A biodegradable metal coordination polyester composite material and a preparation method thereof

Abstract

The application provides a biodegradable metal coordination polyester composite material and a preparation method thereof, and belongs to the field of high polymer composite metal materials. The preparation method of the biodegradable metal coordination polyester composite material comprises the following steps: providing an organic ligand, wherein the organic ligand is selected from imidazole-4,5-dicarboxylic acid or fumaric acid; providing terephthalic acid, dibasic acid, dibasic alcohol and a catalyst, and performing an esterification reaction on the organic ligand to obtain an intermediate product; performing a polycondensation reaction on the intermediate product to obtain a base polyester; and mixing the base polyester with a metal compound to initiate metal coordination to obtain the biodegradable metal coordination polyester composite material. The biodegradable metal coordination polyester composite material is prepared by using an esterification method to prepare a base polyester and then coordinate with metal ions, so that the mechanical strength of the polyester is enhanced, and the biodegradability of the polyester can be retained.

Description

Technical Field

[0001] This invention relates to the field of polymer composite metal materials technology, specifically to a biodegradable metal-coordinated polyester composite material. Background Technology

[0002] Driven by both environmental regulations and the concept of sustainable development, polyester materials, which combine biodegradability and good mechanical properties, have gradually become an important alternative to traditional plastics. The application demand for biodegradable polyester is wide-ranging, and its application areas are expanding from traditional disposable products to high-value-added fields such as biomedicine and smart packaging.

[0003] Currently, the most common biodegradable polymers are aliphatic polymers, such as polylactic acid (PLA), polyhydroxyalkanoates (PHA), and polyglycolic acid (PGA). Due to the lack of rigid aromatic groups in their molecular chains, their mechanical properties are significantly insufficient. Therefore, aromatic groups have been introduced into polymers through chemical copolymerization, leading to the development of biodegradable polybutylene terephthalate (PBST). A high content of aromatic segments reduces the degradation rate of the material, while a high content of aliphatic segments leads to reduced crystallinity and weakened mechanical properties. Balancing the contradictory relationship between the biodegradability and mechanical properties of polyesters is a crucial problem that urgently needs to be solved.

[0004] In view of this, it is necessary to design a biodegradable metal-coordinated polyester composite material to solve the above problems. Summary of the Invention

[0005] In view of the technical problems existing in the background art, the purpose of the present invention is to provide a biodegradable metal-coordinated polyester composite material and its preparation method. The method uses esterification to prepare a matrix polyester and then coordinates it with metal ions, which enhances the mechanical strength of the polyester while retaining its biodegradability.

[0006] To achieve the above objectives, in a first aspect, the present invention proposes a method for preparing a biodegradable metal-coordinated polyester composite material, comprising: providing an organic ligand, wherein the organic ligand is selected from imidazole-4,5-dicarboxylic acid or transbutenedioic acid; Terephthalic acid, a dicarboxylic acid, a diol, and a catalyst are provided to undergo an esterification reaction with the organic ligand to obtain an intermediate product; The intermediate product is subjected to a polycondensation reaction to obtain the base polyester; A metal compound is mixed with the matrix polyester to initiate metal coordination, resulting in a biodegradable metal-coordinated polyester composite material; the metal coordination structure formed by the metal coordination is shown in formula (I) or formula (II): Formula (I): Formula (II): Among them, M 2+ It represents a metal ion.

[0007] Furthermore, the dicarboxylic acid is an alkyl chain dicarboxylic acid; and / or, The diol is an alkyl chain diol; and / or, The catalyst includes at least one of antimony-based catalysts, germanium-based catalysts, tin-based catalysts, and titanium-based catalysts; and / or, Metal compounds include at least one of zinc salts, cobalt salts, nickel salts, and calcium salts.

[0008] Furthermore, the molar ratio of the organic ligand, terephthalic acid, dicarboxylic acid, diol, and catalyst is 1:(0.5-2.5):(1.5-3.5):(6-12):(0.001-0.002).

[0009] Furthermore, the esterification reaction is carried out at a temperature of 160℃-200℃ for 4-5 hours.

[0010] Furthermore, the esterification reaction needs to be stirred and pressurized to 2-5 bar in an inert gas atmosphere and maintained for 10-15 minutes.

[0011] Furthermore, after the esterification reaction is pressurized, it needs to be depressurized to atmospheric pressure at a rate of 0.5 bar / h-4 bar / h, and the depressurization reaction time is 1h-2h.

[0012] Furthermore, the reaction temperature for the polycondensation reaction is 200℃-250℃, and the reaction time is 3h-4h.

[0013] Furthermore, the polycondensation reaction includes a vacuum section and a vacuum section, wherein the reaction time in the vacuum section is 2-3 hours.

[0014] Furthermore, the mixing is carried out under heating and stirring conditions for 0.5h-1h, wherein the heating temperature is 140℃-200℃.

[0015] Secondly, embodiments of this application also provide a biodegradable metal-coordinated polyester composite material, which is prepared by the above-described method for preparing biodegradable metal-coordinated polyester composite materials.

[0016] The beneficial effects of this application are as follows: Metal ions can form coordination bonds with the imidazole ring of imidazole-4,5-dicarboxylic acid and the carboxyl group of fumaric acid, linking the originally linear polymer chains to construct a dynamic network structure. By increasing the connection points between molecular chains, the polymer material's resistance to tensile or compressive forces is significantly improved. The cross-linked network restricts the relative slippage of molecular chains, making polyester materials less prone to permanent deformation under long-term static loads and enhancing their creep resistance. Metal coordination bonds can selectively break under external forces, enhancing the material's toughness through energy consumption and absorption. Metal coordination cross-linking is a physical process that maintains the chemical structure of the polyester backbone and preserves the integrity of ester bonds; therefore, degrading enzymes or water molecules can still attack the ester bonds, achieving material degradation.

[0017] The properties of metal coordination crosslinking systems are tunable. Different metal ions have varying coordination abilities and stability with organic ligands, directly affecting crosslinking strength and degradation rate. Higher density of metal-ligand crosslinking points in the system results in higher material strength and rigidity, but may correspondingly decrease the degradation rate. Specific requirements for material strength and degradation rate can be achieved by selecting different coordinating metals and setting different crosslinking densities.

[0018] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Detailed Implementation

[0019] The following embodiments are only used to illustrate the technical solutions of this application more clearly, and are therefore only examples and should not be used to limit the scope of protection of this application.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion.

[0021] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0022] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0023] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0024] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0025] In the description of the embodiments of this application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the embodiments of this application.

[0026] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0027] To meet environmental protection demands, biodegradable polyesters, due to their excellent biocompatibility and degradability, have expanded from single-use products to high-value-added fields. Despite their promising prospects, their insufficient mechanical strength still limits their practical applications. To meet the needs of a wide range of applications, enhancing the mechanical properties of biodegradable polyester materials has become a key step in their processing.

[0028] Current technologies for enhancing the mechanical properties of biodegradable polyesters primarily employ chemical copolymerization, which involves introducing rigid monomers to alter the polymer's molecular chain structure. For example, introducing aromatic groups into polymers has led to the development of biodegradable polybutylene terephthalate (PBST). However, the sequence distribution of comonomers and the ratio of hydrophilic to hydrophobic segments can affect hydrolysis or enzymatic degradation sites, potentially impacting degradation performance. While simple physical blending methods, such as adding nanofillers, can improve material strength, this is economical and convenient. However, poor material compatibility can result in weak interfacial bonding, potentially reducing impact or tensile strength. Furthermore, added nanofillers or small-molecule plasticizers may migrate to the surface during storage or use, affecting the material's appearance and degradation performance.

[0029] To address the aforementioned technical problems, in a first aspect, embodiments of this application provide a biodegradable metal-coordinated polyester composite material and its preparation method, thereby resolving the above-mentioned issues.

[0030] This invention proposes a method for preparing a biodegradable metal-coordinated polyester composite material, comprising: An organic ligand is provided, wherein the organic ligand is selected from imidazole-4,5-dicarboxylic acid or fumaric acid; Terephthalic acid, a dicarboxylic acid, a diol, and a catalyst are provided to undergo an esterification reaction with the organic ligand to obtain an intermediate product; The intermediate product is subjected to a polycondensation reaction to obtain the base polyester; A metal compound is mixed with the matrix polyester to initiate metal coordination, resulting in a biodegradable metal-coordinated polyester composite material; the metal coordination structure formed by the metal coordination is shown in formula (I) or formula (II): Formula (I): Formula (II): Among them, M 2+ It represents a metal ion.

[0031] In the technical solution of this application, the organic ligand imidazole-4,5-dicarboxylic acid or fumaric acid, due to their two carboxyl groups, participates in esterification and polycondensation reactions, copolymerizing the nitrogen atom or carbonyl oxygen atom of the imidazole ring capable of metal coordination onto the polyester polymer chain, thus forming a stable foundation for subsequent metal coordination. By controlling the balanced ratio of the organic ligand, rigid terephthalic acid, and diacid, a balance between mechanical strength and biodegradability is achieved. Furthermore, by optimizing the conditions of the esterification and polycondensation reactions, the growth of the polyester molecular chain is promoted. Finally, a suitable metal ion is selected and mixed with the matrix polyester and heated to form a metal-coordinated crosslinked network, which improves the mechanical strength of the material while maintaining its biodegradability.

[0032] It can be noted that an organic ligand is provided, selected from imidazole-4,5-dicarboxylic acid or fumaric acid. The two carboxyl groups and two nitrogen atoms on the imidazole ring in the imidazole-4,5-dicarboxylic acid molecule can all donate lone pairs of electrons, and the abundant coordination sites enhance the ligand's coordination ability. Its structural framework has a certain rigidity, which is conducive to forming a well-structured crystalline network. The two carboxyl groups of fumaric acid are located on opposite sides of the double bond, and its symmetrical molecular structure and simple configuration make it an excellent rigid bridging ligand. This structure enables it to firmly bridge and crosslink, constructing a multidimensional framework structure.

[0033] It can be explained that terephthalic acid, a diacid, a diol, and a catalyst are provided to undergo an esterification reaction with the organic ligand, yielding an intermediate product. Terephthalic acid provides two carboxyl groups, which undergo esterification with the hydroxyl groups of the diol to form ester bonds and participate in chain growth. Its benzene ring is a planar rigid group that restricts free rotation; after embedding into the polyester backbone, it restricts the movement of the molecular chain, enhancing chain segment rigidity and creep resistance. Diacids and diols are the basic monomers for synthesizing polyesters. Diacids provide carboxyl groups, and diols provide hydroxyl groups. They are alternately linked through repeated esterification reactions, forming the backbone of the polyester molecular chain and jointly determining the final properties of the polymer. The core role of the catalyst is to increase the reaction rate and molecular weight, enabling the polycondensation reaction to proceed effectively even under conditions of high viscosity and low end-group concentration in the later stages. The purpose of the esterification reaction is to achieve prepolymerization of the diacid and diol through the formation of ester bonds, generating oligomers.

[0034] It can be explained that the intermediate product undergoes a polycondensation reaction to obtain the base polyester. Esterification and polycondensation are chemically similar, both involving the formation of ester bonds, but they have different requirements for reaction conditions. The intermediate product obtained from the initial esterification reaction is an oligomer melt. As the molecular chain grows, the viscosity of the system increases sharply, and the carboxyl and hydroxyl groups are encapsulated in the viscous oligomer melt, making diffusion and collision difficult. Therefore, the rate of ester bond formation is very slow, requiring adjustments to the reaction conditions to promote the effective progress of the polycondensation reaction.

[0035] It can be explained that by mixing a metal compound with the matrix polyester, metal coordination is initiated, resulting in a biodegradable metal-coordinated polyester composite material. The metal ions in the metal compound coordinate with the functional structures in the side groups of the matrix polyester, allowing the metal ions to connect different polymer chains and form a stable three-dimensional network structure. The entangled polymer molecular chains enhance the overall mechanical strength of the material. Formula (I) represents the coordination structure of imidazole-4,5-dicarboxylic acid with metal ions. The two carbonyl oxygen atoms in the imidazole-4,5-dicarboxylic acid molecule and the two nitrogen atoms on the imidazole ring can both undergo metal coordination with the selected metal ions, forming a structurally stable cyclic structure. Formula (II) represents the coordination structure of fumaric acid with metal ions. The carbonyl oxygen atom undergoes metal coordination with the selected metal ion, acting as a bridging ligand to connect two metal ions and form a layered structure.

[0036] In some embodiments, the dicarboxylic acid is an alkyl-chain dicarboxylic acid.

[0037] In this embodiment, the selected diacid is an alkyl-chain diacid, such as succinic acid or adipic acid. The flexible alkyl chain imparts bendability to the polymer backbone. By changing its carbon chain length, the flexibility and network structure of the polymer backbone can be precisely controlled at the molecular level. As the alkyl chain length increases, the lipophilicity of the diacid increases. In polycondensation reactions, alkyl-chain diacids have better compatibility with the polymer melt, are easier to disperse uniformly, and participate in the reaction efficiently. Alkyl-chain diacids generally remain stable at high temperatures, adapting to the high-temperature reaction conditions of polymerization. Compared to rigid aromatic diacids, flexible alkyl chains can effectively reduce the overall crystallinity of the polyester, preventing the material from becoming too brittle, thereby obtaining flexible, transparent, or amorphous products.

[0038] Shorter alkyl chains result in a greater number of ester bonds that can be formed per unit mass, leading to more potential hydrolysis sites and faster degradation. Furthermore, short-chain diacid polyesters exhibit higher hydrophilicity, and their high water absorption rate further accelerates degradation. Conversely, longer alkyl chains are more hydrophobic, making it difficult for water molecules to penetrate and significantly slowing down degradation. On the other hand, short-chain polyester molecules are more regular and prone to crystallization. High crystallinity hinders water molecule diffusion and protects ester bonds in amorphous regions, thus reducing the degradation rate. Therefore, the degradation rate is not simply a monotonic change with chain length, but rather a result of the combined effects of hydrophilicity and crystallinity. Tensile strength typically decreases with increasing chain length. Short-chain polyesters are more rigid and have stronger interchain forces; long-chain polyesters have lower strength. Therefore, considering both degradation rate and mechanical strength, diacids with a carbon number in the C4-C6 range are superior, such as succinic acid and adipic acid.

[0039] In some embodiments, the diol is an alkyl chain diol.

[0040] In this embodiment, the selected diol is an alkyl chain diol, such as ethylene glycol, propylene glycol, and butanediol. In the polyester backbone, rigid cyclic structural units (such as aromatic rings) provide the core framework for the regular arrangement and close packing of chain segments, laying the foundation for the material's high crystallinity and high strength. Based on this, alkyl chain diols are introduced as compliant connecting units; their simple linear methylene structure helps regulate the packing density of the molecular chains. By balancing rigidity and flexibility, the material's mechanical strength can be maintained while imparting necessary processing flexibility. Furthermore, the ester bonds in the backbone can break under specific conditions (such as degrading enzymes or water molecules), giving the material degradability. Generally, longer carbon chains of alkyl diols impart better flexibility to the material, but excessive length leads to a decrease in strength; and during high-temperature polycondensation, longer-chain alkyl diols are prone to cyclization side reactions, disrupting chain regularity. Therefore, in order to balance excellent mechanical strength, thermal properties and controllable degradation rate, C2-C4 short-chain alkyl diols (such as ethylene glycol and 1,4-butanediol) that are not prone to cyclization side reactions are usually preferred during synthesis.

[0041] In some embodiments, the catalyst includes at least one of antimony-based catalysts, germanium-based catalysts, tin-based catalysts, and titanium-based catalysts.

[0042] In this embodiment, the catalyst includes at least one of antimony-based, germanium-based, tin-based, and titanium-based catalysts. Metal-based catalysts exhibit high activity, requiring only trace amounts for efficient catalysis and possessing good thermal stability, making them suitable for the temperature environment of polycondensation reactions. Antimony-based catalysts are widely used in polyester industrial production, achieving a balance between catalytic activity, side reaction control, and cost, effectively promoting polycondensation reactions without excessively catalyzing thermal degradation. Germanium-based catalysts produce products with good color, induce fewer side reactions, and positively impact the heat resistance of the product, making them suitable for producing high-quality, high-value-added polyesters. Tin-based catalysts exhibit high catalytic activity, significantly shortening reaction time and reducing energy consumption, while also producing products with good color. Titanium-based catalysts are abundant in resources, non-toxic, and environmentally friendly, and due to their extremely high catalytic activity, require very small quantities.

[0043] In some embodiments, the metal compound includes at least one of zinc salt, cobalt salt, nickel salt, and calcium salt.

[0044] In this embodiment, the metal compound includes at least one of zinc, cobalt, nickel, and calcium salts. Zinc, cobalt, nickel, and calcium ions have empty valence electron orbitals and act as electron docking acceptors. They tend to accept lone pairs of electrons from ligands to form coordinate bonds, thereby lowering the system energy and achieving a more stable state; their common coordination numbers are between 4 and 6. They can coordinate with the two nitrogen atoms and two oxygen atoms in imidazole to form stable complexes. Fumaric acid has a carboxyl group at each end; after esterification, it loses its hydroxyl group and forms an ester bond with an alcohol. Both oxygen atoms in this ester have lone pairs of electrons, which can serve as coordination sites. This bidentate ligand can bridge two metal ions, facilitating the construction of diverse coordination polymer networks.

[0045] In some embodiments, the molar ratio of the organic ligand, terephthalic acid, dicarboxylic acid, diol, and catalyst is 1:(0.5-2.5):(1.5-3.5):(6-12):(0.001-0.002).

[0046] In this embodiment, the molar ratio of organic ligand, terephthalic acid, diacid, diol, and catalyst is 1:(0.5-2.5):(1.5-3.5):(6-12):(0.001-0.002). The organic ligand, along with terephthalic acid and the diacid, acts as the acid component, undergoing esterification and polycondensation reactions with excess diol. The difference in the ratio of diol to acid components lies in the fact that increasing the concentration of diol can shift the esterification reaction towards polymer formation. Excess alcohol can also act as a solvent in the early stages of the reaction, promoting uniform mixing of the system. The metal-coordinated organic ligand and the rigid benzene ring structure of terephthalic acid together constitute the material's framework, providing high strength and high modulus. The aliphatic chain of the diacid provides necessary flexibility and biodegradability. The balanced ratio of the rigid organic ligand and terephthalic acid to the biodegradable diacid allows for a balanced control of the material's mechanical strength and biodegradability. The catalyst is used in very small amounts. It does not participate as a reactant, but promotes the esterification reaction through dynamic coordination and dissociation equilibrium. Using too much catalyst will hinder the reaction.

[0047] In some embodiments, the esterification reaction is carried out at a temperature of 160°C-200°C for 4-5 hours.

[0048] In this embodiment, the esterification reaction temperature is 160℃-200℃. On the one hand, a temperature above 160℃ allows the reaction mixture to form a uniform molten state, ensuring uniform mass transfer and thus improving the overall reaction efficiency. On the other hand, since the boiling points of commonly used diols are mostly between 190℃ and 230℃, controlling the temperature below 200℃ can effectively suppress the volatilization loss of the diol and its own cyclization and etherification side reactions, maintaining the initial balance of the alcohol and acid ratios and ensuring the smooth progress of the esterification reaction. In addition, the overall reaction time of 4h-5h can achieve a relatively uniform initial linking of rigid diacids (such as terephthalic acid) and flexible diols in the molecular chain segments, reducing the risk of excessive local viscosity, and can also reduce thermal oxidative degradation and side reactions caused by overheating, laying a good foundation for obtaining polyesters with regular structure and stable performance.

[0049] In some embodiments, the esterification reaction is stirred and pressurized to 2-5 bar under an inert atmosphere and held for 10-15 minutes.

[0050] In this embodiment, the boiling point of the diol is between 190°C and 230°C. Applying pressure can raise its boiling point, maintaining the diol in a liquid state within the reaction temperature range. Short-duration high-pressure (10-15 minutes) promotes surface softening and swelling of the solid reactants, ensuring uniform suspension and dispersion within the diol, forming a paste or slurry. At high temperatures (160°C-200°C), if residual air is present in the reaction environment, the terminal hydroxyl groups of the diol are easily oxidized to aldehydes and carboxylic acids, resulting in a yellowish final product. An inert gas can protect the hydroxyl groups and reduce the degree of oxidation.

[0051] It should be noted that an inert atmosphere refers to a gas that does not react chemically with the intermediate product, such as nitrogen, helium, neon, and argon.

[0052] In some embodiments, after the esterification reaction is pressurized, it needs to be depressurized to atmospheric pressure at a rate of 0.5 bar / h-4 bar / h, and the depressurization reaction time is 1h-2h.

[0053] In this embodiment, the water generated during the esterification reaction needs to be drained promptly to promote the forward esterification reaction. Slowly reducing the pressure at a rate of 0.5 bar / h to 4 bar / h helps maintain the stability of the reactants and reduces the possibility of explosive boiling. The required depressurization reaction time at this rate is 1-2 hours.

[0054] In some embodiments, the reaction temperature of the polycondensation reaction is 200℃-250℃, and the reaction time is 3h-4h.

[0055] In this embodiment, the reaction temperature for the polycondensation reaction is 200℃-250℃. After the esterification reaction, the intermediate product in the system is a high-viscosity oligomer melt, and the movement and binding ability of end groups such as carboxyl and hydroxyl groups are limited. Effective reaction of the end groups of oligomer segments requires higher thermal kinetic energy than in the esterification stage. Within the temperature range of 200℃-250℃, polymer molecular chains can move normally, accelerating the reaction rate and allowing for normal molecular weight growth. Within this temperature range, the ester bonds of polyester segments remain stable, and the etherification side reaction is controllable.

[0056] In some embodiments, the polycondensation reaction includes a vacuum section and a vacuum section, wherein the reaction time in the vacuum section is 2-3 hours.

[0057] In this embodiment, the polycondensation reaction includes a vacuum section and a vacuum section. The vacuum section lasts for 1 hour. At the end of the esterification reaction, the system contains a large amount of unreacted free diol, low molecular weight prepolymer, and residual water. Slow vacuuming allows the residual water molecules to escape gently and safely. Polycondensation is a reversible equilibrium reaction. Under vacuum, the concentration of small byproduct molecules drops to extremely low levels, strongly pushing the chemical equilibrium towards higher molecular weights, effectively promoting molecular weight growth and improving the mechanical strength of the polymer. A polycondensation reaction time of 2-3 hours can form a high-polymerization-degree-of-polymerization matrix polyester while reducing the impact of thermal degradation.

[0058] In some embodiments, the mixing is carried out under heating and stirring conditions for 0.5h-1h, wherein the heating temperature is 140℃-200℃.

[0059] In this embodiment, the mixing and heating temperature is 140℃-200℃. At 140℃-200℃, the base polyester is a fluid, viscous liquid, exposing the lone pairs of electrons on the ester groups or imidazole rings, allowing the empty orbitals of the metal ions to coordinate with them. At 140℃-200℃, the coordination bonds between the metal ions and the carbonyl oxygen of the ester are in a reversible equilibrium of binding and dissociation. This facilitates the formation of low-energy, stable coordination structures by the metal ions, resulting in a uniform and robust physical cross-linked network. With a stirring time of 0.5h-1h, the metal ions not only achieve physical homogeneity but also migrate at the microscale to the coordination sites of the polyester chains, forming a coordination network structure of moderate density.

[0060] Secondly, embodiments of this application also provide a biodegradable metal-coordinated polyester composite material, which is prepared by the above-described method for preparing biodegradable metal-coordinated polyester composite materials.

[0061] It is understood that the biodegradable metal-coordinated polyester composite material has all the beneficial effects of all the above-mentioned preparation methods of biodegradable metal-coordinated polyester composite materials, which will not be elaborated here.

[0062] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0063] I. Preparation Method Example 1 1 mol of imidazole-4,5-dicarboxylic acid, terephthalic acid, succinic acid, butanediol, and the catalyst isopropyl titanate in a molar ratio (1:1:3.5:12:0.001) was added to a 500 ml reactor.

[0064] The mixture was purged with nitrogen three times, and stirred thoroughly under a nitrogen atmosphere. It was then heated to 180°C, and heating continued until the pressure inside the reactor reached 3.5 bar. After maintaining this temperature for 10 minutes, the pressure relief valve was opened, and the pressure was reduced to atmospheric pressure for 1 hour. The total time for all stages of the esterification reaction was 4 hours, yielding the esterified product.

[0065] The reactor was evacuated, and then polycondensation was carried out at 220°C under vacuum for 2.5 hours. The total time for each stage of the polycondensation reaction was 3.5 hours, and the reaction yielded polybutylene terephthalate-co-imidazolium-4,5-dicarboxylic acid-co-butylene succinate.

[0066] 1 mol of calcium acetate was added to a sealed reactor and heated and mixed at 200°C for 0.5 h. After cooling, a biodegradable metal-coordinated polyester composite material was obtained.

[0067] Examples 2-6 and Comparative Example 1 Examples 2-6 and Comparative Example 1 respectively provide a method for preparing a biodegradable metal-coordinated polyester composite material. Compared with Example 1, the only difference is the change in the molar ratio of imidazole-4,5-dicarboxylic acid, terephthalic acid, succinic acid, butanediol, and the catalyst isopropyl titanate. The remaining steps are the same as in Example 1 and will not be repeated here. The specific molar ratios of imidazole-4,5-dicarboxylic acid, terephthalic acid, succinic acid, butanediol, and the catalyst isopropyl titanate in Examples 2-6 and Comparative Examples 1-2 are shown in Table 1.

[0068] Table 1 Example 7 Example 7 provides a method for preparing a biodegradable metal-coordinated polyester composite material. Compared with Example 1, the only difference is the choice of organic ligand, which is replaced by imidazole-4,5-dicarboxylic acid with fumaric acid. The molar ratio of fumaric acid, terephthalic acid, succinic acid, butanediol and the catalyst isopropyl titanate is kept at 1:1:3.5:12:0.001. The remaining steps are the same as in Example 1 and will not be repeated here.

[0069] Examples 8-9 and Comparative Examples 2-3 Examples 8-9 and Comparative Examples 2-3 provide a method for preparing a biodegradable metal-coordinated polyester composite material. Compared with Example 1, the only difference is the change in the esterification reaction temperature and the esterification reaction depressurization time. The remaining steps are the same as in Example 1 and will not be repeated here. The esterification reaction temperature and esterification reaction depressurization time in Examples 8-9 and Comparative Examples 2-3 are shown in Table 2.

[0070] Table 2 Examples 10-11 and Comparative Examples 4-5 Examples 10-11 and Comparative Examples 4-5 provide a method for preparing a biodegradable metal-coordinated polyester composite material. Compared with Example 1, the only difference is the change in the temperature of the polycondensation reaction and the reaction time in the vacuum section of the polycondensation reaction. The remaining steps are the same as in Example 1 and will not be repeated here. The temperature of the polycondensation reaction and the reaction time in the vacuum section of the polycondensation reaction in Examples 10-11 and Comparative Examples 4-5 are shown in Table 3.

[0071] Table 3 Examples 12-13 and Comparative Examples 6-7 Examples 12-13 and Comparative Examples 6-7 provide a method for preparing a biodegradable metal-coordinated polyester composite material. Compared with Example 1, the only difference is the change in the temperature and time of metal coordination mixing; the remaining steps are the same as in Example 1 and will not be repeated here. The temperature and time of metal coordination mixing in Examples 12-13 and Comparative Examples 6-7 are shown in Table 4.

[0072] Table 4 Examples 14-17 Examples 14-17 provide a method for preparing a biodegradable metal-coordinated polyester composite material. Compared with Example 1, the only difference is the selection of the metal compound; the remaining steps are the same as in Example 1 and will not be repeated here. The selection of the metal compound in Examples 14-17 is shown in Table 5.

[0073] Table 5 Comparative Example 8 Comparative Example 8 provides a method for preparing a biodegradable metal-coordinated polyester composite material. Compared with Example 1, the only difference is that the organic ligand imidazole-4,5-dicarboxylic acid is not added. The remaining steps are the same as in Example 1 and will not be repeated here.

[0074] Comparative Example 9 Comparative Example 9 provides a method for preparing a biodegradable metal-coordinated polyester composite material. Compared with Example 1, the only difference is that the metal compound calcium acetate is added before the start of the esterification reaction. Calcium acetate is mixed with imidazole-4,5-dicarboxylic acid, terephthalic acid, succinic acid, butanediol, and the catalyst isopropyl titanate in a reaction vessel before the esterification reaction. Calcium acetate is not added in subsequent steps. The remaining steps are the same as in Example 1 and will not be repeated here.

[0075] II. Testing Methods 1. Viscosity tests were conducted on the biodegradable metal-coordinated polyester composite material, and the viscosity values ​​were measured.

[0076] The specific testing process for intrinsic viscosity is as follows: (1) Accurately weigh 125 mg of the biodegradable metal-coordinated polyester composite material using a balance and place it in a dissolution bottle. Add 25 mL of mixed solvent using a pipette. Place the dissolution container in a sealed heating and stirring vessel at 110 °C for 30 min until completely dissolved into a transparent liquid.

[0077] (2) Cool the dissolved solution to room temperature, filter it through a G4 sintered glass funnel, and then inject it into the Ubbelohde viscometer. Fix the viscometer vertically in a constant temperature water bath at 25°C and let it stand at a constant temperature for 20 minutes to ensure that the internal and external temperatures are consistent and to eliminate thermal history.

[0078] (3) Use a syringe bulb to draw the liquid over the upper graduation line, and after releasing it, accurately record the outflow time t from the upper graduation line to the lower graduation line. Repeat steps (2) and (3) with pure solvent to determine the blank outflow time t0 of the pure solvent.

[0079] (4) Substitute the measured time and known concentration into the formula to calculate the intrinsic viscosity η: Where t: outflow time of the polymer solution (measured using an Ubbelohde viscometer, unit: / s) t0: Effluent time of pure solvent (unit: / s) C: Concentration of the polymer solution (common unit is g / dL) 2. The above-mentioned biodegradable metal-coordinated polyester composite material was hot-pressed into dumbbell-shaped specimens and subjected to tensile testing.

[0080] The tensile test process is as follows: (1) Turn on the tensile testing machine and extensometer, and zero the force and deformation under no-load conditions.

[0081] (2) Place the specimen vertically into the upper and lower clamps of the tensile testing machine. Hold the middle of the specimen with your hand to ensure that the axis of the specimen is completely aligned with the direction of the force applied by the tensile testing machine. Then clamp the upper clamp first, and then straighten and clamp the lower clamp.

[0082] (3) Secure the two ends of the parallel section gauge length of the specimen. If it is a contact extensometer, it should be removed in time before the specimen breaks to prevent it from being thrown away and damaged.

[0083] (4) Click “Start” in the control software. The crossbeam will separate at a set speed and the spline will be stretched continuously.

[0084] (5) When the spline breaks, the tensile testing machine will automatically stop or continue running for a short distance after the break. The software will automatically generate a stress-strain curve. Record the yield strength, maximum tensile strength, elongation at break, and elastic modulus.

[0085] 3. Composting biodegradation rate: The above-mentioned biodegradable metal-coordinated polyester composite material was tested for composting biodegradation rate.

[0086] The biodegradation rate testing process for composting is as follows: The above-mentioned biodegradable metal-coordinated polyester composite material was pulverized using a cryogenic pulverizer and passed through a 2 mm standard sieve to obtain powder with a particle size of less than 2 mm. According to GB / T 19277.1-2011, the total organic carbon content of the samples was determined using a total organic carbon analyzer with high-temperature catalytic combustion. Each sample was tested three times, and the average value was taken.

[0087] III. Analysis of Test Results for Each Embodiment and Comparative Example Table 6 shows the test results of mechanical properties and biodegradability of Examples 1-17 and Comparative Examples 1-9. The biodegradable metal-coordinated polyester composites prepared in Examples 1-17 all exhibited better mechanical strength than those in Comparative Examples 1-9, and their biodegradability remained at a good level.

[0088] In Examples 1, 2-3, and Comparative Example 1, the molar ratio of imidazole-4,5-dicarboxylic acid to terephthalic acid was adjusted. When the molar ratio of imidazole-4,5-dicarboxylic acid, succinic acid, butanediol, and isopropyl titanate remained consistent, appropriately increasing the proportion of terephthalic acid was beneficial to improving the viscosity and tensile strength of the metal-coordinated polyester composite material. Although the biodegradability was slightly reduced, it was still at a good level. When the molar ratio of terephthalic acid, succinic acid, butanediol, and isopropyl titanate remained consistent, significantly reducing the proportion of imidazole-4,5-dicarboxylic acid would lead to a significant decrease in the tensile strength of the metal-coordinated polyester composite material.

[0089] In Examples 1 and 4-6, the molar ratios of imidazole-4,5-dicarboxylic acid, succinic acid, butanediol, and the catalyst isopropyl titanate were adjusted, and the resulting metal-coordinated polyester composite materials all exhibited good mechanical properties and biodegradability.

[0090] In Examples 1 and 7, the choice of organic ligand was adjusted; imidazole-4,5-dicarboxylic acid was replaced with fumaric acid. The viscosity and tensile strength of the metal-coordinated polyester composite material decreased slightly, while its biodegradability remained at a good level. Imidazole-4,5-dicarboxylic acid has chelating ability and can form more metal coordination sites than fumaric acid, resulting in stronger binding forces. Therefore, the metal-coordinated polyester composite material prepared from imidazole-4,5-dicarboxylic acid has higher viscosity and better tensile strength.

[0091] In Examples 1, 8-9, and Comparative Examples 2-3, the esterification reaction temperature and depressurization time were adjusted. When the esterification reaction temperature was below 200℃ and the depressurization time was below 2 hours, the viscosity and tensile strength of the obtained metal-coordinated polyester composite material increased to some extent with the increase of esterification reaction temperature and depressurization time, while maintaining a good level of biodegradability. However, an esterification reaction temperature above 200℃ may cause thermal decomposition of ester bonds at high temperatures; a depressurization time greater than 2 hours may cause hydrolytic breakage of ester bonds, thereby reducing the molecular weight and leading to a decrease in the viscosity and tensile strength of the biodegradable metal-coordinated polyester composite material.

[0092] In Examples 1, 10-11, and Comparative Examples 4-5, the temperature and vacuum reaction time of the polycondensation reaction were adjusted. When the polycondensation temperature was below 250°C and the vacuum reaction time was below 3 hours, the viscosity and tensile strength of the obtained metal-coordinated polyester composite material increased to some extent with the increase of both the temperature and the vacuum reaction time, while maintaining a good level of biodegradability. However, a polycondensation temperature above 250°C may cause thermal degradation and breakage of the main chain ester bonds, generating oligomers; a polycondensation reaction time greater than 3 hours may cause the molecular weight of the polycondensation reaction to tend to stabilize, and may even induce degradation, thereby leading to a decrease in the viscosity and tensile strength of the biodegradable metal-coordinated polyester composite material.

[0093] In Examples 1, 12-13, and Comparative Examples 6-7, the temperature and time of metal coordination were adjusted. When the temperature of metal coordination was 200°C and the time was within 1 hour, the viscosity and tensile strength of the metal-coordinated polyester composite increased with increasing temperature and time, while maintaining a good level of biodegradability. Temperatures above 200°C may cause dissociation of coordination bonds, leading to a reduction in crosslinking points in the molecular chains of the metal-coordinated polyester composite. A time exceeding 1 hour may cause stress relaxation at the crosslinking points, resulting in network structure collapse and a decrease in the viscosity and tensile strength of the biodegradable metal-coordinated polyester composite.

[0094] In Examples 1 and 14-17, the selection of metal compounds was adjusted, and the resulting metal-coordinated polyester composite materials all exhibited good mechanical properties and biodegradability.

[0095] Compared to Example 1, Comparative Example 8 did not add organic ligands, thus eliminating metal coordination. As a result, the tensile strength of the resulting polyester material decreased significantly, while its biodegradability remained at the same level as that of the metal-coordinated polyester composite material.

[0096] Compared to Example 1, Comparative Example 9 added a metal compound before the esterification reaction began, and crosslinking occurred before the polyester was formed. This increased the steric hindrance of the esterification reaction, which may have inhibited the formation of the prepolymer, resulting in a decrease in the molecular weight, viscosity, and tensile strength of the biodegradable metal-coordinated polyester composite material.

[0097] Therefore, the method for preparing biodegradable metal-coordinated polyester composite materials of the present invention involves metal coordination between metal ions and organic ligands. By controlling the molar ratio of organic ligands to terephthalic acid, diacid, diol, and catalyst, adjusting the temperature range of metal coordination mixing and heating, selecting different metal ions for coordination, and adjusting the esterification and polymerization reaction temperatures, the tensile strength of the biodegradable metal-coordinated polyester composite material is successfully improved, while maintaining its biodegradable properties.

[0098] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing a biodegradable metal-coordinated polyester composite material, characterized in that, include; An organic ligand is provided, wherein the organic ligand is selected from imidazole-4,5-dicarboxylic acid or fumaric acid; Terephthalic acid, a dicarboxylic acid, a diol, and a catalyst are provided to undergo an esterification reaction with the organic ligand to obtain an intermediate product; The intermediate product is subjected to a polycondensation reaction to obtain the base polyester; A metal compound is mixed with the matrix polyester to initiate metal coordination, resulting in a biodegradable metal-coordinated polyester composite material; the metal coordination structure formed by the metal coordination is shown in formula (I) or formula (II): Formula (I): Formula (II): Among them, M 2+ It represents a metal ion.

2. The method for preparing the biodegradable metal-coordinated polyester composite material according to claim 1, characterized in that, The dicarboxylic acid is an alkyl chain dicarboxylic acid; and / or, The diol is an alkyl chain diol; and / or, The catalyst includes at least one of antimony-based catalysts, germanium-based catalysts, tin-based catalysts, and titanium-based catalysts; and / or, The metal compound includes at least one of zinc salt, cobalt salt, nickel salt, and calcium salt.

3. The method for preparing the biodegradable metal-coordinated polyester composite material according to claim 1, characterized in that, The molar ratio of the organic ligand, terephthalic acid, dicarboxylic acid, diol, and catalyst is 1:(0.5-2.5):(1.5-3.5):(6-12):(0.001-0.002).

4. The method for preparing the biodegradable metal-coordinated polyester composite material according to claim 1, characterized in that, The esterification reaction is carried out at a temperature of 160℃-200℃ for 4-5 hours.

5. The method for preparing the biodegradable metal-coordinated polyester composite material according to claim 4, characterized in that, The esterification reaction needs to be stirred and pressurized to 2-5 bar in an inert gas atmosphere and maintained for 10-15 minutes.

6. The method for preparing the biodegradable metal-coordinated polyester composite material according to claim 5, characterized in that, After the esterification reaction is pressurized, it needs to be depressurized to atmospheric pressure at a rate of 0.5 bar / h-4 bar / h, and the depressurization reaction time is 1h-2h.

7. The method for preparing the biodegradable metal-coordinated polyester composite material according to claim 1, characterized in that, The reaction temperature for the polycondensation reaction is 200℃-250℃, and the reaction time is 3h-4h.

8. The method for preparing the biodegradable metal-coordinated polyester composite material according to claim 7, characterized in that, The polycondensation reaction includes a vacuum section and a vacuum section, and the reaction time in the vacuum section is 2-3 hours.

9. The method for preparing the biodegradable metal-coordinated polyester composite material according to claim 1, characterized in that, The mixing is carried out under heating and stirring conditions for 0.5h-1h, and the heating temperature is 140℃-200℃.

10. A biodegradable metal-coordinated polyester composite material, characterized in that, It is prepared by the method for preparing biodegradable metal-coordinated polyester composite material according to any one of claims 1-9.

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