax and (d) sisal.
In contrast to this, the length of reinforcing
elements in the injection moulding process
must not exceed a few millimetres, but must still
be above the critical length. Moreover, natural
fibres undergo a considerable amount of ther-
mal and mechanical degradation during injec-
tion moulding. Joseph
et al
. (2003) noticed a
fibre shortening of up to 60% for melt-mixed
short sisal fibres in a matrix of polypropylene.
the fibre bundles, while the distribution of the
more strongly retted flax B is narrower. For
cotton, the fineness is very close to a normal
distribution, indicating measurement of mainly
single fibres.
Fineness plays an important role for fibre-
reinforced materials, since the surface in con-
tact with the matrix increases with finer fibres
or fibre bundles. By increasing the contact
surface between the fibres and the matrix, the
stress transfer into the fibres can be improved.
In contrast to natural fibres constituted of sin-
gle fibres like cotton, bast fibre bundles can be
opened during processing due to shear effects.
For this reason, the fineness of bast fibre
bundles after processing can decrease down
to the fineness distribution of single fibres.
10.3.6
Fineness (fibre width)
The results of fineness measurement by means
of the Fibreshape system are presented in
Table 10.6 and Fig. 10.15. The factors influ-
encing the fineness of natural fibres are, for
example, the variety, the method and the
degree of separation. Especially in the case of
bast fibre bundles, fineness can vary depending
greatly on the degree of retting, as the flax vari-
eties in Table 10.6 demonstrate quite clearly.
The distribution of the values for hemp and flax
A indicates an uneven separation degree of
10.4 Integrated Quality
Management for Hemp
Integrated quality management for hemp
fibres is discussed to describe the fibre bundle
