An antibacterial lignin-based biodegradable polyester and its preparation method

Abstract

This invention relates to the field of polymer materials technology, specifically to an antibacterial lignin-based biodegradable polyester and its preparation method. The method includes: 1) dissolving lignin in an alkaline solution and sequentially performing quaternary phosphonium salt functionalization and free radical graft polymerization, followed by precipitation, washing, and drying to obtain modified lignin; 2) uniformly mixing the modified lignin, biodegradable polyester, compatibilizer, and processing aids, followed by melt blending extrusion, granulation, and drying to obtain granules; 3) molding the granules to form the antibacterial lignin-based biodegradable polyester. This invention integrates antibacterial and reactive compatibilizing functions onto lignin molecules through chemical bonding, and then achieves chemical bonding between the modified lignin and the polyester matrix through in-situ interfacial reactions during melt blending, ultimately forming a nanocomposite structure in which antibacterial functional units are uniformly and stably dispersed in the matrix.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to an antibacterial lignin-based biodegradable polyester and its preparation method. Background Technology

[0002] Currently, ecological and environmental protection has received increasing attention. Polymers, as a major source of environmental pollution, are mostly synthesized from petrochemical products and are difficult to biodegrade; when they enter the natural environment, they cause serious harm to wild flora and fauna. Incineration, as the main method of plastic waste disposal, emits harmful gases such as dioxins; while the recycling of plastics is often limited by the high energy consumption of washing and recycling processes. Therefore, developing biodegradable materials that can replace traditional plastics is of significant research importance.

[0003] Biodegradable polyesters, such as polylactic acid (PLA), polybutylene succinate (PBS), and polybutylene terephthalate (PBAT), have wide applications in food packaging, medical devices, and daily necessities, exhibiting good biocompatibility and degradation properties. However, studies have shown that these materials are susceptible to contamination by bacteria, viruses, and other microorganisms, which may increase the risk of infection and affect health after human contact, thus significantly limiting their application in short-term use areas such as packaging materials and toys.

[0004] Lignin, a major component of plant wood structure, is widely available and inexpensive, possessing high impact strength, excellent heat resistance, and water resistance. More importantly, lignin exhibits certain antibacterial activity, the mechanism of which mainly involves phenolic compounds causing cell membrane damage upon contact with bacteria. However, lignin has a complex structure and poor compatibility with polyester matrices; direct blending often leads to a decline in the mechanical properties of the material.

[0005] To improve the compatibility of lignin and polyester, existing technologies mainly employ two strategies: first, esterification or etherification modification of lignin to introduce flexible segments compatible with polyester; second, reactive blending by adding compatibilizers. However, these strategies only focus on improving compatibility and fail to effectively endow the material with antibacterial properties. On the other hand, to impart antibacterial properties to biodegradable polyesters, the conventional method is to directly add small-molecule antibacterial agents (such as silver ions, quaternary ammonium salts, etc.), but small-molecule antibacterial agents are prone to migration and loss, resulting in unsustainable antibacterial effects and potentially causing environmental and biosafety issues. Attempting to combine the natural antibacterial properties of lignin with improved compatibility presents a dilemma: improving compatibility alone cannot achieve sufficient antibacterial performance; while relying solely on the natural antibacterial properties of lignin is ineffective due to limited antibacterial activity and poor dispersibility.

[0006] Furthermore, some existing technologies use quaternary phosphonium salt-modified lignin for antibacterial materials, but only focus on antibacterial properties without addressing the lignin-polyester interfacial compatibility issue. Other existing technologies use maleic anhydride-grafted lignin for polyester compatibility, but do not impart antibacterial functionality. Simply combining the two approaches leads to several problems. First, the separately modified lignins undergo cross-linking deactivation during melt blending due to the random reaction between the active ester groups and the quaternary phosphonium salt groups. Second, the two separately added modified lignins exhibit independent dispersion behavior in the matrix, making it difficult to simultaneously achieve spatial matching between "interfacial anchoring" and "surface antibacterial" properties. This results in the antibacterial groups being embedded within the interfacial layer and becoming ineffective.

[0007] Therefore, how to simultaneously improve the compatibility of lignin and polyester and impart efficient antibacterial function, while ensuring the long-term stability of the antibacterial function, and how to integrate dual functions on a single lignin molecule while avoiding interference between groups, has become a technical challenge that urgently needs to be overcome in this field. Summary of the Invention

[0008] This invention addresses the technical challenges of poor antibacterial properties of traditional biodegradable polyester materials, poor compatibility between lignin and the polyester matrix, and the inability of existing modification strategies to simultaneously solve both antibacterial and compatibility issues. It provides a structurally stable antibacterial lignin-based biodegradable polyester and its preparation method.

[0009] The main objective of this invention is: I. A structurally stable antibacterial lignin-based biodegradable polyester is provided. Through a chemical modification strategy, antibacterial active groups and flexible segments compatible with polyester are introduced into the lignin molecule simultaneously, so as to achieve nanoscale dispersion and strong interfacial bonding of lignin in the polyester matrix. II. A method for preparing a structurally stable antibacterial lignin-based biodegradable polyester is provided, which obtains a composite material with excellent mechanical properties, long-lasting antibacterial effect and complete biodegradability through melt blending and reactive compatibilization synergistic technology. Third, by using lignin derived from agricultural waste to replace part of the petroleum-based polyester raw materials, material costs can be reduced and high-value utilization of waste biomass can be achieved.

[0010] To achieve the above objectives, the present invention adopts the following technical solution.

[0011] A method for preparing an antibacterial lignin-based biodegradable polyester. The method includes: 1) Dissolve lignin in an alkaline solution, add a phosphorus source to carry out a quaternary phosphonium salt functionalization reaction to obtain quaternary phosphonium salt modified lignin, then add an active ester monomer and an initiator to the reaction system to carry out free radical graft polymerization, and after precipitation, washing and drying, obtain modified lignin; 2) After uniformly mixing modified lignin, biodegradable polyester, compatibilizer and processing aid, the mixture is melt-blended, extruded, granulated and dried to obtain granules; 3) The granules are processed into the antibacterial lignin-based biodegradable polyester through a molding process.

[0012] As a preferred option Step 1) The lignin is enzymatically hydrolyzed lignin and / or alkali lignin; The enzymatically hydrolyzed lignin and / or alkali lignin are extracted from corn stalks and / or wheat stalks and / or sugarcane bagasse. Step 1) The lignin is washed and dried before use. Washing is performed by washing with hydrochloric acid solution with pH 2-3 3-5 times, and then washing with deionized water until neutral. Drying is performed by drying under vacuum at 50-70 ℃ for 12-24 h until the moisture content is less than 1 wt%.

[0013] As a preferred option Step 1) The alkaline solution is an aqueous solution of an alkali metal hydroxide with a concentration of 1.0–2.0 mol / L; In step 1), the mass-to-volume ratio of lignin to alkaline solution is 1:(8-12) g / mL.

[0014] As a preferred option The phosphorus source is (3-epoxypropyl)triphenylphosphonium bromide, and its amount is 20-30% of the lignin content.

[0015] As a preferred option Step 1) The quaternary phosphonium salt functionalization reaction is carried out under environmental conditions of 0.08-0.12 MPa pressure and 60-80 ℃ for 4-8 h. After the reaction is completed, the pH is adjusted to 6.5-7.5 with hydrochloric acid solution of 1-2 mol / L.

[0016] As a preferred option Step 1) The active ester monomer is glycidyl methacrylate and / or maleic anhydride, and the amount added is 20-30% of the quaternary phosphonium salt modified lignin. Step 1) The initiator is azobisisobutyronitrile or benzoyl peroxide, and the amount added is 1 to 2% of the mass of the active ester monomer.

[0017] As a preferred option Step 1) The free radical grafting polymerization is carried out under nitrogen atmosphere, pressure 0.08-0.12 MPa, and temperature 80-100℃ for 4-6 h. After the reaction is completed, the reaction solution is poured into anhydrous ethanol to precipitate. The precipitate is filtered and washed with anhydrous ethanol 3-5 times. It is then vacuum dried at 50-70℃ for 12-24 h to obtain modified lignin.

[0018] As a preferred option Step 2) The biodegradable polyester is polylactic acid and / or polycaprolactone and / or polybutylene succinate and / or polybutylene terephthalate; Step 2) The compatibilizer is an epoxy functionalized chain extender and / or maleic anhydride-grafted polylactic acid (MAH-g-PLA). Step 2) The processing aids include antioxidants and lubricants, wherein: The antioxidants are pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and / or tris(2,4-di-tert-butylphenyl) phosphite; The lubricant is calcium stearate and / or ethylene bis-stearamide.

[0019] As a preferred option Step 2) The modified lignin, biodegradable polyester, compatibilizer and processing aid are mixed evenly at a mass ratio of 1:(1.0~4.0):(0.02~0.10):(0.005~0.02); Step 2) The melt blending is carried out using an extrusion device, and the temperature of each section is set as follows: The feeding section is 140–160 °C, the melting section is 160–180 °C, the die head section is 170–190 °C, and the screw speed is 100–300 rpm. Step 2) The drying process involves drying under vacuum at 60–80 °C for 4–8 h until the moisture content is below 0.5 wt%.

[0020] As a preferred option Step 3) The molding process can be any existing polyester granule processing process, such as common injection molding.

[0021] An antibacterial lignin-based biodegradable polyester; The modified lignin is a dual-modified lignin with quaternary phosphonium salt antibacterial groups and active ester compatibilizing groups chemically bonded to the same lignin molecule. The modified lignin is dispersed in the polyester matrix through in-situ reaction of the active ester groups with biodegradable polyester end groups in a chemically bonded manner, forming a nano-dispersion structure with a lignin phase region size ≤200nm.

[0022] The core of this invention lies in the modification of lignin by active ester grafting, introducing flexible segments compatible with polyester, which significantly improves the dispersibility of lignin in the polyester matrix, resulting in strong interfacial bonding and excellent mechanical properties. Simultaneously, the introduction of quaternary phosphonium salt groups endows the material with broad-spectrum antibacterial properties, and the antibacterial mechanism is contact killing, making it safe and environmentally friendly. This effectively solves the problems of biodegradable polyesters being susceptible to microbial contamination and having a short service life during use.

[0023] In the current application context, the technical challenges to be overcome are twofold: firstly, how to endow biodegradable polyesters with efficient and long-lasting antibacterial properties; and secondly, how to overcome the interfacial compatibility problems caused by the significant differences in chemical structure between lignin and the polyester matrix. In existing technologies, improving antibacterial performance often relies on the physical incorporation of small-molecule antibacterial agents (such as silver ions, quaternary ammonium salts, and quaternary phosphonium salts). However, these small molecules are prone to migration and precipitation during material use, leading to a rapid decline in antibacterial efficacy and potentially posing environmental and biosafety risks. Improving interfacial compatibility typically involves esterification or etherification of lignin or the addition of compatibilizers, but these modification methods do not simultaneously introduce antibacterial functionality. If these two strategies are mechanically superimposed—that is, simultaneously adding small-molecule antibacterial agents and compatibilizers—a dual contradiction arises: antibacterial agent migration and weakened interfacial bonding, making it difficult to simultaneously achieve long-lasting antibacterial effects and material structural stability.

[0024] To address existing shortcomings, this invention proposes a "dual chemical modification synergy" technical concept. The core of this concept lies in sequentially modifying the same lignin molecule with quaternary phosphonium salt functionalization and then with reactive ester grafting, thereby enabling the lignin to simultaneously possess both highly efficient antibacterial properties and reactive compatibilizing capabilities. Subsequently, through in-situ interfacial reactions during melt blending, the modified lignin is chemically bonded and firmly anchored within the polyester matrix, constructing a stable composite structure integrating "antibacterial unit - reactive compatibilizing unit - matrix resin."

[0025] The beneficial effects of the technical solution of this invention stem from the synergistic effect of the following two key chemical reactions: One method involves functionalization modification with quaternary phosphonium salts. This invention uses (3-epoxypropyl)triphenylphosphonium bromide as a modifier, whose molecular structure contains both epoxy groups and quaternary phosphonium salt groups. Under alkaline aqueous conditions, the epoxy groups undergo a ring-opening addition reaction with the phenolic or alcoholic hydroxyl groups on the lignin molecule, grafting the quaternary phosphonium salt groups onto the lignin backbone through stable carbon-oxygen covalent bonds. This chemical bonding method makes the quaternary phosphonium salt groups an intrinsic component of the lignin molecular structure, rather than a simple physical blend. The quaternary phosphonium salt groups carry a positive charge; when the material surface comes into contact with bacteria, they can adsorb the negatively charged bacterial cell membrane through electrostatic interactions, thereby interfering with the normal function of the cell membrane phospholipid bilayer, leading to membrane rupture and leakage of intracellular substances, thus achieving contact sterilization. Since the quaternary phosphonium salt is fixed to lignin in the form of covalent bonds, and the lignin molecules are firmly bonded to the polyester matrix after subsequent reactive compatibilization, the quaternary phosphonium salt groups are difficult to migrate and precipitate during use, thus endowing the material with long-lasting and safe antibacterial properties.

[0026] Secondly, there is the active ester grafting modification. This invention selects glycidyl methacrylate or maleic anhydride as grafting monomers, and grafts polymer segments carrying epoxy groups or anhydride groups onto lignin molecules via free radical polymerization under the action of an initiator. The key function of this modification is to introduce active functional groups into lignin that can chemically react with polyester. Specifically, during subsequent melt blending, as the temperature rises, the epoxy groups (or anhydride groups) on the modified lignin undergo ring-opening esterification with the end groups (carboxyl or hydroxyl groups) of the polyester molecular chain, forming a covalently bonded "lignin-polyester" graft copolymer. This in-situ generated copolymer acts as a "molecular bridge": its lignin segments are compatible with the modified lignin matrix, while the polyester segments are compatible with the polyester matrix, thereby embedding lignin particles into the polyester matrix through chemical bonding. The interfacial forces of this type of chemical bonding are much stronger than the van der Waals forces or hydrogen bonds in traditional physical blending, which leads to the refinement of the lignin phase region size from the micrometer scale in traditional blending to the nanometer scale, and significantly improves the interfacial shear strength.

[0027] Furthermore, the coexistence of the aforementioned dual modifications on the same lignin molecule follows a molecular design balance of "steric hindrance-reactivity". The quaternary phosphonium salt group is grafted onto the phenolic hydroxyl sites of lignin via the glycidyl moiety in the C3 alkyl chain, while the active ester grafting occurs primarily at the electron-rich sites of the guaiacol / syringyl side chains of lignin via free radical reactions. These two groups are spatially separated on the lignin aromatic skeleton, avoiding the electrostatic shielding effect of the positive charge of the quaternary phosphonium salt on the free radical grafting reaction, and also preventing the active ester polymer chain from spatially embedding the antibacterial sites of the quaternary phosphonium salt. This intramolecular site-selective distribution ensures that the quaternary phosphonium salt maintains highly efficient contact antibacterial activity, while the active ester chain segments fully extend to participate in interfacial reactions. During melt blending, the active ester group preferentially reacts with the polyester end groups, "anchoring" the lignin carrying the quaternary phosphonium salt group to the interface, forming an interfacial gradient distribution of "antibacterial units enriched towards the surface, and reactive units penetrating towards the matrix." This microstructure cannot be achieved by a single modified lignin or a physical blend system.

[0028] The advantages of this invention lie in its integration of antibacterial and reactive compatibilizing functions onto lignin molecules through chemical bonding. Then, through in-situ interfacial reactions during melt blending, chemical bonds are established between the modified lignin and the polyester matrix, ultimately forming a nanocomposite structure in which antibacterial functional units are uniformly and stably dispersed within the matrix. This technical solution breaks away from the existing mindset of "solving antibacterial and compatibility problems separately," achieving a synergistic unity of antibacterial properties and compatibility from a molecular design perspective. It fundamentally solves the two major technical challenges of small-molecule antibacterial agent migration failure and lignin / polyester interface weakening. Detailed Implementation

[0029] The present invention will be further described clearly and in detail below with reference to specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0030] Unless otherwise specified, all raw materials used in the embodiments of the present invention are commercially available or obtainable by those skilled in the art; unless otherwise specified, all methods used in the embodiments of the present invention are methods mastered by those skilled in the art. Example 1

[0031] A structurally stable antibacterial lignin-based biodegradable polyester is prepared by mixing modified lignin, biodegradable polyester, compatibilizer and processing aid in a mass ratio of 1:1.0:0.02:0.005.

[0032] 1) Take enzymatically hydrolyzed lignin (extracted from corn stalks), wash it three times with hydrochloric acid solution at pH 2.0, then wash it with deionized water until neutral, and dry it under vacuum at 50 ℃ for 24 h until the moisture content is less than 1 wt%. Mix the dried lignin with a 1.0 mol / L sodium hydroxide aqueous solution at a mass-to-volume ratio of 1:8 g / mL, add 20% (3-epoxypropyl)triphenylphosphonium bromide by weight of lignin, and react at 60 ℃ and 0.08 MPa for 8 h. After the reaction, adjust the pH to 6.5 with 1.0 mol / L hydrochloric acid. Add 20% glycidyl methacrylate by weight of quaternary phosphonium salt modified lignin and 1% azobisisobutyronitrile by weight of active ester monomer to the reaction system, and react at 80 ℃ and 0.08 MPa for 6 h under nitrogen protection. After the reaction was completed, the reaction solution was poured into anhydrous ethanol to precipitate. The precipitate was filtered, washed three times with anhydrous ethanol, and dried under vacuum at 50°C for 24 h to obtain modified lignin.

[0033] 2) Weigh the modified lignin, polybutylene terephthalate (PBAT), epoxy functionalized chain extender, and pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (antioxidant 1010) according to the above mass ratio, and mix for 10 min. Add the mixture to the extrusion equipment for melt blending extrusion. The temperatures of each section are set as follows: Zone 1 140 ℃, Zone 2 160 ℃, Zone 3 170 ℃, Zone 4 170 ℃, Die head 170 ℃, and screw speed 100 rpm. The extruded strip is water-cooled and pelletized. The resulting particles are dried under vacuum at 60 ℃ for 8 h until the moisture content is below 0.5 wt%, yielding granules.

[0034] 3) Add the dried granules to the injection molding machine. Set the injection temperature as follows: Zone 1 165 ℃, Zone 2 170 ℃, Zone 3 175 ℃, nozzle 175 ℃; mold temperature 40 ℃, injection pressure 60 MPa, holding pressure 50 MPa, cooling time 30 s. Obtain Type I tensile specimens (total length 150 mm, narrow section length 60 mm, width 10 mm, thickness 4 mm) conforming to GB / T 1040.2-2022 and short beam shear specimens (length 20 mm, width 10 mm, thickness 4 mm) conforming to ASTM D2344 / D2344M-16.

[0035] The materials prepared in the examples were subjected to performance testing. The prepared standard samples were placed in an environment of 23±2 ℃ and 50±5% relative humidity for 48 h before performance testing. The specific characterization results are as follows.

[0036] Tensile strength test: Refer to GB / T 1040.2-2022 test, use type I specimen, tensile speed 50 mm / min, initial clamp spacing 115 mm, and take the average value of 5 specimens in each group of tests.

[0037] Elongation at break test: Refer to GB / T 1040.2-2022 test, use type I specimen, tensile speed 50 mm / min, record the change rate of gauge length at the time of specimen breakage, and take the average value of 5 specimens in each group of tests.

[0038] Antibacterial rate test: Referring to GB / T 31402-2015, the sample was processed into a 50 mm × 50 mm × 4 mm plate, and Escherichia coli bacterial suspension (concentration of 10) was evenly coated on the surface. 5 After incubating the samples (CFU / mL) at 35 ℃ and 90% relative humidity for 24 h, the number of surviving colonies was determined by plate counting. Three samples were tested in each group, and the average value was taken.

[0039] Interfacial shear strength test: Refer to ASTM D2344 / D2344M-16 test, use short beam shear method, sample size 20 mm × 10 mm × 4 mm, span 12 mm, loading speed 1 mm / min, record the maximum load, interfacial shear strength = 0.75 × maximum load / (sample width × sample thickness), take the average value of 5 samples in each group of tests.

[0040]

[0041] Analysis of the above characterization results shows that the antibacterial lignin-based biodegradable polyester prepared by this invention possesses excellent mechanical properties, highly efficient antibacterial effects, and strong interfacial bonding, fully verifying the effectiveness of the "dual chemical modification synergy" technical concept. Specifically, the tensile strength reaches 20.8 MPa and the elongation at break is 325%, indicating that the material maintains good ductility while possessing sufficient structural strength. This is due to the chemical bonding interface formed between the modified lignin and the PBAT matrix through active ester grafting, which effectively inhibits the aggregation and debinding of lignin. The antibacterial rate against Escherichia coli reaches 99.2%, proving that the contact bactericidal mechanism of quaternary phosphonium salt groups is highly efficient and stable. Furthermore, since the quaternary phosphonium salt is covalently fixed to lignin and anchored to the matrix, the migration and loss of small molecule antibacterial agents are avoided. The interfacial shear strength of 10.2 MPa is significantly higher than that of the traditional physical blending system, further confirming that the three-in-one structure of "antibacterial unit-reactive compatibilizing unit-matrix resin" constructed by in-situ interfacial reaction effectively solves the interfacial compatibility problem between lignin and the polyester matrix. Example 2

[0042] A structurally stable antibacterial lignin-based biodegradable polyester is prepared by mixing modified lignin, biodegradable polyester, compatibilizer and processing aid in a mass ratio of 1:2.5:0.06:0.012.

[0043] 1) Take alkali lignin (extracted from sugarcane bagasse), wash it four times with hydrochloric acid solution at pH 2.5, then wash it with deionized water until neutral, and dry it under vacuum at 60 ℃ for 18 h until the moisture content is less than 1 wt%. Mix the dried lignin with a 1.5 mol / L potassium hydroxide aqueous solution at a mass-to-volume ratio of 1:10 g / mL, add 25% (3-epoxypropyl)triphenylphosphonium bromide by weight of lignin, and react at 70 ℃ and 0.10 MPa for 6 h. After the reaction, adjust the pH to 7.0 with 1.5 mol / L hydrochloric acid. Add 25% glycidyl methacrylate by weight of quaternary phosphonium salt modified lignin and 1.5% azobisisobutyronitrile by weight of active ester monomer to the reaction system, and react at 90 ℃ and 0.10 MPa for 5 h under nitrogen protection. After the reaction was completed, the reaction solution was poured into anhydrous ethanol to precipitate. The precipitate was filtered, washed four times with anhydrous ethanol, and dried under vacuum at 60°C for 18 h to obtain modified lignin.

[0044] 2) Weigh the modified lignin, polylactic acid (PLA), maleic anhydride-grafted PLA, and pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid] (antioxidant 1010) according to the above mass ratio, and mix for 6 min. Add the mixture to the extrusion equipment for melt blending extrusion. The temperatures of each section are set as follows: Zone 1 150 ℃, Zone 2 170 ℃, Zone 3 180 ℃, Zone 4 180 ℃, die head 175 ℃, and screw speed 200 rpm. The extruded strip is water-cooled and pelletized. The resulting particles are dried under vacuum at 70 ℃ for 6 h until the moisture content is less than 0.5 wt%, yielding granules.

[0045] 3) Add the dried granules to the injection molding machine. Set the injection temperature as follows: Zone 1 170 ℃, Zone 2 175 ℃, Zone 3 180 ℃, nozzle 180 ℃; mold temperature 50 ℃, injection pressure 70 MPa, holding pressure 55 MPa, cooling time 40 s. Obtain the following: Type I tensile specimens (total length 150 mm, narrow section length 60 mm, width 10 mm, thickness 4 mm) conforming to GB / T 1040.2-2022, heat deformation test specimens (length 80 mm, width 10 mm, thickness 4 mm) conforming to GB / T 1634.2-2019, and short beam shear specimens (length 20 mm, width 10 mm, thickness 4 mm) conforming to ASTM D2344 / D2344M-16.

[0046] The materials prepared in the examples were subjected to performance testing. The prepared standard samples were placed in an environment of 23±2 ℃ and 50±5% relative humidity for 48 h before performance testing. The specific characterization results are as follows.

[0047] Tensile strength test: Refer to GB / T 1040.2-2022 for testing. Type I specimens are used, the tensile speed is 10 mm / min, the initial spacing of the clamps is 115 mm, and the average value of 5 specimens in each group of tests is taken.

[0048] Elongation at break test: Refer to GB / T 1040.2-2022 test, use type I specimen, tensile speed 10 mm / min, record the gauge length change rate when the specimen breaks, and take the average value of 5 specimens in each group test.

[0049] Antibacterial rate test: Referring to GB / T 31402-2015, the sample was processed into a 50 mm × 50 mm × 4 mm plate, and Staphylococcus aureus bacterial suspension (concentration of 10) was evenly coated on the surface. 5After incubation at 35 ℃ and 90% relative humidity for 24 h, the number of surviving colonies was determined by plate counting. The antibacterial rate was calculated as (1 - number of surviving colonies / initial number of colonies) × 100%. The average value of three samples in each group was taken.

[0050] Interfacial shear strength test: Refer to ASTM D2344 / D2344M-16 test, use short beam shear method, sample size 20 mm × 10 mm × 4 mm, span 12 mm, loading speed 1 mm / min, record the maximum load, interfacial shear strength = 0.75 × maximum load / (sample width × sample thickness), take the average value of 5 samples in each group of tests.

[0051] Heat distortion temperature test: Refer to GB / T 1634.2-2019 test, method B (1.8 MPa), sample size 80 mm×10 mm×4 mm, span 64 mm, heating rate 120 ℃ / h, record the temperature when the sample deformation reaches 0.34 mm, and take the average value of 3 samples in each group of tests.

[0052]

[0053] Analysis of the above characterization results shows that the antibacterial lignin-based biodegradable polyester prepared by the present invention exhibits excellent rigidity, high efficiency of antibacterial activity, strong interfacial bonding and good thermal stability in a polylactic acid (PLA) matrix, further verifying the universality and effectiveness of the technical solution. Specifically, the tensile strength reached 48.6 MPa, significantly higher than that of Example 1. This is attributed to the high rigidity of the PLA matrix itself. Simultaneously, the modified lignin, through a covalent cross-linked network formed by epoxy groups and maleic anhydride-grafted PLA compatibilizer, effectively transferred stress, further enhancing the overall strength of the material. The elongation at break was 6.2%, consistent with the inherent brittleness of the PLA matrix, and the uniform dispersion of the modified lignin did not compromise its rigidity. The antibacterial rate against Staphylococcus aureus reached 99.8%, demonstrating that quaternary phosphonium salt groups also have a highly efficient and stable contact bactericidal effect against Gram-positive bacteria. The covalent bond fixation method completely solved the problem of migration and loss of small-molecule antibacterial agents. The interfacial shear strength was 15.8 MPa, far exceeding that of the traditional PLA-lignin physical blend system, confirming that the in-situ interfacial reaction between maleic anhydride-grafted PLA compatibilizer and modified lignin successfully constructed a tightly bound structure of "antibacterial unit-compensating unit-matrix," effectively eliminating interfacial defects between the two phases. The heat distortion temperature was 68.5 °C. The temperature of ℃ meets the basic requirements for heat resistance in daily use scenarios. This is attributed to the heterogeneous nucleation and reinforcing effect of modified lignin in the PLA matrix, which improves the thermal stability of the material.

[0054] This embodiment demonstrates that the technical solution of the present invention can be adapted to different types of biodegradable polyester matrices, and the material properties can be customized and optimized by adjusting the component ratio and process parameters. Example 3

[0055] A structurally stable antibacterial lignin-based biodegradable polyester is prepared by mixing modified lignin, biodegradable polyester, compatibilizer and processing aid in a mass ratio of 1:4.0:0.10:0.02.

[0056] 1) Take enzymatically hydrolyzed lignin (extracted from wheat straw), wash it 5 times with hydrochloric acid solution at pH 3.0, then wash it with deionized water until neutral, and dry it under vacuum at 70 ℃ for 12 h until the moisture content is less than 1 wt%. Mix the dried lignin with a 2.0 mol / L sodium hydroxide aqueous solution at a mass-to-volume ratio of 1:12 g / mL, add 30% (3-epoxypropyl)triphenylphosphonium bromide by weight of lignin, and react at 80 ℃ and 0.12 MPa for 4 h. After the reaction, adjust the pH to 7.5 with 2.0 mol / L hydrochloric acid. Add 30% maleic anhydride by weight of quaternary phosphonium salt modified lignin and 2% benzoyl peroxide by weight of active ester monomer to the reaction system, and react at 100 ℃ and 0.12 MPa for 4 h under argon protection. After the reaction was completed, the reaction solution was poured into anhydrous ethanol to precipitate. The precipitate was filtered, washed five times with anhydrous ethanol, and dried under vacuum at 70 °C for 12 h to obtain modified lignin.

[0057] 2) Weigh the modified lignin, polybutylene succinate (PBS), epoxy functionalized chain extender, and tris(2,4-di-tert-butylphenyl) phosphite (antioxidant 168) according to the above mass ratio, and mix for 3 min. Add the mixture to an extrusion device for melt blending and extrusion. The temperatures of each section are set as follows: Zone 1 160 ℃, Zone 2 180 ℃, Zone 3 190 ℃, Zone 4 190 ℃, die head 190 ℃, and screw speed 300 rpm. The extruded strip is water-cooled and pelletized. The resulting particles are dried under vacuum at 80 ℃ for 4 h until the moisture content is below 0.5 wt%, yielding granules.

[0058] 3) Add the dried granules to the injection molding machine. Set the injection temperature as follows: Zone 1 165 ℃, Zone 2 170 ℃, Zone 3 175 ℃, nozzle 175 ℃; mold temperature 45 ℃, injection pressure 65 MPa, holding pressure 50 MPa, cooling time 35 s. Obtain Type I tensile specimens (total length 150 mm, narrow section length 60 mm, width 10 mm, thickness 4 mm) conforming to GB / T 1040.2-2022 and short beam shear specimens (length 20 mm, width 10 mm, thickness 4 mm) conforming to ASTM D2344 / D2344M-16. Take a portion of the granules for melt flow index testing.

[0059] The materials prepared in the examples were subjected to performance testing. The prepared standard samples were placed in an environment of 23±2 ℃ and 50±5% relative humidity for 48 h before performance testing. The specific characterization results are as follows.

[0060] Tensile strength test: Refer to GB / T 1040.2-2022 test, use type I specimen, tensile speed 50 mm / min, initial clamp spacing 115 mm, and take the average value of 5 specimens in each group of tests.

[0061] Elongation at break test: Refer to GB / T 1040.2-2022 test, use type I specimen, tensile speed 50 mm / min, record the change rate of gauge length at the time of specimen breakage, and take the average value of 5 specimens in each group of tests.

[0062] Antibacterial rate test: Referring to GB / T 31402-2015, the sample was processed into a 50 mm × 50 mm × 4 mm plate, and Escherichia coli bacterial suspension (concentration of 10) was evenly coated on the surface. 5 After incubating at 35℃ and 90% relative humidity for 24 hours, the number of surviving colonies was determined by plate counting. The antibacterial rate was calculated as (1 - number of surviving colonies / initial number of colonies) × 100%. The average value of three samples in each group was taken.

[0063] Interfacial shear strength test: Refer to ASTM D2344 / D2344M-16 test, use short beam shear method, sample size 20 mm × 10 mm × 4 mm, span 12 mm, loading speed 1 mm / min, record the maximum load, interfacial shear strength = 0.75 × maximum load / (sample width × sample thickness), take the average value of 5 samples in each group of tests.

[0064] Melt flow index test: Refer to GB / T 3682.1-2018 for testing. Test temperature is 190 ℃, load is 2.16 kg, preheating time is 5 min, cut once every 1 min, cut continuously for 6 times, and take the average value. Each group of tests is 3 times and the average value is taken.

[0065]

[0066] Analysis of the above characterization results shows that the antibacterial lignin-based biodegradable polyester prepared by the present invention exhibits excellent flexibility, high efficiency of antibacterial activity, good interfacial compatibility and processing fluidity in polybutylene succinate (PBS) matrix, further verifying the adaptability of the technical solution to flexible biodegradable polyester matrix. Specifically, the tensile strength reached 32.8 MPa, and the elongation at break was as high as 285%, indicating that the material achieved a balance between strength and ductility through the covalent cross-linking of modified lignin and epoxy functionalized chain extender on the basis of the inherent flexibility of the PBS matrix. The modified lignin is uniformly dispersed in the matrix, acting as a reinforcing phase to transfer stress without destroying the flexible network of PBS. The antibacterial rate against Escherichia coli reached 99.5%, further confirming that the contact bactericidal mechanism of quaternary phosphonium salt groups is stable and efficient, and the covalent bond fixation effectively avoids the migration and loss of antibacterial agents, ensuring long-term antibacterial performance. The interfacial shear strength was 10.5 MPa, which is significantly better than the traditional PBS-lignin physical blend system, indicating that the in-situ interfacial reaction between maleic anhydride modified lignin and epoxy chain extender successfully constructed a tightly combined structure of "antibacterial unit-chain extender compatibilization unit-matrix", eliminating interfacial defects between the two phases. The melt flow index was 8.5 g / 10min, indicating that the material has good processing fluidity and can meet the requirements of various molding processes such as extrusion and injection molding.

[0067] This embodiment shows that the technical solution of the present invention can be customized and optimized for flexible biodegradable polyester matrix, and the prepared material is suitable for application scenarios with high requirements for flexibility and processability (such as food packaging film, disposable tableware, etc.). Comparative Example 1

[0068] Based on Example 2, this example only modifies the preparation process of the modified lignin; the remaining steps are the same as in Example 2. The specific settings are as follows:

[0069] The performance testing method for the comparative product is completely consistent with that of Example 2. Partial performance characterization was performed, and the characterization results are shown in the table below.

[0070] The size of the lignin phase region was characterized by observing the cross-section using a scanning electron microscope (SEM), and the diameter of 100 particles was statistically analyzed using ImageJ software, with the arithmetic mean ± standard deviation taken.

[0071]

[0072] Analysis of the above characterization results shows that the bifunctionalization process of modified lignin (quaternary phosphonium salt functionalization + active ester grafting) is the core of the technical solution of this invention. Specifically, the antibacterial rates of D1-1 and D1-3 are both below 5.0%, while D1-2 still maintains a high antibacterial rate of 98.9%, confirming that the quaternary phosphonium salt group is the key source of antibacterial activity. Its covalent fixation effectively avoids the migration and loss of antibacterial agents, ensuring stable bactericidal effect.

[0073] Furthermore, the lignin phase region size of D1-1 reached 850±210 nm, significantly larger than the 120±35 nm of Example 2, with an interfacial shear strength of only 8.2 MPa; the phase region size of D1-2 was 420±95 nm, with an interfacial shear strength of 6.5 MPa; and the phase region size of D1-3 was the largest, with the lowest interfacial shear strength (3.8 MPa). This indicates that active ester grafting can significantly improve the interfacial bonding between lignin and the PLA matrix, promote uniform lignin dispersion, and reduce phase separation defects.

[0074] In this scheme, Example 2 simultaneously possesses quaternary phosphonium salt functionalization and active ester grafting, thus exhibiting the best performance in tensile strength, interfacial shear strength, heat distortion temperature, and antibacterial rate. D1-1 fails to perform antibacterially due to the lack of antibacterial groups, D1-2 suffers from decreased mechanical properties due to insufficient interfacial compatibility, and D1-3 performs the worst due to dual defects.

[0075] This comparative example verifies that the bifunctionalization process of modified lignin in this invention is a necessary condition for achieving synergistic improvement in the antibacterial properties, mechanical properties, and interfacial compatibility of the material. The absence of any one of these steps will lead to a significant deterioration in performance.

[0076] Furthermore, this invention supplements experimental groups D1-4 and D1-5. The results of experimental group D1-4 show that a physical blending strategy was employed, in which a single quaternary phosphonium salt modified lignin (treated only in step 1 of Example 2) and a single reactive ester modified lignin (treated only in step 2 of Example 2) were mixed at a mass ratio of 1:1 and then melt-blended with a PLA matrix and a compatibilizer. The experimental results show that although the total amount of the two components added was the same as in Example 2, and theoretically both antibacterial and reactive groups were present, the material properties deteriorated significantly: the antibacterial rate plummeted from 99.8% to 91.6%, the interfacial shear strength decreased from 15.8 MPa to 8.8 MPa, and the lignin phase region size increased from 120±35 nm to 380±95 nm. This is because in the physical blending system, the two modified lignins are dispersed as independent phase regions within the matrix. When single-active ester-modified lignin reacts with PLA / compatibilizer, the single quaternary phosphonium salt-modified lignin cannot participate in interfacial anchoring simultaneously, leading to spatial separation between the antibacterial and compatibilizing units. Some quaternary phosphonium salt groups are embedded inside the polyester matrix rather than enriched on the material surface / interface, resulting in reduced antibacterial contact efficiency. Simultaneously, the unreacted quaternary phosphonium salt-modified lignin has weak interfacial bonding with PLA, easily debonding under shear stress, forming defects, resulting in a 40.5% decrease in interfacial shear strength and a 3.2-fold increase in phase size due to aggregation.

[0077] Even if two modified lignins are present, if they are not on the same molecule, the "anchoring-antibacterial" synergistic effect cannot be achieved, and the dispersibility and interfacial binding force are significantly inferior to those in Example 2.

[0078] In the D1-5 experimental group, the free radical grafting reaction of glycidyl methacrylate was performed first, followed by the functionalization reaction of glycidyl oxypropyltriphenyl quaternary phosphonium salt, with the remaining reaction conditions completely consistent with Example 2. The experimental results showed that reversing the time sequence led to disastrous consequences: the quaternary phosphonium salt grafting rate plummeted from 12.5 mmol / g to 6.3 mmol / g, the antibacterial rate was only 82.7%, the interfacial shear strength was 7.6 MPa, and the phase region size increased to 520±140 nm. This is because the phenolic hydroxyl groups of lignin are the main sites for the ring-opening reaction of quaternary phosphonium salt epoxy and also potential sites for the free radical grafting of reactive esters. When reactive ester grafting is performed first, the reactive ester monomer preferentially occupies the electron-rich carbon adjacent to the phenolic hydroxyl group of lignin, forming polymer side chains. These pre-grafted reactive ester segments produce a significant steric hindrance effect, shielding the reactivity of the phenolic hydroxyl group and hindering the subsequent ring-opening reaction between glycidyl oxypropyltriphenyl quaternary phosphonium salt and the phenolic hydroxyl group. Meanwhile, the epoxy groups of the reactive ester may partially open under free radical reaction conditions, consuming the active hydrogen on the lignin and further reducing the grafting sites of quaternary phosphonium salts. The decrease in grafting rate leads to insufficient density of antibacterial groups, and the pre-grafted flexible reactive ester segments entangle the lignin core, hindering its interfacial reaction with the polyester, resulting in deteriorated dispersibility.

[0079] It is evident that the grafting sequence has strict temporal requirements and is not a simple superposition of steps. Incorrect timing can lead to intramolecular site competition and shielding effects, undermining the coexistence basis of dual modification. Comparative Example 2

[0080] Based on Example 2, this example only modifies the melt blending process; the remaining steps are the same as in Example 2. The specific settings are as follows:

[0081] The performance testing method for the comparative product is completely consistent with that of Example 2. Partial performance characterization was performed, and the characterization results are shown in the table below.

[0082]

[0083] Analysis of the above characterization results shows that precise control of melt blending process parameters is the key to achieving excellent material performance in the technical solution of this invention. Specifically: D2-1 suffered from insufficient melt blending due to an excessively low melt blending temperature, resulting in incomplete melt blending of the PLA matrix and modified lignin. The active ester groups of the modified lignin and the epoxy groups of the compatibilizer did not react completely in situ, leading to a significant increase in the lignin phase region size to 680±150 nm. The interfacial shear strength decreased to 7.6 MPa, and the tensile strength to only 38.4 MPa, resulting in a substantial decline in mechanical properties. D2-2 suffered from an excessively high melt temperature. Although this improved the blending uniformity, the high temperature caused partial thermal decomposition of the quaternary phosphonium salt antibacterial groups, reducing the antibacterial rate to 97.2%. Simultaneously, the PLA matrix experienced slight thermal degradation, and the interfacial bonding force and tensile strength remained lower than in Example 2. D2-3 suffered from insufficient shear force due to a reduced screw speed of 50 rpm, resulting in uneven dispersion of the modified lignin. The phase region size reached 350±85 nm, with an interfacial shear strength of 8.5 MPa and a tensile strength of 41.3 MPa, indicating a significant deterioration in performance compared to Example 2.

[0084] The melt blending process parameters in Example 2 ensure that the PLA matrix is ​​fully melted, the interface reaction between the modified lignin and the compatibilizer is complete and uniformly dispersed, thereby achieving synergistic optimization of antibacterial properties, mechanical properties and interface compatibility.

[0085] This comparative example verifies the decisive influence of reasonable control of melt blending process parameters on material properties. Deviation from optimal parameters can lead to poor phase dispersion, decreased interfacial bonding or deactivation of antibacterial groups, thereby affecting overall performance. Comparative Example 3

[0086] Based on Example 1, this example only modifies the ratio of modified lignin to PBAT; the remaining steps are the same as in Example 1. The specific settings are as follows:

[0087] The performance testing method for the comparative product is completely consistent with that of Example 1. Partial performance characterization was performed, and the characterization results are shown in the table below.

[0088]

[0089] Analysis of the above characterization results shows that the ratio of modified lignin to PBAT has a significant regulatory effect on the overall performance of the material, and there exists an optimal ratio range that balances mechanical equilibrium, antibacterial properties, and processability. Specifically: In D3-1, the proportion of modified lignin is reduced, and due to insufficient lignin content in the reinforcing phase, the tensile strength decreases to 18.6 MPa compared to Example 1; the increased proportion of PBAT matrix significantly enhances the material's flexibility, with the elongation at break increasing to 520%; at the same time, the reduced density of antibacterial groups leads to a slight decrease in the antibacterial rate to 98.5%, and the reduced lignin proportion also improves processing fluidity, with a melt index of 9.5 g / 10min. In D3-2, the lignin proportion is moderately increased, highlighting the reinforcing phase effect and increasing the tensile strength to 24.8 MPa; however, the rigidity of lignin inhibits matrix flexibility, and the elongation at break decreases to 240%; the increased density of antibacterial groups increases the antibacterial rate to 99.9%, while the increased lignin proportion leads to a decrease in processing fluidity, with the melt index decreasing to 3.8 g / 10min. The proportion of lignin in D3-3 is further increased. Although the tensile strength increases slightly to 25.2 MPa, the excessive lignin damages the flexible network of the PBAT matrix, and the elongation at break drops sharply to 95%. The antibacterial rate remains at a high level of 99.9%, but the excessive aggregation of lignin leads to a serious deterioration in processing fluidity, with a melt index of only 1.5 g / 10 min, which is difficult to meet the requirements of conventional molding processes.

[0090] The example formulation achieves synergistic optimization of strength, ductility, antibacterial properties, and processing fluidity, verifying the rationality of the formulation. This comparative example shows that the ratio of modified lignin to PBAT needs to be precisely controlled; too high or too low a ratio will lead to performance imbalance. The optimal ratio is one of the key parameters to ensure the overall performance of the material. Comparative Example 4

[0091] Based on Example 1, this example only compares the durability of antibacterial properties; the remaining steps are the same as in Example 1. The specific settings are as follows:

[0092] Performance testing method for comparative products: The samples of Example 1 and D4-1 were respectively subjected to water immersion treatment (40℃ deionized water, soaking for 30 days, with water changed daily), and the antibacterial rate against Escherichia coli before and after immersion was tested. The characterization results are shown in the table below.

[0093]

[0094] Analysis of the above characterization results shows that the modified lignin using covalently grafted quaternary phosphonium salt groups in this invention can significantly improve the durability of antibacterial properties. Specifically, the antibacterial rate of Example 1 decreased only slightly from 99.2% to 99.0% after 30 days of water immersion, showing almost no change. This is because the quaternary phosphonium salt groups are firmly bound to the lignin skeleton through covalent bonds and are not easily migrated or lost during water immersion, thus maintaining a stable antibacterial effect. In contrast, D4-1, which uses a physically blended antibacterial agent, initially achieved an antibacterial rate of 99.7%, but after 30 days of immersion, it plummeted to 68.3%, indicating that the physically blended antibacterial agent is prone to precipitate from the matrix, leading to a significant decrease in antibacterial activity. This comparative example verifies the effectiveness of the "covalently fixed antibacterial group" strategy in the technical solution of this invention. This strategy avoids the migration problem of traditional physically blended antibacterial agents, ensuring that the material maintains high-efficiency antibacterial performance even under long-term use or water contact, further demonstrating the technical advantages of this invention. Comparative Example 5

[0095] Based on Example 1, this example compares the differences in antibacterial longevity and mechanical properties between physically blended quaternary phosphonium salt antibacterial agents and chemically bonded modified lignin of this application. Specific settings are as follows:

[0096] Performance testing methods for comparative products: The initial mechanical properties and antibacterial rate of each group of samples were tested, and the antibacterial rate was tested again after water immersion treatment (40 ℃ deionized water, soaking for 30 days, with water changed daily). The characterization results are shown in the table below.

[0097]

[0098] Analysis of the above characterization results shows that the technical solution of this invention, which uses chemical bonding to fix quaternary phosphonium salt groups to the lignin framework, has significant advantages in terms of synergistic effects on antibacterial long-term efficacy and mechanical properties. Specifically, the amount of antibacterial agent migration in Example 1 is much lower than that in D5-1, D5-2, and D5-3, confirming that covalent bonding can effectively inhibit the migration of antibacterial groups and ensure that the antibacterial rate remains at a high level of 99.0% after immersion in water for 30 days. At the same time, its tensile strength and elongation at break are better than those of D5-1 and D5-3, and also slightly better than D5-2 with added chain extenders, indicating that the interfacial compatibility between chemically bonded modified lignin and the PBAT matrix is ​​better, and it can better maintain the mechanical properties of the material.

[0099] D5-1, due to its lack of premixing and the use of physically blended antibacterial agents, not only suffers from poor long-term effectiveness due to easy migration and loss of the antibacterial agents, but also experiences a significant decrease in mechanical properties due to insufficient interfacial bonding between the unmodified lignin and the matrix. Although D5-2 improves interfacial compatibility and mechanical properties by adding chain extenders, the physically mixed antibacterial agents still exhibit significant migration, and the long-term antibacterial effect remains unresolved. D5-3, as a commercially available antibacterial blend, has the highest amount of antibacterial agent migration, with an antibacterial rate of only 45.6% after soaking, resulting in the worst long-term effectiveness.

[0100] This comparative example further verifies the core value of the chemical bonding strategy of the present invention: by fixing the antibacterial group to lignin through covalent bonds, it not only solves the migration problem of traditional physical blending antibacterial agents, but also maintains mechanical properties by utilizing the good interfacial bonding between modified lignin and the matrix, achieving synergistic optimization of antibacterial long-term effect and mechanical properties, which is significantly better than physical mixing methods and commercially available similar products.

Claims

1. A method for preparing an antibacterial lignin-based biodegradable polyester, characterized in that, The method includes: 1) Dissolve lignin in an alkaline solution, add a phosphorus source to carry out a quaternary phosphonium salt functionalization reaction to obtain quaternary phosphonium salt modified lignin, then add an active ester monomer and an initiator to the reaction system to carry out free radical graft polymerization, and after precipitation, washing and drying, obtain modified lignin; 2) After uniformly mixing modified lignin, biodegradable polyester, compatibilizer and processing aid, the mixture is melt-blended, extruded, granulated and dried to obtain granules; 3) The granules are processed into the antibacterial lignin-based biodegradable polyester through a molding process.

2. The method for preparing an antibacterial lignin-based biodegradable polyester according to claim 1, characterized in that, Step 1) The lignin is enzymatically hydrolyzed lignin and / or alkali lignin; The enzymatically hydrolyzed lignin and / or alkali lignin are extracted from corn stalks and / or wheat stalks and / or sugarcane bagasse. Step 1) The lignin is washed and dried before use. Washing is performed by washing with hydrochloric acid solution with pH 2-3 3-5 times, and then washing with deionized water until neutral. Drying is performed by drying under vacuum at 50-70 ℃ for 12-24 h until the moisture content is less than 1 wt%.

3. The antibacterial lignin-based biodegradable polyester according to claim 1, characterized in that, Step 1) The alkaline solution is an aqueous solution of an alkali metal hydroxide with a concentration of 1.0–2.0 mol / L; In step 1), the mass-to-volume ratio of lignin to alkaline solution is 1:(8-12) g / mL.

4. The method for preparing an antibacterial lignin-based biodegradable polyester according to claim 1, characterized in that, The phosphorus source is (3-epoxypropyl)triphenylphosphonium bromide, and its amount is 20-30% of the lignin content.

5. A method for preparing an antibacterial lignin-based biodegradable polyester according to claim 1 or 4, characterized in that, Step 1) The quaternary phosphonium salt functionalization reaction is carried out under environmental conditions of 0.08-0.12 MPa pressure and 60-80 ℃ for 4-8 h. After the reaction is completed, the pH is adjusted to 6.5-7.5 with hydrochloric acid solution of 1-2 mol / L.

6. The method for preparing an antibacterial lignin-based biodegradable polyester according to claim 1, characterized in that, Step 1) The active ester monomer is glycidyl methacrylate and / or maleic anhydride, and the amount added is 20-30% of the quaternary phosphonium salt modified lignin quality; Step 1) The initiator is azobisisobutyronitrile or benzoyl peroxide, and the amount added is 1 to 2% of the mass of the active ester monomer.

7. A method for preparing an antibacterial lignin-based biodegradable polyester according to claim 1 or 6, characterized in that, Step 1) The free radical grafting polymerization is carried out under nitrogen atmosphere, pressure 0.08-0.12 MPa, and temperature 80-100 ℃ for 4-6 h. After the reaction is completed, the reaction solution is poured into anhydrous ethanol to precipitate. The precipitate is filtered and washed with anhydrous ethanol 3-5 times. It is then vacuum dried at 50-70 ℃ for 12-24 h to obtain modified lignin.

8. The method for preparing an antibacterial lignin-based biodegradable polyester according to claim 1, characterized in that, Step 2) The biodegradable polyester is polylactic acid and / or polycaprolactone and / or polybutylene succinate and / or polybutylene terephthalate; Step 2) The compatibilizer is an epoxy-functionalized chain extender and / or maleic anhydride-grafted polylactic acid; Step 2) The processing aids include antioxidants and lubricants, wherein: The antioxidants are pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and / or tris(2,4-di-tert-butylphenyl) phosphite; The lubricant is calcium stearate and / or ethylene bis-stearamide.

9. A method for preparing an antibacterial lignin-based biodegradable polyester according to claim 1 or 8, characterized in that, Step 2) The modified lignin, biodegradable polyester, compatibilizer and processing aid are mixed evenly at a mass ratio of 1:(1.0~4.0):(0.02~0.10):(0.005~0.02); Step 2) The melt blending is carried out using an extrusion device, and the temperature of each section is set as follows: The feeding section is 140–160 °C, the melting section is 160–180 °C, the die head section is 170–190 °C, and the screw speed is 100–300 rpm. Step 2) The drying process involves drying under vacuum at 60–80 °C for 4–8 h until the moisture content is below 0.5 wt%.

10. An antibacterial lignin-based biodegradable polyester prepared by any one of claims 1 to 9.

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