Preparation method of carboxymethyl cellulose grafted starch doped urea-formaldehyde resin water-retaining slow-release fertilizer

Abstract

The invention relates to the field of high polymer material preparation, in particular to a preparation method of a carboxymethyl cellulose grafted starch doped urea-formaldehyde resin water-retaining slow-release fertilizer, which comprises the following steps: quickly pouring a gelatinous product obtained by reaction into a beaker which is placed in an ice-water bath in advance, quickly cooling and shaping the product, and drying to obtain the carboxymethyl cellulose grafted starch doped urea-formaldehyde resin water-retaining slow-release fertilizer. Unreacted small molecule raw materials and by-products possibly remain on the surface of the cooled gel product, the gel product is repeatedly washed with absolute ethyl alcohol for 3-5 times, then the washed gel is transferred into a freeze dryer until the gel product reaches constant weight, and the semi-IPN slow-release fertilizer with the water retention function is obtained. Due to the unique structural design, the water absorption performance of the material is remarkably improved, the material shows more excellent water absorption rate in various media, the material is endowed with a slow release function, and slow release of nutrients is achieved.

Description

Technical Field

[0001] This invention relates to the field of polymer material preparation, specifically a method for preparing a carboxymethyl cellulose grafted starch-doped urea-formaldehyde resin water-retaining slow-release fertilizer. Background Technology

[0002] The use of chemical fertilizers plays an important role in increasing crop yields[1]. However, traditional fertilizers are easily lost through volatilization, surface runoff and other means, resulting in low utilization rates[2]. In contrast, slow-release fertilizers achieve slow release of fertilizers through multiple mechanisms such as coating barrier[3], carrier adsorption[4], chemical reaction control[5] and microbial decomposition[6], thereby significantly improving fertilizer utilization, reducing economic costs and environmental pollution.

[0003] Water resources are a key factor affecting fertilizer effectiveness.

[0004] Traditional fertigation technology improves water and fertilizer utilization by drip irrigation with water-soluble fertilizers. However, this method has high requirements for pipeline quality, water quality and the solubility of water-soluble fertilizers, which undoubtedly increases the cost of agricultural production [8]. The use of superabsorbent polymers (SAP) provides an effective way to improve water resource utilization. The three-dimensional network structure of SAP can load and encapsulate fertilizers, thereby improving fertilizer utilization while retaining water. This slow-release fertilizer with SAP as the fertilizer carrier, which has both water retention and slow-release functions, is called super retention fertilizer hydrogels (SRFHs) [9]. It can not only effectively solve the problem of low water and fertilizer utilization, but also enhance the synergistic effect of water and fertilizer.

[0005] Currently, according to the preparation method, slow-release fertilizers (SRFHs) can be divided into coated slow-release fertilizers, loaded slow-release fertilizers and in-situ slow-release fertilizers [9]. Coated fertilizers (CRFs) can reduce fertilizer usage and application frequency, reduce labor intensity, improve soil quality, and regulate nutrient release rate and seed germination rate

[10] . For example, Gou et al.

[11] used cross-linked starch as the core and acrylic acid (AA) and acrylamide (AAm) as the outer slow-release membrane to prepare white granular SMUSMP using the reverse suspension method. In the soil, the material released 10%, 15% and 61% of nitrogen elements at 2 days, 5 days and 30 days, respectively. However, the preparation cost of CRFs is high, and some of the coating materials used to produce CRFs are non-biodegradable, which can easily cause secondary pollution to the soil. In contrast, slow-release fertilizers based on natural polymers (such as cellulose, starch, chitosan, etc.) have the advantages of low cost and biodegradability. The loading method is one of the simplest methods to expand the function of superabsorbent polymers (SAP) due to its simple preparation process, and it does not interfere with the polymerization process of SAP, but it can only load water-soluble fertilizers. Leon et al.

[12] extracted chitosan (CHI) from waste seafood shells, and after mild oxidation and itaconic acid grafting modification, loaded different concentrations of urea (Urea). The results showed that the urea release of the high urea loading CHI slow-release fertilizer remained unchanged for 24 to 96 hours. Semi-interpenetrating polymer networks (semi-IPN) are molecular-scale networks composed of linear and branched macromolecules, and usually have better performance than their constituent polymers. Using a simple production method, a semi-IPN multifunctional fertilizer containing polymer composites can be prepared, which can improve mechanical strength, enhance soil fertility, and reduce fertilizer costs. Liu et al.

[13] loaded urea formaldehyde (UF) into a carboxymethyl cellulose-poly(acrylic acid-co-acrylamide) (CMC-P(AA-co-AM)) network using solution polymerization and semi-interpenetrating network technology, which not only enhanced the water retention performance of the material but also enriched the function of SAP. Experiments showed that the nitrogen accumulation release rate of CMC-P(AA-co-AM) / UF was 83.67% after 30 days. However, acrylic-based materials are difficult to degrade in soil and may cause secondary pollution. Current research on the synthesis of water-retaining slow-release fertilizers (SRFHs) still faces many challenges, such as poor degradability and single nutrient content.

[0006] This invention, based on the principles of sustainable resource utilization, environmental protection, and soil degradability, uses carboxymethyl cellulose (CMC) and starch (St) as natural and renewable framework raw materials. It employs citric acid (CA) as a chemical cross-linking agent for cross-linking modification and introduces urea-formaldehyde resin (UF) as a slow-release fertilizer component to prepare a water-retaining semi-interpenetrating polymer network (semi-IPN) slow-release fertilizer. This material not only possesses high water absorption, excellent slow-release performance, and biodegradability, but also releases nutrients during degradation, promoting plant growth. It is a low-cost, environmentally friendly, novel water-retaining slow-release fertilizer. Summary of the Invention

[0007] This invention relates to a method for preparing a carboxymethyl cellulose-grafted starch-doped urea-formaldehyde resin water-retaining slow-release fertilizer, aiming to solve the problems of complex device structure, inconvenient operation, and insufficient sealing performance in existing technologies. Therefore, this invention adopts the following technical solution:

[0008] This invention provides a method for preparing a carboxymethyl cellulose-grafted starch-doped urea-formaldehyde resin water-retaining slow-release fertilizer, comprising the following steps:

[0009] S1. In a four-necked flask, add 6g of urea (0.1mol) and 13.8g of 37% formaldehyde aqueous solution (0.15mol, molar ratio of urea to formaldehyde is 1:1.5) in sequence, then add 100mL of distilled water that has been pre-adjusted to pH 9 with sodium hydroxide solution (0.1g / L), turn on the stirrer, and carry out the addition reaction at this temperature for 2 hours.

[0010] S2. After the addition reaction is completed, phosphoric acid is slowly added dropwise to adjust the pH of the reaction system to 4-6. At the same time, the temperature of the reaction system is slowly raised from 50℃ to 90℃. The reaction is stirred at a speed of 400r / min to 500r / min for 2 hours. As the reaction system gradually becomes acidic, a white precipitate will gradually precipitate in the solution. This precipitate is urea-formaldehyde resin.

[0011] S3. Take out the reaction solution and use vacuum filtration to repeatedly wash the unreacted raw materials with distilled water until the filtrate is neutral. Then place the solid material obtained by vacuum filtration into a freeze dryer and freeze dry at -50℃ for 48 hours to remove the moisture completely.

[0012] S4. Finally, the dried product is ground in a mortar and passed through a 200-mesh sieve to obtain urea-formaldehyde resin powder for later use.

[0013] S5. Weigh 12g carboxymethyl cellulose, 6g starch, 6g citric acid and 5g urea-formaldehyde resin, and transfer these raw materials together with 200mL deionized water into a four-necked flask. Turn on the stirring device and place the flask in a constant temperature water bath at 65℃ for 3 hours. Stir continuously during the heating process to fully dissolve and disperse the raw materials and form a uniform mixed system.

[0014] S6. After the pre-reaction is completed, the system temperature is slowly increased to 85℃ at a rate of 2℃ / min. At this time, the solution system begins to become viscous. After the temperature stabilizes at 85℃, the reaction system is stirred at a speed of 300r / min. The reaction is continued to be stirred at 85℃ for 3h. During the reaction, the viscosity and color changes of the system are closely monitored to ensure that the cross-linking reaction is fully carried out.

[0015] S7. Quickly pour the gel-like product obtained from the reaction into a beaker that has been placed in an ice-water bath to cool and solidify the product rapidly. Unreacted small molecule raw materials and by-products may remain on the surface of the cooled gel product. Rinse it repeatedly with anhydrous ethanol 3-5 times. Then transfer the cleaned gel to a freeze dryer until the gel product reaches a constant weight to obtain a semi-IPN slow-release fertilizer with water retention function.

[0016] Preferably, in step S1, the stirring speed is controlled at 400 r / min to 500 r / min, and the temperature of the reaction system is raised to 50°C.

[0017] Preferably, in step S2, the concentration of phosphoric acid added slowly is 0.1 mol / g.

[0018] Preferably, in step S5, carboxymethyl cellulose accounts for 5.24 wt% of the total system, starch accounts for 2.62 wt% of the total system, citric acid accounts for 2.62 wt% of the total system, and urea-formaldehyde resin accounts for 2.18 wt% of the total system. Preferably, in step S5, the stirring speed is set to 450 r / min.

[0019] Preferably, in step S6, after the temperature stabilizes at 85°C, citric acid is slowly added over a period of 30 minutes. After the citric acid is added, a cross-linking reaction occurs.

[0020] Preferably, in step S7, the cooling time is 30 minutes.

[0021] Preferably, in step S7, the freeze-drying temperature is set to -50°C and the drying time is 48 hours.

[0022] The beneficial effects of this invention are as follows: the detachable connection structure between the mounting base and the connector, along with the locking mechanism of the locking block and the adjusting arc plate, ensure the stability and reliability of the device during use. The design of the rotating ring makes the disassembly and installation of the connector and the mounting base easier, while the sealing cover effectively protects the internal structure and extends the service life of the device. The lamp body provides medical personnel with a clear field of vision, facilitating the precise insertion of gastric tubes or urinary catheters, and improving the safety and efficiency of medical procedures.

[0023] In particular, the method for preparing a carboxymethyl cellulose-grafted starch-doped urea-formaldehyde resin water-retaining slow-release fertilizer solves the problems existing in the prior art through optimized structural design and functional configuration. The device is compact, easy to operate, and versatile, possessing high practical value and promising prospects for widespread application.

[0024] Furthermore, the components of the method for preparing a carboxymethyl cellulose grafted starch-doped urea-formaldehyde resin water-retaining slow-release fertilizer interact with each other through precise mechanical connections. For example, the elastic element between the pressure block and the mounting groove is made of a highly elastic material to ensure that the pressure block maintains a stable clamping force even after long-term use. The fit between the locking block and the adjusting arc plate is precisely designed to ensure a smooth and reliable locking process. The sealing cover is made of a corrosion-resistant material, enabling it to maintain good sealing performance in various medical environments.

[0025] Specifically, in the preparation method of the carboxymethyl cellulose grafted starch-doped urea-formaldehyde resin water-retaining slow-release fertilizer, the tube body and pressure tube are fixedly connected by welding or threaded connection to ensure that they will not loosen during use. The fit between the mounting block and the mounting groove of the connector is precision machined to ensure a tight and gapless connection. The rotation angle of the rotating ring is strictly limited to avoid damage to the locking block due to excessive rotation.

[0026] Furthermore, the lamp body in the method for preparing a carboxymethyl cellulose grafted starch-doped urea-formaldehyde resin water-retaining slow-release fertilizer uses an LED light source, which features low power consumption and high brightness. The outer shell of the lamp body is made of transparent material to ensure that the light can be evenly irradiated onto the target area. The wires of the lamp body are arranged through a dedicated channel inside the tube to avoid interference between the wires and other components inside the tube.

[0027] Specifically, in the method for preparing a carboxymethyl cellulose grafted starch-doped urea-formaldehyde resin water-retaining slow-release fertilizer, the sealing cover completely covers the mounting groove in the locked state, preventing liquid or dust from entering the device. The sealing cover has a sealing ring on its edge, further improving the device's sealing performance. The sealing ring is made of silicone material, which has good elasticity and durability, and can maintain a good sealing effect even after long-term use.

[0028] This invention employs a semi-interpenetrating structure strategy to enhance the water absorption performance of materials and add nutrient slow-release function. The structural characteristics, functional group features, and synthetic route of CMC-St / UF were confirmed by comparing the XRD, FT-IR, and SEM characterization methods of carboxymethyl cellulose (CMC), starch (St), citric acid (CA), urea-formaldehyde resin (UF), and the modified CMC-St / UF.

[0029] CMC exhibits a rod-like morphology with a relatively loose structure and numerous grooves on its surface. This morphological characteristic endows it with excellent water absorption and solubility, which is beneficial for the reaction synthesis of CMC-St / UF materials. On the other hand, St exhibits a regular spherical granular structure with a relatively uniform particle size distribution. The synthesized CMC-St / UF composite material displays a dense porous structure and a complex network morphology. In addition, the surface of this composite material is coated with UF, increasing the surface roughness and effectively improving its specific surface area, thus providing a physical barrier for better water molecule retention. Combined with the energy dispersive spectroscopy (EDS) analysis results, the nitrogen (N) content in CMC-St / UF is 2.9%, a level that ensures that it can both improve seed germination rate and provide the necessary nitrogen source for plant growth in practical applications.

[0030] The peaks at 3400 cm⁻¹, 3600 cm⁻¹, 2912 cm⁻¹, 1429 cm⁻¹, and 1130 cm⁻¹ correspond to the stretching vibrations of -OH, CH, and β-1,4 glycosidic bonds (COC), respectively. The characteristic peak at 1641 cm⁻¹ is attributed to the stretching vibration of the C=O group. In the infrared spectrum of CMC-St / UF, a broadening of the -OH characteristic absorption peak was observed, while the -COO characteristic absorption peak showed a blue shift compared to CMC-St. These changes are likely due to the introduction of UF, which leads to the formation of hydrogen bonds between UF and CMC and St molecules. This phenomenon strongly demonstrates the role of UF as a physical cross-linking agent. Compared to the spectrum of CMC / St / UF without CA, the CMC-St / UF spectrum and the CMC-St spectrum show a significant C=O stretching vibration peak at 1740 cm⁻¹. This phenomenon is attributed to the chemical cross-linking effect of CA forming ester groups with the -OH groups in the molecular backbone.

[0031] The XRD pattern of CMC shows distinct diffraction peaks at 31.81°, 45.54°, and 56.55°, with a broad peak at 18.61°–22.37° corresponding to the amorphous region of CMC. Similarly, the broad peak of St at 10.53°–25.92° corresponds to the amorphous region of St, with an interplanar spacing of [missing information]. Its molecular arrangement is relatively loose, making it easily affected by water molecules and other solvent molecules, thus exhibiting good water absorption and solubility. The UF spectrum shows a broad diffraction peak, indicating that UF has low crystallinity and its structure is even close to amorphous. Compared to the XRD patterns of CMC and St, the prepared CMC-St / UF shows a new peak shape. Comparing the XRD patterns of CMC-St / UF, CMC-St, and CMC / St / UF, the crystallinity of CMC-St / UF is between that of CMC-St and CMC / St / UF, proving that the introduction of UF can reduce crystallinity, while the CA chemical crosslinking agent increases crystallinity due to its crosslinking effect on the gel network backbone.

[0032] 1. This invention innovatively combines four raw materials—carboxymethyl cellulose (CMC), starch (St), citric acid (CA), and urea-formaldehyde resin (UF)—to construct a semi-interpenetrating polymer network (semi-IPN) structure with water-retaining properties. This combination not only utilizes the natural renewable properties of CMC and St but also achieves multifunctionality through the cross-linking effect of CA and the slow-release properties of UF. Compared with traditional slow-release fertilizers, this raw material combination significantly improves the material's water absorption and slow-release effect while reducing production costs.

[0033] 2. This invention introduces a semi-interpenetrating polymer network (semi-IPN) structure, cleverly interweaving UF within the water-retaining agent network. This unique structural design not only significantly improves the material's water absorption performance, enabling it to exhibit superior water absorption rates in various media, but also endows the material with a slow-release function, achieving the gradual release of nutrients. Furthermore, the chemical cross-linking effect of citric acid further enhances the stability of the material's network structure, optimizing its overall performance.

[0034] 3. Compared with traditional petroleum-based water-retaining agents, the CMC-St / UF slow-release fertilizer of this invention uses natural renewable polymers CMC and St as raw materials, exhibiting superior degradation performance and renewability, and better meeting environmental protection requirements. This material demonstrates good biodegradability in soil, with a degradation rate of up to 22.87% in 7 days, reducing the risk of environmental pollution while promoting the improvement of soil physicochemical properties.

[0035] 4. The CMC-St / UF slow-release fertilizer of this invention not only exhibits excellent water absorption and slow-release performance, but also demonstrates remarkable effects in soil water retention, nutrient release, and plant growth promotion. By optimizing the dosage of each component, the material achieves a water absorption ratio of 67.74 g / g in distilled water and 16.88 g / g in 0.9% NaCl solution. It releases 59.82% of the nitrogen source in water after 7 days and 8.24% of the nitrogen source in simulated soil after 7 days. Pot experiments show that soybean seedlings treated with CMC-St / UF exhibit 76.2% higher aboveground growth and 56.4% greater underground root growth compared to the control group, significantly promoting crop growth.

[0036] 5. This invention employs solution polymerization to prepare CMC-St / UF slow-release fertilizer. The process is simple, the conditions are mild, and it is easy to mass-produce. Single-factor experiments were conducted to optimize the dosage of each component, determining the optimal preparation conditions and ensuring the high performance of the material, thus providing a solid technical foundation for practical applications.

[0037] To make the above and other objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 This is a diagram illustrating the preparation process and synthesis mechanism of CMC-St / UF according to the present invention.

[0040] Figure 2 This is a scanning electron microscope image of the CMC-St / UF of the present invention;

[0041] Figure 3 The infrared spectra of CMC, St, UF, CMC-St, CMC / St / UF and CMC-St / UF of this invention are shown below.

[0042] Figure 4 This is an X-ray diffraction pattern of the CCS-NaAlg / UF material of this invention;

[0043] Figure 5 This is a diagram showing the repeated water absorption ratio of CMC-St / UF of the present invention;

[0044] Figure 6This is a diagram showing the liquid absorption ratio of CMC-St / UF in different salt solutions according to the present invention;

[0045] Figure 7 The liquid absorption performance of CMC-St / UF of the present invention at different pH values;

[0046] Figure 8 The soil water holding capacity and soil water retention rate of CMC-St / UF in this invention;

[0047] Figure 9 The degradation performance of CMC-St / UF of this invention;

[0048] Figure 10 This invention demonstrates the sustained-release properties of CMC-St / UF and UF in still water.

[0049] Figure 11 The slow-release performance of CMC-St / UF in soil according to the present invention;

[0050] Figure 12 This is the result of the CMC-St / UF pot experiment of the present invention;

[0051] Figure 13 This is the result data of the CMC-St / UF pot experiment of the present invention. Detailed Implementation

[0052] This invention provides a method for preparing a carboxymethyl cellulose-grafted starch-doped urea-formaldehyde resin water-retaining slow-release fertilizer, comprising the following steps:

[0053] S1. In a four-necked flask, add 6g of urea (0.1mol) and 13.8g of 37% formaldehyde aqueous solution (0.15mol, molar ratio of urea to formaldehyde 1:1.5) sequentially. Then add 100mL of distilled water pre-adjusted to pH 9 with sodium hydroxide solution (0.1g / L). Turn on the stirrer and control the stirring speed at 400r / min to 500r / min. Raise the temperature of the reaction system to 50℃ and carry out the addition reaction at this temperature for 2 hours. S2. After the addition reaction is complete, slowly add phosphoric acid dropwise to adjust the pH of the reaction system to 4-6. The concentration of phosphoric acid added dropwise is 0.1mol / g. Simultaneously, slowly raise the temperature of the reaction system from 50℃ to 90℃ and continue stirring at 400r / min to 500r / min for 2 hours. As the system gradually becomes acidic, a white precipitate will gradually form in the solution; this precipitate is urea-formaldehyde resin. S3. The reaction solution is removed and vacuum filtered. Unreacted raw materials are repeatedly washed with distilled water until the filtrate is neutral. The solid obtained from the filtration is then placed in a freeze dryer and freeze-dried at -50°C for 48 hours to remove moisture completely. S4. Finally, the dried product is ground in a mortar and passed through a 200-mesh sieve to obtain urea-formaldehyde resin powder for later use. S5. 12g of carboxymethyl cellulose, 6g of starch, 6g of citric acid, and 5g of urea-formaldehyde resin are weighed. Carboxymethyl cellulose accounts for 5.24 wt% of the total system, starch accounts for 2.62 wt%, and citric acid accounts for... The raw materials, comprising 2.62 wt% of the system and 2.18 wt% of urea-formaldehyde resin, were transferred together with 200 mL of deionized water into a four-necked flask. The stirring device was turned on, and the stirring speed was set to 450 rpm. The flask was placed in a constant temperature water bath at 65°C and heated for 3 hours, with continuous stirring during heating to ensure thorough dissolution and dispersion of the raw materials, forming a homogeneous mixture. After the pre-reaction, the system temperature was slowly increased to 85°C at a rate of 2°C / min. At this point, the solution began to thicken. Once the temperature stabilized at 85°C, the reaction system was stirred at 300 rpm. Simultaneously, citric acid was slowly added over a period of 30 minutes. After adding citric acid, a cross-linking reaction occurs. The reaction is continuously stirred at 85°C for 3 hours. During the reaction, the viscosity and color changes of the system are closely monitored to ensure that the cross-linking reaction is fully carried out. S7. The gel-like product obtained from the reaction is quickly poured into a beaker that has been placed in an ice-water bath. The product is rapidly cooled and solidified for 30 minutes. The freeze-drying temperature is set to -50°C and the drying time is 48 hours. Unreacted small molecule raw materials and by-products may remain on the surface of the cooled gel product. It is rinsed repeatedly with anhydrous ethanol 3-5 times. Then, the washed gel is transferred to a freeze dryer until the gel product reaches constant weight, thus obtaining a semi-IPN slow-release fertilizer with water retention function.

[0054] Water absorption performance test method

[0055] This study used the tea bag method to determine the water absorption capacity of the material. 1g of the water-absorbing polymer was placed in a tea bag and completely immersed in distilled water. The weight of absorbed water was then calculated periodically according to formula (1) until an equilibrium state was reached.

[0056]

[0057] w represents the water absorption ratio (g / g); m0 represents the mass of the sample when dried (g); and m represents the mass of the gel when swelling equilibrium is reached (g).

[0058] Repeated water absorption performance test

[0059] Through the above water absorption performance test, the swollen equilibrium sample was placed in a 45℃ oven until the weight remained unchanged. Then, the material was placed in a tea bag and completely immersed in distilled water. Then, according to formula (1), the equilibrium state was reached.

[0060] From the appendix Figure 5 It is evident that the water absorption capacity of CMC-St / UF decreases with increasing cycle number. This is likely because the physical cross-linking points in the polymer network structure are disrupted during the swelling-drying cycle, leading to severe damage to the network structure and weakening the CMC-St / UF water-absorbing network, thus reducing the water absorption rate. In the first repeated water absorption cycle, the swelling ratio of CMC-St / UF in deionized water reached as high as 67.74 g / g, indicating that the material has a strong absorption capacity for deionized water in its initial state, rapidly absorbing large amounts of water and swelling. As the number of repeated water absorption cycles increases, the swelling ratio gradually decreases. It drops to 54.71 g / g in the second cycle, 21.84 g / g in the third, 19.15 g / g in the fourth, and 17.25 g / g in the fifth. Although the swelling ratio continuously decreases, it still absorbs a certain amount of water in each cycle, indicating that CMC-St / UF retains some water absorption capacity even after multiple uses. In 0.9 wt% NaCl, the swelling ratio of CMC-St / UF was 16.88 g / g during the first repeated water absorption cycle, significantly lower than the initial swelling ratio in deionized water. This indicates that the salt in the solution significantly inhibits the material's water absorption capacity. In subsequent cycles, the swelling ratio also showed a decreasing trend: 12.23 g / g in the second cycle, 9.38 g / g in the third, 7.41 g / g in the fourth, and 5.93 g / g in the fifth. The decrease was relatively stable, and the swelling ratio remained lower than in deionized water at each cycle number, further demonstrating the adverse effect of salt on the material's water absorption performance.

[0061] Liquid absorption performance under different ions

[0062] Accurately weigh 1g of sample and place it into several salt solutions prepared with 200ml of NaCl, KCl, MgCl, and NH4Cl, respectively, and with concentrations of 0.1wt%, 0.3wt%, 0.6wt%, and 0.9wt%. After the sample has fully swelled in each solution and reached saturation, filter it using a sieve to remove any unabsorbed liquid from the surface. Then, determine the liquid absorption ratio of each sample according to formula (1).

[0063] In the practical application of slow-release fertilizers for soil water retention, their resistance to ion interference plays a crucial role. (See attached image) Figure 6 The figure shows the water absorption performance of CMC-St / UF under different ion concentrations. The water absorption ratio of CMC-St / UF in different salt solutions is significantly affected by the salt ion concentration, and this effect increases with increasing salt concentration, in the following order: NH4Cl > NaCl > KCl > MgCl2. NH4+ ions partially hydrolyze in aqueous solution to produce H+, increasing the acidity of the solution and thus negatively impacting the water absorption performance of CMC-St / UF. However, due to the relatively low charge density of NH4+ ions, its effect may be less significant than that of Mg2+. Mg2+ ions, due to their high charge density, have the most significant inhibitory effect on the water absorption capacity of CMC-St / UF. High-valence ions are more likely to induce osmotic pressure changes, causing water inside the hydrogel to diffuse outward more easily, thus significantly reducing the water absorption ratio.

[0064] Liquid absorption performance under different pH conditions

[0065] Accurately weigh 1g of sample and place it into multiple 500mL beakers. Then, add 400mL of aqueous solution with different pH values ​​(3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13) to each beaker. After the sample has fully swelled and reached saturation in each solution, filter it using a sieve to remove any unabsorbed liquid from the surface. Then, measure the liquid absorption ratio of each sample.

[0066] As attached Figure 7As shown, with the pH value gradually increasing from 1, the swelling ratio initially rises slowly and then rapidly, reaching a peak of 66.45 g / g at pH 7. Afterward, the swelling ratio gradually decreases with further increases in pH. In acidic to near-neutral environments (pH = 1-6), the swelling ratio gradually increases from 10.49 g / g to 22.79 g / g, with a relatively small increase. This may be because some functional groups in the material partially dissociate or are in a protonated state under acidic conditions, gradually increasing their solvent absorption capacity, but to a limited extent. From pH 6 to 7, the swelling ratio increases sharply from 22.79 g / g to 66.45 g / g. This indicates that in near-neutral environments, the internal chemical equilibrium of the material changes significantly, and the dissociation or protonation of functional groups reaches a state most favorable for solvent absorption, causing the material to absorb a large amount of water and swell. When the pH value exceeds 7 and enters an alkaline environment, the swelling ratio gradually decreases from 66.45 g / g to 14.07 g / g. This may be because in an alkaline environment, the functional groups in the material further dissociate or undergo other chemical reactions, leading to changes in the material structure and a decrease in solvent absorption capacity. Clearly, the sustained-release effect is best at pH 7, reaching 66.4 g / g.

[0067] Soil water holding capacity and water retention rate test

[0068] Samples with different mass fractions (0wt%, 1wt%, 2wt%, and 3wt%) were mixed with 100g of soil and filled into containers with a diameter of 52mm and drainage holes at the bottom to allow for natural drainage. The apparatus was then placed on a conical flask to collect the drained liquid. Tap water was slowly added to the apparatus until no water seeped out from the bottom, at which point the water was weighed and recorded as W1. The soil water holding capacity (WH%) was calculated using formula (2). A control group was also set up to compare and analyze the effects of different samples on soil water holding capacity and water retention rate.

[0069]

[0070] The soil water holding capacity is denoted as W2. The prepared soil mixture is stored in the device at room temperature, and weighed every 48 hours and recorded as W. i Soil without samples was used as a blank control group.

[0071]

[0072] Soil water holding capacity with different CMC-St / UF addition amounts is shown in the attached figure. Figure 8As shown in Figure a, when the CMC-St / UF addition was 0 wt%, the soil water holding capacity was 29.55%, indicating that the natural water holding capacity of the soil without the added material was at a low level. As the addition increased to 1 wt%, the soil water holding capacity rose to 44.98%, a significant increase compared to the unadded group, indicating that the introduction of CMC-St / UF began to have a positive impact on soil water holding capacity. When the addition further increased to 2 wt%, the water holding capacity reached 52.81%, indicating that CMC-St / UF continued to play a role in the soil, continuously improving the soil's water-holding structure. When the addition reached 3 wt%, the soil water holding capacity reached as high as 62.07%, significantly higher than other addition amounts, fully demonstrating that with the increase of CMC-St / UF addition, the soil water holding capacity gradually increased, and the two showed a clear positive correlation.

[0073] Appendix Figure 8 As shown in b, regarding the soil water retention rates with different CMC-St / UF additions, at the beginning of the experiment, the water retention rates of soils with different addition amounts were all at a relatively high level. As time progressed, all curves showed a downward trend, but the soil with a 3wt% addition rate consistently maintained the highest water retention rate, with a smaller decrease compared to other addition rates. The soil with a 0wt% addition rate showed the most significant decrease in water retention rate, indicating that the soil without CMC-St / UF had a poorer ability to retain water. Throughout the observation period, the soil with added CMC-St / UF, due to its special structure and properties, was able to more effectively bind water and reduce water loss. This means that adding CMC-St / UF to the soil not only improves its water-holding capacity but also significantly enhances its water retention performance, which has important application value for maintaining soil moisture stability, reducing irrigation frequency, and improving the survival ability of plants in drought environments.

[0074] Degradation rate test

[0075] 2g of the composite material was placed in a nylon tea bag and then buried in soil (typical sandy soil from Yulin area) at a depth of 5cm for biodegradation experiments. During the experiment, the soil was irrigated with 500g of tap water every 3 days to maintain suitable soil moisture. Every 7 days, the buried sample was taken out of the soil, washed thoroughly with distilled water to remove soil and other impurities adhering to the surface, and then dried at 60℃ until the sample mass no longer changed. Finally, it was weighed. The biodegradation rate was calculated according to formula (4):

[0076]

[0077] In the formula, W t For the net weight of the composite material, W0 and W t0These represent the weights of the membrane before and after it is buried in the soil.

[0078] As attached Figure 9 As shown, the long-term retention of non-biodegradable water-retaining agents in soil can cause soil and environmental pollution problems. However, water-retaining agents containing bio-based components such as St can significantly reduce this environmental impact due to their biodegradability. Under soil burial conditions, the biodegradation process can be divided into three stages: In the first 21 days, soil microorganisms begin to degrade the bio-based components in the water-retaining agent. The degradation rate is relatively fast in this stage because the microorganisms' ability to adapt to and decompose these bio-based components gradually increases. Between 21 and 40 days, the degradation rate slows down, reaching 14.87% and 22.87%, respectively. The reason for the reduced degradation rate in this stage may be due to the increased water content in the soil, which hinders the transport of oxygen to the water-retaining agent network, thus creating an anaerobic environment. This environment inhibits the growth of microorganisms, thereby slowing down the degradation rate. Over time, the water-retaining agent decomposes into smaller fragments, which are more easily attacked by microorganisms, thus entering the rapid degradation stage. This stage is characterized by a significantly increased degradation rate, ultimately completing the biodegradation process of the water-retaining agent.

[0079] Slow-release performance test in still water

[0080] Prior to testing, the total nitrogen content of the composite material formulation was determined using an organic elemental analyzer. These results were used to calculate the amount of material used in the release test. Samples were immersed in water at 25°C and sealed with plastic film to minimize moisture loss through evaporation. Nitrogen content was measured at regular intervals (1, 3, 5, 7, 14, 28, 32, and 46 days). Nitrogen content was determined using the Kjeldahl method.

[0081] As attached Figure 10 As shown, water-retaining slow-release hydrogels require a certain level of soil moisture. Therefore, to more comprehensively analyze the slow-release effect, the nitrogen release rate of CMC-St / UF material in still water was first tested. The slow-release rate of the material in still water (pH=7) for 72 hours was measured. The slow-release graphs of CMC-St / UF and UF show that both have the fastest release rate in the first 0-10 hours. This is because UF, prepared in this study, is a slightly water-soluble oligomer, which is more prone to chain decomposition when moisture is sufficient, resulting in a fast release rate in the initial stage. However, the release rate slows down with time because more C-C bonds cannot break naturally in a short period, leading to a slower release rate. Comparing the release rates of UF and CMC-St / UF, the results indicate that the three-dimensional network structure of CMC-St / UF material significantly inhibits the nitrogen source release of UF, demonstrating a significant effect on practical applications and soil conditions after prolonged release.

[0082] Slow-release performance test in soil

[0083] The sample was placed in a nylon tea bag, which was then buried in the soil, ensuring the soil layer above the tea bag was approximately 5 cm thick. The soil containing the sample was placed in a container with openings of 5 cm at both ends. During the experiment, the soil was irrigated with 50 mL of deionized water every other day to maintain suitable soil moisture. Nitrogen content in the effluent was collected and measured at regular intervals (1, 3, 5, 7, 14, 28, 32, and 46 days). Nitrogen content was determined using the Kjeldahl method.

[0084] As attached Figure 11 As shown, to analyze the nitrogen release of the prepared materials under near-realistic conditions, the release rate in soil was significantly lower than that in water. This may be due to the limited water holding capacity of the soil, restricting the material's water absorption, and the fact that microorganisms had not yet begun to effectively degrade the material. Both UF and CMC-St / UF materials gradually released nitrogen over 7 days, with CMC-St / UF significantly extending the release time. This is because the three-dimensional network structure within CMC-St effectively hinders the degradation of UF by water and microorganisms. Furthermore, the abundant -OH groups within the CMC-St network form hydrogen bonds with the -NH2 groups in UF, slowing down the N release rate.

[0085] Pot experiment

[0086] Soybean seeds were evenly distributed in multiple petri dishes at room temperature. Each dish was filled with 15 mL of water and 0.5 g of a pre-swelled water-retaining agent. Repeated experiments were necessary to ensure the reliability of the results. The petri dishes were then cyclically treated with light for 12 hours followed by 12 hours in the dark at 30±2℃, with 10 mL of water added every two days to maintain humidity. During the experiment, the germination process and growth indicators of the seeds were meticulously measured using calipers on days 1, 3, and 6.

[0087] Appendix Figure 12 The results of a CMC-St / UF pot experiment are presented. The experiment was divided into two groups: a blank control group and a CMC-St / UF treatment group. According to... Figure 13 The average aboveground length of the CMC-St / UF treatment group was 4.67 cm, significantly higher than the 2.65 cm of the control group. Simultaneously, the average underground length of the CMC-St / UF treatment group was 1.83 cm, also higher than the 1.17 cm of the control group. This indicates that CMC-St / UF has a significant promoting effect on plant growth.

[0088] The above are merely embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a carboxymethyl cellulose-grafted starch-doped urea-formaldehyde resin water-retaining slow-release fertilizer, characterized in that, Includes the following steps: S1. In a four-necked flask, add 6g of urea (0.1mol) and 13.8g of 37% formaldehyde aqueous solution (0.15mol, molar ratio of urea to formaldehyde is 1:1.5) in sequence, then add 100mL of distilled water that has been pre-adjusted to pH 9 with sodium hydroxide solution (0.1g / L), turn on the stirrer, and carry out the addition reaction at this temperature for 2 hours. S2. After the addition reaction is completed, phosphoric acid is slowly added dropwise to adjust the pH of the reaction system to 4-6. At the same time, the temperature of the reaction system is slowly raised from 50℃ to 90℃. The reaction is stirred at a speed of 400r / min to 500r / min for 2 hours. As the reaction system gradually becomes acidic, a white precipitate will gradually precipitate in the solution. This precipitate is urea-formaldehyde resin. S3. Take out the reaction solution and use vacuum filtration to repeatedly wash the unreacted raw materials with distilled water until the filtrate is neutral. Then place the solid material obtained by vacuum filtration into a freeze dryer and freeze dry at -50℃ for 48 hours to remove the moisture completely. S4. Finally, the dried product is ground in a mortar and passed through a 200-mesh sieve to obtain urea-formaldehyde resin powder for later use. S5. Weigh 12g carboxymethyl cellulose, 6g starch, 6g citric acid and 5g urea-formaldehyde resin, and transfer these raw materials together with 200mL deionized water into a four-necked flask. Turn on the stirring device and place the flask in a constant temperature water bath at 65℃ for 3 hours. Stir continuously during the heating process to fully dissolve and disperse the raw materials and form a uniform mixed system. S6. After the pre-reaction is completed, the system temperature is slowly increased to 85℃ at a rate of 2℃ / min. At this time, the solution system begins to become viscous. After the temperature stabilizes at 85℃, the reaction system is stirred at a speed of 300r / min. The reaction is continued to be stirred at 85℃ for 3h. During the reaction, the viscosity and color changes of the system are closely monitored to ensure that the cross-linking reaction is fully carried out. S7. Quickly pour the gel-like product obtained from the reaction into a beaker that has been placed in an ice-water bath to cool and solidify the product rapidly. Unreacted small molecule raw materials and by-products may remain on the surface of the cooled gel product. Rinse it repeatedly with anhydrous ethanol 3-5 times. Then transfer the cleaned gel to a freeze dryer until the gel product reaches a constant weight to obtain a semi-IPN slow-release fertilizer with water retention function.

2. The method for preparing a carboxymethyl cellulose-grafted starch-doped urea-formaldehyde resin water-retaining slow-release fertilizer according to claim 1, characterized in that: In step S1, the stirring speed is controlled at 400 r / min to 500 r / min, and the temperature of the reaction system is raised to 50°C.

3. The method for preparing a carboxymethyl cellulose-grafted starch-doped urea-formaldehyde resin water-retaining slow-release fertilizer according to claim 1, characterized in that: In step S2, the concentration of phosphoric acid added slowly is 0.1 mol / g.

4. The method for preparing a carboxymethyl cellulose-grafted starch-doped urea-formaldehyde resin water-retaining slow-release fertilizer according to claim 1, characterized in that: In step S5, carboxymethyl cellulose accounts for 5.24 wt% of the total system, starch accounts for 2.62 wt% of the total system, citric acid accounts for 2.62 wt% of the total system, and urea-formaldehyde resin accounts for 2.18 wt% of the total system.

5. The method for preparing a carboxymethyl cellulose-grafted starch-doped urea-formaldehyde resin water-retaining slow-release fertilizer according to claim 1, characterized in that: In step S5, the stirring speed is set to 450 r / min.

6. The method for preparing a carboxymethyl cellulose-grafted starch-doped urea-formaldehyde resin water-retaining slow-release fertilizer according to claim 1, characterized in that: In step S6, after the temperature stabilizes at 85°C, citric acid is slowly added over a period of 30 minutes. After the citric acid is added, a cross-linking reaction occurs.

7. The method for preparing a carboxymethyl cellulose-grafted starch-doped urea-formaldehyde resin water-retaining slow-release fertilizer according to claim 1, characterized in that: In step S7, the cooling time is 30 minutes.

8. The method for preparing a carboxymethyl cellulose-grafted starch-doped urea-formaldehyde resin water-retaining slow-release fertilizer according to claim 1, characterized in that: In step S7, the freeze-drying temperature is set to -50℃ and the drying time is 48h.

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