In this study,
electrostatic charging of lactose and its mixtures with salbutamol sulphate
(SS) were studied as a function of relative humidity (RH). Powder adhesion onto
a steel pipe surface was also investigated. The powders were charged by sliding
in a steel pipe. Increase in RH decreased the charging of lactose and mixtures,
but the effect on SS was not evident. Furthermore, the charge of the mixtures
reversed from negative to positive as RH was increased and remained positive as
the samples were again dried. Humidification also changed the adhesion behavior
of the mixtures onto the pipe surface.