Rice Hulls for Composites - Introduction to Polymeric Composites with Rice Hulls - page 60

air pollution, water pollution or erosion. Rice hulls do not deplete our reserves of fossil
fuels as do the processes for manufacturing polymeric compounds from petroleum
sources. As an insulation material and utility reinforcement for composites, rice hulls
now rank among the best. Their ready availability and cheap costs are important
factors to consider.
To protect the rice seed during growth, the hull is formed from hard materials, including
opaline silica and the polymer lignin. It is generally accepted that these hulls contain
20% opaline silica but, if they are burnt into ash, test results have shown silica content
of ≤70% of volume. The production of ash goes through two stages: the first is a 'grey'
state when the silica content is at its maximum and then a 'black' state. Rice hulls can
be used to produce mesoporous molecular sieves, which are applied as catalysts for
various chemical reactions as a support system. The ash is also a very fine thermal
insulation material and can have finer particle size, even better than cement, and thus
could have many applications in the building industry. Here, I would like to offer the
theory that using the fine ash of rice hulls as the reinforcing component instead of
rice hull flour would be more beneficial in the production of polymeric composites.
Higher contents of silica, volume to volume, between fine ash and rice hull flour for
added properties such as additional strength and weathering may justify this theory.
Also, combined use of rice hull ash and rice hull flour in the production of polymeric
composites should be tested to yield better products than those being made currently.
5.4 Uses for Rice Hulls
Most countries grow rice, more so in Asian and Eastern countries, where it is their
staple diet. Rice hulls resulting from the growing, harvesting and processing of rice is
a gift of nature as a recyclable resource having many current and potential uses. Up to
recently, this lowly byproduct of growing rice has been regulated to being used only as
animal feedstock and for the poultry industry, with most of it being discarded as waste.
However, due to increasing global environmental concerns, researchers and scientists
have realised the important potential of rice hulls in a wide range of applications,
especially as an ideal substitute for natural wood in the form of lumber. Thus, the use
of rice hulls in the production of polymeric composites is gaining ground fast via the
production of: (i) polymeric composite resins for moulding, and (ii) lumber through
extrusion. Some of the important uses of rice hulls are presented below.
5.4.1 Extrusion, Injection Moulding and Compression Moulding
Polymer resin moulders are always on the lookout for cheaper resins to be able to be
competitive in the market because they also have to battle with rising labour costs