Meaning
Safety evaluations for food contact plastics measure the sum of all non-volatile substances that transfer from the material into a food simulant. This value, known as total migration, serves as a measure of the overall inertness of the polymer and its suitability for packaging applications. It is expressed as the weight of material lost from the plastic per unit of surface area, typically in milligrams per square decimetre.
A high level of migration indicates that the plastic is reacting with the food or that it contains a large amount of soluble residuals. Regulatory limits are set to ensure that the plastic does not change the composition or the sensory qualities of the food. Every food contact material must pass this test before it can be legally sold in most jurisdictions.
Gravimetric Test
Measuring the total amount of material transferred is a straightforward but precise laboratory procedure. The test for total migration involves exposing a plastic sample to a food simulant for a specific time and temperature and then evaporating the liquid to dryness. The weight of the residue that remains after evaporation represents the total amount of material that leached from the plastic.
This method captures all types of substances, including monomers, oligomers and additives, without needing to identify them individually. If the weight of the residue exceeds the legal limit, the material is considered non-compliant. This process provides a clear and objective way to assess the quality of the resin and the moulding process.
Exposure Condition
Simulation of the real-world use of a product is necessary for obtaining a meaningful migration result. The rules for total migration testing specify the time and temperature based on the intended use of the part, such as two hours at seventy degrees Celsius for hot filling. These conditions are designed to be more severe than the actual use to provide a safety margin.
If a part is intended for use in a microwave or an oven, the test must be performed at much higher temperatures. Moulders must ensure that the grade of resin they choose can withstand these conditions without degrading or releasing excessive amounts of material. The selection of the correct test conditions is the responsibility of the manufacturer and is a critical part of the compliance process.
Material Suitability
Performance of a plastic part in a migration test depends on both the chemical nature of the resin and the quality of the manufacturing. A high total migration can be caused by the use of low-purity materials or by the thermal degradation of the polymer during the injection moulding cycle. If the melt temperature is too high, the polymer chains can break down into smaller molecules that are more likely to migrate.
Moulders must balance the need for fast cycle times with the requirement for low migration to produce a safe and profitable product. Regular monitoring of the migration levels helps to identify drifts in the process and ensure that the quality remains consistent. This test is a fundamental tool for protecting the integrity of the food supply chain.
The management of total migration supports the development of safer and more sustainable packaging.
