Preparation of water‐soluble oxidized starch with high carbonyl content by sodium hypochlorite

Abstract

Water-soluble oxidized starch with high carbonyl content (DO CO ¼ 0.40) was prepared using a one-step method with sodium hypochlorite (NaClO) as the primary oxidant and under the mediation of sodium bromide (NaBr) and hydroxylamine hydrochloride (NH 2 OH · HCl). The influences of pH, initial starch concentration, and the amount of NaBr and NH 2 OH · HCl on the carbonyl and carboxyl content were discussed. The molar ratio of carbonyl to carboxyl groups can be adjusted from 0.8 to 2.2 by controlling the dropping speed of NaClO. The formation of carbonyl and carboxyl groups on the oxidized starch was confirmed by Fourier-transform infrared (FT-IR) and 13 C NMR spectroscopy. The molecular weight of the oxidized starch determined by SEC revealed modest degradation. Besides, a good solubility of the oxidized starch in cold water was also proved based on the study of its solubility and swelling properties.

Rapid Preparation of Oxidized Starch with High Carbonyl Contents Using NaBrO as Oxidizer

“…However, the value of the carboxyl content and carbonyl content of oxidized starch as well as the oxidizer utilization rate of NaBrO also decreased when the reaction temperature above 25 °C, which might be due to the fact that starch gelatinization caused the entanglement of starch molecular when the reaction temperature is above 25 °C, resulting in the inhibition of oxidizer molecule to react with starch molecules. In summary, oxidized starch with sodium hypobromite as an oxidizer could be readily obtained at 25 °C, which is a mild condition and easy to control, compared to those reported previously where the reaction temperature was below 5 °C by using sodium hypochlorite as oxidizer . Therefore, reaction temperature 25 °C was chose for the following experiments.…”

“…Combined with Figure a, oxidized starch with a relatively high carbonyl content, carboxyl content, intrinsic viscosity and yield was obtained when the reaction time was 30 min, although the NaBrO utilization did not reach its maximum value. The reaction time with sodium hypobromite as an oxidizer was much shorter than that reported with sodium hypochlorite as an oxidizer where the reaction lasted more than 2 hours . The reaction time 30 min was chosen for the following experiments.…”

“…The attenuated total reflection (ATR) method was employed and the wavelength range was from 4000 to 400 cm −1 . The natural starch and oxidized starch were dried at 130 °C before test …”

“…The natural starch and oxidized starch were dried at 130 C before test. [33,36] 2.8. X-ray Diffraction (XRD)…”

“…As early as 1972, Ziderman et al reported the oxidation kinetics of starch by diluted bromine water, however, the reaction conditions were not studied in detail. Recently reports believed that sodium bromide can be used as a co‐catalyst in the oxidation system such as NaClO/TEMPO/NaBr system and NaClO/NH 2 OH · HCl/NaBr system, where sodium bromide was oxidized by sodium hypochlorite to form sodium hypobromite, which was subsequently used as an oxidizer to react with starch to produce oxidized starch. To the best of our knowledge, few papers focus on the oxidation of starch using NaBrO as oxidizer.…”