High-amylose maize starch (AS) was modified by graft copolymerization with sodium acid maleate and disodium maleate, using the KMnO
4
-NaHSO
3
redox system, and covalently crosslinked with ...N,N'-bismethylene acrylamide in inverse suspension polymerization process. The resulting modified starches were evaluated as absorbent materials for release fertilizers. Firstly, AS was obtained by leaching from native maize starch and posterior precipitation in ethanol. The gelatinized AS, comonomers, redox pair and crosslinker were dissolved in distilled water, which was used as dispersed phase; while paraffin oil was used as the continuous phase and sorbitan esters as stabilizers. In the reacions, parameters such as the AS amount of 10 wt%/v with respect to the dispersed phase; the degree of neutralization of maleic acid of 80%; the ratio NaHSO
3
/KMnO
4
of 2.6; the ratio between crosslinker and comonomers of 8.9 × 10
–4
; the stirring speed of 250 rpm; the reaction temperature at 60 °C; and a reaction time of 3 h, were kept constant. All the resulting amylose modified starches were characterized by potenciometric titration, X-ray diffraction and scanning electronic microscopy. The absorption capacity of these materials was studied by analyzing their swelling in various media and different pHs. Finally, the amylose modified starches were evaluated as systems for release fertilizers by measuring the loaded and released amount of fertilizer by gravimetry and conductimetry, respectively.
Herein, the effectiveness of an itaconic acid (IA) graft copolymer on native corn starch (NCS) as a filter control agent in fresh water-based drilling fluids (WBDFs) was evaluated. The copolymer (S-
...-IA_APS) was synthesized by conventional radical dispersion polymerization using the redox initiation system (NH
)
S
O
/NaHSO
. The modification of the starches was verified by volumetry, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Then, three WBDFs were formulated in which only the added polymer (NCS, S-
-IA_APS, and a commercial starch (CPS)) was varied to control the fluid losses. The physico-chemical, rheological, and filtering properties of the formulated systems were evaluated in terms of density (ρ), pH, plastic viscosity (µ
), apparent viscosity (µ
), yield point (Y
), gel strength (R
), and filtrated volume (V
). In order to evaluate the resistance to temperature and contaminants of the WBDFs, they were subjected to high pressure and high temperature filtering (V
). The filter control agents were also subjected to aging and contamination with cement and salt. The S-
-IA_APS addition improved the filtering behavior at a high pressure and temperature by 38%.
Herein, hydrogels based on starch from corn, sweet cassava and bitter cassava were prepared by a straightforward approach. The hydrogels were obtained by an oxidation process using the redox system ...KMnO4/NaHSO3 which leads to the formation of carbonyl and carboxyl groups with minimum polymer hydrolysis. The resulting oxidized samples as well as the native starches were extensively characterized by scanning electron microscopy, thermogravimetric analysis and wide angle X-ray scattering, among others. High gel fraction values and low degree of crystallinity were obtained in all the cases, which values vary slightly depending on the botanical source. High swelling capacity was observed for all the samples, which behave as hydrogels. The influence of the ionic strength and pH in the swelling capacity of the oxidized starches was also studied. The samples exhibit an anti-polyelectrolyte behavior and the water uptake increases at basic pH as the carboxylic groups become ionized. The hydrogels were also loaded with urea, potassium nitrate and ammonium sulfate as model fertilizers and their potential for controlled release was investigated.
Superabsorbents starches (SASs) were synthesized and characterized starting from native corn starch, bitter cassava and sweet cassava by graft copolymerization with itaconic acid. Additionally, their ...swelling behavior was studied both in water and in buffer solutions with different pHs and saline solutions. Their applicability was tested as environmentally friendly fertilizers in the absorption and release of urea, potassium nitrate and ammonium nitrate at different concentrations of fertilizers. The values of swelling at the equilibrium (H∞) in water and different media of the graft copolymers demonstrated their superabsorbent capacity, polyelectrolyte behavior, and smart response to environmental stimuli. The percentage of fertilizer absorbed and released from the SASs was a function of the initial concentration of the fertilizer in the medium. The loading and release of SASs were depended on the initial concentration of the fertilizer in the medium as well as the nature, structure, and morphology of the starch used.
Different hydrogels based on chitosan were prepared by two environmentally friendly approaches: (i) oxidation under mild conditions and (ii) grafting of itaconic acid. Both procedures guide to it ...success modification leading hydrogels with adequate crosslinked degree. The hydrogels were structurally and chemically characterized and their swelling behavior was evaluated in water, NaCl and buffer solutions at different pHs. In all the cases, the increase of ionic strength decreases the equilibrium swelling. It was also demonstrated a superior swelling percentage at acidic pH. This percentage of swelling is significantly higher in grafted films than in the oxidized chitosans. Besides, the ability as fertilizers and water controlled-release superabsorbent hydrogels was evaluated. Consequently, the absorption and delivery of urea fertilizer was investigated as a function of initial concentration of urea in the media and the pH. These materials can be used in the agriculture as controlled fertilizer delivery as well as water regulators.
Graphical Abstract
Hydrogels based-chitosan were prepared by non-environmentally aggressive approaches. Chitosan was modified by mild oxidation and grafting reaction with itaconic acid. The hydrogels present adequate crosslinked degree and worthy swelling behavior. Hydrogels were evaluated as superabsorbent for urea and water controlled- release.
Succinylated Starches for Dye Removal Soto, Diana; León, Orietta; Muñoz‐Bonilla, Alexandra ...
Starch - Stärke,
January 2021, 2021-01-00, 20210101, Letnik:
73, Številka:
1-2
Journal Article
Recenzirano
Odprti dostop
Succinylated bitter cassava starches are evaluated for the removal of cationic, methylene blue (MB) and anionic, methyl orange (MO) dyes present in water. The native starch (NS) extracted from bitter ...cassava by the dry method, is modified using succinic anhydride (SA) as esterifying agent and sodium hydroxide, sodium carbonate, sodium sulfate, and sodium chloride as non‐toxic and environmentally friendly catalysts. The effect of the type and concentration of catalyst on the modification is evaluated. Starch replacement with SA is confirmed by Fourier transform infrared spectroscopy, wide‐angle X‐ray diffraction, thermogravimetric analysis, and scanning electron microscopy. The degree of substitution in the resulting succinylated starches is determined by volumetric analysis, presenting high values (0.5–0.9). These materials act as superabsorbent gels, sensitive to changes in pH and ionic strength, and mostly with anti‐polyelectrolytic behavior. MB dye has a higher affinity for succinylated starches than the MO dye. The removal capacity of MB is also influenced by the pH and the ionic strength of the solution. The kinetics and adsorption isotherms are satisfactorily adjusted to the pseudo‐second order and Freundlich models, respectively. The esters functionalities of the starch prove to be reusable adsorbents, completing successfully five cycles of adsorption‐desorption.
Bitter cassava starch is modified by esterification with succinic anhydride using non‐toxic and environmentally friendly catalysts. The resulting succinylated starches behave as superabsorbent hydrogels sensitive to variations in pH and ionic strength, and can be used for the removal of dyes from solutions. The modified starches are reusable adsorbents, able to successfully complete five cycles of adsorption‐desorption.
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•Amphiphilic block copolymers are synthesized by ATRP.•Their physico-chemical behaviors in solid state and in solution are analyzed.•These copolymers are chemically modified to obtain ...glycopolymers.•The glucopolymers are able to interact with Concanavalin A lectin.
The preparation of amphiphilic glycopolymers by chemical modification of di- and triblock copolymers based on 2-hydroxyethyl acrylate, HEA, and n-butyl acrylate, BA, is described in this manuscript. For that purpose, initially PBA-b-PHEA and PHEA-b-PBA-b-PHEA block copolymers were synthesized by controlled radical polymerization. After that, glycopolymers containing d-(+)-glucosamine or N-(4-aminobutyl)-d-gluconamide, NABG, were prepared by chemical modification of the HEA units. This process occurs in two consecutive steps: (1) an initial activation of the hydroxyl groups of the HEA units with highly reactive p-nitrophenyl carbonate groups and (2) the carbohydrate incorporation. In addition, the solid state and solution behaviors of PBA-b-PHEA and PHEA-b-PBA-b-PHEA di- and triblock copolymers are described by using differential scanning calorimetry, X-ray diffraction, atomic force microscopy and dynamic light scattering. The results have been compared with those previously obtained with methacrylate derivatives. Finally, the resulting water soluble glycopolymers have been exposed to lectins and the aggregation capacity and the selectivity have been also evaluated.
The stability and fat‐replacer properties of mayonnaise prepared with oxidized sweet cassava starch is studied. In a first step, the oxidation of starch using different conditions, i.e., thermal and ...thermochemical processes with the redox pair system (H2O2/NaHCO3), is analyzed. Oxidized starches can be used to produce food grade emulsions without the addition of surfactant, then, the mayonnaise emulsions are prepared using oxidized starch paste as partial substituent of the fat. They show greater stability with respect to the mayonnaise prepared with the native paste due to electro‐steric effects and Pickering type that the oxidized starch exerts on the emulsion. The rheological performance of mayonnaises with oxidized starches is analyzed and compared with that of full‐fat mayonnaise; demonstrating the oxidized starches applicability as stabilizers and fat‐reducers. Finally, a sensory analysis of the mayonnaise emulsions is carried out where all mayonnaise samples are judged to be sensorially acceptable.
Reduced‐fat mayonnaises are prepared from oxidized starches obtained by using a H2O2/NaHCO3 redox pair. Rheological performance of mayonnaises demonstrates their long‐term stability.
•Oxidized chitosans were developed as novel adsorbents to remove dyes from waste water.•Oxidation introduces carboxyl groups and favors the immobilization of cationic dyes.•The novel adsorbents ...showed the capacity to remove both anionic and cationic dyes.•The adsorbents can be regenerated and reused for various adsorption/desorption cycles.
Different oxidized chitosans were prepared following various approaches, by thermo-acid oxidation or by using KMnO4/NaHSO3, (NH4)2S2O8/NaHSO3 and K2Cr2O7/NaHSO3 redox pairs added sequentially or simultaneously. All these reactions pursue the formation of carboxylic groups which enhance their capability to remove model cationic and anionic dyes such as methylene blue and methyl orange, respectively. The resulting oxidized chitosans were structurally and thermally characterized by elemental analysis, infrared spectroscopy, nuclear magnetic resonance, scanning electron microscopy and thermogravimetry. The swelling capacity of these hydrogels was also determined as well as the remediation ability of dyes in different conditions. The results showed that the adsorption of methylene blue followed a pseudo second-order kinetics model, while the adsorption behavior was in agreement with the Langmuir isotherm model. Remarkably, the oxidized chitosans showed removal ability for both dyes cationic and anionic, which of great importance for application of these materials as versatile bioadsorbents.
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