Abstract:

Cross-linked carboxymethyl corn starch was prepared from carboxymethyl starch with epichlorohydrin as a crosslinking agent in ethanol-water medium. A four-variable, five-level quadratic orthogonal rotation combination design was employed for maximizing apparent viscosity of modified corn starch, and a regression equation describing the relationship of it with four variables was established. The physico-chemical properties of cross-linked carboxymethyl corn starch paste including transparency, expansion, freeze thawing stability, adsorptivity and rheological properties were studied. A maximum apparent viscosity of cross-linked carboxymethyl corn starch of 10.51 Pa·s was obtained under the following conditions: epichlorohydrin amount 0.23%, reaction temperature 53.2 ℃, reaction time 64.6 min, and pH 10, which was increase by 214.67% and 88.35%, respectively, compared with native corn starch and carboxymethyl starch. Cross-linked carboxymethyl starch had significantly higher apparent viscosity, transparency, expansion, thermostability, adsorptivity and freeze thawing stability than native corn starch and carboxymethyl starch and its paste belonged to pseudoplastic fluid and displayed shear thinning characteristics. Under normal temperature, the rheological model obeyed the following law: τ= 105.6γ0.3599 (τ, viscosity; and γ, shearing velocity), R2 = 0.9882, and the adsorption kinetic model was in accordance with Freundlich adsorption isotherm: Q = 0.4152C0.9894 (Q, adsorption capacity; and C, Pb2+ concentration), R2 = 0.9846.

Key words: cross-linked carboxymethyl, physico-chemical characteristics, adsorption, rheological property