Meaning
Chemical mass transfer describes the transport of photoinitiator residues from printed packaging materials through a polymer layer into dry or aqueous food stimulants. Packaging films made from low density polyethylene allow unreacted printing additives to cross the matrix, so benzophenone migration measures the quantity of chemical mass reaching the food contact interface. The phenomenon stops applying when a functional barrier such as aluminum foil or glass completely blocks molecular transport.
Mass Diffusion
Thermal motion drives low molecular weight organic molecules through the amorphous phase of semi-crystalline polymers. When printed ultraviolet inks remain uncurated on outer carton surfaces, benzophenone migration proceeds through print-to-contact set-off during roll storage or through gas-phase diffusion across the air gap inside the package. Higher storage temperatures accelerate transport rates, while thicker polymer layers lengthen the physical pathway that molecules traverse.
Crystallinity in polypropylene reduces total free volume, slowing mass loss into fatty food matrices.
Barrier Permeability
Functional barriers limit mass flux depending on polymer density and layer thickness. Monolayer polyolefin structures fail to prevent benzophenone migration over extended shelf life periods. Coextruded ethylene vinyl alcohol layers restrict non-polar organic movement effectively.
Regulatory Threshold
European union plastic materials regulations establish specific migration limits for substances transferred into food. Testing protocols specify specific migration limits measured in milligrams per kilogram of food simulant, requiring gas chromatography testing for verification. Excessive benzophenone migration renders packaging lots non-compliant, forcing converters to discard affected inventory or substitute low-migration ink formulations.
