Lignin-based polyurethane elastomer as well as preparation method and application thereof

Abstract

The invention relates to the field of lignin recycling, in particular to a lignin-based polyurethane elastomer as well as a preparation method and application thereof. The lignin-based polyurethane elastomer is prepared from the following components in parts by weight: 32 to 40 parts of long-chain polyol, 10 to 17 parts of isocyanate, 0.1 to 0.3 part of a catalyst, 2 to 3 parts of a hydrazide chain extender, 4 to 12 parts of lignin and an organic solvent. The phenolic hydroxyl group content of the lignin is greater than or equal to 5.00 mmol / g. The obtained polyurethane elastomer is good in mechanical property, the tensile strength reaches 87.82 MPa, and the polyurethane elastomer further has good aging resistance and photothermal conversion performance. According to the invention, lignin is adopted to replace petroleum-based polyol, so that the demand and dependence of polyurethane on petrochemical resources are reduced, and high-valued utilization of lignin is realized.

Description

Technical Field

[0001] This invention relates to the field of lignin recycling and reuse, and more specifically, to a lignin-based polyurethane elastomer, its preparation method, and its application. Background Technology

[0002] Polyurethane elastomers are important polymer materials widely used in key sectors of the national economy, such as high-performance tires, seals, and shock-absorbing components, due to their excellent mechanical properties, wear resistance, and adjustability. However, the traditional polyurethane industry heavily relies on polyether or polyester polyols derived from non-renewable petroleum resources, facing challenges to resource sustainability. Therefore, developing and utilizing renewable biomass resources to partially or completely replace petroleum-based raw materials has become a cutting-edge research direction and an inevitable development trend in the polyurethane field.

[0003] Lignin is the most abundant renewable aromatic polymer in nature. Due to its hydroxyl structure, lignin is considered a potential source of polyols. However, due to differences in pulping processes and raw material sources, lignin from different sources exhibits significant variations in molecular structure, molecular weight distribution, and hydroxyl composition. Nevertheless, existing research attempting to introduce lignin into polyurethane systems to reduce the use of petroleum-based raw materials generally faces problems such as poor compatibility and decreased material mechanical properties, thus limiting its practical application in polyurethane elastomers.

[0004] The prior art 201811189140.2 discloses a recyclable thermosetting lignin-based polyurethane elastomer and its preparation method, which uses depolymerized lignin to prepare lignin-based polyurethane elastomer. However, the mechanical properties of the prepared lignin-based polyurethane elastomer are poor, with a tensile strength of 22.3 MPa.

[0005] The prior art (202210761906.X) discloses a reprocessable lignin polyurethane elastomer and a catalyst-free preparation method, which has good reprocessing performance, but its tensile strength is only 12.5 MPa and its mechanical properties are poor. Summary of the Invention

[0006] To overcome the shortcomings of the prior art described above, the present invention provides a lignin-based polyurethane elastomer. The present invention also provides a method for preparing a lignin-based polyurethane elastomer.

[0007] The present invention also provides an application of lignin-based polyurethane elastomer.

[0008] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows: A lignin-based polyurethane elastomer is prepared by comprising a long-chain polyol, an isocyanate, a catalyst, an acyl hydrazine chain extender, lignin, and an organic solvent, wherein the long-chain polyol comprises 32-40 parts by weight, the isocyanate comprises 10-17 parts by weight, the catalyst comprises 0.1-0.3 parts by weight, the acyl hydrazine chain extender comprises 2-3 parts by weight, and the lignin comprises 4-12 parts by weight. The phenolic hydroxyl content of the lignin is greater than or equal to 5.0 mmol / g.

[0009] Preferably, the phenolic hydroxyl content of the lignin is greater than or equal to 5.4 mmol / g.

[0010] Preferably, the lignin comprises phenolic sulfate lignin and sulfate lignin.

[0011] Preferably, the phenolic sulfate lignin is prepared by phenolation reaction of catechol and sulfate lignin.

[0012] Furthermore, the preparation method of the phenolic sulfate lignin is as follows: after mixing and reacting sulfate lignin, catechol and concentrated sulfuric acid, the mixture is separated, washed and dried to obtain the lignin.

[0013] Preferably, the phenolic hydroxyl content of the lignin is 5.0~10.0 mmol / g; More preferably, the phenolic hydroxyl content of the lignin is 5.0~9.5 mmol / g; More preferably, the phenolic hydroxyl content of the lignin is 8.7~9.3 mmol / g; More preferably, the phenolic hydroxyl content of the lignin is 8.9~9.1 mmol / g; Preferably, the weight-average molecular weight (Mw) of the lignin is 2000~4100 g / mol; Preferably, the weight-average molecular weight (Mw) of the lignin is 2000~2200 g / mol; Preferably, the PDI of the lignin is 2.0 to 2.9; Preferably, the PDI of the lignin is 2.0 to 2.2; Preferably, the sulfate lignin is mainly obtained from wood fiber raw materials through sulfate pulping.

[0014] Preferably, the wood fiber raw material includes coniferous wood, broadleaf wood, and grasses.

[0015] Preferably, the wood fiber raw material includes coniferous wood.

[0016] Preferably, the wood fiber raw material is pine wood.

[0017] Preferably, the lignin-based polyurethane elastomer is prepared from long-chain polyol, isocyanate, catalyst, hydrazine chain extender, lignin and organic solvent, wherein the long-chain polyol is 32-34 parts by weight, the isocyanate is 11-13 parts by weight, the catalyst is 0.1-0.3 parts by weight, the hydrazine chain extender is 2-3 parts by weight and the lignin is 6-8 parts by weight.

[0018] Furthermore, the preparation method of the lignin-based polyurethane elastomer includes the following steps: (1) Mix long-chain polyol, isocyanate, catalyst and organic solvent evenly, react at 70 ℃~90 ℃ for 2~4 h, add hydrazide chain extender to react and obtain solution A; (2) Dissolve lignin in an organic solvent, add it to solution A obtained in step (1) to react, cool to room temperature, and solidify to obtain lignin-based polyurethane elastomer.

[0019] Preferably, in step (1), the reaction temperature for adding the hydrazide chain extender is 70 ℃~90 ℃ and the reaction time is 20~60 min.

[0020] Preferably, in step (2), the reaction temperature is 70 ℃~90 ℃ and the time is 10~20 h.

[0021] Preferably, in step (2), the curing temperature is 80 ℃~100 ℃ and the time is 18~24 h.

[0022] Preferably, the long-chain polyol includes at least one of polyethylene glycol, polytetrahydrofuran, polycaprolactone diol, and polycarbonate diol; Preferably, the long-chain polyol is polytetrahydrofuran; Preferably, the number-average molecular weight (Mn) of the long-chain polyol is 1000-4000, and more preferably, it is a polytetrahydrofuran with a number-average molecular weight (Mn) of 1800-2200. Preferably, the isocyanate includes at least one of toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, and hexamethylene diisocyanate; Preferably, the isocyanate includes isophorone diisocyanate; Preferably, the catalyst comprises at least one of dibutyltin dilaurate, stannous octanoate, dioctyltin, and dibutyltin diacetate; Preferably, the catalyst comprises dibutyltin dilaurate; Preferably, the organic solvent includes at least one selected from N,N-dimethylformamide, N,N-dimethylacetamide, tetrahydrofuran, and acetone; Preferably, the organic solvent includes N,N-dimethylacetamide; Preferably, the acylhydrazine chain extender includes at least one of oxalohydrazide, succinylhydrazide, adipylhydrazide, and sebadecylhydrazide; Preferably, the hydrazide chain extender comprises oxalohydrazide; Preferably, in the preparation method of the lignin-based polyurethane elastomer, the amount of NCO: the amount of total hydroxyl (total OH) substances, i.e., the NCO:(total OH) substance ratio is 0.6~1.2:1.

[0023] Preferably, in the preparation method of the lignin-based polyurethane elastomer, the amount of NCO: the amount of total hydroxyl (total OH) substances, i.e., the NCO:(total OH) substance ratio is 0.6~0.8:1.

[0024] Application of a lignin-based polyurethane elastomer in the field of photothermal conversion.

[0025] In this invention, lignin with a phenolic hydroxyl content of not less than 5 mmol / g is used to partially replace petroleum-based polyols in polyurethane elastomers, which can improve the mechanical properties of polyurethane elastomers and reduce the amount of petroleum-based polyols used.

[0026] In this invention, compared with polyurethane elastomers prepared from unphenolized sulfate lignin, phenolized lignin has a lower molecular weight, a smaller degree of dispersion, and a higher content of phenolic hydroxyl groups.

[0027] In this invention, lignin, which has a more uniform structure, lower molecular weight, less dispersion, and more phenolic hydroxyl groups, is used to partially replace petroleum-based polyols. At the same time, hydrazides with multiple hydrogen bond donors and acceptors are introduced as chain extenders, which helps to improve the mechanical properties of polyurethane elastomers, thereby significantly improving the mechanical properties of lignin-based polyurethane elastomers.

[0028] This invention improves the lignin substitution rate in lignin-based polyurethane elastomers, and in particular improves the mechanical properties of lignin-based polyurethane elastomers containing chain extenders.

[0029] Compared with the prior art, the beneficial effects of the technical solution of the present invention are: This invention uses lignin with a phenolic hydroxyl content of not less than 5 mmol / g for the preparation of polyurethane elastomers. The resulting polyurethane elastomers have good mechanical properties, with a tensile strength of up to 87.82 MPa, and exhibit good anti-aging and photothermal conversion properties.

[0030] The technical solution of this invention is used in the preparation of polyurethane elastomers. Lignin can be used to partially replace petroleum-based polyols in polyurethane elastomers, which reduces the demand for and dependence on petrochemical resources of polyurethane and realizes the high-value utilization of lignin. Attached Figure Description

[0031] Figure 1 For KL and CPKL 31 P nuclear magnetic resonance spectroscopy data image Figure 2 Infrared spectral data of the elastomers prepared in Examples 1-4, Example 12, and Comparative Example 1. Figure 3 Stress-strain curve data of the elastomers prepared in Examples 1-4 and Example 12. Figure 4 Stress-strain curve data of the elastomer prepared for Comparative Example 1 Figure 5 Photothermal effect data of the elastomers prepared in Examples 1-4, Example 12, and Comparative Example 1. Figure 6 The graph shows the changes in tensile properties of the elastomers prepared in Examples 3 and 12 after aging at 100 °C for 7 days. Detailed Implementation

[0032] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field.

[0033] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0034] Polytetrahydrofuran (PTMG, Mn=2000), isophorone diisocyanate (IPDI, 99%), oxadiazine (OD, 97%), N,N-dimethylacetamide (DMAc, 99.8%), catechol (99.5%), dibutyltin dilaurate (DBTDL, 95%), and concentrated sulfuric acid (98%) were all purchased from Macklin Reagents Ltd.; 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxocyclopentane (TMDP) was purchased from Sigma.

[0035] The present invention will be further described below: A lignin-based polyurethane elastomer is prepared by comprising a long-chain polyol, an isocyanate, a catalyst, an acyl hydrazine chain extender, lignin, and an organic solvent, wherein the long-chain polyol comprises 32-40 parts by weight, the isocyanate comprises 10-17 parts by weight, the catalyst comprises 0.1-0.3 parts by weight, the acyl hydrazine chain extender comprises 2-3 parts by weight, and the lignin comprises 4-12 parts by weight. The phenolic hydroxyl content of the lignin is greater than or equal to 5.00 mmol / g.

[0036] In a preferred embodiment, the mass ratio of lignin to hydrazide chain extender is (1.6~5.0):1.

[0037] In a preferred embodiment, the lignin-based polyurethane elastomer is prepared from a long-chain polyol, an isocyanate, a catalyst, an acyl hydrazine chain extender, lignin, and an organic solvent, wherein the long-chain polyol comprises 32-34 parts by weight, the isocyanate comprises 11-13 parts by weight, the catalyst comprises 0.1-0.3 parts by weight, the acyl hydrazine chain extender comprises 2-3 parts by weight, and the lignin comprises 6-8 parts by weight.

[0038] Furthermore, the preparation method of the lignin-based polyurethane elastomer includes the following steps: (1) Mix long-chain polyol, isocyanate, catalyst and organic solvent evenly, react at 70 ℃~90 ℃ for 2~4 h, add hydrazide chain extender to react and obtain solution A; (2) Dissolve lignin in an organic solvent, add it to solution A obtained in step (1) to react, cool to room temperature, and solidify to obtain lignin-based polyurethane elastomer.

[0039] In a preferred embodiment, in step (1), the reaction temperature of the added hydrazide chain extender is 70 ℃~90 ℃ and the reaction time is 20~60 min.

[0040] In a preferred embodiment, in step (2), the reaction temperature is 70 ℃~90 ℃ and the time is 10~20 h.

[0041] In a preferred embodiment, in step (2), the curing temperature is 80 ℃~100 ℃ and the time is 18~24h.

[0042] In one preferred embodiment, the long-chain polyol includes at least one of polyethylene glycol, polytetrahydrofuran, polycaprolactone diol, and polycarbonate diol; In one preferred embodiment, the long-chain polyol is polytetrahydrofuran; In one preferred embodiment, the number-average molecular weight (Mn) of the long-chain polyol is 1000-4000, and more preferably, it is a polytetrahydrofuran with a number-average molecular weight (Mn) of 1800-2200. In a preferred embodiment, the isocyanate includes at least one of toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, and hexamethylene diisocyanate; In one preferred embodiment, the isocyanate includes isophorone diisocyanate; In a preferred embodiment, the catalyst comprises at least one of dibutyltin dilaurate, stannous octanoate, dioctyltin, and dibutyltin diacetate; In one preferred embodiment, the catalyst comprises dibutyltin dilaurate; In a preferred embodiment, the organic solvent includes at least one selected from N,N-dimethylformamide, N,N-dimethylacetamide, tetrahydrofuran, and acetone; In one preferred embodiment, the organic solvent includes N,N-dimethylacetamide; In a preferred embodiment, the amount of the organic solvent used is 50 to 200 parts by weight.

[0043] In a preferred embodiment, the acylhydrazine chain extender includes at least one of oxalohydrazide, succinylhydrazide, adipylhydrazide, and sebacatehydrazide; In a preferred embodiment, the hydrazide chain extender comprises oxalohydrazide; In a preferred embodiment, in the preparation method of the lignin-based polyurethane elastomer, the amount of NCO:total hydroxyl (total OH) is in the ratio of NCO:(total OH) = 0.6~1.2:1.

[0044] In a preferred embodiment, in the preparation method of the lignin-based polyurethane elastomer, the amount of NCO:total hydroxyl (total OH) is in the ratio of NCO:(total OH) = 0.6~0.8:1.

[0045] In one preferred embodiment, the lignin comprises phenolic sulfate lignin and sulfate lignin.

[0046] In a preferred embodiment, the phenolic hydroxyl content of the lignin is 5.0~10.0 mmol / g; In a preferred embodiment, the phenolic hydroxyl content of the lignin is 5.0~9.5 mmol / g; In a preferred embodiment, the phenolic hydroxyl content of the lignin is 8.9~9.2 mmol / g; In one preferred embodiment, the weight-average molecular weight (Mw) of the lignin is 2000~4100 g / mol; In a preferred embodiment, the weight-average molecular weight (Mw) of the lignin is 2000~2200 g / mol; In a preferred embodiment, the PDI of the lignin is 2.0 to 2.9; In a preferred embodiment, the PDI of the lignin is 2.0 to 2.2; In one preferred embodiment, the sulfate lignin is mainly obtained from wood fiber raw materials through sulfate pulping.

[0047] In one preferred embodiment, the wood fiber raw material includes coniferous wood, broadleaf wood, and grasses.

[0048] In one preferred embodiment, the wood fiber raw material includes coniferous wood.

[0049] In one preferred embodiment, the wood fiber raw material is pine wood.

[0050] Pine sulfate lignin (KL) can be supplied by Huatai Co., Ltd. (Shandong). The following is one of the sulfate pulping methods for preparing pine sulfate lignin: Pulping of pine wood chips using the sulfate process is carried out in a rotary digester under the following conditions: active alkali content 20% (based on NaOH), liquor ratio (L / kg) 6, degree of sulfidation 30%, temperature increased to 160℃ at a rate of 5℃ / min, held for 60 min, then increased to 170℃ at a rate of 0.4℃ / min, and held at this temperature for another 50 min. Black liquor is collected to remove solid impurities. A 1 mol / L hydrochloric acid solution is added under magnetic stirring until pH=3. The mixture is left to stand in a 4℃ refrigerator for 24 h, centrifuged at 6000 rpm to obtain the precipitate. The precipitate is washed with deionized water until neutral, dried, and pine sulfate lignin is obtained.

[0051] In one preferred embodiment, the phenolic sulfate lignin is prepared by a phenolic reaction of catechol and sulfate lignin.

[0052] As a preferred embodiment, the preparation method of the phenolic sulfate lignin is as follows: after mixing and reacting sulfate lignin, catechol and concentrated sulfuric acid, the mixture is separated, washed and dried to obtain the lignin.

[0053] Example 1 Preparation of phenolic sulfate lignin (CPKL): 10 g of catechol was added to a polytetrafluoroethylene liner and stirred at 120 °C until melted. 5 g of pine sulfate lignin (KL) was added and stirred evenly, wherein the mass ratio of pine sulfate lignin to catechol was 1:2. Then, concentrated sulfuric acid (98% by mass) was added, the mass of which was 5% of the mass of pine sulfate lignin. The reaction was carried out at 120 °C for 3 h. After cooling to room temperature, 200 mL of 1 mol / L NaOH aqueous solution was added to dissolve the reaction product. The pH was then adjusted to 2.0 with 2 mol / L HCl. The product was collected by centrifugation (9000 rpm for 10 minutes), and washed with deionized water until neutral. After drying, phenolic sulfate lignin (CPKL) was obtained.

[0054] A method for preparing lignin-based polyurethane elastomers includes the following steps: (1) Remove moisture by rotary evaporation of polytetrahydrofuran (Mn=2000) at 80 °C for 2 h; weigh 3.6 g of polytetrahydrofuran, 1.02 g of isophorone diisocyanate, 0.024 g of dibutyltin dilaurate and 15 g of N,N-dimethylacetamide into a 100 mL three-necked flask and mix them evenly. After reacting at 70 °C for 3 h, add 0.24 g of oxalohydrazide and continue the reaction for 30 min to obtain solution A; (2) Dissolve 0.4 g of CPKL in 5 g of N,N-dimethylacetamide and add it to solution A obtained in step (1). React at 70°C for 15 h. Cool to room temperature, drop the resulting viscous product into a polytetrafluoroethylene mold, and heat in an 80°C drying oven for 24 h to cure, thereby obtaining lignin-based polyurethane elastomer.

[0055] In this embodiment, the sum of the amount of isocyanate (NCO) in isophorone diisocyanate and the amount of hydroxyl (OH) in polytetrahydrofuran and CPKL is 0.7, that is, the ratio of the amount of NCO to the amount of total hydroxyl (total OH) is 0.7:1.

[0056] Examples 2 to 9 Examples 2 to 9 are similar to Example 1, except that the amount of raw materials used in preparing the lignin-based polyurethane elastomer is different, as detailed in Table 1.

[0057] Example 10 Example 10 is similar to Example 1, except that: (1) Polytetrahydrofuran (Mn=2000) was dried by rotary evaporation at 80 °C for 2 h to remove moisture; 3.4 g of polytetrahydrofuran, 1.25 g of isophorone diisocyanate, 0.024 g of dibutyltin dilaurate and 15 g of N,N-dimethylacetamide were weighed and mixed evenly in a 100 mL three-necked flask, reacted at 90 °C for 2 h, and then 0.24 g of oxalohydrazide was added and the reaction was continued for 60 min to obtain solution A; (2) Dissolve 0.6 g of CPKL in 5 g of N,N-dimethylacetamide and add it to solution A obtained in step (1). React at 90°C for 10 h. Cool to room temperature, drop the resulting viscous product into a polytetrafluoroethylene mold, and heat in a 70°C drying oven for 18 h to cure, thereby obtaining lignin-based polyurethane elastomer.

[0058] The ratio of NCO to total hydroxyl (total OH) is 0.8:1.

[0059] Example 11 Example 11 is similar to Example 1, except that: (1) Polytetrahydrofuran (Mn=2000) was dried by rotary evaporation at 80°C for 2 h to remove moisture; 3.4 g of polytetrahydrofuran, 1.36 g of isophorone diisocyanate, 0.024 g of dibutyltin dilaurate and 15 g of N,N-dimethylacetamide were weighed and mixed evenly in a 100 mL three-necked flask, reacted at 90°C for 4 h, and then 0.24 g of oxalohydrazide was added and the reaction was continued for 20 min to obtain solution A; (2) Dissolve 0.6 g of CPKL in 5 g of N,N-dimethylacetamide and add it to solution A obtained in step (1). React at 90°C for 20 h. Cool to room temperature, drop the resulting viscous product into a polytetrafluoroethylene mold, and heat in a 100°C drying oven for 20 h to cure, thereby obtaining lignin-based polyurethane elastomer.

[0060] The ratio of NCO to total hydroxyl (total OH) is 0.9:1.

[0061] Example 12 Example 12 is similar to Example 1, except that KL is used instead of CPKL. The specific amounts of raw materials used in the preparation of lignin-based polyurethane elastomers are shown in Table 1.

[0062] Comparative Example 1 Comparative Example 1 is similar to Example 1, except that CPKL is not added and the amount of raw materials used in the preparation of polyurethane elastomer is different, as detailed in Table 1.

[0063] Table 1. List of Raw Materials for the Preparation of Lignin-Based Polyurethane Elastomers

[0064] Analysis and testing: Tensile test conditions: The heat-dried elastomer was cut into standard strips with a length of 40 mm, a width of 8 mm, and a thickness of 0.2 mm. The tensile interval was 20 mm. The test was conducted on an Instron 3344 universal testing machine equipped with a 500 N sensor at room temperature (25 ℃) and a tensile rate of 50 mm / min.

[0065] GPC test conditions for lignin: The molecular weight and dispersibility of lignin before and after phenolation were determined by high performance liquid chromatography. The chromatographic column was PLgel MIXED-C, the mobile phase was chromatographically pure tetrahydrofuran, and the flow rate was set to 1 mL / min.

[0066] Lignin 3131P NMR testing conditions: For lignin samples, refer to the literature "Application of quantitative 31P NMR in biomass lignin and biofuel precursors characterization." Energy & Environmental Science, 2011, 4(9), pp. 3154-3166. The lignin samples were fully reacted with 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxophosphazenecyclopentane, and the samples were scanned in a 500M superconducting nuclear magnetic resonance spectrometer. The testing conditions were: room temperature, relaxation delay of 10 s, 256 scans, and scan width of 61.9 ppm.

[0067] Structural characterization of lignin-based polyurethane elastomers was performed using attenuated total reflectance (ATR) analysis. The ATR was measured at room temperature (4000-500 cm⁻¹). -1 The area was scanned 32 times, with a resolution of 4 cm. -1 .

[0068] Antioxidant aging test: The thermo-oxidative aging test was conducted in an air-circulating oven (BPG-9070A), and its antioxidant aging performance was evaluated by the retention rate of tensile strength and elongation at break.

[0069] Photothermal conversion effect: A xenon lamp (PLS-SXE 300+ / UV) was used to simulate solar irradiation, and an infrared camera (MAG14, Magnity, China) was used to monitor temperature changes.

[0070] The test results are shown in the table below: Table 2 Molecular weight data for CPKL and KL

[0071] Table 3. Pine wood sulfate lignin phenolization before and after 31 P NMR (hydroxyl content) data table

[0072] Table 4. Data of Examples and Comparative Cases

[0073] Table 5. Photothermal conversion data (°C) for the examples and comparative examples

[0074] Table 6. Comparison of tensile properties of Examples 3 and 12 after 7 days of aging at 100 °C.

[0075] Results analysis: As can be seen from Table 2, the weight-average molecular weight (Mw) of KL in the examples is 4044, and the weight-average molecular weight (Mw) of CPKL is 2219 g / mol. Compared with KL, CPKL has a smaller molecular weight and a smaller degree of molecular weight dispersion, with the PDI decreasing from 2.82 to 2.09.

[0076] The hydroxyl content of KL and CPKL was determined, and the results are presented in Table 3 (phosphorus spectrum data). Figure 1 It can be clearly seen that CPKL has a higher content of phenolic hydroxyl groups, with fewer alcoholic hydroxyl groups and more phenolic hydroxyl groups, reaching as high as 9.01 mmol / g, accounting for 94.05% of the total hydroxyl content.

[0077] As can be seen from the results of Examples 1-12 and Comparative Example 1, the technical solution of the present invention can be used to partially replace petroleum-based polyols with lignin (phenolic hydroxyl content greater than or equal to 5.00 mmol / g) to prepare lignin-based polyurethane elastomers, with a substitution rate of up to 30%. As can be seen from Table 4 and the results of Example 3, when the substitution rate is 20%, the tensile strength of the prepared lignin-based polyurethane elastomer is 87.82 MPa and the elongation at break is 683.90%.

[0078] The results of the examples show that when the amount of NCO to the amount of total hydroxyl (total OH) is 0.7:1, the polyurethane elastomer obtained under the condition of introducing lignin exhibits superior comprehensive mechanical properties.

[0079] Figure 2 Infrared spectra of the elastomers prepared in Examples 1-4, Example 12, and Comparative Example 1. At 3350 cm⁻¹ -1 and 1560 cm -1 The results, representing NH stretching and bending vibrations respectively, indicate the successful preparation of the polyurethane elastomer; 1509 cm -1 The vibration of the C=C bond in the benzene ring of CPKL indicates that CPKL has been successfully integrated into the polyurethane; 1600-1750 cm- 1 The vibration is C=O stretching vibration, indicating the formation of a dense network of hydrogen bonds; at 2275 cm⁻¹ -1 The absence of a vibrational peak for -NCO indicates that -NCO has completely reacted.

[0080] As shown in Tables 2 and 4, although both KL and CPKL have high phenolic hydroxyl content, they differ significantly in molecular weight and dispersibility. Under the same polyurethane preparation conditions, the mechanical properties of polyurethane elastomers obtained using lignin from different sources and preparation methods differ significantly.

[0081] Figure 5The table shows the photothermal effect of the elastomers prepared in Examples 1-4, Example 12, and Comparative Example 1. Under the same intensity light source, with the increase of CPKL substitution, the heating rate and maximum temperature of the elastomers prepared in Examples 1-4 gradually increased, while Comparative Example 1 showed no significant change (Table 5). This indicates that lignin is the main factor in the photothermal effect, and the photothermal conversion capacity is closely related to the CPKL content. The results of Examples 3 and 12 show that the lignin-based polyurethane elastomers prepared with CPKL have a stronger photothermal effect, possibly due to the enhanced π-π conjugation after phenolation modification, resulting in a better photothermal effect.

[0082] Figure 6 The graph shows the changes in tensile properties of the elastomers prepared in Examples 3 and 12 after aging at 100 °C for 7 days. As can be seen from the comparison of data in Table 6, the tensile strength of Example 3 remains above 90%, while the retention rate of Example 12 is 73.38%.

[0083] As can be seen from Comparative Example 1, when the amount of NCO to the amount of total hydroxyl (total OH) is 0.7:1 without the introduction of lignin, the obtained polyurethane elastomer has poor mechanical properties.

[0084] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A lignin-based polyurethane elastomer, characterized in that, It is prepared by comprising long-chain polyol, isocyanate, catalyst, acyl hydrazine chain extender, lignin and organic solvent, wherein the long-chain polyol is 32-40 parts by weight, the isocyanate is 10-17 parts by weight, the catalyst is 0.1-0.3 parts by weight, the acyl hydrazine chain extender is 2-3 parts by weight and the lignin is 4-12 parts by weight. The phenolic hydroxyl content of the lignin is greater than or equal to 5.0 mmol / g.

2. The lignin-based polyurethane elastomer according to claim 1, characterized in that, The weight-average molecular weight of the lignin is 2000~4100 g / mol; the PDI of the lignin is 2.0~2.

9.

3. The lignin-based polyurethane elastomer according to claim 1, characterized in that, The lignin includes at least one of phenolic sulfate lignin and sulfate lignin.

4. The lignin-based polyurethane elastomer according to claim 1, characterized in that, It is prepared by comprising long-chain polyol, isocyanate, catalyst, acyl hydrazine chain extender, lignin and organic solvent, wherein the long-chain polyol is 32-34 parts by weight, the isocyanate is 11-13 parts by weight, the catalyst is 0.1-0.3 parts by weight, the acyl hydrazine chain extender is 2-3 parts by weight and the lignin is 6-8 parts by weight.

5. A method for preparing the lignin-based polyurethane elastomer according to any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Mix long-chain polyol, isocyanate, catalyst and organic solvent evenly, react at 70 ℃~90 ℃ for 2~4 h, add hydrazide chain extender to react and obtain solution A; (2) Dissolve lignin in an organic solvent, add it to solution A obtained in step (1) to react, cool to room temperature, and solidify to obtain lignin-based polyurethane elastomer.

6. The method for preparing the lignin-based polyurethane elastomer according to claim 5, characterized in that, In step (2), the reaction temperature is 70 ℃~90 ℃ and the time is 10~20 h; the curing temperature is 80 ℃~100 ℃ and the time is 18~24 h.

7. The method for preparing the lignin-based polyurethane elastomer according to claim 5, characterized in that, The ratio of NCO to total hydroxyl content is 0.6 to 1.2:

1.

8. The method for preparing the lignin-based polyurethane elastomer according to claim 5, characterized in that, The ratio of NCO to total hydroxyl content is 0.6 to 0.8:

1.

9. The method for preparing the lignin-based polyurethane elastomer according to claim 5, characterized in that, The long-chain polyol includes at least one of polyethylene glycol, polytetrahydrofuran, polycaprolactone diol, and polycarbonate diol; the isocyanate includes at least one of toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, and hexamethylene diisocyanate; the catalyst includes at least one of dibutyltin dilaurate, stannous octanoate, dioctyltin, and dibutyltin diacetate; the organic solvent includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, tetrahydrofuran, and acetone; and the hydrazide chain extender includes at least one of oxalohydrazide, succinylhydrazide, adipylhydrazide, and sebadecylhydrazide.

10. The application of the lignin-based polyurethane elastomer according to any one of claims 1 to 5 in the field of photothermal conversion.

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