VISCOELASTIC BEHAVIOR OF MICROCRYSTALLINE CELLULOSE HYDROGELS

An extensive study is made of the rheological behaviour of microcrystalline cellulose-sodium carboxymethyl cellulose (MCC-Na-CMC) gels at six different concentrations. The effect of agitation time, storage time, shear rate and temperature on the viscosity-eta of these thixotropic gels is analysed, over 7200 resulting values of eta being available to this effect. The pseudoplastic and thixotropic characteristics of the gels has been established, and a progressive decrease in gel viscosity with increasing storage time was observed, although retaining stability. On the other hand, constant agitation for five minutes was found to reduce gel viscosity by 40 to 50%, regardless of concentration. The Ostwald rheological model was used to derive an empirical equation providing gel viscosity as a function of the abovementioned physical variables. This formula is particularly interesting in that it establishes the viscosity of MCC-NaCMC gels encountered in many kinds of pharmaceutical preparations.