Composite Technology - Introduction to Polymeric Composites with Rice Hulls - page 27

3 Composite Technology
3.1 Principles of Composites
The general principle of a composite is the combination of ≥2 different components
with a common base, which acts as the matrix. The new material will have the base
properties of both components but better properties such as light weight, higher
strength, aesthetic finishes, and wider end-applications depending on the design of
the composite. In general, composites may cost more but polymeric composites with
rice hulls (PCRH) will yield composites that are less expensive than standard ones
(especially as a biomass waste); in this case, rice hulls are used as the constituent
component. Composites with rice hulls will be considered in two segments: PCRH
as pellets and PCRH as extruded profiles.
Composites are usually made up of fibres and a matrix. Most commonly used fibres
have been glass-fibres, Kevlar, carbon-fibres, and steel whereas, more recently, other
reinforcement materials (e.g., biomasses) are being used. The fibre is embedded in
the matrix to make the matrix stronger. Fibre-reinforced composites (FRC) have
two special properties in that they are lighter and stronger, with some special
composites being even stronger than steel but weighing much less. One of the main
advantages of these types of composites is their ability to make automobiles and other
vehicles lighter and thus fuel-efficient as well as lessening environmental concerns.
Matrices provide a common base for holding together whichever reinforcements are
used. Although some fibres are strong, they can be brittle. A matrix can absorb energy
by deforming under stress (i.e., a matrix adds strength and toughness to a composite).
Fibres may have good tensile strength (i.e., they are strong if pulled) but they usually
have weak compression strength, and this is countered by the matrix. When making
composites, the designers use different matrices for different end applications. If a
cost-effective composite is desired, some cheap matrices can be used that will yield
decent properties. The unsaturated polyester/styrene system is a good example.
Cheap matrices are fine for everyday applications but have drawbacks. They shrink
if cured, absorb water easily, have low impact strength, and are not very resistant to
chemicals. However, with the advent of new technologies, as discussed in this topic,
whereby common polymers such as polyethylene (PE); polypropylene (PP); vinyls;
and high-density polyethylene (HDPE) coupled with rice hulls (which contain high
contents of silica) have opened up a vast array of possibilities.