Prof Edward Kosior at Nextek and Paul Marshall at NEXTLOOPP have recently conducted a multi-phase project to develop a comprehensive Polyolefin Challenge Test Guide. This aims to help the industry validate the decontamination performance of recycling processes to produce recycled polyolefins for contact-sensitive applications.
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Polyolefins (PO), primarily HDPE and PP, represent the dominant fraction of household plastic packaging. Unlike PET, however, polyolefins have faced regulatory limitations for direct food-contact applications. This is due to insufficient evidence of adequate decontamination performance in PCR systems based on historical published data regarding incidental contamination rates in 2005.
To meet the UK Plastics Pact target of 30% average recycled content across all plastic packaging by 2025 and PPWR requirements by 2030, recycled polyolefins must be safely used in sensitive applications, including those with direct food contact.
To achieve this, WRAP and Innovate UK led a three-year, multi-phase project, conducted by Nextek’s Recycled Plastics Food Contact Plastics Specialist, Paul Marshall. A standardised challenge test protocol has recently been completed to evaluate the cleaning efficiency of mechanical and non-mechanical polyolefin recycling processes.
Whilst the concept of testing recycling processes is not new, current guidance focuses mainly on the principles of testing and provides less guidance on how to design and perform tests practically. Our project developed a structured, laboratory-scalable challenge test protocol structured across seven key phases.
The outcome provides a basis for progressing regulatory submissions supporting the closed-loop and semi-closed-loop use of recycled HDPE and PP in high-value applications.
Bridging regulatory gaps for recycled polyolefins
We started with a desk-based study, examining the history of challenge tests to better define what worked well and what appeared to be missing. We wanted to ensure that guidance delivered at least the information required by UK and EU regulations, as well as drawing on advice from the US FDA. The regulatory context was complex. EU Regulation 2022/1616 establishes requirements for recycled plastics intended for food contact, but lacks validated opinions for HDPE and PP mechanical recycling systems.
EFSA has issued inconclusive data positions for HDPE mechanical recycling processes due to varied feedstock streams, limited contamination datasets from real-world feedstocks and variable migration behaviours. The FDA guidance (2006) remained unchanged and is primarily PET-centric.
If we are to progress polyolefin circularity, regulators require robust, process-specific evidence of decontamination efficiency, demonstrated through a controlled surrogate challenge test.
Two years into our project, in 2024, EFSA updated its guidance following challenge tests on PET. Even with this progress, it was clear that the sector still lacked a practical, accessible challenge test approach tailored specifically to polyolefins.
Designing a practical and reproducible challenge test
A challenge test works by intentionally contaminating plastic with known chemicals, running the material through a recycling decontamination process and analysing how much contamination remains compared to the starting level. For polyolefins, the chemicals used in testing had to realistically reflect substances that plastics may encounter in real-world use.
The work began by considering the nature of polyolefins and where they’re used. While food-contact grades avoid harmful additives, non-food applications such as electrical goods may contain flame retardants and other substances that should not carry over into recycled food-contact materials. Additionally, inks, coatings and labels can introduce degradation products or residues if not properly removed before or during recycling.
The project assessed the types of products commonly stored in polyolefin packaging, such as bleach, cleaning agents and personal care products, and examined potential migration of these ingredients into plastic. Co-mingled recycling streams showed superficial cross-contamination (e.g., milk bottles in contact with shampoo residues), whereas polyolefins sourced from residual waste streams posed a higher risk of deeper contamination from both organic and inorganic compounds. These findings reinforced the importance of robust sourcing, traceability and controlled feedstock streams.
Selecting representative surrogates
The next step was to select surrogate chemicals that could reliably mimic their behaviour. The aim was to cover a realistic spread of volatility and polarity while avoiding substances with problematic hazard classifications. We also considered availability and cost to ensure the test could be widely adopted by recyclers.
Once the surrogates were chosen, the team evaluated contamination methods. The Fraunhofer IVV-style conditioning method, where a concentrated mixture of surrogates is heated with the plastic, has historically delivered consistent contamination across molecular weight ranges.
Contrarily, the FDA-style method introduces weaker contamination and is useful for modelling packaging misuse. However, it shows lower absorption of higher molecular weight substances. This difference demonstrates that such substances have limited migration potential in real-world packaging use.
To verify robustness, both contamination approaches were compared alongside classic and new surrogate sets at the lab scale.
Scaling to commercial processes
Challenge tests were conducted at commercial scale across multiple recycling technologies and polyolefin types, producing test batches of tens of kilograms. Both the new surrogate set and the traditional surrogate group demonstrated comparable removal behaviour, confirming the suitability of the selected surrogates.
During this phase, analytical methods and sampling plans were refined to ensure efficient testing and reliable interpretation of decontamination performance.
The final surrogate group intentionally spanned a broad molecular weight range, from low-volatility substances to higher-weight compounds representing additive-like contaminants.
Fraunhofer-style conditioning was adopted because it provides more consistent and measurable absorption of higher molecular weight substances than the FDA-style approach. This ensures that the decontamination performance reflects how polyolefins behave in real recycling environments.
Multiple commercial recycling plants, processing HDPE, PP, and emerging technologies, were tested. The results showed that alternative surrogate chemicals performed the same as classical surrogates, validating their use in routine challenge testing.
Conclusion
This project establishes a clear, practical and scientifically robust protocol for evaluating recycled HDPE and PP intended for high-value and sensitive applications. It provides:
- A shared, validated standard for assessing food-grade recycled polyolefins
- A pathway toward regulatory acceptance in the UK and EU
- A means for recyclers to demonstrate performance without needing proprietary test systems
- Support for investment in higher-grade recycled content capacity
It opens the door to true closed-loop recycling for everyday packaging –– food-grade milk bottles into milk bottles, contact-sensitive shampoo bottles into shampoo bottles –– rather than wasteful downcycling. The loop can now begin to close with greater confidence and human safety through practical science applied to the demonstration of measurable decontamination of polyolefins.