Important Stages of the Production Process - Introduction to Polymeric Composites with Rice Hulls - page 86

• Freeze dryers are used to dry heat-sensitive material such as chemicals in small
batches.
• Gas dryers use gas to heat and dry a material as desired. These dryers are quite
common.
• Industrial dryers are used for removing moisture from materials in a business or
manufacturing process.
• IR dryers are used most often for the curing of water-based inks and coatings.
• Rotary or drum dryers can be gas, liquid or solid fuel fired and pass material
through a heated rotating drum. Sometimes these drums will have multiple
chambers that allow longer passes to get through the drum.
• Spray dryers take a material such as wet powder and spin it centrifugally, then
direct a line of spray of the material into a drying chamber, which rapidly dries
the material. This type of dryer is also called a dispersion dryer .
• Vacuum rotary dryers are used for applications in which low-temperature drying
of a material is desired, as in the chemical and pharmaceutical industries.
7.3 Mixing and Compounding
Mixing and compounding is a very important stage in the production of composites
with rice hulls. Formulation must be carried out carefully with the end application in
mind. Selection of the polymer matrix, the minimum specifications for the rice hull flour
or rice hull fibre, the additives and colour requirements become very important for a
successful composite. Once the formulation has been finalised, the next step is mixing
and compounding to obtain a homogenous mass that can be fed into an extruding
system for further processing as pellets or profiled extrusions. Depending on the volume
of production, there are many types of mixers and compounding systems, which may
comprise a single-screw extruder, twin-screw extruder or multiple-screw compounding.
7.3.1 Industrial Mixers
Blenders and dispensers are used throughout the composite manufacturing industry.
Basic applications include simple blending of dry powders to the sophisticated
dispersion of solids into high-viscosity fluids. Some in the range of mixers include
double planetary mixers, planetary dispensers, high-shear mixers, horizontal ribbon,
tumble and vertical blenders. The success of composite chemistry can go so far as