Meaning
A predictive formula determines the duration required for a migrating substance to traverse a functional barrier and begin entering the packaged product. In packaging design, lag time calculation helps engineers determine the shelf life of a food product by estimating when exposure to contaminants begins.
Analytical Methodology
The calculation is derived from Fick’s laws of diffusion and incorporates the barrier thickness and diffusion coefficient. When performing a lag time calculation, the time is proportional to the square of the barrier thickness and inversely proportional to the diffusion coefficient of the migrant. This mathematical relationship highlights the importance of layer thickness in barrier design.
Process Application
Moulders use these mathematical tools to optimize the cost and thickness of multi-layer structures. By utilizing the lag time calculation, designers can reduce the thickness of expensive barrier polymers if the required shelf life of the package is shorter than the calculated time to breakthrough. This optimization allows for more economical material usage without compromising the chemical safety of the product.
Model Boundary
The method assumes that the diffusion coefficient remains constant throughout the shelf life of the product. If matrix swelling occurs, the results of the lag time calculation will underestimate the rate of migration.
