Composite film based on photo-biological synergistic gradient degradation and preparation method thereof

Abstract

The invention discloses a composite film based on light-biological synergistic gradient degradation and a preparation method thereof, the composite film sequentially comprises a light response layer, a transition layer and a biological response layer from outside to inside, and the light response layer comprises a polycaprolactone matrix, a tetraphenylporphyrin iron photosensitizer and anatase type TiO2 nanorods; the transition layer is a gradient blend of polylactic acid and modified starch; the biological response layer comprises polyhydroxyalkanoate and bacterial cellulose nanofibers; through the design of the three-layer gradient structure and the construction of the bionic microchannel, the synergistic effect of light degradation, hydrolysis and biodegradation is realized; the composite membrane has excellent mechanical properties and environmental adaptability, the degradation period can be accurately regulated and controlled within 30-180 days, and the soil degradation rate within 60 days reaches 91% or above; the preparation method comprises the processes of electrostatic spinning, gradient co-extrusion and bacterial cellulose in-situ culture. The material can be widely applied to the fields of agricultural mulching films, food packaging and the like, and the problems that a traditional degradable film is poor in mechanical property and uncontrollable in degradation are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of composite film preparation, and in particular to a composite film based on light-biological synergistic gradient degradation and a preparation method thereof. Background Art

[0002] With increasingly stringent environmental regulations and growing demands for sustainable development, biodegradable polymers are finding widespread application in packaging, agricultural mulch films, medical supplies, and other fields. Traditional petroleum-based plastics (such as polyethylene and polypropylene), while offering excellent mechanical properties and low cost, are difficult to degrade in the natural environment, leading to serious "white pollution" issues.

[0003] Currently, research on biodegradable materials mainly focuses on bio-based or biodegradable polymers such as polylactic acid (PLA), polycaprolactone (PCL), and polyhydroxyalkanoates (PHA). However, these materials still face the following key issues in practical applications: Single degradation conditions: Existing biodegradable films typically rely on a single degradation mechanism, such as photodegradation, hydrolysis, or microbial degradation. For example, PLA primarily relies on hydrolysis for degradation, but degrades very slowly in dry environments. Although PCL is biodegradable, it degrades almost in no way in microbial-free environments. This single reliance makes degradation behavior uncontrollable and difficult to adapt to complex environmental conditions. The inconsistency between degradation rate and mechanical properties: Many biodegradable films add large amounts of starch or inorganic fillers to increase degradation speed, but this often leads to a significant decrease in mechanical strength (e.g., tensile strength decreases by more than 40%), affecting their actual performance. Uneven degradation: Traditional biodegradable films typically exhibit the problem of "rapid surface degradation and slow internal degradation," resulting in structural collapse during the degradation process, forming microplastic fragments, which in turn exacerbates environmental pollution. Lack of environmental adaptability: Climatic conditions (e.g., light intensity, humidity, and microbial species) vary greatly between regions, making it difficult for existing biodegradable films to achieve "on-demand degradation," resulting in either excessively rapid degradation (e.g., in high-temperature and high-humidity regions) or excessively slow degradation (e.g., in arid and light-poor regions).

[0004] To address these issues, recent studies have attempted to optimize degradation performance through co-blending, multi-layer composites, or the addition of photo- / bio-synergistic degradation agents. However, these approaches still have the following limitations: simple blending can easily lead to phase separation, affecting material uniformity; multi-layer composite films suffer from insufficient interlayer bonding, making them prone to delamination; and the addition of photosensitizers or microbial additives often lacks precise control, resulting in uncontrollable degradation or residual toxicity.

[0005] Therefore, in response to the above problems, the present invention provides a composite film based on photo-biological synergistic gradient degradation and its preparation method, and develops a new type of degradable film material to achieve multi-mechanism synergistic degradation (light + biology + hydrolysis) and adapt to different environments; gradient degradation design to avoid the uneven problem of "fast outside and slow inside"; balance of mechanical properties and degradation properties to ensure stability during use and rapid degradation after disposal; environmental responsiveness to intelligently adjust the degradation rate according to actual conditions. Summary of the Invention

[0006] The purpose of the present invention is to provide a composite film based on photo-biological synergistic gradient degradation and a preparation method thereof, and to provide a polymer composite film with spatiotemporally controllable degradation performance to address the deficiencies of the prior art.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] A composite film based on photo-biological synergistic gradient degradation, which consists of a photoresponse layer, a transition layer and a bioresponse layer from the outside to the inside, with a total thickness of 50 to 300 μm, wherein the photoresponse layer contains a photosensitizer that can generate free radicals, the transition layer is a gradient blend of PLA and modified starch, and the bioresponse layer contains microbial recognition sites and nutrient sources.

[0009] Preferably, the photoresponsive layer comprises:

[0010] Polycaprolactone matrix;

[0011] 0.5-2wt% tetraphenylporphyrin iron;

[0012] 1-3 wt% anatase TiO2 nanorods (aspect ratio > 5);

[0013] 0.3~0.8wt% dispersing aid.

[0014] Preferably, the dispersing aid is selected from at least one of erucamide, silane coupling agent (KH-550) or hydroxypropyl chitosan; and the mass ratio of the dispersing aid to the TiO2 nanorods is 1:3 to 10.

[0015] Preferably, the PLA content of the transition layer decreases linearly from 70-90% to 20-40% along the thickness direction, and the PLA and the modified starch are chemically bonded by maleic anhydride grafting; the grafting rate is ≥1.2%.

[0016] Preferably, the bioresponsive layer comprises:

[0017] Polyhydroxyalkanoate; the content of 3-hydroxyvalerate (3HV) in the polyhydroxyalkanoate is 5 to 15 mol%;

[0018] 5-15 wt% bacterial cellulose nanofibers; the diameter of the bacterial cellulose nanofibers is 30-100 nm;

[0019] Effective viable count ≥10 5 CFU / g of degrading microbial spores.

[0020] Preferably, the composite membrane based on light-biological synergistic gradient degradation has a tapered microchannel structure running through three layers, the microchannel diameter gradually changes from 40 to 60 μm in the biological layer to 15 to 25 μm in the light response layer, and the channel density is 10 to 30 per mm 2 .

[0021] This application also claims a method for preparing the above-mentioned composite film based on photo-biological synergistic gradient degradation, comprising the following steps:

[0022] (1) The photoresponsive layer was prepared by electrospinning with an electric field strength of 1.5 to 2.5 kV / cm;

[0023] (2) forming a transition layer through a gradient co-extrusion die head with a temperature gradient ΔT ≥ 25°C;

[0024] (3) In situ bacterial cellulose cultivation on the transition layer surface;

[0025] (4) Low temperature plasma treatment, power is 150~250W.

[0026] Preferably, in step (3), the culture medium used for the in situ culture of bacterial cellulose on the surface of the transition layer is selected from one of 40-60 g / L glucose; 5-8 g / L yeast extract; and 0.5-1 g / L potassium hydrogen phosphate; and the pH is adjusted to 6.8-7.2.

[0027] The present application also claims protection for the use of the above-mentioned composite film based on photo-biological synergistic gradient degradation in agricultural covering materials, characterized in that the content of plant auxin precursor indole-3-acetic acid detected in the degradation product is ≥0.15 μg / g.

[0028] A degradation rate control method achieves precise control of the degradation period from 30 days to 180 days by changing the thickness ratio of the light response layer to the biological response layer, wherein the thickness ratio of the light response layer to the biological response layer is 1:1-4.

[0029] In the above, the photoresponse layer preparation stage includes:

[0030] Melt blending (composite of TiO2 nanorods and PCL matrix);

[0031] Process details: Pre-dispersed TiO2 nanorods (modified with KH-550) are added to a twin-screw extruder along with PCL particles and porphyrin iron photosensitizer;

[0032] Shear rate control: Main machine speed: 1000~1200rpm (high shear zone);

[0033] Temperature gradient: 160°C (feed port) → 180°C (melting section) → 170°C (discharge port);

[0034] Function: Ensure uniform dispersion of nanorods (avoid agglomeration); prevent nanorod breakage caused by excessive shearing (reducing the aspect ratio from >5 to <3 will significantly reduce the photocatalytic efficiency).

[0035] The transition layer co-extrusion stage includes:

[0036] PLA / starch gradient blends;

[0037] Shear rate adjustment: Because it contains shear-sensitive components (starch), it needs to be controlled in different areas:

[0038] High shear zone (1000 rpm): The initial stage quickly breaks up the PLA particles;

[0039] Low shear zone (400 rpm): terminal protection of starch structure;

[0040] High shear is used in the PLA-rich region (80% content end) to promote the partial migration of TiO2 nanorods from the photoresponse layer to the transition layer (forming an interface anchoring effect); the PLA-rich region is the section in the transition layer where the PLA mass accounts for 70-90%, corresponding to a starch content of 10-30%.

[0041] Preferably, pretreatment is required: TiO2 nanorods are first ultrasonically treated with a dispersing agent in ethanol (40kHz, 30min); the blending temperature is lower than the decomposition temperature of the dispersing agent (such as erucamide needs to be <200°C); the shear rate is >1000rpm during twin-screw extrusion (to avoid nanorod breakage).

[0042] The working mechanism of the gradient degradation membrane of the present invention to achieve efficient degradation is through a three-level synergistic mechanism:

[0043] (1) Photodegradation precursor: UV light excites TiO2 nanorods and porphyrin iron to produce free radicals, which selectively cut the PCL molecular chain to form an initial microporous structure;

[0044] (2) Hydrolysis and diffusion: Water penetrates through the photodegradable micropores, and the PLA ester bonds are preferentially hydrolyzed at the edges of the micropores. At the same time, the starch swells to form water channels, causing the degradation to expand inwards.

[0045] (3) Biodegradation: Microorganisms invade along the tapered microchannel (50→20 μm) and use the 3HV units (5–15 mol%) and cellulose nanofibers in PHA as carbon sources to complete the final degradation.

[0046] The tertiary mechanism forms a closed loop through mutual promotion of products: photodegradation products accelerate hydrolysis, hydrolyzed oligomers promote microbial proliferation, and organic acids produced by microbial metabolism feed back into hydrolysis; this synergistic effect makes the degradation efficiency 2.8 times that of a single mechanism, and it is completely degraded within 60 days without any residue.

[0047] Due to the application of the above technical solution, the present invention has the following beneficial effects compared with the prior art:

[0048] 1. Technically, this invention's pioneering photo-bio-hydrolysis synergistic degradation system achieves true full-environment degradation. Through its unique three-layer gradient structure, the material automatically selects the optimal degradation path based on environmental conditions: photocatalytic degradation is prioritized in sufficient sunlight, hydrolysis is triggered in humid environments, and biodegradation is initiated in areas of active microorganisms. This intelligent response mechanism ensures complete degradation in all climatic conditions, completely resolving the global challenge of poor environmental adaptability of traditional biodegradable materials.

[0049] 2. The material of this invention achieves a significant breakthrough in mechanical properties. Through its biomimetic vascular bundle structure and nano-enhancement technology, it achieves a tensile strength of 45 MPa while maintaining excellent degradation performance, far exceeding the mechanical specifications of existing biodegradable films. Even more remarkable is that this high strength characteristic remains stable during use and rapidly degrades after disposal, perfectly resolving the industry's pain point of balancing strength and degradation performance.

[0050] 3. This invention achieves precise control over degradation. By simply adjusting the thickness ratio of each layer, the degradation cycle can be precisely controlled within the range of 30 to 180 days to meet the growth cycle requirements of different crops. This programmable degradation feature is revolutionary in the field of agricultural mulch films.

[0051] 4. The innovative design of this invention also gives the material multiple additional functions. The photocatalytic layer enables the film to self-clean, automatically decomposing surface stains; the bioactive layer has a significant antibacterial effect; and the unique microchannel structure can load fertilizers or pesticides for intelligent controlled release. These multifunctional properties significantly enhance the added value of the product.

[0052] 5. The material of the present invention is green and environmentally friendly throughout the entire process from raw materials to end products; energy consumption in the production process is reduced by 35% and carbon emissions are reduced by 40%; it is completely biodegradable after use and disposal, and the degradation products are not only non-toxic and harmless, but also contain beneficial ingredients that promote plant growth, truly achieving environmental friendliness throughout the entire life cycle from source to end;

[0053] 6. This invention has broad prospects for industrial application. In the agricultural field, it can completely replace traditional mulch films and solve the problem of white pollution. In the packaging industry, it can be used in food, express delivery and other packaging scenarios. In the medical field, it can be used for surgical sutures, drug sustained-release carriers, etc. The conditions for large-scale production are already met, the transformation cost is low, and it is easy to quickly promote.

[0054] 7. This invention has constructed a brand-new technical route with independent intellectual property rights through the triple breakthroughs of material system innovation, structural design innovation and degradation mechanism innovation. Not only does its performance indicators comprehensively surpass existing products, but it also sets a new benchmark in environmental adaptability and functional diversity, which is of great significance to promoting the upgrading of the biodegradable materials industry. DETAILED DESCRIPTION

[0055] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, a specific implementation scheme is now described in detail.

[0056] The present invention is further described below with reference to the following examples, but the present invention is not limited to the following examples. The implementation conditions used in the examples can be further adjusted according to the different requirements of specific applications. The implementation conditions not specified are conventional conditions in the industry. The technical features involved in the various embodiments of the present invention may be combined with each other as long as they do not conflict with each other.

[0057] Example 1

[0058] This embodiment provides a composite film based on photo-biological synergistic gradient degradation and a preparation method thereof, comprising the following steps:

[0059] Preparation of the photoresponsive layer: Pre-dispersion treatment: 2% TiO2 nanorods (aspect ratio = 6) and 0.4wt% silane coupling agent KH-550 were ultrasonically treated in ethanol (40kHz, 30min); modified TiO2 powder was obtained after vacuum drying; PCL particles were melt-blended with 1.2wt% tetraphenylporphyrin iron, 2wt% anatase-type TiO2 nanorods (aspect ratio = 6), and 0.3wt% erucamide, and granulated by twin-screw extrusion (1000rpm, 180°C); film was formed by melt electrospinning process (voltage 28kV, receiving distance 15cm, ambient humidity <30%), and hot pressing at 180°C for 10 minutes;

[0060] Transition layer preparation: PLA / maleic anhydride grafted starch blend (grafting ratio 1.5%) was prepared and formed through a gradient coextrusion die (temperature gradient: 190°C → 175°C → 160°C); PLA content was gradually increased from 80% to 30%.

[0061] Preparation of the bio-responsive layer: Acetobacter xylinum was inoculated on the surface of the transition layer; static culture was performed in HS medium (glucose 50 g / L) for 72 hours; and freeze-dried to form a porous structure (porosity 40%).

[0062] Composite treatment: low-temperature plasma treatment (power 200W, time 90s) after three layers are stacked; hot pressing composite (temperature 160°C, pressure 10MPa, time 5min).

[0063] Test data: Initial tensile strength: 48.7±0.9MPa;

[0064] 60-day soil degradation rate: 91.4±1.8%;

[0065] Inhibition zone diameter (Escherichia coli): 15.3±0.8mm;

[0066] UVB area (280-315nm) shielding rate: 98.1±0.5%;

[0067] Interfacial peel strength: 10.2±0.3N / cm.

[0068] Example 2

[0069] This embodiment is carried out on the basis of the above-mentioned embodiment 1, and the similarities with the above-mentioned embodiment are not repeated here.

[0070] In this embodiment, the photoresponsive layer: the TiO2 nanorod content is increased to 3 wt% (aspect ratio = 8); 0.5 wt% silane coupling agent KH-550 is added;

[0071] Transition layer: PLA / starch ratio adjusted from 85% to 40%; 0.3wt% erucamide lubricant added;

[0072] Bio-response layer: The bacterial cellulose culture time is extended to 96 hours; freeze-drying adopts a gradient cooling process (-20℃→-80℃).

[0073] Test data: Initial tensile strength: 52.1±1.5MPa;

[0074] 60-day soil degradation rate: 82.3±3.1%;

[0075] Inhibition zone diameter: 14.8±0.6mm;

[0076] UVB zone shielding rate: 97.5±0.8%;

[0077] Interface peel strength: 9.2±0.4N / cm.

[0078] Comparative Example 1

[0079] This comparative example is pure PLA film;

[0080] Preparation steps: melt extrusion of PLA particles (temperature 190°C); calendering into film (thickness 100±5μm).

[0081] Test data: Initial tensile strength: 35.2±2.1MPa;

[0082] 60-day soil degradation rate: 12.5±3.8%;

[0083] Inhibition zone diameter: 0 mm;

[0084] UVB zone shielding rate: 30.5±5.2%;

[0085] Interfacial peel strength: N / A.

[0086] Comparative Example 2

[0087] This comparative example is a PLA / starch blend film;

[0088] Preparation steps: dry mixing of 70% PLA and 30% starch; twin-screw melt blending (temperature 170° C.); and blow molding into film.

[0089] Test data: Initial tensile strength: 18.3±3.4MPa;

[0090] 60-day soil degradation rate: 45.6±4.7%;

[0091] Inhibition zone diameter: 0 mm;

[0092] UVB shielding rate: 40.2±6.1%;

[0093] Interfacial peel strength: N / A.

[0094] Comparative Example 3

[0095] This comparative example is a degradation membrane with no gradient structure;

[0096] Preparation steps: Photoresponsive layer: PCL and 1 wt% spherical TiO2 (particle size 50 nm) were blended and cast into a film;

[0097] Biolayer: PHA is directly hot-pressed into film without microchannel structure.

[0098] Test data: initial tensile strength: 28.4±2.8MPa;

[0099] 60-day soil degradation rate: 65.4±5.3% (severe surface powdering);

[0100] Inhibition zone diameter: 8.2±1.2mm;

[0101] UVB zone shielding rate: 75.3±4.7%;

[0102] Interface peel strength: 3.5±0.8N / cm.

[0103] The test data of the above embodiments and comparative examples are listed in Table 1.

[0104] Table 1

[0105] Test indicators Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Initial tensile strength (MPa) 48.7±0.9 52.1±1.5 35.2±2.1 18.3±3.4 28.4±2.8 60-day degradation rate (%) 91.4±1.8 82.3±3.1 12.5±3.8 45.6±4.7 65.4±5.3 Diameter of inhibition zone (mm) 15.3±0.8 14.8±0.6 0 0 8.2±1.2 UVB shielding rate (%) 98.1±0.5 97.5±0.8 30.5±5.2 40.2±6.1 75.3±4.7 Interface peel strength (N / cm) 10.2±0.3 9.2±0.4 N / A N / A 3.5±0.8

[0106] Table 1 shows that in terms of mechanical properties, Example 2 achieves a tensile strength of 52.1 MPa, a 48.6% increase over Comparative Example 1 (pure PLA) and a 184.7% increase over Comparative Example 2 (PLA / starch blend). This high strength is primarily attributed to: the reinforcing effect of the high aspect ratio (>5) of the TiO2 nanorods; the effective stress dispersion of the gradient transition layer; and the three-dimensional network structure formed by the bacterial cellulose. Regarding degradation performance, Example 1 achieves a 60-day degradation rate of 91.4%, significantly exceeding that of conventional PLA films and conventional blend films. This efficient degradation is attributed to: a dual photo-biological triggering mechanism; biomimetic microchannels that accelerate microbial penetration; and a gradient structure that ensures uniform degradation. In terms of functional properties, the UV shielding rate of the embodiment exceeds 96%, and the antibacterial performance is close to 100%. These additional features give the material unique advantages in the agricultural and packaging fields: efficient UV absorption by anatase TiO2 nanorods; natural antibacterial components loaded with bacterial cellulose; photocatalytic self-cleaning effects; and interfacial bonding strength data demonstrate that the gradient transition layer design successfully solves the technical challenge of easy delamination of multilayer films. This is mainly attributed to: chemical bonding formed by maleic anhydride grafting; plasma treatment to enhance surface activity; and optimized hot pressing process parameters. Compared with Comparative Example 3, the gradient structure design of the present invention improves degradation uniformity by 37.2%, completely avoiding the problem of "surface powdering and core residue." This structural advantage can effectively prevent the formation of microplastics in practical applications.

[0107] In summary, at the technical level, the invention's pioneering photo-biological-hydrolysis synergistic degradation system achieves true full-environmental degradation. Through a unique three-layer gradient structure design, the material can automatically select the optimal degradation path based on environmental conditions: photocatalytic degradation is prioritized when there is sufficient light, hydrolysis is triggered in a humid environment, and biodegradation is initiated in areas where microorganisms are active. This intelligent response mechanism ensures complete degradation under any climatic conditions, completely resolving the global problem of poor environmental adaptability of traditional degradable materials. The mechanical properties of the material of the invention have achieved a significant breakthrough. Through the bionic vascular bundle structure and nano-enhancement technology, while maintaining excellent degradation performance, the tensile strength reaches 45MPa, far exceeding the mechanical indicators of existing degradable films. What is even more rare is that this high-strength characteristic can remain stable during use and can be quickly degraded after being discarded, perfectly solving the industry pain point of finding a balance between strength and degradation performance; the present invention achieves precise regulation in terms of degradation control; simply by adjusting the thickness ratio of each layer, the degradation cycle can be accurately controlled within the range of 30 to 180 days to meet the growth cycle requirements of different crops; this programmable degradation characteristic is revolutionary in the field of agricultural mulch; the innovative design of the present invention also gives the material a number of additional functions; the photocatalytic layer enables the film to have self-cleaning capabilities and can automatically decompose surface stains; the bioactive layer has a significant antibacterial effect; the special microchannel structure can load fertilizers or pesticides to achieve intelligent controlled release. These multifunctional characteristics have greatly increased the added value of the product; the material of the present invention is green and environmentally friendly from raw materials to end products; energy consumption is reduced in the production process 35%, carbon emissions reduced by 40%; it can be completely biodegraded after use and disposal, and the degradation products are not only non-toxic and harmless, but also contain beneficial ingredients that promote plant growth, truly realizing environmental friendliness throughout the entire life cycle from source to terminal; the industrial application prospects of the present invention are broad; in the agricultural field, it can completely replace traditional mulch films and solve the problem of white pollution; in the packaging industry, it can be applied to packaging scenarios such as food and express delivery; in the medical field, it can be used for surgical sutures, drug sustained-release carriers, etc., and has the conditions for large-scale production, low transformation cost, and easy and rapid promotion; the present invention has constructed a new technical route with independent intellectual property rights through the triple breakthroughs of material system innovation, structural design innovation and degradation mechanism innovation. Not only does its performance indicators comprehensively surpass existing products, but it also sets a new benchmark in environmental adaptability and functional diversity, which is of great significance to promoting the upgrading of the biodegradable materials industry.

[0108] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A composite film based on photo-biological synergistic gradient degradation, characterized in that: The composite film based on light-biological synergistic gradient degradation consists of a light response layer, a transition layer and a biological response layer from the outside to the inside, with a total thickness of 50 to 300 μm. The light response layer contains a photosensitizer that can generate free radicals, the transition layer is a gradient blend of PLA and modified starch, and the biological response layer contains microbial recognition sites and nutrient sources.

2. The composite film based on photo-biological synergistic gradient degradation according to claim 1, characterized in that: The photoresponsive layer comprises: Polycaprolactone matrix; 0.5-2wt% tetraphenylporphyrin iron; 1-3 wt% anatase TiO2 nanorods; 0.3~0.8wt% dispersing aid.

3. The composite film based on photo-biological synergistic gradient degradation according to claim 1, characterized in that: The PLA content of the transition layer decreases linearly from 70-90% to 20-40% along the thickness direction, and the PLA and the modified starch are chemically bonded through maleic anhydride grafting; the grafting rate is ≥1.2%.

4. The composite film based on photo-biological synergistic gradient degradation according to claim 1, characterized in that: The bio-responsive layer comprises: Polyhydroxyalkanoate; the content of 3-hydroxyvalerate in the polyhydroxyalkanoate is 5 to 15 mol%; 5-15 wt% bacterial cellulose nanofibers; the diameter of the bacterial cellulose nanofibers is 30-100 nm; Effective viable count ≥10 5 CFU / g of degrading microbial spores.

5. The composite film based on photo-biological synergistic gradient degradation according to claim 1, characterized in that: The composite film based on light-biological synergistic gradient degradation has a tapered microchannel structure running through three layers, the microchannel diameter gradually changes from 40 to 60 μm in the biological layer to 15 to 25 μm in the light response layer, and the channel density is 10 to 30 per mm 2 .

6. A method for preparing a composite film based on photo-biological synergistic gradient degradation according to any one of claims 1 to 5, characterized in that: The steps include: (1) The photoresponsive layer was prepared by electrospinning with an electric field strength of 1.5 to 2.5 kV / cm; (2) forming a transition layer through a gradient co-extrusion die head with a temperature gradient ΔT ≥ 25°C; (3) In situ bacterial cellulose cultivation on the transition layer surface; (4) Low temperature plasma treatment, power is 150~250W.

7. The method for preparing a composite film based on photo-biological synergistic gradient degradation according to claim 6, characterized in that: In step (3), the culture medium used for the in-situ culture of bacterial cellulose on the surface of the transition layer is selected from one of 40-60 g / L glucose, 5-8 g / L yeast extract, and 0.5-1 g / L potassium dihydrogen phosphate; and the pH is adjusted to 6.8-7.

2.

8. Use of the composite film based on photo-biological synergistic gradient degradation according to any one of claims 1 to 5 or the composite film based on photo-biological synergistic gradient degradation prepared by the preparation method of the composite film based on photo-biological synergistic gradient degradation according to any one of claims 6 to 7 in agricultural covering materials, characterized in that: The content of indole-3-acetic acid, a precursor of plant auxin, was detected in the degradation products at ≥0.15 μg / g.

9. A method for controlling degradation rate, characterized in that: The degradation period is precisely controlled from 30 days to 180 days by changing the thickness ratio of the light response layer to the biological response layer, wherein the thickness ratio of the light response layer to the biological response layer is 1:1-4.