Preparation method of bamboo-based multifunctional biomass high-water-absorption hydrogel composite material

Abstract

The invention provides a preparation method of a bamboo-based multifunctional biomass high-water-absorption hydrogel composite material, which comprises the following steps: 1, mixing bamboo powder with water, and carrying out ultrasonic treatment for 1 minute to prepare a bamboo powder suspension; 2, acrylic acid neutralized by a NaOH solution, dissolved diacetone acrylamide, a cross-linking agent N 'N-methylene bisacrylamide and an initiator ammonium persulfate are sequentially added into the bamboo powder suspension; and 3, performing ultrasonic mixing on the suspension in the step 2 by using an ultrasonic instrument to obtain a mixed solution, vacuumizing a vessel filled with the mixed solution to remove oxygen, performing graft polymerization in a nitrogen atmosphere to synthesize a hydrogel product, and after the reaction is finished, cooling, washing by using a solvent, and drying to obtain the target compound. The bamboo-based multifunctional biomass high-water-absorption hydrogel composite material is obtained. The prepared high-water-absorption gel can efficiently absorb and maintain moisture, the water absorption capacity of the high-water-absorption gel in pure water can reach 1401.5 g / g at most, and the high-water-absorption gel can be used for slow release of nutrient substance urea and has wide application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of superabsorbent hydrogels, and particularly to a preparation method of a bamboo-based multifunctional biomass superabsorbent hydrogel composite material. Background Art

[0002] Natural superabsorbent polymer materials prepared from agricultural residue biomass show excellent performance in terms of sustainability, environmental friendliness, biocompatibility, and specific functionality. Superabsorbent hydrogels are a class of cross-linked polymer materials that can absorb and retain a large amount of water. They are usually prepared by free radical polymerization of hydrophilic monomers and have a three-dimensional network structure.

[0003] Bamboo resources are abundant and have great application potential. It is a biomass material with broad research prospects and high cellulose content. Cellulose is a linear polysaccharide formed by β-1,4-glucose units linked by glycosidic bonds. Each glucose unit contains three hydroxyl groups, which endow cellulose with good hydrophilicity and the ability to react chemically with other molecules. The hydrophilic functional groups such as hydroxyl and carboxyl groups rich in bamboo can form hydrogen bonds with water molecules, increasing the water absorption capacity of the hydrogel. At the same time, they can form a stable three-dimensional network structure through cross-linking reactions with other polymers, further improving the water retention capacity of the superabsorbent hydrogel. The superabsorbent hydrogel forms a gel-like substance after swelling and has good water retention performance. Such materials are widely used in agriculture (such as soil moisturizers), sanitary products (such as diapers and sanitary napkins), food packaging, and environmental remediation, etc., and have attracted much attention due to their high water absorption and water retention capabilities.

[0004] Therefore, it is necessary to provide a new preparation method of a bamboo-based multifunctional biomass superabsorbent hydrogel composite material to solve the above problems. Summary of the Invention

[0005] The technical problem solved by the present invention is to provide a preparation method of a bamboo-based multifunctional biomass superabsorbent hydrogel composite material that can efficiently absorb and retain water, with a maximum water absorption capacity of up to 1401.5 g / g in pure water, and can be used for the slow release of the nutrient urea.

[0006] To solve the above technical problems, the preparation method of the bamboo-based multifunctional biomass superabsorbent hydrogel composite provided by the present invention comprises the following steps: Step 1: Mix bamboo powder with water, put it into a three-necked flask, and perform ultrasonic mixing with an ultrasonic instrument to obtain a pretreated bamboo powder suspension; Step 2: Sequentially add acrylic acid neutralized by an NaOH solution, dissolved diacetone acrylamide, crosslinking agent N,N'-methylenebisacrylamide, and initiator ammonium persulfate to the pretreated bamboo powder suspension; Step 3: Then use an ultrasonic instrument to perform ultrasonic mixing on the suspension in Step 2 to obtain a mixed solution. After evacuating and deoxygenating the vessel containing the mixed solution, carry out graft polymerization under a nitrogen atmosphere to synthesize a hydrogel product. After the reaction ends, cool, wash with a solvent, and dry to obtain the target compound, namely the bamboo-based multifunctional biomass superabsorbent hydrogel composite (abbreviated as BP-AD).

[0007] Preferably, in Step 2, the molar ratio of the acrylic acid to the diacetone acrylamide is 0.025 - 0.1.

[0008] Preferably, in Step 2: the neutralization degree of the acrylic acid is 60 - 75%; the mass of N,N'-methylenebisacrylamide is 0.025 - 0.175% of the mass of the acrylic acid, and the mass of ammonium persulfate is 0.25 - 1.75% of the mass of the acrylic acid.

[0009] Preferably, in Step 3, the reaction temperature of the graft polymerization is 65 °C.

[0010] Preferably, in Step 1 and Step 3, the ultrasonic mixing time is 1 minute for both.

[0011] Preferably, the washing solvent is anhydrous ethanol, and the drying temperature is 60 °C.

[0012] The bamboo-based multifunctional biomass superabsorbent hydrogel composite prepared according to the above method can be applied to water absorption and retention and urea slow release. The rich carboxyl functional groups of acrylic acid endow the hydrogel with excellent hydrophilicity and water absorption capacity. As a multifunctional monomer, diacetone acrylamide can undergo a graft copolymerization reaction with acrylic acid during the polymerization process. At the same time, the two ketone groups in the molecule can participate in the crosslinking reaction to form a stable three-dimensional network structure, adjust the pore structure of the hydrogel, and optimize the water absorption rate and capacity. At the same time, the carbonyl group in diacetone acrylamide can form a hydrogen bond interaction with the amino group in the urea molecule, adsorb urea and effectively control the urea release rate.

[0013] Free radical reaction is a type of chemical reaction that proceeds through free radical intermediates. In free radical reactions, free radicals initiate and propagate reaction chains by losing, gaining, or rearranging electrons. Superabsorbent hydrogels prepared by free radical polymerization show great potential for a wide range of applications in multiple fields, but there are still certain limitations in water absorption capacity and water retention ability. In this invention, bamboo powder cellulose is grafted with hydrophilic monomers diacetone acrylamide and acrylic acid through free radical polymerization, which not only increases the types and amounts of surface hydrophilic functional groups of the superabsorbent hydrogel, but also regulates the three-dimensional network structure of the superabsorbent hydrogel, and at the same time solves the problem of low water absorption capacity of bio-based superabsorbent hydrogels.

[0014] Compared with related technologies, the preparation method of the bamboo-based multifunctional biomass superabsorbent hydrogel composite provided by this invention has the following beneficial effects: (1) The preparation method of the biomass superabsorbent hydrogel uses aqueous solution free radical polymerization, which is clean and environmentally friendly, simplifies the process steps, and reduces the process cost; (2) The bamboo-based multifunctional biomass superabsorbent hydrogel composite (BP-AD) prepared by the preparation method can efficiently absorb and retain water. Among them, the maximum water absorption capacity in pure water is 1401.5 g / g, and it can efficiently absorb water within a wide pH range; (3) The biomass superabsorbent hydrogel has multifunctionality and can be applied to aspects such as water absorption and retention and slow release of urea nutrients. Description of the Drawings

[0015] Figure 1 It is the reaction synthesis route of the preparation method of the bamboo-based multifunctional biomass superabsorbent hydrogel composite provided by this invention; Figure 2 It is the FTIR spectra of AA, DAAM, BP-AD, after 5 cycles of water absorption of BP-AD, and BP-AD after adsorbing urea; Figure 3 It is the water retention ability diagram of BP-AD under different (a) pH (b) salt concentration conditions; Figure 4 It is the water retention ability diagram of BP-AD at different temperatures. Specific Embodiments

[0016] The following further illustrates this invention in conjunction with the drawings and multiple embodiments.

[0017] Example 1: Weigh 0.18 g of bamboo powder, mix it with 35 mL of water, put it into a three-necked flask, and ultrasonicate it for 1 minute with an ultrasonic instrument to obtain a pretreated bamboo powder suspension; neutralize 0.1 mol of acrylic acid (abbreviated as AA) with a 300 g / L NaOH solution, with a neutralization degree of 60%. Dissolve 0.42 g of diacetone acrylamide (abbreviated as DAAM), 0.018 g of crosslinking agent N,N'-methylenebisacrylamide, and 0.0018 g of initiator ammonium persulfate in 5 mL of water respectively, and then add them to the pretreated bamboo powder suspension in sequence to obtain a mixture; ultrasonicate the mixture for 1 minute to thoroughly mix it to obtain a mixed solution. After evacuating and deoxygenating the vessel containing the mixed solution, carry out graft polymerization in a 65 °C oil bath under a nitrogen atmosphere to synthesize a hydrogel product. After the reaction is completed, cool it, wash it with anhydrous ethanol solvent, and dry it in an oven at 60 °C to obtain a bamboo-based multifunctional biomass superabsorbent hydrogel composite material (BP-AD).

[0018] Example 2: Weigh 0.36 g of bamboo powder, mix it with 35 mL of water, put it into a three-necked flask, and ultrasonicate it for 1 minute with an ultrasonic instrument to obtain a pretreated bamboo powder suspension; neutralize 0.1 mol of acrylic acid with a 300 g / L NaOH solution, with a neutralization degree of 65%. Dissolve 0.85 g of diacetone acrylamide, 0.054 g of crosslinking agent N,N'-methylenebisacrylamide, and 0.0054 g of initiator ammonium persulfate in 5 mL of water respectively, and then add them to the pretreated bamboo powder suspension in sequence to obtain a mixture; ultrasonicate the mixture for 1 minute to thoroughly mix it to obtain a mixed solution. After evacuating and deoxygenating the vessel containing the mixed solution, carry out graft polymerization in a 65 °C oil bath under a nitrogen atmosphere to synthesize a hydrogel product. After the reaction is completed, cool it, wash it with anhydrous ethanol solvent, and dry it in an oven at 60 °C to obtain a bamboo-based multifunctional biomass superabsorbent hydrogel composite material (BP-AD).

[0019] Example 3: Weigh 0.54 g of bamboo powder, mix it with 35 mL of water, put it into a three-necked flask, and ultrasonicate it for 1 minute with an ultrasonic instrument to obtain a pretreated bamboo powder suspension; neutralize 0.1 mol of acrylic acid with a 300 g / L NaOH solution, with a neutralization degree of 70%. Dissolve 1.27 g of diacetone acrylamide, 0.090 g of crosslinking agent N,N'-methylenebisacrylamide, and 0.0090 g of initiator ammonium persulfate in 5 mL of water respectively, and then add them to the pretreated bamboo powder suspension in sequence to obtain a mixture; ultrasonicate the mixture for 1 minute to thoroughly mix it to obtain a mixed solution. After evacuating and deoxygenating the vessel containing the mixed solution, carry out graft polymerization in a 65 °C oil bath under a nitrogen atmosphere to synthesize a hydrogel product. After the reaction is completed, cool it, wash it with anhydrous ethanol solvent, and dry it in an oven at 60 °C to obtain a bamboo-based multifunctional biomass superabsorbent hydrogel composite material (BP-AD).

[0020] Example 4: Weigh 0.72 g of bamboo powder, mix it with 35 mL of water, put it into a three-necked flask, and ultrasonicate it for 1 minute with an ultrasonic instrument to obtain a pretreated bamboo powder suspension; neutralize 0.1 mol of acrylic acid with a 300 g / L NaOH solution, with a neutralization degree of 75%. Dissolve 1.69 g of diacetone acrylamide, 0.126 g of crosslinking agent N,N'-methylenebisacrylamide, and 0.0126 g of initiator ammonium persulfate in 5 mL of water respectively, and then add them to the pretreated bamboo powder suspension in sequence to obtain a mixture; ultrasonicate the mixture for 1 minute to thoroughly mix it to obtain a mixed solution. After evacuating and deoxygenating the vessel containing the mixed solution, carry out graft polymerization in a 65 °C oil bath under a nitrogen atmosphere to synthesize a hydrogel product. After the reaction is completed, cool it, wash it with anhydrous ethanol solvent, and dry it in an oven at 60 °C to obtain a bamboo-based multifunctional biomass superabsorbent hydrogel composite material (BP-AD).

[0021] The preparation conditions of the bamboo-based multifunctional biomass superabsorbent hydrogel composite material were based on the monomer ratio of acrylic acid (0.1 mol) to conduct an orthogonal experiment on the addition amount of bamboo powder, the monomer ratio of diacetone acrylamide, the neutralization degree, the initiator content, and the crosslinking agent content. The above-mentioned addition amount of bamboo powder was 2.50%, 5.00%, 7.50%, and 10.00% of the mass of acrylic acid, the neutralization degree of acrylic acid was 60%, 65%, 70%, and 75%, the molar ratio (n:n) of AA to DAAM was 1:0.025, 1:0.05, 1:0.075, and 1:0.1, the dosage of N,N'-methylenebisacrylamide was 0.025%, 0.075%, 0.125%, and 0.175% of the mass of acrylic acid, and the content of ammonium persulfate was 0.25%, 0.75%, 1.25%, and 1.75% of the mass of acrylic acid.

[0022] Next, the bamboo-based multifunctional biomass superabsorbent hydrogel composite material (BP-AD) prepared with the optimal results of the example, with a bamboo powder addition amount of 10% (0.72 g), a ratio of AA to DAAM (n:n) of 1:0.05 (0.85 g), a neutralization degree of 75%, an initiator content of 0.25% (0.018 g), and a crosslinking agent content of 0.075% (0.0054 g), was subjected to structural characterization and test result analysis.

[0023] (1) FTIR The presence of groups and chemical structure of the sample were analyzed by infrared. As shown in the attached instructions of the specification Figure 2 For acrylic acid, as shown, a sharp peak at 1721 cm -1 was observed, which can be attributed to the stretching vibration of the carboxylic acid C=O, and 1046 cm -1The nearby peak is attributed to the stretching vibration of -C-O-C-. Diacetone acrylamide exhibits a series of specific infrared characteristic peaks. The FTIR spectrum of diacetone acrylamide shows three characteristic peaks of NH 2 namely, the symmetric stretching vibration at 3283 cm -1 , the shear bending vibration at 1621 cm -1 , and the rocking vibration peak at 812 cm -1 . The peaks at 1718 cm -1 and 1657 cm -1 reflect the C=O stretching vibrations of the ketone group and amide I of diacetone acrylamide respectively. The peak at 1560 cm -1 is attributed to the mixed vibration of the N-H bending vibration and C-N stretching vibration in the amide group.

[0024] The peak at 1723 cm -1 in the prepared sample BP-AD indicates the vibration of the carboxyl C=O of acrylic acid. The peak at 1717 cm -1 represents the vibration of the ketone group C=O of diacetone acrylamide. The C=O stretching vibration of the DAAM amide I band moves from 1657 cm -1 to 1629 cm -1 due to the connection with acrylic acid. The above characteristic peaks indicate the graft polymerization of acrylic acid and diacetone acrylamide on bamboo powder. After 5 water absorption cycles of BP-AD, the stretching vibrations of the carboxyl group of acrylic acid and the ketone group C=O of diacetone acrylamide appear at 1708 cm -1 and 1702 cm -1 respectively. The stretching vibration of the C=O in the amide I band of diacetone acrylamide and the -N-H bending vibration of NH2 in the amide II band are redshifted to 1639 cm -1 and 1577 cm -1 respectively.

[0025] In the sample after urea adsorption, peaks are observed at 1676 cm -1 and 1463 cm -1 . These peaks are related to the stretching vibrations of -C=O and C-N in -CONH 2 respectively. The enhancement of the C=O vibration of the amide at 1625 cm -1 can be attributed to the combination of the carbonyl group with urea, indicating the interaction between urea molecules and the polymer.

[0026] (2) Influence of pH and salt concentration on water absorption effect As described in the attached instructions Figure 3As shown, in the range of acidic pH values from 3 to 5, the water absorption rate gradually increases. When the pH value turns neutral and enters the alkaline range (6 to 11), stable water retention is observed. However, when the pH value reaches 12, the water absorption ability significantly decreases. BP-AD is characterized by the presence of keto carbonyl and carboxyl functional groups, which have specific interactions with water molecules. When the keto carbonyl part encounters water molecules, the oxygen atom in the water molecule starts to attack the carbon atom in the carbonyl group, ultimately forming a transient intermediate. Subsequently, the oxygen atom in the carbonyl group forms a hydrogen bond with the hydrogen atom of the water molecule, finally generating alcohol and carboxylic acid derivatives. In an acidic solution with pH < 5, most carboxylic acid anions are protonated, and strong hydrogen bonds result in polymer-polymer interactions dominating. In a solution close to neutral or slightly alkaline, BP-AD exhibits higher swelling performance because most hydrophilic groups are in a bound state and there is electrostatic repulsion between the groups. The electrostatic repulsion between them further expands the network and increases the swelling rate of the hydrogel. Under overly alkaline conditions, the charge screening effect weakens the repulsion between polymer chains and reduces the swelling ability of the polymer.

[0027] As the salt ion concentration increases, the swelling potential of BP-AD rapidly decreases and finally reaches a stable state. This significant attenuation of the swelling ability can be attributed to the following main mechanisms. The presence of salt ions creates a charge screening effect between the ions themselves and the water-absorbing functional groups in the water environment. As the salt concentration increases, this screening effect proportionally strengthens, effectively weakening the electrostatic interactions that drive the hydration and swelling processes of the water-retaining agent. Therefore, the ability of BP-AD to attract and retain water molecules is greatly weakened. In addition, the introduction of salt ions changes the osmotic pressure dynamics between BP-AD and the surrounding liquid environment. The increase in ionic strength generates a counterforce, thereby reducing the tendency of the water-absorbing polymer to absorb water and swell. In particular, when BP-AD is exposed to a solution containing NaCl or Na 2 SO 4 , the Na + ions exhibit a strong affinity and can bind to the carboxyl and other functional groups in the complex hydrogel structure of BP-AD. This competitive binding disrupts the hydrogen bond network and weakens the hydrophilic interactions crucial for effective water absorption and swelling.

[0028] (3) Influence of temperature on water retention As shown in the attached instructions Figure 4 , as the temperature increases, the water loss rate of BP-AD significantly accelerates, and over time, the water retention rate continuously decreases. At 35 °C, the curve becomes sharply steeper, while at 65 °C, this indicates an accelerated rate of water evaporation. From Figure 4It can be clearly seen that after BP-AD is heated at 35°C for 8 hours, its initial water content remains at about 80%, while at 65°C, this figure drops to 35%. The change in this water retention behavior is mainly determined by two factors. First, after entering BP-AD, water molecules bind to hydrophilic groups, hindering their migration. At the same time, an interaction occurs between water molecules and the BP-AD matrix, and the bound water is retained in the interconnected cross-linked structure through hydrogen bonds and dipole interactions between water molecules and hydrophilic parts, thus delaying the evaporation of water. At lower temperatures, BP-AD shows a stable release of the stored water, maintaining long-term hydration. On the contrary, when the temperature rises, the water absorbed by BP-AD is quickly released into the environment. BP-AD accelerates the release of the absorbed water under high-temperature conditions, which is beneficial for crops in arid and warm environments to quickly replenish water.

[0029] The above are only embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of the present invention.

Claims

1. A method for preparing a bamboo-based multifunctional biomass highly absorbent hydrogel composite material, characterized in that: The steps include: Step 1: Mix bamboo powder and water, put them into a three-necked flask, and use an ultrasonic device to perform ultrasonic mixing to obtain a pretreated bamboo powder suspension; Step 2: adding acrylic acid neutralized by NaOH solution and dissolved diacetone acrylamide, crosslinking agent N'N-methylenebisacrylamide, and initiator ammonium persulfate to the pretreated bamboo powder suspension in sequence; Step 3: Then use an ultrasonic instrument to ultrasonically mix the suspension in step 2 to obtain a mixed solution, evacuate the container containing the mixed solution to deoxygenate, and then carry out graft polymerization in a nitrogen atmosphere to synthesize a hydrogel product. After the reaction is completed, cool, wash with a solvent, and dry to obtain the target compound, that is, a bamboo-based multifunctional biomass highly absorbent hydrogel composite material.

2. The method for preparing the bamboo-based multifunctional biomass highly absorbent hydrogel composite material according to claim 1, characterized in that: In step 2, the molar ratio of the acrylic acid to the diacetone acrylamide is 1:0.025-1:0.

1.

3. The method for preparing the bamboo-based multifunctional biomass highly absorbent hydrogel composite material according to claim 1, characterized in that: In step 2: the neutralization degree of acrylic acid is 60-75%; the mass of N'N-methylenebisacrylamide is 0.025-0.175% of the mass of acrylic acid, and the mass of ammonium persulfate is 0.25-1.75% of the mass of acrylic acid.

4. The method for preparing the bamboo-based multifunctional biomass highly absorbent hydrogel composite material according to claim 1, characterized in that: In step three, the reaction temperature of the graft polymerization is 65°C.

5. The method for preparing the bamboo-based multifunctional biomass highly absorbent hydrogel composite material according to claim 1, characterized in that: In step 1 and step 3, the ultrasonic mixing time is 1 minute.

6. The method for preparing the bamboo-based multifunctional biomass highly absorbent hydrogel composite material according to claim 1, characterized in that: In step three, the washing solvent is anhydrous ethanol, and the drying temperature is 60°C.

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