Bamboo fiber-based composite foam material as well as preparation method and application thereof

Abstract

The invention discloses a bamboo fiber-based composite foam material as well as a preparation method and application thereof, and belongs to the field of biomass chemical engineering technologies and environmental remediation. The preparation method comprises the following steps: mixing bamboo fibers with micron fibers, polyvinyl alcohol and starch, stirring and foaming to form wet foam, freezing, carrying out freeze-thaw replacement on a solvent, and drying at normal pressure to prepare the bamboo fiber-based composite foam material. The composite foam material prepared by the invention has super-efficient capturing capability on micro-nano plastics, the filtering efficiency reaches 100%, the filtering flux reaches 7200 L / m < 2 > / h, the adsorption capacity reaches 734 mg / g, the removal efficiency is high, the composite foam material can be repeatedly utilized, and the removal cost is greatly reduced.

Description

Technical Field

[0001] The present invention belongs to the fields of biomass chemical engineering technology and environmental remediation, and particularly relates to a bamboo fiber-based composite foam material, a preparation method thereof, and an application thereof. Background Art

[0002] Micro-nano plastic (referring to plastic particles <5 mm) pollution, as an important threat to the Earth system boundary, has currently become one of the topics attracting much attention in global environmental issues. Micro-nano plastics are almost present in all parts of the abiotic (including water bodies, land, and atmosphere) and biotic (including plants, animals, and humans) ecosystems on the Earth. Due to the continuous increase in the annual production and waste emissions of plastic products, while the recycling and reuse rates are limited, and the degradability of the materials is poor, the micro-nano plastic pollution problem has become a major global environmental challenge. Micro-nano plastics may affect environmental quality and biological health through their own physical and chemical properties, as well as their interactions with chemical substances and microorganisms in the environmental medium. In particular, the pollutants carried by these particles, such as chemical substances and microorganisms, will spread between biotic and abiotic ecosystems, resulting in a combined pollution effect. Micro-nano plastics have a high degree of variability in physical and chemical properties, including particle size, shape, polymer type, additives, aging time, and the substances attached to them. So far, a large number of studies have shown that micro-nano plastics are widely present in rivers, lakes, and urban sewage.

[0003] Currently, physical means such as conventional coagulation and flocculation, chemical means such as photocatalysis, and microbial degradation have been successfully used to remove micro-nano plastics. Among them, coagulation and flocculation require the addition of a large amount of chemical reagents, which not only easily cause secondary pollution, but also have poor effects on plastics with smaller sizes or special surface properties (less than 10%). Photocatalytic degradation requires a large amount of energy input, while microbial degradation is slow and has limited efficiency, restricting its large-scale application. Therefore, it is necessary to develop a material for efficient, high-throughput, and multi-cycle removal.

[0004] In recent years, there have been some studies on the removal of micro-nano plastics. For example, in the patent of Chen Lidong et al. (CN 118223330A), a vacuum filtration method is used to load TEMPO-oxidized nanocellulose on the surface of filter paper, and a nanocellulose filter paper composite paper-based material is obtained through glutaraldehyde cross-linking treatment. The filtration efficiency reaches 96%, but the filtration flux is only 784 L / m 2 / h. Another example is the patent of Zhu Gaojian et al. (CN118440391A), in which polydopamine and quaternary ammonium salt-modified nanocellulose are freeze-dried to prepare a polydopamine-nanocellulose composite aerogel material, and the filtration flux of micro-nano plastics is 1748 L / m 2 / h. Therefore, how to further improve the filtration flux of the material on the basis of ensuring the removal efficiency to meet the requirements of large-scale application. Summary of the Invention

[0005] The first technical problem to be solved by the present invention is to provide a preparation method of a bamboo fiber-based composite foam material, which has the advantages of simple preparation process, low cost, etc.; the second technical problem to be solved by the present invention is to provide a bamboo fiber-based composite foam material obtained by the above method, which can efficiently filter and adsorb micro-nano plastics in water and has a broad-spectrum effect in terms of size and type; the third technical problem to be solved by the present invention is to provide the application of the above bamboo fiber-based composite foam material in micro-nano plastic filtration.

[0006] To solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0007] A preparation method of a bamboo fiber-based composite foam material, which mixes bamboo fiber with microfiber, polyvinyl alcohol, and starch, forms wet foam through stirring and foaming, then freezes it, replaces the solvent through freeze-thaw, and dries it under normal pressure to obtain the bamboo fiber-based composite foam material.

[0008] Further, the mass ratio of the microfiber to the bamboo fiber is 1-3:9-7, the polyvinyl alcohol accounts for 12-16 wt% of the total mass of the bamboo fiber and the microfiber, the starch accounts for 14-18 wt% of the total mass of the microfiber and the bamboo fiber, and the foam slurry concentration is 2-4%.

[0009] Further, the freezing temperature is -20 °C and the freezing time is 6 h.

[0010] Further, the method of solvent freeze-thaw replacement is: successively use 50% ethanol solution, 100% ethanol solution, 50% tert-butanol / ethanol solution, and 100% tert-butanol solution for solvent replacement, and the replacement time for each time is 1 h.

[0011] Further, the normal pressure drying temperature is 25 °C and the drying time is 24 h.

[0012] Further, a bamboo fiber-based composite foam material is prepared by any of the above preparation methods of the bamboo fiber-based composite foam material.

[0013] Further, the application of the above bamboo fiber-based composite foam material in filtering and adsorbing micro-nano plastics.

[0014] Further, the micro-nano plastics for filtration are selected from any one or at least two combinations of polystyrene, carboxylated polystyrene, aminoated polystyrene, polypropylene, polyethylene, and polyethylene terephthalate, and the filtration concentration is 25-100 ppm; the size of the micro-nano plastics is 500-10000 nm.

[0015] Further, the number of cycles of the composite foam material is 1-12 times.

[0016] Furthermore, the micro-nano plastics used for adsorption are selected from any one or a combination of at least two of polystyrene, carboxylated polystyrene, and amino-functionalized polystyrene, the adsorption temperature is 25 °C; the size of the micro-nano plastics is 500-10,000 nm.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] (1) The present invention prepares a foam material using bamboo fiber, microfiber, starch, and polyvinyl alcohol as substrates to replace petroleum-based foam, which can achieve the purpose of environmental friendliness.

[0019] (2) The present invention uses bamboo fiber as the main component of the foam, and microfiber and starch as reinforcing agents to realize the regulation of the pore size of the composite foam material. The ultra-high efficiency capture of micro-nano plastics has a broad-spectrum effect in terms of type, size, and concentration, the filtration efficiency reaches 100%, and the filtration flux reaches 7200 L / m 2 / h, and the adsorption capacity reaches 734 mg / g.

[0020] (3) The bamboo fiber-based composite foam material of the present invention has excellent filtration efficiency and flux, has very little dependence on pressure driving, and has excellent adsorption capacity, further ensuring low energy consumption. Description of the Drawings

[0021] Figure 1 is the physical property diagram of the orthogonal test of the bamboo fiber-based composite foam material prepared in Examples 2-10; among them, Figure (a) is the density diagram of the sample OE1-9 foam material, Figure (b) is the volume change diagram of the sample OE1-9 wet foam before and after stirring, Figure (c) is the stress-strain curve diagram of the sample OE1-9 foam material, and Figure (d) is the Young's modulus diagram of the sample OE1-9 foam material;

[0022] Figure 2 is the physical property diagram of the bamboo fiber-based composite foam materials with different pulp concentrations prepared in Example 8 and Comparative Examples 1-2; among them, Figure (a) is the stress-strain curve diagram of the composite foam materials with different pulp concentrations, Figure (b) is the Young's modulus diagram of the composite foam materials with different pulp concentrations, Figure (c) is the bubble microscope diagram of BF-4% wet foam, Figure (d) is the FE-SEM image of BF-2% composite foam, Figure (e) is the FE-SEM image of BF-3% composite foam, and Figure (f) is the FE-SEM image of BF-4% composite foam;

[0023] Figure 3Filtration performance diagrams of bamboo fiber-based composite foams with different pulp concentrations prepared in Example 8 and Comparative Examples 1-2 for micro-nano plastics; among them, Figure (a) is the fluorescence curve images of composite foams with different pulp concentrations before and after filtering 50 ppm PS (Ф2μm), Figure (b) is the filtration efficiency and filtration flux diagrams of composite foams with different pulp concentrations for 50 ppm PS (Ф2μm), Figure (c) is the filtration efficiency and filtration flux diagrams of BF-4% composite foam for PS (Ф2μm), PS-COOH (Ф2μm) and PS-NH 2 (Ф2μm), Figure (d) is the filtration efficiency and filtration flux diagrams of BF-4% composite foam for PS of different sizes, Figure (e) is the filtration efficiency and filtration flux diagrams of BF-4% composite foam for PS of different concentrations, Figure (f) is the filtration efficiency and filtration flux diagrams of BF-4% composite foam for 50 ppm PS (Ф2μm) under different pH conditions, Figure (g) is the FE-SEM diagram of BF-4% composite foam after filtering 50 ppm PS (Ф2μm), Figure (h) is the FE-SEM diagram of BF-4% composite foam after filtering 50 ppm PS-COOH (Ф2μm), Figure (i) is the FE-SEM diagram of BF-4% composite foam after filtering 50 ppm PS-NH 2 (Ф2μm);

[0024] Figure 4 Diagrams of the cycling performance and general performance of the bamboo fiber-based composite foam material prepared in Example 8; among them, Figure (a) is the filtration efficiency diagram of BF-4% composite foam for cyclic filtration of 50 ppm PS (Ф2μm) 12 times, Figure (b) is the filtration flux of BF-4% composite foam for cyclic filtration of 50 ppm PS (Ф2μm) 12 times, Figure (c) is the filtration efficiency and filtration flux of BF-4% composite foam for PE, PET, and PP;

[0025] Figure 5 Adsorption performance diagrams of the bamboo fiber-based composite foam material prepared in Example 8 for micro-nano plastics; among them, Figure (a) is the adsorption capacity diagram of BF-4% composite foam for micro-nano plastics with different charges (50 ppm Ф500nm), Figure (b) is the adsorption capacity diagram of BF-4% composite foam for PS of different sizes (50 ppm, Ф500nm) in cycles. Detailed implementation methods

[0026] The following combines specific examples to further clarify the present invention. The examples are implemented on the premise of the technical solution of the present invention. It should be understood that these examples are only used to illustrate the present invention and not to limit the scope of the present invention.

[0027] In the following examples, MFC is microfiber, PVA is polyvinyl alcohol, CS is starch, MNPs is micro-nano plastic, OE1 - 9 are samples of orthogonal test numbers 1 - 9, BF2 - 4% are foam samples prepared with different fiber pulp concentrations under the OE - 7 process, PS is polystyrene, PS - COOH is carboxylated polystyrene, and PS - NH 2 is aminated polystyrene, PE is polyethylene, PP is polypropylene, and PET is polyethylene terephthalate.

[0028] The bleached Neosinocalamus affinis pulp fibers were purchased from Sichuan Yongfeng Paper Co., Ltd.

[0029] Mechanically ground cellulose microfibers (length 20 - 40 μm) were purchased from Tianjin Wood Elf Biotechnology Co., Ltd.

[0030] Example 1

[0031] A preparation method of a bamboo fiber - based composite foam material specifically includes the following steps:

[0032] (1) First, prepare 300 g of a 10% bamboo pulp fiber suspension. After defibrating the bamboo fibers with a defibrator and then grinding them with a PFI refiner to 10000 rpm, after equilibrating the moisture of the ground bamboo pulp suspension at room temperature for 3 days, measure the moisture using a 4 h, 105 °C oven, and then mix the microfibers (where the mass ratio of microfibers to bamboo fibers is 1:9, 2:8, 3:7) to prepare 2%, 3%, and 4% fiber suspensions respectively.

[0033] (2) Add 1.6 g of CS particles to 38.4 g of deionized water at 75 °C, dissolve for 1 h, prepare 14, 16, 18 wt% CS solutions, and place them in a 4 °C refrigerator for 12 h to remove air bubbles.

[0034] (3) Mix the 14, 16, 18 wt% CS solutions with the 2%, 3%, 4% fiber suspensions (where the mass ratio of microfibers to bamboo fibers is 1:9, 2:8, 3:7), add an appropriate amount of deionized water to make the system reach 10 g, stir evenly, then add 12, 14, 16 wt% PVA particles and stir at 10000 rpm for 1 min to obtain wet foam.

[0035] (4) Place the wet foam in a - 20 °C refrigerator and freeze for 6 h. Then, place the frozen sample in 25 °C water to equilibrate to room temperature. Successively use 50% ethanol solvent, 100% ethanol solvent, 50% tert - butanol / ethanol solvent, and 100% tert - butanol solvent for solvent replacement, with each replacement time being 1 h. After the replacement is completed, take out the sample and dry it at normal pressure at a temperature of 25 °C for 24 h to obtain the bamboo fiber - based composite foam material.

[0036] Example 2

[0037] When preparing the bamboo fiber-based composite foam material, 14 wt% of CS solution was mixed with 2% fiber suspension (where the mass ratio of microfiber to bamboo fiber was 1:9), 12 wt% of PVA particles were added and stirred, and the remaining preparation methods and parameters were the same as those in Example 1. OE-1 foam was prepared, and the main pore size distribution was 12.3 μm.

[0038] Example 3

[0039] When preparing the bamboo fiber-based composite foam material, 16 wt% of CS solution was mixed with 2% fiber suspension (where the mass ratio of microfiber to bamboo fiber was 2:8), 14 wt% of PVA particles were added and stirred, and the remaining preparation methods and parameters were the same as those in Example 1. OE-2 foam was prepared, and the main pore size distribution was 11.1 μm.

[0040] Example 4

[0041] When preparing the bamboo fiber-based composite foam material, 18 wt% of CS solution was mixed with 2% fiber suspension (where the mass ratio of microfiber to bamboo fiber was 3:7), 16 wt% of PVA particles were added and stirred, and the remaining preparation methods and parameters were the same as those in Example 1. OE-3 foam was prepared, and the main pore size distribution was 9.1 μm.

[0042] Example 5

[0043] When preparing the bamboo fiber-based composite foam material, 16 wt% of CS solution was mixed with 3% fiber suspension (where the mass ratio of microfiber to bamboo fiber was 3:7), 12 wt% of PVA particles were added and stirred, and the remaining preparation methods and parameters were the same as those in Example 1. OE-4 foam was prepared, and the main pore size distribution was 16.0 μm.

[0044] Example 6

[0045] When preparing the bamboo fiber-based composite foam material, 18 wt% of CS solution was mixed with 3% fiber suspension (where the mass ratio of microfiber to bamboo fiber was 1:9), 14 wt% of PVA particles were added and stirred, and the remaining preparation methods and parameters were the same as those in Example 1. OE-5 foam was prepared, and the main pore size distribution was 15.1 μm.

[0046] Example 7

[0047] When preparing the bamboo fiber-based composite foam material, 14 wt% of CS solution was mixed with 3% fiber suspension (where the mass ratio of microfiber to bamboo fiber was 2:8), 16 wt% of PVA particles were added and stirred, and the remaining preparation methods and parameters were the same as those in Example 1. OE-6 foam was prepared, and the main pore size distribution was 14.5 μm.

[0048] Example 8

[0049] When preparing the bamboo fiber-based composite foam material, 18 wt% of CS solution was mixed with 4% fiber suspension (where the mass ratio of microfiber to bamboo fiber was 2:8), 12 wt% of PVA particles were added and stirred, and the remaining preparation methods and parameters were the same as those in Example 1. OE-7 foam was prepared, and the main pore size distribution was 15.4 μm.

[0050] Example 9

[0051] When preparing the bamboo fiber-based composite foam material, 14 wt% of CS solution was mixed with 4% fiber suspension (where the mass ratio of microfiber to bamboo fiber was 3:7), 14 wt% of PVA particles were added and stirred, and the remaining preparation methods and parameters were the same as those in Example 1. OE-8 foam was prepared, and the main pore size distribution was 14.9 μm.

[0052] Example 10

[0053] When preparing the bamboo fiber-based composite foam material, 16 wt% of CS solution was mixed with 4% fiber suspension (where the mass ratio of microfiber to bamboo fiber was 1:9), 16 wt% of PVA particles were added and stirred, and the remaining preparation methods and parameters were the same as those in Example 1. OE-9 foam was prepared, and the main pore size distribution was 14.1 μm.

[0054] The physical properties of the bamboo fiber-based composite foam materials prepared in Examples 2-10 were characterized. As shown in Table 1, they were the effects of different factors on the foam density, foaming volume, elastic modulus, compressive strength, and average pore size. As Figure 1 shown, they were (a) the density image of the sample OE1-9 foam material; (b) the change diagram of the foaming volume of the sample OE1-9 wet foam; (c) the stress-strain curve of the sample OE1-9 foam material; (d) the Young's modulus diagram of the sample OE1-9 foam material.

[0055] Table 1 Range analysis results of the orthogonal experiment of the bamboo fiber-based composite foam material

[0056]

[0057] As can be seen from Table 1, the pulp concentration has the greatest influence on density, foaming volume, elastic modulus and compressive strength, and the amount of microfiber has the greatest influence on the average pore size of the foam. From Figure 1 it can be seen that when the pulp concentration and the amount of microfiber are small, the composite foam material has a large density, a large foaming volume, and small compressive strength and elastic modulus. This is because there are few fibers in the system, and large wet foams cannot stably form composite foam materials, resulting in a dense local structure of the material, reduced and uneven pores, and a large apparent density of the system. As the pulp concentration, microfiber and PVA content increase, the structure of the foam material gradually changes from densification to a three-dimensional fluffy structure, the density decreases, the elastic modulus and compressive strength increase, and the pores are more uniform. Therefore, the optimal process conditions determined by combining physical properties and range analysis are: the CS dosage is 14 wt%, the PVA dosage is 16 wt%, the pulp concentration is 4%, and the mass ratio of microfiber to bamboo fiber is 2:8.

[0058] The results of range analysis of the orthogonal experiments in Examples 2-10 show that the pulp concentration and the amount of microfiber have the greatest influence on the physical properties and pore structure of the composite foam. Therefore, bamboo fiber-based composite foams with a CS dosage of 14 wt%, a PVA dosage of 12 wt%, and a pulp concentration of 2-4% are selected for micro-nano plastic filtration experiments.

[0059] Comparative Example 1

[0060] When preparing the bamboo fiber-based composite foam material, an 18 wt% CS solution was mixed with a 2% fiber suspension (where the mass ratio of microfiber to bamboo fiber is 2:8), 12 wt% PVA particles were added and stirred, and the remaining preparation methods and parameters were the same as those in Example 1, and BF-2% foam was prepared.

[0061] Comparative Example 2

[0062] When preparing the bamboo fiber-based composite foam material, an 18 wt% CS solution was mixed with a 3% fiber suspension (where the mass ratio of microfiber to bamboo fiber is 2:8), 12 wt% PVA particles were added and stirred, and the remaining preparation methods and parameters were the same as those in Example 1, and BF-3% foam was prepared.

[0063] The physical properties of the composite foam materials prepared in Example 8 and Comparative Examples 1 and 2 were compared, as Figure 2 shown, (a) stress-strain curves of composite foam materials with different pulp concentrations; (b) Young's modulus diagrams of composite foam materials with different pulp concentrations; (c) microscopic images of bubbles in BF-4% wet foam; (d) FE-SEM images of BF-2% composite foam; (e) FE-SEM images of BF-3% composite foam; (f) FE-SEM images of BF-4% composite foam.

[0064] FromFigure 2 (a) and Figure 2 As can be seen from (b), as the pulp concentration increases, the compressive strength increases from 9.5 kPa to 21.2 kPa, and the Young's modulus increases from 82.7 kPa to 383.5 kPa. This is attributed to the increase of fibers in the composite foam stabilizing the three-dimensional structure of the foam, making the foam structure stable and uniform, and enhancing the mechanical strength. From Figure 2 (c), it can be found that under high-speed stirring, there are a large number of uniform and stable bubbles in the BF-4% wet foam, and the pore size distribution is in the range of 10 - 210 μm, with an average size of 68.9 μm. Figure 2 (d), Figure 2 and Figure 2 (f) are the SEM images of BF-2%, BF-3% and BF-4% respectively. It can be seen that with the increase of fiber content, more microfibers are intertwined to form a network structure, the pore size decreases and the three-dimensional morphology of the foam is stabilized, which is beneficial to improving the mechanical properties.

[0065] Example 11

[0066] Experiment on filtering microplastics with bamboo fiber-based composite foam materials: Take a composite foam sample with a height of 10 mm and a diameter of 15 mm as the filtering matrix and fill it at the bottom of the filter tube of the filtering device, and firmly connect the filter tube and the filter element gasket. Weigh 20 mL of the ultrasonic-dispersed micro-nano plastic suspension, pour the suspension containing micro-nano plastics from above the filter tube under a pressure of 0.1 bar and start timing. Stop timing after filtration ends and collect the filtrate. Calculate the filtration efficiency and filtration flux according to the filtration area of the filtration device, filtration time, volume of the micro-nano plastic suspension, initial concentration of micro-nano plastics and residual concentration after filtration;

[0067]

[0068]

[0069] Among them, μ is the filtration efficiency (%), C 0 and C f are the micro-nano plastic concentrations (ppm) of the suspension before and after filtration respectively, J is the filtration flux (L / m 2 / h), V f is the effective filtration volume (L) of micro-nano plastics, S a is the effective filtration area (m 2 ) of the composite foam material, and t is the filtration time (h).

[0070] Example 12

[0071] The bamboo fiber-based composite foam materials prepared in Example 8 and Comparative Examples 1 and 2 were subjected to a test for filtering micro-nano plastics. In order to study the effect of the composite foam pulp concentration on the filtering performance of micro-nano plastics, the filtering efficiency and filtering flux of different pulp concentrations for 50 ppm PS (Ф2μm) were measured using the measurement method of Example 11. The results are as Figure 3 shown in Figure 3 (a) and

[0072] As can be seen from Figure 3 (a) and Figure 3 (b), the filtering efficiencies of the BF-2%, BF-3% and BF-4% composite foams for PS were 91.7%, 97.4% and 99.4% respectively, and the corresponding filtering fluxes were 17240, 12857 and 7257 L / m 2 / h. As the pulp concentration increased, the fluorescence intensity of the filtered water sample decreased, and the filtering efficiency gradually increased, indicating that more network structures were formed by the fibers, providing more capture sites and enhancing the ability to intercept PS. Therefore, BF-4% was selected for subsequent filtering tests.

[0073] Example 13

[0074] The bamboo fiber-based composite foam materials prepared in Example 8 and Comparative Examples 1 and 2 were subjected to a test for filtering micro-nano plastics. Since CS is a cationic starch, the prepared composite foam material is positively charged. In order to study the effect of electrostatic interaction on the filtering performance of micro-nano plastics, the filtering efficiency and filtering flux of PS, PS-COOH and PS-NH 2 (50 ppm, Ф2μm) were measured using the measurement method of Example 11. The results are as Figure 3 shown in

[0075] As can be seen from Figure 3 (c), the filtering efficiencies of the BF-4% composite foam material for negatively charged PS and PS-COOH were 99.4% and 96.0% respectively, and the filtering fluxes were 7257 and 8518 L / m 2 / h. The filtering efficiency of the BF-4% composite foam material for positively charged PS-NH 2 was 87.1%, and the filtering flux was 15340 L / m 2 / h. Figure 3 (g)-(i) are the SEM images of BF-4% filtering PS, PS-COOH and PS-NH 2 respectively. It can be clearly seen that there is an obvious electrostatic attraction effect on negatively charged PS and PS-COOH, and the microplastic microspheres are adsorbed on the fibers in large quantities. For positively charged PS-NH 2 , there is more interception by the foam network structure.

[0076] Example 14

[0077] The bamboo fiber-based composite foam materials prepared in Example 8 and Comparative Examples 1 and 2 were subjected to a test for filtering micro-nano plastics. To study the effect of the size of micro-nano plastics on the filtering performance, the filtering efficiency and filtering flux for different sizes of 50 ppm PS (Ф500 nm, Ф2 μm, Ф5 μm, Ф10 μm) were measured using the measurement method of Example 11. The results are as Figure 3 shown in (d).

[0078] As can be seen from Figure 3 (d), the filtering efficiencies of BF-4% for PS with sizes of 500 nm, 2 μm, 5 μm, and 10 μm were 81.8%, 99.4%, 99.5%, and 99.2% respectively, and the filtering fluxes were 9409, 7257, 4038, and 2585 L / m 2 / h. It can be clearly seen that as the size of PS increases, the filtering efficiency increases, but the filtering flux decreases. This is because the increase in the size of PS will gradually block the pores in the upper layer of the foam, forming a dense micro-nano plastic layer on the upper layer, resulting in a decrease in its filtering flux.

[0079] Example 15

[0080] The bamboo fiber-based composite foam materials prepared in Example 8 and Comparative Examples 1 and 2 were subjected to a test for filtering micro-nano plastics. To study the effect of the concentration of micro-nano plastics on the filtering performance, the filtering efficiency and filtering flux for different concentrations of PS (Ф2 μm 25 ppm, 50 ppm, 75 ppm, 100 ppm) were measured using the measurement method of Example 11. The results are as Figure 3 shown in (e).

[0081] As can be seen from Figure 3 (e), the filtering efficiencies of BF-4% for PS with concentrations of 25 ppm, 50 ppm, 75 ppm, and 100 ppm were 98.8%, 99.4%, 98.5%, and 98.5% respectively, and the filtering fluxes were 18149, 7252, 5385, and 3264 L / m 2 / h.

[0082] Example 16

[0083] The bamboo fiber-based composite foam materials prepared in Example 8 and Comparative Examples 1 and 2 were subjected to a test for filtering micro-nano plastics. To study the effect of the pH value of the water body on the filtering performance of micro-nano plastics, the filtering efficiency and filtering flux of the composite foam for PS (Ф2 μm) at different pH values (3, 7, 11) were measured using the measurement method of Example 11. The results are as Figure 3 shown in (f).

[0084] As can be seen from Figure 3As can be seen from (f), when the pH is 3, 7, and 11, the filtration efficiency of BF-4% for PS is 83.1%, 95.7%, and 71.9% respectively, and the filtration fluxes are 10507, 12293, and 6144 L / m 2 / h. It can be clearly seen that when the pH is neutral, the filtration performance is the best.

[0085] Example 17

[0086] The BF-4% composite foam prepared in Example 8 and Comparative Examples 1 and 2 was used for a cyclic filtration test of 50 ppm PS (Ф2μm). The filtration efficiency and filtration flux at different cyclic times were measured by the measurement method of Example 11.

[0087] The results are as Figure 4 shown in (a) and Figure 4 (b). As the number of cycles increases, the filtration efficiency of the BF-4% composite foam for PS always remains above 99%, but the filtration flux gradually decreases and tends to be stable, and finally remains at 1000 L / m 2 / h, indicating that the bamboo fiber-based composite foam material has stable cyclic use performance.

[0088] Example 18

[0089] The BF-4% composite foam prepared in Example 8 was used to filter different types of micro-nano plastics, and the filtration efficiency and filtration flux were measured by the measurement method of Example 11.

[0090] The results are as Figure 4 shown in (c). The filtration efficiencies of the BF-4% composite foam for PE, PET, and PP are 99.3%, 98.4%, and 97.7% respectively, and the filtration fluxes are 6633, 10696, and 7517 L / m 2 / h. The above results indicate that the bamboo fiber-based composite foam material has a broad-spectrum effect on filtering micro-nano plastics.

[0091] Example 19

[0092] Adsorption test of bamboo fiber-based composite foam material for micro-nano plastics: The bamboo fiber-based composite foam material dried at normal pressure for 24 h was cut into a cube with a weight of 3 mg and a length, width, and height of 6 mm. Weigh 3 mL of the ultrasonically dispersed micro-nano plastic suspension into a centrifuge tube. After adding the composite foam material to the centrifuge tube, place it in a water bath thermostatic oscillator at 100 rpm for adsorption for 24 h. After the adsorption ends, stop timing and collect the suspension. The adsorption capacity was calculated based on the concentration of micro-nano plastics before and after adsorption, the volume of the micro-nano plastic water body, and the mass of the composite foam material:

[0093]

[0094] where Q is the adsorption capacity (mg / g), C 0 and C f are the concentrations of micro-nano plastics in the suspension (ppm) before and after adsorption, respectively, V is the volume of the micro-nano plastic suspension (mL), and m is the weight of the composite foam (g).

[0095] Example 20

[0096] The bamboo fiber-based composite foam material prepared in Example 8 was used for the experiment of adsorbing micro-nano plastics. In order to study the influence of electrostatic interaction on the adsorption performance of micro-nano plastics, the adsorption capacities of the composite foam for PS (50 ppm, Ф500nm), PS-COOH (50 ppm, Ф500nm) and PS-NH 2 (50 ppm, Ф500nm) were measured by the measurement method of Example 19, and the results are as Figure 5 shown in (a).

[0097] As can be seen from Figure 5 (a), the adsorption capacities of the BF-4% composite foam for negatively charged PS and PS-COOH are 743.1 mg / g and 933.9 mg / g respectively, and the adsorption capacity for positively charged PS-NH 2 is 251.9 mg / g, indicating that the composite foam has a better adsorption effect on negatively charged micro-nano plastics.

[0098] Example 21

[0099] The bamboo fiber-based composite foam material prepared in Example 8 was used for the experiment of adsorbing micro-nano plastics. In order to study the influence of the size of micro-nano plastics on the adsorption performance, the adsorption capacities of the composite foam for PS (Ф500nm), PS (Ф2000nm), PS (Ф5000nm) and PS (Ф10000nm) were measured by the measurement method of Example 19, and the results are as Figure 5 shown in (b).

[0100] As can be seen from Figure 5 (b), the smaller the size of PS, the better the adsorption effect of the composite foam and the larger the adsorption capacity. Among them, when the size of PS is 10000 nm, the adsorption capacity is 276.9 mg / g. When the size of PS is reduced to 500 nm, the corresponding adsorption capacity increases to 734.1 mg / g.

[0101] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a bamboo fiber-based composite foam material, characterized in that: The bamboo fiber is mixed with micron fiber, polyvinyl alcohol and starch, stirred and foamed to form wet foam, then frozen, the solvent is freeze-thawed and replaced, and the mixture is dried under normal pressure to prepare a bamboo fiber-based composite foam material.

2. The method for preparing the bamboo fiber-based composite foam material according to claim 1, characterized in that: The mass ratio of the micron fiber to the bamboo fiber is 1-3:9-7, the polyvinyl alcohol accounts for 12-16 wt % of the total mass of the bamboo fiber and the micron fiber, the starch accounts for 14-18 wt % of the total mass of the micron fiber and the bamboo fiber, and the foam pulp concentration is 2-4%.

3. The method for preparing the bamboo fiber-based composite foam material according to claim 1, characterized in that: The freezing temperature is -20°C and the freezing time is 6 hours.

4. The method for preparing the bamboo fiber-based composite foam material according to claim 1, characterized in that: The solvent freeze-thaw replacement method is: using 50% ethanol solution, 100% ethanol solution, 50% tert-butanol / ethanol solution and 100% tert-butanol solution to replace the solvent in sequence, and each replacement time is 1 hour.

5. The method for preparing the bamboo fiber-based composite foam material according to claim 1, characterized in that: The normal pressure drying temperature is 25°C and the drying time is 24 h.

6. A bamboo fiber-based composite foam material is prepared according to the method for preparing a bamboo fiber-based composite foam material according to any one of claims 1 to 5.

7. Use of the bamboo fiber-based composite foam material according to claim 6 in filtering and adsorbing micro-nano plastics.

8. The use of the bamboo fiber-based composite foam material according to claim 7, characterized in that: The micro-nano plastic used for filtration is selected from any one of polystyrene, carboxylated polystyrene, amino polystyrene, polypropylene, polyethylene, polyethylene terephthalate, or a combination of at least two thereof, and the filtration concentration is 25-100 ppm; the size of the micro-nano plastic is 500-10000 nm.

9. The use of the bamboo fiber-based composite foam material according to claim 7, characterized in that: The number of cycles for composite foam materials ranges from 1 to 12 times.

10. The use of the bamboo fiber-based composite foam material according to claim 7, characterized in that: The micro-nano plastic used for adsorption is selected from any one of polystyrene, carboxylated polystyrene, and amino polystyrene, or a combination of at least two thereof, and the adsorption temperature is 25°C; the size of the micro-nano plastic is 500~10000 nm.

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