Page 41 - Plastics News December 2020

blue tint helps to mask the yellowness and create a virgin PET. Because the PCR is darker, it more readily
more uniform color. Green, amber, or other colors also absorbs heat from the blow molding oven lamps, so
effectively mask the effects of high percentages of PCR, lamp profiles often need to be adjusted. Small particles
but they also mean the bottle can't be recycled again of contamination in PCR also can cause pinholes and
into a clear bottle. If you do your own blending of PCR leaks when blow molding the bottle. As the walls of the
with virgin resin, you may be able to adjust the ratio of bottles are stretched during molding, particles of
PCR to maintain acceptable color in the final container. contamination can cause weaknesses that result in
holes in the bottle wall. The number of defects will
In addition to black specs, larger contaminant particles
depend on the amount of contamination in the PCR
in PCR can cause problems in injection molding the
preform. These contaminants are usually caused by resin and the design and wall thickness of the preform
some malfunction in the washing or melt-filtering and final bottle.
process, such as a blown filter screen, and are not part Infrastructure
of normal day-to-day operation. Otherwise, there is
For packaging materials such as aluminum, glass, and
little difference in the injection molding process when paper, today's economics and manufacturing processes
producing a preform made of PCR.
often support the use of post-consumer recycled
materials. With plastics, including PET, the demand for
PCR is increasing, but the infrastructure to recycle and
preprocess post-consumer plastics is not as well
developed.
Using PCR to make new bottles starts with sourcing the
right PCR for your application. At the converting plant
there may be some infrastructure needed to store,
handle, and blend the PCR resin. There generally won't
need to be modifications to the injection and blow
molding equipment, but processes will probably need
to be developed or at least fine-tuned. Using larger
percentages of PCR may require colorants or ongoing
management of the supply or of blend ratios to achieve
consistent output.
Blow molding bottles with PCR usually requires a (Courtesy: Plastics Technology)
different set of process parameters than is typical for

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DECEMBER 2020 41 Plastics News