(273d) Experimental and Multi-Scale Modelling to Understand Electrostatic Behavior of Pharmaceutical Powders

Naik, S. S., University of Connecticut
Sarkar, S., University of Connecticut
Hancock, B. C., Pfizer Worldwide Research and Development
Yu, W., Pfizer
Abramov, Y., Pfizer Global Research & Development
Gupta, V., University of Connecticut
Chaudhuri, B., University of Connecticut

In pharmaceutical formulation processes, particle charging is often a nuisance and can cause problems in the manufacture of products, such as affecting powder flow, and reducing fill and dose uniformity. For a fundamental understanding of the powder triboelectrification, it is essential to study charge transfer under well-defined conditions. Hence all experiments were conducted in a humidity controlled glove box at 20%rh.  To understand tribocharging materials, different surface viz. PVC, aluminum, Teflon, PMMA were used along with two pharmaceutical excipients and two API’s. The experiments were performed in V-blender at a prescribed speed of 13 rpm. A triboelectric series of pharmaceutical materials was generated. For the pharmaceutical materials the work function was determined using MOPAC. MOPAC is a general-purpose semi-empirical molecular orbital package for the study of solid state and molecular structures and reactions providing band gap and ionization potential of molecules. In addition a discrete element method (DEM), including charge transfer and screened coulombic forces was developed for the V-blender system.  There are different competing mechanisms involved in tribocharging. The two most important ones are electron transfer and ion transfer. Electron transfer has been well established for metal-metal and to some extent for insulator-metal contacts. There is still an ongoing debate for insulator-insulator charging whether the charge carriers are electrons or ions. As per work function hypothesis or established tribo-electric series powders should charge negatively against Alumimium, PMMA surfaces and positively against Teflon surfaces and PVC surfaces. According to the experiments in V-blender both the excipients (lactose and MCC) and API’s charged negatively against PMMA and Aluminum and positively against Teflon and PVC surfaces