Gellan gum-O,O ′-bis(2-aminopropyl)-polyethylene glycol hydrogel for controlled fertilizer release

Natural gums and their derivatives based hydrogels: in biomedical, environment, agriculture, and food industry

The hydrogels based on natural gums and chemically derivatized natural gums have great interest in pharmaceutical, food, cosmetics, and environmental remediation, due to their: economic viability, sustainability, nontoxicity, biodegradability, and biocompatibility. Since these natural gems are from plants, microorganisms, and seaweeds, they offer a great opportunity to chemically derivatize and modify into novel, innovative biomaterials as scaffolds for tissue engineering and drug delivery. Derivatization improves swelling properties, thereby developing interest in agriculture and separating technologies. This review highlights the work done over the past three and a half decades and the possibility of developing novel materials and technologies in a cost-effective and sustainable manner. This review has compiled various natural gums, their source, chemical composition, and chemically derivatized gums, various methods to synthesize hydrogel, and their applications in biomedical, food and agriculture, textile, cosmetics, water purification, remediation, and separation fields.

Hydrogels Based on Natural Polymers Loaded with Bentonite and/or Halloysite: Composition Impact on Spectroscopic, Thermal, and Swelling Properties

Hydrogels are characterized by their property of absorbing and releasing a high content of water and water-based liquids; thus, they can be applied in agriculture as controlled-release water and fertilizer products. The focus of this research was efficient and low-cost natural polymer-based hydrogels obtained by crosslinking gellan gum (GGLA) and starch (ST) with acetic acid (CA) and loading them with either bentonite (BET) and/or halloysite (HAL). The hydrogels were obtained by mixing 100, 75, 50, 25, and 0 wt.% of GGLA with 0, 25, 50, 75, and 100 wt.% ST water solutions. To obtain the networks, they were crosslinked with 10, 5, and 2 wt.% of CA and loaded with 2, 5, and 10 wt.% of BET and/or HAL. The samples were analyzed by infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), their swelling in water, and the state of bound water properties. The results of these analyses point to the formation of a polymeric network with a decomposition temperature of >250 °C, and tailorable swelling properties that vary between 3 and 77, depending on the hydrogel composition. In summary, GGLA-ST-BET/HAL hydrogels are a good option for eco-friendly agriculture materials.

Improved Conductivity in Gellan Gum and Montmorillonite Nanocomposites Electrolytes

Nanocomposite polymer electrolytes (NPEs) were obtained using gellan gum (GG) and 1 to 40 wt.% of montmorillonite (Na⁺SYN-1) clay. The NPEs were crosslinked with formaldehyde, plasticized with glycerol, and contained LiClO₄. The samples were characterized by impedance spectroscopy, thermal analyses (TGA and DSC), UV-vis transmittance and reflectance, X-ray diffraction (XRD), and continuous-wave electron paramagnetic resonance (CW-EPR). The NPEs of GG and 40 wt.% LiClO₄ showed the highest conductivity of 2.14 × 10^-6 and 3.10 × 10^-4 S/cm at 30 and 80 °C, respectively. The samples with 10 wt.% Na⁺SYN-1 had a conductivity of 1.86 × 10^-5 and 3.74 × 10^-4 S/cm at 30 and 80 °C, respectively. TGA analyses revealed that the samples are thermally stable up to 190 °C and this did not change with clay addition. The transparency of the samples decreased with the increase in the clay content and at the same time their reflectance increased. Finally, CW-EPR was performed to identify the coordination environment of Cu²⁺ ions in the GG NPEs. The samples doped with the lowest copper concentration exhibit the typical EPR spectra due to isolated Cu²⁺ ions in axially distorted sites. At high concentrations, the spectra become isotropic because of dipolar and exchange magnetic effects. In summary, GG/clay NPEs presented good ionic conductivity results, which qualifies them for electrochemical device applications.

Advances in fermentative production, purification, characterization and applications of gellan gum

Multiple microbial exopolysaccharides have been reported in recent decade with their structural and functional features. Gellan gum (GG) is among these emerging biopolymers with versatile properties. Low production yield, high downstream cost, and abundant market demand have made GG a high cost material. Hence, an understanding on the various possibilities to develop cost-effective gellan gum bioprocess is desirable. This review focuses on details of upstream and downstream process of GG from an industrial perspective. It emphasizes on GG producing Sphingomonas spp., updates on biosynthesis, strain and media engineering, kinetic modeling, bioreactor design and scale-up considerations. Details of the downstream operations with possible modifications to make it cost-effective and environmentally sustainable have been discussed. The updated regulatory criteria for GG as a food ingredient and analytical tools required to validate the same have been briefly discussed. Derivatives of GG and their applications in various industrial segments have also been highlighted.

Reclaiming Phosphate from Waste Solutions with Fe(III)-Polysaccharide Hydrogel Beads for Photo-Controlled-Release Fertilizer

Photoresponsive hydrogels from polysaccharides and Fe(III) were used as a new system to capture and release PO43- from waste solutions. Uptake of 0.6-1.5 mg of phosphate per gram of hydrogels was determined from 800 ppm phosphate solutions (pH 4.8-9.0). These beads also captured 1.2 mg g-1 of phosphate from animal waste (raw manure, 727 ppm phosphate, pH 7.6), which accounted for above 80% phosphate uptake. Irradiation of phosphate-loaded hydrogels degraded the gels due to the photochemistry of the Fe(III)-carboxylates, giving controlled phosphate release (∼81% after 7 days). No release (<2% after 7 days) was seen in the dark. Kale plant trials showed complete degradation of the hydrogels in ∼2 weeks under greenhouse conditions. Biomass analysis of kale treated with phosphate-loaded beads compared to controls indicated no signs of toxicity. These results show that Fe(III)-polysaccharide hydrogels were able to reclaim phosphates from waste solutions and can be used as a controlled-release fertilizer.

Controlled-release urea encapsulated by ethyl cellulose/butyl acrylate/vinyl acetate hybrid latex

Fertilizer encapsulation through polymer membranes can reduce fertilizer losses and minimize environmental pollution. In this paper, an emulsion of ethyl cellulose (EC)/vinyl acetate (VAc)/butyl acrylate (BA) was successfully prepared by pre-emulsified semi-continuous seed emulsion polymerization. EC/BA/VAc films showed biodegradability. The influence of the EC content on the properties of EC/BA/VAc films was also investigated by DSC, a water absorbency analysis, etc. Controlled-release urea encapsulated by EC/BA/VAc latex was prepared in a film coating machine and conformed to the standards for slow-release fertilizers of the Committee of European Normalization. The release of urea from controlled-release urea encapsulated by EC/BA/VAc latex containing 0%, 5%, 10%, and 15% EC was 75.1%, 65.8%, 70.1% and 84.1%, respectively, after 42 days, and controlled-release urea encapsulated by EC/BA/VAc latex (5% EC) had the best controlled-release ability. Therefore, controlled-release urea encapsulated by EC/BA/VAc latex has many potential applications in agricultural industry.