EFFECT OF PORE-SIZE ON THE GASEOUS ADSORPTION OF ETHENZAMIDE ON POROUS CRYSTALLINE CELLULOSE AND THE PHYSICOCHEMICAL STABILITY OF ETHENZAMIDE AFTER STORAGE

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 a t various relative humidities (RHs) were investigated by powder S-ray diffractometry, differential scanning calorimetry, specific surface ar ea and pore size distribution measurements, After heating a mixture of PCC-EZ, which contained less than 7% EZ, at 70 degrees C at reduced p ressure, 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 s urface area of PCC was 82.3 m(2)/g, while the specific surface areas o f the heated mixtures of PCC-3% EZ, PCC-5% EZ and PCC-7% EZ were 74.1, 72.7 and 63.8 m(2)/g, respectively, The specific surface area of the heated mixture of PCC-EZ decreased with an increase in the mixing rati o of EZ, In the pore size distribution curves of the heated mixtures o f PCC-EZ, the pore volumes in the range of pore diameters from 2 to 40 nm decreased compared with the pore volume of PCC, The volumes of por es with diameters ranging from 3 to 10 nm decreased markedly with an i ncrease in the mixing ratio of EZ, These results Indicate that the ads orption of EZ on the pore surfaces of PCC occurred principally in the range of diameters from 3 to 10 nm, After storage of the heated mixtur es of PCC-7% EZ at various RHs for 7 d at 30 degrees C, recrystallizat ion of EZ was observed in the X-ray diffraction spectrum when the mixt ures were stored above RH 72.8% due to condensation of water vapor in pores.