Preparation method of nanocellulose enhanced wet adhesion hydrogel

Abstract

The invention discloses a preparation method of nanocellulose enhanced wet adhesion hydrogel, and belongs to the technical field of hydrogel. The method comprises the following steps: controlling a solution environment to enable polydopamine to grow on nanocellulose in an oriented manner; the preparation method comprises the following steps: adding an acrylic acid matrix, a conductive substance and a drug into a nano cellulose solution with an adhesion property, and then stirring for a period of time; and adding an initiator and a cross-linking agent, standing, and polymerizing in a thermal environment to prepare the composite conductive hydrogel material with wet adhesion. The preparation process is simple, the reaction condition is mild, and the problem that the flexible sensing underwater conductive hydrogel is poor in adhesion performance is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of hydrogels, and in particular relates to a nanocellulose-reinforced wet-state adhesive hydrogel. Background Art

[0002] Hydrogel is a polymer material with a three-dimensional cross-linked network structure formed by chemical cross-linking or physical entanglement. It is used in many fields, such as tissue engineering, drug sustained release, artificial skin, water resource treatment, medical rehabilitation, flexible wearable devices, etc. Conductive hydrogel is the most important of flexible devices. It is formed by combining various different matrices and conductive media. It has high sensitivity, strong self-healing properties, adjustable mechanical strength and customizable electronic properties. At present, most conductive hydrogels have adhesion properties. In the absence of external force, they directly adhere to the surface of the substrate, reducing the possibility of signal blocking, thereby capturing tiny sensor signals during transmission. It has been applied in the fields of human motion monitoring, clinical diagnosis and human-computer interaction. However, the application of conductive hydrogel underwater is limited. The water absorption of hydrogel will cause it to absorb water and swell, causing the internal structure of the gel to collapse rapidly, losing its adhesion properties, causing the hydrogel to fall off from the surface of the skin, making it difficult for the outside world to detect the physical condition of the user, which may lead to tragedy.

[0003] At present, it is generally believed that the main reasons affecting the application of hydrogels in wet environments are the formation of a hydration layer and water swelling. It is necessary to destroy the formation of a hydration layer, and hydrophobic groups can solve this problem. The hydration layer is removed from the interface through hydrophobic interactions, and the hydrogel is kept away from the contact interface when adhering underwater, thereby adhering. Mussels are a type of marine organism that lives in a humid environment and can achieve long-term adhesion in an aquatic environment. Inspired by them, small molecules containing catechol groups are combined with nanocellulose to give nanocellulose adhesion properties, further enhancing the adhesion properties of hydrogels underwater. There are few reports on giving nanocellulose adhesion properties in a humid environment through catechol groups. Summary of the invention

[0004] Aiming at the problems of internal structure collapse and reduced adhesion of existing conductive hydrogel sensing materials in a humid environment, the present invention provides a method for preparing nanocellulose-reinforced wet adhesive hydrogel, which is simple to operate and economically feasible.

[0005] In order to achieve the above technical objectives, the technical solution adopted by the present invention is:

[0006] S1. Take a certain amount of nanocellulose in a beaker, adjust the pH, add dopamine hydrochloride, seal and avoid light, and stir;

[0007] S2, after stirring for a period of time, centrifuging to obtain polydopamine-modified nanocellulose;

[0008] S3, dispersing the modified nanocellulose into solutions with different mass fractions, taking appropriate amounts of methacrylate sulfobetaine, aluminum chloride, tannic acid and acrylic acid, etc., adding the above solutions, and stirring evenly at room temperature;

[0009] S4. Weigh a small amount of initiator (ammonium persulfate, N,N-methylenebisacrylamide), add to the above solution, stir for 3 hours, transfer to a mold, and let stand at 60°C for 6 hours to obtain nanocellulose reinforced wet adhesion hydrogel.

[0010] Furthermore, in step S1, the nanocellulose is derived from one or more of nanocellulose crystals, nanocellulose filaments, and bacterial cellulose, the mass ratio of nanocellulose to dopamine hydrochloride is 10-1, and the polymerization environment of dopamine hydrochloride requires pH to be controlled at 6-10.

[0011] Furthermore, in step S2, centrifugation is performed multiple times, each time for 10 to 100 minutes, and the rotation speed is controlled at 3000 to 12000 r / min.

[0012] Furthermore, in step S2, the polydopamine-modified nanocellulose is dispersed into solutions with different cellulose contents, with a mass fraction of 0.005 to 0.5%.

[0013] Furthermore, in step S3, in the drugs added to the solution, the mass ratio of methacrylic acid sulfobetaine to acrylic acid is 0.1-5, the total molar concentration of the two is controlled at 0.5-5 mol / L, the mass fraction of aluminum chloride is 0.5%-5%, and the amount of tannic acid is controlled at 100-500 mg.

[0014] Furthermore, in step S4, the ammonium persulfate in the mixed solution accounts for 0.01% to 0.05% of the solution mass fraction, and the N,N-methylenebisacrylamide accounts for 0.01% to 0.1% of the total solution mass.

[0015] The nanocellulose in the present invention is green and environmentally friendly, and has a wide source. By adjusting the pH of the solution to create an alkaline environment, polydopamine is guided to grow on the nanocellulose, so that the hydrogel can adhere even in a humid environment, thereby improving the adhesion performance of the composite hydrogel.

[0016] The invention prepares the nanocellulose hydrogel sensing material by a thermal polymerization method, the reaction conditions are mild, and relatively few chemical substances are used. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The actual picture shows the adhesion of the composite hydrogel containing polydopamine-modified nanocellulose in the air and underwater;

[0018] Figure 2This is a comparison of the adhesion of the composite hydrogel material to different substrates in the air and underwater;

[0019] Figure 3 This is a comparison diagram of the mechanical properties of polydopamine-modified nanocellulose composite hydrogel and nanocellulose composite hydrogel;

[0020] Figure 4 The mechanical properties of nanocellulose composite hydrogels modified with different contents of polydopamine; DETAILED DESCRIPTION

[0021] The technical solution of the present invention is further described below in conjunction with specific embodiments, but is not limited thereto.

[0022] Example 1

[0023] 1) Take 100g of nanocellulose and place it in a beaker. Use hydrochloric acid-Tris system to adjust the pH of the nanocellulose solution to 8.5. After uniform mixing, add an equal amount of dopamine hydrochloride according to the ratio of nanocellulose to dopamine hydrochloride of 1:1. Stir for 6 hours in a dark place and centrifuge for washing. Add appropriate amount of liquid for washing in the order of stock solution, water, alcohol and water. The rotation speed is 10000r / min and centrifuge for 20min.

[0024] 2) Take 2.25g of polydopamine-modified nanocellulose (solid content 1.14%) and add it to 15g of water, mix it evenly on a magnetic stirrer, control the mass ratio of methacrylic acid sulfobetaine to acrylic acid to be 1:5, use a pipette to take the mixed solution, 0.6g of aluminum chloride and 1.05g of tannic acid, stir at room temperature for 20min, add 0.4%wt N,N-methylenebisacrylamide and 0.2%wt initiator ammonium persulfate, stir at room temperature for 3h, transfer to molds of different shapes, and let stand at 60°C for 6h to obtain a wet-viscous hydrogel material.

[0025] Example 2

[0026] 1) Take 100g of nanocellulose and place it in a beaker. Use hydrochloric acid-Tris system to adjust the pH of the nanocellulose solution to 8.5. After uniform mixing, add an equal amount of dopamine hydrochloride according to the ratio of nanocellulose to dopamine hydrochloride of 1:1. Stir for 6 hours in a dark place, and centrifuge and wash in the order of stock solution, water, alcohol, and water. The speed is 10000r / min and the centrifugation is carried out for 20 minutes.

[0027] 2) Take 1.76g of polydopamine-modified nanocellulose (solid content 2.18%) and add it to 15g of water, mix it evenly on a magnetic stirrer, control the mass ratio of methacrylic acid sulfobetaine to acrylic acid to be 1:5, take the solution with a pipette, add 0.6g of aluminum chloride and 1.05g of tannic acid, stir at room temperature for 20min, then add 0.4%wt N,N-methylenebisacrylamide and 0.2%wt initiator ammonium persulfate, stir at room temperature for 3h, transfer to molds of different shapes, and let stand at 60°C for 4h to obtain a wet-viscous hydrogel material.

[0028] The prepared composite hydrogel was subjected to an adhesion test on a real object (e.g. Figure 1 As shown in the figure, it can be seen that the prepared composite hydrogel can adhere well to the surface of various objects, which can prove that the prepared material has good adhesion.

[0029] Example 3

[0030] 1) Take 100g of nanocellulose and place it in a beaker. Use hydrochloric acid-Tris system to adjust the pH of the nanocellulose solution to 8.5. After uniform mixing, add an equal amount of dopamine hydrochloride according to the ratio of nanocellulose to dopamine hydrochloride of 1:1. Stir for 6 hours in a dark place, and centrifuge and wash in the order of stock solution, water, alcohol, and water. The speed is 10000r / min and the centrifugation is carried out for 20 minutes.

[0031] 2) Take 5.29g of polydopamine-modified nanocellulose (solid content 0.97%) and add it to 15g of water, mix it evenly on a magnetic stirrer, control the mass ratio of methacrylic acid sulfobetaine to acrylic acid to be 1:5, use a pipette to take the solution, 0.6g of aluminum chloride, 1.05g of tannic acid, stir at room temperature for 15min, add 0.4%wt N,N-methylenebisacrylamide, 0.2%wt initiator ammonium persulfate, stir at room temperature for 3h, transfer to molds of different shapes, and stand at 60°C for 5h to obtain a wet viscous hydrogel material.

[0032] The adhesion and tensile properties of the prepared composite hydrogel were tested (such as Figure 2 , 4 shown).

[0033] Comparative Example 1

[0034] Take 1.82 nanocellulose (solid content 1.4%) and add it to 15g water, mix it evenly on a magnetic stirrer, control the mass ratio of methacrylate sulfobetaine to acrylic acid to be 1:5, add 0.6g aluminum chloride and 1.05g tannic acid to the solution, stir at room temperature for 30min, then add 0.4%wt N,N-methylenebisacrylamide and 0.2%wt initiator ammonium persulfate, stir at room temperature for 4h, transfer to molds of different shapes, and let stand at 60°C for 5h to obtain a hydrogel material.

[0035] Comparative Example 2

[0036] Take 1.18g of polydopamine-modified nanocellulose (solid content 2.18%) and add it to 15g of water, mix it evenly on a magnetic stirrer, control the mass ratio of methacrylate sulfobetaine to acrylic acid to be 1:5, add 0.6g of aluminum chloride and 0.75g of tannic acid to the solution, stir at room temperature for 15min, then add 0.4%wt N,N-methylenebisacrylamide and 0.2%wt initiator ammonium persulfate, stir at room temperature for 3h, transfer to molds of different shapes, and let stand at 60°C for 4h to obtain a hydrogel material.

[0037] Comparative Example 3

[0038] Take 1.18g of polydopamine-modified nanocellulose (solid content 2.18%) and add it to 15g of water, mix it evenly on a magnetic stirrer, control the mass ratio of methacrylate sulfobetaine to acrylic acid to be 1:5, add 0.75g of aluminum chloride and 1.05g of tannic acid to the solution, stir at room temperature for 15min, then add 0.4%wt N,N-methylenebisacrylamide and 0.2%wt initiator ammonium persulfate, stir at room temperature for 3h, transfer to molds of different shapes, and let stand at 60°C for 4h to obtain a hydrogel material.

[0039] It can be seen from Tables 1 and 2 that the addition of polydopamine-modified nanocellulose and tannic acid can improve the adhesion of the composite hydrogel relative to the nanocellulose hydrogel. Figure 2 It is not difficult to see that the adhesion on different substrates is generally higher than that of Comparative Example 1, among which Example 2 is the most obvious, especially the improvement of wet adhesion. Compared with the same content of polydopamine-modified nanocellulose, the adhesion is improved with the increase of tannic acid addition; Al 3+ The content is increased and the tensile properties are improved. Figure 3 , Figure 4 From the stress-strain data, we can see that polydopamine modified nanocellulose can improve the elongation and stress of hydrogel. As the amount of addition increases, the change in the tensile properties of hydrogel generally shows that the elongation first increases and then decreases, while the stress increases. See the figure for details.

[0040] Performance Testing

[0041] Table 1 Adhesion of polydopamine-modified nanocellulose hydrogels to different substrates (kPa)

[0042]

[0043] Table 2 Wet adhesion of nanocellulose modified with different contents of polydopamine to different substrates (kPa)

[0044]

[0045] It should be noted that the above embodiments are only partial embodiments of the preferred methods of implementing the present invention, rather than all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

Claims

1. A method for preparing a nanocellulose-enhanced wet adhesive hydrogel, characterized in that: Follow these steps: S1. Take a certain amount of nanocellulose in a beaker, adjust the pH, add dopamine hydrochloride, seal and avoid light, and stir; S2, after stirring for a period of time, centrifuging to obtain polydopamine-modified nanocellulose; S3, dispersing the modified nanocellulose into solutions with different mass fractions, taking appropriate amounts of methacrylate sulfobetaine, aluminum chloride, tannic acid and acrylic acid, etc., adding the above solutions, and stirring evenly at room temperature; S4. Weigh a small amount of initiator (ammonium persulfate, N,N-methylenebisacrylamide), add to the above solution, stir for 3 hours, transfer to a mold, and let stand at 60°C for 6 hours to obtain nanocellulose reinforced wet adhesion hydrogel.

2. The method for preparing a nanocellulose enhanced wet adhesive hydrogel according to claim 1, characterized in that: In the step S1, the nanocellulose is derived from one or more of nanocellulose crystals, nanocellulose filaments, and bacterial cellulose, the mass ratio of nanocellulose to dopamine hydrochloride is 10-1, and the polymerization environment of dopamine hydrochloride requires the pH to be controlled at 6-10.

3. The method for preparing a nanocellulose enhanced wet adhesive hydrogel according to claim 1, characterized in that: In step S2, centrifugation is performed multiple times, each time for 10 to 100 minutes, and the rotation speed is controlled at 3000 to 12000 r / min.

4. The method for preparing a nanocellulose enhanced wet adhesive hydrogel according to claim 1, characterized in that: In the step S2, the polydopamine-modified nanocellulose is dispersed into solutions with different cellulose contents, with a mass fraction of 0.005 to 0.5%.

5. The method for preparing a nanocellulose enhanced wet adhesive hydrogel according to claim 1, characterized in that: In step S3, in the drugs added to the solution, the mass ratio of methacrylic acid sulfobetaine to acrylic acid is 0.1-5, the total molar concentration of the two is controlled at 0.5-5 mol / L, the mass fraction of aluminum chloride is 0.5%-5%, and the amount of tannic acid is controlled at 100-500 mg.

6. The method for preparing a nanocellulose-enhanced wet adhesive hydrogel according to claim 1, characterized in that: In step S4, the ammonium persulfate in the mixed solution accounts for 0.01% to 0.05% of the solution mass fraction, and the N,N-methylenebisacrylamide accounts for 0.01% to 0.1% of the total solution mass fraction.

7. Nanocellulose reinforced wet adhesive hydrogel prepared by the preparation method according to any one of claims 1 to 6.

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