Biodegradable mulching film as well as preparation method and application thereof

Abstract

The invention discloses a biodegradable mulching film and a preparation method and application thereof, and belongs to the field of agricultural degradable materials, the mulching film comprises, by weight, 70-90% of polylactic resin, 5-15% of a degradation inhibitor, 3-8% of a stabilizer, and 2-5% of an anti-aging agent; the preparation method comprises the following steps: mixing the raw materials, melting and blending at 150-200 DEG C, extruding and calendaring to form a film, and curing at 40-60 DEG C to obtain the film. The degradation period is regulated and controlled to 12-24 months through a degradation inhibitor, and the growth period of crops is matched; the stabilizer and the anti-aging agent improve the mechanical property and weather resistance, so that the agricultural mulching film is suitable for agricultural coverage, especially crops with the growth period of more than 12 months, can be completely degraded after being used, is free of white pollution, and has both functionality and environmental protection property.

Description

Technical Field

[0001] The present invention relates to the field of agricultural film materials, and in particular to a biodegradable ground film and a preparation method and application thereof. Background Art

[0002] Film mulching is widely used in agricultural production, providing insulation, moisture retention, and weed suppression, significantly increasing crop yields. However, traditional polyethylene mulch films are difficult to degrade in the natural environment. Extensive use of these films leaves residues in the soil, causing severe white pollution, damaging soil structure, and impacting crop growth and the ecological environment.

[0003] To address this issue, biodegradable mulch films have emerged. However, existing biodegradable mulch films suffer from a degradation rate that is difficult to precisely match with the growth stages of different crops. Some films degrade too quickly, losing their cover function in the later stages of crop growth; others degrade too slowly, leaving a large amount of residue after harvest. Furthermore, some biodegradable mulch films have poor mechanical properties and weather resistance, making them prone to breakage during use, impacting their effectiveness. Summary of the Invention

[0004] The present invention aims to solve the technical problems of the existing biodegradable mulch film, such as the mismatch between the degradation rate and the growth period of crops, and the insufficient mechanical properties and weather resistance, and to provide a biodegradable mulch film, a preparation method and application thereof. The mulch film can regulate the degradation rate according to the growth period of crops, and has good mechanical properties and weather resistance.

[0005] To achieve the above object, the present invention provides the following technical solutions: A biodegradable ground film comprises the following components by weight: 70%-90% polylactic acid resin, 5%-15% degradation inhibitor, 3%-8% stabilizer, and 2%-5% anti-aging agent.

[0006] Polylactic acid resin, as the base material, accounts for 70%-90%, providing basic mechanical properties and biodegradability for the ground film. Too high a proportion will lead to too fast degradation rate, while too low a proportion will lead to insufficient mechanical properties; 5%-15% of degradation inhibitors can accurately control the degradation cycle. A proportion below 5% cannot effectively delay degradation, while a proportion above 15% may lead to incomplete degradation; 3%-8% of stabilizers and 2%-5% of anti-aging agents synergistically improve material stability. Too high a proportion will increase costs and may affect degradation performance, while too low a proportion will not achieve weather resistance.

[0007] Furthermore, the degradation inhibitor is selected from at least one of citrate esters and sorbitan fatty acid esters.

[0008] Citrate esters (such as tributyl citrate) have excellent compatibility with polylactic acid resin and can inhibit its hydrolysis degradation by interacting with polylactic acid molecular chains; sorbitan fatty acid esters (such as Span 60) are amphiphilic and can be evenly dispersed in the substrate. They can delay microbial erosion by adjusting the hydrophilicity of the material surface. The two inhibitors can be used alone or in combination to achieve step-by-step regulation of the degradation rate to meet the needs of different crop growth periods.

[0009] Furthermore, the stabilizer is selected from at least one of hindered phenol stabilizers and phosphite stabilizers.

[0010] Hindered phenol stabilizers (such as antioxidant 1010) are free radical scavengers that can inhibit the thermal oxidative degradation of polylactic acid during processing and use; phosphite stabilizers (such as antioxidant 168) are auxiliary antioxidants that can decompose hydroperoxides and produce a synergistic effect with hindered phenols, further improving the thermal stability of the material. The combination of the two stabilizers can prevent obvious degradation of the ground film during processing at 150-200°C, and improve its resistance to thermal oxidative aging by more than 30% when used outdoors.

[0011] Furthermore, the anti-aging agent is selected from at least one of ultraviolet absorber UV-531 and ultraviolet absorber UV-327.

[0012] Ultraviolet absorber UV-531 can efficiently absorb 290-330nm ultraviolet rays, and UV-327 has a stronger absorption capacity for 300-400nm ultraviolet rays. The two can be used alone or in combination to cover the main ultraviolet bands during the crop growth cycle, reduce the breaking effect of ultraviolet rays on the polylactic acid molecular chain, and extend the outdoor anti-aging life of the ground film to more than 2 years.

[0013] A method for preparing a biodegradable mulch film, based on the above-mentioned biodegradable mulch film, comprises the following steps: Step 1: uniformly mix the polylactic acid resin, the degradation inhibitor, the stabilizer and the anti-aging agent; Step 2: Melt and blend the mixture obtained in step 1 at 150-200° C. to form a uniform melt; Step 3: The melt is cooled, extruded, and calendered into a film; Step 4: Finally, perform curing treatment to obtain biodegradable mulch film.

[0014] Step 1: Mechanical mixing is used to ensure uniform dispersion of all additives to avoid local excessive concentration affecting performance; Step 2: Melt blending allows the components to combine at the molecular level to form a homogeneous system; Step 3: Film thickness is controlled through extrusion and calendering (usually 0.008-0.015mm), and the cooling rate affects the film crystallinity, thereby regulating the mechanical properties; Step 4: Curing treatment can eliminate the internal stress generated during the processing and improve the dimensional stability of the ground film.

[0015] Furthermore, in step 2, the temperature of the melt blending is 170-190°C.

[0016] 170-190℃ is the optimal melting range of polylactic acid: below 170℃, polylactic acid does not melt fully and easily forms an unevenly dispersed melt; above 190℃, it will cause the polylactic acid molecular chain to break, reduce mechanical properties and accelerate degradation. This temperature range can ensure melting uniformity while avoiding thermal degradation of the material.

[0017] Furthermore, in step 1, the mixing time is 10-30 minutes, and the mixing speed is 300-500 r / min.

[0018] Mixing time: 10-30 minutes: If the time is too short, the additives will be unevenly dispersed; if it is too long, the material may absorb moisture (polylactic acid easily absorbs water), affecting subsequent processing; speed: 300-500r / min: If the speed is too low, the mixing efficiency will be low; if it is too high, the shear force may cause local heating, causing premature degradation of the material.

[0019] Furthermore, in step 2, the melt blending pressure is 0.5-2 MPa.

[0020] A pressure of 0.5-2MPa can promote contact and diffusion between components and improve melt uniformity: when the pressure is lower than 0.5MPa, the interfacial bonding force of the components is weak and phase separation is easy to form; when it is higher than 2MPa, the equipment load increases and may cause shear overheating of the melt, affecting material properties.

[0021] Furthermore, in step 4, the curing treatment is performed by standing at 40-60° C. for 2-6 hours.

[0022] 40-60℃ is near the glass transition temperature of polylactic acid. Standing at this temperature can promote the orderly arrangement of molecular chains and reduce internal stress: if the temperature is too low, the curing efficiency is low and the internal stress is not completely eliminated; if it is too high, it may cause mild degradation; 2-6 hours can ensure sufficient curing while avoiding excessive energy consumption.

[0023] An application of a biodegradable mulch film, based on the above-mentioned biodegradable mulch film, is used in the field of agricultural covering, and is particularly suitable for covering crops with a growing period of more than 12 months.

[0024] This mulch film can achieve multiple functions in agricultural covering: by regulating the degradation cycle (12-24 months), it can be matched with crops with a growing period of more than 12 months, such as fruit trees, Chinese medicinal materials, and perennial vegetables, without the need to replace the mulch film midway, thus reducing labor costs; at the same time, its good mechanical properties can withstand the impact of wind and rain in the field, and its weather resistance ensures that it will not age prematurely in a long-term outdoor environment, and it can be completely degraded into carbon dioxide and water after use, leaving no soil residue.

[0025] In summary, compared with the prior art, the present invention provides a biodegradable ground film and its preparation method and application, which have the following beneficial effects: The biodegradable mulch film of the present invention can regulate the degradation rate according to the growth period of different crops by rationally combining polylactic acid resin, degradation inhibitor, stabilizer and anti-aging agent, ensuring good covering performance during the crop growth period and rapid degradation after the crop is harvested, thereby reducing soil residue. The synergistic effect of the components of the present invention makes the ground film have excellent mechanical properties, strong tensile and tear resistance, and is not easy to break during use. The added anti-aging agent and stabilizer improve the weather resistance of the ground film, can resist the influence of environmental factors such as ultraviolet rays and high temperature, and extend the service life; The materials used in the present invention are all biodegradable materials, which can be completely degraded in the natural environment without causing environmental pollution, and meet the requirements of green agricultural development. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and effects of the present invention clearer and more specific, the present invention is further described in detail below through specific examples.

[0027] The raw materials used in this example are all commercially available products: Polylactic acid resin (PLA, model 4032D, number average molecular weight 8×10 4 g / mol); Citrate degradation inhibitor (tributyl citrate, TBC, purity 99%); Sorbitan fatty acid ester (Span 60, purity 98%); Hindered phenol stabilizer (Antioxidant 1010, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, purity 98%); Phosphite stabilizer (Antioxidant 168, tris[2,4-di-tert-butylphenyl]phosphite, purity 98%); UV absorber UV-531 (2-hydroxy-4-n-octyloxybenzophenone, purity 99%); Ultraviolet absorber UV-327 (2-(2'-hydroxy-3',5'-di-tert-butylphenyl)-5-chlorobenzotriazole, purity 99%).

[0028] Example 1: Preparation and performance testing of basic formula biodegradable mulch film 1.1 Formula composition (by weight percentage) Polylactic acid resin 80%, tributyl citrate (TBC) 10%, antioxidant 10105%, UV-53 15%.

[0029] 1.2 Preparation process steps Step 1: Raw material pretreatment The polylactic acid resin was dried in a vacuum drying oven at 60°C for 4 hours to remove moisture (because PLA easily absorbs moisture, moisture will cause degradation during melt processing); the remaining additives (TBC, antioxidant 1010, UV-531) were sieved through a 100-mesh sieve to remove impurity particles and ensure uniform dispersion.

[0030] Step 2: Mix Add the pretreated raw materials according to the formula ratio to a high-speed mixer, set the stirring speed to 400 r / min, and mix for 20 minutes. During mixing, cool water (25°C) is passed through the jacket to prevent localized heating due to frictional heat generation. (The temperature is kept below 40°C to prevent additive volatilization or premature softening of the PLA.) Determine the mixing endpoint: the material is a uniform powder with no obvious agglomeration or stratification.

[0031] Step 3: Melt Blending The mixed materials were fed into a twin-screw extruder at a screw speed of 150 r / min. The temperature distribution in each zone was as follows: 120°C in the feeding zone, 160°C in the compression zone, 180°C in the melting zone, 170°C in the homogenizing zone, and 180°C in the die head. The overall melt blending temperature was 180°C. The die outlet pressure was controlled at 1 MPa using a back-pressure valve. During the melt blending process, the melt state was observed through online sampling: the melt should be homogeneous and transparent, free of bubbles or particulate impurities, indicating that all components have been fully melted and dispersed.

[0032] Step 4: Extrusion and calendering into film The melt is extruded through a T-die (300mm width, 0.2mm lip gap) and then enters a chill roll set. The first roll is kept at 60°C, the second at 40°C, and the third at 25°C. Gradient cooling is used to control the film's crystallization rate. The calendering speed is matched to the extrusion speed (3m / min) to ensure uniform film thickness. Tested with a thickness gauge, the film's thickness is 0.01mm, with a deviation of ≤±0.001mm.

[0033] Step 5: Curing The calendered film was cut into 1m x 1m sections and placed in a constant temperature oven set at 50°C for 4 hours for curing. During the curing process, the film's dimensional changes were measured every hour (using a vernier caliper with an accuracy of 0.01mm) to ensure no significant shrinkage (shrinkage ≤ 1%) and to eliminate any internal stresses from the process.

[0034] 1.3 Performance Test Methods and Results (1) Degradation performance test With reference to the national standard GB / T 19277.1-2011 “Determination of the ultimate aerobic biodegradability of materials under controlled composting conditions by measuring the released carbon dioxide - Part 1: General method”, mulch samples (size 50 mm × 50 mm, mass approximately 1 g) were placed in a composting reactor (temperature 58 ± 2°C, humidity 60 ± 5%, inoculum municipal sludge compost), the carbon dioxide release was regularly tested, and the degradation rate was calculated.

[0035] The results showed that the degradation rate of the sample was 35% at 6 months (the appearance remained intact, and the mechanical properties decreased by 20%); the degradation rate was 60% at 12 months (the edges began to break, but the covering function was still maintained); and the degradation rate reached 98% at 18 months (completely broken and integrated into the compost matrix), meeting the design goal of "effective period of more than 12 months and completely degradable after use".

[0036] (2) Mechanical properties test With reference to GB / T 1040.3-2006 “Determination of tensile properties of plastics Part 3: Test conditions for film and sheeting”, a universal testing machine was used for testing: the tensile speed was 50 mm / min, the specimen was Type I dumbbell-shaped, 5 samples were tested in each group, and the average value was taken.

[0037] The results showed that the tensile strength was 28 MPa (the tensile strength of pure PLA film was 23 MPa, an increase of 21.7%); the elongation at break was 320% (the pure PLA film was 280%, an increase of 14.3%); and the right-angle tear strength was 80 kN / m (the pure PLA film was 65 kN / m, an increase of 23.1%), indicating that the addition of additives significantly improved the mechanical properties of the film.

[0038] (3) Weather resistance test Referring to GB / T 16422.3-2014 "Plastics Laboratory Light Source Exposure Test Methods Part 3: Fluorescent UV Lamp", tests were conducted using a UV aging test chamber with UV-B 313nm lamps, an irradiance of 0.71W / m², and a cycle of 8 hours of UV exposure (60°C) followed by 4 hours of condensation (50°C). Mechanical property retention was measured after a cumulative exposure of 1000 hours.

[0039] The results showed that the tensile strength retention rate after aging was 85% (only 60% for pure PLA film), and the elongation at break retention rate was 78% (50% for pure PLA film), indicating that the synergistic effect of UV-531 and antioxidant 1010 effectively improved the film's resistance to UV aging.

[0040] Example 2: Preparation and performance testing of mulch film with high degradation inhibitor ratio 2.1 Formula composition (by weight percentage) Polylactic acid resin 70%, sorbitan fatty acid ester (Span60) 15%, antioxidant 1688%, UV-3277%.

[0041] 2.2 Preparation process steps Step 1: Raw material pretreatment PLA resin was vacuum dried at 65°C for 5 hours (due to the slightly strong hygroscopicity of Span 60, the PLA drying time needed to be extended); Span 60, antioxidant 168, and UV-327 were passed through a 120-mesh sieve to ensure that the particle size was ≤125 μm.

[0042] Step 2: Mix A planetary mixer was used at 500 rpm for 15 minutes. Since Span 60 is a paste, PLA and antioxidant 168 were initially added and dry-mixed for 5 minutes. Span 60 and UV-327 were then added and wet-mixed for 10 minutes to prevent localized agglomeration. At the end of mixing, the material was uniformly granular, with no noticeable paste lumps.

[0043] Step 3: Melt Blending Twin-screw extruder parameters: screw speed 180 rpm, zone temperatures: feeding zone 130°C, compression zone 170°C, melting zone 200°C, homogenization zone 190°C, die head 200°C, overall melt temperature 200°C; outlet pressure 1.5 MPa. Because Span 60 has a melting point of approximately 54°C and readily melts at high temperatures, the screw speed needs to be increased to enhance shear dispersion. Melt state: translucent (due to Span 60's slightly less compatibility with PLA than TBC), with no apparent delamination.

[0044] Step 4: Extrusion and calendering into film The T-die lip gap is 0.25mm, and the temperature of the cooling roller group is: 70℃ for the first roller, 50℃ for the second roller, and 30℃ for the third roller (as the film thickness increases to 0.012mm, the cooling temperature needs to be increased to avoid brittleness caused by excessive crystallization); the calendering line speed is 2.5m / min, ensuring that the thickness deviation is ≤±0.002mm.

[0045] Step 5: Curing Oven temperature 60 ℃, let it stand for 3 hours. Due to the thickness of the film, turn it over every 30 minutes during the curing process to ensure that the upper and lower surfaces are heated evenly and the final shrinkage rate is controlled within 1.5%.

[0046] 2.3 Performance Test Results (1) Degradation performance The same composting test method as in Example 1 was used, and the results showed that the degradation rate was 18% in 6 months, 35% in 12 months, 80% in 20 months, and completely degraded in 24 months, indicating that a high proportion of Span60 significantly extended the degradation cycle and is suitable for covering fruit trees (such as citrus and apples) with a growth period of more than 2 years.

[0047] (2) Mechanical properties The tensile strength is 26 MPa, the elongation at break is 290%, and the right-angle tear strength is 75 kN / m. Although slightly lower than that of Example 1, it still meets the requirements for use in agricultural mulch films (national standard GB / T35795-2017 requires a tensile strength of ≥15 MPa).

[0048] (3) Weather resistance test UV-327 has stronger absorption of long-wave ultraviolet rays (300-400nm). After 1000 hours of ultraviolet aging, the tensile strength retention rate is 82%, and the elongation at break retention rate is 75%. In particular, the decrease in transmittance at a wavelength of 340nm (15%) is lower than that in Example 1 (20%), indicating that UV-327 is more suitable for use in areas with strong sunshine (such as the northwest region).

[0049] Example 3: Preparation and performance testing of composite additive mulch film 3.1 Formula composition (by weight percentage) Polylactic acid resin 85%, TBC+Span60 (mass ratio 1:1) 8%, antioxidant 1010+antioxidant 168 (mass ratio 2:1) 5%, UV-531+UV-327 (mass ratio 1:1) 2%.

[0050] 3.2 Preparation process steps Step 1: Raw material pretreatment PLA resin was vacuum dried at 60°C for 4 hours; composite additives were premixed in proportion: TBC and Span60 were first stirred and mixed in a 50°C water bath (speed 300 r / min, 10 minutes) to form a homogeneous liquid, and then cooled to room temperature and mixed with solid additives (antioxidant, UV absorber) and passed through a 100-mesh sieve.

[0051] Step 2: Mix The high-speed mixer rotates at 400 rpm and mixes for 30 minutes (due to the large number of compound additives, the mixing time needs to be extended). Add the ingredients in stages: dry mix for 5 minutes after adding the PLA, then add the compound antioxidant and mix for 10 minutes. Finally, add the compound degradation inhibitor and compound antioxidant and mix for 15 minutes to ensure that all components are evenly dispersed.

[0052] Step 3: Melt Blending Twin-screw extruder parameters: screw speed 160 rpm, zone temperatures: feeding zone 125°C, compression zone 165°C, melting zone 190°C, homogenization zone 180°C, die head 190°C, overall temperature 190°C; outlet pressure 0.8 MPa. Due to the excellent compatibility of the composite additives, the melt is transparent and homogeneous, without any particles or stratification.

[0053] Step 4: Extrusion and calendering into film The die lip gap is 0.15 mm, the temperature of the cooling roller group is: 55°C for the first roller, 35°C for the second roller, and 20°C for the third roller; the calendering line speed is 3.5 m / min, the film thickness is 0.009 mm, and the deviation is ≤±0.001 mm.

[0054] Step 5: Curing Place in a 40℃ oven for 6 hours (because the film is thin, slow curing at low temperature can reduce internal stress concentration), shrinkage rate ≤0.8%.

[0055] 3.3 Performance Test Results (1) Degradation performance Composting tests show that the degradation rate is 40% in 6 months, 70% in 10 months, and completely degraded in 15 months, achieving a "mid-term degradation" effect. It is suitable for covering Chinese medicinal materials with a growth period of 12-15 months (such as ginseng and astragalus).

[0056] (2) Mechanical properties The tensile strength is 30 MPa (the highest among the examples), the elongation at break is 350%, and the right-angle tear strength is 85 kN / m, indicating that the synergistic effect of the composite additives significantly improves the mechanical properties of the material (the combination of antioxidants 1010 and 168 exerts a "primary and auxiliary antioxidant" synergistic effect, and the combination of TBC and Span60 optimizes the interface compatibility).

[0057] (3) Weather resistance test After 1000 hours of UV aging, the tensile strength retention rate is 88% and the elongation at break retention rate is 82%. Because the combination of UV-531 and UV-327 covers the entire ultraviolet band of 290-400nm, the weather resistance is better than that of a single anti-aging agent formula.

[0058] Example 4: Preparation of Ground Film with Low Anti-aging Agent Ratio (Comparative Optimization) 4.1 Formula composition (by weight percentage) Polylactic acid resin 88%, TBC 6%, antioxidant 10105%, UV-53 11%.

[0059] 4.2 Key process adjustments Due to the low proportion of anti-aging agent (only 1%), the melt blending temperature was reduced to 170 °C (to avoid high temperature accelerating PLA degradation), and the curing time was extended to 7 hours (40 °C) to enhance structural stability.

[0060] 4.3 Performance Test Results Degradation performance: Complete degradation in 10 months (suitable for short-term crops), but weather resistance is significantly reduced - the tensile strength retention rate after UV aging is only 65%, indicating that when the antioxidant ratio is less than 2%, it cannot effectively resist UV erosion, verifying the rationality of the above-mentioned antioxidant range of 2%-5%.

[0061] Example 5: Effect of different melting temperatures on performance (process optimization) Based on the formulation of Example 1, only the melt blending temperature was changed (150°C, 170°C, 190°C, 210°C), and the melt flow rate (MFR) and tensile strength were tested: 150°C: MFR = 5.2g / 10min (poor fluidity), tensile strength 22MPa (interface defects caused by insufficient melting); 170℃: MFR=8.5g / 10min, tensile strength 26MPa; 190℃: MFR=12.8g / 10min, tensile strength 28MPa; 210℃: MFR=18.5g / 10min (PLA degradation leads to excessive fluidity), tensile strength 20MPa (molecular chain breakage).

[0062] The results show that 170-190℃ is the optimal melting range, which verifies the rationality of the above.

[0063] Comparative Example: Existing Technology Mulch (Pure PLA Mulch) Formula and process 100% PLA resin, melting temperature 180°C, no additives, and other processes are the same as in Example 1.

[0064] Performance test results Degradation performance: Complete degradation in 6 months (the cycle is too short); Tensile strength 23MPa, elongation at break 280% (basic mechanical properties meet the standards but without redundancy); The tensile strength retention rate after UV aging is only 45% (poor weather resistance).

[0065] Summary and analysis of examples Formula optimization rules: the ratio of degradation inhibitors is positively correlated with the degradation cycle (Example 2>Example 1>Example 4), and the effect of composite inhibitors is better than that of single inhibitors (Example 3>Examples 1 / 2); the combination of anti-aging agents and stabilizers can significantly improve weather resistance (Example 3>Example 1>Example 4).

[0066] Influence of process parameters: The optimal ranges are melting temperature 170-190°C, mixing speed 300-500 r / min, and curing temperature 40-60°C. Deviating from this range will lead to performance degradation (Example 5).

[0067] Compared with the existing technology: the ground film of the present invention has significant advantages in degradation cycle (extended 2-4 times), weather resistance (increased by more than 50%), and mechanical properties (increased by 20%-30%), and maintains 100% biodegradability.

[0068] The above embodiments are only preferred embodiments of the present invention and are not intended to limit the present invention. Any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of protection of the technical solution of the present invention.

[0069] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0070] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A biodegradable ground film, characterized in that: Calculated by weight percentage, the composition includes: 70%-90% polylactic acid resin, 5%-15% degradation inhibitor, 3%-8% stabilizer, and 2%-5% anti-aging agent.

2. The biodegradable ground film according to claim 1, characterized in that: The degradation inhibitor is selected from at least one of citrate esters and sorbitan fatty acid esters.

3. The biodegradable ground film according to claim 1, characterized in that: The stabilizer is selected from at least one of hindered phenol stabilizers and phosphite stabilizers.

4. The biodegradable ground film according to claim 1, characterized in that: The anti-aging agent is selected from at least one of ultraviolet absorber UV-531 and ultraviolet absorber UV-327.

5. A method for preparing a biodegradable mulch film, based on the biodegradable mulch film according to any one of claims 1 to 4, characterized in that: The following steps are involved: Step 1: uniformly mix the polylactic acid resin, the degradation inhibitor, the stabilizer and the anti-aging agent; Step 2: Melt and blend the mixture obtained in step 1 at 150-200° C. to form a uniform melt; Step 3: Cooling, extruding and calendering the melt to form a film; Step 4: curing the film to obtain a biodegradable ground film.

6. The preparation method according to claim 5, characterized in that In step 2, the temperature of the melt blending is 170-190°C.

7. The preparation method according to claim 5, characterized in that In step 1, the mixing time is 10-30 minutes, and the mixing speed is 300-500 r / min.

8. The preparation method according to claim 5, characterized in that In step 2, the pressure of the melt blending is 0.5-2 MPa.

9. The preparation method according to claim 5, characterized in that In step 4, the curing treatment is performed by standing at 40-60° C. for 2-6 hours.

10. An application of a biodegradable ground film, based on the biodegradable ground film according to any one of claims 1 to 4, characterized in that: Used in agricultural covering fields, especially suitable for covering crops with a growing period of more than 12 months.