A method for preparing modified biochar / PBAT mulch with high water vapor barrier performance

Abstract

The present invention discloses a method for preparing a modified biochar / PBAT mulch film with high water vapor barrier performance, comprising the following steps: S1, preparation of flaky biochar; S2, preparation of modified biochar; S3, preparation of composite film. The present invention combines flaky biochar, modified biochar and PBAT mulch film. The addition of flaky biochar material can form more barrier layers in the film, making the effective path of water vapor passing through the film more tortuous, reducing the water vapor transmission rate, and utilizing the multiple epoxy groups contained in epoxidized soybean oil. At high temperatures, some epoxy groups will open the ring and react with the hydroxyl and carboxyl groups on the surface of biochar, so that the surface of biochar will be grafted with epoxy groups, and the epoxy groups grafted with biochar will open the ring and react with the hydroxyl and carboxyl groups at both ends of the PBAT and PPC molecular chains during twin-screw melt blending, achieving a cross-linking effect, thereby improving the water vapor barrier performance of the PBAT mulch film.

Description

Technical Field

[0001] The present invention relates to the technical field of modified PBAT mulch film preparation, and in particular to a method for preparing a modified biochar / PBAT mulch film with high water vapor barrier performance. Background Art

[0002] Ground film plays an important role in my country's agricultural production and life. At present, traditional polyethylene (PE) ground film is difficult to degrade, resulting in serious residual film pollution problems, which has led to an increasing demand for biodegradable ground film. Polybutylene terephthalate-adipate (PBAT) has excellent film-forming properties and is one of the best choices for preparing biodegradable ground film. However, its poor water vapor barrier properties limit its application in agricultural production, so it is necessary to improve its barrier properties through modification methods.

[0003] Defects and shortcomings of existing technologies: At present, the barrier properties of PBAT are mainly improved through molecular chain regulation, blending or surface modification; molecular chain regulation achieves the purpose of improving barrier properties by grafting monomers with better barrier properties onto the main chain of the polymer, however, this method has fewer monomers to choose from and a narrow operating window, which cannot meet the requirements of use; the blending method improves its barrier properties by blending with polymers with better barrier properties. The method is simple and easy to implement, but the gas barrier capacity of the blend is often between the polymers used, and it is difficult to achieve a significant improvement; surface modification of the film can improve its barrier properties, but the operation method is too complicated and the cost is generally high, which is not in line with the actual production of large-scale use of ground films; the filling method by adding inorganic materials such as biochar has gradually been recognized. These inorganic materials are widely available, low-priced, and will not cause secondary pollution to the land. They are an excellent choice for improving PBAT films.

[0004] However, in the prior art, there is no method for using biochar to regulate the water vapor barrier performance of PBAT mulch, because the larger particle size of biochar will destroy the continuity of PBAT and reduce its mechanical properties. In addition, simply adding unmodified biochar does not significantly improve the water vapor barrier performance of PBAT film, which is difficult to meet actual production needs; therefore, to solve this problem, the present invention proposes a method for preparing a modified biochar / PBAT mulch with high water vapor barrier performance, and applies biochar to the modification of PBAT mulch, which greatly improves its water vapor barrier performance. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing a modified biochar / PBAT mulch film with high water vapor barrier performance, so as to solve the problem raised in the above background technology that in the prior art, there is no method for using biochar to regulate the water vapor barrier performance of PBAT mulch films, because the larger particle size of biochar will destroy the continuity of PBAT and reduce its mechanical properties. In addition, simply adding unmodified biochar will not significantly improve the water vapor barrier performance of PBAT film, which is difficult to meet actual production needs.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for preparing a modified biochar / PBAT mulch film with high water vapor barrier performance comprises the following steps:

[0008] S1. Preparation of flaky biochar, comprising the following steps:

[0009] S1a, crushing plant straw into straw powder, adding the straw powder into a container containing sodium hydroxide solution and stirring evenly, then pouring the sodium hydroxide solution mixed with the straw powder into a ball mill for wet ball milling to obtain a mixed slurry;

[0010] S1b, washing the obtained mixed slurry with deionized water until it is neutral and drying it to obtain activated straw powder, and then placing the activated straw powder in a tubular furnace for carbonization to obtain flaky biochar;

[0011] S2. Preparation of modified biochar, comprising the following steps:

[0012] S2a, biochar preparation, crushing plant straw into straw powder, washing the straw powder with deionized water to remove water-soluble impurities and drying, then adding the dried straw powder to a tubular furnace for carbonization to obtain straw biochar, and then placing the straw biochar in a ball mill for ball milling to obtain ball-milled biochar;

[0013] S2b, biochar modification, adding the prepared ball-milled biochar to a container containing epoxidized soybean oil and heating and stirring, so that the epoxy groups open and react with the functional groups on the surface of the biochar, until the ball-milled biochar and the epoxidized soybean oil react, after the liquid in the container cools down, adding n-hexane and stirring, dissolving the excess epoxidized soybean oil in n-hexane, the epoxidized soybean oil is viscous and cannot be separated by centrifugation, the epoxidized soybean oil can be dissolved in n-hexane for separation, and then the biochar is separated by centrifugation, and then ethanol is added thereto for cleaning and centrifugation, retaining the bottom product and drying it to obtain modified biochar;

[0014] S3, the preparation of the composite membrane comprises the following steps:

[0015] S3a, mixing the PBAT material with flaky biochar and modified biochar, melt blending through a twin-screw extruder granulator to obtain modified biochar / PBAT composite particles, and then placing the composite particles in a film blowing machine for film blowing to obtain a modified biochar / PBAT ground film.

[0016] In the aforementioned method for preparing a modified biochar / PBAT mulch film with high water vapor barrier properties, in step S1a and step S2a, the plant straw is one of wheat straw, corn straw, rice straw and soybean straw.

[0017] In the aforementioned method for preparing a modified biochar / PBAT mulch film with high water vapor barrier performance, in step S1a, the plant straw is crushed to 500 mesh and 5-10 g is taken, the molar concentration of the sodium hydroxide solution is 0.1-1 mol / L, and the amount of the sodium hydroxide solution added is 20-50 ml.

[0018] In the aforementioned method for preparing a modified biochar / PBAT mulch film with high water vapor barrier properties, in step S1a, the sodium hydroxide solution mixed with straw powder is processed in a ball mill at a rotation speed of 100-300 rpm, and the wet ball milling is performed for 3-5 hours.

[0019] In the aforementioned method for preparing a modified biochar / PBAT mulch film with high water vapor barrier properties, in step S1b and step S2a, the carbonization treatment temperature is 300-600°C, and the carbonization is carried out under nitrogen protection for 3-5 hours.

[0020] In the aforementioned method for preparing a modified biochar / PBAT mulch film with high water vapor barrier performance, in step S2a, the plant straw is crushed to 500-1000 mesh, and the straw powder is washed at least three times with deionized water.

[0021] In the aforementioned method for preparing a modified biochar / PBAT mulch film with high water vapor barrier properties, in step S2a, the straw biochar is placed in a ball mill at a rotation speed of 100-300 rpm and ball milled for 2-5 hours, and the obtained ball-milled biochar particle size is 200-300 nm.

[0022] In the aforementioned method for preparing a modified biochar / PBAT mulch film with high water vapor barrier properties, in step S2b, the ball-milled biochar is taken in an amount of 1-10 g, the epoxy soybean oil is added in an amount of 10-50 g, and the n-hexane is added in an amount of 50-200 g.

[0023] In the aforementioned method for preparing a modified biochar / PBAT mulch film with high water vapor barrier properties, in step S2b, the ball-milled biochar is mixed with epoxidized soybean oil and stirred at 100-200° C. for 1-3 hours.

[0024] In the aforementioned method for preparing a modified biochar / PBAT mulch film with high water vapor barrier properties, in step S1b, step S2a and step S2b, the drying treatment conditions are all drying at 60° C. for 24 hours.

[0025] The beneficial effects of the present invention are:

[0026] 1. The present invention combines flaky biochar, modified biochar and PBAT mulch film. The addition of flaky biochar material can form more barrier layers in the film, making the effective path for water vapor to pass through the film more tortuous, reducing the water vapor transmission rate, and utilizing the multiple epoxy groups contained in epoxidized soybean oil. At high temperatures, some epoxy groups will open the ring and react with the hydroxyl and carboxyl groups on the surface of biochar. Therefore, epoxy groups will be grafted on the surface of biochar. The epoxy groups grafted on biochar will open the ring and react with the hydroxyl and carboxyl groups at both ends of the PBAT and PPC molecular chains during twin-screw melt blending, achieving a cross-linking effect, thereby improving the water vapor barrier performance of the PBAT mulch film;

[0027] 2. The present invention has opened up a new method for modifying PBAT mulch with biochar, which not only greatly improves the water vapor barrier performance of the PBAT mulch, facilitating its application in the field of agricultural mulch, but also uses low-cost biochar for filling, reducing the cost of materials. DETAILED DESCRIPTION

[0028] The present invention will be further described below with reference to the embodiments.

[0029] A method for preparing a modified biochar / PBAT mulch film with high water vapor barrier performance of the present invention comprises the following steps:

[0030] S1. Preparation of flaky biochar, comprising the following steps:

[0031] S1a, crushing plant straw into straw powder, adding the straw powder into a container containing sodium hydroxide solution and stirring evenly, then pouring the sodium hydroxide solution mixed with the straw powder into a ball mill for wet ball milling to obtain a mixed slurry;

[0032] The plant straw is one of wheat straw, corn straw, rice straw and soybean straw, the plant straw is crushed to 500 mesh and 5-10 g is taken, the molar concentration of the sodium hydroxide solution is 0.1-1 mol / L, and the amount of the sodium hydroxide solution added is 20-50 ml; the sodium hydroxide solution mixed with the straw powder is processed in a ball mill at a rotation speed of 100-300 rpm, and the wet ball milling is performed for 3-5 hours;

[0033] S1b, washing the obtained mixed slurry with deionized water until it is neutral and drying it, the drying treatment conditions are all drying at 60°C for 24 hours to obtain activated straw powder, and then placing the activated straw powder in a tubular furnace for carbonization treatment to obtain flaky biochar, wherein the carbonization treatment temperature is 300-600°C, and the carbonization is carried out under nitrogen protection for 3-5 hours;

[0034] The formation process of biochar with flake structure is as follows: first, the lignin part of straw powder is removed under alkaline solution conditions to make the structure soft, and then the alkaline solution and straw powder are added into the ball mill under wet ball milling conditions, and the zirconium oxide balls rub and crush the remaining part of the straw powder into flake structure during high-speed rotation;

[0035] The addition of flaky biochar material can form more barrier layers in the film, making the effective path for water vapor to pass through the film more tortuous, reducing the rate of water vapor transmission, and thus improving the water vapor barrier performance of the composite film;

[0036] S2. Preparation of modified biochar, comprising the following steps:

[0037] S2a, biochar preparation, crushing plant straw into straw powder, then washing the straw powder with deionized water to remove water-soluble impurities and drying the straw powder, the drying condition is drying at 60°C for 24 hours, then adding the dried straw powder to a tubular furnace for carbonization treatment to obtain straw biochar, then placing the straw biochar in a ball mill for ball milling treatment to obtain ball-milled biochar, wherein the carbonization temperature is 300-600°C, and the carbonization is carried out under nitrogen protection for 3-5 hours;

[0038] The plant straw is one of wheat straw, corn straw, rice straw and soybean straw, the plant straw is crushed to 500-1000 mesh, and the straw powder is washed at least three times with deionized water; the straw biochar is placed in a ball mill at a rotation speed of 100-300 rpm, ball milled for 2-5 hours, and the obtained ball-milled biochar particle size is 200-300 nm;

[0039] S2b, biochar modification, adding the prepared ball-milled biochar to a container containing epoxidized soybean oil for heating and stirring until the ball-milled biochar and the epoxidized soybean oil react, adding n-hexane and stirring after the liquid in the container cools down, dissolving the excess epoxidized soybean oil in n-hexane, separating the biochar by centrifugation, adding ethanol to the biochar for washing and centrifugation, retaining the bottom product and drying it to obtain modified biochar, and the drying conditions are all at 60°C for 24 hours;

[0040] The ball-milled biochar is 1-10 g, the amount of epoxy soybean oil added is 10-50 g, and the amount of n-hexane added is 50-200 g; the ball-milled biochar and the epoxy soybean oil are mixed and stirred at 100-200° C. for 1-3 hours;

[0041] S3, the preparation of the composite membrane comprises the following steps:

[0042] S3a, mixing the PBAT material with the flaky biochar and the modified biochar, and melt blending them through a twin-screw extruder granulator to obtain modified biochar / PBAT composite particles, and then placing the composite particles in a film blowing machine for film blowing to obtain a modified biochar / PBAT ground film;

[0043] Epoxidized soybean oil contains multiple epoxy groups. At high temperatures, some epoxy groups will open their rings and react with the hydroxyl and carboxyl groups on the surface of biochar, so epoxy groups will be grafted onto the surface of biochar. The epoxy groups grafted onto biochar will open their rings and react with the hydroxyl and carboxyl groups at both ends of the PBAT and PPC molecular chains during twin-screw melt blending, achieving a cross-linking effect, thereby improving the performance of the mulch film.

[0044] The specific process is as follows:

[0045] Epoxidized soybean oil is a kind of substance containing multiple epoxy groups. Epoxy groups can open the ring and react with hydroxyl and carboxyl groups at high temperature. There are hydroxyl and carboxyl groups on the surface of ball-milled biochar, so one or several epoxy groups in epoxidized soybean oil will react with the hydroxyl and carboxyl groups on the surface of biochar, and the remaining epoxy functional groups will be grafted on the surface of biochar. In this way, the surface of the modified biochar will have multiple epoxy functional groups. The PBAT polyester molecular chain contains terminal hydroxyl and terminal carboxyl groups. After we add the modified biochar, during the high-temperature melt blending of the twin-screw extruder, the epoxy functional groups on the surface of the modified biochar will also open the ring and react with the hydroxyl and carboxyl groups at both ends of the PBAT molecular chain to form a cross-linked structure, thereby reducing the free volume between molecules, slowing down the penetration of water molecules, and enhancing the water vapor barrier performance.

[0046] Comparative Examples of the Present Invention

[0047] 80 parts of PBAT and 20 parts of PPC are mixed evenly, wherein PBAT is polybutylene terephthalate-adipate, and PPC is polypropylene carbonate, and melt blending is performed through a twin-screw extruder, and the temperature of the twin-screw extruder is adjusted to 140 degrees in zone 1, 145 degrees in zone 2, 150 degrees in zone 3, 160 degrees in zone 4, 150 degrees in zone 5, and 150 degrees in zone 6, and fully biodegradable particles are obtained by pelletizing, and the particles are added to a film blowing machine for film blowing, and the temperature of the film blowing machine is adjusted to 150 degrees in zone 1, 155 degrees in zone 2, 160 degrees in zone 3, 165 degrees in zone 4, 165 degrees in zone 5, and 160 degrees in zone 6 to obtain a fully biodegradable mulch film;

[0048] The water vapor permeability of the ground film was tested to be 623g / m 2 ·After 24 hours, the tensile strength is 23.5MPa and the elongation at break is 407%.

[0049] Embodiment 1 of the present invention

[0050] The wheat straw was crushed into 500 meshes, 5 g of straw powder was added into 50 ml of 1 mol / L sodium hydroxide solution, stirred evenly, and wet-milled in a ball mill at 300 rpm for 5 hours to obtain a mixed slurry, which was washed with deionized water until neutral, and dried at 60 degrees for 24 hours; the dried and activated straw powder was placed in a tubular furnace, and carbonized at 600 degrees under nitrogen protection for 5 hours to obtain flaky biochar;

[0051] After 80 parts of PBAT, 20 parts of PPC, and 10 parts of flaky biochar are uniformly mixed, melt blended in a twin-screw extruder granulator, the temperature of the twin-screw extruder is adjusted to 140 degrees in zone 1, 145 degrees in zone 2, 150 degrees in zone 3, 160 degrees in zone 4, 150 degrees in zone 5, and 150 degrees in zone 6, and fully biodegradable particles are obtained by pelletizing. The particles are added to a film blowing machine for film blowing, and the temperature of the film blowing machine is adjusted to 150 degrees in zone 1, 155 degrees in zone 2, 160 degrees in zone 3, 165 degrees in zone 4, 165 degrees in zone 5, and 160 degrees in zone 6 to obtain a biochar-modified fully biodegradable mulch film;

[0052] The film was tested and found to have a water vapor weight of 326 g / m2 per unit area within 24 hours. 2 , the tensile strength is 25.4MPa and the elongation at break is 413%.

[0053] Embodiment 2 of the present invention

[0054] The wheat straw was crushed into 500 mesh, and then the straw powder was washed three times with deionized water to remove water-soluble impurities, dried at 60 degrees for 24 hours, and an appropriate amount of straw powder was carbonized in a tubular furnace at 450 degrees under nitrogen protection for 5 hours to obtain wheat straw biochar;

[0055] The wheat straw biochar was placed in a ball mill and ball-milled at 300 rpm for 5 hours to obtain ball-milled biochar with a particle size of about 200 nm; 1 g of the ball-milled biochar was added to 10 g of epoxidized soybean oil and stirred at 140 degrees for 3 hours to allow the epoxy groups of the epoxidized soybean oil to open and react with the functional groups on the surface of the biochar; after cooling, 50 g of n-hexane was added and stirred to allow the excess epoxidized soybean oil to dissolve in the n-hexane; the biochar was separated by centrifugation, and then ethanol was added to the mixture for cleaning and centrifugation, the bottom product was retained, and dried to obtain modified biochar;

[0056] 80 parts of PBAT, 20 parts of PPC, and 10 parts of modified biochar are uniformly mixed, and then melt-blended by a twin-screw extruder granulator. The temperature of the twin-screw extruder is adjusted to 140 degrees in zone 1, 145 degrees in zone 2, 150 degrees in zone 3, 160 degrees in zone 4, 150 degrees in zone 5, and 150 degrees in zone 6. Fully biodegradable particles are obtained by pelletizing, and the particles are added to a film blowing machine for film blowing. The temperature of the film blowing machine is adjusted to 150 degrees in zone 1, 155 degrees in zone 2, 160 degrees in zone 3, 165 degrees in zone 4, 165 degrees in zone 5, and 160 degrees in zone 6 to obtain a biochar-modified fully biodegradable mulch film.

[0057] The film was tested and found to have a water vapor weight of 207.3 g / m2 per unit area within 24 hours. 2 The tensile strength is 26.1MPa and the elongation at break is 481.6%. All performances have been improved, among which the water vapor barrier performance has been significantly improved.

[0058] Embodiment 3 of the present invention

[0059] The wheat straw was crushed into 500 meshes, 10 g of straw powder was added into 50 ml of 0.1 mol / L sodium hydroxide solution, stirred evenly, and wet-milled in a ball mill at 200 rpm for 5 hours to obtain a mixed slurry, which was washed with deionized water until neutral, and dried at 60 degrees for 24 hours; the dried and activated straw powder was placed in a tubular furnace, and carbonized at 600 degrees under nitrogen protection for 5 hours to obtain flaky biochar;

[0060] Then, a portion of the straw powder was washed three times with deionized water to remove water-soluble impurities, dried at 60 degrees for 24 hours, and an appropriate amount of straw powder was carbonized in a tubular furnace at 450 degrees under nitrogen protection for 5 hours to obtain wheat straw biochar; the wheat straw biochar was placed in a ball mill and ball-milled at 200 revolutions for 3 hours to obtain ball-milled biochar with a particle size of about 300 nm;

[0061] 5 g of the ball-milled biochar was added to 30 g of epoxidized soybean oil and stirred at 140 degrees for 3 hours to allow the epoxy groups of the epoxidized soybean oil to open and react with the functional groups on the surface of the biochar. After cooling, 100 g of n-hexane was added and stirred to dissolve the excess epoxidized soybean oil in the n-hexane. The biochar was separated by centrifugation, and then ethanol was added to the mixture for cleaning and centrifugation. The bottom product was retained and dried to obtain modified biochar.

[0062] 80 parts of PBAT, 20 parts of PPC, 10 parts of flaky biochar and 10 parts of modified biochar are uniformly mixed, melt blended by a twin-screw extruder granulator, the temperature of the twin-screw extruder is adjusted to 140 degrees in zone 1, 145 degrees in zone 2, 150 degrees in zone 3, 160 degrees in zone 4, 150 degrees in zone 5 and 150 degrees in zone 6, and fully biodegradable particles are obtained by pelletizing, and the particles are added to a film blowing machine for film blowing, and the temperature of the film blowing machine is adjusted to 150 degrees in zone 1, 155 degrees in zone 2, 160 degrees in zone 3, 165 degrees in zone 4, 165 degrees in zone 5 and 160 degrees in zone 6 to obtain a biochar-modified fully biodegradable mulch film;

[0063] The water vapor permeability of the ground film was tested to be 183g / m 2 ·After 24 hours, the tensile strength is 26.7MPa and the elongation at break is 482%.

[0064] Embodiment 4 of the present invention

[0065] According to the flake biochar and modified biochar prepared in Example 3, 20 parts of flake biochar and 20 parts of modified biochar were taken;

[0066] 80 parts of PBAT, 20 parts of PPC, 20 parts of flaky biochar and 20 parts of modified biochar are uniformly mixed, melt blended by a twin-screw extruder granulator, the temperature of the twin-screw extruder is adjusted to 140 degrees in zone 1, 145 degrees in zone 2, 150 degrees in zone 3, 160 degrees in zone 4, 150 degrees in zone 5 and 150 degrees in zone 6, and fully biodegradable particles are obtained by pelletizing, and the particles are added to a film blowing machine for film blowing, and the temperature of the film blowing machine is adjusted to 150 degrees in zone 1, 155 degrees in zone 2, 160 degrees in zone 3, 165 degrees in zone 4, 165 degrees in zone 5 and 160 degrees in zone 6 to obtain a biochar-modified fully biodegradable mulch film;

[0067] The water vapor permeability of the ground film was tested to be 161g / m 2 ·After 24 hours, the tensile strength is 27.4MPa and the elongation at break is 507%.

[0068] In summary, the mulch films prepared by adding flaky biochar and modified biochar in Example 3 and Example 4 have lower water vapor permeability and stronger water vapor barrier ability. After being modified with biochar, the water vapor barrier performance of the mulch films can be significantly improved, which is beneficial to their application in the field of agricultural mulch films. In addition, the use of low-cost biochar for filling reduces the cost of materials.

[0069] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for preparing a modified biochar / PBAT mulch film with high water vapor barrier performance, characterized in that: The following steps are involved: S1. Preparation of flaky biochar, comprising the following steps: S1a, crushing plant straw into straw powder, adding the straw powder into a container containing sodium hydroxide solution and stirring evenly, then pouring the sodium hydroxide solution mixed with the straw powder into a ball mill for wet ball milling to obtain a mixed slurry; S1b, washing the obtained mixed slurry with deionized water until it is neutral and drying it to obtain activated straw powder, and then placing the activated straw powder in a tubular furnace for carbonization to obtain flaky biochar; S2. Preparation of modified biochar, comprising the following steps: S2a, biochar preparation, crushing plant straw into straw powder, washing the straw powder with deionized water to remove water-soluble impurities and drying, then adding the dried straw powder to a tubular furnace for carbonization to obtain straw biochar, and then placing the straw biochar in a ball mill for ball milling to obtain ball-milled biochar; S2b, biochar modification, adding the prepared ball-milled biochar to a container containing epoxidized soybean oil, heating and stirring, until the ball-milled biochar and the epoxidized soybean oil react, adding n-hexane and stirring after the liquid in the container cools, dissolving excess epoxidized soybean oil in n-hexane, separating the biochar by centrifugation, adding ethanol to the biochar for washing and centrifugation, retaining the bottom product and drying it to obtain modified biochar; In step S2b, the ball-milled biochar is used in an amount of 1-10 g, the epoxy soybean oil is added in an amount of 10-50 g, and the n-hexane is added in an amount of 50-200 g; In step S2b, the ball-milled biochar and epoxidized soybean oil are mixed and stirred at 100-200° C. for 1-3 hours; S3, the preparation of the composite membrane comprises the following steps: S3a, mixing the PBAT material with flaky biochar and modified biochar, melt blending through a twin-screw extruder granulator to obtain modified biochar / PBAT composite particles, and then placing the composite particles in a film blowing machine for film blowing to obtain a modified biochar / PBAT ground film.

2. The method for preparing a modified biochar / PBAT mulch film with high water vapor barrier performance according to claim 1, characterized in that: In step S1a and step S2a, the plant straw is one of wheat straw, corn straw, rice straw and soybean straw.

3. The method for preparing a modified biochar / PBAT mulch film with high water vapor barrier performance according to claim 2, characterized in that: In step S1a, the plant straw is crushed to 500 mesh and 5-10 g is taken, the molar concentration of the sodium hydroxide solution is 0.1-1 mol / L, and the amount of the sodium hydroxide solution added is 20-50 ml.

4. The method for preparing a modified biochar / PBAT mulch film with high water vapor barrier performance according to claim 3, characterized in that: In step S1a, the sodium hydroxide solution mixed with the straw powder is processed in a ball mill at a rotation speed of 100-300 rpm, and the wet ball milling is performed for 3-5 hours.

5. The method for preparing a modified biochar / PBAT mulch film with high water vapor barrier performance according to claim 4, characterized in that: In step S1b and step S2a, the carbonization treatment temperature is 300-600°C, and the carbonization is carried out under nitrogen protection for 3-5 hours.

6. A method for preparing a modified biochar / PBAT mulch film with high water vapor barrier performance according to claim 1 or 5, characterized in that: In step S2a, the plant straw is crushed to 500-1000 mesh, and the straw powder is washed at least three times with deionized water.

7. The method for preparing a modified biochar / PBAT mulch film with high water vapor barrier performance according to claim 6, characterized in that: In step S2a, the straw biochar is placed in a ball mill for treatment at a rotation speed of 100-300 rpm and ball milled for 2-5 hours, and the obtained ball-milled biochar has a particle size of 200-300 nm.

8. A method for preparing a modified biochar / PBAT mulch film with high water vapor barrier performance according to claim 1 or 7, characterized in that: In step S1b, step S2a and step S2b, the drying treatment conditions are all drying at 60° C. for 24 hours.