Page 40 - Plastics News December 2020

Processing PCR: How it is Done

There are several challenges to making bottles with from contaminants in the PET. Some of the contaminants
recycled PET, and they increase with the percentage that affect PCR color are oxygen scavengers, reheat
of PCR used enhancers, or other additives used in the original
containers. Contaminants can also be microscopic
David Clark
pieces of foreign material such as other plastics, glass,
Many food and beverage companies are either using or sand, or metals. These small particles are bound in the
thinking about using recycled materials in their plastic and don't pose a hazard in food containers, but
packaging. In addition to enhancing brand equity, using can sometimes be seen as black specs in the resin pellets
post-consumer recycled (PCR) plastics has a number of or in the container. The color and amount of
environmental benefits. Recycling reduces the amount contamination in recycled PET depends on the source of
of plastic sent to landfills, and using PCR helps support the recycled bottles—deposit or curbside—and also the
the recycling infrastructure. Using recycled PET means technology used to sort, wash, and grind the bottles.
that less petroleum is needed to make new, virgin resin.
Recycled PET also requires less energy to produce and Processing PCR
has a lower carbon footprint than virgin PET. For PET containers, PCR is used in varying amounts from
less than 10% to 100%. At ratios below 25%, there are
There are several challenges to making bottles with
usually only slight differences when using PCR versus
recycled PET, and they increase with the percentage of
PCR used. In general, there are no modifications 100% virgin. At higher percentages, the use of PCR has a
required to machinery or molds, except for the greater impact.
additional equipment needed to store, handle, and Using PCR requires some additional infrastructure
blend PCR. However, using PCR often introduces subtle compared with running 100% virgin PET. First, you need a
challenges and process considerations. Most often, the place to hold the PCR. Smaller amounts can be handled
quality of the PCR resin will have the most impact on the in gaylord boxes or Super Sacks. Larger amounts of PCR
challenges you'll face in production. usually warrant a separate resin silo to store the PCR,
which can be delivered in bulk trucks or railcars.
Why PCR is challenging
Blending equipment, such as a gravimetric blender, is
For PET bottle processors, the source of almost all PCR is required to mix the PCR with virgin resin at the desired
carbonated soft-drink, water, and other beverage ratio. It's also possible to purchase PCR preblended with
bottles. Most soft-drink bottles are collected by one of virgin resin, but this limits your options to one ratio.
two methods. Some states have deposit or redemption Preblending also increases your risk if the PCR turns out
systems to encourage consumers to recycle their to have unacceptable levels of contamination.
bottles. These return systems usually result in the best
quality recovered PET because the bottles are kept
separate from other types of plastic and paper, glass,
and other potential contaminants. Most bottles
collected outside of the deposit or redemption systems
are from curbside recycling programs. The PET bottles,
and sometimes other containers made from PET, are
often mixed with other types of plastic, metal, and glass
containers that can contaminate the PET.
The PET resin used for carbonated soft drinks is not
identical to the grades typically used for isotonic
beverages and most water bottles. The most important
difference is the intrinsic viscosity (IV) of the various
resins. The IV of a resin increases with the length of its
polymer chains, which have an effect on the strength Probably the most noticeable difference when using PCR
and stretch characteristics of the PET bottle. The ratio instead of 100% virgin PET is the color. When attempting
of carbonated soft-drink to water bottles will have an to make clear bottles from PCR, you will notice they will
impact on the resulting IV in the recycled PET.
be somewhat darker and often yellower than those made
In addition to IV, the two most critical quality variables of virgin PET. Because of variation in the sources of the
when using PCR are color and contamination. Recycled PCR, it can be difficult to maintain a consistent color
PET tends to be darker and more yellow than virgin PET. from batch to batch. Some food and beverage companies
Some of the color comes from reheating, but most comes overcome these problems by adding colorant. A slight

DECEMBER 2020 40 Plastics News