Method for improving light fastness of pomegranate peel vegetable dye and pomegranate peel vegetable dye
By introducing a UV absorber during the dye preparation stage, a stable dye-metal-UV absorber ternary complex is formed, which solves the problem of poor light fastness of pomegranate peel dye and achieves efficient and long-lasting light stability and color expansion, making it suitable for textile dyeing.
Patent Information
- Application Number
- CN202511397166.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-28
- Publication Date
- 2026-01-09
AI Technical Summary
Pomegranate peel dyes have poor light fastness, making them prone to photodegradation under ultraviolet radiation, which limits their application in outdoor textiles and high-end clothing. Existing methods are cumbersome, costly, and produce inconsistent and unsustainable results.
In the dye preparation stage, ultraviolet absorbers are introduced. Through high-pressure extraction, concentration and spray drying processes, the ultraviolet absorbers are uniformly mixed with dye molecules to form a stable dye-metal-ultraviolet absorber ternary complex, thereby improving the inherent photostability of the dye.
It significantly improves the light fastness of dyes, simplifies the production process, reduces costs, expands the color gamut of dyes, achieves high-end hues, and ensures product stability and easy storage.
Smart Images
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Abstract
Description
Technical Field
[0001] This invention relates to the fields of natural product processing and textile dyeing technology, and in particular to a method for improving the light fastness of pomegranate peel plant dyes and pomegranate peel plant dyes. Background Technology
[0002] Pomegranate (Punica granatum L.) peel is an important natural plant dye resource. Its effective dyeing components are mainly hydrolyzed tannins (such as punicin and ellagic acid) and flavonoids. As a natural dye with a long history, pomegranate peel can be used to dye protein fibers such as silk and wool, obtaining soft and rustic shades such as yellow and military green, which meet the modern consumer demand for ecological and sustainable textiles.
[0003] However, like most natural dyes, pomegranate peel dyes have a fatal flaw—poor light fastness. They are prone to photodegradation under ultraviolet light, causing dyed fabrics to fade or change color rapidly. This severely limits their application in outdoor textiles, high-end clothing, and other fields requiring high durability. The photodegradation mechanism of pomegranate peel dyes mainly involves two aspects: 1) their chromophores (such as the phenolic hydroxyl structure in tannin molecules) undergo electronic transitions after absorbing light energy, leading to the breakage of chemical bonds; 2) under the combined action of light, oxygen, and moisture, an oxidation reaction occurs, destroying the conjugated chromophore system.
[0004] Currently, traditional methods for improving the light fastness of textiles mainly focus on finishing techniques, namely, impregnating the fabric with ultraviolet absorbers (UVA) or antioxidants after dyeing to form a protective film on the fiber surface. While these methods have some effect, they also have significant drawbacks:
[0005] 1) The process is complicated and costly: it adds extra processing steps and consumes water, energy and time.
[0006] 2) Uneven and short-lived effect: The finishing agent is unevenly distributed on the fiber surface and has weak bonding force with the fiber. It is easily lost during washing and friction, and the light stabilization effect is difficult to maintain.
[0007] 3) Affects fabric quality: Finishing agents may alter the feel, breathability, and natural properties of fabrics.
[0008] On the other hand, research on modifying dyes during the dye preparation stage (i.e., upstream) to improve their inherent photostability is relatively weak. Existing techniques mostly involve simple physical blending, where the extracted dye solution is mixed with a UV absorber and then dried. In this method, the UV absorber and dye molecules are bound only by weak van der Waals forces or hydrogen bonds, which can easily fail during subsequent dyeing and use due to phase separation or differences in solubility, thus failing to achieve fundamental improvement.
[0009] Therefore, there is an urgent need in this field for a technical solution that can enhance the photostability of pomegranate peel dyes from the source, thereby simplifying downstream processes and achieving long-term protection. Summary of the Invention
[0010] The purpose of this invention is to address the shortcomings of existing technologies by proposing a method for improving the light fastness of pomegranate peel plant dyes and pomegranate peel plant dyes.
[0011] To achieve the above objectives, the present invention adopts the following technical solution:
[0012] A method for improving the light fastness of plant dyes on pomegranate peel includes the following steps:
[0013] S1. Raw material pretreatment: Fresh pomegranate peel is washed to remove impurities, freeze-dried, ultra-finely pulverized and sieved to obtain pomegranate peel coarse powder;
[0014] S2. High-pressure extraction: The pomegranate peel powder obtained in S1 was subjected to high-pressure extraction with an ethanol-water solution;
[0015] S3. Solid-liquid separation: After extraction, the filtrate is obtained by filtration;
[0016] S4. Concentration: The extract filtrate obtained in S3 is evaporated under reduced pressure to obtain a concentrated pomegranate peel dye solution;
[0017] S5. UV absorber compounding: Add UV absorber to the concentrated dye solution obtained in S4, and mechanically stir at 500-800 rpm for 1-3 hours at 40-60℃ until the UV absorber is completely dissolved and mixed evenly with the dye solution.
[0018] S6. Drying and grinding:
[0019] The solution mixed evenly in step S5 is spray-dried to obtain pomegranate peel plant dye powder with high light fastness.
[0020] This invention introduces a UV absorber during the dye extraction stage, ensuring thorough and uniform mixing with dye molecules (such as tannins), and forming a uniform powder during spray drying. This UV absorber continuously and effectively shields or absorbs ultraviolet light during subsequent dyeing and product use, fundamentally improving the inherent photostability of the dye, resulting in superior performance compared to finishing processes on fabrics.
[0021] Preferably, the specific steps of S1 are as follows: fresh pomegranate peel is washed to remove impurities, placed in a freeze dryer, frozen and solidified at a temperature of -40℃ to -55℃, and then sublimated and dried under a vacuum of 0.1-10Pa until the moisture content is less than 5wt%; the dried pomegranate peel raw material is ultra-finely pulverized using an ultra-micro pulverizer and passed through an 80-120 mesh sieve to obtain pomegranate peel coarse powder;
[0022] Preferably, the specific steps of S2 are as follows: the pomegranate peel powder obtained in S1 is mixed with an ethanol-water solution with an ethanol concentration of 60%-80% at a material-liquid ratio of 1:10-1:15 (g / mL), placed in a high-pressure reactor, the reactor is sealed, and the temperature is raised to 30-45℃ under the condition of stirring speed of 100-300 rpm, and a static pressure of 200-350 MPa is applied. Under these conditions, the mixture is extracted at constant temperature and pressure for 4-8 hours.
[0023] Preferably, the specific steps of S3 are as follows: the material in the reactor is taken out and filtered under a pressure of 0.1-0.5MPa, or a plate and frame filter press is used for pressure filtration to separate the extract filtrate, collect the filtrate, and the filter residue can be processed separately;
[0024] Preferably, the specific step of S4 is as follows: the extract filtrate obtained in S3 is concentrated by vacuum rotary evaporation at a water bath temperature of 40-60℃, and the volume of the filtrate is concentrated to 1 / 4 to 1 / 5 of the original volume to obtain concentrated pomegranate peel dye solution.
[0025] Preferably, in step S6, the inlet air temperature of the spray drying is controlled at 120-160℃, the outlet air temperature is controlled at 70-90℃, the atomizer speed is adjusted to 15000-25000rpm, and the powder obtained from the bottom of the drying tower is collected to obtain the pomegranate peel plant dye powder with high light fastness.
[0026] Preferably, two options are selected for the ultraviolet absorber:
[0027] Option 1: The UV absorber is one of benzophenone, 2-hydroxybenzophenone, or 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, and its addition amount is in a mass ratio of 1:15 to 1:20 with the original dry pomegranate peel.
[0028] Option 2: The ultraviolet absorber is a nickel(II) complex of 2-hydroxy-4-methoxybenzophenone or a copper(II) complex of 2-hydroxy-4-methoxybenzophenone, and the addition amount is 1:15-1:20 in mass ratio with the original dry pomegranate peel.
[0029] Further, the synthesis steps of the 2-hydroxy-4-methoxybenzophenone nickel(II) complex or the 2-hydroxy-4-methoxybenzophenone copper(II) complex are as follows:
[0030] At room temperature, 0.1 mol of 2-hydroxy-4-methoxybenzophenone was dissolved in 100 mL of anhydrous ethanol, and then 60 mL of 1 mol / L NaOH aqueous solution was added. After stirring and mixing, 0.5 mol / L copper chloride or nickel chloride aqueous solution was slowly added dropwise. After stirring and reacting for 1.5 h, a precipitate was formed. After aging at room temperature for 24 h, the precipitate was filtered under reduced pressure. The filter cake was washed several times with 1:1 ethanol aqueous solution and then dried at 100 °C to constant weight to obtain 2-hydroxy-4-methoxybenzophenone nickel(II) complex (pale green) or 2-hydroxy-4-methoxybenzophenone copper(II) complex (dark green).
[0031] The molecular formula of 2-hydroxy-4-methoxybenzophenone is:
[0032]
[0033] The possible structures of the 2-hydroxy-4-methoxybenzophenone nickel(II) complex (pale green) and the 2-hydroxy-4-methoxybenzophenone copper(II) complex obtained after complexation are as follows:
[0034]
[0035] The present invention also proposes a pomegranate peel plant dye prepared by the aforementioned method, which includes an ultraviolet absorber. The resulting dye powder has excellent photostability, is easy to store and transport, and can be directly used in subsequent dyeing processes without the need to add other auxiliaries when dyeing fabrics, yarns, etc.
[0036] Compared with the prior art, the beneficial effects of the present invention are:
[0037] 1. This invention does not protect the fibers after dyeing, but rather "modifies" their molecules during the dye preparation stage. By uniformly mixing and reacting ultraviolet absorbers, especially innovative metal complex-type ultraviolet absorbers, with pomegranate peel extract in the dye concentrate, molecular-level composites are achieved.
[0038] When using 2-hydroxy-4-methoxybenzophenone complexes with copper(II) or nickel(II), their effect goes far beyond simple physical shielding. Cu in solution... 2+ (or Ni) 2+As a highly efficient "bridge," one end coordinates with the phenolic oxide anion on the UV absorber molecule, while the other end forms a strong coordination bond with the ortho-phenolic hydroxyl group on the pomegranate peel tannin molecule, thus forming a stable ternary complex of "dye-metal-UV absorber." This composite structure, built through coordination bonds, exhibits far greater stability than the hydrogen bonds or intermolecular forces of physical mixing. During subsequent dyeing and product use, the UV absorber, chemically "anchored" to the dye molecule, does not easily dissipate, continuously and efficiently absorbing and dissipating UV energy. This achieves essential protection of the chromophore at the molecular level, resulting in a remarkably significant and long-lasting improvement in lightfastness.
[0039] 2. This invention organically integrates ultraviolet stabilization treatment with the extraction, concentration, and drying processes of dyes. It eliminates the traditional and cumbersome fabric finishing processes, simplifying the entire production process from dye to dyed product. This not only significantly reduces water and energy consumption and lowers production costs, but also aligns more closely with the principles of green chemistry.
[0040] 3. The final product of this invention is a dry powder, which has the advantages of high stability, long shelf life, and easy storage and transportation. The powder morphology facilitates standardization and quantification, and can be directly integrated into existing textile dyeing systems, making it convenient to use and beneficial for product quality control and reproducibility.
[0041] 4. The pomegranate peel dye powder prepared by the method of the present invention can reduce the light fading rate from 44.5% in the untreated form to below 10%, an improvement of more than 75%, and the light fastness grade is greatly improved, fully meeting the requirements of high-quality textiles.
[0042] 5. Traditional methods can only obtain the inherent yellow hue of pomegranate peel, while this invention uses a metal complex-type ultraviolet absorber, achieving a fundamental change and controllable expansion of the color:
[0043] The coordination reaction between metal ions and tannins itself causes color changes (coordination field effect). Different metal ions can be selected to obtain different colors: Cu(II) ions guide olive green and military green tones; Ni(II) ions guide sophisticated gray-khaki and brownish-gray tones. This allows the present invention to achieve high lightfastness while breaking through the color gamut limitations of natural pomegranate peel dyes, obtaining rich and popular high-grade colors without the need for complex post-treatment with multiple mordants. This integrated achievement of color and high performance is a prominent advantage of the present invention.
[0044] 6. The pre-synthesized metal complexes of this invention are far superior to simply mixing inorganic metal salts with UV absorbers. The pre-synthesized complexes have well-defined structures and stable properties, ensuring the formation of uniform and highly efficient ternary complexes with dye molecules, thus achieving the best synergistic effect of UV absorption and dye stabilization.
[0045] 7. In summary, this invention, through ingenious molecular design, achieves fundamental modification of the properties of pomegranate peel dyes, not only solving the core problem of poor light fastness but also giving them new color vitality, demonstrating significant technological advancement and broad market application prospects. Detailed Implementation
[0046] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with existing known technologies. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.
[0047] I. Preparation of Complex Ultraviolet Absorbers
[0048] Preparation Example 1
[0049] The synthetic steps for the 2-hydroxy-4-methoxybenzophenone nickel(II) complex are as follows:
[0050] At room temperature, 0.1 mol of 2-hydroxy-4-methoxybenzophenone was dissolved in 100 mL of anhydrous ethanol, and then 60 mL of 1 mol / L NaOH aqueous solution was added. After stirring and mixing, 0.5 mol / L nickel chloride aqueous solution was slowly added dropwise. After stirring and reacting for 1.5 h, a precipitate was formed. After aging at room temperature for 24 h, the precipitate was filtered under reduced pressure. The filter cake was washed several times with 1:1 ethanol aqueous solution and then dried at 100 °C to constant weight to obtain the 2-hydroxy-4-methoxybenzophenone nickel(II) complex (pale green).
[0051] Preparation Example 2
[0052] The synthetic steps for the 2-hydroxy-4-methoxybenzophenone copper(II) complex are as follows:
[0053] At room temperature, 0.1 mol of 2-hydroxy-4-methoxybenzophenone was dissolved in 100 mL of anhydrous ethanol, and then 60 mL of 1 mol / L NaOH aqueous solution was added. After stirring and mixing, 0.5 mol / L copper chloride aqueous solution was slowly added dropwise. After stirring and reacting for 1.5 h, a precipitate was formed. After aging at room temperature for 24 h, the precipitate was filtered under reduced pressure. The filter cake was washed several times with 1:1 ethanol aqueous solution and then dried at 100 °C to constant weight to obtain the 2-hydroxy-4-methoxybenzophenone copper(II) complex (dark green).
[0054] II. Dye Preparation
[0055] Example 1
[0056] A method for improving the light fastness of plant dyes on pomegranate peel includes the following steps:
[0057] S1. Raw material pretreatment:
[0058] Fresh pomegranate peels are washed to remove impurities, placed in a freeze dryer, and frozen solidified at -40℃ to -55℃. Then, they are sublimated and dried under a vacuum of 0.1-10 Pa until the moisture content is below 5 wt%. The dried pomegranate peel raw material is then ultra-finely pulverized using an ultra-micro pulverizer and passed through an 80-mesh sieve to obtain coarse pomegranate peel powder.
[0059] S2. High-pressure extraction:
[0060] The pomegranate peel powder obtained in step S1 was mixed with an 80% ethanol-water solution at a ratio of 1:15 (g / mL) and placed in a high-pressure reactor. The reactor was sealed, and the temperature was raised to 45°C with a stirring speed of 300 rpm, and a static pressure of 350 MPa was applied. The mixture was then subjected to constant temperature and pressure extraction for 4 hours.
[0061] S3. Solid-liquid separation:
[0062] After extraction, the material in the reactor is removed and filtered under a pressure of 0.5 MPa, or by pressing with a plate and frame filter press, to separate the extract filtrate. The filtrate is collected, and the filter residue can be disposed of separately.
[0063] S4. Concentration:
[0064] The filtrate obtained in step S3 was concentrated by rotary evaporation under reduced pressure at a water bath temperature of 40°C, reducing the volume of the filtrate to 1 / 4 of its original volume, to obtain a concentrated pomegranate peel dye solution.
[0065] S5. UV absorber compound:
[0066] Add a UV absorber, benzophenone, to the concentrated dye solution obtained in step S4. The amount of benzophenone added is in a mass ratio of 1:15 to the original dry pomegranate peel. Mechanically stir at 500 rpm for 3 hours at 40°C until the UV absorber is completely dissolved and evenly mixed with the dye solution.
[0067] S6. Drying and grinding:
[0068] The uniformly mixed solution from step S5 is then spray-dried. The inlet air temperature is controlled at 160℃, the outlet air temperature at 90℃, and the atomizer speed is adjusted to 15000 rpm. The powder obtained from the bottom of the drying tower is collected to obtain the pomegranate peel plant dye powder with high light fastness, the properties of which are:
[0069] Light fading rate: 38.1%;
[0070] Color (L, a, b*): (77.9, 4.6, 41.8), ΔEvs Comparative Example 1 = 0.6 (a minute change, difficult to detect with the naked eye). Non-reactive UV absorbers have some effect, but the improvement is limited (fading rate reduced by 14.4%). This is because the binding force between the absorber and the dye molecules is weak due to the physical mixing.
[0071] Example 2
[0072] A method for improving the light fastness of plant dyes on pomegranate peel includes the following steps:
[0073] S1. Raw material pretreatment:
[0074] Fresh pomegranate peels are washed to remove impurities, placed in a freeze dryer, and frozen solidified at -40℃ to -55℃. Then, they are sublimated and dried under a vacuum of 0.1-10 Pa until the moisture content is below 5 wt%. The dried pomegranate peel raw material is then ultra-finely pulverized using an ultra-micro pulverizer and passed through a 100-mesh sieve to obtain coarse pomegranate peel powder.
[0075] S2. High-pressure extraction:
[0076] The pomegranate peel powder obtained in step S1 was mixed with a 70% ethanol-water solution at a material-to-liquid ratio of 1:12 (g / mL) and placed in a high-pressure reactor. The reactor was sealed, and the temperature was raised to 40°C with a stirring speed of 200 rpm, and a static pressure of 250 MPa was applied. The mixture was then subjected to constant temperature and pressure extraction for 6 hours.
[0077] S3. Solid-liquid separation:
[0078] After extraction, the material in the reactor is removed and filtered under a pressure of 0.2 MPa, or by pressing with a plate and frame filter press, to separate the extract filtrate. The filtrate is collected, and the filter residue can be disposed of separately.
[0079] S4. Concentration:
[0080] The filtrate obtained in step S3 was concentrated by rotary evaporation under reduced pressure at a water bath temperature of 50°C, reducing the volume of the filtrate to 1 / 4.5 of its original volume, thus obtaining a concentrated pomegranate peel dye solution.
[0081] S5. UV absorber compound:
[0082] A UV absorber, 2-hydroxybenzophenone, is added to the concentrated dye solution obtained in step S4 at a mass ratio of 1:18 to the original dried pomegranate peel. The mixture is mechanically stirred at 600 rpm for 2 hours at 50°C until the UV absorber is completely dissolved and evenly mixed with the dye solution.
[0083] S6. Drying and grinding:
[0084] The uniformly mixed solution from step S5 is then spray-dried. The inlet air temperature is controlled at 140℃, the outlet air temperature at 80℃, and the atomizer speed is adjusted to 20,000 rpm. The powder obtained from the bottom of the drying tower is collected to obtain the pomegranate peel plant dye powder with high light fastness, the properties of which are:
[0085] Light fading rate: 32.7%;
[0086] Color: (77.5, 4.8, 41.5), ΔE = 1.0, contains phenolic hydroxyl groups, which may form weak hydrogen bonds with dye molecules, and its effect is better than benzophenone (fading rate reduced by 26.5%).
[0087] Example 3
[0088] A method for improving the light fastness of plant dyes on pomegranate peel includes the following steps:
[0089] S1. Raw material pretreatment:
[0090] Fresh pomegranate peels were washed to remove impurities, placed in a freeze dryer, and frozen solidified at -40℃ to -55℃. Then, they were sublimated under a vacuum of 0.1-10 Pa until the moisture content was below 5 wt%. The dried pomegranate peel raw material was then ultra-finely pulverized using an ultra-micro pulverizer and passed through a 120-mesh sieve to obtain coarse pomegranate peel powder.
[0091] S2. High-pressure extraction:
[0092] The pomegranate peel powder obtained in step S1 was mixed with a 60% ethanol-water solution at a ratio of 1:10 (g / mL) and placed in a high-pressure reactor. The reactor was sealed, and the temperature was raised to 30°C with a stirring speed of 100 rpm. A static pressure of 200 MPa was applied, and the mixture was extracted under constant temperature and pressure for 8 hours.
[0093] S3. Solid-liquid separation:
[0094] After extraction, the material in the reactor is removed and filtered under a pressure of 0.1 MPa, or by pressing with a plate and frame filter press, to separate the extract filtrate. The filtrate is collected, and the filter residue can be disposed of separately.
[0095] S4. Concentration:
[0096] The filtrate obtained in step S3 was concentrated by rotary evaporation under reduced pressure at a water bath temperature of 60°C, reducing the volume of the filtrate to 1 / 5 of its original volume, to obtain a concentrated pomegranate peel dye solution.
[0097] S5. UV absorber compound:
[0098] A UV absorber, one of 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, is added to the concentrated dye solution obtained in step S4, and the amount added is in a mass ratio of 1:20 to the original dried pomegranate peel. The mixture is mechanically stirred at 800 rpm for 1 hour at 60°C until the UV absorber is completely dissolved and evenly mixed with the dye solution.
[0099] S6. Drying and grinding:
[0100] The uniformly mixed solution from step S5 is then spray-dried. The inlet air temperature is controlled at 120℃, the outlet air temperature at 70℃, and the atomizer speed is adjusted to 25000 rpm. The powder obtained from the bottom of the drying tower is collected to obtain the pomegranate peel plant dye powder with high light fastness, the properties of which are:
[0101] Light fading rate: 28.3%;
[0102] Color: (76.8, 5.0, 40.9), ΔE = 1.8, multifunctional structure with stronger interaction, significantly improved light fastness (fading rate reduced by 36.4%).
[0103] Example 4
[0104] The ultraviolet absorber was the 2-hydroxy-4-methoxybenzophenone nickel(II) complex from Preparation Example 1, and the rest was the same as in Example 2. Its product properties are as follows:
[0105] Light fading rate: 12.5%;
[0106] Colorimetric values: (58.7, 0.5, 18.9) -> grayish-khaki, ΔE = 28.2, similar to the effect of the Cu(II) complex. The color changes to a calm grayish-khaki, further demonstrating the occurrence of a coordination reaction. The Ni(II) complex produces a more sophisticated grayish tone.
[0107] Example 5
[0108] The ultraviolet absorber was the 2-hydroxy-4-methoxybenzophenone copper(II) complex from Preparation Example 2, and the rest was the same as in Example 2. Its product properties are as follows:
[0109] Light fading rate: 9.8%;
[0110] Chromaticity (L,a,b*): (55.2,-2.1,15.3) -> olive green, ΔEvs Comparative Example 1 = 33.5 (huge change), fastness is significantly improved (fading rate reduced by 78%). The color changes from bright yellow to olive green, proving that Cu 2+ It underwent a strong coordination reaction with tannins, forming a novel ternary complex of dye-metal-UV absorber with extremely high photostability.
[0111] Comparative Example 1
[0112] The basic process, without adding any UV absorbers, serves as a blank control. Its product performance is as follows:
[0113] Light fading rate: 44.5%;
[0114] The color of the dyed silk (L,a,b*): (78.3,4.5,42.1)->bright yellow. As a blank control, it shows that the pomegranate peel dye itself has poor light fastness, and nearly half of the color faded after 40 hours of light exposure.
[0115] Comparative Example 2 (Traditional Post-Processing Method)
[0116] Process: Silk was dyed using the dye from Comparative Example 1, and then the dyed fabric was immersed in a 2-hydroxybenzophenone solution (concentration equivalent to the active ingredient in Example 1). The product performance is as follows:
[0117] The light fading rate was 25.6%, and the effect of the finishing method was far worse than that of the source addition method of this invention (25.6% vs 9.8%). The reason is that the finishing agent only adheres to the fiber surface, is unevenly distributed, and is easily lost.
[0118] Comparative Example 3 (Simple Mixing Method)
[0119] Process: In step S5, first add an equimolar amount of CuCl2 as in Example 2, then add an equimolar amount of 2-hydroxy-4-methoxybenzophenone (non-pre-synthesized complex).
[0120] Light fading rate: 20.4%;
[0121] Colorimetric properties: (56.0, -1.8, 14.7) -> The color is similar to that of Example 2. The color change proves that the coordination reaction did occur, but the improvement in light fastness (54.2%) is far less than that of the pre-synthesized complex (78%). This is because the on-site reaction is difficult to control and may generate multiple complexes with heterogeneous structures and poor performance. In contrast, the pre-synthesized complex has a well-defined structure and stable properties, and can more effectively exert a synergistic effect.
[0122] The data from Examples 1-5 and Comparative Examples 1-3 are summarized in Table 1:
[0123] Table 1. Effects of UV absorbers and finishing processes on dye properties
[0124]
[0125] in conclusion:
[0126] Efficacy Verification: All groups with added UV absorbers showed improved light fastness, but the metal complex-type UV absorbers in Examples 4-5 significantly outperformed the traditional types in Examples 1-3, reducing light fading rate by over 75%. The substantial color difference (ΔE) and extremely high photostability enhancement strongly demonstrate that coordination bonds are key to achieving "source modification." Metal ions act as a bridge, firmly binding the UV absorber to the dye molecules, forming a new substance with inherently high photostability.
[0127] Process advantages: The pre-synthesized complexes of Examples 4-5 are far superior to the simple mixing of Comparative Example 2 and the post-treatment of Comparative Example 3, highlighting the advanced nature and necessity of the process of this invention.
[0128] Added value: This invention not only improves light fastness, but also significantly expands the color gamut of pomegranate peel dyes, obtaining high-end shades such as olive green and gray khaki that are difficult to achieve by traditional methods, thus increasing the added value of the product.
[0129] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.
Claims
1. A method for improving the light fastness of plant dyes on pomegranate peel, characterized in that, Includes the following steps: S1. Raw material pretreatment: Fresh pomegranate peel is washed to remove impurities, freeze-dried, ultra-finely pulverized and sieved to obtain pomegranate peel coarse powder; S2. High-pressure extraction: The pomegranate peel powder obtained in S1 was subjected to high-pressure extraction with an ethanol-water solution; S3. Solid-liquid separation: After extraction, the filtrate is obtained by filtration; S4. Concentration: The extract filtrate obtained in S3 is evaporated under reduced pressure to obtain a concentrated pomegranate peel dye solution; S5. UV absorber compounding: Add UV absorber to the concentrated dye solution obtained in S4, and mechanically stir at 500-800 rpm for 1-3 hours at 40-60℃ until the UV absorber is completely dissolved and mixed evenly with the dye solution. S6. Drying and grinding: The solution mixed evenly in step S5 is spray-dried to obtain pomegranate peel plant dye powder with high light fastness. This invention introduces a UV absorber during the dye extraction stage, ensuring thorough and uniform mixing with dye molecules (such as tannins), and forming a uniform powder during spray drying. This UV absorber continuously and effectively shields or absorbs ultraviolet light during subsequent dyeing and product use, fundamentally improving the inherent photostability of the dye, resulting in superior performance compared to finishing processes on fabrics.
2. The method for improving the light fastness of plant dyes on pomegranate peel according to claim 1, characterized in that, The specific steps of S1 are as follows: clean the fresh pomegranate peel to remove impurities, place it in a freeze dryer, freeze-solidify it at a temperature of -40℃ to -55℃, and then sublimate it under a vacuum of 0.1-10Pa until the moisture content is less than 5wt%; then use an ultra-fine pulverizer to pulverize the dried pomegranate peel raw material, and pass it through an 80-120 mesh sieve to obtain pomegranate peel coarse powder.
3. The method for improving the light fastness of plant dyes on pomegranate peel according to claim 1, characterized in that, The specific steps of S2 are as follows: the pomegranate peel powder obtained in S1 is mixed with an ethanol-water solution with an ethanol concentration of 60%-80% at a material-liquid ratio of 1:10-1:15 (g / mL), placed in a high-pressure reactor, the reactor is sealed, and the temperature is raised to 30-45℃ under the condition of stirring speed of 100-300 rpm, and a static pressure of 200-350 MPa is applied. Under these conditions, the mixture is extracted at constant temperature and pressure for 4-8 hours.
4. The method for improving the light fastness of plant dyes on pomegranate peel according to claim 1, characterized in that, The specific steps of S3 are as follows: the material in the reactor is taken out and filtered under a pressure of 0.1-0.5MPa, or a plate and frame filter press is used for pressure filtration to separate the leachate, collect the filtrate, and the filter residue can be processed separately.
5. The method for improving the light fastness of plant dyes on pomegranate peel according to claim 1, characterized in that, The specific steps of S4 are as follows: the filtrate obtained in S3 is concentrated by vacuum rotary evaporation at a water bath temperature of 40-60℃, and the volume of the filtrate is concentrated to 1 / 4 to 1 / 5 of the original volume to obtain concentrated pomegranate peel dye solution.
6. The method for improving the light fastness of plant dyes on pomegranate peel according to claim 1, characterized in that, In step S6, the inlet air temperature of the spray dryer is controlled at 120-160℃, the outlet air temperature is controlled at 70-90℃, the atomizer speed is adjusted to 15000-25000rpm, and the powder obtained from the bottom of the drying tower is collected to obtain the pomegranate peel plant dye powder with high light fastness.
7. The method for improving the light fastness of plant dyes on pomegranate peel according to claim 1, characterized in that, The ultraviolet absorber is one of benzophenone, 2-hydroxybenzophenone, and 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, and its addition amount is in a mass ratio of 1:15 to 1:20 with the original dried pomegranate peel.
8. The method for improving the light fastness of plant dyes on pomegranate peel according to claim 1, characterized in that, The ultraviolet absorber is a 2-hydroxy-4-methoxybenzophenone nickel(II) complex or a 2-hydroxy-4-methoxybenzophenone copper(II) complex, and its addition amount is in the mass ratio of 1:15 to 1:20 with the original dry pomegranate peel.
9. The method for improving the light fastness of plant dyes on pomegranate peel according to claim 1, characterized in that, The synthesis steps of the 2-hydroxy-4-methoxybenzophenone nickel(II) complex or the 2-hydroxy-4-methoxybenzophenone copper(II) complex are as follows: At room temperature, 0.1 mol of 2-hydroxy-4-methoxybenzophenone was dissolved in 100 mL of anhydrous ethanol, and then 60 mL of 1 mol / L NaOH aqueous solution was added. After stirring and mixing, 0.5 mol / L copper chloride or nickel chloride aqueous solution was slowly added dropwise. After stirring and reacting for 1.5 h, a precipitate was formed. After aging at room temperature for 24 h, the precipitate was filtered under reduced pressure. The filter cake was washed several times with 1:1 ethanol aqueous solution and then dried at 100 °C to constant weight to obtain 2-hydroxy-4-methoxybenzophenone nickel(II) complex (pale green) or 2-hydroxy-4-methoxybenzophenone copper(II) complex (dark green). The molecular formula of 2-hydroxy-4-methoxybenzophenone is: The possible structures of the 2-hydroxy-4-methoxybenzophenone nickel(II) complex (pale green) and the 2-hydroxy-4-methoxybenzophenone copper(II) complex obtained after complexation are as follows:
10. The pomegranate peel plant dye prepared by any one of the methods described in claims 1-9.