Eco‐Friendly Synthesis of Hydrogels from Starch, Citric Acid, and Itaconic Acid: Swelling Capacity and Metal Chelation Properties

Abstract

In this study, eco‐friendly superabsorbent hydrogels are prepared by the grafting and crosslinking reactions of itaconic acid and citric acid with starch, using potassium persulfate as the free radical initiator. The structure and morphology of the hydrogels are studied using Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis. The effect of the citric acid to starch ratio on the swelling properties is evaluated, and it is found that equal parts of citric acid and starch produced the highest swelling ratio of 188 g distilled water per g hydrogel. The hydrogels also exhibit pH‐dependent behavior, such that the maximum swelling ratio of 232 g/g is obtained at pH 8. Finally, the metal chelation properties of the hydrogel are tested in solutions of copper, nickel, and zinc, and the adsorption capacity followed the trend Cu > Ni > Zn based on the Freundlich parameter KF.

Triticale Starch-Based pH-Responsive Hydrogel: Synthesis, Characterization, Diffusion & New Perspective of Triticale Crop as Sustainable Source for Stimuli-Response Hydrogels

“…Wang & Wang, 42 where an anionic group and a polyglycol were also added. Besides, non-porous surfaces were also reported by Duquette et al 33 on a natural citrate-crosslinked starch-based hydrogel. Moreover, Yoon, Lee & Lim 43 reported that the retrogradation process in refrigeration (4°C) decreased its porosity, which improved the enzymatic resistance to hydrolysis by αamylases.…”

“…The presence of a new well-defined band due to carbonyl bond vibration was confirmed (C=O, 1721-1755 cm -1 ) by the extrapolation of FT-IR spectra of the hydrogels and the raw material (Figure 3), indicative of cross-linking starch-citrate in anionic hydrogels. 33,35,36 A higher vibration intensity was present in hydrogels within absorbance range of 500-1220 cm -1 due to the bending of C-OH and C-O bonds, related to the decrease in the semicrystalline zone after the gelatinization process. 27 Furthermore, a higher intensity band were presented at 1639 cm -1 in the control hydrogel, representative of the vibration of water retained in the amorphous zone of the starches.…”

“…The study of Wu et al 30 showed that citrate crosslinking (5-20% w/w) on starch/chitosanbased films did not present significant difference in thermal stability (Tp~279.2°C) compared to non-crosslinked film, similar to the results of the present study, where the thermal stability and the kinetic parameter of degradation are similar between the native hydrogel and the experimental ones (Table 2). Duquette et al 33 reported that citrate-crosslinked starch-based hydrogel had better thermal stability (378°C, 50% degradation) than native corn starch (306°C, 50%), and on the other hand starch crosslinking with itaconic acid reduced the thermal stability of the hydrogel; despite this, their study reported only the DTG thermogram, which does not allow the analysis behavior of weight loss, since a similar pattern could be observed in the decay curves. The Ea of the hydrogels was lower compared to the starch due to the previous gelatinization process, where the water and glycerol molecules influenced the separation of the polysaccharide chains, being retained between them through the retrogradation process.…”

Triticale Starch-Based pH-Responsive Hydrogel: Synthesis, Characterization, Diffusion & New Perspective of Triticale Crop as Sustainable Source for Stimuli-Response Hydrogels

“…The presence of a new well-defined band due to carbonyl bond vibration was confirmed (C=O, 1721-1755 cm -1 ) by the extrapolation of FT-IR spectra of the hydrogels and the raw material (Figure 3), which is indicative of the starch-citrate cross-linking in anionic hydrogels. 33,35,36 A higher vibration intensity was presented in hydrogels within absorbance range of 500-1220 cm -1 due to the bending of C-OH and C-O bonds, related to the decrease in the semicrystalline zone after the gelatinization process. 27 Furthermore, the control hydrogel showed a higher intensity band at 1639 cm -1 , representative of the vibration of the water retained in the amorphous zone of native starches.…”

“…The hydrothermal treatment at 90°C was a non-destructive process that allowed the gelatinization of the granules and subsequent formation of the starch-citrate. The synthesis was performed based on the effective citrate cross-linked hydrogels reported by Wu et al 30 and Duquette et al 33 Refrigerated storage (120h/5°C) maintained humidity and prevented abrupt rupture of the hydrogel allowing better stability in the natural retrogradation process (20-25°C),…”