Agriculture Reference
In-Depth Information
natural colour or self-coloured. Moulders will also have the choice of polymeric
composite resins with wood fibre. Excellent products can be made with these new
types of resins.
12.4.2 Thermosetting Polymeric Composite Resins
'Rice hull ash' is a general term describing all types of ash produced from burning rice
husks used in various operations (e.g., steam-boiler fuel in agricultural projects). The
nature of the ash produced depends on the burning conditions of rice husks. The silica
in the ash undergoes structural transformations depending on the conditions, such as
the duration and temperature of the burning process. The resulting ash will be of two
types: (i) black and coarse powder, and (ii) grey and fine powder. Rice husks are high
in ash compared with other biomass fuels. In the form of ash, the silica content can
be ≥70-80%, highly porous and lightweight. This ash is absorbent and its insulating
properties are useful for many industrial and building construction applications.
Another use is the extraction of silica from rice hull ash for the manufacture of
sodium silicate for adhesives.
Initially, compression-moulded products were made by virgin thermosetting polymer
resins. Over the years, this trend has changed to the use of composites. Composite
boards are commonly produced by combining a fibrous material (e.g., wood chips
or flakes) as the reinforcement and a thermosetting synthetic resin (e.g., urea-
formaldehyde) as the polymer matrix and curing the mass under heat and pressure.
Further developments in this trend have produced composite resins with other
thermosetting resins, such as phenol formaldehyde and melamine formaldehyde,
combined with rice hull ash, as suitable for compression moulding. The ratio of
polymer matrix to the reinforcing constituents depends on the end-product application.
Many large parts can be made using these thermosetting composites with rice hull
ash, but one important application is composite boards as walls and floors in the
construction of buildings (enhanced strength and moisture resistance). They can also
be used in the manufacture of furniture and many industrial applications.
12.5 Dangers and Safety Information
In general, compression-moulding machines are very large and dangerous if used
inappropriately. These machines usually have safeguards that are activated if a part
malfunctions. The safeguards must be installed appropriately, maintained regularly,
and the heating systems checked often. Because the moulds mostly work with
thermosetting plastics, the products can come out of the mould at high temperatures.
Precautions must be taken at the time of part removal to prevent burns to operators.
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