WETTING PROPERTIES AND WATER VAPOR PERMEABILITY OF WHEY-PROTEIN-COATED PAPER

Abstract

Water-related properties of whey-protein-coated pulp paper were measured. The properties measured wereinitial contact angle of a water drop, dynamic change of the contact angle with time, water absorption rate, maximumwater absorptiveness, and water vapor permeability (WVP). Whey protein isolate (WPI) solutions with WPI:glycerol =6:4 were spread on pulp papers to produce final coating weights of 5, 10, and 18 g/m2 of WPI on the paper. Initial contactangle of water was decreased by increasing coating weight, which indicated that WPI coating increased homogeneity andsmoothness of the paper surface by filling the porous structure of the paper. Increasing coating weight increased the rateof the contact angle change with time, which is associated with a water absorption rate. WPI coating also increased themaximum amount of water absorbed by the paper. These results suggest that the printability of water-based ink on WPIcoatedpaper would increase, with faster and greater ink absorption. Even though WPI coating on the paper surfaceaccelerated water absorption, it also increased the water vapor barrier property (water vapor resistance). The WVPs ofpaper coated with 5, 10 and 18 g WPI/m2 were 70.5%, 55.2% and 51.2% of that of uncoated pulp paper, respectively.