CS@ZIF-8 / PLA composite electrospun fiber membrane with rapid degradation in water, high antibacterial properties, and high filtration efficiency.

Abstract

The application discloses a kind of CS@ZIF-8 / PLA composite electrostatic spinning fiber membranes with fast degradation in water, high antibacterial and filtration efficiency, by in-situ growth method synthesis MOFs composite material with positive electricity, namely CS@ZIF-8;It is mixed with polylactic acid to make spinning fluid, electrostatic spinning is carried out, so as to obtain composite electrostatic spinning fiber membrane.Because the fiber membrane of the application contains polylactic acid and chitosan, it has the characteristics of simple preparation process, easy degradation, green environmental protection, the self-charge of MOFs composite material not only makes the application have excellent bactericidal effect, and it also has better adsorption to PM pollutants in air;Its chemical property is stable, can adapt to different temperature and humidity environment, has wide practical application prospect in medical material, antibacterial filter material field.

Description

TECHNICAL FIELD

[0001] The application relates to the field of MOFs composite material mixed electrostatic spinning, and relates to a CS@ZIF-8 / PLA composite electrostatic spinning fiber membrane with rapid degradation in water, high antibacterial property and filtration efficiency and a preparation method. BACKGROUND

[0002] A mask plays an important protective role in blocking haze and preventing highly contagious diseases, and the amount used is huge. The mask is generally composed of a fly-proof layer, a filter layer (i.e. filter material) and a moisture absorption layer, wherein the filter material is the core layer and key material of the mask, and determines the performance of the mask. At present, the filter material widely used in the national standard is a polypropylene non-woven fabric material (commonly known as melt-blown fabric) treated by electrostatic treatment, which has very good effect, but also has the problems of coarse melt-blown fabric fibers (diameter is about 0.1 mm) and attenuation of electrostatic adsorption characteristics with time, temperature, humidity and breathing. In addition, most of the current mask filter materials do not have antibacterial and other functional properties, are difficult to degrade in the environment, and cause environmental pollution after being discarded after use. Therefore, the current mask filter material is developing towards multi-functionality, high filtration and green environmental protection.

[0003] Polylactic acid (PLA) is a recognized environmentally friendly material, and the ester group in its molecular structure formula is easy to hydrolyze, can be degraded in vivo or soil by microorganisms, and can be completely degraded in 3-6 months. Metal-organic framework material (Metal-organic frameworks, MOFs) is a kind of very rapidly developing organic-inorganic hybrid material, which has great application value in antibacterial, gas adsorption, catalysis and drug delivery. Due to the specificity of its composition and structure, MOFs are widely used for modification of antibacterial agents (Zhang YM, et al. Nanomaterials 2019, 9, 1579.). At the same time, chitosan as a degradable material has a large number of active hydroxyl and amino groups, which have strong chemical reaction ability and certain antibacterial property. Therefore, the modification of chitosan by MOFs will play a synergistic antibacterial effect of the two, and can be widely applied to the preparation of textiles and the development of biological materials.

[0004] However, in the existing background, most of the mask filter materials cannot simultaneously achieve high filtration efficiency, antibacterial property and easy degradation in water. For example, the PU@ZIF-15 electrospun fiber membrane prepared by Wang et al. (ACS Appl. Polym. Mater. 2021, 3, 710-719) has high filtration performance for PM2.5, but it cannot be degraded because the base material used is polyurethane PU. The filtration membrane using polyacrylonitrile (PAN), polystyrene (PS) and polyvinylpyrrolidone (PVP) as the base material by Zhang et al. (J. Am. Chem. Soc. 2016, 138, 5785-5788) also cannot be degraded. In addition, although the polyvinyl alcohol (PVA)-tannic acid (TA) composite nanofiber membrane prepared by Cui et al. (J. Colloid Interface Sci. 2021, 597, 48-55) can achieve easy degradation in nature, it has the defect of being unable to resist bacteria. SUMMARY

[0005] In order to solve the problems of poor antibacterial performance, adsorption decreasing over time, and difficulty in degradation of the current mask filter material, the purpose of the present application is to provide a CS@ZIF-8 / PLA (CS-chitosan, ZIF-8-a metal organic framework, PLA-poly lactic acid) composite electrospun fiber membrane with rapid degradation in water, high antibacterial property and filtration efficiency and a preparation method. The method uses the positively charged MOFs composite material CS@ZIF-8 as an antibacterial agent, and a degradable material poly lactic acid resin to prepare a multifunctional fiber membrane with filtration performance, sterilization performance and degradability by mixing electrospinning technology, to solve the problems of poor antibacterial performance of the current mask filter material and decreased filtration in a high humidity environment.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical scheme: a CS@ZIF-8 / PLA composite electrospun fiber membrane with rapid degradation in water, high antibacterial property and filtration efficiency and a preparation method, a positively charged MOFs composite material CS@ZIF-8 is synthesized by in-situ growth method; it is mixed with poly lactic acid to prepare a spinning solution, and electrospinning is carried out, so as to obtain a solid mask filter material, which specifically comprises the following steps:

[0007] Step 1, disperse CS@ZIF-8 into a mixed solvent of N,N-dimethylformamide and dichloromethane, add polyvinylpyrrolidone as a dispersant, stir, ultrasonic, and prepare a suspension; then pour the suspension into a poly lactic acid solution, stir uniformly to prepare a mixed spinning solution, wherein the mass percentage of poly lactic acid and CS@ZIF-8 is (99-95):(1-5);

[0008] Step 2, electrospinning the above mixed spinning solution, the spinning process parameters: voltage 20kV, push injection speed is 1.5-2.0mL / h, receiving distance is 15-17cm, drum speed 70rpm, ambient temperature is 30-40℃, ambient humidity is 40-60%RH; after spinning, oven drying, to prepare CS@ZIF-8 / PLA composite fiber membrane.

[0009] Preferably, in step 1, the molar ratio of CS to ZIF-8 in CS@ZIF-8 is 1:100.

[0010] Preferably, in step 1, the Zeta potential value of CS@ZIF-8 is +13.8±1.45mV.

[0011] Preferably, in step 1, the polylactic acid solution is a dichloromethane solution of polylactic acid.

[0012] Preferably, in step 1, the mass fraction of polylactic acid in the mixed spinning solution is 12%.

[0013] Preferably, in step 1, the mass ratio of N,N-dimethylformamide to dichloromethane is 1:4.

[0014] Preferably, in step 1, the mass ratio of CS@ZIF-8 to polyvinylpyrrolidone is 1:5.

[0015] Preferably, in step 2, the injection pump flow rate is 1.9mL / h, and the receiving distance is 15cm.

[0016] Compared with the prior art, the advantages of the present application are:

[0017] The present application provides a kind of CS@ZIF-8 / PLA composite electrospinning fiber membrane of quick degradation in water, high antibacterial and filtration efficiency and preparation method, with PLA as matrix material, MOFs composite material CS@ZIF-8 is added as antibacterial material, using electrospinning method is prepared, in filtration, with PM2.5 And PM10 as filter object, the filtration rate of the fiber membrane can reach 100% in ten minutes, with good filtration performance.

[0018] In terms of antibacterial, the fiber membrane can achieve more than 100% antibacterial effect on escherichia coli and staphylococcus in 4h contact time, which has filtering and antibacterial effect that ordinary melt-blown cloth material on the market cannot achieve.In terms of thickness, the thickness of the membrane is about 40 microns, which achieves ultra-thin effect, compared with the thickness of about 100 microns of ordinary melt-blown cloth material, greatly reducing the consumption of materials.

[0019] In terms of degradation, due to the presence of CS, the degradation performance of the CS@ZIF-8 / PLA composite fiber membrane in river water environment is better than that of the ordinary melt-blown cloth and the polylactic acid fiber membrane, and the weight loss rate of the CS@ZIF-8 / PLA composite fiber membrane is about 2 times that of the polylactic acid fiber membrane. At 90 days, the CS@ZIF-8 / PLA composite fiber membrane is severely broken in appearance, the total area is significantly reduced, the weight loss rate is high, and the quality is significantly decreased, while the ordinary melt-blown cloth material has no obvious change in appearance and quality, and the degradation performance is poor. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The scanning electron microscope image of the fiber membrane of Example 1.

[0021] Figure 2 The scanning electron microscope image of the fiber membrane of Example 2.

[0022] Figure 3 The scanning electron microscope image of the fiber membrane of Example 3. DETAILED DESCRIPTION

[0023] In order for those skilled in the art to better understand the technical solutions of the present application, some non-limiting examples are further disclosed below to further illustrate the present application.

[0024] The MOFs composite material is compounded with a completely biodegradable polymer, and a mask filter material is prepared by using an electrospinning technology: (1) the nano MOFs fixed and limited on the surface of the filter material fiber are charged, have a super-high specific surface area, porosity and open sites, and the electrostatic adsorption does not decay with time, temperature, humidity and breathing; (2) in the electrospinning process, the nano MOFs and the spinning conditions jointly act on the diameter, porosity and pore size of the electrospinning fiber. By compounding the antibacterial self-charged nano MOFs composite material with the completely biodegradable polylactic acid, the filtration of air pollutants and the antibacterial performance of the filter material can be improved, and the material can also be well degraded in the environment.

[0025] The present application utilizes the positively charged MOFs composite material as an antibacterial agent to be compounded with a completely biodegradable polymer such as polylactic acid, and a mask filter material is prepared by using an electrospinning technology, and the degradation performance of the prepared mask filter material is studied.

[0026] The CS@ZIF-8 according to the present application is prepared by the following operation steps:

[0027] Chitosan was ball-milled for 4 hours. 0.163 g of chitosan was dispersed in 50 mL of methanol and magnetically stirred for 2 hours to form a suspension. Then, 1.602 g of 2-methylimidazole was dissolved in 50 mL of methanol and added to the chitosan suspension after complete dissolution. The mixture was stirred for 5 minutes. 1.487 g of zinc nitrate hexahydrate was dissolved in 50 mL of methanol and added to the above solution at room temperature. The reaction mixture was stirred for 2 hours, ultimately producing a white product. The molar ratio of chitosan, zinc nitrate hexahydrate, 2-methylimidazole, and methanol was 1:100:800:80000. After the reaction, the product was filtered and washed three times with methanol. Finally, it was dried overnight in a 50°C oven to obtain CS@ZIF-8.

[0028] The CS@ZIF-8 / PLA composite electrospun fiber membrane of the present invention is prepared by the following steps:

[0029] Step 1: First, put the dried PLA granules and dichloromethane into a flask and dissolve them by magnetic stirring. At the same time, weigh N,N-dimethylformamide and dichloromethane into a small beaker, add CS@ZIF-8 and polyvinylpyrrolidone, and stir magnetically to prepare a suspension. After the PLA is completely dissolved in the round-bottom flask, use a dropper to add the suspension from the small beaker to the round-bottom flask. Seal the mouth of the round-bottom flask with plastic wrap and continue stirring to prepare the spinning solution.

[0030] Step 2: Electrospinning is performed at a voltage of 20kV, a jetting speed of 1.5–2.0 mL / h, a receiving distance of 15–17 cm, a roller speed of 70 rpm, an ambient temperature of 30–40℃, and an ambient humidity of 40–60% RH. Under the action of the electric field, the jet can be stably deposited on the roller, and the electrostatic nozzle performs reciprocating linear motion according to the computer-designed path.

[0031] Step 3: Place the obtained CS@ZIF-8 / PLA composite electrospun fiber membrane in a fume hood for 24 hours to dry and remove excess organic solvents, and obtain the sample.

[0032] The specific operation method of the filtration experiment in this invention is as follows:

[0033] The fiber membrane sample was cut into 6cm×6cm squares and fixed at the interface of two sealed containers. A laser dust meter was placed in the upper and lower containers respectively to detect PM concentration. PM particles were generated by burning mosquito coils in the upper container. The lower container was connected to an air pump to draw polluted air from the upper container through the fiber membrane into the lower container. The filtration time was 20 minutes, and the filtration efficiency was measured.

[0034] The specific operating method for the antibacterial experiment in this invention is as follows:

[0035] The fiber membrane and control sample were cut into circular pieces with a diameter of approximately 5 cm to prepare three experimental groups. The antibacterial properties of the fiber membrane were determined according to GB-T20944.3-2008 Evaluation of Antibacterial Properties of Textiles Part 3 - Shaking Method. The experimental bacterial solution concentration was selected as (2-3)×10⁻⁶. 5 The antibacterial properties were measured at CFU / mL for contact times of 1, 2, and 4 hours, and the antibacterial rate was calculated.

[0036] The specific operation method of the degradation experiment in this invention is as follows:

[0037] The samples were cut into 4×4cm squares and placed in the experimental river water. The river water temperature was maintained at 25-30℃. A booster pump was used to keep the water flowing to simulate the real environment. Samples were taken from the river water after 90 days. Impurities on the surface of the fiber membrane were washed away with deionized water. The membranes were dried in a forced-air drying oven at 40℃ for 12 hours until constant weight. The appearance changes of the fiber membranes were recorded. The mass of the fiber membranes after degradation was weighed and recorded. The weight loss rate of the samples was calculated to evaluate their degradation and weight loss.

[0038] Example 1

[0039] Weigh 1.8 g PLA and 7.11 g dichloromethane into a round-bottom flask and stir magnetically until fully dissolved to prepare a PLA solution. Simultaneously, weigh 0.018 g CS@ZIF-8 and 0.09 g polyvinylpyrrolidone and disperse them into 2.64 g N,N-dimethylformamide and 3.45 g dichloromethane, respectively. Stir for 1 h and then sonicate for 30 min to prepare a suspension. Finally, add the suspension dropwise to the PLA solution, seal the flask, and stir overnight for 24 h to obtain a mixed spinning solution.

[0040] The spinning solution was injected into two 5mL syringes, each fitted with a 19G needle. The electrospinning parameters were set as follows: voltage 20kV, injection speed 1.9mL / h, receiving distance 15cm, roller speed 70rpm, ambient temperature 30-40℃, ambient humidity 40-60%RH, and spinning time 100min. After spinning, the fiber membrane was dried in a 40℃ forced-air oven for 1 day to obtain the CS@ZIF-8 / PLA composite fiber membrane.

[0041] exist Figure 1 It can be observed that the MOF composite material CS@ZIF-8 was successfully loaded onto a single fiber without agglomeration, and the fiber diameter distribution was uniform with an average diameter of 630 nm. The composite fiber membrane achieved adsorption efficiencies of 95.16% and 97.58% for PM2.5 and PM10 within 4 minutes, respectively, and remained stable at around 97% throughout the adsorption process. Regarding antibacterial properties, the composite fiber membrane exhibited a 100% inhibition rate against Escherichia coli and Staphylococcus aureus after a 4-hour contact time.

[0042] Example 2

[0043] Weigh 1.8 g PLA and 7.36 g dichloromethane into a round-bottom flask and stir magnetically until fully dissolved to prepare a PLA solution. Simultaneously, weigh 0.054 g CS@ZIF-8 and 0.27 g polyvinylpyrrolidone and disperse them in 2.64 g N,N-dimethylformamide and 3.20 g dichloromethane, respectively. Stir for 1 h and then sonicate for 30 min to prepare a suspension. Finally, add the suspension dropwise to the PLA solution, seal the flask, and stir overnight for 24 h to obtain a mixed spinning solution.

[0044] The spinning solution was injected into two 5mL syringes, each fitted with a 19G needle. The electrospinning parameters were set as follows: voltage 20kV, injection speed 1.9mL / h, receiving distance 15cm, roller speed 70rpm, ambient temperature 30-40℃, ambient humidity 40-60%RH, and spinning time 100min. After spinning, the fiber membrane was dried in a 40℃ forced-air oven for 1 day to obtain the CS@ZIF-8 / PLA composite fiber membrane.

[0045] exist Figure 2 It can be observed that the MOF composite material CS@ZIF-8 was successfully loaded onto a single fiber without agglomeration, and the fiber diameter distribution was uniform with an average diameter of 580 nm. The composite fiber membrane achieved adsorption efficiencies of 99.09% and 99.38% for PM2.5 and PM10 within 4 minutes, respectively, with the highest adsorption rate reaching 100% within 14 minutes, and remaining stable at around 99% throughout the adsorption process. In terms of antibacterial properties, after a 4-hour contact time, the composite fiber membrane achieved a 100% inhibition rate against Escherichia coli and Staphylococcus aureus, indicating that the composite fiber membrane achieved an antibacterial effect. Degradation experiments showed that after 90 days, the CS@ZIF-8 / PLA composite fiber membrane had broken into multiple small fragments, with a significant reduction in total area and a weight loss rate of approximately 24% in the river water.

[0046] Example 3

[0047] Weigh 1.8 g PLA and 7.24 g dichloromethane into a round-bottom flask and stir magnetically until fully dissolved to prepare a PLA solution. Simultaneously, weigh 0.09 g CS@ZIF-8 and 0.45 g polyvinylpyrrolidone and disperse them into 2.64 g N,N-dimethylformamide and 3.32 g dichloromethane, respectively. Stir for 1 h and then sonicate for 30 min to prepare a suspension. Finally, add the suspension dropwise to the PLA solution, seal the flask, and stir overnight for 24 h to obtain a mixed spinning solution.

[0048] The spinning solution was injected into two 5mL syringes, each fitted with a 19G needle. The electrospinning parameters were set as follows: voltage 20kV, injection speed 1.9mL / h, receiving distance 15cm, roller speed 70rpm, ambient temperature 30-40℃, ambient humidity 40-60%RH, and spinning time 100min. After spinning, the fiber membrane was dried in a 40℃ forced-air oven for 1 day to obtain the CS@ZIF-8 / PLA composite fiber membrane.

[0049] exist Figure 3 It was observed that the MOF composite material CS@ZIF-8 was successfully loaded onto a single fiber without agglomeration, and the fiber diameter distribution was uniform with an average diameter of 890 nm. The composite fiber membrane achieved adsorption efficiencies of 92.20% and 92.39% for PM2.5 and PM10 within 14 minutes, respectively, and remained stable at around 90% throughout the adsorption process. Regarding antibacterial properties, the composite fiber membrane exhibited a 100% inhibition rate against Escherichia coli and Staphylococcus aureus after a 4-hour contact time.

[0050] Comparative Example 1

[0051] Polylactic acid fiber membrane control group

[0052] Weigh 1.8g PLA and 7.81g dichloromethane into a round-bottom flask, stir until fully dissolved, then add 2.64g N,N-dimethylformamide and 2.75g dichloromethane, seal and stir overnight for 24h to obtain a mixed spinning solution.

[0053] The spinning solution was injected into two 5mL syringes, each fitted with a 19G needle. The electrospinning parameters were set as follows: voltage 20kV, injection speed 1.9mL / h, receiving distance 15cm, roller speed 70rpm, ambient temperature 30-40℃, ambient humidity 40-60%RH, and spinning time 100min. After spinning, the fiber membrane was dried in a 40℃ forced-air oven for 1 day to obtain a polylactic acid fiber membrane.

[0054] Polylactic acid (PLA) fibers have a smooth surface and a uniform fiber diameter distribution, with an average diameter of 970 nm. Within a 20-minute adsorption time, the highest adsorption efficiencies for PM2.5 and PM10 reached 88.61% and 89.77%, respectively, and remained above 85%. The adsorption rate was slightly lower than that of composite fiber membranes with added MOFs (Examples 1, 2, and 3), indicating that the addition of charged MOFs improved the adsorption performance to some extent. Regarding antibacterial properties, after a 4-hour contact time, the fiber membrane showed no inhibition against Escherichia coli and Staphylococcus aureus. This indicates that the PLA fiber membrane has no antibacterial effect. Degradation experiments showed that after 90 days, the PLA fiber membrane maintained a good appearance in river water, but due to the colonization of diatoms and microorganisms, many green spots appeared on the surface, and the weight loss in river water was approximately 12%.

[0055] Comparative Example 2

[0056] The PP meltblown fabric used in the middle layer of disposable medical masks purchased from the market showed that, during a 20-minute adsorption test, its adsorption efficiency for PM2.5 and PM10 remained around 80%, with a maximum of only 88.56% and 90.26% respectively, indicating no antibacterial effect. Degradation experiments showed that after 90 days, the meltblown fabric exhibited no significant change in appearance, but its weight loss in river water was approximately -2%, attributed to the colonization of diatoms and microorganisms, resulting in a slight increase in mass.

[0057] This invention utilizes an in-situ growth method to load ZIF-8 onto chitosan, using safe, environmentally friendly, inexpensive, and readily available raw materials. It is expected that the positive charge on ZIF-8 will cause CS@ZIF-8 to become positively charged, thereby enhancing the antibacterial properties of chitosan. The prepared membrane possesses structural characteristics such as fine fiber diameter, high porosity, large specific surface area, and self-charged structure, resulting in better interception and adsorption effects, thus achieving high filtration efficiency, low air resistance, and low basis weight.

Claims

1. A preparation method of a CS@ZIF-8 / PLA composite electrospun fiber membrane with rapid degradation in water, high antibacterial property and filtration efficiency, characterized in that, A positively charged MOFs composite material, CS@ZIF-8, is synthesized by in-situ growth method; the composite electrospun fiber membrane is prepared by mixing the CS@ZIF-8 with polylactic acid to prepare a spinning solution and then electrospinning, specifically including the following steps: Step 1: dispersing the CS@ZIF-8 into a mixed solvent of N,N-dimethylformamide and dichloromethane, adding polyvinylpyrrolidone as a dispersant, stirring, and ultrasonicating to prepare a suspension; then pouring the suspension into a polylactic acid solution and stirring to prepare a mixed spinning solution, wherein the mass percentage of polylactic acid and CS@ZIF-8 is (99-95):(1-5); Step 2: electrospinning the mixed spinning solution, and the spinning process parameters are as follows: voltage 20 kV, injection speed 1.5-2.0 mL / h, receiving distance 15-17 cm, roller speed 70 rpm, ambient temperature 30-40℃, and ambient humidity 40-60% RH; after spinning, drying in an oven to prepare a composite electrospun fiber membrane; In step 1, the molar ratio of CS to ZIF-8 in CS@ZIF-8 is 1:

100.

2. The method of claim 1, wherein, In step 1, the Zeta potential value of CS@ZIF-8 is +13.8±1.45 mV.

3. The method of claim 1, wherein, In step 1, the polylactic acid solution is a dichloromethane solution of polylactic acid.

4. The method of claim 1, wherein, In step 1, the mass fraction of polylactic acid in the mixed spinning solution is 12%.

5. The method of claim 1, wherein, In step 1, the mass ratio of N,N-dimethylformamide to dichloromethane is 1:

4.

6. The method of claim 1, wherein, In step 1, the mass ratio of CS@ZIF-8 to polyvinylpyrrolidone is 1:

5.

7. The method of claim 1, wherein, In step 2, the injection pump flow rate is 1.9 mL / h, and the receiving distance is 15 cm.

8. The composite electrospun fiber membrane prepared by the method of any one of claims 1-7.

9. The use of the composite electrospun fiber membrane prepared by the method of any one of claims 1-7 as filter material.

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