Introduction - Introduction to Polymeric Composites with Rice Hulls - page 5

(finely ground wood waste). Some producers are also using other bio-mass wastes.
These combinations produce strong boards, and have been replacing traditional
materials used for outdoor applications such as decking, fencing, and park benches.
These products are, in general, available in solid rectangular or hollow profiles and
other pre-determined shapes with varying dimensions, and can be ≤5 m in length.
1.3.4 High-density Polyethylene Resin Composites with Rice Hulls
These eco-friendly composites are made from HDPE polymer resin with ground rice
hull powder as the reinforcement fibre in the matrix. The mix can be 30-40% HDPE
resin and 70-60% rice hull powder plus additives to achieve any special properties
desired as required in the end application. An extrusion process is used to produce
board lengths of desired profile sections. Additives are used singly but very often in
combinations of two, three or more. Some of the common additives used are lubricants,
binders, and crosslinking agents. It is also possible to use small percentages of other
biomass wastes with rice hull content but this is dependent upon the producer.
1.3.5 Polymer Composites with Recycled Plastics
This is a class of composites made with the wastes of recycled plastics, rice hull powder
or other biomass and made into extruded profiled products. Here, the important
factor is compatibility between the different grades of plastic wastes. Though most
thermoplastic grades are compatible, a few grades may not be. A combination of
thermoplastic and thermosetting grades is to be avoided because they will not be
compatible and pose problems when being processed. With these composite mixtures,
achieving the desired properties and finishes may be difficult unless they are used as
a small percentage of the matrix comprising virgin polymers. However, products
made from 100% recycled material may be suitable for certain low-end applications.
1.3.6 Fibre-reinforced Polymers
Fibre-reinforced polymers include carbon-fibre reinforced plastics and glass-
reinforced plastics (GRP). If classified by matrix, then they are termed 'thermoplastic
composites', 'short-fibre thermoplastics', 'long-fibre thermoplastics' or 'long
fibre-reinforced thermoplastics'. There are several thermoplastic composites but
advanced systems usually incorporate aramid fibre and carbon fibre in an epoxy
resin matrix. Good examples of carbon-fibre composites are aircraft parts, whereas
glass-reinforced composites include marine boats manufactured using a lay-down
production method.