Activated carbon filled polyvinyl alcohol hydrogel for soilless culture and preparation method thereof

Abstract

The invention discloses activated carbon filled polyvinyl alcohol hydrogel for soilless culture and a preparation method of the activated carbon filled polyvinyl alcohol hydrogel, and belongs to the technical field of polyvinyl alcohol hydrogel. The preparation method comprises the following steps: mixing polyvinyl alcohol and ultrapure water according to a mass ratio of 1: 9 to prepare a polyvinyl alcohol matrix solution, adding activated carbon into the polyvinyl alcohol matrix solution according to the mass content of the activated carbon of 1-5% to prepare a composite solution, ultrasonically dispersing the composite solution, and performing three freeze-thaw cycles on the dispersed composite solution. The active carbon filled polyvinyl alcohol hydrogel has the beneficial effects that the active carbon filled polyvinyl alcohol hydrogel can be prepared from the raw materials which are low in cost and easy to obtain through a simple process, complicated equipment is not needed, the production cost and the production difficulty are reduced, and large-scale application is facilitated; the prepared activated carbon filled polyvinyl alcohol hydrogel is high in water and fertilizer retention capacity and excellent in mechanical property, seed germination and plant growth can be effectively promoted, and continuous physical support is provided for plant growth.

Description

Technical Field

[0001] This invention relates to a hydrogel and its preparation method, specifically to an activated carbon-filled polyvinyl alcohol hydrogel for hydroponics and its preparation method, belonging to the field of polyvinyl alcohol hydrogel technology. Background Technology

[0002] Soilless cultivation, as a core technology of modern agriculture, can eliminate dependence on soil and has significant advantages in areas with limited space, poor soil or salinization.

[0003] Hydrogels, with their three-dimensional network structure and excellent hydrophilicity, have been widely studied as a novel substrate for soilless cultivation, enabling slow release of water, controlled release of nutrients, and regulation of the root environment.

[0004] Polyvinyl alcohol hydrogel, as a biocompatible material, has advantages such as being non-toxic and easy to prepare. However, pure polyvinyl alcohol hydrogel has poor mechanical properties and is prone to breakage during plant cultivation due to root growth or stress during operation, making it unable to provide stable support for plants. At the same time, its water and fertilizer retention capacity is limited, making it difficult to meet the water and nutrient requirements of plants for long-term growth. These two factors limit its application in complex cultivation environments.

[0005] Researchers have enhanced the mechanical properties of hydrogels by adding rigid fillers such as carbon fiber and nano-clay, or improved the water and fertilizer retention capacity of hydrogels by blending with natural polymers (such as chitosan and sodium alginate). However, these fillers have problems such as high cost and insufficient compatibility with polyvinyl alcohol matrix, making it difficult to balance performance improvement and economy.

[0006] Activated carbon, as a low-cost, porous, and non-toxic material, has been applied in the fields of adsorption and enhancement. However, there is still little research on activated carbon-polyvinyl alcohol composite hydrogel systems for soilless cultivation, especially a lack of systematic exploration of the relationship between activated carbon content and hydrogel performance and plant growth.

[0007] Based on this, the present invention aims to balance performance improvement and economy, and to develop a low-cost and high-performance activated carbon-filled polyvinyl alcohol hydrogel, so that the application of polyvinyl alcohol hydrogel in complex cultivation environments is no longer limited. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide a low-cost activated carbon-filled polyvinyl alcohol hydrogel with strong water and fertilizer retention capacity and excellent mechanical properties (tensile strength, compression resistance, and puncture resistance), as well as a method for preparing the activated carbon-filled polyvinyl alcohol hydrogel.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing activated carbon-filled polyvinyl alcohol hydrogel for hydroponics includes the following steps: (1) Preparation of polyvinyl alcohol matrix solution: Mix polyvinyl alcohol and ultrapure water at a mass ratio of 1:9, and stir magnetically in a water bath until the polyvinyl alcohol is completely dissolved to form a uniform polyvinyl alcohol matrix solution; (2) Preparation of composite solution: Weigh out the corresponding mass of activated carbon with an activated carbon content of 1-5%, and then add it to the polyvinyl alcohol matrix solution. Continue stirring until the activated carbon is mixed evenly to form a uniform composite solution. (3) Ultrasonic dispersion: The composite solution is placed in an ultrasonic cleaner for ultrasonic treatment to make the activated carbon evenly dispersed. (4) Freeze-thaw cycle: Pour the dispersed composite solution into a mold and place it in a refrigerator for 3 freeze-thaw cycles to form activated carbon-filled polyvinyl alcohol hydrogel.

[0010] Preferably, in step (1), the temperature of the water bath is 90°C.

[0011] Preferably, in step (2), activated carbon is weighed according to a mass content of 3%.

[0012] Preferably, in step (3), the parameters for ultrasonic treatment are: ultrasonic treatment at 40KHz frequency at 25℃ for 1h.

[0013] Preferably, in step (4), each freeze-thaw cycle lasts 24 hours.

[0014] An activated carbon-filled polyvinyl alcohol hydrogel for hydroponics is prepared by the aforementioned preparation method.

[0015] The advantages of this invention are: (1) The present invention utilizes the porous structure and rigidity of activated carbon to form a synergistic effect with the polyvinyl alcohol matrix: On the one hand, activated carbon, as a rigid filler, can enhance the mechanical strength (tensile strength, compression strength, and puncture resistance) of hydrogel, improve its easy breakage defects, and provide stable support for plants for a long time; on the other hand, the porous structure of activated carbon can optimize the adsorption and slow release capacity of hydrogel for water and nutrients, thereby improving the water and fertilizer retention performance of hydrogel, realizing the efficient use of water and nutrients, and reducing irrigation frequency and nutrient loss.

[0016] (2) By adjusting the activated carbon content (0%, 1%, 3%, 5%), the present invention screened out 3% activated carbon content as the optimal ratio, and achieved a balance between the mechanical properties, water retention and fertilizer retention of polyvinyl alcohol hydrogel and the germination and growth promotion effect of plants (such as sesame, tomatoes, etc.), thus breaking through the application limitations of pure polyvinyl alcohol hydrogel in complex cultivation environments.

[0017] (3) The present invention uses low-cost, readily available, non-toxic, and biodegradable raw materials (polyvinyl alcohol and activated carbon) to prepare composite hydrogels—activated carbon-filled polyvinyl alcohol hydrogels—through a simple process (solution blending-freeze-thaw cycle). No complex equipment is required, which reduces both production costs and production difficulty, facilitates large-scale application, and has good social and environmental benefits. Attached Figure Description

[0018] Figure 1 These are scanning electron microscope (SEM) images of composite hydrogels with different activated carbon contents. Among them, a is an SEM image of pure polyvinyl alcohol hydrogel with 0% activated carbon content, b is an SEM image of composite hydrogel with 1% activated carbon content, c is an SEM image of composite hydrogel with 3% activated carbon content, and d is an SEM image of composite hydrogel with 5% activated carbon content. Figure 2 These are force-depth curves of composite hydrogels with different activated carbon contents subjected to puncture tests using pointed, round, and flat-headed blades. Among them, a is the force-depth curve of composite hydrogels with different activated carbon contents subjected to puncture tests using pointed blades, b is the force-depth curve of composite hydrogels with different activated carbon contents subjected to puncture tests using round-headed blades, and c is the force-depth curve of composite hydrogels with different activated carbon contents subjected to puncture tests using flat-headed blades. Detailed Implementation

[0019] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0020] I. Preparation method of activated carbon-filled polyvinyl alcohol hydrogel This invention uses polyvinyl alcohol as the matrix material and introduces activated carbon as a functional filler to prepare a composite hydrogel—activated carbon-filled polyvinyl alcohol hydrogel—using a solution blending-cycle freeze-thaw method.

[0021] 1. Preparation of polyvinyl alcohol matrix solution Polyvinyl alcohol and ultrapure water were mixed at a mass ratio of 1:9, and then magnetically stirred in a 90°C water bath until the polyvinyl alcohol was completely dissolved, forming a homogeneous polyvinyl alcohol matrix solution.

[0022] 2. Preparation of composite solution Weigh out the corresponding amounts of activated carbon with a content of 0%, 1%, 3%, and 5%, respectively, and then add them to the polyvinyl alcohol matrix solution. Continue stirring until the activated carbon is evenly mixed to form a uniform composite solution.

[0023] 3. Ultrasonic dispersion The composite solution was placed in a KQ-400DE CNC ultrasonic cleaner and ultrasonically treated at 25℃ and 40KHz for 1 hour to ensure uniform dispersion of activated carbon.

[0024] 4. Freeze-thaw cycle The dispersed composite solution was poured into a mold and placed in a refrigerator for three freeze-thaw cycles, each lasting 24 hours, to form activated carbon-filled polyvinyl alcohol hydrogel.

[0025] II. Structural Characterization of Activated Carbon-Filled Polyvinyl Alcohol Hydrogels The microstructure of the composite hydrogels filled with activated carbon at concentrations of 0%, 1%, 3%, and 5% was investigated by scanning electron microscopy to explore the activated carbon filling situation.

[0026] Scanning electron microscope images of composite hydrogels with different activated carbon contents are shown below. Figure 1 .

[0027] Depend on Figure 1 It can be seen that: (1) All hydrogels exhibited a porous network structure, which indicates that a hydrogel with a three-dimensional network structure has been prepared through freeze-thaw cycles.

[0028] (2) Pure polyvinyl alcohol hydrogel (0% activated carbon content, a) has a certain pore structure, but the pore distribution is relatively disordered, and the size and shape are not uniform. The surface is relatively rough, but there are no obvious particles and special structures.

[0029] (3) The composite hydrogels (b, c, d) with added activated carbon have more pores and are rougher. As the activated carbon content increases, the pores in the composite hydrogel gradually increase and become denser. There are no obvious uneven phenomena such as activated carbon agglomeration on the surface of the composite hydrogel, indicating that there is good compatibility between activated carbon and polyvinyl alcohol hydrogel.

[0030] The well-developed porous structure of activated carbon facilitates the transport of water and air, which is crucial for plant growth and can effectively promote seed germination and plant growth.

[0031] III. Mechanical Properties of Activated Carbon-Filled Polyvinyl Alcohol Hydrogel To evaluate the mechanical properties of activated carbon-filled polyvinyl alcohol hydrogels used in hydroponics, puncture tests were conducted using pointed, round, and flat-headed knives.

[0032] Force-depth curves of composite hydrogels with different activated carbon contents, obtained from puncture tests using pointed, rounded, and flat-headed scalpels, are shown below. Figure 2 .

[0033] Depend on Figure 2It can be seen that the composite hydrogels with added activated carbon (1%, 3%, and 5% activated carbon content, respectively) exhibited significantly higher puncture resistance under all three tools than the pure polyvinyl alcohol hydrogel (0% activated carbon content). This indicates that the addition of activated carbon enhances the polyvinyl alcohol hydrogel's ability to resist structural damage, ensuring that plant roots can penetrate the hydrogel without causing local tearing, while maintaining the integrity of the overall hydrogel structure.

[0034] When the composite hydrogel with added activated carbon is used in hydroponics (as a hydroponics substrate), the above-mentioned properties ensure that the hydrogel maintains a stable porous structure during seedling root growth, preventing loss of water retention or failure of support function due to mechanical damage, thereby providing continuous physical support for plant growth. The effective interaction between activated carbon and the polyvinyl alcohol matrix significantly improves the mechanical properties of the polyvinyl alcohol hydrogel. This synergistic enhancement ensures that the polyvinyl alcohol hydrogel is suitable as a hydroponics substrate in hydroponic plant cultivation applications.

[0035] IV. Plant Germination and Growth Promotion Effects of Activated Carbon-Filled Polyvinyl Alcohol Hydrogel 1. Seed disinfection Select tomato or sesame seeds that are uniform in size, plump, and without broken skin. Wash them with 70% (v / v) ethanol for 1 minute, then rinse them with a 2.5% sodium hypochlorite solution for 10 minutes. Finally, rinse them with distilled water and dry them with absorbent paper.

[0036] 2. Seed germination and growth experiment Seed germination and growth experiments were conducted in a light incubator at a constant temperature of 26℃. The culture media used were composite hydrogels with activated carbon contents of 0%, 1%, 3%, and 5%, respectively. Each group had three replicates, and each culture medium contained 5 seeds.

[0037] When a seed develops a 2-3 mm embryo, it is considered to have germinated. In the early stages of the experiment, the number of germinated seeds was recorded, and the germination rate was calculated.

[0038] Harvest the seedlings on the 8th day after germination and record the root length and stem length.

[0039] The seed germination rates of tomatoes and sesame seeds in composite hydrogel culture media with different activated carbon contents are shown in Table 1.

[0040] Table 1. Calculation results of seed germination rates for tomatoes and sesame seeds.

[0041] The statistical results of root length and stem length of tomatoes and sesame in composite hydrogel culture media with different activated carbon contents are shown in Tables 2 and 3, respectively.

[0042] Table 2. Statistical results of root and stem length of tomatoes

[0043] Table 3. Statistical results of root and stem length of sesame.

[0044] As shown in Tables 1, 2 and 3, when the activated carbon content is 3%, the composite hydrogel can significantly improve the seed germination rate and significantly promote the growth of plants (sesame and tomato).

[0045] In summary, by adjusting the activated carbon content (0%, 1%, 3%, 5%), this invention screened out 3% activated carbon content as the optimal ratio, achieving a balance between the mechanical properties, water and fertilizer retention of polyvinyl alcohol hydrogel and the germination and growth promotion effect of plants (such as sesame, tomatoes, etc.), thus breaking through the application limitations of pure polyvinyl alcohol hydrogel in complex cultivation environments.

[0046] It should be noted that the above embodiments are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is impossible to exhaustively list all possible implementations here. All obvious variations or modifications derived from the technical solutions of this invention are still within the scope of protection of this invention.

Claims

1. A method for preparing activated carbon-filled polyvinyl alcohol hydrogel for hydroponics, characterized in that, Includes the following steps: (1) Preparation of polyvinyl alcohol matrix solution: Mix polyvinyl alcohol and ultrapure water at a mass ratio of 1:9, and stir magnetically in a water bath until the polyvinyl alcohol is completely dissolved to form a uniform polyvinyl alcohol matrix solution; (2) Preparation of composite solution: Weigh out the corresponding mass of activated carbon with an activated carbon content of 1-5%, and then add it to the polyvinyl alcohol matrix solution. Continue stirring until the activated carbon is mixed evenly to form a uniform composite solution. (3) Ultrasonic dispersion: The composite solution is placed in an ultrasonic cleaner for ultrasonic treatment to make the activated carbon evenly dispersed. (4) Freeze-thaw cycle: Pour the dispersed composite solution into a mold and place it in a refrigerator for 3 freeze-thaw cycles to form activated carbon-filled polyvinyl alcohol hydrogel.

2. The preparation method according to claim 1, characterized in that, In step (1), the temperature of the water bath is 90°C.

3. The preparation method according to claim 1, characterized in that, In step (2), the corresponding mass of activated carbon is weighed according to the activated carbon mass content of 3%.

4. The preparation method according to claim 1, characterized in that, In step (3), the parameters for ultrasonic treatment are: ultrasonic treatment at 40KHz frequency at 25℃ for 1h.

5. The preparation method according to claim 1, characterized in that, In step (4), each freeze-thaw cycle lasts 24 hours.

6. An activated carbon-filled polyvinyl alcohol hydrogel for hydroponics, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 5.

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