A method for determining fiber microplastics in textile aqueous solutions based on fluorescence spectrometry

Abstract

This invention discloses a method for determining fiber microplastics in aqueous textile solutions based on fluorescence spectrophotometry, belonging to the field of textile pollutant detection technology. The method includes: S1, collecting wastewater and filtering it through a filter membrane; S2, rinsing the filter membrane with sodium hypochlorite solution; S3, rinsing the fiber microplastics on the filter membrane into a separatory funnel; S4, pouring out a portion of the fiber microplastics from the upper end of the separatory funnel and collecting another portion from the lower end; S5, repeating S1-S4, rinsing the filter membrane with hydrochloric acid during this process, and collecting the remaining fiber microplastics; S6, dyeing the three solutions obtained; S7, preparing standard series solutions using polyester, polyamide, and polypropylene standard liner; S8, measuring and plotting a standard curve of fluorescence intensity versus fiber microplastic concentration using a fluorescence spectrophotometer; S9, measuring the fluorescence intensity of the three solutions obtained in S6. This invention is applicable to the field of aqueous textile solutions, enabling quantitative analysis of unknown samples, and can analyze both single and mixed samples with minimal detection bias.

Description

Technical Field

[0001] This invention relates to the field of textile pollutant detection technology, and in particular to a method for determining fiber microplastics in aqueous textile solutions based on fluorescence spectrometry. Background Technology

[0002] Plastics are an indispensable material in our daily lives and production. Due to their lightweight, strength, durability, and corrosion resistance, plastic products have become a highly versatile material. Their low price also makes them easy to manufacture widely, finding applications in industry, agriculture, daily necessities, medicine, military, and aerospace. As early as the 1970s, the scientific community began to pay attention to microplastic pollution. In 2004, Thompson et al. first proposed the term microplastics (MPs), drawing widespread attention to tiny plastic particles in the environment. Based on size, the International Symposium on Microplastics defines microplastics as plastic fragments with a diameter of less than 5 mm. In the past decade or so, microplastics have become a hot topic and frontier in environmental science research, experiencing rapid development. Currently, the most abundant type found in research is fibrous microplastics.

[0003] Fibrous microplastics, also known as fiber microplastics, are primarily produced in the textile industry by the breaking of non-degradable fibers from textiles during production, dyeing, finishing, wearing, and washing due to mechanical friction, collisions, and chemical agents. These fibers are then exposed to light, rain, and water flow, transforming into microplastics smaller than 5 mm in size. Due to their recalcitrant nature and bioaccumulation, they pose a significant threat to the environment, plants, animals, and even humans. Common types include polyester fibers, polyamide fibers, and polypropylene fibers. Other recalcitrant microplastics, such as polyvinyl chloride and polystyrene, are rarely used in textile products and therefore do not generate corresponding fiber microplastics. Polyester and polyamide fibers are the most commonly used textile fibers, produced as pure spun synthetic fibers or blended with cotton, viscose, linen, and other fibers to create textiles of various styles and designs. Polypropylene fibers are generally used in the textile industry as textile fillings, clothing linings, or disposable hygiene products, with relatively smaller usage.

[0004] For the detection of microplastics in fibers, the current ISO / DIS 4484-2-2023(E) standard, "Textiles and textile products - Microplastics from textile sources - Part 2: Qualitative and quantitative evaluation of microplastics," employs optical microscopy for examination, followed by qualitative and quantitative analysis of microplastics from textiles using Fourier transform infrared spectroscopy and Raman spectroscopy. Both DB 37 / T4323-2021, "Technical Specification for Environmental Microplastic Monitoring in Marine Aquaculture Areas," and DB 21 / T 2751-2017, "Determination of Microplastics in Seawater - Fourier Transform Infrared Spectroscopy," use stereomicroscopy for examination, followed by Fourier transform infrared spectroscopy to determine the material composition of the microplastic particles. The aforementioned standards all employ large-scale instruments such as Fourier transform infrared spectrometers or Raman spectrometers. Sample preparation is complex, the detection cycle is long, professional operation is required, and costs are high. Furthermore, when the amount of fiber microplastics is slightly large, they tend to aggregate, which complicates counting and infrared and Raman spectroscopy scanning. The varying lengths of fiber microplastics also make it difficult to accurately describe their quantity using quantitative methods.

[0005] A Chinese invention patent with publication number CN112730368A discloses a thermal cycling method and concentration analysis method for preparing fluorescently stained microplastics. The method includes the following steps: 1. Mixing a dye and an organic solvent to prepare a staining working solution; 2. Mixing the staining working solution with microplastics, thermally cycling and shaking for staining, filtering and drying to obtain fluorescently stained microplastics; 3. Staining an unknown sample and measuring the fluorescence intensity, using a standard curve between the concentration of fluorescently stained microplastics and the fluorescence intensity to analyze the mass concentration of microplastics in the unknown sample. This invention provides a short, rapid and convenient method for quantitative analysis of microplastics.

[0006] However, while this technical solution enables quantitative analysis of fiber microplastics without the use of large-scale instruments, it requires prior qualitative analysis to determine the specific microplastics present in the unknown sample before selecting the appropriate standard curve. This makes it unsuitable for quantitative analysis of unknown samples without prior qualitative analysis. Furthermore, this method is only applicable to quantitative analysis of single-type unknown samples, such as those containing only polyethylene or polyethylene terephthalate microplastics. It cannot be used for quantitative analysis of mixed samples containing multiple microplastics. Therefore, this fiber microplastic quantitative analysis method has significant limitations and is difficult to apply in practice.

[0007] Furthermore, we know that microplastics come in various types, classified by morphology as flakes, microspheres, foams, fibers, films, etc. The standard curve provided in this technical solution can be understood as applicable to all forms of microplastics. However, for particulate microplastics, their particle size directly affects the fluorescence intensity after dyeing, and the standard curve differs for each size range of microplastics. In other words, applying the standard curve in this technical solution for quantitative analysis of certain specific forms of microplastics will result in significant biases. Therefore, applying this technical solution to the determination of microplastics in textile wastewater is unlikely to yield reliable quantitative analysis results.

[0008] In addition to the above, in the determination of fiber microplastics in textile wastewater, we know that textile wastewater also contains other biodegradable fibers such as cotton, viscose, flax, sheep wool, silk, and polyacrylonitrile fiber. These biodegradable fibers can interfere with the determination of fiber microplastics, resulting in inaccurate measurements. This technical solution also struggles to solve these problems.

[0009] Therefore, there is an urgent need to invent a method that is less restrictive, reliable, accurate, and applicable to the determination of fiber microplastics in textile wastewater. Summary of the Invention

[0010] The purpose of this invention is to address the shortcomings of existing technologies by proposing a method for determining fiber microplastics in textile aqueous solutions based on fluorescence spectrometry.

[0011] To achieve the above objectives, the present invention adopts the following technical solution:

[0012] A method for determining microplastics in textile fibers in aqueous solution based on fluorescence spectrometry includes the following steps:

[0013] S1. Collect wastewater from the environment and filter the wastewater sample using a micro-glass filtration device with a glass fiber filter membrane.

[0014] S2. Rinse the filter membrane with sodium hypochlorite solution, turn off the vacuum filtration device, and allow the fiber microplastics to be fully immersed in the sodium hypochlorite solution. After standing for a period of time, wash the filter membrane with plenty of water until it is neutral.

[0015] S3. Rinse the fiber microplastics on the filter membrane into the tertiary water, add it to the separatory funnel, and let it stand until clear separation occurs.

[0016] S4. Pour the fiber microplastics floating on the surface of the solution out from the upper port of the separatory funnel, and collect the fiber microplastics deposited at the bottom from the lower port. The liquid collected at the upper port is the test solution 1, and the liquid collected at the lower port is the test solution 2.

[0017] S5. Repeat S1-S2, then rinse the filter membrane with hydrochloric acid to remove any small amount of fiber microplastics that may be present. Collect the remaining fiber microplastics, rinse the filter membrane with plenty of water until neutral, and then repeat S3-S4. Collect the fiber microplastics deposited at the bottom from the lower end of the separatory funnel and label it as test solution 3.

[0018] S6. Filter the three solutions 1, 2 and 3 obtained for testing respectively, and stain them with the prepared Nile Red dye solution.

[0019] S7. Take the dyed and filtered polyester, polyamide, and polypropylene standard lining fiber microplastics and prepare them into a series of standard solutions with concentration gradients.

[0020] S8. Take appropriate amounts of standard series solutions from low to high in sequence, place them in cuvettes, start the fluorescence spectrophotometer to measure and plot the standard curve of fluorescence intensity versus fiber microplastic concentration. After performing exponential fitting on the standard curve, obtain the standard curve fitting equation.

[0021] S9. After dispersing the three solutions obtained in S6 evenly, measure their fluorescence intensity on a fluorescence spectrophotometer, and calculate the concentration of fiber microplastics in the aqueous solution by combining the standard curve fitting equation.

[0022] Furthermore, in step S2, the rinsing volume of sodium hypochlorite solution is 20 mL to 50 mL, and the concentration of sodium hypochlorite solution is 0.9 mol / L to 1.0 mol / L.

[0023] Furthermore, the separating funnel is a cylindrical separating funnel.

[0024] Furthermore, in step S5, the amount of hydrochloric acid is 20mL-50mL, and the filter bottle for receiving the filtrate is replaced before rinsing the filter membrane with hydrochloric acid.

[0025] Furthermore, the Nile Red dyeing step in S6 is as follows: the three types of fiber microplastics are rinsed into the dyeing solution with 80mL-150mL of the prepared Nile Red dyeing solution and left to stand at room temperature for 20min-40min; wherein the concentration of Nile Red fluorescent dye is 80ug / mL.

[0026] Furthermore, in S7, 0.5000g ± 0.0002g of polyester, polyamide, and polypropylene standard linings are weighed and crushed into various fiber microplastics with a length of <2mm.

[0027] The dyeing process includes: placing various types of fiber microplastics into conical flasks, adding tertiary water and Nile red dye, and letting them stand at room temperature for a period of time, wherein the concentration of Nile red dye is 160ug / mL;

[0028] The filtration process includes rinsing with a 1:1 solution of water and acetone, followed by drying before use.

[0029] Furthermore, in step S7, the preparation process of the standard series solutions with concentration gradients is as follows:

[0030] Weigh 0.2500g±0.0002g of dyed polyester and polyamide standard lining fiber microplastics respectively, add them to an aqueous solution containing surfactant to prepare standard solutions, and dilute them into at least 6 solutions with concentration gradients.

[0031] Weigh 0.2500g ± 0.0002g of dyed polypropylene standard lining fiber microplastics, add them to liquid paraffin to prepare a standard solution, and dilute them to prepare at least 6 solutions with concentration gradients.

[0032] Furthermore, the standard curve fitting equation in S8 is: I = aC + b; where I is the fluorescence intensity of the single-fiber microplastic, C is the concentration of the single-fiber microplastic in the sample to be tested, and a and b are the working curve coefficients of the single-fiber microplastic.

[0033] Furthermore, in S9:

[0034] The fluorescence intensity of test solution 1 was measured as I1. This fluorescence intensity I1 was substituted into the fitting equation for the standard curve of polypropylene fiber microplastics. PP =a PP C PP +b PP The concentration C1 of the fiber microplastics in the test solution 1 was obtained;

[0035] The fluorescence intensity of test solution 3 was measured to be I3. This fluorescence intensity I3 was substituted into the fitting equation for the standard curve of polyester fiber microplastics. PET =a PET C PET +b PET The concentration C3 of polyester fiber microplastics was obtained;

[0036] For test solution 2, the fluorescence intensity was measured to be I2. Substituting C1, C3, and I2 into the following formula, the total amount of fiber microplastics in the concentrated or diluted aqueous solution can be obtained:

[0037]

[0038] C = KC 总

[0039] C — Concentration of fiber microplastics in aqueous solution (ug / mL);

[0040] C 总 —Total concentration of fiber microplastics in the concentrated or diluted aqueous solution (ug / mL);

[0041] K – the factor of concentration or dilution. When there is no concentration or dilution, K = 1 / 10.

[0042] Furthermore, in S9, the solution is dispersed evenly by placing it in a turbine disperser or by hand-cranking it.

[0043] Compared with the prior art, the beneficial effects of the present invention are:

[0044] This invention provides a method for determining fiber microplastics in textile aqueous solutions based on fluorescence spectrophotometry. Applied to the field of textile wastewater, this method enables the determination of unknown samples of textile wastewater without prior qualitative analysis. The unknown samples can be single or mixed samples, both suitable for this method. Furthermore, it effectively eliminates interference from other fibers besides microplastics in the textile wastewater. Additionally, since the standard curve equation is based on standard profiles for several types of fiber microplastics in textile aqueous solutions, its deviation is small when applied to the determination of these types of fiber microplastics in textile aqueous solutions, resulting in more accurate measurement results.

[0045] In summary, the method for determining fiber microplastics in textile aqueous solutions based on fluorescence spectrometry provided by this invention not only eliminates the need for large instruments such as Fourier transform infrared spectrometers and Raman spectrometers, but also simplifies operation, reduces time consumption, and helps improve detection efficiency. Furthermore, it is applicable to unknown samples in the field of textile aqueous solutions, and can analyze both single and mixed samples with higher detection accuracy. Attached Figure Description

[0046] Figure 1 This is a schematic diagram illustrating the effect of fiber microplastic length on fluorescence intensity in Experiment Example 1 of this invention;

[0047] Figure 2 This is a schematic diagram of the fluorescence intensity of microplastics made from shredded 500µm polyester fibers in Experiment 1a of the present invention. Figure 2 .b is a schematic diagram of the fluorescence intensity of 50µm polyester fiber microplastics;

[0048] Figure 3 The image shows the fluorescence intensity test results of polyester fiber microplastics with different diameters in Experiment Example 2 of this invention.

[0049] Figure 4 The image shows the fluorescence intensity test results of polyamide fiber microplastics with different diameters in Experiment Example 2 of this invention.

[0050] Figure 5 To demonstrate that the relationship between the concentration of polyethylene fiber microplastics and fluorescence intensity conforms to the standard curve of polypropylene fiber microplastics in this invention. Detailed Implementation

[0051] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0052] The embodiments provided in this application use wastewater from washing knitted fabrics made of blue polyacrylonitrile and polyester blends and wastewater from washing trousers made of beige viscose and nylon blends as wastewater samples to determine fiber microplastics. The wastewater samples are not limited to these; they can also be aqueous solutions of other textiles, such as wastewater from washing mats made of polyacrylonitrile and hemp blends. It should be noted that the selection of wastewater samples is diverse and can be chosen according to actual needs.

[0053] The implementation principle of this invention is as follows: The above-mentioned textile wastewater is used as an unknown sample. The unknown sample does not need to be pre-identified for fiber microplastics. It can be a sample mixed with a single fiber microplastic or a sample mixed with multiple fiber microplastics. The unknown sample is filtered, rinsed with sodium hypochlorite solution, and then the fiber microplastics are separated into two parts with densities less than water and greater than water using a cylindrical separatory funnel to obtain two aqueous solutions. Then, Nile red dye is used for staining, and after secondary dispersion with reagents, the fluorescence intensity is tested. Then, the content of fiber microplastics in the unknown aqueous solution is obtained by referring to the standard curve.

[0054] This invention is applied to the detection of fiber microplastics in aqueous solutions of textiles. The fiber microplastics to be measured are polypropylene fiber microplastics, polyethylene fiber microplastics, polyester fiber microplastics, and polyamide fiber microplastics. That is to say, regardless of whether the unknown sample contains a single polypropylene fiber microplastic, polyethylene fiber microplastic, polyester fiber microplastic, or polyamide fiber microplastic, or contains any two, three, or a combination of three of the polypropylene fiber microplastic, polyethylene fiber microplastic, polyester fiber microplastic, and polyamide fiber microplastic, the fiber microplastic determination method provided by this invention can determine the concentration of fiber microplastics. In other words, this invention is applied to the determination of polypropylene fiber microplastic, polyethylene fiber microplastic, polyester fiber microplastic, and polyamide fiber microplastic in aqueous solutions of textiles, and is applicable not only to the detection of unknown samples, but also to the determination of single samples or mixed samples.

[0055] Furthermore, the standard curves provided in this invention are obtained by fitting the measured standard curves using standard substrates of polypropylene fiber microplastics, polyester fiber microplastics, and polyamide fiber microplastics. The provided standard curves are only applicable to polypropylene fiber microplastics, polyester fiber microplastics, and polyamide fiber microplastics. Therefore, when applying the standards of this invention to the quantitative analysis of textile aqueous solutions, serious deviations in the results are avoided, and reliable quantitative analysis results can be achieved.

[0056] It should be noted that there are currently no standard fiber materials for polyethylene fibers. Furthermore, most polyethylene fibers are high-modulus, making them impossible to cut with scissors and hindering the production of fiber microplastics within the desired length range. Subsequent collection of various low-modulus polyethylene fibers and two types of high-modulus polyethylene fibers, processed through cutting and low-temperature grinding, yielded short fibers within the microplastic length range. After staining with Nile Red fluorescent dye, the relationship between its concentration and fluorescence intensity was found to conform to the standard curve for polypropylene fiber microplastics. (See...) Figure 5 . Figure 5 The two curves in the figure represent the linear relationship between the fluorescence intensity of polypropylene fibers and the concentration of fiber microplastics in two wavelength bands. The black data points in the figure represent the relationship between fluorescence intensity and polyethylene fiber microplastic concentration measured using multiple batches of polyethylene fiber microplastics. Therefore, a standard curve between fiber microplastic concentration and fluorescence intensity is no longer required for the determination of polyethylene fiber microplastics.

[0057] Example 1

[0058] This embodiment is a method for determining fiber microplastics in textile aqueous solutions based on fluorescence spectrometry. The textile aqueous solution is wastewater from the washing of knitted fabrics blended with blue polyacrylonitrile and polyester fibers. The method includes the following steps:

[0059] S1. Use a water sampler to collect 2L of washing wastewater from blue polyacrylonitrile fiber and polyester fiber blended plush fabric, stir to obtain a homogeneous water sample, and collect parallel samples at the same time; filter the wastewater sample using a micro-volume glass filtration device with a glass fiber filter membrane; the specific method for collecting parallel samples refers to the sample collection and storage section of GB 17378.3 Marine Monitoring Specification Part 3, which is collected by the water sampler during transportation, and will not be repeated here.

[0060] S2. Rinse the filter membrane with sodium hypochlorite solution, turn off the vacuum filtration device, and allow the fiber microplastics to be fully impregnated in the sodium hypochlorite solution. Let it stand for 10 minutes, then rinse the filter membrane with plenty of water until it is neutral. The rinsing volume of sodium hypochlorite solution is 20 mL to 50 mL, and the concentration of sodium hypochlorite solution is 0.9 mol / L to 1.0 mol / L.

[0061] S3. Rinse the fiber microplastics on the filter membrane into the tertiary water, add it into the cylindrical separatory funnel, and let it stand for 1 hour.

[0062] S4. Pour the fiber microplastics floating on the surface of the solution out from the upper port of the cylindrical separatory funnel, and collect the fiber microplastics deposited at the bottom from the lower port. The liquid collected at the upper port is the test solution 1, and the liquid collected at the lower port is the test solution 2.

[0063] S5. Repeat S1-S2, then rinse the filter membrane with hydrochloric acid to remove any remaining fiber microplastics. Collect the remaining fiber microplastics and rinse the filter membrane with plenty of water until neutral. Then repeat S3-S4. Collect the fiber microplastics deposited at the bottom from the lower end of the separatory funnel and label it as test solution 3. Note that the filter bottle for receiving the filtrate should be replaced before rinsing the filter membrane with hydrochloric acid.

[0064] S6. Filter the three solutions 1, 2 and 3 obtained for testing respectively, and rinse the three types of fiber microplastics into the dye solution with 80mL-150mL of the prepared Nile Red dye solution respectively, and let them stand at room temperature for 20min-40min; wherein the concentration of Nile Red fluorescent dye is 80ug / mL.

[0065] S7. Weigh 0.5000g ± 0.0002g (accurate to 0.0001g) of various fiber microplastics with a length <2mm (polyester standard liner, polyamide standard liner, and polypropylene standard liner), put them into conical flasks, add 25ml of grade III water and 25ml of Nile Red dye (160ug / mL), let stand at room temperature for 30min, after dyeing, filter the three types of fiber microplastics, and rinse with 50ml of water:acetone = 1:1 solution during filtration, dry and set aside for use;

[0066] Weigh 0.2500g ± 0.0002g (accurate to 0.0001g) of dyed polyester and polyamide standard lining fiber microplastics respectively, add them to 500ml of aqueous solution containing 0.3% surfactant, and prepare standard solutions.

[0067] Weigh 0.2500g ± 0.0002g (accurate to 0.0001g) of dyed polypropylene standard lining fiber microplastics and add them to 500ml of liquid paraffin with a density of 0.86-0.89g / cm3 to prepare a standard solution; wherein, the liquid paraffin is used as a dispersant.

[0068] Preparation of two calibration solutions, polyester fiber microplastics and polyamide fiber microplastics, involves diluting at least six standard solutions in a 250 mL Erlenmeyer flask with tertiary water containing 0.3% surfactant.

[0069] The polypropylene fiber microplastic correction solution was prepared by adding a solution with a density of 0.86 g / cm³ to a 250 mL Erlenmeyer flask. 3 -0.89g / cm 3 At least six solutions in the liquid paraffin dilution standard solution;

[0070] in:

[0071] 10 mL standard solution to 100 mL, containing 50 μg / mL fiber microplastics;

[0072] 15 mL standard solution to 100 mL, containing 75 μg / mL fiber microplastics;

[0073] 20 mL standard solution to 100 mL, containing 100 μg / mL fiber microplastics;

[0074] 25 mL standard solution to 100 mL, containing 125 μg / mL fiber microplastics;

[0075] 30 mL standard solution to 100 mL, containing 150 μg / mL fiber microplastics;

[0076] 35 mL standard solution to 100 mL, containing 175 μg / mL fiber microplastics;

[0077] 40 mL standard solution to 100 mL, containing 200 μg / mL fiber microplastics;

[0078] 45 mL standard solution to 100 mL, containing 225 μg / mL fiber microplastics;

[0079] 50 mL standard solution to 100 mL, containing 250 ug / mL fiber microplastics;

[0080] 55 mL standard solution to 100 mL, containing 275 μg / mL fiber microplastics;

[0081] 60 mL standard solution to 100 mL, containing 300 μg / mL fiber microplastics;

[0082] S8. Take appropriate amounts of standard series solutions from low to high in sequence, place them in cuvettes, start the analysis and testing system to measure and plot the standard curve of fluorescence intensity versus fiber microplastic concentration. After performing exponential fitting on the standard curve, obtain the standard curve fitting equation.

[0083] in:

[0084] Fitting equation curve for polyester fiber microplastics

[0085] I PET =a PET C PET +b PET Formula (1)

[0086] Fitting equation curve for polyamide fiber microplastics

[0087] I PA =a PA C PA +b PA Formula (2)

[0088] Fitting equation curve for polypropylene fiber microplastics

[0089] I PP =a PP C PP +b PP Formula (3)

[0090] In the above formula:

[0091] I PET —Fluorescence signal value (fluorescence intensity) of polyester fiber microplastics;

[0092] I PA — Fluorescence signal value (fluorescence intensity) of polyamide fiber microplastics;

[0093] I PP — Fluorescence signal value (fluorescence intensity) of polypropylene fiber microplastics;

[0094] C PET —The concentration of polyester fiber microplastics in the sample to be tested, (ug / mL);

[0095] C PA — The concentration of polyamide fiber microplastics in the sample to be tested, (ug / mL);

[0096] C PP —The concentration of polypropylene fiber microplastics in the sample to be tested, (ug / mL);

[0097] a PET ,b PET —Working curve coefficients of polyester fiber microplastics;

[0098] a PA ,b PA —Working curve coefficients of polyamide fiber microplastics;

[0099] a PP ,b PP —Working curve coefficients of polypropylene fiber microplastics;

[0100] S9. The three solutions obtained in S6 are respectively placed in a turbine disperser or manually dispersed until uniform, and their fluorescence intensity is measured on a fluorescence spectrophotometer. The concentrations of the three fiber microplastics are calculated by combining the standard curve fitting equation. Specifically:

[0101] The fluorescence intensity of test solution 1 was measured as I1. This fluorescence intensity I1 was substituted into the fitting equation for the standard curve of polypropylene fiber microplastics. PP =a PP C PP +b PP The concentration C1 of the fiber microplastics in the test solution 1 was obtained;

[0102] The fluorescence intensity of test solution 3 was measured to be I3. This fluorescence intensity I3 was substituted into the fitting equation for the standard curve of polyester fiber microplastics. PET =a PET C PET +b PET The concentration C3 of polyester fiber microplastics was obtained;

[0103] For test solution 2, the fluorescence intensity was measured to be I2. Substituting C1, C3, and I2 into the following formula, the total amount of fiber microplastics in the concentrated or diluted aqueous solution can be obtained:

[0104]

[0105] C = KC 总

[0106] C — Concentration of fiber microplastics in aqueous solution (ug / mL);

[0107] C 总 —Total concentration of fiber microplastics in the concentrated or diluted aqueous solution (ug / mL);

[0108] K – the factor of concentration or dilution; when undiluted, K = 1 / 10.

[0109] It should also be noted that the fibers collected from the lower end of the separatory funnel include not only fiber microplastics but also some potentially biodegradable fibers. However, these fibers have little effect on the determination in this application and are therefore not considered here.

[0110] To avoid uneven distribution of fiber microplastics, each solution was tested in triplicate to obtain three fiber microplastic concentrations, and the average of these three concentrations was taken as the final fiber microplastic concentration. If the difference between the parallel test results was greater than 3.0%, a fourth test was conducted, and the data with the largest differences were discarded. The final result was the arithmetic mean of the three tests. The final result was rounded to two decimal places according to GB / T 8170.

[0111] Example 2

[0112] This embodiment is a method for determining fiber microplastics in textile aqueous solutions based on fluorescence spectrometry. The textile aqueous solution is wastewater from washing trousers, a blend of 40% beige viscose fiber and 60% nylon fiber. The method includes the following steps:

[0113] S1. Use a water sampler to collect 5L of washing wastewater from blue polyacrylonitrile fiber and polyester fiber blended plush fabric, and stir to obtain a homogeneous water sample; at the same time, collect parallel samples, and filter the wastewater using a micro-volume glass filtration device with a glass fiber filter membrane; the specific method for collecting parallel samples refers to the sample collection and storage section of GB 17378.3 Marine Monitoring Specification Part 3, which is collected by the water sampler during transportation, and will not be repeated here.

[0114] Following the same steps as in Example 1, repeat steps S2-29 to obtain C1, C3, and C1 respectively. 总 This allows us to obtain the concentration of fiber microplastics in the aqueous solution being tested.

[0115] Test Example 1

[0116] Fiber microplastics are fibrous microplastics smaller than 5 mm in size, formed when non-degradable fibers detach from textiles during pretreatment, dyeing, finishing, wearing, and washing due to mechanical action and abrasion. These fibers are then exposed to wind, rain, sun, and microorganisms. The length of fiber microplastics is not entirely uniform, ranging from nanometers and micrometers to some larger millimeters. For unknown samples, the size distribution is unknown, making the length of fiber microplastics a significant factor influencing dyeing processes.

[0117] Based on this, the dyeing method for fiber microplastics provided in this application was used to dye fiber microplastics of different lengths and types. The fiber microplastics measured included polyester fibers, polyamide fibers, and polypropylene fibers.

[0118] The three standard fiber linings were cut into lengths of 500um, 1mm, 2mm, 3mm and 4mm. In addition, the fibers were ground into 50um microplastic fibers using a cryogenic grinder.

[0119] The effect of fiber microplastic length on fluorescence intensity was obtained, as shown in the figure. Figure 1 As shown.

[0120] Depend on Figure 1 As can be seen from A, fiber length has little effect on the fluorescence intensity of polyamide fiber microplastics and polypropylene fiber microplastics. Polyester fiber microplastics have stronger fluorescence intensity at a length of about 50 μm. This is because polyester fibers have a compact structure, making it difficult for dye molecules to enter the fiber interior at room temperature. In contrast, fiber microplastics with a length of about 50 μm obtained by grinding cause most of the fibers to break.

[0121] like Figure 2 As shown, Figure 2 .a represents shredded 500µm polyester fiber microplastics. Figure 2 .b represents milled 50µm polyester fiber microplastics, such as... Figure 2In sample .b, the specific surface area of ​​polyester fiber microplastics increases dramatically, enhancing their dye adsorption capacity and resulting in higher fluorescence intensity compared to fibers of other lengths. However, some fiber microplastics are less than 0.7 μm in length and will be filtered out by the glass fiber membrane during filtration. Another important reason is that the small length of the fiber microplastics makes them prone to aggregation, causing fluctuating fluorescence intensity test results and making it impossible to obtain accurate results. However, since the unknown sample of fiber microplastics is composed of fibers of various sizes, and it is difficult to damage the fiber surface, subsequent sample preparation methods were used, with the following results... Figure 1 As shown in B.

[0122] Therefore, using the determination method of this application, the length of the fiber microplastics has little effect on the fluorescence intensity after staining, and its influence can be eliminated. Staining unknown samples yields relatively stable fluorescence intensity.

[0123] Test Example 2

[0124] During the spinning and weaving process of textiles, the production, design, and weaving are based on the style and pattern of the textiles. Therefore, the diameter of the fibers used will vary. Some ultrafine fibers are spun using special processes, and the fiber diameter can be as small as a few micrometers, while the diameter of larger fibers can be as large as nearly 100 micrometers. Therefore, whether the diameter of different fibers will affect the fluorescence intensity after dyeing is also a key factor affecting the feasibility of this method.

[0125] Nile red fluorescent dye was applied to polyester fiber microplastics and polyamide fibers of different diameters, and the fluorescence intensity was then tested. The results are as follows: Figure 3 As shown Figure 4 As shown, Figure 3 The images shown are fluorescence intensity test results for polyester fiber microplastics with different diameters. Figure 4 The image shows fluorescence intensity test results for polyamide fiber microplastics with different diameters.

[0126] Depend on Figure 3 , Figure 4 The results showed that polyester fiber microplastics and polyamide fibers of different diameters did not affect the final fluorescence intensity, and the fluorescence intensity and fiber concentration still followed the above linear relationship.

[0127] Meanwhile, using the measurement method of this application, polyester fiber microplastics and polyamide fiber microplastics with different diameters were used for verification, as shown in Tables 1 and 2.

[0128] Table 1 Verification of polyester fiber microplastics with different diameters

[0129]

[0130] Table 2 Verification of polyamide fiber microplastics with different diameters

[0131]

[0132]

[0133] As can be verified by Tables 1 and 2, using the measurement method of this application, polyester fiber microplastics and polyamide fibers of different diameters do not affect the final fluorescence intensity, and the concentration of fiber microplastics calculated from the fluorescence intensity is highly consistent with the known concentration.

[0134] Experimental Example 3

[0135] Textile products undergo a series of dyeing and finishing processes, including dyeing, printing, and finishing. Therefore, most microplastics formed from textiles through mechanical, sun-drying, and biological processes carry dyes, resulting in a wide variety of colors. Whether the different types of dyes carried by the microplastics affect the uptake of Nile Red dye is crucial for the qualitative and quantitative identification of microplastics using this method. Below, textiles of various colors were selected, cut into microplastics approximately 50 μm in length, and their solutions were analyzed, resulting in Table 3.

[0136] Table 3. Results verification of fiber microplastics of different colors

[0137]

[0138]

[0139] As shown in the table above, the dye color of the fiber itself does not affect the dyeing of Nile Red dye, nor does it affect the fluorescence intensity of the limiting microplastics. The concentration of fiber microplastics calculated from the fluorescence intensity is highly consistent with the known concentration.

[0140] Test Example 4

[0141] There are more than a dozen types of fibers commonly used in textiles. Most of these fibers, once released into the environment, will degrade under the influence of light, rain, and microorganisms. These include natural fibers such as cotton, linen, wool, and silk, as well as some chemically synthesized fibers such as viscose, modal, lyocell, protein-modified polyvinyl alcohol (soybean fiber), protein-modified polyacrylonitrile (milk fiber), vilan, and polyacrylonitrile fibers that take 20 to 30 years to degrade. Of course, this also includes polyester, polyamide, polypropylene, and polyethylene fibers, which are difficult to degrade and belong to the category of fiber microplastics.

[0142] To improve the performance of textiles, apparel manufacturers often use blends of two or more fibers during production. Therefore, the aqueous solutions containing fiber microplastics we collect often contain a variety of fiber microplastics, including not only recalcitrant ones but also incompletely degraded or undegraded biodegradable fibers. Whether the presence of these fibers interferes with the testing of fiber microplastics is a problem that urgently needs to be addressed.

[0143] When Nile Red was used to dye various biodegradable fibers, it was found that protein fibers such as silk and wool would be dyed and obtain higher fluorescence intensity. Therefore, during the pretreatment, the fibers were soaked and rinsed in a 0.9-1.0 mol / L sodium hypochlorite solution to remove the influence of protein fibers.

[0144] Polyamide fiber microplastics and polyacrylonitrile fibers with a length of about 500 μm were manually mixed in the following proportions, and their fluorescence intensity was tested. The concentration of fiber microplastics in the solution was calculated and compared with the mixing results in Table 4.

[0145] Table 4 Polyamide fiber microplastics blended with polyacrylonitrile fibers

[0146]

[0147] Table 4 shows that the calculated concentration of polyamide fiber microplastics is close to the actual blending concentration, indicating that the presence of polyacrylonitrile fibers did not affect the concentration determination of polyamide fiber microplastics. Nile red dye does not dye degradable polyacrylonitrile fibers, so its influence can be ignored.

[0148] Therefore, the influence of other fibers on the determination method of this application can be ignored.

[0149] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for determining fiber microplastics in aqueous textile solutions based on fluorescence spectrometry, characterized in that, Includes the following steps: S1. Collect wastewater from the environment and filter the wastewater sample using a micro-glass filtration device with a glass fiber filter membrane. S2. Rinse the filter membrane with sodium hypochlorite solution, turn off the vacuum filtration device, and allow the fiber microplastics to be fully immersed in the sodium hypochlorite solution. After standing for a period of time, wash the filter membrane with plenty of water until it is neutral. S3. Rinse the fiber microplastics on the filter membrane into the tertiary water, add it to the separatory funnel, and let it stand until clear separation occurs. S4. Pour the fiber microplastics floating on the surface of the solution out from the upper port of the separatory funnel, and collect the fiber microplastics deposited at the bottom from the lower port. The liquid collected at the upper port is the test solution 1, and the liquid collected at the lower port is the test solution 2. S5. Repeat S1-S2, then rinse the filter membrane with hydrochloric acid to remove any small amount of fiber microplastics that may be present. Collect the remaining fiber microplastics, rinse the filter membrane with plenty of water until neutral, and then repeat S3-S4. Collect the fiber microplastics deposited at the bottom from the lower end of the separatory funnel and label it as test solution 3. S6. Filter the three solutions 1, 2 and 3 obtained for testing respectively, and stain them with the prepared Nile Red dye solution. S7. Take the dyed and filtered polyester, polyamide, and polypropylene standard lining fiber microplastics and prepare them into a series of standard solutions with concentration gradients. S8. Take appropriate amounts of standard series solutions from low to high in sequence, place them in cuvettes, start the fluorescence spectrophotometer to measure and plot the standard curve of fluorescence intensity versus fiber microplastic concentration. After performing exponential fitting on the standard curve, obtain the standard curve fitting equation. S9. After dispersing the three solutions obtained in S6 evenly, measure their fluorescence intensity on a fluorescence spectrophotometer, and calculate the concentration of fiber microplastics in the aqueous solution by combining the standard curve fitting equation.

2. The method for determining fiber microplastics in aqueous textile solutions based on fluorescence spectrometry according to claim 1, characterized in that, In step S2, the rinsing volume of sodium hypochlorite solution is 20 mL to 50 mL, and the concentration of sodium hypochlorite solution is 0.9 mol / L to 1.0 mol / L.

3. The method for determining fiber microplastics in aqueous textile solutions based on fluorescence spectrometry according to claim 2, characterized in that, The separating funnel is a cylindrical separating funnel.

4. The method for determining fiber microplastics in aqueous textile solutions based on fluorescence spectrometry according to claim 1, characterized in that, In step S5, the amount of hydrochloric acid is 20mL-50mL, and the filter bottle for receiving the filtrate is replaced before rinsing the filter membrane with hydrochloric acid.

5. The method for determining fiber microplastics in aqueous textile solutions based on fluorescence spectrometry according to claim 1, characterized in that, The dyeing steps in S6 using Nile Red dye solution are as follows: rinsing the three types of fiber microplastics into the dye solution with 80mL-150mL of the prepared Nile Red dye solution, and letting them stand at room temperature for 20min-40min; wherein the concentration of Nile Red fluorescent dye is 80ug / mL.

6. The method for determining fiber microplastics in aqueous textile solutions based on fluorescence spectrometry according to claim 1, characterized in that, In S7, 0.5000g ± 0.0002g of polyester, polyamide, and polypropylene standard linings are weighed and crushed into various fiber microplastics with a length of <2mm. The dyeing process includes: placing various types of fiber microplastics into conical flasks, adding tertiary water and Nile red dye, and letting them stand at room temperature for a period of time, wherein the concentration of Nile red dye is 160ug / mL; The filtration process includes rinsing with a 1:1 solution of water and acetone, followed by drying before use.

7. The method for determining fiber microplastics in aqueous textile solutions based on fluorescence spectrometry according to claim 1, characterized in that, In step S7, the preparation process of the standard series solutions with concentration gradients is as follows: Weigh 0.2500g±0.0002g of dyed polyester and polyamide standard lining fiber microplastics respectively, add them to an aqueous solution containing surfactant to prepare standard solutions, and dilute them into at least 6 solutions with concentration gradients. Weigh 0.2500g ± 0.0002g of dyed polypropylene standard lining fiber microplastics, add them to liquid paraffin to prepare a standard solution, and dilute them to prepare at least 6 solutions with concentration gradients.

8. The method for determining fiber microplastics in textile aqueous solutions based on fluorescence spectrometry according to claim 1, characterized in that, The standard curve fitting equation in S8 is: I = aC + b; where I is the fluorescence intensity of the single-fiber microplastic, C is the concentration of the single-fiber microplastic in the sample to be tested, and a and b are the working curve coefficients of the single-fiber microplastic.

9. The method for determining fiber microplastics in aqueous textile solutions based on fluorescence spectrometry according to claim 1, characterized in that, In S9: The fluorescence intensity of test solution 1 was measured as I1. This fluorescence intensity I1 was substituted into the fitting equation for the standard curve of polypropylene fiber microplastics. PP =a PP C PP +b PP The concentration C1 of the fiber microplastics in the test solution 1 was obtained; The fluorescence intensity of test solution 3 was measured to be I3. This fluorescence intensity I3 was substituted into the fitting equation for the standard curve of polyester fiber microplastics. PET =a PET C PET +b PET The concentration C3 of polyester fiber microplastics was obtained; For test solution 2, the fluorescence intensity was measured to be I2. Substituting C1, C3, and I2 into the following formula, the total amount of fiber microplastics in the concentrated or diluted aqueous solution can be obtained: C=KC 总 C — Concentration of fiber microplastics in aqueous solution (ug / mL); C 总 —Total concentration of fiber microplastics in the concentrated or diluted aqueous solution (ug / mL); K – the factor of concentration or dilution. When there is no concentration or dilution, K = 1 / 10.

10. The method for determining fiber microplastics in aqueous textile solutions based on fluorescence spectrometry according to claim 1, characterized in that, The method for uniformly dispersing the solution in S9 is as follows: Place the solution in a turbine disperser or shake it by hand.

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