Preparation and characterization of carboxymethyl starch under ultrasound‐microwave synergistic interaction

Abstract

ABSTRACTUsing native cassava starch as raw materials, carboxymethyl starch (CMS) was prepared by ethanol solvent method under the ultrasound‐microwave synergistic interaction. And the structure of CMS was characterized employing Fourier transform infrared (FTIR) spectrometer, scanning electron microscopy (SEM), X‐ray diffraction (XRD) and thermogravimetric analyzer. Typically, the optimal synthesis conditions for the preparation process confirmed by orthogonal experiment L18 (61 × 36) were shown as follows: the ultrasonic treatment temperature was fixed to 35°C and two steps alkalization was employed; the ultrasonic time was 40 min before alkalizing and the ultrasonic power was 220 W; the amount of sodium hydroxide was 8.8 g, the microwave alkalization time was 2 min; the amount of monochloroacetic acid was 11.34 g; the amount of 95% (v/v) ethanol was 70 mL; the microwave etherification time was 3 min. The degree of substitution of prepared CMS was 1.089 ± 0.041, which was increased 30.4% compared with the prepared sample without ultrasound‐microwave synergistic treatment. FTIR results showed that the strong COO characteristic absorption peaks of the stretching vibration were observed at 1613 and 1421 cm−1, which proved that the carboxymethylation of cassava starch was occurred. SEM results suggested that there were many cracks and dents on CMS granules; and, XRD results indicated that the carboxymethylation of starch occurred both in amorphous region and crystalline region, the noticeable damage of crystalline region by carboxymethylation was observed. Thermogravimetric analysis (TG) and derivative TG showed that thermal stability of CMS changed better compared with native starch. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40906.