Evaluating Packaging Sterilisation Efficacy Using Computational Fluid Dynamics

Abstract

Sterilisation of packaging with vapour hydrogen peroxide (VHP) is commonly used across the consumer-packaged goods (CPG), food, beverage, and pharmaceutical industries to prevent product contamination from bacteria, viruses and fungi, and for the removal of chemical residues and particulate matter. To verify the efficacy of sterilisation, experimental testing is undertaken whereby bacterial cultures are deposited prior to VHP exposure and then monitored to see if they remain and grow after VHP exposure. While this test indicates a pass or fail outcome, and where in the bottle the failure occurred, the test does not give insight into why the failure occurred. As companies increasing aim to introduce more sustainable packaging concepts through lightweighting and geometry optimisation, understanding the "why" helps to assure safety and quality whilst accelerating the delivery of more sustainable packaging concepts to the consumer.

To that end, modelling and simulation serve as valuable tools to complement laboratory measurements, providing insights prior to physical testing. By understanding the flow of VHP during sterilisation and the concentration of VHP on the exposed surfaces, these techniques can provide greater confidence in the safety of the packaging. Moreover, with virtual Design of Experiments (DOE) analysis, sensitivities to manufacturability tolerances can also be assessed.

The purpose of this study is to show how Computational Fluid Dynamics (CFD) can be used to achieve these objectives. To do so, this study compares typical and representative (but generic) bottle designs and processing conditions, highlighting differences in outcomes and complexities despite the geometric similarities. The differences are numerically quantified by calculating the Sterility Assurance Level (SAL) and other metrics from relevant CFD output variables. The following observations were made from the analyses: a) given fixed sterilisation processing conditions, the absolute dimensions of bottles and associated geometric features can significantly influence the transient flow during the bottle fill up process; b) the combined effects of the geometric features and the mass flow rate of VHP lead to non-negligible changes in VHP surface coverage which impact sterilisation efficacy. These observations can have a significant impact on products where the sterilisation processing conditions remain fixed but different bottle volumes (500mL, 1L, etc) are used.