WETTING PROPERTIES AND WATER VAPOR PERMEABILITY OF WHEY-PROTEIN-COATED PAPER
Water-related properties of whey-protein-coated pulp paper were measured. The properties measured were 
initial contact angle of a water drop, dynamic change of the contact angle with time, water absorption rate, maximum 
water 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 contact 
angle of water was decreased by increasing coating weight, which indicated that WPI coating increased homogeneity and 
smoothness of the paper surface by filling the porous structure of the paper. Increasing coating weight increased the rate 
of the contact angle change with time, which is associated with a water absorption rate. WPI coating also increased the 
maximum amount of water absorbed by the paper. These results suggest that the printability of water-based ink on WPIcoated 
paper would increase, with faster and greater ink absorption. Even though WPI coating on the paper surface 
accelerated water absorption, it also increased the water vapor barrier property (water vapor resistance). The WVPs of 
paper coated with 5, 10 and 18 g WPI/m2 were 70.5%, 55.2% and 51.2% of that of uncoated pulp paper, respectively.