Page 31 - Plastics News November 2021

FEATURE

extrusion equipment. This will ensure displaced virgin content and thus more In general, the properties of high-quality
that most contaminants are filtered out ideal. This alignment is driving many to PCR resins correlate well with similar
in their process and will not result in investigate closed-loop opportunities, virgin grades and can have minimal
processing issues at your extruder. The where specific packages or articles are impact on finished article performance,
processability of PCR can be affected collected to be incorporated back into especially with the right approach to
by contaminants. The breadth of the the same type of product. It is helpful product design. For property retention, it
molecular-weight distribution can be to try to source PCR from the same or is essential that the stream be significantly
approximated by the MFR and is a good similar stream as the anticipated end free of contamination, especially from
indication of processability. A higher use. Similarly, the best PCR source for polymers such as PP and PET. Although
number generally indicates that it is food-contact applications currently is PP melts at the temperatures used
easier to process. If mineral fillers such one that’s directly traceable to a food- in PE extrusion, it can affect impact
as talc or calcium carbonate are present, contact application in the first lifetime, performance of the final part, which
the density reported on the product even if the form factor is different. A is especially important in many rigid
data sheet may appear to be higher well-known example is recycled HDPE articles. The first step in comparing the
than the actual base polymer density. sourced from milk jugs. As this stream is physical property performance of an
The presence of mineral fillers can be highly sought after and in short supply, article or film with PCR content to an
determined through ash testing, with a we are seeing that issues such as MI article made with 100% virgin content is
rough rule of thumb being for every mismatch and homopolymer density are to make sure you choose the right resin
1% ash content the density will shift by being overcome in diverse end uses such for a fair comparison. It is always best
approximately 0.01 g/cc, and then true as flexible film and caps and closures. to compare performance of the PCR
PCR density can be calculated from there. Sourcing PCR from a product made against a virgin resin with similar MI
with the same conversion process is and density. Physical property retention
What Should You Look for in Your another good strategy. Recycled content can be quite good provided the PCR is
PCR to Ensure the Best Quality produced by blown film extrusion will high quality and free of contamination.
Finished Goods? be easier to incorporate back into blown Since most PCR is being used as a
Consistent pellet color and size, low film than it would in cast film, which blend component, it is also possible to
odor, and minimal contamination are requires a higher melt index. The same is consider changing the other resins in
all indicators of high-quality PCR. true for injection molding, which requires the composition to overcome the slight
Consistency of MI will drive consistency an even higher MI, so starting with an reduction in performance. Using higher
in processing the PCR, and is highly article that was made by blow molding performance virgin resins, or resins
sought after by converters. On the would present processing challenges. specifically formulated to compensate
supply side, this is being addressed by for PCR properties, can also result in a
controlled sourcing, material sortation, What Impact on Performance product that does not compromise on
and blending. Blending can occur both Should You Expect When Using performance. For example, if MD tear
on the incoming source stream as well as PCR? performance is affected through the
the final PCR pellets to achieve a higher inclusion of PCR, a high-tear virgin resin
degree of homogenization. Blending can be used to compensate for the loss
silos and a high degree of testing and in performance.
monitoring can allow a recycler to
deliver a consistent MI that can even How Do You Know If a PCR Resin
be comparable to wide-spec virgin resin Will Have Sufficient Stability?
(±30%). In addition, it is helpful to try Be sure to ask your supplier whether
to source PCR from the same or similar it is including additional antioxidants
stream as the anticipated end use—this (AOs) in the formulation. Testing for the
is called “like-for-like” recycling. For a presence and consumption of additives
flexible film such as shrink film, looking is relatively easy and will determine
to source PCR from film sources such as whether there is sufficient stabilization in
back-of-store or distribution-center film, the PCR stream. Through collaborations
or even agricultural film, will ensure that Shrink film in this type of application has been with resin suppliers and converters,
the properties are more similar to the made with up to 40% PCR content. recyclers are beginning to understand

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