Dissolution of unmodified waxy starch in ionic liquid and solution rheological properties
Résumé
Dissolution of waxy corn starch in 1-ethyl-3-methylimidazolium acetate (EMIMAc) was qualitatively studied and compared with gelatinisation process in water. The rheological properties of starch-EMIMAc solutions were investigated in dilute and semi-dilute regions, from 0.1 to 10 wt% over temperature range from 20 °C to 100 °C. The values of zero shear viscosity were obtained by applying Carreau-Yasuda model to shear-thinning flow curves and plotted vs. polymer concentration. Power law exponents in viscosity-concentration dependence in semi-dilute region were compared with the ones reported previously for microcrystalline cellulose. Intrinsic viscosity was obtained as a function of temperature and compared with the one of microcrystalline cellulose; starch was found to be much less temperature sensitive than cellulose. Amylopectin overlap concentration in EMIMAc was compared with the one in water and 0.5 M NaOH-water. Based on these comparisons it was suggested that starch conformation in EMIMAc is similar to the one in water (compact ellipsoid). The activation energy was calculated for starch-EMIMAc solutions and demonstrated to obey power-law concentration dependence.