A novel fresh-keeping degradable bio-based plastic film and a preparation method thereof

Abstract

The application provides a novel fresh-keeping degradable bio-based plastic film, which comprises chemically modified cellulose, lignin and lignin derivatives and natural polymer materials, is prepared by crosslinking of the chemically modified cellulose, lignin and lignin derivatives and the natural polymer materials containing amino groups, and is prepared from lignocellulose biomass as raw material through a green pretreatment technology to obtain cellulose, lignin and lignin derivatives, and then the cellulose, lignin and lignin derivatives are chemically modified and crosslinked with the natural polymer materials containing amino groups to prepare the film, and a multiple network structure is constructed, so that the mechanical properties of the film are significantly improved.

Description

Technical Field

[0001] This invention relates to biofilm technology, specifically to a novel biodegradable bio-based plastic film for food preservation and its preparation method. Background Technology

[0002] With the increasing prominence of plastic pollution and fossil resource shortages, the development of fully biodegradable and environmentally friendly polymer materials has become an important direction for development in packaging, agriculture, and biomedicine. Traditional petroleum-based plastic films are difficult to degrade naturally, and the large amounts of waste they produce cause serious "white pollution," damaging the ecological environment and threatening biosecurity. Lignocellulosic biomass, such as crop straw and forestry waste, is one of the most abundant renewable resources in nature, with a huge annual output. Fully utilizing these agricultural and forestry wastes to produce high-value-added bio-based plastics has significant environmental and economic value.

[0003] Natural polysaccharides, due to their wide availability, excellent biocompatibility, and complete biodegradability, have become core raw materials for preparing biodegradable films. In recent years, the construction of green cross-linked networks using aldehyde-modified polysaccharides and amino-containing polymers via Schiff base reactions has become a research hotspot. However, existing reports mostly focus on binary cross-linking systems, resulting in films with relatively limited functionality. Aromatic compounds (such as vanillin, cinnamaldehyde, and anisaldehyde) are widely available naturally and possess both antibacterial and reactive activities, showing promise in introducing functional groups through Schiff base reactions. However, systematic research on their synergistic construction of multifunctional composite films with oxidized cellulose / chitosan systems is currently lacking. Therefore, developing a bio-based cross-linked biodegradable film with a simple preparation process, excellent mechanical properties, and antibacterial function has significant application value.

[0004] Patent CN104892969B provides a chitosan-cellulose composite membrane and its preparation method. The method uses electrostatic spraying to coat the surface of a regenerated cellulose membrane with a chitosan solution to prepare the composite membrane. Although it has certain biocompatibility and biodegradability, the method is essentially a physical coating and does not achieve covalent bonding between the two polysaccharides. This results in weak interfacial bonding, poor mechanical properties and stability of the membrane material. At the same time, the electrostatic spraying process is complex and energy-intensive, making it difficult to achieve low-cost, green, large-scale production. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a novel biodegradable bio-based plastic film for food preservation and its preparation method.

[0006] The present invention provides a novel biodegradable bio-based plastic film for food preservation, comprising chemically modified cellulose, lignin and lignin derivatives interacting with natural polymer materials.

[0007] Furthermore, cellulose and lignin are obtained from lignocellulose biomass through pretreatment methods.

[0008] Furthermore, lignocellulosic biomass includes at least one of wheat straw, corn straw, agricultural and forestry waste, rice straw, sorghum straw, soybean straw, forestry waste, recycled wood pulp fiber, sawdust, softwood, hardwood, aquatic plants, algae, or animal excrement.

[0009] Furthermore, both cellulose and lignin were chemically modified by adding oxidants for oxidation.

[0010] Furthermore, the oxidizing agent includes at least one of sodium periodate, hydrogen peroxide, ozone, or potassium periodate.

[0011] Furthermore, the lignin derivatives include at least one of oligolignin, vanillin, cinnamaldehyde, salicylic acid, eugenol, protocatechuic acid, or p-hydroxybenzaldehyde.

[0012] Furthermore, the natural polymeric material includes at least one of chitosan, carboxymethyl chitosan, hydroxypropyl chitosan, polypeptide, soybean protein, or cottonseed protein.

[0013] A method for preparing a novel biodegradable bio-based plastic film for food preservation, as described above, includes the following steps: S1: Take lignocellulose biomass, crush and sieve it, add a mixed solvent of 2-methyltetrahydrofuran and water at a solid-liquid ratio of 1:9, and add acetic acid or glyoxylic acid into a high-temperature and high-pressure reactor. S2: After the reaction in the reactor is completed, centrifuge and filter to obtain cellulose solid and supernatant containing lignin; S3: The cellulose solid was washed with water until neutral and then dried to obtain high-purity cellulose; the supernatant was adjusted to pH 2, centrifuged, filtered, washed with water, and then dried to obtain pure lignin; S4: Take equal amounts of the high-purity cellulose from step S3 and disperse them separately in water. Add sodium periodate to each, and stir the mixture at 800 r / min in the dark at 30°C. After the reaction is complete, filter the solid and wash it three times with water. Dry it at 40°C to obtain aldehyde cellulose.

[0014] S5: Dissolve carboxymethyl chitosan in a 3% (v / v) aqueous solution of acetic acid to obtain a carboxymethyl chitosan solution; S6: Carboxymethyl chitosan solution is mixed with aldehyde cellulose, and 1% carboxylated lignin is added. The mixture is stirred at 800 r / min in the dark at 30℃. After ultrasonic defoaming, the solution is cast onto a glass petri dish, dried at 40℃, and then flattened and dried at room temperature to obtain a novel biodegradable preservative plastic film.

[0015] Furthermore, in step S1, the reaction temperature inside the reactor is 160°C, and the reaction time is 3 hours.

[0016] Furthermore, the cellulose solids were washed with water until neutral and then dried at 60°C for 12 hours. The pH of the supernatant was adjusted to 2, and after centrifugation, filtration, and washing with water, it was dried at 60°C for 12 hours.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention uses lignocellulose biomass as raw material, obtains cellulose and lignin and their derivatives through green pretreatment technology, and then chemically modifies them before crosslinking with amino-containing natural polymers to prepare films, constructing a multi-network structure that significantly improves the mechanical properties of the films.

[0018] 2. The raw materials of this invention are all natural biomass, which not only endows the film with multiple functions such as biodegradability and antibacterial properties, but also realizes the high-value utilization of agricultural and forestry waste.

[0019] 3. The preparation process of this invention is mild, simple, green and safe, with low energy consumption and simple operation, suitable for large-scale production, and has good economic and environmental benefits. Attached Figure Description

[0020] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 The yield of cellulose and lignin extracted from lignocellulose biomass.

[0021] Figure 2 This is a comparison chart of the degradation performance of the thin films.

[0022] Figure 3 This is a comparison chart of the antibacterial properties of the films. Detailed Implementation

[0023] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0024] A novel biodegradable bio-based plastic film for food preservation comprises chemically modified cellulose, lignin, and lignin derivatives interacting with natural polymer materials.

[0025] Cellulose and lignin are obtained from lignocellulose biomass through pretreatment methods.

[0026] Lignocellulose biomass includes at least one of the following: wheat straw, corn straw, agricultural and forestry waste, rice straw, sorghum straw, soybean straw, forestry waste, recycled wood pulp fiber, sawdust, softwood, hardwood, aquatic plants, algae, or animal excrement.

[0027] Both cellulose and lignin were chemically modified by adding oxidants for oxidation.

[0028] Oxidizing agents include at least one of sodium periodate, hydrogen peroxide, ozone, or potassium periodate.

[0029] Lignin derivatives include at least one of oligolignin, vanillin, cinnamaldehyde, salicylic acid, eugenol, protocatechuic acid, or p-hydroxybenzaldehyde.

[0030] Natural polymer materials include at least one of chitosan, carboxymethyl chitosan, hydroxypropyl chitosan, polypeptides, soybean protein, or cottonseed protein.

[0031] A method for preparing a novel biodegradable bio-based plastic film for food preservation, as described above, includes the following steps: S1: Take lignocellulose biomass, crush and sieve it, add a mixed solvent of 2-methyltetrahydrofuran and water at a solid-liquid ratio of 1:9, and add acetic acid or glyoxylic acid into a high-temperature and high-pressure reactor. S2: After the reaction in the reactor is completed, centrifuge and filter to obtain cellulose solid and supernatant containing lignin; S3: Cellulose solids were washed with water until neutral and then dried to obtain high-purity cellulose; the supernatant was adjusted to pH 2, centrifuged, filtered, washed with water, and then dried to obtain carboxylated lignin; S4: Take equal amounts of the high-purity cellulose from step S3 and disperse them separately in water. Add sodium periodate to each, and stir the mixture at 800 r / min in the dark at 30°C. After the reaction is complete, filter the solid and wash it three times with water. Dry it at 40°C to obtain aldehyde cellulose and carboxylated lignin.

[0032] S5: Dissolve carboxymethyl chitosan in a 3% (v / v) aqueous solution of acetic acid to obtain a carboxymethyl chitosan solution; S6: Carboxymethyl chitosan solution is mixed with aldehyde cellulose, and 1% carboxylated lignin is added. The mixture is stirred at 800 r / min in the dark at 30℃. After ultrasonic defoaming, the solution is cast onto a glass petri dish, dried at 40℃, and then flattened and dried at room temperature to obtain a novel biodegradable preservative plastic film.

[0033] In step S1, the reaction temperature inside the reactor is 160°C, and the reaction time is 3 hours.

[0034] After washing the cellulose solids with water until neutral, they were dried at 60°C for 12 hours. The pH of the supernatant was adjusted to 2, and after centrifugation, filtration, and washing with water, it was dried at 60°C for 12 hours.

[0035] Based on this, the present invention conducted several comparative experiments.

[0036] Example 1 Corn stalks were crushed and sieved. A mixed solvent of 2-methyltetrahydrofuran and water (mass ratio 2:7) was added at a solid-liquid ratio of 1:9. Acetic acid or glyoxylic acid was added to a high-temperature and high-pressure reactor and reacted at 160℃ for 3 hours. After the reaction, the mixture was centrifuged and filtered to obtain cellulose solid and a supernatant containing lignin. The cellulose solid was washed with water until neutral and dried at 60℃ for 12 hours to obtain high-purity cellulose. The supernatant was adjusted to pH 2, centrifuged, filtered, washed with water, and dried at 60℃ for 12 hours to obtain a pure lignin derivative. 10g of cellulose and lignin were separately dispersed in 100mL of water, 12g of sodium periodate were added, and the mixture was stirred at 800r / min in the dark at 30℃ for 8h. After the reaction was completed, the solid was filtered, washed three times with water, and dried at 40℃ for 12h to obtain aldehyde cellulose and aldehyde lignin. Dissolve 10g of carboxymethyl chitosan in 100mL of 3% (v / v) acetic acid aqueous solution to obtain carboxymethyl chitosan solution; 2, 4, 6, 8 and 10% (wt / wt) of aldehyde cellulose were mixed with the obtained carboxymethyl chitosan solution, and 1% (wt / wt) of carboxylated lignin was added. The mixture was stirred at 800 r / min at 30 °C in the dark for 8 h. The reacted solution was ultrasonically defoamed and then cast onto a glass petri dish, which was dried at 40°C for 24 hours. After being flattened and air-dried at room temperature, a novel biodegradable, food-preserving plastic film was obtained. The PE plastic film, chitosan film, and experimental group purchased from the market were placed in moist soil and sprayed with water every two days to observe the degradation of the film.

[0037] The biodegradable bio-based films prepared by the method of this invention have excellent mechanical properties, with a tensile strength of up to 98.3 MPa and a fracture strain of 23.8% (Table 1). Table 1 Example 2 LB medium: Dissolve 5g yeast extract, 10g peptone, and 10g sodium chloride in 1L of deionized water, adjust the medium to 7.0 with sodium hydroxide, and autoclave at 121℃ for 20min; transfer Escherichia coli and Staphylococcus aureus into LB medium for activation and incubate for 12 hours. The commercial PE film, chitosan film and experimental group were crushed and added to LB medium. Activated Escherichia coli and Staphylococcus aureus were inoculated into the three groups of medium containing the film and cultured for 12 hours. Dissolve 5g yeast extract, 10g peptone, 10g sodium chloride, and 15g agar powder in 1L of deionized water, and adjust the medium to 7.0 using sodium hydroxide. Autoclave at 121℃ for 20min. After autoclaving, transfer to petri dishes, cool, and set aside. Dilute the LB medium that has been cultured for 12 hours and spread it onto the solid medium in S4, and culture for another 12 hours.

[0038] Combination Figures 1 to 3 The results showed that in Example 1, the experiment of obtaining lignin and cellulose by pretreating corn stalks with two-phase solvents containing different types of protons showed that the two-phase solvent pretreatment containing glyoxylic acid yielded the highest lignin and cellulose yields, which were 83.4% and 98.3%, respectively.

[0039] The degradation performance of the prepared biodegradable bio-based film, pure chitosan film, and commercially available PE film was tested, such as... Figure 2 As shown, the pure chitosan film completely decomposed within seven days. The prepared biodegradable bio-based film showed slight degradation after 21 days, while no degradation was observed in commercially available PE films.

[0040] The antibacterial properties of the biodegradable bio-based film, chitosan film, and commercially available PE film prepared in Example 2 were tested. Figure 3 As shown, the biodegradable bio-based film prepared in Example 2 has antibacterial function due to the introduction of lignin, and the antibacterial rate against Escherichia coli and Staphylococcus aureus reaches 100%.

[0041] In summary, this invention overcomes the shortcomings of traditional cellulose / chitosan binary physical composites by using a ternary chemical grafting of aldehyde polysaccharide, amino polymer, and aromatic lignin derivative, forming a dual network of covalent and hydrogen bonds. This results in a strong film bond and significantly improved mechanical properties, water resistance, and structural stability.

[0042] Using straw and agricultural and forestry waste as the main raw materials, it turns waste into treasure. The raw materials are cheap and readily available, eliminating dependence on petroleum-based raw materials. The entire composition is natural biomass, which can be completely biodegraded after disposal, eliminating white pollution.

[0043] In-situ grafting of lignin aromatic derivatives into the membrane structure eliminates the need for external antibacterial agents, and the film itself possesses highly efficient antibacterial and preservation capabilities, making it suitable for fruit and vegetable preservation packaging scenarios.

[0044] The entire reaction process is carried out at low temperatures and mainly at atmospheric pressure, with no high-risk reagents. Casting, casting, and hot pressing can all be industrialized. It has low energy consumption, simple process, and is suitable for large-scale production line production.

[0045] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A novel fresh-keeping degradable bio-based plastic film, characterized in that, This includes the interaction between chemically modified cellulose, lignin, and lignin derivatives and natural polymer materials.

2. The novel fresh-keeping biodegradable bio-based plastic film according to claim 1, characterized in that, The cellulose and lignin are obtained from lignocellulose biomass through a pretreatment method.

3. The novel fresh-keeping biodegradable bio-based plastic film according to claim 2, characterized in that, The lignocellulosic biomass includes at least one of the following: wheat straw, corn straw, agricultural and forestry waste, rice straw, sorghum straw, soybean straw, forestry waste, recycled wood pulp fiber, sawdust, softwood, hardwood, aquatic plants, algae, or animal excrement.

4. The novel fresh-keeping biodegradable bio-based plastic film according to claim 1, characterized in that, Both the cellulose and the lignin were chemically modified by adding an oxidizing agent.

5. The novel fresh-keeping biodegradable bio-based plastic film according to claim 4, characterized in that, The oxidant includes at least one of sodium periodate, hydrogen peroxide, ozone, or potassium periodate.

6. The novel fresh-keeping biodegradable bio-based plastic film according to claim 1, characterized in that, The lignin derivatives include at least one of oligolignin, vanillin, cinnamaldehyde, salicylic acid, eugenol, protocatechuic acid, or p-hydroxybenzaldehyde.

7. The novel fresh-keeping biodegradable bio-based plastic film according to claim 1, characterized in that, The natural polymeric material includes at least one of chitosan, carboxymethyl chitosan, hydroxypropyl chitosan, polypeptide, soybean protein, or cottonseed protein.

8. A process for the preparation of a novel fresh-keeping biobased degradable plastic film as claimed in any one of claims 1 to 7, characterized in that, Including the following steps: S1: Take lignocellulose biomass, crush and sieve it, add a mixed solvent of 2-methyltetrahydrofuran and water at a solid-liquid ratio of 1:9, and add acetic acid or glyoxylic acid into a high-temperature and high-pressure reactor. S2: After the reaction in the reactor is completed, centrifuge and filter to obtain cellulose solid and supernatant containing lignin; S3: Cellulose solids were washed with water until neutral and then dried to obtain high-purity cellulose; the supernatant was adjusted to pH 2, centrifuged, filtered, washed with water, and then dried to obtain carboxylated lignin; S4: Take equal amounts of the high-purity cellulose from step S3 and disperse them separately in water. Add sodium periodate to each, and stir the mixture at 800 r / min in the dark at 30°C. After the reaction is complete, filter the solid and wash it three times with water. Dry it at 40°C to obtain aldehyde cellulose. S5: Dissolve carboxymethyl chitosan in a 3% (v / v) aqueous solution of acetic acid to obtain a carboxymethyl chitosan solution; S6: Carboxymethyl chitosan solution is mixed with aldehyde cellulose, and 1% carboxylated lignin is added. The mixture is stirred at 800 r / min in the dark at 30℃. After ultrasonic defoaming, the solution is cast onto a glass petri dish, dried at 40℃, and then flattened and dried at room temperature to obtain a novel biodegradable preservative plastic film.

9. A process for the preparation of novel fresh-keeping biodegradable bio-based plastic film as claimed in claim 8, wherein, In step S1, the reaction temperature inside the reactor is 160°C, and the reaction time is 3 hours.

10. The method for preparing the novel biodegradable bio-based plastic film for food preservation according to claim 8, characterized in that, Cellulose solids were washed with water until neutral and then dried at 60°C for 12 hours. The pH of the supernatant was adjusted to 2, and the solids were centrifuged, filtered, washed with water, and then dried at 60°C for 12 hours.

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