Composite mulching film with high mechanical property, high biodegradation rate and low permeable rate and preparation method thereof

Abstract

The invention discloses a composite mulching film with high mechanical property, high biodegradation rate and low permeable rate and a preparation method of the composite mulching film, and belongs to the technical field of high polymer material modification and environmental degradation plastics. The composite mulching film with the high mechanical property, the high biodegradation rate and the low permeable rate comprises a laminated structure composed of a core layer and an outer layer; the raw materials of the outer layer comprise polyethylene resin as well as an oxygen-promoting degradation agent and a compatilizer which are dispersed in the polyethylene resin; the raw material of the core layer comprises poly (butylene adipate-co-terephthalate) resin. The invention aims to overcome the inherent defect that in the prior art, the biodegradation rate, the mechanical property of a film and the low permeable rate are difficult to consider at the same time, the easily biodegradable PBAT material is used as the core layer, the core layer is preferentially degraded in the degradation process, and high-activity chemical species are continuously generated and provided; the PE layers containing the oxygen-promoting degradation agent are arranged on the two sides of the core layer and serve as the main place of the oxidative degradation reaction.

Description

Technical Field

[0001] This invention relates to the field of polymer material modification and environmentally degradable plastics technology, and in particular to a composite mulch film with high mechanical properties, high biodegradability and excellent moisture retention (low permeability) and its preparation method. Background Technology

[0002] Currently, there is still room for improvement in the physical and performance aspects of fully biodegradable materials. Polyethylene (PE) plastics are widely used due to their stable chemical structure and physical properties, but their difficulty in degrading in the natural environment has led to a serious "white pollution" problem. Improving the environmental absorbability of traditional polyethylene plastics has become a global challenge. The two main technical approaches currently available are chemical degradation and physical blending.

[0003] The chemical degradation pathway involves adding transition metal salts (such as cobalt stearate and zinc stearate) to PE as pro-oxidative degradation agents, thereby breaking the PE chains through catalytic oxidation. Its fundamental drawback is that the oxidation reaction is difficult to initiate and lacks sufficient depth; the resulting film only achieves about 40% biodegradation rate under standard composting conditions after 6 months, leaving a large amount of PE residue in the form of microplastics.

[0004] The physical blending approach involves melt blending PE with modified starch, biodegradable polyesters (such as PBAT), etc., to reduce the amount of PE used. Its fundamental drawback is that PE (a non-polar crystalline polymer) and PBAT (a polar polyester) are thermodynamically incompatible, resulting in a fragile interphase bond and a significant decrease in the mechanical properties of the film (especially tear strength), failing to meet practical application requirements. Simultaneously, the phase separation structure confines the degradation activity of PBAT to its own phase region, making it difficult to effectively initiate the degradation of the PE phase. The overall degradation efficiency is limited by the PBAT content, and the PE phase still degrades slowly.

[0005] More importantly, existing fully biodegradable mulch films generally suffer from poor mechanical properties and excessively high water vapor permeability (typically 300-800 g / m²) due to the inherent characteristics of their materials. 2 The low humidity (over 24 hours) results in poor soil warming and moisture retention properties, which can easily lead to significant crop yield reduction when applied in arid and semi-arid regions, becoming a significant drawback that limits its widespread application.

[0006] In summary, this field has long faced the following technical dilemma: pursuing high biodegradability rates leads to a decline in the physical properties of the mulch film and a significant increase in water vapor permeability, while maintaining good physical properties makes it difficult to achieve deep and rapid biodegradation. Current technologies have not yet provided an effective solution that can simultaneously overcome the performance and degradation challenges, and further improvements are needed. Summary of the Invention

[0007] The purpose of this invention is to provide a composite mulch film with high mechanical properties, high biodegradability, and low water permeability, and its preparation method, to solve the aforementioned problems in the prior art. This invention aims to overcome the inherent deficiency in the prior art where it is difficult to simultaneously achieve optimal mechanical properties, biodegradability, and moisture retention performance of the film. By using easily biodegradable PBAT material as the core layer, which preferentially degrades during the degradation process and continuously generates and provides highly active chemical species; simultaneously, PE layers containing pro-oxidative degradation agents are disposed on both sides of the core layer, serving as the main sites for oxidative degradation reactions and improved moisture retention performance.

[0008] To achieve the above objectives, the present invention provides the following technical solution: One of the technical solutions of the present invention is to provide a composite mulch film with high mechanical properties, high biodegradability and low water permeability. The composite mulch film includes a stacked structure consisting of a core layer (PBAT layer) and an outer layer (PE layer), with the core layer sandwiched between the upper and lower outer layers to form a stacked structure. The outer layer contains polyethylene (PE) resin and an oxygen-promoting degradation agent and a compatibilizer dispersed therein. The core layer is made of polybutylene adipate / terephthalate (PBAT) resin.

[0009] Preferably, the pro-oxidative degradation agent is a transition metal carboxylate, preferably cobalt stearate and / or manganese stearate.

[0010] Preferably, the amount of the pro-oxidative degradation agent added is 0.5%-2.5% of the mass of the polyethylene resin.

[0011] Preferably, the compatibilizer is maleic anhydride-grafted polyethylene, and the amount added is 1-3% of the mass of polyethylene resin; the total thickness of the composite mulch film is 6-25 μm.

[0012] Preferably, the water vapor transmission rate of the composite mulch film is less than 80 g / m³. 2 • 24h, preferably below 60 g / m 2 ·24h.

[0013] The second technical solution of the present invention provides a method for preparing the above-mentioned composite mulch film with high mechanical properties, high biodegradability and low water permeability, comprising the following steps: Prepare the raw materials for the preparation of the outer layer to obtain component A; Prepare the raw materials for the preparation of the core layer to obtain component B; Two parts of component A and one part of component B are melted and plasticized, then co-extruded into a laminated structure, blown in, and cooled to set, thus obtaining the composite mulch film.

[0014] Preferably, the amount of component B added is 40%-75% of the sum of the masses of components A and B.

[0015] Preferably, the melting and plasticizing temperature is 150℃-190℃.

[0016] The third technical solution of the present invention provides an application of the above-mentioned composite mulch film with high mechanical properties, high biodegradability and low water permeability in the field of agricultural mulch film.

[0017] The technical principle of this invention is as follows: 1. Primary initiation (core layer initiation): In a composting environment, the core layer PBAT of the composite mulch film of the present invention undergoes hydrolysis and microbial erosion first. This process continuously generates a large number of highly active chemical species, including free radicals (R·), peroxides (ROOH), and small molecule organic acids.

[0018] 2. Interfacial transport: These highly reactive chemical species diffuse efficiently into the interior of the outer polyethylene (PE) layers on both sides through the tight interlayer interface.

[0019] 3. Secondary catalytic activation (deep oxidation of the outer layer): Exogenous reactive species (such as free radicals, peroxides, and organic acids) diffuse into the PE layer and encounter the existing pro-oxidative degradation agents (transition metal ions) in the PE layer, producing a significant synergistic catalytic effect. The metal ions are activated by the organic acids, thus efficiently catalyzing the decomposition of oxides diffused from the outside and generated by the oxidation of the PE itself. This produces a burst of highly reactive substances such as hydroxyl radicals (·OH), which launch a strong attack on the long PE chain from within the molecule, achieving deep oxidation.

[0020] 4. Chain reaction and complete disintegration: Under intense oxidation, the PE molecular chains undergo chain breakage, resulting in an exponential decrease in molecular weight. Simultaneously, the complete degradation of the core PBAT layer leads to the loss of structural support, fully exposing and fracturing the deeply oxidized and embrittled PE layer. This significantly increases the specific surface area, allowing for rapid assimilation by environmental microorganisms and complete biodegradation.

[0021] The beneficial technical effects of the present invention are as follows: This invention provides a composite mulch film with high mechanical properties, high biodegradability and low water permeability, and a preparation method thereof, aiming to overcome the inherent defects of existing technologies where it is difficult to simultaneously achieve the desired mechanical properties, biodegradability and low water permeability of the film.

[0022] The composite mulch film designed in this invention uses readily biodegradable PBAT material as the core layer, which preferentially degrades during the degradation process and continuously generates and provides highly reactive chemical species (such as free radicals, peroxides, and organic acids). Simultaneously, PE layers containing pro-oxidative degradation agents are placed on both sides of the core layer as the main sites for oxidative degradation reactions, and the outer PE layer serves as a highly efficient water vapor barrier. This results in a composite mulch film with high mechanical properties, a high biodegradability rate (≥90%), and low permeability (down to approximately 52 g / m²). 2 (24h) Its moisture retention performance is 5-10 times better than existing fully biodegradable mulch films, solving the application bottleneck of poor water retention of fully biodegradable mulch films. By using co-extrusion molding to form a tight interlayer interface, the active substances generated by the degradation of the core layer can be efficiently and directionally diffused into the interior of the two PE layers, and have a synergistic effect with the oxygen-promoting degradation agents therein, thereby effectively initiating and significantly accelerating the chain oxidation degradation reaction in the PE phase.

[0023] First, this invention achieves a significant improvement in degradation performance, increasing the biodegradation rate of the film under standard composting conditions (58±2℃, 6 months) from approximately 40% in existing technologies to over 90%. Second, this composite film also achieves excellent physical and mechanical properties and moisture retention. Its performance indicators (such as tensile load, elongation at break, tear load, and water vapor transmission rate) fully meet or exceed relevant national standards for mulch films (such as GB / T 35795-2017), achieving significant advantages in high biodegradability, high mechanical properties, and low water vapor transmission rate.

[0024] This method can be stably prepared through a three-layer co-extrusion blown film process. The preparation method is simple, the process window is wide, the product performance is stable and reliable, and it is easy to achieve stable and large-scale manufacturing. It is suitable for agricultural mulch films and other fields, and has great commercial value. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the composite mulch film of the present invention.

[0027] Figure 2 This is a schematic diagram illustrating the degradation active substance delivery mechanism of the composite mulch film of the present invention.

[0028] Figure 3 The mechanical performance test results are for the composite mulch film of Example 1.

[0029] Figure 4 The results show the water permeability test results of the composite mulch film in Example 1.

[0030] Figure 5 The results show the biodegradation rate of the composite mulch film in Example 1. Detailed Implementation

[0031] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0032] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0033] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. It should be noted that any aspects of this invention not described in detail are conventional practices in the art and are not the focus of this invention.

[0034] The terms “comprising,” “including,” “having,” “containing,” etc., used in this invention are all open-ended terms, meaning that they include but are not limited to.

[0035] This invention discloses a composite mulch film with high mechanical properties, high biodegradability and low water permeability. The composite mulch film includes a sandwich structure consisting of a core layer (PBAT layer) and an outer layer (PE layer), with the core layer sandwiched between the upper and lower outer layers to form a stacked structure. The outer layer contains polyethylene (PE) resin and an oxygen-promoting degradation agent and a compatibilizer dispersed therein. The core layer is made of polybutylene adipate / terephthalate (PBAT) resin.

[0036] The core layer is sandwiched between two outer layers, forming a symmetrical A / B / A three-layer laminated structure. The layers are bonded together through melt co-extrusion to form a tight interface.

[0037] Furthermore, the pro-oxidative degradation agent is cobalt stearate and / or manganese stearate.

[0038] Furthermore, the amount of the pro-oxidative degradation agent added is 0.5%-2.5% of the mass of the polyethylene resin.

[0039] Furthermore, the total thickness of the composite mulch film is 6-25 μm.

[0040] Furthermore, maleic anhydride-grafted polyethylene (PE-g-MAH) is added between the layers of the composite mulch film as a binder to further enhance interfacial adhesion and compatibility, and promote the transport of active substances during the degradation process.

[0041] This invention also discloses a method for preparing the above-mentioned composite mulch film with high mechanical properties, high biodegradability, and low water permeability, comprising the following steps: S1. Ingredients: Mix the raw materials used to prepare the outer layer to obtain component A; mix the raw materials used to prepare the core layer to obtain component B; S2. Three-layer co-extrusion: Using a co-extrusion blown film equipment with three independent extruders, 2 parts of component A and 1 part of component B are melted and plasticized respectively, and then introduced into the three-layer co-extrusion die. In the die, the melt is distributed and merged into a preset A / B / A layered structure, and then extruded, blown, cooled and shaped by the die to obtain the composite mulch film.

[0042] Furthermore, the amount of component B added is 40%-75% of the sum of the masses of components A and B. This ratio range is a balance point to ensure sufficient supply of "active species" and maintain the overall structural strength; if the proportion is too high, it is difficult to ensure the high mechanical properties and low water permeability of the composite membrane; if the proportion is too low, it is difficult to ensure the biodegradability rate of the composite membrane is ≥90%.

[0043] The melting and plasticizing temperature is 150℃-190℃.

[0044] All raw materials used in the following embodiments and comparative examples of the present invention are commercially available products.

[0045] Figure 1 This is a schematic diagram of the composite mulch film of the present invention.

[0046] Figure 2 This is a schematic diagram illustrating the degradation active substance delivery mechanism of the composite mulch film of the present invention.

[0047] Example 1 A method for preparing the above-mentioned composite mulch film with high mechanical properties, high biodegradability, and low water permeability comprises the following steps: S1. Ingredients: Commercially available linear low-density polyethylene (LLDPE, grade 7042N), pro-oxidative degradation agent (cobalt stearate, added at 1.5 wt% of LLDPE) and maleic anhydride grafted polyethylene (PE-g-MAH, added at 2 wt% of LLDPE) are mixed to obtain component A.

[0048] Prepare commercially available PBAT resin (brand name A400) to obtain component B.

[0049] S2. Three-layer co-extrusion: A co-extrusion blown film machine with three independent extruders is used. The thickness ratio of the three layers A / B / A is set to 4μm / 4μm / 4μm, and the amount of component B added is 41% of the sum of the masses of components A and B. Two parts of component A and one part of component B are melted and plasticized to obtain the corresponding melt A and melt B, and then introduced into the three-layer co-extrusion die (die temperature 175℃). In the die, the melt is distributed and merged into the preset A / B / A layered structure, and then extruded through the die (extrusion temperature 150-185℃), blown, cooled and shaped, and wound up to obtain a composite mulch film with a total thickness of about 12μm.

[0050] Performance test results of the composite mulch film in Example 1: Physical and mechanical properties: Tested by China Merchants Xinjiang Quality Inspection Technology Research Institute Co., Ltd., the results are as follows: Figure 3-5 As shown.

[0051] Figure 3 The mechanical performance test results are for the composite mulch film of Example 1.

[0052] Figure 4 The results show the water permeability test results of the composite mulch film in Example 1.

[0053] Figure 5 The results show the biodegradation rate of the composite mulch film in Example 1.

[0054] Depend on Figure 3 It is evident that all indicators of the composite mulch film of this invention far exceed the requirements of national standards such as GB / T 35795-2017, proving its superior mechanical properties. The tensile load (longitudinal / transverse) of the product in Example 1 is 5.11 N / 2.76 N (national standard requirement: ≥2.00 N), the elongation at break (longitudinal / transverse) is 458% / 806% (national standard requirement: ≥150% / ≥250%), and the right-angle tear load (longitudinal / transverse) is 1.20 N / 2.14 N (national standard requirement: ≥0.80 N).

[0055] It can be seen that the present invention achieves an ultra-high biodegradability rate without sacrificing the basic performance of the material, and successfully solves the long-standing problem of the mutual exclusion between "performance and degradation".

[0056] Permeability: Tested according to GB / T 1037 standard, the result is 52.7 g / (m²). 2 •24h).

[0057] Biodegradation rate: Tested under controlled composting conditions at (58±2)℃ according to ISO 14855-1 standard. After 5 months of testing, the biodegradation rate was calculated to be 90.3% based on the measured CO2 released.

[0058] Comparative Example 1 (Single-layer oxygen-promoting PE membrane) The specific preparation method is as follows: S1. Ingredients: Commercially available linear low-density polyethylene (LLDPE, grade 7042N), pro-oxidative degradation agent (cobalt stearate, added at 1.5 wt% of LLDPE) and maleic anhydride grafted polyethylene (PE-g-MAH, added at 2 wt% of LLDPE) are mixed to obtain component A.

[0059] S2. Molding: Component A is melted and plasticized, then introduced into the die head (die head temperature 175℃), and then extruded through the die head (extrusion temperature 150-185℃), blown, cooled and shaped, and wound up to obtain a single-layer film with a total thickness of about 12μm.

[0060] Testing revealed that the biodegradation rate of the monolayer membrane prepared in Comparative Example 1 was only 41.2% under the same biodegradation rate test conditions as in Example 1 of this invention, which was far lower than the 90.3% in Example 1.

[0061] Comparative Example 2 (Simple blend of PE and PBAT membrane) The specific preparation method is as follows: S1. Ingredients: Commercially available linear low-density polyethylene (LLDPE, grade 7042N), an oxygen-promoting degradation agent (cobalt stearate, added at 1.5 wt% of LLDPE), and maleic anhydride grafted polyethylene (PE-g-MAH, added at 2 wt% of LLDPE) are mixed to obtain component A; commercially available PBAT resin (grade A400) is prepared to obtain component B; Component A and component B are mixed at a mass ratio of 60:40 to obtain component C.

[0062] S2. Molding: Component C is melted and plasticized, then introduced into the die head (die head temperature 165℃), and then extruded through the die head (extrusion temperature 150-185℃), blown, cooled and shaped, and wound up to obtain a blend film with a total thickness of about 12μm.

[0063] Testing revealed that the blend membrane prepared in Comparative Example 2, under the same biodegradation rate test conditions as Example 1 of this invention, achieved a biodegradation rate of only about 65%, and its mechanical properties were significantly reduced.

[0064] Comparative Example 3 (PE three-layer film without oxygen promoter) The only difference from Example 1 is that the addition of cobalt stearate in component A is omitted.

[0065] Tests showed that its biodegradability was 58.4% and its water vapor transmission rate was 53.1 g / (m²). 2 • 24h). This indicates that after removing the oxygenation promoter, the biodegradation rate decreased significantly because only PBAT provided the active species.

[0066] The performance comparison between Example 1 and Comparative Examples 1-3 is shown in Table 1.

[0067] Table 1 Note: The sample in Example 1 had reached a degradation rate of 90.3% after 150 days, meeting the national standard requirements. Therefore, no further testing for longer degradation times was conducted.

[0068] In summary, the composite mulch film solution designed in this invention not only meets all national standards for the physical properties of agricultural mulch film products, but also achieves a significant leap forward over existing technologies in core environmental attributes—biodegradability and water permeability. This demonstrates that the specific layered structure of this invention (containing an oxygen-promoting PE layer / PBAT layer / containing an oxygen-promoting PE layer) produces a unique synergistic effect, exhibiting significant performance advantages. It provides a new direction for solving the problems of the difficulty in degrading polyethylene mulch films and the poor warming and moisture-retaining properties of fully biodegradable mulch films.

[0069] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A composite mulch film with high mechanical properties, high biodegradability, and low water permeability, characterized in that, The composite mulch film comprises a stacked structure consisting of a core layer and an outer layer; The raw materials of the outer layer include polyethylene resin and an oxygen-promoting degradation agent and a compatibilizer dispersed therein; The raw material of the core layer includes poly(butylene adipate / terephthalate) resin.

2. The composite mulch film with high mechanical properties, high biodegradability, and low water permeability according to claim 1, characterized in that, The pro-oxidative degradation agent is a transition metal carboxylate.

3. The composite mulch film with high mechanical properties, high biodegradability, and low water permeability according to claim 1, characterized in that, The amount of the pro-oxidative degradation agent added is 0.5%-2.5% of the mass of the polyethylene resin.

4. The composite mulch film with high mechanical properties, high biodegradability, and low water permeability according to claim 1, characterized in that, The compatibilizer is maleic anhydride-grafted polyethylene.

5. The composite mulch film with high mechanical properties, high biodegradability, and low permeability according to claim 1, characterized in that, The total thickness of the composite mulch film is 6-25 μm.

6. A method for preparing a composite mulch film with high mechanical properties, high biodegradability, and low permeability as described in any one of claims 1-5, characterized in that, Includes the following steps: Prepare the raw materials for the preparation of the outer layer to obtain component A; Prepare the raw materials for the preparation of the core layer to obtain component B; Two parts of component A and one part of component B are melted and plasticized, then co-extruded into a laminated structure, blown in, and cooled to set, thus obtaining the composite mulch film.

7. The preparation method according to claim 6, characterized in that, The amount of component B added is 40%-75% of the sum of the masses of components A and B.

8. The preparation method according to claim 6, characterized in that, The melting and plasticizing temperature is 150℃-190℃.

9. The application of a composite mulch film with high mechanical properties, high biodegradability and low water permeability as described in any one of claims 1-5 in the field of agricultural mulch films.

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