Whisker growth of l-menthol in coexistence with various excipients

The purpose of the present study was to clarify the mechanism for l-menthol whisker growth, l-Menthol was mixed with an excipient, and the interaction was examined by IR measurement, thermal analysis and powder X-ray diffract ion. Then we examined the involvement of the capillary condensation using t he pore size distribution measurement. By mixing l-menthol with an excipien t with whisker growth, the hydroxyl group stretching band of l-menthol was shifted to the higher wavenumber in the IR Spectrum, the melting point and heat of fusion of l-menthol became lower in the thermal analysis, and the d iffraction intensity of l-menthol became lower in the powder X-ray diffract ion. The excipients with whisker growth showed the tendency to have the mes o-pore involved in the capillary condensation in the pore size distribution measurement. From the above results, the whisker growth mechanism is consi dered as follows. When l-menthol was mixed with an excipient with whisker g rowth, the crystallinity of l-menthol was lowered and the vapor pressure wa s increased by the interaction mainly consisting of the hydrogen bond. The generated l-menthol vapor entered meso-pore, the saturated vapor pressure w as lowered by the capillary condensation, and the nucleation occurred. The vapor was further supplied, generating the growth of whisker. (C) 2000 Else vier Science B.V. All rights reserved.