Steam Cracker Co-Processing Mass Balance Basics
Co-processing plastic pyrolysis oil in steam crackers requires yield-based mass balance attribution under ISCC PLUS rules to substantiate circular claims.
Overall Migration Limits
Meaning
Maximum allowable thresholds for the transfer of non-volatile chemical substances from a plastic article into food or simulants protect consumers from contamination. Under food-contact regulations, overall migration limits define the maximum permissible quantity of all substances combined that may migrate from a polymer into food. This threshold is set at a standard level of sixty milligrams of substances per kilogram of foodstuff, or ten milligrams per square decimetre of food-contact surface.
The boundary of these limits applies to the finished plastic article under its intended conditions of use, including specific temperature and time exposures.
Safety Standard
Establishing a high level of chemical inertness in plastic packaging ensures that the material does not alter the food in an unacceptable way. Compliance with overall migration limits ensures that the plastic does not transfer enough of its constituents to cause organoleptic changes. This parameter measures the cumulative transfer of all mobile species.
Extraction Test
Laboratory assessments use standardized food simulants to measure the release of chemical substances from the polymer matrix. To verify that overall migration limits are met, plastic parts are exposed to liquids like distilled water, ethanol solutions, acetic acid or vegetable oil. The test run is executed at temperatures that match or exceed the worst-case exposure scenarios of real-world use.
Gravimetric analysis then determines the mass of residue left after evaporation of the simulant.
Moulding Influence
Processing variables during injection moulding or extrusion directly influence the migration behaviour of the finished part. High melt temperatures during processing can cause polymer degradation, generating low molecular weight species that increase the risk of failing overall migration limits. Residual stresses and poor crystallization in the moulded part also create pathways that allow additives to migrate more freely to the surface.
Optimizing cooling times and screw speeds helps to minimize polymer degradation, ensures compliance with migration thresholds and prevents structural failures in thin-walled packaging.