Preparation method of high-strength transparent non-hydrolytic lignin / polyvinyl alcohol composite hydrogel

Abstract

The invention discloses a preparation method of high-strength transparent non-hydrolytic lignin / polyvinyl alcohol composite hydrogel, and belongs to the field of functional materials. The method comprises the following steps: dissolving polyvinyl alcohol (PVA) in deionized water, and uniformly stirring to obtain a solution A; dissolving sodium polyacrylate (PAANa) in deionized water, and uniformly stirring to obtain a solution B; dissolving alkaline lignin (AL) in deionized water, and uniformly stirring to obtain a solution C; dissolving potassium hydroxide (KOH) in deionized water, and uniformly stirring to obtain a solution D; sequentially mixing and heating the solution A, the solution B, the solution C and the solution D, and pouring the mixture into a mold for casting molding to obtain composite hydrogel; the mass ratio of the PVA to the PAANa to the AL to the KOH is (0.5 to 1.5 g) to (0.01 to 0.2 g) to (0.01 to 0.2 g) to (0.1 to 1.0 g). The polyvinyl alcohol composite hydrogel provided by the invention has a non-hydrolytic function, can be soaked in water for a long time, the soaking time can be as long as 1 year or even longer, no structural change occurs, the form of the hydrogel cannot be damaged, and the hydrogel can be recycled.

Description

Technical Field

[0001] The invention belongs to the field of functional materials, and in particular relates to a method for preparing a high-strength, transparent, non-hydrolyzable lignin / polyvinyl alcohol composite hydrogel. Background Art

[0002] Polyvinyl alcohol (PVA) is a water-soluble synthetic polymer. PVA hydrogel has good biocompatibility, stability, porous structure, low friction coefficient and water content similar to human tissue. It has broad application prospects in tissue replacement and repair materials, drug carriers, cartilage and skin substitutes, skin wound dressings and cell culture scaffolds. However, traditional PVA hydrogel is very easy to hydrolyze without adding any plasticizer, curing agent, acid or alkali, and cannot maintain the original morphology and function, resulting in difficulty in operation. This is also a problem that PVA hydrogel urgently needs to solve. The solubility of PVA is affected by the degree of alcoholysis and degree of polymerization. The lower the degree of alcoholysis and degree of polymerization, the faster it dissolves. Although the PVA hydrogel with the addition of potassium hydroxide achieves the hydrogel without hydrolysis, its transparency is significantly reduced, forming a milky white hydrogel state. In addition, since the mechanical properties of PVA hydrogel are not ideal, it is difficult to meet some high requirements in related fields. Therefore, the current main goal is to improve the transparency and mechanical properties of PVA hydrogel while maintaining its non-hydrolysis performance.

[0003] Hydrogels can be physically or chemically cross-linked. Due to the presence of these chemical, covalent, ionic or physical cross-links, hydrogels become insoluble. Physical methods have a significant advantage, that is, no cross-linking residues are left in the gel matrix. Therefore, by incorporating reinforcing materials into PVA hydrogels to form composite hydrogels, the various properties of PVA hydrogels can be improved while maintaining non-hydrolysis. Sodium polyacrylate (PAANa) is an electronegative polymer. There is a potential ionic interaction between it and PVA, and the two can be directly mixed to obtain a homogeneous PVA / PAANa sol solution. PAANa has high water absorption performance, and the water absorption can reach 200-300 times its own weight. This makes the hydrogel formed by PAANa and other polymers have good water absorption and water retention, and is often used to construct self-healing hydrogels and highly absorbent hydrogels. However, alkaline PVA hydrogels have poor water retention and their transparency decreases after salting out, which seriously limits their application in some fields. Therefore, the direct blending of PVA and PAANa in alkaline aqueous solution to prepare mechanical performance enhancing materials has certain research and application value.

[0004] Lignin is the most abundant aromatic biopolymer, accounting for about 30% of the organic carbon in the biosphere, and has been shown to have interesting properties not only in terms of energy but also in the synthesis of new bio-based materials. It is also a major byproduct of the paper industry, agriculture and forestry. However, basic and applied research on lignin has been slow, mainly due to the heterogeneity of lignin, including a wide molecular weight distribution and a complex chemical structure. The homogenization of lignin is beneficial not only to the development of theoretical research on lignin, but also to its commercialization and standardized application. This molecule has a wide range of applications and good prospects in various fields. Lignin has a highly branched structure and has multiple functional groups such as carbonyl (C=O), hydroxyl (-OH), carboxyl (-COOH) and methoxyl (-CH3O), which directly affect its reactivity. Due to its large molecular weight, large steric hindrance and few active sites, the reactivity of this biopolymer is usually not high enough. Therefore, it is sometimes necessary to blend it with other high molecular weight polymers as a raw material or additive for adjusting the properties of functional materials, or to modify some chemical sites, as well as to prepare some composite materials with specific functions by synthesizing graft copolymers with it.

[0005] In summary, traditional PVA hydrogels are very easy to hydrolyze without adding any plasticizers, curing agents, acids or alkalis, and cannot maintain their original morphology and functions. This is also a problem that PVA hydrogels need to solve urgently. Although PVA hydrogels with potassium hydroxide added can prevent hydrogels from hydrolyzing, their transparency is significantly reduced, and their mechanical properties are not ideal, making it difficult to meet some high requirements in related fields. Summary of the invention

[0006] The purpose of the present invention is to solve the problems of traditional polyvinyl alcohol hydrogel being extremely easy to hydrolyze, being relatively hard, having poor transparency, and having low water retention, and to provide a method for preparing a high-strength, transparent, non-hydrolyzable lignin / polyvinyl alcohol composite hydrogel. A non-hydrolyzable PVA composite hydrogel is prepared, and the composite hydrogel is non-toxic and harmless. Compared with the traditional PVA hydrogel, the composite hydrogel has the advantages of high transparency, stable structure, non-hydrolysis, high tensile strength, good flexibility, suitable for covering in various shapes, good skin adhesion, and can be recycled. The preparation method is green and environmentally friendly, and the experimental operation is simple and convenient, and it is convenient to use at any time.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a high-strength, transparent, non-hydrolyzable lignin / polyvinyl alcohol composite hydrogel, the method comprising:

[0009] Step 1: dissolving polyvinyl alcohol (PVA) in deionized water and stirring evenly to obtain solution A;

[0010] Step 2: dissolving sodium polyacrylate (PAANa) in deionized water and stirring evenly to obtain solution B;

[0011] Step 3: dissolving alkaline lignin (AL) in deionized water and stirring evenly to obtain solution C;

[0012] Step 4: Dissolve potassium hydroxide (KOH) in deionized water and stir evenly to obtain solution D;

[0013] Step 5: After mixing solutions A, B, C, and D in sequence and heating them, pouring them into a mold for cast molding to obtain a composite hydrogel; the mass ratio of the PVA, PAANa, AL, and KOH is 0.5-1.5g: 0.01-0.2g: 0.01-0.2g: 0.1-1.0g.

[0014] Furthermore, the step 1 is specifically as follows: polyvinyl alcohol (PVA) is put into a glass container, deionized water is added and ultrasonically stirred, and a solution A of 25.0 wt% to 50.0 wt% is obtained.

[0015] Furthermore, in step 1, deionized water is ultrasonicated for 15 to 25 minutes, heated at 70 to 90° C. for 0.5 to 1.5 hours, and stirred evenly.

[0016] Furthermore, the step 2 is specifically as follows: sodium polyacrylate (PAANa) is put into a glass container, deionized water is added and ultrasonically stirred, and a solution B of 1.0 wt% to 8.0 wt% is obtained.

[0017] Furthermore, in step 2, deionized water is ultrasonicated for 15 to 25 minutes, and heated at 30 to 50° C. for 0.1 to 1.0 hour and stirred evenly.

[0018] Furthermore, the step three is specifically as follows: alkaline lignin (AL) is placed in a glass container, deionized water is added for ultrasonic stirring, and the mixture is stirred evenly to obtain a solution C with a concentration of 0.1 wt% to 4.0 wt%.

[0019] Furthermore, in step three, deionized water is sonicated for 15 to 25 minutes, and heated at 30 to 50° C. for 0.1 to 0.5 hours to stir and dissolve.

[0020] Furthermore, the step 4 is specifically as follows: potassium hydroxide (KOH) is put into a glass container, deionized water is added, ultrasonically stirred, and uniformly stirred to obtain a solution D of 5.0 wt%-30.0 wt%.

[0021] Furthermore, in step 4, deionized water is ultrasonically dissolved for 15 to 25 minutes, and heated at 70 to 90° C. for 0.1 to 2.5 hours to stir evenly.

[0022] Furthermore, in step five, the masses of the components are: PVA is 1 g; PAANa is 0.12 g; AL is 0.05 g; and KOH is 0.5 g.

[0023] The beneficial effects of the present invention compared to the prior art are:

[0024] (1) The present invention chelates alkaline lignin (AL) with a rigid structure with potassium ions, and then cross-links two linear polymers, polyvinyl alcohol (PVA, type 1788) and sodium polyacrylate (PAANa), through hydrogen bonds and charge interactions, to prevent the two linear polymers from being tightly entangled and precipitating or forming films. The selected AL, PVA and PAANa are all abundant, readily available and non-toxic materials. The hydrogen bond interaction between lignin and PVA makes the prepared hydrogel have better flexibility and strength than pure PVA hydrogel. The hydrogen bond effect between lignin and PAANa not only strengthens the network structure of the hydrogel, but also makes the hydrogel have certain water retention properties. There is a charge interaction between PVA and PAANa, which combines the two network structures more closely together and enhances the mechanical strength of the hydrogel. In addition, the complexation of KOH and AL not only realizes the non-hydrolysis property of the PVA composite hydrogel, but also greatly improves the transparency of the PVA composite hydrogel. The PVA composite hydrogel can maintain its appearance and function in water for a long time. Only when the complexation of KOH and AL exists, the hydrogel has both the characteristics of non-hydrolysis and good transparency. This easy-to-prepare, high-strength, transparent, non-hydrolyzed lignin / polyvinyl alcohol composite hydrogel can be used in various occasions with high light transmittance requirements. It is simple to prepare, can be run quickly, has high strength, is non-hydrolyzed, and has high light transmittance. It is a hydrogel material with excellent performance.

[0025] (2) The polyvinyl alcohol composite hydrogel in the present invention has high strength. Among them, polyvinyl alcohol interacts with sodium polyacrylate and alkaline lignin to form a double network structure. Its storage modulus (G') reaches a maximum of 80537.066Pa, and within a shear strain of 24%, the difference between its storage modulus G' and loss modulus G" reaches a maximum of 75694.600Pa. The maximum tensile fracture strength of the composite hydrogel reaches 738.54kPa, and the fracture strain can reach 774.02%.

[0026] (3) The polyvinyl alcohol composite hydrogel in the present invention has the function of not being hydrolyzed and can be immersed in water for a long time, up to 1 year or even longer, without any structural change, without destroying the morphology of the hydrogel, and can be recycled.

[0027] (4) Compared with the traditional opaque alkaline PVA hydrogel, the polyvinyl alcohol composite hydrogel in the present invention is added with alkaline lignin with a rigid structure. The alkaline lignin can be cross-linked with polyvinyl alcohol and sodium polyacrylate polymer chains to support the three-dimensional network structure of the hydrogel, giving the hydrogel good light transmittance and maintaining a light-transmitting state for a long time.

[0028] (5) The polyvinyl alcohol composite hydrogel in the present invention is added with sodium polyacrylate with high water absorption, which has a higher water retention rate than the traditional alkaline PVA hydrogel and can keep water from being lost for a long time. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The following is a comparison chart of the appearance and transparency of the lignin / polyvinyl alcohol composite hydrogel under various concentration conditions in Examples 1 to 3.

[0030] Figure 2 The following is a comparison chart of the appearance and transparency of the polyvinyl alcohol composite hydrogel with different added ingredients in Comparative Examples 1 to 4.

[0031] Figure 3 This is a comparison chart of the tensile test of lignin / polyvinyl alcohol composite hydrogel under various concentration conditions in Examples 1 to 3.

[0032] Figure 4 This is the infrared analysis diagram of the high-strength, transparent, non-hydrolyzed lignin / polyvinyl alcohol composite hydrogel of Example 3.

[0033] Figure 5 This is the rheological test diagram of the high-strength, transparent, non-hydrolyzed lignin / polyvinyl alcohol composite hydrogel of Example 3.

[0034] Figure 6 This is a comparison chart of the fit test between the high-strength, transparent, non-hydrolyzed lignin / polyvinyl alcohol composite hydrogel of Example 3 and the pure PVA hydrogel. DETAILED DESCRIPTION

[0035] In order to further understand the present invention, the preferred embodiments of the present invention are described below in conjunction with examples, but it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than for limiting the claims of the present invention. It should be noted that, unless otherwise specified, the meaning of the scientific and technological terms used in the present invention is the same as that generally understood by those skilled in the art. If not otherwise stated, the raw materials in the examples of the present application are purchased through commercial channels.

[0036] The present invention chelates AL with a rigid structure with potassium ions, and then cross-links two linear polymers, PVA and PAANa, through hydrogen bonds and charge interactions, to prepare a high-strength, transparent, and non-hydrolyzable lignin / polyvinyl alcohol composite hydrogel. Not only does the non-hydrolyzable property of the PVA hydrogel be achieved, but the transparency of the PVA hydrogel is also well improved. The PVA composite hydrogel can maintain its appearance and function for a long time in water. The composite hydrogel is non-toxic and harmless. Compared with traditional PVA hydrogels, it has high transparency, stable structure and non-hydrolysis, high tensile strength, good flexibility, and the preparation method is green and environmentally friendly. It also has good skin conformability, is suitable for covering environments of various shapes, and can be recycled. This easy-to-prepare, high-strength, transparent, and non-hydrolyzable lignin / polyvinyl alcohol composite hydrogel is a hydrogel material with excellent performance.

[0037] Example 1

[0038] Weigh 1 g of polyvinyl alcohol and dissolve it in 10 ml of water. Ultrasonicate and stir for 10 minutes to disperse it.

[0039] Weigh 0.04 g of sodium polyacrylate and dissolve it in 5 ml of deionized water. Ultrasonicate and stir for 10 minutes to disperse it.

[0040] 0.02 g of alkaline lignin was weighed and placed in a reaction bottle, dissolved in 5 ml of deionized water, and dispersed by ultrasonication and stirring for 5 minutes.

[0041] Weigh 0.2 g of potassium hydroxide into a reaction bottle, dissolve it in 10 ml of deionized water, and stir and sonicate for 5 minutes to dissolve it.

[0042] The above solutions were mixed in order, heated with stirring at 70°C for 30 minutes, and after the reaction was completed, 1.5 ml of the reaction solution was poured into a 5cm×5cm×5cm flat plate mold, placed for 12 hours, taken out, washed with deionized water 3 times, and then immersed in deionized water for 2 hours to obtain a composite hydrogel material. The maximum tensile fracture stress of the hydrogel was 161.20 kPa, the tensile fracture strain was 513.41%, the transparency was low, and it did not hydrolyze.

[0043] Example 2

[0044] Weigh 1 g of polyvinyl alcohol and dissolve it in 10 ml of water. Ultrasonicate and stir for 10 minutes to disperse it.

[0045] Weigh 0.08 g of sodium polyacrylate and dissolve it in 5 ml of deionized water. Ultrasonicate and stir for 10 minutes to disperse it.

[0046] 0.04 g of alkaline lignin was weighed and placed in a reaction bottle, dissolved in 5 ml of deionized water, and dispersed by ultrasonication and stirring for 5 minutes.

[0047] Weigh 0.4 g of potassium hydroxide into a reaction bottle, dissolve it in 10 ml of deionized water, and stir and sonicate for 5 minutes to dissolve it.

[0048] The above solutions were mixed in order, heated at 80°C with stirring for 1 hour, and after the reaction, 1.5 ml of the reaction solution was poured into a 5cm×5cm×5cm flat plate mold, placed for 12 hours, taken out, washed with deionized water 3 times, and then immersed in deionized water for 2 hours to obtain a composite hydrogel material. The maximum tensile fracture stress of the hydrogel was 513.41 kPa, the tensile fracture strain was 710.60%, the transparency was low, and it did not hydrolyze.

[0049] Example 3

[0050] Weigh 1 g of polyvinyl alcohol and dissolve it in 10 ml of water. Ultrasonicate and stir for 10 minutes to disperse it.

[0051] Weigh 0.12 g of sodium polyacrylate and dissolve it in 5 ml of deionized water. Ultrasonicate and stir for 10 minutes to disperse it.

[0052] Weigh 0.05 g of alkaline lignin into a reaction bottle, dissolve it in 5 ml of deionized water, and disperse it by ultrasonication and stirring for 5 minutes.

[0053] Weigh 0.5 g of potassium hydroxide into a reaction bottle, dissolve it in 10 ml of deionized water, and stir and sonicate for 5 minutes to dissolve it.

[0054] The above solutions were mixed in order, heated at 85°C with stirring for 2 hours, and after the reaction, 1.5 ml of the reaction solution was poured into a 5cm×5cm×5cm flat plate mold, placed for 12 hours, taken out, washed with deionized water 3 times, and then immersed in deionized water for 2 hours to obtain a composite hydrogel material. The maximum tensile fracture stress of the hydrogel was 738.54 kPa, the tensile fracture strain was 772.98%, the transparency was high, and it did not hydrolyze.

[0055] Figure 4 The infrared analysis spectrum of the hydrogel in Example 3. PVA, PAANa, and AL polymers all contain a large number of hydrogen bond-forming groups, which can form hydrogen bonds with each other. -1 The left and right are the stretching vibration peaks of the hydroxyl-OH bond, -NH2, and NH group. Figure 4 The characteristic peaks of PVA are located at 2938, 1333 and 1254 cm -1 , belonging to -CH2-, -CH-OH- and -CH- resonance respectively. ~1099cm -1 The peak at 1405 cm is caused by the presence of terminal polyethylene hydrocarbon groups. The symmetric stretching vibration of carboxylate (-COO) and C=O in PAANa is at 1405 cm -1~1718cm -1 The peak at is caused by the stretching vibration of the -C=O band in the -COOH group. The peak of the plane rocking vibration of the -(CH2)n- structure is at ~1455cm -1 ~1563cm -1 The peak at 1316 cm is caused by the stretching vibration of C=C in the polymer structure. -1 The reason for the characteristic peak at 1250-830cm is the skeleton vibration of the CC bond in the polymer. -1 A series of moderately intense absorption peaks appeared in the region, which are related to the helical arrangement of the molecular chain. -1 The broad vibrations in the range are associated with hydroxyl groups in phenolic and fatty compounds. -1 The vibration at 1710 cm-1 is attributed to the carbon-hydrogen vibration of the aromatic methoxy and methylene groups on the side chains. -1 The absorbance band corresponding to the non-conjugated carbonyl / carboxyl stretching in lignin is 1595 cm -1 The peaks at ∼1330 and ∼1125 cm are due to the presence of different amounts of phenylpropane skeletons in the samples. -1 The absorbance signal at 1259 cm represents the syringyl unit (S), while the -1 The peak at 1300-1000cm is due to the combination with guaiacyl units (G), confirming that lignin is composed of S and G basic units. -1 The bonds between indicate that there are different numbers of CC, C=O, and CO groups in the lignin samples. Compared with the three polymers, the absorption peaks of PVA-PAANa-AL hydrogel retain the absorption peaks of each polymer at 3300 cm -1 Characteristic absorption peak near 1546cm -1 and ~1448cm -1 The formed hydrogel also retains some characteristic peaks of the three polymers at 2900 cm -1 In summary, due to the cross-linking of the three polymers by hydrogen bonds, the formed hydrogels all retain some characteristic peaks of PVA, PAANa, and AL, but the vibration intensity changes. This shows that the three polymers are mainly cross-linked by hydrogen bonds.

[0056] Figure 5 The rheological properties analysis spectrum of the hydrogel in Example 3. Figure 5(a) Analysis of the viscoelastic properties of PVA-PAANa-AL hydrogel when the angular frequency is constant at 10rad / s and the shear strain ranges from 0.1% to 100%. The storage modulus (G') of PVA-PAANa-AL hydrogel reached a maximum of 80537.066Pa, and within the shear strain of 24%, the maximum difference between its G' and G" reached 75694.600Pa. As the shear rate gradually increases, its G' and G" intersect at the shear strain of 24%. As the shear rate continues to increase, its G" is greater than G'. This is because the shear rate is too high and water gradually seeps out of the hydrogel. These results show that PVA-PAANa-AL hydrogel has good elasticity, low viscosity, and water can be gradually released as the shear rate increases. It is a material with strong mechanical properties. Figure 5 (b) Analysis of the viscoelastic properties of PVA-PAANa-AL hydrogel when the shear rate is constant at 10% and the angular frequency ranges from 0.1 to 100 rad / s. It can also be seen that the G' and G" of PVA-PAANa-AL hydrogel maintain a large difference. As the angular frequency gradually increases, the G' and G" of PVA-PAANa-AL hydrogel are very stable, and there is no Figure 6 This indicates that the PVA-PAANa-AL hydrogel can resist large shear stress without any change and has strong viscoelasticity.

[0057] Example 4

[0058] Weigh 1 g of polyvinyl alcohol and dissolve it in 10 ml of water. Ultrasonicate and stir for 10 minutes to disperse it.

[0059] Weigh 0.12 g of sodium polyacrylate and dissolve it in 5 ml of deionized water. Ultrasonicate and stir for 10 minutes to disperse it.

[0060] Weigh 0.1 g of alkaline lignin into a reaction bottle, dissolve it in 5 ml of deionized water, and disperse it by ultrasonication and stirring for 5 minutes.

[0061] Weigh 0.5 g of potassium hydroxide into a reaction bottle, dissolve it in 10 ml of deionized water, and stir and sonicate for 5 minutes to dissolve it.

[0062] The above solutions were mixed in order, heated with stirring at 85°C for 2 hours, and after the reaction, 1.5 ml of the reaction solution was poured into a 5 cm × 5 cm × 5 cm flat plate mold, placed for 12 hours, taken out, washed with deionized water 3 times, and then immersed in deionized water for 2 hours to obtain a composite hydrogel material. A large amount of alkaline lignin was washed away from the hydrogel during the washing process, indicating that the alkaline lignin was added excessively.

[0063] In Examples 1-4, the present invention studies the effects of different addition amounts of alkaline lignin, sodium polyacrylate and potassium hydroxide on the hydrogel. In Example 3, under the conditions of 1 g of polyvinyl alcohol, 0.05 g of alkaline lignin, 0.12 g of sodium polyacrylate and 0.5 g of potassium hydroxide, the mechanical properties and visible light transmittance of the hydrogel are optimal.

[0064] Comparative Example 1

[0065] Weigh 1 g of polyvinyl alcohol and dissolve it in 20 ml of water. Ultrasonicate and stir for 10 minutes to disperse it.

[0066] Weigh 0.5 g of potassium hydroxide into a reaction bottle, dissolve it in 10 ml of deionized water, and stir and sonicate for 5 minutes to dissolve it.

[0067] The above solutions were mixed in order, heated at 85℃ with stirring for 2h, and after the reaction, 1.5ml of the reaction solution was poured into a 5cm×5cm×5cm flat plate mold, placed for 12h, taken out, washed with deionized water for 3 times, and then soaked in deionized water for 2h to obtain a PVA hydrogel material. It does not hydrolyze but has low transparency.

[0068] Comparative Example 2

[0069] Weigh 1 g of polyvinyl alcohol and dissolve it in 10 ml of water. Ultrasonicate and stir for 10 minutes to disperse it.

[0070] Weigh 0.12 g of sodium polyacrylate and dissolve it in 5 ml of deionized water. Ultrasonicate and stir for 10 minutes to disperse it.

[0071] Weigh 0.5 g of potassium hydroxide into a reaction bottle, dissolve it in 15 ml of deionized water, and stir and sonicate for 5 minutes to dissolve it.

[0072] The above solutions were mixed in order, heated with stirring at 85°C for 2 hours, and after the reaction, 1.5 ml of the reaction solution was poured into a 5cm×5cm×5cm flat plate mold, placed for 12 hours, taken out, washed with deionized water for 3 times, and then immersed in deionized water for 2 hours to obtain a composite hydrogel material. It does not hydrolyze but has low transparency.

[0073] Comparative Example 3

[0074] Weigh 1 g of polyvinyl alcohol and dissolve it in 10 ml of water. Ultrasonicate and stir for 10 minutes to disperse it.

[0075] Weigh 0.12 g of sodium polyacrylate and dissolve it in 5 ml of deionized water. Ultrasonicate and stir for 10 minutes to disperse it.

[0076] Weigh 0.05 g of carboxymethyl cellulose into a reaction bottle, dissolve it in 5 ml of deionized water, and disperse it by ultrasonication and stirring for 5 minutes.

[0077] Weigh 0.5 g of potassium hydroxide into a reaction bottle, dissolve it in 10 ml of deionized water, and stir and sonicate for 5 minutes to dissolve it.

[0078] The above solutions were mixed in order, heated with stirring at 85°C for 2 hours, and after the reaction, 1.5 ml of the reaction solution was poured into a 5cm×5cm×5cm flat plate mold, placed for 12 hours, taken out, washed with deionized water for 3 times, and then immersed in deionized water for 2 hours to obtain a composite hydrogel material. It does not hydrolyze but has low transparency.

[0079] Comparative Example 4

[0080] Weigh 1 g of polyvinyl alcohol and dissolve it in 10 ml of water. Ultrasonicate and stir for 10 minutes to disperse it.

[0081] Weigh 0.12 g of sodium polyacrylate and dissolve it in 5 ml of deionized water. Ultrasonicate and stir for 10 minutes to disperse it.

[0082] Weigh 0.05 g of dealkalized lignin into a reaction bottle, dissolve it in 5 ml of deionized water, and disperse it by ultrasonication and stirring for 5 minutes.

[0083] Weigh 0.5 g of potassium hydroxide into a reaction bottle, dissolve it in 10 ml of deionized water, and stir and sonicate for 5 minutes to dissolve it.

[0084] The above solutions were mixed in order, heated at 85°C with stirring for 2 hours, and after the reaction was completed, 1.5 ml of the reaction solution was poured into a 5 cm × 5 cm × 5 cm flat plate mold, placed for 12 hours, taken out, washed with deionized water for 3 times, and then immersed in deionized water for 2 hours to obtain a composite hydrogel material. The hydrogel produced many pores, did not hydrolyze, but had low transparency.

[0085] Comparative Example 5

[0086] Weigh 1 g of polyvinyl alcohol and dissolve it in 15 ml of water. Ultrasonicate and stir for 10 minutes to disperse it.

[0087] Weigh 0.12 g of sodium polyacrylate and dissolve it in 10 ml of deionized water. Ultrasonicate and stir for 10 minutes to disperse it.

[0088] Weigh 0.05 g of alkaline lignin into a reaction bottle, dissolve it in 5 ml of deionized water, and disperse it by ultrasonication and stirring for 5 minutes.

[0089] Mix the above solutions in order, heat at 85℃ with stirring for 2h, and after the reaction, pour 1.5ml of the reaction solution into a 5cm×5cm×5cm flat plate mold, and take it out after leaving it for 12h. It has high transparency but is easily hydrolyzed.

[0090] Comparative Example 6

[0091] Weigh 1 g of polyvinyl alcohol and dissolve it in 15 ml of water. Ultrasonicate and stir for 10 minutes to disperse it.

[0092] Weigh 0.12 g of sodium polyacrylate and dissolve it in 10 ml of deionized water. Ultrasonicate and stir for 10 minutes to disperse it.

[0093] Weigh 0.05 g of carboxymethyl cellulose into a reaction bottle, dissolve it in 5 ml of deionized water, and disperse it by ultrasonication and stirring for 5 minutes.

[0094] Mix the above solutions in order, heat at 85℃ with stirring for 2h, and after the reaction, pour 1.5ml of the reaction solution into a 5cm×5cm×5cm flat plate mold, and take it out after leaving it for 12h. It has high transparency but is easily hydrolyzed.

[0095] In the above comparative examples 1-6, the effects of Example 3 are far from being achieved in terms of both the mechanical properties and the light transmittance of the hydrogels.

Claims

1. A method for preparing a high-strength, transparent, non-hydrolyzable lignin / polyvinyl alcohol composite hydrogel, characterized in that: The method is: Step 1: dissolving polyvinyl alcohol (PVA) in deionized water and stirring evenly to obtain solution A; Step 2: dissolving sodium polyacrylate (PAANa) in deionized water and stirring evenly to obtain solution B; Step 3: dissolving alkaline lignin (AL) in deionized water and stirring evenly to obtain solution C; Step 4: Dissolve potassium hydroxide (KOH) in deionized water and stir evenly to obtain solution D; Step 5: After mixing solutions A, B, C, and D in sequence and heating them, pouring them into a mold for cast molding to obtain a composite hydrogel; the mass ratio of the PVA, PAANa, AL, and KOH is 0.5-1.5g: 0.01-0.2g: 0.01-0.2g: 0.1-1.0g.

2. The method for preparing a high-strength, transparent, non-hydrolyzable lignin / polyvinyl alcohol composite hydrogel according to claim 1, characterized in that: The step 1 is specifically as follows: polyvinyl alcohol (PVA) is put into a glass container, deionized water is added, ultrasonically stirred, and uniformly stirred to obtain a solution A of 25.0 wt% to 50.0 wt%.

3. The method for preparing a high-strength, transparent, non-hydrolyzable lignin / polyvinyl alcohol composite hydrogel according to claim 1 or 2, characterized in that: In step 1, deionized water is ultrasonicated for 15 to 25 minutes, heated at 70 to 90° C. for 0.5 to 1.5 hours, and stirred evenly.

4. The method for preparing a high-strength, transparent, non-hydrolyzable lignin / polyvinyl alcohol composite hydrogel according to claim 1, characterized in that: The step 2 is specifically as follows: sodium polyacrylate (PAANa) is put into a glass container, deionized water is added, ultrasonically stirred, and uniformly stirred to obtain a solution B of 1.0 wt% to 8.0 wt%.

5. A method for preparing a high-strength, transparent, non-hydrolyzable lignin / polyvinyl alcohol composite hydrogel according to claim 1 or 4, characterized in that: In step 2, deionized water is ultrasonicated for 15 to 25 minutes, and heated at 30 to 50° C. for 0.1 to 1.0 hour and stirred evenly.

6. The method for preparing a high-strength, transparent, non-hydrolyzable lignin / polyvinyl alcohol composite hydrogel according to claim 1, characterized in that: The step three is specifically as follows: alkaline lignin (AL) is placed in a glass container, deionized water is added and ultrasonically stirred to obtain a solution C of 0.1 wt% to 4.0 wt%.

7. A method for preparing a high-strength, transparent, non-hydrolyzable lignin / polyvinyl alcohol composite hydrogel according to claim 1 or 6, characterized in that: In step 3, deionized water is sonicated for 15 to 25 minutes, and heated at 30 to 50° C. for 0.1 to 0.5 hours to stir and dissolve.

8. The method for preparing a high-strength, transparent, non-hydrolyzable lignin / polyvinyl alcohol composite hydrogel according to claim 1, characterized in that: The step 4 is specifically as follows: potassium hydroxide (KOH) is put into a glass container, deionized water is added, ultrasonically stirred, and uniformly stirred to obtain a solution D of 5.0 wt% to 30.0 wt%.

9. The method for preparing a high-strength, transparent, non-hydrolyzable lignin / polyvinyl alcohol composite hydrogel according to claim 1 or 8, characterized in that: In step 4, dissolve in deionized water by ultrasonic treatment for 15 to 25 minutes, heat at 70 to 90° C. for 0.1 to 2.5 hours, and stir evenly.

10. The method for preparing a high-strength, transparent, non-hydrolyzable lignin / polyvinyl alcohol composite hydrogel according to claim 1, characterized in that: In step five, the masses of the components are: PVA is 1 g; PAANa is 0.12 g; AL is 0.05 g; and KOH is 0.5 g.

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