Abstract

MOLLEGA, Sebastián et al. CHEMICAL MODIFICATION OF CASSAVA STARCH BY CARBOXYMETHYLATION REACTION IN AQUEOUS MEDIA. Rev. Fac. Ing. UCV [online]. 2011, vol.26, n.1, pp.117-128. ISSN 0798-4065.

In this work, a study was performed on the carboxymethylation of cassava starch in aqueous media by employing monochloroacetic acid as the modification reagent. All the variables that can affect the process of chemical modification were systematically studied. The five selected reaction variables were: activation time, activation temperature, starch/solvent ratio (w/v %) and the molar ratio between the following reactants: activating agent:modifying agent:anhydroglucose units (NaOH:MCAA:AGU). These variables were analyzed with the aim of optimizing the reaction conditions which could yield the highest degrees of substitution (DS) and the highest viscosity values in aqueous solution. This represents a novel approach to the chemical modification of starch since it balances the degree of substitution obtained with the minimization of chemical degradation during the reaction. It was observed that even though factors like temperature increases or longer reaction times favored higher DS values, they also lead to viscosity reductions. The conditions that yield the products with the highest viscosities are: a starch concentration of 5% in water, 50 ºC as activation temperature, 2 hours of activation, 3 hours of reaction and a molar relationship between reactants equal to 2:1:1 (NaOH:MCAA:AGU). The maximum viscosity value at low shear rates obtained was 0.26 Pa•s when it was measured in a saline solution at 3% w/w of modified starch and 0.1 M of NaCl

Keywords : Starch; Carboxymethylation; Carboxymethyl starch; Monochloroacetic acid; Rheological properties.