Recycled PET under the microscope: NIAS research findings need to be put into context

An interlaboratory study involving 13 laboratories shows how strongly the research methods used and the reporting approach can affect NIAS analysis results. As the use of recycled PET increases, knowledge about the material's origin and processing conditions is also becoming increasingly important.

NIAS screening, covering substances that are not intentionally added or that form in the material, helps to characterise the chemical composition of plastics intended for food contact. It provides a broader picture of the compounds present, including those whose occurrence was not anticipated at the material design stage. However, the results of such analyses require interpretation that takes account of the method used, the scope of the study and the approach to substance identification and reporting.

13 laboratories, different results

The interlaboratory study involving 13 laboratories showed that NIAS analysis results may differ depending on the method used and the way in which the data are processed. The study used commercial analytical techniques, including GC-MS, GC-MS/FID and LC-(HR)MS. The results were affected by factors including the availability of analytical standards, the spectral libraries used and the approach to substance identification and reporting. This indicates the importance of harmonising analytical approaches to improve data comparability.

In practice, results from different NIAS screening studies should not be compared without considering differences in methods, analytical scope and data processing.

"For NIAS, the analysis result alone is not enough. We need to know how it was obtained, which method was used and on what basis a given substance was identified. Discrepancies between laboratories do not necessarily mean that one of the results is incorrect. This is why data quality and comparability are so important," says Bernd Schwarz, Chief Chemical Officer at Kör.

An analytical result should also be distinguished from a material safety assessment. Differences in screening results do not in themselves determine whether a plastic is safe or unsafe. They require interpretation that considers the capabilities and limitations of the method used, as well as the properties of the material under examination.

Material history matters

The interpretation of results is affected not only by analytical methods but also by the material's origin, recycled content and processing conditions.

A separate study analysed PET containing between 0 and 100% recycled material, rPET, processed using different extrusion technologies. The researchers assessed both intentionally added substances and NIAS. The migration profiles of cyclic oligomers varied according to the proportion of rPET and the processing technology used. Multivariate analysis also identified potential markers that may help to detect specific relationships.

The results show that the composition of a sample alone is not always sufficient to explain the observed effects fully. Information about the origin of the plastic and its processing history is also relevant.

"As the use of rPET increases, knowledge of the material's history becomes increasingly important. To develop the circular economy, we need to understand not only which substances were detected in the sample, but also where the material came from and how it was processed. Only by combining this information with the analytical results can we better understand the observed differences," says Raphaël Jaumotte, Technical Manager at Petcore Europe.

From data to knowledge, the role of GeNi

As analytical methods develop, more results become available. However, collecting data alone does not guarantee that they will be easier to compare or that reliable conclusions can be drawn from them. It is essential to organise the data and enable the comparison of results obtained for different samples and under different conditions.

Multivariate analysis can support this process by identifying recurring patterns and examining relationships between material composition, processing conditions and analytical results. In the PET and rPET study, this approach was used to identify potential markers that may facilitate further analysis of the observed differences.

"We obtain the greatest value when we can consider results in a broader context. Comparing data from multiple samples makes it possible to identify recurring relationships and examine which factors may be responsible for them. This provides many more opportunities than analysing each result separately," says Bernd Schwarz.

In a circular economy, a material may pass repeatedly through successive stages of use, collection and recycling. Information about its properties and processing history may therefore be relevant at different stages of its life cycle. If data remain dispersed and are difficult to link to a specific material or process, their potential remains unused.

GeNi addresses this challenge. It is an initiative of Petcore Europe and Kör intended to support the collection and use of analytical data and to convert them into knowledge useful throughout the PET value chain.

"In a circular economy, a material's history does not end after one use. The same should apply to information about it. The more complex the value chain becomes, the more important it is to link data and draw conclusions from experience gained at different stages of material circulation. GeNi is intended to help connect dispersed information and make it more useful for participants across the value chain," says Raphaël Jaumotte.

Combining analytical results with information about the material's origin and processing conditions may support a more comprehensive assessment of PET intended for food contact. It is important not only to detect individual substances, but also to understand the relationships that influence the results. Appropriate use of data may help the industry to improve its understanding of materials and processes at successive stages of the PET life cycle.