News Items - International Association of Packaging Research Institutes
Migration testing for paper-based packaging

As the focus on renewable raw materials for packaging intensifies, there is a growing need to find more consistent and accurate ways of testing paper and board to ensure compliance with regulations and to evaluate potential migration into food.

That at least is the view at the Fraunhofer IVV institute in Germany, where a team began work at the start of the year on the MigPAP multi-partner project. The premise is that conventional test methods, such as applying hot or cold water or solvent extracts to paper-based packaging can result in overestimates of the real level of migration into food. That in turn can lead to incorrect judgements of non-compliance, says project leader Angela Störmer, who works in the institute’s product safety and analytics department.
 
“One example would be the dialkylketones occurring in papers with AKD [alkyl ketene dimer] sizings,” she tells IAPRI. Potential disqualification on the basis of isooctane extraction testing has reportedly been discussed on several occasions by Germany’s Federal Institute for Risk Assessment (BfR). “We have shown in a publication that isooctane and also vegetable oil overestimate real migration into cheese, salami or croissant by [a sizeable margin],” says Störmer.
 
“The aim of our project is to allow the setting, for example, of a maximum shelf-life during which migration levels will stay below the relevant limits, based on more realistic migration simulation tools,” she explains, adding that the objective is to make this achievable via either an experimental or a theoretical, modelled route.
 
The institute’s role in the project will include investigating material transfer processes through migration and permeation tests, basing these initially on well-defined paper samples. This will allow researchers to estimate diffusion and distribution coefficients for the substances as they are influenced by environmental and materials-related factors such as moisture.
 
Model-based simulations can then be used to generate kinetic data. These findings, along with experimental outcomes, are expected to suggest ways of making migration testing more realistic.
 
Ambitions and challenges
 
Störmer does not minimize the challenges. “Mobility of migrants within paper and board materials, and transfer into food, is a very complex process which depends on a number of physico-chemical and material-related parameters,” she says, contrasting this complexity with the migration dynamics of plastics.
 
“Plastics are usually homogeneous polymeric networks, in which the migratable organic substances are dissolved and, at a given temperature, diffusion of an organic substance depends mainly on its molecular volume,” Störmer explains. “In paper and board, we have cellulose fibers of different sizes building a non-homogeneous network with air-filled pores.”
 
In this type of network, the mobility of a migrating substance will depend on a sequence of diffusion-adsorption-desorption-diffusion steps, she points out, where polar substances behave differently from non-polar ones and fiber length, pore size, humidity and substance volatility all play a part.
 
Despite a huge amount of literature having been published in recent decades, much of it is fragmented in terms of areas of focus, and Fraunhofer IVV claims there is still no overall quantitative understanding of the dominant transport processes. “Our approach is to generate three-dimensional theoretical fiber-pore models in order to better understand the processes and figure out the main driving parameters,” Störmer says. “These complex models will be simplified for industry applicability in a later step.”
 
Summing up, she believes that the challenges will start with the benchmark defined papers, and the need to characterize them in such a way that material-related parameters can be extrapolated.
 
“The second challenge is to experimentally generate migration and/or permeation data, using selected test substances, which is precise enough to parametrize the three-dimensional model,” Störmer explains.
 
The third challenging area will be building the model in such a way that it is able to explain the influencing parameters and describe the experimental values, she adds.
 
Fraunhofer IVV is working with the Technical Universities of Darmstadt and Munich on the MigPAP  project, which will run until mid-2025.
 
Mineral oil risks
 
The specific risks associated with mineral oil migration into food have, in recent years, become a major concern, leading to stricter regulation and increased testing – at least, in certain markets. “For instance, in Germany, there is a decree [going through] the legislative process which requires functional barriers for paper food packaging to reduce the transfer of aromatic mineral oil components to non-detectable levels,” says Störmer.

These moves are just one example of more intensive efforts to protect the consumer from unwanted materials migrating from packaging materials. “This comes into conflict with the aim to increase the use of recycled materials,” she points out. “At the same time, barriers might influence the recyclability.”
 
Specifically with regard to mineral oils in Europe, different national safety bodies have been approaching the question in different ways. That may be about to change, given that the European Food Safety Authority (EFSA) is widely expected to be about to provide a revised scientific opinion on this topic to replace the current one, which is now 10 years old. The EU is understood to be intent on introducing restrictions on mineral oil content in – and migration into – food.
 
At last year’s IAPRI Conference, Nestlé’s research team presented a paper examining the issue of mineral oil barrier and how to measure its effectiveness. As the abstract says: “While the determination of mineral oil migration is complex and time-consuming, it has been shown that Hexane Vapor Transmission Rate (HVTR) could be a good proxy for the screening of mineral oil barrier in packaging materials.”
 
The Nestlé team worked at developing an automated gravimetric method to determine the HVTR of barrier papers. At the same time, they tried to avoid possible pitfalls linked to the sample setup and to the hygroscopic nature of paper. The aim was to be able to test entire packages, including seals, leaks and other defects from the converting process, as well as the paper-based material per se.
 
“The results show that by understanding and avoiding common artefacts of paper testing, a method with significantly improved robustness compared to those commonly reported for the HVTR  testing of paper-based materials could be developed for flat materials and adapted to test complete packages,” says the presentation.
 
The complexities of paper and board packaging pose some particular food safety problems. But, referring to the general issue of migration from these materials into food, Störmer at Fraunhofer IVV concludes: “By better understanding the transport mechanisms in paper substrates, including barriers, our project wants to provide tools which will help to develop solutions for packaging systems with sufficiently effective barriers.”
 
 

Published: 04/27/23