A lignin dispersion system, and a preparation method and application thereof

Abstract

This invention discloses a lignin dispersion system, its preparation method, and its application, belonging to the fields of biomass material utilization and textile dyeing and finishing technology. This invention proposes a simple metal-free dyeing strategy. The preparation method of the dye bath includes: adding lignin to an alcohol-water mixed solvent to form a mixed system; heat treatment to disperse the lignin at high temperature; and then cooling to room temperature to form dispersed lignin aggregates in the system, thereby obtaining a lignin dispersion system suitable for fabric dyeing. The dispersion system can dye fabrics at room temperature without the need for metal mordants. Compared with existing technologies, the process steps of this invention are simple, the conditions are controllable, and the resulting fabrics have better dyeing effects and wash resistance.

Description

Technical Field

[0001] This invention belongs to the field of biomass material utilization and textile dyeing and finishing technology, specifically relating to a lignin dispersion system and its preparation method and application. Background Technology

[0002] Lignin is an abundant aromatic polymer found in plant biomass, produced in large quantities as a byproduct of the pulping and biorefining industries. Despite being a highly promising renewable carbon resource, lignin's complex and heterogeneous structure presents challenges for its high-value conversion. Over the past few decades, researchers have developed various depolymerization and chemical modification methods for lignin value enhancement. Lignin is rich in polyphenols, and its conjugated aromatic groups exhibit strong absorption capacity in the ultraviolet region, demonstrating antioxidant activity. Based on its UV shielding and free radical scavenging properties, lignin has been explored as a bio-based additive in sunscreens, coatings, and UV-resistant materials. In the textile industry, these properties not only endow fabrics with multifunctional properties such as UV resistance and flame retardancy but also contribute to improving the sustainability of the dyeing process.

[0003] However, due to the weak interaction between lignin and textile fibers, it is difficult to apply it directly to dyeing processes. To improve the fixation effect of lignin on fibers, researchers have explored a variety of strategies.

[0004] One common approach is cationization modification of fabrics. This method introduces positively charged sites into cellulose fibers through chemical modification, thereby enhancing their adsorption capacity for anionic lignin. Even so, the dyeing performance is still unsatisfactory; sulfate lignin dyed from cationized cotton fibers exhibits only limited color depth.

[0005] Another commonly used strategy is metal salt mordant dyeing. This method uses polyvalent metal salts to pre-mordine untreated fibers (especially wool) to enhance lignin deposition on the fiber surface. For example, lignin sulfonates can only slightly color wool, while to obtain significant color depth and good wash fastness, Cu is usually introduced. 2+ or Fe 2+ / Fe 3+ Mordants. A study showed that wool dyed with 5% lignin sulfonate had extremely low color intensity, while copper mordant treatment could increase the K / S value to 4.21 and improve wash fastness to grade 4–5. Without the assistance of metal salts, lignin adsorption on fibers is generally weak; however, the introduction of metal ions not only makes the dyeing tone greenish, but the use of metal mordants also contradicts environmental protection principles.

[0006] In addition to the two methods mentioned above, there are strategies to improve the solubility and dyeing properties of lignin itself. For example, lignin nanoparticles (LNPs) prepared by ultrafine grinding or solvent / non-solvent methods are used as natural brown pigments. However, these attempts still rely on metal-based mordants to achieve acceptable color depth and color fastness. Although the characteristic size of lignin nanoparticles (LNPs) is in the nanometer range, their size in solution is still too small to allow for direct physical fixation of fibers, considering that traditional dyeing studies have shown that larger pigment particles can improve pigment uptake, rubbing fastness, and washing fastness.

[0007] Therefore, developing a metal-free lignin dyeing strategy to improve the dyeing effect and wash resistance of fabrics has become one of the important issues that urgently need to be addressed. Summary of the Invention

[0008] Therefore, the purpose of this invention is to provide a method for preparing a lignin dispersion system and its application in fabric dyeing.

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] In a first aspect, the present invention provides a lignin dispersion, characterized in that it comprises the following components: 0.1~0.3 g / ml of lignin raw material; and anhydrous ethanol:water = 1:20~20:1 as the solvent.

[0011] Based on the above technical solution, the lignin is further uniformly dispersed in the dispersion medium; the particle size of the dispersion is 180~320nm, and the absolute value of the ζ point is 25~28mV.

[0012] Based on the above technical solution, the lignin raw material is further described as alkali lignin.

[0013] Secondly, the present invention provides a method for preparing the lignin dispersion described above, characterized by comprising the following steps: (1) Pretreatment of alkali lignin: Alkali lignin is purified by acid precipitation, transferred to a petri dish, and dried in a vacuum oven at 110~130℃ for 20~28h; (2) Preparation of dispersion: Disperse the alkali lignin described in step (1) in a solvent of anhydrous ethanol and water; (3) High-temperature reaction: The dispersion described in step (2) is sealed in a stainless steel high-pressure reactor and heated in an oil bath at 150~250℃ for 1~4h; (4) Filtration to remove impurities: After cooling to room temperature, the reaction mixture is centrifuged and filtered to remove undissolved lignin residue. The resulting supernatant is used directly as a dye bath.

[0014] Based on the above technical solution, further, the ratio of anhydrous ethanol to water in step (2) is 1:20~20:1.

[0015] Based on the above technical solution, the lignin raw material content in the dispersion is further 0.1~0.3g / ml.

[0016] Thirdly, the present invention provides an application of the lignin dispersion in fabric dyeing, characterized in that the fabric dyeing includes placing a cotton fabric sample in a dye bath and soaking it at room temperature for about 5 to 10 minutes; after dyeing, taking out the fabric, washing it with room temperature running water 1 to 3 times, each time for 1 to 5 minutes, and then placing it in a drying oven at 42 to 48°C to dry.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. Compared with traditional solvent exchange or antisolvent methods for lignin nanoparticles, this method is a simple one-pot process that requires no additional particle preparation steps. The resulting suspension can be directly used as a dye bath to dye cotton fabrics within 10 minutes at room temperature, without the need for fiber pretreatment or the addition of mordants.

[0018] 2. Compared with existing methods, the K / S value of cotton fabrics dyed with the lignin dispersion prepared by this invention is increased by more than 80%, reaching 7.79~8.69, and it also exhibits good wash fastness. This durability is mainly attributed to physical fixation: mesoscale particles are deposited on the fiber surface and retained through van der Waals forces, hydrogen bonding, and mechanical interlocking effects with the fiber microstructure. Syringaldehyde generated during lignin depolymerization was detected in the dye bath, which can effectively promote pigment uptake.

[0019] 3. Fabrics dyed with the lignin dispersion prepared by the present invention exhibit excellent ultraviolet protection properties (UPF > 40), highlighting its application potential in the field of sustainable textile finishing. Attached Figure Description

[0020] To more clearly illustrate the embodiments of the present invention, the accompanying drawings involved in the embodiments will be briefly described below.

[0021] Figure 1 The particle size distribution of DLS in dye baths with different ethanol concentrations is shown.

[0022] Figure 2 Images of TB50 under 200x and 400x optical microscopes.

[0023] Figure 3 The images show the FT-IR spectra of alkali lignin (AL) and mesoscale lignin particles (MLPs).

[0024] Figure 4Comparison of HSQC nuclear magnetic resonance spectra of AL and MLPs.

[0025] Figure 5 This is the GC-MS detection spectrum of TB50.

[0026] Figure 6 The results of dyeing fabrics in TB50 dye bath.

[0027] Figure 7 The effect of pH on staining performance.

[0028] Figure 8 The results show the staining performance under different treatment times and temperatures.

[0029] Figure 9 The results show the staining performance at different ethanol concentrations.

[0030] Figure 10 The changes in sediment amount and K / S value over storage time.

[0031] Figure 11 The images show the SEM results of the original fabric and the dyed fabric, where (A1-A2) are the original fabric; (B1-B2) are the TB50 dyed fabric; and (C1-C2) are the TB50 dyed fabric with added eugenol.

[0032] Figure 12 The graph shows the carbon yield results derived from thermogravimetric analysis. Detailed Implementation

[0033] The present invention will be described in detail below with reference to the embodiments. However, the implementation of the present invention is not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments can be obtained without creative effort and all fall within the protection scope of the present invention.

[0034] The reagents used in this embodiment of the invention are as follows: Alkali lignin (AL) and sodium lignin sulfonate (SL) were purchased from Sinopharm Chemical Reagent Co., Ltd. Anhydrous ethanol (99.5%), benzoic acid (99%), syringol (98%), vanillin (99%), syringaldehyde (98%), acetylsuccione (98%), and eugenolacetone (95%) were all purchased from Shanghai Maclean Biochemical Technology Co., Ltd. Except for alkali lignin, all other reagents were used directly without further purification.

[0035] Example 1: Preparation of lignin dispersion and method for fabric dyeing First, alkali lignin (AL) was purified by acid precipitation, and then transferred to a petri dish and dried in a vacuum oven at 120°C for 24 hours.

[0036] Measure 0, 5, 10, 15 and 20 mL of anhydrous ethanol respectively and add them to 50 mL polytetrafluoroethylene (PTFE) containers; then add deionized water to each container to make the total solvent volume reach 20 mL.

[0037] Then, 2.0g of dried alkali lignin (AL) was added to each container, and the polytetrafluoroethylene (PTFE) container was sealed in a stainless steel high-pressure reactor at a pressure of 2.35MPa and heated in an oil bath at 200℃ for 4 hours.

[0038] After cooling to room temperature, the reaction mixture was centrifuged and filtered to remove undissolved lignin residue. The resulting supernatant was used directly as a dye bath.

[0039] Place the cotton fabric sample (1×2cm) in the dye bath and soak it at room temperature for about 8 minutes. After dyeing, take out the fabric, wash it twice with room temperature running water for 3 minutes each time, and then dry it in a 45℃ drying oven.

[0040] Dyeing performance was evaluated using the K / S value and the color difference (ΔE) between the dyed fabric and the original lignin. The dyeing results are as follows: Figure 6 As shown. Compared with existing technologies, this method can increase the K / S value by at least 50%, while reducing the staining time from 60-90 minutes to 5-10 minutes.

[0041] Photographs of dyed fabrics were taken in a standard light box equipped with a D65 light source. As shown in Equations 1 and 2, Kubelka-Munk color intensity (K / S) and CIE La... b The color difference (ΔE) in the color space was used to evaluate the color performance of dyed fabrics. All tests were performed using an X-Rite EyeOne spectrophotometer.

[0042]

[0043] Where r represents the reflectivity at a wavelength of 400 nm.

[0044]

[0045] like Figure 9 As shown, the ethanol-water composition has a significant impact on dyeing performance. When the ethanol volume fraction increases from 0% to 50%, the K / S value of the dyed fabric significantly increases from approximately 2.2 to 7.8, while the color difference (ΔE) between the dyed fabric and lignin decreases to its lowest value, indicating that the fabric color is closer to the intrinsic color of lignin at this point. In contrast, studies reported on dyeing with metal mordants (such as Cu) have shown a different effect. 2+ Fe 2+ The dyeing method often makes the fabric appear greenish or blackish, rather than the color of lignin itself.

[0046] Example 2 Characterization of the dye bath performance of lignin dispersion The performance of the lignin dispersion prepared in Example 1 was tested: (1) Average particle size, polydispersity index (PDI), and zeta potential of the dye bath The average particle size, polydispersity index (PDI), and zeta potential of the dye bath were determined using a Zetasizer Nano ZS nanoparticle potentiometer (Malvin Panaco) based on the principle of dynamic light scattering. Particle size and PDI were measured using 14 mm square polystyrene cuvettes (DTS0014), while zeta potential was measured using a disposable folded capillary sample cell (DTS1070). All tests were performed at room temperature. Each sample was measured in triplicate, and the results are expressed as averages.

[0047] Dynamic light scattering results as follows Figure 1 As shown, the results indicate that the lignin particle size distribution varies significantly with ethanol content. In a pure water system (without ethanol solvent), the suspension exhibits a single peak distribution centered at 300 nm; the solution is pale yellow due to the small amount of lignin dispersed in the medium. When a lower volume fraction of ethanol (<25%, v / v) is introduced, the particle size decreases to below 200 nm, indicating that ethanol can reduce the polarity mismatch between lignin and the solvent, thereby improving its dispersibility. When the ethanol volume fraction reaches 50%, the particle size distribution shifts to larger sizes, with a main peak of approximately 4 μm and a minor subpeak at approximately 200 nm. This result suggests that when the ethanol volume fraction reaches 50%, the interactions between lignin molecules in the TB50 system (such as hydrophobic interactions and aromatic π-π stacking) compete with the interactions between lignin and the solvent, thus promoting the aggregation of smaller primary particles into mesoscale aggregates.

[0048] Meanwhile, the 50% ethanol suspension had the lowest polydispersity index (PDI) value, as shown in Table 1, indicating that the particle size distribution range in this system was narrower and more easily deposited uniformly on the fabric surface. When the ethanol volume fraction was further increased (75% and 100%), the particle size distribution shifted back to the nanoscale. This is because the increased ethanol content improved the solubility of lignin, thereby inhibiting its large-scale aggregation.

[0049] Table 1. Polydispersity index (PDI) and zeta potential of dye baths prepared in different ethanol-water systems

[0050] As shown in Table 1, the zeta potentials of each sample are all close to... 30 mV, close to the generally accepted stability threshold (|ζ| ≥ 30 mV), with the TB50 sample showing the highest absolute value, reaching... 29.6 mV. The negative charge on the surface of lignin particles mainly originates from the ionization of phenolic hydroxyl groups, carboxyl groups, and interfacial OH groups. - The contribution of adsorption is relatively small. This surface charge not only provides moderate electrostatic repulsion but also acts as an electron-rich site to form hydrogen bonds with cellulose hydroxyl groups, thereby promoting dye adsorption. The TB50 system is in a critical electrostatically stable state, maintaining stable dyeing performance for at least 24 hours. Figure 6 , Figure 10 As shown. Considering its staining performance, TB50 was selected as the representative dye bath for subsequent characterization.

[0051] (2) Optical microscope and scanning electron microscope Mesoscale lignin pigments (MLPs) in TB50 were observed using an optical microscope (Nikon ECLIPSE 8i). 30 μL of TB50 was dropped onto a clean glass slide, covered with a coverslip, and observed and imaged under the microscope.

[0052] The surface morphology of the dyed fabric was characterized using a scanning electron microscope (JEOL JSM-6460LV). Before observation, the fabric was washed and dried, and then fixed to the sample stage with conductive adhesive.

[0053] The results are as follows Figure 2 As shown, the results indicate that TB50 mesoscale lignin particles (MLPs) are dispersed throughout the field of view. At 200x magnification, these particles exhibit irregular morphology, dispersed across the entire background, while some degree of aggregation is also observed. The observed mesoscale characteristics are consistent with dynamic light scattering (DLS) results. Figure 1 The main peak shown in the figure is consistent with the particle group of about 4 μm.

[0054] At 400x magnification, individual aggregates exhibit a distinct "secondary structure," i.e., dense aggregates formed by the stacking of smaller subunits. The zeta potential of TB50 is approximately... The value of 29.6 mV, close to the stability threshold (|ζ|≥30 mV), indicates that electrostatic repulsion provides only limited colloidal stability. Therefore, particles in the dye bath readily contact and aggregate through non-covalent intermolecular interactions. This "dispersible but easily aggregated" state is consistent with the observed storage behavior: the dye bath is essentially stable within the first 12–24 hours, but significant precipitation occurs after prolonged standing, accompanied by a decrease in staining capacity.

[0055] (3) Fourier transform infrared spectroscopy and two-dimensional heteronuclear single-quantum coherent nuclear magnetic resonance detection The structural changes of lignin during EWS heat treatment were analyzed using Fourier transform infrared spectroscopy (ANTAIRS). TB50 prepared in Example 1 was subjected to rotary evaporation to obtain lignin and a colorless, transparent condensate. The extracted lignin was identified as mesoscale lignin particles (MLPs), distinct from the original alkali lignin (AL). After drying the alkali lignin (AL) and mesoscale lignin pigments (MLPs) separately, they were mixed with potassium bromide, ground, and pressed into tablets for infrared spectroscopy analysis. The spectral acquisition range was 4000–400 cm⁻¹. -1 The resolution is 4cm. -1 Each sample was scanned 16 times and the average value was taken. Two-dimensional heteronuclear single-quantum coherent NMR spectra were acquired using a Bruker AvanceIII 400 NMR spectrometer (Bruker Corporation, USA). 50 mg of alkali lignin and mesoscale lignin pigment were dissolved in 0.6 mL of deuterated dimethyl sulfoxide (DMSO-d6) for analysis. NMR data were processed using MestReNova software, and HSQC spectra were calibrated using the solvent peak (DMSO-d6, δC / δH 39.5 / 2.49 ppm).

[0056] like Figure 3 As shown, the FT-IR spectra of alkali lignin (AL) and mesoscale lignin particles (MLPs) at 3448 cm⁻¹ -1 Broad absorption peaks appear at all locations, corresponding to the OH stretching vibrations of aliphatic and phenolic hydroxyl groups. 2930 cm⁻¹ -1 and 2850 cm -1 The absorption peak at 1695 cm⁻¹ is attributed to the symmetric and asymmetric stretching vibrations of the C–H bonds between the methyl and methylene groups. -1 The shoulder peak at this location originates from the stretching vibration of C=O in conjugated aldehydes or carboxylic acids. It is noteworthy that, after treatment, the 1458 cm⁻¹... -1 (CH3 / CH2 deformation vibration), 1328 cm -1 and 1215 cm -1 The spectral changes of the characteristic peaks of phenols associated with guaiacol and syringyl units were slight. These results indicate that the aromatic skeleton and major functional groups of lignin were largely preserved under the treatment conditions, with no significant degradation.

[0057] However, two-dimensional HSQC nuclear magnetic resonance spectra ( Figure 4The study revealed subtle structural changes. In the side-chain region, the signals of β-O–4 bonds, β–β bonds, and γ–OMe were clearly visible without significant attenuation. In the aromatic region, the characteristic cross-peaks of the guaiacolyl unit (G), syringyl unit (S), and p-hydroxyphenyl unit (H) appeared at δC / δH = 111 / 6.9 ppm (G2), 104 / 6.7 ppm (S2,6), and 128 / 7.2 ppm (H2,6), respectively. Quantitative integration of the three structural units using literature methods showed that the H unit content decreased significantly (by 2.11%), while the relative contents of the S and G units increased slightly (from 77.26% to 77.91% and from 18.24% to 19.69%, respectively).

[0058] Given that the direct conversion from the H-type structure to the S / G-type structure is thermodynamically unfavorable, this change can be attributed to the breakage of the H-type units during the treatment process, leading to an increase in the relative S / G content in MLPs. This indicates that lignin underwent partial depolymerization, resulting in the formation of low molecular weight aromatic products.

[0059] (4) GC-MS analysis Degradation products in the dye bath were analyzed using an Agilent 7890A gas chromatograph coupled with an Agilent 5975C mass spectrometer (GC-MS). Quantitative analysis was performed using an Agilent 7890A gas chromatograph equipped with a flame ionization detector (GC-FID), with n-tetradecane as the internal standard. Gas chromatographic separation was performed using an HP-5MS capillary column (60 m × 0.25 mm × 0.25 μm), with high-purity helium as the carrier gas, a flow rate of 1.0 mL / min, and a split ratio of 10:1. The column oven temperature program was set as follows: initial temperature 50 °C (held for 2 min), increased to 250 °C at a rate of 6 °C / min, and held at 250 °C for 8 min; the injection port temperature was set to 250 °C. Mass spectrometry conditions were as follows: full scan mode was used, the electron ionization (EI) source temperature was 200 °C, and the ionization energy was 70 eV. Mass spectra were identified using the NIST08 mass library.

[0060] like Figure 5 As shown, GC-MS identified a variety of phenolic aromatic compounds, with seven major products summarized in this figure. Among these components, syringaldehyde was shown to effectively promote lignin deposition on the matrix, such as... Figure 12 As shown. Especially for dye baths stored for 3-5 days, adding eugenol can partially restore their dyeing properties. Figure 7 This highlights the role of eugenol as an effective interface promoter.

[0061] It is worth noting that the formation of MLPs is not sensitive to the cooling method. Whether rapidly quenched in cold water or naturally cooled at room temperature, the generated particles are basically the same, and the K / S values ​​of the dyed fabrics are not significantly different.

[0062] (5) Thermogravimetric analysis The thermal decomposition behavior of the prepared samples was evaluated using a TA Instruments Q50 thermogravimetric analyzer. The tests were conducted under a high-purity nitrogen atmosphere (flow rate 50 mL / min). -1 The heating process was carried out at a temperature ranging from 25 to 700°C, with a heating rate of 10°C / min. -1 .

[0063] Thermogravimetric analysis (TGA) results are as follows Figure 12 As shown, the carbon residue rate of undyed cotton fabric at 700℃ is only 11.4%, while after being dyed by this system, the carbon residue rate of cotton fabric increases to 13.15%, which is significantly higher than that of blank cotton fabric, indicating that the lignin component has been successfully dyed onto the fiber surface.

[0064] Example 3: Effect of dye bath pH on dyeing performance The pH of TB50 was adjusted to 1-9 using hydrochloric acid aqueous solution and sodium hydroxide aqueous solution. The resulting solution was used for fabric dyeing to evaluate the effect of pH on dyeing performance.

[0065] The staining performance is significantly dependent on the pH of the staining bath; both excessively acidic and excessively alkaline conditions lead to a significant decrease in the K / S ratio. Figure 6 and Figure 7 As shown, the maximum color intensity is obtained when pH ≈ 4.7 (corresponding to the natural pH of TB50). In the TB50 system, the addition of acid or base will result in visible precipitation, and even a slight shift in pH (from 4.7 to 5.0) is sufficient to cause a significant decrease in the K / S value.

[0066] In strongly acidic media, phenolic hydroxyl and carboxyl groups undergo protonation, reducing the surface charge of lignin particles and weakening their electrostatic stability. Conversely, under high pH conditions, deprotonation is enhanced, increasing the negative charge density of both lignin particles and cellulose fibers, generating stronger electrostatic repulsion and thus hindering particle deposition. When pH ≈ 4.7, the system is near its critical state, where colloidal stability and interfacial adhesion reach equilibrium, and this equilibrium is easily disrupted by small pH deviations.

[0067] Example 4: Effect of dye bath preparation temperature and time on dyeing performance A lignin dispersion was prepared as a dye bath. The temperature inside the reactor was 150, 180, 200, 230, and 250°C, and the reaction time was 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, and 4.0 hours, respectively. The remaining operating conditions were the same as in Example 1. The prepared dye bath was cooled to room temperature for dyeing.

[0068] like Figure 8 As shown, the dyeing performance initially improves with increasing treatment time, then gradually stabilizes after about 4 hours. In the initial stage, extending the treatment time promotes lignin deposition on the fibers, significantly increasing the color depth; when the treatment time approaches 4 hours, adsorption tends to saturate, and the dyeing performance enters a stable state. The effect of temperature is also significant. At lower temperatures, lignin is not sufficiently dispersed in the dye bath, resulting in limited dye uptake; however, when the temperature rises to around 200℃ or higher, lignin is effectively dissolved, forming a stable dye bath, thus achieving efficient dyeing. Further increasing the temperature not only does not benefit the dyeing performance but also triggers excessive degradation and carbonization of lignin, indicating that the system has approached the optimal process window.

[0069] Example 5: Effect of dye bath storage time on dyeing performance The TB50 prepared in Example 1 was stored at room temperature for 1 to 5 days; the suspension was centrifuged every 24 hours, and the recovered lignin was weighed after the precipitate was dried. The corresponding supernatant was used as a dye bath for dyeing cotton fabrics.

[0070] The staining performance of TB50 remained relatively stable during the first 24 hours. During this period, the K / S value decreased slightly, and the visual color difference was negligible (ΔE≈3.0). Figure 6 and Figure 10 As shown in the figure. In contrast, the amount of lignin precipitation increased significantly during the same period, with the total precipitation in the first 24 hours accounting for 70% of the total precipitation in 5 days. This decoupling phenomenon indicates that the initial precipitation preferentially removed larger aggregates with poor dyeing effect, while particles and interfacial promoters associated with cotton fabric deposition were retained. In contrast, during long-term aging, the slight increase in precipitation was accompanied by a sharp decrease in the K / S value (from 7.17 to 2.75), which is due to the continuous aggregation of effective particles and their loss of dyeing ability.

[0071] Example 6: Effect of eugenol on dye bath performance To investigate the effects of eugenol and other lignin degradation-derived phenolic aromatic compounds, benzoic acid, 2,6-dimethoxyphenol, vanillin, and eugenol were added to the dye bath at a concentration of 1 mg / mL, and fabric dyeing experiments were conducted according to the dyeing method described in Example 2.

[0072] Scanning electron microscopy (SEM) observations and thermogravimetric analysis (TGA) char residue data indicate that the addition of syringaldehyde can promote the deposition and retention of lignin.

[0073] SEM results are as follows Figure 11 As shown in Figures B1-B2, the results indicate that the fiber surface and interfiber spaces of fibers dyed in the TB50 dye bath are covered with a large number of lignin aggregates, forming a film-like layer. This deposition phenomenon results in a high degree of color matching between the dyed fabric and the lignin. In contrast, fibers dyed in the TB50 dye bath with added eugenol... Figure 11 As shown in C1-C2, larger and more continuous lignin aggregates are observed, resulting in a more uniform and complete coating on the fabric surface.

[0074] Thermogravimetric analysis (TGA) further revealed the effects of syringaldehyde. For example... Figure 12 As shown, undyed cotton fabrics had a lower char residue rate (10.1%) at 700℃, while lignin had a char residue rate of 35.8%.

[0075] After TB50 dyeing, the residual mass of the fabric increased from 10.1% to 13.2%, indicating that lignin was successfully loaded onto the fiber surface. Notably, the fabric dyed with TB50 under the condition of adding syringaldehyde showed a slight but identifiable increase in char yield (13.9%), further confirming the increase in lignin loading on the fiber, a result consistent with scanning electron microscopy observations.

[0076] Example 7: UV resistance and wash fastness of fabrics after dyeing in a dye bath The ultraviolet transmittance (UVA) and ultraviolet protection factor (UPF) of the fabric were determined using a UV-Vis spectrophotometer (Cary 300, Varian, USA) according to AATCC 183:2010 standard. The test scanning range was 290–400 nm ultraviolet wavelength. The UVA and UPF values ​​were calculated according to formulas (Equations 3 and 4) specified in GB / T 18830-2009 standard.

[0077]

[0078]

[0079] Where E(λ), ε(λ), and T(λ) represent solar spectral irradiance (W·m²), respectively. -2 ·nm -1 ), relative erythema spectral efficacy and spectral transmittance, where λ represents the wavelength interval (nm).

[0080] The color fastness to rubbing of TB50 dye bath-dyed fabrics was evaluated according to ISO 105-X12:2016 standard. During testing, undyed cotton fabric was attached to the rubbing head, and the dyed sample was subjected to 10 cycles of rubbing. Before the wet rubbing test, the cotton fabric was thoroughly wetted to 100% liquid retention. The degree of staining was assessed using a grey scale rating (GS 1-5), where 1 indicates the worst performance and 5 indicates the best performance.

[0081] Color fastness to washing was determined according to ISO 105-C10:2006 (EN) standard. The dyed fabric was immersed in a soap solution (0.5 wt%) and stirred at 40°C for 30 min using a color fastness tester. After drying, the color change of the fabric was rated using an ISO gray scale in a standard light source box.

[0082] Lignin, rich in aromatic structures such as syringyl and guaiacol, exhibits significant absorption capacity in the 280–400 nm ultraviolet band. Based on this, this study evaluated the UV protection properties of lignin-dyed fabrics. As shown in Table 3, the UV protection factor (UPF) of undyed cotton fabric was 32.26, while after TB50 dyeing, the UPF value increased to 45.98. According to GB / T 18830-2009 standard, this improvement is sufficient to classify the dyed fabric as having UV protection function. Table 3 also summarizes the wash fastness and rubbing fastness of TB50-dyed fabrics. The results show that the dyed fabrics have high stain fastness but low colorfastness.

[0083] Table 3 UV resistance and wash fastness of TB50 dyed fabrics

[0084] The low colorfastness is mainly attributed to the alkali sensitivity of lignin. Under alkaline soaping conditions, some lignin dissolves, leading to a significant decrease in the color depth of the dyed fabric. In contrast, the stain fastness remains at grade 4, indicating low migration of detached lignin and a low likelihood of redeposition.

[0085] The rubbing fastness is less affected by soaping, mainly because the deposition of lignin on cotton fibers is dominated by physical interactions; in addition, alkali lignin itself is insoluble in water, which can effectively inhibit particle migration, thereby maintaining good rubbing fastness.

[0086] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A lignin dispersion, characterized in that, It includes the following components: 0.1~0.3g / ml lignin raw material; solvent is anhydrous ethanol:water = 1:20~20:

1.

2. The lignin dispersion according to claim 1, characterized in that, The lignin raw material is uniformly dispersed in the dispersion medium; the particle size of the dispersion is 180~320nm, and the absolute value of the ζ point is 25~28mV.

3. The lignin dispersion according to claim 1, characterized in that, The lignin raw material is alkali lignin.

4. A method for preparing the lignin dispersion according to any one of claims 1 to 3, characterized in that, Includes the following steps: (1) Pretreatment of alkali lignin: Alkali lignin is purified by acid precipitation, transferred to a petri dish, and dried in a vacuum oven at 110~130℃ for 20~28h; (2) Preparation of dispersion: Disperse the alkali lignin described in step (1) in a solvent of anhydrous ethanol and water; (3) High-temperature reaction: The dispersion described in step (2) is sealed in a stainless steel high-pressure reactor with a reactor pressure of 2.3~2.4MPa and heated in an oil bath at 150~250℃ for 1~4h; (4) Filtration to remove impurities: After cooling to room temperature, the reaction mixture is centrifuged and filtered to remove undissolved lignin residue. The resulting supernatant is used directly as a dye bath.

5. The preparation method according to claim 4, characterized in that, The ratio of anhydrous ethanol to water in step (2) is 1:20 to 20:

1.

6. The preparation method according to claim 4, characterized in that, The lignin raw material content in the dispersion is 0.1~0.3g / ml.

7. The application of the lignin dispersion according to any one of claims 1 to 3 in fabric dyeing, characterized in that, The fabric dyeing process involves placing a cotton fabric sample in a dye bath and soaking it at room temperature for 5-10 minutes. After dyeing, the fabric is removed, washed with room temperature running water 1-3 times for 1-5 minutes each time, and then dried in a drying oven at 42-48°C.

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