Specifying PCR? Find Answers to These Eight Questions

Eliminating plastic waste in the environment is critical to the health of our planet and the health of our industry. Circularity is being advanced with downgauging and lightweighting, and processors are working with brand owners to redesign packaging for recyclability and to incorporate post-consumer resin (PCR) and other recycled content.

As you embark on this endeavor, learn as much as you can about the PCR that is available today. Understanding what to expect when working with recycled resin is critical as we continue to drive improvements of both the quality and quantity of recycled plastics. It will give you more confidence and improve your success in incorporating this sustainable material into new packaging and products.  Here are eight questions whose answers will help put you on the right track.
  

1. How is PCR Different from PIR and Rework?

PCR is defined as plastic that has served its defined purpose. After its intended use, it is collected, cleaned and repelletized to be used in new plastic articles or packaging. Post-industrial (PIR) resin, on the other hand, is typically resin that has been converted into a product that is out of specification or not saleable, and thus has never reached the customer or consumer. This product can still be collected and diverted from landfill and used in new products or packaging.

Rework is waste generated within a manufacturing process that is reused within the same process rather than sold to another manufacturer. The ability to use rework as a feedstock is considered a best practice in manufacturing. This resin is very close to virgin resin in quality since it has only experienced one additional heat or processing history. Examples include tips and tails from blow molding, runners from injection molding, and edge trim from film or sheet production. Rework is considered distinct from PCR and PIR, as it is reused back in the same process that created it. As such, it is not considered a recycled product.

Products must be designed to be recycled or upcycled rather than downcycled or landfilled; and to fully close the loop, the materials in them must be incorporated back into new products. PCR is the primary focus for most participants in the value chain, and reincorporating it into new products and packaging is critical to circularity.  
 

2. What Properties and Processibility Should You Expect from PCR Resins?

Melt index (MI), melt-flow ratio (MFR) and density are basic properties that should be communicated on every lot of PCR. Since PCR is often used as a blend component, these properties will affect blend compatibility, which will affect overall performance.

For PE-PCR, sophisticated rheology curves are more commonly used with virgin resin, but understanding whether LDPE is present in a LLDPE PCR is important to predict the shear-thinning behavior and melt strength during processing. While it is difficult to quantify the level of LDPE in a specific batch of LLDPE PCR, understanding whether it is present in the incoming recovered plastic stream is a good start.

The processability of PCR can be affected by contaminants, especially if they do not melt at temperatures used for PE extrusion. PET is a good example, as its higher melt temperature will result in blockage of the extruder screen pack, building up backpressure and potentially causing downtime. Foreign contaminants such as cellulose or wood fibers can also result in screen-pack buildup. A good rule of thumb is that your PCR supplier should be using mesh filtration one step finer than that which is used on your extrusion equipment. This will ensure that most contaminants are filtered out in their process and will not result in processing issues at your extruder.

The processability of PCR can be affected by contaminants.

The breadth of the molecular-weight distribution can be approximated by the MFR and is a good indication of processability. A higher number generally indicates that it is easier to process.

If mineral fillers such as talc or calcium carbonate are present, the density reported on the product data sheet may appear to be higher than the actual base polymer density. The presence of mineral fillers can be determined through ash testing, with a rough rule of thumb being for every 1% ash content the density will shift by approximately 0.01 g/cc, and then true PCR density can be calculated from there.

3. What Should You Look for in Your PCR to Ensure the Best Quality Finished Goods?

Consistent pellet color and size, low odor, and minimal contamination are all indicators of high-quality PCR. Consistency of MI will drive consistency in processing the PCR, and is highly sought after by converters.

On the supply side, this is being addressed by controlled sourcing, material sortation, and blending. Blending can occur both on the incoming source stream as well as the final PCR pellets to achieve a higher degree of homogenization. Blending silos and a high degree of testing and monitoring can allow a recycler to deliver a consistent MI that can even be comparable to wide-spec virgin resin (±30%).

In addition, it is helpful to try to source PCR from the same or similar stream as the anticipated end use—this is called “like-for-like” recycling. For a flexible film such as shrink film, looking to source PCR from film sources such as back-of-store or distribution-center film, or even agricultural film, will ensure that the properties are more similar to the displaced virgin content and thus more ideal. This alignment is driving many to investigate closed-loop opportunities, where specific packages or articles are collected to be incorporated back into the same type of product.

It is helpful to try to source PCR from the same or similar stream as the anticipated end use.

Similarly, the best PCR source for food-contact applications currently is one that’s directly traceable to a food-contact application in the first lifetime, even if the form factor is different. A well-known example is recycled HDPE sourced from milk jugs. As this stream is highly sought after and in short supply, we are seeing that issues such as MI mismatch and homopolymer density are being overcome in diverse end uses such as flexible film and caps and closures.

Sourcing PCR from a product made with the same conversion process is another good strategy. Recycled content produced by blown film extrusion will be easier to incorporate back into blown film than it would in cast film, which requires a higher melt index. The same is true for injection molding, which requires an even higher MI, so starting with an article that was made by blow molding would present processing challenges.

4. What Impact on Performance Should You Expect When Using PCR?

In general, the properties of high-quality PCR resins correlate well with similar virgin grades and can have minimal impact on finished article performance, especially with the right approach to product design. For property retention, it is essential that the stream be significantly free of contamination, especially from polymers such as PP and PET. Although PP melts at the temperatures used in PE extrusion, it can affect impact performance of the final part, which is especially important in many rigid articles.

The first step in comparing the physical property performance of an article or film with PCR content to an article made with 100% virgin content is to make sure you choose the right resin for a fair comparison. It is always best to compare performance of the PCR against a virgin resin with similar MI and density. Physical property retention can be quite good provided the PCR is high quality and free of contamination.  

Since most PCR is being used as a blend component, it is also possible to consider changing the other resins in the composition to overcome the slight reduction in performance. Using higher performance virgin resins, or resins specifically formulated to compensate for PCR properties, can also result in a product that does not compromise on performance. For example, if MD tear performance is affected through the inclusion of PCR, a high-tear virgin resin can be used to compensate for the loss in performance.
 

5. How Do You Know If a PCR Resin Will Have Sufficient Stability?

Be sure to ask your supplier whether it is including additional antioxidants (AOs) in the formulation. Testing for the presence and consumption of additives is relatively easy and will determine whether there is sufficient stabilization in the PCR stream.

Through collaborations with resin suppliers and converters, recyclers are beginning to understand the value of additional stabilization. Crosslinking, which is a common result of insufficiently stabilized resin, will bring the MI down and make processing more difficult. Having additional AO added during production by your PCR supplier is ideal to protect the resin through at least its third heat history to ensure minimal degradation occurs and the MI is preserved.
 

6. Are There Tactics to Reduce Odors Commonly Associated with PCR?

Most plastic converters report that PCR has more odor than virgin plastic. Good PCR suppliers address odor early in the recycling process. It is critical to remove paper labels and cellulosic/organic contamination in the wash step to prevent particles from charring during the extrusion process.

Devolatilization is an additional step that occurs at some recyclers to drive off volatile organic compounds and can result in a noticeable reduction in odor. Deodorizing additives can also be used to improve perceived odors. Ask your supplier if any of these steps are included in their process.
 

7. How Do You Know Whether Recycled Resin Will Meet Special Criteria for Your Application?

If you have a special criterion such as absence declarations, California Prop 65, Toxins in Packaging Clearinghouse (TPCH) or food-contact statements, you must work with your supplier to address these needs. Food-contact PCR is in particularly high demand as brand owners work to achieve packaging sustainability goals.

Globally, there are differences in how the use of PCR is regulated for food-contact applications. In the U.S. and Canada, the PCR material must meet all the same legal requirements as virgin material. The Food and Drug Administration (FDA) in the U.S. and the Health Products and Food Branch (HPFB) in Canada will review the recycling process and material source(s), and then issue letters of non-objection (LNO or LONO), which are opinions on the recycling process used to produce material for food-contact applications and will include food type or use restrictions for the resulting PCR.

However, the LNO is just one criterion that must be met in order to comply with food-contact requirements. To be considered suitable for the final application from a regulatory perspective, the PCR will typically go through additional testing and obtain additional regulatory statements.

For cleanliness and gel level, ask your supplier about its cleaning steps and melt-filtration capabilities. 

The EU has a similar approach, but also requires only food-contact material be recycled for use in food-contact applications. Similarly to the FDA and HPFB, The European Food Safety Authority (EFSA) will review a recycling process to assess its suitability in producing food-contact PCR. To date, however, opinions have only been issued for rPET. It is anticipated that this may change with the recent push in the EU to develop a comprehensive strategy to include plastic in a circular economy.
 

8. How Do You Determine the Maximum PCR Content You Can Use in Your Product or Package Design?

Exploring how much PCR can be incorporated into your product design is a key component of application development and should be determined on a case-by-case basis through trial evaluations and modeling. The ultimate PCR content can depend on the level of gels or impurities, physical-property retention, and aesthetics.

For cleanliness and gel level, ask your supplier about its cleaning steps and melt-filtration capabilities. For physical property retention, matching density is important, as previously noted. If this is not possible, consider what can be done to offset the resulting change in performance. With regards to aesthetics, our advice is to embrace the ugly! PCR can look very good but is not likely to look the same as virgin resin, even if the utmost care is taken in its production. Let the different aesthetic start telling the story for the consumer to understand that PCR is being used in your product design – the sustainability messaging is a key component to driving growth in the circular economy!

We have seen levels of PCR in excess of 70% for some can liners and around 40% for shrink film. For more sensitive applications with stringent requirements, starting at a lower dosage such as 10% and building confidence and experience before targeting higher loadings is a good strategy. Higher loadings will be limited by required part performance and/or aesthetics. Burying the PCR in a core layer in a multi-layer structure can help overcome PCR aesthetics to some extent, and relying on high-performance blend components can offset a reduction in physical performance.
 

ABOUT THE AUTHORS: Anna Rajkovic is the circular economy market manager at Nova Chemicals, Calgary, Alta. In her role, she is responsible for the company’s PCR product portfolio, and more broadly driving circularity with plastic converter customers and across the entire plastics value chain. Rajkovic also serves on the Association of Plastics Recyclers (APR) Film Technical Committee and the Alliance to End Plastic Waste Thematic Expert Group, as well as representing Nova Chemicals at IPANA, RIBCA, PDA, PPI, ASTM and CSA. Contact: 403-250-0635; anna.rajkovic@novachem.com; novachem.com.

Tammy Rucker is v.p. of sustainable materials at Revolution, a plastics recycler based in Little Rock, Ark., where her focus is on the transition of post-consumer polyethylene from internal use to external sale. She joined the company in October of 2020, bringing over 27 years of materials and plastics experience to the firm’s recycled plastic business. Rucker has worn many hats in her career, including quality-lab chemist, sales, market and product management, and marketing communications in several Fortune 500 companies: GE Plastics (now SABIC), Union Carbide (now Dow Chemical), and Avery Dennison. Contact: 312-520-7461; trucker@revolutioncompany.com;  revolutioncompany.com