A method for preparing modified lignin composite films and their applications

Abstract

This invention relates to the field of fully biodegradable composite film technology, and discloses a method for preparing a modified lignin composite film and its application. The preparation method includes mixing lignin modified with phenolic and aliphatic hydroxyl groups with a biodegradable polymer material, extruding, hot pressing, and blow molding. The fully biodegradable composite film consists of 50-70% modified lignin and 30-50% biodegradable polymer material. This invention, by modifying and increasing the proportion of lignin in the biodegradable polymer, can reduce the material cost of the fully biodegradable composite film while maintaining high mechanical properties (tensile strength ≥20MPa, elastic modulus ≥200MPa, elongation at break ≥200%). This composite film overcomes the mechanical property defects of traditional fully biodegradable films while ensuring blow molding, and can be widely used in the production of mulch films, food preservation films, vest bags, or packaging bags.

Description

Technical Field

[0001] This invention relates to the field of fully biodegradable composite film technology, and in particular to a method for preparing and applying a modified lignin composite film. Background Technology

[0002] The widespread use of plastics has led to white pollution, posing a serious threat to the environment and human health. Therefore, developing a fully biodegradable plastic material to replace traditional non-biodegradable plastics has become an urgent problem to be solved. Currently, the main fully biodegradable plastics on the market include PBAT, PHA, PLA, PCL, and PBS; however, their high production costs and poor mechanical properties limit their large-scale application in agriculture and daily necessities. Based on this situation, this invention proposes a method for preparing a fully biodegradable and low-cost composite membrane material using modified lignin as a filler, combined with PBAT, PHA, PLA, PCL, or PBS, which is expected to solve the current technical and industrial bottlenecks of fully biodegradable plastics. Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing and applying a modified lignin composite film. Compared with PBAT, PHA, PLA, PCL or PBS films, the composite film prepared by this invention overcomes the defects of mechanical properties of traditional fully biodegradable films and ensures the blow molding of the composite film. It can be widely used in the production of mulch film, food preservation film, vest bags or packaging bags.

[0004] To achieve the above objectives, the present invention provides a method for preparing a modified lignin composite film, comprising the following steps:

[0005] S1. Modification of aliphatic and phenolic hydroxyl groups in lignin: A modifier is added to lignin, and the mixture is reacted at 25℃~160℃ for 4-48h. After the reaction, the solution is added dropwise to a solution with pH 2~4 to precipitate lignin. Modified lignin is obtained by centrifugation, washing, and freeze-drying.

[0006] S2. Mixing and granulation: Biodegradable polymer materials and modified lignin are mixed in a mass ratio, an interface compatibilizer is added to the mixture, and after being mixed evenly, the mixture is put into a twin-screw extruder for granulation to obtain masterbatch.

[0007] S3. Hot pressing film formation: The masterbatch obtained by granulation in step S2 is hot pressed at 120-180℃ and 2-15MPa for 1-5min to obtain a composite film.

[0008] S4. Blow molding film: The masterbatch obtained from granulation in step S2 is blow molded into a film at 130-180℃.

[0009] Furthermore, the lignin in step 1 includes one or a combination of several of the following: alkali lignin, organic solvent lignin, DES lignin, ionic liquid lignin, sulfate lignin, lignin sulfonate, and groundwood lignin.

[0010] Further, in step 1, the modifier is a mixture of acetic anhydride, propionic anhydride or butyric anhydride, maleic anhydride, acyl chloride or polyethylene glycol and pyridine, and the volume ratio of acetic anhydride, propionic anhydride, butyric anhydride, maleic anhydride, acyl chloride or polyethylene glycol to pyridine is 1:1-5.

[0011] Furthermore, in step 1, the ratio of lignin to modifier is 1g:5-10ml.

[0012] Furthermore, in step 2, the biodegradable polymer material is one or more of PBAT, PHA, PLA, PCL, or PBS.

[0013] Furthermore, in step 2, the biodegradable polymer material accounts for 30-50% of the total mass of the biodegradable polymer material and modified lignin, and the modified lignin accounts for 50-70% of the total mass of the biodegradable polymer material and modified lignin.

[0014] Furthermore, in step 2, the interface compatibilizer accounts for 1-9% of the total mass of the masterbatch. The interface compatibilizer includes one or a combination of several of the following: dibutyl adipate, diisodecyl phthalate, dioctyl phthalate, triphenyl phosphate, tributyl citrate, trioctyl citrate, glycerol, polyethylene glycol, glucose, ethyl lactate, sodium benzoate, sodium dodecyl sulfate, tannic acid, and Twenty-80.

[0015] The present invention also provides a modified lignin composite film, which is prepared by the above preparation method.

[0016] Furthermore, the modified lignin composite film has a tensile strength ≥20MPa, an elastic modulus ≥200MPa, and an elongation at break ≥200%.

[0017] The present invention also provides the application of the above-mentioned modified lignin composite film in the production of mulch film, cling film, vest bags or packaging bags.

[0018] The present invention employs the above-described method for preparing a modified lignin composite film and its application, the beneficial effects of which are as follows:

[0019] 1. This invention modifies the phenolic and aliphatic hydroxyl groups of lignin to obtain modified lignin. The intermolecular forces between the modified lignin and PBAT, PHA, PLA, PCL or PBS are enhanced. Compared with pure PBAT, PHA, PLA, PCL or PBS films, the composite film provided by this invention has excellent mechanical properties.

[0020] 2. This invention utilizes dibutyl adipate, diisodecyl phthalate, dioctyl phthalate, triphenyl phosphate, tributyl citrate, trioctyl citrate, glycerol, polyethylene glycol, glucose, ethyl lactate, sodium benzoate, sodium dodecyl sulfate, tannic acid, and Twenty-80 as interfacial compatibilizers. After adding the interfacial compatibilizers, the amount of modified lignin added to the composite film can reach 70%. The addition of the interfacial compatibilizers not only improves the interfacial bonding force between modified lignin and biodegradable polymers, but also promotes the dispersion of modified lignin in biodegradable polymers, reduces stress concentration, and greatly improves the mechanical properties of the fully biodegradable composite film material.

[0021] 3. The composite film provided by this invention has good mechanical properties, barrier properties and fully biodegradable properties. It can be used not only as a mulch film, but also in vest bags, packaging bags or plastic wrap and other fields. While maintaining the fully biodegradable characteristics, it greatly reduces the production cost.

[0022] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0023] Figure 1 The figures represent the changes in soil temperature and humidity when rapeseed is covered with different plastic film in the embodiments of the present invention, where A represents the change in soil humidity and B represents the change in soil temperature. Detailed Implementation

[0024] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0025] The present invention will be explained in more detail through the following embodiments. The purpose of disclosing the present invention is to protect all changes and modifications within the scope of the present invention. The present invention is not limited to the following embodiments.

[0026] Unless otherwise defined, the alkali lignin, organic solvent lignin, DES lignin, ionic liquid lignin, sulfate lignin, lignin sulfonate and groundwood lignin, PBAT, PHA, PLA, PCL or PBS used in this invention are all commercially available.

[0027] Unless otherwise defined, the reagents used in this invention, such as dibutyl adipate, diisodecyl phthalate, dioctyl phthalate, triphenyl phosphate, tributyl citrate, trioctyl citrate, glycerol, polyethylene glycol, glucose, ethyl lactate, sodium benzoate, sodium dodecyl sulfate, tannic acid, and Twenty-80, are all commercially available.

[0028] Example 1

[0029] A method for preparing a modified lignin composite film includes the following steps:

[0030] S1. Modification of aliphatic and phenolic hydroxyl groups in lignin: Add a mixed solution of acetic anhydride and pyridine (50 mL: 50 mL) to 10 g of sulfate lignin and react at 25 °C for 48 h. After the reaction is complete, add the solution dropwise to a solution with pH 2 to 4, then centrifuge the resulting mixed solution, wash with ultrapure water, and freeze-dry for 24 h to 48 h to obtain modified lignin.

[0031] S2. Mixing and Granulation: 40% by mass of PBAT and 10% by mass of PHA are mixed with 50% by mass of modified lignin to obtain a mixture. 3% by mass of tributyl citrate is added to the mixture as an interfacial compatibilizer. After mixing, the mixture is placed in a dual planetary mixer for stirring, and then fed into a twin-screw extruder for granulation to obtain masterbatch. The temperature of the twin screw is 130-175℃, and the rotation speed is 20-33 rpm / min.

[0032] S3. Hot pressing film formation: The masterbatch is hot pressed at 140℃~175℃ and 2~15MPa for 1~5min to obtain a composite film.

[0033] S4. Blow molding film formation: Blow molding the masterbatch into a film at a temperature of 135℃~175℃ and a rotation speed of 400-800rpm / min.

[0034] Example 2

[0035] A method for preparing a modified lignin composite film includes the following steps:

[0036] S1. Modification of aliphatic and phenolic hydroxyl groups in lignin: A mixed solution of propionic anhydride and pyridine (propionic anhydride:pyridine = 30 mL: 40 mL) was added to 10 g of sulfate lignin and reacted at 35 °C for 36 h. After the reaction was completed, the solution was added dropwise to a solution with pH 2 to 4. The resulting mixed solution was then centrifuged, washed, and freeze-dried for 24 h to 48 h to obtain modified lignin.

[0037] S2. Mixing and Granulation: 37% by mass of PBAT, 3% by mass of PLA, and 60% by mass of modified lignin are mixed to obtain a masterbatch. 5% by mass of sodium dodecyl sulfate is added to the masterbatch as an interfacial compatibilizer. After mixing, the mixture is placed in a dual planetary mixer for stirring, and then fed into a twin-screw extruder for granulation. The temperature of the twin screw is 130-175℃, and the rotation speed is 20-33 rpm / min.

[0038] S3. Hot pressing film formation: The masterbatch is hot pressed at 140℃~175℃ and 2~15MPa for 1~5min to obtain a composite film.

[0039] S4. Blow molding film formation: Blow molding the masterbatch into a film at a temperature of 130℃~175℃ and a rotation speed of 400-800rpm / min.

[0040] Example 3

[0041] A method for preparing a modified lignin composite film includes the following steps:

[0042] S1. Modification of aliphatic and phenolic hydroxyl groups in lignin: Polyethylene glycol was added to 10g of organic solvent lignin and reacted at 150℃ for 6h. After the reaction was completed, the solution was added dropwise to a solution with pH 2-4. The resulting mixed solution was then centrifuged, washed, and freeze-dried for 24h-48h to obtain modified lignin.

[0043] S2. Mixing and Granulation: 40% by mass of PBAT and 60% by mass of modified lignin are mixed to obtain a mixture. 3% by mass of sodium dodecyl sulfate is added to the mixture as an interfacial compatibilizer. After mixing, the mixture is placed in a dual planetary mixer for stirring, and then granulated in a twin-screw extruder to obtain masterbatch. The temperature of the twin screw is 130-170℃, and the rotation speed is 20-33 rpm / min.

[0044] S3. Hot pressing film formation: The masterbatch is hot pressed at 140℃~175℃ and 2~15MPa for 1~5min to obtain a composite film.

[0045] S4. Blow molding film formation: Blow molding the masterbatch into a film at a temperature of 130℃~170℃ and a rotation speed of 400-800rpm / min.

[0046] Comparative Example 1

[0047] The method for preparing PBAT thin films includes the following steps:

[0048] S1. Hot pressing film formation: PBAT is hot pressed at 140℃~150℃ and 2~15MPa to obtain a composite film.

[0049] Comparative Example 2

[0050] A method for preparing a lignin composite film includes the following steps:

[0051] S1. Mixing and granulation: PBAT and lignin are mixed at a mass ratio of 1:1. The mixture is then fed into a twin-screw extruder for granulation to obtain masterbatch. The temperature of the twin screw is 130-145℃ and the rotation speed is 20-33 rpm / min.

[0052] S2. Hot pressing film formation: The masterbatch is hot pressed at 140℃~150℃ and 2~15MPa for 1~5min to obtain a composite film.

[0053] Performance testing

[0054] The mechanical properties of the composite films (hot-pressed films) prepared in Examples 1-3 and Comparative Examples 1-2 were tested, and the results are shown in Table 1.

[0055] Table 1 Mechanical Properties of Composite Membranes

[0056] Tensile strength (MPa) Elongation at break (%) Young's modulus (MPa) Example 1 25.4±0.8 297.6±17.6 218.1±20 Example 2 23.5±1.1 236.5±5.2 197.6±5.2 Example 3 20.2±1.2 306.5±12.6 203.5±10.5 Comparative Example 1 28.7±2.0 795.9±78.1 58.5±3.9 Comparative Example 2 21.3±1.2 100.3±2.9 245.4±28

[0057] As shown in Table 1, the tensile strength and elongation at break of Comparative Example 2 are lower than those of Comparative Example 1, while the Young's modulus is much higher than that of Comparative Example 1. This indicates that the addition of lignin can increase the Young's modulus, but the tensile strength and elongation at break will decrease.

[0058] To address this issue, modified lignin was added in the examples. Compared to Comparative Example 2, Examples 1 and 2 added modified lignin and an interfacial compatibilizer to promote fusion between the two phases, maintaining a high Young's modulus while improving tensile strength and elongation at break. This demonstrates that the modified lignin composite film overcomes the weakness of traditional PBAT films, ensuring both blow molding and strength, while significantly reducing costs.

[0059] Therefore, the present invention employs the above-described method for preparing and applying a modified lignin composite film. Compared to PBAT, PHA, PLA, PCL, or PBS films, the fully biodegradable composite film prepared by the present invention exhibits superior mechanical properties. This composite film overcomes the defects in the mechanical properties of traditional fully biodegradable films while ensuring the blow molding process of the composite film, making it widely applicable in the production of mulch films, food preservation films, vest bags, or packaging bags.

[0060] Application examples

[0061] Using the fully biodegradable membrane prepared in Example 1 as the experimental material, practical applications of mulching were carried out on rapeseed, cabbage, tomato, corn, and cotton. Rapeseed was used as an example to illustrate the changes in soil temperature and humidity after mulching. Figure 1 As shown, from Figure 1 As can be seen from the example, the thermal insulation and entropy-increasing performance of the fully biodegradable composite film in Example 1 is better than that of the traditional fully biodegradable PBAT film and close to that of the PE film, which proves the application potential of this composite film in mulch film.

[0062] Finally, it should be noted that the above embodiments and application examples are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a modified lignin composite film, characterized in that, Includes the following steps: S1. Modification of aliphatic and phenolic hydroxyl groups in lignin: A modifier is added to lignin, and the mixture is reacted at 25℃~160℃ for 4-48 hours. After the reaction, the solution is added dropwise to a solution with a pH of 2~4 to precipitate lignin. Modified lignin is obtained by centrifugation, washing, and freeze-drying. S2. Mixing and granulation: Biodegradable polymer materials and modified lignin are mixed in proportion, an interface compatibilizer is added to the mixture, and after being mixed evenly, the mixture is granulated through a twin-screw extruder to obtain masterbatch. S3. Hot pressing film formation: The masterbatch obtained in step S2 is hot pressed at 120-180℃ and 2-15MPa for 1-5min to obtain a composite film; S4. Blow molding film formation: The masterbatch obtained in step S2 is blow molded into a film at 130-180℃. In step 1, the modifier is acetic anhydride, propionic anhydride, butyric anhydride, maleic anhydride or a mixture of polyethylene glycol and pyridine, and the volume ratio of acetic anhydride, propionic anhydride, butyric anhydride, maleic anhydride or polyethylene glycol to pyridine is 1:1-5. The ratio of lignin to modifier is 1g:5-10ml; In step 2, biodegradable polymer materials account for 30-50% of the total mass of biodegradable polymer materials and modified lignin, and modified lignin accounts for 50-70% of the total mass of biodegradable polymer materials and modified lignin. In step 2, the interface compatibilizer accounts for 1-9% of the total mass of the masterbatch, and the interface compatibilizer is tributyl citrate or sodium dodecyl sulfate.

2. The method for preparing a modified lignin composite film according to claim 1, characterized in that: In step 1, the lignin includes one or a combination of several of the following: alkali lignin, organic solvent lignin, DES lignin, ionic liquid lignin, sulfate lignin, lignin sulfonate, or ground wood lignin.

3. The method for preparing a modified lignin composite film according to claim 1, characterized in that: The biodegradable polymeric materials in step 2 include one or more of PBAT, PHA, PLA, PCL, and PBS.

4. A modified lignin composite film, characterized in that: It is prepared by the preparation method according to any one of claims 1-3.

5. The modified lignin composite film according to claim 4, characterized in that: The modified lignin composite film has a tensile strength ≥20MPa, an elastic modulus ≥200MPa, and an elongation at break ≥200%.

6. The application of the modified lignin composite film as described in claim 5 in the production of mulch film, cling film, vest bags or packaging bags.

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