LAUSR

Abstract A thermodynamically consistent model for multiphase flow in swelling cellulose based material is adopted. The material is decomposed into a fiber phase, a gas phase and an inter-fiber water phase, where the fiber phase consists of a fiber water and a dry fiber constituent and the gas phase is an ideal gas mixture of water vapor and dry air. The model is derived within mixture theory and includes local non-equilibrium mass exchange between inter-fiber water, fiber water and water vapor. From assumptions on the microscale structure a novel model is derived to account for spatially varying hydrophobicity. An finite element implementation is made and employed to solve boundary value problems for edge wicking to investigate the water transport in paperboard with varying hydrophobicity. The results are analysed with the aim to better understand the mechanisms of interaction between water and fiber/cellulose. Simulations with spatially varying hydrophobicity reveals different regimes of the macroscopic water uptake made accessible by the decomposition of the water into inter-fiber water and fiber water contributions.