Effect of surfactants on water sorption and barrier properties of hydroxypropyl methylcellulose films

Moisture sorption isotherms and water barrier properties of films made from hydroxypropyl methylcellulose (HPMC) containing surfactant mixtures of sorbitan monostearate (SPAN 60) and sucrose palmitate (sucrose ester P-1570) were evaluated at 10 °C. The effect of hydrocolloid/surfactant ratio (H/S) (0.5, 1.0 and 1.5) and the hydrophilic/lipophilic balance of the mixture (HLB: 4.7, 6.0 and 8.0) was analysed. GAB and BET sorption models were tested to fit the experimental data. The equilibrium moisture content of films increased dramatically above aw=0.6. Films with greater H/S ratio have greater water binding capacity. For a specific hydrocolloid/surfactant ratio, equilibrium moisture content of the coatings decreased as the HLB of the surfactant mixture increased. Equilibrium moisture contents of the composite films could be predicted from the corresponding values of pure compounds and the respective component mass fractions by a linear model, in the water activity range of 0.11–0.75. At the high relative humidity at which water permeability of the films was evaluated, the water vapour barrier was effective when the films reached a critical amount of surfactants (H/S=0.5).