Cellulose-reinforced polyacrylic acid composite hydrogel and preparation method thereof

Abstract

This invention discloses a cellulose-reinforced polyacrylic acid composite hydrogel, its preparation method, and its applications. The composite hydrogel comprises a three-dimensional polyacrylic acid network and short cellulose fibers derived from waste toilet paper. The short cellulose fibers are physically embedded within the polyacrylic acid network, and the two are bonded together by hydrogen bonds, forming a macroporous network microstructure. The preparation method involves mixing and dispersing acrylic acid, waste toilet paper-based cellulose short fibers, 2-ketoglutaric acid, and N,N'-methylenebisacrylamide in deionized water according to a specific ratio, followed by curing under ultraviolet light, washing, soaking to remove impurities, drying, and pulverizing. This invention uses waste toilet paper as raw material, resulting in low cost and a simple, green process. The obtained product exhibits strong structural toughness and resistance to swelling and collapse; the swelling rate after 1 hour of soaking reaches 831.88 g⋅g⁻¹, and the water retention rate after 24 hours reaches 64.41%. It can be widely used in fields such as farmland water conservation, sandy land water conservation, ecological sand fixation, and green vegetation maintenance.

Description

Technical Field

[0001] This invention relates to the field of polymer water-absorbing materials technology, specifically a cellulose-reinforced polyacrylic acid composite hydrogel prepared from waste toilet paper, which is suitable for fields such as farmland water conservation, sandy land water retention, ecological sand fixation, and green vegetation maintenance. Background Technology

[0002] Polyacrylic acid hydrogels, due to the large number of hydrophilic carboxyl groups in their molecular chains, possess extremely high water absorption capacity and are widely used in hygiene products, agricultural water retention, desertification control, and other fields. However, the three-dimensional network structure of pure polyacrylic acid hydrogels has low mechanical strength and poor toughness. Under repeated water absorption-release cycles or when subjected to external pressure, the network structure is prone to breakage or permanent deformation, leading to a decline in its water absorption and retention properties and a shortened service life.

[0003] To improve its mechanical properties, researchers often introduce reinforcing phases through physical blending or chemical crosslinking. Cellulose, as a widely available, biodegradable natural polymer with good biocompatibility and mechanical strength, is an ideal reinforcing material. The large amount of waste toilet paper generated in daily life is mainly composed of cellulose. Utilizing it as a raw material can not only realize the resource recovery of solid waste but also reduce the production cost of hydrogels, aligning with the concept of green and sustainable development.

[0004] Currently, research on the preparation of polyacrylic acid composite hydrogels using waste toilet paper as a cellulose source and ultraviolet light curing is insufficient. Traditional methods for preparing composite hydrogels may suffer from problems such as complex processes, high costs, or low waste utilization rates. Therefore, developing a cellulose-reinforced polyacrylic acid composite hydrogel that is simple to process, low in cost, and has excellent performance is of significant practical importance. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing cellulose-reinforced polyacrylic acid composite hydrogels using waste toilet paper as raw material, which is simple to process and produces products with excellent structural strength. To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a cellulose-reinforced polyacrylic acid 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 waste toilet paper as a natural cellulose reinforcing phase. The method includes the following steps: (1) Dissolve acrylic acid, toilet paper-based cellulose, 2-ketoglutaric acid and N,N'-methylenebisacrylamide in water and stir to mix evenly to obtain a precursor solution; the toilet paper-based cellulose is short fiber obtained by crushing waste toilet paper; (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 cellulose-reinforced composite hydrogel.

[0006] 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, cellulose, 2-ketoglutaric acid, and N,N'-methylenebisacrylamide are 1:(0.008~0.025):(0.005~0.012):(0.0005~0.0012). More preferably, this mass ratio is 1:(0.014~0.016):(0.007~0.008):(0.0007~0.0008). The amount of water used is preferably 3 to 8 times the mass of acrylic acid. At this ratio, the short cellulose fibers can be uniformly dispersed and physically embedded within the polyacrylic acid network, achieving the best reinforcing effect.

[0007] The UV curing irradiation time is preferably 15-25 minutes, more preferably 19-22 minutes. Room temperature UV curing avoids the high energy consumption of traditional thermal polymerization, making the process green and simple. 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, preferably at a temperature of 60-80℃, more preferably 65-75℃. The dried material can be pulverized to obtain a granular finished product.

[0008] The cellulose-reinforced composite hydrogel prepared by the above method has a typical macroporous network structure. Short cellulose fibers, formed from the shearing and pulverizing of waste toilet paper, are uniformly distributed within the three-dimensional network of polyacrylic acid. The fibers are physically intercalated and bonded to the polymer matrix, with the two tightly connected by numerous hydrogen bonds. This structure endows the gel with excellent resistance to breakage and swelling / collapse, effectively overcoming the poor toughness of pure polyacrylic acid hydrogels. Performance tests show that the swelling rate of the composite hydrogel particles after soaking for 1 hour is no less than 830 g·g⁻¹, and the water retention rate after being left open at room temperature for 24 hours is no less than 64%, exhibiting both good water absorption and retention properties and structural strength. Furthermore, this invention uses household waste as raw material, resulting in low production costs and an environmentally friendly preparation process, making it suitable for large-scale promotion and use.

[0009] Compared with the prior art, the present invention has the following advantages: (1) Enhanced structural performance: This invention utilizes short cellulose fibers from waste toilet paper as a reinforcing skeleton, which are combined with the polyacrylic acid matrix through physical intercalation and abundant hydrogen bonding, significantly improving the overall structural toughness of the hydrogel and effectively solving the problems of fragility and lack of durability of traditional polyacrylic acid hydrogels. While maintaining a high swelling rate (1h swelling rate ≥830 g / g), the product also has excellent water retention capacity (24h water retention rate ≥64%).

[0010] (2) Waste resource utilization: This invention uses household waste - waste toilet paper as raw material to realize the resource utilization and high-value utilization of solid waste, and significantly reduce the cost of raw materials.

[0011] (3) Green and efficient process: The present invention adopts ultraviolet curing technology, and the polymerization reaction can be completed in a short time at room temperature or near room temperature. The process is simple, energy consumption is low, and there is no emission of volatile organic solvents. It is an environmentally friendly preparation process and is easy to scale up for industrial production. Attached Figure Description

[0012] Figure 1 A scanning electron microscope image of the composite hydrogel prepared in Example 1; Figure 2 The infrared spectrum of the composite hydrogel prepared in Example 1 is shown. Detailed Implementation

[0013] The technical solution of 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 to these embodiments.

[0014] Example 1 To a beaker containing 30 mL of deionized water, add 6.480 g of acrylic acid, 0.100 g of shredded and crushed waste toilet paper (cellulose source), 0.050 g of 2-ketoglutaric acid, and 0.005 g of N,N'-methylenebisacrylamide sequentially. Stir magnetically at room temperature until all materials are completely and uniformly dispersed to form a precursor solution. Place the precursor solution under a 100 W UV lamp for 20 min to allow it to completely solidify, obtaining a nascent hydrogel. Wash the nascent hydrogel three times with deionized water, then soak it in sufficient deionized water at room temperature for 24 hours to remove impurities. After removal, dry it in a 70°C forced-air oven to constant weight, and finally mechanically pulverize and sieve to obtain a granular cellulose-reinforced polyacrylic acid composite hydrogel product.

[0015] Testing showed that the product obtained in this embodiment had a swelling rate of 831.88 g⋅g⁻¹ after 1 hour and a water retention rate of 64.41% after 24 hours at room temperature. Scanning electron microscopy observation showed ( Figure 1 ), short cellulose fibers are uniformly embedded and dispersed within the macroporous network structure of polyacrylic acid. Infrared spectroscopy shows ( Figure 2 ), at 3400 cm -1 A broad and strong OH stretching vibration absorption peak is observed at 1720 cm⁻¹, which is due to the formation of hydrogen bonds between a large number of hydroxyl groups in the sample. A C=O stretching vibration peak is observed at 1720 cm⁻¹, which is caused by the -COOH group in PAA. Asymmetric and symmetric COO⁻ stretching vibration peaks are observed at 1600 cm⁻¹ and 1400 cm⁻¹, which are caused by the -COO⁻ in SA. No new characteristic absorption peaks were observed, proving that the components are bound together only by physical interactions such as hydrogen bonds.

[0016] Example 2 The preparation steps in this embodiment are exactly the same as in Example 1, except that the UV irradiation curing time is adjusted to 22 min. The resulting product, after testing, showed a swelling rate of 828.62 g⋅g⁻¹ after 1 hour and a water retention rate of 64.17% after 24 hours. The gel structure exhibited good strength, meeting the application requirements.

[0017] Example 3 The preparation steps in this embodiment are exactly the same as in Example 1, except that the oven drying temperature is adjusted to 68°C. The resulting product was tested and showed a swelling rate of 830.14 g⋅g⁻¹ after 1 hour and a water retention rate of 64.29% after 24 hours. The performance indicators are basically consistent with those of Example 1, indicating that the process parameters have good stability within the given range.

[0018] The above description is only a partial embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a cellulose-reinforced polyacrylic acid composite hydrogel, characterized in that, Includes the following steps: (1) Dissolve acrylic acid, toilet paper-based cellulose, 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 cellulose-reinforced composite hydrogel.

2. The production method according to claim 1, characterized by, In step (1), the toilet paper-based cellulose is short fiber obtained by crushing waste toilet paper.

3. The production method according to claim 1, characterized by, In step (1), the mass ratio of acrylic acid, cellulose, 2-ketoglutaric acid and N,N'-methylenebisacrylamide is 1 : (0.008~0.025) : (0.005~0.012) : (0.0005~0.0012).

4. The production method according to claim 3, characterized by, The mass ratio of acrylic acid, cellulose, 2-ketoglutaric acid and N,N'-methylenebisacrylamide is 1 : (0.014~0.016) : (0.007~0.008) : (0.0007~0.0008).

5. 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.

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

7. The preparation method according to claim 1, characterized in that, In step (3), the soaking time for impurity removal is 20-28 hours; the drying temperature is 60-80℃.

8. A cellulose-reinforced polyacrylic acid composite hydrogel prepared by the method according to any one of claims 1-7, characterized in that, In the hydrogel, cellulose is physically embedded in the three-dimensional network of polyacrylic acid in the form of short fibers. The two are bonded by hydrogen bonds, and the whole presents a macroporous network microstructure.

9. The cellulose-reinforced polyacrylic acid 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 830 g·g⁻¹, and the water retention rate after being placed at room temperature for 24 hours is not less than 64%.

10. The application of the cellulose-reinforced polyacrylic acid composite hydrogel as described in claim 8 or 9 in water conservation in farmland, water retention in sandy areas, or ecological sand fixation.

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