Introduction - Introduction to Polymeric Composites with Rice Hulls - page 4

1.3.1 Composite Resins with Rice Hulls
Rapid developments are taking place in the production of composite resins in pellet
form by combining a polymer matrix with rice hulls ground to a fine powder. These
resins can be made in small volumes using manual operations but, for large-volume
and quality resins, it is imperative that advanced technological equipment is employed.
This process can be done in two stages: the rice hulls are ground, dried, compounded
with the polymer matrix and then put through an extrusion process, resulting in a
pellet form. Alternatively, this process can be set up with a continuous processing
line, whereby the entire process is completed in one operation. These composite
resins can be made with various plastics (e.g., PE, PP and polystyrene). Also, these
WPC are just one category of an emerging family of materials termed thermoplastic
bio-composite resins. Although these bio-composite resins can be made with fibres
such as flax, palm-fibre wastes, wood flour, and rice-straw wastes, laboratory testing
and practical applications have shown that PCRH elicit better overall properties
(e.g., better structural strength) and capabilities.
These resins are slightly transparent to yellow in colour. Properties are decided by
the types of constituents and additives used, whereas pellet sizes can be varied during
pelletising. Colouring is an option but can also be carried out during conversion
to the final product. The second option has benefits in that, whichever process is
used, different finishes can be obtained by adding master-batches, dyes, pigments, or
combinations of dyes/pigments to get the desired effects.
1.3.2 Composite Profiles with Rice Hulls
A wide range of profiles can be produced using an extrusion process in which the
composite resins of choice can be converted to profiled length boards. A specially
designed die at the end/head of the extruder will determine the profile shape of the
extrudate (i.e., whether the cross-section is round, rectangular, octagonal, or hollow).
In general, the thicknesses of these boards can range from 15-25 mm and widths
≤1,000 mm and almost any desired lengths which are determined by a pre-set vertical
cutting saw. Addition of extra additives during processing will enable a producer
to achieve any special properties desired and incorporation of single colours or in
combination to obtain aesthetically pleasing finishes.
1.3.3 Wood Polymer Composites
WPC have been available for some time and very popular for outdoor applications,
especially for decking. The two main constituents are a polymer matrix and wood flour