Hydroxyl Groups Of Starch Research Articles

Facile fabrication of a starch-based wood adhesive showcasing water resistance, flame retardancy, and antibacterial properties via a dual crosslinking strategy

The demand for non-toxic, environmentally friendly, easily processable, water-resistant, flame-retardant and antimicrobial adhesives in the wood processing industry is becoming increasingly urgent. Few adhesives can both simultaneously possess these functions and synthesis easily. This paper presents a one-pot process utilizing corn starch, sodium hypochlorite, itaconic acid, and borax to synthesize a starch-based adhesive with dual crosslinking. Initial crosslinking takes place between the carboxyl groups of itaconic acid and hydroxyl groups on oxidized starch due to the formation of ester bonds. Secondary crosslinking occurs borate ester bonds between starch hydroxyl groups and boric acid. The entire reaction process is environmentally benign, generating no waste, with all reactants converted into final products, aligning with “green” chemistry principles. When used to bond wooden boards, this adhesive achieved a dry shear strength of 5.34 ± 0.24 MPa, and a wet shear strength of 1.22 ± 0.06 MPa after soaking in water. Additionally, this starch-based adhesive exhibited antibacterial properties against Escherichia coli (ATCC 8739) and Staphylococcus aureus. Moreover, with borax incorporated, the adhesive demonstrated flame-retardancy. The limiting oxygen index for bonded wooden boards was 30.9 %, qualifying it as a flame-retardant material. These multiple functions render it promising for applications in the wood processing industry.

Mechanical activation-enhanced metal-organic coordination strategy to fabricate high-performance starch/polyvinyl alcohol films by extrusion blowing

The production of high-performance starch-based packaging films by extrusion blowing is challenging, ascribed to poor processability of the blend precursors. In this study, a new strategy of mechanical activation (MA)-enhanced metal-organic coordination was proposed to improve the processability of starch (St)/polyvinyl alcohol (PVA) blend precursor, with calcium acetate (CA) as a chelating agent and glycerol as a plasticizer. MA pretreatment activated the hydroxyl groups of starch and PVA for constructing strong metal-organic coordination between CA and St/PVA during reactive extrusion, which effectively enhanced the melt processing properties of the blend precursor, contributing to the fabrication of high-performance St/PVA films by the extrusion-blowing method. The as-prepared St/PVA films exhibited excellent mechanical properties (tensile strength of 34.5 MPa; elongation at break of 271.8 %), water vapor barrier performance (water vapor permeability of 0.704 × 10−12 g·cm−1·s−1·Pa−1), and oxygen barrier performance (oxygen transmission rate of 0.7 cm3/(m2·day·bar)), along with high transmittance and good uniformity. These outstanding characteristics and performances can be attributed to the improved interfacial interaction and compatibility between the two matrix phases. This study uncovers the mechanism of MA-enhanced metal-organic coordination for improving the properties of starch-based films, which provides a convenient and eco-friendly technology for the preparation of high-performance biodegradable films.

Injection molding of biodegradable polyester blends filled with mineral and sustainable fillers: Performance evaluation

AbstractThis research focuses on the melt processing of biocomposites from a biodegradable polymer blend mixed with hybrid fillers through injection molding technique. An optimized blend ratio (60/40 wt%) poly(butylene succinate‐co‐butylene adipate) (PBSA) and poly(butylene adipate‐co‐terephthalate) (PBAT) demonstrated promising results after blending with a mixture of walnut shell powder (WSP), corn starch and talc in various proportions for use in rigid packaging. The addition of hybrid fillers (i) 10% WSP with 15% talc and (ii) 5% WSP with 5% starch and 15% talc to the polymer blend (60%PBSA/40%PBAT) improved tensile modulus (160% and 162%, respectively) and flexural modulus (147% and 153%, respectively) because of the dispersion of stiffer talc and WSP. Following the addition of fillers, tensile strength of the composites decreased. However, flexural strength improved significantly after filler introduction because of better stress transfer ability. Rheological analysis of filled composites with starch or WSP (25%) depicted similar characteristics of the polymer blend, indicating lower viscosity than hybrid composites. The abundant hydroxyl groups in starch explained the increased water absorption and decreased contact angle compared with other composites. This research's novelty encompasses utilizing low‐cost biomasses with mineral filler into an under‐researched biodegradable polymer blend suitable for single‐use rigid packaging applications.

Eggshell powder as a bio-filler for starch and gelatin: Ternary biodegradable composite films manufactured by extrusion compression molding

Recovery of food waste eggshell powder (ESP) as a bio-filler for biopolymer matrix to develop sustainable composites is an attractive recycling strategy nowadays. Herein, biodegradable composite films based on potato starch/gelatin (PS/G) containing different concentrations (0%–50%, w/w, of the total mass of PS/G) of ESP were manufactured using thermal extrusion followed by compression molding. Interaction and compatibility of film components were evaluated by using Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). Color, opacity, mechanical properties, water vapor and oxygen permeability, and biodegradability of the composite films were also systematically characterized. The existence of hydrogen bonding interactions between the amino groups of organic compounds on ESP surface and the hydroxyl groups of starch and gelatin was confirmed by FTIR, and the ESP particles were uniformly dispersed in the film matrix with good adhesion as observed by SEM. More importantly, the incorporation of ESP at appropriate amount greatly improved water resistance, tensile properties, water vapor and oxygen barrier properties of composite films compared to the control PS/G films. Optimal ESP content in the composite films was found to be ∼30 % w/w in terms of their mechanical and barrier properties, showing a tensile strength of 4.54 MPa, elongation at break of 27.23%, water vapor permeability of 4.16 × 10−10 g m·m−2·s−1·Pa−1 and oxygen permeability of 8.15 × 10−15kg m·m−2·s−1·Pa−1, respectively. Moreover, all the films were able to completely degrade within one month. Thermo-processed PS/G/ESP composite films with desirable physicochemical properties and favorable biodegradability hold great application potential in biodegradable packaging systems.

Preparation of Starch‐Fatty Acid Esters from Agro‐Based Raw Materials (Corn Starch, Cassava Starch, Coconut Oil, and Castor Seed Oil)

AbstractThe preparation of starch‐fatty acid esters is investigated for corn starch and cassava starch. The fatty acid contents are obtained from the hydrolysis of coconut oil and castor oil respectively and are characterized by GC/MS techniques. The major fatty acid component of coconut oil is found to be lauric acid (34%) while that of castor oil is ricinoleic acid (84%). Four different starch‐fatty esters are prepared, namely cassava starch‐coconut fatty acid esters (CacoFAE), cassava starch‐castor fatty acid ester (CacaFAE), corn starch‐coconut fatty acid ester (CocoFAE), and corn starch‐castor fatty acid ester (CocaFAE). The starch‐fatty acid esters are analyzed using FT‐IR and liquid chromatography‐mass spectrometer techniques. All the esterified starch‐fatty acid esters contain the C=O absorption peak at 1707 cm−1 which is the peak corresponding to the ester group formed between the starch hydroxyl and fatty acid carboxylic functions. The major fatty acid eluted from LC‐MS for CacoFAE and CocoFAE is lauric (dodecanoic) acid with 67.4% and 74% respectively while ricinoleic acid (58%) is obtained for CacaFAE. The data for CocaFAE are mainly dominated by the ester of the fatty acids.

Enhancing I0/I− Conversion Efficiency by Starch Confinement in Zinc–Iodine Battery

The redox couple of I0/I− in aqueous rechargeable iodine–zinc (I2‐Zn) batteries is a promising energy storage resource since it is safe and cost‐effective, and provides steady output voltage. However, the cycle life and efficiency of these batteries remain unsatisfactory due to the uncontrolled shuttling of polyiodide (I3− and I5−) and side reactions on the Zn anode. Starch is a very low‐cost and widely sourced food used daily around the world. “Starch turns blue when it encounters iodine” is a classic chemical reaction, which results from the unique structure of the helix starch molecule–iodine complex. Inspired by this, we employ starch to confine the shuttling of polyiodide, and thus, the I0/I− conversion efficiency of an I2‐Zn battery is clearly enhanced. According to the detailed characterizations and theoretical DFT calculation results, the enhancement of I0/I− conversion efficiency is mainly originated from the strong bonding between the charged products of I3− and I5− and the rich hydroxyl groups in starch. This work provides inspiration for the rational design of high‐performance and low‐cost I2‐Zn in AZIBs.

Antimicrobial thermoplastic starch reactive blend with chlorhexidine gluconate and epoxy resin

An antimicrobial thermoplastic starch (TPS) was developed by melt-mixing TPS with chlorhexidine gluconate (CHG) and epoxy resin (Er). The tensile strength and hardness of the TPSCh blend increased with the addition of Er (TPSCh/Er), especially at 5 wt% Er (TPSCh/Er5) (19.5 MPa and 95 %, respectively). The water contact angle of TPSCh/Er was higher than those of TPS and TPSCh because of the improved interfacial tension. Fourier transform infrared and nuclear magnetic resonance analyses confirmed the reaction between the epoxy groups of Er, hydroxyl groups of starch, and amino groups of CHG. TPSCh/Er5 exhibited a significantly lower CHG release than TPSCh owing to the rearrangement of TPSCh chains via Er crosslinking. TPSCh/Er0.5 and TPSCh/Er1 showed inhibition zones against both tested bacteria (Staphylococcus aureus and Bacillus cereus), whereas TPSCh/Er2.5, TPSCh/Er5, and TPSCh/Er10 showed inhibition zones only against S. aureus. Moreover, TPSCh and TPSCh/Er0.5–2.5 exhibited inhibition zones with Saccharomyces cerevisiae.

Increasing the interaction of calcium carbonate with cellulosic fibers

Çalışmada, selülozik liflerin çok fazla tüketildiği kâğıt endüstrisinde dolgu maddesinin kullanım miktarını artırarak lifsel kaynakların tüketiminin azaltılması araştırılmıştır. Nişasta/stearik asit ile kalsiyum karbonat yüzeyinin modifiyesi partikül yüzeylerinin lif yüzeyindeki hidroksil gruplarıyla uyumluluğunun artırılması için kullanılmıştır. Nişasta moleküllerindeki hidroksil gruplarına ilaveten katyonik gruplara sahip olması modifiye edilmiş kalsiyum karbonat partiküllerinin selülozik liflere ve kâğıt üretiminde kullanılacak iyonik diğer kimyasallarla etkileşimini kolaylaştırmıştır. Böylece, inorganik partiküllerin lif/lif ara yüzeyinde meydana gelen bağ sayısındaki düşmelerin önüne geçilerek kalsiyum karbonat kullanımı ile ortaya çıkacak direnç kayıpları azaltılması hedeflenmiştir. Dolgu maddesi tutunumu, dolgu maddesinin iyonitesindeki değişim, boyut ve üretilen kâğıtların kopma mukavemetindeki değişimler incelenmiştir. Retansiyon değerleri incelendiğinde modifikasyondan sonra kalsiyum karbonat partiküllerinin liflere tutunumunun artığı ve ilave edilen retansiyon kimyasalları ile bu değerlerin daha ileriye çekildiği görülmüştür. Bununla birlikte, modifikasyon işleminden sonra kalsiyum karbonat kullanımının kâğıt kopma mukavemetine pozitif etkisi belirlenmiştir.

Synthesis, characterization, and antibacterial activities of novel starch derivatives against E. coli and S. aureus

AbstractThree novel starch derivatives with antibacterial properties are synthesized through a rather simple multistep synthesis route. In a first step, sodium periodate oxidation of the hydroxyl groups (C2–C3) of starch yields a di‐aldehyde structure, which is used to attach N,N‐dimethylbenzylamine by Schiff base formation. Then, the amino groups of aminated starch are quaternized with three different ammonium salts (4‐bromobutyl‐pyridinium bromide, 4‐bromobutyl‐benzalkonium bromide, and 4‐bromobutyl‐quinolinium bromide). The different resulting products are fully characterized by FTIR, 1H NMR, and SEC analysis. Their antibacterial properties are evaluated against Escherichia coli and Staphylococcus aureus in vitro to obtain minimum inhibitory and bactericidal concentrations. All the starch derivatives show strong antibacterial activities against Gram‐negative E. coli strain and Gram‐positive S. aureus. Finally, hemolysis assays show that two of the starch derivatives obtained have no significant hemolytic effect on isolated human red cells.

High antibacterial activity of new eco‐friendly and biocompatible polyurethane nanocomposites based on Fe3O4/Ag and starch moieties

AbstractControl of microbial infections is one of the growing concerns in modern societies due to the increasing presence and risk of pathogenic bacterial spread. Therefore, there is a strong demand to design new antibacterial agents to overcome these problems. The aim of this study is the preparation of a new series of biocompatible starch‐based polyurethane (PU) nanocomposites with a unique combination of magnetic nanoparticles (MNPs) and silver nanoparticles (AgNPs). In order to perform the study, first, a new synthetic diisocyanate was synthesized by a three‐step reaction and grafted into bis(2‐hydroxyethyl terephthalate) (BHET) and starch as a covering agent of MNPs containing different amounts of AgNPs. Afterward, the diisocyanate containing two active isocyanate moieties was reacted with hydroxyl groups of BHET and starch to form stable urethane linkages. Subsequently, the antibacterial activity of the pure synthetic PU and the produced nanocomposites were investigated against Escherichia coli and Staphylococcus aureus as Gram‐negative and Gram‐positive microorganism models, respectively. The obtained results exhibited that the nanocomposites have a synergistic effect on the antibacterial activity, which decreased with increasing of the Ag content. Such results may be related to the AgNPs agglomeration in the nanocomposite.

Modeling and Optimization of the Shear Strength of Cassava Starch-Based Adhesives Using Artificial Intelligence Methods

With the exponential growth of the computing power, machine learning techniques have been successfully used in various applications. This paper intended to predict and optimize the shear strength of single lap cassava starchbased adhesive joints for comparison with the application of artificial intelligence (AI) methods. The shear strength was firstly determined by the experiment with three independent experimental variables (starch content, NaOH concentration and reaction temperature). The analysis of range (ANORA) and analysis of variance (ANOVA) were applied to investigate the optimal combination and the significance of each factor for the shear strength based on the orthogonal experiment. The performance of all AI models was characterized by mean absolute error (MAE), root mean square error (RMSE) and regression coefficient (R2 ) compared with the experimental ones. The GA-optimized ANN model was combined with the genetic algorithm (GA) to find the optimal combination of factors for the finalized optimized cassava starch adhesives (CSA-OP). The physicochemical properties of the cassava starch and CSA-OP were determined by the FTIR, TGA and SEM-EDS, respectively. The results showed that the numerical optimized condition of the GA-optimized ANN model was superior to the orthogonal experimental optimized condition. The sensitivity analysis revealed that the relative importance of variables was consistent with the results from ANOVA. FTIR results showed that there were high hydroxyl groups in cassava starch. TGA results showed that the residue of CSA-OP was higher than the cassava starch. SEM-EDS results showed that both the cassava starch and CSA-OP had abundant carbon and oxygen functional groups. Consequently, the obtained results revealed that the use of AI methods was an adequate approach to model and optimize the experimental variables of the shear strength of single lap cassava starch-based adhesive joints.

Effect of nixtamalization with Ca(OH)2, CaCl2, and CaCO3 on the protein secondary structure, rheological, and textural properties of soft wheat flour doughs

The effect of dough formation using dynamic rheology, thixotropy, zeta-potential, and FT-IR properties of soft wheat dough as a function of Ca(OH)2, and Ca-salts contents (0.3%, 0.7%, and 1.1%) was investigated. Physical data were further supplemented by measurements of dough texture profile analysis, wet gluten, and pH. Additional information provided by structure-sensitive properties, such as the zeta-potential, thixotropic index, and slopes of rheo-destroyed and complex viscosity curves using Cox–Merz rule, can comprise complementary instances of evidence of the ability of dough self-regeneration or build-up after rheodestruction to certain limits. There is a different behavior of the dough properties above and below pH 7.0. Above pI ≈ 5.2, dough (pH 5.5–7.0) has zeta-potential with negative charge from ionizing hydroxyl groups of starch and proteins that favor protein unfolding and that increase α-helix, wet gluten, and functionality. Weak non-covalent bonds and electrostatic forces induce strong entanglement and interaction with water, increase swelling, and preserve the chemical structure. However, at pH > 7.0, Ca(OH)2 treatment changed to negative charge tendency of the dough system, specifically of starch. The effects provided by nixtamalization are essential for its application in improvement of wheat flour with limited functionality, such as soft wheat flour and other grains or materials.

Effects of nanocellulose fiber and thymol on mechanical, thermal, and barrier properties of corn starch films

This study explores the preparation of corn starch (CS) films incorporated with nanocellulose fiber (NCF) and different concentrations of thymol (0.1, 0.3, and 0.5% weight of thymol/volume of solution (% w/v)) via the solvent casting method. The resulting films were characterized by the functional chemistry, crystallinity, morphology, mechanical, thermal, and barrier properties. The Fourier transform infrared spectroscopy analysis confirmed the presence of intermolecular hydrogen bonding between the thymol and starch, as well as the thymol and glycerol, via hydroxyl groups of glycerol, starch, and thymol. The film crystallinity decreased with increasing concentration of thymol. The addition of NCF at 1.5% weight of starch increased the tensile strength (TS) and Young's Modulus (YM), but decreased the elongation at break (EAB), oxygen permeability, and water vapor permeability of the CS films. The thermal stability of the CS films was also improved with the addition of NCF. The addition of thymol to the CS/NCF bio-nanocomposite films decreased the TS and YM, respectively but increased the EAB due to the plasticizing effect of thymol. The addition of thymol also improved the thermal stability but reduced the barrier properties of the films. The effects on the mechanical, thermal, and barrier properties were more pronounced at higher concentrations of thymol. In conclusion, the inclusion of both NCF and thymol led to the improvement of the flexibility and thermal stability of the CS films.

Interactions between caffeic acid and corn starch with varying amylose content and their effects on starch digestion

This study aimed to evaluate the physical-chemical interaction between caffeic acid (CA) and gelatinized corn starch with varying amylose and its potential effect on starch digestion. Iodine binding reaction indicated that the absorbance of starch-iodine complex was lower than that in the starch-CA sample. Furthermore, the decrease of absorbance in high amylose corn starch was the most obvious. The affinity constant for CA obtained by isothermal titration calorimetry analysis increased with the amylose content. In the 1H NMR analysis, the peaks of starch hydroxyl groups at 5.4 and 5.5 ppm became broader after the addition of CA, demonstrating that CA interacted with the selected starches via the hydroxyl groups to form hydrogen bonds. In vitro digestibility studies revealed that the interaction between CA and starch had different effects on starch with different amylose content. Moreover, it was revealed that 2% of CA promoted the hydrolytic process, but a drastic reduction of the hydrolytic process occurred upon increasing the CA to 10% for CS. These results suggested that amylose content and certain interactions with CA was a potential reason affecting the mode of interaction, thus altering the digestion.

Interactions between tapioca starch and Mesona chinensis polysaccharide: Effects of urea and NaCl

Non-starch polysaccharide and starch interactions have been extensively studied. However, few researches focus on their interactions mechanism. In this study, the effects of hydrogen bond and electrostatic interactions on the tapioca starch-Mesona chinensis polysaccharide (TM) gels were investigated. The results of pasting and thermal experiments (heating phase) showed that the peak viscosity (PV) of TM gels increased with the addition of urea. The addition of urea caused the hydrogen bonds to be destroyed and the rearrangement of starch during cooling was inhibited, which led to the final viscosity of TM gels decreased. The interactions between 0.5% NaCl and starch hydroxyl groups resulted in a significant increase in PV, while excessive addition of NaCl produced an electrostatic shielding effect, resulting in a decrease in PV, but still higher than TM gels. The results of rheological, texture, and particle size experiments (gel cooling stage) showed that hydrogen bond played a decisive role in the final texture of TM gels. Scanning electronic microscopy results showed that the addition of urea loosened the starch structure, and the high concentration of urea caused the structure appear fragmented.

Oligo(lactic acid)-grafted starch: A compatibilizer for poly(lactic acid)/thermoplastic starch blend

The objective of this study was to improve the compatibility between poly(lactic acid) (PLA) and thermoplastic starch (TPS) in PLA/TPS blown films by incorporating oligo(lactic acid)-grafted starch (OLA-g-starch) as a compatibilizer. OLA-g-starch with a degree of substitution of 1.2 and degree of polymerization of 2.0 was synthesized via a ring-opening polymerization of lactide initiated by hydroxyl groups of starch. The PLA/TPS blends containing OLA-g-starch were prepared using a twin-screw extruder with a constant weight proportion of PLA to TPS of 50:50 and various concentrations of OLA-g-starch, i.e., 1, 2, 3, and 5%. The obtained blends were blown into thin films using a blown film extruder. SEM confirmed the droplet/matrix morphology of the PLA/TPS blends both with and without OLA-g-starch. Incorporating OLA-g-starch improved the compatibility between the TPS dispersed phase and PLA matrix, as evidenced by the smaller size and better distribution of the TPS phase. As a result, the blends containing OLA-g-starch exhibited up to 280% greater extensibility as well as enhanced water vapor and oxygen barrier properties, water resistance, melt flowability, and thermal stability. The Tg, Tcc, and Tm of PLA in the blends shifted to higher temperatures when OLA-g-starch was incorporated. The obtained PLA/TPS blown film containing OLA-g-starch has the potential to be used as flexible packaging.

Pine Resin Derivatives as Sustainable Additives to Improve the Mechanical and Thermal Properties of Injected Moulded Thermoplastic Starch

Fully bio-based materials based on thermoplastic starch (TPS) were developed starting from corn starch plasticized with glycerol. The obtained TPS was further blended with five pine resin derivatives: gum rosin (GR), disproportionated gum rosin (dehydroabietic acid, RD), maleic anhydride modified gum rosin (CM), pentaerythritol ester of gum rosin (LF), and glycerol ester of gum rosin (UG). The TPS–resin blend formulations were processed by melt extrusion and further by injection moulding to simulate the industrial conditions. The obtained materials were characterized in terms of mechanical, thermal and structural properties. The results showed that all gum rosin-based additives were able to improve the thermal stability of TPS, increasing the degradation onset temperature. The carbonyl groups of gum rosin derivatives were able to interact with the hydroxyl groups of starch and glycerol by means of hydrogen bond interactions producing a significant increase of the glass transition temperature with a consequent stiffening effect, which in turn improve the overall mechanical performance of the TPS-resin injected moulded blends. The developed TPS–resin blends are of interest for rigid packaging applications.

Enhanced and Selective Adsorption of Zn(II), Pb(II), Cd(II), and Hg(II) Ions by a Dumbbell- and Flower-Shaped Potato Starch Phosphate Polymer: A Combined Experimental and DFT Calculation Study.

Microwave–ultrasound-assisted facile synthesis of a dumbbell- and flower-shaped potato starch phosphate (PSP) polymer, hereafter PSP, was carried out by cross-linking the hydroxyl groups of native potato starch (NPS) using phosphoryl chloride as a cross-linking agent. Structural and morphological analysis manifested the successful formation of the dumbbell- and flower-shaped PSP biosorbent with enhanced specific surface area and thermal stability. Viscoelastic behavior of NPS and PSP suggested increased rigidity in PSP, which helped the material to store more deformation energy in an elastic manner. The synthesized PSP biosorbent material was successfully tested for efficient and quick uptake of Zn(II), Pb(II), Cd(II), and Hg(II) ions from aqueous medium under competitive and noncompetitive batch conditions with qm values of 130.54, 106.25, 91.84, and 51.38 mg g–1, respectively. The adsorption selectivity was in consonance with Pearson’s hard and soft acids and bases (HSAB) theory in addition to their order of hydrated radius. Adsorption of Zn(II), Pb(II), Cd(II), and Hg(II) followed a second-order kinetics and the adsorption data fitted well with the Langmuir isotherm model. Quantum computations using density functional theory (DFT) further supported the experimental adsorption selectivity, Zn(II) > Pb(II) > Cd(II) > Hg(II), in terms of metal–oxygen binding energy measurements. What was more intriguing about PSP was its reusability over multiple adsorption cycles by treating the metal(II)-complexed PSP with 0.1 M HCl without any appreciable loss of its adsorption capacity.

Synthesis and characterization of starch sulfates obtained by the sulfamic acid-urea complex

The process of sulfation of starch with sulfamic acid in the presence of urea was studied. The sulfur content of starch sulfate increases with increasing sulfation temperature from 70 to 100 °C. To obtain starch sulfates with a high sulfur content (about 10 wt%), It is advisable to carry out the sulfation process at a temperature of 100 °C for 120 min. Mathematical modeling of the process of sulfation of starch with sulfamic acid in the presence of urea was carried out. The introduction of a sulfate group in the structure of starch is confirmed by FTIR spectroscopy. In the FTIR spectra of sulfated starch, in contrast to the original starch, there are absorption bands at 1255 cm−1, 808-817 cm−1 and 859-867 cm−1, corresponding to sulfate groups. Sulfation of starch with a complex of sulfamic acid - urea can improve the environmental safety and efficiency of the process in comparison with the known methods of sulfation. Initial starch and sulfated starch were analyzed by gel permeation chromatography. The initial starch was shown to have a main peak with Mn 139 kDa and Mw 382 kDa, and sulfated starch has a peak in the chromatogram relating to Mn 44 kDa and Mw 60 kDa. Besides, the quantum chemical calculations of the starch and sulfated starches (in dimer forms) formed when different number of hydroxyl groups in starch were replaced with sulfate groups were performed using the DFT/B3LYP method with 6-31+G (d, p) basis set in the ground state. Firstly, these molecules were optimized. Then, from the optimized geometry of the starch and sulfated starches, frontier molecular orbitals (FMOs), molecular electrostatic potential (MEP) surfaces, bond parameters, chemical reactivity descriptors such as chemical potential, electron affinity, electronegativity, ionization energy, electrophilicity index and chemical hardness have been calculated theoretically. In addition, spectroscopic analyzes of starch and sulfated starches such as FTIR and 1H NMR were theoretically performed using the same method and compared with each other.

Baked hydrogel from corn starch and chitosan blends cross‐linked by citric acid: Preparation and properties

Citric acid (CA)–modified hydrogels from corn starch and chitosan were synthesized using a semidry condition. This strategy has great benefits of friendly environment because of the absence of organic solvents and compatible with the industrial process. The hydrogel blends were prepared with starch/chitosan ratios of 75/25, 50/50, and 25/75. The thermal stability, morphology, water absorption, weight loss in water, and methylene blue absorption were determined. Multi‐carboxyl structure of CA could result in a chemical cross‐linking reaction between starch, chitosan, and CA. The cross‐linking reaction between free hydroxyl groups of starch, amino groups of chitosan, and carboxyl groups of CA has been confirmed by attenuated total reflectance infrared (ATR‐IR) spectroscopy, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) analysis. The water absorption properties of CA‐modified hydrogel blends were increased significantly compared with the native starch and chitosan. Moreover, the hydrogel blends modified with CA showed good water resistance and gel content. The morphology study confirmed the complete chemical cross‐linking and porous structure of hydrogel blends. The hydrogel blend with the starch/chitosan ratio of 50/50 presented powerful absorption of methylene blue as well as chemical cross‐linking reaction and dense structure. In sum, the hydrogel blend comprising 50% starch and 50% chitosan has the potential to be applied for water maintaining at large areas, for example, in agriculture.