Preparation method of type Ⅱ crystal of bacterial cellulose, and product and application thereof

Abstract

This invention discloses a method for preparing bacterial cellulose type II crystals, the resulting product, and its applications. The method involves washing, granulating, removing impurities, soaking in alkali, synthesizing, filtering, centrifuging, washing, and drying bacterial cellulose gel to obtain cellulose type II crystals. This invention achieves solid-phase transformation of bacterial cellulose to prepare cellulose type II crystals by controlling the conditions of the medium. The process is simple, and all reagents used are recyclable. This method can also be extended to plant and animal cellulose. The obtained cellulose type II crystals have a particle size of 0.1-500 μm, are non-agglomerated, and have good dispersibility, making them a suitable replacement for plastic microbeads in cosmetics, chemicals, materials, and medical fields.

Description

Technical Field

[0001] This invention relates to a method for preparing bacterial cellulose type II crystals, the resulting product, and its applications, belonging to the field of green material processing and application technology. Background Technology

[0002] Natural cellulose is the most abundant biomass resource on Earth and the most widely distributed biopolymer in nature, found in plants, animals, and some bacteria. Cellulose nanocrystals (CNCs) are nanoscale cellulose extracted from natural fibers. They not only possess the characteristics of nanoparticles but also exhibit unique strength and optical properties. The most common preparation processes for CNCs are acid hydrolysis and enzymatic hydrolysis. In these methods, the amorphous regions of cellulose are preferentially hydrolyzed, while the crystalline regions remain intact due to their inherent structural stability. Common CNCs are type I cellulose crystals, characterized by large specific surface area, high crystallinity and surface activity, modifiable hydroxyl groups, and excellent mechanical properties, giving CNCs broad application prospects in various fields.

[0003] Plastic microbeads are commonly used in daily chemical products for their exfoliating, scrubbing, and cleaning functions. However, considering the slow degradation of plastics and their environmental harm, finding alternatives is extremely important. CNC particles, being too small, are ineffective for these functions. Therefore, there is an urgent need to develop large-particle cellulose crystal materials to replace plastic microbeads. Summary of the Invention

[0004] To address the problem of the difficulty in degrading plastic microbeads, this invention provides a method and product for preparing bacterial cellulose type II crystals to meet market demand. This method uses bacterial cellulose as raw material to obtain micron-sized large-particle cellulose type II crystals through solid-phase conversion. The process is simple, and all reagents used can be recycled and reused. The resulting cellulose type II crystals have a particle size of 0.1-500 μm, which is adjustable and controllable. They can replace plastic microbeads in cosmetics, pharmaceuticals, chemicals, and composite materials.

[0005] The specific technical solution of this invention is as follows: A method for preparing cellulose type II crystals, wherein bacterial cellulose gel is subjected to rinsing, granulation, impurity removal, alkali soaking, synthesis, filtration, centrifugation, washing and drying to obtain cellulose type II crystals.

[0006] Furthermore, the bacterial cellulose gel used in this invention is obtained by the bio-fermentation of Acetic Acid Bacillus. It is in gel form and can be commercially available or prepared by methods disclosed in the prior art.

[0007] Furthermore, the rinsing refers to washing the bacterial cellulose gel with water to remove surface contaminants.

[0008] Furthermore, the granulation involves cutting the rinsed bacterial cellulose gel into granules with a particle size of less than or equal to 8 mm using equipment such as a cutting machine. For example, it can be cut into granules with a particle size of 1 mm × 1 mm × 1 mm, 5 mm × 5 mm × 5 mm, 8 mm × 8 mm × 8 mm, or irregular granules.

[0009] Furthermore, the impurity removal involves adding the granulated bacterial cellulose particles to an alkaline solution to obtain an alkaline / bacterial cellulose particle system with an alkaline content of 0.5-1 wt%. The system is then boiled at 100°C for 1-1.5 hours. After boiling, the mixture is filtered and washed with water. Filtration can be performed using a filter cloth. Filtration removes impurities such as proteins and bacterial cells entrained in the bacterial cellulose gel, while also removing excess alkali. Preferably, the alkaline solution is a sodium hydroxide solution.

[0010] Furthermore, the alkali soaking process involves mixing the purified bacterial cellulose particles with an alkaline solution to obtain an alkali / bacterial cellulose system with an alkali content of 1-2 wt%. This system is then boiled under microwave for 10-30 minutes, followed by the addition of more alkaline solution until the alkali content reaches 3-8 wt%, and then boiled under ultrasonication for 10-20 minutes. The microwave power is 50-70 W. The alkaline solution is preferably a sodium hydroxide solution. This invention combines microwave and ultrasonic treatment during the alkali soaking process, using two stages of alkali with different concentrations to treat the bacterial cellulose. This helps reduce the intermolecular and chain-related forces within the bacterial cellulose, thus facilitating the subsequent solid-phase transformation of cellulose.

[0011] Furthermore, the synthesis refers to adding a poor solvent of alkali to the alkali / bacterial cellulose granule system after alkali impregnation, shaking well, and allowing the reaction to stand for about 3-24 hours, with a reaction temperature of less than or equal to 80°C, such as 20°C, 25°C, 30°C, 50°C, or 80°C.

[0012] Furthermore, the unsuitable solvent for the alkali is one insoluble, sparingly soluble, or slightly soluble in the solvent, and miscible with water. For example, it can be at least one of dimethyl sulfoxide, acetone, and acetonitrile, preferably a mixture of dimethyl sulfoxide and acetone. Preferably, the mass ratio of dimethyl sulfoxide to acetone is 1:3-5. Bacterial cellulose undergoes a simultaneous transformation from type I to type II in the unsuitable solvent of the alkali, changing from a filamentous fibrous morphology to irregular crystals.

[0013] Furthermore, the amount of undesirable solvent used for the alkali is approximately 3-7 times that of the alkali / bacterial cellulose granule system, for example, 3, 4, 5, or 7 times. If the amount of undesirable solvent used for the alkali is too low, the synthesis reaction time will be too long; if the amount is too high, the product will contain amorphous cellulose and the reagent recovery cost will be high.

[0014] Furthermore, after synthesis, unreacted alkali-condensing bacterial cellulose granules are removed by filtration using a 20-mesh filter. The filtrate is then centrifuged to obtain cellulose type II crystals and a clear liquid at 2000-5000 rpm. The clear liquid obtained by centrifugation is then separated from water, the unsuitable solvent (alkali), and the alkali itself by distillation or fractional distillation, thereby recovering the chemical reagents for recycling.

[0015] Furthermore, the cellulose type II crystal samples obtained by centrifugation were washed sequentially with dilute acid and ethanol until neutral. The washed samples were then spray-dried to obtain cellulose crystal products with a particle size of 0.1-500 μm. These cellulose crystals are a green, biodegradable material that can replace plastic microbeads in cosmetics, pharmaceuticals, chemicals, and composite materials.

[0016] This invention has the following advantages: 1. This invention prepares type II cellulose crystals by solid-phase conversion method. The crystal particle size is 0.1-500μm, the particle size is controllable, there is no adhesion and the dispersion is good. The obtained product can replace plastic microbeads in cosmetics, pharmaceuticals, chemicals and composite materials.

[0017] 2. The process of this invention is simple, all reagents used can be recycled and reused, no special equipment is required, it is green and environmentally friendly, low in cost, and has significant economic benefits and huge ecological and environmental benefits. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating the preparation process of bacterial cellulose type II crystals according to the present invention.

[0019] Figure 2 This is a diagram of 18*8*8mm bacterial cellulose gel particles from Example 1.

[0020] Figure 3 This is a SEM image of bacterial cellulose gel particles from Example 1.

[0021] Figure 4 SEM images of cellulose type II crystals from Examples 1 and 5: a. Example 1, b. Example 5.

[0022] Figure 5 This is a SEM image of the product of Comparative Example 1.

[0023] Figure 6 XRD patterns of type II cellulose crystals obtained in Example 1 and raw material bacterial cellulose are shown. a. Bacterial cellulose, b. Type II cellulose crystals. Detailed Implementation

[0024] The present invention will be further explained and illustrated below through specific embodiments. The following descriptions are merely exemplary and do not limit its content. In the following embodiments, unless otherwise specified, all concentrations are mass concentrations.

[0025] Example 1 1. Rehydrate the compressed bacterial cellulose gel, rinse with tap water to remove impurities from the surface of the fine cellulose gel, and cut it into 8*8*8mm gel particles using a cutter. Figure 2 As shown.

[0026] 2. Add bacterial cellulose gel particles to a sodium hydroxide solution and let it stand for 8 hours to obtain an alkali / bacterial cellulose gel particle system with a sodium hydroxide content of 1%. Boil at 100°C for 1 hour. Filter using a filter cloth and rinse with pure water to remove proteins, bacterial cells, and sodium hydroxide entrained in the bacterial cellulose gel particles, obtaining neutral bacterial cellulose gel particles.

[0027] 3. Add the above neutral bacterial cellulose gel particles to a sodium hydroxide solution and stir continuously to obtain a sodium hydroxide / bacterial cellulose gel particle system with a sodium hydroxide content of 2%. Microwave the system at a power of 60W and a temperature of 100℃ for 20 minutes. Then add sodium hydroxide solution to adjust the alkali concentration to obtain a sodium hydroxide / bacterial cellulose gel particle system with a sodium hydroxide content of 8%. Continue to boil the system under ultrasound for 15 minutes.

[0028] 4. Add 7 times its mass of anhydrous dimethyl sulfoxide and a mixture of acetone in a mass ratio of 1:4 to the above sodium hydroxide / bacterial cellulose gel particle system, stir well, let stand at room temperature for 3 hours, and filter with a 20-mesh filter to remove unreacted BC particles.

[0029] 5. Take the filtrate obtained by filtration, centrifuge at 5000 r / min for 5 min to obtain a precipitate, wash the precipitate with dilute acid and ethanol until neutral, and then disperse it with anhydrous ethanol to obtain an ethanol dispersion of cellulose crystals.

[0030] 6. Spray dry the above cellulose crystal ethanol dispersion to obtain cellulose type II crystals, and package them to obtain cellulose type II crystal products with a crystal diameter of about 100 μm.

[0031] SEM image of bacterial cellulose gel raw material as shown below Figure 3 As shown, the SEM image of the obtained cellulose type II crystals is as follows. Figure 4 As shown in Figure a, the XRD patterns of bacterial cellulose and cellulose type II crystals are as follows. Figure 6 As shown in the figure, the filamentous fibers are transformed into irregular blocky cellulose crystals, and the cellulose crystals are of type II.

[0032] Example 2 1. Take the compressed bacterial cellulose gel, rehydrate it, rinse it with tap water to remove dirt from the surface of the fine cellulose gel, and cut it into 5*5*5mm gel particles using a cutting machine.

[0033] 2. Add the bacterial cellulose gel particles to a sodium hydroxide solution and let it stand for 8 hours to obtain a sodium hydroxide / bacterial cellulose gel particle system with a sodium hydroxide content of 1%. Boil at 100°C for 1 hour, then filter with a filter cloth and rinse with pure water to remove the protein, bacterial cells and sodium hydroxide encapsulated in the bacterial cellulose gel particles, and obtain neutral bacterial cellulose gel particles.

[0034] 3. Add the above neutral bacterial cellulose gel particles to a sodium hydroxide solution and stir continuously to obtain a sodium hydroxide / bacterial cellulose gel particle system with a sodium hydroxide content of 2%. Microwave the system at a power of 50W and a temperature of 100℃ for 30 minutes. Then add sodium hydroxide solution to adjust the alkali concentration to obtain a sodium hydroxide / bacterial cellulose gel particle system with a sodium hydroxide content of 7%. Continue to boil the system under ultrasound for 10 minutes.

[0035] 4. Add 5 times its mass of anhydrous dimethyl sulfoxide to the above sodium hydroxide / bacterial cellulose gel particle system, stir well, let stand for 6 hours, and filter with a 20-mesh filter to remove unreacted BC particles.

[0036] 5. Take the filtrate, centrifuge at 4000 r / min for 5 min to obtain a precipitate, wash the precipitate with dilute acid and ethanol until neutral, and then disperse it with anhydrous ethanol to obtain an ethanol dispersion of cellulose crystals.

[0037] 6. Spray dry the above cellulose crystal ethanol dispersion to obtain cellulose crystals, and package them to obtain a cellulose type II crystal product with a crystal diameter of about 200 μm.

[0038] Example 3 1. Take the compressed bacterial cellulose gel, rehydrate it, rinse it with tap water to remove dirt from the surface of the fine cellulose gel, and cut it into 2*2*2mm gel particles using a cutting machine.

[0039] 2. Add the bacterial cellulose gel particles to a sodium hydroxide solution and let them stand for 5 hours to obtain a sodium hydroxide / bacterial cellulose gel system with a sodium hydroxide content of 1%. Boil at 100°C for 1 hour, then filter with a filter cloth and rinse with pure water to remove the protein, bacterial cells and sodium hydroxide encapsulated in the bacterial cellulose gel, and obtain neutral bacterial cellulose gel particles.

[0040] 3. Add the above neutral bacterial cellulose gel particles to sodium hydroxide solution and stir continuously to obtain a sodium hydroxide / bacterial cellulose gel system with a sodium hydroxide content of 2%. Microwave treat it for 10 min at a microwave power of 75 W and a temperature of 100 °C. Then add sodium hydroxide solution to adjust the alkali concentration to obtain a sodium hydroxide / bacterial cellulose gel particle system with a sodium hydroxide content of 6%. Continue to boil it under ultrasound for 20 min.

[0041] 4. Add 4 times the mass of acetone to the above sodium hydroxide / bacterial cellulose system, stir well, let stand for 12 hours, and filter with a 20-mesh filter to remove unreacted BC particles.

[0042] 5. Take the above clear liquid, centrifuge at 3000 r / min for 5 min to obtain a precipitate, wash the precipitate with dilute acid and ethanol until neutral, and then disperse it with anhydrous ethanol to obtain an ethanol dispersion of cellulose crystals.

[0043] 6. Spray dry the above cellulose crystal ethanol dispersion to obtain cellulose crystals, and package them to obtain a cellulose type II crystal product with a crystal diameter of about 300 μm.

[0044] Example 4 1. Take the compressed bacterial cellulose gel, rehydrate it, rinse it with tap water to remove dirt from the surface of the fine cellulose gel, and cut it into irregular gel particles with a diameter of less than 5mm using a cutting machine.

[0045] 2. Add the bacterial cellulose gel particles to a sodium hydroxide solution and let it stand for 5 hours to obtain a sodium hydroxide / bacterial cellulose gel particle system with a sodium hydroxide content of 0.5%. Boil at 100°C for 1 hour, then filter with a filter cloth and rinse with pure water to remove the protein, bacterial cells and sodium hydroxide encapsulated in the bacterial cellulose gel particles, and obtain neutral bacterial cellulose gel particles.

[0046] 3. Add the above neutral bacterial cellulose gel particles to a sodium hydroxide solution and stir continuously to obtain a sodium hydroxide / bacterial cellulose gel particle system with a sodium hydroxide content of 1%. Microwave the system at a power of 60W and a temperature of 100℃ for 20 minutes. Then add sodium hydroxide solution to adjust the alkali concentration to obtain a sodium hydroxide / bacterial cellulose gel particle system with a sodium hydroxide content of 5%. Continue to boil the system under ultrasound for 15 minutes.

[0047] 4. Add three times the mass of anhydrous dimethyl sulfoxide and a mixture of acetonitrile in a mass ratio of 1:4 to the above sodium hydroxide / bacterial cellulose gel particle system, stir well, let stand for 18 hours, and remove unreacted BC particles using a 20-mesh filter.

[0048] 5. Take the filtrate, centrifuge at 2000 r / min for 5 min to obtain a precipitate, wash the precipitate with dilute acid and ethanol until neutral, and then disperse it with anhydrous ethanol to obtain an ethanol dispersion of cellulose crystals.

[0049] 6. Spray dry the above cellulose crystal ethanol dispersion to obtain cellulose type II crystals, and package them to obtain cellulose type II crystal products with a crystal diameter of about 400 μm.

[0050] Example 5 1. Take the compressed bacterial cellulose gel, rehydrate it, rinse it with tap water to remove dirt from the surface of the fine cellulose gel, and cut it into 1*1*1mm gel particles using a cutting machine.

[0051] 2. Add the bacterial cellulose gel particles to a sodium hydroxide solution and let it stand for 12 hours to obtain a sodium hydroxide / bacterial cellulose gel particle system with a sodium hydroxide content of 1%. Boil at 100°C for 1 hour, then filter with a filter cloth and rinse with pure water to remove the protein, bacterial cells and sodium hydroxide encapsulated in the bacterial cellulose gel particles, and obtain neutral bacterial cellulose gel particles.

[0052] 3. Add the above neutral bacterial cellulose gel particles to a sodium hydroxide solution and stir continuously to obtain a sodium hydroxide / bacterial cellulose gel particle system with a sodium hydroxide content of 1%. Microwave the system at a power of 60W and a temperature of 100℃ for 20 minutes. Then add sodium hydroxide solution to adjust the alkali concentration to obtain a sodium hydroxide / bacterial cellulose gel particle system with a sodium hydroxide content of 3%. Continue to boil the system under ultrasound for 15 minutes.

[0053] 4. Add 3 times the mass of acetone and acetonitrile in a 1:1 mass ratio to the above sodium hydroxide / bacterial cellulose gel particle system, stir well, let stand for 24 hours, and use a 40-mesh filter to remove unreacted BC particles.

[0054] 5. Take the filtrate, centrifuge at 2000 r / min for 5 min to obtain a precipitate, wash the precipitate with dilute acid and ethanol until neutral, and then disperse it with anhydrous ethanol to obtain an ethanol dispersion of cellulose crystals.

[0055] 6. The above cellulose crystal ethanol dispersion was spray-dried to obtain cellulose type II crystals, which were then packaged to obtain a cellulose type II crystal product with a crystal diameter of approximately 500 μm, such as... Figure 4 As shown in b.

[0056] Comparative Example 1 The procedure was followed according to Example 1, except that in step 3, neutral bacterial cellulose gel particles were added to a sodium hydroxide solution and stirred continuously to obtain a sodium hydroxide / bacterial cellulose gel particle system with a sodium hydroxide content of 10%, which was then boiled for 60 minutes. The final product consisted of amorphous particles with a diameter less than 10 μm, such as... Figure 5 As shown.

[0057] Comparative Example 2 The procedure was followed as described in Example 1, except that in step 3, neutral bacterial cellulose gel particles were added to a sodium hydroxide solution and stirred continuously to obtain a sodium hydroxide / bacterial cellulose gel particle system with a sodium hydroxide content of 1%, which was then boiled for 60 minutes. The results showed that in step 5, after centrifuging the filtrate at 5000 r / min for 5 minutes, no precipitate formed, and no cellulose crystal particles were obtained.

[0058] Comparative Example 3 The procedure was followed as described in Example 1, except that in step 4, a mixture of anhydrous dimethyl sulfoxide and N,N-dimethylformamide in a mass ratio of 1:4 (twice their mass) was added, stirred thoroughly, and allowed to stand at room temperature for 3 hours. Unreacted BC particles were then removed by filtration through a 20-mesh screen. The results showed that in step 5, after centrifuging the filtrate at 5000 rpm for 5 minutes, no precipitate formed, and no cellulose crystal particles were obtained.

Claims

1. A method for preparing type II crystals of bacterial cellulose, characterized by: Bacterial cellulose gel was subjected to rinsing, granulation, impurity removal, alkali soaking, synthesis, filtration, centrifugation, washing, and drying to obtain bacterial cellulose type II crystals.

2. The method of claim 1, wherein: The rinsing process involves washing the bacterial cellulose gel with water to remove surface contaminants.

3. The method of claim 1 wherein: The granulation process involves cutting the rinsed bacterial cellulose gel into granules with a particle size of 8 mm or less.

4. The method of claim 1 wherein: The impurity removal process involves adding the granulated bacterial cellulose particles to an alkaline solution to obtain an alkaline / bacterial cellulose particle system with an alkaline content of 0.5-1 wt%, followed by boiling, filtration, and water washing.

5. The method of claim 1 wherein: The alkali soaking process involves mixing the purified bacterial cellulose particles with an alkaline solution to obtain an alkali / bacterial cellulose system with an alkali content of 1-2 wt%. The system is then boiled under microwave for 10-30 minutes, and then an alkaline solution is added until the alkali content in the system is 3-8 wt%. The system is then boiled under ultrasonication for 10-20 minutes. Preferably, the microwave power is 50-75 W.

6. The method of claim 1 wherein: The synthesis involves adding a poor solvent of alkali to the alkali / bacterial cellulose granule system after alkali impregnation, stirring evenly, and then allowing it to stand for treatment; preferably, the treatment temperature is less than or equal to 80°C, and the treatment time is 3-24 hours; the mass ratio of the alkali solution and bacterial cellulose granule mixture after alkali impregnation to the poor solvent of alkali is 1:3-7.

7. The method of claim 6, wherein: The unsuitable solvent for the alkali is at least one of dimethyl sulfoxide, acetone, and acetonitrile, preferably a mixture of dimethyl sulfoxide and acetone.

8. The method of claim 1 wherein: After synthesis, the mixture was filtered to obtain the supernatant. The supernatant was centrifuged to obtain a precipitate. The precipitate was washed with acid and ethanol in sequence until neutral. Then, the neutral bacterial cellulose was dispersed with ethanol and spray-dried to obtain bacterial cellulose type II crystals.

9. Bacterial cellulose type II crystals prepared by the method according to any one of claims 1-8, wherein the crystal particle size is 0.1-500 μm.

10. The application of the bacterial cellulose powder according to claim 9 in the fields of cosmetics, pharmaceuticals, chemicals and composite materials.

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