Antibacterial composite resin as well as preparation method and application thereof

Abstract

The invention provides antibacterial composite resin and a preparation method and application thereof, and belongs to the technical field of composite resin.The preparation method of the antibacterial composite resin comprises the steps that lignin is dissolved in dimethyl sulfoxide, then methacrylic anhydride is added, a catalyst is added for a catalytic reaction at the first preset temperature for the first preset time, and the antibacterial composite resin is obtained; the preparation method comprises the following steps: adding methacrylic anhydride into lignin to obtain a reaction solution, partially esterifying aromatic and aliphatic hydroxyl groups of lignin by controlling the dosage of methacrylic anhydride to be 0.15-0.25 time equivalent weight of the hydroxyl content in lignin, and then carrying out impurity removal treatment on the reaction solution to obtain M-lignin (methacrylic acid lignin), then dissolving 5-20 parts by weight of M-lignin in 65-75 parts by weight of polyurethane acrylate, then adding 10-40 parts by weight of an active diluent and 0.5-2.5 parts by weight of a photoinitiator, and uniformly mixing to obtain an antibacterial composite resin precursor; and finally, carrying out photocuring molding on the antibacterial composite resin precursor to obtain the antibacterial composite resin.

Description

Technical Field

[0001] The present invention relates to the technical field of composite resins, and particularly relates to an antibacterial composite resin, a preparation method thereof, and an application thereof. Background Art

[0002] Composite resin is a composite material composed of a resin matrix and a reinforcing material. Different reinforcing materials doped in the resin matrix will endow the composite resin with different characteristics. Therefore, the application fields of composite resin products are very wide. For example, in the field of pet products, a large amount of bacterial dirt will exist on the surfaces of related composite resin products such as dog houses, cat litter boxes, and pet feeders. These bacterial dirt will not only cause bacterial infections in pets using related composite resin products but also have an adverse impact on human health;

[0003] Traditionally, in order to endow related composite resin products with antibacterial properties, manufacturing enterprises have added a large amount of antibacterial agents, such as bactericides, antibiotics, and metal nanoparticles, to prevent bacterial contamination and reduce the risk of infection. However, when the above antibacterial agents are applied to composite resin products, the following problems will occur: on the one hand, since the above antibacterial agents cannot have effective adhesion with the resin matrix, the antibacterial agents cannot maintain an effective concentration on the material surface continuously and have release properties. As time goes by, the antibacterial properties of related composite resin products will continuously decay, thereby gradually enhancing the drug resistance of bacteria. On the other hand, due to the non-degradability of the above antibacterial agents themselves, not only will the antibacterial agents cause persistent cytotoxicity to tissue cells when the related resin products are in direct contact with the skin, but also they will cause secondary pollution to the environment and hinder the growth of beneficial microorganisms. Summary of the Invention

[0004] In view of this, in order to overcome the above deficiencies, it is necessary to provide an antibacterial composite resin, a preparation method thereof, and an application thereof;

[0005] The technical solution adopted by the present invention to solve the technical problems is as follows:

[0006] In the first aspect, the present invention provides a preparation method of an antibacterial composite resin, comprising the following steps:

[0007] Step 1: Dissolve lignin in dimethyl sulfoxide, then add methacrylic anhydride, and then add a catalyst to carry out a catalytic reaction at a first preset temperature and a first preset time to obtain a reaction solution, and perform impurity removal treatment on the reaction solution to obtain M-lignin (methylacrylated lignin), wherein the dosage of methacrylic anhydride is 0.15 - 0.25 times the equivalent of the hydroxyl content in lignin;

[0008] Step 2: Dissolve 5 - 20 parts by weight of M - lignin in 65 - 75 parts by weight of polyurethane acrylate, then add 10 - 40 parts by weight of active diluent and 0.5 - 2.5 parts by weight of photoinitiator, and mix evenly to obtain an antibacterial composite resin precursor;

[0009] Step 3: Carry out photocuring molding on the antibacterial composite resin precursor to obtain an antibacterial composite resin.

[0010] Preferably, the lignin in Step 1 is obtained by the following method:

[0011] A 11 : Dissolve the lignin raw material in dimethylformamide to obtain a mixed solution A, where the ratio of the lignin raw material to dimethylformamide is 5 - 10 g: 90 - 100 mL;

[0012] A 12 : Add the mixed solution A to a methanol solution for precipitation, filter out the precipitate A, and then rinse the precipitate A with distilled water to obtain the initial lignin, where the volume ratio of the mixed solution to the methanol solution is 1:(4 - 5);

[0013] A 13 : Place the initial lignin in a vacuum environment at 35 - 45 °C and dry it to a constant weight to obtain lignin.

[0014] Preferably, Step 1 is specifically as follows:

[0015] S 11 : Put 2 - 5 g of lignin into a flask and pour 20 - 50 mL of dimethyl sulfoxide to fully dissolve the lignin to obtain a dissolved solution A;

[0016] S 12 : Add 0.29 - 1.2 mL of methacrylic anhydride to the dissolved solution A, and then add a catalyst and react in an environment with a first preset temperature of 40 - 80 °C for a first preset time of 12 - 48 hours to obtain a reaction solution.

[0017] Preferably, in Step 1, the catalyst is one or more of 4 - dimethylaminopyridine, triethylamine, diisopropylethylamine, dicyclohexylcarbodiimide, and dicyclohexylamine.

[0018] Preferably, in Step 1, the impurity removal treatment is specifically as follows: Add the reaction solution to a methanol solution for precipitation, filter out the precipitate B, wash the precipitate B with deionized water, and place it in a vacuum environment at 35 - 45 °C and dry it to a constant weight to obtain M - lignin.

[0019] Preferably, in the step 2, the reactive diluent is one or more of 4-acryloylmorpholine, 2-hydroxyethyl acrylate, 2-phenoxyethyl acrylate, tripropylene glycol diacrylate, and diethylene glycol diacrylate.

[0020] Preferably, in the step 2, the photoinitiator is one or more of 2,4,6-trimethylbenzoyl diphenylphosphine oxide, 2-hydroxy-2-methylphenylpropanone, and 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone.

[0021] Preferably, the step 2 is specifically as follows:

[0022] S 21 : Dissolve 5-20 g of M-lignin in 65-75 g of polyurethane acrylate to obtain a solution B;

[0023] S 22 : Add 10-40 g of 4-acryloylmorpholine and 0.5-2.5 g of 2,4,6-trimethylbenzoyl diphenylphosphine oxide to the solution B, mix well and remove bubbles to obtain an antibacterial composite resin precursor.

[0024] In a second aspect, the present invention provides an antibacterial composite resin prepared according to the preparation method described in the first aspect.

[0025] In a third aspect, the present invention provides an antibacterial composite resin obtained according to the preparation method described in the first aspect and applied to photocuring 3D printing.

[0026] As can be seen from the above technical solutions, for a preparation method of an antibacterial composite resin provided by the present invention, first, lignin is dissolved in dimethyl sulfoxide, then methacrylic anhydride is added, and then a catalyst is added to carry out a catalytic reaction at a first preset temperature and a first preset time to obtain a reaction solution. On the one hand, methacrylic anhydride can replace the hydroxyl groups of the lignin macromolecule with methacrylate groups for chemical modification, ensuring that when photocuring molding is carried out subsequently, the modified lignin can form a large number of stable and strong covalent bonds with other components in the entire crosslinking network, thereby improving the adhesion of lignin and the mechanical properties of the overall composite resin. On the other hand, by controlling the dosage of methacrylic anhydride to be 0.15 - 0.25 times the equivalent of the hydroxyl group content in lignin, partial esterification of the aromatic hydroxyl group and aliphatic hydroxyl group of lignin occurs, so as to retain part of the phenolic hydroxyl group of lignin to achieve the inherent antibacterial property and high biocompatibility of lignin. Subsequently, the reaction solution is subjected to impurity removal treatment to obtain M-lignin (methacrylated lignin). Then, 5 - 20 parts by weight of M-lignin is dissolved in 65 - 75 parts by weight of polyurethane acrylate, and then 10 - 40 parts by weight of an active diluent and 0.5 - 2.5 parts by weight of a photoinitiator are added and mixed evenly to obtain an antibacterial composite resin precursor. Among them, the methacrylate functional group in M-lignin ensures its good compatibility in polyurethane acrylate, and further makes the properties of the composite resin after photocuring molding uniform and consistent. Finally, the antibacterial composite resin precursor is subjected to photocuring molding to obtain an antibacterial composite resin that has persistent antibacterial property and high biocompatibility without adding antibacterial agents. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a flowchart of a preparation method of an antibacterial composite resin provided by an embodiment of the present invention.

[0028] Figure 2 It is a process diagram of the lignin catalytic reaction in the present invention.

[0029] Figure 3 It is a diagram of the chemical structure detection results of lignin and methacrylated lignin in the present invention.

[0030] Figure 4 It is a diagram of the antibacterial property detection results of the antibacterial composite resin of the present invention.

[0031] Figure 5 It is a diagram of the biocompatibility detection results of the antibacterial composite resin of the present invention.

[0032] Figure 6 It is a diagram of the mechanical property detection results of the antibacterial composite resin of the present invention.

[0033] Figure 7This is the stability test result diagram of the antibacterial composite resin of the present invention.

[0034] Figure 8 This is the surface feature test result diagram of the antibacterial composite resin of the present invention. Detailed implementation manners

[0035] To better understand the present invention, the following describes the present invention in combination with embodiments, but the scope claimed by the present invention is not limited to the scope described in the embodiments.

[0036] The raw materials used in the present invention are all conventional commercially available products without special instructions. The methods used in the present invention are all conventional methods in the art without special instructions. The masses of various substances used in the present invention are all conventional usage masses.

[0037] Please refer to Figure 1 , in the first aspect, the present invention provides a preparation method of an antibacterial composite resin, including the following steps:

[0038] Step 1: Dissolve lignin in dimethyl sulfoxide, then add methacrylic anhydride, and then add a catalyst to carry out a catalytic reaction at a first preset temperature and a first preset time to obtain a reaction solution, and perform impurity removal treatment on the reaction solution to obtain M-lignin (methacrylated lignin), wherein the dosage of methacrylic anhydride is 0.15-0.25 times the equivalent of the hydroxyl content in lignin;

[0039] Step 2: Dissolve 5-20 parts by weight of M-lignin in 65-75 parts by weight of polyurethane acrylate, then add 10-40 parts by weight of an active diluent and 0.5-2.5 parts by weight of a photoinitiator, and mix evenly to obtain an antibacterial composite resin precursor;

[0040] Step 3: Carry out photocuring molding on the antibacterial composite resin precursor to obtain an antibacterial composite resin.

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0042] In this application, lignin is first dissolved in dimethyl sulfoxide, then methacrylic anhydride is added, and then a catalyst is added to carry out a catalytic reaction at a first preset temperature and a first preset time to obtain a reaction solution. On the one hand, methacrylic anhydride can replace the hydroxyl groups of the lignin macromolecule with methacrylate groups for chemical modification, ensuring that when photocuring molding is carried out subsequently, the modified lignin can form a large number of stable and strong covalent bonds with other components in the entire crosslinked network, thereby improving the adhesion of lignin and the mechanical properties of the composite resin as a whole. On the other hand, by controlling the amount of methacrylic anhydride to be 0.15 - 0.25 times the equivalent of the hydroxyl group content in lignin, partial esterification of the aromatic hydroxyl group and aliphatic hydroxyl group of lignin occurs, thereby retaining some phenolic hydroxyl groups of lignin to achieve the inherent antibacterial properties and high biocompatibility of lignin. Subsequently, the reaction solution is subjected to impurity removal treatment to obtain M-lignin (methacrylated lignin). Then, 5 - 20 parts by weight of M-lignin is dissolved in 65 - 75 parts by weight of polyurethane acrylate, and then 10 - 40 parts by weight of active diluent and 0.5 - 2.5 parts by weight of photoinitiator are added and mixed evenly to obtain an antibacterial composite resin precursor. Among them, the methacrylate functional group in M-lignin ensures its good compatibility in polyurethane acrylate, thereby making the properties of the composite resin after photocuring molding uniform and consistent. Finally, the antibacterial composite resin precursor is subjected to photocuring molding to obtain an antibacterial composite resin with persistent antibacterial properties and high biocompatibility without adding antibacterial agents.

[0043] The reason why the phenolic hydroxyl group structure in lignin endows lignin with natural antibacterial properties is that the phenolic hydroxyl group structure in lignin is hydrophobic, which can destroy the phospholipid structure on the bacterial cell membrane and mitochondria and enhance the permeability of the cell membrane, thereby causing the leakage of ions and other substances inside the cell to disrupt the metabolism of bacteria and ultimately leading to the flocculation and death of bacteria.

[0044] In the present invention, the amount of methacrylic anhydride is 0.15 - 0.25 times the equivalent of the hydroxyl group content in lignin, where the equivalent represents the amount of substance. For example, when the hydroxyl group content in 1 g of lignin is 5 - 7 mmol, the amount of methacrylic anhydride is 0.75 - 1.75 mmol. The process diagram of the catalytic reaction of lignin in step 1 can be as Figure 2 shown, where methacrylic anhydride is represented as MA, lignin is represented as Lignin, and M-lignin (methacrylated lignin) is represented as M-lignin. And according to Figure 2 it can be seen that by controlling the amount of methacrylic anhydride, partial esterification of the aromatic hydroxyl group and aliphatic hydroxyl group of lignin can occur to generate a-lignin and b-lignin respectively, thereby retaining the phenolic hydroxyl group of b-lignin, where M-lignin includes a-lignin and b-lignin.

[0045] In one embodiment, to ensure the uniform molecular weight of the lignin used and improve the success rate of chemically modified lignin, the lignin in step 1 is obtained in the following manner to further screen and purify the lignin raw material:

[0046] A 11 : Dissolve the lignin raw material in dimethylformamide to obtain a mixed solution A, where the ratio of the lignin raw material to dimethylformamide is 5 - 10 g: 90 - 100 mL;

[0047] A 12 : Add the mixed solution A to a methanol solution for precipitation, filter out the precipitate A, and then wash the precipitate A with distilled water to obtain the initial lignin, where the volume ratio of the mixed solution to the methanol solution is 1:(4 - 5);

[0048] A 13 : Place the initial lignin in a vacuum environment at a temperature of 35 - 45 °C and dry it to a constant weight to obtain the lignin.

[0049] In one embodiment, step 1 is specifically as follows:

[0050] S 11 : Put 2 - 5 g of lignin into a flask and pour in 20 - 50 mL of dimethyl sulfoxide to fully dissolve the lignin to obtain a dissolved solution A;

[0051] S 12 : Add 0.29 - 1.2 mL of methacrylic anhydride to the dissolved solution A, and then add a catalyst and react in an environment with a first preset temperature of 40 - 80 °C for a first preset time of 12 - 48 hours to obtain a reaction solution.

[0052] In one embodiment, in step 1, the catalyst is one or several of 4 - dimethylaminopyridine, triethylamine, diisopropylethylamine, dicyclohexylcarbodiimide, and dicyclohexylamine.

[0053] In one embodiment, in step 1, the impurity removal treatment is specifically as follows: Add the reaction solution to a methanol solution for precipitation, filter out the precipitate B, wash the precipitate B with deionized water, and place it in a vacuum environment at a temperature of 35 - 45 °C and dry it to a constant weight to obtain M - lignin.

[0054] In one embodiment, in step 2, the reactive diluent is one or several of 4 - acryloylmorpholine, 2 - hydroxyethyl acrylate, 2 - phenoxyethyl acrylate, tripropylene glycol diacrylate, and diethylene glycol diacrylate.

[0055] In one embodiment, in step 2, the photoinitiator is one or more of 2,4,6-trimethylbenzoyl diphenylphosphine oxide, 2-hydroxy-2-methylphenylpropanone, and 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone.

[0056] In one embodiment, step 2 is specifically:

[0057] S 21 : Dissolve 5 - 20 g of M-lignin in 65 - 75 g of polyurethane acrylate to obtain a solution B;

[0058] S 22 : Add 10 - 40 g of 4-acryloylmorpholine and 0.5 - 2.5 g of 2,4,6-trimethylbenzoyl diphenylphosphine oxide (TPO) to solution B, mix well and remove air bubbles to obtain an antibacterial composite resin precursor; during the photocuring process of the obtained antibacterial composite resin precursor under light irradiation with a wavelength of 405 nm, TPO will generate two active free radicals, thereby initiating the free radical polymerization between M-lignin and PAO to form a chemical crosslinking network in the polyurethane acrylate. At this time, both M-lignin and PAO play a dual role, being both monomers and crosslinking agents, further improving the adhesion of M-lignin.

[0059] In a second aspect, the present invention provides an antibacterial composite resin prepared according to the preparation method described in the first aspect.

[0060] In a third aspect, the present invention provides an antibacterial composite resin obtained according to the preparation method described in the first aspect and applied to photocuring 3D printing.

[0061] The preparation process of the antibacterial composite resin is shown through the following examples and comparative examples of the method of the present invention.

[0062] Example 1: Dissolve 10 g of purchased lignin raw material in 100 mL of dimethylformamide to obtain a mixed solution A; add the mixed solution A to 500 mL of methanol solution for precipitation, and after filtering out the precipitate A, rinse the precipitate A with distilled water to obtain the initial lignin; place the initial lignin in a vacuum environment at 40 °C and dry it to constant weight to obtain lignin; put 3 g of lignin into a 100 mL three-necked flask and pour in 30 mL of dimethyl sulfoxide to completely dissolve and mix, obtaining a solution A, where the hydroxyl content in the lignin is 6.54 mmol / g; add 0.58 mL (3.92 mmol) of methacrylic anhydride (MA) to the solution A, and then add 0.03 g (0.26 mmol) of 4-dimethylaminopyridine (DMAP), heat it in an oil bath to 60 °C and react for 48 hours to obtain a reaction solution, add the reaction solution to the methanol solution for precipitation, filter out the precipitate B, wash the precipitate B with deionized water, and place it in a vacuum environment at 40 °C and dry it to constant weight to obtain M-lignin. Subsequently, dissolve 5 g of M-lignin in 70 g of polyurethane acrylate (PAO) to obtain a solution B; add 30 g of 4-acryloylmorpholine (ACMO) and 2 g of 2,4,6-trimethylbenzoyl diphenylphosphine oxide (TPO) to the solution B, completely mix for 1 hour and remove the bubbles to obtain an antibacterial composite resin precursor; use a digital light processing-based DLP 3D printer (Accufab-D1s, Shining 3D Technology Co., Ltd.) to perform photocuring and molding 3D printing on the antibacterial composite resin precursor, with a printing layer thickness of 50 μm. After printing, carefully remove the printed model from the building platform with a spatula, thoroughly rinse it with a large amount of ethanol to remove impurities and residual solvents, and then place it in an ultraviolet curing chamber (Fabcure 1.0, Shining 3D Technology Co., Ltd.) to completely harden it to obtain the antibacterial composite resin LCR-1.

[0063] Example 2: Compared with Example 1, the M-lignin added to the solution B is 10 g, and other components and conditions are the same as those in Example 1, obtaining the antibacterial composite resin LCR-2.

[0064] Example 3: Compared with Example 1, the M-lignin added to the solution B is 15 g, and other components and conditions are the same as those in Example 1, obtaining the antibacterial composite resin LCR-3.

[0065] Example 4: Compared with Example 1, the M-lignin added to the solution B is 20 g, and other components and conditions are the same as those in Example 1, obtaining the antibacterial composite resin LCR-4.

[0066] Comparative example: Compared with Example 1, 0 g of M-lignin was added to the dissolution solution B, and other components and conditions were the same as those in Example 1, obtaining the antibacterial composite resin LCR-0.

[0067] Table 1 Component contents of the antibacterial composite resins obtained in each example and comparative example

[0068]

[0069]

[0070] Specifically, in order to verify whether the modification of lignin by methacrylic anhydride was successful, the chemical structure detection process and results of lignin and M-lignin are as follows:

[0071] The protons (1H) and phosphorus (31P) in lignin and M-lignin were respectively detected by nuclear magnetic resonance (NMR) spectroscopy, thereby obtaining the NMR spectra of lignin and M-lignin. The chemical structure of M-lignin was analyzed using the NMR spectra, and the NMR spectra were recorded by a Bruker Avance spectrometer (300 MHz);

[0072] ① Detection method for protons (1H): 50 mg of dry lignin or M-lignin was completely dissolved in 500 μL of deuterated dimethyl sulfoxide, and then transferred to an NMR tube for NMR acquisition. The detection results are as Figure 3 (a) shown;

[0073] ② Detection method for phosphorus (31P): 20 mg of dry lignin or M-lignin was completely mixed with 400 μL of a prepared mixture of anhydrous pyridine and deuterated chloroform with a volume ratio of 1:1. Then, 50 μL of deuterated methylene sulfide and 31P NMR were added. Finally, 50 μL of 2-chloro-4,4,5,5-tetramethyl-1,2,3-dioxaphospholane, 100 μL of endo-N-hydroxy-5-norbornene-2,3-dicarboximide solution (10 mg / mL), and 40 μL of chromium(III) acetylacetonate solution (5.6 mg / mL) were added as a phosphating reagent, an internal standard, and a relaxation reagent respectively. After stirring with a vortex mixer for 5 minutes, it was transferred to an NMR tube for NMR acquisition. The detection results are as Figure 3 (b) shown;

[0074] Table 2 Quantitative analysis of different hydroxyl groups (-OH) in lignin and M-lignin

[0075]

[0076] Please refer to Figure 3(a), The unmodified lignin shows two broad peaks located at 2.9 - 4.2 ppm and 6.5 - 7.6 ppm, corresponding to the methoxy groups and aromatic groups in lignin respectively. In contrast, two new chemical shifts for the methylene (a) and methyl (b) groups of the methacrylic anhydride molecule appear in the ranges of 5.4 - 6.5 ppm and 1.4 - 2.2 ppm, preliminarily proving the successful methacrylation of the hydroxyl groups in lignin by methacrylic anhydride;

[0077] Please refer to Figure 3 (b) and Table 2. The quantitative analysis by phosphorus (31P) NMR further determines the contents of various hydroxyl groups in lignin and M - lignin. Although the 31P NMR spectra are from two samples of lignin and M - lignin, their appearances are very similar. The characteristic signals of carboxyl, phenolic, and aliphatic hydroxyl groups are located at 133 - 136 ppm, 136 - 144 ppm, and 145 - 150 ppm respectively, once again proving the successful methacrylation of the hydroxyl groups in lignin by methacrylic anhydride, and partial esterification of the aromatic hydroxyl and aliphatic hydroxyl groups in lignin has occurred.

[0078] Specifically, for the performance detection processes and results of the antibacterial composite resins LCR - 0, LCR - 1, LCR - 2, LCR - 3, LCR - 4 obtained from the above respective examples and comparative examples are as follows:

[0079] (1) Antibacterial performance detection of the antibacterial composite resin: The plate count method is used to evaluate the antibacterial properties of the antibacterial composite resins LCR - 0, LCR - 1, LCR - 2, LCR - 3, LCR - 4 against the Gram - positive Staphylococcus aureus and Gram - negative Escherichia coli strains. The Gram - positive Staphylococcus aureus and Gram - negative Escherichia coli are respectively inoculated into agar plates and cultured in Mueller Hinton broth medium at 37 °C until the logarithmic growth phase, and then diluted to a concentration of 1×10 7 colony - forming units (CFU) / milliliter. Then, 10 μL of the diluted bacterial suspension is smeared on the surfaces of the sterilized antibacterial composite resin LCR - 0, LCR - 1, LCR - 2, LCR - 3, LCR - 4 samples (10 mm × 10 mm) in a 24 - well plate, as sample group 1; at the same time, the same bacterial suspension is added to the wells without any samples, as control group 1. The culture plates of sample group 1 and control group 1 are cultured at 37 °C and a relative humidity of 90% for 2 hours, then 1 mL of phosphate - buffered saline (PBS, pH = 7.4) is added to restore the bacterial survival rate. The bacterial suspension is diluted 10 - fold with PBS, and then the bacterial colonies are counted by an optical microscope after culturing on Luria - Bertani agar (LB medium) at 37 °C for 24 hours. The calculation formula for the reduction in bacteria is as follows:

[0080]

[0081] Where A and B are the CFUs of control group 1 and sample group 1 respectively, and the mean and standard deviation are calculated based on at least three sets of data for each sample;

[0082] The test results are as Figure 4 shown, where Figure 4 (a) represents the reduction of Staphylococcus aureus in the antibacterial composite resins LCR-0, LCR-1, LCR-2, LCR-3, and LCR-4, where Figure 4 (b) represents the reduction of Escherichia coli in the antibacterial composite resins LCR-0, LCR-1, LCR-2, LCR-3, and LCR-4, where Figure 4 (c) and Figure 4 (e) are the images of Staphylococcus aureus on the surfaces of the antibacterial composite resins LCR-0 and LCR-4 respectively; where Figure 4 (d) and Figure 4 (f) are the images of Escherichia coli on the surfaces of the antibacterial composite resins LCR-0 and LCR-4 respectively;

[0083] Please refer to Figure 4 (a-b). LCR-0 without added M-lignin has little antibacterial activity against Staphylococcus aureus and Escherichia coli, but LCR-1, LCR-2, LCR-3, and LCR-4 with added M-lignin all show strong antibacterial activity, where the bacterial survival rate is reduced by at least 85%. LCR-4 containing 20 g of M-lignin reduces the most Staphylococcus aureus (96.5 ± 3.2%) and Escherichia coli (95.2 ± 2.8%). By observing the number and morphology of bacterial cells attached to the surfaces of LCR-0 and LCR-4 using a field emission scanning electron microscope ( Figure 4 (c-f)), it can be clearly seen that a large number of Staphylococcus aureus and Escherichia coli adhere to the surface of LCR-0, while the amount of bacteria adhering to the surface of LCR-4 is significantly reduced. Thus, it can be known that the antibacterial activity of the antibacterial composite resin gradually increases with the increase in the content of M-lignin, which confirms that the inherent antibacterial property of lignin is retained after being converted into M-lignin.

[0084] (2) Biocompatibility testing of antibacterial composite resin: The cytotoxicity of antibacterial composite resins LCR-0, LCR-1, LCR-2, LCR-3, and LCR-4 to cells was studied through extraction tests. NIH / 3T3 mouse fibroblasts were inoculated into 96-well plates at a density of the optimal cell number (104 cells / well). The antibacterial composite resins LCR-0, LCR-1, LCR-2, LCR-3, and LCR-4 were all soaked and disinfected to obtain the corresponding extracts. Then, the cells cultured with 200 μL of a mixed solution composed of 50% complete medium and 50% extract were used as sample group 2, while 200 μL of complete medium was added to one well as control group 2. Both sample group 2 and control group 2 were cultured in a humid environment at 37 °C and 5% CO 2 2. After growing for 1, 3, 5, and 7 days, 100 μL of 1 mg / mL 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) solution was added to each well, and then cultured at 37 °C for another 4 hours. Fresh formazan crystals appeared and precipitated at the bottom. Subsequently, the formazan crystals were dissolved in 100 μL of dimethyl sulfoxide, and the absorbance (optical density, OD) was measured at a wavelength of 570 nm using a microplate reader (Bio-Rad, Philadelphia, PA). The cell viability calculation formula is as follows:

[0085]

[0086] where the mean and standard deviation were calculated based on at least three sets of data for each sample. The test results are as Figure 5 shown;

[0087] Please refer to Figure 5 . There was no significant difference in cell viability among the samples of antibacterial composite resins LCR-0, LCR-1, LCR-2, LCR-3, and LCR-4. Even after culturing for 7 days, the cell viability was still higher than 90%, indicating that the antibacterial composite resins LCR-0, LCR-1, LCR-2, LCR-3, and LCR-4 have no cytotoxic effect on cultured cells and have good biocompatibility.

[0088] (3) Mechanical properties of antibacterial composite resin: The mechanical properties of samples of antibacterial composite resins LCR-0, LCR-1, LCR-2, LCR-3, and LCR-4 were tested respectively using a universal testing machine (YL-1109, Yuelian Testing Machine Co., Ltd., Dongguan, China), including tensile and flexural properties. For the tensile test, rectangular specimens with a length of 125 mm, a width of 10 mm, and a thickness of 4 mm were used, and the crosshead speed was kept constant at 5 mm / min; for the flexural test, specimens with a length of 80 mm, a width of 10 mm, and a thickness of 4 mm were used, and the crosshead speed was kept constant at 2 mm / min. The mean and standard deviation were calculated based on at least three sets of data for each specimen;

[0089] The test results are as Figure 6 shown, where Figure 6 (a) is the tensile strength table of the antibacterial composite resin samples LCR-0, LCR-1, LCR-2, LCR-3, and LCR-4, where Figure 6 (b) is the tensile modulus table of the antibacterial composite resin samples LCR-0, LCR-1, LCR-2, LCR-3, and LCR-4, where Figure 6 (c) is the flexural strength table of the antibacterial composite resin samples LCR-0, LCR-1, LCR-2, LCR-3, and LCR-4, where Figure 6 (d) is the flexural modulus table of the antibacterial composite resin samples LCR-0, LCR-1, LCR-2, LCR-3, and LCR-4;

[0090] Please refer to Figure 6 , as the content of M-lignin increases, on the one hand, the tensile strength and flexural strength of the antibacterial composite resins LCR-0, LCR-1, LCR-2, LCR-3, and LCR-4 increase significantly, from 28.6 ± 3.1 MPa of the control group LCR-0 to 37.3 ± 3.1 MPa of LCR-4, and the tensile strength increases by about 30%. Similarly, the flexural strength also increases from 44.8 ± 4.7 MPa of the control group LCR-0 to 58.6 ± 5.4 MPa of LCR-4. On the other hand, the tensile modulus and flexural modulus of the antibacterial composite resins LCR-0, LCR-1, LCR-2, LCR-3, and LCR-4 decrease significantly, from 1228.7 ± 49.3 MPa and 1026.8 ± 47.7 MPa to 1096.1 ± 54.3 MPa and 894.6 ± 36.7 MPa respectively. It can be seen that the antibacterial composite resin has successfully changed from brittle to tough. This huge change is due to the addition of M-lignin in the resin matrix, and the functional side chains of M-lignin weaken the intermolecular forces and reduce the crosslinking density of the composite resin, resulting in M-lignin playing the role of a plasticizer in the resin matrix.

[0091] (4) Stability of the antibacterial composite resin: According to the ASTM F1980-21 standard, the stability of the antibacterial composite resin is tested through an accelerated aging test. The antibacterial composite resin samples LCR-0, LCR-1, LCR-2, LCR-3, and LCR-4 are stored in an environmental chamber at a temperature of 60 °C (accelerated aging temperature T AA ) and a relative humidity of 50% for 7 days (accelerated aging time AAT), and then their antibacterial properties and mechanical properties are tested respectively according to the above (1) antibacterial property detection of the antibacterial composite resin and (3) detection steps of the mechanical properties of the antibacterial composite resin. The average value and standard deviation are calculated based on at least three sets of data for each sample;

[0092] According to ASTM F1980-21, the calculation formula for Real-Time Aging (RT) is as follows:

[0093]

[0094] Where Q 10 = 2 is the most commonly used coefficient, indicating that for every 10°C increase in temperature, the reaction rate doubles. The ambient temperature (T RT ) is 22°C, and the relative humidity is 50%;

[0095] The test results are as Figure 7 shown, the mechanical properties ((a) tensile strength, (b) tensile modulus, (c) flexural strength, and (d) flexural modulus) and antibacterial properties ((e) CFU reduction of Staphylococcus aureus and (f) Escherichia coli) of the antibacterial composite resins LCR-0, LCR-1, LCR-2, LCR-3, and LCR-4 after 7 days of accelerated aging at 60°C.

[0096] Please refer to Figure 7 , as the M-lignin content increases, the tensile strength and flexural strength of the aged antibacterial composite resins also increase, while the tensile modulus and flexural modulus decrease ( Figure 7 (a-d)). More precisely, the addition of M-lignin increases the tensile strength and flexural strength from 27.9 ± 2.8 MPa and 43.9 ± 3.6 MPa to 36.7 ± 2.9 MPa and 57.9 ± 5.2 MPa respectively, while the tensile modulus and flexural modulus decrease from 1217.8 ± 46.7 MPa and 1088.8 ± 48.4 MPa to 1003.8 ± 50.4 MPa and 891.2 ± 38.9 MPa respectively. At the same time, except for LCR-0, the antibacterial composite resins LCR-1, LCR-2, LCR-3, and LCR-4 all maintain an antibacterial activity of more than 85% after aging, and the antibacterial activity gradually increases with the increase of M-lignin content ( Figure 8 (e-f)). According to the numerical results extracted from Figure 3 , Figure 6 and Figure 7 , it can be concluded that the mechanical properties and antibacterial properties of the antibacterial composite resins LCR-0, LCR-1, LCR-2, LCR-3, LCR-4 and the aged antibacterial composite resins LCR-0, LCR-1, LCR-2, LCR-3, LCR-4 show almost the same trend of change with the M-lignin content. Figure 7 The tensile and flexural strengths, tensile and flexural moduli, and CFU reduction of the aged antibacterial composite resins shown in Figure 3 and Figure 6The initial values are not very different, indicating that the performance hardly degrades after 7 days of accelerated aging treatment at 60°C. Through the conversion of the real-time aging formula (3), it can be known that accelerating aging for 7 days at 60°C is equivalent to accelerating aging for about 98 days at room temperature of 22°C. In short, the antibacterial composite resin prepared by the present invention exhibits stable performance throughout the aging process, ensuring its reliability in applications for pet products.

[0097] (5) Surface characteristics of the antibacterial composite resin: The surface characteristics of the antibacterial composite resin were analyzed using a JSM-6701F field emission scanning electron microscope. Samples of the antibacterial composite resin LCR-0, LCR-1, LCR-2, LCR-3, and LCR-4 were vacuum dried at 40°C for 24 hours, and then directly pasted onto the FESEM column using a conductive double-sided adhesive carbon tape. A thin layer of platinum was gently coated to reduce the charging effect. Microscopic photographs were taken under vacuum conditions with an acceleration voltage of 5 kV and a working distance of 10 mm.

[0098] The test results are as Figure 8 shown. The FESEM images of the surface morphology of the antibacterial composite resin are (a) LCR-0, (b) LCR-1, (c) LCR-2, (d) LCR-3, and (e) LCR-4, respectively.

[0099] Please refer to Figure 8 , the surface morphology of the control sample (LCR-0) without M-lignin is the best, with a smooth, dense, and uniform surface ( Figure 8 (a)). In contrast, introducing M-lignin into the resin matrix results in many poorly fused areas, manifested as voids on the surface ( Figure 8 (b - e)). In addition, as the content of M-lignin increases, the number and size of the voids and the surface roughness also gradually increase. This is because the cross-linking effect between M-lignins disrupts the assembly of the polyurethane acrylate network, leading to the aggregation of voids, proving the successful mixing of M-lignin and polyurethane acrylate.

[0100] The above-disclosed are only the preferred embodiments of the present invention. Of course, the scope of the rights of the present invention cannot be limited thereby. Those of ordinary skill in the art can understand the entire or partial processes of implementing the above embodiments, and the equivalent changes made according to the claims of the present invention still fall within the scope covered by the invention.

Claims

1. A method for preparing an antibacterial composite resin, characterized in that: The following steps are involved: Step 1: dissolving lignin in dimethyl sulfoxide, then adding methacrylic anhydride, and then adding a catalyst to carry out a catalytic reaction at a first preset temperature and a first preset time to obtain a reaction solution, and removing impurities from the reaction solution to obtain M-lignin (methacrylated lignin), wherein the amount of methacrylic anhydride used is 0.15-0.25 times the equivalent of the hydroxyl content in the lignin; Step 2: dissolving 5-20 parts by weight of M-lignin in 65-75 parts by weight of polyurethane acrylate, adding 10-40 parts by weight of active diluent and 0.5-2.5 parts by weight of photoinitiator, and mixing them evenly to obtain an antibacterial composite resin precursor; Step 3: Photocuring the antibacterial composite resin precursor to obtain the antibacterial composite resin.

2. The method for preparing the antibacterial composite resin according to claim 1, characterized in that: The lignin in step 1 is obtained by the following method: A 11 : Dissolve the lignin raw material in dimethylformamide to obtain a mixed solution A, wherein the ratio of the lignin raw material to dimethylformamide is 5-10 g: 90-100 mL; A 12 : Adding the mixed solution A into the methanol solution for precipitation, filtering out the precipitate A, and then washing the precipitate A with distilled water to obtain the initial lignin, wherein the volume ratio of the mixed solution to the methanol solution is 1: (4-5); A 13 : The initial lignin is placed in a vacuum environment at a temperature of 35-45° C. and dried to a constant weight to obtain lignin.

3. The method for preparing the antibacterial composite resin according to claim 1 or 2, characterized in that: The step 1 is specifically as follows: S 11 : Add 2-5 g of lignin into a flask and pour in 20-50 mL of dimethyl sulfoxide to fully dissolve the lignin to obtain a solution A; S 12 : Add 0.29-1.2 mL of methacrylic anhydride to the dissolving solution A, then add a catalyst, and react at a first preset temperature of 40-80° C. for a first preset time of 12-48 hours to obtain a reaction solution.

4. The method for preparing the antibacterial composite resin according to claim 1, characterized in that: In the step 1, the catalyst is one or more of 4-dimethylaminopyridine, triethylamine, diisopropylethylamine, dicyclohexylcarbodiimide, and dicyclohexylamine.

5. The method for preparing the antibacterial composite resin according to claim 1, characterized in that: In the step 1, the impurity removal treatment is specifically as follows: adding the reaction solution into a methanol solution for precipitation, filtering out the precipitate B, washing the precipitate B with deionized water, and drying it in a vacuum environment at a temperature of 35-45° C. to a constant weight to obtain M-lignin.

6. The method for preparing the antibacterial composite resin according to claim 1, characterized in that: In the step 2, the active diluent is one or more of 4-acryloylmorpholine, 2-hydroxyethyl acrylate, 2-phenoxyethyl acrylate, tripropylene glycol diacrylate, and diethylene glycol diacrylate.

7. The method for preparing the antibacterial composite resin according to claim 6, characterized in that: In the step 2, the photoinitiator is one or more of 2,4,6-trimethylbenzoylphenylphosphine oxide, 2-hydroxy-2-methylphenylacetone, and 2-hydroxy-4-(2-hydroxyethoxy)-2-methylphenylacetone.

8. The method for preparing the antibacterial composite resin according to claim 7, characterized in that: The step 2 is specifically as follows: S 21 : Dissolve 5-20 g of M-lignin in 65-75 g of polyurethane acrylate to obtain solution B; S 22 : Add 10-40 g of 4-acryloylmorpholine and 0.5-2.5 g of 2,4,6-trimethylbenzoylphenylphosphine oxide to the dissolving solution B, mix well and remove bubbles to obtain an antibacterial composite resin precursor.

9. An antibacterial composite resin prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the antibacterial composite resin obtained by the preparation method according to any one of claims 1 to 8 in photocuring 3D printing.

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