Elucidating the mechanisms of liquid and vapour transport during drying of porous coatings

The influence of the coating composition of a porous paper coating on the evaporation rate of water contained in the sample has been studied experimentally. For low-content latex samples, drying was found to be mainly controlled by capillarity, perhaps also in the form of thin film pore surface feature/wall wetting, which drew water from the connected pores to the drying surface or near the surface. This led to a lengthy constant drying rate period (CDRP) where nearly 70 % of the saturated water was evaporated. High-content latex samples, characterized by low porosity and permeability showed shorter CDRP and lengthy falling drying rate period. The drying rate curve varied as the square root of time, indicating a diffusive controlled mechanism. Low latex content samples took less time to dry, which can be inferred to mean they require less drying energy.