Meaning
Mass transfer variables determine the rate at which molecules migrate through a polymer layer designed to isolate contents from external contaminants. Food safety depends on functional barrier kinetics to ensure that recycled content in a multilayer structure does not allow chemicals to reach the internal product. Barrier layers prevent the passage of mineral oils or volatile organic compounds from the outer regrind layers.
Diffusion Rate
Molecular movement follows Fickian laws where the concentration of the migrant and the temperature of storage drive the speed of penetration. Higher temperatures accelerate functional barrier kinetics and reduce the shelf life of the packaged goods.
Compliance Threshold
Regulatory bodies define the maximum migration levels allowed for food contact materials. Testing functional barrier kinetics involves measuring the specific migration of surrogate molecules over a set period. Compliance results confirm that the barrier layer effectively blocks substances below the legal limit.
Layer Thickness
Engineering the wall structure requires a balance between material cost and protection. A thicker layer of ethylene vinyl alcohol provides slower functional barrier kinetics than a thin skin of the same material. Nylon is often used in automotive fuel tanks to stop the permeation of hydrocarbons through the high density polyethylene.
Calculating the required thickness involves modeling the solubility and the diffusion coefficient of the most mobile species.
