materials feature | Colourants Co-extruded
potable water pipes with a skin layer on the outside can be far cheaper than pipe that is coloured all the way through
masterbatch used for an outer shell layer is much less than it would be to colour the whole structure. For potable water applications, co-extrusion is advisable as colour pigments can influence the taste of water that passes through it. It could also avoid costly toxicology testing required by NSF for drinking water system components (NSF Standards # 42/53). And while most polyolefin pipe in North America is HDPE, some speciality applications use polypropylene (PP). When extruding high-performance pressure pipe from PP, it is not advisable to use masterbatches in PE carriers. While the polarities of the olefins make them compatible as polymers, the melt viscosities and other characteristics can be quite dissimilar. For pressure
Colour coding/designations of PE pipe for US and Canada
Pressure-rated pipe Yellow = Fuel gas Blue = Potable water Lavender = Re-claimed water Green = Geothermal Grey = Slip lining of older pipe
Non-pressure Pipe Orange = Communications conduit Red = Electrical conduit
applications, only masterbatches using a PP carrier should be used in PP pipe.
Summary Although the factors outlined here play a role in the manufacturing of high quality polyolefin pipe, failures are more commonly caused by poor extrusion – or improper handling and installation of the pipe – than by poor quality materials. It is essential, however, that masterbatch formulators and pipe producers under- stand and adhere to fundamental material guidelines. l Joseph Serbaroli is strategic business manager at Ampacet (
www.ampacet.com)
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