Date of Completion

11-18-2014

Embargo Period

11-17-2014

Keywords

Triboelectrification, work function, milling, damage accumulation, Discrete Element Method

Major Advisor

Dr. Bodhisattwa Chaudhuri

Associate Advisor

Dr. Robin Bogner

Associate Advisor

Dr. Ramesh Malla

Associate Advisor

Dr. Montgomery Shaw

Field of Study

Pharmaceutical Science

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

Abstract

In the pharmaceutical industry, over 75 percent of all products are in the solid dosage form. Considering their prevalence, the aim of this study was to employ experimental methods and process modeling tools viz. Discrete Element Method (DEM) to ascertain the effect of powder flow and material properties during triboelectrification and particle size reduction. Considering electron exchange to be the dominant mechanism for charge transfer, work function all powders viz. Ibuprofen, theophylline, microcrystalline cellulose and lactose was estimated from quantum chemical calculations. Tribocharging of individual powders in a V-blender revealed a higher specific charge for Ibuprofen against all surfaces. Moreover, for mixtures, charge mitigation was observed. To facilitate model development, a hopper-chute assembly was employed to investigate the effect of coefficient of friction (COF) and coefficient of restitution (COR). The specific charge increased with COF due to longer contact time and greater particle-wall collisions. Secondly, the specific charge increased as COR was decreased, suggesting that continuous contacts transfer more charge than bouncing contacts. The model was able to capture the collisional nature of tribocharging although discrepancies were observed between numerical results and experimental observations. Thus, a collective experimental and simulation approach was found to be beneficial in identifying gaps and enabling a comprehensive interpretation of an intricate process.

To study the effect of process parameters on milling, dynamic mechanical analyzer was employed to investigate the effect of damage accumulation during breakage. Damage accumulation was found to be low since the change in breakage force upon repeated impacts was insignificant. High feed rates at lower speeds resulted in flood feed conditions, which changed the mode of breakage from fragmentation to attrition. Additionally, this effect was verified from the velocity profiles obtained from simulations that revealed stagnation of the powder bed, which consequently reduced the breakage rate. Although, the DEM model does not account for any attrition, simulations could qualitatively capture the effect of impeller speed and feed rate on the average particle size. Consequently, a combined experimental and simulations approach can be employed to direct experiment and equipment design thereby providing a better understanding of a process.

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