No abstract

Corn starch has been modified with naturally occurring compounds, maleic acid (MA) and itaconic acid (IA), by esterification in an aqueous medium catalyzed by NaOH to produce adsorbents for heavy metals removal in water. The ester formation has been confirmed by wide angle x-ray scattering (WAXS), thermogravimetric analysis (TGA), Fourier Transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The effect of the mono and di-substitution with both acids, on the solubility and the swelling capacity of the modified starch have been investigated. The materials modified with maleic acid exhibited high water solubility, fact that made difficult their characterization and thus their application as adsorbents. In contrast, itaconate esters derivatives demonstrated superabsorbent characteristics and a typical polyelectrolyte behavior. Semiester derivative with greater content of carboxylic acid groups underwent the highest water uptake (H 1 ¼ 1292%). Additionally, the capability of the modified starches with itaconic acid to adsorb aqueous metal cations such as Ni 2þ , Zn 2þ , Cd 2þ , and Pb 2þ was investigated and the results were compared with the native corn starch. The modified and native starches exhibited reasonable adsorption capacity for all the cations. It was demonstrated that the native starch does not exhibit selectivity for any of the cations, whereas the itaconate starches remove higher content of Pb 2þ with the lowest hydration radius in comparison with other ions.

Superabsorbent materials based on natural products have been synthesized by free radical oxidation of corn starch using a redox system consisting of potassium permanganate and sodium bisulfite. The resulting oxidized starches were characterized by analyzing the variation of carbonyl and carboxyl contents. The swelling ability of these samples has been determined by gravimetric method in water and in saline solutions. The effect of oxidant concentration and bleaching procedure on the water absorption capacity has been studied. The ability to remove heavy metals in water solution has been tested against Cd2+, Ni2+, Pb2+ and Zn2+ ions, showing higher percentage of remotion for the unbleached oxidized starches, in particular against nickel ions. Copyright © 2014 John Wiley & Sons, Ltd.

The use of potentiometric titration for the analysis and characterization of native and modified starches is highlighted. The polyelectrolytic behavior of oxidized starches (thermal and thermal-chemical oxidation), a graft copolymer of itaconic acid (IA) onto starch, and starch esters (mono- and diester itaconate) was compared with the behavior of native starch, the homopolymer, and the acid employed as a graft monomer and substituent. Starch esters showed higher percentages of acidity, followed by graft copolymer of itaconic acid and finally oxidized starches. Analytical techniques and synthesis of modified starches were also described.