Dissolution of starch in urea/NaOH aqueous solutions

Dissolution of starch in urea/NaOH aqueous solutions was studied by using polarizing microscope and viscometry. The experimental results revealed that starch could dissolve in urea (2-20 wt %) and NaOH (10-1 wt %) aqueous solutions at temperature ranging from -12 to 25 degrees C, where the optimized dissolution condition was in the aqueous solution of mixed urea 14% and NaOH 4% at 0 degrees C for 30 min or above. Under the conditions, the starch solubility could be 99.0 and 92.1% as the starch weight percent was 1 and 10%, respectively. Measurements for the molecular weight and amylose content of the starch before and after the dissolution indicated that there was no serious degradation during the process. The results from determinations of X-ray diffraction, Fourier transform infrared, and rapid visco analysis revealed that the recovered starch from the starch solutions was an amorphous solid with a part of V-type pattern (single-helix). The urea/NaOH aqueous solvent may have potential significance for starch processing and modification. (c) 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43390.