Biodegradable plastic film as well as preparation method and application thereof

Abstract

The invention relates to the technical field of biodegradable plastic films, in particular to a biodegradable plastic film as well as a preparation method and application thereof, and the biodegradable plastic film comprises the following components in parts by weight: 30-50 parts of modified polyvinyl alcohol, 1-5 parts of nano magnesium oxide, 35-60 parts of modified starch and 5-15 parts of plant fiber. According to the biodegradable plastic film as well as the preparation method and the application thereof, the prepared biodegradable plastic film has relatively good mechanical property, water resistance, barrier property and antibacterial property, can be used in the field of food packaging, and has a good fresh-keeping effect.

Description

Technical Field

[0001] The present invention relates to the technical field of degradable plastic films, and in particular to a biodegradable plastic film and a preparation method and application thereof. Background Art

[0002] Plastic films have been widely used in the packaging industry due to their lightness, durability, low cost, and excellent protection and sealing properties, but they have also brought many negative impacts to the environment, such as resource consumption, pollution problems, and the death of marine life. In addition, as a synthetic material, the manufacturing process of plastic not only consumes a lot of energy, but also consumes a lot of water resources. Due to the huge amount of plastic packaging used, the demand for raw materials is also increasing, which has aggravated the consumption of natural resources. Secondly, discarded plastic packaging is usually piled up in landfills or incinerated, which not only produces harmful gases and wastewater, but also pollutes soil and water bodies. A large amount of plastic waste piled up in the natural environment will also destroy the balance of the ecosystem and cause harm to wild animals and plants. In contrast, biodegradable plastic films come from renewable resources and can be rapidly degraded naturally under certain conditions, reducing the negative impact on the environment. Therefore, the research on biodegradable plastic films has become the focus of research and attention.

[0003] Biodegradable materials refer to molecular chains that can be decomposed by microorganisms (such as bacteria, mold, algae, etc.) in garbage disposal or natural environments to produce pollution-free water, CO 2 Or methane and other materials. The materials used to prepare biodegradable plastic films mainly include natural polymer materials (such as starch, cellulose, lignin, protein, etc.) and synthetic polymer materials (such as polylactic acid, polyvinyl alcohol, etc.). However, due to the different sources of natural polymers, the properties of different natural polymer-based plastic films are different. Starch-based plastic films have higher transparency, while cellulose-based plastic films and lignin-based plastic films have better mechanical properties, and cellulose-based plastic films and protein-based plastic films have better permeability resistance. In addition, starch easily absorbs water and swells in a humid environment, cellulose is difficult to process, and lignin and protein degrade slowly. These characteristics limit the preparation and application of biodegradable plastic films; compared with natural polymer-based plastic films, synthetic polymer-based plastic films have high transparency and better mechanical properties. Both can be naturally degraded in nature and will not cause pollution to the environment. However, the degradation rate of synthetic polymer-based plastic films is slow. In addition, polylactic acid-based plastic films are easily affected by sunlight and turn yellow and brittle, while polyvinyl alcohol-based plastic films are easily deformed by moisture and have poor heat resistance. In addition, their preparation costs are high, which is not conducive to industrial production. Therefore, it is of great significance to develop a new biodegradable plastic film. Summary of the invention

[0004] The purpose of the present invention is to provide a biodegradable plastic film and a preparation method and application thereof. The prepared biodegradable plastic film has good mechanical properties, water resistance, barrier properties and antibacterial properties, can be used in the field of food packaging, and has a good preservation effect.

[0005] To achieve the above object, the present invention provides a biodegradable plastic film, which comprises the following components by weight: 30-50 parts of modified polyvinyl alcohol, 1-5 parts of nano magnesium oxide, 35-60 parts of modified starch and 5-15 parts of plant fiber.

[0006] Preferably, the modified polyvinyl alcohol is modified with polyethylene glycol.

[0007] Preferably, the modified starch is modified using octenyl succinic anhydride.

[0008] The method for preparing the above-mentioned biodegradable plastic film comprises the following steps: S1. Preparation of modified polyvinyl alcohol S1.1, dissolving polyvinyl alcohol in deionized water, heating and swelling to obtain a polyvinyl alcohol aqueous solution; S1.2, dissolving polyethylene glycol in deionized water, heating to dissolve, to obtain a polyethylene glycol aqueous solution; S1.3, adding the polyethylene glycol aqueous solution to the polyvinyl alcohol aqueous solution to obtain a blended solution, adjusting the pH of the blended solution to 1-3, then adding a cross-linking agent, and stirring the reaction to obtain modified polyvinyl alcohol; S2. Preparation of modified starch Dissolve starch in deionized water, heat and stir to obtain a starch suspension, adjust the pH of the starch suspension to 8-9, dilute octenyl succinic anhydride and add it to the starch suspension, stir and react to obtain a mixture, adjust the pH of the mixture to 6.5, centrifuge, wash, dry and sieve to obtain modified starch; S3, repeatedly mixing the modified polyvinyl alcohol, nano magnesium oxide, modified starch and plant fiber, and vacuum drying to obtain a film-forming mixture; S4, melt-extrude the film-forming mixture, cool it, and pelletize it to obtain film-forming particles; S5. Add the film-forming particles into a film blowing machine for blow molding to obtain a biodegradable plastic film.

[0009] Preferably, in S1.1, the concentration of the polyvinyl alcohol aqueous solution is 2-6% (w / v), and the swelling is carried out by stirring in an oil bath at 90° C. for 30-60 min.

[0010] Preferably, in S1.2, the concentration of the polyethylene glycol aqueous solution is 1-3% (w / v), and the temperature is raised to dissolve by stirring in an oil bath at 90° C. for 5-30 min.

[0011] Preferably, S1.3, the mass of polyethylene glycol in the blended solution is 15% to 35% of the mass of polyvinyl alcohol, the cross-linking agent is cinnamaldehyde, and the amount of the cross-linking agent is 12% to 40% of the mass of polyvinyl alcohol; the stirring reaction is carried out in an oil bath at 90°C for 120 minutes.

[0012] Preferably, the dilution in S2 is dilution with anhydrous alcohol, and the stirring reaction is stirring at 25° C. for 4 to 6 hours.

[0013] Preferably, the temperature of melt extrusion in S4 is 200-230°C; and the temperature of film blowing in S5 is 170-200°C.

[0014] The above-mentioned biodegradable plastic film is used in food packaging, cosmetic packaging, planting greenhouses, and ground films.

[0015] Beneficial effects of the present invention: (1) In the present invention, hydrogen bonds are formed between the primary alcohol in the modified starch and the modified polyvinyl alcohol molecules to form a three-dimensional network structure, thereby improving the mechanical properties. Polyvinyl alcohol is blended and modified with polyethylene glycol to form a cross-linked network structure with excellent thermal stability and good tensile strength. Octenyl succinic anhydride undergoes nucleophilic addition with the alcohol in the starch to form an esterification product, thereby enhancing the mechanical properties and barrier properties of the film. (2) In the present invention, polyvinyl alcohol is doped with cinnamaldehyde through a cross-linking reaction to improve its mechanical properties and transparency; the water vapor permeability and water solubility of the obtained plastic film are also reduced, so that the obtained plastic film has excellent water resistance. Although part of the cinnamaldehyde participates in the cross-linking reaction, the free cinnamaldehyde in the cross-linked film exhibits good antibacterial properties, so that the obtained plastic film has a longer shelf life and a good preservation effect; (3) Nano magnesium oxide and plant cellulose are also added in the present invention to further improve the antibacterial and ultraviolet shielding properties of the film, so that the prepared film has good mechanical properties, barrier properties, heat resistance and antibacterial properties.

[0016] The technical solution of the present invention is further described in detail below through embodiments. DETAILED DESCRIPTION

[0017] The present invention is further described below in conjunction with the examples. The various chemicals and reagents used in the examples are commercially available unless otherwise specified. The present invention is further described below in conjunction with the examples. Unless otherwise defined, the technical terms or scientific terms used in the present invention should be the usual meanings understood by people with ordinary skills in the field to which the present invention belongs. The above-mentioned features mentioned in the present invention or the features mentioned in the specific examples can be combined arbitrarily, and these specific embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0018] Example 1

[0019] The invention provides a biodegradable plastic film, which comprises the following components in parts by weight: 30 parts of modified polyvinyl alcohol, 1 part of nano magnesium oxide, 35 parts of modified starch and 5 parts of plant fiber.

[0020] The method for preparing the above-mentioned biodegradable plastic film comprises the following steps: S1. Preparation of modified polyvinyl alcohol S1.1. Dissolve polyvinyl alcohol in deionized water, stir in an oil bath at 90°C for 30 min, and swell to obtain a polyvinyl alcohol aqueous solution with a concentration of 2% (w / v); S1.2, dissolve polyethylene glycol in deionized water, stir in an oil bath at 90°C for 5 min, and dissolve to obtain a 1% (w / v) polyethylene glycol aqueous solution; S1.3, adding a polyethylene glycol aqueous solution to a polyvinyl alcohol aqueous solution to obtain a blended solution, wherein the mass of the polyethylene glycol accounts for 15% of the mass of the polyvinyl alcohol, adjusting the pH of the blended solution to 1, and then adding cinnamaldehyde accounting for 12% of the mass of the polyvinyl alcohol, stirring in an oil bath at 90° C. for 120 min to obtain a modified polyvinyl alcohol; S2. Preparation of modified starch Dissolve starch in deionized water, heat and stir to obtain a starch suspension, adjust the pH of the starch suspension to 8, dilute octenyl succinic anhydride 3 times with anhydrous alcohol and add it to the starch suspension, stir at 25°C for 4 hours to obtain a mixture, adjust the pH of the mixture to 6.5, centrifuge, wash, dry and sieve to obtain modified starch; S3, repeatedly mixing the modified polyvinyl alcohol, nano magnesium oxide, modified starch and plant fiber, and vacuum drying to obtain a film-forming mixture; S4, melt-extrude the film-forming mixture at a temperature of 200° C., cool it, and pelletize it to obtain film-forming particles; S5. Add the film-forming particles into a film blowing machine, and perform blow molding at a temperature of 170° C. to obtain a biodegradable plastic film.

[0021] Example 2

[0022] The invention provides a biodegradable plastic film, which comprises the following components in parts by weight: 40 parts of modified polyvinyl alcohol, 2 parts of nano magnesium oxide, 45 parts of modified starch and 10 parts of plant fiber.

[0023] The method for preparing the above-mentioned biodegradable plastic film comprises the following steps: S1. Preparation of modified polyvinyl alcohol S1.1. Dissolve polyvinyl alcohol in deionized water, stir in an oil bath at 90°C for 45 minutes, and swell to obtain a polyvinyl alcohol aqueous solution with a concentration of 3% (w / v); S1.2, dissolve polyethylene glycol in deionized water, stir in an oil bath at 90°C for 20 min, and dissolve to obtain a 2% (w / v) polyethylene glycol aqueous solution; S1.3, adding a polyethylene glycol aqueous solution to a polyvinyl alcohol aqueous solution to obtain a blended solution, wherein the mass of the polyethylene glycol accounts for 25% of the mass of the polyvinyl alcohol, adjusting the pH of the blended solution to 2, and then adding cinnamaldehyde accounting for 20% of the mass of the polyvinyl alcohol, stirring in an oil bath at 90° C. for 120 min to obtain a modified polyvinyl alcohol; S2. Preparation of modified starch Dissolve starch in deionized water, heat and stir to obtain a starch suspension, adjust the pH of the starch suspension to 8, dilute octenyl succinic anhydride 3 times with anhydrous alcohol and add it to the starch suspension, stir at 25°C for 5 hours to obtain a mixture, adjust the pH of the mixture to 6.5, centrifuge, wash, dry and sieve to obtain modified starch; S3, repeatedly mixing the modified polyvinyl alcohol, nano magnesium oxide, modified starch and plant fiber, and vacuum drying to obtain a film-forming mixture; S4, melt-extrude the film-forming mixture at a temperature of 210° C., cool it, and pelletize it to obtain film-forming particles; S5. Add the film-forming particles into a film blowing machine, and perform blow molding at a temperature of 180° C. to obtain a biodegradable plastic film.

[0024] Example 3

[0025] The invention provides a biodegradable plastic film, which comprises the following components in parts by weight: 50 parts of modified polyvinyl alcohol, 5 parts of nano magnesium oxide, 60 parts of modified starch and 15 parts of plant fiber.

[0026] The method for preparing the above-mentioned biodegradable plastic film comprises the following steps: S1. Preparation of modified polyvinyl alcohol S1.1, dissolve polyvinyl alcohol in deionized water, stir in an oil bath at 90°C for 60 min, and swell to obtain a polyvinyl alcohol aqueous solution with a concentration of 6% (w / v); S1.2, dissolve polyethylene glycol in deionized water, stir in an oil bath at 90°C for 30 min, and dissolve to obtain a 3% (w / v) polyethylene glycol aqueous solution; S1.3, adding a polyethylene glycol aqueous solution to a polyvinyl alcohol aqueous solution to obtain a blended solution, wherein the mass of the polyethylene glycol accounts for 35% of the mass of the polyvinyl alcohol, adjusting the pH of the blended solution to 3, and then adding cinnamaldehyde accounting for 40% of the mass of the polyvinyl alcohol, stirring in an oil bath at 90° C. for 120 min to obtain a modified polyvinyl alcohol; S2. Preparation of modified starch Dissolve starch in deionized water, heat and stir to obtain a starch suspension, adjust the pH of the starch suspension to 9, dilute octenyl succinic anhydride 3 times with anhydrous alcohol and add it to the starch suspension, stir at 25°C for 6 hours to obtain a mixture, adjust the pH of the mixture to 6.5, centrifuge, wash, dry and sieve to obtain modified starch; S3, repeatedly mixing the modified polyvinyl alcohol, nano magnesium oxide, modified starch and plant fiber, and vacuum drying to obtain a film-forming mixture; S4, melt-extrude the film-forming mixture at a temperature of 230° C., cool it, and pelletize it to obtain film-forming particles; S5. Add the film-forming particles into a film blowing machine, and perform blow molding at a temperature of 200° C. to obtain a biodegradable plastic film.

[0027] Comparative Example 1 A biodegradable plastic film comprises the following components in parts by weight: 40 parts of modified polyvinyl alcohol, 2 parts of nano magnesium oxide and 10 parts of plant fiber.

[0028] The method for preparing the above-mentioned biodegradable plastic film comprises the following steps: S1. Preparation of modified polyvinyl alcohol S1.1. Dissolve polyvinyl alcohol in deionized water, stir in an oil bath at 90°C for 45 minutes, and swell to obtain a polyvinyl alcohol aqueous solution with a concentration of 3% (w / v); S1.2, dissolve polyethylene glycol in deionized water, stir in an oil bath at 90°C for 20 min, and dissolve to obtain a 2% (w / v) polyethylene glycol aqueous solution; S1.3, adding a polyethylene glycol aqueous solution to a polyvinyl alcohol aqueous solution to obtain a blended solution, wherein the mass of the polyethylene glycol accounts for 25% of the mass of the polyvinyl alcohol, adjusting the pH of the blended solution to 2, and then adding cinnamaldehyde accounting for 20% of the mass of the polyvinyl alcohol, stirring in an oil bath at 90° C. for 120 min to obtain a modified polyvinyl alcohol; S2, repeatedly mixing the modified polyvinyl alcohol, nano magnesium oxide and plant fiber, and vacuum drying to obtain a film-forming mixture; S4, melt-extrude the film-forming mixture at a temperature of 210° C., cool it, and pelletize it to obtain film-forming particles; S5. Add the film-forming particles into a film blowing machine, and perform blow molding at a temperature of 180° C. to obtain a biodegradable plastic film.

[0029] Comparative Example 2 A biodegradable plastic film comprises the following components by weight: 2 parts of nano magnesium oxide, 45 parts of modified starch and 10 parts of plant fiber.

[0030] The method for preparing the above-mentioned biodegradable plastic film comprises the following steps: S1. Preparation of modified starch Dissolve starch in deionized water, heat and stir to obtain a starch suspension, adjust the pH of the starch suspension to 8, dilute octenyl succinic anhydride 3 times with anhydrous alcohol and add it to the starch suspension, stir at 25°C for 5 hours to obtain a mixture, adjust the pH of the mixture to 6.5, centrifuge, wash, dry and sieve to obtain modified starch; S2, repeatedly mixing nano magnesium oxide, modified starch and plant fiber, and vacuum drying to obtain a film-forming mixture; S3, melt-extrude the film-forming mixture at a temperature of 210° C., cool, and pelletize to obtain film-forming particles; S4. Add the film-forming particles into a film blowing machine, and perform blow molding at a temperature of 180° C. to obtain a biodegradable plastic film.

[0031] The biodegradable plastic films prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to performance tests. The tensile properties of the biodegradable plastic films were tested according to standard ASTM D882-02. The hygroscopic properties of the biodegradable plastic films were tested according to standard GB / T 1034-2008, and the films were placed in an environment with an ambient humidity of 53% for 24 hours to test their moisture absorption rate. The oxygen permeability of the biodegradable plastic films was tested according to standard GB / T 19789-2005. The results are shown in Table 1.

[0032] Table 1 Performance data of biodegradable plastic films ; As can be seen from Table 1, the tensile strength and elongation at break of the biodegradable plastic films prepared in Examples 1-3 of the present invention are better than those in Comparative Examples 1-2, indicating that the biodegradable plastic films prepared in the present invention have better mechanical properties; while the moisture absorption rate and oxygen permeability of the biodegradable plastic films prepared in Examples 1-3 of the present invention are lower than those in Comparative Examples 1-2, indicating that the biodegradable plastic films prepared in the present invention have better water resistance and barrier properties.

[0033] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A biodegradable plastic film, characterized in that: The composition comprises the following components in parts by weight: 30-50 parts of modified polyvinyl alcohol, 1-5 parts of nano magnesium oxide, 35-60 parts of modified starch and 5-15 parts of plant fiber.

2. A biodegradable plastic film according to claim 1, characterized in that: Modified polyvinyl alcohol is modified with polyethylene glycol.

3. The biodegradable plastic film according to claim 1, characterized in that: The modified starch is modified with octenyl succinic anhydride.

4. A method for preparing a biodegradable plastic film according to any one of claims 1 to 3, characterized in that: The following steps are included: S1. Preparation of modified polyvinyl alcohol S1.1, dissolving polyvinyl alcohol in deionized water, heating and swelling to obtain a polyvinyl alcohol aqueous solution; S1.2, dissolving polyethylene glycol in deionized water, heating to dissolve, to obtain a polyethylene glycol aqueous solution; S1.3, adding the polyethylene glycol aqueous solution to the polyvinyl alcohol aqueous solution to obtain a blended solution, adjusting the pH of the blended solution to 1-3, then adding a cross-linking agent, and stirring the reaction to obtain modified polyvinyl alcohol; S2. Preparation of modified starch Dissolve starch in deionized water, heat and stir to obtain a starch suspension, adjust the pH of the starch suspension to 8-9, dilute octenyl succinic anhydride and add it to the starch suspension, stir and react to obtain a mixture, adjust the pH of the mixture to 6.5, centrifuge, wash, dry and sieve to obtain modified starch; S3, repeatedly mixing the modified polyvinyl alcohol, nano magnesium oxide, modified starch and plant fiber, and vacuum drying to obtain a film-forming mixture; S4, melt-extrude the film-forming mixture, cool it, and pelletize it to obtain film-forming particles; S5. Add the film-forming particles into a film blowing machine for blow molding to obtain a biodegradable plastic film.

5. The method for preparing a biodegradable plastic film according to claim 4, characterized in that: S1.1, the concentration of the polyvinyl alcohol aqueous solution is 2~6% (w / v), and the temperature swelling is stirred in an oil bath at 90℃ for 30~60min.

6. The method for preparing a biodegradable plastic film according to claim 4, characterized in that: S1.2, the concentration of polyethylene glycol aqueous solution is 1~3% (w / v), and the temperature is raised to dissolve by stirring in an oil bath at 90℃ for 5~30min.

7. The method for preparing a biodegradable plastic film according to claim 4, characterized in that: S1.3, the mass of polyethylene glycol in the blend solution is 15%~35% of the mass of polyvinyl alcohol, the cross-linking agent is cinnamaldehyde, and the amount of the cross-linking agent is 12%~40% of the mass of polyvinyl alcohol; the stirring reaction is stirred in an oil bath at 90°C for 120 minutes.

8. The method for preparing a biodegradable plastic film according to claim 4, characterized in that: The dilution in S2 is dilution with anhydrous alcohol, and the stirring reaction is stirred at 25°C for 4 to 6 hours.

9. The method for preparing a biodegradable plastic film according to claim 4, characterized in that: The temperature of melt extrusion in S4 is 200-230°C; the temperature of film blowing in S5 is 170-200°C.

10. An application of a biodegradable plastic film as claimed in any one of claims 1 to 3, characterized in that: Used in food packaging, cosmetic packaging, greenhouses, and mulch films.