Multi-scale simulation of paperboard edge wicking using a fiber-resolving virtual paper model

When liquid packaging board is made aseptic in the filling machine, the unsealed edges of the board are exposed to hydrogen peroxide. A high level of liquid penetration may lead to aesthetic as well as functional defects. The ability to make a priori predictions about the edge wicking properties of a certain paperboard material is therefore of great interest to the paper industry, as well as to packaging manufacturers. In this paper, a multi-scale framework is proposed that allows for detailed simulation of the edge wicking process. On the fiber micro-scale, virtual paper models are generated based on input from tomographic and scanning electron microscope (SEM) images. A pore morphology method is used to calculate capillary pressure curves, and on the active pores, one-phase flow simulations are performed for relative permeabilities. The results as functions of saturation and porosity are stored in a database. The database is used as input for two-phase flow simulations on the paper macro-scale. The resulting fluid penetration is validated against pressurized edge wick measurements on paper lab sheets with very good agreement. The proposed multi-scale approach can be used to increase the understanding of how edge wicking in paperboard packages depends on the micro-structure.