Introduction - Introduction to Polymeric Composites with Rice Hulls - page 8

1.4.1 Polymeric Composite Resins in Injection Moulding
Wood fibre/thermoplastic blends are employed in extruded decking and fencing
boards, but are now being used in injection moulding and compression moulding.
Initially, some injection moulders were reluctant to accept this new concept. However,
recent developments in the manufacture of composite resin compounds have vastly
improved their quality, consistency and capabilities, and moulders are now using these
environmentally friendly composite resins with more confidence, with cheaper costs
playing a major part. The latest generation of WPC can be run smoothly through
traditional injection-moulding equipment with minimal adjustments to process
settings, and modifications to hardware are not needed. However, these composite
materials have some processing characteristics that distinguish them from the standard
moulding resins.
1.4.2 Polymeric Composite Resins in Extrusion
WPC with wood flour have been in use for some years, but composites with rice hulls
are comparatively new. WPC have been used in extrusion processes to make solid
boards of different profiles, mainly for decking and fencing. With the emergence
of composites with rice hulls, the possibilities have widened. Due to the unique
presence of a high content of silica in rice hull wastes, products with higher strengths,
very low maintenance and excellent finishes can be achieved. These products are
emerging as ideal substitutes for natural wood, and their end uses are spreading
from outdoor applications (e.g., decking, fencing and benches) to furniture and
building construction.
1.4.3 Polymeric Composites in Compression Moulding
Compression moulding is a simple and effective way to manufacture large plastic
parts, especially for the automotive industry. This type of moulding involves heating
of a plastic powder to remove moisture before introduction into one-half of a mould
cavity, and then closing the mould and moulding under compression. Plastic raw
materials used for this process are in powder form. They absorb moisture from the
air during their shelf-life and must be heated before being moulded. Use of polymeric
composite resins in pellet form will eliminate this stage and give the additional
properties of strength and rigidity.