| Plastic pipes are increasingly used for pressure
applications such as potable water supply etc.
Higher pressure ratings, particularly of PE pipes,
have been increasingly gaining higher market share.
For instance, most of the recent PE pipes fall
in the category of P100 pressure ratings. To meet
the requirements of enhanced pressure rating,
weathering is the most crucial property primarily
dependent on the quality of Carbon black. All
the major Carbon black suppliers have been developing
improved grades. The critical requirements of
Carbon black are:
 Long-term
weatherability
The end product is required by utility companies
to provide long service life without failure,
despite being exposed to ultraviolet light. This
requires very fine prime particles, which present
more surfaces to incident light, and hence have
greater UV light absorbing efficiency than a coarser
particle size.
Extremely
low levels of moisture absorption
Compounds containing carbon black usually
absorb moisture when exposed to air. This can
create processing problems, surface defects or
internal cavities in the finished part. The high
purity of the carbon black grades developed for
this application has resulted in very low moisture
absorption during the compounding process.
Dispersability
This performance measure depends primarily on
the fundamental characteristics of carbon black
and relates to the attractive force needed to
separate the agglomerates into discrete carbon
black aggregates. It is also an indicator of the
relative yields that can be achieved on compounding
equipment with different carbon black grades.
The P-types show much better dispersability than
a conventional grade, resulting in better wetting
with the polymer and subsequent de-agglomeration.
Microscopic
dispersion
Undispersed carbon black agglomerates in the pipe
wall can lead to premature failure and also reduce
fluid flow properties. These problems are recognised
in the industry, and most standards for pressure
pipes specify a microscopic dispersion rating
of no greater than 3 under ISO 11420, NFT51 -
142. Conventional blacks typically rate between
5 and 6.
Chemical
cleanliness
Chemical impurities, particularly sulphur, ash
and toluene extract, when present in the compounds
used to make pipes for drinking water, can impart
unpleasant tastes or odours. All carbon blacks
include some residues of these materials, but
in the P-type grades the amounts have been greatly
reduced. For example, sulphur content - typically
around 10,000 ppm in a conventional black - is
some 600 ppm in the new grades.
|