Total Immersion Extraction

Test Condition

Procedure for a migration test is defined by the choice of simulant and the duration of the contact period. A plastic sample of known surface area and weight is placed in a glass container filled with a simulant that mimics the properties of a specific food type. The container is then held at a constant temperature in an oven or incubator for a period ranging from a few hours to several days.

This setup ensures that the migration process reaches a point that represents the actual shelf life of the final product. For total immersion extraction, the ratio of the simulant volume to the plastic surface area must be carefully controlled to ensure the results can be accurately scaled. If the temperature is too high, the plastic may swell or deform, leading to results that do not reflect normal use.

Solvent Interaction

Ability of the liquid to penetrate the polymer matrix determines how much of the internal additives will be released. In a total immersion extraction, the simulant comes into contact with the cut edges and the interior surfaces of the plastic, which might not be exposed in a real world application. This can lead to higher migration values than a one sided test where only the food contact surface is exposed.

Some solvents, like hexane or ethanol, are very aggressive and can cause the polymer chains to relax, speeding up the diffusion of migrants. This interaction is useful for rapid screening and quality control but must be interpreted with care when comparing to legal limits. The stability of the migrant within the solvent also affects the final measurement, as some chemicals may degrade or evaporate before they can be quantified.

Migration Boundary

Compliance is determined by weighing the residue left after the simulant has been evaporated or by analyzing the liquid for specific chemicals. The total immersion extraction result is usually expressed in milligrams per square decimeter or milligrams per kilogram of food. If the total migration exceeds the legal limit, the material must be reformulated or the thickness of the part must be changed.

This testing boundary ensures that the plastic does not release enough material to alter the composition of the food or pose a health risk to the consumer. For many moulders, these results provide a definitive pass or fail grade for a new resin or a change in a processing variable. Regular use of this technique is a primary tool for maintaining the safety and quality of plastic articles.