Multifunctional full-biodegradable mulching film capable of being controllably degraded in subareas and preparation method of multifunctional full-biodegradable mulching film

Abstract

The invention relates to the technical field of high polymer materials, and discloses a partition controllable degradation multifunctional full-biodegradable mulching film and a preparation method thereof.The partition controllable degradation multifunctional full-biodegradable mulching film is of a three-layer co-extrusion structure, and the middle layer and the inner layer are transversely divided into a soil covering area and an exposed area; the formula of the exposed area contains PGA and modified foaming master batch, and the barrier and tear resistance are improved by using the high compactness and micro-foaming structure of PGA; the formula of the soil covering area contains PPC and plant fibers, and degradation is accelerated by utilizing the moisture absorption expansion effect of the fibers; the invention relates to a preparation method of a multifunctional full-biodegradable mulching film capable of realizing partition controllable degradation. The preparation method adopts multi-runner independent temperature control plasticizing and radial flow choking rib die head partition co-extrusion. According to the invention, the contradiction that the degradation rate of the mulching film is not matched with the growth cycle of crops is solved, the synchronization of long-acting soil moisture conservation in an exposed area and rapid disintegration in an earthing area is realized, and the problem of integrated processing of high-melting-point PGA and heat-sensitive filler is solved.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a multifunctional, fully biodegradable mulch film with zoned and controllable degradation and its preparation method. Background Technology

[0002] Fully biodegradable mulch films have become an important way to solve agricultural white pollution. However, most existing products are homogeneous in structure, making it difficult to adapt to the drastically different environmental conditions and functional requirements of the "bare area" and the "soil-covered area" after field application. The bare area requires high strength and high barrier properties to ensure effective coverage during crop growth, while the soil-covered area requires rapid degradation after harvest to avoid hindering cultivation. The single formulation of homogeneous mulch films cannot simultaneously address these differences, often leading to premature rupture and failure in the bare area or delayed degradation and residue in the soil-covered area. Although physical splicing technologies have attempted to solve the zoning problem, they suffer from drawbacks such as low seam strength, poor production efficiency, and difficulty in large-scale application.

[0003] Furthermore, there is a serious conflict in processing temperature between high-melting-point components (such as PGA) introduced to improve specific properties and heat-sensitive components (such as PPC and biomass fillers) introduced to promote degradation. Conventional co-extrusion processes cannot achieve integrated and stable molding while ensuring material properties.

[0004] Therefore, this invention proposes a multifunctional, fully biodegradable mulch film with zoned controllable degradation and its preparation method to overcome the shortcomings of the prior art. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a multifunctional fully biodegradable mulch film with zoned controllable degradation and its preparation method. This solves the problem that existing fully biodegradable mulch films have a mismatch between degradation rate and crop growth cycle in practical applications, and that the high-barrier components and high-degradable components have significant differences in melt processing temperature, making it difficult to balance them in a single formulation or conventional co-extrusion process.

[0006] To address the above problems, the present invention provides the following technical solution:

[0007] In a first aspect, the present invention provides a multifunctional, fully biodegradable mulch film with zoned controllable degradation, employing the following technical solution:

[0008] A multifunctional, fully biodegradable mulch film with zoned controllable degradation is disclosed. The mulch film has a three-layer co-extruded structure, comprising an outer layer, a middle layer, and an inner layer stacked sequentially. The middle and inner layers are both laterally divided into a soil-covered zone and a bare zone. The composition of each layer and zone is as follows:

[0009] Outer layer: made of raw materials comprising the following parts by weight: 70-80 parts PBAT, 20-30 parts PLA, and UV absorbers and antioxidants;

[0010] Middle layer - exposed area: made from raw materials containing the following parts by weight: 60-70 parts PBAT, 20-25 parts PLA, and 10-15 parts PGA modified foaming masterbatch;

[0011] Middle layer - soil cover zone: made from raw materials containing the following parts by weight: 50-65 parts PBAT, 18-25 parts PPC, 10-30 parts plant fiber filler, and compatibilizer;

[0012] Inner layer - exposed area: made from raw materials containing the following parts by weight: 25-45 parts PBAT, 50-70 parts PGA, and anti-hydrolysis agent;

[0013] Inner layer - soil cover zone: made from raw materials containing the following parts by weight: 50-60 parts PBAT, 35-40 parts PPC, 2-5 parts biodegradable inducing masterbatch, and 3-10 parts plant fiber filler.

[0014] By adopting the above technical solution, this invention utilizes differences in material properties and spatial distribution control to achieve regionalized functional regulation of mulch film:

[0015] The soil-covered and bare areas exhibited different degradation characteristics. In the soil-covered area, PPC had a lower glass transition temperature and was easily hydrolyzed. Combined with a high content of plant fiber filler, in a high-humidity soil environment, the plant fibers absorbed moisture and expanded, generating microcracks inside the polymer matrix. This increased the contact area between water molecules and soil microorganisms, accelerating the material's disintegration. In the bare area, the high crystallinity of PGA and the hydrophobicity of PLA, combined with anti-hydrolysis agents, slowed down the rate of hydrolysis and weathering in the surface environment, maintaining the integrity of the cover during the crop growth period.

[0016] It achieves a combination of high barrier and high strength; the high content of PGA distributed in the inner layer-exposed area uses its dense crystal structure to block water vapor transmission and reduce soil moisture evaporation; the PGA modified foaming masterbatch in the middle layer-exposed area forms a closed-cell micro-foamed structure inside the film, which can blunt the crack tip and change the crack propagation path, thereby improving the transverse tear strength of the mulch film.

[0017] The problem of mismatched processing temperatures has been solved; the outer layer uses a PBAT / PLA universal formula as the bonding layer; the exposed area uses PLA with good heat resistance combined with PGA to adapt to high-temperature processing above 220℃; the soil covering area uses PPC with good fluidity and low processing temperature combined with plant fiber to adapt to low-temperature processing below 150℃; this zoned formula design allows materials with different melting characteristics to coexist stably in the same mulch film.

[0018] Preferably, the PGA-modified foaming masterbatch comprises 80-90 parts of PGA resin, 9-18.1 parts of PBAT resin, 0.8-1.5 parts of high-temperature foaming agent, 0.1-0.3 parts of nucleating agent, and 0.1 parts of chain extender. By adopting the above technical solution, the chain extender reacts with the PGA end groups to improve melt strength, and the nucleating agent provides heterogeneous nucleation points to refine the pores. This modified masterbatch improves the extrusion foaming stability of PGA, helps to form a uniform closed-cell structure, and enhances the heat insulation and toughening effects of the mulch film.

[0019] Preferably, the biodegradation inducing masterbatch is one of starch-based biodegradation inducing masterbatch, microbial-based biodegradation inducing masterbatch, or composite biodegradation inducing masterbatch; more preferably, the starch-based masterbatch is made of starch, glycerol, and PBAT; the microbial-based masterbatch is made of PBAT, Bacillus amyloliquefaciens spore powder, and a dispersant; and the composite masterbatch combines the components of both.

[0020] By adopting the above technical solutions, exogenous additives further regulate the degradation rate of the soil covering area; starch, as a carbon source, promotes microbial attachment and consumption, disrupting the continuity of the matrix; Bacillus spores are protected during processing, and after entering the soil environment, they revive and secrete esterases or keratinases, promoting the breaking of ester bonds in the polymer molecular chain, thus achieving endogenous degradation of the material.

[0021] Preferably, the plant fiber filler is wood flour or straw powder with a particle size D50 of 20-40 μm and a moisture content of less than 2%. By adopting the above technical solution, the micron-sized particle size ensures the dispersibility of the filler in the film and avoids the generation of stress concentration points. The low moisture content prevents the generation of bubbles and the hydrolysis of polyester resin during the processing.

[0022] Secondly, the present invention provides a method for preparing a multifunctional, fully biodegradable mulch film with zoned controllable degradation, employing the following technical solution:

[0023] A method for preparing a multifunctional, fully biodegradable mulch film with zoned controllable degradation includes the following steps:

[0024] S1. Material feeding and plasticizing: Provide multiple extruders to add the corresponding formulation materials for the outer layer, middle layer-exposed area, middle layer-covered area, inner layer-exposed area, and inner layer-covered area to their respective extruders for melting and plasticizing, resulting in multiple melt streams;

[0025] S2, Partitioned Co-extrusion: The multiple melt streams obtained in step S1 are introduced into a three-layer partitioned co-extrusion die head with radial flow-blocking ribs; the radial flow-blocking ribs are used to separate the melt streams of the middle layer and the inner layer, so that the formula melt of the exposed area and the formula melt of the covered area enter different fan-shaped flow channels.

[0026] S3, blow molding: The melt from each zone converges before the die lip exit, and after being extruded through the die lip, it is blow molded to obtain the mulch film.

[0027] Preferably, in step S1, the extruder temperature for processing PGA or PGA-modified foaming masterbatch is controlled at 220℃~240℃; the extruder temperature for processing plant fiber filler and PPC is controlled at 135℃~155℃.

[0028] By adopting the above technical solution, differentiated processing temperature windows are set; the high-temperature zone ensures that PGA is fully melted and plasticized; the low-temperature zone utilizes the low-temperature flow characteristics of PPC to prevent plant fiber scorching and maintain the melt pressure matching with the high-temperature zone, ensuring the stability of the film bubble in the co-extrusion process.

[0029] Preferably, in step S2, the temperature of the partitioned co-extrusion die is controlled to be 155℃~170℃; by adopting the above technical solution, the die temperature is set to the equilibrium point; at this temperature, the PGA fluid can still maintain flow by utilizing shear heat and thermal inertia; at the same time, this temperature is within the thermal stability range of plant fibers, and short-term residence will not cause material deformation.

[0030] Preferably, before step S1, the method further includes a step of preparing the biodegradation-inducing masterbatch; wherein, when preparing the starch-containing biodegradation-inducing masterbatch, starch and glycerol are mixed at 80°C in advance to prepare a thermoplastic starch precursor; by adopting the above technical solution, the starch is transformed from a granular state to a thermoplastic state, which improves the interfacial compatibility between starch and PBAT matrix and reduces the pore phenomenon during the blown film process.

[0031] Preferably, in step S3, the blow-up ratio is controlled to be 2.8 to 3.5, and the traction speed is 8 to 15 m / min; by adopting the above technical solution, the orientation of polymer molecular chains is promoted, and the mechanical strength and barrier properties of the film are improved.

[0032] This invention provides a multifunctional, fully biodegradable mulch film with zoned controllable degradation and its preparation method.

[0033] It has the following beneficial effects:

[0034] 1. This invention divides the middle and inner layers of the mulch film into a soil-covered zone and an exposed zone in the horizontal direction, and designs targeted formulations for each zone. The soil-covered zone uses a PPC and plant fiber filler system, utilizing the micro-crack effect generated by the moisture absorption and expansion of plant fibers and the easy hydrolysis characteristics of PPC to allow the buried part to quickly disintegrate in moist soil, avoiding residual film from hindering cultivation. The exposed zone uses a high-content PGA and PLA system, utilizing the high crystallinity and density of PGA to give the surface part excellent resistance to ultraviolet rays and weathering. This structural design solves the problem that traditional mulch films cannot simultaneously meet the dual requirements of "long-term surface coverage" and "rapid underground degradation".

[0035] 2. This invention concentrates a high proportion of PGA in the inner layer-exposed zone, utilizing PGA's excellent gas barrier properties to construct a highly efficient moisture-retaining layer, reducing the soil moisture evaporation rate; simultaneously, PGA-modified foaming masterbatch is introduced into the middle layer-exposed zone, forming a micro-foamed closed-cell structure inside the mulch film; this structure can blunt the tear tips and hinder the linear propagation of cracks, thereby significantly improving the transverse tear strength of the mulch film and enhancing its wind uplift resistance and puncture resistance during field use.

[0036] 3. To address the significant temperature difference between PGA and plant fiber / PPC during processing, this invention develops a zoned co-extrusion process based on radial flow-blocking ribs. Through multi-channel independent temperature control and plasticization, combined with physical isolation and conveying inside the die head, the scorching or degradation of heat-sensitive biomass fillers caused by high-temperature melts is avoided. At the same time, by adjusting the proportion of low-viscosity components such as PPC, the rheological differences between high and low temperature melts at the confluence point are balanced, achieving stable molding with strong interfacial bonding and uniform thickness. Attached Figure Description

[0037] Figure 1 This is a density comparison diagram of the exposed area and the soil-covered area in this invention;

[0038] Figure 2 This is a diagram showing the trade-off between the mechanical strength and barrier properties of the present invention.

[0039] Figure 3 This is a graph showing the change in soil degradation weight loss rate over time according to the present invention.

[0040] Figure 4 This is a cross-sectional schematic diagram of the three-layer partitioned co-extrusion die head of the present invention;

[0041] Figure 5 This is a schematic diagram of the radial flow-blocking rib structure of the present invention;

[0042] Figure 6 This is a flowchart of the preparation process of the present invention.

[0043] Among them, 1. flow-blocking reinforcement; 2. exposed area; 3. soil-covered area. Detailed Implementation

[0044] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0046] Polybutylene adipate / terephthalate (PBAT): CAS No. 55231-08-8, weight-average molecular weight (Mw) 120,000-130,000 g / mol, melt flow rate (190℃, 2.16 kg) 3.0-5.0 g / 10 min, terminal carboxyl group content ≤30 mol / ton; Polylactic acid (PLA): CAS No. 26100-51-6, D-lactic acid content ≤1.5%, melt flow rate Melt flow rate (190℃, 2.16kg): 2.0-4.0 g / 10min; Polyglycolic acid (PGA): CAS No. 26124-68-5, melt flow rate (230℃, 2.16kg): 20-30 g / 10min; Polypropylene carbonate (PPC): CAS No. 25511-85-7; Chain extender ADR-4368: Styrene-glycidyl acrylate copolymer, epoxy equivalent: 280-310 g / mol; Maleic anhydride grafted PBAT (PBAT-g-MAH): grafting rate: 0.8-1.2%; Bacillus amyloliquefaciens spore powder: viable count ≥ 1.0 × 10⁻⁶ 10 CFU / g; In this invention, the plant fiber filler is a commercially available product, including but not limited to natural plant fiber powders such as wood flour, straw powder, bamboo powder, rice husk powder, and hemp fiber; Wood flour: particle size D50 is 20-40μm, and moisture content is less than 2%; Straw powder: particle size D50 is 20-40μm, and moisture content is less than 2%.

[0047] Preparation Example 1: PGA-modified foaming masterbatch A1

[0048] This preparation example provides a modified masterbatch focusing on high foaming ratio, including the following steps:

[0049] Weigh out 80 parts of dried PGA resin, 18.1 parts of PBAT resin, 1.5 parts of high-temperature foaming agent (modified azodicarbonamide), 0.3 parts of nucleating agent (ultrafine talc), and 0.1 parts of chain extender ADR-4368 by weight.

[0050] After the above raw materials are premixed evenly in a high-speed mixer, they are fed into a twin-screw extruder through the main feed port. Considering the high melting point of PGA, the temperatures of each zone of the extruder are set as follows: Zone 1 210℃, Zone 2 225℃, Zone 3 230℃, Zone 4 225℃, and Die head 220℃; the screw speed is set to 200 rpm; after the melt is extruded, it is granulated by hot cutting of the air-cooled die surface and dried in a vacuum oven at 60℃ for 6 hours to obtain PGA modified foaming masterbatch A1.

[0051] Preparation Example 2: PGA-modified foaming masterbatch A2

[0052] This preparation example provides a modified masterbatch with balanced performance, including the following steps:

[0053] The preparation process parameters are the same as those in Preparation Example 1, except that the weight ratio of raw materials is different: 85 parts of PGA resin, 13.6 parts of PBAT resin, 1.2 parts of high-temperature foaming agent, 0.1 parts of nucleating agent, and 0.1 parts of chain extender ADR-4368; PGA modified foaming masterbatch A2 is obtained.

[0054] Preparation Example 3: PGA-modified foaming masterbatch A3

[0055] This preparation example provides a modified masterbatch that focuses on high rigidity support, including the following steps:

[0056] The preparation process parameters are the same as those in Preparation Example 1, except that the weight ratio of raw materials is different: 90 parts of PGA resin, 9 parts of PBAT resin, 0.8 parts of high-temperature foaming agent, 0.1 parts of nucleating agent, and 0.1 parts of chain extender ADR-4368; PGA modified foaming masterbatch A3 is obtained.

[0057] Preparation Example 4: Biodegradation-Inducing Masterbatch B1

[0058] This preparation example provides a high-content starch-based degradation inducer, comprising the following steps:

[0059] Weigh out 60 parts starch, 20 parts glycerol, 19.5 parts PBAT resin, and 0.5 parts chain extender ADR-4368 by weight.

[0060] First, starch and glycerol were stirred at high speed in a high-speed mixer at 80°C for 30 minutes to obtain a thermoplastic starch (TPS) precursor. Then, the TPS precursor was mixed with PBAT resin and chain extender and added to a twin-screw extruder. The extruder temperature was set at 110°C-135°C and the screw speed was 150 rpm. The extruded strip was air-cooled and pelletized to obtain starch-based biodegradable inducing masterbatch B1.

[0061] Preparation Example 5: Biodegradation-Induced Masterbatch B2

[0062] This preparation example provides a degradation inducer containing active microorganisms, comprising the following steps:

[0063] Weigh out 92 parts of PBAT resin, 5 parts of Bacillus amyloliquefaciens spore powder, 0.5 parts of chain extender ADR-4368, and 2.5 parts of calcium stearate by weight.

[0064] The above components were mixed evenly in a low-speed mixer; then added to a twin-screw extruder for granulation; to ensure the activity of the microbial agent, the shear heat and barrel temperature were strictly controlled, and the temperatures of each zone were set to 110℃, 115℃, 120℃, and 125℃ (drill head), and the screw speed was 100 rpm; underwater pelleting and rapid air drying were used to obtain microbial biodegradation inducing masterbatch B2.

[0065] Preparation Example 6: Biodegradation-Inducing Masterbatch B3

[0066] This preparation example provides a composite degradation inducer that synergistically induces starch and microorganisms, comprising the following steps:

[0067] Weigh out 50 parts starch, 10 parts glycerol, 35 parts PBAT resin, 3 parts Bacillus amyloliquefaciens spore powder, and 2 parts chain extender ADR-4368 by weight.

[0068] First, starch and glycerol were premixed to prepare a TPS precursor; the precursor was then mixed with the remaining components and fed into a twin-screw extruder; the extrusion temperature was controlled between 120℃ and 130℃ and the screw speed was 120 rpm; the composite biodegradable inducible masterbatch B3 was obtained by air-cooled die hot cutting granulation.

[0069] Example 1: Refer to Appendix Figure 6 This embodiment provides a multifunctional, fully biodegradable mulch film with zoned controllable degradation, which is divided into a left soil-covered zone, a central bare zone, and a right soil-covered zone in the horizontal direction, and into an outer layer, a middle layer, and an inner layer in the vertical direction. The preparation of the mulch film in this embodiment includes the following steps:

[0070] Material preparation: A co-extrusion system consisting of five extruders (A, B, C, D, E) was used; according to the formulation of “Example 1” shown in Table 1, the components were mixed evenly and then added to the corresponding extruder hoppers.

[0071] Five extruders were used to control five different formulations. However, in actual production, if the formulations of the middle layer-cover zone and the inner layer-cover zone are similar or the same, they can be combined and used in the same extruder for plasticization. The plasticizer can then be used to distribute the plasticizer to the middle layer and the inner layer through the flow channel distributor, thus completing the preparation using four extruders.

[0072] Melt plasticizing: Each extruder independently controls its temperature to adapt to the melting characteristics of different materials.

[0073] Extruder A (outer layer): Processes PBAT / PLA general formulations, temperature set at 160℃-170℃.

[0074] Extruder B (middle layer - covering zone) and extruder D (inner layer - covering zone): To prevent wood flour and starch from scorching and to take advantage of the good low-temperature fluidity of PPC, the temperature is set to 140℃-150℃.

[0075] Extruder C (middle layer - exposed zone): To ensure that the PGA foaming masterbatch is fully plasticized, the temperature is set to 220℃-230℃.

[0076] Extruder E (inner layer - exposed area): Processes high-content PGA barrier layers, with the temperature set at 225℃-235℃.

[0077] Zoned co-extrusion: The melt enters a three-layer zoned co-extrusion die with radial flow-blocking ribs; the die temperature is set to 165℃. (See attached diagram.) Figure 4 -Appendix Figure 5 The core feature of the three-layer zoned co-extrusion die is the flow channel structure design of the middle and inner layers. Inside the annular flow channels of the middle and inner layers, radial flow-blocking ribs 1 (or physical partitions) are set along the extrusion direction. The radial flow-blocking ribs 1 physically divide the continuous annular flow channels into non-communicating fan-shaped flow channels in the circumferential direction, corresponding to the exposed area 2 and the soil-covered area 3 of the mulch film, respectively. This structure ensures that the formula melt in the exposed area and the formula melt in the soil-covered area are in a state of thermal and physical isolation within the die body, and lateral welding only occurs in the confluence area before the die lip exit.

[0078] Lateral fusion and molding: The melts from each zone converge before the die lip exit, resulting in lateral fusion. After extrusion through the die lip, the melt is blown up, with the blow-up ratio (BUR) controlled at 3.0, the traction speed at 10m / min, and the frosting height at 400mm.

[0079] Post-processing: After being flattened by herringbone plates, pulled, trimmed and rolled up, a finished mulch film with a total thickness of 10μm is obtained.

[0080] Example 2: This example provides a multifunctional, fully biodegradable mulch film with zoned controllable degradation. This example focuses on verifying low cost and rapid degradation performance under high filler content. The preparation steps are as follows:

[0081] Material preparation: According to the formula shown in Table 1, the plant fiber content in the soil covering area is increased to 30%, and PPC is used in the inner layer instead of PGA to meet the requirements of low-temperature degradation.

[0082] Melt plasticization and extrusion:

[0083] Extruder B / D (covered zone): Due to the high shear heat of the high-content wood flour, the set temperature is reduced to 135℃-145℃, and the back pressure is increased.

[0084] Extruder C / E (exposed zone): Maintain 225°C-235°C for processing PGA-containing materials.

[0085] Molding: The die temperature is set to 155℃. Due to the high filler content and low melt strength, the traction speed is reduced to 8m / min, and the blow-up ratio is set to 2.8. The remaining steps are the same as in Example 1.

[0086] Example 3: This example provides a multifunctional, fully biodegradable mulch film with zoned and controllable degradation. This example focuses on verifying its high barrier and high strength performance. The preparation steps are as follows:

[0087] Material preparation: According to the formula shown in Table 1, the PGA content in the inner layer of the exposed area is as high as 70%.

[0088] Melt plasticization and extrusion:

[0089] Extruder E (inner layer - exposed area): Temperature increased to 230℃-240℃ to reduce the viscosity of high PGA content.

[0090] Extruder A (outer layer): PLA content is high, temperature is set at 170℃-180℃.

[0091] Molding: The die temperature is set to 170℃ to prevent premature crystallization of PGA. The traction speed is increased to 12m / min, and the blow-up ratio is set to 3.2. The remaining steps are the same as in Example 1.

[0092] Example 4: This example provides a multifunctional fully biodegradable mulch film with zoned controllable degradation. This example mainly verifies the limit production efficiency of process parameters, and its formula is exactly the same as that of Example 1.

[0093] Process adjustments:

[0094] The blow-up ratio (BUR) has been increased to 3.5.

[0095] The traction speed has been increased to 15 m / min.

[0096] The cooling airflow was increased by 20%, and the frost line was controlled at 450mm.

[0097] Results: The membrane vesicles were stable, and the interfaces of each zone were well bonded, with no rupture or delamination observed.

[0098] Table 1: Weight ratio of components in each layer and zone of Examples 1-3

[0099]

[0100]

[0101] Comparative Example 1:

[0102] Compared to Example 1, the differences are as follows: instead of using a partitioned die, a conventional three-layer co-extrusion die (without flow-blocking ribs) is used; the formulation of each layer is the average value of the formulation of the soil-covered area and the exposed area in Example 1, weighted by the area ratio (3:4:3); for example, the inner layer formulation is uniformly: 48 parts PBAT, 46 parts PGA / PPC mixture, 1.5 parts masterbatch B1, 0.9 parts wood flour, 0.4 parts anti-hydrolysis agent, etc.; the process parameters adopt a compromise temperature (180℃-190℃). All other steps are the same.

[0103] Comparative Example 2:

[0104] Compared to Example 1, the difference lies in that: integrated co-extrusion molding is not used; two single-layer films are blown separately: film A (corresponding to the average formulation of the soil-covered area in Example 1) and film B (corresponding to the average formulation of the exposed area in Example 1); then, film A is cut into two pieces and film B is cut into one piece, and the three are hot-pressed together longitudinally using a heat sealing machine to form a "film A-film B-film A" structure. Everything else is the same.

[0105] Comparative Example 3

[0106] Compared to Example 1, the difference lies in that although a partitioned die head is used, the formulation design is reversed. No wood flour or biodegradable inducing masterbatch is added to the soil-covered zone; only pure PBAT / PPC substrate is used. No PGA high-barrier component or foaming masterbatch is added to the exposed zone, and 30% wood flour is added. All other process parameters and structures remain the same.

[0107] Comparative Example 4

[0108] Compared to Example 1, the difference lies in that the mulch film structure is simplified to a single-layer partition. The formulation of the inner layer in Example 1 is directly used as a single-layer formulation for partition blow molding, and the outer layer (UV-resistant layer) and the middle layer (transition layer) are removed. All other process parameters are the same.

[0109] Comparative Example 5

[0110] The difference from Example 1 is that the PGA-modified foaming masterbatch A1 is not used in the middle layer-exposed zone formulation; instead, an equal amount of unmodified PGA resin is used directly. All other aspects are the same.

[0111] Test Example 1:

[0112] This test case aims to verify the processing stability and film quality of the multi-channel zoned co-extrusion process when handling materials with significant rheological differences (such as high-melting-point PGA and low-heat-resistant PPC / wood flour).

[0113] The experimental steps are as follows:

[0114] According to GB / T-6672-2001 standard, after the extruder enters a stable production state, the traction process is continuously observed for 4 hours, and the operating status of the film bubble is recorded. A film bubble that is upright, without rupture, and with a sway amplitude of less than 10mm is recorded as Grade 1; occasional sway amplitude of 10-30mm that does not affect winding is recorded as Grade 2; frequent and violent swaying or rupture that makes winding impossible is recorded as Grade 3.

[0115] The thickness is measured at 50mm intervals along the transverse direction (TD) of the mulch film. The percentage difference between the maximum and minimum thicknesses relative to the nominal thickness is calculated as the limit thickness deviation. Measurements are taken at the boundaries of the coverage zones.

[0116] According to GB / T-1033.1-2008, the actual density of the "exposed area" and "soil-covered area" of the finished mulch film were tested by the immersion method.

[0117] A 10-meter-long sample of the mulch film was cut, unfolded, and laid flat. The maximum distance that the color boundary line of different areas deviated from the theoretical straight line was measured to characterize the interfacial stability of the melt confluence.

[0118] The experimental results are shown in Table 2 below.

[0119] Table 2: Test data on process stability and molding quality

[0120]

[0121] Conclusion: Refer to Appendix Figure 1 Based on the data in Table 2, Examples 1, 3, and 4 exhibited first-order bubble stability during processing, with lateral thickness deviation controlled within ±8%. The processing temperature in the exposed zone exceeded 220°C to melt PGA, while the processing temperature in the covered zone was controlled below 150°C to protect PPC and wood flour, resulting in a significant temperature difference between the two. Experimental results show that the temperature regulation of the independent flow channels inside the die head and the back pressure effect generated by the radial flow-blocking ribs enabled the two melts at different temperatures to achieve flow rate matching and pressure balance at the die confluence point. In Example 1, the density of the exposed zone was 0.842 g / cm³. 3 The density of the soil covering area is 1.265 g / cm³. 3 The significant difference in density indicates that the high-temperature foamed masterbatch introduced into the middle layer of the exposed area forms a closed-cell structure, achieving material lightweighting, while the high density of the soil-covered area originates from the filling of mineral or biomass fillers, verifying the zoning structure of the mulch film's microstructure.

[0122] In Example 2, the wood flour content in the covering zone was increased to 30%, which reduced the melt ductility and caused the film bubble stability to drop to level two. The interface straightness deviation increased to 7.2 mm, but no cracking occurred. This indicates that the co-extrusion system can adapt to the processing of high-viscosity and high-filler materials by adjusting the extrusion back pressure and traction speed. In Comparative Example 3, the formulation design did not consider the differences in polymer melting characteristics, and high-flowability components were not used for rheological balance in the low-temperature zone. This caused turbulence and coating of the melt at the confluence point, with a thickness deviation of more than 20%, making continuous production impossible. This shows that in the partitioned co-extrusion process, the selection of substrates for each partition must simultaneously meet the functional requirements and the rheological matching principle.

[0123] Test Example 2:

[0124] This test case mainly examines the differences in mechanical strength of mulch film in different functional zones and the key moisture retention index (water vapor barrier property), and verifies whether the zone formula design meets the design goal of "high strength and high barrier in exposed areas and basic operational requirements in soil-covered areas".

[0125] The experimental steps are as follows:

[0126] The samples were conditioned for 48 hours at 23±2℃ and 50±5%RH. Avoiding the transition zone, long strip samples were cut from the exposed area of ​​the mulch film and the soil-covered area along the longitudinal (MD) and transverse (TD) directions, respectively. Comparative Example 1 was sampled at any location, Comparative Example 2 was sampled avoiding the weld seam, and Comparative Example 3 was sampled according to the physical location.

[0127] According to GB / T-1040.3-2006 standard, tensile properties were tested using a universal testing machine with a specimen width of 15 mm, a clamp spacing of 100 mm, and a tensile speed of 500 mm / min. The tensile strength at break and the elongation at break were recorded, and the arithmetic mean of 5 parallel samples was taken.

[0128] The right-angle tear strength was tested according to the QB / T-1130-1991 standard at a test speed of 200 mm / min, with a focus on testing the exposed area.

[0129] According to the cup method of GB / T-1037-2021, the water vapor transmission rate was tested at 38℃ and 90%RH, with a focus on the data of the exposed area.

[0130] The experimental results are summarized in Table 3.

[0131] Table 3: Summary of test data on mechanical and barrier properties of mulch film in different zones

[0132]

[0133]

[0134] Note: In the tensile data of Comparative Example 2, fractures mostly occurred at the edges of the heat-sealed welds, resulting in lower elongation data.

[0135] in conclusion:

[0136] Combined with appendix Figure 2 Based on the data in Table 3 and membrane structure analysis, the water vapor permeation rate in the exposed area of ​​Example 1 was 115.4 g / (m²). 2 •24h), lower than Comparative Example 1's 286.5g / (m 2 • 24h); Comparative Example 1 dispersed the PGA component throughout the membrane layer, failing to form a continuous, highly dense barrier layer; Example 1 concentrated PGA in the inner layer of the exposed area, increasing the local barrier layer density and extending the water molecule permeation path; Example 3 increased the PGA content to 70%, reducing the water vapor permeation rate to 65.3 g / (m²). 2 • 24h); Comparative Example 3: In the exposed area without a PGA layer, the water vapor permeation reached 652.1 g / (m²). 2 • 24h), the barrier performance drops significantly.

[0137] In Example 2, adding 30% wood flour to the soil-covered area reduced the longitudinal tensile strength to 11.8 MPa; the increased amount of plant fiber filling reduced the continuity of the matrix resin, resulting in a decrease in tensile strength; the soil-covered area is mainly fixed by soil compaction, and the tensile strength requirement is lower than that of the bare area; the bare area in Example 2 retained a tensile strength of 26.9 MPa, which can meet the requirements of mulch film covering operations and wind resistance.

[0138] In Example 1, the right-angle tear strength of the exposed area was 84.5 kN / m, higher than the 58.3 kN / m of the single-layer structure in Comparative Example 4. The difference in modulus between the layers in the multilayer co-extruded structure altered the stress distribution during crack propagation, hindering the crack from penetrating in a straight line. Comparison between Example 1 and Comparative Example 5 showed that the tensile strength of the unfoamed sample was slightly higher (30.5 MPa), but the tear strength was lower (71.2 kN / m). The microporous structure of the middle layer disrupted the continuous phase of the material, causing a deflection of the crack propagation path and improving tear resistance. Simultaneously, the foaming treatment reduced the material density, which is beneficial for reducing the amount of raw material used per unit area.

[0139] Test Example 3:

[0140] This test case aims to verify the differences in degradation rates among different functional zones of the mulch film in order to evaluate the actual effect of its "zoned controlled degradation" characteristic; the focus is on examining the rapid degradation capacity of the soil-covered zone in the soil environment and the stability of the exposed zone during the functional period.

[0141] The experimental steps are as follows:

[0142] The experiment used topsoil (0-20cm deep), which was sieved through a 2mm sieve to remove stones, and the soil moisture content was adjusted to 45%±5%, pH value to 6.8-7.2, and the ambient temperature was controlled at 25℃±2℃.

[0143] From the finished mulch films of each embodiment and comparative example, samples of "exposed area" and "soil-covered area" with a size of 50mm×50mm were cut out respectively. The samples were washed in anhydrous ethanol to remove surface grease, and vacuum dried at 40°C to constant weight. The initial weight M0 was recorded.

[0144] The samples were buried in the soil to a depth of 10 cm. Samples were retrieved on days 30, 60, and 90 after burial, rinsed with deionized water to remove adhering soil, and severely broken samples were collected by filtration through a 200-mesh sieve. The samples were then vacuum-dried again at 40℃ to constant weight, and the residual weight Mt was recorded.

[0145] Calculate the weightlessness rate using the formula:

[0146] Weight loss rate (%) = (M0 - Mt) / M0 × 100%.

[0147] The experimental results are shown in Table 4.

[0148] Table 4: Summary of Test Data on Weight Loss Rate of Mulch Film in Soil Landfill in Different Zones

[0149]

[0150]

[0151] in conclusion:

[0152] From the appendix Figure 3 As shown in Table 4, the mulch films of Examples 1-4 exhibited a significantly higher degradation rate in the soil-covered area than in the bare area. Taking Example 1 as an example, the weight loss rate in the soil-covered area reached 88.4% on day 90, while that in the bare area was 15.6%. The soil-covered area contains hydrophilic wood flour and starch-based inducing masterbatch, which absorbs water and swells in the high-humidity soil environment, increasing the contact area and reaction sites for microorganisms and promoting the hydrolysis of the PBAT / PPC matrix. The bare area contains highly crystalline PGA and hydrophobic PLA, and has a closed-cell foam structure, which delays water penetration and enzymatic hydrolysis, maintaining the covering function.

[0153] Comparing Examples 2 and 3, the weight loss rate of the soil-covered area in Example 2 reached 26.8% on day 30, while the weight loss rate of the soil-covered area in Example 3 was 72.1% on day 90. Adjusting the ratio of plant fiber to degradation-inducing masterbatch can change the degradation induction period of the soil-covered area.

[0154] The degradation rates of the two zones in Comparative Example 1 (homogeneous mulch) were basically the same, failing to simultaneously meet the requirements for moisture retention during the covering period and degradation after harvest. In Comparative Example 3 (reverse formulation), the weight loss rate in the exposed zone reached 91.2% after 90 days, indicating insufficient weather resistance; the weight loss rate in the soil-covered zone was only 18.4%, resulting in soil residue. In Comparative Example 5 (no wood flour), the degradation rate in the soil-covered zone was lower than that in Example 1, indicating that plant fibers promote water conduction during soil degradation.

[0155] Examples show that the mulch film of the present invention mineralizes or disintegrates in the soil-covered area at the end of crop growth (90 days), which is conducive to tillage; the exposed area remains macroscopically intact, which is convenient for recycling or subsequent natural degradation, thus realizing differentiated regulation of degradation cycle in different areas.

[0156] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A multifunctional full-biodegradable mulching film with controllable degradation in different regions, characterized in that, The mulch film is a three-layer co-extrusion structure, including an outer layer, a middle layer and an inner layer which are stacked in sequence; wherein the middle layer and the inner layer are both divided into a covering area and a bare area in the transverse direction; the component of each layer and area is as follows: The outer layer is made of raw materials containing PBAT 70-80 parts, PLA 20-30 parts, and ultraviolet absorber 0.5-3 parts and antioxidant 0.1-1 part by weight; The middle layer-bare area is made of raw materials containing PBAT 60-70 parts, PLA 20-25 parts, and PGA modified foaming master batch 10-15 parts by weight; The middle layer-covering area is made of raw materials containing PBAT 50-65 parts, PPC 18-25 parts, plant fiber filler 10-30 parts, and compatibilizer 0.5-2 parts by weight; The inner layer-bare area is made of raw materials containing PBAT 25-45 parts, PGA 50-70 parts, and anti-hydrolysis agent 0.5-2 parts by weight; The inner layer-covering area is made of raw materials containing PBAT 50-60 parts, PPC 35-40 parts, biodegradation inducing master batch 2-5 parts, and plant fiber filler 3-10 parts by weight.

2. The multifunctional full-biodegradable mulching film with controllable degradation in different regions according to claim 1, characterized in that, The PGA modified foaming master batch contains the following components by weight: PGA resin 80-90 parts, PBAT resin 9-18.1 parts, high-temperature foaming agent 0.8-1.5 parts, nucleating agent 0.1-0.3 parts, and chain extender 0.1 part.

3. The multifunctional full-biodegradable mulching film with controllable degradation in different regions according to claim 1, and a preparation method thereof, characterized in that, The biodegradation inducing master batch is one of starch-based biodegradation inducing master batch, microbial-based biodegradation inducing master batch or composite biodegradation inducing master batch.

4. The multi-functional and fully biodegradable mulching film with controllable degradation in different zones according to claim 3, wherein, The starch-based biodegradation inducing master batch is made of raw materials containing starch, glycerol and PBAT; the microbial-based biodegradation inducing master batch is made of raw materials containing PBAT, Bacillus amyloliquefaciens spore powder and dispersing agent; and the composite biodegradation inducing master batch is made of raw materials containing starch, glycerol, PBAT and Bacillus amyloliquefaciens spore powder.

5. The multifunctional full-biodegradable mulching film with controllable degradation in different regions according to claim 1, and a preparation method thereof, characterized in that, The plant fiber filler is wood powder or straw powder, with particle size D50 of 20-40 μm and water content less than 2%.

6. A method for preparing the multifunctional full-biodegradable mulching film with controllable degradation in different zones according to any one of claims 1-5, characterized in that, The method comprises the following steps: S1, feeding and plasticizing: providing at least four extruders, and feeding the corresponding formula materials of the outer layer, the middle layer-bare area, the middle layer-covering area, the inner layer-bare area and the inner layer-covering area into the respective extruders for melting and plasticizing to obtain multiple melt streams; S2, zone co-extrusion: introducing the multiple melt streams obtained in step S1 into a three-layer zone co-extrusion die provided with radial resistance ribs; the radial resistance ribs are used to separate the melt streams of the middle layer and the inner layer, so that the bare area formula melt and the covering area formula melt enter different fan-shaped flow channels; S3, blow molding: the zone melts are combined before the die lip outlet, and then blow molded after extrusion through the die lip to obtain the mulch film.

7. The preparation method of the multifunctional full-biodegradable mulching film with controllable degradation in different regions according to claim 6, characterized in that, In step S1, the temperature of the extruder for processing PGA or PGA modified foaming master batch is controlled to be 220-240°C; and the temperature of the extruder for processing plant fiber filler and PPC is controlled to be 135-155°C.

8. The preparation method of the multifunctional full-biodegradable mulching film with controllable degradation in different regions according to claim 6, characterized in that, In step S2, the temperature of the zone co-extrusion die is controlled to be 155-170°C.

9. The preparation method of the multifunctional full-biodegradable mulching film with controllable degradation in different regions according to claim 6, characterized in that, Before step S1, a step of preparing the biodegradation-inducing master batch is further included; wherein, when preparing the starch-containing biodegradation-inducing master batch, starch is mixed with glycerol at 80 DEG C in advance to prepare a thermoplastic starch precursor.

10. The preparation method of the multifunctional full-biodegradable mulching film with controllable degradation in different regions according to claim 6, characterized in that, In step S3, the blow-up ratio is controlled to be 2.8-3.5, and the drawing speed is 8-15 m / min.

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