The Thermal Stability and Rheological Properties of Alkylated Carboxymethyl Starch

Several alkylated carboxymethyl starches (CMS) with different alkyl chain lengths were prepared. The influence of the number of alkyls on the thermal stability and rheological properties, such as thickening properties, salt-tolerance, temperature sensitivity and time-dependent rheological behavior, are discussed. The initial decomposition temperature (IDT) of alkylated CMS reached 263°C ～293°C which, as compared to the IDT for CMS itself (230°C), indicated that the thermal stability of CMS was improved after being alkylated. The solution viscosities of the alkylated carboxymethyl starch increased with the increasing of alkyl length. With the alkyl chain length increasing from C₂ to C₈, the viscosity increased from 400 mPa·s to 38000 mPa·s. The weak hydrophobic aggregation of the alkyl groups did not improve the shear-resistance and relative hysteresis area. But the temperature sensitivity of alkylated CMS was improved as the chain length of the alkyl groups increased, as the activation energy (E_a) value decreased from 2.082 kJ·mol^?1 to 0.077 kJ·mol^?1; Improving the rigidity of the molecular chains and reducing the network structure of the hydrophobic contribution to the viscosity of the solution are benefits for improving the salt-tolerance and shear-resistance of the aqueous solution.