Preparation and swelling properties of a starch-g-poly(acrylic acid)/organo-mordenite hydrogel composite

Structure Effects on Swelling Properties of Hydrogels Based on Sodium Alginate and Acrylic Polymers

Hydrogels based on sodium alginate (SA) and partially neutralised poly(acrylic acid) were obtained by radical polymerisation. The hydrogels were cross-linked with N,N'-methylenebisacrylamide (MBA), simultaneously grafting the resulting polymer onto SA. The findings of the FTIR spectroscopy showed that all of the hydrogels were effectively synthesized and sodium alginate was chemically bonded with the poly(sodium acrylate) matrix. DSC analysis of the melting heat and glass transition parameters indicated that the hydrogel structure had changed as a result of the cross-linking process. Sodium alginate and MBA were tested at different concentrations to determine how they affected the hydrogel properties. A very high content of the biopolymer, i.e., sodium alginate, was used in our research, up to 33 wt%. This resulted in durable and stable hydrogels with a very high ability to uptake water, comparable to hydrogels based on synthetic polymers only. The ability to swell is inversely proportional to the quantity of MBA present. By increasing the amount of sodium alginate in the hydrogel, the ability of the hydrogel to absorb water is reduced. However, water uptake remains relatively high at 350 g·g-1, even for the hydrogel with the highest SA content.

Wettability of HPMC/PEG/CS Thermosensitive Porous Hydrogels

Thermosensitive hydrogels have been receiving attention in the development of fire extinguishing agents due to their stimuli responsivity. Conventional hydrogels are limited by their slow response rate, and their wettability has not been studied systematically. In the present study, a concentrate of a thermosensitive porous system has been successfully synthesized by adding Na2CO3/CH3COOH as a foaming agent into the mixture of hydroxypropyl methylcellulose (HPMC)/polyethylene glycol (PEG)/chitosan (CS). The systems with different concentrations were obtained by diluting the concentrate with water. Thermosensitivity, surface tension and contact angle were characterized. In addition, spreadability, wettability and adhesivity were investigated systematically. Results showed that the systems with a concentration greater than 15 wt% exhibited outstanding performance of thermosensitivity and coagulability. A total of 20 wt% of the system has the best spreadability and wettability on the wood surface, most likely due to favorable contributions brought by both adequate viscosity and hydrophilicity. The adhesive force and surface-free energy of the pre-gel droplet that reached deposition on the wood surface decreased by 46.78% and 20.71%, respectively. The gel has a great capacity of water retention over a long period of time, which makes this porous gel the best system when it comes to its wettability and adhesiveness towards the chosen wood surface. The equilibrium surface tension decreased by 45.50% compared with water. HPMC/PEG/CS thermosensitive porous hydrogel with excellent wettability presented wide-ranging possibilities for the further development of fire suppression agents of fast phase-transition thermosensitive hydrogel.

Adsorption kinetics of methylene blue from wastewater using pH-sensitive starch-based hydrogels

In this work, starch/poly(acylic acid) hydrogels were synthesized through a free radical polymerization technique. The molar ratios of acrylic acid to N,N'-methylenebisacrylamide were 95:5, 94:6, and 93:7. The samples exhibited an amorphous porous structure, indicating that the size of the pores was contingent upon the amount of cross-linking agent. The quantity of acrylic acid in structure rose with a little increase in the amount of the cross-linking agent, which improved the hydrogels' heat stability. The swelling characteristics of the hydrogels were influenced by both the pH level and the amount of cross-linking agent. The hydrogel with a ratio of 94:6 exhibited the highest degree of swelling (201.90%) at a pH of 7.4. The dominance of the Fickian effect in regulating water absorption in the synthesized hydrogels was demonstrated, and the kinetics of swelling exhibited agreement with Schott's pseudo-second order model. The absorption of methylene blue by the hydrogels that were developed was found to be influenced by various factors, including the concentration of the dye, the quantity of the cross-linking agent, the pH level, and the duration of exposure. The hydrogel 95:5 exhibited the highest adsorption effectiveness (66.7%) for the dye solution with a concentration of 20 mg/L at pH 10.0. The examination of the kinetics and isotherms of adsorption has provided evidence that the process of physisorption takes place on heterogeneous adsorbent surfaces and can be explained by an exothermic nature.

Synthesis and Characterization of Novel Magnetic Nano-Biocomposite Hydrogels Based on Starch-g-poly(acrylic acid) Reinforced by Cellulose Nanofibers for Cu2+ Ion Removal

One of the crucial challenges of the adsorption process is to recapture the adsorbent from the solution, especially for adsorbents in powder form. This study synthesized a novel magnetic nano-biocomposite hydrogel adsorbent to successfully remove Cu²⁺ ions, followed by convenient recovery and reusability of the adsorbent. The Cu²⁺ adsorption capacity of starch-g-poly(acrylic acid)/cellulose nanofibers (St-g-PAA/CNFs) composite hydrogel and magnetic composite hydrogel (M-St-g-PAA/CNFs) was investigated and compared in both bulk and powder forms. Results showed that Cu²⁺ removal kinetics and swelling rate were improved by grinding the bulk hydrogel into powder form. The kinetic data and adsorption isotherm were best correlated with the pseudo-second-order and Langmuir models, respectively. The maximum monolayer adsorption capacity values of M-St-g-PAA/CNFs hydrogels loaded with 2 and 8 wt % Fe₃O₄ nanoparticles in 600 mg/L Cu²⁺ solution were found to be 333.33 and 555.56 mg/g, respectively, compared to 322.58 mg/g for the St-g-PAA/CNFs hydrogel. Vibrating sample magnetometry (VSM) results demonstrate that the magnetic hydrogel that included 2 and 8 wt % magnetic nanoparticles exhibited paramagnetic behavior with the magnetization of 0.6-0.66 and 1-1.04 emu/g at the plateau, respectively, which showed a proper magnetic property and good magnetic attraction in the magnetic field for separating the adsorbent from the solution. Also, the synthesized compounds were characterized by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and Fourier transform infrared spectroscopy (FTIR). Finally, the magnetic bioadsorbent was successfully regenerated and reused for four treatment cycles.

A review of advances over 20 years on polysaccharide-based polymers applied as enhanced efficiency fertilizers

Over the last 20 years, polysaccharide-based materials have garnered attention in the enhanced efficiency fertilizers (EEFs) research. Biodegradability, non-toxicity, water-solubility, swellability, and ease of chemical modification make these polymers suitable for agricultural applications. In this review, the polysaccharides-based EEFs advances are summarized over the polymer and co-materials selection, the methods, and the chemical/structure aspects necessary for an appropriate production. We also briefly discuss terminologies, nutrient release mechanisms, biodegradation, and future trends. The most used polysaccharides are chitosan, starch, and alginate, and the non-Fickian model most describes the release mechanism. It is dependent on the relaxation of polymer chains by the matrix swelling followed by the nutrient diffusion. EEFs-polymers-based should be designed as more packed and less porous structures to avoid the immediate contact of the fertilizer with the surrounding water, improving fertilizer retention. Furthermore, the preparation methods will determine the scale-up of the material.

Effect of Diaminosilane Derivative on Thermal and Swelling Behaviour of Acrylic Acid Based Hydrophilic Composites

Organic-inorganic hydrophilic composites based on sodium polyacrylate (PAANa) and poly-N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (PAPTMS) showed the improved swelling capacity at incorporation of PAPTMS. Changing of non-Fickian to Super case II swelling behaviour is observed at 20 wt % PAPTMS content. Enhancing of thermal stability and heat-resistance index of composite hydrogels compared to PAA is shown.

Adsorption of copper (II) and cadmium (II) ions by in situ doped nano-calcium carbonate high-intensity chitin hydrogels

Most natural polymers exhibit limited functional groups, which is not favourable for the adsorption of various ions and their utilisation. To overcome this drawback, a novel in-situ-doped nano-calcium carbonate (CaCO₃) chitin hydrogel was synthesised as an efficient adsorbent for Cu (II) and Cd (II) ions. Scanning electron microscopy and Brunauer-Emmett-Teller results revealed that the synthesised CaCO₃/chitin hydrogel exhibited loose macropores and mesopores. Subsequently, Fourier transform infrared, Raman, and X-ray diffraction characterisation characterisation proved that chitin was successfully doped with nano-CaCO₃. The mechanical properties of CaCO₃/chitin hydrogel were superior to those of the unmodified chitin hydrogel and could efficiently adsorb Cu (II) and Cd (II) ions in water. The effect of pH, initial concentration, adsorbent dosage, and temperature was assessed to determine the adsorption properties of the hydrogel. Under suitable experimental conditions, the maximum adsorption rate of the CaCO₃/chitin hydrogel was approximately 96%. The time-dependent adsorption kinetics followed a quasi-second order model, and the adsorption process followed the Langmuir model. The maximum adsorption capacities of Cu (II) and Cd (II) according to the Langmuir curve were 194.61 and 191.58 mg/g, respectively. Compared with the binary competitive system, the material exhibited a specific selectivity to the adsorption of Cu (II). X-ray photoelectron spectroscopy (XPS) revealed that nitrogen and oxygen atoms were involved in chelation with the metal ions. The successful compounding of calcium carbonate nanoparticles provided more active adsorption sites for the gel. The novel material exhibited excellent adsorption effects on Cu (II) and Cd (II) ions when applied to a water sample. Thus, the novel material exhibits excellent potential for application. The Cu (II) and Cd (II)ion removal efficiencies after five successive adsorption cycles were higher than 90%, which indicated that the composite material exhibited excellent stability and reproducibility.

Phosphates-Containing Interpenetrating Polymer Networks (IPNs) Acting as Slow Release Fertilizer Hydrogels (SRFHs) Suitable for Agricultural Applications

Novel, phosphorus-containing slow release fertilizer hydrogels (SRFHs) composed of interpenetrating polymer networks (IPNs) with very good swelling and mechanical properties have been obtained and characterized. It was found that introducing organophosphorus polymer based on a commercially available monomer, 2-methacryloyloxyethyl phosphate (MEP), as the IPN’s first component network results in much better swelling properties than for a terpolymer with acrylic acid (AAc), 2-methacryloyloxyethyl phosphate (MEP) and bis[2-(methacryloyloxy)ethyl] phosphate (BMEP) when the same weight ratios of monomers are employed. The procedure described in this paper enables the introduction of much larger amounts of phosphorus into polymer structures without significant loss of water regain ability, which is crucial in the application of such materials in the agricultural field.

Transformation of non-water sorbing fly ash to a water sorbing material for drought management

Securing water in the soil through suitable amendments is one of the methods for drought management in arid regions. In this study, a poor water sorbing fly ash was transformed into a high water-absorbing material for improving soil water retention during the drought period. The fly ash water absorbent (FAWA) exhibited high water-absorbing capacity (WAC) of 310 g/g at par with commercially available superabsorbent hydrogel (SAH). The FAWA showed excellent re-swelling behavior for more than eight alternate wetting–drying cycles. The WAC of FAWA was sensitive to salt type, pH, and ionic strength of the solution. At maximum salinity level permitted for plant growth, the WAC of FAWA was 80 g/g indicating its suitability for drought management. There was only a marginal WAC variation in the range of pH (5.5–7.5) considered most suitable for plant growth. The drying characteristics of FAWA amended soil exhibited an increase in desaturation time by 3.3, 2.2, and 1.5 times for fine sand, silt loam, and clay loam, respectively. The study demonstrates the success of using a low rate of FAWA for drought management with the advantage of offering a non-toxic and eco-friendly solution to mass utilization of industrial solid waste for agricultural applications.

Advancements in applications of nanotechnology in global food industry

Nanotechnology has several applications in food industry and it significantly helps in characterization, fabrication, and manipulation of nanostructures. The nanostructures improve the solubility of food ingredients in vivo, along with enhancement in their bioavailability and controlled release at the target site. These nanostructures also serve as anticaking agents, nano-additives, delivery systems for nutraceuticals, etc. Present study highlights different forms of nanoengineered structures applied in food nanotechnology to tune the characteristics of conventional food ingredients and their applications. Literature survey highlighted the application of various types of nanostructures in the food industry. The study focusses on recent advancements in preparation methods of nanostructures as food additives and packaging stuffs along with pros and cons of their application in food industry. The shortcomings associated to nanotechnology in food science have illustrated along with its tentative future perespective. The impact of eco-toxicity due to application of nanostructures has also been discussed based on recent observations. This can suppressed by the application of bioedible polymers instead of synthetic polymers.

Starch-based semi-IPN hydrogel nanocomposite integrated with clinoptilolite: Preparation and swelling kinetic study

Semi-interpenetrating polymer network (semi-IPN) of starch-graft-poly(acrylic acid-co-acrylamide)/polyvinyl alcohol/clinoptilolite (starch-g-p(AA-co-AAm)/PVA/clino) superabsorbent nanocomposite was synthesized by free-radical graft co-polymerization technique in an aqueous solution. Taguchi method was used to optimize the synthesis reaction condition based on the equilibrium swelling capacity of the hydrogels. FTIR, XRD, and SEM analyses were used to study the chemical and structural properties of the hydrogel samples. The equilibrium swelling capacity of the semi-IPN superabsorbent nanocomposite (364.82 g/g) was higher than that of neat hydrogel (286.21 g/g) and in both of them water penetration into hydrogel network occurred through non-Fickian diffusion mechanism. Incorporation of clino into the polymeric matrix not only increased the equilibrium swelling capacity of the hydrogel, but also induced a substantial enhancement in its mechanical strength. Semi-IPN superabsorbent nanocomposite showed reasonable water absorbency under different loads, good salt and pH-sensitive swelling behavior, and better water retention capability, which make it potentially useful for hygiene products.

Recent Advances in Edible Polymer Based Hydrogels as a Sustainable Alternative to Conventional Polymers

The over increasing demand of eco-friendly materials to counter various problems, such as environmental issues, economics, sustainability, biodegradability, and biocompatibility, open up new fields of research highly focusing on nature-based products. Edible polymer based materials mainly consisting of polysaccharides, proteins, and lipids could be a prospective contender to handle such problems. Hydrogels based on edible polymer offer many valuable properties compared to their synthetic counterparts. Edible polymers can contribute to the reduction of environmental contamination, advance recyclability, provide sustainability, and thereby increase its applicability along with providing environmentally benign products. This review is highly emphasizing on toward the development of hydrogels from edible polymer, their classification, properties, chemical modification, and their potential applications. The application of edible polymer hydrogels covers many areas including the food industry, agricultural applications, drug delivery to tissue engineering in the biomedical field and provide more safe and attractive products in the pharmaceutical, agricultural, and environmental fields, etc.

Preparation and Characterization of Superabsorbent Polymers Based on Starch Aldehydes and Carboxymethyl Cellulose

Superabsorbent polymers (SAPs) are crosslinked hydrophilic polymers that are capable of absorbing large amounts of water. Commercial SAPs are mostly produced with acrylic acid that cannot be easily biodegraded. Therefore, in this study, polysaccharide-based SAPs using carboxymethyl cellulose as a major component were prepared. Starch aldehydes and citric acid were selected due to their environment-friendly, non-toxic, and biodegradable properties compared to conventional crosslinking agents. Starch aldehydes were prepared by periodate oxidation, which forms aldehyde groups by taking the places of C–OH groups at C-2 and C-3. Furthermore, starch aldehydes were analyzed through the change in FT-IR spectra, the aldehyde quantitation, and the morphology in FE-SEM images. In the crosslinking of polysaccharide-based SAPs, the acetal bridges from starch aldehydes led to a large amount of water entering the network structure of the SAPs. However, the ester bridges from citric acid interfered with the water penetration. In addition, the swelling behavior of the SAPs was analyzed by the Fickian diffusion model and the Schott’s pseudo second order kinetics model. The relationship between swelling behavior and morphology of the SAPs was analyzed by FE-SEM images. In conclusion, polysaccharide-based SAPs were well prepared and the highest equilibrium swelling ratio was 87.0 g/g.

Swelling Properties and Environmental Responsiveness of a Superabsorbent Composite Microsphere Based on Starch-g-Poly(acrylic acid)/Organo-Mordenite

Starch-g-poly(acrylic acid)/organo-mordenite superabsorbent composite microsphere, was prepared by grafting partially neutralized acrylic acid onto starch in the presence of organo-mordenite as an inorganic component. The morphology was characterized with scanning electron microscope (SEM). The swelling properties of the superabsorbent composite microsphere were evaluated in distilled water, various NaCl solutions, solutions with different pH values, and urea solutions. Swelling kinetics of the superabsorbent composite microsphere in above environments were discussed by means of a Schott's second-order model. The results showed that the incorporation of 10 wt% organo-mordenite enhanced the water absorbency by 144% (from 268 to 655 g · g−1) and possessed the maximum swelling absorbency (75 g · g−1) in the 0.9% NaCl solution and (667 g · g−1) in 0.04 mol · l−1 urea solution. Moreover, swelling of starch-g-poly(acrylic acid)/organo-mordenite (with 10 wt% organo-mordenite) in distilled water and in all other environments followed Schott's second order kinetics. Swelling was extremely environmental-responsive to the concentration of the NaCl solution, the pH values, and urea solutions, respectively. The overall results inferred that the novel superabsorbent composite can be exploited for many potential applications.