Full-bio-based super-absorbent gel and preparation method thereof

Abstract

The invention discloses full-bio-based super-absorbent gel and a preparation method thereof, and relates to the technical field of polymer hydrogel materials. The preparation method comprises the following steps: adding carboxymethyl cellulose, starch and beta-cyclodextrin into deionized water, adding citric acid and sodium hypophosphite, reacting, washing a product, and drying to obtain the full-bio-based super-absorbent gel. In the preparation process, not only is the use of a synthetic cross-linking agent completely avoided, but also the cost of raw materials is greatly reduced; the prepared full-bio-based super-absorbent gel has high water absorption, excellent mechanical properties and complete biodegradability, and can be widely applied to the fields of agricultural water retention, medical dressings, hygienic products and the like; the water absorption rate to deionized water is larger than or equal to 1200 g / g, the water absorption rate to normal saline is larger than or equal to 100 g / g, the compression strength is larger than or equal to 8 kPa, and the elongation at break is larger than or equal to 1000%.

Description

Technical Field

[0001] This invention relates to the field of polymer hydrogel materials technology, specifically a fully bio-based superabsorbent hydrogel and its preparation method. Background Technology

[0002] Superabsorbent hydrogels have wide applications in agriculture, medicine, and sanitation due to their excellent water absorption and retention properties. Traditional hydrogels are mostly prepared using synthetic polymers such as polyvinyl alcohol (PVA) or acrylic monomers, which have problems such as poor biodegradability and environmental unfriendliness.

[0003] With increasing environmental awareness, the green modification of hydrogels has become a challenging problem that industry technicians must overcome. Starch, as a natural polysaccharide, is widely available, inexpensive, and completely biodegradable; however, its gelling and mechanical properties are poor, making it difficult to meet practical application requirements. Crosslinking modification is needed to improve its performance. Existing technologies involve compounding starch with polyvinyl alcohol and using physical crosslinking to create hydrogel materials with certain environmental properties. However, these hydrogel materials have poor structural stability and mechanical properties, and are not completely environmentally friendly and biodegradable.

[0004] Based on this, this invention designs a method that completely replaces traditional raw materials such as polyvinyl alcohol with starch and performs green modification on it to prepare a hydrogel material with excellent comprehensive performance. In the exploration of modification technology, the researchers successively introduced carboxymethyl cellulose, β-cyclodextrin, and starch in combination, and discovered that citric acid, as a natural polyacid, can act as a green crosslinking agent, forming a crosslinking network with polysaccharide molecules through esterification. Sodium hypophosphite can act as a highly efficient catalyst for esterification, significantly improving crosslinking efficiency. Finally, a fully bio-based superabsorbent hydrogel with a ternary crosslinking system of carboxymethyl cellulose-starch-β-cyclodextrin was prepared, which is of great significance. Summary of the Invention

[0005] The purpose of this invention is to provide a fully bio-based superabsorbent gel and its preparation method to solve the problems mentioned in the background art.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A method for preparing a fully bio-based superabsorbent gel involves adding carboxymethyl cellulose, starch, and β-cyclodextrin to deionized water, adding citric acid and sodium hypophosphite, reacting, washing the product, and drying to obtain the gel.

[0007] Furthermore, the raw materials of the all-bio-based superabsorbent gel include the following components: 1-5 wt% carboxymethyl cellulose, 1-4 wt% starch, 0.5-3 wt% β-cyclodextrin, 5-15 wt% citric acid, 1-5 wt% sodium hypophosphite, and the remainder is deionized water.

[0008] Furthermore, the raw materials of the all-bio-based superabsorbent hydrogel include the following components: 2.5-4 wt% carboxymethyl cellulose, 1-3 wt% starch, 1-2 wt% β-cyclodextrin, 8-12 wt% citric acid, 2.4-3.6 wt% sodium hypophosphite, and the remainder is deionized water.

[0009] Furthermore, the starch includes, but is not limited to, one or more combinations of potato starch, cassava starch, corn starch, wheat starch, and sweet potato starch.

[0010] Furthermore, during the reaction, the temperature is 80~100℃ and the reaction time is 1~3h.

[0011] Furthermore, the preparation method of the all-bio-based superabsorbent gel is as follows: S1: At 55~65℃, add carboxymethyl cellulose, starch and β-cyclodextrin to deionized water and stir for 1~3 hours; S2: Add citric acid and sodium hypophosphite to the solution of S1, stir and mix for 20-40 minutes to obtain a mixed solution; S3: Heat the mixed solution obtained in S2 to 80~100℃ and react for 1~3 hours. After the reaction system forms a uniform gel-like substance, stop heating and allow it to cool naturally to room temperature. Collect the gel-like substance. S4: The gel material collected in S3 was washed with deionized water until it was neutral, and then dried at 60~80℃ to constant weight to obtain a fully bio-based superabsorbent gel.

[0012] Furthermore, the fully bio-based superabsorbent gel has an absorption rate of ≥1200g / g for deionized water and ≥100g / g for physiological saline.

[0013] Furthermore, the fully bio-based superabsorbent gel has a compressive strength ≥8kPa and an elongation at break ≥1000%.

[0014] Furthermore, the fully bio-based superabsorbent gel can be applied in fields such as agricultural water retention, medical dressings, and hygiene products.

[0015] Compared with the prior art, the beneficial effects achieved by the present invention are: (1) The present invention uses starch instead of traditional polyvinyl alcohol, which reduces the preparation cost and improves the environmental friendliness and biodegradability of the product.

[0016] (2) Citric acid is used as a crosslinking agent in this invention. The multiple carboxyl groups contained in its molecule can undergo esterification with the hydroxyl groups in starch to form a three-dimensional network structure. Sodium hypophosphite is further added as a crosslinking catalyst, which can effectively promote the esterification reaction and improve the crosslinking density and gel strength.

[0017] (3) In this invention, carboxymethyl cellulose, β-cyclodextrin and starch are further added to enhance the crosslinking density and structural stability of the three-dimensional network structure. In addition, the cavity structure of β-cyclodextrin can encapsulate water molecules, which enhances the water absorption performance of the all-bio-based superabsorbent gel.

[0018] (4) The bio-based superabsorbent gel prepared by the present invention has a water absorption rate of ≥1200g / g for deionized water, a water absorption rate of ≥100g / g for physiological saline, a compressive strength of ≥8kPa, and an elongation at break of ≥1000%.

[0019] (5) The preparation process of this invention not only completely avoids the use of synthetic crosslinking agents, but also greatly reduces the cost of raw materials; the prepared all-bio-based superabsorbent gel has high water absorption rate, excellent mechanical properties and complete biodegradability, and can be widely used in agricultural water retention, medical dressings, hygiene products and other fields.

[0020] In summary, this invention uses citric acid-sodium hypophosphite as a crosslinking catalytic system to achieve stable crosslinking of carboxymethyl cellulose, starch, and β-cyclodextrin, ultimately preparing a fully bio-based superabsorbent gel with dense crosslinking, stable structure, and high gel strength. Attached Figure Description

[0021] Figure 1 The graph shows the change in water absorption rate of the hydrogel prepared in Example 1 in deionized water. Figure 2 The graph shows the change in water absorption rate of the hydrogel prepared in Example 2 in deionized water. Figure 3 The graph shows the change in water absorption rate of the hydrogel prepared in Example 3 in deionized water. Figure 4 The graph shows the change in water absorption rate of the hydrogel prepared in Example 4 in deionized water. Figure 5 The graph shows the change in water absorption rate of the hydrogel prepared in Example 5 in deionized water. Figure 6 The graph shows the change in water absorption rate of the hydrogel prepared in Example 6 in deionized water. Figure 7The graph shows the change in water absorption rate of the hydrogel prepared in Example 7 in deionized water. Figure 8 This is a SEM image of the hydrogel prepared in Example 1. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] It should be noted that there are no special restrictions on the suppliers of the raw materials involved in this invention; exemplarily, they include: In the following examples, the raw materials such as carboxymethyl cellulose, potato starch, β-cyclodextrin, citric acid, and sodium hypophosphite were all commercially available; Polyvinyl alcohol hydrogel, catalog number R-BX-517, was purchased from Ruixi Biotechnology Co., Ltd.

[0024] Example 1: A method for preparing a fully bio-based superabsorbent gel: S1: Based on a total mass of 100g, add 3.0g carboxymethyl cellulose, 2.0g potato starch, and 1.5g β-cyclodextrin to deionized water at 60℃ and stir for 2 hours; S2: Add 10.0g citric acid and 3.0g sodium hypophosphite to the solution of S1, stir and mix for 30min to obtain a mixed solution; S3: Heat the mixed solution obtained in S2 to 90℃ and react for 2 hours. After the reaction system forms a uniform gel-like substance, stop heating and allow it to cool naturally to room temperature. Collect the gel-like substance. S4: The gel material collected in S3 was washed with deionized water until it was neutral, and then dried at 70°C to constant weight to obtain a fully bio-based superabsorbent gel.

[0025] The following is based on Example 1, with Examples 2-7 configured as follows: Example 2: A method for preparing a fully bio-based superabsorbent gel: S1: Based on a total mass of 100g, add 3.0g carboxymethyl cellulose, 1.0g potato starch, and 1.5g β-cyclodextrin to deionized water at 60℃ and stir for 2 hours; S2: Add 10.0g citric acid and 3.0g sodium hypophosphite to the solution of S1, stir and mix for 30min to obtain a mixed solution; S3: Heat the mixed solution obtained in S2 to 90℃ and react for 2 hours. After the reaction system forms a uniform gel-like substance, stop heating and allow it to cool naturally to room temperature. Collect the gel-like substance. S4: The gel material collected in S3 was washed with deionized water until it was neutral, and then dried at 70°C to constant weight to obtain a fully bio-based superabsorbent gel.

[0026] Example 3: A method for preparing a fully bio-based superabsorbent gel: S1: Based on a total mass of 100g, add 3.0g carboxymethyl cellulose, 3.0g potato starch, and 1.5g β-cyclodextrin to deionized water at 60℃ and stir for 2 hours; S2: Add 10.0g citric acid and 3.0g sodium hypophosphite to the solution of S1, stir and mix for 30min to obtain a mixed solution; S3: Heat the mixed solution obtained in S2 to 90℃ and react for 2 hours. After the reaction system forms a uniform gel-like substance, stop heating and allow it to cool naturally to room temperature. Collect the gel-like substance. S4: The gel material collected in S3 was washed with deionized water until it was neutral, and then dried at 70°C to constant weight to obtain a fully bio-based superabsorbent gel.

[0027] Example 4: A method for preparing a fully bio-based superabsorbent gel: S1: Based on a total mass of 100g, add 3.0g carboxymethyl cellulose, 2.0g potato starch, and 1.0g β-cyclodextrin to deionized water at 60℃ and stir for 2 hours; S2: Add 10.0g citric acid and 3.0g sodium hypophosphite to the solution of S1, stir and mix for 30min to obtain a mixed solution; S3: Heat the mixed solution obtained in S2 to 90℃ and react for 2 hours. After the reaction system forms a uniform gel-like substance, stop heating and allow it to cool naturally to room temperature. Collect the gel-like substance. S4: The gel material collected in S3 was washed with deionized water until it was neutral, and then dried at 70°C to constant weight to obtain a fully bio-based superabsorbent gel.

[0028] Example 5: A method for preparing a fully bio-based superabsorbent gel: S1: Based on a total mass of 100g, add 3.0g carboxymethyl cellulose, 2.0g potato starch, and 2.0g β-cyclodextrin to deionized water at 60℃ and stir for 2 hours; S2: Add 10.0g citric acid and 3.0g sodium hypophosphite to the solution of S1, stir and mix for 30min to obtain a mixed solution; S3: Heat the mixed solution obtained in S2 to 90℃ and react for 2 hours. After the reaction system forms a uniform gel-like substance, stop heating and allow it to cool naturally to room temperature. Collect the gel-like substance. S4: The gel material collected in S3 was washed with deionized water until it was neutral, and then dried at 70°C to constant weight to obtain a fully bio-based superabsorbent gel.

[0029] Example 6: A method for preparing a fully bio-based superabsorbent gel: S1: Based on a total mass of 100g, add 3.0g carboxymethyl cellulose, 2.0g potato starch, and 1.5g β-cyclodextrin to deionized water at 60℃ and stir for 2 hours; S2: Add 8.0g citric acid and 3.0g sodium hypophosphite to the solution of S1, stir and mix for 30 minutes to obtain a mixed solution; S3: Heat the mixed solution obtained in S2 to 90℃ and react for 2 hours. After the reaction system forms a uniform gel-like substance, stop heating and allow it to cool naturally to room temperature. Collect the gel-like substance. S4: The gel material collected in S3 was washed with deionized water until it was neutral, and then dried at 70°C to constant weight to obtain a fully bio-based superabsorbent gel.

[0030] Example 7: A method for preparing a fully bio-based superabsorbent gel: S1: Based on a total mass of 100g, add 3.0g carboxymethyl cellulose, 2.0g potato starch, and 1.5g β-cyclodextrin to deionized water at 60℃ and stir for 2 hours; S2: Add 12.0g citric acid and 3.0g sodium hypophosphite to the solution of S1, stir and mix for 30min to obtain a mixed solution; S3: Heat the mixed solution obtained in S2 to 90℃ and react for 2 hours. After the reaction system forms a uniform gel-like substance, stop heating and allow it to cool naturally to room temperature. Collect the gel-like substance. S4: The gel material collected in S3 was washed with deionized water until it was neutral, and then dried at 70°C to constant weight to obtain a fully bio-based superabsorbent gel.

[0031] Based on Example 1, the following control experiments were conducted, setting up comparative examples 1 to 4, as detailed below: Comparative Example 1: Comparative Example 1 is based on Example 1, with the following adjustment: citric acid is not added, while other processes remain unchanged. Specifically: A method for preparing a fully bio-based superabsorbent gel: S1: Based on a total mass of 100g, add 3.0g carboxymethyl cellulose, 2.0g potato starch, and 1.5g β-cyclodextrin to deionized water at 60℃ and stir for 2 hours; S2: Add 3.0g of sodium hypophosphite to the solution of S1, stir and mix for 30min to obtain a mixed solution; S3: Heat the mixed solution obtained in S2 to 90℃ and react for 2 hours. After the reaction system forms a uniform gel-like substance, stop heating and allow it to cool naturally to room temperature. Collect the gel-like substance. S4: The gel material collected in S3 was washed with deionized water until it was neutral, and then dried at 70°C to constant weight to obtain a fully bio-based superabsorbent gel.

[0032] Comparative Example 2: Comparative Example 2 is based on Example 1, with the following adjustment: β-cyclodextrin is not added, while other processes remain unchanged. Specifically: A method for preparing a fully bio-based superabsorbent gel: S1: Based on a total mass of 100g, add 3.0g of carboxymethyl cellulose and 2.0g of potato starch to deionized water at 60℃ and stir for 2 hours; S2: Add 10.0g citric acid and 3.0g sodium hypophosphite to the solution of S1, stir and mix for 30min to obtain a mixed solution; S3: Heat the mixed solution obtained in S2 to 90℃ and react for 2 hours. After the reaction system forms a uniform gel-like substance, stop heating and allow it to cool naturally to room temperature. Collect the gel-like substance. S4: The gel material collected in S3 was washed with deionized water until it was neutral, and then dried at 70°C to constant weight to obtain a fully bio-based superabsorbent gel.

[0033] Comparative Example 3: Comparative Example 3 is based on Example 1, with the following adjustment: sodium hypophosphite is not added, while other processes remain unchanged. Specifically: A method for preparing a fully bio-based superabsorbent gel: S1: Based on a total mass of 100g, add 3.0g carboxymethyl cellulose, 2.0g potato starch, and 2.0g β-cyclodextrin to deionized water at 60℃ and stir for 2 hours; S2: Add 10.0g of citric acid to the solution of S1, stir and mix for 30 minutes to obtain a mixed solution; S3: Heat the mixed solution obtained in S2 to 90℃ and react for 2 hours. After the reaction system forms a uniform gel-like substance, stop heating and allow it to cool naturally to room temperature. Collect the gel-like substance. S4: The gel material collected in S3 was washed with deionized water until it was neutral, and then dried at 70°C to constant weight to obtain a fully bio-based superabsorbent gel.

[0034] Comparative Example 4: Commercially available polyvinyl alcohol hydrogel.

[0035] Performance Test 1: The water absorption performance of the fully bio-based superabsorbent gels prepared in Examples 1-7 and Comparative Examples 1-4 was tested according to the test methods specified in GB / T 461.3-2005. The specific test method is as follows: The prepared product was weighed (m1), and placed vertically in a reagent bath containing deionized water or physiological saline at room temperature. Samples were taken out and weighed at certain time intervals (every 100 minutes). The water absorption rate was calculated according to the following formula: R = (m2 - m1) / m1 * 100%. The water absorption rate change curve in deionized water is shown below. Figures 1-7 As shown.

[0036] Table 1 Conclusion: The test results in Table 1 above show that the fully bio-based superabsorbent gels prepared in Examples 1-7 of this invention all exhibit excellent high water absorption performance and structural integrity, with Example 1 being the optimal example. The test results fully demonstrate the feasibility and advancement of replacing traditional polyvinyl alcohol with starch and using a green crosslinking system of citric acid and β-cyclodextrin.

[0037] Performance Test 2: Since Example 1 is the optimal embodiment, the present invention further uses a compression tester and a tensile tester to test the compressive strength and elongation at break of the all-bio-based superabsorbent gel prepared in Example 1. The specific test results are shown in Table 2 below: Table 2 Conclusion: The test results in Table 2 above show that the all-bio-based superabsorbent gel prepared by this invention has excellent overall performance and good application prospects.

[0038] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for preparing a fully bio-based superabsorbent gel, characterized in that: Carboxymethyl cellulose, starch, and β-cyclodextrin were added to deionized water, along with citric acid and sodium hypophosphite. The mixture was reacted, the product was washed, and dried to obtain a fully bio-based superabsorbent gel.

2. The method for preparing a fully bio-based superabsorbent gel according to claim 1, characterized in that: The raw materials of the fully bio-based superabsorbent hydrogel include the following components: 1-5 wt% carboxymethyl cellulose, 1-4 wt% starch, 0.5-3 wt% β-cyclodextrin, 5-15 wt% citric acid, 1-5 wt% sodium hypophosphite, and the remainder is deionized water.

3. The method for preparing a fully bio-based superabsorbent gel according to claim 1, characterized in that: The starch includes one or more of potato starch, cassava starch, corn starch, wheat starch, and sweet potato starch.

4. The method for preparing a fully bio-based superabsorbent gel according to claim 1, characterized in that: During the reaction, the temperature is 80~100℃ and the reaction time is 1~3h.

5. The method for preparing a fully bio-based superabsorbent hydrogel according to claim 2, characterized in that: The raw materials of the all-bio-based superabsorbent hydrogel include the following components: 2.5-4 wt% carboxymethyl cellulose, 1-3 wt% starch, 1-2 wt% β-cyclodextrin, 8-12 wt% citric acid, 2.4-3.6 wt% sodium hypophosphite, and the remainder is deionized water.

6. The all-bio-based superabsorbent gel prepared by any one of the preparation methods of the all-bio-based superabsorbent gel according to any one of claims 1 to 5.

7. The all-bio-based superabsorbent gel according to claim 6, characterized in that: The fully bio-based superabsorbent gel has an absorption rate of ≥1200g / g for deionized water and ≥100g / g for physiological saline.

8. The all-bio-based superabsorbent gel according to claim 6, characterized in that: The fully bio-based superabsorbent gel has a compressive strength ≥8kPa and an elongation at break ≥1000%.

9. An application of a bio-based superabsorbent gel, characterized in that: The all-bio-based superabsorbent gel described in claim 6 can be applied to fields such as agricultural water retention, medical dressings, and hygiene products.

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