Agriculture Reference
In-Depth Information
1
Introduction
1.1 History of Composite Materials
In ancient times, natural wood from trees and plants (e.g., palms and bamboo)
were the 'natural' composite materials used by mankind, followed by straw and
mud in the production of bricks and wattle by the Egyptians for the construction of
buildings. As the needs of humans widened, other composite materials (e.g., papyrus;
plywood; volcanic sands; lime mortars; and combinations of paper and glues) were
used. Concrete began to be used 25 BC and, as time progressed, the natural polymer
shellac began to be employed until the birth of the first 'plastic': bakelite.
Many 'developing' countries produce huge quantities of agricultural residues and
plastic wastes but their uses have been small compared with the large volumes
produced, thus causing extensive pollution to the environment. Some of the major
agricultural residues are rice husks (hulls); coffee husks; coir pith; jute sticks; bagasse;
groundnut shells; mustard stalks; rice stalks; and sawdust. The major plastic wastes are
films, bottles, parts and containers. Apart from the problems of collection, transport,
storage and handling, the direct burning of loose biomass in conventional grates is
associated with very low thermal efficiency and widespread pollution. To some extent,
plastic wastes are recycled and re-used but two of the major constraints have been
the limited number of times they can be recycled and the lack of bio-degradation in
landfill sites.
Historically, agricultural biomass wastes have been used as important energy sources in
industrial and domestic settings. These have been used for heating; cooking; lighting;
insulation; composites; and fuel for steam boilers. Plastic wastes have been recycled
and fed back into production on a limited basis. Agricultural wastes are being used
ideally as briquettes; logs; chips; and ash. In the manufacture of versatile briquettes
in various shapes and sizes, two main methods have been used: ram/piston press
and extrusion screw press. Both processes have their merits and demerits but, over
the years, it has become universally accepted that screw-pressed briquettes are far
superior in terms of storability and combustibility. Worldwide, both technologies
are being used for the briquetting of sawdust and other agricultural residues. The
importance of biomass briquettes as a substitute fuel for wood, coal and lignite is
well recognised, but numerous limitations with regard to machinery and production
may be the reasons for the slow expansion in this sector.
