Introduction - Introduction to Polymeric Composites with Rice Hulls - page 3

ester; epoxy, phenols; polyimide; polypropylene (PP); polyethylene (PE); high-density
polyethylene (HDPE); and polyvinyl chloride (PVC). Reinforcement materials are very
often fibres but also ground minerals. In polymeric composites, the polymer matrix can
also be considered a 'carrier' for processing an end product, as in extrusion.
The ratio of the resin matrix to reinforcements used is important to the end product
and the targeted special properties. As a rule of thumb, a 60% resin and 40% fibre
may be considered a good starting point. The main aim is to reduce the resin content
in the final product while achieving the special properties required, and additives go
a long way in helping in this area. There is a limit to the reduction of resin content
because the strength of the final product may be dependent upon the ratio of the
constituents. Also, too little resin may also cause problems or completely prevent
smooth processing of the composite. Polymeric composites can be made with a wide
range of natural fibres, such as rice hulls, wood flour, palm-fibre wastes, flax, rice
straw and other biomass wastes. This emerging 'family' of composites with such great
possibilities can be categorised as 'thermoplastic bio-composites'.
1.2.1 Engineered Composites
Engineered composites are, in general, made to be shaped. The matrix material can
be introduced before or after the reinforcement materials are placed into a mould
cavity or onto a mould surface, as in the production of fibre-glass products. The
matrix material undergoes melting and then the part shape is set. Depending on the
nature of the matrix material, this melting phase can occur in various ways, such as
chemical polymerisation or solidification from the melted state.
Various moulding methods can be used according to the design of the end-product.
The principal factors affecting the methodology are the nature of the matrices chosen.
Another important factor is the quantity of composite material to be produced. Large
volumes may justify high capital investment for rapid and automated manufacturing.
This chapter is mainly about the new technological field of PCRH and the methodology
that can be used to produce composite resin pellets as well as how to process them
to make composite profiled boards.
1.3 Types of Composites
Many types of materials are suitable for combination with a range of polymers for
making composites for different applications. Due to technological advances, polymers
can be used singly, in combination, or as modified polymers, depending on the final
objective in regard to a particular application(s).