Polymeric Composite Resins in Injection Moulding - Introduction to Polymeric Composites with Rice Hulls - page 136

11.6 Selection of Polymeric Composite Resins
Processing composite resins (and especially injection moulding composite resins) have
had teething problems but over the years have settled down and these difficulties
have been overcome. Although PCRH may be accepted as better composite resins,
processing them needs a little more caution. For starters, one must be aware of the
extra inherent heat-generating property and its natural abrasiveness as compared with
standard polymer resins. Also, the probability is that rice hulls at the initial stages
may contain a high content of moisture due to exposure to the weather. For ease of
processing and to achieve good-quality products it is important to use high-quality
pellets. Sections 11.6.1-11.6.3 describe some of the basic areas vital for selection of
these pellets.
11.6.1 Moisture Content
Surface moisture content should be <1.5%. Moisture content within the pellet should
ideally be <1.0%. Increased moisture content and failure to control moisture content
during processing results in 'splay' (whitish patches) and excessive brittleness.
11.6.2 Pellet Characteristics
Pellets should be clean and relatively consistent in size and shape. There should
be no chads or streamers. Powdery residues indicate the use non-standard pellet
manufacturing equipment and poor maintenance of the equipment on the part of the
manufacturer. Generally, a supplier of composite resins will include information in
his/her datasheets. Large-volume producers may have their own in situ laboratories
where tests can be carried out.
11.6.3 Correct Grades
One of the benefits of PCRH is that they can be blended with additional pure resins
while maintaining levels of polymer rice hulls. Through blending, moulders also can
achieve different performance characteristics in addition to what is basically offered,
such as flame-retardants, colouring, and extra-glossy grades. Thus, moulders have
the option of selecting the correct grade(s) of these composite resins to suit particular
applications.