Effect of nicotinamide on the properties of aqueous HPMC solutions

The effect of nicotinamide on the properties of aqueous hydroxypropylmethyl cellulose (HPMC) solutions was studied. Rheological studies showed that sol utions of HPMC of concentration less than 3.0 w/v.% did not form gels and e xhibited Newtonian flow patterns at 25 degreesC. The inclusion of nicotinam ide increased the viscosity of HPMC solutions, which indicates that nicotin amide expanded the HPMC coils in aqueous solution. When the temperature of the solutions was raised, they formed gels that were detected by viscometry and oscillation tests as abrupt increases in viscosity, storage modulus an d loss modulus and an abrupt decrease in loss angle. Nicotinamide exhibited a salting in effect on the HPMC solutions resulting in an increase in gela tion temperatures and cloud points. These effects are considered to be due to the hydrogen-bonding of nicotinamide to HPMC molecules, which was sugges ted by a shift to a longer wavelength of the UV spectra of aqueous nicotina mide solutions by the addition of HPMC. These results suggested that nicoti namide has affinity with the hydrophilic groups of HPMC. (C) 2001 Elsevier Science B.V. All rights reserved.