Triboelectrification of spray-dried lactose prepared from different feedstock concentrations

Powder systems may acquire electrostatic charge during various pharmaceutical processing operations and may give rise to difficulties in handling and powder flow, mainly due to adhesion/cohesion effects. We have investigated the electrostatic charging of spray-dried lactose prepared from different feedstock concentrations using a laboratory spray-dryer. Triboelectrification of the spray-dried lactose samples was effected through contact with the stainless steel surface of either a mixing vessel or a cyclone separator. Results from both techniques showed differences in charge accumulation and particle-steel adhesion between the spray-dried lactose samples. As the feedstock concentration used to produce the spray-dried lactose was increased in the range 10-50% w/v, the mean charge on the lactose decreased from -20.8 to -1.3 nC g(-1) and -54.9 to -4.1 nC g(-1) for the mixing vessel and cyclone separator, respectively, with a corresponding decrease in adhesion. In addition, as the feedstock concentration was increased from 10 to 50% w/v, decreases were obtained in surface area values (1.06 to 0.56 m(2) g(-1)), pore diameter (198.7 to 83.5 mu m) and pore volume (1.09 to 0.75 cm(3) g(-1)), and together with differences in crystal form correlated with the charge and adhesion results. The results suggested that the feedstock concentration could have a considerable influence on the charging and adhesional properties of spray-dried lactose. This may have relevance during pharmaceutical processing and manufacturing operations.