Preparation method and application of a cyanobacterial polysaccharide-pva composite material

Abstract

The application discloses a kind of cyanobacterial polysaccharide and PVA composite material preparation method, comprising the following steps: S1: PVA and cyanobacterial polysaccharide are dissolved in deionized water to obtain premixed solution;S2: crosslinking agent ethylene glycol diglycidyl ether is added to the premixed solution prepared in step S1 and heated to react, to obtain mixed solution;S3: tannic acid is added dropwise to the mixed solution prepared in step S2 to obtain film forming liquid, and the film forming liquid is laid flat and dried to obtain a cyanobacterial polysaccharide and PVA composite film.The application forms a crosslinked network structure by PVA, cyanobacterial polysaccharide and ethylene glycol diglycidyl ether through ring-opening reaction, while meeting biocompatibility and mechanical properties, it can greatly improve the barrier property of the material, and can be used as functional packaging film, fresh-keeping adsorption gasket, etc. for fresh fruits and vegetables, livestock and poultry meat food storage and transportation.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a method for preparing and applying a composite material of cyanobacterial polysaccharide and PVA. Background Technology

[0002] Food preservation is a key technology in the storage and transportation of fresh fruits, vegetables, and meat. With the rapid development of e-commerce and cold chain logistics, the scale of agricultural and sideline product exports continues to expand, leading to a year-on-year increase in market demand for environmentally friendly, high-performance food packaging materials. Traditional plastic preservation packaging is difficult to degrade naturally, and discarded packaging easily pollutes soil and water bodies. Furthermore, most petrochemical-based films have limited barrier properties, water absorption, and antioxidant capacity. Problems such as seepage accumulation in meat, oxidation and spoilage of food, and dehydration and shriveling of fruits and vegetables are prominent during the storage and transportation of fresh produce, resulting in significant food waste and hindering the long-distance circulation of agricultural products. Therefore, the development of fully bio-based biodegradable functional packaging has become a hot research topic in the industry.

[0003] Biodegradable polymer packaging is gradually replacing traditional plastics due to its environmental friendliness, safety, and non-toxicity. Natural polysaccharides, with their wide availability, excellent biocompatibility, and complete biodegradability, are preferred raw materials for preparing green food packaging. Sacran polysaccharides derived from cyanobacteria have extremely high molecular weights and their molecular chains are rich in hydrophilic anionic groups such as carboxyl groups, sulfonic acid groups, and hydroxyl groups. They exhibit outstanding moisturizing, water-absorbing, and biocompatibility properties and have already been applied in medical dressings and skincare raw materials. Theoretically, they are suitable for the water-absorbing and preservation of fresh produce. However, the intermolecular forces of individual Sacran polysaccharides are relatively weak, resulting in poor independent film-forming mechanical properties, fragile films, and insufficient water resistance. Consequently, they cannot be directly used to make films for food packaging, severely limiting their application.

[0004] Polyvinyl alcohol (PVA) is an industrially mature biodegradable polymer with excellent film-forming properties, tensile toughness, and mechanical strength. It is often used as a matrix material to improve the film-forming defects of natural polysaccharides. However, PVA films have abundant hydrophilic groups, making them prone to swelling and breakage in pure water environments. When used alone, their water vapor barrier and moisture absorption and control performance do not meet the standards for fresh food preservation. Existing technologies mostly use physically blended modified polysaccharide / PVA films, relying solely on intermolecular hydrogen bonds. The film structure is loose, easily dissolving and disintegrating in aquatic environments, resulting in poor ability to block water vapor and absorb fresh food exudates.

[0005] Among existing modification methods, ordinary small molecule crosslinking agents have low crosslinking efficiency and are difficult to construct a stable three-dimensional network structure between polysaccharides and PVA, resulting in limited improvement in the overall performance of the film. At the same time, most biodegradable packaging on the market only has basic water-proof or water-absorbing functions and lacks endogenous antioxidant components. It cannot inhibit the oxidation of oils and deterioration of nutrients during the storage of fresh food and often requires additional spraying of antioxidants, which poses a risk of food safety contamination due to the migration of these additives.

[0006] In summary, addressing the technical pain points of existing food packaging such as its difficulty in degradation, mechanical shortcomings, and limited preservation functions, the development of a Sacran / PVA composite food packaging material with green raw materials, simple processing, and high water absorption, high barrier properties, and long-lasting antioxidant effects has significant value for industrial application.

[0007] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0008] This invention aims to provide a method for preparing and applying a composite material of cyanobacterial polysaccharides and PVA. By adding PVA, the mechanical properties of the cyanobacterial polysaccharide membrane are enhanced. The water resistance and mechanical properties of the composite membrane are strengthened by utilizing a cross-linking network. The antioxidant properties of the composite membrane are provided by tannic acid.

[0009] To achieve the above objectives, the present invention provides a method for preparing a composite material of cyanobacterial polysaccharides and PVA, characterized by comprising the following steps: S1: Dissolve PVA and cyanobacterial polysaccharides in deionized water to obtain a premixed solution; S2: Add the crosslinking agent ethylene glycol diglycidyl ether to the premixed solution obtained in step S1 and heat to react, to obtain a mixed solution; S3: Add tannic acid dropwise to the mixed solution prepared in step S2 to obtain a film-forming solution. After the film-forming solution is spread out, allowed to stand, and dried, a composite film of cyanobacterial polysaccharide and PVA is obtained.

[0010] Preferably, the degree of polymerization of the PVA used in step S1 is 1500-1900, and the molecular weight of the cyanobacterial polysaccharide used is 1×10⁻⁶. 7 -2.5×10 7 .

[0011] Preferably, the mass ratio of PVA to cyanobacterial polysaccharide is 10:1-7:1.

[0012] Preferably, in step S1, PVA and cyanobacterial polysaccharides are mixed at 30-40°C.

[0013] Preferably, in step S2, the mass of ethylene glycol diglycidyl ether is 10-20% of the total amount of PVA and cyanobacterial polysaccharides, and the heating temperature is 100-120℃.

[0014] Preferably, the amount of tannic acid added in step S3 is 5-20% of the total amount of PVA and cyanobacterial polysaccharides.

[0015] Preferably, in step S3, tannic acid is added dropwise at 0-5°C.

[0016] Preferably, the drying temperature in step S3 is 30-40°C, and the drying is carried out under vacuum.

[0017] Preferably, the composite material is used in food preservation packaging.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention forms a cross-linked network structure by means of PVA, cyanobacterial polysaccharide and ethylene glycol diglycidyl ether through ring-opening reaction, which can significantly improve the barrier performance of the material while satisfying biocompatibility and mechanical properties. (2) The present invention also introduces tannic acid, which can greatly improve the scavenging rate of free radicals, thereby giving the material antioxidant properties, so that it can achieve good preservation ability as food packaging; (3) The preparation method adopted in this invention is simple, concise, efficient and environmentally friendly, with mild conditions and safe and environmentally friendly raw materials. The preparation process is non-toxic and pollution-free, and no special equipment is required during the production process. It is easy to operate. Attached Figure Description

[0019] Figure 1 This is a scanning electron microscope image of the sample from the present invention; Figure 2 This is a stress-strain diagram of the sample from the present invention; Figure 3 This is a test diagram of the water absorption performance of the sample of the present invention; Figure 4 This is a water vapor permeation test diagram of the sample of the present invention; Figure 5 This is a sample antioxidant test diagram of the present invention; Figure 6 This is a sample meat preservation test diagram for the present invention. Detailed Implementation

[0020] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0021] The following provides a brief overview of one or more aspects to offer a basic understanding of them. This overview is not an exhaustive summary of all conceived aspects, nor is it intended to identify key or decisive elements of all aspects, nor to define the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form to prepare for the more detailed descriptions that follow.

[0022] Example 1:

[0023] A method for preparing a composite material of cyanobacterial polysaccharide and PVA includes the following steps: S1: Weigh 0.9g of PVA and 0.1g of cyanobacterial polysaccharide Sacran. Add PVA to 25ml of deionized water and heat to 90℃ to dissolve. At the same time, add Sacran to 25ml of deionized water to dissolve. Mix the PVA aqueous solution and Sacran aqueous solution evenly and stir at 35℃ for 12h to obtain a premixed solution. S2: Weigh 0.15g of ethylene glycol diglycidyl ether, dissolve it in 3ml of anhydrous ethanol, and add it dropwise to the premixed solution prepared in S1. React at 120℃ for 3-4h. S3: Weigh 5% of the total amount of PVA and Sacran tannic acid, i.e. 0.05g, dissolve it in deionized water, and slowly add it dropwise to the mixed solution in step S2. The dropwise addition is carried out under the conditions of ice-water bath and high-speed stirring, and the dropwise addition time is 15-20min. S4: Place the sample solution from S3 at 4℃ and let it stand for 1-2 hours. Then place it in a vacuum drying oven and remove air bubbles at 30℃ to obtain a composite membrane of PVA and Sacran.

[0024] The degree of polymerization of PVA is 1700, and the molecular weight of Sacran is 1.5 × 10⁻⁶. 7 .

[0025] Example 2:

[0026] A method for preparing a composite material of cyanobacterial polysaccharide and PVA includes the following steps: S1: Weigh 0.9g of PVA and 0.1g of cyanobacterial polysaccharide Sacran. Add PVA to 25ml of deionized water and heat to 90℃ to dissolve. At the same time, add Sacran to 25ml of deionized water to dissolve. Mix the PVA aqueous solution and Sacran aqueous solution evenly and stir at 35℃ for 12h to obtain a premixed solution. S2: Weigh 0.15g of ethylene glycol diglycidyl ether, dissolve it in 3ml of anhydrous ethanol, and add it dropwise to the premixed solution prepared in S1. React at 120℃ for 3-4h. S3: Weigh 0.1g of tannic acid, which is 10% of the total amount of PVA and Sacran, dissolve it in deionized water, and slowly add it dropwise to the mixed solution in step S2. The dropwise addition is carried out under the conditions of ice-water bath and high-speed stirring, and the dropwise addition time is 15-20min. S4: Place the sample solution from S3 at 4℃ and let it stand for 1-2 hours. Then place it in a vacuum drying oven and remove air bubbles at 30℃ to obtain a composite membrane of PVA and Sacran.

[0027] The degree of polymerization of PVA is 1700, and the molecular weight of Sacran is 1.5 × 10⁻⁶. 7 .

[0028] Example 3:

[0029] A method for preparing a composite material of cyanobacterial polysaccharide and PVA includes the following steps: S1: Weigh 0.9g of PVA and 0.1g of cyanobacterial polysaccharide Sacran. Add PVA to 25ml of deionized water and heat to 90℃ to dissolve. At the same time, add Sacran to 25ml of deionized water to dissolve. Mix the PVA aqueous solution and Sacran aqueous solution evenly and stir at 35℃ for 12h to obtain a premixed solution. S2: Weigh 0.15g of ethylene glycol diglycidyl ether, dissolve it in 3ml of anhydrous ethanol, and add it dropwise to the premixed solution prepared in S1. React at 120℃ for 3-4h. S3: Weigh 20% of the total amount of PVA and Sacran tannic acid, i.e. 0.2g, dissolve it in deionized water, and slowly add it dropwise to the mixed solution in step S2. The dropwise addition is carried out under the conditions of ice-water bath and high-speed stirring, and the dropwise addition time is 15-20min. S4: Place the sample solution from S3 at 4℃ and let it stand for 1-2 hours. Then place it in a vacuum drying oven and remove air bubbles at 30℃ to obtain a composite membrane of PVA and Sacran.

[0030] The degree of polymerization of PVA is 1700, and the molecular weight of Sacran is 1.5 × 10⁻⁶. 7 .

[0031] Example 4:

[0032] A method for preparing a composite material of cyanobacterial polysaccharide and PVA includes the following steps: S1: Weigh 0.9g of PVA and 0.1g of cyanobacterial polysaccharide Sacran. Add PVA to 25ml of deionized water and heat to 90℃ to dissolve. At the same time, add Sacran to 25ml of deionized water to dissolve. Mix the PVA aqueous solution and Sacran aqueous solution evenly and stir at 35℃ for 12h to obtain a premixed solution. S2: Weigh 0.15g of ethylene glycol diglycidyl ether, dissolve it in 3ml of anhydrous ethanol, and add it dropwise to the premixed solution prepared in S1. React at 120℃ for 3-4h. S3: Weigh 5% of the total amount of PVA and Sacran tannic acid, i.e. 0.05g, dissolve it in deionized water, and slowly add it dropwise to the mixed solution in step S2. The dropwise addition is carried out under the conditions of ice-water bath and high-speed stirring, and the dropwise addition time is 15-20min. S4: Place the sample solution from S3 at 4℃ and let it stand for 1-2 hours. Then place it in a vacuum drying oven and remove air bubbles at 30℃ to obtain a composite membrane of PVA and Sacran.

[0033] The degree of polymerization of PVA is 1500, and the molecular weight of Sacran is 1.5 × 10⁻⁶. 7 .

[0034] Example 5:

[0035] A method for preparing a composite material of cyanobacterial polysaccharide and PVA includes the following steps: S1: Weigh 0.9g of PVA and 0.1g of cyanobacterial polysaccharide Sacran. Add PVA to 25ml of deionized water and heat to 90℃ to dissolve. At the same time, add Sacran to 25ml of deionized water to dissolve. Mix the PVA aqueous solution and Sacran aqueous solution evenly and stir at 35℃ for 12h to obtain a premixed solution. S2: Weigh 0.15g of ethylene glycol diglycidyl ether, dissolve it in 3ml of anhydrous ethanol, and add it dropwise to the premixed solution prepared in S1. React at 120℃ for 3-4h. S3: Weigh 5% of the total amount of PVA and Sacran tannic acid, i.e. 0.05g, dissolve it in deionized water, and slowly add it dropwise to the mixed solution in step S2. The dropwise addition is carried out under the conditions of ice-water bath and high-speed stirring, and the dropwise addition time is 15-20min. S4: Place the sample solution from S3 at 4℃ and let it stand for 1-2 hours. Then place it in a vacuum drying oven and remove air bubbles at 30℃ to obtain a composite membrane of PVA and Sacran.

[0036] The degree of polymerization of PVA is 1900, and the molecular weight of Sacran is 1.5 × 10⁻⁶. 7 .

[0037] Comparative Example 1: A method for preparing a composite material of cyanobacterial polysaccharide and PVA includes the following steps: S1: Weigh 0.9g of PVA and 0.1g of Sacran, add PVA to 25ml of deionized water and heat to 90℃ to dissolve, while adding Sacran to 25ml of deionized water to dissolve, mix the PVA aqueous solution and Sacran aqueous solution evenly, and stir at 35℃ for 12h to obtain a mixed solution. S2: The mixed solution was placed at 4℃ and allowed to stand for 1-2 hours, then placed in a vacuum drying oven and the bubbles were removed at 30℃ to obtain a composite membrane of PVA and Sacran.

[0038] The degree of polymerization of PVA is 1700, and the molecular weight of Sacran is 1.5 × 10⁻⁶. 7 .

[0039] Comparative Example 2: A method for preparing a composite material of cyanobacterial polysaccharide and PVA includes the following steps: S1: Weigh 0.9g of PVA and 0.1g of cyanobacterial polysaccharide Sacran. Add PVA to 25ml of deionized water and heat to 90℃ to dissolve. At the same time, add Sacran to 25ml of deionized water to dissolve. Mix the PVA aqueous solution and Sacran aqueous solution evenly and stir at 35℃ for 12h to obtain a premixed solution. S2: Weigh 0.15g of ethylene glycol diglycidyl ether, dissolve it in 3ml of anhydrous ethanol, and add it dropwise to the premixed solution prepared in S1. React at 120℃ for 3-4h. S3: Place the sample solution of S2 at 4℃ and let it stand for 1-2 hours. Then place it in a vacuum drying oven and remove the air bubbles at 30℃ to obtain a composite membrane of PVA and Sacran.

[0040] The degree of polymerization of PVA is 1700, and the molecular weight of Sacran is 1.5 × 10⁻⁶. 7 .

[0041] Comparative Example 3: A method for preparing PVA material includes the following steps: S1: Weigh 1g of PVA, add it to 25ml of deionized water, and heat to 90℃ to dissolve it to obtain a PVA aqueous solution; S2: Weigh 0.15g of ethylene glycol diglycidyl ether, dissolve it in 3ml of anhydrous ethanol, and then add it dropwise into PVA aqueous solution. React at 120℃ for 3-4h. S3: Weigh 5% of the weight of PVA tannic acid, i.e. 0.05g, dissolve it in deionized water and slowly add it dropwise to the mixed solution in step S2. The dropwise addition is carried out under the conditions of ice water bath and high-speed stirring, and the dropwise addition time is 15-20min. S3: Place the sample solution of S2 at 4℃ and let it stand for 1-2 hours. Then place it in a vacuum drying oven and remove the air bubbles at 30℃ to obtain a composite membrane of PVA and Sacran.

[0042] The degree of polymerization of PVA is 1700, and the molecular weight of Sacran is 1.5 × 10⁻⁶. 7 .

[0043] Comparative Example 4: A method for preparing a composite material of cyanobacterial polysaccharide and PVA includes the following steps: S1: Weigh 0.8g of PVA and 0.2g of cyanobacterial polysaccharide Sacran. Add PVA to 25ml of deionized water and heat to 90℃ to dissolve. At the same time, add Sacran to 25ml of deionized water to dissolve. Mix the PVA aqueous solution and Sacran aqueous solution evenly and stir at 35℃ for 12h to obtain a premixed solution. S2: Weigh 0.15g of ethylene glycol diglycidyl ether, dissolve it in 3ml of anhydrous ethanol, and add it dropwise to the premixed solution prepared in S1. React at 120℃ for 3-4h. S3: Place the sample solution of S2 at 4℃ and let it stand for 1-2 hours. Then place it in a vacuum drying oven and remove the air bubbles at 30℃ to obtain a composite membrane of PVA and Sacran.

[0044] The degree of polymerization of PVA is 1700, and the molecular weight of Sacran is 1.5 × 10⁻⁶. 7 .

[0045] Comparative Example 5: A method for preparing a composite material of cyanobacterial polysaccharide and PVA includes the following steps: S1: Weigh 0.67g of PVA and 0.33g of cyanobacterial polysaccharide Sacran. Add PVA to 25ml of deionized water and heat to 90℃ to dissolve. At the same time, add Sacran to 25ml of deionized water to dissolve. Mix the PVA aqueous solution and Sacran aqueous solution evenly and stir at 35℃ for 12h to obtain a premixed solution. S2: Weigh 0.15g of ethylene glycol diglycidyl ether, dissolve it in 3ml of anhydrous ethanol, and add it dropwise to the premixed solution prepared in S1. React at 120℃ for 3-4h. S3: Place the sample solution of S2 at 4℃ and let it stand for 1-2 hours. Then place it in a vacuum drying oven and remove the air bubbles at 30℃ to obtain a composite membrane of PVA and Sacran.

[0046] The degree of polymerization of PVA is 1700, and the molecular weight of Sacran is 1.5 × 10⁻⁶. 7 .

[0047] Comparative Example 6: A method for preparing a composite material of cyanobacterial polysaccharide and PVA includes the following steps: S1: Weigh 0.5g of PVA and 0.5g of cyanobacterial polysaccharide Sacran. Add PVA to 25ml of deionized water and heat to 90℃ to dissolve. At the same time, add Sacran to 25ml of deionized water to dissolve. Mix the PVA aqueous solution and Sacran aqueous solution evenly and stir at 35℃ for 12h to obtain a premixed solution. S2: Weigh 0.15g of ethylene glycol diglycidyl ether, dissolve it in 3ml of anhydrous ethanol, and add it dropwise to the premixed solution prepared in S1. React at 120℃ for 3-4h. S3: Place the sample solution of S2 at 4℃ and let it stand for 1-2 hours. Then place it in a vacuum drying oven and remove the air bubbles at 30℃ to obtain a composite membrane of PVA and Sacran.

[0048] The degree of polymerization of PVA is 1700, and the molecular weight of Sacran is 1.5 × 10⁻⁶. 7 .

[0049] Comparative Example 7: A method for preparing a composite material of cyanobacterial polysaccharide and PVA includes the following steps: S1: Weigh 0.9g of PVA and 0.1g of cyanobacterial polysaccharide Sacran. Add PVA to 25ml of deionized water and heat to 90℃ to dissolve. At the same time, add Sacran to 25ml of deionized water to dissolve. Mix the PVA aqueous solution and Sacran aqueous solution evenly and stir at 35℃ for 12h to obtain a premixed solution. S2: Weigh 0.15g of ethylene glycol diglycidyl ether, dissolve it in 3ml of anhydrous ethanol, and add it dropwise to the premixed solution prepared in S1. React at 120℃ for 3-4h. S3: Place the sample solution of S2 at 4℃ and let it stand for 1-2 hours. Then place it in a vacuum drying oven and remove the air bubbles at 30℃ to obtain a composite membrane of PVA and Sacran.

[0050] The degree of polymerization of PVA is 1400, and the molecular weight of Sacran is 1.5 × 10⁻⁶. 7 .

[0051] Comparative Example 8: A method for preparing a composite material of cyanobacterial polysaccharide and PVA includes the following steps: S1: Weigh 0.9g of PVA and 0.1g of cyanobacterial polysaccharide Sacran. Add PVA to 25ml of deionized water and heat to 90℃ to dissolve. At the same time, add Sacran to 25ml of deionized water to dissolve. Mix the PVA aqueous solution and Sacran aqueous solution evenly and stir at 35℃ for 12h to obtain a premixed solution. S2: Weigh 0.15g of ethylene glycol diglycidyl ether, dissolve it in 3ml of anhydrous ethanol, and add it dropwise to the premixed solution prepared in S1. React at 120℃ for 3-4h. S3: Place the sample solution of S2 at 4℃ and let it stand for 1-2 hours. Then place it in a vacuum drying oven and remove the air bubbles at 30℃ to obtain a composite membrane of PVA and Sacran.

[0052] The degree of polymerization of PVA is 2000, and the molecular weight of Sacran is 1.5 × 10⁻⁶. 7 .

[0053] Various performance tests were conducted on Examples 1-5 and Comparative Examples 1-8, and the test results are as follows: Figure 1 The images are scanning electron microscope (SEM) images of different samples. The testing method was as follows: after sputtering gold onto the cross-section of the functional packaging material composed of Sacran and PVA, the morphology and structure of the cross-section were observed under a scanning electron microscope.

[0054] SP(a) is the sample of Comparative Example 1, SPE(b) is the sample of Comparative Example 2, and SPE(ce) is the sample of Examples 1-3. The cross-section of SP membrane(a) shows some wrinkles and particles, but still has a compact structure, and the physical mixing of sacran polysaccharide and PVA is relatively uniform. The cross-section of SPE(b) membrane is smoother and denser because the three-dimensional network formed by cross-linking makes the membrane structure more compact. After adding tannic acid (ce), the cross-sectional morphology of the membrane changes significantly. At this time, the cross-section shows depressions and delamination. With the increase of the amount added, TA agglomerates and destroys the integrity of the cross-linked membrane, making the delamination and defects of the membrane cross-section more serious. When the amount of tannic acid added is 5%, the cross-linked membrane can still maintain its integrity.

[0055] Figure 2 The stress-strain diagram of the sample is obtained by the following test method: the prepared functional packaging material specimen of Sacran and PVA composite is placed on the platform of a universal testing machine for tensile property testing. During the test, a load is continuously applied at a fixed tensile rate until the sample breaks significantly. The stress-strain curve is recorded and analyzed.

[0056] SP represents the sample of Comparative Example 1, SPE represents the sample of Comparative Example 2, SPE-5%TA represents the sample of Example 1, SPE-10%TA represents the sample of Example 2, SPE-20%TA represents the sample of Example 3, 1:4 represents the sample of Comparative Example 4, 1:2 represents the sample of Comparative Example 5, and 1:1 represents the sample of Comparative Example 6. After the addition of EDGE (ethylene glycol diglycidyl ether) as a crosslinking agent, the SPE membrane has a denser structure than the SP membrane. The formation of the three-dimensional crosslinked network enhances the tensile stress of the membrane and restricts the free movement of molecular chains, thus reducing the elongation at break. Through least squares linear regression fitting, selecting the linear elastic stage of 0%-5% strain, the Young's modulus of the SPE membrane is found to be 660 MPa. According to the formula ν = E / (3ρRT) (ρ = 1200 kg / m³), the Young's modulus of the SPE membrane is 660 MPa. 3(R = 8.314; T = 298K) The crosslinking density was calculated to be 74 mol / m3, which is on the same order of magnitude as the crosslinking density calculated by swelling degree, indicating that the SPE membrane was successfully crosslinked. After TA modification, the tensile strength of the composite film decreased, while the elongation at break showed a trend of first increasing and then slowly decreasing. This may be because the method of using ice water bath and low temperature drying to form film allows an appropriate amount of small TA molecules to insert into the gaps between polymer chains, weakening the intermolecular forces and keeping the elongation at break at a high level. However, excessive TA leads to the aggregation of small molecules, causing local defects and weakening the toughness. When the ratio of PVA to Sacran is 4:1 to 1:1, the nominal strain decreases significantly, meaning that the elongation and toughness decrease significantly. This is because Sacran is a macromolecular rigid polysaccharide with an extremely high hydroxyl density. The higher the content, the more intermolecular hydrogen bond crosslinking points there are, and the membrane crosslinking density increases, resulting in a simultaneous increase in tensile strength and rigidity. However, the polysaccharide chains lack flexibility, and the movement of chain segments is restricted, leading to a decrease in membrane plasticity, a decrease in elongation at break, and an increase in brittleness. It exhibits superior stress-strain capability when the ratio of PVA to Sacran is 9:1.

[0057] In addition, separate tests were conducted on Comparative Examples 7 and 8. The stress in Comparative Examples 7 and 8 was less than 15 MPa and the strain was less than 20%. This is because when the PVA molecular chain is too short, the cross-linking network is sparse and the stability of the membrane mechanical properties is insufficient. When the PVA molecular chain is too long, it becomes excessively entangled, its compatibility with Sacran deteriorates, and severe phase separation occurs, making the membrane brittle and extremely difficult to process.

[0058] Figure 3 For the water absorption performance test, the test method is as follows: weigh the completely dried sample and record it as K0, then place the sample in a pH 7.4 solution at 60℃, take out the sample at predetermined time intervals and weigh it as K1, and calculate the dynamic swelling of the sample: q = K1 / K0.

[0059] Three sets of samples from Example 1 were prepared, dried for 3 days, and then soaked in 60°C warm water. The swelling weight was measured at different time intervals, the data were recorded, and the cross-linking density was calculated. As shown in the figure, as the soaking time increased, the swelling degree of the cross-linked membrane gradually increased, and the final volume swelling degree tended to stabilize at about 630%. This indicates that the cross-linked membrane has a certain water absorption capacity, but the three-dimensional network restricts the water absorption and swelling of the membrane, and will not cause the membrane to collapse due to excessive water absorption.

[0060] Based on this, the crosslinking density can be calculated to be 33.4 mol / m³. 3The crosslinking density further confirmed the stability of the crosslinking network. SPE has a certain binding effect on the molecular chains in the membrane, which is consistent with the change law of the swelling performance curve, indicating that the prepared SPE crosslinked membrane has good water environment stability.

[0061] Figure 4 The diagram shows the water vapor permeability test results. The test method is as follows: a circular sample with a diameter of 90 mm is used to test its barrier performance using a water vapor permeability testing system.

[0062] Among them, PVA was a pure PVA film sample, SP was a sample of Comparative Example 1, SPE was a sample of Comparative Example 2, SPE-5%TA was a sample of Example 1, SPE-10%TA was a sample of Example 2, and SPE-20%TA was a sample of Example 3. Since the SP film contains sacran, its WVP is slightly higher than that of the pure PVA film due to the superhydrophilicity of sacran. However, the WVP of the SPE film with the introduction of cross-linked network is significantly reduced, indicating that the dense cross-linked network effectively improves the compactness of the film and reduces the permeation path of water vapor. In all experimental groups, although the addition of TA showed an increase in water vapor permeability, it still had excellent water-blocking performance and is an ideal candidate for food packaging materials.

[0063] Figure 5 The antioxidant test results are shown in the figure. The test method is as follows: the sample is immersed in DPPH and ABTS free radical solutions respectively. The DPPH free radical system is reacted at room temperature in the dark for 30 minutes and the absorbance is measured at 517 nm. The ABTS free radical system is incubated at 37°C for 30 minutes and the absorbance is measured at 730 nm. The antioxidant performance of the hydrogel is evaluated by the change in absorbance.

[0064] Among them, PVA is a pure PVA film sample, SP is the sample of Comparative Example 1, SPE is the sample of Comparative Example 2, SPE-5%TA is the sample of Example 1, SPE-10%TA is the sample of Example 2, and SPE-20%TA is the sample of Example 3. Through the two free radical scavenging experiments of DPPH (a) and ABTS (b), it can be seen that the introduction of TA successfully endows the Sacran / PVA composite film with excellent antioxidant properties, and the free radical scavenging rate can reach more than 90%, which can effectively delay the oxidative deterioration of food and further improve the preservation effect.

[0065] Figure 6 The image shows a test of meat preservation using a composite film. The test method is as follows: pork of similar size and thickness is co-cultured with a sample used as a pad for 5 days. Filter paper is used to prevent direct contact between the pork and the sample. The sample is taken out and weighed at predetermined time intervals, and photographs are taken for comparison.

[0066] Among them, blank was a PVA film sample, SP was a sample of Comparative Example 1, SPE was a sample of Comparative Example 2, SPE-5%TA was a sample of Example 1, SPE-10%TA was a sample of Example 2, and SPE-20%TA was a sample of Example 3. Meat pad preservation experiments were carried out. The pork preservation experiment showed that the preservation pad prepared by the composite film can effectively extend the shelf life of pork and reduce the weight loss of pork, proving the feasibility of the composite film in actual food preservation. Although the integrity of the cross-linked film is somewhat damaged as the amount of TA increases, the degree of cross-linking is still sufficient for food preservation applications.

[0067] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for preparing a composite material of cyanobacterial polysaccharide and PVA, characterized in that, Includes the following steps: S1: Dissolve PVA and cyanobacterial polysaccharides in deionized water to obtain a premixed solution; S2: Add the crosslinking agent ethylene glycol diglycidyl ether to the premixed solution obtained in step S1 and heat to react, to obtain a mixed solution; S3: Add tannic acid dropwise to the mixed solution prepared in step S2 to obtain a film-forming solution. After the film-forming solution is spread out, allowed to stand, and dried, a composite film of cyanobacterial polysaccharide and PVA is obtained.

2. The method for preparing a cyanobacterial polysaccharide and PVA composite material according to claim 1, characterized in that, The degree of polymerization of the PVA used in step S1 is 1500-1900, and the molecular weight of the cyanobacterial polysaccharide used is 1×10⁻⁶. 7 -2.5×10 7 .

3. The method for preparing a cyanobacterial polysaccharide and PVA composite material according to claim 2, characterized in that, The mass ratio of PVA to cyanobacterial polysaccharide is 10:1-7:

1.

4. The method for preparing a cyanobacterial polysaccharide and PVA composite material according to claim 1, characterized in that, In step S1, PVA and cyanobacterial polysaccharides are mixed at 30-40°C.

5. The method for preparing a cyanobacterial polysaccharide and PVA composite material according to claim 1, characterized in that, In step S2, the mass of ethylene glycol diglycidyl ether is 10-20% of the total amount of PVA and cyanobacterial polysaccharides, and the heating temperature is 100-120℃.

6. The method for preparing a cyanobacterial polysaccharide and PVA composite material according to claim 1, characterized in that, In step S3, the amount of tannic acid added is 5-20% of the total amount of PVA and cyanobacterial polysaccharides.

7. The method for preparing a cyanobacterial polysaccharide and PVA composite material according to claim 1, characterized in that, In step S3, tannic acid is added dropwise at 0-5°C.

8. The method for preparing a cyanobacterial polysaccharide and PVA composite material according to claim 1, characterized in that, In step S3, the drying temperature is 30-40℃, and the drying is carried out under vacuum.

9. The method for preparing a cyanobacterial polysaccharide and PVA composite material according to claim 1, characterized in that, The composite material is used in food preservation packaging.

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