Bacterial cellulose dry film and preparation process thereof

Abstract

The invention provides a bacterial cellulose dry film and a preparation process thereof, and relates to the field of biopolymer materials, and the preparation process comprises the following steps: culturing bacterial strains capable of producing bacterial cellulose to obtain a bacterial cellulose wet film; cleaning the bacterial cellulose wet film, and removing thalli and a culture medium which are left on the surface and in the bacterial cellulose wet film; pressing the bacterial cellulose wet film to 1.5-2mm in thickness by using a film pressing machine, and cutting the bacterial cellulose wet film to a preset size to obtain a wet film sheet; a polyol solution or a hydroxyl-rich compound is distributed to the surface of the wet membrane in a smearing, spraying or infiltrating mode to serve as a drying protective agent; and treating the wet film added with the protective agent in an air drying, hot air drying or microwave drying manner to obtain the bacterial cellulose dry film. According to the preparation method of the dry film, the high-rehydration and high-swelling dry film can be prepared within a short time, the method is simple, cheap and rapid, and expensive special equipment is not needed.

Description

Technical Field

[0001] The invention relates to the field of biopolymer materials, and in particular to a bacterial cellulose dry film and a preparation process thereof. Background Art

[0002] Bacterial cellulose (BC) is a nano-scale biopolymer synthesized by microbial fermentation. Glucose monomers are connected by β-1,4 glycosidic bonds to form fiber filaments, and many fiber filaments are self-assembled to form a three-dimensional network structure. Bacterial cellulose has many excellent properties such as high purity, strong water retention, high mechanical strength and good biocompatibility. It has shown broad application prospects in many fields such as biomedicine, chemical industry, food, environmental protection, etc., and also shows huge market potential. In the process of realizing the present invention, the applicant found that the water content of the bacterial cellulose hydrogel directly obtained by fermentation is extremely high, which can reach 100-500 times the dead weight of bacterial cellulose. Even after mechanical water pressure treatment, the water content in the membrane is still maintained above 95%. The high water content of the wet film increases the transportation cost on the one hand, and the easy contamination of bacteria on the other hand will also increase the antiseptic cost. If the bacterial cellulose film is dried by conventional heat to remove moisture, a large number of hydroxyl groups in the bacterial cellulose molecules can form strong intramolecular and intermolecular hydrogen bonds, causing the three-dimensional network structure to collapse. When rehydrated, it is difficult for water molecules to re-enter the cellulose network. The rehydration rate of this dry film can only reach 3-5 times the dry weight of bacterial cellulose, and it cannot be restored to a hydrogel state. Therefore, the preparation technology of bacterial cellulose dry film is the technical bottleneck for the current large-scale and industrial promotion of bacterial cellulose. There are three main drying methods for the existing cellulose dry film preparation technology: thermal drying, vacuum freeze drying, and microwave vacuum drying. The thermal drying method is to increase the temperature through a heat source to promote the loss of water in the film, thereby achieving a drying effect. However, it will cause uneven heating inside and outside the film, and heat loss will cause fiber flocculation, resulting in the collapse of the three-dimensional network structure, and the rehydration ability is very poor. In addition, the final dry film will cause the edge of the film to curl and the surface to wrinkle due to uneven heating. The vacuum freeze drying method uses the low-pressure environment of the vacuum to reduce the boiling point of water and achieve water evaporation at a lower temperature. The membrane is frozen into a solid state, retaining the original three-dimensional structure, and a foamy bacterial cellulose dry membrane is obtained after drying. This method has high equipment investment costs, complex processes, high energy consumption, high production costs, slow water loss efficiency of the cellulose membrane, and usually requires the addition of retention and filtration aids, which makes the production cost high and is not suitable for industrial production. The microwave vacuum drying method combines the internal heating characteristics of microwave heating and the low-pressure environment of vacuum drying, making the drying process more efficient. Under the action of microwaves, the internal temperature of cellulose rises rapidly. At the same time, in a vacuum environment, the evaporation pressure of water molecules decreases, accelerating the evaporation rate of water molecules. However, this method has a great damage to the three-dimensional network structure of bacterial cellulose, which may be related to factors such as material size, microwave power, vacuum degree and microwave working mode that affect the effect of microwave vacuum drying. In addition, there is a method for chemically modifying the hydroxyl groups of bacterial cellulose.First, the treated membrane is etherified, and the etherified membrane is neutralized to obtain a hydroxypropylated bacterial cellulose membrane. The dried hydroxypropylated bacterial cellulose membrane has high rehydration and reswelling ability. However, this method requires the use of an etherifying agent, which increases the risk of environmental pollution and processing costs, and is also not suitable for the industrial production of bacterial cellulose dry membranes. Therefore, there is an urgent need for a cheap, simple, high-quality and efficient dry membrane production technology. Summary of the invention

[0003] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art or related art, and provides a bacterial cellulose dry film and a preparation process thereof, which can prepare a high rehydration and high swelling dry film in a short time, and the method is simple, cheap, fast, and does not require expensive special equipment. The dried bacterial cellulose film has low water content, light weight, convenient transportation, is not easy to be contaminated, has a long storage time, and can be expanded to the fields of medicine, packaging, beauty, etc., and has wide applicability.

[0004] The first aspect of the present invention discloses a method for preparing a bacterial cellulose dry film, comprising: culturing a strain capable of producing bacterial cellulose to obtain a bacterial cellulose wet film; cleaning the bacterial cellulose wet film to remove residual bacteria and culture medium on the surface and inside; using a film press to press the bacterial cellulose wet film to a thickness of 1.5 mm to 2 mm and cut it to a predetermined size to obtain a wet film sheet; distributing a polyol solution or a hydroxyl-containing compound to the surface of the wet film sheet by applying, spraying or soaking as a drying protective agent; treating the wet film sheet to which the protective agent is added by air drying, hot air drying or microwave drying to obtain a bacterial cellulose dry film.

[0005] In this technical solution, polyols and other substances rich in hydroxyl groups (-OH) are used as three-dimensional network protective agents for bacterial cellulose. After the water is lost during the drying process, new hydrogen bonds can be formed with the bacterial cellulose to protect the three-dimensional network structure from being destroyed. When rehydrated, water molecules can easily re-enter the cellulose network. Based on this principle, other non-polyol compounds rich in hydroxyl groups (-OH), such as sodium hyaluronate, trehalose, glucose and its derivatives, ceramide, etc., can play the same role in protecting bacterial cellulose from drying. In addition, compounding with different polyol compounds, or compounding with polyols and other substances can also achieve the same drying protection effect. Anyone who adopts the basic principle of protecting the bacterial cellulose network with polyols, even if the method of adding the protective agent and the choice of drying method are changed, still belongs to the protection scope of the present invention. In addition, it is a consensus that polyols have antiseptic effects, so the bacterial cellulose dry film prepared by the present invention has a good antiseptic effect.

[0006] According to the method for preparing bacterial cellulose dry film provided by the present invention, preferably, the strain capable of producing bacterial cellulose is Enterobacter.

[0007] According to the method for preparing bacterial cellulose dry film provided by the present invention, preferably, the strain capable of producing bacterial cellulose is Enterobacter or Acetobacter xylinum.

[0008] According to the method for preparing bacterial cellulose dry film provided by the present invention, preferably, the polyol solution includes but is not limited to butanediol solution, propylene glycol solution, xylitol solution and sorbitol solution, and the hydroxyl-containing compound includes but is not limited to sodium hyaluronate, trehalose, glucose, glucose derivatives and ceramide.

[0009] According to the method for preparing bacterial cellulose dry film provided by the present invention, preferably, the mass concentration of 1,3-butanediol in the butanediol solution is 60%; the mass concentration of glycerol in the glycerol solution is 40%; the mass concentration of xylitol in the xylitol solution is 40%; and the mass concentration of sorbitol in the sorbitol solution is 40%.

[0010] According to the method for preparing the bacterial cellulose dry film provided by the present invention, preferably, for a dry film having a thickness of 1.5 mm to 2 mm and an area of ​​100 cm 2 The wet film is evenly distributed with the following amounts of polyol solution: 1.2g~2.5g of 60% concentration butanediol solution, 1.2g~2.5g of 40% concentration propylene glycol solution, 1.2g~2.5g of 40% concentration xylitol solution or 1.2g~2.5g of 40% concentration sorbitol solution.

[0011] According to the preparation method of bacterial cellulose dry film provided by the present invention, preferably, the step of cleaning the bacterial cellulose wet film specifically includes: cleaning the bacterial cellulose wet film with clean water to remove the bacteria and culture medium remaining on the surface; soaking the bacterial cellulose wet film with 0.3M NaOH at 80°C for 2 hours to lyse the internal bacteria and remove excess culture medium; neutralizing the NaOH with dilute hydrochloric acid until the pH value of the soaking solution is weakly acidic; soaking the BC wet film with deionized water at room temperature until it is neutral.

[0012] According to the method for preparing bacterial cellulose dry film provided by the present invention, preferably, air drying includes: natural air drying at room temperature; hot air drying specifically includes: drying in a blast oven at 50°C for 20min~40min; microwave drying specifically includes: using a microwave vacuum tunnel dryer, 3kW drying for 8 minutes.

[0013] According to the method for preparing a bacterial cellulose dry film provided by the present invention, preferably, the method for preparing a bacterial cellulose wet film comprises:

[0014] S1, Streak the Enterobacter bacterial suspension on a LB solid medium plate containing 0.1% Congo red and culture at 30°C for 24 h;

[0015] S2, pick a single red colony, streak densely on LB slant medium, and culture at 30°C for 24 h;

[0016] S3, picking a portion of the thin bacterial cellulose film containing active bacteria from the slant culture medium obtained in step S2, densely streaking it onto the LB slant culture medium, and culturing it at 30° C. for 24 hours;

[0017] S4, washing the slant culture medium obtained in step S3 with 100 ml of distilled water, repeatedly washing until the bacterial cellulose membrane containing a large number of bacteria on the slant culture medium is detached, and placing it in the distilled water and mixing it to form a seed solution;

[0018] S5, preparing HS-XGK fermentation medium: xanthan gum 1.0 g / L, yeast powder 7.5 g / L, peptone 10 g / L, Na2HPO4 10 g / L, KNO3 1.0 g / L, glucose 25 g / L, pH does not need to be adjusted, and the HS-XGK fermentation medium is obtained after high-pressure sterilization;

[0019] S6, taking the seed solution prepared in step S4, inoculating it into the HS-XGK fermentation medium prepared in step S5 at a ratio of 1%, mixing evenly and placing in an incubator, culturing and fermenting at 30° C. for 24 hours to obtain a bacterial cellulose wet film.

[0020] The second aspect of the present invention further discloses a bacterial cellulose dry film, which is prepared according to the preparation method of the bacterial cellulose dry film disclosed in any of the above technical solutions.

[0021] The beneficial effects achieved by the present invention include at least:

[0022] The present invention uses polyols and other substances rich in hydroxyl groups (-OH) as three-dimensional network protective agents for bacterial cellulose. After the water is lost during the drying process, new hydrogen bonds can be formed between the bacterial cellulose to protect the three-dimensional network structure from being destroyed. When rehydrated, water molecules can easily re-enter the cellulose network to restore the hydrogel properties of the bacterial cellulose, and achieve high rehydration and high swelling properties of the bacterial cellulose dry film. The present invention uses butanediol as a diol representative, propylene glycol as a triol representative, xylitol as a pentaol representative, and sorbitol as a hexaol representative, thereby deducing the scalability and applicability of using polyols and other substances rich in hydroxyl groups as three-dimensional network protective agents for bacterial cellulose.

[0023] The present invention can prepare a high rehydration and high swelling dry film in a short time through a simple polyol addition method (spraying, coating, soaking) and a simple drying method (oven drying, air drying, microwave drying). The method is simple, cheap, fast, and does not require expensive special equipment. The dried bacterial cellulose film has a low water content (about 10%), light weight, convenient transportation, not easy to be contaminated, and a long storage time. It can be expanded to the fields of medicine, packaging, and beauty, and has a wide range of applicability.

[0024] Based on the antiseptic effect of polyols, the bacterial cellulose dry film prepared by the present invention has a good antiseptic effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic diagram showing the rehydration weight of a bacterial cellulose dry film prepared with butanediol as a drying protective agent according to an embodiment of the present invention is shown.

[0026] Figure 2 A schematic diagram showing the rehydration weight of a bacterial cellulose dry film prepared with glycerol as a drying protective agent according to an embodiment of the present invention is shown.

[0027] Figure 3 A schematic diagram showing the rehydration weight of a bacterial cellulose dry film prepared with xylitol as a drying protective agent according to an embodiment of the present invention is shown.

[0028] Figure 4 A schematic diagram showing the rehydration weight of a bacterial cellulose dry film prepared with sorbitol as a drying protective agent according to an embodiment of the present invention is shown.

[0029] Figure 5 A schematic diagram of the rehydration weight of bacterial cellulose dry films prepared by adding different drying protective agents according to an embodiment of the present invention is shown.

[0030] Figure 6 A schematic diagram showing the rehydration weight of bacterial cellulose dry films prepared by different drying methods according to an embodiment of the present invention is shown.

[0031] Figure 7 A schematic diagram showing the rehydration weight of a bacterial cellulose dry film prepared without adding a drying protective agent according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0032] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] Example 1

[0034] According to one embodiment of the present invention, a method for preparing a bacterial cellulose wet film is disclosed, comprising:

[0035] (1) Streak the Enterobacter bacterial culture onto a LB solid medium plate containing 0.1% Congo red and incubate at 30°C for 24 hours;

[0036] (2) Pick a large red colony and streak it densely on LB slant medium and culture it at 30℃ for 24 hours;

[0037] (3) Picking a portion of the thin bacterial cellulose film containing a large number of active bacteria from the slant culture medium obtained in step (2), streaking densely on the LB slant culture medium, and culturing at 30°C for 24 hours;

[0038] (4) Rinse the slant culture medium obtained in step (3) with 100 ml of distilled water, repeatedly rinse until the bacterial cellulose membrane containing a large number of bacteria on the slant culture medium is detached, and place it in the distilled water and mix well as the seed solution;

[0039] (5) Preparation of HS-XGK fermentation medium: xanthan gum 1.0 g / L, yeast powder 7.5 g / L, peptone 10 g / L, Na2HPO4 10 g / L, KNO3 1.0 g / L, glucose 25 g / L, pH adjustment is not required. After high-pressure sterilization, the HS-XGK fermentation medium was obtained;

[0040] (6) Take the seed liquid prepared in step (4) and inoculate it into the HS-XGK fermentation medium prepared in step (5) at a ratio of 1%. After mixing evenly, place it in an incubator and culture and ferment it at 30°C for 24 hours to obtain a bacterial cellulose wet film.

[0041] Example 2

[0042] According to another embodiment of the present invention, a preparation process for preparing a bacterial cellulose dry film by using the bacterial cellulose wet film provided in Example 1 is disclosed, comprising:

[0043] (1) Wash the bacterial cellulose wet film (BC wet film) with clean water to remove the residual bacteria and culture medium on the surface.

[0044] (2) Soak the BC wet membrane in 0.3 M NaOH at 80°C for 2 h to lyse the internal bacteria and remove excess culture medium.

[0045] (3) Neutralize NaOH with dilute hydrochloric acid until the pH value of the soaking solution is weakly acidic.

[0046] (4) Soak the BC wet film in deionized water at room temperature until it becomes neutral.

[0047] (5) Use a pneumatic laminating machine to press the BC wet film to a thickness of 1.5~2 mm.

[0048] (6) Cut the BC membrane into 10 cm × 10 cm sizes.

[0049] (7) BC dry films were prepared by adding different types and concentrations of polyols, by different polyol addition methods (spraying, coating, and wetting), and by different drying methods (oven drying, air drying, and microwave drying).

[0050] In this embodiment, the polyols that can be added include diols, triols, pentaols and hexaols. Taking butanediol as the diol representative, propylene glycol as the triol representative, xylitol as the pentaol representative, and sorbitol as the hexaol representative: the mass concentration of 1,3-butanediol in the butanediol solution is 60%; the mass concentration of propylene glycol in the propylene glycol solution is 40%; the mass concentration of xylitol in the xylitol solution is 40%; the mass concentration of sorbitol in the sorbitol solution is 40%, and different amounts of polyols are selected according to the area of ​​the wet film as a three-dimensional network protective agent during the drying process of bacterial cellulose. After the BC dry film is obtained, the swelling rate can be calculated as follows: the BC dry film is placed in distilled water, soaked at room temperature for 5 days, the weight is recorded every day, and the swelling rate is calculated:

[0051]

[0052] Among them, m 湿重 Represents the mass of bacterial cellulose membrane after water absorption, m BC干重 Indicates the quality of bacterial cellulose dry film.

[0053] Example 3

[0054] like Figure 1 As shown, according to another embodiment of the present invention, the effects of different amounts of 1,3-butanediol on the preparation of bacterial cellulose dry film are also disclosed. The specific experimental process includes:

[0055] (1) Take 60 mL of 1,3-butanediol solution and add 40 mL of distilled water to prepare a 60% butanediol solution.

[0056] (2) Take three 10 cm × 10 cm wet membranes, weigh them by dripping liquid on a balance, and use a rubber-tipped dropper to drip 1.2–1.3 g of 60% 1,3-butanediol solution onto the surface of each membrane and spread it evenly. This is recorded as the low-concentration butanediol group.

[0057] (3) Take three 10 cm × 10 cm wet membranes, weigh them by dripping liquid on a balance, and use a rubber-tipped dropper to drip 1.8–1.9 g of 60% 1,3-butanediol solution onto the surface of each membrane. Apply it evenly and record it as the medium-concentration butanediol group.

[0058] (4) Take three 10 cm × 10 cm wet membranes, weigh them by dripping liquid on a balance, and use a rubber-tipped dropper to drip 2.4–2.5 g of 60% 1,3-butanediol solution onto the surface of each membrane and spread it evenly. This is recorded as the high-concentration butanediol group.

[0059] (5) The nine films were placed in a 50°C forced air oven and dried for 20 to 40 min to obtain the BC dry film.

[0060] (6) Place the BC dry films of the above three concentration groups in distilled water and soak them at room temperature for 5 days. Record the weight every day.

[0061] The rehydration results are as follows Figure 1 As shown: the three adjacent bars in each group represent low concentration, medium concentration and high concentration from left to right. On the fifth day, the rehydrated weight of the low-concentration butanediol group was 30.27 g, and the swelling rate was 13059%; the rehydrated weight of the medium-concentration butanediol group was 43.67 g, and the swelling rate was 18888%; the rehydrated weight of the high-concentration butanediol group was 52.35 g, and the swelling rate was 22662%.

[0062] Example 4

[0063] like Figure 2 According to another embodiment of the present invention, the effects of different amounts of glycerol on the preparation of bacterial cellulose dry film are also disclosed. The specific experimental process includes:

[0064] (1) Take 40 mL of propylene glycol solution and add 60 mL of distilled water to prepare a 40% propylene glycol solution.

[0065] (2) Take three pieces of 10 cm × 10 cm wet membranes, weigh them by dripping liquid on a balance, and use a rubber-tipped dropper to drip 1.2–1.3 g of 40% propylene glycol solution onto the surface of each membrane and spread it evenly. This is recorded as the low-concentration propylene glycol group.

[0066] (3) Take three pieces of 10 cm × 10 cm wet membranes, weigh them by dripping liquid on a balance, and use a rubber-tipped dropper to drip 1.8–1.9 g of 40% propylene glycol solution onto the surface of each membrane and spread it evenly. This is recorded as the medium propylene glycol concentration group.

[0067] (4) Take three pieces of 10 cm × 10 cm wet membranes, weigh them by dripping liquid on a balance, and use a rubber-tipped dropper to drip 2.4–2.5 g of 40% propylene glycol solution onto the surface of each membrane and spread it evenly. This is recorded as the high-concentration propylene glycol group.

[0068] (5) The nine films were placed in a 50°C forced air oven and dried for 20 to 40 min to obtain the BC dry film.

[0069] (6) Place the BC dry films of the above three concentration groups in distilled water and soak them at room temperature for 5 days. Record the weight every day.

[0070] The rehydration results are as follows Figure 2 As shown: the three adjacent bars in each group represent low concentration, medium concentration and high concentration from left to right. On the fifth day, the rehydrated weight of the low-concentration glycerol group was 10.87 g, and the swelling rate was 46.25%; the rehydrated weight of the medium-concentration glycerol group was 12.92 g, and the swelling rate was 55.17%; the rehydrated weight of the high-concentration glycerol group was 16.71 g, and the swelling rate was 71.64%.

[0071] Example 5

[0072] like Figure 3 According to another embodiment of the present invention, the effects of different amounts of xylitol on the preparation of bacterial cellulose dry film are also disclosed. The specific experimental process includes:

[0073] (1) Weigh 60.6 g of xylitol and dissolve it in 60 mL of distilled water to prepare a 40% xylitol solution.

[0074] (2) Take three pieces of 10 cm × 10 cm wet membranes, weigh them by dripping liquid on a balance, and use a rubber-tipped dropper to drip 1.2-1.3 g of 40% xylitol solution onto the surface of each membrane and spread it evenly. This is recorded as the low-concentration xylitol group.

[0075] (3) Take three pieces of 10 cm × 10 cm wet membranes, weigh them by dropping liquid on a balance, and use a rubber-tipped dropper to drop 1.8–1.9 g of 40% xylitol solution onto the surface of each membrane. Apply it evenly and record it as the xylitol medium concentration group.

[0076] (4) Take three pieces of 10 cm × 10 cm wet membranes, weigh them by dripping liquid on a balance, and use a rubber-tipped dropper to drip 2.4–2.5 g of 40% xylitol solution onto the surface of each membrane and spread it evenly. This is recorded as the high-concentration xylitol group.

[0077] (5) The nine films were placed in a 50°C forced air oven and dried for 20 to 40 min to obtain the BC dry film.

[0078] (6) Place the BC dry films of the above three concentration groups in distilled water and soak them at room temperature for 5 days. Record the weight every day.

[0079] The rehydration results are as follows Figure 3As shown: the three adjacent bars in each group represent low concentration, medium concentration and high concentration from left to right. On the fifth day, the rehydrated weight of the low-concentration xylitol group was 33.68 g, and the swelling rate was 14542%; the rehydrated weight of the medium-concentration xylitol group was 45.56 g, and the swelling rate was 19710%; the rehydrated weight of the high-concentration xylitol group was 16.14 g, and the swelling rate was 6919%.

[0080] Example 6

[0081] like Figure 4 As shown, according to another embodiment of the present invention, the effects of different amounts of sorbitol on the preparation of bacterial cellulose dry film are also disclosed. The specific experimental process includes:

[0082] (1) Weigh 51.2 g of xylitol and dissolve it in 60 mL of distilled water to prepare a 40% sorbitol solution.

[0083] (2) Take three pieces of 10 cm × 10 cm wet membranes, weigh them by dripping liquid on a balance, and use a rubber-tipped dropper to drop 1.2–1.3 g of 40% sorbitol solution onto the surface of each membrane and spread it evenly. This is recorded as the low-concentration sorbitol group.

[0084] (3) Take three pieces of 10 cm × 10 cm wet membranes, weigh them by dripping liquid on a balance, and use a rubber-tipped dropper to drop 1.8–1.9 g of 40% sorbitol solution onto the surface of each membrane and spread it evenly. This is recorded as the medium sorbitol concentration group.

[0085] (4) Take three pieces of 10 cm × 10 cm wet membranes, weigh them by dripping liquid on a balance, and use a rubber-tipped dropper to drip 2.4–2.5 g of 40% sorbitol solution onto the surface of each membrane and spread it evenly. This is recorded as the high-concentration sorbitol group.

[0086] (5) The nine films were placed in a 50°C forced air oven and dried for 20 to 40 min to obtain the BC dry film.

[0087] (6) Place the BC dry films of the above three concentration groups in distilled water and soak them at room temperature for 5 days. Record the weight every day.

[0088] The rehydration results are as follows Figure 4 As shown: the three adjacent bars in each group represent low concentration, medium concentration and high concentration from left to right. On the fifth day, the rehydrated weight of the low-concentration sorbitol group was 13.86 g, and the swelling rate was 5925%; the rehydrated weight of the medium-concentration sorbitol group was 19.68 g, and the swelling rate was 8457%; the rehydrated weight of the high-concentration sorbitol group was 20.05 g, and the swelling rate was 8616%.

[0089] Example 7

[0090] like Figure 5As shown, according to another embodiment of the present invention, the effects of different protective agent addition methods on the preparation of bacterial cellulose dry film are disclosed, and the specific experimental process includes:

[0091] (1) Take 40 mL of propylene glycol solution and add 60 mL of distilled water to prepare a 40% propylene glycol solution.

[0092] (2) Take three pieces of 10 cm × 10 cm wet membranes, weigh them by dripping liquid on a balance, and use a rubber-tipped dropper to drip 1.8–1.9 g of 40% propylene glycol solution onto the surface of each membrane. Apply it evenly and record it as the smearing addition group.

[0093] (3) Take three pieces of 10 cm × 10 cm wet membranes and spray 1.8-1.9 g of 40% propylene glycol on the surface of each piece of membrane using a spray bottle on a balance. This group is recorded as the spray addition group.

[0094] (4) Take three pieces of 10 cm × 10 cm wet membranes and soak them in 40% propylene glycol solution for 10 min. This is recorded as the infiltration addition group.

[0095] (5) The nine films were placed in a 50°C forced air oven and dried for 20 to 40 min to obtain the BC dry film.

[0096] (6) The BC dry films of the above three treatment groups were placed in distilled water and soaked at room temperature for 5 days. The weight was recorded every day.

[0097] The rehydration results are as follows Figure 5 As shown: the three adjacent bars in each group represent smearing, spraying and infiltration from left to right. On the fifth day, the rehydrated weight of the smearing group was 12.92 g, and the swelling rate was 5437%; the rehydrated weight of the spraying group was 14.25 g, and the swelling rate was 6006%; the rehydrated weight of the infiltration group was 22.18 g, and the swelling rate was 9406%.

[0098] Example 8

[0099] like Figure 6 As shown, according to another embodiment of the present invention, the influence of different drying methods on the preparation of bacterial cellulose dry film is disclosed, and the specific experimental process includes:

[0100] (1) Take 40 mL of propylene glycol solution and add 60 mL of distilled water to prepare a 40% propylene glycol solution.

[0101] (2) Take 9 pieces of 10 cm × 10 cm wet membranes, weigh them by dripping liquid on a balance, and use a rubber-tipped dropper to drip 1.8-1.9 g of 40% propylene glycol solution onto the surface of each membrane and spread it evenly.

[0102] (3) Place the three sheets in a 50°C forced air oven and dry them for 20–40 min to obtain the BC dry film, which is recorded as the drying group.

[0103] (4) Place the three pieces of film under outdoor air-drying conditions to obtain the BC dry film, which is recorded as the air-dried group.

[0104] (5) Place the three pieces in a microwave vacuum tunnel dryer and dry them at 3 kW for 8 minutes, which is recorded as the microwave group.

[0105] (6) The BC dry films of the above three treatment groups were placed in distilled water and soaked at room temperature for 5 days. The weight was recorded every day.

[0106] The rehydration results are as follows Figure 6 As shown: the three adjacent bars in each group represent the drying group, air-drying group and microwave group from left to right. On the fifth day, the rehydrated weight of the drying group was 35.60 g, and the swelling rate was 15480%; the rehydrated weight of the air-drying group was 40.04 g, and the swelling rate was 17407%; the rehydrated weight of the microwave group was 47.10 g, and the swelling rate was 20477%.

[0107] Example 9

[0108] like Figure 7 As shown, according to another embodiment of the present invention, the swelling rate of the bacterial cellulose dry film prepared without adding polyol as a drying protective agent is disclosed as a control group, and the specific experimental process includes:

[0109] (1) Take three pieces of 10 cm × 10 cm wet film without adding polyol, place them in a 50 °C forced air oven and dry them for 20-40 min to prepare BC dry film, which is recorded as the unprotected group.

[0110] (2) Place the three BC dry films mentioned above in distilled water and soak them at room temperature for 5 days. Record the weight every day.

[0111] The rehydration results are as follows Figure 7 As shown: On the fifth day, the rehydrated weight of the unprotected group was 2.90 g and the swelling rate was 1144%. Compared with the polyol-protected group, the rehydrated weight and swelling rate were significantly reduced, and it was impossible to return to the hydrogel state.

[0112] It can be seen from the above examples that the present invention uses hydroxyl-rich substances such as polyols as three-dimensional network protective agents in the drying process of bacterial cellulose. The protective agent addition method is simple, the drying method is simple, no expensive special equipment is required, and the applicability is wide. The prepared bacterial cellulose film has high rehydration and high swelling properties, and can restore the hydrogel properties after rehydration.

[0113] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a bacterial cellulose dry film, characterized in that: include: Cultivating a bacterial strain capable of producing bacterial cellulose to obtain a wet bacterial cellulose film; Cleaning the bacterial cellulose wet film to remove the bacterial cells and culture medium remaining on the surface and inside; The wet bacterial cellulose film is pressed to a thickness of 1.5 mm to 2 mm using a film press and cut to a predetermined size to obtain a wet film sheet; Distributing a polyol solution or a hydroxyl-containing compound onto the surface of the wet film by applying, spraying or soaking as a drying protective agent; The wet film sheet with the protective agent added is treated by air drying, hot air drying or microwave drying to obtain a bacterial cellulose dry film.

2. The method for preparing a bacterial cellulose dry film according to claim 1, characterized in that: The bacterial strain capable of producing bacterial cellulose is Enterobacter.

3. The method for preparing a bacterial cellulose dry film according to claim 1, characterized in that: The bacterial strain capable of producing bacterial cellulose is Acetobacter xylinum.

4. The method for preparing a bacterial cellulose dry film according to claim 1, characterized in that: The polyol solution includes: butanediol solution, glycerol solution, xylitol solution and sorbitol solution, and the hydroxyl-containing compound includes: sodium hyaluronate, trehalose, glucose, glucose derivatives and ceramide.

5. The method for preparing a bacterial cellulose dry film according to claim 4, characterized in that: The mass concentration of 1,3-butanediol in the butanediol solution is 60%; the mass concentration of glycerol in the glycerol solution is 40%; the mass concentration of xylitol in the xylitol solution is 40%; and the mass concentration of sorbitol in the sorbitol solution is 40%.

6. The method for preparing a bacterial cellulose dry film according to claim 1, characterized in that: For thickness of 1.5mm~2mm and area of ​​100cm 2 The wet film is evenly distributed with the following amounts of polyol solution: 1.2g~2.5g of 60% concentration butanediol solution, 1.2g~2.5g of 40% concentration propylene glycol solution, 1.2g~2.5g of 40% concentration xylitol solution or 1.2g~2.5g of 40% concentration sorbitol solution.

7. The method for preparing a bacterial cellulose dry film according to claim 1, characterized in that: The step of cleaning the bacterial cellulose wet film specifically comprises: Wash the wet bacterial cellulose film with clean water to remove the residual bacteria and culture medium on the surface; Soak the wet bacterial cellulose film in 0.3M NaOH at 80°C for 2 hours to lyse the internal bacteria and remove excess culture medium; Neutralize NaOH with dilute hydrochloric acid until the pH value of the soaking solution is weakly acidic; Soak the BC wet film in deionized water at room temperature until it becomes neutral.

8. The method for preparing a bacterial cellulose dry film according to claim 1, characterized in that: The air drying includes: natural air drying at room temperature; the hot air drying specifically includes: drying in a blast oven at 50° C. for 20 min to 40 min; the microwave drying specifically includes: using a microwave vacuum tunnel dryer, 3 kW drying for 8 minutes.

9. The method for preparing a bacterial cellulose dry film according to claim 1, characterized in that: The preparation method of the bacterial cellulose wet film comprises: S1, Streak the Enterobacter bacterial suspension on a LB solid medium plate containing 0.1% Congo red and culture at 30°C for 24 h; S2, pick a single red colony, streak densely on LB slant medium, and culture at 30°C for 24 h; S3, picking a portion of the thin bacterial cellulose film containing active bacteria from the slant culture medium obtained in step S2, densely streaking it onto the LB slant culture medium, and culturing it at 30° C. for 24 hours; S4, washing the slant culture medium obtained in step S3 with 100 ml of distilled water, repeatedly washing until the bacterial cellulose membrane containing a large number of bacteria on the slant culture medium is detached, and placing it in the distilled water and mixing it to form a seed solution; S5, prepare HS-XGK fermentation medium: xanthan gum 1.0 g / L, yeast powder 7.5 g / L, peptone 10 g / L, Na2HPO4 10 g / L, KNO3 1.0 g / L, glucose 25 g / L, pH does not need to be adjusted, and the HS-XGK fermentation medium is obtained after high-pressure sterilization; S6, taking the seed solution prepared in step S4, inoculating it into the HS-XGK fermentation medium prepared in step S5 at a ratio of 1%, mixing evenly and placing in an incubator, culturing and fermenting at 30° C. for 24 hours to obtain a bacterial cellulose wet film.

10. The bacterial cellulose dry film obtained by the preparation method according to any one of claims 1 to 9.

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