Introduction - Introduction to Polymeric Composites with Rice Hulls - page 7

certain materials are deemed hazardous and are banned (e.g., lead) or if secondary
costs (e.g., machining, finishing, coating) are a factor.
1.3.11 Structured Composites
A sandwich-structured composite is a special class of composite material fabricated
by attaching two thin (but stiff) skins to a lightweight (but thick) core. Usually,
the core material is a low-strength material but its higher thickness provides the
sandwich composite with high bending stiffness with overall low density. A very
common sandwich composite involves the combination of two layers of cotton with
a polymer or rubber. Cotton comprises a natural polymer called cellulose, whereas
rubber is also known as 'polyisoprene'. The two layers of cotton fabrics embedded
in a polymer or rubber matrix makes an ideal material that can be used for rainwear
or protective materials.
1.3.12 Natural Composite - Wood
Wood is a naturally occurring composite comprising cellulose fibre in a lignin and
hemicellulose matrix. 'Engineered wood' includes a wide variety of products such as
wood fibre board, plywood, oriented strand board, WPC with wood flour, WPC with
sawdust powder- or plastic-impregnated paper or textiles as well as other laminated
boards with brand names such as Aborite and Formica. Other engineered wood
laminated composites such as Mallite use a central core of balsa wood bonded to the
surface skin of a light alloy or GRP. These produce low-weight, highly rigid materials.
1.4 Uses for Composites
The ever-increasing material, agricultural and other wastes (e.g., plastics) due to global
population growth is causing environmental concerns because disposing of them is
an enormous problem. Resin manufacturers are using bio-degradable additives to
enable faster degradation in landfills but this is a slow process. Research has focused
on finding solutions, and biomass wastes from different activities are being used in
composites. Many types of composites are in use and continuing research and
development are enabling the combination of plastic resins and biomass wastes. One
of the most common and popular composites are WPC. New technology is enabling
combination of plastic resins with rice hulls, which is opening up a wide range of
possibilities with much better properties than the WPC available currently.