Composite Technology - Introduction to Polymeric Composites with Rice Hulls - page 28

Fibre-reinforced plastics involve polymers (matrices) whose properties have been
enhanced by introducing a reinforcement (fibres) of higher stiffness and strength.
Such a resulting material is called a 'fibre-reinforced polymer' (FRP) or a FRC. One
of the main purposes of introducing a fibre into a matrix is to transfer the load
from the weaker material to the stronger one. This load transfer occurs over the
length of the fibre. If the fibre lengths are short, the composites are referred to
as 'short-fibre composites'. If the fibre lengths are long, the composites are referred
to as 'long-fibre composites'. The lengths of the fibres and their orientation in the
matrices play a key part in the final quality of a composite. In the case of PCRH
fibres, the two main important factors are water content (the less the better) and the
particle size of the ground rice hulls (the smaller the better).
Although the term reinforced plastics is not very descriptive of polymeric composites,
it implies that another agent(s) has been added to the plastic material to improve or
strengthen the matrix, which will result in a superior product. In this context, terms
such as advanced, high strength, engineered or structural composites came into being.
PCRH, irrespective of whether they are in the form of resin pellets or processed
products, will have the added advantage of being cost-effective as compared with
standard products.
3.1.1 Principles of Polymeric Composite Resins
Traditionally, the production of polymer resins have been based on crude oil as
a starting source with the by-product (liquefied ethylene gas) used as the base for
most polymers. However, due to rising costs, polymer engineers and scientists have
been suggesting alternative sources such as minerals, vegetable oils and biomasses.
Nevertheless, the average prices of most polymer resins to product manufacturers
have been increasing, and resin manufacturers are always on the lookout for cheaper
sources. The concept of composites has been based on 'finished' composite materials,
but the industry has been shifting to polymer resins with fillers, fibres and other
constituent components to produce cheaper resins similar to normal standard ones.
The principle of producing PCRH, as presented here, is the compounding of common
and popular polymers such as PE, PP and HDPE with finely ground rice hull powder
with the addition of fillers, lubricants, stabilisers and colourants. This mixture is
processed by extrusion and finally a process to make it into pellets for easy processing
into products. Theoretically, the process looks straightforward but the entire process
needs close attention and control because there are variants that must be controlled to
achieve acceptable resins by the end producers. These composite resins are now being
made and used by manufacturers of extruded, injection-moulded and compression-
moulded products. This process is presented in detail in the chapters that follow.