THE INFLUENCE OF STARCH ON THE RHEOLOGICAL BEHAVIOR OF MICROCRYSTALLINE CELLULOSE HYDROGELS

A study has been made of the influence of physical factors such as tem perature, agitation time and shear rate upon the rheological behaviour of hydrogels composed of 2.5% microcrystalline cellulose - sodium car boxymethyl cellulose (Avicel RC 591(R), American Viscose Div., FMC Cor p.) and different percentages of corn starch (0-3% by weight, w/w). Th e pseudoplasticity of the gels was demonstrated regardless of the star ch concentration employed; an increased presence of starch elevated ge l viscosity but did not modify its pseudoplasticity. The gels investig ated corresponded to Ostwald's rheological model, with high correlatio n coefficients. The coefficients characterizing the model have been de termined as a function of the different physical parameters introduced in the experiment. Thus, a mathematical expression was developed from which the rheological behaviour of these gels can be established. Fin ally, the thixotropic behaviour of the gels was studied, demonstrating that at a given temperature an increase in starch concentration produ ces an increase in thixotropic area. The latter increases with agitati on time at lower temperatures, although at higher temperatures the thi xotropic behaviour is lost after relatively short agitation times.