Whisker growth of l-menthol in coexistence with various excipients.

Abstract 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 diffraction. Then we examined the involvement of the capillary condensation using the pore size distribution measurement. By mixing l -menthol with an excipient 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 diffraction intensity of l -menthol became lower in the powder X-ray diffraction. The excipients with whisker growth showed the tendency to have the meso -pore involved in the capillary condensation in the pore size distribution measurement. From the above results, the whisker growth mechanism is considered as follows. When l -menthol was mixed with an excipient with whisker growth, the crystallinity of l -menthol was lowered and the vapor pressure was increased by the interaction mainly consisting of the hydrogen bond. The generated l -menthol vapor entered meso -pore, the saturated vapor pressure was lowered by the capillary condensation, and the nucleation occurred. The vapor was further supplied, generating the growth of whisker.