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Compounding is the process by which colour or additives are added to the basic
thermoplastics material. This usually involves melting the thermoplastics
material then mixing it with the required pigments and/or additive material in
an extruder. The polymer melt is then extruded and chopped into pellets as it
cools, which can then be used directly by the plastics processor. An
associated process is masterbatch. This is where a high concentration of
pigment and/or additives are dispersed in a carrier medium which can then be
used directly by the processor in small quantities to pigment or modify the
virgin polymer material. The thermoplastics compounding industry forms a
vital interface between resin production and the plastics converter. Most
processors require the polymers they use to be coloured or modified in some
way (e.g. with the addition of additives such as flame retardants or UV light
stabilisers) and in the case of PVC, all resin has to be compounded before it
can be processed. Whilst a few very large processors carry out their own
compounding, particularly PVC processors, the majority buy-in ready compounded
material either direct from the polymer supplier or through an independent
compounder. It is this “free” market, i.e. compounds sourced externally by the
processor, which will be covered in this chapter.
Browse more:
Compounding Problems
Compounding Process
Methods of Compounding |
Molding
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