Meaning
Molecular diffusion through semi-crystalline plastic matrices carries additives or monomers from the bulk material to the surface. The phenomenon of polyolefin migration is most common with slip agents, antistatic chemicals and antioxidants. These molecules move because they are not chemically bonded to the polymer chains and have low solubility in the resin.
Diffusive Flux
Temperature and concentration gradients determine the speed at which chemicals move toward the part surface. Higher temperatures increase the kinetic energy of the molecules and accelerate the polyolefin migration process. Movement continues until a chemical equilibrium is reached between the surface and the core.
Food Contact
Chemicals that reach the surface can transfer into the contents of a package or container. Managing polyolefin migration is a primary concern for the safety of bottled water and fatty foods. Limits are set on the total amount of material that can leave the plastic during the shelf life of the product.
Organoleptic Effect
Changes in the taste or smell of a product occur when migrated substances dissolve into the stored liquid. Even if the migrating chemicals are non-toxic, polyolefin migration can ruin the consumer experience by introducing a plastic-like odor. Selecting high-purity resins reduces the risk of these sensory defects.
Finished parts stored in warm warehouses are more susceptible to these changes than those kept in climate-controlled environments. Testing for these defects often involves sensory panels or specialized gas chromatography to detect trace levels of volatile compounds.
