Environmental Engineering Reference
In-Depth Information
affordable furniture and kitchens. The smallest particle sizes, that is, wood flour,
are used for medium-density fibreboard (MDF), which has the advantage of show-
ing a smooth surface after cutting, avoiding the need for a plastic covering on the
edges (as particleboard does).
Urea-formaldehyde resins are used for applications in which the panel is not in
contact with water. For applications with a high level of humidity, phenol-formal-
dehyde resins are required. In all cases, free formaldehyde constitutes a dangerous
pollutant that is slowly released and can be particularly toxic in confined environ-
ments. Recent research has been carried out into the possibility of substituting this
type of resin by natural binders such as cross-linkable proteins [54, 55].
6.4.4.2
Wood Boards without External Binder
In this case, water is sprayed on sawdust instead of a synthetic binder. Hot-
pressing of the material is carried out to partially hydrolyse some macromolecules
contained in the wood, and thermally degrade some of the free sugars and other
small molecules. The degradation products contribute to the cohesion of the
particles.
Depending on the pressure applied, more or less rigid boards are obtained. The
boards of lowest density (0.15-0.5 kg m
-3
), processed with the lowest pressure,
are called insulation board. As the name indicates, they are used in housing for
thermal and phonic insulation of the walls and ceilings. In practice, they are used
alongside more rigid materials to obtain a stronger product.
If the pressure used in the fabrication is increased, the density of the product is
higher (0.5-1.45 kg m
-3
);
hardboard
is then obtained. This kind of board is used in
furniture parts in which the mechanical resistance required is not very high, such
as the back panel of inexpensive bookcases for example.
6.4.5
Materials for Construction
Apart from wood- and fibreboards, many agricultural products, by-products and
waste are now used in construction materials; these applications concern more
industrial applications, however. Although the scientific literature on this subject
is sparse, some studies and reviews have recently been published including a
paper [56] from the Visvesvaraya National Institute of Technology (India)
The types of material used in this domain include the following.
•
Insulation materials:
as a substitution for glass wool and polyurethane, which
are both of fossil origin and bear a high amount of grey energy, many natural
fibres are now used in commercial products (e.g. paper waste, hemp fibres,
wood fibres, palm leave fibres, etc.). Their use is mainly in fibre panels obtained
after carding and bounding with thermoplastic fibres but other methods are
possible, including wet projection or waste paper blowing.
