Light-resistant dispersed tannin as well as preparation method and application thereof

Abstract

The invention belongs to the field of leather auxiliaries, and particularly relates to light-resistant dispersed tannin as well as a preparation method and application thereof. The preparation method comprises the following steps: dissolving hydrolytic tannin (the molecular weight is 500-3000Da) into water, and sterilizing to obtain a 5-8wt% tannin solution; dissolving chitosan in 1-2wt% of acetic acid to obtain a 2-3wt% chitosan solution; quercetin is dissolved in ethyl alcohol, and a 10-12 mg / mL solution is obtained. Mixing the three solutions according to the mass ratio of (5-6): (2-3): (0.5-0.6), stirring for 30-40 minutes at the temperature of 25-30 DEG C and the speed of 60-80 r / min, adjusting the pH value to 6.5, performing self-assembly, performing micro-jet homogenization (1000-1200 bar) to obtain a dispersion liquid with the particle size of 130-170 nm, performing centrifugation at the speed of 8000-10000 r / min, and performing freeze-drying at the temperature of-50 DEG C to obtain the light-resistant dispersed tannin. The obtained product is light-resistant and excellent in dispersity, retains tannin activity, and can be used for preparing leather auxiliaries.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of leather auxiliaries, and particularly relates to a light-resistant dispersed tannin as well as a preparation method and application thereof. BACKGROUND

[0002] Tannins, as natural polyphenolic compounds widely existing in plants, have irreplaceable application value in the fields of food, medicine, cosmetics and especially leather auxiliaries due to their excellent antioxidant, antibacterial and ultraviolet absorption capabilities. In leather processing, tannins can not only realize tanning function to improve the flexibility of leather, but also can delay the aging and discoloration of leather by absorbing ultraviolet rays, and are natural auxiliaries meeting the current environmental protection trend.

[0003] However, the phenolic hydroxyl groups in the molecular structure of tannins are extremely sensitive to light, which becomes a key obstacle for the large-scale application of tannins in the leather field. During the storage and use of leather, ultraviolet irradiation will cause tannins to rapidly degrade or polymerize, on the one hand, causing the loss of antioxidant and antibacterial activity, and failing to continuously protect the leather; on the other hand, it will cause the deepening of the color of leather (such as browning), which seriously affects the appearance consistency of the product.

[0004] The current technical paths for improving the light resistance of tannins in the industry all have significant defects, which are difficult to meet the actual needs of leather auxiliaries: Chemical modification method (such as acetylation, esterification): this method reduces the light sensitivity by blocking the phenolic hydroxyl groups of tannins, but needs to be carried out under strong acid (such as concentrated sulfuric acid) or high temperature (80-120℃) conditions. Strong acid will destroy the polyphenolic skeleton of tannins, resulting in the loss of tanning and antibacterial activity. High temperature is easy to cause carbonization of tannins, and the impurities generated will form spots on the surface of leather. In addition, the organic waste liquid generated during the reaction process needs to be treated additionally, which does not meet the green leather processing standard.

[0005] Physical embedding method (such as microencapsulation, liposome wrapping): the existing technology mostly uses β-cyclodextrin, gum arabic and the like as wall materials to isolate ultraviolet rays, but due to the compatibility of the wall material with tannins, the embedding efficiency is generally lower than 60%, and a large amount of unembedded tannins will still be ineffective under light. At the same time, mechanical stirring (the rotation speed is usually 300-500 r / min) and pH fluctuation (the pH of leather tanning is mostly 3-8) in the leather processing process are easy to cause the rupture of microcapsules, and the released tannins will excessively combine with collagen in leather, causing the leather to be hard and brittle.

[0006] Additive compounding method: synthetic UV absorbers such as benzotriazole and benzophenone are added to enhance light resistance, but the compatibility of such synthetic additives with tannins is poor, and delamination is easy to occur during the leather finishing process. Moreover, with the use of leather, the additives will gradually migrate and precipitate to the surface, forming white powder (i.e. "white spots"), which seriously reduces the commercial value of leather.

[0007] In addition, the particle size of the tannin particles prepared by the traditional process is generally greater than 1 mu m, the specific surface area is too high (> 5 m 2 / g), which further increases the contact probability with ultraviolet light and accelerates degradation; at the same time, the large particle size particles are not uniformly dispersed in the leather finishing liquid, which can cause differences in the gloss of the leather surface and affect the product quality stability.

[0008] With the tightening of global environmental regulations, there is an urgent need for natural, efficient and stable leather auxiliaries in the market, and the existing technology cannot solve the problem of "retaining tannin activity" and "improving light resistance and dispersibility", so it is urgent to develop a mild, efficient and suitable tannin modification technology for leather processing scene.

[0009] Therefore, based on this, the technical scheme of the present application is proposed. SUMMARY

[0010] The traditional dispersed tannin has the problems of poor light stability, easy loss of activity and uneven dispersion in application. Specifically, the existing chemical modification method needs to be carried out under strong acid / high temperature conditions, which leads to the destruction of the natural active structure of tannin; the addition of exogenous light stabilizer can easily cause poor compatibility and uneven dispersion; at the same time, the particle size of the tannin particles prepared by the traditional process is too large (> 1 mu m), and the specific surface area is high, which makes it more susceptible to ultraviolet light attack and degradation.

[0011] In view of these problems, the present application provides a mild and controllable preparation method, which significantly improves the light resistance and dispersion stability of tannin while retaining the activity of tannin through nano-dispersion technology and natural ingredient compounding, and the preparation method comprises the following steps: (1) dissolving tannin in water to obtain a tannin solution; (2) dissolving chitosan in acetic acid solution to obtain a chitosan solution; (3) dissolving quercetin in ethanol to obtain a quercetin solution; (4) mixing the tannin solution, the chitosan solution and the quercetin solution, stirring and adjusting the pH value of the system to trigger the electrostatic self-assembly of tannin-chitosan to obtain a mixed solution; (5) homogeneously dispersing the mixed solution to obtain a dispersion liquid; (6) centrifuging the dispersion liquid to remove unembedded components, and then drying to obtain the light-resistant dispersed tannin.

[0012] Preferably, in step (1), the tannin is a hydrolyzed tannin, and the molecular weight of the hydrolyzed tannin is 500-3000 Da; and / or, the concentration of the tannin solution is 5-8 wt%; and / or, dissolving tannin in water, sterilizing through a 0.22 mu m filter membrane to obtain a tannin solution.

[0013] Preferably, in step (2), the degree of deacetylation of the chitosan is greater than or equal to 90%. And / or, the concentration of the acetic acid solution is 1-2 wt%. And / or, the concentration of the chitosan in the chitosan solution is 2-3 wt%.

[0014] Preferably, in step (3), the concentration of the quercetin solution is 10-12 mg / mL.

[0015] Preferably, in step (4), the mass ratio of the tannin solution, the chitosan solution and the quercetin solution is 5-6:2-3:0.5-0.6.

[0016] Preferably, in step (4), the stirring speed is 60-80 r / min, the stirring temperature is 25-30 DEG C, and the stirring time is 30-40 min. And / or, the pH value of the adjusting system is 6.5.

[0017] Preferably, in step (5), the homogenously dispersed manner is that the dispersion liquid with a particle size of 130-170 nm is obtained by circulating 3-4 times under the condition of a pressure of 1000-1200 bar through a microfluidic homogenizer.

[0018] Preferably, in step (6), the centrifugation speed is 8000-10000 r / min, and the centrifugation time is 10-15 min. And / or, the drying manner is freeze-drying at-50 DEG C for 24-28 h.

[0019] Based on the same technical concept, another aspect of the present application provides a light-resistant dispersed tannin obtained by the preparation method.

[0020] Based on the same technical concept, another aspect of the present application provides an application of the light-resistant dispersed tannin in preparing a leather auxiliary agent.

[0021] The present application has the following advantages: The preparation method of the light-resistant dispersed tannin provided by the present application solves the core problems of "difficult to retain tannin activity, poor light resistance and uneven dispersion" in the prior art through the synergistic design of "natural ingredient compounding + nanodispersion technology + mild self-assembly process", and the prepared product not only has excellent light resistance, dispersion stability and biological activity, but also does not require strong acid and high temperature, and does not contain synthetic additives, which meets the requirements of green leather processing and can be directly used for large-scale production of leather auxiliary agents.

[0022] 1. Mild process retains full activity of tannin, avoids defects of chemical modification method: The present application uses normal temperature (25-30℃) and neutral pH (6.5) conditions throughout, without the need for strong acid or high temperature - the polyphenol skeleton and phenolic hydroxyl groups of tannin are not destroyed, and the tanning, antibacterial and antioxidant activity retention rate is over 90%, solving the problems of activity loss and hard and brittle leather caused by chemical modification method.

[0023] 2. High embedding efficiency + anti-breakage, breaking through the bottleneck of physical embedding method: Through the combination process of "tannin-chitosan electrostatic self-assembly + microfluidic homogenization", chitosan (degree of deacetylation ≥ 90%) can form a stable core-shell structure with tannin, and the embedding efficiency is improved to more than 85%; microfluidic homogenization (1000-1200 bar, 3-4 cycles) further controls the particle size of the complex to 130-170 nm, and the particle size uniformity can effectively resist mechanical stress and pH fluctuations in leather processing. Acid and alkali resistance tests show that the product has no precipitation and stratification in hydrochloric acid, formic acid, sulfuric acid and ammonia water environments, completely avoiding the "low embedding efficiency and easy leakage" problem of physical embedding method.

[0024] 3. Natural compounding without migration, solving the compatibility problem of additive compounding method: The present application selects natural polyphenolic compound quercetin as a synergistic light-resistant component, the hydroxyl groups in its molecular structure can form hydrogen bonds with tannin and chitosan, and the three have excellent compatibility; and the ultraviolet absorption band of quercetin and tannin (280-380 nm) is complementary, which can synergistically improve light resistance; at the same time, the combination of quercetin with tannin and chitosan is stable and has no migration and precipitation, completely eliminating the "white spot" problem in leather use.

[0025] 4. Nanoparticle size optimizes performance, improves dispersion defects of traditional particles: The product particle size is controlled at 130-170 nm, the specific surface area is significantly reduced compared to traditional tannin particles (>1 μm), the contact probability with ultraviolet light is reduced, and the light resistance is greatly improved; and the nano-level particles are uniformly dispersed in the leather finishing liquid, with a maximum agglomeration size of only 50 μm, and a dispersion level of "excellent".

[0026] 5. Process adapts to industrial production, balancing efficiency and cost: The preparation steps of the present application (dissolution-mixing-self-assembly-homogenization-centrifugation-drying) are simple and controllable, and the raw materials (tannin, chitosan, quercetin) used are all industrialized mass production products, with low cost; freeze-drying (-50℃, 24-28h) can realize long-term storage of the product (shelf life more than 12 months under sealed conditions), and the dried product is a light yellow powder, easy to measure and transport, which can be directly connected to the existing leather additive production line without additional equipment modification, and has the potential for large-scale application. DETAILED DESCRIPTION

[0027] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described in detail below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work belong to the scope of protection of the present application.

[0028] Embodiment 1 The present embodiment provides a preparation method of light-resistant dispersed tannin, which comprises the following steps: (1) Preparation of tannin solution (ensure that the raw materials are pure and avoid microbial contamination) 952.4g of deionized water was added to a reaction bottle, and stirring was started (speed 500r / min, room temperature 25℃), and 47.6g of hydrolyzed tannin was slowly added (to ensure that the concentration is 5wt%); stirring for 30min to completely dissolve the tannin; the solution was sterilized by 0.22μm organic filter membrane - effect: remove microorganisms (such as bacteria, mold) in water and tannin, avoid microbial degradation of tannin during subsequent storage and reaction, ensure product activity and stability, at the same time, filter out the undissolved tannin impurities, ensure the uniformity of subsequent solution mixing; collect the filtrate, which is 5wt% tannin solution, for standby.

[0029] (2) Preparation of chitosan solution (dissolved in weak acid environment to retain chitosan amino activity) 980.4g of deionized water was added to another reaction bottle, and stirring was started (speed 300r / min, room temperature 25℃), and 19.6g of analytical pure acetic acid was slowly added, and stirring was started for 10min to completely dissolve the acetic acid; then 2.04g of chitosan was added, and stirring was continued for 60min to completely dissolve the chitosan - effect: 1wt% acetic acid is a weak acid environment, which can protonate the amino group (-NH2) of chitosan to -NH3 + , which ensures complete dissolution of chitosan and avoids destruction of the amino group structure by strong acid, laying a foundation for subsequent electrostatic self-assembly with tannin.

[0030] (3) Preparation of quercetin solution (ensure complete dissolution of quercetin and avoid interference of solid particles) Into another reaction bottle, 100 mL of anhydrous ethanol was added, and the ultrasonic (power 300 W, frequency 20 kHz) was turned on. Then, 1.01 g of quercetin was slowly added. The ultrasonic was applied for 10 min to ensure the complete dissolution of quercetin. The anhydrous ethanol was a good solvent for quercetin, which could ensure its complete dissolution and avoid the formation of impurities from undissolved quercetin solid particles in the subsequent mixing. The ultrasonic-assisted dissolution could shorten the dissolution time (from 60 min of conventional stirring to 10 min) and improve the industrial production efficiency. The solution was collected, which was a 10 mg / mL quercetin solution, ready for use.

[0031] (4) Mixing and electrostatic self-assembly (precise control of ratio and conditions to form stable complexes) Into the reaction bottle, 500 g of tannin solution, 200 g of chitosan solution, and 50 g of quercetin solution (mass ratio 5:2:0.5, meeting the formula requirements) were added. The stirring was started (speed 60 r / min), and the temperature in the reaction bottle was controlled at 25°C. The stirring was continued for 30 min. After the stirring was completed, 0.1 M sodium hydroxide aqueous solution was slowly added by a dropping pump to adjust the pH of the system to 6.5 (real-time monitoring by an online pH meter, pH fluctuation range ±0.1). The stirring was continued for 5 min to trigger the electrostatic self-assembly of tannin-chitosan. The ratio of 5:2:0.5 could make the carboxyl group (-COOH) of tannin and the -NH3 + of chitosan form hydrogen bonds, ensuring the stability of the complex structure. The low-speed stirring of 60 r / min could avoid the generation of bubbles during the mixing process (bubbles would affect the subsequent homogenization effect). The normal temperature of 25°C could retain the activity of each component. The pH of 6.5 was the best balance point for the protonation of chitosan and the dissolution of tannin, which could maximize the self-assembly efficiency. The mixed liquid was obtained and ready for use.

[0032] (5) Microfluidic homogenization (refining particle size, improving dispersibility and embedding stability) The mixed liquid was transferred into a microfluidic homogenizer, and the homogenization pressure was set to 1000 bar. The device was turned on to circulate the mixed liquid for 3 times (monitored by the device flow meter and pressure sensor, and each cycle time was about 1 h). During the homogenization process, the online particle size analyzer was used for real-time monitoring to ensure that the particle size of the dispersed liquid was stable at 150±20 nm. The high pressure of 1000 bar could make the complex particles in the mixed liquid undergo shearing and collision, thereby refining the particle size to the nanoscale. Three cycles could ensure the uniformity of the particle size (CV value <10%), avoiding the existence of large particles. The nanoscale particle size not only improved the dispersibility, but also enhanced the tightness of chitosan wrapping tannin, reducing the exposure of tannin under light. The dispersed liquid was obtained and ready for use.

[0033] (6) Centrifugal purification (removing unembedded components, improving product purity) The dispersion liquid is transferred into a high-speed centrifuge, the centrifugal speed is set to 8000 r / min, and the centrifugal time is 10 min (monitored by the centrifuge speed controller and timer); after centrifugation, the supernatant is collected (the lower sediment is un-embedded tannin, chitosan and quercetin, which can be recycled and used) - effect: the centrifugal force of 8000 r / min can effectively separate the free components that do not participate in self-assembly, avoiding their influence on the light resistance and dispersibility of the product; recycling the sediment can reduce the loss of raw materials, and the utilization rate of raw materials in industrial production can be improved to more than 92%; the purified dispersion liquid is obtained and ready for use.

[0034] (7) Freeze-drying (low-temperature drying, retaining activity, facilitating storage and transportation) The purified dispersion liquid is transferred into an industrial freeze-drier (freeze-drying area 10 m 2 , cold trap temperature -80℃), pre-frozen at -50℃ for 2h (to completely freeze the dispersion liquid and avoid particle agglomeration during drying), and then freeze-dried at -50℃ and a vacuum degree of 10 Pa for 24h (monitored by the freeze-drier temperature sensor and vacuum gauge) - effect: -50℃ low-temperature drying can avoid the degradation of tannin due to high temperature, maximizing the retention of its activity; the vacuum environment can accelerate the sublimation of water, and the product moisture content can be reduced to less than 3% in 24h, meeting the storage requirements of leather auxiliaries (moisture content > 5% is prone to moisture absorption and caking); the dried product is a light yellow powder with good flowability, facilitating subsequent metering, packaging and transportation; the powder collected is the light-resistant dispersed tannin product.

[0035] Example 2 The present embodiment provides a preparation method of light-resistant dispersed tannin, which comprises the following steps (brief description): (1) Dissolve tannin (hydrolyzed type, average molecular weight about 2000 Da) in deionized water, sterilize through a 0.22μm filter membrane, and obtain a tannin solution with a concentration of 8wt%; (2) Dissolve chitosan (degree of deacetylation ≥90%) in a 2wt% acetic acid solution to obtain a 3wt% chitosan solution; (3) Dissolve quercetin in ethanol to obtain a quercetin solution with a concentration of 12mg / mL; (4) Mix the tannin solution, chitosan solution and quercetin solution according to a mass ratio of 6:3:0.6, magnetically stir at 30℃ and 80r / min for 40min, adjust the pH of the system to 6.5 with a 0.1M NaOH solution, trigger the electrostatic self-assembly of tannin-chitosan, and obtain a mixed solution; (5) Pass the mixed solution through a microfluidizer (pressure 1200bar, cycle 4 times) to obtain a dispersion liquid with a particle size of 150±20nm; (6) The dispersion liquid is centrifuged (10000 r / min, 15 min) to remove the unembedded components, and then freeze-dried at -50°C for 28 h to obtain the light-resistant dispersed tannin (light yellow powder).

[0036] Example 3 The present example provides a preparation method of light-resistant dispersed tannin, which comprises the following steps (briefly described): (1) Dissolve tannin (hydrolyzed type, average molecular weight about 3000 Da) in deionized water, sterilize through a 0.22 μm filter membrane, and obtain a tannin solution with a concentration of 6 wt%; (2) Dissolve chitosan (degree of deacetylation ≥90%) in a 2 wt% acetic acid solution to obtain a 3 wt% chitosan solution; (3) Dissolve quercetin in ethanol to obtain a quercetin solution with a concentration of 11 mg / mL; (4) Mix the tannin solution, chitosan solution and quercetin solution according to a mass ratio of 6:2:0.6, magnetically stir at 28°C and 70 r / min for 35 min, adjust the pH of the system to 6.5 with a 0.1M NaOH solution, and trigger the electrostatic self-assembly of tannin-chitosan to obtain a mixed solution; (5) Pass the mixed solution through a microfluidic homogenizer (pressure 1100 bar, cycle 4 times) to obtain a dispersion liquid with a particle size of 150±20 nm; (6) Centrifuge the dispersion liquid (9000 r / min, 12 min) to remove the unembedded components, and then freeze-dry at -50°C for 26 h to obtain the light-resistant dispersed tannin (light yellow powder).

[0037] Verification Example The dispersed tannin obtained in Examples 1-3 is compared with a commercially available similar product (comparative example) for testing, and the results are shown in Tables 1-4.

[0038] Table 1 Acid and alkali resistance test data

[0039] Table 2 Tear resistance data

[0040] Table 3 Light resistance performance data

[0041] Table 4 Dispersion performance data

[0042] The above merely illustrates the specific embodiments of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of the changes or replacements within the technical range disclosed by the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for preparing a light-resistant dispersed tannin, characterized by, The preparation method comprises the following steps: (1) dissolving tannin in water to obtain a tannin solution; (2) dissolving chitosan in an acetic acid solution to obtain a chitosan solution; (3) dissolving quercetin in ethanol to obtain a quercetin solution; (4) mixing the tannin solution, the chitosan solution and the quercetin solution, stirring and adjusting the pH value of the system to trigger the electrostatic self-assembly of tannin-chitosan to obtain a mixed solution; (5) homogeneously dispersing the mixed solution to obtain a dispersion liquid; (6) removing un-embedded components from the dispersion liquid by centrifugation, and then drying to obtain the light-resistant dispersed tannin.

2. The method for producing light-resistant dispersed tannin according to claim 1, characterized by, In step (1), the tannin is a hydrolyzed tannin, and the molecular weight of the hydrolyzed tannin is 500-3000 Da; And / or, the concentration of the tannin solution is 5-8 wt%; And / or, the tannin is dissolved in water, sterilized through a 0.22 μm filter membrane to obtain the tannin solution.

3. The method for preparing light-resistant dispersed tannins according to claim 1, characterized in that, In step (2), the degree of deacetylation of the chitosan is ≥90%; And / or, the concentration of the acetic acid solution is 1-2 wt%; And / or, in the chitosan solution, the concentration of chitosan is 2-3 wt%.

4. The method for preparing light-resistant dispersed tannins according to claim 1, characterized in that, In step (3), the concentration of the quercetin solution is 10-12 mg / mL.

5. The method for preparing light-resistant dispersed tannins according to claim 1, characterized in that, In step (4), the mass ratio of the tannin solution, the chitosan solution and the quercetin solution is 5-6:2-3:0.5-0.

6.

6. The method for preparing light-resistant dispersed tannins according to claim 1, characterized in that, In step (4), the stirring speed is 60-80 r / min, the stirring temperature is 25-30℃, and the stirring time is 30-40 min; And / or, the pH value of the system is adjusted to 6.

5.

7. The method for preparing light-resistant dispersed tannins according to claim 1, characterized in that, In step (5), the homogenously dispersed manner is: circulating 3-4 times through a microfluidic homogenizer under a pressure of 1000-1200 bar to obtain a dispersion liquid with a particle size of 130-170 nm.

8. The method for preparing light-resistant dispersed tannins according to claim 1, characterized in that, In step (6), the centrifugation speed is 8000-10000 r / min, and the centrifugation time is 10-15 min; And / or, the drying manner is: freeze-drying at-50℃ for 24-28 h.

9. The light-resistant dispersed tannin obtained by the preparation method of any one of claims 1-8.

10. The use of the light-resistant dispersed tannin of claim 9 in preparing a leather aid.

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