Slow-release NPK fertilizer encapsulated by carboxymethyl cellulose-based nanocomposite with the function of water retention in soil

Synergistic Effect of Hydrogen Bonds and Chemical Bonds to Construct a Starch-Based Water-Absorbing/Retaining Hydrogel Composite Reinforced with Cellulose and Poly(ethylene glycol)

The hydrogel prepared by graft copolymerization of starch (ST) and acrylamide (AM) is a commonly used absorbent material; however, due to their irregular network structure and a limited number of hydrophilic groups, starch-based hydrogels have poor water absorption and water retention. To overcome this, here, we provide a new preparation method for starch-based hydrogels. Using cerium ammonium nitrate (CAN) as an initiator, the starch-acrylamide-cellulose (CMC)/poly(ethylene glycol) (S-A-M/PEG) superabsorbent hydrogel was prepared by graft copolymerization. The starch-acrylamide-cellulose/poly(ethylene glycol) hydrogel network is constructed through the synergistic effect of hydrogen bonds and chemical bonds. The experimental results showed that the starch-acrylamide-cellulose/poly(ethylene glycol) superabsorbent hydrogel has a complete network structure that does not easily collapse due to its superior mechanical properties. The water swelling rate reached 80.24 times, and it reached 50.61% water retention after 16 days. This hydrogel has excellent water-absorbing and water-retaining properties, biocompatibility, and degradability, making it useful for further studies in medical, agricultural, and other fields.

Synthesis and Characterization of Slow-Release Fertilizer Hydrogel Based on Hydroxy Propyl Methyl Cellulose, Polyvinyl Alcohol, Glycerol and Blended Paper

In this study, biodegradable slow-release fertilizer (SRF) hydrogels were synthesized from hydroxyl propyl methyl cellulose (HPMC), polyvinyl alcohol (PVA), glycerol and urea (SRF1) and HPMC, PVA, glycerol, urea and blended paper (SRF2). The fertilizer hydrogels were characterized by SEM, XRD and FTIR. The swelling capacity of the hydrogels in both distilled and tap water as well as their water retention capacity in sandy soil were evaluated. The hydrogels had good swelling capacity with maximum swelling ratio of 17.2 g/g and 15.6 g/g for SRF1 and SRF2 in distilled, and 14.4 g/g and 15.2 g/g in tap water, respectively. The water retention capacity of the hydrogels in sandy soil exhibited higher water retention when compared with soil without the (SRFs). The soil with the hydrogels was found to have higher water retention than the soil without the hydrogels. The slow-release profile of the hydrogels was also evaluated. The result suggested that the prepared fertilizer hydrogels has a good controlled release capacity. The blended paper component in SRF2 was observed to aid effective release of urea, with about 87.01% release in soil at 44 days compared to the pure urea which was about 97% release within 4 days. The addition of blended paper as a second layer matrix was found to help improve the release properties of the fertilizer. The swelling kinetic of the hydrogel followed Schott's second order model. The release kinetics of urea in water was best described by Kormeye Peppas, suggesting urea release to be by diffusion via the pores and channels of the SRF, which can be controlled by changing the swelling of the SRF. However, the release mechanism in soil is best described by first order kinetic model, suggesting that the release rate in soil is depended on concentration and probably on diffusion rate via the pores and channels of the SRF.

Synthesis, classification and properties of hydrogels: their applications in drug delivery and agriculture

Absorbent polymers or hydrogel polymer materials have an enhanced water retention capacity and are widely used in agriculture and medicine. The controlled release of bioactive molecules (especially drug proteins) by hydrogels and the encapsulation of living cells are some of the active areas of drug discovery research. Hydrogel-based delivery systems may result in a therapeutically advantageous outcome for drug delivery. They can provide various sequential therapeutic agents including macromolecular drugs, small molecule drugs, and cells to control the release of molecules. Due to their controllable degradability, ability to protect unstable drugs from degradation and flexible physical properties, hydrogels can be used as a platform in which various chemical and physical interactions with encapsulated drugs for controlled release in the system can be studied. Practically, hydrogels that possess biodegradable properties have aroused greater interest in drug delivery systems. The original three-dimensional structure gets broken down into non-toxic substances, thus confirming the excellent biocompatibility of the gel. Chemical crosslinking is a resource-rich method for forming hydrogels with excellent mechanical strength. But in some cases the crosslinker used in the synthesis of the hydrogels may cause some toxicity. However, the physically cross-linked hydrogel preparative method is an alternative solution to overcome the toxicity of cross-linkers. Hydrogels that are responsive to stimuli formed from various natural and synthetic polymers can show significant changes in their properties under external stimuli such as temperature, pH, light, ion changes, and redox potential. Stimulus-responsive hydrogels have a wider range of applications in biomedicine including drug delivery, gene delivery and tissue regeneration. Stimulus-responsive hydrogels loaded with multiple drugs show controlled and sustained drug release and can act as drug carriers. By integrating stimulus-responsive hydrogels, such as those with improved thermal responsiveness, pH responsiveness and dual responsiveness, into textile materials, advanced functions can be imparted to the textile materials, thereby improving the moisture and water retention performance, environmental responsiveness, aesthetic appeal, display and comfort of textiles. This review explores the stimuli-responsive hydrogels in drug delivery systems and examines super adsorbent hydrogels and their application in the field of agriculture.

New directions for agricultural wastes valorization as hydrogel biocomposite fertilizers

The tremendous amount of waste is an environmental and social problem worldwide. The agri-food sector is the largest producer of waste and requires the extensive use of fertilizers, which entails the need to look for innovative solutions in waste management. Properly recycled bio-waste can be reused as fertilizer. Polymer capsules with immobilized waste biomass can be applied as carriers for fertilizer nutrients. The amount of components exerts a certain influence on the effectiveness of copper ions binding. The most important physicochemical properties of biocomposites, such as swelling, SEM (Scanning Electron Microscopy) and FTIR (Fourier Transform Infrared Spectroscopy) were investigated. FTIR analyzes revealed that carboxyl and hydroxyl groups play a key role in Cu²⁺ ion binding. Morphology analysis showed that ion binding leads to homogenization of the composite surface, while coating the structure makes it more regular and cohesive. The sorption kinetics and the determination of the process's equilibrium parameters (Q_max = 29.4 ± 0.493 mg g^-1) play an important role. The study of Cu²⁺ ion release in different media showed that the chitosan layer slowed down the diffusion of cations by about 50% in NaNO₃ (1% m/m) solution. Preliminary studies of the applicability of the capsules in germination tests demonstrate that the biocomposites have no phytotoxic effects on the test plant. The chitosan coating slows the release of Cu²⁺ ions by about 20% compared to uncoated capsules. New fertilizer formulations containing chitosan-encapsulated hydrogel with biomass-immobilized micronutrients can be applied for precision agriculture to minimize the loss of fertilizer nutrients to the environment. These fertilizers could be used to cultivate houseplants and greenhouse crops.

Cellulose nanocrystals-filled poly (vinyl alcohol) nanocomposites as waterborne coating materials of NPK fertilizer with slow release and water retention properties

Effective fertilizers management is essential for sustainable agricultural practices. One way to improve agronomic practices is by using slow-release fertilizers (SRF) that have shown interesting role in optimizing nutrients availability for plants growth. Considering the current ecological concerns, coated SRF using ecofriendly materials continue to attract great attention. In this context, novel waterborne and biodegradable coating nanocomposite formulations were elaborated from cellulose nanocrystals (CNC)-filled poly (vinyl alcohol) (PVA) for slow release NPK fertilizer with water retention property. CNC were extracted from hemp stalks using sulfuric acid hydrolysis process and their physico-chemical characteristics were investigated. CNC with various weight loadings (6, 10, 14.5 wt%) were incorporated into PVA polymer via solvent mixing method to produce viscous coating nanocomposite formulations with moderated shear viscosity. Uniform PVA@CNC coating microlayer was applied on the surface of NPK fertilizer granules in Wurster chamber of a fluidized bed dryer at controlled spraying and drying parameters. The nitrogen, phosphorus and potassium release profiles from coated NPK fertilizer were determined in water and soil. It was found that the coating materials extended the N-P-K nutrients release time from 3 days for uncoated fertilizer to 10 and 30 days for neat PVA- and CNC/PVA-coated fertilizer in soil medium, indicating the positive role of the presence of CNC in the PVA-based coatings. The morphology, coating rate and crushing strength of the as-prepared coated products were investigated in addition to their effect on water holding capacity and water retention of the soil. Enhanced crushing strength and water retention with a positive effect on the soil moisture were observed after coating NPK fertilizer, mainly with high CNC content (14.5 wt%). Therefore, these proposed nanocomposite coating materials showed a great potential for producing a new class of SRF with high nutrients use efficiency and water retention capacity, which could be beneficial to sustainable crop production.

Regenerated Cellulose Products for Agricultural and Their Potential: A Review

Cellulose is one of the most abundant natural polymers with excellent biocompatibility, non-toxicity, flexibility, and renewable source. Regenerated cellulose (RC) products result from the dissolution-regeneration process risen from solvent and anti-solvent reagents, respectively. The regeneration process changes the cellulose chain conformation from cellulose I to cellulose II, leads the structure to have more amorphous regions with improved crystallinity, and inclines towards extensive modification on the RC products such as hydrogel, aerogel, cryogel, xerogel, fibers, membrane, and thin film. Recently, RC products are accentuated to be used in the agriculture field to develop future sustainable agriculture as alternatives to conventional agriculture systems. However, different solvent types and production techniques have great influences on the end properties of RC products. Besides, the fabrication of RC products from solely RC lacks excellent mechanical characteristics. Thus, the flexibility of RC has allowed it to be homogenously blended with other materials to enhance the final products' properties. This review will summarize the properties and preparation of potential RC-based products that reflect its application to replace soil the plantation medium, govern the release of the fertilizer, provide protection on crops and act as biosensors.

Decomposition and Nutrient Releasing of Biochar Compound Materials in Soil with Different Textures

Combining biochar with chemical fertilizers or compost not only improves the shortcomings of biochar’s lack of fertility, but also extends the benefits of the compost. The application of biochar composite materials will be a future agricultural management strategy. In this study bagasse compost was mixed with wood biochar (w/w) at rates of 0% (B), 25% (BC), 50% (BC3), and 100% (no biochar, C) to produce four types of particle biochar compound materials (pBCM). These materials were applied to two types of soil (sandy soil and clayey soil) for a 180-day incubation to determine the decomposition rate and the nutrient release efficiency of the pBCMs. The results showed that C treatment had the highest decomposition rate in both types of soil. Overall, the materials decomposed faster in the sandy soil than in the clayey soil. Plants were grown over two 30-day crop periods. The plant yields of treatments C and BC3 were the highest in the first period and respectively decreased and increased in the second period. The experiment results revealed that in the biochar–compost compounds, compost increased the use efficiency of nitrogen and phosphorus in the soil, and biochar increased the nutrient use efficiency in the second period. These compound materials had greater capacity for long-term supply of nutrients in soil than did single-component ones.

Current and future perspectives on the use of nanofertilizers for sustainable agriculture: the case of phosphorus nanofertilizer

Over the last century, the demand for food resources has been continuously increasing with the rapid population growth. Therefore, it is critically important to adopt sustainable farming practices that can enhance crop production without the excessive use of fertilizers. In this regard, there is a growing interest in the use of nanomaterials for improving plant nutrition as an alternative to traditional chemical or mineral fertilizers. Using this technology, the efficiency of micro- and macro-nutrients in plants can increase. Various nanomaterials have been successfully applied in agricultural production, compared to conventional fertilizers. Among the major plant nutrients, phosphorus (P) is the least accessible since most farmlands are frequently P deficient. Hence, P use efficiency should be maximized to conserve the resource base and maintain agricultural productivity. This review summarizes the current research and the future possibilities of nanotechnology in the biofortification of plant nutrition, with a focus on P fertilizers. In addition, it covers the challenges, environmental impacts, and toxic effects that have been explored in the area of nanotechnology to improve crop production. The potential uses and benefits of nanoparticle-based fertilizers in precision and sustainable agriculture are also discussed.

Construction of Porous Starch-Based Hydrogel via Regulating the Ratio of Amylopectin/Amylose for Enhanced Water-Retention

The performance of hydrogels prepared with traditional natural starch as raw materials is considerable; the fixed ratio of amylose/amylopectin significantly limits the improvement of hydrogel structure and performance. In this paper, starch hydrogels were prepared by physical blending and chemical grafting, with the aid of ultrasonic heating. The effects of different amylose/amylopectin ratios on the microstructure and water retention properties of starch hydrogels were studied. The results show that an increase in amylopectin content is beneficial to improve the grafting ratio of acrylamide (AM). The interaction between the AM grafted on amylopectin and amylose molecules through hydrogen bonding increases the pores of the gel network and thins the pore walls. When the amylopectin content was 70%, the water absorption (swelling 45.25 times) and water retention performance (16 days water retention rate 44.17%) were optimal. This study provides new insights into the preparation of starch-based hydrogels with excellent physical and chemical properties.

Synthesis of a novel superabsorbent with slow-release urea fertilizer using modified cellulose as a grafting agent and flexible copolymer

In this work, a number of glucose unites in polymeric structure of cellulose was converted to 2,4-dihydroxy-3-(1-hydroxy-2-oxoethoxy)butanal (cellulose containing di aldehyde units (CCDAUs)) by oxidation with sodium periodate, followed by condensation with acetone to produce 5,7-dihydroxy-6-((1-hydroxy-4-oxopent-2-en-1-yl)oxy)hept-3-en-2-one unites (cellulose containing di ene units (CCDEUs)). This modified cellulose was characterized by different methods and applied as a copolymer and grafting agent to synthesize an eco-friendly (CCDEUs-g-poly(AA)/urea) superabsorbent with slow-release urea fertilizer. The created double bonds in C₂ and C₃ positions of β-d-glucose units increased the linkage between cellulose and acrylic acid, leading to the formation of a strong network for slow-release urea fertilizer. Also, this modification created an expanded network for storage a high amount of water by increasing the cellulose flexibility. The reaction conditions for modification and synthesis of the superabsorbent, the oxidation degree value of glucose units, kinetics models, the effect of different saline solutions, various pH and reswelling time on the water absorbency, water retention capacity, reusability, biodegradability, and slow-release property were investigated. Also, the effect of synthesized CCDEUs-g-poly(AA)/urea on plant growth was tested and excellent results were obtained.

Synthesis of a slow-release fertilizer composite derived from waste straw that improves water retention and agricultural yield

To enhance waste straw utilization and improve fertilizer efficiency, a novel semi-interpenetrating polymer network fertilizer (CMCK-g-PAA/PDMUP) was prepared from straw cellulose and linear polymer by solution polymerization. Polydihydroxymethyl-urea potassium phosphate (PDMUP) was included to supply nitrogen, phosphorus, and potassium nutrients. Characterization of CMCK-g-PAA/PDMUP with FTIR, XPS, XRD, and SEM techniques provided evidence for semi-interpenetrating polymer networks (semi-IPNs) and component interactions. The prepared product exhibited excellent water absorbency (681.3 g/g) and enhanced the soil's water-retention capacity. Cumulative release of N, P, and K was 56.1%, 64.3%, and 74.1%, respectively, after 40 days-meeting a Committee of European Normalization (CEN) standard. Agricultural application of CMCK-g-PAA/PDMUP promoted wheat growth. Desirable water retention, slow-release properties, and wheat growth effects highlight the product's potential for improving agriculture.

Controlled Release Fertilizers: A Review on Coating Materials and Mechanism of Release

Rising world population is expected to increase the demand for nitrogen fertilizers to improve crop yield and ensure food security. With existing challenges on low nutrient use efficiency (NUE) of urea and its environmental concerns, controlled release fertilizers (CRFs) have become a potential solution by formulating them to synchronize nutrient release according to the requirement of plants. However, the most significant challenge that persists is the "tailing" effect, which reduces the economic benefits in terms of maximum fertilizer utilization. High materials cost is also a significant obstacle restraining the widespread application of CRF in agriculture. The first part of this review covers issues related to the application of conventional fertilizer and CRFs in general. In the subsequent sections, different raw materials utilized to form CRFs, focusing on inorganic and organic materials and synthetic and natural polymers alongside their physical and chemical preparation methods, are compared. Important factors affecting rate of release, mechanism of release and mathematical modelling approaches to predict nutrient release are also discussed. This review aims to provide a better overview of the developments regarding CRFs in the past ten years, and trends are identified and analyzed to provide an insight for future works in the field of agriculture.

Guar gum based hydrogel as controlled micronutrient delivery system: Mechanism and kinetics of boron release for agricultural applications

A boron loaded super-absorbent hydrogel (BLSAH) was developed through in situ incorporation of boron (B) in a guar gum-based hydrogel and characterized with FTIR, thermo-gravimetric analysis (TGA), scanning electron microscopy (SEM), and swelling studies, showing maximum absorption up to 356 g/g. The release pattern of B from the BLSAH and its kinetics was studied in water as well as soil. The B release pattern of the BLSAH was also compared with the commercial B fertilizer, boronated single super phosphate (bSSP). The BLSAH, following the Fickian mechanism, released 38% B, as compared with 51% of the bSSP, during the incubation period of 30 days in soil. The half-life period for the BLSAH (96.25 days) in soil was almost triple that of the bSSP's half-life (33.32 days), which is indicative of the slow and controlled release of B from the BLSAH. Thus, owing to its sustained nutrient release ability, the synthesized BLSAH exhibited wide potential for applications in agriculture sector.

Novel alginate-cellulose nanofiber-poly(vinyl alcohol) hydrogels for carrying and delivering nitrogen, phosphorus and potassium chemicals

Novel nanocomposite hydrogels were successfully prepared by blending and crosslinking sodium alginate (SA), poly(vinyl alcohol) (PVA) and cellulose nanofibers (CNFs) in the presence of a fertilizer formulation containing nitrogen (N), phosphorus (P) and potassium (K). The hydrogels had a macroporous flexible core and a microporous semi- interpenetrating polymer network (IPN) shell. The crystalline nature of the NPK chemicals was retained in the hydrogel nanocomposite network. Furthermore, the SA/CNF/PVA-based hydrogels showed a higher water-retention capacity in both deionized water and mixed soil. The swelling behavior in various physiological pH, salt and alkali solutions exhibited good sensitivity. The NPK release from SA/CNF/NPK and SA/CNF/PVA/NPK hydrogels was controlled by Fickian diffusion in both water and soil based on the Korsmeyer-Peppas release kinetics model (n < 0.5). Therefore, the prepared hydrogels have the potential for applications in drought-prone and/or fertilizer-loss regions for future development of precision agriculture and horticulture.

Development of polymer composites and encapsulation technology for slow-release fertilizers

The fertilizer manufacturing faces an ongoing challenge to develop its products to raise the effectiveness of their application, mainly of nitrogenous fertilizers, as well as to reduce any probable adverse ecological effect. In general, chemical fertilizers are very necessary for agricultural lands to provide the essential nutrients for plant growth, which are lost and leached into the surrounding environment during irrigation, which then leads to unwanted side effects, such as crop failure or increased losses to the environment. To solve this problem of nutrients being wasted, the most effective way is to use slow or controlled-release fertilizers (S/CRFs). The current review provides an insight vision into the methods used to save agricultural fertilizers from being wasted due to irrigation. The functional materials or physical techniques are used to maintain a steady release of nutrients. Fertilizers are encapsulated with various compounds based on synthetic or natural polymers to be used as SRFs. In this review paper, a comprehensive survey is presented on SRFs as an effective method in dealing with the problem of fertilizer wastage during irrigation. This review discusses the technology and applications of the latest research findings in this field.

Sustainable coating material based on chitosan-clay composite and paraffin wax for slow-release DAP fertilizer

The coating of fertilizers by polymers is one of the most efficient tools for their slow and control release into soil. This strategy avoids excessive use of the fertilizers and increases their availability to the crops needs. In the present paper, hydro-soluble diammonium phosphates (DAP) fertilizer was double coated following the dip-coating process by chitosan-clay composites as inner coating and paraffin wax as an outer coating. The chitosan composite preparation and characterization were deeply investigated. The montmorillonite (MMT) clay incorporation as filler improves the water barrier diffusion, mechanical properties, and thermal stability of the composite. The combination of the swelling behavior of the chitosan-clay composite (inner coating) and the hydrophobic property of paraffin wax (outer coating) was confirmed by the water holding capacity evaluation and the phosphorus release essays in water and soil. Indeed, the phosphorus dissolution from the coated DAP granules was significantly delayed compared to the uncoated DAP. Moreover, the biodegradation study of composite material in soil and the biochemical oxygen demand (BOD) tests revealed that the coating system proposed could be considered as a carbon source for microorganisms after the fertilization process, which confirms its sustainability.

Nanocomposites for Delivering Agrochemicals: A Comprehensive Review

Excessive application of fertilizers negatively affects soil health, causes low nutrient utilization efficiency in plants, and leads to environmental pollution. The application of controlled-release fertilizer is gaining momentum to overcome this crisis. Engineered nanocomposites (ENCs) have shown tremendous promise for need-based delivery of agrochemicals (macro- and micronutrients, pesticides, and other agrochemicals). This review provides comprehensive coverage of synthesis of nanocomposites, their physical-chemical characterization, and techniques to achieve sustained release and targeted delivery to the crops, emphasizing their beneficial role in plant production and protection. Related aspects like feasibility of the application, commercialization of the nanoformulations, and biosafety concerns are also highlighted. This will be helpful to develop a critical understanding of the current state of the art in the controlled release of agrochemicals through nanocomposites. The pressing issues like scale up production, cost analyses, field-based trials, and environmental safety concerns should be given greater attention in future studies.

Salt-Free Dyeing of Modified Cotton through Graft Polymerization with Highly Enhanced Dye Fixation and Good Strength Properties

Modification of cotton fabric with 2-methacryloyloxyethyltrimethyl ammonium chloride (DMC) was achieved through free-radical initiated graft polymerization with K₂S₂O₈/NaHSO₃ as the initiator. Grafting of DMC was confirmed by ATR-IR of the modified cotton. The optimal grafting reaction conditions, including DMC dosage, mole ratio of initiator to DMC, temperature, and time, were determined by cation content and dye fixation results of the modified cotton. The modified fibers were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and whiteness measurement. Salt-free dyeing of the modified cotton with commonly used C. I. Reactive Blue 19, C. I. Reactive Yellow 145, and C. I. Reactive Red 195 presented high fixation of 96.8%, 98.7%, and 97.3%, respectively. These results indicated that the modification is effective for changing the surface charge of the fiber and increasing the dye-fiber reactivity. The color fastness and strength property were still very satisfactory. With excellent properties, this dyeing method shows promise in real application for eliminating the usage of salt and reducing environmental pollution.

Cellulose based materials for controlled release formulations of agrochemicals: A review of modifications and applications

Controlled release formulations (CRFs) of agrochemicals have been attracted considerable attention due to their friendliness to environment. The commercial supporting materials for CRFs of agrochemicals are non-degradable, leading to secondary pollution issue. Cellulose, as the most abundant natural materials in the world, is regarded as one of the most ideal substitutes for non-degradable supporting materials thanks to its good biocompatibility and biodegradability. As raw cellulose materials suffer several problems, such as poor mechanical strength, fast release rate, etc., chemical modifications are commonly performed to improve their properties. In this review, modification methods of cellulose materials for CRFs of agrochemicals were introduced. The relationships between release rate and cellulose based materials were discussed in detail. The applications of cellulose materials for CRFs of agrochemicals were also expounded.

Novel Semi-IPN Nanocomposites with Functions of both Nutrient Slow-Release and Water Retention. 2. Effects on Soil Fertility and Tomato Quality

So far, the effects of the semi-interpenetrating polymer network (semi-IPN) composites with functions of both nutrient slow-release and water retention on soil physicochemical properties, yield, and quality of crops have not been studied. In Part 1 of this paper ( Song, J.; Zhao, H.; Zhao, G.; Xiang, Y.; Liu, Y. J. Agric. Food Chem. 2019 , DOI: 10.1021/acs.jafc.9b00888 ), superabsorbent polymers SAP_WS (grafting wheat straw (WS) to poly(acrylic-co-acrylamide), which is WS-g-P(AA-co-AM)) and SAP_HEC (HEC (hydroxyethyl cellulose)-g-P(AA-co-AM)), and their semi-IPN nanocomposites SI-PSRF/SAP_WS and SI-PSRF/SAP_HEC (formed by chemical bonding of SAP_WS or SAP_HEC with PSRF (NPK-containing polymeric slow-release fertilizer)) were prepared, and their microstructures and degradation performances were systematically studied. In this study, effects of these two nanocomposites on soil physicochemical properties, crop yield, and quality as well as soil fertility, especially the relationships between these effects and the degradation performances of the materials themselves, were investigated by a pot experiment of the tomato. Results show that SI-PSRF/SAP nanocomposites can regulate the pH values of weak alkaline soils close to 7.0. The changes of soil pH values, in our study, are basically synchronized with the degradation rates of SI-PSRF/SAP, the higher the degradation rate of SI-PSRF/SAP, the lower the pH value of the alkaline soil treated. Compared with PSRF+SAP (the simple physically mixed system of PSRF and SAP) and PSRF, during the whole growth period of the tomato, SI-PSRF/SAP treatments have the lowest nitrogen release amounts, 4.74 g for SI-PSRF/SAP_WS and 4.88 g for SI-PSRF/SAP_HEC, the highest nitrogen contents of soils after day 40, and the highest nitrogen contents of plants on day 100, 1.16 and 1.68 g for SI-PSRF/SAP_WS and 1.26 and 1.86 g for SI-PSRF/SAP_HEC. While for PSRF+SAP_WS, PSRF+SAP_HEC, and PSRF, they are 5.16 g, 0.81 g, 0.63 g and 5.26 g, 0.87 g, 0.66 g and 5.17 g, 0.63 g, 0.52 g, respectively. There is a significant positive correlation between the material degradation rates and their nitrogen release amounts in this study, while SI-PSRF/SAP systems have the highest correlation coefficient, 0.950. In addition, compared to the control blank, the SI-PSRF/SAP system significantly increases tomato yield, 270.1% for SI-PSRF/SAP_WS and 301.7% for SI-PSRF/SAP_HEC. Compared with PSRF+SAP, the SI-PSRF/SAP system can make the soil treated become a high-quality soil by influencing the soil pH value, conductivity, cation exchange capacity, and the contents of nitrogen, phosphorus, organic carbon, and active organic carbon, which have significant impact on the soil quality. The chemical-bonded functional nanocomposites with a semi-IPN three-dimensional network structures formed by hydrogen-bonding interactions among functional groups of their components can more efficiently improve soil fertility, increase soil nutrient supply capacity, and promote plants growth and development as well as solve the environmental pollution caused by traditional fertilizers. The technology reported in this paper is simple and feasible for large-scale production of fertilizer with both water retention and nutrient slow-release, even nanofertilizer, which has great application potential.

How rheological behaviors of concentrated starch affect graft copolymerization of acrylamide and resultant hydrogel

Corn starches with different amylose/amylopectin ratios were used to explore the effect of rheological behaviors of concentrated system on the graft copolymerization of acrylamide and resultant hydrogels, which sheds a light on their reactive extrusion process. The viscoelastic moduli of starch melts increased with increasing amylose content (AC), leading to a decreased extent of micro-mixing detected by a reduced rheokinetic rate. With increasing AC, the graft efficiency was decreased but with almost similar monomer conversion (about 87.5%) and nearly equivalent graft content. XRD and SAXS spectra revealed that the extent of retrogradation of the starches were increased and two-phase separation was enhanced for hydrogels with increasing AC. Interestingly, microscopic analysis showed the superabsorbent hydrogel from the starch with AC of 50% exhibited a gridding membrane porous structure, resulting in a higher water absorbent capacity of 550 g/g. This was attributed to the moderate crosslinking and the slightly greater graft content.

Potential Sustainable Slow-Release Fertilizers Obtained by Mechanochemical Activation of MgAl and MgFe Layered Double Hydroxides and K₂HPO₄

This study describes the behavior of potential slow-release fertilizers (SRF), prepared by the mechanochemical activation of calcined Mg₂Al-CO₃ or Mg₂Fe-CO₃ layered double hydroxides (LDH) mixed with dipotassium hydrogen phosphate (K₂HPO₄). The effects of LDH thermal treatment on P/K release behavior were investigated. Characterizations of the inorganic composites before and after release experiments combined X-Ray diffraction (XRD), Fourier-transform infra-red spectroscopy (FTIR), solid-state nuclear magnetic resonance (NMR), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The best release profile (<75% in 28 days and at least 75% release) was obtained for MgAl/K₂HPO₄ (9 h milling, 2:1 molar ratio, MR). Compared to readily used K₂HPO₄, milling orthophosphate into LDH matrices decreases its solubility and slows down its release, with 60% and 5.4% release after 168 h for MgAl/K₂HPO₄ and MgFe/K₂HPO₄ composites, respectively. Mechanochemical addition of carboxymethylcellulose to the LDH/K₂HPO₄ composites leads to a noticeable improvement of P release properties.

Slow release fertilizer hydrogels: a review

Slow release fertilizer hydrogels combine fertilizer and hydrogel into one system.

Carboxylated nanocellulose foams as superabsorbents

HYPOTHESIS

Carboxylated nanocellulose fibres formed into foam structures can demonstrate superabsorption capacity. Their performance can be engineered by changing process variables.

EXPERIMENTS

TEMPO-oxidised cellulose nanofibres of varying concentration and surface charge are produced from hardwood kraft pulp. Foams were prepared through a 2-step freezing and lyophilisation process. The absorption capacity of water and saline solution (0.9 wt%) were measured as a function of time and related to the foam structure.

FINDINGS

The absorption capacity of nanocellulose foams can be manipulated from initial gel properties and processing conditions. Pore structure and distribution of nanocellulose foams are dictated by fibre content and charge density and freezing rate. The best performing foams are at 0.3-0.5 wt%, with a carboxylate concentration of 1.2 mmol/g and frozen at -86 °C before freeze-drying, which can absorb 120 g H₂O/g fibre. Fibre surface charge influences the absorption capacity of the foams by dictating the amount of participating carboxylate groups. Absorption capacity in saline (60 g/g) is lower than in deionised water (120 g/g); but is only slightly lower than that of a commercial polyacrylic acid (PAA) SAPs (80 g/g). Nanocellulose foams are attractive renewable alternatives for superabsorbent applications, contributing to a reduction of plastic microspheres.