Abstract
The effect of pore size on the gaseous adsorption of ethenzamide (EZ) on porous crystalline cellulose (PCC) in a mixture of PCC-EZ, and the physicochemical stability of EZ in a mixture of PCC-EZ after storage at various relative humidities (RHs) were investigated by powder X-ray diffractometry, differential scanning calorimetry, specific surface area and pore size distribution measurements. After heating a mixture of PCC-EZ, which contained less than 7% EZ, at 70°C at reduced pressure, the EZ became amorphous. The specific surface areas and pore size distribution curves of PCC and the heated mixtures of PCC-EZ were calculated from the nitrogen gas adsorption isotherms. The specific surface area of PCC was 82.3m2/g, while the specific surface areas of the heated mixtures of PCC-3% EZ, PCC-5% EZ and PCC-7% EZ were 74.1, 72.7 and 63.8m2/g, respectively. The specific surface area of the heated mixture of PCC-EZ decreased with an increase in the mixing ratio of EZ. In the pore size distribution curves of the heated mixtures of PCC-EZ, the pore volumes in the range of pore diameters from 2 to 40nm decreased compared with the pore volume of PCC. The volumes of pores with diameters ranging from 3 to 10nm decreased markedly with an increase in the mixing ratio of EZ. These results indicate that the adsorption of EZ on the pore surfaces of PCC occurred principally in the range of diameters from 3 to 10nm. After storage of the heated mixtures of PCC-7% EZ at various RHs for 7d at 30°C, recrystallization of EZ was observed in the X-ray diffraction spectrum when the mixtures were stored above RH 72.8% due to condensation of water vapor in pores.
