Influences of Mixing on Product Properties

The incorporation of additives is carried out to achieve a technical specification, some of which will be more sensitive to extruder mixing performance than others. Technical specifications are normally covered by standards testing, whether to recognised standards or in-house specifications. A concern here is to recognise the extruder s mixing contribution to achieving, or (more likely), the failure to meet standards such as fire retardancy and impact tests described in Chapter 1. 

Where agglomerates appear to be causing, for example, impact and electrical failures, the first suspect is the masterbatch or compound supplier. As a first step, it may be advisable to check whether the undispersed specks are one of the following  

1) Dirt or other contaminants such as packing material, incompatible polymeric bits from scrap granulation. (Even dandruff has been found in optically clear film). Burnt and degraded polymers 

2) Gels due to oxidation during extrusion, possibly caused by long coextrusion feed pipes and dead corners in film dies (see Chapter 14). Pigmented gels can easily be mistaken for agglomerates. 

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