Biodegradable mulching film raw material composition, biodegradable mulching film and preparation method of biodegradable mulching film

Abstract

The invention relates to a biodegradable mulching film raw material composition, a biodegradable mulching film and a preparation method of the biodegradable mulching film. The invention relates to a raw material composition for a biodegradable mulching film. Comprising the following components in parts by weight: 50 to 90 parts of poly (butylene terephthalate)-adipate, 5 to 20 parts of composite powder, 0.2 to 1 part of a coupling agent, 0.2 to 1 part of a lubricant, 5 to 30 parts of polypropylene carbonate and a modifier, 0.1 to 1 part of a hydrolysis time regulator, 0.4 to 1 part of a hindered amine light stabilizer, 0.2 to 0.5 part of an antioxidant and 0.2 to 0.8 part of a compatilizer. Wherein the composite powder comprises calcium carbonate and talcum powder; the crystal diameter of the calcium carbonate is 2-5 nanometers, and the crystal is needle-shaped or fibrous; the crystal size of the talcum powder is 2-5 nanometers, the crystal is in a sheet shape or a scale shape, and the length-diameter ratio of the crystal is larger than or equal to 20: 1. The biodegradable mulching film formed by the raw material composition has low water vapor permeability, and the biodegradation time and the degradation rate can be regulated and controlled.

Description

Technical Field

[0001] This invention relates to the field of biodegradable film technology, and in particular to a biodegradable mulch film raw material composition, a biodegradable mulch film, and a method for preparing the same. Background Art

[0002] In the 1950s, with the development of plastics science, plastic film mulching technology was introduced into agricultural planting, initially mainly for strawberry cultivation. Because mulching can significantly increase soil temperature, prevent soil moisture evaporation, maintain soil looseness, and control weeds, it helps promote seed germination and crop growth. Therefore, the types of crops using it have gradually expanded from cash crops to major food crops such as corn, wheat, and rice, with its application scope and area continuously expanding, effectively improving agricultural productivity. However, mulching has also brought about serious problems of residual mulch pollution, causing severe "white pollution."

[0003] In recent years, the development of fully biodegradable plastics has offered a possible solution to this problem. Because biodegradable polymers are broken down by microorganisms into water and carbon dioxide, mulch films made from them will gradually degrade in the soil after use, preventing large-scale accumulation and thus avoiding pollution of the soil and surrounding environment. Biodegradable mulch films based on polyester materials (such as PLA, PBS, and PBAT) have become an alternative. Among them, PBAT (polybutylene terephthalate) has become one of the mainstream raw materials due to its good flexibility, high ductility, and wide processing adaptability.

[0004] However, existing PBAT-based biodegradable mulch films still have the following significant drawbacks: Excessive water vapor transmission rate: PBAT molecular chains have weaker polarity, and its water vapor barrier properties (WVTR) are significantly lower than those of PE (usually 2-5 times higher), resulting in insufficient moisture retention and weed suppression, especially in arid areas where frequent irrigation is required; Uncontrollable degradation behavior: PBAT relies on microbial enzymatic hydrolysis in soil. Its degradation rate is greatly affected by environmental temperature and humidity and microbial community. It may disintegrate prematurely (loss of function) or remain (not completely degraded for more than 2 years), which cannot match the needs of crop growth cycle. Summary of the Invention

[0005] Therefore, it is necessary to provide a biodegradable mulch film raw material composition, a biodegradable mulch film, and a method for preparing the same, which have low water vapor permeability and adjustable biodegradation time and rate.

[0006] A biodegradable mulch film raw material composition, comprising the following components in parts by weight: 50 to 90 parts of polybutylene terephthalate (PET); 5 to 20 parts of composite powder; 0.2 to 1 part coupling agent; Lubricant 0.2 to 1 part; 5 to 30 parts of polypropylene carbonate and its modifiers; Hydrolysis time regulator: 0.1 to 1 part; 0.4 to 1 part hindered amine light stabilizer; Antioxidant 0.2 to 0.5 parts; and Compatibilizer: 0.2 to 0.8 parts; The composite powder comprises calcium carbonate and talc; the calcium carbonate has a crystal diameter of 2-5 nanometers and a crystal morphology of needle-like or fibrous; the talc has a crystal size of 2-5 nanometers and a crystal morphology of platy or scaly, with an aspect ratio ≥20:1; the mass ratio of calcium carbonate to talc is (1-5):1. The lubricant includes an internal lubricant and an external lubricant, and the mass ratio of the internal lubricant to the external lubricant is 1:(2~5). The hydrolysis time regulator includes one or a mixture of multiple polyimide anti-hydrolysis agents and epoxy chain extenders.

[0007] In the above-mentioned biodegradable mulch film raw material composition, two different crystal forms of calcium carbonate and talc crystals are intercalated within each other, effectively reducing the intermolecular porosity in PBAT, thereby reducing the water vapor transmission rate of the PBAT agricultural film. Polypropylene carbonate and its modified chain segments provide rapid hydrolysis sites, while the hydrolysis time regulator, through anti-hydrolysis agents capturing carboxyl groups or chain extenders repairing molecular chains, dynamically controls the ester bond breaking rate. An internal lubricant promotes the dispersion of nanoparticles, while an external lubricant reduces melt-equipment friction. A hindered amine light stabilizer quenches ultraviolet free radicals; an antioxidant inhibits processing heat oxidation; and a compatibilizer enhances the interfacial bonding between the raw materials. The combination of these components and the aforementioned mass ratio range of each component were determined through extensive experimentation. This combination and mass ratio range enable the biodegradable mulch film formed from the biodegradable mulch film raw material composition of the present invention to have the advantages of low water vapor transmission rate and adjustable biodegradation time and rate.

[0008] In one embodiment, the coupling agent includes one or a mixture of more than one of silane coupling agents, phosphate coupling agents, and titanate coupling agents.

[0009] In one embodiment, the internal lubricant comprises one or a mixture of multiple polyhydroxyalkyl aluminum salts and stearates.

[0010] In one embodiment, the external lubricant comprises one or more of silicone resins and polyol lubricants.

[0011] In one embodiment, the polypropylene carbonate and its modifiers include one or a mixture of PPC, PPCP, and PPC-TPU.

[0012] In one embodiment, the antioxidant is BASF Irganox 1010; The compatibilizer is a maleic anhydride-based graft compatibilizer.

[0013] A method for preparing a biodegradable mulch film includes the following steps: According to parts by weight, any of the above-mentioned biodegradable mulch film raw material compositions are mixed evenly, and then extruded and granulated to obtain masterbatch; and The masterbatch is melt-co-extruded and blown into film to obtain a biodegradable mulch film.

[0014] The above-mentioned method for preparing biodegradable mulch film is simple, and the prepared biodegradable mulch film has the advantages of low water vapor permeability and adjustable biodegradation time and degradation rate, which is conducive to its widespread application.

[0015] In one embodiment, the extrusion granulation includes a material feeding section, a material melting section, a plasticizing section, and a conveying section arranged in sequence. The temperature of the material feeding section is 80°C to 120°C, the temperature of the material melting section is 120°C to 140°C, the temperature of the plasticizing section is 140°C to 150°C, and the temperature of the conveying section is 145°C to 150°C.

[0016] In one embodiment, the melt co-extrusion blown film includes a material feeding section, a material melting section, a plasticizing section, and a conveying section arranged sequentially. The temperature of the material feeding section is 80℃~120℃, the temperature of the material melting section is 120℃~140℃, the temperature of the plasticizing section is 140℃~145℃, the temperature of the conveying section is 145℃~155℃, the temperature of the die head is 140℃~150℃, the expansion ratio is 2.5~3.5, and the draw ratio is 2.5~3.5.

[0017] A biodegradable mulch film is prepared using the above-described method for preparing biodegradable mulch films.

[0018] Through experimental verification, the biodegradable mulch film of the present invention has the advantages of low water vapor permeability and adjustable biodegradation time and degradation rate, which is conducive to its widespread application. Attached Figure Description

[0019] Figure 1This is a flowchart of a method for preparing a biodegradable mulch film according to one embodiment of the present invention. Detailed Implementation

[0020] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0022] One embodiment of the biodegradable mulch film raw material composition comprises, by weight parts: 50 to 90 parts of polybutylene terephthalate (PET); 5 to 20 parts of composite powder; 0.2 to 1 part coupling agent; Lubricant 0.2 to 1 part; 5 to 30 parts of polypropylene carbonate and its modifiers; Hydrolysis time regulator: 0.1 to 1 part; 0.4 to 1 part hindered amine light stabilizer; Antioxidant 0.2 to 0.5 parts; and Compatibilizer: 0.2 to 0.8 parts.

[0023] The composite powder comprises calcium carbonate and talc; the crystal diameter of calcium carbonate is 2-5 nanometers, and the crystal morphology is needle-like or fibrous; the crystal size of talc is 2-5 nanometers, and the crystal morphology is platy or scaly, with an aspect ratio ≥20:1; the mass ratio of calcium carbonate to talc is (1-5):1. Further, the aspect ratio is preferably 20:1-50:1, and can be, but is not limited to, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1, or 50:1; the mass ratio of calcium carbonate to talc can be, but is not limited to, 1:1, 2:1, 3:1, 4:1, or 5:1.

[0024] The lubricant includes an internal lubricant and an external lubricant, with a mass ratio of internal lubricant to external lubricant of 1:(2~5). Further, the mass ratio of internal lubricant to external lubricant may be, but is not limited to, 1:2, 1:3, 1:4, or 1:5.

[0025] The hydrolysis time regulator includes one or more of the following: polyimide anti-hydrolysis agents and epoxy chain extenders. In other words, the hydrolysis time regulator can be a polyimide anti-hydrolysis agent, an epoxy chain extender, or a mixture of both.

[0026] In the biodegradable mulch film raw material composition of the above embodiments, the flake talc mainly plays a labyrinth effect, prolonging the water vapor diffusion path; while the needle-shaped calcium carbonate plays a supporting and cross-linking role, synergistically forming a denser network with the talc flakes. These two different crystal forms of calcium carbonate and talc, "flake-needle," are intercalated within each other, effectively reducing the intermolecular porosity in PBAT, thereby reducing the water vapor permeability of the PBAT agricultural film.

[0027] In the biodegradable mulch film raw material composition of the above embodiments, the coupling agent acts as an interfacial bridge between inorganic fillers and organic matter, inhibiting the performance degradation caused by filler agglomeration and optimizing the processing rheological behavior.

[0028] In the biodegradable mulch film raw material composition of the above embodiments, polypropylene carbonate and its modifiers play a carbon fixation role, and their chain segments can provide rapid hydrolysis sites. The hydrolysis activation energy of the carbonate bond (-OC(O)-O-) in the molecular chain of polypropylene carbonate and its modifiers (approximately 50 kJ / mol) is significantly lower than that of the ester bond (>80 kJ / mol) in PBAT, making it more susceptible to water molecule attack. Therefore, it can preferentially hydrolyze in the soil, forming microporous channels (increasing specific surface area), accelerating water / microbial infiltration, and initiating initial degradation. Polypropylene carbonate and its modifiers can reduce the water vapor permeability of the mulch film and improve its toughness. By adding these substances, the water vapor permeability of the mulch film can be significantly reduced to a low level, and the longitudinal and transverse elongation at break of the mulch film can be increased to ≥300%.

[0029] In the biodegradable mulch film raw material composition of the above embodiments, the polyimide anti-hydrolysis agent can control the ester bond breaking rate by capturing carboxyl groups, and the epoxy chain extender can dynamically control the ester bond breaking rate by repairing molecular chains. Depending on different regions and crop growth cycle requirements, different proportions of polyimide anti-hydrolysis agents or epoxy chain extenders can be added to the mulch film to regulate its degradation time.

[0030] In the biodegradable mulch film raw material composition of the above embodiments, the internal lubricant promotes the dispersion of nanoparticles, and the external lubricant reduces the friction between the melt and the equipment.

[0031] In the biodegradable mulch film raw material composition of the above embodiments, hindered amine light stabilizers are used to quench ultraviolet free radicals, antioxidants are used to inhibit processing heat oxidation, and compatibilizers are used to enhance the interfacial bonding between the raw materials. Depending on the climatic conditions and solar radiation intensity of different regions, different proportions of hindered amine light stabilizers and antioxidants can be added to the mulch film to regulate the photodegradation time of the mulch film and achieve the purpose of controlling the degradation induction period of the mulch film.

[0032] In the biodegradable mulch film raw material composition of the above embodiments, the combination of each component and the above-mentioned mass ratio range of each component were determined through a large number of experiments. The above combination and mass ratio range enable the biodegradable mulch film formed by the biodegradable mulch film raw material composition of the present invention to have the advantages of low water vapor permeability and controllable biodegradation time and degradation rate.

[0033] Based on the aforementioned embodiments, the coupling agent includes one or a mixture of more than one of silane coupling agents, phosphate coupling agents, and titanate coupling agents. Silane coupling agents have strong bonds with the -OH groups on the filler surface, which can improve the filler-polymer interfacial strength; phosphate coupling agents can reduce the polymer melt viscosity and improve processing fluidity; titanate coupling agents have flame retardant and hydrolysis-resistant properties, which can delay initial degradation.

[0034] Based on the aforementioned embodiments, the internal lubricant comprises one or a mixture of multiple polyhydroxyalkyl aluminum salts and stearates. The aluminum ions of the polyhydroxyalkyl aluminum salt can complex PBAT ester bonds, and the hydroxyl groups shield inter-chain friction, reducing viscosity. The metal ions of the stearate interact with the filler, and the long alkyl chains promote chain slippage, thereby inhibiting interfacial friction between the filler and the polymer, and reducing viscosity.

[0035] Based on the aforementioned embodiments, the external lubricant includes one or a mixture of silicone resin and polyol lubricants. Silicone resin can form a molecular adsorption layer on the metal surface, reducing the coefficient of friction between the melt and the die; polyol lubricants can migrate to the surface of the film bubble, reducing the surface tension of the melt and decreasing the surface roughness of the film.

[0036] Based on the aforementioned embodiments, polypropylene carbonate and its modifiers include one or a mixture of PPC (poly(propylene carbonate)), PPCP (maleic anhydride-grafted poly(propylene carbonate)), and PPC-TPU (poly(propylene carbonate)-thermoplastic polyurethane block copolymer). Further, PPC is obtained by ring-opening polymerization of carbon dioxide and epoxy compounds (such as ethylene oxide, propylene oxide, and cyclohexane oxide) under the action of a catalyst. It is a carbon-negative carbon dioxide-based polymer, and the production of one ton of the above-mentioned carbon dioxide-based polymer will absorb 500 kg of carbon dioxide.

[0037] Based on the aforementioned embodiments, the antioxidant is BASF Irganox 1010 (chemical name: pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]). BASF Irganox 1010 provides irreplaceable comprehensive protective efficacy in biodegradable mulch film systems. On one hand, its molecule contains four hindered phenolic units, each containing a sterically hindered tert-butyl group, which can capture four free radical chains, thus achieving synergistic antioxidant activity across four functional groups. On the other hand, the benzene ring in its molecule forms a conjugation with the carbonyl group of PBAT, resulting in electron delocalization and dispersion, significantly improving antioxidant efficiency.

[0038] Based on the aforementioned embodiments, the compatibilizer is a maleic anhydride-based grafted compatibilizer. Maleic anhydride-based grafted compatibilizers (such as maleic anhydride-grafted polyolefin elastomers) can solve multiphase incompatibility problems in biodegradable mulch film systems through precise interface engineering.

[0039] In the above-mentioned biodegradable mulch film raw material composition, two different crystal forms of calcium carbonate and talc crystals are intercalated within each other, effectively reducing the intermolecular porosity in PBAT, thereby reducing the water vapor transmission rate of the PBAT agricultural film. Polypropylene carbonate and its modified chain segments provide rapid hydrolysis sites, while the hydrolysis time regulator, through anti-hydrolysis agents capturing carboxyl groups or chain extenders repairing molecular chains, dynamically controls the ester bond breaking rate. An internal lubricant promotes the dispersion of nanoparticles, while an external lubricant reduces melt-equipment friction. A hindered amine light stabilizer quenches ultraviolet free radicals; an antioxidant inhibits processing heat oxidation; and a compatibilizer enhances the interfacial bonding between the raw materials. The combination of these components and the aforementioned mass ratio range of each component were determined through extensive experimentation. This combination and mass ratio range enable the biodegradable mulch film formed from the biodegradable mulch film raw material composition of the present invention to have the advantages of low water vapor transmission rate and adjustable biodegradation time and rate.

[0040] Please see Figure 1 The method for preparing a biodegradable mulch film according to one embodiment of the present invention includes the following steps: S10. Mix any of the above biodegradable mulch film raw material compositions evenly according to the mass fraction, and then extrude and granulate to obtain masterbatch.

[0041] In step S10, the extrusion granulation process is typically carried out in a twin-screw extruder, meaning that the extruder can granulate the material into blown film particles. A twin-screw extruder is usually divided into multiple heating zones along the material conveying direction to achieve precise temperature control of the material under different physical states (such as solid conveying, melting, plasticizing, and homogenization). Furthermore, the blown film particles can be further dehydrated to obtain masterbatch.

[0042] In one embodiment, the extrusion granulation operation is as follows: raw and auxiliary materials of different components are weighed separately using a loss-in-weight scale, fed into a twin-screw extruder through a metering screw, a vacuum device is set in the middle and rear of the screw to remove the moisture and low molecular weight substances generated in the screw, the material strip is cooled by an air-cooling device, and then cut into particles of 3mm to 5mm size by a pelletizer, which are the masterbatches.

[0043] In one embodiment, extrusion granulation includes a material feeding section, a material melting section, a plasticizing section, and a conveying section arranged in sequence. The temperature of the material feeding section is 80°C to 120°C, the temperature of the material melting section is 120°C to 140°C, the temperature of the plasticizing section is 140°C to 150°C, and the temperature of the conveying section is 145°C to 150°C.

[0044] It should be noted that twin-screw extruders typically have several heating zones. The "material feeding zone" usually corresponds to zones 1-2 near the feed inlet, mainly responsible for preheating and conveying the material. The "material melting zone" corresponds to the subsequent zones and is the key area for material melting and blending. The "plasticizing zone" corresponds to the homogenization zone after the melting zone, ensuring that the components are fully dispersed and plasticized. The "conveying zone" corresponds to the high-temperature zone in front of the die head or prongs, ensuring that the melt is output in a uniform and stable flow pattern.

[0045] S20. The masterbatch obtained in step S10 is melt-co-extruded and blown into film to obtain a biodegradable mulch film.

[0046] In step S20, the melt co-extrusion blown film process is usually carried out in a single-layer or multi-layer co-extrusion blown film equipment. The single-layer or multi-layer co-extrusion blown film equipment is usually divided into multiple heating zones along the material conveying direction in order to achieve precise temperature control of the material under different physical states (such as solid conveying, melting, plasticizing, and homogenization).

[0047] Specifically, the melt co-extrusion blown film step can be carried out using single-layer, double-layer, or triple-layer co-extrusion blown film equipment. When using a single-layer extrusion blown film process, the process is the simplest and lowest cost, suitable for applications with general requirements for film uniformity and mechanical properties. When using a double-layer co-extrusion blown film process, the film can be endowed with certain asymmetric structural potential; for example, the inner and outer surface properties of the film can be optimized by adjusting the processing temperature or rate of the two melt layers, or functional differentiation can be achieved in future formulation expansion. Preferably, a triple-layer co-extrusion blown film process is used. This process can significantly improve melt strength and film bubble stability, greatly improve film thickness uniformity, and reduce performance degradation caused by local defects, thereby obtaining a high-quality film with the most consistent and reliable mechanical properties, barrier properties, and degradation behavior. The three-layer structure also provides a direct technological basis for the future development of functionally graded film products (such as adding different additives to the inner and outer layers).

[0048] In one embodiment, the melt co-extrusion blown film includes a material feeding section, a material melting section, a plasticizing section, and a conveying section arranged sequentially. The temperature of the material feeding section is 80℃~120℃, the temperature of the material melting section is 120℃~140℃, the temperature of the plasticizing section is 140℃~145℃, the temperature of the conveying section is 145℃~155℃, the temperature of the die head is 140℃~150℃, the expansion ratio is 2.5~3.5, and the draw ratio is 2.5~3.5.

[0049] It should be noted that co-extrusion blown film equipment typically has several heating zones. The "material input zone" usually corresponds to zones 1-2 near the feed inlet of the equipment, mainly responsible for preheating and conveying the material; the "material melting zone" corresponds to several subsequent zones and is the key area for the material to achieve melt blending; the "plasticizing zone" corresponds to the homogenization zone after the melting zone, ensuring that each component is fully dispersed and plasticized; and the "conveying zone" corresponds to the high-temperature zone in front of the die head or prong, ensuring that the melt is output in a uniform and stable flow state.

[0050] The aforementioned temperature, expansion ratio, and draw ratio ranges were optimized through extensive experimentation. Within these ranges, good dispersion of the nanoparticles and stability of the film bubbles can be ensured, resulting in a biodegradable mulch film with uniform thickness, excellent mechanical properties, and high water vapor barrier properties. Furthermore, in the melt co-extrusion blown film operation of the masterbatch, the expansion ratio can be, but is not limited to, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, or 3.5, and the draw ratio can be, but is not limited to, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, or 3.5.

[0051] The biodegradable mulch film prepared by the method of this embodiment has a significantly reduced water vapor permeability to a low level, which can be as low as <300g / (㎡.24h), longitudinal and transverse tensile strength ≥2N, elongation at break ≥300%, and tear strength ≥1.8kn / m.

[0052] The above-mentioned method for preparing biodegradable mulch film is simple, and the prepared biodegradable mulch film has the advantages of low water vapor permeability and adjustable biodegradation time and degradation rate, which is conducive to its widespread application.

[0053] One embodiment of the biodegradable mulch film is prepared using the above-described method for preparing biodegradable mulch film.

[0054] Through experimental verification, the biodegradable mulch film of the present invention has the advantages of low water vapor permeability and adjustable biodegradation time and degradation rate, which is conducive to its widespread application.

[0055] Referring to the above embodiments, in order to make the technical solution of the present invention more specific, clear and easy to understand, examples of the technical solution of the present invention are given below. However, it should be noted that the content to be protected by the present invention is not limited to the following embodiments.

[0056] The raw materials used in the following embodiments include: Polybutylene terephthalate (PET) adipate, manufactured by Sinopec Yizheng Chemical Fiber Co., Ltd., product code TA200; Composite powder (calcium carbonate + talc), manufactured by Liaoning Jinghua New Materials Co., Ltd., product code Ta-1008; Silane coupling agent, manufactured by Hangzhou Haiyi Polymer Materials Co., Ltd., product code HY-3525G; Internal lubricant, polyhydroxyalkyl aluminum salt, manufactured by Hangzhou Haiyi Polymer Materials Co., Ltd., product code HY-418L; External lubricant... Lubricant, manufactured by Hangzhou Haiyi Polymer Materials Co., Ltd., product code HY-5501; Polypropylene carbonate and its modifiers, manufactured by Taizhou Jinlong New Materials Co., Ltd., product code T-9; Hydrolysis time regulator, manufactured by Nanjing Baitong New Materials Co., Ltd., product code BTWR-500(CN); Hindered amine light stabilizer, manufactured by Suqian Liansheng Technology Co., Ltd., product code 783G; Antioxidant, manufactured by BASF, product code Irganox 1010; Compatibilizer, manufactured by Shanghai Xiuyuan Chemical Co., Ltd., product code P-303.

[0057] Examples 1-5 and Comparative Examples 1-4 According to Table 1, weigh each raw material, mix them evenly, and then granulate them into blown film particles through a twin-screw extruder. The process temperature of the twin-screw extruder granulation is set according to the material process as follows: material feeding section (zone I to II) 80℃ / 100℃, material melting section (zone III to V) 120℃ / 135℃ / 140℃, plasticizing section (zone VI) 145℃, conveying section (zone VII) 150℃. After the particles are cooled, masterbatch is obtained. The above masterbatch was melt-co-extruded and blown into film using a three-layer co-extrusion blown film mill. The process temperature of the three-layer co-extrusion blown film mill was set according to the material process as follows: material input section (zones I to II) 120℃ / 125℃, material melting section (zones III to IV) 130℃ / 140℃, plasticizing section (zone V) 145℃, conveying section (zone VI) 155℃, die temperature 150℃, expansion ratio 3.5, and draw ratio 2.5, to obtain the biodegradable mulch films of Examples 1 to 5 and Comparative Examples 1 to 4.

[0058] Table 1. Raw material list for the examples and comparative examples Performance testing: The water vapor transmission rate, induction period, service life, longitudinal and transverse tensile strength, elongation at break and tear strength of the above embodiments were tested. The test methods are as follows, and the test results are shown in Table 2.

[0059] Water vapor transmission rate: Test method or test standard "GBT 35795-2017 Fully biodegradable agricultural ground cover film".

[0060] Induction period: The period during which the mulch film maintains its effective covering function. After the mulch film is laid, samples are taken from the field to test the tensile strength and elongation at break of the mulch film. The milestone is when the tensile strength and elongation at break of the film are ≥50% of the initial tensile strength and elongation at break.

[0061] Use period: The period during which the plastic film can effectively perform its main agronomic functions, specifically the point in time when the plastic film in the field breaks down over a large area and loses its ability to provide continuous coverage.

[0062] Longitudinal and transverse tensile strength: GBT 35795-2017 "Fully biodegradable agricultural ground cover film".

[0063] Elongation at break: GBT 35795-2017 "Fully biodegradable agricultural ground cover film".

[0064] Tear strength: GBT 35795-2017 "Fully biodegradable agricultural ground cover film".

[0065] Table 2 Performance test results of the examples and comparative examples As can be clearly seen from the performance test results in Table 2, by adjusting the proportion of key components in the raw material composition of the present invention, the water vapor transmission rate, induction period and service period of the biodegradable mulch film can be effectively controlled, thereby achieving precise design of the degradation behavior and agronomic function of the mulch film.

[0066] This demonstrates that the present invention possesses excellent controllability. For example: Example 3 demonstrates the best overall performance: it has the lowest water vapor transmission rate (220 g / (㎡·24h)) and the longest induction period (120 days) and application period (180 days), indicating that the formulation has a slow degradation rate, the best functional durability, and is suitable for crops with long growth cycles. Examples 1, 2, 4, and 5 demonstrate different combinations of performance: by changing the content of components such as polypropylene carbonate and its modifiers, and composite powders, different barrier properties and degradation cycles were obtained to meet the needs of different application scenarios. In contrast, Comparative Example 1 (without added polypropylene carbonate and modifiers) had an extremely high water vapor transmission rate (1200 g / (㎡·24h)) and a significantly shortened induction period and service life, proving that PPC and its modifiers are crucial for reducing water permeability and regulating the degradation initiation point. Comparative Examples 2-4 (excessive composite powder content) show that although fillers help reduce costs, excessive addition (exceeding the range of 5-20 parts required by this invention) can lead to agglomeration, which in turn increases water vapor permeability and seriously impairs the mechanical properties (reduction in tensile strength and elongation at break) and durability (shortened induction period and service life) of the material.

[0067] The above results fully demonstrate that the present invention, through the raw material composition and its proportion range, can produce biodegradable mulch films with low water vapor permeability, excellent mechanical properties, and flexible controllable degradation time and rate, thereby adapting to the needs of different crop growth cycles, planting areas and climatic environments.

[0068] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0069] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A biodegradable mulch film raw material composition, characterized in that, Based on parts by mass, it includes the following components: 50 to 90 parts of polybutylene terephthalate (PET); 5 to 20 parts of composite powder; 0.2 to 1 part coupling agent; Lubricant 0.2 to 1 part; 5 to 30 parts of polypropylene carbonate and its modifiers; Hydrolysis time regulator: 0.1 to 1 part; 0.4 to 1 part hindered amine light stabilizer; Antioxidant 0.2 to 0.5 parts; as well as Compatibilizer: 0.2 to 0.8 parts; The composite powder comprises calcium carbonate and talc; the calcium carbonate has a crystal diameter of 2-5 nanometers and a crystal morphology of needle-like or fibrous; the talc has a crystal size of 2-5 nanometers and a crystal morphology of platy or scaly, with an aspect ratio ≥20:1; the mass ratio of calcium carbonate to talc is (1-5):

1. The lubricant includes an internal lubricant and an external lubricant, and the mass ratio of the internal lubricant to the external lubricant is 1:(2~5). The hydrolysis time regulator includes one or a mixture of multiple polyimide anti-hydrolysis agents and epoxy chain extenders.

2. The biodegradable mulch film raw material composition according to claim 1, characterized in that, The coupling agent includes one or a mixture of more than one of silane coupling agents, phosphate coupling agents, and titanate coupling agents.

3. The biodegradable mulch film raw material composition according to claim 1, characterized in that, The internal lubricant comprises one or a mixture of multiple polyhydroxyalkyl aluminum salts and stearates.

4. The biodegradable mulch film raw material composition according to claim 1, characterized in that, The external lubricant includes one or a mixture of silicone resins and polyol lubricants.

5. The biodegradable mulch film raw material composition according to claim 1, characterized in that, The polypropylene carbonate and its modifiers include one or a mixture of PPC, PPCP and PPC-TPU.

6. The biodegradable mulch film raw material composition according to claim 1, characterized in that, The antioxidant is BASF Irganox 1010; The compatibilizer is a maleic anhydride-based graft compatibilizer.

7. A method for preparing a biodegradable mulch film, characterized in that, Includes the following steps: The biodegradable mulch film raw material composition according to any one of claims 1 to 6 is mixed evenly according to parts by weight, and then extruded and granulated to obtain masterbatch; and The masterbatch is melt-co-extruded and blown into film to obtain a biodegradable mulch film.

8. The method for preparing biodegradable mulch film according to claim 7, characterized in that, The extrusion granulation includes a material feeding section, a material melting section, a plasticizing section, and a conveying section arranged in sequence. The temperature of the material feeding section is 80℃~120℃, the temperature of the material melting section is 120℃~140℃, the temperature of the plasticizing section is 140℃~150℃, and the temperature of the conveying section is 145℃~150℃.

9. The method for preparing the biodegradable mulch film according to claim 7, characterized in that, The melt co-extrusion blown film comprises a material feeding section, a material melting section, a plasticizing section, and a conveying section arranged in sequence. The temperature of the material feeding section is 80℃~120℃, the temperature of the material melting section is 120℃~140℃, the temperature of the plasticizing section is 140℃~145℃, the temperature of the conveying section is 145℃~155℃, the temperature of the die head is 140℃~150℃, the expansion ratio is 2.5~3.5, and the draw ratio is 2.5~3.

5.

10. A biodegradable mulch film, characterized in that, The biodegradable mulch film is prepared using the method described in any one of claims 7 to 9.

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