Moisture sorption of cellulose-based porous media containing co-solvents and its impact on pore-fiber transport rates of co-solvent solutions

Water-based inkjet inks typically contain non-volatile, polar compounds - referred to as co-solvents - such as glycerol and ethylene glycol oligomers, which constitute approximately 5-50 wt% of the total ink. The hygroscopic nature of both paper and co-solvents makes their interplay with atmospheric moisture a critical factor in controlling the penetration and drying dynamics of ink, as well as the long-term mechanical and morphological stability of the printed paper. In this study, we systematically investigate how co-solvent deposition influences equilibrium moisture uptake and how the ambient humidity influences the ink absorption dynamics into cellulose fibers. We find that co-solvent addition substantially increases moisture uptake and eliminates the sorption hysteresis present in paper. The moisture sorption of co-solvent-infused paper is well-predicted by the mass-weighted average of the individual, single-material sorption isotherms of paper and co-solvent. The rate of pore-fiber transport of co-solvents was observed to depend sensitively on ambient humidity, the presence of predeposited liquids as well as the addition of surfactants and divalent salts.