Breakthroughs for Clean, Recycled Food-Grade PP ResinsBreakthroughs for Clean, Recycled Food-Grade PP Resins

New trace-free labels, decontamination processes, and other emerging technologies are shaping the future of recycled polypropylene resins.

Joanna Cosgrove, Freelance Writer

January 29, 2025

5 Min Read
FTR Soap suds representing cleaning during recycling of polypropylene (PP)
MiguelMalo/iStock; Canva

At a Glance

  • Edward Kosior highlights breakthroughs in removing labels and labeling adhesives when recycling polyproplene.
  • New label and decontamination technologies make recycled PP safe for food-grade use.
  • New methods have been developed to detect and remove very low-level toxic substances.

Labeling and labeling adhesives can cause sticky problems in post-consumer films and rigids recycling but breakthroughs in trace-free labels and decontamination technologies are helping to eliminate toxic substances from recycled polypropylene (rPP) resins.

Below is Part Two of an interview with Edward Kosior, CEO and Founder of Nextek Ltd and NextLooPP. Below, he discusses how these new technologies work to turn post-consumer films and rigids back into safe recycled content for food-grade rPP; and the role of new trace-free labeling and adhesives in the process. (Part One revealed advances in using artificial intelligence to sort food-grade PP.)

Tell us about the new breed of trace-free labeling and adhesives. How do they connect to decontamination advancements and are they accessible to most brands?

Kosior: In a circular economy where materials are recovered at the end of one lifecycle, we must go beyond our old recycling boundaries to eliminate unintended build-up of package elements that might travel with the plastics during recycling. These include the inks, adhesives, binders, and labels as well as the pigments that must be reduced and optimized for recycling to boost rather than hinder the circular economy. This starts with ensuring that all on-pack decorative material is totally removable, everything from adopting labeling systems that detach from the pack-through to stable formulations for inks and binders must be proven to be suitable for the subsequent recycling operations at the early stages of packaging design.

Related:Recycling’s Next Frontier: Artificial Intelligence

Adhesives need to separate from the package and must remain with the label when being recycled. NextLooPP participant Bostik has developed a next-generation range of wash-off label solutions for PP, HDPE, and PET that ensures complete removal during the recycling process, preventing contamination of rPP streams.

Another NextLooPP participant, MCC Verstraete addresses the IML issue with its NextCycle removable IML solution tailored for rigid polypropylene packaging. This system allows decorated packaging to be recycled with minimal interference. During recycling, the labels are designed to shrink and then separate from the PP containers in the hot washing phase, preserving the integrity of both materials. These innovative technologies have been successfully trialed and are already commercially available.

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What specific testing methods are most efficient in terms of ensuring no toxic substances remain in recycled PP resin? How do these methods improve on previous/traditional testing methods?

Kosior: Proving the absence of potentially harmful substances in recycled resins can’t always be easily demonstrated with classical chemical analysis testing due to the very low levels of detection required for substances that might be of concern. This issue led to a Europe-wide initiative, SafeCycle, whose goal to tackle potential contamination in recycled plastics focuses on materials intended for food contact and cosmetics packaging.

SafeCycle, which is coordinated by partners such as Fraunhofer IVV, OFI, and FH Campus Wien, has been investigating testing methodologies to determine DNA-reactive substances that arose in some recycled plastics and not in others after extrusion and were considered toxicologically significant. These very low-level contaminants, which are challenging to detect and characterize with traditional analytical methods, have been found to create a response in a modified Ames test for mutagenicity.

Following their initial findings, SafeCycle dug deeper to identify exactly what was causing the issue by developing a comprehensive testing protocol utilizing high-resolution mass spectrometry, liquid chromatography, and bioassays. These methodologies aim to identify and categorize contaminants, thereby helping to develop guidelines for safer recycling processes that prevent these substances from entering recycled materials.

Unprinted polyolefin film that is re-extruded did not cause a problem, however, where packaging was printed — or had labels, glues, binders, and inks — the extrusion step triggered the release of decomposition products that were identified as mutagenic responsive triggers to the modified Ames Test.

Refining findings further, it was established that the re-extrusion of nitrocellulose binders was one of the main contributors. As for inks, each color comes with its own spectrum of challenges with organic yellow being one of the most concerning. Whilst inks are strictly regulated and fit-for-purpose during their application, meaning nitrocellulose binders would never be used in packaging that requires high-heat exposure such as ovenable packaging, once in the recycling stream, with no control of the input, they will be heated to T >250°C [482°F] during extrusion. In these conditions, the inks will degrade, making the recycled material unsuitable for contact-sensitive applications due to safety concerns.

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Can recycled material derived from printed packaging be decontaminated to an acceptable level for safe use in food-grade packaging, even after going through the extrusion process?

Kosior: We are making good progress in this direction. Whilst more work needs to be done to validate our findings, NextLooPP’s high-performance decontamination process, which relies on extracting volatile and semi-volatile materials in the melt stage and the solid state and the PPristine food-grade resins, has passed the modified Ames test showing no mutagenic responses.

Furthermore, Nextek’s novel technology, COtooCLEAN uses a supercritical CO2 process to extract contaminants from polyolefin films at very high rates.

One of NextLooPP’s participants, HydroDyn, the innovative cleaning technology company, has developed an advanced approach for removing labels, adhesives, inks, and other contaminants from recycled plastics. This process centers on its innovative HydroCleaner and HydroSeparator technologies, which can eliminate up to 99.9% of extrinsic contaminants, including ink from labels.

Inks and coating specialists, Siegwerk have been running in-depth studies to investigate the de-inkability of direct-printed PP cups. Adhering to DIN SPEC 91496, the tests resulted in complete ink removal with undetectable color differences in the final resin.

In order to address these more complex circular economy recycling issues we must continually reassess our guidelines for Design for Recycling, taking these findings into account and re-aligning with the latest recycling technologies that overcome these hurdles.

With so many different substrates, how can this be done automatically?

Kosior: In reality, there are not that many substrates used in packaging in most markets. The plastics used in packaging are mainly polyethylene (LDPE and HDPE), polypropylene, and polyethylene terephthalate (PET). Sorting into individual polymer streams is an important initial step prior to introducing any of these technologies. No doubt there will be important integrations occurring in the way we initially design products so that the treatments during recycling can become integrated into the standardized recycling systems for the plastics. The various treatments only require adjustment mainly based on whether the products are thin films or thicker rigid packaging so this is not a limiting step.

About the Author

Joanna Cosgrove

Freelance Writer

Joanna Cosgrove has enjoyed writing about the packaging industry for more than 20 years.

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