(357e) Spatially Resolved Characterization of Capping Using Nondestructive Ultrasonics and Finite Element Modeling

Capping is one of the mechanical defects in tableting process in which catastrophic failure of the compact can occur. Understanding what influences capping in terms of process variables, mechanical properties, and density/stress distributions in compacts and developing specialized techniques to quantitatively correlate these variables to capping/lamination tendencies of formulations are practical interests of the pharmaceutical industry. In this talk, we will present a nondestructive ultrasonic method to quantitatively evaluate the capping tendencies of single-component, binary, tertiary mixtures as well as real-life formulations. The speeds of pressure (longitudinal) and shear (transverse) waves in uni-axially compressed tablets were measured in different directions using the developed ultrasonic method. Average elastic (E) and shear (G) moduli of each tablet in these directions were characterized. The ultrasonic measurements revealed that elastic and shear modulus values vary with different testing orientations which indicate elastic and shear moduli anisotropy in compacts. The extent of capping tendency (EG) was quantified by using a dimensionless ratio. It was found that EG values increase with increasing anisotropic mechanical properties of the compressed powder. The presented method is an attractive tool for process and formulation scientists since it has the advantages of being nondestructive, fast (measurement time less than 15 microseconds), requiring no calibration and requiring a small amount of material thus it supports material-sparing development (< 1g). This talk also focuses on finite element modeling of powder compaction when approaching this problem using case studies. The results of the current study point out that the nondestructive ultrasonics coupled with finite element analysis provide insight into tablet capping.