Characterization of the hydroxypropylmethylcellulose-nicotinamide binary system

The effect of hydroxypropylmethylcellulose (HPMC) on the thermal behaviour of nicotinamide was studied. Binary mixtures of nicotinamide and HPMC, comp osed of various weight fractions of HPMC (X-HPMC), were heated, cooled and subsequently re-heated. HPMC dissolved in fused nicotinamide at 140 degrees C. The binary mixture at compositions 0 less than or equal to X-HPMC less t han or equal to 0.3 formed a film structure on cooling. At X-HPMC greater t han or equal to 0.4, the molten nicotinamide at 140 degreesC was saturated with HPMC. These heated mixtures did not form a homogeneous film by cooling to ambient temperature. At X-HPMC < 0.4. differential scanning calorimetry peaks originating from recrystallization and melting of nicotinamide were observed in the cooling and re-heating scans, respectively. These peaks bec ame smaller with increase in X-HPMC and disappeared at X-HPMC <similar to> 0.4. Decrease in crystallinity with increase in X-HPMC was confirmed by X-r ay diffraction. The glass transition temperature of the cooled mixture ( T- g) increased with increase in X-HPMC. When the enthalpy of melting of nicot inamide and 1/T-g were plotted against X-HPMC, inflections were observed at similar X-HPMC values, 0.37-0.38. Dissolution of HPMC in molten nicotinami de was accompanied by hydrogen bond formation, which was confirmed by infra red studies. (C) 2001 Elsevier Science B.V. All rights reserved.