Agriculture Reference
In-Depth Information
0.08
0.075
0.065
0.06
0.055
0.05
0.045
0.04
0.035
0.03
20
40
60
80
100
Density (kg/m
3
)
Fig. 17.3.
Variation in thermal conductivity of hemp wool as a function of density. Comparison with
a trial undertaken using predictions issuing from a self-consistent homogenization approach
(Cerezo, 2005).
Table 17.1.
Characteristic values of the materials.
influence the mechanical performance of the
wool. A very high resistance to traction is seen
(Fig. 17.4): the breaking point of hemp wool
with a density of 60 kg/m
3
and a thickness of
45 cm is 900 kN. It would therefore be possible
to hang a weight of 90 kg from a 9 cm wide
strip. This means that the installation and use of
these products is relatively easy and does not
necessitate any particular precautions. The high
degree of mechanical resistance does, however,
mean that this material is very tough to cut up!
The compression and extension tests of
hemp wool, as illustrated in Fig. 17.5, dem-
onstrate their marked elastic properties with
little residual distortion. It is therefore possible
to reach levels of compression of 60%. It
would appear, however, that above 60% the
friction between plant fibres results in some
significant permanent distortion. A compres-
sion of 70% will thus result in a permanent
distortion of 15%. In other words, a wool with
an initial thickness of 10 cm that is com-
pressed to 3 cm during conditioning will,
when installed and decompressed, have a
thickness of 8.5 cm.
Hemp
wool
Synthetic
wool
Air
Water
Density
ρ
(kg/m
3
)
1.2
1000
35
35
Thermal
conductivity
λ
(W/m/K)
0.025
0.602
0.047
0.041
Thermal
resistance
R = e/
λ
m
2
/K/W/)
4
0.2
2.1
2.4
They therefore must not be changed easily or
modified. That said, during conditioning, and
to reduce transport costs, these materials are
heavily compressed. The wool must be able to
withstand these compressive forces and recover
its original shape and geometry in order to
regain its properties. During installation, the
fibres are often placed under traction. Once
again, the wool must be able to resist such
abuses to preserve its performance.
Laboratory tests have been undertaken to
characterize the behaviour of these fibres dur-
ing compression and extension, as well as to
evaluate the traction resistance of hemp wool.
These experiments demonstrate that the
intrinsic properties of the hemp wool (high
traction resistance and mechanical 'power')
17.3.3
Areas of application
Among the main fields of use for hemp wool,
we can list the following:
