The compliance of two-thirds of packaging or plastic materials in contact with food is tested by calculation. This possibility was introduced into European regulations as early as Directive 2002/72/EC, extended today by Regulation (EU) No. 10/2011 and its successive amendments.
The predictive power of the migration calculation tools on offer is highly dependent on the quality of the mathematical or molecular models linking the structure of molecules to their thermodynamic or transport properties.
These computational tools are progressively enriched with new molecular models and theories for predicting chemical affinity and diffusion coefficients of substances as a function of their structure and polymer properties.
.Measurement methods and calculation models can be applied immediately to the evaluation of thermoplastic polymer recycling processes, the redesign of additives (e.g. plasticizers, antioxidants) with lower migration risks, and the assessment of consumer exposure to substances from packaging.
.Key points on diffusion coefficients in polymers (thermoplastics, thermosets, elastomers)
Diffusion coefficients are essential properties for evaluating the performance of functional barriers and for assessing migration kinetics in foods.
Diffusion coefficients are strongly affected by migrant size: volume effects dominate for bulk and rigid solutes (e.g. aromatic solutes), the number of rigid subunits dominates in flexible solutes.
Diffusion activation follows an Arrhenius relationship only far from the glass transition temperature (Tg). In the vicinity of Tg, free-volume effects dominate, and apparent activation energies depend on both temperature and the size of the diffusants.
For compliance testing, it is recommended to use overestimates of diffusion coefficients to reduce the risk of underestimating migration.
When modeling is used to validate polymer mechanical recycling processes, it is recommended to use either realistic estimates or probabilistic modeling.
Key points on sorption and partitioning properties
Aside from diffusion properties, sorption and partition coefficients are essential properties for assessing migration kinetics in foods.
Parallel to fugacities, partial pressures offer the best representation of the force allowing a substance to transfer from one phase to another. Approximations are given for all practical cases of material transfer (from a material to a liquid, from a material to a gas phase, etc.) and possible substances (volatile or not).
Partition coefficients are defined respectively as activity coefficients.
Binary and ternary Flory isotherms offer estimates of activity coefficients for all migration modeling applications: blending of food simulants, wet or plasticized polymers, homo and copolymers.
The effects of temperature are less significant between two condensed phases, but dominant between a condensed phase and a gas phase.
Activity coefficients and their activation by temperature can be calculated on an atomistic scale for arbitrary (uncharged) solutes.
The projects
"FoodSafeBioPack" project: Evaluating and managing the migration of contaminants from cellulosic materials
"FITNess" project: Food packaging open courseware for higher education and staff of companies
"SafeFoodPackDesign" project: Rational design of safe food packaging
Thesis "Engineering food packaging safety"
Thesis "Predicting packaging material compliance by integrating deformation methods and partition coefficient modeling"
List of scientific articles
Thermodynamic properties
Transport properties