A high water-retention sodium alginate-polyacrylic acid binary composite hydrogel and a preparation method thereof

Abstract

The application discloses a kind of high water-retention sodium alginate-polyacrylic acid binary composite hydrogel and preparation method thereof.The preparation method uses acrylic acid as monomer, sodium alginate as natural modifier, 2-ketoglutaric acid as photoinitiator, N,N'-methylene bisacrylamide as crosslinking agent, deionized water as solvent, is prepared through the steps of mixing, ultraviolet irradiation curing, washing, soaking, drying and crushing.By optimizing the mass ratio of each component, sodium alginate and polyacrylic acid form a dense interpenetrating network structure through hydrogen bonding and weak electrostatic interaction.The method uses ultraviolet light normal temperature curing, and the process is simple, low in energy consumption and environmentally friendly.The obtained hydrogel has excellent water absorption and water retention performance, with a 1-hour swelling rate of more than 926.30 g·g⁻¹, a room temperature 24-hour water retention rate of more than 74.53%, and good biocompatibility, and can be widely used in agricultural soil water retention, water and fertilizer slow release and saline-alkali soil improvement.

Description

Technical Field

[0001] This invention belongs to the field of polymer functional materials technology, specifically relating to a UV-curable sodium alginate-modified polyacrylic acid binary composite hydrogel, its preparation method and application. This material is particularly suitable for agricultural soil water retention, slow-release fertilizer, saline-alkali land improvement and vegetation cultivation. Background Technology

[0002] Sodium alginate is a natural polysaccharide polymer extracted from seaweed. Its molecular chain is rich in hydroxyl and carboxyl groups, exhibiting excellent hydrophilicity, biocompatibility, and biodegradability. Introducing sodium alginate into a polyacrylic acid network can theoretically form interpenetrating or semi-interpenetrating network structures through intermolecular interactions (such as hydrogen bonding), thereby enhancing the mechanical strength, water retention, and environmental friendliness of the hydrogel. Currently, the preparation of such composite hydrogels mostly employs thermally initiated free radical polymerization processes, which suffer from high energy consumption, long reaction cycles, and numerous byproducts.

[0003] Ultraviolet (UV) curing technology boasts advantages such as rapid reaction speed, low energy consumption, room temperature operation, and minimal pollution, demonstrating immense potential in materials preparation. 2-Ketoglutaric acid, as a highly efficient photoinitiator, is suitable for photopolymerization in aqueous systems. However, existing technologies lack mature and optimized solutions for combining UV curing technology with sodium alginate / polyacrylic acid composite systems to prepare hydrogels with ultra-high water retention and stable structures through precise formulation design and process control.

[0004] Therefore, developing a simple, energy-saving, and high-performance method for preparing sodium alginate-polyacrylic acid binary composite hydrogels is of great significance for promoting their practical application in arid agriculture, ecological restoration, and other fields. Summary of the Invention

[0005] The primary objective of this invention is to provide a method for preparing a highly water-retaining sodium alginate-polyacrylic acid binary composite hydrogel that is simple to process, has low energy consumption, and produces a product with excellent water retention properties.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a highly water-retaining sodium alginate-polyacrylic acid binary composite hydrogel uses deionized water as a solvent, acrylic acid as a polymerizing monomer, 2-ketoglutaric acid as a photoinitiator, N,N'-methylenebisacrylamide as a chemical crosslinking agent, and is modified with natural high-molecular-weight sodium alginate. The specific steps are as follows: (1) Dissolve acrylic acid, sodium alginate, 2-ketoglutaric acid and N,N'-methylenebisacrylamide in water and stir to mix evenly to obtain a precursor solution; (2) The precursor liquid is placed under ultraviolet light for curing to form a primary hydrogel; (3) The nascent hydrogel is washed, soaked to remove impurities, dried and pulverized to obtain the binary composite hydrogel.

[0007] As a preferred technical solution, the proportions of each reactant are crucial in determining the final performance of the product. By mass ratio, the proportions of acrylic acid, sodium alginate, 2-ketoglutaric acid, and N,N'-methylenebisacrylamide are 1:(0.02~0.08):(0.002~0.008):(0.0002~0.0008). More preferably, this mass ratio is 1:(0.04~0.05):(0.004~0.005):(0.0004~0.0005). The amount of water is preferably 3~8 times the mass of acrylic acid. Under this ratio, sodium alginate can be uniformly dispersed and penetrate the polyacrylic acid network, forming an interpenetrating network hydrogel with the most complete structure and superior performance.

[0008] The UV curing irradiation time is preferably 15-25 minutes, more preferably 19-21 minutes. Room temperature curing avoids heating, resulting in extremely low energy consumption and uniform reaction. The nascent hydrogel after curing needs to be washed and soaked to remove unreacted monomers and soluble impurities. The soaking time is preferably 20-28 hours, more preferably 24 hours. The cleaned hydrogel needs to be dried at a temperature preferably 60-80℃, more preferably 68-72℃. The dried material can be pulverized to obtain a granular finished product.

[0009] The binary composite hydrogel prepared by the above method exhibits a dense and uniform interpenetrating porous network structure. Infrared spectroscopy analysis confirmed that sodium alginate and polyacrylic acid molecules are bonded only through numerous hydrogen bonds and weak electrostatic forces, without undergoing a chemical reaction to form new covalent bonds. This interpenetrating network structure, with both physical and chemical cross-linking, endows the material with excellent water absorption, water retention, and mechanical stability. Performance tests show that the swelling rate of the composite hydrogel particles after soaking for 1 hour is not less than 920 g·g⁻¹, and the water retention rate after being left open at room temperature for 24 hours is not less than 74%, demonstrating extremely excellent rapid water absorption and long-term water retention capabilities. Simultaneously, the introduction of the natural component sodium alginate significantly improves the biocompatibility and biodegradability of the material, making it environmentally friendly and pollution-free for long-term application. Therefore, the high water-retention binary composite hydrogel described in this invention can be widely used in agricultural and ecological fields such as soil water retention, slow-release fertilization, and saline-alkali land improvement.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Green and efficient process: The process adopts ultraviolet light room temperature curing technology to replace the traditional thermally initiated polymerization, which greatly reduces energy consumption, shortens the production cycle, and avoids side reactions that may be caused by high temperature. The process is free of secondary pollution.

[0011] 2. Significantly improved performance: By introducing sodium alginate and optimizing the ratio, a stable physical interpenetrating network is formed with polyacrylic acid, which significantly improves the water absorption rate, swelling ratio and long-term water retention capacity of the hydrogel, and solves the problems of insufficient water retention and easy collapse of the structure of single polyacrylic acid hydrogel.

[0012] 3. Environmentally friendly product: The formula contains sodium alginate, a natural biodegradable component, which improves the product's biocompatibility, making it safer for agricultural applications and environmentally friendly to the soil with long-term use.

[0013] 4. Broad application prospects: The product has excellent performance, simple preparation method, and controllable cost, and has huge market application potential in the fields of agricultural water conservation, soil improvement, and ecological restoration. Attached Figure Description

[0014] Figure 1 The infrared spectrum of the composite hydrogel prepared in Example 1; Figure 2 The image shows a scanning electron microscope (SEM) image of the composite hydrogel prepared in Example 1. Detailed Implementation

[0015] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0016] Example 1 Add 6.48 g of acrylic acid, 0.30 g of sodium alginate, 0.03 g of 2-ketoglutarate, and 0.003 g of N,N'-methylenebisacrylamide (mass ratio 1:0.0463:0.00463:0.000463) sequentially to 30 g of deionized water, and stir until completely dissolved. Irradiate the mixture under 100W ultraviolet light for 20 min to complete curing. Wash the resulting hydrogel three times with deionized water, soak it at room temperature for 24 h, and then dry it in a 70℃ oven. Finally, pulverize the dried product to obtain granular material.

[0017] Performance tests were conducted on the finished product: A certain mass (m0) of dry gel particles was weighed, soaked in excess deionized water for 1 hour, drained through a sieve until no water dripped, and weighed (m1). The swelling ratio (SR) was calculated as (m1 - m0) / m0. The fully swollen gel was then placed in an open environment at room temperature for 24 hours and weighed (m2). The water retention rate (WR) was calculated as (m2 / m1) × 100%. The test results were: a swelling ratio (SR) of 926.30 g·g⁻¹ after 1 hour, and a water retention rate (WR) of 74.53% after 24 hours. The infrared spectrum of the composite hydrogel is shown below. Figure 1 A broad and strong OH stretching vibration absorption peak is observed at 3400 cm⁻¹, due to hydrogen bonds formed between numerous hydroxyl groups in the sample. A C=O stretching vibration peak is observed at 1720 cm⁻¹, caused by the -COOH group in PAA. Asymmetric and symmetric COO⁻ stretching vibration peaks are observed at 1600 cm⁻¹ and 1400 cm⁻¹, respectively, due to the -COO⁻ group in SA. No new characteristic absorption peaks were observed, indicating that the components are bound together solely by physical interactions such as hydrogen bonds. Scanning electron microscopy (SEM) observations confirm this. Figure 2 The cross-section after freeze-drying shows that its interior has a dense and uniform porous interpenetrating network structure.

[0018] Example 2 6.0 g of acrylic acid, 0.24 g of sodium alginate, 0.024 g of 2-ketoglutaric acid, and 0.0024 g of N,N'-methylenebisacrylamide (mass ratio 1:0.04:0.004:0.0004) were added sequentially to 30 g of deionized water. After stirring and dissolving, the solution was irradiated with ultraviolet light for 19 min, cured, washed, soaked for 24 h, dried at 68℃, and pulverized. Test results: swelling ratio of 922.18 g·g⁻¹ at 1 h, water retention rate of 74.26% at 24 h, and microstructure similar to that of Example 1.

[0019] Example 3 7.0 g of acrylic acid, 0.42 g of sodium alginate, 0.042 g of 2-ketoglutaric acid, and 0.0042 g of N,N'-methylenebisacrylamide (mass ratio 1:0.06:0.006:0.0006) were added sequentially to 35 g of deionized water. After stirring and dissolving, the solution was irradiated with ultraviolet light for 21 min, cured, washed, soaked for 24 h, dried at 72℃, and pulverized. Test results: swelling rate of 924.55 g·g⁻¹ at 1 h, water retention rate of 74.39% at 24 h, performance meets the requirements.

[0020] Example 4 The raw materials and procedures were the same as in Example 1, except that the UV irradiation time was adjusted to 19 min and the drying temperature to 70℃. The resulting hydrogel had a swelling ratio of 923.40 g·g⁻¹ after 1 h and a water retention rate of 74.10% after 24 h.

[0021] Comparative Example 1 Without adding sodium alginate, and using the same raw materials and steps as in Example 1, pure polyacrylic acid hydrogel was prepared. Its swelling rate after 1 hour was 615 g·g⁻¹, and its water retention rate after 24 hours was only 52%, significantly lower than the product of this invention.

[0022] The above embodiments demonstrate that, under the mass ratio and process conditions specified in this invention, the prepared hydrogels all possess high swelling ratio and high water retention rate, and exhibit good reproducibility, making them suitable for the agricultural field.

Claims

1. A method for preparing a highly water-retaining sodium alginate-polyacrylic acid binary composite hydrogel, characterized in that, Includes the following steps: (1) Dissolve acrylic acid, sodium alginate, 2-ketoglutaric acid and N,N'-methylenebisacrylamide in water and stir to mix evenly to obtain a precursor solution; (2) The precursor liquid is placed under ultraviolet light for curing to form a primary hydrogel; (3) The nascent hydrogel is washed, soaked to remove impurities, dried and pulverized to obtain the binary composite hydrogel.

2. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of acrylic acid, sodium alginate, 2-ketoglutaric acid and N,N'-methylenebisacrylamide is 1 : (0.02~0.08) : (0.002~0.008) : (0.0002~0.0008).

3. The preparation method according to claim 2, characterized in that, The mass ratio of acrylic acid, sodium alginate, 2-ketoglutarate and N,N'-methylenebisacrylamide is 1 : (0.04~0.05) : (0.004~0.005) : (0.0004~0.0005).

4. The preparation method according to claim 1, characterized in that, In step (1), the amount of water used is 3 to 8 times the mass of acrylic acid.

5. The preparation method according to claim 1, characterized in that, In step (2), the UV irradiation curing time is 15-25 minutes.

6. The preparation method according to claim 1, characterized in that, In step (3), the soaking time for removing impurities is 20 to 28 hours.

7. The preparation method according to claim 1, characterized in that, In step (3), the drying temperature is 60~80℃.

8. A highly water-retaining sodium alginate-polyacrylic acid binary composite hydrogel prepared by the method according to any one of claims 1-7, characterized in that, The hydrogel has a dense and uniform interpenetrating porous network structure, and the sodium alginate and polyacrylic acid molecules are bonded together by hydrogen bonds and weak electrostatic forces, without the formation of covalent bonds.

9. The highly water-retaining sodium alginate-polyacrylic acid binary composite hydrogel according to claim 8, characterized in that, The swelling rate of the hydrogel particles after soaking for 1 hour is not less than 920 g·g⁻¹, and the water retention rate after being placed at room temperature for 24 hours is not less than 74%.

10. The application of the high water-retaining sodium alginate-polyacrylic acid binary composite hydrogel as described in claim 8 or 9 in soil water retention, slow release of water and fertilizer, or improvement of saline-alkali land.

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