Civil Engineering Reference
In-Depth Information
fire-resistant chemical treatment is often applied to vegetable fibres to resist heat
and increase their combustion property. However, although vegetable fibres are
not naturally combustion resistant, they commonly contain high amounts of silica,
which could be beneficial for fire retardancy applications (Ardanuy et al.
2012
).
4.4 Hygroscopic Properties
Vegetable fibres are very hygroscopic generally and they can absorb or release
moisture in response to their environment (Patel et al.
2012
). This property is
especially favoured for winter season when low indoor air humidity is presented
for a long period. However, high moisture level in vegetable fibre can have
negative effects and health risk.
Cellulose and hemicellulose in vegetable fibre contribute largely to the high
moisture absorption, since they absorb water as hydroxyl groups held by hydrogen
bonding within the fibre cell wall. This leads to a fibre swelling which can cause
the changes of hygroscopic nature of the cell wall leading to dimensional insta-
bility and poor mechanical and thermal properties (Rowell
1992
). As the thermal
conductivity increases with increasing moisture, thermal losses become higher and
insulating properties are poorer. High moisture absorption is also prone to
microbiological growth (Bisanda and Ansell
1992
) and increases risks to the
environment or human health. Controlling the moisture content of fibrous material
is essential for manufacturing processors and buildings. The vegetable fibres
should always be controlled since moisture into the material during processing
procedures is inevitable. Similarly, accurately identifying and control moisture
levels in fibreous insulation in buildings is paramount in order to ensure healthy
buildings.
Rode (
1998
) conducted an investigation into the hygrothermal behaviour of
wall constructions and the occupied spaces when an organic insulation material,
such as vegetable fibres and animal wool, was used to verify the common belief
that ''a vapour barrier is not needed when using organic insulation materials'' and
''organic insulation materials have a stabilizing effect on the indoor humidity''.
The analyses revealed interesting results. Not surprisingly, it shows that unless
there is no vapour retarder or other material between the insulation layers of the
wall and the adjacent space, the hygroscopic capacity of the insulation material
cannot act as a buffer for the indoor relative humidity level. Moisture diffusion
through the wall might desiccate the room by a small amount under winter con-
ditions in a Nordic climate if there is little or no vapour diffusion resistance
between the insulation and the indoor space. Furthermore, the same conditions
may cause high humidity levels in the exterior wall leading to fungal attack on
wood-based materials that are in contact with the insulation.
Based on Finnish and Swedish sources, some of the commonly used vegetable
fibres in Finland and Sweden are given in Table
5
.(
http://www.nordicnaturfibre.se/
