PHOTOACOUSTIC EVALUATION OF ELASTICITY AND INTEGRITY OF PHARMACEUTICAL TABLETS

A nondestructive method based on pulse photoacoustics was applied for evaluation of elasticity and integrity of pharmaceutical tablets. Vari ations in porosity, density and sodium chloride content of microcrysta lline cellulose tablets were found to be related to parameters extract ed from the through-transmitted ultrasonic wave forms. By using the am plitudes and ultrasonic velocities of these wave forms, it was possibl e to obtain values of a transverse to longitudinal amplitude ratio, an d also elastic parameters, such as Young's and shear moduli, for the t ablets. Poisson's ratio was calculated from the elastic moduli as well as from the amplitudes. An exponential relationship between tablet po rosity and the attenuation of longitudinal wave form was noticed. The transverse to longitudinal amplitude ratio and the amplitudinal Poisso n's ratio were indicative of structural variations, e.g., changes in t he porosity and the sodium chloride content of tablets. Young's and sh ear moduli of microcrystalline cellulose tablets were found to follow similar porosity trends to those in previously published beam bending and twisting studies, although the absolute values and the values extr apolated to zero porosity were slightly smaller. The Poisson's ratio c alculated from the experimental Young's and shear modulus values was a lso in agreement with earlier studies, but the values extrapolated to zero porosity differed significantly. The method is a promising tool f or evaluating the elastic properties of tableting materials and the st ructural variations in tablets.