Preparation of temperature-sensitive lignin with controllable lcst by williamson method and preparation method and application thereof
By activating lignin sulfonate via the Williamson method and preparing highly active thiol radicals and modified N-vinylcaprolactam using azobisisobutyronitrile and iodide catalysts, the problem of large controllable amounts in the synthesis of thermosensitive lignin in existing technologies was solved, and the synthesis and thermosensitive transformation of thermosensitive lignin with LCST control was realized.
Patent Information
- Application Number
- CN202311582681.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-11-24
- Publication Date
- 2026-08-25
- Estimated Expiration
- 2043-11-24
AI Technical Summary
Existing thermosensitive lignin synthesis processes require significant control of quantities, making the reaction difficult to manage.
Using the Williamson method, highly active thiol radicals were prepared by activating lignin sulfonate and increasing the content of phenolic hydroxyl groups in lignin sulfonate using a mixed solution of urea and sodium hydroxide. Combined with azobisisobutyronitrile as an initiator and iodide as a catalyst, graft copolymerization was carried out with modified N-vinylcaprolactam to form ether bonds.
The synthesis of thermosensitive lignin with controllable LCST was achieved, which improved the controllability of the reaction and the thermosensitivity of the product. The prepared thermosensitive lignin can transform from hydrophilic to hydrophobic at a specific temperature.
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Figure CN117510870B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of thermosensitive lignin synthesis technology, specifically relating to a method for preparing LCST-controlled thermosensitive lignin using the Williamson method, and its application. Background Technology
[0002] Thermosensitive polymers are intelligent polymeric materials that respond to temperature stimuli. At a specific temperature, these polymers transition from hydrophilic to hydrophobic properties; this temperature is called the lowest critical phase transition temperature (LCST). The thermosensitivity of thermosensitive polymers originates from their thermosensitive monomers. Currently, the most commonly used thermosensitive monomer is N-isopropylacrylamide (PNIPAM), whose LCST is around 33°C, close to human physiological temperature. Numerous polymers and block compounds use PNIPAM as their thermosensitive monomer. In recent years, as research on PNIPAM has deepened, some reports have indicated that PNIPAM-related polymers contain residual monomers and exhibit local toxicity. Therefore, researchers are placing increasing emphasis on the biocompatibility and non-toxicity of thermosensitive monomers.
[0003] Researchers are currently focusing on N-vinylcaprolactam (NVCL), which has lower toxicity. This is because NVCL hydrolysis only produces polymeric carboxylic acids and does not generate small-molecule ammonium, which has certain biotoxicity. The LCST of NVCL is between 30 and 40 °C, and its LCST can be adjusted according to the concentration of the synthesized polymer in aqueous solution and the molecular weight of the polymer. Lignin, due to its unique structure and diverse functional groups, possesses antioxidant, UV-resistant, antibacterial, and biocompatible properties. In recent years, researchers have conducted extensive and in-depth studies on the preparation of thermosensitive materials using lignin as a raw material. Since the active functional group of NVCL is vinyl, it cannot be directly grafted onto the active functional groups in lignin. The most active functional group in lignin is the aromatic hydroxyl group, therefore, NVCL needs to be structurally modified to enable it to bind with lignin. Current literature reports on lignin grafted with NVCL, using a controlled-activity free radical polymerization-electron transfer activated regeneration catalyst atom transfer radical polymerization (ARGET-ATRP) to graft copolymerize lignin and thermosensitive monomers. This method involves adding ascorbic acid as a reducing agent to complex Cu in the solution. 2+ Reduce it to Cu +， This process promotes the formation of carbon radicals from lignin intermediates into lignin macromolecules. These carbon radicals attack the olefin bonds of NVCLs, leading to chain propagation. Throughout the process, the addition of excess ascorbic acid can continuously generate Cu radicals. However, this method requires careful control of the reaction amounts to synthesize thermosensitive lignin. Summary of the Invention
[0004] The purpose of this invention is to provide a method for preparing LCST-controlled thermosensitive lignin using the Williamson method to solve the technical problem of requiring large amounts of controlled quantities in existing thermosensitive lignin synthesis processes.
[0005] A second objective of this invention is to provide a thermosensitive lignin.
[0006] A third objective of this invention is to provide an application of thermosensitive lignin.
[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:
[0008] The Williamson method for preparing LCST-controlled thermosensitive lignin includes the following steps:
[0009] Step 1): Activation of lignin sulfonate: The lignin sulfonate is activated using an activation reagent, which is a mixed solution of urea and sodium hydroxide;
[0010] Step 2): Modification of N-vinylcaprolactam: Dissolve the initiator, N-vinylcaprolactam, and modifier in solvent one and then heat to obtain the modified poly-N-vinylcaprolactam.
[0011] Step 3): Preparation of thermosensitive lignin: Dissolve the activated lignin sulfonate in solvent 2, then add the modified polyN-vinylcaprolactam, pH adjuster, and catalyst from step 2), and heat to obtain the final product.
[0012] Further, the modification of N-vinylcaprolactam in step 2) involves adding the initiator, N-vinylcaprolactam, modifier, and solvent to a reaction vessel. After the initiator, N-vinylcaprolactam, and modifier dissolve, the vessel is sealed and reacted at 70–95°C for 6–10 hours to obtain a reaction solution. The reaction solution is then purified to obtain the final product. The modifier is one of 3-chloro-1-propanethiol, 1,3-dichloro-1-propanethiol, or 2-(2-chloroethylthioalkyl)ethanethiol.
[0013] Furthermore, the molar ratio of N-vinylcaprolactam, modifier, and initiator is 30–122:10.8–15:1; the mass of N-vinylcaprolactam added to each mL of solvent one is 0.03–0.08 g; solvent one is one of dimethyl sulfoxide, tetrahydrofuran, and chloroform; and the initiator is azobisisobutyronitrile.
[0014] Furthermore, after recrystallizing the N-vinylcaprolactam in hexane, the recrystallized N-vinylcaprolactam is modified; the purification step of the reaction solution is to dialyze the reaction solution through a cellulose membrane and then freeze-dry it.
[0015] Furthermore, after nitrogen gas is introduced into the reaction vessel for deoxygenation, the initiator, N-vinylcaprolactam, 3-chloro-1-propanethiol, and solvent are added to the reaction vessel; the nitrogen gas is introduced for 15 to 30 minutes.
[0016] Further, the method for preparing the thermosensitive lignin in step 3) is as follows: after dissolving the activated lignin sulfonate in solvent two, the modified poly-N-vinylcaprolactam, pH adjuster, and catalyst are added, and the reaction is carried out at 70-95°C for 6-10 hours to obtain a thermosensitive lignin solution. The thermosensitive lignin solution is dialyzed through a cellulose membrane and then freeze-dried to obtain the final product. The lignin sulfonate is one of sodium lignin sulfonate, calcium lignin sulfonate, and magnesium lignin sulfonate.
[0017] Furthermore, the molar ratio of the phenolic hydroxyl group, pH adjuster, and halogen in the activated lignin sulfonate is 1:3:12-15; the solvent is one of anhydrous dimethyl sulfoxide, dimethylformamide, and tetrahydrofuran; the pH adjuster is one of sodium bis(trimethylsilyl)amino, potassium bis(trimethylsilyl)amino, and lithium bis(trimethylsilyl)amino; the catalyst is potassium iodide or sodium iodide; and the molar ratio of the catalyst to the modified polyN-vinylcaprolactam is 0.3-1:1.
[0018] Further, the activation step of lignin sulfonate in step 2) is as follows: after mixing lignin sulfonate with an activation reagent, react at -20 to -5°C for 24 to 72 hours to obtain the product; the activation reagent includes 6 to 10% w / v sodium hydroxide solution and 8 to 16% w / v urea solution; each g of the lignin sulfonate corresponds to 15 to 35 mL of the activation reagent.
[0019] A thermosensitive lignin was prepared using the Williamson method described above for preparing LCST-controlled thermosensitive lignin.
[0020] An application of thermosensitive lignin is disclosed, wherein the thermosensitive lignin is used in the preparation of thermosensitive lignin-based hydrogels. The preparation method of the thermosensitive lignin-based hydrogels is as follows: the thermosensitive lignin is dissolved in water, an alkaline adjuster is added to adjust the pH to 8-12, ultrasonication is performed, polyethylene glycol diglycidyl ether is added and stirred, and the mixture is kept at a constant temperature of 25-45°C for 48-72 hours to obtain the hydrogel. The mass ratio of polyethylene glycol diglycidyl ether to the thermosensitive lignin is 0.625-0.83:1. The alkaline adjuster is one of sodium hydroxide, potassium hydroxide, and sodium bicarbonate, and the concentration of the alkaline adjuster is 10-20 wt%.
[0021] The beneficial effects of this invention are:
[0022] This invention uses azobisisobutyronitrile (AIBN) as an initiator to separate protons from thiol groups. When the temperature rises to the reaction temperature, highly reactive thiol radicals are generated. These highly reactive thiol radicals can effectively attack the olefinic bonds of N-vinylcaprolactam, generating carbon-centered radicals, and finally synthesizing modified polyN-vinylcaprolactam.
[0023] This invention utilizes a mixed solution of urea and sodium hydroxide to activate lignin sulfonate, thereby increasing the content of phenolic hydroxyl groups in lignin sulfonate. Simultaneously, it modifies N-vinylcaprolactam, enabling highly reactive thiol radicals to effectively attack the olefin bonds of N-vinylcaprolactam, generating carbon-centered radicals. Finally, the Williamson ether synthesis reaction is used to allow the halogens in the modified poly-N-vinylcaprolactam to combine with the phenolic hydroxyl groups in the activated lignin sulfonate to form ethers.
[0024] This application utilizes organic bases to create alkaline conditions for the synthesis of thermosensitive lignin, thereby increasing the activity of phenolic hydroxyl groups in lignin sulfonates.
[0025] This invention uses iodine-containing inorganic salts as catalysts. The iodine element in the iodide replaces the chlorine element in the modified poly-N-vinylcaprolactam during the reaction, thus promoting the synthesis reaction of thermosensitive lignin in the forward direction. Attached Figure Description
[0026] Figure 1 Digital photographs of the thermosensitive lignin in Example 1 at 25°C and 37°C;
[0027] Figure 2 The UV transmittance of the thermosensitive lignin aqueous solution in Example 2 at different temperatures;
[0028] Figure 3 The states of the thermosensitive lignin-based hydrogel prepared in Example 4 at different temperatures;
[0029] Figure 4 The viscosity of the thermosensitive lignin-based hydrogel prepared in Example 5 varies at different temperatures.
[0030] Figure 5 The equilibrium swelling ratio of the thermosensitive lignin-based hydrogel prepared in Example 6 at different temperatures is shown in the graph.
[0031] Figure 6 Digital photographs of the temperature-sensitive lignin in Comparative Example 1 at 25°C and 37°C. Detailed Implementation
[0032] The present invention will be further described below with reference to the embodiments and accompanying drawings.
[0033] Example 1
[0034] The Williamson method for preparing LCST-controlled thermosensitive lignin in this embodiment includes the following steps:
[0035] 1. Lignosulfonate activation treatment
[0036] Prepare a mixed solution of 8% w / v sodium hydroxide and 12% w / v urea. Mix sodium lignosulfonate with the mixed solution at a ratio of 1 / 25 (w / v). Stir and react at -10℃ for 24 h. Purify by dialysis for 5 days. Freeze dry to obtain activated sodium lignosulfonate.
[0037] 2. Modification of N-vinylcaprolactam (NVCL)
[0038] NVCL was recrystallized in n-hexane to remove impurities, yielding pure white NVCL crystals. A 250 mL three-necked flask was purged with nitrogen for 15 min to remove oxygen. Then, 0.304 mmol of azobisisobutyronitrile (AIB), 3.278 mmol of 3-chloro-1-propanethiol (3-chloro-1-propanethiol), 5.21 g of NVCL crystals, and 90 mL of dimethyl sulfoxide (DMSO) were added to the flask. After the AIB, 3-chloro-1-propanethiol, and NVCL crystals were completely dissolved, the mixture was reacted at 70 °C for 8 h in a sealed three-necked flask to obtain the reaction solution. The reaction solution was dialyzed against a 1000 kDa cellulose membrane for two days to remove impurities and unreacted AIB, 3-chloro-1-propanethiol, and NVCL crystals. The solution was then freeze-dried to obtain the modified poly(N-vinylcaprolactam).
[0039] 3. Preparation of thermosensitive lignin
[0040] Activated sodium lignin sulfonate was weighed and dissolved in anhydrous dimethyl sulfoxide. Modified poly(N-vinylcaprolactam) was added at 15 times the molar amount of phenolic hydroxyl groups in the activated sodium lignin sulfonate, along with sodium bis(trimethylsilyl)amino at 3 times the molar amount of phenolic hydroxyl groups in the activated sodium lignin sulfonate. Finally, potassium iodide was added as a catalyst at 30% molar amount of the modified poly(N-vinylcaprolactam). The reaction was carried out at 85°C for 8 hours to obtain a thermosensitive lignin solution. The thermosensitive lignin solution was dialyzed through a 1000 kDa cellulose membrane for 2 days and then freeze-dried to obtain thermosensitive lignin.
[0041] Example 2
[0042] The Williamson method for preparing LCST-controlled thermosensitive lignin in this embodiment includes the following steps:
[0043] 1. Activation treatment of lignin sulfonate
[0044] Prepare a mixed solution of 10% w / v sodium hydroxide and 8% w / v urea. Mix calcium lignosulfonate with the mixed solution at a ratio of 1 / 15 (w / v). Stir and react at -5℃ for 48 h. Purify by dialyzing for 5 days. Freeze dry to obtain activated calcium lignosulfonate.
[0045] 2. Modification of N-vinylcaprolactam
[0046] NVCL was recrystallized in n-hexane to remove impurities, yielding pure white NVCL crystals. A 250 mL three-necked flask was purged with nitrogen for 20 min to remove oxygen. Then, 0.304 mmol of azobisisobutyronitrile (AIB), 4.56 mmol of 1,3-dichloro-1-propanethiol, 2.5 g of NVCL crystals, and 83 mL of tetrahydrofuran were added to the flask. After the AIB, 1,3-dichloro-1-propanethiol, and NVCL crystals were completely dissolved, the mixture was reacted at 80 °C for 10 h in a sealed three-necked flask to obtain the reaction solution. The reaction solution was dialyzed against a 1000 kDa cellulose membrane for two days to remove impurities and unreacted AIB, 1,3-dichloro-1-propanethiol, and NVCL crystals. The solution was then freeze-dried to obtain the modified poly(N-vinylcaprolactam).
[0047] 3. Preparation of thermosensitive lignin
[0048] Activated calcium lignin sulfonate was weighed and dissolved in dimethylformamide. Modified poly(N-vinylcaprolactam) was added at 12 times the molar amount of phenolic hydroxyl groups in the activated calcium lignin sulfonate, along with potassium bis(trimethylsilyl)amino at 3 times the molar amount of phenolic hydroxyl groups in the activated calcium lignin sulfonate. Finally, sodium iodide was added as a catalyst at 50% molar amount of the modified poly(N-vinylcaprolactam). The reaction was carried out at 70°C for 10 hours to obtain a thermosensitive lignin solution. The thermosensitive lignin solution was dialyzed through a 1000 kDa cellulose membrane for 2 days and then freeze-dried to obtain thermosensitive lignin.
[0049] Example 3
[0050] 1. Lignosulfonate activation treatment
[0051] A mixed solution of 6% w / v sodium hydroxide and 16% w / v urea was prepared. Magnesium lignosulfonate was mixed with the mixed solution at a ratio of 1 / 35 (w / v). The mixture was stirred at -15℃ for 72 h, purified by dialysis for 5 days, and then freeze-dried to obtain activated magnesium lignosulfonate.
[0052] 2. Modification of N-vinylcaprolactam
[0053] NVCL was recrystallized in n-hexane to remove impurities, yielding pure white NVCL crystals. A 250 mL three-necked flask was purged with nitrogen for 30 min to remove oxygen. Then, 0.304 mmol of azobisisobutyronitrile (AIB), 3.59 mmol of 2-(2-chloroethylthioalkyl)ethanethiol, 1.25 g of NVCL crystals, and 25 mL of chloroform were added to the flask. After the AIB, 2-(2-chloroethylthioalkyl)ethanethiol, and NVCL crystals were completely dissolved, the mixture was reacted at 95 °C for 6 h in a sealed three-necked flask to obtain the reaction solution. The reaction solution was dialyzed against a 1000 kDa cellulose membrane for two days to remove impurities and unreacted AIB, 2-(2-chloroethylthioalkyl)ethanethiol, and NVCL crystals. The solution was then freeze-dried to obtain the modified poly(N-vinylcaprolactam).
[0054] 3. Preparation of thermosensitive lignin
[0055] Activated magnesium lignin sulfonate was weighed and dissolved in tetrahydrofuran. Modified poly(N-vinylcaprolactam) was added at a molar ratio of 13.5 times the molar ratio of phenolic hydroxyl groups in the activated magnesium lignin sulfonate. Simultaneously, bis(trimethylsilyl)aminolithium was added at a molar ratio of 3 times the molar ratio of phenolic hydroxyl groups in the activated magnesium lignin sulfonate. Finally, potassium iodide was added at a molar ratio of 100% of the modified poly(N-vinylcaprolactam) as a catalyst. The reaction was carried out at 95°C for 6 hours to obtain a thermosensitive lignin solution. The thermosensitive lignin solution was dialyzed through a 1000 kDa cellulose membrane for 2 days and then freeze-dried to obtain thermosensitive lignin.
[0056] Example 4
[0057] The thermosensitive lignin prepared in Example 1 was dissolved in 4.25 mL of water, and the pH was adjusted to 12 by adding 20 wt% sodium hydroxide solution. The mixture was stirred and vortexed for 10 min, then sonicated for 10 min. Polyethylene glycol diglycidyl ether (PEGDGE) was then added, and the mixture was stirred and vortexed for 20 min. The mixture was then placed in a constant temperature incubator at 30 °C for 48 h to obtain a thermosensitive lignin-based hydrogel. In Example 4, the mass ratio of polyethylene glycol diglycidyl ether to the thermosensitive lignin of Example 1 was 0.625:1, and the mass of thermosensitive lignin added in Example 1 was 0.75 g.
[0058] Example 5
[0059] The thermosensitive lignin prepared in Example 1 was dissolved in 3.58 mL of water, and the pH was adjusted to 8 by adding 10 wt% potassium hydroxide solution. The mixture was stirred and vortexed for 15 min, then sonicated for 20 min. Polyethylene glycol diglycidyl ether was then added, and the mixture was stirred and vortexed for 15 min. The mixture was then placed in a constant temperature incubator at 25 °C for 72 h to obtain a thermosensitive lignin-based hydrogel. In Example 5, the mass ratio of PEGDGE to the thermosensitive lignin in Example 1 was 0.83:1, and the mass of thermosensitive lignin added in Example 1 was 1.42 g.
[0060] Example 6
[0061] The thermosensitive lignin prepared in Example 3 was dissolved in 3.85 mL of water, and the pH was adjusted to 10 by adding 15 wt% sodium bicarbonate solution. The mixture was stirred and vortexed for 15 min, then sonicated for 20 min. Polyethylene glycol diglycidyl ether was then added, and the mixture was stirred and vortexed for 15 min. The mixture was then placed in a 45°C incubator for 60 h to obtain a thermosensitive lignin-based hydrogel. In Example 6, the mass ratio of PEGDGE to the thermosensitive lignin in Example 3 was 0.75:1, and the mass of the thermosensitive lignin added in Example 3 was 1.15 g.
[0062] Comparative Example 1
[0063] 1. Sodium lignosulfonate was not activated.
[0064] Sodium lignosulfonate was purified by dialysis for 5 days and then freeze-dried to obtain purified sodium lignosulfonate.
[0065] 2. Modification of N-vinylcaprolactam (NVCL)
[0066] NVCL was recrystallized in n-hexane to remove impurities, yielding pure white NVCL crystals. A 250 mL three-necked flask was purged with nitrogen for 15 min to remove oxygen. Then, 0.304 mmol of azobisisobutyronitrile (AIB), 3.278 mmol of 3-chloro-1-propanethiol (3-chloro-1-propanethiol), 5.21 g of NVCL crystals, and 90 mL of dimethyl sulfoxide (DMSO) were added to the flask. After the AIB, 3-chloro-1-propanethiol, and NVCL crystals were completely dissolved, the mixture was reacted at 70 °C for 8 h in a sealed three-necked flask to obtain the reaction solution. The reaction solution was dialyzed against a 1000 kDa cellulose membrane for two days to remove impurities and unreacted AIB, 3-chloro-1-propanethiol, and NVCL crystals. The solution was then freeze-dried to obtain the modified poly(N-vinylcaprolactam).
[0067] 3. Preparation of thermosensitive lignin
[0068] Purified sodium lignin sulfonate was weighed and dissolved in anhydrous dimethyl sulfoxide. Modified poly(N-vinylcaprolactam) was added at 15 times the molar amount of phenolic hydroxyl groups in the purified sodium lignin sulfonate, along with sodium bis(trimethylsilyl)amino at 3 times the molar amount of phenolic hydroxyl groups in the purified sodium lignin sulfonate. Finally, potassium iodide was added as a catalyst at 30% molar amount of the modified poly(N-vinylcaprolactam). The reaction was carried out at 85°C for 8 hours to obtain a thermosensitive lignin solution. The thermosensitive lignin solution was dialyzed through a 1000 kDa cellulose membrane for 2 days and then freeze-dried to obtain thermosensitive lignin.
[0069] Comparative Example 2
[0070] 1. Activation of lignin sulfonate
[0071] Prepare a mixed solution of 8% w / v sodium hydroxide and 10% w / v urea. Mix sodium lignosulfonate with the mixed solution at a ratio of 1 / 25 (w / v). Stir and react at -10℃ for 24 h. Purify by dialysis for 5 days. Freeze dry to obtain activated sodium lignosulfonate.
[0072] 2. Modification of N-vinylcaprolactam (NVCL)
[0073] NVCL was recrystallized in n-hexane to remove impurities, yielding pure white NVCL crystals. A 250 mL three-necked flask was purged with nitrogen for 15 min to remove oxygen. Then, 0.304 mmol of azobisisobutyronitrile (AIB), 3.278 mmol of 3-chloro-1-propanethiol (3-chloro-1-propanethiol), 5.21 g of NVCL crystals, and 90 mL of dimethyl sulfoxide (DMSO) were added to the flask. After the AIB, 3-chloro-1-propanethiol, and NVCL crystals were completely dissolved, the mixture was reacted at 70 °C for 8 h in a sealed three-necked flask to obtain the reaction solution. The reaction solution was dialyzed against a 1000 kDa cellulose membrane for two days to remove impurities and unreacted AIB, 3-chloro-1-propanethiol, and NVCL crystals. The solution was then freeze-dried to obtain the modified poly(N-vinylcaprolactam).
[0074] 3. Preparation of thermosensitive lignin
[0075] Sodium lignin sulfonate was weighed and dissolved in anhydrous dimethyl sulfoxide. Modified poly(N-vinylcaprolactam) was added at a rate of 9 times the molar amount of phenolic hydroxyl groups in the activated sodium lignin sulfonate, along with sodium bis(trimethylsilyl)amino at a rate of 3 times the molar amount of phenolic hydroxyl groups in the activated sodium lignin sulfonate. Finally, potassium iodide was added as a catalyst at a rate of 30% of the molar amount of the modified poly(N-vinylcaprolactam). The reaction was carried out at 85°C for 8 hours to obtain a thermosensitive lignin solution. The thermosensitive lignin solution was dialyzed through a 1000 kDa cellulose membrane for 2 days and then freeze-dried to obtain thermosensitive lignin.
[0076] The temperature-responsive lignins prepared by the methods in Examples 1-3 above all exhibit temperature responsiveness. Figure 1 It can be seen that the thermosensitive lignin prepared in Example 1 is soluble in water at temperatures below 33°C, but when the temperature rises above 33°C, the water solubility of the thermosensitive lignin deteriorates and the solution becomes turbid.
[0077] The prepared thermosensitive lignin possesses a minimum phase transition temperature. Below this temperature, it exhibits hydrophilicity, high solubility in water, and high UV transmittance. Above this temperature, it becomes hydrophobic, exhibiting low solubility in water and low UV transmittance. The UV transmittance of the thermosensitive lignin prepared in Example 2 at different temperatures is shown below. Figure 2 As shown, the lowest phase transition temperature of the thermosensitive lignin prepared in Example 2 is 39.1°C.
[0078] The thermosensitive lignin-based hydrogels prepared by the methods in Examples 4-6 above all exhibit temperature responsiveness. Figure 3 As can be seen, the thermosensitive lignin-based hydrogel of Example 4 is in a fluid state at room temperature. When the temperature rises to 37°C, the thermosensitive lignin-based hydrogel becomes hydrophobic, the internal water is squeezed out, and phase separation occurs, resulting in a gel state.
[0079] Example 5: Preparation of thermosensitive lignin-based hydrogels and their viscosity changes at different temperatures. Figure 4 As shown, when the temperature rises to 33°C, the viscosity of the hydrogel increases sharply and then drops sharply, indicating that the thermosensitive lignin-based hydrogel prepared in Example 5 exhibits a significant hydrophilic state below the LCST temperature. Subsequently, the thermosensitive lignin-based hydrogel changes from a sol state to a gel state, and the viscosity of the gel increases.
[0080] The swelling ratio of the thermosensitive lignin-based hydrogel prepared in Example 6 at different temperatures is as follows: Figure 5 As shown, the swelling rate of the thermosensitive lignin-based hydrogel gradually decreases with increasing temperature.
[0081] The sodium lignin sulfonate selected in Comparative Example 1 was not activated, and the resulting thermosensitive lignin did not exhibit responsiveness. Figure 6 It can be seen that the sample prepared by grafting modification of unactivated sodium lignosulfonate is in a dissolved state below 33℃, and does not become turbid after the temperature is increased.
[0082] The modified lignin prepared in Comparative Example 2 did not exhibit thermosensitivity. Elemental analysis of the thermosensitive lignin prepared in Comparative Example 2 showed a nitrogen content of 6.43%. The low proportion of modified poly-N-vinylcaprolactam and the small amount of grafted thermosensitive polymer resulted in the lack of thermosensitivity in the prepared lignin.
Claims
1. A method for preparing LCST-controlled thermosensitive lignin using the Williamson process, characterized in that, Includes the following steps: Step 1): Activation of lignin sulfonate: Activate lignin sulfonate using an activation reagent, wherein the activation reagent is a mixed solution of urea and sodium hydroxide; Step 2): Modification of N-vinylcaprolactam: The initiator, N-vinylcaprolactam, and modifier are dissolved in solvent one and then heated to obtain the modified poly-N-vinylcaprolactam; the modifier is one of 3-chloro-1-propanethiol, 1,3-dichloro-1-propanethiol, and 2-(2-chloroethylthioalkyl)ethanethiol; Step 3): Preparation of thermosensitive lignin: Dissolve the activated lignin sulfonate in solvent two, then add the modified polyN-vinylcaprolactam, pH adjuster, and catalyst from step 2), and heat to obtain the final product; the molar ratio of phenolic hydroxyl groups, pH adjuster, and halogens in the activated lignin sulfonate is 1:3:12-15; the molar ratio of the catalyst to the modified polyN-vinylcaprolactam is 0.3-1:
1.
2. The method for preparing LCST-controlled thermosensitive lignin according to claim 1, characterized in that, Step 2) The modification of N-vinylcaprolactam is carried out by adding the initiator, N-vinylcaprolactam, modifier and solvent into a reaction vessel. After the initiator, N-vinylcaprolactam and modifier are dissolved, the vessel is sealed and reacted at 70-95 °C for 6-10 h to obtain a reaction solution. The reaction solution is then purified to obtain the final product.
3. The method for preparing LCST-controlled thermosensitive lignin according to claim 1 or 2, characterized in that, The molar ratio of N-vinylcaprolactam, modifier and initiator is 30-122:10.8-15:1; the mass of N-vinylcaprolactam added to each mL of solvent one is 0.03-0.08 g; solvent one is one of dimethyl sulfoxide, tetrahydrofuran and chloroform, and the initiator is azobisisobutyronitrile.
4. The method for preparing LCST-controlled thermosensitive lignin according to claim 2, characterized in that, The N-vinylcaprolactam is recrystallized in hexane, and the recrystallized N-vinylcaprolactam is then modified. The purification step of the reaction solution is to dialyze the reaction solution through a cellulose membrane and then freeze-dry it.
5. The method for preparing LCST-controlled thermosensitive lignin according to claim 2, characterized in that, After nitrogen gas is introduced into the reaction vessel to remove oxygen, the initiator, N-vinylcaprolactam, 3-chloro-1-propanethiol, and solvent are added to the reaction vessel; the nitrogen gas is introduced for 15 to 30 minutes.
6. The method for preparing LCST-controlled thermosensitive lignin according to claim 1, characterized in that, Step 3) describes the preparation method of thermosensitive lignin as follows: after dissolving the activated lignin sulfonate in solvent two, the modified poly-N-vinylcaprolactam, pH adjuster, and catalyst are added. After reacting at 70-95 °C for 6-10 h, a thermosensitive lignin solution is obtained. The thermosensitive lignin solution is dialyzed through a cellulose membrane and then freeze-dried to obtain the final product. The lignin sulfonate is one of sodium lignin sulfonate, calcium lignin sulfonate, and magnesium lignin sulfonate.
7. The method for preparing LCST-controlled thermosensitive lignin according to claim 6, characterized in that, The solvent is one of anhydrous dimethyl sulfoxide, dimethylformamide, and tetrahydrofuran; the pH adjuster is one of sodium bis(trimethylsilyl)amino, potassium bis(trimethylsilyl)amino, and lithium bis(trimethylsilyl)amino; and the catalyst is potassium iodide or sodium iodide.
8. The method for preparing LCST-controlled thermosensitive lignin according to claim 6, characterized in that, Step 1) The activation step of lignin sulfonate is as follows: after mixing lignin sulfonate with an activation reagent, react at -20 to -5 °C for 24 to 72 h to obtain the lignin sulfonate; the activation reagent includes 6 to 10% w / v sodium hydroxide solution and 8 to 16% w / v urea solution; each g of lignin sulfonate corresponds to 15 to 35 mL of the activation reagent.
9. A thermosensitive lignin, characterized in that, The LCST-controlled thermosensitive lignin was prepared using the Williamson method described in claim 1.
10. An application of the thermosensitive lignin as described in claim 9, characterized in that, The thermosensitive lignin is used in the preparation of thermosensitive lignin-based hydrogels. The preparation method of the thermosensitive lignin-based hydrogels is as follows: the thermosensitive lignin is dissolved in water, an alkaline adjuster is added to adjust the pH to 8-12, ultrasonication is performed, polyethylene glycol diglycidyl ether is added and stirred, and the mixture is kept at a constant temperature of 25-45 °C for 48-72 h to obtain the hydrogel. The mass ratio of polyethylene glycol diglycidyl ether to the thermosensitive lignin is 0.625-0.83:
1. The alkaline adjuster is one of sodium hydroxide, potassium hydroxide, and sodium bicarbonate, and the concentration of the alkaline adjuster is 10-20 wt%.