Preparation method and application of biodegradable material based on gamma-polyglutamic acid

Abstract

The invention discloses a preparation method of a biodegradable material based on gamma-polyglutamic acid, which comprises the following steps: (1) preparing a low-molecular-weight polyglutamic acid aqueous solution, adjusting the pH value to be acidic to obtain a carboxylic acid group protonated polyglutamic acid solution, then adding a metal ion solution into the polyglutamic acid solution, and uniformly stirring and mixing to obtain a mixed solution; and (2) adjusting the pH value of the mixed solution obtained in the step (1) to be alkaline while stirring, then adding a cross-linking agent into the mixed solution, and carrying out cross-linking curing to obtain the biodegradable material. The material disclosed by the invention has mechanical properties, tensile strength, toughness and the like can be improved, so that the material can better meet the requirements of different application scenes, the application range of the material is widened, and meanwhile, the material has relatively good degradation performance, adsorption performance, antibacterial performance and moisture retention performance, can be produced by utilizing renewable resources, is wide in raw material source and sustainable, and is suitable for industrial production. The dependence on non-renewable resources such as petroleum is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of polymer material preparation, and in particular to a preparation method and application of a biodegradable material based on gamma-polyglutamic acid. Background Art

[0002] In the process of rapid global industrialization, the contradiction between material use and environmental protection has become increasingly prominent, and the environmental problems caused by traditional plastic products are particularly severe. Ordinary plastic products are mostly made of petroleum-based polymers, with stable chemical structures and extremely difficult to degrade in the natural environment. Every year, more than 300 million tons of plastic waste are produced worldwide. They remain in the soil for hundreds or even thousands of years, seriously damaging the soil structure, reducing fertility, and affecting the growth of crops; after flowing into the water body, they threaten the survival of aquatic organisms, block waterways, and destroy the ecological balance of the ocean. "White pollution" has become a global environmental problem, endangering ecological security and human sustainable development. my country has actively responded and clearly made strengthening environmental protection and promoting green development an important goal. Vigorously developing the green materials industry has become a key task. The research and development of new biodegradable materials to replace traditional non-degradable materials is urgent, which is of great significance to ensuring national ecological security and promoting high-quality economic development.

[0003] γ-Polyglutamic acid is a material with excellent biodegradability. It can respond well to the plastic ban and fill the gap in the biodegradable material market. Its preparation raw materials are renewable, the synthesis process is mild, the energy consumption is low, the carbon emissions are low, and the degradation products are harmless, which is conducive to the sustainable development of agriculture. At the same time, it also has antibacterial properties, can form a film to inhibit the growth of microorganisms, and has good biocompatibility. It can be used in biomedical fields such as drug carriers and tissue engineering scaffolds to avoid the risk of long-term residues in the body.

[0004] γ-polyglutamic acid (γ-PGA), also known as natto gum and polyglutamic acid, is a biopolymer composed of α-amine and γ-carboxyl groups via amide bonds. It is a homogeneous polypeptide polymerized with left- and right-handed optically active glutamic acid as units and amide bonds at the γ-position. Common ions such as calcium ions, magnesium ions, and iron ions can coordinate with glutamic acid, and different metal ions will give the material different properties.

[0005] In addition, γ-polyglutamic acid (γ-PGA) can be obtained through microbial fermentation. Under specific fermentation conditions, Bacillus natto can utilize nutrients such as carbon sources and nitrogen sources in the culture medium to synthesize and secrete γ-polyglutamic acid through intracellular metabolic pathways. For example, in a culture medium with glucose as the carbon source and soy peptone as the nitrogen source, Bacillus natto can synthesize a large amount of γ-polyglutamic acid. Under appropriate fermentation conditions, Bacillus licheniformis can also convert nutrients into γ-polyglutamic acid through its own metabolic mechanism, making large-scale production possible. However, the current γ-polyglutamic acid-related material technology still needs to be improved. Summary of the invention

[0006] Purpose of the invention: In view of the shortcomings of the prior art, the present invention aims to innovate the preparation method, provide a preparation method and application of a biodegradable material based on γ-polyglutamic acid, and further synthesize γ-polyglutamic acid mineralized plastics with excellent performance to meet market demand and promote the green development of the industry.

[0007] In order to solve the above technical problems, the present invention discloses a method for preparing a biodegradable material based on γ-polyglutamic acid, comprising the following steps:

[0008] (1) preparing a low molecular weight polyglutamic acid aqueous solution, adjusting the pH of the polyglutamic acid aqueous solution to acidity to obtain a polyglutamic acid solution with protonated carboxylic acid groups, and then adding a metal ion solution thereto, stirring and mixing to obtain a mixed solution, wherein the metal ion solution is a solution containing calcium ions or a mixture of calcium ions and iron ions;

[0009] (2) adjusting the pH of the mixed solution obtained in step (1) to alkaline while stirring, and then adding a cross-linking agent thereto to perform cross-linking and curing to obtain a biodegradable material.

[0010] Preferably, in step (1), the weight average molecular weight of the polyglutamic acid is 5000-20000 Da, and the molar concentration of the polyglutamic acid aqueous solution is 0.2-0.3 M. Low molecular weight polyglutamic acid is easily soluble in water and degrades quickly.

[0011] Preferably, in step (1), the pH of the polyglutamic acid aqueous solution is adjusted to 2.5-3.0, preferably to 2.8. Since low molecular weight PGA contains carboxylic acid groups, under acidic conditions, the carboxylic acid groups are protonated, making them in a relatively dispersed state in the solution, which is conducive to subsequent uniform mixing and reaction with other ions. Preferably, the pH is adjusted by slowly adding 1M HCl solution.

[0012] Wherein, the total cation molar concentration of the metal ion solution is 0.1mol / L to 0.5mol / L, wherein, in the mixture of calcium ions and iron ions, the molar ratio of iron ions to calcium ions is 100 to 9:1. Wherein, preferably, the metal ion solution is slowly added to the PGA solution while the PGA solution is vigorously stirred. Continue stirring to fully mix the two solutions. Violent stirring can provide sufficient power to evenly disperse the metal ions into the PGA solution system, create good conditions for the subsequent cross-linking reaction, and ensure that the cross-linking reaction is evenly carried out in the entire solution system. Preferably, the stirring rate is 1200-1500rpm.

[0013] The volume ratio of the polyglutamic acid aqueous solution to the metal ion solution is 1:0.8 to 1. The preferred ratio is 1:1.

[0014] In step (2), the pH of the mixed solution is adjusted to 8-9, preferably to 8. Preferably, a 1M NaOH solution is slowly added dropwise to the mixed solution, stirred while adding dropwise, and the pH value change is closely observed. When the pH is raised to alkaline, the carboxylic acid group of PGA loses protons and becomes a carboxylate anion. The negatively charged carboxylate anion can react with the positively charged Ca 2 + Ions combine through electrostatic action to form ionic bonds, thereby achieving cross-linking and building a three-dimensional network structure.

[0015] Preferably, the cross-linking agent is isopropanol, and the volume ratio of the mixed solution to isopropanol is 1:1 to 1.2. Preferably, isopropanol is added to the mixed solution slowly and evenly at a rate of 1 to 1.5 mL / s through a syringe pump.

[0016] The biodegradable material based on γ-polyglutamic acid prepared by the above preparation method is also within the protection scope of the present invention.

[0017] The present invention further protects a mineralized plastic, which is obtained by further molding and processing a marketed biodegradable material, and then drying it. Specifically, the mixture after the reaction is poured into a mold, and solidified and molded by natural drying, hot pressing molding, injection molding, etc. to obtain a γ-polyglutamic acid mineral plastic. The drying treatment includes any one of vacuum drying, freeze drying or hot air drying. The molded material is dried in an oven to remove residual moisture and solvent, thereby improving the performance and stability of the material.

[0018] Furthermore, according to actual application requirements, the material can be surface treated, such as coating, plating, etc., to improve the surface properties of the material, such as waterproofness and wear resistance.

[0019] The present invention further proposes the use of the mineralized plastic in manufacturing automobile interior trims, automobile exterior trims, building pipes, profiles, electrical housings, wire and cable insulation layers, plastic furniture, plastic tableware, plastic toys or biomedical materials.

[0020] The glutamic acid unit in polyglutamic acid can coordinate with metal ions to form a material with specific properties. This material not only has the advantages of ordinary mineralized plastics, such as being hard, non-flammable, and can be produced in room temperature water, and can be reshaped and recycled after being formed by adding water, but also overcomes the key defect of ordinary mineralized plastics that they are difficult to biodegrade.

[0021] The biodegradable material prepared by the invention has good toughness and mechanical properties, antibacterial performance with an antibacterial rate of 98%, extremely low rejection reaction, and a cell survival rate of 90% and biocompatibility.

[0022] Beneficial effects: Compared with the prior art, this application has the following advantages:

[0023] (1) γ-polyglutamic acid itself has good biodegradability and can be decomposed into harmless substances such as carbon dioxide and water by microorganisms in the natural environment. Compared with traditional materials, it greatly reduces the pollution to the environment and helps to alleviate the problem of "white pollution";

[0024] (2) γ-polyglutamic acid can be produced from renewable resources through methods such as microbial fermentation. The raw material sources are extensive and sustainable, reducing dependence on non-renewable resources such as petroleum;

[0025] (3) γ-polyglutamic acid has strong adsorption properties and can effectively adsorb metal ions and other substances in γ-polyglutamic acid mineral plastics, thereby improving the stability and durability of the materials. It can also be used to adsorb pollutants such as heavy metal ions in the environment, thereby playing a role in purifying the environment.

[0026] (4) Adding γ-polyglutamic acid can improve the mechanical properties of mineralized plastics, such as tensile strength and toughness, so that they can better meet the needs of different application scenarios and broaden the scope of use of the material;

[0027] (5) γ-polyglutamic acid has excellent moisturizing properties, which can keep the performance of mineralized plastics stable in some environments with certain humidity requirements, and prevent the material from cracking, brittleness and other problems due to drying and other reasons;

[0028] (6) γ-Polyglutamic acid has certain antibacterial properties. When added to mineralized plastics, it can inhibit the growth and reproduction of microorganisms and reduce the growth of bacteria on the surface of the material. When used in food packaging, medical and other fields, it helps to extend the shelf life of the product and improve its safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The preliminary γ-polyglutamic acid mineral fiber obtained in Example 1 is shown in Figure A. Figure A is a physical picture of a polyglutamic acid mineral product with 100% calcium ions, Figure B is a physical picture of a polyglutamic acid mineral product with an iron-calcium ratio of 1:99, Figure C is a physical picture of a polyglutamic acid mineral product with an iron-calcium ratio of 1:49, and Figure D is a physical picture of a polyglutamic acid mineral product with an iron-calcium ratio of 1:9. Figure E is a physical picture of a polyglutamic acid mineral product stretched into a film;

[0030] Figure 2The preliminary polyglutamic acid mineral fiber in Example 2 is stretched after kneading for 5 minutes. Figure A is a stretching diagram of a polyglutamic acid mineral product with a calcium ion ratio of 100%, Figure B is a stretching diagram of a polyglutamic acid mineral product with an iron-calcium ratio of 1:99, and Figure C is a stretching diagram of a polyglutamic acid mineral product with an iron-calcium ratio of 1:49. Figure D is a combustion diagram of a polyglutamic acid mineral product with an iron-calcium ratio of 1:99;

[0031] Figure 3 The line graphs are made of the rheological data of each product measured in Example 3, wherein Figure a is a rheological test graph of a polyglutamic acid mineral product with a calcium ion ratio of 100%, Figure b is a rheological test graph of a polyglutamic acid mineral product with an iron-calcium ratio of 1:99, Figure c is a rheological test graph of a polyglutamic acid mineral product with an iron-calcium ratio of 1:49, and Figure d is a rheological test graph of a polyglutamic acid mineral product with an iron-calcium ratio of 1:9;

[0032] Figure 4 The differential scanning calorimetry (DSC) spectrum obtained in the test of Example 4;

[0033] Figure 5 This is a curve chart of the test results of the biodegradability of the polyglutamic acid mineral fiber material in Example 5. DETAILED DESCRIPTION

[0034] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments, and the above and / or other advantages of the present invention will become more clear.

[0035] If the specific techniques or conditions are not specified in the examples, they are carried out according to the techniques or conditions described in the literature in the field or according to the product instructions. If the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be purchased through regular channels.

[0036] The polyglutamic acid used in the following examples was purchased from Nanjing Xuankai Biotechnology Co., Ltd., with a purity of cosmetic grade (≥95%) and a molecular weight of 5000-20000 Da.

[0037] The vortex oscillator used in the following examples was purchased from SCILOGEX Instruments, model SCI-VS.

[0038] The components of the liquid culture medium used in the following examples are: 17.0 g / L trypticase peptone, 3.0 g / L soybean papain hydrolyzate, 5.0 g / L sodium chloride, 2.5 g / L potassium dihydrogen phosphate, 2.5 g.

[0039] Example 1 Preparation of polyglutamic acid mineral product.

[0040] Accurately weigh an appropriate amount of low molecular weight PGA (Nanjing Xuankai Biological, 5000-20000Da), dissolve it in 5mL of deionized water, and prepare a PGA solution with a concentration of 0.2M according to the average molecular weight. During the dissolution process, stir with a magnetic stirrer to accelerate the dissolution. Subsequently, 1M HCl solution was slowly added dropwise, and the pH value of the solution was monitored in real time with a pH meter until the pH value reached 2.8. Since low molecular weight PGA contains carboxylic acid groups, under acidic conditions (pH = 2.8), the carboxylic acid groups are protonated, making them in a more dispersed state in the solution, which is conducive to subsequent uniform mixing and reaction with other ions.

[0041] Take another portion of pure CaCl2 and prepare a 0.2M CaCl2 solution. While vigorously stirring the PGA solution at 1400rpm, use a pipette to accurately measure the CaCl2 solution of the same volume as the PGA solution and slowly add it to the PGA solution. Continue stirring to mix the two solutions thoroughly. Vigorous stirring can provide enough power to make the CaCl2 solution 2 + ions are evenly dispersed into the PGA solution system, creating good conditions for the subsequent cross-linking reaction and ensuring that the cross-linking reaction proceeds evenly throughout the solution system.

[0042] After mixing evenly, slowly add 1M NaOH solution to the mixed solution, stirring while adding, and closely observe the change in pH value. Stop adding when the pH value reaches 8.0. At this point, the carboxylic acid group of PGA is deprotonated and reacts with Ca 2 + ions undergo cross-linking reaction. When the pH rises to 8.0, the carboxylic acid group of PGA loses protons and becomes a carboxylate anion. The negatively charged carboxylate anion can cross-link with the positively charged Ca 2 + Ions combine through electrostatic action to form ionic bonds, thereby achieving cross-linking and building a three-dimensional network structure.

[0043] Then, isopropanol was added to the mixed solution at a uniform rate of 1 mL / s through a syringe pump. . With the addition of isopropanol, the solution gradually formed a viscous white gel. The flow rate of the syringe pump was controlled at 1-2 mL per minute to ensure that the isopropanol was evenly dispersed in the mixed solution and promote the uniform formation of the gel. The addition of isopropanol changed the polarity and solvent environment of the solution, causing the cross-linked PGA-Ca network structure to further aggregate and entangle, and the intermolecular force was enhanced, eventually forming a gel with a certain viscosity and shape retention ability. After the isopropanol was completely added (the volume ratio with the mixed solution was 1:1) and a white gel was obtained, an anchor stirring paddle was used, the speed was set to 50-80 rpm, and the gel was stirred for 5 minutes. During the stirring process, the stirring state of the gel was closely observed. If the gel was found to be sticky to the wall, the stirring could be stopped, and the sticky gel could be scraped off with a glass rod or other tool, and then the stirring could be continued to ensure that the gel was uniform everywhere, and finally the PGA / Ca mineral plastic (MP) was obtained.

[0044] With other conditions remaining unchanged, polyglutamate mineral products with different calcium-iron ratios were obtained by replacing the CaCl2 solution with a mixed solution of CaCl2 solution and FeCl3, wherein the iron-calcium ratios were 1:99, 1:49 and 1:9, respectively.

[0045] Kneading and stirring can further destroy the local uneven structure that may exist inside the gel, and make the molecular chains and cross-linking points inside the gel more evenly distributed through external force, thereby improving the consistency of the overall performance of the material.

[0046] like Figure 1 As shown, Figure A is a physical picture of a polyglutamate mineral product with a calcium ion ratio of 100%, and the product is milky white. Figure B is a physical picture of a polyglutamate mineral product with an iron-calcium ratio of 1:99, and the product is yellow. Figure C is a physical picture of a polyglutamate mineral product with an iron-calcium ratio of 1:49, and the product is dark yellow. Figure D is a physical picture of a polyglutamate mineral product with an iron-calcium ratio of 1:9, and the product is dark yellow.

[0047] The product with an iron-calcium ratio of 1:99 can be stretched to obtain the film material shown in Figure E. This material can be used for (1) wound dressings, which can keep wounds moist and promote healing by virtue of its good water absorption and water retention; (2) water treatment: used for seawater desalination, sewage treatment, etc., through the principle of selective permeation, intercepting salts, large molecular impurities, etc., to purify water quality; (3) chemical separation: separation of mixtures in chemical production, such as separation of different components in organic solutions, to achieve material purification and recovery.

[0048] Example 2 Tensile properties, viscosity, toughness and flame retardancy of polyglutamic acid mineral products.

[0049] The polyglutamic acid mineral product obtained in Example 1 was kneaded, and it was found that the toughness of the product increased and the hardness increased during the kneading process. Then it was stretched. Figure 2 A in the figure is a tensile diagram of a polyglutamic acid mineral product in which calcium ions account for 100%. Figure 2 Figure B is a tensile diagram of a polyglutamic acid mineral product with an iron-calcium ratio of 1:99. Figure 2 Figure C in the figure is a tensile diagram of a polyglutamic acid mineral product with an iron-calcium ratio of 1:49. During the stretching, it was found that the less iron ions added, the lower the viscosity of the product, the stronger the toughness, and the more difficult it is to stretch. And when too much iron is added, the iron-calcium ratio is 1:9, Figure 1 As shown in Figure D, a flocculent product is formed, which is difficult to knead together. The practical value is not high, so it is easiest to form when the iron-calcium ratio is 1:99. From the combustion of the material with an iron-calcium ratio of 1:99 in Figure D, it can be seen that the material is also flame retardant and can be used for sofas and mattresses: the use of flame retardant fabrics and filling materials can reduce the burning speed of furniture when it comes into contact with fire, reduce fire hazards, and clothing. Firefighters,

[0050] Example 3 Rheological test of polyglutamic acid mineral product.

[0051] In order to further explore the properties of the product, the product was subjected to rheological testing. The test steps are as follows:

[0052] Adjust the rheometer parameters, use a rotor with a diameter of 40.0 mm, adjust the gap to 45000.0 μm, trim the gap offset to 50.0 μm, take out 0.8 g of each of the four polyglutamic acid mineral products with different calcium-iron ratios, carefully place the sample at the center of the lower parallel plate of the rheometer, adjust the height of the upper parallel plate so that the sample is in light contact with the upper parallel plate. Start the test, and the rheometer loads the sample with sinusoidal oscillations at the set frequency and strain amplitude, and record the storage modulus (G') and loss modulus (G") of the sample at each frequency. Figure 3As shown, Figure a is a rheological test diagram of a polyglutamic acid mineral product with a calcium ion ratio of 100%, Figure b is a rheological test diagram of a polyglutamic acid mineral product with an iron-calcium ratio of 1:99, Figure c is a rheological test diagram of a polyglutamic acid mineral product with an iron-calcium ratio of 1:49, and Figure d is a rheological test diagram of a polyglutamic acid mineral product with an iron-calcium ratio of 1:9. The results show that Figure a: As the shear rate increases from 0.01, the viscosity decreases rapidly, reaching a relatively stable low value between the shear rate of about 0.1-1, and then the stress begins to rise rapidly after the shear rate is greater than 1, while the viscosity continues to decrease slowly. This shows that the material has a shear-thinning property, that is, as the shear effect increases, the viscosity of the material decreases, and when the shear rate reaches a certain level, the stress increases rapidly. Figure b: In the range of shear rate from 0 to about 0.05, both stress and viscosity show a trend of first increasing and then decreasing, and the peak values ​​of the two are relatively close. As the shear rate increases further, the stress and viscosity continue to decrease. Figure c: When the shear rate increases from 0.01, the stress and viscosity first increase, reaching their respective peaks at a shear rate of about 0.1, and then both decrease. After the shear rate is greater than 1, the stress rises with a small fluctuation, then decreases, while the viscosity tends to be stable and remains at a low value. Figure d: When the shear rate increases from 0.001, the change trends of stress and viscosity are more complicated, with multiple fluctuations of increase and decrease. When the shear rate is close to 1, both stress and viscosity increase significantly. There is an intersection in pictures a, b, and c. The storage modulus (G') and loss modulus (G") before and after the intersection are different, so it has a wide range of applications. The material before the intersection has obvious shear thinning characteristics, that is, as the shear rate increases, the structure inside the material that hinders the flow is destroyed, the interaction between molecules is weakened, and the viscosity decreases rapidly. This property has important applications in industries such as coatings and inks. During production and storage, the material needs to have a certain viscosity to prevent precipitation and stratification; during construction, such as spraying and printing, the applied shear force will reduce its viscosity, allowing it to flow and coat better. Ensure uniformity and smoothness of construction. The stress rises sharply after the intersection, and the material's resistance to further increased shear rate is significantly enhanced. The internal structure of the material is reorganized at a high shear rate, forming a new structure that hinders flow. The viscosity continues to decrease but the speed slows down, indicating that the destruction of the internal structure of the material at a high shear rate has reached its limit. In the plastic processing industry, when the plastic melt is subjected to a high shear rate, its stress-viscosity characteristics will affect the flow and filling behavior of the melt in the mold. Understanding these characteristics of the material at high shear rates can help optimize the injection molding process parameters and ensure the quality of plastic products.

[0053] Example 4 is a study on the phase change, reaction heat and other properties of polyglutamic acid mineralized plastic (product with an iron-calcium ratio of 1:99).

[0054] Differential scanning calorimetry (DSC) was used to study the phase transition, reaction heat and other properties of polyglutamic acid mineralized plastics. Figure 4 As shown in the figure, Chanawu has an obvious endothermic peak at around 50℃, and the material undergoes thermal transitions such as melting near this temperature, reflecting its thermal sensitivity at lower temperatures. The endothermic peak appears again at 200-250℃, indicating that the material has different thermal behaviors in different temperature ranges.

[0055] Phase change characteristics: The endothermic peak in the spectrum corresponds to the phase change process of this material, indicating that the material has at least two different phase changes, showing that the material's microstructure changes with temperature and the molecular thermal motion inside the material gradually intensifies.

[0056] This material can be developed into a new type of heat dissipation material. When the temperature of electronic components rises to the range of 200-250℃, the material absorbs heat through endothermic transformation to prevent components from overheating and ensure the normal operation of the equipment.

[0057] At the same time, it can also be made into building coatings or wall panel filling materials. When the indoor and outdoor temperatures change, the thermal transformation of the material can be used to absorb or release heat, adjust the indoor temperature, and reduce the energy consumption of air conditioning and heating systems.

[0058] Example 5: Testing of biodegradability of polyglutamic acid mineral fiber material.

[0059] Film preparation: Dissolve polyglutamic acid mineralized plastic with an iron-calcium ratio of 1:99 in dimethyl sulfoxide, dissolving 2g of polyglutamic acid mineralized plastic per milliliter of dimethyl sulfoxide to prepare a fully dissolved uniform solution. Then slowly pour the solution onto a clean, flat surface such as a glass sheet, and use a scraper or other tool to evenly spread the solution into a film. Wait until the solvent evaporates naturally to obtain a polyglutamic acid mineralized plastic film.

[0060] Powder preparation: A bulk sample of polyglutamic acid mineralized plastic with an iron to calcium ratio of 1:99 was placed in a mortar or grinder and ground into a gravel-sized powder by mechanical grinding.

[0061] Block preparation: fully mix the polyglutamic acid mineralized plastic powder with an iron-calcium ratio of 1:99 and the plasticizer phenolic resin with a mass ratio of 20:1. Put the mixed materials into a block mold, press at a pressure of 10MPa and a temperature of 150℃, and demold after maintaining the pressure for 30 minutes to obtain a block sample.

[0062] Soil collection: Collect soil rich in microbial species at a depth of 5-20 cm and put it into a sterile sampling bag.

[0063] Under sterile conditions, take several conical flasks, add appropriate amounts of beef extract peptone culture medium, take appropriate amounts of organic-rich soil, put them into a clean beaker, add distilled water about 2-3 times the volume of the soil, stir evenly, and fully dissolve the microorganisms and soluble substances in the soil into the water. Then let the mixed solution stand for 30 minutes to allow the soil particles to settle. Then filter the upper clear liquid with filter paper or gauze, and the filtrate obtained is the soil leachate. Put the treated fiber material samples of different specifications into conical flasks to completely immerse the samples, set up multiple parallel groups under different acid-base conditions, set the pH to 3.0 and 9.5 respectively, and set the concentration of 0.3mg / mL of polyglutamic acid hydrolase for parallel experiments. At the same time, set a blank control group with traditional plastics, cultured at 30℃, and observed every 24 hours. It was found that the materials in the experimental group were completely degraded before the control group, indicating that the biodegradability of polyglutamic acid mineral fiber materials is good. By placing the degradation products in a closed environment and measuring the changes in air composition, it was found that polyglutamic acid mineral fiber materials are decomposed into harmless substances such as carbon dioxide and water by microorganisms in the natural environment. Replacing traditional materials with polyglutamic acid mineral fiber materials can reduce the long-term environmental pollution problems caused by traditional materials, especially in the fields of packaging, agricultural mulch, etc. that are easily discarded after one-time use. The advantages are obvious and can greatly reduce the pressure of environmental pollution.

[0064] The present invention provides a preparation idea and method of a biodegradable material based on γ-polyglutamic acid. There are many methods and approaches to implement the technical solution. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the protection scope of the present invention. All components not specified in this embodiment can be implemented by existing technologies.

Claims

1. A method for preparing a biodegradable material based on γ-polyglutamic acid, characterized in that: The steps include: (1) preparing a low molecular weight polyglutamic acid aqueous solution and adjusting the pH to acidic to obtain a polyglutamic acid solution with protonated carboxylic acid groups, then adding a metal ion solution thereto, stirring and mixing to obtain a mixed solution, wherein the metal ion solution is a solution containing calcium ions or a mixture of calcium ions and iron ions; (2) The pH of the mixed solution obtained in step (1) is adjusted to alkaline while stirring, and then a cross-linking agent is added thereto to perform cross-linking and curing to obtain a biodegradable material.

2. The preparation method according to claim 1, characterized in that: In step (1), the weight average molecular weight of the low molecular weight polyglutamic acid is 5000-20000 Da, and the molar concentration of the polyglutamic acid aqueous solution is 0.2-0.3 M.

3. The preparation method according to claim 1, characterized in that: In step (1), the pH of the polyglutamic acid aqueous solution is adjusted to 2.5-3.

0.

4. The preparation method according to claim 1, characterized in that: The total cation molar concentration of the metal ion solution is 0.1 mol / L to 0.5 mol / L, wherein the molar ratio of calcium ions to iron ions in the mixture is 100 to 9:

1.

5. The preparation method according to claim 1, characterized in that: The volume ratio of the polyglutamic acid aqueous solution to the metal ion solution is 1:0.8~1.

6. The preparation method according to claim 1, characterized in that: In step (2), the pH of the mixed solution is adjusted to 8-9.

7. The preparation method according to claim 1, characterized in that: The cross-linking agent is isopropanol, and the volume ratio of the mixed solution to isopropanol is 1:0.9-1.

1.

8. The biodegradable material based on γ-polyglutamic acid prepared by the preparation method according to any one of claims 1 to 7.

9. A mineralized plastic, characterized in that: The biodegradable material according to claim 8 is obtained by further molding and drying the biodegradable material.

10. Use of the mineralized plastic according to claim 9 in manufacturing automobile interior trims, automobile exterior trims, building pipes, profiles, electrical housings, wire and cable insulation layers, plastic furniture, plastic tableware, plastic toys or biomedical materials.

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