Black biodegradable mulching film for weeding and preparation method thereof

Abstract

The present application relates to the technical field of degradable agricultural mulching film, and particularly discloses a black biodegradable weeding mulching film and a preparation method thereof. The black biodegradable weeding mulching film is prepared by using biodegradable resin as a base material, replacing traditional carbon black with oil shale semi-coke as a core black functional filler, and compounding plasticizers, nucleating agents, antioxidants and other additives, and then through raw material pretreatment, mixed modification, melt blending, granulation and blow molding. The oil shale semi-coke contains carbon black components and inorganic minerals such as quartz and illite, which can not only endow the mulching film with excellent light-shielding and weeding performance, but also improve the mechanical strength and controllable degradation of the mulching film. Meanwhile, the oil shale semi-coke realizes the resource utilization of industrial solid waste and reduces the production cost of the biodegradable mulching film. The preparation process of the present application is compatible with the existing mulching film production line, is suitable for large-scale production, and has environmental protection value, economic value and agricultural application value.

Description

Technical Field

[0001] This invention relates to the field of new materials, and particularly to the field of biodegradable agricultural mulch film materials, specifically providing a black biodegradable weed control mulch film and its preparation method. Background Technology

[0002] Since my country introduced plastic film mulching technology in 1978, it has been rapidly promoted and upgraded on a large scale in agricultural production. Agricultural plastic film, by precisely regulating soil temperature and humidity and reducing water evaporation and nutrient loss, effectively overcomes crop growth limitations under different climate and soil conditions due to its core advantages of "water conservation, soil conservation, and fertilizer conservation," becoming a key agricultural technology for ensuring high and stable crop yields. With the increasing demand for green agricultural development, the problem of weed infestation caused by traditional transparent plastic film has become increasingly prominent. Weeds compete with crops for sunlight, water, and nutrients, leading to a 10%-30% reduction in crop yields, while the extensive use of herbicides causes soil pollution and pesticide residues. Against this backdrop, black plastic film with weed-suppressing functions has emerged, becoming an important solution to the contradiction between "weed control" and "green production."

[0003] The core advantage of black weed control mulch lies in its dual value of highly efficient weed control and environmental friendliness: Significant shading and weed suppression effects: Black mulch film typically has a light transmittance of less than 20%, which can effectively block the light conditions required for weed photosynthesis, causing weeds to wither and die due to insufficient energy supply during the germination stage. The weed suppression rate in the field can reach more than 85%. Better temperature and humidity control: Black mulch film has poor permeability to radiant heat, which can smooth out the daily temperature fluctuations of the soil. During the peak growth period of crops, the soil temperature in the covered area is 1-3℃ lower than that of transparent mulch film, which avoids the high temperature of the soil from scorching the crop roots. At the same time, it maintains stable soil moisture, which is more conducive to the robust growth of crops. Reduce chemical pollution: By replacing herbicides with physical shading, the amount of pesticides used is greatly reduced, and pesticide residues in the soil and crops are reduced, which is in line with the concept of green agriculture development.

[0004] Existing publicly disclosed patents for weed control films primarily revolve around a combination of "substrate + light-blocking / herbicide" in their core material system design, which can be divided into three categories: Traditional non-degradable systems: using general-purpose plastics such as polyethylene (PE) and polypropylene (PP) as the base material, combined with carbon black or herbicides, is the mainstream solution in early patents, such as patents CN117866307A and CN117322264A. It has the advantages of excellent base material performance, mature processing, controllable cost, and stable weeding and temperature and humidity control effects. However, it has the disadvantages of serious residual film pollution, difficult recycling, environmental and safety hazards of the combined ingredients, and single function, which makes it difficult to adapt to the needs of modern agricultural green development.

[0005] Biodegradable weed control systems: These systems use biodegradable polymers such as polybutylene adipate / terephthalate (PBAT) and polylactic acid (PLA) as base materials, combined with herbicide components. This is a mainstream innovative solution under the current agricultural orientation, as exemplified by patents CN118163454A and CN117487264A. They have advantages such as no residual film pollution, high weed control efficiency, and strong processing adaptability. However, they also have problems such as safety hazards caused by herbicide migration, high raw material costs, difficulty in controlling degradation rate, and insufficient mechanical and weather resistance, which limit their large-scale promotion and application.

[0006] Biodegradable shading systems: These systems use biodegradable polymers such as poly(butylene adipate / terephthalate) (PBAT) and polylactic acid (PLA) as the base material, and carbon black as the main shading filler. Some patents have attempted to add inorganic pigments such as iron oxide black and manganese black to assist in shading, such as patents CN115260708A and CN114801268A. They have the advantages of no residual film pollution, safe and efficient shading and weed suppression, and strong processing adaptability. However, they have problems such as high cost of core fillers, poor compatibility with the base material, potential impact on degradation performance, and insufficient weather resistance, which limit their large-scale market application.

[0007] On the other hand, oil shale semi-coke, as an industrial solid waste, is the main solid by-product of the oil shale refining process. Oil shale semi-coke is formed from the non-volatile part of oil shale as the temperature rises during the pyrolysis process. It contains a large amount of carbon and other inorganic mineral components. The formation process involves complex chemical reactions, including the pyrolysis and cracking of organic matter, carbonization process, and thermal decomposition and recombination of inorganic minerals.

[0008] Currently, the annual emissions of oil shale semi-coke in China exceed ten million tons. Large-scale accumulation not only occupies land resources but also risks heavy metal migration due to rainwater leaching, leading to soil or water pollution. Existing research indicates that oil shale semi-coke contains carbon black and is rich in inorganic minerals such as quartz and illite, possessing excellent light-shielding properties, thermal stability, and mechanical strengthening potential. Therefore, how to utilize oil shale semi-coke in biodegradable mulch films to reduce costs while optimizing film performance is one of the urgent problems to be solved by those skilled in the art. Summary of the Invention

[0009] The purpose of this invention is to address the dual pain points of existing biodegradable weed control films, namely "environmental pollution caused by herbicides" and "high cost due to reliance on expensive carbon black and environmental pollution from oil shale semi-coke," by providing a black biodegradable weed control film and its preparation method. This achieves the triple goals of "solid waste resource utilization, cost reduction, and performance optimization," thereby promoting the large-scale application of biodegradable weed control films.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A black biodegradable weed control film, the raw material composition by mass parts includes: 40-95 parts biodegradable resin, 2-5 parts polylactic acid, 1-35 parts oil shale semi-coke, 5-12 parts plasticizer, 0.5-2 parts nucleating agent, 0.2-0.8 parts antioxidant, 0.1-0.4 parts lubricant, and 0.2-0.8 parts ultraviolet absorber.

[0011] Further preferred, the raw material composition by mass parts includes: 72 parts biodegradable resin, 3 parts polylactic acid (PLA), 15 parts oil shale semi-coke, 5 parts plasticizer, 2 parts nucleating agent, 0.4 parts antioxidant, 0.2 parts lubricant, and 0.6 parts ultraviolet absorber.

[0012] The biodegradable resin is one or more of polybutylene succinate (PBS), propylene glycol phthalate-propylene carbonate copolymer (PPCP), polyhydroxyalkanoate (PHA), or polybutylene adipate / terephthalate (PBAT), preferably PPCP.

[0013] The molecular weight of the polylactic acid (PLA) is 200,000-300,000 g / mol.

[0014] The plasticizer is one or a combination of two of the following: tributyl citrate (TBC) and acetylated tributyl citrate (ATBC), with a mass ratio of 1:1-2, preferably tributyl citrate (TBC).

[0015] The nucleating agent is one of magnesium silicate, calcium carbonate, calcium oxide, montmorillonite, and silicon dioxide, with a particle size of 20,000-40,000 mesh, preferably calcium carbonate.

[0016] The antioxidant is one or a combination of antioxidant 1010 and antioxidant 168, with a mass ratio of 1:1-1.5, preferably antioxidant 1010.

[0017] The lubricant is one or a mixture of two of erucamide and oleamide, with a mass ratio of 1:1-2, preferably erucamide.

[0018] The ultraviolet absorber is one or more of UV-531, UV-326, and UV-400, preferably UV-531.

[0019] The specific steps for preparing the aforementioned black biodegradable composite mulch film are as follows: (1) After drying, the oil shale semi-coke is ball-milled and sieved to obtain pretreated oil shale semi-coke; (2) The pretreated oil shale semi-coke obtained in step (1) is added to a high-speed mixer along with plasticizer and lubricant to obtain surface-modified oil shale semi-coke; (3) The biodegradable resin, PLA, nucleating agent, antioxidant and ultraviolet absorber are dried, and then added together with the modified oil shale semi-coke obtained in step (2) into a twin-screw extruder. After melt blending, they are extruded and pelletized to obtain special granules for mulch film, and then dried. (4) Blow molding: The granules obtained in step (3) are added to a blow molding machine and extruded and blow molded to obtain a black biodegradable grass cutter film.

[0020] Further, in step (1), the drying temperature is 70-100℃ and the time is 8-12h; the agate beads filling rate in the ball mill jar is 40%-60% of the volume, the oil shale semi-coke filling rate is 25%-40% of the volume, the ball mill speed is 40-80Hz, the ball milling time is 40-180min, and it passes through a 20000-40000 mesh sieve.

[0021] The pretreated oil shale semi-coke has a particle size of 20,000-40,000 mesh and a specific surface area ≥20 m². 2 / g, moisture content ≤0.5%.

[0022] In step (2), the oil shale semi-coke is mixed with plasticizer and lubricant at high speed at a temperature of 90-130℃ and a speed of 800-1200r / min for 20-30min to obtain a preliminary mixed surface-modified oil shale semi-coke, thus preventing uneven mixing.

[0023] In step (2), the plasticizer coats the surface of oil shale semi-coke with polar groups, and can subsequently be compatible with the substrate (biodegradable resin) through non-polar segments, improving interfacial bonding and dispersibility; the lubricant forms a lubricating film between the oil shale semi-coke particles, assisting in dispersion and reducing processing resistance. Together, they achieve uniform dispersion and stable bonding of oil shale semi-coke in the biodegradable substrate, laying the foundation for the excellent shading, mechanical and weather resistance properties of the mulch film.

[0024] The drying conditions for the biodegradable resin, PLA, nucleating agent, antioxidant, and UV absorber in step (3) are: drying in a forced-air drying oven at 60-80℃ for 6-10 hours. The material is added to a twin-screw extruder with a feed rate set to 50-200 g / min, a screw speed set to 60-100 rpm, and barrel temperatures controlled at 140-160℃ (zone 1), 160-175℃ (zone 2), 175-185℃ (zone 3), 175-185℃ (zone 4), 175-185℃ (zone 5), 160-175℃ (zone 6), and 165-180℃ (die head). After melt blending, the material is extruded and pelletized to obtain granules specifically for mulch film. The drying conditions for these granules are: drying in a 60-80℃ oven for 6-10 hours to remove surface adsorbed water.

[0025] In step (4), the granules are added to the blow molding machine, and the barrel temperature is set to 165-175℃ (zone 1), 170-185℃ (zone 2), 180-190℃ (zone 3), and 165-185℃ (die head). The blow ratio is 2.5-3.0. After blow molding, cooling and shaping, and edge trimming, a black biodegradable weed film with a thickness of 6-12µm is obtained.

[0026] The mulch film prepared by the above method has a thickness of 6-12µm, a light transmittance of ≤8%, a tensile strength of ≥18MPa, an elongation at break of ≥400%, and a biodegradation rate of ≥60% under soil composting conditions for 6-12 months.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Resource and environmental value: Converting industrial solid waste oil shale semi-coke into high-value mulch film filler can solve the problem of industrial solid waste resource utilization and reduce the production cost of biodegradable mulch film. At the same time, through the synergistic effect of inorganic minerals and biodegradable resin, the mechanical properties and degradation controllability of mulch film are optimized. Mulch film can be biodegraded in soil for 6-12 months without "white pollution", which meets the development needs of "green agriculture" and "circular economy".

[0028] (2) Economic value: Oil shale semi-coke, as an industrial waste, can replace carbon black and reduce the cost of raw materials for mulch film (calculated according to the conventional formula of biodegradable mulch film, the cost of each ton of mulch film can be reduced by RMB 1,500-3,000), which significantly enhances the market competitiveness of biodegradable mulch film.

[0029] (3) Performance advantages: Shading and weed control: The carbon black in oil shale semi-coke works synergistically with illite, quartz and calcite in oil shale semi-coke, resulting in a shading rate of ≥92% and a weed suppression rate of ≥88% in the field, which is superior to traditional carbon black mulch (shading rate of about 88%-90%). Mechanical properties: The reinforcing effect of inorganic minerals in oil shale semi-coke enables the mulch film to have a tensile strength ≥18MPa and an elongation at break ≥400%, meeting the tensile and tearing requirements during agricultural mulching. Oil shale semi-coke improves rigidity support through formula optimization, which is 5%-12% higher than that of carbon black film.

[0030] Controllable degradation: Trace metal ions in oil shale semi-coke can regulate microbial activity, allowing the mulch film to maintain its integrity during the crop growing season (3-6 months) and degrade rapidly within 6 months after harvest, preventing residual film from affecting the next season's cultivation. Furthermore, oil shale semi-coke is rich in beneficial soil elements and can be used as a soil conditioner. It contains not only essential elements for crop growth such as C, N, P, and K, but also trace elements such as Ca, Mg, Si, and Fe. Field trials have shown that appropriate application of this material can increase soil organic matter, improve cation exchange capacity, enhance soil enzyme activity, and ultimately significantly increase crop yield.

[0031] (4) Process compatibility: The preparation process is fully compatible with existing mulch film production lines. No additional equipment modification is required. Only parameters such as temperature and rotation speed need to be adjusted, which is suitable for enterprises to quickly scale up production. Attached Figure Description

[0032] Figure 1 This is a diagram of a weeding experiment in the experimental examples; Figure 2 The transmittance and haze test results are shown in the experimental example. Figure 3 This is a graph showing the water vapor transmission rate in the experimental example. Figure 4 The image shows the tensile strength test results from the experimental example. Figure 5 The image shows the elongation at break test in the experimental example; Figure 6 The image shows the UV accelerated aging performance test results in the experimental example. Detailed Implementation

[0033] Other materials used in this invention, unless otherwise stated, are commercially available. Other terms used in this invention, unless otherwise specified, generally have the meanings commonly understood by those skilled in the art. The invention is further described in detail below with reference to specific embodiments and data. The following embodiments are merely illustrative and not intended to limit the scope of the invention in any way.

[0034] Unless otherwise specified, all raw materials used in the following embodiments were commercially available. The oil shale semi-coke was purchased from Yantai Jiahe Plastics Technology Co., Ltd. This oil shale semi-coke contains 10%-20wt% carbon black. In addition to carbon black, it also contains other minerals such as quartz, potassium feldspar, calcite, illite, plagioclase, hematite, gypsum, and kaolinite. The specific composition may vary depending on the source of the oil shale, but as long as it contains 10%-20wt% carbon black, it is suitable for use in this application.

[0035] Example 1: A method for preparing a black biodegradable weed control film, the specific steps of which are as follows: (1) The oil shale semi-coke was placed in an oven and dried at 80°C for 8 hours. Then it was ground. The agate beads in the ball mill were 50% filled and the oil shale semi-coke was 30% filled. The ball milling speed was 60 Hz and the ball milling time was 120 min. The semi-coke was passed through a 20,000 mesh sieve to obtain the pretreated oil shale semi-coke.

[0036] (2) Take 7 parts of the pretreated oil shale semi-coke from step (1) and mix them with 5 parts of tributyl citrate and 0.2 parts of erucamide at high speed. The temperature is 100℃, the speed is 1000r / min, and the mixture is stirred for 30min to obtain surface-modified oil shale semi-coke.

[0037] (3) Place 86.8 parts PPCP, 3 parts PLA, 2 parts calcium carbonate, 0.2 parts antioxidant 1010 and 0.5 parts UV-531 in an 80℃ forced-air drying oven and dry for 8 hours to remove surface adsorbed water; then add the surface modified oil shale semi-coke obtained in step (2) together to a twin-screw extruder, set the feed rate to 100g / min, set the screw speed to 65rpm, and control the barrel temperature to 150℃ (zone 1), 170℃ (zone 2), 175℃ (zone 3), 185℃ (zone 4), 175℃ (zone 5), 170℃ (zone 6), and 170℃ (drill head), melt-blend and then extrude and granulate to obtain granules for mulch film; then place the granules for mulch film in an 80℃ oven and dry for 8 hours to remove surface adsorbed water.

[0038] (4) Add the special granules for mulch film to the blown film machine, set the barrel temperature to 170℃ (zone 1), 180℃ (zone 2), 185℃ (zone 3), and 170℃ (die head), and the blow-up ratio to 2.7. After blow molding, cooling and shaping, and edge trimming, a black biodegradable weed control film with a thickness of 10µm is obtained.

[0039] Example 2: A method for preparing a black biodegradable weed control film, the specific steps of which are as follows: The operation methods for steps (1) and (2) are the same as in Example 1, except that in step (2), 10 portions of pretreated oil shale semi-coke are taken; (3) Place 83.8 parts PPCP, 3 parts PLA, 2 parts calcium oxide, 0.2 parts antioxidant 168, and 0.5 parts UV absorber UV-326 in an 80℃ forced-air drying oven for 8 hours to remove surface adsorbed water. Then, add the surface-modified oil shale semi-coke obtained in step (2) to a twin-screw extruder. Set the feed rate to 150 g / min, the screw speed to 75 rpm, and the barrel temperature to 170℃ (zone 1), 175℃ (zone 2), 185℃ (zone 3), 175℃ (zone 4), 175℃ (zone 5), 170℃ (zone 6), and 170℃ (drill head). After melt blending, extrude and granulate to obtain granules for mulch film. Then, place the granules for mulch film in an 80℃ oven for 8 hours to remove surface adsorbed water. (4) Add the special granules for mulch film to the blown film machine, set the barrel temperature to 170℃ (zone 1), 180℃ (zone 2), 180℃ (zone 3), and 170℃ (die head), and the blow-up ratio to 2.6. After blow molding, cooling and shaping, and edge trimming, a black biodegradable weed control film with a thickness of 10µm is obtained.

[0040] Example 3: A method for preparing a black biodegradable weed control film, the specific steps of which are as follows: The operation methods for steps (1) and (2) are the same as in Example 1, except that in step (2), 15 portions of pretreated oil shale semi-coke are taken; (3) Place 78.8 parts PPCP, 3 parts PLA, 2 parts silica, 0.2 parts antioxidant (antioxidant 1010 and antioxidant 168 are compounded in a mass ratio of 1:1), and 0.5 parts UV-400 in an 80℃ forced-air drying oven for 8 hours to remove surface adsorbed water. Then, add the surface-modified oil shale semi-coke obtained in step (2) to a twin-screw extruder. Set the feed rate to 160 g / min, the screw speed to 85 rpm, and the barrel temperature to 150℃ (zone 1), 170℃ (zone 2), 175℃ (zone 3), 185℃ (zone 4), 175℃ (zone 5), 170℃ (zone 6), and 170℃ (drill head). After melt blending, extrude and granulate to obtain granules for mulch film. Then, place the granules for mulch film in an 80℃ oven for 6 hours to remove surface adsorbed water. (4) Add the special granules for mulch film to the blown film machine, set the barrel temperature to 170℃ (zone 1), 180℃ (zone 2), 180℃ (zone 3), and 170℃ (die head), and the blow-up ratio to 2.6. After blow molding, cooling and shaping, and edge trimming, a black biodegradable weed control film with a thickness of 10µm is obtained.

[0041] Comparative Example 1: A method for preparing a plastic film, the specific steps of which are as follows: (1) Take 93.8 parts of PPCP, 3 parts of PLA, 2 parts of calcium carbonate, 0.2 parts of antioxidant 1010 and 0.5 parts of UV-531 and dry them in an oven at 80℃ for 8 hours to remove surface adsorbed water. Add them to a twin-screw extruder, set the feed rate to 100 g / min, set the screw speed to 65 rpm, and control the barrel temperature to 150℃ (zone 1), 170℃ (zone 2), 175℃ (zone 3), 185℃ (zone 4), 175℃ (zone 5), 170℃ (zone 6), and 170℃ (drill head). After melt blending, extrude and granulate to obtain special granules for mulch film. (2) Add the special granules for mulch film to the blown film machine, set the barrel temperature to 170℃ (zone 1), 180℃ (zone 2), 183℃ (zone 3), and 173℃ (die head), and the blow-up ratio to 2.7. After blow molding, cooling and shaping, and edge trimming, a composite mulch film with a thickness of 8µm is obtained.

[0042] Comparative Example 2: A method for preparing a plastic film, the specific steps of which are as follows: (1) Take 83.8 parts of PPCP, 3 parts of PLA, 10 parts of carbon black, 2 parts of calcium oxide, 0.2 parts of antioxidant 168 and 0.5 parts of UV-326 and dry them in an oven at 80℃ for 8 hours to remove surface adsorbed water. Add them to a twin-screw extruder, set the feed rate to 100 g / min, set the screw speed to 65 rpm, and control the barrel temperature to 150℃ (zone 1), 170℃ (zone 2), 175℃ (zone 3), 185℃ (zone 4), 175℃ (zone 5), 170℃ (zone 6) and 170℃ (drill head). After melt blending, extrude and granulate to obtain special granules for mulch film. (2) Add the special granules for mulch film to the blown film machine, set the barrel temperature to 170℃ (zone 1), 180℃ (zone 2), 180℃ (zone 3), and 170℃ (die head), and the blow-up ratio to 2.6. After blow molding, cooling and shaping, and edge trimming, a composite mulch film with a thickness of 10µm is obtained.

[0043] Experimental Example (1) Weeding experiment: A potted weed control experiment was conducted using ryegrass as the test subject: 50g of ryegrass seeds were sown into each of the six flowerpots containing 4kg of planting soil and treated. Six treatment groups were set up, namely, no mulch (blank group), mulch covered with comparative example 1, comparative example 2, example 1, example 2, and example 3. After the mulch was fixed, the plants were placed in the same environment for cultivation. Photos were taken on the 15th and 45th days, and the film was removed on the 45th day for observation.

[0044] The results are as follows Figure 1 As shown, the ryegrass in the control group germinated rapidly in 15 days and grew vigorously in 45 days; in the film group of Comparative Example 1, a small number of weeds germinated after 15 days, and the potting soil was covered with weeds after the film was removed in 45 days; in the film group of Comparative Example 2, weed germination was suppressed in 15 days, and only a small number of weeds were found after the film was removed in 45 days; while in the film groups of Examples 1, 2, and 3, a small number of weeds germinated in 15 days, and the potting soil had only trace amounts or no weeds after the film was removed in 45 days, and the weed control effect was significantly better than that of the control group and Comparative Examples 1 and 2.

[0045] (2) Transmittance and haze tests: Using a standard C-light source, performance tests were conducted on five types of plastic film samples (Comparative Examples 1-2 and Examples 1-3). Eight different test locations were selected for each sample, and the tests were performed in parallel eight times, with the average value taken. The test error was controlled within 10%. The results are as follows: Figure 2 As shown.

[0046] Depend on Figure 2It can be seen that Comparative Example 1 has the highest light transmittance (approximately 90%) and the lowest haze (approximately 30%); Comparative Example 2 has a light transmittance reduced to around 18% and a haze increased to over 70%; Example 1 has a light transmittance below 20% and a haze around 70%; Examples 2 and 3 have light transmittance below 10% and haze maintained between 80% and 90%. Based on the weed control test results, the low light transmittance and high haze of the mulch films in Examples 1-3 are key performance indicators for achieving efficient shading and weed suppression, with overall optical performance superior to Comparative Example 1 and comparable to Comparative Example 2.

[0047] (3) Water vapor permeability test This test was conducted according to the cup method of national standard GB / T 1037-2021: the plastic film samples of Comparative Examples 1-2 and Examples 1-3 were cut into pieces with an area of ​​3.3 × 10⁻⁶. -3 m 2 The circular membrane was preheated for 1 hour at 38°C and 90%RH. Each sample was tested in parallel at least three times, and the average value was used to obtain the water vapor transmission rate (WVT) data. The results are as follows: Figure 3 As shown.

[0048] Depend on Figure 3 It can be seen that the water vapor permeability of both comparative examples 1 and 2 is close to 500 g / (m²). 2 In Examples 1 and 2, the permeability was slightly reduced to about 450 g / (m²·24h), while in Example 3 it returned to a level close to that of the comparative example. This indicates that the mulch film of Examples 1-3 can maintain a certain water vapor permeability (avoiding diseases caused by excessive soil moisture) and reduce the rapid evaporation of water, which meets the needs of "water retention and air permeability" in agricultural production.

[0049] (3) Mechanical property testing This test was conducted in accordance with GB / T1040.3-2006 standard: The plastic film samples from Comparative Examples 1-2 and Examples 1-3 were cut into strips with a standard length of 100 mm and a width of 15 mm using a long strip mold. The samples were tested at a tensile rate of 500 mm / min. Each sample was tested at least 8 times, and the average value was taken. The test error was controlled within 10%. The results are as follows: Figure 4 and 5 As shown.

[0050] Depend on Figure 4 and 5It can be seen that the longitudinal and transverse tensile strengths of each film sample remained between 18-25 MPa, and the elongation at break was higher than 400%. Among them, the longitudinal tensile strength of Examples 2 and 3 was slightly higher than that of the comparative example, and the elongation at break of the example series was not significantly different from that of the comparative example. This result shows that the mulch film of the examples still maintained good mechanical properties after the addition of oil shale semi-coke, and the longitudinal and transverse tensile strengths and toughness could meet the mechanical operation requirements of field laying and crop growth.

[0051] (4) Ultraviolet accelerated aging performance test This test was conducted using an indoor accelerated aging chamber with ultraviolet light: The mulch film samples from Comparative Examples 1-2 and Examples 1-3 were placed in the chamber, and the cycling conditions were set as "60℃ ultraviolet light (UVA light source) irradiation for 8 hours + 50℃ darkness condensation for 4 hours", with 12 hours constituting one cycle, repeated 10 times (the experimental period was 10 days). Samples were removed on the 5th and 10th days of the experiment, naturally air-dried, and the elongation at break retention rate was measured. The results are as follows: Figure 6 As shown.

[0052] Depend on Figure 6 It can be seen that the retention rate of elongation at break of each film sample decreased with the extension of aging time, but the performance of the examples and the comparative examples was similar. On the 5th day, the retention rate of elongation at break of all film samples remained above 70%; on the 10th day, the retention rate dropped to the range of 17%-23%. This indicates that the mulch film of Examples 1-3 did not show significant deterioration in its resistance to ultraviolet aging after the addition of oil shale semi-coke, and can meet the short-term (about 1-3 months) weather resistance requirements in the field.

[0053] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art can utilize the above technical content to make changes or modifications to create equivalent embodiments. Any simple modifications, equivalent changes, and modifications made to the above embodiments without departing from the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A black biodegradable mulch film for weed control, characterized by, The raw material composition, by mass parts, includes: 40-95 parts of biodegradable resin, 2-5 parts of polylactic acid, 1-35 parts of oil shale semi-coke, 5-12 parts of plasticizer, 0.5-2 parts of nucleating agent, 0.2-0.8 parts of antioxidant, 0.1-0.4 parts of lubricant, and 0.2-0.8 parts of ultraviolet absorber.

2. The black biodegradable mulch film according to claim 1, characterized in that, The raw material composition, by mass parts, includes: 72 parts biodegradable resin, 3 parts polylactic acid, 15 parts oil shale semi-coke, 5 parts plasticizer, 2 parts nucleating agent, 0.4 parts antioxidant, 0.2 parts lubricant, and 0.6 parts ultraviolet absorber.

3. The black biodegradable weed control film according to claim 1, characterized in that, The biodegradable resin is one or more of polybutylene succinate, propylene glycol phthalate-propylene carbonate copolymer, polyhydroxyalkanoate, or poly(butylene adipate / terephthalate); the polylactic acid has a molecular weight of 200,000-300,000. g / mol; the plasticizer is one or a combination of two of tributyl citrate and acetylated tributyl citrate, with a mass ratio of 1:1-2; the nucleating agent is one of magnesium silicate, calcium carbonate, calcium oxide, montmorillonite, and silicon dioxide, with a particle size of 20,000-40,000 mesh; the antioxidant is one or a combination of antioxidant 1010 and antioxidant 168, with a mass ratio of 1:1-1.5; the lubricant is one or a combination of erucamide and oleamide, with a mass ratio of 1:1-2; the ultraviolet absorber is one or more of UV-531, UV-326, and UV-400.

4. The black biodegradable weed control film according to claim 3, characterized in that, The biodegradable resin is a propylene glycol phthalate-propylene carbonate copolymer; the plasticizer is tributyl citrate; the nucleating agent is calcium carbonate; the antioxidant is antioxidant 1010; the lubricant is erucamide; and the ultraviolet absorber is UV-531.

5. The method for preparing the black biodegradable composite mulch film according to claim 1, characterized in that, The specific steps are as follows: (1) The oil shale semi-coke is dried, then ball-milled and sieved to obtain pretreated oil shale semi-coke; (2) The pretreated oil shale semi-coke obtained in step (1) is added to a high-speed mixer along with plasticizer and lubricant to obtain surface-modified oil shale semi-coke; (3) The biodegradable resin, PLA, nucleating agent, antioxidant and ultraviolet absorber are dried, and then added together with the modified oil shale semi-coke obtained in step (2) into a twin-screw extruder. After melt blending, they are extruded and pelletized to obtain special granules for mulch film, and then dried. (4) Blow molding: The granules obtained in step (3) are added to a blow molding machine and extruded and blow molded to obtain a black biodegradable grass cutter film.

6. The method for preparing the black biodegradable composite mulch film according to claim 5, characterized in that, In step (1), the drying temperature is 70-100℃, and the time is 8-12h; the agate beads filling rate in the ball mill jar is 40%-60% of the volume, the oil shale semi-coke filling rate is 25%-40% of the volume, the ball mill speed is 40-80Hz, the ball milling time is 40-180min, and it is passed through a 20000-40000 mesh sieve; the particle size of the pretreated oil shale semi-coke is 20000-40000 mesh, and the specific surface area is ≥20m². 2 / g, moisture content ≤0.5%.

7. The method for preparing the black biodegradable composite mulch film according to claim 5, characterized in that, In step (2), oil shale semi-coke is mixed with plasticizer and lubricant at high speed at a temperature of 90-130℃ and a rotation speed of 800-1200r / min for 20-30min to obtain preliminarily mixed surface-modified oil shale semi-coke.

8. The method for preparing the black biodegradable composite mulch film according to claim 5, characterized in that, The drying conditions for the biodegradable resin, PLA, nucleating agent, antioxidant, and UV absorber in step (3) are as follows: drying in a 60-80℃ forced-air drying oven for 6-10 hours, then adding them to a twin-screw extruder with a feed rate of 50-200 g / min, a screw speed of 60-100 rpm, and barrel temperatures of 140-160℃ in zone 1, 160-175℃ in zone 2, 175-185℃ in zone 3, 175-185℃ in zone 4, 175-185℃ in zone 5, 160-175℃ in zone 6, and 165-180℃ at the die head. After melt blending, the mixture is extruded and pelletized to obtain granules for mulch film. The drying conditions for the granules for mulch film are as follows: drying in a 60-80℃ oven for 6-10 hours to remove surface adsorbed water.

9. The method for preparing the black biodegradable composite mulch film according to claim 5, characterized in that, In step (4), the granules are added to the blow molding machine, and the barrel temperature is set to 165-175℃ in zone 1, 170-185℃ in zone 2, 180-190℃ in zone 3, and 165-185℃ in the die head. The blow ratio is 2.5-3.

0. After blow molding, cooling and shaping, and edge trimming, a black biodegradable weed control film is obtained.

10. The method for preparing the black biodegradable composite mulch film according to any one of claims 5-9, characterized in that, The prepared mulch film has a thickness of 6-12µm, a light transmittance of ≤8%, a tensile strength of ≥18MPa, an elongation at break of ≥400%, and a biodegradation rate of ≥60% under soil composting conditions for 6-12 months.

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