Agriculture Reference
In-Depth Information
3.1.2 Principles of Polymeric Composite Extruded Profiles
In principle, profiled extrusions can be made from the already available composite
resins or by starting from scratch. In the latter scenario, the rice hulls are made into
a powder form, dried and then compounded with selected polymers with additives,
with all operations being carried out in one production line.
Use of these profiled extrusions was intended originally to elicit a better material
with improved properties for decking and outdoor applications. However, due to
the versatility of the material, its uses are now expanding into other areas. This
process will basically be a complete extrusion line consisting of drying (rice hulls),
mixing with polymer, extrusion, cooling of extrudate, haul-off and cutting to desired
lengths. A manufacturer will have the option of using one of these complete online
operations or starting with the already compounded resins in pellet form, in which
case the machinery costs will be much less. In China rapid developments are taking
place with these types of extruded profiles. While maintaining the basic principle of
composites, and by varying the additives used, many products are being made that
have a wide range of applications, such as building construction and furniture.
3.1.3 Principles of Polymeric Composites in Injection Moulding
Injection moulders have been using standard polymers and plastic-recycled materials.
Moulders have been experiencing frequent increases in the prices of raw materials, which
limits profitability. The advent of polymeric composite resins in pellet form is starting
to ease this problem. At the beginning, processors were cautious in using these new
resins but, with time, they are now beginning to use them with confidence. In principle,
use of these composite resins is more or less the same as for using standard resins. The
same machines can be used but with slightly different temperatures, injection time and
cooling time. Due to lower amount of polymer in the resin, the distinct advantages
are: lower melt temperatures, shorter dwell time (cooling), lighter part weights and
lower power consumption. These factors lead to lower costs of the injection cycles
in addition to lower material costs. However, one disadvantage may be the limitation in
wall thicknesses, and very thin walls may not be possible due to the presence of fibres.
3.1.4 Principles of Polymeric Composites in Compression Moulding
Polymeric composite resins can be used readily in compression moulding. The
principle of compression moulding in plastics is the introduction of a plastic resin
into the bottom-half of a horizontal pre-designed mould cavity with the top-half
clamped hydraulically and the entire mould heated. Compression moulding used to
 
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