Full-biodegradable bag and preparation method thereof

Abstract

The invention discloses a full-biodegradable bag and a preparation method thereof in the technical field of biodegradable materials.According to the full-biodegradable bag, polylactic acid and poly (butylene adipate-co-terephthalate) serve as matrixes, and performance optimization is achieved by adding a specially-made nanofiber interpenetrating network compatibilizer and a star-shaped structure bio-based plasticizer; wherein the nanofiber interpenetrating network compatibilizer is prepared by grafting polylactic acid and poly (butylene adipate-co-terephthalate) chain segments on cellulose nanofibers through an atom transfer radical polymerization technology, and the star-shaped structure bio-based plasticizer is prepared through ring opening polymerization and melt grafting technologies. In addition, the formula also comprises a maleimide modified lignin filler, an ethylene bis stearamide lubricant and an antioxidant. Through the synergistic effect of the two specially-made modified compounds, the compatibility of all the components is remarkably improved, the preparation process is simple and reliable and suitable for industrial production, and the problem of white pollution of traditional plastic products can be effectively solved.

Description

Technical Field

[0001] This invention relates to the field of biodegradable materials technology, specifically to a fully biodegradable bag and its preparation method. Background Technology

[0002] With the increasingly severe global plastic pollution problem, the control of white pollution has become a common challenge faced by countries around the world. Traditional petroleum-based plastic products, such as polyethylene and polypropylene, are extremely difficult to degrade in the natural environment and can persist for hundreds of years, posing a long-term and serious threat to soil, marine ecosystems, and human health. Against this backdrop, developing alternative materials that can completely degrade in the natural environment and return to the ecological cycle has become an urgent task for scientific research and industry. Currently, bio-based or biodegradable polyesters, represented by polylactic acid (PLA) and polybutylene terephthalate (PET), have become one of the mainstream alternatives to traditional plastics. They are derived from renewable resources or have degradable ends, theoretically meeting the requirements of environmentally friendly materials. However, these two materials themselves have obvious performance defects; although PLA has good rigidity, it is brittle and lacks toughness, while PET, although highly flexible, has low modulus and strength, making it difficult to meet the comprehensive mechanical performance requirements of practical applications when used alone. While blending the two is an ideal strategy for complementary advantages, the poor compatibility caused by differences in molecular structure makes simple blending prone to phase separation, which in turn degrades the mechanical properties of the material, becoming the primary technical bottleneck restricting its widespread application.

[0003] To overcome the aforementioned compatibility challenges, existing technologies primarily focus on adding a third component as a compatibilizer or solubilizer. Common strategies include using maleic anhydride-grafted polymers or simple copolymers to act as "molecular bridges" in the blend system. However, these traditional compatibilizers often have limited functionality and solubilizing effects, making it difficult to establish strong and durable interfacial interactions between polylactic acid and polybutylene adipate terephthalate. On the other hand, introducing small-molecule plasticizers is a common practice to improve processing flow and finished product flexibility, but these small molecules are prone to migration and precipitation during material use, leading not only to gradual embrittlement but also potential environmental pollution and food safety issues. Furthermore, adding biomass fillers such as lignin is a common choice to reduce costs or impart specific functions to materials, but unmodified lignin has weak interfacial bonding with the polymer matrix, also facing problems of uneven dispersion and acting as stress defect points. Therefore, the solutions provided by existing technologies are often isolated and patchy, lacking a comprehensive approach that can systematically and synergistically resolve the contradictions between compatibility, mechanical properties, and degradation performance at the molecular level.

[0004] Currently, the market demand for fully biodegradable bags is not limited to their degradable and environmentally friendly attributes, but also places high demands on their mechanical strength, durability, and processing adaptability throughout their service life, comparable to traditional plastics. Recent standards released by the Guangdong Plastics Industry Association clearly reflect this trend, establishing specific indicators for the physical and mechanical properties of fully biodegradable plastic shopping bags and garbage bags. This means that developing a fully biodegradable material that simultaneously meets the requirements of excellent mechanical properties, controllable degradation rate, and good processing performance is key to breaking through current industrial technology bottlenecks and promoting its large-scale replacement application. Based on this urgent technological need, this invention aims to overcome the technical barriers of existing biodegradable materials in terms of compatibility, comprehensive mechanical properties, and functionalization by designing and synthesizing two modified compounds with novel molecular structures to construct a highly efficient multi-component synergistic system. Summary of the Invention

[0005] The purpose of this invention is to provide a fully biodegradable bag and its preparation method, which solves the technical problems of insufficient mechanical properties caused by poor compatibility between PLA and PBAT in existing biodegradable bags, as well as the impact on material durability and safety caused by the easy migration and precipitation of small molecule plasticizers.

[0006] The present invention achieves the above objectives through the following technical solutions: A method for preparing a fully biodegradable bag, comprising the following steps: S1. Polylactic acid and polybutylene adipate terephthalate are vacuum dried at 78-82℃; the dried polylactic acid and polybutylene adipate terephthalate are mixed with nanofiber interpenetrating network compatibilizer, star-shaped bio-based plasticizer, maleimide modified lignin, ethylene bis-stearamide and antioxidant in a high-speed mixer to obtain a well mixed material; S2. The mixed materials are fed into a twin-screw extruder for melt blending and granulation. The extruder temperature range is 160-180℃ to obtain granules. The granules are blown into film by a single-screw blown film unit. The blown film is cut and heat-sealed by a bag making machine.

[0007] According to a preferred embodiment of the present invention, the preparation steps of the maleimide-modified lignin include: dissolving 10 parts by weight of alkali lignin in dimethyl sulfoxide, adding 3 parts by weight of N-(2-aminoethyl)maleimide hydrochloride and 1.5 parts by weight of catalyst N,N'-diisopropylcarbodiimide, reacting at 85°C for 12 hours under nitrogen protection, precipitating the product in a large amount of deionized water and filtering it, washing it three times with deionized water, and then vacuum drying it at 50°C for 24 hours to obtain maleimide-modified lignin.

[0008] According to a preferred embodiment of the present invention, the antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

[0009] In this invention, the preparation process of the fully biodegradable bag involves a complex synergistic mechanism of multiple components under the combined action of thermodynamics and kinetics. During the melt blending stage, each component undergoes a series of physicochemical changes under heat and shear force. After the nanofiber interpenetrating network compatibilizer is dispersed in the melt, its different segments specifically interact with the two matrix resins, forming a strong transition layer at the phase interface through intermolecular forces and segment entanglement, significantly reducing interfacial energy and promoting compatibility between components. The star-shaped bio-based plasticizer, through its three-dimensional spatial configuration, interpenetrates between polymer chains, effectively increasing the intermolecular distance and reducing intersegmental interactions. Simultaneously, its terminal epoxy groups react with the polyester end groups to form a mildly cross-linked network structure. With the assistance of the compatibilizer, the biomass filler is uniformly dispersed in the matrix, and its surface active groups form strong hydrogen bonds with the cellulose backbone of the compatibilizer, jointly constructing a reinforcing network. During blown film forming, this multi-component synergistic system undergoes molecular chain orientation and crystallization under tensile stress. The interfacial interaction between the compatibilizer and the matrix ensures effective stress transfer, while the star-shaped plasticizer provides the necessary melt strength and flexibility, enabling the film to achieve balanced mechanical properties in both longitudinal and transverse directions. The resulting material possesses a stable three-dimensional network structure, maintaining excellent performance during use. After disposal, the natural components in the compatibilizer and the ester bonds in the plasticizer provide pathways for microbial erosion and hydrolysis, achieving complete biodegradation.

[0010] According to a preferred embodiment of the present invention, in step S1, the vacuum drying time at 78-82°C is 12-14 hours.

[0011] According to a preferred embodiment of the present invention, in step S2, the temperature for blown film forming is 150-170°C.

[0012] According to a preferred embodiment of the present invention, the preparation method of the nanofiber interpenetrating network compatibilizer includes: A1, dispersing a nanofiber suspension in N,N-dimethylformamide, adding α-bromoisobutyryl bromide, and reacting under nitrogen protection at -2~2℃ to obtain a macromolecular initiator; A2, adding L-lactide and adipic acid / butyl terephthalate copolymer macromonomers and pentamethyldiethylenetriamine, and carrying out an atom transfer radical polymerization reaction at 78-82℃; after the reaction is completed, precipitating the product with methanol and drying under vacuum.

[0013] According to a preferred embodiment of the present invention, the preparation steps of the nanofiber suspension include: mixing 5 parts by weight of microcrystalline cellulose with 100 parts by weight of 8% sulfuric acid solution at 45°C, reacting at a mechanical stirring speed of 300 rpm for 30 minutes, then adding a large amount of deionized water to terminate the reaction, separating the mixture by high-speed centrifugation, collecting the precipitate and dialysis until the suspension is neutral, and finally treating it with ultrasonic cell disruption for 20 minutes to obtain a nanofiber suspension with a solid content of 3%.

[0014] In this invention, the preparation reaction mechanism of the nanofiber interpenetrating network compatibilizer is based on a precisely controlled process of atom transfer radical polymerization. The reaction uses nanofibers obtained from the hydrolysis of natural cellulose as the backbone, with abundant hydroxyl functional groups on their surface providing active sites for subsequent modification. At low temperatures, the nanofibers react with specific acyl bromide compounds, introducing bromine atoms firmly onto the fiber surface through esterification, forming a macromolecular initiator with initiating activity. This step lays the foundation for subsequent polymerization, ensuring that polymer chains can grow directionally from the fiber surface. Subsequently, at a suitable temperature, lactide monomers and copolymer macromonomers with specific structures are added to the system. Atom transfer radical polymerization is achieved through copper salt catalysis in the presence of organic amine ligands. This polymerization process is highly reactive, allowing for controllable growth of the polymer chains, ultimately resulting in the simultaneous grafting of polylactic acid segments and matrix-compatible polymer segments onto the nanofiber surface. This ingenious molecular design enables the resulting compatibilizer to possess triple affinity: strong hydrogen bonds are formed between the cellulose backbone and the biomass filler, polylactic acid segments co-crystallize with the polylactic acid matrix, and compatible polymer segments form molecular chain entanglements with another matrix resin, thereby constructing a stable interpenetrating network structure in the blend system and effectively preventing phase separation.

[0015] According to a preferred embodiment of the present invention, in step A1, the reaction time at -2~2℃ is 12-14h.

[0016] According to a preferred embodiment of the present invention, in step A2, the atom transfer radical polymerization reaction is carried out at 78-82°C for 24-30 hours.

[0017] According to a preferred embodiment of the present invention, the method for preparing the star-shaped bio-based plasticizer includes: B1, performing a ring-opening polymerization reaction of γ-valerolactone and trimethylolpropane at 145-155°C under the catalysis of stannous octoate to generate a three-armed star-shaped polyvalerolactone prepolymer; B2, performing a ring-opening esterification reaction of itaconic acid and epichlorohydrin at 78-82°C under the catalysis of tetrabutylammonium bromide, followed by the addition of an aqueous sodium hydroxide solution to generate itaconic acid diglycidyl ester; and performing a melt grafting reaction of itaconic acid diglycidyl ester and the three-armed star-shaped polyvalerolactone prepolymer at 110-130°C.

[0018] In this invention, the synthetic reaction mechanism of the star-shaped bio-based plasticizer revolves around the stepwise construction and functionalization of a bio-based platform compound. The process begins with the ring-opening polymerization of a biomass-derived lactone monomer and a polyol under a metal catalyst. The polyol, as the core molecule, has multiple hydroxyl functional groups that can simultaneously initiate the ring-opening of the lactone monomer, forming multiple polymer arms radiating outwards from the core molecule, constituting a basic polymer with a star-shaped topology. This unique star configuration endows the molecule with excellent steric hindrance and molecular chain mobility. Subsequently, this star-shaped prepolymer undergoes melt polycondensation with a bio-based olefin compound containing dicarboxyl groups. Through esterification of the carboxyl groups with the terminal hydroxyl groups of the polymer, the carboxyl groups are introduced to the ends of the star-shaped molecule. The key step lies in the subsequent epoxidation reaction. In the presence of a phase-transfer catalyst, the terminal carboxyl groups undergo a specific reaction with the epoxidizing agent, precisely introducing epoxy groups to the ends of the molecular chains. This series of chemical transformations ultimately forms a reactive star-shaped plasticizer. Its star structure can effectively prevent the close packing of polymer molecular chains, while the terminal epoxy groups can react chemically with the end groups of polyester materials to form stable chemical bonds, thereby avoiding the migration problem of traditional small molecule plasticizers and achieving a long-lasting plasticizing effect.

[0019] According to a preferred embodiment of the present invention, in step B1, the ring-opening polymerization reaction is carried out at 145-155°C for 8-10 hours.

[0020] According to a preferred embodiment of the present invention, in step B2, the reaction time at 78-82°C is 8-10 hours.

[0021] The present invention also provides a method for preparing the fully biodegradable bag described above. The fully biodegradable bag prepared by the method comprises the following raw materials in parts by weight: 30-50 parts by weight of polylactic acid; 20-40 parts by weight of polybutylene adipate terephthalate; 5-15 parts by weight of nanofiber interpenetrating network compatibilizer; 3-10 parts by weight of star-shaped bio-based plasticizer; 5-15 parts by weight of maleimide-modified lignin; 0.5-2 parts by weight of ethylene bis-stearamide; and 0.1-0.5 parts by weight of antioxidant.

[0022] The beneficial effects of this invention are as follows: The fully biodegradable bag provided by this invention achieves a breakthrough in comprehensive material performance by introducing two newly designed modified compounds. The nanofiber interpenetrating network compatibilizer, with its unique molecular structure, constructs a stable bridge at the interface between polylactic acid and polybutylene terephthalate (PET). Its cellulose nanofiber skeleton forms strong hydrogen bonds with the lignin filler, while the grafted polymer segments generate molecular chain entanglement and co-crystallization effects with both matrix resins. This multi-level, multi-mechanism synergistic effect fundamentally solves the core problem of poor compatibility in traditional biodegradable blend systems. Simultaneously, the star-shaped bio-based plasticizer not only effectively prevents the tight packing of polymer molecular chains through its three-dimensional topological configuration, significantly improving molecular chain mobility, but also forms stable chemical bonds through the chemical reaction of the terminal epoxy groups with the end groups of the polyester material, completely avoiding the migration and precipitation of small molecule plasticizers. The synergistic effect of these two modified compounds results in a fully biodegradable bag that maintains high tensile strength while significantly improving elongation at break, achieving a perfect balance between rigidity and toughness. Its comprehensive mechanical properties fully meet or even exceed the requirements for traditional polyethylene plastic bags.

[0023] While achieving excellent mechanical properties, this invention also cleverly regulates the degradation behavior of the material. The naturally derived cellulose nanofibers in the nanofiber interpenetrating network compatibilizer, together with the maleimide-modified lignin filler, construct hydrophilic degradation channels. These natural components are preferentially recognized and eroded by microorganisms in soil or compost environments, thus forming a degradation front from the surface inwards. The introduction of the star-shaped bio-based plasticizer not only does not hinder the degradation process, but its unique ester bond density and spatial structure create a microenvironment more conducive to hydrolysis, producing a synergistic effect with the degradation channels in the compatibilizer, jointly accelerating the overall disintegration process of the material. This degradation mechanism ensures that the fully biodegradable bag maintains stable performance throughout its service life, and after disposal, it can quickly initiate and complete the degradation process under suitable composting or soil conditions, ultimately converting into carbon dioxide, water, and biomass, without causing any persistent pollution to the environment. Degradation tests under standard conditions have verified that the fully biodegradable bag prepared by this invention achieves the majority of its mass loss within 180 days, with a biodegradation rate far exceeding relevant standard requirements, truly realizing environmentally friendly characteristics throughout its entire life cycle from use to disposal.

[0024] In addition to its excellent performance and controllable degradation characteristics, the fully biodegradable bag of this invention also exhibits superior processing applicability and comprehensive benefits. The addition of two modified compounds significantly improves the rheological properties of the blend system, enhances melt strength, and stabilizes melt flow rate. This makes the process of preparing uniformly thick films via blown film processing smoother, effectively avoiding problems such as bubble breakage and uneven thickness that are common in traditional biodegradable materials during blown film production, thus greatly improving production efficiency and product yield. Each component in the formulation fully considers the feasibility and economy of industrial production. In particular, the introduction of maleimide-modified lignin effectively reduces overall raw material costs while improving material rigidity and promoting degradation, thereby enhancing the product's market competitiveness. In summary, this invention, through careful molecular design and component formulation, successfully prepares a fully biodegradable bag with excellent mechanical properties, controllable degradation behavior, good processing performance, and reasonable cost. It provides a practical technical solution for replacing traditional plastic products and solving the problem of white pollution, possessing significant social benefits and broad market application prospects. Detailed Implementation

[0025] The following detailed embodiments are only used to further illustrate this application and should not be construed as limiting the scope of protection of this application. Those skilled in the art can make some non-essential improvements and adjustments to this application based on the above application content.

[0026] The main suppliers of related equipment and materials are as follows: The polylactic acid was purchased from Yangzhou Huitong Biomaterials Co., Ltd.

[0027] The poly(butylene adipate) terephthalate was purchased from Chongqing Jianfeng Chiyuan Chemical Co., Ltd.

[0028] The ethylene bis-stearamide was purchased from Shandong Qiangsen Chemical Co., Ltd.

[0029] The α-bromoisobutyryl bromide was purchased from Changyi Fengrun Fine Chemical Co., Ltd.

[0030] The L-lactide was purchased from Wuhan Qiaofeng Chemical Technology Co., Ltd.

[0031] The adipic acid / butyl terephthalate copolymer macromonomer was purchased from Jiangsu Ruizheng Biomaterials Co., Ltd.

[0032] The pentamethyldiethylenetriamine was purchased from Puyang Shengquan Chemical Co., Ltd.

[0033] The γ-valerol was purchased from Anhui Xuelang Biotechnology Co., Ltd.

[0034] The trimethylolpropane was purchased from Jinan Century Tongda Chemical Co., Ltd.

[0035] The stannous octoate was purchased from Shandong Tonglan Chemical Co., Ltd.

[0036] The itaconic acid was purchased from Qingdao Chengxin Hongfeng Chemical Co., Ltd.

[0037] The epichlorohydrin was purchased from Shandong Jinshengrun Chemical Co., Ltd.

[0038] The tetrabutylammonium bromide was purchased from Weifang Hengfeng Chemical Co., Ltd.

[0039] Example 1 Preparation of nanofiber interpenetrating network compatibilizer: 50g of microcrystalline cellulose was mixed with 1000g of 8% sulfuric acid solution at 45℃ and reacted with mechanical stirring at 300rpm for 30min. The reaction was terminated by adding 2000mL of deionized water. The mixture was centrifuged at 10000rpm for 10min, and the precipitate was collected and dialyzed using a dialysis bag with a molecular weight cutoff of 8000Da until the conductivity was less than 10μS / cm. The precipitate was then treated with an ultrasonic cell disruptor at 800W for 20min to obtain a nanofiber suspension with a solid content of 3%. 100g of this suspension was dispersed in 500g of N,N-dimethylformamide, and... 20g of α-bromoisobutyryl bromide was reacted at 0℃ for 13h under nitrogen protection to obtain a macromolecular initiator; 200g of L-lactide and 50g of adipic acid / butyl terephthalate copolymer macromonomers and 5g of pentamethyldiethylenetriamine were added, and after purging with nitrogen to remove oxygen, 0.5g of cuprous bromide catalyst was added, and atom transfer radical polymerization reaction was carried out at 80℃ with a stirring speed of 400rpm for 26h; after the reaction, the product was precipitated with 2000mL of methanol, filtered through a Buchner funnel, and vacuum dried at 80℃ for 24h to obtain a nanofiber interpenetrating network compatibilizer; preparation of star-shaped bio-based plasticizer: 150g of γ-valerolactone and 30g of trimethylolpropane were reacted at 1.A three-armed star-shaped polyvalerone prepolymer was generated by ring-opening polymerization of 5g stannous octoate at 150℃ for 9h. 50g itaconic acid and 80g epichlorohydrin were subjected to ring-opening esterification at 80℃ under the catalysis of 4g tetrabutylammonium bromide, followed by slow dropwise addition of 40g of 10% sodium hydroxide aqueous solution, maintaining the reaction at 80℃ for 9h to generate itaconic acid diglycidyl ester. The obtained itaconic acid diglycidyl ester was then melt-grafted with the three-armed star-shaped polyvalerone prepolymer at a mass ratio of 1:2 at 120℃ with stirring at 200rpm for 6h to obtain a star-shaped bio-based plasticizer. Preparation of fully biodegradable bags: 400g polylactic acid and 300g polybutylene adipate-terephthalate were vacuum-dried at 80℃ for 13h. The dried polylactic acid and polybutylene adipate-terephthalate were then mixed with 100g nanofibers. A network compatibilizer, 50g of star-shaped bio-based plasticizer, 100g of maleimide-modified lignin, 10g of ethylene bis-stearamide, and 3g of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid] were mixed in a high-speed mixer at 600 rpm for 12 minutes to obtain a well-mixed material. The well-mixed material was then fed into a twin-screw extruder for melt blending and granulation. The extruder temperatures were set at 160℃, 165℃, 170℃, 175℃, and 180℃, with a screw speed of 250 rpm, to obtain granules. The granules were then blown into film at 165℃ using a single-screw blown film extruder with a blow-up ratio of 3:1 and a traction speed of 8 m / min. The blown film was then cut and heat-sealed using a bag-making machine at 170℃ for 2 seconds to obtain a fully biodegradable bag with a thickness of 0.05 mm.

[0040] Example 2 The specific implementation method is the same as in Example 1, except that the preparation of the nanofiber interpenetrating network compatibilizer is as follows: 60g of microcrystalline cellulose and 1200g of 8% sulfuric acid solution are mixed at 45°C and reacted with mechanical stirring at 300rpm for 30min. 2400mL of deionized water is added to terminate the reaction. The mixture is centrifuged at 10000rpm for 10min, the precipitate is collected, and dialyzed using a dialysis bag with a molecular weight cutoff of 8000Da until the conductivity is less than 10μS / cm. The mixture is then treated with an ultrasonic cell disruptor at 800W power for 20min to obtain a nanofiber suspension with a solid content of 3%. 120g of this suspension is dispersed in 600g of N,N-dimethylformamide, and 24g of α-bromoisobutyryl bromide is added. The mixture is reacted at 0°C for 13h under nitrogen protection to obtain a macromolecular initiator. 240g of... L-lactide, 60g of adipic acid / butyl terephthalate copolymer macromonomer, and 6g of pentamethyldiethylenetriamine were subjected to atom transfer radical polymerization at 80℃ and 400rpm for 26h after purging with nitrogen to remove oxygen. After the reaction, the product was precipitated with 2400mL of methanol, filtered through a Buchner funnel, and vacuum dried at 80℃ for 24h to obtain a nanofiber interpenetrating network compatibilizer. Preparation of star-shaped bio-based plasticizer: 120g of γ-valerolactone and 24g of trimethylolpropane were subjected to ring-opening polymerization at 150℃ for 9h under the catalysis of 1.2g of stannous octoate to generate a three-armed star-shaped polyvalerolactone prepolymer; 40g of itaconic acid and 64g of epichlorohydrin were subjected to atom transfer radical polymerization at 3.A ring-opening esterification reaction was carried out at 80℃ under the catalysis of 2g tetrabutylammonium bromide, followed by the slow dropwise addition of 32g of 10% sodium hydroxide aqueous solution, maintaining the reaction at 80℃ for 9h to generate itaconic acid diglycidyl ester; the obtained itaconic acid diglycidyl ester was melt-grafted with a three-arm star-shaped polyvalerone prepolymer at a mass ratio of 1:2 at 120℃ with a stirring speed of 200rpm for 6h to obtain a star-shaped bio-based plasticizer; preparation of fully biodegradable bags: 350g of polylactic acid and 350g of polybutylene adipate-terephthalate were vacuum dried at 80℃ for 13h; the dried polylactic acid and polybutylene adipate-terephthalate were then mixed with 120g of nanofiber interpenetrating network compatibilizer, 40g of star-shaped bio-based plasticizer, and 120g of maleic acid... Imine-modified lignin, 12g of ethylene bis-stearamide, and 2g of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid] were mixed in a high-speed mixer at 600 rpm for 12 min to obtain a well-mixed material. The well-mixed material was then fed into a twin-screw extruder for melt blending and granulation. The temperatures of each section of the extruder were set to 160℃, 165℃, 170℃, 175℃, and 180℃, with a screw speed of 250 rpm, to obtain granules. The granules were then blown into film at 165℃ using a single-screw blown film unit, with a blow-up ratio of 3:1 and a traction speed of 8 m / min. The blown film was then cut and heat-sealed using a bag-making machine at 170℃ for 2 seconds to obtain a fully biodegradable bag with a thickness of 0.05 mm.

[0041] Example 3 The specific implementation method is the same as in Example 1, except that the preparation of the nanofiber interpenetrating network compatibilizer is as follows: 40g of microcrystalline cellulose and 800g of 8% sulfuric acid solution are mixed at 45°C and reacted with mechanical stirring at 300rpm for 30min. 1600mL of deionized water is added to terminate the reaction. The mixture is centrifuged at 10000rpm for 10min, the precipitate is collected, and dialyzed using a dialysis bag with a molecular weight cutoff of 8000Da using a dialysis membrane until the conductivity is less than 10μS / cm. The mixture is then treated with an ultrasonic cell disruptor at 800W power for 20min to obtain a nanofiber suspension with a solid content of 3%. 80g of this suspension is dispersed in 400g of N,N-dimethylformamide, and 16g of α-bromoisobutyryl bromide is added. The mixture is reacted at 0°C for 13h under nitrogen protection to obtain a macromolecular initiator. 160g of... L-lactide, 40g of adipic acid / butyl terephthalate copolymer macromonomer, and 4g of pentamethyldiethylenetriamine were subjected to atom transfer radical polymerization at 80℃ and 400rpm for 26h after purging with nitrogen to remove oxygen. After the reaction, the product was precipitated with 1600mL of methanol, filtered through a Buchner funnel, and vacuum dried at 80℃ for 24h to obtain a nanofiber interpenetrating network compatibilizer. Preparation of star-shaped bio-based plasticizer: 180g of γ-valerolactone and 36g of trimethylolpropane were subjected to ring-opening polymerization at 150℃ for 9h under the catalysis of 1.8g of stannous octoate to generate a three-armed star-shaped polyvalerolactone prepolymer; 60g of itaconic acid and 96g of epichlorohydrin were subjected to atom transfer radical polymerization at 4℃.A ring-opening esterification reaction was carried out at 80℃ under the catalysis of 8g tetrabutylammonium bromide, followed by the slow dropwise addition of 48g of 10% sodium hydroxide aqueous solution, maintaining the reaction at 80℃ for 9h to generate itaconic acid diglycidyl ester; the obtained itaconic acid diglycidyl ester was melt-grafted with a three-arm star-shaped polyvalerone prepolymer at a mass ratio of 1:2 at 120℃ with a stirring speed of 200rpm for 6h to obtain a star-shaped bio-based plasticizer; preparation of fully biodegradable bags: 450g polylactic acid and 250g polybutylene adipate-terephthalate were vacuum dried at 80℃ for 13h; the dried polylactic acid and polybutylene adipate-terephthalate were then mixed with 80g of nanofiber interpenetrating network compatibilizer, 70g of star-shaped bio-based plasticizer, and 80g of maleimide. Amine-modified lignin, 8g of ethylene bis-stearamide, and 4g of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid] were mixed in a high-speed mixer at 600 rpm for 12 min to obtain a well-mixed material. The well-mixed material was then fed into a twin-screw extruder for melt blending and granulation. The temperatures of each section of the extruder were set to 160℃, 165℃, 170℃, 175℃, and 180℃, with a screw speed of 250 rpm, to obtain granules. The granules were then blown into film at 165℃ using a single-screw blown film mill, with a blow-up ratio of 3:1 and a traction speed of 8 m / min. The blown film was then cut and heat-sealed using a bag-making machine at 170℃ for 2 seconds to obtain a fully biodegradable bag with a thickness of 0.05 mm.

[0042] Comparative Example 1 The specific implementation method is the same as in Example 1, except that the preparation of the fully biodegradable bag is as follows: 400g of polylactic acid and 300g of polybutylene adipate-terephthalate are vacuum dried at 80°C for 13h; the dried polylactic acid, polybutylene adipate-terephthalate, 100g of maleimide-modified lignin, 10g of ethylene bis-stearamide, and 3g of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid] are placed in a high-speed mixer and mixed at 600rpm for 12min to obtain the mixture. The mixed materials are fed into a twin-screw extruder for melt blending and granulation. The temperatures of each section of the extruder are set to 160℃, 165℃, 170℃, 175℃, and 180℃, and the screw speed is 250 rpm to obtain granules. The granules are then blown into film at 165℃ using a single-screw blown film extruder with a blow-up ratio of 3:1 and a traction speed of 8 m / min. The blown film is then cut and heat-sealed by a bag-making machine at a heat-sealing temperature of 170℃ and a heat-sealing time of 2 seconds to obtain a fully biodegradable bag with a thickness of 0.05 mm.

[0043] Comparative Example 2 The specific implementation method is the same as in Example 1, except that the preparation of the fully biodegradable bag is as follows: 400g of polylactic acid and 300g of polybutylene adipate-terephthalate are vacuum dried at 80°C for 13h; the dried polylactic acid, polybutylene adipate-terephthalate, 100g of nanofiber interpenetrating network compatibilizer, 100g of maleimide-modified lignin, 10g of ethylene bis-stearamide, and 3g of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid] are placed in a high-speed mixer and mixed at 600rpm for 1 hour. After 2 minutes, a well-mixed material is obtained. The well-mixed material is fed into a twin-screw extruder for melt blending and granulation. The temperatures of each section of the extruder are set to 160℃, 165℃, 170℃, 175℃, and 180℃, and the screw speed is 250 rpm to obtain granules. The granules are blown into film at 165℃ using a single-screw blown film unit with a blow-up ratio of 3:1 and a traction speed of 8 m / min. The blown film is cut and heat-sealed by a bag-making machine at a heat-sealing temperature of 170℃ and a heat-sealing time of 2 seconds to obtain a fully biodegradable bag with a thickness of 0.05 mm.

[0044] Comparative Example 3 The specific implementation method is the same as in Example 1, except that the preparation of the fully biodegradable bag is as follows: 400g of polylactic acid and 300g of polybutylene adipate-terephthalate are vacuum dried at 80°C for 13 hours; the dried polylactic acid, polybutylene adipate-terephthalate, 50g of star-shaped bio-based plasticizer, 100g of maleimide-modified lignin, 10g of ethylene bis-stearamide, and 3g of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid] are placed in a high-speed mixer and mixed at 600 rpm for 12 hours. The mixture is then fed into a twin-screw extruder for melt blending and granulation. The extruder temperatures are set at 160℃, 165℃, 170℃, 175℃, and 180℃, and the screw speed is 250 rpm to obtain granules. The granules are then blown into film at 165℃ using a single-screw blown film extruder with a blow-up ratio of 3:1 and a traction speed of 8 m / min. The blown film is then cut and heat-sealed using a bag-making machine at 170℃ for 2 seconds to obtain a fully biodegradable bag with a thickness of 0.05 mm.

[0045] Performance testing The performance of the fully biodegradable bags provided in the above embodiments and comparative examples was tested using the following methods: The fully biodegradable bags obtained in Examples 1-3 and Comparative Examples 1-3 were systematically evaluated according to national and industry standard testing specifications. Performance testing methods: Mechanical property testing was performed using a universal testing machine. Samples were cut into standard dumbbell-shaped specimens with a working width of 10 mm, a thickness of 0.05 mm, and a gauge length of 50 mm. After equilibration for 24 hours at 23℃ and 50% relative humidity, the test was conducted. The tensile speed was set to 50 mm / min. The load-displacement curve was automatically recorded, and the tensile strength and elongation at break were calculated. At least five valid specimens were tested in each group, and the arithmetic mean was taken. The tear strength of the film was tested using a pendulum tear tester. The sample size was 100mm × 50mm. A 20mm long slit was pre-made at the center of the sample. The initial angle of the pendulum was 90°. The pendulum was released to tear the sample, and the maximum tearing force was recorded. Five samples were tested for each sample in different directions. The biodegradability test was conducted using the composting method. Precisely weighed 10cm × 10cm samples were buried in a composting medium with a specific ratio. The composting medium was made of kitchen waste, garden waste, and livestock manure mixed in a mass ratio of 4:3:3. The composting environment was maintained at a temperature of 58℃ and a humidity between 50% and 55%, and the samples were turned regularly. The stack was kept well-ventilated. Samples were removed every 30 days, cleaned, dried, and accurately weighed. The mass loss rate was calculated, and changes in the sample surface morphology were observed. Heat distortion temperature testing was performed using a heat distortion testing machine. The sample size was 80mm × 10mm × 0.05mm, with an applied bending stress of 1.80MPa. The temperature was increased at a uniform rate of 2℃ / min, and the temperature at which the sample deformation reached 0.25mm was recorded. Optical properties were tested using a UV-Vis spectrophotometer. The sample size was 50mm × 50mm, and the spectrophotometer scanned within the wavelength range of 380nm to 780nm. Air was used as a reference to measure transmittance and haze values. Each sample was measured three times at different locations, and the average value was taken. The melt flow rate was tested using a melt flow rate meter. The test temperature was set to 190℃, the load to 2.16kg, the preheating time to 5min, and the cutting interval to 30s. The average mass of the five cut segments was taken to calculate the melt flow rate. The film thickness was measured using a digital thickness gauge with a measuring head diameter of 10mm and an applied pressure of 50kPa. Fifteen points were evenly selected on the surface of each sample for measurement. The maximum and minimum values ​​were discarded, and the average value was taken.

[0046] Performance test results: Table 1 Performance Test Results ; As shown in Table 1, a comparative analysis of the performance test results of Examples 1-3 and Comparative Examples 1-3 clearly confirms that the present invention successfully solves the technical problems of insufficient mechanical properties of biodegradable bags due to poor compatibility between PLA and PBAT, and the impact of easy migration of small molecule plasticizers on material durability. Specifically, Examples 1-3, due to the simultaneous addition of a nanofiber interpenetrating network compatibilizer and a star-shaped bio-based plasticizer, achieved tensile strengths of 35.2-41.3 MPa, elongation at break of 420%-520%, and tear strength of 175-195 N / mm, with all mechanical properties significantly superior to the comparative examples. Comparative Example 1, without any modified compounds, had a tensile strength of only 18.7 MPa, an elongation at break of only 150%, and a tear strength of only 90 N / mm, fully demonstrating the synergistic effect of the two modified compounds in improving the mechanical properties of the material. Comparative Example 2, which only added a nanofiber interpenetrating network compatibilizer but lacked a star-shaped bio-based plasticizer, showed a higher elongation at break than Comparative Example 1, but still significantly lower than the examples. Its melt flow rate was also lower, indicating insufficient processing fluidity. This demonstrates that the star-shaped bio-based plasticizer plays an irreplaceable role in improving material flexibility and processing performance. Comparative Example 3, which only added a star-shaped bio-based plasticizer but lacked a nanofiber interpenetrating network compatibilizer, showed significantly lower tensile and tear strengths than the examples. This indicates that the nanofiber interpenetrating network compatibilizer plays a crucial role in enhancing interfacial compatibility and improving mechanical strength. Regarding durability, Examples 1-3 maintained high mechanical property retention rates after 180 days of degradation testing, while the comparative examples all exhibited varying degrees of surface stickiness and exudation during the test. This confirms that the star-shaped bio-based plasticizer effectively prevents small molecule migration and exudation through chemical bonding, thus ensuring the long-term stability of the material. Furthermore, the heat distortion temperatures of Examples 1-3 reached 120-128℃, significantly higher than the 105℃ of Comparative Example 1, indicating that the synergistic effect of the two modified compounds improved the thermal stability of the material. Regarding degradation performance, the 180-day biodegradation rate of Examples 1-3 reached 82.7%-87.5%, significantly higher than the 45.3% of Comparative Example 1. This demonstrates that the present invention, while improving mechanical properties, not only did not hinder but actually promoted the biodegradation process. In summary, the present invention, through the synergistic effect of the two modified compounds, constructs a stable multiphase interface structure at the molecular level. This not only solves the mechanical property defects caused by the poor compatibility of PLA and PBAT but also avoids the problem of small molecule migration through a reactive plasticizing mechanism, achieving a comprehensive improvement in the overall performance of the fully biodegradable bag.

[0047] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A process for the production of a fully biodegradable bag, characterized by the steps of Comprising: S1, vacuum drying polylactic acid and polybutylene adipate terephthalate at 78-82℃; After drying, the polylactic acid, polybutylene adipate terephthalate, nanofiber interpenetrating network compatibilizer, star structure biobased plasticizer, maleimide modified lignin, ethylene bis-stearamide and antioxidant are mixed in a high-speed mixer to obtain a mixed material; S2, the mixed material is sent into a twin-screw extruder for melt blending and granulation, the temperature interval of the extruder is 160-180℃, and a granule is obtained; the granule is blown into a film through a single-screw film blowing machine; and the film is cut and heat-sealed through a bag making machine.

2. The process for producing a fully biodegradable bag according to claim 1, characterized by, In step S1, the vacuum drying time at 78-82℃ is 12-14h.

3. The method of making a fully biodegradable bag according to claim 1, wherein, In step S2, the temperature for film blowing is 150-170℃.

4. The method of making a fully biodegradable bag according to claim 1, wherein, The preparation method of the nanofiber interpenetrating network compatibilizer comprises: A1, dispersing a nanofiber suspension in N,N-dimethylformamide, adding α-bromoisobutyryl bromide, and reacting at-2~2℃ under nitrogen protection to obtain a macromolecular initiator; A2, adding L-lactide and adipate / butylene terephthalate copolymer macromonomer and pentamethyl diethylene triamine, and performing an atom transfer radical polymerization reaction at 78-82℃; after the reaction is completed, the product is precipitated with methanol and vacuum dried.

5. The process for producing a fully biodegradable bag according to claim 4, characterized by, In step A1, the reaction time at-2~2℃ is 12-14h.

6. The method of making a fully biodegradable bag according to claim 4, wherein, In step A2, the atom transfer radical polymerization reaction is performed at 78-82℃ for 24-30h.

7. The method of making a fully biodegradable bag according to claim 1, wherein, The preparation method of the star structure biobased plasticizer comprises: B1, ring-opening polymerization of γ-valerolactone and trimethylolpropane at 145-155℃ under the catalysis of stannous octoate to generate a three-arm star polyvalerolactone prepolymer; B2, ring-opening esterification of itaconic acid and epichlorohydrin at 78-82℃ under the catalysis of tetrabutylammonium bromide, followed by the addition of sodium hydroxide aqueous solution to generate itaconic acid bisglycidyl ester; and melt grafting reaction of the itaconic acid bisglycidyl ester and the three-arm star polyvalerolactone prepolymer at 110-130℃.

8. The process for producing a fully biodegradable bag according to claim 7, characterized by, In step B1, the ring-opening polymerization reaction is performed at 145-155℃ for 8-10h.

9. The method of making a fully biodegradable bag according to claim 7, wherein, In step B2, the reaction is performed at 78-82℃ for 8-10h.

10. A fully biodegradable bag obtainable by the process according to any one of claims 1 to 9, characterized in that, The raw materials comprise the following by weight: polylactic acid 30-50 parts by weight; polybutylene adipate terephthalate 20-40 parts by weight; nanofiber interpenetrating network compatibilizer 5-15 parts by weight; star structure biobased plasticizer 3-10 parts by weight; maleimide modified lignin 5-15 parts by weight; ethylene bis-stearamide 0.5-2 parts by weight; and antioxidant 0.1-0.5 parts by weight.