Controllable light-oxygen and biological dual-degradation label and preparation method and degradation control method thereof

Abstract

The invention discloses a controllable light-oxygen and biological dual-degradation label and a preparation method and a degradation control method thereof, and belongs to the technical field of environment-friendly materials, the controllable light-oxygen and biological dual-degradation label comprises an upper surface layer, a core layer and a lower surface layer, the upper surface layer comprises 1500-3000 ppm of an anti-blocking agent, 5-10 wt% of a photocatalytic material and the balance of a polypropylene homopolymer; the core layer is prepared from the following components in percentage by weight: 5 to 15 percent of degradable master batch, 20 to 40 percent of nano calcium carbonate, 2 to 5 percent of light-oxygen degradation regulator and the balance of polypropylene homopolymer; the lower surface layer is prepared from 10 to 20 weight percent of polypropylene grafted maleic anhydride, 5 to 10 weight percent of degradable master batch and the balance of polypropylene homopolymer. According to the scheme, efficient and controllable degradation is achieved through a light-oxygen-biological dual-degradation synergistic mechanism, light-oxygen degradation preferentially breaks polymer chains, biodegradation relay mineralization is achieved, an adjustable degradation window within 180-270 days is achieved, and the problem of micro-plastic residues is thoroughly solved.

Description

Technical Field

[0001] This invention relates to the field of environmental protection materials technology, specifically to a controllable photo-oxidation and biodegradable label, its preparation method, and degradation control method. Background Technology

[0002] Self-adhesive labels (such as BOPP film labels) are widely used in the food, pharmaceutical, and daily chemical industries. However, their slow degradation results in discarded labels persisting in the natural environment for extended periods, causing environmental pollution. Therefore, the development of labels that can be controlled for both photo-oxidation and biodegradation has become a current research hotspot.

[0003] Chinese patent CN112143101A discloses a biodegradable masterbatch for BOPP film and its preparation method. The biodegradable masterbatch comprises polypropylene resin (45-96.3%), a pre-oxidant (photodegradant such as titanium dioxide or thermal degradant such as ferric stearate, 0.2-10%), natural biomass (such as plant fiber, 1-30%), plasticizer, compatibilizer, and lubricant. It is used to produce BOPP film through melt blending and biaxial stretching processes, with the biodegradable masterbatch added at a rate of 0.1-1%, aiming to achieve a synergistic effect of photodegradation, thermal degradation, and biodegradation. However, this prior art has significant limitations: The degradation rate is uncontrollable: it depends on environmental conditions (such as light and temperature), and the degradation time window cannot be preset, which may lead to premature degradation (such as during transportation) or slow degradation (accumulation pollution).

[0004] Insufficient performance balance: Adding natural biomass may reduce the thermal stability (glass transition temperature <100℃) and mechanical strength (Young's modulus <2GPa) of the material, making it difficult to meet the requirements of high-performance labels.

[0005] It is evident that existing biodegradable labels mostly use bio-based materials such as polylactic acid (PLA) or polybutylene adipate / terephthalate (PBAT), but these materials suffer from problems such as uncontrollable degradation rates, poor mechanical properties, and high costs. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a controllable photo-oxidation and biodegradable tag, along with its preparation and degradation control methods. This tag combines photo-oxidation and biodegradation mechanisms to achieve rapid degradation under specific conditions (such as light exposure and microbial activity), reducing environmental burden. Photo-oxidation degradation breaks down high-molecular polymers into smaller fragments through photocatalytic reactions, while biodegradation utilizes microorganisms to further mineralize these fragments into CO2 and H2O. The synergistic effect of these two mechanisms improves degradation efficiency and controllability.

[0007] The technical means adopted in this solution are as follows: A controllable photo-oxidation and biodegradable label includes: an upper surface layer, a core layer and a lower surface layer, wherein the upper surface layer includes 1500~3000ppm of an anti-blocking agent and 5~10wt% of a photocatalytic material, with the balance being polypropylene homopolymer; The core layer comprises 5-15 wt% biodegradable masterbatch, 20-40 wt% nano-calcium carbonate and 2-5 wt% photo-oxidation degradation regulator, with the balance being polypropylene homopolymer. The lower surface layer comprises 10-20 wt% polypropylene grafted with maleic anhydride and 5-10 wt% biodegradable masterbatch, with the remainder being polypropylene homopolymer.

[0008] Furthermore, the anti-blocking agent is silicon dioxide with a particle size of 0.5~0.8 micrometers; the photocatalytic material is graphitic carbon nitride g-C3N4; The biodegradable masterbatch is a blend of PLA and PBAT in a mass ratio of 30:70 to 70:30. The photo-oxidative degradation regulator is a blend of g-C3N4 and Bi2O2CO3 composite catalyst and cyclic olefin copolymer in a mass ratio of 50:50 to 70:30.

[0009] Furthermore, the preparation method of the g-C3N4 and Bi2O2CO3 composite catalyst is as follows: Step 1, Pretreatment: Dispersion and activation of g-C3N4: Take 2g of g-C3N4 and add it to 100ml of solution containing CTAB and Na2CO3; sonicate for 40 minutes; Step 2, Mixing reaction: Dissolve 1.712g of Bi2O2CO3·5H2O in 10mL of 10M nitric acid and stir magnetically until completely dissolved to obtain a bismuth salt solution; slowly add the bismuth salt solution dropwise to a solution containing g-C3N4 in CTAB and Na2CO3, controlling the addition time to 10 minutes, and then stir for 2 hours to obtain a mixed solution; Step 3, hydrothermal reaction: Transfer the mixture to a 100mL polytetrafluoroethylene-lined high-pressure reactor, seal it, and place it in an oven; heat to 160℃ at 5℃ / min, maintain the temperature for 12 hours; allow it to cool naturally to room temperature; Step 4, purification and activation: Filter and collect the precipitate, wash it three times alternately with deionized water and ethanol; dry it in an oven at 80℃ for 12 hours; then grind it to a particle size of less than 50μm, sieve it and store it.

[0010] A controllable photo-oxidation and biodegradable label, further comprising an ink layer and an adhesive layer; The ink layer is printed on the upper surface layer, using UV ink or water-based ink, with 5~10wt% of g-C3N4 and Bi2O2CO3 composite catalyst added, which initiates ink degradation under light irradiation; The adhesive layer, coated on the lower surface, contains 17-19 wt% biodegradable masterbatch.

[0011] A method for preparing a controllable photo-oxidation and biodegradable tag includes the following steps: Step S1: Prepare the raw material components for the upper surface layer, core layer, and lower surface layer, and dry them to ensure uniform dispersion and degradation activity; Step S2, melt co-extrusion: The raw materials for each layer are processed separately using different extruders and then merged through a flow channel distributor to achieve multi-layer co-extrusion; Step S3, casting and biaxial stretching: After the melt is extruded, it is cooled into a thick sheet, and then stretched longitudinally and transversely to form a microporous structure and increase the specific surface area for degradation; after stretching, it is shaped at 190~205℃ to stabilize the molecular chain orientation; the heat setting time is <10s. Step S4, Surface treatment and coating: After stretching, the film is subjected to corona treatment and coated with an adhesive layer; Step S5: After the film is wound up, it needs to be aged: stored at 25°C and 50% humidity for 24 hours to release internal stress.

[0012] Further, in step S1, the preparation of the biodegradable masterbatch is a blend of PLA and PBAT in a mass ratio of 30:70 to 70:30. After mixing PLA and PBAT, 1 to 5 wt% of glycerol plasticizer and 1 to 5 wt% of polypropylene grafted maleic anhydride compatibilizer are added, and the mixture is mixed in a high-speed mixer at 50 to 60°C for 30 minutes. Preparation of photo-oxidative degradation regulator: g-C3N4 and Bi2O2CO3 composite catalyst were blended with cyclic olefin copolymer at a mass ratio of 50:50~70:30, and then ball-milled to a particle size of <100nm in an inert gas atmosphere. The biodegradable masterbatch and the photo-oxidation degradation regulator are pre-blended and then ball-milled to achieve nanocomposite properties, so that the photo-oxidation degradation regulator can uniformly coat the surface of the biodegradable masterbatch.

[0013] Furthermore, in step S2, the extrusion temperature of the core layer is 230~260℃, and the extrusion temperature of the upper and lower surface layers is 220~240℃; the extrusion rate of all extruders is 100~300kg / h, and the screw speed is 300~600rpm.

[0014] The preparation method of the controllable photo-oxidation and biodegradable label also includes a degradation control method: for the ink layer, the ink base material and the remaining treatment components are stirred in a high-speed mixer for 30 minutes, and then coated on the upper surface of the label with a wet thickness of 10~15μm.

[0015] Furthermore, based on the different shelf lives of the labels, three types of ink layers are designed: rapidly degradable ink layers, generally degradable ink layers, and rapidly degradable ink layers. For rapidly degradable ink layers, suitable for labels requiring a degradation rate of ≥90% within 180 days, the ink layer comprises: 5~10wt% of g-C3N4 and Bi2O2CO3 composite catalyst, 10~15wt% of degradable masterbatch, 5~8wt% of laccase-loaded microspheres, 2~4wt% of urethane compound, 2~3wt% of polyvinyl alcohol, 0.5~1wt% of ferric stearate, and the remainder being ink base material; For general degradable ink layers, suitable for labels requiring a 75% degradation rate within 220 days; the ink layer includes: 6-8 wt% g-C3N4 and Bi2O2CO3 composite catalyst, 10-12 wt% degradable masterbatch, 3-5 wt% laccase-loaded microspheres, 1.5-2.5 wt% maleic anhydride graft, 2-3 wt% nano-silica, 3-5 wt% cyclic olefin copolymer, 1-2 wt% polyvinyl alcohol, 0.1-0.3 wt% antioxidant BHT, and the balance being ink base material; For slow-degrading ink layers, suitable for ink layers where the degradation rate can be controlled below 50% within 270 days; the ink layer includes: 5-6 wt% of g-C3N4 and Bi2O2CO3 composite catalyst, 1-2 wt% of rutile TiO2, 0.1-0.5 wt% of antioxidant BHT, 3-5 wt% of hydrophobic modifier OTS, 1-2 wt% of carbonyl compound, 5-8 wt% of cyclic olefin copolymer, 2-3 wt% of nano silica, and the remainder is ink base material.

[0016] This invention provides a controllable photo-oxidation and biodegradable tag, its preparation method, and degradation control method, which have the following advantages: Breakthrough in degradation performance: This solution achieves efficient and controllable degradation through a photo-oxidation-biological dual degradation synergistic mechanism. Photo-oxidation degradation preferentially breaks down polymer chains, while biological degradation follows up with mineralization, achieving an adjustable degradation window of 180~270 days and completely solving the problem of microplastic residues.

[0017] Balanced mechanical properties: While maintaining degradability, it meets the strength and durability requirements of high-performance labels.

[0018] Significant environmental benefits: Green throughout the entire life cycle, with no microplastic residue, in line with the concept of circular economy. Attached Figure Description

[0019] Figure 1 This is a schematic diagram illustrating the degradation mechanism. Detailed Implementation

[0020] The technical solutions of 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.

[0021] Terminology Explanation: BOPP (Biaxially Oriented Polypropylene) is a film formed by biaxially stretching polypropylene (PP) in both the longitudinal and transverse directions.

[0022] Polypropylene homopolymer is a polymer compound produced by the polymerization of pure propylene monomers. Its molecular chain contains only propylene structural units and no other comonomers. In this design, polypropylene homopolymer serves as the matrix material and is a core component of the label's upper, core, and lower layers.

[0023] Biodegradable masterbatch is a high-molecular functional material, a concentrated mixture obtained by melt blending a biodegradable polymer matrix, degradation promoters, and processing aids. In the controlled photo-oxidation and biodegradable label described in this scheme, the biodegradable masterbatch, as the core functional component for biodegradation, can be enzymatically hydrolyzed by microorganisms under natural environmental conditions through easily degradable bonds in its molecular structure, ultimately mineralizing into CO2 and H2O; it can be a blend of PLA (polylactic acid) and PBAT (polybutylene adipate / terephthalate). The biodegradable masterbatch can be commercially available Polymateria Recycle V31, or a blend of PLA (polylactic acid) and PBAT (polybutylene adipate / terephthalate).

[0024] Laccase-loaded microspheres are composite materials used to immobilize laccase, designed to improve enzyme stability and reusability. The carrier typically consists of a hydrogel porous microcarrier and laccase covalently bonded together. The hydrogel porous microcarrier is a chitosan-filled methacrylic acid hydrogel microcarrier, providing abundant loading sites. Laccase-loaded microspheres are existing technology; for example, the technical solution in Chinese patent application CN202310486974.4 can be used. Laccase is a copper-containing polyphenol oxidase with strong substrate specificity, capable of catalyzing various phenols, anilines, and aromatic compounds.

[0025] Nano-silica is easy to surface modify, with a particle size of 40~100nm.

[0026] The antioxidant BHT (Butylated Hydroxytoluene) is a synthetic phenolic antioxidant with the chemical name 2,6-di-tert-butyl-4-methylphenol.

[0027] Cyclic olefin copolymers (COCs) are high-performance transparent polymer materials made by copolymerizing cyclic olefins (such as norbornene) with ethylene. They have high transparency (transmittance > 90%), low hygroscopicity (water absorption < 0.01%), excellent chemical stability, and a wide glass transition temperature range (80~170℃).

[0028] OTS is an abbreviation for Octadecyltrichlorosilane, with the chemical formula C64. 18 H 37 SiCl3 is a commonly used hydrophobic modifier.

[0029] ESP stands for Electron Surface Potential.

[0030] A controllable photo-oxidation and biodegradable label includes: an upper surface layer, a core layer, a lower surface layer, an ink layer, and an adhesive layer.

[0031] The upper surface is the printing surface of the label, which is in direct contact with the external environment and has good printability, abrasion resistance and photocatalytic activity.

[0032] The upper surface layer includes 1500~3000ppm of anti-blocking agent and 5~10wt% of photocatalytic material, with the balance being polypropylene homopolymer; The melt index of the polypropylene homopolymer is 2.8~3.8 g / 10 min; The anti-blocking agent is silica with a particle size of 0.5~0.8 micrometers. The refractive index of silica is highly matched with that of polypropylene, and its effect on the light transmittance and haze of BOPP film is negligible. The anti-blocking mechanism of silica is as follows: it forms fine, hard protrusions on the film surface, significantly reducing the actual contact area between films (by 60-70%), thus reducing the coefficient of friction on the film surface. Simultaneously, the protrusion structure creates continuous air gaps, disrupting the vacuum adsorption effect and making the film easier to open, thereby preventing film adhesion and ensuring printing quality.

[0033] The photocatalytic material is graphitic carbon nitride g-C3N4, which has a graphene-like two-dimensional layered structure and can absorb blue-violet light with wavelengths ≤475nm (visible light response). Under illumination, it generates -OH and O2. - Free radicals attack polymer chains, achieving initial degradation.

[0034] The top surface is corona treated to increase surface energy and promote ink adhesion.

[0035] The core layer is the support layer of the label, accounting for more than 60% of the thickness. It dominates the mechanical properties (such as stiffness and tensile strength) and degradation controllability. By adding biodegradable masterbatch and nanofillers, the synergy of photo-oxidation and biodegradation is achieved.

[0036] The core layer comprises 5-15 wt% biodegradable masterbatch, 20-40 wt% nano-calcium carbonate, and 2-5 wt% photo-oxidative degradation regulator, with the balance being polypropylene homopolymer. The components are melt-blended to form an island structure, with PLA as the dispersed phase, preferentially degrading in the environment and triggering overall disintegration.

[0037] The biodegradable masterbatch is a blend of PLA (polylactic acid) and PBAT (polybutylene adipate / terephthalate) in a mass ratio of 30:70 to 70:30, combining the high strength of PLA with the flexibility of PBAT, while optimizing compatibility through a twin-screw extrusion process. As the core of biodegradation, the ester bonds in the biodegradable masterbatch are easily degraded by microbial enzymes.

[0038] The nano-calcium carbonate has a particle size of 40-100 nm, forming a vacancy structure, increasing the specific surface area, and promoting photocatalytic reactions and microbial attachment.

[0039] The photo-oxidative degradation regulator is a blend of g-C3N4 and Bi2O2CO3 composite catalyst and cyclic olefin copolymer in a mass ratio of 50:50 to 70:30. g-C3N4 is graphitic carbon nitride with a planar two-dimensional sheet structure and a moderate band gap, enabling it to absorb blue-violet light with wavelengths less than 475 nm in the solar spectrum.

[0040] Cyclic olefin copolymers (COCs) are amorphous transparent polymers formed by the polymerization of ethylene and cyclic olefin monomers. They have excellent optical properties and heat resistance. Their cyclic structure helps to reduce oxygen permeability, thereby delaying the rapid loss of material strength in the early stages of degradation, achieving "controllable" regulation of the degradation process, and producing a synergistic effect with the photocatalytic effect of the g-C3N4 and Bi2O2CO3 composite catalyst.

[0041] The preparation method of g-C3N4 and Bi2O2CO3 composite catalyst is as follows: Step 1, Pretreatment: Dispersion and activation of g-C3N4: Take a predetermined mass of g-C3N4 (e.g., 2g) and add it to 100ml of a solution containing CTAB (hexadecyltrimethylammonium bromide) and Na2CO3 (CTAB concentration 0.01526mol / L, Na2CO3 concentration 0.314mol / L); ultrasonically disperse for 40 minutes.

[0042] g-C3N4 has a two-dimensional layered structure that is prone to aggregation due to van der Waals forces. Microjets generated through ultrasonic cavitation can peel it off into monolayer or few-layer sheet-like structures. CTAB, as a cationic surfactant, adsorbs onto the g-C3N4 surface to form a positively charged layer, preventing re-aggregation through electrostatic repulsion. Simultaneously, CTAB acts as a template agent, guiding the directional growth of Bi2O2CO3 on the g-C3N4 surface and promoting heterojunction formation.

[0043] Step 2, Mixing reaction: Dissolve Bi2O2CO3·5H2O (1.712g) in 10mL nitric acid (10M) and stir magnetically until completely dissolved to obtain a bismuth salt solution; slowly add the bismuth salt solution dropwise to a CTAB / Na2CO3 solution containing g-C3N4, controlling the addition time to 10 minutes, and then stir for 2 hours to obtain a mixed solution.

[0044] The purpose of slow dripping is twofold: 1. To avoid localized oversaturation: Rapid addition of bismuth salt will instantly generate Bi₂O₂CO₃ nuclei, leading to uneven particle size; 2. To control the nucleation rate: Slow dripping allows Bi₂O₂CO₃ to be added more gradually. 3+ With CO3 2- Ions combine in an orderly manner and preferentially nucleate on the g-C3N4 surface, achieving "in-situ coating".

[0045] After stirring for 2 hours, weak chemical bonds are formed between the nitrogen-containing groups (such as CN bonds) of g-C3N4 and the Bi-O bonds of Bi2O2CO3. The addition of nitric acid maintains an acidic environment (pH≈3) and inhibits Bi... 3+ Premature hydrolysis can generate impurity phases (such as BiOCl).

[0046] Step 3, hydrothermal reaction: Transfer the mixture to a 100mL polytetrafluoroethylene-lined high-pressure reactor, seal it, and place it in an oven; heat it to 160℃ at 5℃ / min and keep it at that temperature for 12 hours; then cool it naturally to room temperature.

[0047] Under high temperature and high pressure, enhanced atomic diffusion at the interface between g-C3N4 and Bi2O2CO3 leads to Type-II band alignment, achieving effective separation of photogenerated electron-hole pairs and significantly improving photocatalytic degradation efficiency. Hydrothermal treatment at 160℃ causes Bi2O2CO3 to form petal-like nanosheets, which intertwine with the porous structure of g-C3N4, increasing the specific surface area (BET reaches 42.64 m² after composite formation). 2 / g). The reaction time is 12 hours. If the reaction time is too short, the crystal growth will be incomplete; if it is too long, it may cause g-C3N4 to decompose. The temperature is 160°C: the reaction is incomplete below 150°C, and side reactions are triggered above 180°C.

[0048] Step 4, Purification and Activation: Filter and collect the precipitate, wash it three times alternately with deionized water and ethanol; dry it in an oven at 80℃ for 12 hours; then grind it to a particle size of less than 50μm, sieve it (400 mesh) and store it.

[0049] Washing removes impurities such as CTAB and sodium nitrate, preventing residual ions from blocking active sites; ethanol washing removes moisture, reducing agglomeration after drying. Drying at 80℃ balances efficiency and material stability: excessively high temperatures may damage the hydrogen bond network of g-C3N4. Grinding to the micron level improves processability and ensures uniformity during coating or molding.

[0050] The composite catalyst of g-C3N4 and Bi2O2CO3 achieves synergistic enhancement through Type-II band alignment. The principle can be divided into the following stages: 1. Band alignment and charge separation.

[0051] Type-II heterojunction formation: The conduction band of g-C3N4 (-1.1eV) is higher than that of Bi2O2CO3 (-0.3eV), while the valence bands (g-C3N4: +1.6eV; Bi2O2CO3: +3.0eV) are staggered. The band shift generates an internal electric field, driving photogenerated electrons to migrate from the g-C3N4 conduction band to the Bi2O2CO3 conduction band, while holes migrate in the opposite direction.

[0052] Charge separation effect: Electrons are enriched on the Bi2O2CO3 side and holes are enriched on the g-C3N4 side. Spatial isolation reduces the electron-hole recombination rate by more than 50%, and the degradation rate is increased by 10-15% after recombination.

[0053] 2. Visible light absorption expansion.

[0054] Spectral complementarity: g-C3N4 absorbs blue-violet light (λ≤475nm), Bi2O2CO3 absorbs ultraviolet light (λ≤375nm), and the combined light response range covers 300~475nm.

[0055] Improved photon utilization efficiency: The composite catalyst captures twice as many photons under visible light as the single component.

[0056] Therefore, the core photocatalytic principle of the g-C3N4 and Bi2O2CO3 composite catalyst lies in the charge space separation effect induced by Type-II band alignment. The visible light capture capability of g-C3N4 combined with the strong adsorption of Bi2O2CO3 achieves efficient electron-hole pair separation through the heterojunction interface, significantly improving the free radical yield and pollutant degradation efficiency.

[0057] The lower surface layer is the adhesive layer bonding surface, which has high adhesion and degradation compatibility. Polar components are introduced to enhance the bonding force with the adhesive layer, and biodegradation promoters are added.

[0058] The lower surface layer comprises 10-20 wt% polypropylene grafted with maleic anhydride and 5-10 wt% biodegradable masterbatch, with the remainder being polypropylene homopolymer.

[0059] For polypropylene grafted with maleic anhydride, such as Dow Polybond® 3150, the polypropylene main chain is grafted with polar maleic anhydride groups. The anhydride groups react with the hydroxyl and amino groups in the adhesive layer to form covalent bonds, increasing the adhesive strength by 50-80%. Although its own degradation is weak, the anhydride groups hydrolyze to produce carboxylic acids, promoting microbial adhesion. The hydrolysis products (maleic acid) can serve as a carbon source to promote microbial growth. The lower surface layer promotes adhesive adhesion through polar components (polypropylene grafted with maleic anhydride), preventing delamination during the service life.

[0060] The addition of biodegradable masterbatch accelerates the biodegradation of the lower surface layer, allowing the degradation of the lower surface layer and the core layer to occur simultaneously. Photo-oxidative degradation begins from the surface layer, while biodegradation penetrates from the bottom layer, forming a hierarchical synergy.

[0061] The ink layer is printed on the upper surface layer, using UV ink or water-based ink, with 5~10wt% of g-C3N4 and Bi2O2CO3 composite catalyst added, which initiates ink degradation under light irradiation.

[0062] The adhesive layer, coated on the lower surface layer, contains 17-19 wt% biodegradable masterbatch, is biodegradable, and works synergistically with the biodegradable masterbatch in the lower surface layer to form a continuous degradation interface.

[0063] Each layer achieves complementary functions through component design: the upper layer initiates photocatalytic degradation; the core layer's biodegradable masterbatch and nano-calcium carbonate regulate the degradation rate; and the polar components in the lower layer ensure stability throughout the service life. The small molecular fragments generated by photocatalytic degradation provide nutrients for microorganisms, accelerating biodegradation and forming a "photocatalytic-biological" cascade reaction.

[0064] A method for preparing a controllable photo-oxidation and biodegradable tag includes the following steps: Step S1: Prepare the raw material components for the upper surface layer, core layer, and lower surface layer, and dry them to ensure uniform dispersion and degradation activity.

[0065] The biodegradable masterbatch is prepared by blending PLA (polylactic acid) and PBAT (polybutylene adipate / terephthalate) in a mass ratio of 30:70 to 70:30. After mixing PLA and PBAT, 1-5 wt% glycerol plasticizer and 1-5 wt% polypropylene-grafted maleic anhydride compatibilizer are added. The mixture is then stirred in a high-speed mixer at 50-60°C for 30 minutes. The plasticizer lowers the glass transition temperature of PLA and improves processing fluidity. Simultaneously, the compatibilizer improves the compatibility between PLA and polypropylene and prevents phase separation.

[0066] The photocatalytic degradation regulator was prepared by blending a g-C3N4 and Bi2O2CO3 composite catalyst with a cyclic olefin copolymer at a mass ratio of 50:50 to 70:30, followed by ball milling to a particle size <100 nm in an inert gas atmosphere. The nanoscale size increases the specific surface area and improves photocatalytic efficiency. The inert gas prevents oxidation of g-C3N4 or degradation of the cyclic olefin copolymer.

[0067] Synergistic pretreatment: The biodegradable masterbatch is pre-blended with a photo-oxidation degradation regulator, and then ball-milled (40℃) to achieve nanocomposite processing, ensuring that the photo-oxidation degradation regulator uniformly coats the surface of the biodegradable masterbatch. This step ensures that the photocatalytic sites and biodegradation sites are adjacent during subsequent extrusion, resulting in synergy during degradation: the reactive oxygen species generated by photolysis attack the PLA chains, generating low molecular weight fragments that are more easily utilized by microorganisms.

[0068] Step S2, melt co-extrusion: Different extruders are used to process the raw materials of each layer separately, and they are combined through a flow channel distributor to achieve multi-layer co-extrusion.

[0069] The extrusion temperature of the core layer is 230~260℃, and the extrusion temperature of the upper and lower surface layers is 220~240℃. The extrusion rate of all extruders is 100~300kg / h, and the screw speed is 300~600rpm. High temperature ensures the melting of biodegradable masterbatch, but the residence time must be controlled to <5 minutes to prevent thermal degradation of the biodegradable masterbatch.

[0070] The core layer accounts for 60% of the thickness. During extrusion, a compatibilizer (such as polypropylene grafted with maleic anhydride) promotes the interfacial bonding between the biodegradable masterbatch and the polypropylene homopolymer, forming a microscopic island structure. The biodegradable masterbatch is an island phase, which acts as a "weak point" in the early stages of degradation, inducing cracking; the photo-oxidation degradation regulator is a continuous phase, ensuring the efficiency of the photoreaction.

[0071] Step S3, casting and biaxial stretching: After the melt is extruded, it is cooled into a thick sheet, and then stretched longitudinally and laterally to form a microporous structure and increase the specific surface area for degradation.

[0072] Casting: The melt is cast through a 25-40℃ chilled roller with a cooling rate >50℃ / s to form an amorphous thick sheet. Rapid cooling inhibits the crystallization of degradable masterbatch (high crystallinity of degradable masterbatch reduces the degradation rate), maintaining the amorphous region as easily degradable.

[0073] Biaxial stretching: First, longitudinal stretching (temperature 140~180℃, stretching ratio 3.3~4.8 times), then transverse stretching (temperature 150~180℃, stretching ratio 3.0~3.2 times). During stretching, cavities are formed at the interface between nano-calcium carbonate and the biodegradable masterbatch, with a cavity size of 100~500nm, increasing the permeation pathways for oxygen and moisture, and promoting photo-oxidation and biodegradation. The stretching ratio controls the degradation rate: a high ratio (e.g., transverse stretching >5 times) generates more micropores, accelerating degradation, but may reduce mechanical strength; a balance needs to be struck.

[0074] Heat setting: After stretching, the material is set at 190~205℃ to stabilize the molecular chain orientation. Heat setting time should be <10s to avoid decomposition of the biodegradable masterbatch. This step fixes the microporous structure, ensuring controllable degradation.

[0075] Step S4, Surface treatment and coating: After stretching, the film is subjected to corona treatment and coated with an adhesive layer to complete the label preparation.

[0076] Corona treatment: Corona power 50~100W, processing speed 100m / min. Corona treatment increases surface energy to over 40mN / m, improving ink adhesion by 50%. Simultaneously, corona treatment introduces oxygen-containing groups (such as carboxyl groups), enhancing surface hydrophilicity, facilitating microbial adhesion, and promoting biodegradation.

[0077] Adhesive coating: The adhesive coating is applied to the lower surface layer. The coating solution contains 17-19 wt% biodegradable masterbatch and 5-10 wt% g-C3N4 and Bi2O2CO3 composite catalyst. The coating thickness is 3-6 μm, and after drying it is 1-1.8 μm.

[0078] Synergistic effect of corona treatment and photocatalytic layer: The active sites generated by corona treatment can adsorb photogenerated electrons, extending the lifetime of photo-oxidative degradation regulators. The biodegradable masterbatch in the coating layer and the biodegradable masterbatch in the core layer form a degradation network, ensuring overall degradation consistency.

[0079] Step S5: After the film is wound up, it needs to undergo aging treatment: stored at 25℃ and 50% humidity for 24 hours to release internal stress and stabilize dimensions. After aging, it is slit into finished products. The entire preparation process must be carried out in a clean environment to prevent impurities from being introduced into the degradation "dead zone".

[0080] In this preparation method, pretreatment ensures component dispersion; co-extrusion and stretching construct a porous structure, increasing the degradation interface; and surface treatment enhances the photo-biodegradation linkage. The photo-oxidative degradation regulator (g-C3N4 and cyclic olefin copolymer) achieves a specific surface area of ​​40-80 m² after stretching. 2 / g, a similar structure can improve the efficiency of tag degradation.

[0081] Figure 1 A schematic diagram of the degradation mechanism, such as Figure 1As shown, the product prepared by this method achieves highly efficient synergy between photo-oxidative degradation and biodegradation through innovative hierarchical structure design and component optimization. Its hierarchical degradation mechanism is as follows: Primary degradation (photo-oxidation dominant): The upper surface g-C3N4 and Bi2O2CO3 composite catalyst generates active oxygen (-OH and -O2) under light irradiation. - Within 7 days, the polymer molecular weight was reduced from 200,000 Da to below 10,000 Da; Deep degradation (bio-driven): The ester bonds of the core PLA / PBAT masterbatch are degraded by microbial enzymes, increasing the degradation rate by 30% within 180 days; Complete mineralization: The final products are CO2, H2O and biomass, with no microplastic residue.

[0082] Mechanical property analysis: Tensile strength: longitudinal ≥45MPa, transverse ≥40MPa (ASTM D882 standard); Young's modulus: 2.1~3.5GPa (adjustable according to degradation type); elongation at break: 100~300%; interlaminar peel strength: ≥4N / cm.

[0083] Mechanical property retention rate: Mechanical properties retention rate >95% during storage period (12 months); good dimensional stability within temperature range of -40~120℃; tensile strength retention rate >80% after 1000 hours of UV aging.

[0084] Optical performance: Light transmittance: ≥85% (visible light range of 400~700 m); Haze: ≤5%, maintaining the transparent texture of the label; Color difference: ΔE≤1.5, high color reproduction accuracy.

[0085] As the printing surface of the label, the ink layer is directly exposed to environmental factors (such as light and humidity), acting as a "trigger" for degradation control. To address different application needs (such as short or long shelf life), differentiated ink layer compositions are proposed. Through the synergistic design of photosensitizers, biodegradation promoters, and functional groups, graded control of photo-oxidative degradation and biodegradation rates is achieved. This solution ensures that the label completes degradation within a specific time window (such as rapid degradation within 180 days or slow degradation within 270 days) while maintaining mechanical stability throughout its service life.

[0086] A degradation control method for controlled photo-oxidation and biodegradable tags includes the following steps: For the ink layer, mix the ink base (water-based ink or UV ink) with the remaining treatment components in a high-speed mixer (60°C, 500 rpm) for 30 minutes, then apply to the top surface of the label to a wet thickness of 10-15 μm. For water-based inks, dry with hot air at 80°C for 5 minutes; for UV inks, cure with ultraviolet light (wavelength 365 nm, intensity 10 mW / cm²). 2 After coating, the film is aged for 24 hours at 25°C and 50% humidity (30s) to release internal stress.

[0087] Depending on the shelf life of the label, there are three types of ink layers: rapidly degradable ink layer, generally degradable ink layer, and rapidly degradable ink layer.

[0088] For rapidly degradable ink layers, suitable for labels with short shelf lives (such as fresh food labels, requiring a degradation rate of ≥90% within 180 days), the ink layer is dominated by highly reactive components, preferentially initiating photo-oxidative degradation and coupling with biodegradation. This ink layer includes: 5~10wt% of g-C3N4 and Bi2O2CO3 composite catalyst, 10~15wt% of degradable masterbatch, 5~8wt% of laccase-loaded microspheres, 2~4wt% of urethane compounds, 2~3wt% of polyvinyl alcohol, 0.5~1wt% of ferric stearate, and the remainder is ink base material (water-based ink or UV ink).

[0089] The g-C3N4 and Bi2O2CO3 composite catalyst, as a photo-oxidative degradation regulator, has an ultraviolet absorption peak of 254nm and rapidly generates reactive oxygen species.

[0090] The biodegradable masterbatch, as the main biodegradation promoter, rapidly hydrolyzes to produce lactic acid, which attracts microorganisms and increases the degradation rate by 30%.

[0091] Laccase-loaded microspheres act as co-biodegradation promoters, releasing the enzyme when humidity is >70%, directly cleaving ester bonds.

[0092] Cyano compounds, such as sulfonated polystyrene, serve as functional group modifiers, exhibiting a high ESP value (29.28 kcal / mol), reducing electron density, and accelerating the initial rate of photolysis.

[0093] Polyvinyl alcohol (PVA), as an auxiliary component, forms a hydrophilic coating that exhibits humidity-triggered swelling, promoting microbial penetration.

[0094] Ferric stearate, as an auxiliary component and thermo-oxidative synergist, is activated above 50°C to compensate for degradation efficiency in low-temperature environments.

[0095] Both water-based inks and UV inks are commercially available conventional inks. For example, water-based inks are water-based inks made from acrylic resins or polyurethane dispersions; UV inks are UV inks made from epoxy acrylates or polyester acrylates.

[0096] Degradation control mechanism of rapidly degrading ink layers: 1. Photo-oxidative degradation preferentially triggered: Under UV irradiation (intensity > 5mW / cm²), 2 Under the conditions of g-C3N4 and Bi2O2CO3 composite catalyst, the molecular weight of ink layer was reduced to below 5000 Da within 7 days.

[0097] 2. Biodegradation relay: The carboxylic acid produced by the hydrolysis of the biodegradable masterbatch lowers the local pH, activates laccase, and increases the adhesion efficiency of microorganisms (such as white rot fungi) by 50%.

[0098] 3. Synergistic effect: The styrene-based modification increases the ESP value of the ink layer, increases the photogenerated electron mobility, and improves the degradation rate by 40% compared with the standard formulation.

[0099] Applicable scenarios: Fresh produce packaging labels, which need to be completely degraded within 180 days after disposal; outdoor event labels (such as event tickets), which are exposed to strong sunlight.

[0100] Rapidly degradable inks are based on high photosensitizers, urethane modifiers, and bio-accelerators to meet the requirements of short shelf life, with a degradation rate of ≥90% within 180 days.

[0101] For general degradable ink layers, suitable for labels with medium shelf life (such as daily chemical product packaging, requiring a degradation rate of 75% within 220 days), a balance needs to be struck between degradation rate and mechanical properties. A general degradable ink layer includes: 6-8 wt% g-C3N4 and Bi2O2CO3 composite catalyst, 10-12 wt% biodegradable masterbatch, 3-5 wt% laccase-loaded microspheres, 1.5-2.5 wt% maleic anhydride graft, 2-3 wt% nano-silica, 3-5 wt% cyclic olefin copolymer (COC), 1-2 wt% polyvinyl alcohol (PVA), 0.1-0.3 wt% antioxidant BHT, with the balance being ink base material.

[0102] The g-C3N4 and Bi2O2CO3 composite catalyst, as a photosensitizer, has a visible light response (300~475nm) and extended light coverage.

[0103] Biodegradable masterbatch, as the main biodegradation promoter, attracts microorganisms through hydrolysis products, thereby improving biodegradation efficiency.

[0104] Laccase-loaded microspheres act as co-biodegradation promoters, releasing the enzyme and cleaving ester bonds when humidity is >60%.

[0105] Maleic anhydride grafts (carbonyl compounds), as functional group modifiers, have a moderate ESP value (17.33 kcal / mol) and regulate the degradation initiation energy barrier.

[0106] Nano-silica, as the main stabilizer, fills micropores, reduces microbial adhesion, and delays premature degradation.

[0107] Cyclic olefin copolymers (COCs), used as co-stabilizers, have low oxygen permeability (<10 cm). 3 / m 2 •day), extending the induction period.

[0108] Polyvinyl alcohol (PVA), as an auxiliary component, hydrophilic coating, humidity-triggered swelling (RH>70%).

[0109] Antioxidant BHT, as an auxiliary component, inhibits oxidative degradation during storage.

[0110] Ink base, water-based acrylic resin or UV epoxy acrylate, provides printability and adhesion.

[0111] Its core design principle is: Synergistic effect of photo-oxidation and biodegradation: Controlled degradation is achieved through moderately active photosensitizers and biodegradation promoters.

[0112] Functional group electron density regulation: Carbonyl compounds (ESP value 17.33 kcal / mol) are used to provide moderate reactivity and avoid degradation that is too fast or too slow.

[0113] In this scheme, the total amount of photosensitizer is 8-11 wt%, lower than that of the fast-degrading ink layer (13-15 wt%) but higher than that of the slow-degrading ink layer (6-8 wt%), ensuring a moderate photo-oxidative degradation rate. The total amount of biodegradation promoters (13-17 wt% of degradable masterbatch and starch microspheres) promotes microbial mineralization, but is partially inhibited by nano-SiO2 and COC to avoid excessively rapid degradation. Functional group selection: carbonyl compounds (rather than ternary groups) provide controlled degradation with a moderate ESP value, balancing reactivity and stability.

[0114] For slow-degrading ink layers, suitable for long-term stability scenarios (such as electronic product labels, requiring degradation rates to be controlled below 50% within 270 days), the ink layer is dominated by barrier and stabilizing components to inhibit premature degradation. This ink layer includes: 5~6wt% of g-C3N4 and Bi2O2CO3 composite catalyst, 1~2wt% of TiO2 (rutile type), 0.1~0.5wt% of antioxidant BHT, 3~5wt% of hydrophobic modifier OTS, 1~2wt% of carbonyl compound (such as maleic anhydride graft), 5~8wt% of cyclic olefin copolymer (COC), 2~3wt% of nano silica, and the remainder is ink base material (water-based ink or UV ink).

[0115] The g-C3N4 and Bi2O2CO3 composite catalyst, as a photo-oxidative degradation regulator, is designed at low concentrations to provide only basic photoresponsiveness.

[0116] TiO2 (rutile type) acts as a photosensitizer, blocking some ultraviolet rays and reducing the depth of light penetration.

[0117] The antioxidant BHT, as a degradation inhibitor, captures free radicals and inhibits oxidative degradation during storage.

[0118] The hydrophobic modifier OTS acts as a degradation inhibitor with a contact angle >150°, thus slowing down water and oxygen permeation.

[0119] Carbonyl compounds (such as maleic anhydride grafts), as functional group modifiers, provide a moderate ESP value (17.33 kcal / mol) and offer an energy barrier for the initiation of controlled degradation.

[0120] Cyclic olefin copolymers (COCs), as stabilizing components, have low oxygen permeability (<5 cm³ / m²·day), thus prolonging the photo-oxidative degradation induction period.

[0121] Nano-silica, as a stabilizing component, fills micropores, reduces specific surface area, and lowers the adhesion rate of microorganisms.

[0122] Both water-based inks and UV inks are commercially available conventional inks. For example, water-based inks are water-based inks made from acrylic resins or polyurethane dispersions; UV inks are UV inks made from epoxy acrylates or polyester acrylates.

[0123] Degradation control mechanism of slow-degrading ink layer: Photo-oxidative degradation delay: Hydrophobic modifier OTS prevents water from penetrating in advance and causing degradation; and COC blocks oxygen penetration, which increases the activation threshold of photosensitizer, requiring continuous light exposure for more than 100 hours to start degradation.

[0124] Biodegradation inhibition: Nano-SiO2 filling reduces microbial habitat sites, and enzyme activation requires pH > 7.

[0125] Dynamic regulation: After the antioxidant BHT is consumed during the storage period, the carbonyl functional groups gradually respond to light, and the degradation rate increases linearly, avoiding abrupt changes.

[0126] Applicable scenarios: Electronic product labels (shelf life > 2 years), requiring tolerance to temperature fluctuations of -40~120℃. Chemical product packaging, subject to long-term exposure to low light environments.

[0127] Slow-degrading inks extend the degradation induction period and ensure long-term stability through barrier layers, stabilizers, and carbonyl modification.

[0128] The degradation control method for controllable photo-oxidation and biodegradable labels focuses on the ink layer, utilizing functional group electron density to regulate the degradation threshold. Combined with an environmental response mechanism, this solves the problem of uncontrollable degradation in traditional labels. The degradation control mechanism includes: Mechanism 1: Photo-oxidation-biodegradation cascade reaction.

[0129] Stage 1 (Photo-oxidation dominant): The photosensitizer in the ink layer absorbs photons, generating -OH free radicals that attack the polymer chains (especially CH bonds adjacent to ternary or carbonyl groups). In rapidly degrading inks, the molecular weight drops below 10,000 Da within 7 days; slow-degrading inks require more than 30 days.

[0130] Phase 2 (Bio-dominant): The hydrophilicity of photolysis products (carboxylic acids, aldehydes) increases, and microorganisms (such as Pseudomonas) secrete hydrolytic enzymes to complete mineralization (the final products are CO2 and H2O). The bio-phase of fast inks is completed within 20 days, while that of slow inks extends to 200 days.

[0131] Mechanism 2: Regulation of functional group electron density.

[0132] Sulpho-based (high ESP): The sulfur atom with strong electron-attracting ability reduces the electron density of the reaction site, making the C=O bond easier to break, and increasing the photolysis rate by 50%.

[0133] Carbonyl group (ESP): Provides moderate reactivity, combined with the COC barrier layer, to achieve a degradation curve that is "slowed down but not stopped".

[0134] ESP calculations show that the degradation rate of tannin-modified ink is ≥90% after 180 days, while that of carbonyl-modified ink is 60% after 180 days.

[0135] Mechanism 3: Environmentally responsive design.

[0136] Temperature triggering: Ferric stearate is activated at temperatures above 50°C to compensate for insufficient degradation in low-temperature environments.

[0137] Humidity triggering: Polyvinyl alcohol (PVA) swells when RH > 70%, with a porosity > 30%, accelerating biodegradation.

[0138] Experimental conditions: Photo-oxidative degradation (UV irradiation, 254 nm, intensity 5 mW / cm²) 2 Biodegradation (composting environment, temperature 50℃, humidity 60%).

[0139] Comparison of degradation performance. Table 2 is a comparison table of the performance of the three ink layers.

[0140] Ink type Degradation time (days) Photo-oxidative degradation rate (%) Biodegradation rate (%) Total degradation rate (%) Test Standards Rapidly degradable ink layer 180 60 40 ≥90 ISO 14855-1 General degradation ink layer 220 40 35 75 ISO 14855-1 Slow-degrading ink layer 270 20 30 ≤50 ISO 14855-1 Generally, the total degradation rate of degradable ink layers reaches 75% within 180 days, which is between rapid (90%) and slow (50%) degradation rates.

[0141] In the early stage, photo-oxidative degradation dominates: the rapid ink layer has a relatively high photo-oxidative degradation rate of 60% due to its high photosensitizer content; the general ink layer has a rate of 40%, which reflects its controllability.

[0142] Biodegradation relay: Generally, the ink layer is biodegradable in a composting environment with a rate of 35% through biodegradable masterbatch and microspheres, avoiding residue.

[0143] The Young's modulus (2.8 GPa) and glass transition temperature (105 °C) of general degradable ink layers are higher than those of rapid ink layers, thanks to the reinforcing effect of COC and nano SiO2, which meets the mechanical requirements of daily chemical labels.

[0144] Excellent adhesion and abrasion resistance ensure that the printed pattern will not peel off during use.

[0145] Generally, the ink layer exhibits a degradation rate of 20% under UV irradiation, reflecting moderate activity of the photosensitizer; in a composting environment, the biodegradation rate is 50%, demonstrating a balanced design of biological components.

[0146] Temperature and humidity triggering: PVA swells when RH is greater than 70%, increasing porosity by 15% and accelerating biodegradation; BHT inhibits oxidation during storage, ensuring stability.

[0147] Advantages of generally degradable ink layers: Degradation controllability: By adjusting the carbonyl group (ESP 17.33 kcal / mol) and photosensitizer concentration, the degradation rate increases linearly, avoiding abrupt changes and matching the 180~270 day degradation window.

[0148] Performance balance: COC and nano-SiO2 maintain mechanical strength (Young's modulus 2.8 GPa), which is better than fast ink layer (2.1 GPa) and close to slow ink layer (3.5 GPa).

[0149] Cost-effectiveness: The amount of photosensitizer used is lower than that of the fast ink layer, reducing raw material costs by about 20%.

[0150] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. Controlled photo-oxidation and biodegradable labels, including: The upper surface layer, the core layer, and the lower surface layer are characterized in that the upper surface layer comprises 1500-3000 ppm of an anti-blocking agent and 5-10 wt% of a photocatalytic material, with the balance being polypropylene homopolymer. The core layer comprises 5-15 wt% biodegradable masterbatch, 20-40 wt% nano-calcium carbonate and 2-5 wt% photo-oxidation degradation regulator, with the balance being polypropylene homopolymer. The lower surface layer comprises 10-20 wt% polypropylene grafted with maleic anhydride and 5-10 wt% biodegradable masterbatch, with the remainder being polypropylene homopolymer.

2. The controllable photo-oxidation and biodegradable label according to claim 1, characterized in that, The anti-blocking agent is silicon dioxide with a particle size of 0.5~0.8 micrometers; the photocatalytic material is graphitic carbon nitride g-C3N4; The biodegradable masterbatch is a blend of PLA and PBAT in a mass ratio of 30:70 to 70:

30. The photo-oxidative degradation regulator is a blend of g-C3N4 and Bi2O2CO3 composite catalyst and cyclic olefin copolymer in a mass ratio of 50:50 to 70:

30.

3. The controllable photo-oxidation and biodegradable label according to claim 2, characterized in that, The preparation method of the g-C3N4 and Bi2O2CO3 composite catalyst is as follows: Step 1, Pretreatment: Dispersion and activation of g-C3N4: Take 2g of g-C3N4 and add it to 100ml of solution containing CTAB and Na2CO3; Disperse ultrasonically for 40 minutes; Step 2, Mixing reaction: Dissolve 1.712g of Bi2O2CO3·5H2O in 10mL of 10M nitric acid and stir magnetically until completely dissolved to obtain a bismuth salt solution; slowly add the bismuth salt solution dropwise to a solution containing g-C3N4 in CTAB and Na2CO3, controlling the addition time to 10 minutes, and then stir for 2 hours to obtain a mixed solution; Step 3, hydrothermal reaction: Transfer the mixture to a 100mL polytetrafluoroethylene-lined high-pressure reactor, seal it, and place it in an oven; heat to 160℃ at 5℃ / min, maintain the temperature for 12 hours; allow it to cool naturally to room temperature; Step 4, purification and activation: Filter and collect the precipitate, wash it three times alternately with deionized water and ethanol; dry it in an oven at 80℃ for 12 hours; then grind it to a particle size of less than 50μm, sieve it and store it.

4. The controllable photo-oxidation and biodegradable label according to claim 3, characterized in that, It also includes an ink layer and an adhesive layer; The ink layer is printed on the upper surface layer, using UV ink or water-based ink, with 5~10wt% of g-C3N4 and Bi2O2CO3 composite catalyst added, which initiates ink degradation under light irradiation; The adhesive layer, coated on the lower surface, contains 17-19 wt% biodegradable masterbatch.

5. The method for preparing the controllable photo-oxidation and biodegradable label as described in claim 4, characterized in that, Includes the following steps: Step S1: Prepare the raw material components for the upper surface layer, core layer, and lower surface layer, and dry them to ensure uniform dispersion and degradation activity; Step S2, melt co-extrusion: The raw materials for each layer are processed separately using different extruders and then merged through a flow channel distributor to achieve multi-layer co-extrusion; Step S3, casting and biaxial stretching: After the melt is extruded, it is cooled into a thick sheet, and then stretched longitudinally and transversely to form a microporous structure and increase the specific surface area for degradation; after stretching, it is shaped at 190~205℃ to stabilize the molecular chain orientation; the heat setting time is <10s. Step S4, Surface treatment and coating: After stretching, the film is subjected to corona treatment and coated with an adhesive layer; Step S5: After the film is wound up, it needs to be aged: stored at 25°C and 50% humidity for 24 hours to release internal stress.

6. The method for preparing the controllable photo-oxidation and biodegradable label according to claim 5, characterized in that, In step S1, the preparation of biodegradable masterbatch is a blend of PLA and PBAT in a mass ratio of 30:70 to 70:

30. After mixing PLA and PBAT, 1 to 5 wt% of glycerol plasticizer and 1 to 5 wt% of polypropylene grafted maleic anhydride compatibilizer are added, and the mixture is mixed in a high-speed mixer at 50 to 60°C for 30 minutes. Preparation of photo-oxidative degradation regulator: g-C3N4 and Bi2O2CO3 composite catalyst were mixed with cyclic olefin copolymer at a mass ratio of 50:50~70:30, and then ball-milled to a particle size of <100nm in an inert gas atmosphere. The biodegradable masterbatch and the photo-oxidation degradation regulator are pre-blended and then ball-milled to achieve nanocomposite properties, so that the photo-oxidation degradation regulator can uniformly coat the surface of the biodegradable masterbatch.

7. The method for preparing the controllable photo-oxidation and biodegradable label according to claim 6, characterized in that, In step S2, the extrusion temperature of the core layer is 230~260℃, and the extrusion temperature of the upper and lower surface layers is 220~240℃; the extrusion rate of all extruders is 100~300kg / h, and the screw speed is 300~600rpm.

8. The method for preparing the controllable photo-oxidation and biodegradable label according to claim 7, characterized in that, It also includes degradation control methods: for the ink layer, the ink base material and the remaining treatment components are stirred in a high-speed mixer for 30 minutes, and then coated on the top surface of the label with a wet thickness of 10~15μm.

9. The method for preparing the controllable photo-oxidation and biodegradable label according to claim 8, characterized in that, Depending on the label's shelf life, there are three types of ink layers: rapidly degradable ink layer, generally degradable ink layer, and rapidly degradable ink layer. For rapidly degradable ink layers, suitable for labels requiring a degradation rate of ≥90% within 180 days, the ink layer comprises: 5~10wt% of g-C3N4 and Bi2O2CO3 composite catalyst, 10~15wt% of degradable masterbatch, 5~8wt% of laccase-loaded microspheres, 2~4wt% of urethane compound, 2~3wt% of polyvinyl alcohol, 0.5~1wt% of ferric stearate, and the remainder being ink base material; For general degradable ink layers, suitable for labels requiring a 75% degradation rate within 220 days; the ink layer includes: 6-8 wt% g-C3N4 and Bi2O2CO3 composite catalyst, 10-12 wt% degradable masterbatch, 3-5 wt% laccase-loaded microspheres, 1.5-2.5 wt% maleic anhydride graft, 2-3 wt% nano-silica, 3-5 wt% cyclic olefin copolymer, 1-2 wt% polyvinyl alcohol, 0.1-0.3 wt% antioxidant BHT, and the balance being ink base material; For slow-degrading ink layers, suitable for ink layers where the degradation rate can be controlled below 50% within 270 days; the ink layer includes: 5-6 wt% of g-C3N4 and Bi2O2CO3 composite catalyst, 1-2 wt% of rutile TiO2, 0.1-0.5 wt% of antioxidant BHT, 3-5 wt% of hydrophobic modifier OTS, 1-2 wt% of carbonyl compound, 5-8 wt% of cyclic olefin copolymer, 2-3 wt% of nano silica, and the remainder is ink base material.

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