THE USE OF THE WASHBURN METHOD IN DETERMINING THE CONTACT ANGLES OF LACTOSE POWDER

This paper studies the contact angles of lactose powder determined by the Washburn method based on liquid intrusion into the powder bed. The liquids used were water, methanol, 1-propanol, 1-butanol, 1-octanol a nd n-hexane. Liquid intrusion was studied with saturated solutions. Li quid flow to the powder column was controlled with a technique allowin g constant liquid flow with zero hydrodynamic pressure. Packing of the lactose powder into glass tubes was done manually by tapping in a ver tical motion. The packing of the powder columns was studied with diffe rent packing times (3, 6 and 12 min) and different size fractions (> 2 12 mum, 106-212 mum and < 106 mum) of lactose. Packing time was not fo und to be critical with optimal shaped lactose particles and the short est packing time, 3 min, was adequate. Liquid intrusion rate diminishe d with diminishing particle size. The intrusion rates of the liquids v aried significantly. The slope values of intrusion distance squared vs intrusion time were 0.798 (n-hexane), 0.414 (methanol), 0.179 (water) , 0.123 (1-propanol), 0.099 (1-butanol) and 0.036 (1-octanol). n-Hexan e was found to be the best wetting liquid. Estimating the n-hexane con tact angle to be 0-degrees, the following values for the other liquids were obtained: water 61.7-degrees, methanol 38.7-degrees, propanol 39 .2-degrees, butanol 33.4-degrees and octanol 36.2-degrees.