Important Stages of the Production Process - Introduction to Polymeric Composites with Rice Hulls - page 81

7 Important Stages of the Production Process
A producer of polymeric composites, whether using rice hulls or wood fibres, must
have a thorough knowledge of polymers to be used as matrices and also the production
process. The design and formulation of the composite mix and the additives, in keeping
with the requirements of the end application, is very important in producing good
composites. The basic stages of the process are: particle-size reduction, drying to
reduce moisture levels of the fibres; mixing and compounding; pelletising; extrusion.
Many options are available for the set-up of a processing line, such as individual
machinery for each stage or a complete online operation from feeding of the raw
fibres to final extrusion of the composite. Here, extrusion is mentioned because
probably 75% of polymeric composites with rice hulls (PCRH) are extruded, whereas
pelletised composites are injection moulded and this subject is dealt in another chapter.
Companies supply rice hull fibres and rice hull flour to customer's specifications, such
as moisture levels, particle size, and density, which may have advantages but the cost
must be evaluated.
7.1 Reduction of Particle Size
The chemical, pharmaceutical, food, mining and plastic industries rely on size
reduction. This process uses methods such as shredding, grinding of polymers for
recycling, extraction of a valuable constituent from ores to facilitate separation of
grain components and production of particles of an appropriate size for a given use.
There are many methods for particle-size reduction and different equipment which
are often developed empirically to handle specific materials.
Knowing the properties of the material to be processed is essential. Probably the most
important characteristic governing size reduction is hardness because almost all size-
reduction methods involve creating new surface areas, and this requires adding energy
proportional to the bonds holding the feed particles together. In industrial terms,
hardness can be gauged on a scale from 1 (soft) to 10 (hard). Whether a material
is tough or brittle (with brittle materials being easier to fracture) is also important.
Other characteristics include particle-size distribution, bulk density, abrasiveness and
temperature-sensitivity. Flow properties can also be a major factor because many size-
reduction processes are continuous but often have 'choke points', at which bridging
and flow interruption can occur. For example, some size-reduction equipment is