Hemp-based full-degradable mulching film for biological enzyme control in cold region and preparation method

Abstract

The invention discloses a hemp-based full-degradable mulching film for biological enzyme control in a cold region and a preparation method, and belongs to the technical field of agricultural environment-friendly materials. The mulching film is composed of a high-molecular polymer, modified fibrilia and bio-enzyme microcapsules. By adding the nano fibrilia subjected to hydrophobic modification, the flexibility and tear resistance of the mulching film at low temperature are remarkably improved, and the problem of low-temperature embrittlement in cold regions is effectively solved. According to the invention, a sodium alginate-calcium chloride-chitosan system is adopted to embed degrading enzyme to form microcapsules, so that the performance of the mulching film is stable in the growth period of crops, the enzymatic reaction can be activated through farming operation after the crops are harvested, rapid and controllable degradation is realized, and complete decomposition in a limited window period in a cold region is ensured. The mulching film disclosed by the invention has excellent low-temperature use performance and precise degradation time sequence control capability, is biodegradable in all components, is environment-friendly and is particularly suitable for cold regions.

Description

Technical Field

[0001] This invention relates to the field of agricultural mulch film and environmentally friendly materials technology, and in particular to a bio-enzyme-controlled fully degradable hemp-based mulch film for cold regions and its preparation method. Background Technology

[0002] Mulching technology plays an important role in modern agricultural production, but traditional polyethylene mulch film is difficult to degrade, causing serious "white pollution." While fully biodegradable mulch films, such as those based on starch, bamboo, and straw, have solved the pollution problem to some extent, they have two prominent drawbacks in cold-climate environments: First, there is the problem of low-temperature embrittlement: cold regions have low accumulated temperature and large diurnal temperature differences. The main components of existing fully degradable mulch films (such as starch, PLA, PBAT, etc.) have significantly reduced flexibility at low temperatures, making them prone to embrittlement and cracking. They cannot form a complete covering layer and are prone to holes or tears in the early stages of crop growth, thus failing to play a good role in water retention and moisture conservation.

[0003] Second, there is the issue of mismatched degradation cycles: Cold-region crops have short growing seasons, with limited time from harvest to soil freezing or the following spring sowing. Ordinary fully degradable mulch films rely on microbial degradation, which is extremely slow in low-temperature environments, often leaving large amounts of residue at the time of the following spring sowing, severely impacting subsequent cultivation.

[0004] Therefore, there is an urgent need to develop a new type of mulch film that can maintain good performance in cold and low-temperature environments and can degrade rapidly after use. Summary of the Invention

[0005] In view of the above problems, the present invention provides a bio-enzyme-controlled fully degradable hemp-based mulch film for cold regions and its preparation method. The present invention solves the problems of poor low-temperature toughness and rapid degradation characteristics of mulch films in the prior art.

[0006] This invention provides a bio-enzyme-controlled fully degradable hemp-based mulch film for cold regions, comprising, by weight, 50-99 parts of polymer, 1-50 parts of modified hemp fiber, 1-5 parts of bio-enzyme, and 0-10 parts of other additives. The polymer is at least one of polybutylene terephthalate, polybutylene succinate, polycaprolactone, polylactic acid, and starch; The mulch film also includes bio-enzyme microcapsules with a particle size of 1-5 μm; the bio-enzyme microcapsules are prepared from bio-enzymes.

[0007] Optionally, the mass ratio of modified hemp fiber to polymer is...

[0008] in, Reference temperature; Reference relative humidity; The average annual temperature of the area where the film-laying zone has been located for N consecutive years; The average annual relative humidity of the area where the film-laying zone has been located for N consecutive years; It is a natural constant.

[0009] Optionally, the mass relationship between bio-enzymes, modified hemp fibers, and polymers. for: =

[0010] in, =Bioenzyme / (Modified hemp fiber + polymer); deg is the target degradation time of the mulch film.

[0011] Optionally, the modified hemp fiber is sourced from at least one of ramie, jute, kenaf, flax, hemp, sisal, or Apocynum venetum.

[0012] This invention also discloses a method for preparing a hemp-based fully degradable mulch film, comprising the following steps: S1. Hemp fiber pretreatment; S2. Modify hemp fibers to obtain nano-hemp fiber powder; S3. Preparation of bioenzyme microcapsules; S4. Prepare a film-forming slurry by mixing nano-hemp fiber powder and bio-enzyme microcapsules; S5. The film-forming slurry obtained in step S4 is extruded in an extruder to obtain hemp base film biodegradable masterbatch; S6. A hemp-based fully biodegradable mulch film is produced by using a blown film machine to process biodegradable masterbatch.

[0013] Optionally, the hemp fiber modification in step S2 includes pulverizing the pretreated hemp fiber to a mesh size of 600 or larger, and then preparing nano-hemp fiber powder by a combination of grinding and acid hydrolysis after alkali treatment and siloxane modification.

[0014] Optionally, the alkali treatment involves using 5%-8% sodium hydroxide and reacting at 80-100°C for 3-10 hours to treat the hemp fibers.

[0015] Optionally, the preparation of the bio-enzyme microcapsules in step S3 includes mixing the degrading enzyme with sodium alginate solution, adding it dropwise to calcium chloride solution, preparing microcapsule precursors by ion cross-linking, and then immersing them in chitosan solution for secondary encapsulation.

[0016] Optionally, the concentration of siloxane is 1%-5%.

[0017] Optionally, the specific steps of step S5 are as follows: after the film-forming slurry is mixed evenly by a high-speed mixer, it is extruded in a twin-screw extruder at 120℃~150℃, cooled and pelletized to obtain hemp base film biodegradable masterbatch.

[0018] Compared with the prior art, the present invention has at least the following beneficial effects: 1. Excellent low-temperature toughness: The mulch film made from nano-hemp cellulose extracted from hemp fibers grown in cold regions can still maintain excellent flexibility and mechanical strength in cold and low-temperature environments, effectively avoiding the embrittlement problem of existing fully degradable mulch films at low temperatures, and ensuring continuous water retention and moisture retention functions.

[0019] 2. Rapid and controllable degradation characteristics: The innovative introduction of bio-enzyme microcapsules as degradation accelerators isolates and protects enzyme activity during crop growth, ensuring stable mulch film performance; after crop harvest, enzyme activity can be activated through simple agricultural operations to achieve rapid degradation of the mulch film, ensuring that degradation is completed within a short degradation window and does not affect the spring sowing of the following year.

[0020] 3. Environmentally friendly: Made primarily from natural hemp fiber, it is completely biodegradable, with the final degradation products being water, carbon dioxide, and humus. It not only returns to nature completely but also improves the soil. Detailed Implementation

[0021] To better understand the above-described objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to specific embodiments. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other. Furthermore, the present invention can also be implemented in other ways different from those described herein; therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0022] One specific embodiment of the present invention discloses a bio-enzyme-controlled fully degradable hemp-based mulch film for cold regions, comprising, by mass parts, 50-99 parts of polymer, 1-50 parts of modified hemp fiber, 1-5 parts of bio-enzyme, and 0-10 parts of other additives.

[0023] Preferably, the polymer is one or more of the following: polybutylene terephthalate (PBAT), polybutylene succinate (PBS), polycaprolactone (PCL), polylactic acid (PLA), starch, etc.

[0024] Furthermore, when the polymer is a combination of multiple raw materials, it includes at least polybutylene terephthalate (PBAT), and the mass ratio of PBAT to other polymer raw materials is 7:3-9:1.

[0025] Furthermore, the mass ratio of modified hemp fiber to polymer... ,in, Reference temperature; Reference relative humidity; The average annual temperature of the area where the film-laying zone is located over the past N years; The average annual relative humidity of the area where the film-laying zone is located over the past N years; It is a natural constant.

[0026] Furthermore, the reference temperature is the average annual temperature in China over the past N years or the laboratory set temperature; the reference relative humidity is the average annual relative humidity in China over the past N years or the laboratory set relative humidity.

[0027] Furthermore, the "nearly N years" refers to the past 5 years, such as the current year being 2025, and the past 5 years being 2020-2024; the region refers to extremely cold regions such as Qiqihar City in Heilongjiang Province, Baicheng City in Jilin Province, Heihe City in Heilongjiang Province, or Zhalantun in Inner Mongolia Autonomous Region.

[0028] Furthermore, the mass relationship between bio-enzymes, modified hemp fibers, and polymers... for: =Bioenzyme / (Modified hemp fiber + polymer); where deg is the target degradation time of the mulch film.

[0029] Furthermore, other additives include one or more of the following: antioxidants 2,6-di-tert-butyl-p-cresol, acetylated tributyl citrate, tris[2,4-di-tert-butylphenyl]phosphite, plasticizers epoxidized soybean oil, Irganox 1010, Irganox 1076, etc., which contribute to film formation in biodegradable materials.

[0030] Another specific embodiment of the present invention discloses a method for preparing a bio-enzyme-controlled fully degradable hemp-based mulch film for cold regions, comprising the following steps: S1. Hemp fiber pretreatment; Specifically, the hemp fibers were pretreated by reacting the hemp fiber suspension with the silane coupling agent KH560 at room temperature for 2 hours to increase their water contact angle to over 90 degrees. This reduced the hydrophilicity of the hemp fibers, improved their compatibility with PBAT resin, and enhanced the mechanical properties of the composite mulch film.

[0031] Hemp fiber mainly comes from hemp crops such as ramie, jute, kenaf, flax, hemp, sisal, and apocynum.

[0032] Furthermore, the diameter of the nanofiber cellulose is less than 10 nm.

[0033] S2. Modify hemp fibers to obtain nano-hemp fiber powder; Specifically, the pretreated hemp fibers are pulverized to a fineness of 600 mesh or higher, then treated with alkali and modified with siloxane to remove impurities such as pectin and lignin; subsequently, a combination of mechanical grinding and acid hydrolysis is used to prepare nanoscale hemp fiber powder. Specifically, the alkali treatment steps are as follows: use 5%-8% sodium hydroxide and react at 80-100℃ for 3-10 hours; modify with 1%-5% siloxane.

[0034] Preferably, the concentration of sodium hydroxide is 5% and the concentration of siloxane is 2%.

[0035] S3. Preparation of bioenzyme microcapsules; Specifically, one or more of the following enzymes, such as keratinase, cellulase, laccase, and pectinase, are used as the core degrading enzymes. They are mixed with a 2% sodium alginate solution and then added dropwise to a 3% calcium chloride solution to prepare bio-enzyme microcapsules using an ion cross-linking method.

[0036] Furthermore, the ion crosslinking method specifically involves: adding a mixture containing enzymes and sodium alginate dropwise into a calcium chloride solution to form microcapsule precursors, and then immersing them in a chitosan solution for secondary encapsulation to prepare bioenzyme microcapsules.

[0037] Furthermore, the types and proportions of core degrading enzymes depend on the soil microbial environment, such as 80% cutinase and 20% laccase.

[0038] Furthermore, the particle size of the bioenzyme microcapsules is 1-5 μm.

[0039] S4. Preparation of film-forming slurry; The nanofiber powder obtained in step S2 is dispersed in water to form a matrix solution; the bio-enzyme microcapsules, biodegradable polymer and other additives prepared in step S3 are added to it and the mixture is stirred at high speed until homogeneous.

[0040] Furthermore, the biodegradable polymers include PBAT (polybutylene terephthalate), PBS (polybutylene succinate), PCL (polycaprolactone), PLA (polylactic acid), starch, and other suitable for preparing biodegradable mulch film materials. Other additives include antioxidants, plasticizers, and other film-forming aids that contribute to the biodegradable material.

[0041] Further, the plasticizer is glycerin, and the amount added is 1%-5% of the total mass of the film-forming slurry, preferably 3%; the reinforcing agent is starch or polylactic acid short fiber, and the amount added is 1%-5% of the total mass of the film-forming slurry, preferably 3%.

[0042] Furthermore, the amount of the added bio-enzyme microcapsules is 1%-10% of the dry weight of the nano-hemp cellulose, preferably 2%.

[0043] S5. Masterbatch extrusion: The film-forming slurry obtained in step S4 is mixed evenly by a high-speed mixer; the mixed material is extruded in a twin-screw extruder at an extrusion temperature of 120℃~150℃ (preferably 135℃), cooled and pelletized to obtain hemp base film biodegradable masterbatch.

[0044] S6. Post-processing: The biodegradable masterbatch is blown into a film using a blown film machine to obtain a 6μm~20μm (preferably 10μm) hemp-based fully biodegradable mulch film.

[0045] The mulch film of the present invention has excellent anti-brittleness and crack resistance at a low temperature of 10°C, and its degradation cycle can be accelerated within 60-180 days by activating the built-in biological enzymes.

[0046] To illustrate the effectiveness of the method proposed in this invention, the following detailed description of the above technical solution is provided through a specific embodiment. The specific implementation steps are as follows: Example 1 S1. Pulverize hemp fibers to a fineness of 600 mesh or higher, treat with 5% sodium hydroxide solution at 80°C for 3 to 10 hours to extract cellulose, and use KH-550 coupling agent to improve the hydrophobicity of hemp fibers.

[0047] S2. Obtain all raw materials, including 70 parts of PBAT and 12.2 parts of PLA as high molecular polymers; 15 parts of modified hemp fiber and 1 part of cellulase; and other additives including 1 part of epoxidized soybean oil and 0.8 parts of antioxidant.

[0048] S3. Dissolve cellulase (activity ≥1000 U / g) in a 2% sodium alginate solution. Add the mixture dropwise to a 4% calcium chloride solution using a syringe to form microcapsules. After standing and solidifying for 30 minutes, filter and collect the microcapsules, then immerse them in a 0.5% chitosan acetate solution for 10 minutes to obtain bioenzyme microcapsules.

[0049] S4. Mix all raw materials thoroughly in a high-speed mixer; S5. Add the mixed components to a twin-screw extruder, extrude at 140°C, and prepare biodegradable masterbatch using a pelletizer; S6. The biodegradable masterbatch is blown into a film using a single-screw blown film machine, with a blown film thickness of 12μm.

[0050] Example 2 S1. Pulverize hemp fibers to a fineness of 800 mesh or higher, treat with 5% sodium hydroxide solution at 80°C for 3-10 hours to extract cellulose, and use KH-560 coupling agent to improve the hydrophobicity of hemp fibers.

[0051] S2. Obtain all raw materials, including 60 parts of PBAT and 12.5 parts of PLA, 24 parts of modified hemp fiber, and 2 parts of keratinase. Other additives include 0.5 parts of epoxidized soybean oil, 0.5 parts of antioxidant, and 0.5 parts of carbon black.

[0052] S3. Dissolve keratinase (activity ≥1000 U / g) in 50 mL of 2% sodium alginate solution. Add the mixture dropwise to 4% calcium chloride solution using a syringe to form microcapsules. After standing and solidifying for 30 minutes, filter and collect the microcapsules, then immerse them in 0.5% chitosan acetate solution for 10 minutes to obtain bioenzyme microcapsules.

[0053] S4. Mix all raw materials thoroughly in a high-speed mixer; S5. Add the mixed components to a twin-screw extruder, extrude at 140°C, and prepare biodegradable masterbatch using a pelletizer; S6. Hydroxyapatite biodegradable masterbatch is blown into a film using a twin-screw blown film machine, with a blown film thickness of 10μm.

[0054] Example 3 S1. Pulverize hemp fibers to a fineness of 1000 mesh or finer, treat with 5% sodium hydroxide solution at 80°C for 3 to 10 hours to extract cellulose, and use KH-550 coupling agent to improve the hydrophobicity of hemp fibers.

[0055] S2. Obtain all raw materials. Calculations are made based on weather conditions for 5 years from 2020 to 2024, i.e., N=5. Then, using meteorological values ​​for Nenjiang (annual average temperature t=-2.2℃, annual average relative humidity h=63%) and China (annual average temperature Tem=10.5℃, annual average relative humidity Hum=65%) for the same 5 years, the formula is used to obtain Rat=21.01%. The required degradation days for the Nenjiang mulch film are deg=85 and Pec=3.12%. The final formula composition is as follows: 75 parts PBAT polymer, 20 parts modified hemp fiber, and 3 parts keratinase. Other additives include 1 part epoxidized soybean oil and 1 part antioxidant.

[0056] S3. Dissolve the keratinase in 50 mL of 2% sodium alginate solution. Add the mixture dropwise to 4% calcium chloride solution using a syringe to form microcapsule spheres. After standing and solidifying for 30 minutes, filter and collect the microcapsules, then immerse them in 0.5% chitosan acetate solution for 10 minutes to obtain bioenzyme microcapsules.

[0057] S4. Mix all raw materials thoroughly in a high-speed mixer; S5. Add the mixed components to a twin-screw extruder, extrude at 140°C, and prepare biodegradable masterbatch using a pelletizer; S6. The biodegradable masterbatch is blown into a film using a single-screw blown film machine, with a film thickness of 10μm.

[0058] Performance testing: The mulch films prepared in Examples 1, 2, and 3 of this invention were compared with commercially available starch-based fully degradable mulch films (Comparative Example 1) and PLA / PBAT fully degradable mulch films (Comparative Example 2) under simulated cold-climate conditions (constant temperature 10℃) for performance testing. 1. Low-temperature mechanical property testing: Comparative Example 1 (starch-based): It becomes brittle at 10°C, with an elongation at break of less than 5%, and breaks easily under slight stress.

[0059] Comparative Example 2 (PLA / PBAT): The flexibility is acceptable, but the tensile strength is significantly reduced.

[0060] Example 1: Mulch film: Tensile strength and elongation at break both retained >85%.

[0061] Example 2: Mulch film: Tensile strength and elongation at break both retained >90%.

[0062] Example 3: Mulch film: Tensile strength and elongation at break both retained >92%.

[0063] 2. Degradation performance test (10℃, 90 days): Comparative Example 1: The quality loss rate is approximately 10%.

[0064] Comparative Example 2: Quality loss rate <15%.

[0065] Example 1: After activation, the quality loss rate reached over 35%.

[0066] Example 2: After activation, the quality loss rate exceeds 40%.

[0067] Example 3: After activation, the quality loss rate exceeds 45%.

[0068] Test results show that the mulch film prepared by this invention successfully solves the technical problems of low-temperature embrittlement and slow degradation of mulch film in cold environments.

[0069] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A bio-enzyme-controlled, fully biodegradable hemp-based mulch film for use in cold regions, characterized in that, By weight, it includes 50-99 parts of high molecular polymer, 1-50 parts of modified hemp fiber, 1-5 parts of biological enzyme, and 0-10 parts of other additives; The polymer is at least one of polybutylene terephthalate, polybutylene succinate, polycaprolactone, polylactic acid, and starch; The mulch film also includes bio-enzyme microcapsules with a particle size of 1-5 μm; the bio-enzyme microcapsules are prepared from bio-enzymes.

2. The hemp-based fully degradable mulch film according to claim 1, characterized in that, Mass ratio of modified hemp fiber to polymer in, Reference temperature; Reference relative humidity; The average annual temperature of the area where the film-laying zone is located in year N; The average annual relative humidity of the area where the film-laying zone is located in year N; It is a natural constant.

3. The hemp-based fully degradable mulch film according to claim 2, characterized in that, Mass relationship between bio-enzymes, modified hemp fibers and polymers for: = in, =Bioenzyme / (Modified hemp fiber + polymer); deg is the target degradation time of the mulch film.

4. The hemp-based fully degradable mulch film according to any one of claims 1-3, characterized in that, The modified hemp fiber is derived from at least one of ramie, jute, kenaf, flax, hemp, sisal, or Apocynum venetum.

5. A method for preparing a hemp-based fully degradable mulch film according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Hemp fiber pretreatment; S2. Modify hemp fibers to obtain nano-hemp fiber powder; S3. Preparation of bioenzyme microcapsules; S4. Prepare a film-forming slurry by mixing nano-hemp fiber powder and bio-enzyme microcapsules; S5. The film-forming slurry obtained in step S4 is extruded in an extruder to obtain hemp base film biodegradable masterbatch; S6. A hemp-based fully biodegradable mulch film is produced by using a blown film machine to process biodegradable masterbatch.

6. The preparation method according to claim 5, characterized in that, The modification of hemp fibers in step S2 includes pulverizing the pretreated hemp fibers to a mesh size of 600 or larger, and then preparing nano-hemp fiber powder by a combination of grinding and acid hydrolysis after alkali treatment and siloxane modification.

7. The preparation method according to claim 6, characterized in that, The alkaline treatment involves using 5%-8% sodium hydroxide and reacting at 80-100℃ for 3-10 hours to treat the hemp fibers.

8. The preparation method according to claim 5, characterized in that, The preparation of the bio-enzyme microcapsules in step S3 includes mixing the degrading enzyme with sodium alginate solution, adding it dropwise to calcium chloride solution, preparing microcapsule precursors by ion cross-linking, and then immersing them in chitosan solution for secondary encapsulation.

9. The preparation method according to claim 6, characterized in that, The concentration of siloxane is 1%-5%.

10. The preparation method according to claim 5, characterized in that, The specific steps of step S5 are as follows: after the film-forming slurry is mixed evenly by a high-speed mixer, it is extruded in a twin-screw extruder at 120℃~150℃, cooled and pelletized to obtain hemp base film biodegradable masterbatch.