Hybrid filler for polylactic acid composites and method for its preparation

Abstract

The application discloses a kind of hybrid fillers for polylactic acid composite and its preparation method and application, belong to polymer composite technical field. Stick HA is synthesized using hydrothermal method, and then HA is used as carrier, and ZIF-8 is loaded on its surface by in-situ growth method, to obtain HA-ZIF-8 hybrid filler;The hybrid filler can be compounded with polylactic acid by melt blending, to prepare antibacterial toughening polylactic acid composite material.The application utilizes HA surface group to adsorb Zn 2+ , realizes ZIF-8 uniform loading, effectively inhibits nanoparticle agglomeration, improves the interface compatibility of filler and PLA matrix;Meanwhile, the HA-ZIF-8 hybrid filler has excellent pH-responsive antibacterial performance, in neutral environment, ZIF-8 slowly releases Zn 2+ , realize long-acting bacteriostasis;In slightly acidic environment, ZIF-8 occurs acidolysis and quickly releases Zn 2+ , bacteriostatic rate is fast, and bacteriostatic effect is excellent.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials technology, specifically to a hybrid filler for polylactic acid composite materials and its preparation method. Background Technology

[0002] Polylactic acid (PLA) is a biodegradable polymer material prepared from renewable resources. It possesses good biocompatibility, processability, and environmental friendliness, and is widely used in food packaging, biomedical materials, and 3D printing. However, the relatively rigidity of PLA molecular chains leads to problems such as high brittleness, poor impact resistance, and insufficient antibacterial properties, thus limiting its further application in the field of high-performance functional materials.

[0003] Currently, to improve the overall performance of PLA materials, researchers typically use inorganic nanofillers to reinforce and modify PLA. Among them, hydroxyapatite (HA) is widely used in PLA composite systems due to its good biocompatibility, mechanical reinforcing properties, and surface activity. However, HA has a highly polar surface, making it prone to aggregation, and its interfacial compatibility with the PLA matrix is ​​poor, resulting in uneven dispersion of the filler in the polymer matrix, thus affecting the mechanical properties of the composite material.

[0004] In recent years, metal-organic frameworks (MOFs) have attracted widespread attention due to their large specific surface area, high porosity, and tunable structure. Among them, the zeolite imidazole ester framework material ZIF-8 is particularly noteworthy for its good thermal stability, biocompatibility, and Zn content. 2+ The sustained-release antibacterial properties of ZIF-8 have shown promising application prospects in the field of antibacterial materials. Currently, studies have reported the use of ZIF-8 in antibacterial coatings or polymer composite systems. However, when ZIF-8 is directly added to the polymer matrix, it is prone to aggregation, and its interfacial bonding with the polymer is weak, affecting its reinforcing and antibacterial effects.

[0005] Therefore, how to construct a functionalized hybrid filler that combines good interfacial compatibility, antibacterial properties, and mechanical reinforcement properties, and apply it to PLA composite materials to achieve a synergistic improvement in the antibacterial properties and ductility of PLA materials, remains a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing polylactic acid (PLA) materials, such as insufficient antibacterial properties and poor interfacial compatibility between inorganic fillers and the PLA matrix. This invention provides a hybrid filler for PLA composites and its preparation method, and applies it to PLA composites. By utilizing an in-situ growth method to load ZIF-8 onto the HA surface, this invention constructs an HA-ZIF-8 hybrid filler with good dispersibility and interfacial compatibility, achieving a synergistic effect between the inorganic reinforcing phase and the antibacterial functional phase.

[0007] The technical solution provided by this invention is as follows: In a first aspect, the present invention provides a method for preparing a hybrid filler for polylactic acid composite materials, comprising the following steps: S1. Synthesis of HA Dissolve EDTA-2Na·2H2O and Ca(NO3)2·4H2O in deionized water, stir until completely clear, and adjust the pH to 12 to obtain solution A; dissolve sodium dihydrogen phosphate in deionized water to obtain solution B; Under continuous stirring, solution B was added dropwise to solution A at a uniform rate, and the pH of the system was maintained at 12 throughout the addition process. After the addition was completed, the reaction was carried out at 50-70℃. The reaction solution was then transferred to a high-pressure reactor and subjected to a hydrothermal reaction at 180-200℃. After the reaction was completed, the solution was allowed to cool naturally to room temperature. After centrifugation, washing, and drying, rod-shaped HA powder was obtained. S2. Synthesis of HA-ZIF-8 hybrid filler Zn(NO3)2·6H2O and the rod-shaped HA powder prepared in step S1 were dissolved in anhydrous methanol to obtain solution C; 2-methylimidazole was dissolved in anhydrous methanol to obtain solution D; Solution D was added to solution C and reacted at 60-80℃. After the reaction was completed, the mixture was naturally cooled to room temperature, washed, allowed to stand and separate into layers, and the precipitate was dried to obtain HA-ZIF-8 hybrid filler.

[0008] Furthermore, in step S1, the pH of the system is maintained at 12 using sodium hydroxide solution.

[0009] Furthermore, in step S1, the molar ratio of EDTA-2Na·2H2O and Ca(NO3)2·4H2O is 1:(0.5-1.5), and the concentration of solution B is (0.09-0.10) mol / L.

[0010] Furthermore, after adding solution B dropwise to solution A, the mixture was stirred at 60°C for 30 minutes.

[0011] Furthermore, in step S1, the hydrothermal reaction temperature is 190°C and the reaction time is 5 hours.

[0012] Furthermore, in step S2, the mass ratio of Zn(NO3)2·6H2O to rod-shaped HA powder is (0.5-1):1,2-methylimidazolium to anhydrous methanol is (0.12-0.14) g / mL.

[0013] Furthermore, the reaction temperature in step S2 is 70°C, and the reaction time is 15 min.

[0014] In a second aspect, the present invention provides a hybrid filler for polylactic acid composite materials, which is prepared by a method for preparing a hybrid filler for polylactic acid composite materials as described in any of the preceding claims.

[0015] Thirdly, the present invention provides an antibacterial and toughened polylactic acid composite material, wherein the antibacterial and toughened polylactic acid composite material comprises polylactic acid and HA-ZIF-8 hybrid filler.

[0016] Furthermore, the preparation method of the antibacterial and toughened polylactic acid composite material involves mixing HA-ZIF-8 hybrid filler with polylactic acid using a melt blending method.

[0017] Fourthly, the present invention provides the application of the hybrid filler for polylactic acid composite materials as described above in the preparation of antimicrobial food packaging materials, biomedical materials or biodegradable functional materials.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention uses an in-situ growth method to uniformly load ZIF-8 onto the surface of rod-shaped HA, forming an HA-ZIF-8 hybrid structure. This structure not only preserves the crystal integrity of HA but also significantly inhibits the aggregation of ZIF-8 nanoparticles, improving the dispersion stability of the filler in the polymer matrix.

[0019] 2. Rod-shaped HA has a high aspect ratio, which can effectively transfer stress, hinder crack propagation and promote energy dissipation in the PLA matrix, thereby significantly improving the strength, modulus and toughness of PLA composite materials and overcoming the problem of poor interfacial bonding between traditional inorganic fillers and PLA.

[0020] 3. This HA-ZIF-8 hybrid packing material can achieve Zn under neutral conditions. 2+ Its slow release provides long-lasting antibacterial activity; under slightly acidic conditions, ZIF-8 undergoes acid decomposition, releasing a large amount of Zn. 2+ It exhibits rapid antibacterial rate and excellent effect, demonstrating pH-responsive antibacterial properties.

[0021] 4. The HA-ZIF-8 hybrid filler prepared by this invention can be melt-blended with PLA to prepare antibacterial and toughened composite materials, which are suitable for antibacterial food packaging, biomedical materials and biodegradable functional materials, effectively broadening the application range of PLA materials in high-performance functional materials. Attached Figure Description

[0022] Figure 1 The infrared spectra of HA and HA-ZIF-8 are shown.

[0023] Figure 2 X-ray diffraction patterns of HA and HA-ZIF-8.

[0024] Figure 3 This is a transmission electron microscope image of HA.

[0025] Figure 4 This is a transmission electron microscope image of HA-ZIF-8. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. It should be noted that, unless otherwise specified, all chemical reagents involved in this invention are purchased through commercial channels.

[0027] The English abbreviation and the full Chinese name used in this invention are as follows: Polylactic acid (PLA), hydroxyapatite (HA), and zeolite imidazole ester skeleton (ZIF-8).

[0028] The antibacterial mechanism of the HA-ZIF-8 hybrid packing material prepared in this invention is as follows: HA, as a biocompatible inorganic material, can not only serve as a reinforcing phase to improve the mechanical properties of PLA composites, but also as a support for the in-situ growth of ZIF-8. The hydroxyl and phosphate groups on the HA surface can adsorb Zn. 2+ This promotes the nucleation and growth of ZIF-8 on its surface, thereby forming a uniform and stable HA-ZIF-8 hybrid structure. The rod-shaped HA has a high aspect ratio, which effectively improves stress transfer efficiency, hinders crack propagation, and promotes energy dissipation in the PLA matrix, thus enhancing the strength, modulus, and ductility of the PLA material. Furthermore, HA has a good loading effect on ZIF-8, effectively reducing the aggregation of ZIF-8 nanoparticles and improving their dispersion stability in the PLA matrix.

[0029] The antibacterial mechanism of ZIF-8 mainly comes from its release of Zn. 2+ The behavior of Zn and the synergistic antibacterial effect resulting from its nanostructure. ZIF-8 is a typical metal-organic framework material, composed of Zn... 2+ ZIF-8 forms a three-dimensional porous structure through coordination with a 2-methylimidazolium ligand. When the material is exposed to humid, weakly acidic, or bacterial environments, ZIF-8 undergoes some surface degradation, slowly releasing Zn. 2+ The released Zn 2+ Zn can interact with proteins and phospholipids on the bacterial cell membrane surface, altering cell membrane permeability, damaging the cell membrane structure, and causing leakage of intracellular ions and proteins, thereby disrupting normal bacterial physiological activities. Furthermore, Zn... 2+ It can also enter the bacterial cell and bind to the sulfhydryl (-SH) and amino (-NH2) groups in enzyme molecules, inhibiting the activity of related metabolic enzymes, interfering with the bacterial energy metabolism and DNA replication process, and ultimately leading to bacterial death.

[0030] On the other hand, ZIF-8 possesses a large specific surface area and a nanoscale porous structure, allowing for sufficient contact with bacterial cells and thus enhancing its surface contact bactericidal effect. During bacterial attachment, ZIF-8 can also induce the generation of reactive oxygen species (ROS), including hydroxyl radicals (•OH) and superoxide anions (O2). ⁻ Reactive oxygen species (ROS) such as hydrogen peroxide (H2O2) can further oxidize lipids and proteins in bacterial cell membranes and cause oxidative damage to DNA, thereby accelerating bacterial inactivation. Furthermore, due to the presence of Zn in ZIF-8... 2+ The release process of ZIF-8 exhibits certain sustained-release characteristics, and its antibacterial effect is continuous and long-lasting. After loading ZIF-8 onto the HA surface, HA can further improve the dispersion stability of ZIF-8 and slow down the degradation of Zn. 2+ The release rate is adjusted to achieve a more stable and longer-lasting antibacterial effect.

[0031] ZIF-8 exhibits a significant pH-responsive antibacterial behavior. The core reason for this is that the Zn-N coordination bonds in ZIF-8 become less stable under acidic conditions, leading to acidolysis and the release of Zn. 2+ The degradation rate of ZIF-8 and Zn under different pH conditions. 2+ The release behaviors differ significantly, resulting in substantial differences in their antibacterial properties. A pH of 7.4 is typically used to simulate the normal physiological environment of the human body, while a pH of 5.5 is often used to simulate the slightly acidic environment formed at bacterial infection sites, inflamed areas, or after bacterial metabolism.

[0032] At pH 7.4, the overall structure of ZIF-8 is relatively stable, and the Zn-N coordination framework is not prone to rapid fracture. Therefore, Zn...2+ The release rate is low. At this point, ZIF-8 primarily exhibits a sustained-release antibacterial mechanism: a small amount of Zn is released. 2+ It slowly diffuses into the surrounding environment of bacteria, binding to proteins and phospholipids on the cell membrane, altering cell membrane permeability, and inhibiting the activity of related enzymes within the bacteria, thus achieving a sustained antibacterial effect. Simultaneously, the nanostructure on the surface of ZIF-8 allows for sufficient contact with bacteria, producing a certain contact bactericidal effect. Furthermore, due to Zn... 2+ With a slower release rate, the material exhibits better stability and lower cytotoxicity under neutral conditions, making it more suitable for long-term antimicrobial applications, such as long-lasting antimicrobial systems in biomedical materials or food packaging materials.

[0033] When the ambient pH drops to 5.5, the H in the system... + The concentration increased significantly, H + It will preferentially attack the Zn-N coordination bonds in ZIF-8, causing the 2-methylimidazolium ligand to gradually protonate, leading to coordination structure instability and acidolysis. As the ZIF-8 skeleton gradually disintegrates, a large amount of Zn... 2+ Rapid release within a short time significantly enhances antibacterial activity. This acid-responsive behavior gives ZIF-8 a "release-on-demand" characteristic in bacterial growth zones. High concentrations of Zn 2+ It quickly adheres to the surface of bacterial cells, disrupting the integrity of the cell membrane and causing leakage of cell contents; simultaneously, Zn 2+ Once inside the cell, it inhibits DNA replication and protein synthesis, ultimately leading to bacterial death. Furthermore, the Zn released during acid hydrolysis... 2+ It can also induce the generation of a large amount of reactive oxygen species, including hydroxyl radicals (•OH) and superoxide anions (O2). ⁻ These reactive oxygen species (ROS) include hydrogen peroxide (H2O2), which can oxidize lipids, proteins, and nucleic acids in bacterial cell membranes, accelerating cell inactivation. Therefore, ZIF-8 typically exhibits stronger and faster antibacterial properties at pH 5.5 than in a neutral environment.

[0034] The following are specific embodiments of the present invention. Example

[0035] A method for preparing a hybrid filler for polylactic acid composites includes the following steps: S1. Synthesis of HA Dissolve 14.9g EDTA-2Na·2H2O and 9.5g Ca(NO3)2·4H2O in 45ml of deionized water and stir until completely clear. Then adjust the pH of the system to 12 with sodium hydroxide solution to obtain solution A; separately dissolve 3.4g sodium dihydrogen phosphate in 45ml of deionized water to prepare solution B. Under continuous stirring, solution B was slowly added dropwise to solution A at a constant rate, and sodium hydroxide solution was used to maintain the pH of the reaction system at 12. After the addition was completed, the reaction was stirred at 60°C for 30 minutes to ensure that the system reacted fully and uniformly. The reaction solution was then transferred to a high-pressure reactor with a polytetrafluoroethylene liner and subjected to a hydrothermal reaction at 190°C for 5 hours. After the reaction was completed, the solution was naturally cooled to room temperature, centrifuged, washed three times with deionized water, and dried at 70°C for 6 hours to obtain rod-shaped HA powder. S2. Synthesis of HA-ZIF-8 hybrid filler 0.81 g Zn(NO3)2·6H2O and 1.024 g of rod-shaped HA powder prepared in step S1 were dissolved in 16.2 ml of anhydrous methanol to obtain solution C; 2.25 g 2-methylimidazole was dissolved in 16.2 ml of anhydrous methanol to obtain solution D; Solution D was added to solution C and reacted at 70℃ for 15 min to allow ZIF-8 to grow and load on the HA surface in situ. After the reaction was completed, the mixture was naturally cooled to room temperature, washed three times with methanol, allowed to stand, the supernatant was discarded, and dried in an oven at 70℃ for 6 h to obtain the HA-ZIF-8 hybrid filler. Example

[0036] The HA and HA-ZIF-8 prepared in Example 1 were characterized by FTIR, XRD and TEM.

[0037] Depend on Figure 1 It can be seen that HA is at 1022 cm. -1 and 568 / 603 cm -1 PO4 appears at [location]. 3- The characteristic peaks confirmed the formation of the inorganic framework of hydroxyapatite; compared with pure HA, HA-ZIF-8 showed characteristic peaks at 2927 / 2843 cm⁻¹. -1 (CH) and 1584 cm -1 A new peak appeared at (C=N), which can be attributed to ZIF-8, indicating that ZIF-8 has been successfully loaded onto the HA surface.

[0038] Depend on Figure 2 It can be seen that the diffraction peak positions of HA are highly consistent with those of the standard card (JCPDS: 96-900-2215), indicating that the prepared HA sample has good crystallinity. In the HA-ZIF-8 spectrum, the characteristic peaks of HA are still present, while strong diffraction peaks unique to ZIF-8 appear in the low-angle region (2θ < 20°), which proves that ZIF-8 has been successfully loaded onto the HA matrix and that the recombination process has not destroyed the original crystal structure of HA.

[0039] Depend on Figure 3 and Figure 4It can be seen that HA is rod-shaped, and ZIF-8 in HA-ZIF-8 is a regular hexahedron, which is uniformly loaded on the surface of HA. Example

[0040] The antibacterial properties of the HA-ZIF-8 hybrid packing material prepared in Example 1 were tested, and its antibacterial effects in neutral and slightly acidic environments were compared.

[0041] 1. Preparation of bacterial culture (1) Take 1 ml of the original bacterial culture (Staphylococcus aureus) and put it into a 5 ml centrifuge tube, and centrifuge at 4000 rpm for 5 min; (2) After centrifugation, discard the supernatant and retain the bacterial culture at the bottom; (3) Add 1 ml of sterile water to the centrifuge tube again, remove impurities, and dilute to a concentration of 10. 8 cfu / ml; (4) Transfer 1 ml of bacterial culture to 9 ml of sterile water to dilute to 10. 7 cfu / ml; (5) Dilute the bacterial solution to 10 using this method. 3 cfu / ml.

[0042] 2. Preparation of antibacterial solution (1) Preparation of MES buffer solution Dissolve 0.29 g of MES in 20 ml of sterile water, adjust the pH to 5.5 with 1 M sodium hydroxide solution, and then add water to make up to 30 ml. (2) Preparation of antibacterial stock solution Take 50 mL of sterile water, add 30 mL of MES buffer solution, test and confirm that the pH is 5.5, and then add water to make up to 100 mL. (3) Preparation of gradient antibacterial solution Take 0.2 g of HA-ZIF-8 hybrid packing material and add 10 ml of antibacterial stock solution to prepare antibacterial solution 1 with a concentration of 20 mg / ml; Take 5 mL of antibacterial solution 1 and place it in a sterile tube, then add 5 mL of antibacterial stock solution to prepare antibacterial solution 2 with a concentration of 10 mg / mL. Following the same gradient dilution method, antibacterial solutions with concentrations of 5 mg / ml (antibacterial solution 3), 2.5 mg / ml (antibacterial solution 4), 1.25 mg / ml (antibacterial solution 5), and 0.625 mg / ml (antibacterial solution 6) were prepared sequentially.

[0043] 3. Plate count antibacterial test Take a concentration of 10 3For each CFU / ml bacterial suspension, 900 μL of each concentration of inhibitory solution was mixed with 100 μL of the bacterial suspension. Two experimental environments were set up: an acidic environment with pH 5.5 and a neutral environment with pH 7.4. The mixtures were cultured under the corresponding pH conditions, spread onto culture media, and cultured for a further period. The number of colonies was observed and counted.

[0044] 4. Experimental Results Table 1 Comparison of antibacterial rates

[0045] Table 1 shows that the number of colonies in the blank control group was 110 in a neutral environment and 130 in an acidic environment. After adding HA-ZIF-8 hybrid packing material, the minimum inhibitory concentration (MIC) in the acidic environment was 5 mg / ml, at which point zinc ions were released rapidly, resulting in a fast inhibition rate and excellent antibacterial effect. In the neutral environment, the MIC was 20 mg / ml, with zinc ions released slowly, providing long-lasting antibacterial ability. This HA-ZIF-8 hybrid packing material exhibits significant pH-responsive antibacterial properties.

[0046] The present invention and its embodiments have been described above. This description is not restrictive, and the embodiments shown are only one of the embodiments of the present invention. The actual structure is not limited to this. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A method for preparing a hybrid filler for polylactic acid composite materials, characterized in that, Includes the following steps: S1. Synthesis of HA: Stir until completely clear, adjust pH to 12, and obtain solution A; Sodium dihydrogen phosphate was dissolved in deionized water to obtain solution B; Under continuous stirring, solution B was added dropwise to solution A at a uniform rate, and the pH of the system was maintained at 12 throughout the addition process. After the addition was completed, the reaction was carried out at 50-70℃. The reaction solution was then transferred to a high-pressure reactor and subjected to a hydrothermal reaction at 180-200℃. After the reaction was completed, the solution was allowed to cool naturally to room temperature. After centrifugation, washing, and drying, rod-shaped HA powder was obtained. S2. Synthesis of HA-ZIF-8 hybrid filler Zn(NO3)2·6H2O and the rod-shaped HA powder prepared in step S1 were dissolved in anhydrous methanol to obtain solution C; 2-methylimidazole was dissolved in anhydrous methanol to obtain solution D; Solution D was added to solution C and reacted at 60-80℃. After the reaction was completed, the mixture was naturally cooled to room temperature, centrifuged, washed, and dried to obtain the HA-ZIF-8 hybrid packing material.

2. The method for preparing a hybrid filler for polylactic acid composite materials according to claim 1, characterized in that, In step S1, the pH of the system is maintained at 12 using sodium hydroxide solution.

3. The method for preparing a hybrid filler for polylactic acid composite materials according to claim 1, characterized in that, In step S1, the molar ratio of EDTA-2Na·2H2O and Ca(NO3)2·4H2O is 1:(0.5-1.5), and the concentration of solution B is (0.09-0.10) mol / L.

4. The method for preparing a hybrid filler for polylactic acid composite materials according to claim 1, characterized in that, In step S1, solution B is added dropwise to solution A, and the mixture is stirred at 60°C for 30 minutes.

5. The method for preparing a hybrid filler for polylactic acid composite materials according to claim 1, characterized in that, In step S1, the hydrothermal reaction temperature is 190℃ and the reaction time is 5 hours.

6. The method for preparing a hybrid filler for polylactic acid composite materials according to claim 1, characterized in that, In step S2, the mass ratio of Zn(NO3)2·6H2O to rod-shaped HA powder is (0.5-1): the mass-volume ratio of 1,2-methylimidazole to anhydrous methanol is (0.12-0.14) g / mL.

7. The method for preparing a hybrid filler for polylactic acid composite materials according to claim 1, characterized in that, The reaction temperature in step S2 is 70℃, and the reaction time is 15 min.

8. A hybrid filler for polylactic acid composite materials, characterized in that, It is prepared by the method for preparing a hybrid filler for polylactic acid composite materials according to any one of claims 1-7.

9. An antibacterial and toughened polylactic acid composite material, characterized in that, The antibacterial and toughened polylactic acid composite material comprises polylactic acid and the hybrid filler as described in claim 8.

10. The application of the hybrid filler for polylactic acid composite materials as described in claim 8 in the preparation of antibacterial food packaging materials, biomedical materials or biodegradable functional materials.

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