Moisture transport in paper and paper coatings

On applying water based adhesive coating on a silicone-coated paper, water from the coating permeates through the layer of silicone coating and is absorbed by paper. During drying, water evaporates from both the coating and the paper layers simultaneously; there is also transport of moisture between the coating and paper layers through the silicone layer. Initially, the water evaporation rate from the coating is dominant, but at longer time period the water evaporation rate from paper dominates. Mathematical models for moisture transport in an adhesive coating layer and a paper layer are developed and experimentally validated. Models for moisture transport in coating layer, paper layer and a pseudo steady state (PSS) model for moisture transport in a silicone layer are combined with appropriate boundary conditions to model drying of adhesive coating applied on silicone-coated paper. The mathematical model is solved using the Galerkin's finite element method. To extend the model for drying of adhesive coating applied on silicone-coated paper to drying of adhesive coating applied on un-coated paper, a constitutive model of paper to predict the effect of moisture on the physical and transport properties of paper is required. A constitutive model for paper is developed by mapping the results from Single fiber deformation model to predict cross-sectional shape of a paper fiber at varying stages of drying and/or moisturization, onto Unit cell models of paper structure. A method for predicting the macroscopic properties of paper from the fiber geometry in idealized structural arrangement is presented.