Functional full-biodegradable mulching film with multi-layer composite structure and preparation method of functional full-biodegradable mulching film

Abstract

The invention relates to the technical field of biodegradable material processing, and discloses a functional full-biodegradable mulching film with a multi-layer composite structure and a preparation method thereof, the mulching film has a three-layer co-extrusion structure, and an outer layer and an inner layer take poly (adipic acid) / butylene terephthalate resin as a matrix; the core layer comprises poly (butylene adipate / terephthalate), polypropylene carbonate, surface-activated fine plant fibers, a reactive compatibilizer containing an epoxy group and an endothermic foaming agent. According to the preparation method, a differential temperature co-extrusion process is adopted, the extrusion temperature of the core layer is set to be higher than that of the outer layer and the inner layer, and a compatibilizer at an interface is activated by temperature difference to initiate a chemical bonding reaction between the core layer and the surface layer. According to the invention, through cooperation of in-situ reaction compatibilization and micro-foaming technologies, the technical problems of mechanical property reduction and interlayer stripping of the high-filling mulching film are solved, and low cost, light weight and high strength of the mulching film are realized.

Description

Technical Field

[0001] This invention relates to the field of biodegradable material processing technology, specifically to a multi-layer composite functional fully biodegradable mulch film and its preparation method. Background Technology

[0002] Fully biodegradable mulch film is one way to solve the problem of residual mulch film pollution in farmland. Resins such as poly(butylene adipate) / poly(terephthalate) terephthalate are biodegradable, but their raw material costs are higher than those of polyethylene mulch film. To reduce costs, fillers such as starch, calcium carbonate, or plant fibers are usually added to the resin matrix.

[0003] The addition of fillers affects the continuity of the resin matrix. Polyester materials mainly rely on molecular chain entanglement to maintain melt viscosity; fillers hinder the interaction of molecular chains, leading to a decrease in melt strength. During blown film processing, the melt is unable to withstand the tensile forces generated by traction and inflation, easily resulting in film bubble instability or rupture. This situation limits the thinning of mulch films, making it difficult to produce thinner products.

[0004] Furthermore, biomass fillers such as plant fibers contain hydroxyl groups on their surface, exhibiting hydrophilicity, while the polyester matrix is ​​hydrophobic, resulting in poor interfacial compatibility. In physical blending systems, the fillers are unevenly dispersed in the matrix, easily leading to agglomeration. These agglomeration points cause stress concentration when the mulch film is under stress, resulting in a decrease in tensile strength, tear resistance, and elongation at break, making it difficult to meet the coverage requirements for the crop growth cycle. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a multi-layer composite structure functional fully biodegradable mulch film and its preparation method, which solves the technical problems of existing fully biodegradable mulch films, such as difficulty in stably blowing ultra-thin films and severe degradation of mechanical properties due to decreased melt strength and insufficient interfacial bonding force, when reducing costs through high filling.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A multi-layer composite functional fully biodegradable mulch film has a three-layer co-extruded structure, wherein the three layers are an outer layer, a core layer, and an inner layer. The outer layer and the inner layer are made from raw materials comprising the following parts by weight: Poly(butylene adipate) / terephthalate resin: 90-95 parts UV-531: 0.2-1.0 parts; Silica: 1.0-2.0 parts; Erucamide: 0.2-1.0 parts; Degradation regulator: 2.0-6.0 parts; The core layer is made from raw materials comprising the following parts by weight: Poly(butylene adipate) / butylene terephthalate resin: 40-55 parts; Polypropylene carbonate resin: 15-30 parts; Surface-activated microfibers: 20-35 parts; Styrene-acrylate-glycidyl methacrylate copolymer: 0.5-2.0 parts; Environmentally friendly heat-absorbing foaming agent: 0.5-2.5 parts; Erucamide: 0.2-0.8 parts.

[0007] By adopting the above technical solution, this invention utilizes the synergistic effect of multi-layer structural design and reactive blending system to achieve a balance between high filler content, lightweight, and high strength of the mulch film. The specific mechanism is as follows: Reactive compatibilization and enhancement mechanism: The styrene-acrylate-glycidyl methacrylate copolymer introduced into the core layer serves as a reactive compatibilizer. Utilizing the ring-opening of the epoxy groups on its molecular chain, it chemically bonds with the hydroxyl or carboxyl groups at the ends of poly(adipic acid / butylene terephthalate) resin and polypropylene carbonate resin, respectively. Simultaneously, the epoxy groups undergo grafting reactions with residual active groups on the surface of surface-activated micro-plant fibers. These chemical reactions construct a chemical cross-linking network between the resin, compatibilizer, and fibers, increasing the bonding strength at the phase interface, improving the stress concentration problem caused by poor interfacial compatibility between plant fibers and the polyester matrix, and enhancing the tensile strength and tear resistance of the mulch film.

[0008] Microporous toughening and lightweight mechanism: The environmentally friendly endothermic foaming agent decomposes when heated in the core layer to generate microbubbles, forming a structure in the polymer matrix that blunts the crack tips. When the film is torn by external force, the microporous structure induces the generation of silver crazing and absorbs the impact energy, thereby improving the right-angle tear strength. At the same time, the bubbles reduce the core layer density, thereby reducing the amount of material per unit area while keeping the total thickness unchanged.

[0009] Interlayer synergistic effect: The outer and inner layers use high-content PBAT resin combined with slip agents and anti-blocking agents to provide the integrity, weather resistance and slip-opening properties of the mulch film surface, protect the core layer from direct external erosion, and bear the main tensile load.

[0010] Preferably, the surface-activated microfiber is wheat straw powder whose surface has been modified by 3-aminopropyltriethoxysilane or aluminate coupling agent, and the D98 particle size of the surface-activated microfiber is 5-15 μm.

[0011] By employing the above technical solutions, the particle size of plant fibers is controlled within the range of 5-15 μm, avoiding the formation of defect points in large fiber particles during the blown film stretching process and ensuring film continuity at a thickness of 10-15 μm. After treatment with 3-aminopropyltriethoxysilane or aluminate coupling agents, the hydrophilic hydroxyl groups on the fiber surface are blocked by hydrophobic groups, reducing fiber hygroscopicity, improving its dispersibility in the hydrophobic polyester matrix, and reducing agglomeration.

[0012] Preferably, the thickness ratio of the outer layer, core layer, and inner layer is (15-20)%:(60-70)%:(15-20)%; the total thickness of the mulch film is 10-15 μm, and the density of the core layer is 0.75-0.90 g / cm³. 3 .

[0013] By adopting the above technical solution, the contribution rate of low-cost fibers and foamed structures is increased by utilizing a core layer with a proportion of 60-70%, thereby reducing the overall cost of the mulch film; the core layer density is controlled at 0.75-0.90 g / cm³. 3 This allows the same weight of raw materials to cover a larger land area.

[0014] Preferably, the degradation regulator comprises the following components in parts by weight: Polycarbodiimide: 0.5-1.5 parts; Polylactic acid: 1.0-3.0 parts; Calcium stearate: 0.5-1.5 parts.

[0015] By adopting the above technical solution, polycarbodiimide, as an anti-hydrolysis agent, can capture the terminal carboxyl groups generated by polyester hydrolysis and delay the degradation of the mulch film in the early stage of use; polylactic acid and calcium stearate, as degradation inducers, accelerate the disintegration in the later stage through water absorption and swelling and catalytic ester bond breaking. The three work together to achieve the controllable degradation characteristics of the mulch film, which is stable during its service life and rapidly degrades after disposal.

[0016] Preferably, the environmentally friendly heat-absorbing foaming agent comprises the following components in parts by weight: Sodium bicarbonate: 0.2-1.0 parts; Sodium citrate: 0.2-1.0 parts; Ultrafine calcium carbonate: 0.1-0.5 parts.

[0017] By adopting the above technical solution, the compound foaming system is an endothermic foaming system with a stable decomposition process. The endothermic effect helps to cool the melt and prevent polymer degradation caused by excessive shear heat. The generated cells are fine and uniform and will not damage the continuity of the film.

[0018] Secondly, the present invention provides a method for preparing a multi-layer composite structure functional fully biodegradable mulch film, employing the following technical solution: A method for preparing a multi-layer composite functional fully biodegradable mulch film, applied to the aforementioned multi-layer composite functional fully biodegradable mulch film, employs a three-layer co-extrusion blown film process, and includes the following steps: The raw materials for the outer layer, the core layer, and the inner layer are respectively added to the corresponding outer layer extruder, core layer extruder, and inner layer extruder, and plasticized to form each layer melt; The plasticized melt layers are conveyed to the co-extrusion die via the die connector at the end of their respective extruders; During the conveying process, the process temperature is controlled so that the temperature setpoint at the die head connector of the core extruder is 10-20°C higher than the temperature setpoint at the die head connector of the outer and inner extruders. The three-layer melt flows into the co-extrusion die. The temperature difference between the core melt and the outer and inner melts activates the styrene-acrylate-glycidyl methacrylate copolymer in the core melt, initiating an interfacial chemical bonding reaction between the core and the outer and inner layers. The multilayer melt after the reaction is extruded and blown through the die, cooled and shaped by the internal cooling system and air ring, and then pulled and wound to obtain the finished mulch film.

[0019] By adopting the above technical solution, the present invention employs a differentiated temperature co-extrusion process, the principle of which and its technical effects are as follows: In-situ reaction enhancement mechanism at the interface: The core melt temperature is set 10-20℃ higher than that of the outer / inner layer to form a temperature gradient. When the high-temperature core melt comes into contact with the relatively low-temperature outer / inner layer melt in the die head, heat is transferred to the interlayer interface, activating the epoxy groups of the styrene-acrylate-glycidyl methacrylate copolymer enriched at the interface. This induces a cross-interface chemical bonding reaction between the epoxy groups and the PBAT resin molecular chains of the outer / inner layer. This mechanism forms chemical anchors between the layers, improving the interlayer delamination problem caused by the large core filling amount in multilayer co-extruded mulch films.

[0020] Melt strength and processing stability: The relatively low temperature and high melt viscosity of the outer and inner melt layers support the core melt, encapsulating the fluid, bubble-containing core melt. This structure allows the melt to withstand a blow-up ratio of 4.0-5.0 times without rupturing after leaving the die, enabling thin-walled processing of high-filling mulch films.

[0021] Reaction time control: By establishing a temperature difference at the die head connector, the reactive compatibilizer reaches reactive activity before entering the die head confluence, avoiding premature reaction that leads to excessive cross-linking and screw blockage, and ensuring that the interfacial reaction is completed within the time it stays in the die.

[0022] Preferably, the temperature of the die head connector of the outer extruder and the inner extruder is set to 150-160℃; the temperature of the die head connector of the core extruder is set to 165-175℃; and the temperature of the co-extrusion die head is set to 165-175℃.

[0023] By adopting the above technical solution, this temperature range ensures that the PBAT matrix is ​​plasticized and does not undergo thermal degradation, while being within the kinetic temperature range of the glycidyl methacrylate epoxy ring-opening reaction, thus ensuring the chemical reaction proceeds.

[0024] Preferably, the blow-up ratio of the multilayer melt after reaction during extrusion and blowing through the die is controlled between 4.0 and 5.0, and the traction speed during traction and winding is controlled between 15 and 25 m / min.

[0025] By adopting the above technical solution, a blow-up ratio of 4.0-5.0 is used to orient the polymer molecular chains and micro-plant fibers along the circumferential direction of the membrane bubble, thereby improving the transverse mechanical strength of the mulch film.

[0026] Preferably, the raw material for the core layer is pre-prepared into a highly active composite masterbatch for the core layer, and the preparation steps of the highly active composite masterbatch for the core layer include: The poly(butylene adipate / terephthalate) resin, the polypropylene carbonate resin, the surface-activated microfiber, the styrene-acrylate-glycidyl methacrylate copolymer, the environmentally friendly heat-absorbing foaming agent, and the erucamide are mixed evenly to obtain a mixture. The mixture is then added to a twin-screw extruder for melt blending and granulation, followed by air-cooled die hot cutting and drying to obtain the core layer high-activity composite masterbatch. The die head temperature of the twin-screw extruder is set to 130°C.

[0027] By adopting the above technical solution and using a 130℃ extrusion granulation process, only the physical dispersion of each component is completed in the masterbatch preparation stage, thus inhibiting the chemical reactivity of the reactive compatibilizer. This preserves the epoxy group activity of the compatibilizer and the decomposition potential of the foaming agent, allowing them to be released during the subsequent high-temperature blown film stage, preventing loss of masterbatch flowability due to premature cross-linking.

[0028] Preferably, in the preparation of the core layer high-activity composite masterbatch, the preparation step of the surface-activated microfiber includes: pulverizing dried wheat straw powder with airflow to obtain microfiber with a D98 particle size of 5-15 μm; feeding the microfiber into a mixer, adding a treatment liquid or coupling agent under stirring conditions, heating to 105-120℃ and maintaining mixing for 10-15 minutes, discharging and cooling to room temperature to obtain the surface-activated microfiber.

[0029] By adopting the above technical solution and utilizing a high-temperature and high-speed mixing process, the chemical adsorption and condensation reaction of the coupling agent on the surface of the fine powder is promoted to form a hydrophobic coating layer, which improves the surface energy of the plant fiber and enables it to achieve micron-level dispersion when blended with hydrophobic resin.

[0030] This invention provides a multi-layered composite functional fully biodegradable mulch film and its preparation method. It possesses the following beneficial effects: 1. This invention introduces a reactive compatibilizer and an endothermic foaming agent containing epoxy groups into the core layer, and constructs a cross-linked network of resin, compatibilizer and plant fiber through in-situ chemical reaction, forming a micro-foamed structure in the matrix. This technical solution reduces the density of the mulch film and the cost of raw materials, while strengthening the interfacial bonding force through chemical bonding and passivating the crack tip through micropores, thereby improving the tensile strength and right-angle tear strength under high-filling system, solving the problem that fully biodegradable mulch films are difficult to balance with low cost and high mechanical performance.

[0031] 2. This invention employs a differentiated co-extrusion process where the core layer temperature is higher than that of the outer and inner layers. By utilizing the melt temperature difference, reactive compatibilizers at the interface are directionally activated within the manifold die. This process induces cross-interfacial chemical bonding between the core layer and the surface layer resin molecular chains, forming interlayer chemical connections. This improves the interlayer bonding force of the multilayer structure and avoids interlayer delamination. At the same time, the relatively low temperature of the surface melt restricts the flow of the high-temperature core layer, ensuring the processing stability of the bubble during the blowing process.

[0032] 3. This invention uses fine plant fibers modified with coupling agents as fillers, which seals the hydrophilic groups on the fiber surface, improves its compatibility and dispersibility with the hydrophobic polyester matrix. This treatment method avoids the formation of stress concentration points or particle defects by the aggregation of plant fibers in the matrix, ensures the continuity of film formation during thin-wall processing of the mulch film, and improves the weather resistance and barrier properties of the finished product. Attached Figure Description

[0033] Figure 1 This is a comparison chart of the overall performance of each component of the present invention; Figure 2 This is a biaxial graph showing the right-angle tear strength versus cost of the present invention. Detailed Implementation

[0034] Preparation Examples 1-5: Preparation Example 1: This preparation example provides a surface-activated microfiber F-1, comprising the following steps: Dry wheat straw powder was fed into a fluidized bed jet mill for ultrafine grinding. The particle size was controlled by the speed of the classifier wheel, and fine powder with a D98 particle size of 8.2 μm was collected. A treatment solution was prepared by hydrolyzing a 2.0% (w / w) 3-aminopropyltriethoxysilane (KH550) ethanol aqueous solution at a volume ratio of 9:1 for 20 minutes. The fine powder was fed into a high-speed mixer and the treatment solution was added in the form of a spray at a stirring speed of 2000 rpm. The amount of treatment solution added was such that the effective content of KH550 was 1.0% of the powder mass. The temperature was raised to 110℃ and high-speed mixing was maintained for 12 minutes. The material was discharged and cooled to room temperature to obtain surface-activated micro-plant fiber F-1.

[0035] Preparation Example 2: This preparation example provides a surface-activated microfiber F-2, comprising the following steps: Dry wheat straw powder was fed into a fluidized bed air jet mill for pulverization. The grading parameters were adjusted to collect fine powder with a D98 particle size of 12.5 μm. The fine powder was then fed into a high-speed mixer. Under the condition of stirring speed of 1500 rpm, an aluminate coupling agent was added at a rate of 1.5% of the powder mass. The temperature was raised to 115℃ and high-speed mixing was maintained for 15 minutes. The material was discharged and cooled to room temperature to obtain surface-activated fine plant fiber F-2.

[0036] Preparation Example 3: This preparation example provides a core layer high-activity composite masterbatch M-1, including the following steps: Weighing each component: 52.5 parts by weight of poly(butylene adipate) / butylene terephthalate resin, 20 parts by weight of polypropylene carbonate resin, parts by weight of surface-activated microfiber F-125 obtained in Preparation Example 1, 1.0 part by weight of styrene-acrylate-glycidyl methacrylate copolymer (reactive compatibilizer), 0.4 parts by weight of sodium bicarbonate, 0.4 parts by weight of sodium monocitrate, and 0.2 parts by weight of ultrafine calcium carbonate (the above three constitute an environmentally friendly heat-absorbing foaming agent, totaling 1.0 parts by weight); The above components were premixed in a low-speed mixer for 5 minutes; the mixture was added to a twin-screw extruder for melt blending and granulation. The temperatures of each zone of the extruder were set as follows: Zone 1 125℃, Zone 2 135℃, Zone 3 140℃, Zone 4 140℃, Zone 5 135℃, and the die head 130℃. The screw speed was 280 rpm. After air-cooled die surface hot cutting and drying, the core layer high-activity composite masterbatch M-1 was obtained.

[0037] Preparation Example 4: This preparation example provides a core layer high-activity composite masterbatch M-2, including the following steps: Weighing each component: 41 parts by weight of poly(butylene adipate / terephthalate) resin, 25 parts by weight of polypropylene carbonate resin, 1.5 parts by weight of surface-activated microfiber F-130 obtained in Preparation Example 1, 1.5 parts by weight of styrene-acrylate-glycidyl methacrylate copolymer (reactive compatibilizer), 0.8 parts by weight of sodium bicarbonate, 0.8 parts by weight of sodium monocitrate, 0.4 parts by weight of ultrafine calcium carbonate (the above three constitute an environmentally friendly heat-absorbing foaming agent, totaling 2.0 parts by weight), and 0.5 parts by weight of erucamide; The above components were premixed in a low-speed mixer for 5 minutes; the mixture was added to a twin-screw extruder for melt blending and granulation. The temperatures of each zone of the extruder were set as follows: Zone 1 125℃, Zone 2 135℃, Zone 3 140℃, Zone 4 140℃, Zone 5 135℃, and the die head 130℃. The screw speed was 300 rpm. After air-cooled die surface hot cutting and drying, the core layer high-activity composite masterbatch M-2 was obtained.

[0038] Preparation Example 5: This preparation example provides a core layer common composite masterbatch M-3 for subsequent comparative experiments, including the following steps: Weigh the following components: 53.5 parts by weight of poly(butylene adipate / terephthalate) resin, 20 parts by weight of polypropylene carbonate resin, parts by weight of surface-activated microfiber F-125 obtained in Preparation Example 1, 0.4 parts by weight of sodium bicarbonate, 0.4 parts by weight of monosodium citrate, 0.2 parts by weight of ultrafine calcium carbonate (the above three constitute an environmentally friendly heat-absorbing foaming agent, totaling 1.0 parts by weight), and 0.5 parts by weight of erucamide; Note: No reactive compatibilizer was added in this Preparation Example 5; The above components were premixed in a low-speed mixer for 5 minutes; the mixture was added to a twin-screw extruder for melt blending and granulation. The temperatures of each zone of the extruder were set as follows: Zone 1 125℃, Zone 2 135℃, Zone 3 140℃, Zone 4 140℃, Zone 5 135℃, and the die head 130℃. The screw speed was 280 rpm. After air-cooled die surface hot cutting and drying, the core layer ordinary composite masterbatch M-3 was obtained.

[0039] Examples 1-4: Example 1: This embodiment provides a multi-layer composite structure functional fully biodegradable mulch film with a total thickness of 12 μm, including the following steps: (1) Preparation of special materials: Special materials for outer and inner layers: Mix 93.5 parts by weight of poly(butylene adipate / terephthalate) resin, 0.5 parts by weight of UV-531, 1.5 parts by weight of silica, 0.5 parts by weight of erucamide, 1.0 part by weight of polycarbodiimide, 2.0 parts by weight of polylactic acid, and 1.0 part by weight of calcium stearate (the above three constitute a degradation regulator, totaling 4.0 parts by weight) evenly; Core layer special material: The high-activity composite masterbatch M-1 of the core layer obtained in Preparation Example 3 was used directly; (2) Differentiated plasticizing extrusion: A three-layer co-extrusion blown film unit is used. The above-mentioned special materials are added to the corresponding extruders respectively. The temperatures of the outer and inner extruders are set as follows: Zone 1 140℃, Zone 2 150℃, Zone 3 155℃, and Die head connection 155℃, to maintain a lower melt temperature to preserve melt strength. The temperatures of the core extruder are set as follows: Zone 1 150℃, Zone 2 165℃, Zone 3 175℃, and Die head connection 170℃. The core melt temperature is 15℃ higher than that of the outer / inner layers to thermally activate the reactive compatibilizer in the masterbatch. (3) In-mold interface reaction and molding: The three-layer melt flows into the co-extrusion die at a temperature of 170℃. The layer thickness ratio of the outer layer, core layer and inner layer is controlled at 20%:60%:20%. The high temperature of the core layer and the temperature difference of the surface layer are used to initiate the in-situ chemical bonding reaction at the interface during the residence time in the die. The melt is extruded through the die, the blow-up ratio is set to 4.5 and the traction speed is set to 20m / min. (4) Cooling and winding: Turn on the internal cooling system (IBC) and the double air outlet ring, set the air temperature to 18°C, cool and shape quickly, and after stabilizing the bubble and corona treatment, wind it up to obtain the finished mulch film.

[0040] Example 2: This embodiment provides a multi-layer composite structure of a functional, fully biodegradable mulch film with a total thickness of 10 μm, designed to verify the preparation of an extreme film under high filler content, including the following steps: (1) Preparation of special materials: Special materials for outer and inner layers: 93.5 parts by weight of poly(butylene adipate / terephthalate) resin, 0.5 parts by weight of UV-531, 1.5 parts by weight of silica, 0.5 parts by weight of erucamide and 0.8 parts by weight of polycarbodiimide, 2.0 parts by weight of polylactic acid, and 1.2 parts by weight of calcium stearate (totaling 4.0 parts by weight of degradation regulator) are mixed evenly; Core layer special material: The core layer high-activity composite masterbatch M-2 obtained in Preparation Example 4 contains a higher proportion of fibers and reactive compatibilizers; (2) Differentiated plasticizing extrusion: The temperature settings for the outer and inner extruders are: 155℃ at the die connection; the temperature settings for the core extruder are: 150℃ in zone 1, 170℃ in zone 2, 180℃ in zone 3, and 175℃ at the die connection. The core melt temperature is 20℃ higher than that of the outer / inner layers, which can maximize the activation of the high-content compatibilizer in a very short time. (3) In-mold interface reaction and molding: The three-layer melt flows in the die head at a temperature of 175℃, and the layer thickness ratio of the outer layer, core layer and inner layer is controlled at 15%:70%:15%. The melt is extruded through the die, and the blow-up ratio is increased to 5.0. High stretching ratio combined with the high fiber content of the core layer is used to induce micropore formation to the greatest extent. (4) Cooling and winding: Increase cooling airflow to 2800m³ / h 3 / h, the remaining steps are the same as in Example 1, to obtain the finished mulch film.

[0041] Example 3: This embodiment provides a multi-layer composite functional fully biodegradable mulch film with a total thickness of 15 μm. The implementation effect under mild processing conditions is verified through the following steps: (1) Preparation of special materials: Special materials for outer and inner layers: Mix 93.5 parts by weight of poly(butylene adipate / terephthalate) resin, 0.5 parts by weight of UV-531, 1.5 parts by weight of silica, 0.5 parts by weight of erucamide, 1.2 parts by weight of polycarbodiimide, 1.6 parts by weight of polylactic acid, and 1.2 parts by weight of calcium stearate (totaling 4.0 parts by weight of degradation regulator) evenly; Core layer special material: The high-activity composite masterbatch M-1 of the core layer obtained in Preparation Example 3 was used directly; (2) Differentiated plasticizing extrusion: The temperature settings for the outer and inner extruders are: 155℃ at the die head connection; the temperature settings for the core extruder are: 145℃ in zone 1, 160℃ in zone 2, 170℃ in zone 3, and 165℃ at the die head connection. The core melt temperature is 10℃ higher than that of the outer / inner layers. (3) In-mold interface reaction and molding: The three-layer melt flows into the die at a temperature of 165℃, and the thickness ratio of the outer layer, core layer and inner layer is controlled at 20%:60%:20%. The melt is extruded through the die, and the blow-up ratio is reduced to 4.0 to obtain a thicker physical structure; (4) Cooling and winding: Turn on the internal cooling system (IBC) and the double air outlet ring, set the air temperature to 18°C, cool and shape quickly, and after stabilizing the bubble and corona treatment, wind it up to obtain the finished mulch film.

[0042] Example 4: This embodiment provides a multi-layer composite structure functional fully biodegradable mulch film, designed to support a comprehensive range of fiber particle sizes, including the following steps: (1) Preparation of special materials: Special materials for outer and inner layers: Mix 93.5 parts by weight of poly(butylene adipate / terephthalate) resin, 0.5 parts by weight of UV-531, 1.5 parts by weight of silica, 0.5 parts by weight of erucamide, 1.0 part by weight of polycarbodiimide, 2.0 parts by weight of polylactic acid, and 1.0 part by weight of calcium stearate (the above three constitute a degradation regulator, totaling 4.0 parts by weight) evenly; Core layer material: The preparation method is the same as in Preparation Example 3, except that 25 parts by weight of surface-activated micro-plant fiber F-1 is replaced with surface-activated micro-plant fiber F-2 (D98 particle size 12.5 μm) obtained in Preparation Example 2. (2) Differentiated plasticizing extrusion: The process parameters are set exactly the same as in Example 1, with the core layer die head connection temperature being 170°C, the outer layer and inner layer being 155°C, and the temperature difference being 15°C. (3) In-mold interface reaction and molding: The thickness ratio of the three layers is controlled at 20%:60%:20%. The melt is extruded through the die, and the blow-up ratio is set to 4.2; (4) Cooling and winding: Turn on the internal cooling system (IBC) and the double air outlet ring, set the air temperature to 18°C, cool and shape quickly, and after stabilizing the bubble and corona treatment, wind it up to obtain the finished mulch film.

[0043] Comparative Examples 1-5: Comparative Example 1: This comparative example provides a single-layer fully biodegradable mulch film. Compared with Example 1, the difference is that a three-layer co-extrusion process is not used. Instead, the core layer high-activity composite masterbatch M-1 obtained in Preparation Example 3 is directly added to a single-screw extruder for single-layer blown film production. The extrusion temperature is set to 165-175℃ and the blow-up ratio is 4.5 to obtain a single-layer film.

[0044] Comparative Example 2: This comparative example provides a multi-layer fully biodegradable mulch film without density gradient. Compared with Example 1, the difference is that the core layer material does not contain surface-activated micro-plant fiber F-1 and environmentally friendly heat-absorbing foaming agent, but is replaced by an equal amount of PBAT / PPC resin mixture in a mass ratio of 2:1. That is, the core layer is a solid resin layer that is not lightweight, while the structure and process parameters of the remaining layers are the same.

[0045] Comparative Example 3: This comparative example provides a multi-layer fully biodegradable mulch film lacking a chemical bonding mechanism. The difference from Example 1 is that the core layer material uses the ordinary composite masterbatch M-3 obtained in Preparation Example 5. This masterbatch does not contain styrene-acrylate-glycidyl methacrylate copolymer as a reactive compatibilizer; all other raw materials and process parameters are the same.

[0046] Comparative Example 4: This comparative example provides a multi-layer fully biodegradable mulch film without employing a temperature gradient process. The difference from Example 1 is that the temperature setting in the plasticizing extrusion process is changed, and the high-temperature setting for the core layer is eliminated. The temperatures of each zone of the core layer extruder and the die connection are all set to 155°C, consistent with the outer / inner layer temperature, ensuring the core layer melt is in a relatively low-temperature state. All other raw materials and steps remain the same.

[0047] Comparative Example 5: This comparative example provides a multilayer fully biodegradable mulch film using large-particle-size fiber filler. The difference from Example 1 is that the plant fiber raw material used was not subjected to airflow ultrafine grinding, but only to ordinary mechanical grinding and sieving, with a D98 particle size of approximately 45 μm. It was then processed using the same coupling modification process for core layer masterbatch preparation, with the remaining raw material ratios and process parameters remaining the same.

[0048] Test Example 1-2: Test Example 1: This test case aims to verify the processing feasibility, bubble stability, and density characteristics of the final product of the above embodiments and comparative examples on actual industrial blown film equipment.

[0049] Experimental steps: After the extrusion process stabilized, a continuous 120-minute blown film operation was conducted, recording the number of film breaks due to bubble rupture. During this time, an online laser diameter gauge was used to record the bubble fold diameter every 10 minutes, calculating the standard deviation of the fold diameter to characterize the bubble dimensional stability, and visually inspecting the film surface for defects such as crystal points, holes, or flow lines. Subsequently, according to ISO 1183-1 standard, the overall density of the finished mulch film was measured using the impregnation method with anhydrous ethanol as the medium. For multi-layer samples, the density was determined by combining the mass flow rate ratio of each extruder layer and the theoretical density of the surface layer (set to 1.24 g / cm³). 3 The actual density of the core layer is calculated by subtracting the surface mass contribution from the overall density.

[0050] Experimental data: Table 1: Test results of processing stability and density parameters of each group of samples

[0051] in conclusion: Based on the data in Table 1, no film breakage occurred during the overall processing of the mulch film in Examples 1 to 3, the standard deviation of the folded diameter was controlled at a low level, and the calculated core density was between 0.77 and 0.86 g / cm³. 3 Between. Data shows that by introducing reactive compatibilizers into the core layer and setting a processing temperature 10-20°C higher than that of the surface layer, the continuity and strength of the filler-containing melt can be effectively improved, thereby maintaining bubble stability and achieving density reduction at a higher blow-up ratio.

[0052] Comparative data shows that the single-layer structure of Comparative Example 1 could not withstand high-ratio stretching and broke, indicating that the outer and inner layers are necessary to maintain the integrity of the highly filled film. In Comparative Example 3, the reactive compatibilizer was removed, resulting in unstable film bubbles and an increased number of film breakages, confirming that physical blending cannot provide sufficient melt strength. Comparative Example 4 used a low-temperature homogenization process, and its core layer density was significantly higher than that of Example 1, indicating that without sufficient temperature activation, the compatibilizer reaction efficiency was low and the foaming agent decomposed incompletely, limiting the lightweight effect. Comparative Example 5 caused frequent film breakage due to excessively large fiber particle size, confirming that the filler size needs to be controlled at the micron level to match the film thickness.

[0053] Test Example 2: Experimental steps: The prepared mulch film samples were conditioned for 24 hours under standard conditions (23±2℃, relative humidity 50±5%). According to GB / T1040.3-2006 standard, the longitudinal and transverse tensile strength and elongation at break were determined using an electronic universal testing machine at a tensile speed of 100 mm / min. The right-angle tear strength was determined using the trouser tear method according to GB / T16578.1-2008 standard. The interlayer bonding performance was evaluated using a heat-sealing-tensile failure mode: two inner layers of the mulch film were placed face-to-face and heat-sealed for 1 second at 130℃ and 0.2 MPa, followed by T-shaped peeling to observe whether failure occurred in the material bulk or at the interlayer interface. Weather resistance testing was conducted according to GB / T16422.2 standard, with the elongation at break retention rate measured after 300 hours of treatment in a xenon lamp aging chamber. Economic evaluation was performed based on the average market price of each component and the measured density, calculating the material cost per unit area.

[0054] Experimental data: Table 2: Mechanical properties, peeling modes, and economic test results of each group of samples

[0055] in conclusion: Based on the data in Table 2, the longitudinal and transverse tensile strengths of Example 1 both exceeded 20 MPa, the elongation at break exceeded 380%, and the failure mode was material bulk fracture, indicating that the interlayer bonding force was greater than the material's own strength.

[0056] To more intuitively demonstrate the advantages of this invention in terms of overall performance, Figure 1 It provides a normalized comparison of the overall performance of each component, such as... Figure 1As shown, although the gray column in Comparative Example 2 exhibits outstanding mechanical strength and weather resistance, its cost advantage index is extremely low. Conversely, although the white column in Comparative Example 3 has a significant cost advantage, its mechanical properties and weather resistance are extremely weak. In contrast, the black column in Example 1 shows no weaknesses in any dimension. In particular, while maintaining high mechanical properties such as a tensile strength normalized index close to 0.8, its cost advantage index is also maintained at a high level. This verifies that the present invention has successfully overcome the technical bias that high performance and low cost of fully biodegradable mulch films cannot be achieved simultaneously through multi-layer structure and interface reaction technology.

[0057] Furthermore, regarding the crucial trade-off between tear resistance and economic efficiency in the application of plastic film, Figure 2 A biaxial analysis demonstrating cost advantages and tear strength was presented. Figure 2 As can be seen, the bar chart on the left axis represents the cost per acre, and the line chart on the right axis represents the right-angle tear strength. Comparative Example 2 is in the high-cost, high-strength range, while Comparative Example 3 is in the unusable range of low cost and low strength. The data points for Examples 1-3 clearly fall within the optimal balance zone of low cost and medium-high strength. In particular, Example 1's gray cost bar is significantly lower than that of Comparative Example 2, while its black strength line does not drop significantly with the decrease in cost, remaining at a relatively high level of 88 N / mm. This intuitively demonstrates that the reactive compatibilization system effectively transfers stress, allowing the mulch film under high fill levels to still possess excellent tear resistance.

[0058] Although Comparative Example 4 contains compatibilizers, it uses a low-temperature process. Its mechanical properties are between those of Example 1 and Comparative Example 3, and it exhibits a mixed failure mode. This indicates that the temperature gradient is a key process parameter for activating interfacial reactions and achieving optimal performance. Weather resistance test results show that the aging retention rate of Example 1 is significantly higher than that of Comparative Example 3, indicating that the dense interfacial bonding helps to block water and oxygen penetration and delay material degradation. In summary, through the synergistic design of components and processes, the mechanical strength and performance of the mulch film are guaranteed while reducing costs and density.

Claims

1. A multi-layered composite functional fully biodegradable mulch film, characterized in that, It has a three-layer co-extrusion structure, wherein the three layers are an outer layer, a core layer, and an inner layer; The outer layer and the inner layer are made from raw materials comprising the following parts by weight: Poly(butylene adipate) / butylene terephthalate resin: 90-95 parts; UV-531: 0.2-1.0 parts; Silica: 1.0-2.0 parts; Erucamide: 0.2-1.0 parts; Degradation regulator: 2.0-6.0 parts; The core layer is made from raw materials comprising the following parts by weight: Poly(butylene adipate) / butylene terephthalate resin: 40-55 parts; Polypropylene carbonate resin: 15-30 parts; Surface-activated microfibers: 20-35 parts; Styrene-acrylate-glycidyl methacrylate copolymer: 0.5-2.0 parts; Environmentally friendly heat-absorbing foaming agent: 0.5-2.5 parts; Erucamide: 0.2-0.8 parts.

2. The multi-layer composite functional fully biodegradable mulch film according to claim 1, characterized in that, The surface-activated microfibers are wheat straw powder whose surface has been modified with 3-aminopropyltriethoxysilane or aluminate coupling agent, and the D98 particle size of the surface-activated microfibers is 5-15 μm. The thickness ratio of the outer layer, the core layer, and the inner layer is 15-20%:60-70%:15-20%. The total thickness of the mulch film is 10-15 μm, and the density of the core layer is 0.75-0.90 g / cm³. 3 .

3. The multi-layer composite functional fully biodegradable mulch film according to claim 1, characterized in that, The degradation regulator comprises the following components in parts by weight: Polycarbodiimide: 0.5-1.5 parts; Polylactic acid: 1.0-3.0 parts; Calcium stearate: 0.5-1.5 parts.

4. The multi-layer composite structure functional fully biodegradable mulch film according to claim 1, characterized in that, The environmentally friendly heat-absorbing foaming agent comprises the following components in parts by weight: Sodium bicarbonate: 0.2-1.0 parts; Sodium citrate: 0.2-1.0 parts; Ultrafine calcium carbonate: 0.1-0.5 parts.

5. A method for preparing a multi-layered composite functional fully biodegradable mulch film, characterized in that, The functional, fully biodegradable mulch film with a multi-layer composite structure as described in any one of claims 1-4, using a three-layer co-extrusion blown film process, includes the following steps: The raw materials for the outer layer, the core layer, and the inner layer are respectively added to the corresponding outer layer extruder, core layer extruder, and inner layer extruder, and plasticized to form each layer melt; The plasticized melt layers are conveyed to the co-extrusion die via the die connector at the end of their respective extruders; during the conveying process, the process temperature is controlled so that the temperature setpoint at the die connector of the core extruder is 10-20°C higher than the temperature setpoint at the die connector of the outer and inner extruders. The three-layer melt converges in the co-extrusion die, and the temperature difference between the core melt and the outer and inner melts is used to activate the styrene-acrylate-glycidyl methacrylate copolymer in the core melt, initiating an interfacial chemical bonding reaction between the core layer and the outer and inner layers. After the reaction, the multi-layer melt is extruded and blown through a die, cooled and shaped by the internal cooling system and air ring, and then pulled and wound to obtain the finished mulch film.

6. The method for preparing a multi-layer composite functional fully biodegradable mulch film according to claim 5, characterized in that, The temperature of the die connector between the outer extruder and the inner extruder is set to 150-160℃; The temperature of the die connector of the core extruder is set to 165-175℃; The temperature of the co-extrusion die is set to 165-175℃.

7. The method for preparing a multi-layer composite functional fully biodegradable mulch film according to claim 5, characterized in that, The blow-up ratio of the multilayer melt after reaction during extrusion and blowing through the die is controlled between 4.0 and 5.0, and the traction speed during traction and winding is controlled between 15 and 25 m / min.

8. The method for preparing a multi-layer composite functional fully biodegradable mulch film according to claim 5, characterized in that, The raw materials for the core layer are pre-prepared into a highly active composite masterbatch for the core layer. The preparation steps of the highly active composite masterbatch for the core layer include: The mixture is prepared by uniformly mixing poly(butylene adipate / terephthalate) resin, polypropylene carbonate resin, surface-activated micro-plant fibers, styrene-acrylate-glycidyl methacrylate copolymer, environmentally friendly heat-absorbing foaming agent and erucamide. The mixture is added to a twin-screw extruder for melt blending and granulation, followed by air-cooled die surface hot cutting and drying to obtain the core layer high-activity composite masterbatch; The die head temperature of the twin-screw extruder is set to 130°C.

9. The method for preparing a multi-layer composite functional fully biodegradable mulch film according to claim 8, characterized in that, In the preparation of the core layer highly active composite masterbatch, the preparation steps of the surface-activated microfibers include: Dry wheat straw powder is pulverized by airflow into fine powder with a D98 particle size of 5-15μm; The fine powder is fed into a mixer, and a treatment liquid or coupling agent is added under stirring conditions. The mixture is heated to 105-120°C and kept mixed for 10-15 minutes. The material is then discharged and cooled to room temperature to obtain the surface-activated fine plant fibers.

10. The method for preparing a multi-layer composite functional fully biodegradable mulch film according to claim 8, characterized in that, The treatment solution is a 2.0% (w / w) aqueous solution of 3-aminopropyltriethoxysilane in ethanol, added in such an amount that the effective content of 3-aminopropyltriethoxysilane is 1.0% of the powder mass; or the coupling agent is an aluminate coupling agent, added in an amount of 1.5% of the powder mass, the air jet milling is performed using a fluidized bed air jet mill; the mixing speed of the mixer is 1500-2000 rpm.

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