Knowing how to use the PCR available today is critical, as packaging and other products are being redesigned to achieve circulation.

Consistent sediment color and size, low odor and minimal contamination are all indicators of high-quality PCR. 

Eliminating plastic waste in the environment is vital to the health of our planet and the health of our industry. Recycling is being promoted through thinning and weight reduction, and processors are working with brand owners to redesign packaging to achieve recyclability and include post-consumer resin (PCR) and other recyclable ingredients.

When you start this work, please learn as much as possible about the PCRs available today. As we continue to push to improve the quality and quantity of recycled plastics, it is important to understand what happens when recycled resins are used. When incorporating this sustainable material into new packaging and products, it will give you more confidence and increase your success rate. Here are eight questions whose answers will help you get on the right track.   

1. How is PCR different from PIR and rework?

PCR is defined as plastic that has reached its intended use. After its intended use, it is collected, cleaned and repelletized for use in new plastic products or packaging. On the other hand, post-industrial (PIR) resins are usually resins that have been converted into products that do not meet specifications or are unsaleable, and therefore never reach customers or consumers. The product can still be collected and transferred from landfills for use in new products or packaging.

Rework is waste generated during the manufacturing process, reused in the same process rather than sold to another manufacturer. The ability to use rework as a raw material is considered a best practice in manufacturing. This resin is very close to the original resin in quality because it has only undergone an additional heating or processing history. Examples include blow-molded tips and tails, injection-molded runners, and edge trimming for film or sheet production. Rework is considered different from PCR and PIR because it is reused in the same process that it was created. Therefore, it is not considered a recycled product.

The product must be designed to be recyclable or upgradeable, not downgrade recycling or landfill; in order to completely close the cycle, the materials in it must be reintegrated into the new product. PCR is the main focus of most participants in the value chain, and its reintegration into new products and packaging is critical to circularity.    

The plant food bag prototype is manufactured by Nova, and the PCR content is 20%.

2. What characteristics and processability do you want the PCR resin to have?

Melt index (MI), melt flow ratio (MFR) and density are the basic attributes that should be communicated in each batch of PCR. Since PCR is usually used as a mixed component, these characteristics affect the compatibility of the mix and thus the overall performance.

For PE-PCR, complex rheological curves are more commonly used for raw resins, but understanding whether LDPE is present in LLDPE PCR is important for predicting shear thinning behavior and melt strength during processing. Although it is difficult to quantify the level of LDPE in a specific batch of LLDPE PCR, understanding whether it is present in the incoming recycled plastic stream is a good start.

The processability of PCR can be affected by contaminants, especially when they do not melt at the PE extrusion temperature. PET is a good example, because its higher melt temperature can cause blockage of the extruder screen components, creating back pressure and possible shutdowns. Foreign contaminants such as cellulose or wood fibers can also cause the filter to accumulate. A good rule of thumb is that your PCR supplier should use a finer screen filter than the one used on your extrusion equipment. This will ensure that most contaminants are filtered out during its processing and will not cause processing problems in the extruder.

The processability of PCR is affected by contaminants.

The width of the molecular weight distribution can be approximated by MFR, which is a good indicator of processing performance. A higher number usually means easier processing.

If mineral fillers such as talc or calcium carbonate are present, the density reported in the product data sheet may be higher than the density of the actual base polymer. The presence of mineral fillers can be determined by ash test. A rough rule of thumb is that for every 1% increase in ash, the density will change by about 0.01 g/cc, and then the true PCR density can be calculated from there.

3. What should you look for in PCR to ensure the highest quality finished product?

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

On the supply side, this is being resolved through controlled procurement, material sorting and mixing. Mixing can occur on the incoming source stream as well as the final PCR particles to achieve a higher degree of homogenization. Testing and monitoring of mixing silos and heights allows recyclers to provide consistent MI, even comparable to wide-spec virgin resins (±30%).

In addition, it is helpful to try to obtain PCR from streams that are the same or similar to the intended end use-this is called "homogeneous" recycling. For flexible films such as shrink films, it is desirable to obtain PCR from film sources such as store or distribution center films, or even agricultural films, which will ensure that its characteristics are more similar to the original components being replaced, so it is more ideal. This consistency has prompted many people to study closed-loop opportunities, in which specific packages or items are collected to be re-incorporated into the same type of product.

It is helpful to try to obtain PCR from a stream that is the same or similar to the intended end use.

Similarly, the current best source of PCR for food contact applications is PCR that can be directly traced back to food contact applications during the first life cycle, even if the shape is different. A well-known example is HDPE recovered from milk tanks. Since this flow is highly sought after and in short supply, we see that problems such as MI mismatch and homopolymer density are being overcome in various end uses such as flexible films, bottle caps and bottle caps.

Purchasing PCR from products made using the same transformation process is another good strategy. Compared with cast films that require a higher melt index, the recycled components produced by blown film extrusion are easier to re-add to the blown film. The same is true for injection molding, which requires a higher MI, so products made from blow molding will pose processing challenges.

The shrink film in this type of application has a PCR content of up to 40%.

4. When using PCR, what impact should you expect on performance?

In general, the properties of high-quality PCR resins are related to similar original grades and have the least impact on the performance of the finished product, especially if the product design method is correct. In order to maintain performance, the logistics must be completely free of pollution, especially from polymers such as PP and PET. Although PP will melt at the temperature used in PE extrusion, it will affect the impact properties of the final part, which is particularly important in many rigid products.

The first step in comparing the physical properties of an item or film with PCR content to an item with 100% original content is to ensure that you choose the correct resin for a fair comparison. It is best to compare the performance of PCR with the original resin with similar MI and density. If the PCR is high quality and pollution-free, the physical property retention can be very good.  

Since most PCR is used as a blending component, it is also possible to consider changing other resins in the composition to overcome the slight decrease in performance. Using higher-performance original resins or specially formulated resins to compensate for PCR characteristics can also produce products that do not affect performance. For example, if MD tear performance is affected by the inclusion of PCR, a high tear virgin resin can be used to compensate for the loss of performance.  

5. How to know whether the PCR resin has sufficient stability?

Be sure to ask your supplier if they have added additional antioxidants (AO) to the formula. Testing for the presence and consumption of additives is relatively easy and will determine whether there is sufficient stability in the PCR stream.

Through cooperation with resin suppliers and processors, recyclers are beginning to understand the value of additional stability. Cross-linking is a common result of insufficient resin stability, reducing MI and making processing more difficult. Adding additional AO during the production process by your PCR supplier is ideal for protecting the resin through at least its third heating process to ensure minimal degradation and retention of MI.  

6. Is there a strategy to reduce common odors in PCR?

Most plastic processors report that PCR has more odor than virgin plastic. Good PCR suppliers will solve the odor problem early in the recycling process. It is important to remove paper labels and cellulose/organic contaminants during the washing step to prevent charring of the particles during the extrusion process.

Devolatilization is an additional step performed by some recyclers to remove volatile organic compounds and can significantly reduce odors. Deodorant additives can also be used to improve the perceived odor. Ask your supplier if any of these steps are included in their process.  

7. How do you know whether the recycled resin meets the specific standards of your application?

If you have special standards, such as declarations of absence, California Proposition 65, toxins or food contact declarations in the Packaging Information Exchange (TPCH), you must work with your supplier to meet these needs. As brand owners strive to achieve packaging sustainability goals, the demand for food contact PCR is particularly high.

Globally, there are differences in how to regulate the use of PCR in food contact applications. In the United States and Canada, PCR materials must meet all the same legal requirements as the original materials. The US Food and Drug Administration (FDA) and Canada’s Health Products and Food Department (HPFB) will review the recycling process and material sources, and then issue a letter of no objection (LNO or LONO) regarding the recycling of materials used in the production of food contact applications Opinions on the process and will include the type of food or the resulting PCR usage restrictions.

However, LNO is only a standard that must be met in order to meet food contact requirements. In order to be suitable for the final application from a regulatory perspective, PCR usually undergoes additional tests and obtains additional regulatory declarations.

Regarding cleanliness and gel level, please consult your supplier for its cleaning procedures and melt filtering capabilities. 

The EU has a similar method, but only requires the recycling of food contact materials for food contact applications. Similar to the FDA and HPFB, the European Food Safety Agency (EFSA) will review the recycling process to assess its suitability for the production of food contact PCR. However, so far, opinions have only been expressed on rPET. It is expected that this situation may change as the European Union recently promoted the development of a comprehensive strategy to incorporate plastics into the circular economy.  

The PCR content of the trash bags and tank linings produced is as high as 70%.

8. How do you determine the maximum PCR content that can be used in your product or packaging 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 experimental evaluation and modeling. The final PCR content may depend on the level of gel or impurities, retention of physical properties and aesthetics.

Regarding cleanliness and gel level, please consult your supplier for its cleaning procedures and melt filtering capabilities. As mentioned earlier, the matching density is very important for maintaining physical properties. If this is not possible, consider what measures can be taken to offset the resulting performance changes. Regarding aesthetics, our advice is to embrace the ugliness! PCR looks very good, but it looks unlikely to be the same as the original resin, even with great care during its production. Let different aesthetics begin to tell stories and let consumers know that PCR is being used in your product design—sustainability information is a key part of promoting circular economy growth!

We have seen that some can linings have a PCR level of over 70%, and shrink film has a PCR level of over 40%. For more sensitive applications with strict requirements, starting with a lower dose, such as 10%, and building confidence and experience before aiming at higher loads is a good strategy. Higher loads will be limited by the required part performance and/or aesthetics. Buried PCR in the core layer of the multilayer structure can overcome the beauty of PCR to a certain extent, while relying on high-performance mixed components can offset the decline in physical properties.  

About the author: Anna Rajkovic is a circular economy marketing manager for Nova Chemicals in Calgary, Alta. In her position, she is responsible for the company's PCR product portfolio and promotes the cycle with plastic processors and customers and the entire plastic value chain more broadly. Rajkovic also serves on the Plastic Recyclers Association (APR) Film Technical Committee and the Expert Group Alliance on Ending Plastic Waste, and represents Nova Chemicals at IPANA, RIBCA, PDA, PPI, ASTM and CSA. Contact: 403-250-0635; anna.rajkovic@novachem.com; novachem.com.

Tammy Rucker is the vice president of sustainable materials for Revolution, a plastic recycler based in Little Rock, Arkansas. Her focus is on converting post-consumer polyethylene from internal use to external sales. She joined the company in October 2020 and brings more than 27 years of materials and plastics experience to the company's recycled plastics business. Rucker has held many positions in her career, including quality laboratory chemist, sales, marketing and product management, and marketing communications for several Fortune 500 companies: GE Plastics (now SABIC), Union Carbide (now Dow Chemical) and Avery Dennison. Contact: 312.520-7461; Trucker@revolutioncompany.com; Revolution Company website

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