The crystallinity and several Spanish kaolins; correlation with sodium amylobarbitone release

Six Spanish kaolins were studied to determine the potential application of their crystallinity for pharmaceutical purposes. Particular attention was paid to the effect of crystallinity on sodium amylobarbitone release in water, when the drug was prepared as granulates with kaolin. Crystallinity was estimated empirically in various granulometric kaolin fractions by examining X-ray diffraction (XRD) patterns, infrared spectra and morphology as shown by scanning electron microscopy (SEM). Crystallinity was usually moderate with a mean Hinckley index of 0.69. Statistically significant relationships were found between the XRD indices and other kaoline characteristics such as total iron content and mean particle size. The different degrees of crystallinity also appear to be related to the fabric type and morphology of individual aggregates and particles (SEM). The release of sodium amylobarbitone increases with kaolin crystallinity, as estimated by the indices HBI (Hughes & Brown, 1979) and RWI (Range & Weiss, 1969), according to the formula y = 43.668 + 3.631 HBI -84.711 RWI. Our findings suggest the possibility of preparing sustained-release formulations with controlled drug release by using kaolins of different degrees of crystallinity as excipients.