Method for preparing degradable straw mulch by enzyme

Abstract

The application provides a method for preparing degradable straw mulch by using enzymes, and comprises the following steps: crushing straw, then adding the straw into a NaOH solution, heating and cooking, washing the cooked straw to neutral, drying to obtain straw powder for standby; adding the straw powder into an acetic acid-sodium acetate buffer solution with pH 4.5-5.0 and dissolved with biological enzymes, treating at 45-55 DEG C for 12-16 hours to obtain an enzymolysis mixture; stirring and treating the obtained enzymolysis mixture with a polyvinyl alcohol solution at 70-90 DEG C for 25-35 minutes, adding a crosslinking agent and a plasticizer to continue reacting at 70-90 DEG C for 55-65 minutes to obtain a film solution; and preparing straw degradable film from the film solution. The straw degradable film prepared by the application has excellent hydrophobic property, is beneficial to the film to be quickly broken in the use process without being affected by the external humid environment, and the use stability of the film is enhanced.

Description

Technical Field

[0001] This invention belongs to the field of biodegradable membrane material manufacturing technology, specifically relating to an enzymatic method for preparing biodegradable straw mulch film. Background Technology

[0002] China is a major agricultural country, producing approximately 670 million tons (dry weight) of crop straw annually. Crop straw contains natural macromolecules such as cellulose, lignin, and polysaccharides, which can be converted into organic fertilizer under environmental conditions. It also contains trace elements like iron and zinc, giving it significant economic value. However, due to limited recycling channels and complex utilization methods, farmers and small factories cannot afford the costs of recycling, leading to the burning of most straw, causing environmental pollution and resource waste. To address these problems caused by straw burning, current comprehensive utilization of straw mainly involves its use as feed, fuel, fertilizer, industrial raw material, and substrate—a process known as "five-fold utilization."

[0003] China has a vast land area and a large crop cultivation area, often using plastic film mulching to assist crop growth. Plastic film mulching refers to a cultivation method that uses different types of plastic film to cover the soil surface. Plastic films are characterized by good light transmission, poor thermal conductivity, and impermeability to air. Covering the soil surface with plastic film can improve the relationship between water, fertilizer, air, heat, and biological factors in the topsoil, creating a favorable ecological environment for plant growth and development. However, the polyethylene plastic film currently used is not completely biodegradable. With the increase in the amount of plastic film used and the increase in its service life, a large amount of plastic film fragments remain in the soil, causing not only environmental pollution but also damaging the soil structure, affecting crop growth, and reducing yield.

[0004] Currently, biodegradable mulch films are mainly divided into photodegradable mulch films, fully biodegradable mulch films, and photo-biodegradable mulch films. Photodegradable mulch films and photo-biodegradable mulch films are highly dependent on the environment and exhibit incomplete degradation, and have gradually faded from the market. Biodegradable mulch films have become a major development trend. Currently, the most researched biodegradable mulch films both domestically and internationally are starch films, which are made from starch as a raw material and processed with some additives. However, starch films have problems such as poor water resistance and low mechanical properties, making large-scale use difficult. Cellulose, also a natural polymer material, has great utilization value.

[0005] In recent years, biodegradable mulch films made from straw have developed rapidly, but they also have certain drawbacks. For example, their relatively hard texture makes mechanical laying difficult, and their brittleness prevents them from adhering tightly to the soil, reducing their heat and moisture retention effects. These technical problems urgently need to be solved to ensure the widespread use of straw mulch films.

[0006] Chinese patent document CN 103061182A (application number 201310049537.2) discloses an enzymatic clean production method for straw spinning pulp. The steps are as follows: The straw is crushed into small pieces no longer than 1.5 cm, washed, and placed in a reaction vessel. Pulp enzyme and clean water are added, and the pH is adjusted to 8.0–8.9. The mixture is stirred under normal pressure at a speed of 60–80 rpm and a reaction temperature of 50–55°C for 45–60 minutes. Then, a non-polluting alkaline hydrogen peroxide solution is added to dissolve the pulp. The mixture is stirred under normal pressure at a speed of 80–150 rpm and a reaction temperature of 50–75°C for 150–210 minutes. Under the synergistic effect of pulp enzyme and non-polluting alkaline hydrogen peroxide, coarse spinning pulp is produced. The pulp is then purified, bleached, rinsed, and dried using a pollution-free process to produce a finished product of straw spinning pulp suitable for producing degradable plastic film.

[0007] Chinese patent document CN106750564A (application number 201710035656.0) discloses a high-barrier biodegradable mulch film, the raw materials of which are made from the following components in parts by weight: 9-12 parts wheat straw fiber, 25-35 parts corn starch, 3-5 parts sodium hydroxide, 1-2 parts polyvinyl alcohol, 1-2 parts carboxymethyl cellulose, 3-5 parts glyoxal, 5-10 parts glycerol, 0.5-1 part cellulase, 1-2 parts stabilizer, and 90-100 parts deionized water. The raw material composition involved in this invention is complex, which is not conducive to market promotion and application.

[0008] In the above-described invention, neither straw spinning pulp nor high-barrier biodegradable mulch film effectively utilizes the lignin, hemicellulose, and other components contained in the straw after enzyme treatment in the treatment solution, resulting in a certain waste of resources. Summary of the Invention

[0009] To address the shortcomings of existing technologies, this invention provides a method for preparing biodegradable straw mulch film using an enzymatic process.

[0010] The technical problem solved by this invention is to provide a biodegradable mulch film that fully utilizes straw components, has high mechanical strength, soft texture, simple processing, and is environmentally friendly. This film can enhance the softness of the mulch film while meeting the requirements of mechanical mulching in the field, thereby achieving better heat preservation, moisture retention, and weed suppression effects.

[0011] The technical solution of the present invention is as follows:

[0012] A method for preparing biodegradable straw mulch film using an enzymatic process includes the following steps:

[0013] (1) Crush the straw, then add the straw to NaOH solution, heat and cook, wash the cooked straw until neutral, and dry to obtain straw powder for later use;

[0014] (2) Add the straw powder from step (1) to an acetate-sodium acetate buffer solution with pH 4.5-5.0 containing biological enzymes, and treat at 45-55℃ for 12-16h to obtain an enzymatic hydrolysis mixture.

[0015] (3) The enzymatic hydrolysis mixture obtained in step (2) is stirred with polyvinyl alcohol solution at 70-90℃ for 25-35 min, and crosslinking agent and plasticizer are added at 70-90℃ and the reaction is continued for 55-65 min to obtain membrane solution;

[0016] (4) Prepare a biodegradable straw membrane from the membrane solution in step (3).

[0017] According to a preferred embodiment of the present invention, the NaOH mass concentration in step (1) is 15-20 g / L, and the mass-volume ratio of straw to NaOH solution is (0.8-1.5):30 (g / mL).

[0018] According to a preferred embodiment of the present invention, the cooking temperature in step (1) is 75-95°C and the cooking time is 7-9 hours.

[0019] According to a preferred embodiment of the present invention, the straw in step (1) is corn straw.

[0020] According to a preferred embodiment of the present invention, in step (1), the straw is crushed through an 80-100 mesh sieve.

[0021] According to a preferred embodiment of the present invention, the mass-to-volume ratio of the bio-enzyme to the buffer solution in step (2) is (0.7-2):50 (g / mL), and the bio-enzyme is laccase or xylanase.

[0022] More preferably, the mass ratio of laccase to xylanase is (0.8-1.2):2.

[0023] Further preferred, the mass-to-volume ratio of straw powder to buffer solution, based on dry weight, is 1:(45-55)(g / mL).

[0024] According to a preferred embodiment of the present invention, the mass concentration of the polyvinyl alcohol solution in step (3) is 0.08-0.12 g / mL, the mass ratio of polyvinyl alcohol to straw powder on a dry weight basis is 1:(4.5-5.5), the crosslinking agent is glutaraldehyde, the mass ratio of glutaraldehyde to polyvinyl alcohol is (0.4-1):10, and the plasticizer is glycerol, the mass ratio of glycerol to polyvinyl alcohol is (1-2.2):10.

[0025] More preferably, the mass ratio of glutaraldehyde to polyvinyl alcohol is (0.4-0.6):10; the plasticizer is glycerol, and the mass ratio of glycerol to polyvinyl alcohol is (1.8-2.2):10.

[0026] According to a preferred embodiment of the present invention, in step (4), the membrane liquid from step (3) is poured into a polytetrafluoroethylene plate, coated with a scraper, dried in an oven, and then the membrane is peeled off to obtain a biodegradable straw membrane.

[0027] The biodegradable straw film prepared by the above method can be used in crop cultivation.

[0028] Beneficial effects

[0029] 1. This invention provides a biodegradable mulch film that fully utilizes straw components, has high mechanical strength, is soft in texture, is simple to process, and is environmentally friendly. While meeting the requirements of mechanical mulching in the field, it can enhance the softness of the mulch film and achieve better heat preservation, moisture retention, and weed suppression effects.

[0030] 2. The biodegradable straw film prepared by this invention has significant advantages in mechanical strength and can be promoted and applied in the market.

[0031] 3. The biodegradable straw membrane prepared by this invention has excellent hydrophobic properties, which helps the membrane to break quickly without being affected by the external humid environment during use, thus enhancing the stability of the membrane. Attached Figure Description

[0032] Figure 1 These are surface hydrophilicity test images of the straw biodegradable films prepared in Examples 1-2 and Comparative Examples 1-3. Detailed Implementation

[0033] The present invention will be further described below with reference to embodiments, but the scope of protection of the present invention is not limited thereto.

[0034] All details not described in the embodiments are based on existing technology in the field.

[0035] Source of materials

[0036] The laccase used in the experiment was purchased from Shanghai Yuanye Biotechnology Co., Ltd., and the xylanase and cellulase were purchased from Beijing Solarbio Technology Co., Ltd.

[0037] Example 1

[0038] A method for preparing biodegradable mulch film using an enzymatic process includes the following steps:

[0039] (1) Use a straw crusher to crush corn stalks and select stalks that have been screened through an 80-100 mesh standard sieve for later use.

[0040] (2) Take 2g of the straw after sieving in step (1) and add it to 60mL of 15g / L NaOH solution. Heat it to 80℃ and boil it for 8h. After boiling, wash the straw with deionized water until it is neutral and dry it to obtain straw powder for later use.

[0041] (3) Take 1g of the straw powder obtained by drying in step (2) and add it to 50mL of acetic acid-sodium acetate buffer solution with pH 4.6. Add 0.5g of laccase and 1g of xylanase and react at 50℃ for 12h to obtain an enzymatic hydrolysis mixture.

[0042] (4) Heat 5g of polyvinyl alcohol to dissolve in 50mL of deionized water to make a polyvinyl alcohol solution, add it to the enzymatic hydrolysis mixture prepared in step (3), react at 90℃ for 30min, add 1mL of glycerol and 1mL of glutaraldehyde with a mass concentration of 25% at 90℃, and continue to react for 60min to obtain the membrane solution.

[0043] (5) Pour the membrane liquid obtained in step (4) onto a polytetrafluoroethylene plate for scraper coating, and then dry and peel off the membrane to obtain straw biodegradable membrane F-1. The thickness of the straw biodegradable membrane is 0.02 mm.

[0044] Example 2

[0045] A method for preparing biodegradable mulch film using an enzymatic process includes the following steps:

[0046] (1) Use a straw crusher to crush corn stalks and select stalks that have been screened through an 80-100 mesh standard sieve for later use.

[0047] (2) Take 2g of the straw after sieving in step (1) and add it to 60mL of 20g / L NaOH solution. Heat to 95℃ and boil for 8h. Wash the straw after boiling with deionized water until neutral and dry to obtain straw powder for later use.

[0048] (3) Take 1g of the straw powder obtained by drying in step (2) and add it to 50mL of acetic acid-sodium acetate buffer solution with pH 4.6. Add 0.25g of laccase and 0.5g of xylanase and react at 50℃ for 16h to obtain an enzymatic hydrolysis mixture.

[0049] (4) Heat 5g of polyvinyl alcohol to dissolve in 50mL of deionized water to make a polyvinyl alcohol solution, add it to the enzymatic hydrolysis mixture prepared in step (3), react at 90℃ for 30min, add 1mL of glycerol and 1mL of glutaraldehyde with a mass concentration of 25% at 90℃, and continue to react for 60min to obtain the membrane solution.

[0050] (5) Pour the membrane liquid obtained in step (4) onto a polytetrafluoroethylene plate and coat it with a scraper. After drying, peel off the membrane to obtain straw biodegradable membrane F-2. The thickness of the straw biodegradable membrane is 0.02 mm.

[0051] Comparative Example 1

[0052] The difference from Example 1 is that the corn stalks in Example 1 are replaced with wheat stalks, while everything else is the same, to obtain the straw biodegradable film F-3.

[0053] Comparative Example 2

[0054] The difference from Example 1 is that the laccase in Example 1 is replaced with cellulase, while everything else is the same, to obtain straw biodegradable film F-4.

[0055] Comparative Example 3

[0056] The difference from Example 1 is that the enzymatic hydrolysis mixture obtained in step (3) is separated into solid and liquid parts, and the liquid part is replaced by an equal amount of water. The water and solid parts are mixed to replace the enzymatic hydrolysis mixture for subsequent reactions. Everything else is the same, and the straw biodegradable membrane F-5 is obtained.

[0057] Example 1

[0058] The straw biodegradable films prepared in Examples 1-2 and Comparative Examples 1-3 had their tensile loads of 0.02 mm films measured according to GB / T 1040.1-2006. The results are shown in the table below:

[0059]

[0060]

[0061] The above results show that the straw biodegradable films prepared in Examples 1-2 and Comparative Examples 2-3 all meet the mechanical property requirements of GB 13735-2017 (polyethylene blown agricultural ground covering film), which states that the tensile load of a 0.02mm film should be ≥3.0. The straw biodegradable film prepared by Comparative Example 1 using wheat straw has the worst mechanical strength. The mechanical strength of the straw biodegradable films F-1 and F-2 prepared by this invention is significantly better than that of the comparative examples.

[0062] Example 2

[0063] The straw biodegradable films prepared in Examples 1-2 and Comparative Examples 1-3 were tested for softness according to GB / T 8942-2016. The results are shown in Table 2 below:

[0064] Table 2

[0065] sample Softness (mN) F-1 54 F-2 62 F-3 49 F-4 42 F-5 43

[0066] The results in Table 2 show that the straw biodegradable films F-1 and F-2 prepared by the present invention can maintain a certain level of softness while ensuring film strength, which meets the application requirements. The biodegradable films prepared by comparative examples 1-3 have lower softness.

[0067] Example 3

[0068] The biodegradable straw films prepared in Examples 1-2 and Comparative Examples 1-3 had their surface hydrophilicity determined according to GB / T30693-2014. The results are as follows... Figure 1 As shown, the hydrophobicity of the membrane surface is represented by the static contact angle θ. A larger contact angle indicates a more hydrophobic membrane surface, making it less prone to wetting. The hydrophobicity of the straw biodegradable membranes F-1 and F-2 prepared by this invention is superior to that of the biodegradable membranes prepared in Comparative Examples 1-3, especially superior to the biodegradable membrane F-5 prepared in Comparative Example 3 using water instead of the enzymatic hydrolysis liquid portion. The straw biodegradable membrane prepared by this invention exhibits excellent hydrophobic properties, which facilitates rapid rupture during use without being affected by external humid environments, thus enhancing the membrane's stability.

[0069] The straw biodegradable films F-1 and F-2 prepared by this invention have significant advantages in mechanical strength. Through market promotion and application, the straw biodegradable films F-1 and F-2 prepared by this invention can maintain a certain level of softness while ensuring film strength, which meets the needs of application. The straw biodegradable films prepared by this invention have excellent hydrophobic properties, which is conducive to the rapid rupture of the film during use without being affected by the external humid environment, thus enhancing the stability of the film in use.

Claims

1. A method for preparing degradable straw mulch by enzymatic method, characterized in that, It comprises the following steps: (1) crushing the straw, then adding the straw into NaOH solution, heating and cooking, washing the cooked straw to neutral, drying to obtain straw powder for standby; the straw is corn straw; (2) adding the straw powder in step (1) into acetic acid-sodium acetate buffer solution with pH 4.5-5.0 and dissolved with biological enzyme, treating at 45-55℃ for 12-16h to obtain enzyme hydrolysis mixture; the biological enzyme is laccase and xylanase; (3) stirring the enzyme hydrolysis mixture obtained in step (2) with polyvinyl alcohol solution at 70-90℃ for 25-35min, adding crosslinking agent and plasticizer to continue reacting at 70-90℃ for 55-65min to obtain film solution; (4) obtaining straw degradable film from the film solution in step (3).

2. The method of claim 1, wherein, The mass concentration of NaOH in step (1) is 15-20g / L, and the mass-volume ratio of straw to NaOH solution is (0.8-1.5):30 (g / mL).

3. The method of claim 1, wherein, The cooking temperature in step (1) is 75-95℃, and the cooking time is 7-9h.

4. The method of claim 1, wherein, The straw is crushed to pass through 80-100 mesh sieve.

5. The method of claim 1, wherein, In step (2), the mass-volume ratio of biological enzyme to buffer solution is (0.7-2):50 (g / mL).

6. The method of claim 1, wherein, The mass ratio of laccase to xylanase is (0.8-1.2):

2.

7. The method of claim 1, wherein, In step (2), the mass-volume ratio of straw powder to buffer solution is 1:(45-55) (g / mL) in dry weight.

8. The method of claim 1, wherein, In step (3), the mass concentration of polyvinyl alcohol solution is 0.08-0.12g / mL, the mass ratio of polyvinyl alcohol to straw powder is 1:(4.5-5.5) in dry weight, the crosslinking agent is glutaraldehyde, the mass ratio of glutaraldehyde to polyvinyl alcohol is (0.4-1):10, and the plasticizer is glycerol, the mass ratio of glycerol to polyvinyl alcohol is (1-2.2):

10.

9. The method of claim 8, wherein, The mass ratio of glutaraldehyde to polyvinyl alcohol is (0.4-0.6):10, and the plasticizer is glycerol, the mass ratio of glycerol to polyvinyl alcohol is (1.8-2.2):

10.

10. The method of claim 1, wherein, In step (4), pouring the film solution in step (3) into a polytetrafluoroethylene plate for doctor blade coating, drying in an oven, and then peeling off the film to obtain straw degradable film.

11. The straw degradable film prepared by the method of any one of claims 1-10 is applied to crop planting.

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