KR102842674B1 - Bacteria Cellulose-Milk Protein Complex and Method Thereof - Google Patents

Abstract

The present invention relates to a bacterial cellulose-milk protein particle complex comprising a porous structure including bacterial cellulose fibers; and milk protein particles provided in pores within the porous structure or on the surface of the porous structure; and a method for producing the same. The bacterial cellulose-milk protein complex according to the present invention has excellent dimensional stability, wash fastness, wrinkle resistance, water resistance, and flame retardancy, and thus can replace animal leather, and can be used in flame retardant articles made of leather.

Description

Bacteria Cellulose-Milk Protein Complex and Method Thereof

The present invention relates to a bacterial cellulose-milk protein complex and a method for producing the same.

Natural leather is widely used in products such as clothing, furniture, and accessories. However, limited resources cannot fully meet demand, and various environmental and animal welfare issues are further reducing supply. Artificial leather is being used as a substitute for natural leather. Artificial leather is an artificial imitation of leather made from nonwoven fabric and polyurethane. However, existing artificial leather does not offer the flexibility and wrinkle resistance of animal leather, making it difficult to replace it. Furthermore, some natural leathers exhibit flame-retardant properties, making them useful for items such as welding tool storage boxes and firefighting gloves and boots. However, animal welfare and environmental concerns have made their availability difficult. Therefore, there is a need for a leather substitute that is flame-retardant and similar to animal leather.

Republic of Korea Registration No. 10-2192110 (December 10, 2020)

One aspect is to provide a porous structure including bacterial cellulose fibers; a bacterial cellulose-milk protein complex including milk protein particles provided in pores within the porous structure or on the surface of the porous structure; and artificial leather including the same.

Another aspect provides a method for producing a bacterial cellulose-milk protein complex, and a cellulose-milk protein complex produced thereby, comprising the steps of: producing a milk protein solution by mixing milk protein in purified water; producing a mixture by adding a cross-linking agent and a catalyst to the milk protein solution; immersing a porous structure including bacterial cellulose fibers in the mixture to produce a complex in which milk protein is provided in at least a portion of the internal pores or surface of the porous structure; and drying the complex.

As used herein, the term 'composite' refers to an object comprising two or more components. For example, a 'bacterial cellulose-milk protein particle complex' comprises bacterial cellulose and milk protein particles.

One aspect is to provide a bacterial cellulose-milk protein complex comprising a porous structure comprising bacterial cellulose fibers; and milk protein particles provided in pores within the porous structure or on the surface of the porous structure.

The porous structure including the bacterial cellulose fibers can be manufactured by a method known to those skilled in the art. For example, the porous structure can be manufactured by culturing bacterial cellulose gel (BC gel) with yeast extract, or can be a porous structure manufactured from a symbiotic culture of bacteria and yeast (SCOBY). For example, the steps of mixing carbon source powders such as glucose, sucrose, and mannitol with nitrogen sources such as yeast extract and peptone powder together with distilled water, heating, and cooling at 25°C, adding bacterial cellulose gel (BC gel) to the mixture and culturing for 8 days, then washing with NaOH, neutralizing with acetic acid, bleaching with H2O2, and drying can be repeated. Specifically, the method can be manufactured by repeating the steps of [Han, Shim, and Kim. Effects of cultivation, washing, and bleaching conditions on bacterial cellulose fabric production. You can refer to the method described in [Textile Research Journal 2018, 89(6): 1094-1104].

The cellulose of the porous structure including the above bacterial cellulose fibers is manufactured by a cellulose-producing fungus, and any fungus capable of producing cellulose can be used.

According to one specific example, the bacterial cellulose may be prepared from Acetobacter xylinum, Komagataeibacter xylinus , or Gluconacetobacter xylinus .

According to one specific example, the milk protein may be whey protein isolate (WPI) or casein.

According to one specific example, the milk protein particles may be present in an amount of 30 to 70 parts by weight, 40 to 60 parts by weight, or 45 to 55 parts by weight, based on 100 parts by weight of the bacterial cellulose porous structure. The composite may have the best flame retardancy when the milk protein particles are present in an amount of 45 to 55 parts by weight, based on 100 parts by weight of the bacterial cellulose porous structure.

The above bacterial cellulose-milk protein particle complex may exhibit flame retardant properties. Flame retardancy refers to the property of a material that is difficult to combust, and may play a role in slowing or stopping the spread of a fire.

According to one specific example, the bacterial cellulose-milk protein complex may further comprise a cross-linking agent.

The crosslinking agent may be citric acid, glucose, glyoxal, glutaraldehyde, polyacrylic acid, or BTCA (1,2,3,4-butanetetracarboxylic acid). For example, citric acid may be used.

The cross-linking agent may be present at a concentration of 5% to 15% of the total, or may be present at a concentration of 50 to 150 parts by weight based on 100 parts by weight of bacterial cellulose. For example, citric acid may be present at a concentration of 70 to 130 parts by weight based on 100 parts by weight of bacterial cellulose.

Another aspect provides an artificial leather comprising a porous structure comprising bacterial cellulose fibers; and a bacterial cellulose-milk protein complex comprising milk protein particles provided in pores within the porous structure or on the surface of the porous structure.

According to one specific example, the milk protein particles may be whey protein isolate (WPI) or casein.

According to one specific example, the milk protein particles may be present in an amount of 30 to 70 parts by weight, 40 to 60 parts by weight, or 45 to 55 parts by weight, based on 100 parts by weight of the bacterial cellulose porous structure. The composite may have the best flame retardancy when the milk protein particles are present in an amount of 45 to 55 parts by weight, based on 100 parts by weight of the bacterial cellulose porous structure.

The above artificial leather may exhibit flame retardant properties. Flame retardancy refers to the property of a material that is difficult to combust, and can play a role in slowing or stopping the spread of a fire.

The above artificial leather can be manufactured by laminating an elastic sheet attached to the opposite side of the outer skin and an inner skin attached to the back side of the elastic sheet. The outer skin can be coated with an acrylic or urethane resin to improve texture, and the outer skin can be embossed to create a natural leather pattern or geometric pattern.

Another aspect provides a method for producing a bacterial cellulose-milk protein complex, comprising the steps of: mixing milk protein in purified water to produce a milk protein solution; adding a cross-linking agent and a catalyst to the milk protein solution to produce a mixture; immersing a porous structure including bacterial cellulose fibers in the mixture to produce a composite having milk protein particles in at least a portion of the internal pores or surface of the porous structure; and drying the composite.

According to one specific example, the step of producing the mixture may further include a protein denaturation process. The protein denaturation process may be a step of adjusting the pH to 9 to 11 and performing shaking culture, and the shaking culture may be performed at 75 to 85°C. In addition, the shaking culture may be performed at 60 to 100 rpm for 10 to 30 minutes.

According to one specific example, the milk protein may be whey protein isolate (WPI) or casein.

According to one specific example, the composition ratio of the crosslinking agent and the catalyst may be 4:3 to 1:2.

According to one embodiment, it was confirmed that the flame retardancy significantly increased when the composition ratio of the crosslinking agent and the catalyst was changed from 2:1 to 1:1, and that the flame retardancy gradually decreased when the composition ratio was changed from 1:1 to 1:2.

According to one specific example, the crosslinking agent may be citric acid, glucose, glyoxal, glutaraldehyde, polyacrylic acid, or BTCA (1,2,3,4-butanetetracarboxylic acid). For example, it may be citric acid.

The cross-linking agent may be present at a concentration of 5% to 15% of the total, or may be present at a concentration of 50 to 150 parts by weight based on 100 parts by weight of bacterial cellulose. For example, citric acid may be present at a concentration of 70 to 130 parts by weight based on 100 parts by weight of bacterial cellulose.

In one specific example, the catalyst may be sodium hypophosphite, titanium dioxide, hydrogen chloride, sulfuric acid, or potassium persulfate. For example, it may be sodium hypophosphite.

Another aspect provides a bacterial cellulose-milk protein complex produced by a method for producing a bacterial cellulose-milk protein complex, comprising the steps of: producing a milk protein solution by mixing milk protein in purified water; producing a mixture by adding a cross-linking agent and a catalyst to the milk protein solution; immersing a porous structure including bacterial cellulose fibers in the mixture to produce a composite having milk protein particles in at least a portion of the internal pores or surface of the porous structure; and drying the composite.

The steps for producing the mixture, the crosslinking agent, and the catalyst are the same as those described above.

The above bacterial cellulose-milk protein complex can be used as artificial leather, and the artificial leather can be manufactured by laminating an elastic sheet attached to the opposite side of the outer skin and an inner skin attached to the back side of the elastic sheet. The outer skin can be coated with an acrylic or urethane resin to improve texture, and can be embossed to create a natural leather pattern or geometric pattern on the outer skin.

The bacterial cellulose-milk protein complex according to the present invention has excellent dimensional stability, wash fastness, wrinkle resistance, water resistance, and flame retardancy, and can replace animal leather, and can be used in flame retardant articles made of leather.

Figure 1 is a schematic diagram of a method for producing a bacterial cellulose-milk protein complex using a physical encapsulation method.
Figure 2 is a schematic diagram of a method for producing a bacterial cellulose-milk protein complex through cross-linking.
Figure 3 is a schematic diagram of a method for producing a bacterial cellulose-milk protein complex through physical inclusion and cross-linking.
Figure 4A is data confirming the appropriate content of isolated whey protein that can significantly exhibit flame retardant properties when producing a bacterial cellulose-milk protein complex, and Figure 4B is data confirming the appropriate content of casein that can significantly exhibit flame retardant properties when producing a bacterial cellulose-milk protein complex.
Figure 5 shows data confirming the flame retardant properties of bacterial cellulose-milk protein complexes by changing the order of physical inclusion and cross-linking methods.
Figure 6 shows data showing the surface of a bacterial cellulose-milk protein complex manufactured by changing the type of cross-linking agent and the shape when the complex is folded.
Figure 7 is data confirming the degree of flame retardancy according to the content of citric acid, a cross-linking agent, in the production of bacterial cellulose-milk protein complex.
Figure 8 is data confirming the degree of flame retardancy according to the ratio of cross-linking agent and catalyst during the production of bacterial cellulose-milk protein complex.
Figure 9 shows data analyzing the chemical structure by FT-IR, where A is the FT-IR analysis result of bacterial cellulose-milk protein complex (BC-WPI-ent) manufactured by physical inclusion using a bacterial cellulose porous structure and whey protein isolate, and bacterial cellulose-milk protein complex (BC-WPI-x) manufactured by physical inclusion and cross-linking using whey protein isolate, and B is the FT-IR analysis result of bacterial cellulose-milk protein complex (BC-casein-ent) manufactured by physical inclusion using a bacterial cellulose porous structure and casein, and bacterial cellulose-milk protein complex (BC-casein-x) manufactured by physical inclusion and cross-linking using casein.
Figure 10 is data analyzed for crystallinity by XRD, where A is the XRD analysis result of a bacterial cellulose-milk protein complex (BC-WPI-ent) manufactured by physical inclusion using a bacterial cellulose porous structure and whey protein isolate, and a bacterial cellulose-milk protein complex (BC-WPI-x) manufactured by physical inclusion and cross-linking using whey protein isolate, and B is the XRD analysis result of a bacterial cellulose-milk protein complex (BC-casein-ent) manufactured by physical inclusion using a bacterial cellulose porous structure and casein, and a bacterial cellulose-milk protein complex (BC-casein-x) manufactured by physical inclusion and cross-linking using casein.
Figure 11 is a photograph of the surface structure of a bacterial cellulose porous structure and a bacterial cellulose-milk protein complex observed by SEM.
Figure 12 shows data obtained by analyzing the surface elements of a bacterial cellulose porous structure and a bacterial cellulose-milk protein complex using EDS.
Figure 13 shows data confirming the flame retardant properties of a bacterial cellulose porous structure and a bacterial cellulose-milk protein complex.
Figure 14 shows data confirming the contact angle of a bacterial cellulose porous structure and a bacterial cellulose-milk protein complex.
Figure 15 is data confirming the degree of water absorption (degree of waterproofness) of a bacterial cellulose porous structure and a bacterial cellulose-milk protein complex.
Figure 16 is data confirming the degree of flexibility of bacterial cellulose porous structures and bacterial cellulose-milk protein complexes.
Figure 17 shows data confirming the spindle structure of bacterial cellulose porous structure and bacterial cellulose-milk protein complex.
Figure 18 is data confirming the morphological stability of a bacterial cellulose porous structure and a bacterial cellulose-milk protein complex.
Figure 19 shows data confirming the washing fastness of a bacterial cellulose porous structure and a bacterial cellulose-milk protein complex.

Hereinafter, one or more specific examples will be described in more detail through examples. However, these examples are intended to exemplify one or more specific examples, and the scope of the present invention is not limited to these examples.

Example 1. Preparation of a porous structure comprising bacterial cellulose fibers

Porous structures (bacterial cellulose structures) containing bacterial cellulose fibers were fabricated, washed, and bleached according to the method described in the paper [Han, Shim, and Kim. Effects of cultivation, washing, and bleaching conditions on bacterial cellulose fabric production. Textile Research Journal 2018, 89(6): 1094-1104], and swelling pretreatment was performed according to the method described in the paper [Song JE, Su J, Loureiro A, Martins M, Cavaco-Paulo A, Kim HR, Silva C (2017) Ultrasound-assisted swelling of bacterial cellulose. Engineering in Life Science 17(10): 1108-1117.].

Example 2. Preparation of bacterial cellulose-milk protein complex through physical inclusion.

Bacterial cellulose-milk protein complexes through physical entrapment were prepared according to the procedure shown in Fig. 1. Whey protein isolate (WPI, Purunsan Agricultural Corp.) or casein extracted from bovine milk (Sigma-Aldrich) was placed in a beaker in an amount of 0 to 60 wt% relative to 100 wt% of the bacterial cellulose structure prepared in Example 1, and 10 times the amount of distilled water was added and mixed. Thereafter, the mixture was denatured at 80°C for 20 minutes at 80 rpm to a pH of 9.5 to 10.5, and 100 wt% of the bacterial cellulose structure was immersed and sonicated at 25°C for 30 minutes. To prepare a bacterial cellulose complex entrapping whey protein or casein, the mixture was shaken and cultured at 30°C for 1 hour at 80 rpm. Afterwards, it was dried at 20℃ for 24 hours to produce a bacterial cellulose-milk protein complex through physical inclusion.

Example 3. Preparation of bacterial cellulose-milk protein complex through cross-linking

Bacterial cellulose-milk protein complexes through cross-linking were prepared through the same procedure as in Fig. 2. Whey protein isolate (WPI, Purunsan Agricultural Corp.) or casein extracted from bovine milk (Sigma-Aldrich) was placed in a beaker in an amount of 0 to 60 wt% relative to 100 wt% of the bacterial cellulose structure prepared in Example 1, and distilled water was added in an amount 10 times that of the mixture and mixed. Citric acid as a cross-linking agent was mixed in an amount of 10 to 200 wt% relative to 100 wt% of the bacterial cellulose structure, and sodium hypophosphite was mixed in an amount of 5 to 100 wt% relative to 100 wt% of the bacterial cellulose. Afterwards, the mixture was denatured at 80°C for 20 minutes at 80 rpm to a pH of 9.5 to 10.5, and 100 wt% of the bacterial cellulose structure was immersed in the mixture. After 30 minutes, the immersed bacterial cellulose was taken out and cured at 160°C for 5 minutes to induce a cross-linking reaction. Afterwards, it was dried at 20°C for 24 hours to produce a bacterial cellulose-milk protein complex through cross-linking.

Example 4. Preparation of bacterial cellulose-milk protein complex through physical inclusion and cross-linking.

Bacterial cellulose-milk protein complexes through physical inclusion and cross-linking were prepared in the following sequence as shown in Fig. 3. Whey protein isolate (WPI, Purunsan Agricultural Corp.) or casein extracted from bovine milk (Sigma-Aldrich) was placed in a beaker in an amount of 0 to 60 wt% relative to 100 wt% of the bacterial cellulose structure prepared in Example 1, and 10 times the amount of distilled water was added and mixed. Thereafter, citric acid as a cross-linking agent was mixed in an amount of 10 to 200 wt% relative to 100 wt% of the bacterial cellulose, and sodium hypophosphite was mixed in an amount of 5 to 100 wt% relative to 100 wt% of the bacterial cellulose. The bacterial cellulose structure was denatured at 80°C for 20 minutes at 80 rpm to pH 9.5 to 10.5, and 100 wt% of the bacterial cellulose structure was immersed and sonicated at 25°C for 30 minutes to physically encapsulate the protein. To prepare a bacterial cellulose complex encapsulating isolated whey protein or casein, it was shaken and cultured at 30°C for 1 hour at 80 rpm. Afterwards, it was cured at 160°C for 5 minutes to induce a cross-linking reaction. After that, it was dried at 20°C for 24 hours to prepare a bacterial cellulose-milk protein complex through physical encapsulation and cross-linking.

Example 5. Selection of optimal content conditions for isolated whey protein and casein.

To determine the optimal content of whey protein isolate and casein, thermogravimetric analysis (TGA) was performed. TGA is the simplest method used to analyze flame retardancy. Using a thermogravimetric analyzer (TA Instruments, Discovery SDT 650, USA), the weight ratio of the residue remaining after burning at a high temperature of 1000°C was determined and compared.

As shown in Fig. 4, it was confirmed that the residue was the largest when the isolated whey protein and casein were 50 wt%, and thus the flame retardancy was confirmed to be the best when the amount was 50 wt% relative to the weight of bacterial cellulose.

Example 6. Selection of production method

In order to identify the production method with the best flame retardancy using TGA in the same manner as in Example 5, thermogravimetric analysis was performed on bacterial cellulose fibers, bacterial cellulose-milk protein complexes using only physical inclusion, bacterial cellulose-milk protein complexes in which cross-linking was performed before and after physical inclusion, and bacterial cellulose-milk protein complexes in which cross-linking was performed simultaneously with physical inclusion as in Example 4.

As a result, as shown in Fig. 5, it was confirmed that the bacterial cellulose-milk protein complex that was cross-linked simultaneously with physical inclusion had significantly better flame retardancy, and next, the bacterial cellulose-milk protein complex that was cross-linked after physical inclusion had significantly better flame retardancy than other fibers or protein complexes.

Example 7. Selection of cross-linker

To select a suitable cross-linking agent for cross-linking, bacterial cellulose-milk protein complexes were prepared using citric acid, sorbitol, polyethylene glycol (PEG 400), ethylene glycol, and glucose as cross-linking agents. After preparation, thermogravimetric analysis (TGA) was performed on the bacterial cellulose-milk protein complexes prepared with each cross-linking agent. In the case of citric acid, sodium hypophosphite was used as a catalyst.

As a result, as shown in Table 1 below, it was confirmed that the flame retardancy was the highest when glucose was used as a crosslinking agent, and that the flame retardancy was high when ethylene glycol and citric acid were used as crosslinking agents in that order.

Sample Protein Crosslinker Catalyst Residual wt% at 1,000℃ Crosslinking only WPI Citric acid Sodium hypophosphite 15.255 Crosslinking only WPI Sorbitol - 11.012 Crosslinking only WPI PEG 400 - 5.708 Crosslinking only WPI Ehylene glycol - 16.224 Crosslinking only WPI Glucose - 27.531

However, as shown in Fig. 6, the bacterial cellulose-milk protein (WPI) complex manufactured using citric acid as a cross-linking agent and sodium hypophosphite as a catalyst was confirmed to be very flexible and have a texture similar to that of conventional bacterial cellulose fibers, but in the case of the bacterial cellulose-milk protein (WPI) complex manufactured using other cross-linking agents, all had a paper-like appearance and texture and were stiff, and when bent, they were confirmed to fold in half rather than bend flexibly.

Therefore, flame retardancy was highest when glucose was used as a cross-linking agent, but it was confirmed that the bacterial cellulose-milk protein complex that had flame retardancy while maintaining the leather texture was a bacterial cellulose-milk protein complex manufactured using citric acid as a cross-linking agent and sodium hypophosphate as a catalyst.

Example 8. Selection of optimal citric acid content

To determine the optimal citric acid content for the production of a bacterial cellulose-milk protein complex exhibiting flame-retardant properties, flame retardancy was assessed based on citric acid content. Flame retardancy was determined using thermogravimetric analysis (TGA). Citric acid content was expressed as a percentage of the mixture.

As a result, as shown in Fig. 7, it was confirmed that both isolated whey protein and casein had the highest flame retardancy when the concentration of citric acid was 10%, and that at higher concentrations, the flame retardancy decreased or was at a similar level.

Example 9. Selection of the ratio of crosslinking agent and catalyst

In order to determine the optimal ratio conditions of cross-linking agent and catalyst when manufacturing a bacterial cellulose-milk protein complex exhibiting flame retardant properties, the conditions were evaluated through TGA analysis.

As a result, as shown in Fig. 8, it was confirmed that the flame retardancy was significantly increased when the ratio of crosslinking agent and catalyst was 1:1.

Example 10. Surface analysis of bacterial cellulose-milk protein complexes

10-1. FT-IR analysis

The chemical structure of the bacterial cellulose-milk protein complex was analyzed using an FT-IR spectrophotometer (Nicolet IS50; Thermo Fisher Scientific, Waltham, MA, USA). 32 scans were performed at a resolution of 0.4 cm ^-1 and the range from 650 to 4000 cm -1 was 4000 cm ^-1. FT-IR spectra were collected over a range of wavelengths. Each spectrum was baseline normalized using OMNIC software (Thermo Fisher Scientific, Waltham, MA, USA).

The results of chemical structure analysis are shown in Fig. 9, and it was confirmed that an amide peak was observed at 1500-1700 cm ^-1 in the bacterial cellulose-milk protein complex produced only by the physical inclusion method, but it was not observed after cross-linking. This is confirmed because the chemical structure changes as the bacterial cellulose structure and milk protein molecules combine due to cross-linking, and it was confirmed that bacterial cellulose and milk protein are effectively chemically bonded through cross-linking.

10-2. XRD analysis

The crystallinity of the bacterial cellulose-milk protein complex was confirmed using XRD (X-ray diffraction, D8 ADVANCE diffractometer; Bruker AXS Inc.).

As shown in Fig. 10, it was confirmed that the intensity of the cellulose peak decreased overall after cross-linking. In addition, as shown in Table 2 below, it was confirmed that the crystallinity decreased after cross-linking compared to the physical inclusion or existing bacterial cellulose structure. This phenomenon was presumed to occur because the OH groups of bacterial cellulose were cross-linked with isolated whey protein or casein molecules.

Additionally, as shown in Table 2 below, it was confirmed that although the degree of crystallinity was somewhat reduced, it did not affect the strength of the bacterial cellulose-milk protein complex itself. Therefore, it was confirmed that bacterial cellulose and isolated whey protein or casein molecules were effectively cross-linked.

Sample Crystallinity (%) Original BC 89.3±6.9 BC-WPI-ent 88.0±1.1 BC-WPI-x 60.2±3.1 BC-casein-ent 89.9±0.8 BC-casein-x 62.4±4.6

10-3. FE-SEM analysis

To analyze the surface structure of the bacterial cellulose-milk protein complex, the surface was observed using FE-SEM (JSM-7800F Prime; JEOL Ltd.).

As shown in Fig. 11, the surface structure was observed, and it was confirmed that the cross-linked bacterial cellulose-milk protein complex had a tightly coated surface, whereas the bacterial cellulose-milk protein complex prepared using only a physical encapsulation method had a visible internal fiber structure, and it was confirmed that the whey protein isolate or casein molecules were not evenly distributed within the fiber structure. Therefore, it was confirmed that the flame retardancy of the bacterial cellulose complex was improved because the whey protein isolate or casein was tightly coated on the surface of the bacterial cellulose structure through cross-linking.

10-4. EDS Analysis

To analyze the elements on the surface of the bacterial cellulose-milk protein complex, EDS (JSM-7800F Prime; JEOL Ltd.) was used.

As shown in Fig. 12 and Table 3, it was confirmed that the content of nitrogen (N) and phosphorus (P) elements increased significantly after cross-linking, and the content of sulfur (S) also increased. At this time, the increased nitrogen and phosphorus are the main components of the flame retardant, and it was confirmed that the elemental content of phosphorus and nitrogen in the bacterial cellulose-milk protein complex increased significantly during cross-linking, resulting in a flame retardant effect.

Elements (wt%) Sample C N O P S Original BC 48.74 - 40.79 - - BC-WPI-ent 60.57 3.46 35.05 0.14 0.77 BC-WPI-x 52.02 6.62 32.18 8.26 0.92 BC-casein-ent 49.59 - 50.10 0.23 0.08 BC-casein-x 44.04 5.04 43.68 7.13 0.12

Example 11. Comparison of weight, thickness, and flame retardancy of bacterial cellulose-milk protein complexes.

Thickness, weight, and flame retardancy of bacterial cellulose-milk protein complexes were compared according to the manufacturing method.

As a result, as shown in Table 4 below, it was confirmed that the thickness of the bacterial cellulose-milk protein complex subjected to physical inclusion and cross-linking was significantly increased compared to the thickness of the bacterial cellulose-milk protein complex subjected to only physical inclusion, and it was confirmed that the thickness of the bacterial cellulose-milk protein complex subjected to physical inclusion and cross-linking was similar to the thickness of bovine leather, but it was confirmed that the weight was significantly heavier than bovine leather of similar thickness.

In addition, as shown in Fig. 13, it was confirmed that the bacterial cellulose-milk protein complex subjected to physical inclusion and cross-linking had significantly superior flame retardant properties than the bacterial cellulose-milk protein complex subjected to physical inclusion only and bovine leather of similar thickness.

Fabric Thickness (mm) Weight (g/m ² ) Original BC 0.92±0.13 186.67±12.47 Cowhide leather 0.72±0.14 466.67±18.26 BC-WPI-ent 0.20±0.03 127.80±8.61 BC-WPI-x 0.76±0.08 1036.80±92.89 BC-casein-ent 0.27±0.10 171.73±41.61 BC-casein-x 0.76±0.05 1053.2±76.60

Example 12. Durability Verification

12-1. Contact angle analysis

To analyze the water contact angle on the surface, water was dropped on the bacterial cellulose-milk protein complex, and the water contact angle (WCA) was determined.

As shown in Fig. 14, the complex using only physical inclusion and whey protein isolate (BC-WPI-ent) had a smaller contact angle than that of general bovine leather, whereas the complex using only physical inclusion and casein (BC-casein-ent) had a larger contact angle than that of general bovine leather. However, the complexes manufactured using both physical inclusion and cross-linking (BC-WPI-x and BC-casein-x) had significantly larger contact angles than that of general bovine leather.

12-2. Checking the waterproof effect

To confirm the waterproofing effect, water was dropped on the bacterial cellulose structure, cowhide, and bacterial cellulose-milk protein complex, and then the absorbency was confirmed.

As shown in Fig. 15, the bacterial cellulose-milk protein complex produced by the physical encapsulation method was confirmed to have completely absorbed water within 5 to 10 minutes. On the other hand, in the case of the bacterial cellulose-milk protein complex produced by both the physical encapsulation method and the cross-linking method, no water was absorbed even after 10 minutes after water was dropped, and it was confirmed that completely absorbed after 30 minutes.

Therefore, it was confirmed that the bacterial cellulose-milk protein complex produced by physical inclusion and cross-linking methods absorbs relatively less water.

12-3. Check flexibility

To determine flexibility, the flexibility of bacterial cellulose structures, cowhide, and bacterial cellulose-milk protein complexes was measured.

To determine flexibility, the KS K 0538 heart-loop method was used. The sample size was modified to 5 cm × 10 cm, and the experimental time was modified to 1 minute. A loop was created, and the changes in each sample were observed after 1 minute. Each experiment was performed five times, and the results were expressed as an average value. The more flexible the sample, the longer the difference between the loop length after 1 minute and the initial loop length.

As a result, as shown in Fig. 16, it was confirmed that the bacterial cellulose-milk protein complex manufactured only by the physical encapsulation method was more flexible than the bacterial cellulose structure, but not as flexible as bovine leather. On the other hand, the bacterial cellulose-milk protein complex manufactured using physical encapsulation and cross-linking showed a length difference of about twice that of bovine leather, confirming that it had significantly superior flexibility.

12-4. Check the spindle (crease recovery)

Spindle stiffness is the property of a sample to return to its original state without damage when bent and then straightened. The better the spindle stiffness, the better the durability of the composite. Therefore, to check the spindle stiffness, the recovery angle method of KS K 0550 was used. The sample size was 5 cm × 10 cm, and the experimental time was modified to 1 minute. The wrinkle recovery rate was calculated according to the following formula. All experiments were performed 5 times, and the results are presented as the average value.

[ceremony]

Crease recovery (spindle degree %) = crease recovery angle (wrinkle recovery angle °) / 180° x 100

As a result of the spindle measurement, as shown in Fig. 17, it was confirmed that the bacterial cellulose-milk protein complexes, except for the bacterial cellulose-milk protein complex prepared using the physical encapsulation method with casein, showed a significantly improved spindle rate compared to the existing bacterial cellulose structure. In the case of the bacterial cellulose-milk protein complex prepared using the physical encapsulation method with casein, it was impossible to measure the spindle rate due to its stiffness. In addition, it was confirmed that the bacterial cellulose-milk protein complex prepared through physical encapsulation and cross-linking showed a better spindle rate than bovine hide of similar thickness.

12-5. Checking Dimensional Stability

Shape stability is the property of an object to not change in dimension and shape under conditions such as temperature and humidity. To confirm the shape stability, KS K ISO 7771:1985 Determination of dimensional changes of fabrics induced by cold-water immersion was used. The sample size was modified to 5 cm X 10 cm, and the experimental time was 60 to 180 minutes. To analyze the shape stability, each sample was immersed in a wetting agent, sodium dodecylbenzenesulfonate (C18H29NaO3S), for a certain period of time, and then dried to measure the degree of shape change. The shape stability was calculated according to the following formula, and all experiments were performed five times, and the results were presented as the average value.

[ceremony]

Dimensional stability (%) = (Dimensions of sample after immersion/Dimensions of sample before immersion) × 100

As shown in Fig. 18, the shape stability of the bacterial cellulose-milk protein complex prepared by physically enclosing and cross-linking whey protein isolate was confirmed to remain constant even after immersion in a wetting agent for 180 minutes and drying, similar to that of bovine leather of similar thickness. In addition, the shape of the bacterial cellulose-milk protein complex prepared by physically enclosing and cross-linking casein was maintained constant when dried after immersion for 120 minutes, but a slight deformation occurred in the shape after immersion for 180 minutes. In addition, the shape stability of the bacterial cellulose-milk protein complex prepared by the physical enclosing method was confirmed to be lower than that of the bacterial cellulose-milk protein complex prepared by physical enclosing and cross-linking, and it was confirmed that the bacterial cellulose-milk protein complex prepared by the physical enclosing method using whey protein isolate changed significantly when dried after immersion for 180 minutes.

Therefore, it was confirmed that the bacterial cellulose-milk protein complex produced by physical inclusion and cross-linking had significantly better morphological stability than the bacterial cellulose-milk protein complex produced using only physical inclusion.

12-6. Measurement of color fastness to water washing

Washing fastness was measured as the extent to which flame retardant properties remained after washing.

The fabricated bacterial cellulose-milk protein complex was tested for color fastness to water washing according to the water washing fastness test method of the paper [Kim, Song, and Kim. Ex situ Coloration of Laccase-Entrapped Bacterial Cellulose with Natural Phenolic Dyes. Journal of the Korean Society of Clothing and Textiles 2021, 45(5): 866-880.]. The complex was immersed in distilled water 50 times the weight of the bacterial cellulose-milk protein complex, and then washed in a water bath at 25°C for 30 minutes at a speed of 110 rpm. The washed bacterial cellulose-milk protein complex was dried at 25°C for 2 hours, cut into 1.5 × 1.5 cm pieces, and exposed to a flame for 5 seconds. The burning area was measured, and the area ratio of the sample before and after combustion was calculated.

As shown in Fig. 19, the bacterial cellulose-milk protein complex produced by physically enclosing and cross-linking isolated whey protein was found to maintain its flame retardancy even after washing up to two times, and the bacterial cellulose-milk protein complex produced by physically enclosing and cross-linking casein was found to be able to withstand repeated washing up to three times. On the other hand, the bacterial cellulose-milk protein complex produced by the physical enclosing method was found to have a significantly reduced flame retardancy after washing. This means that the milk protein is firmly bound to the bacterial cellulose due to cross-linking, and thus the flame retardancy is maintained even after washing.

Example 13. Comparison of flame retardancy of bacterial cellulose-milk protein complexes according to cross-linking and physical inclusion.

In order to compare flame retardancy according to the manufacturing method, bacterial cellulose-milk protein complexes using isolated whey protein were manufactured using different manufacturing methods and their flame retardancy was compared.

As a result, as shown in Table 5 below, it was confirmed that the flame retardancy of the bacterial cellulose-milk protein complex using only crosslinking (Crosslinking only) was significantly higher than that of the bacterial cellulose-milk protein complex using only physical entrapment (Entrapment only), and it was confirmed that the flame retardancy of the bacterial cellulose-milk protein complex using both physical entrapment and crosslinking (Entrapment+Crosslinking) was significantly increased compared to that of the bacterial cellulose-milk protein complex using only physical entrapment or crosslinking.

Sample Protein Crosslinker Catalyst Residual wt% at 1,000℃ Original BC WPI - - 3.080 Entrapment only WPI - - 7.524 Crosslinking only WPI Citric acid Sodium hypophosphite 15.255 Entrapment+ Crosslinking WPI Citric acid Sodium hypophosphite 56.298

Example 14. Comparison of the components of bacterial cellulose-milk protein complexes according to cross-linking and physical inclusion.

To determine the cause of the difference in flame retardancy according to the manufacturing method, bacterial cellulose-milk protein complexes using isolated whey protein were manufactured using different manufacturing methods and subjected to EDS analysis.

As a result, as shown in Table 6 below, the contents of nitrogen (N), phosphorus (P), and sulfur (S) elements increased in the bacterial cellulose-milk protein complex produced using both physical inclusion and cross-linking methods, and in particular, the phosphorus content was confirmed to have increased significantly.

Sample Elements (wt%) C N O P S Original BC 48.74 - 40.79 - - Entrapment only 60.57 3.46 35.05 0.14 0.77 Crosslinking only 58.49 7.97 32.21 1.05 0.28 Entrapment + Crosslinking 52.02 6.62 32.18 8.26 0.92

Claims (12)

A porous structure comprising bacterial cellulose fibers; and
A bacterial cellulose-milk protein complex comprising milk protein particles provided in pores within the porous structure or on the surface of the porous structure,
A bacterial cellulose-milk protein complex, wherein the bacterial cellulose fibers and the milk protein particles form a bacterial cellulose-milk complex through physical inclusion and cross-linking.
In the first paragraph,
The above milk protein is whey protein isolate (WPI) or casein.
Bacterial cellulose-milk protein complex.
Artificial leather comprising the complex of claim 1 or 2.
A step of creating a milk protein solution by mixing milk protein into purified water;
A step of creating a mixture by adding a cross-linking agent and a catalyst to the above milk protein solution;
A step of denaturing the mixture, immersing the bacterial cellulose structure, and sonicating to physically encapsulate the milk protein;
A step of producing a bacterial cellulose complex that encapsulates the milk protein by shaking and culturing the bacterial cellulose structure; and
A method for producing a bacterial cellulose-milk protein complex, comprising: a step of curing the bacterial cellulose complex to induce a cross-linking reaction;
In paragraph 4,
The above milk protein is whey protein isolate (WPI) or casein.
Method for producing bacterial cellulose-milk protein complex.
In paragraph 4,
A method for producing a bacterial cellulose-milk protein complex, wherein the milk protein is 45 to 55 wt% relative to the weight of bacterial cellulose.
In paragraph 4,
The composition ratio of the crosslinking agent and the catalyst is 4:3 to 1:2,
Method for producing bacterial cellulose-milk protein complex.
In paragraph 4,
The crosslinking agent is citric acid, glucose, glyoxal, glutaraldehyde, polyacrylic acid or BTCA (1,2,3,4-butanetetracarboxylic acid).
Method for producing bacterial cellulose-milk protein complex.
In paragraph 4,
The catalyst is sodium hypophosphite, titanium dioxide, hydrogen chloride, sulfuric acid or potassium persulfate.
Method for producing bacterial cellulose-milk protein complex.
In paragraph 4,
The crosslinking agent is citric acid, and the catalyst is sodium hypophosphite.
Method for producing bacterial cellulose-milk protein complex.
In paragraph 4,
The crosslinking agent is present in a concentration of 5 to 15% relative to the weight of the mixture.
Method for producing bacterial cellulose-milk protein complex.
A bacterial cellulose-milk protein complex manufactured by any one of the manufacturing methods of claims 4 to 11.