Detection method of ethylene-vinyl acetate copolymer in water

Abstract

The present application discloses a method for detecting ethylene-vinyl acetate copolymer in water, and relates to the field of water quality detection, comprising the following steps: S1. pretreatment: filtering a water sample; S2. separation of ethylene-vinyl acetate copolymer and polyurethane: adding a flotation agent and a sorting agent to 50 parts by volume of the filtered water sample, stirring and standing, and the upper portion of the liquid is a separated liquid containing ethylene-vinyl acetate copolymer; S3. digestion: the digester is mixed with the separated liquid containing ethylene-vinyl acetate copolymer and heated to obtain a detection liquid; S4. detection: the detection liquid is filtered, the filter membrane is dried, and the ethylene-vinyl acetate copolymer on the dried filter membrane is counted to obtain the abundance of ethylene-vinyl acetate copolymer in the water sample. The present application has the effect of improving the problem of long detection cycle and high detection cost when detecting ethylene-vinyl acetate copolymer in water.

Description

Technical Field

[0001] The present application relates to the field of water quality detection, and in particular to a method for detecting ethylene-vinyl acetate copolymer in water. Background Art

[0002] Currently, polyurethane and ethylene-vinyl acetate copolymer are commonly used as soles for making shoes. As people's health concepts change, outdoor walking and running have become new ways of exercise and relaxation. When exercising outdoors, people often look for places with beautiful environments such as lakes and trees to improve the comfort of outdoor sports.

[0003] As people engage in more outdoor sports, substances such as polyurethane and ethylene-vinyl acetate copolymer produced by shoe sole wear will diffuse and disperse into outdoor environments such as lakes and rivers, accumulate in water bodies, and thus cause water pollution. Ethylene-vinyl acetate copolymer is widely used in sports shoes due to its high resilience and tensile strength. It is particularly important to understand its pollution to water bodies.

[0004] Since water contains both polyurethane and ethylene-vinyl acetate copolymer, when it is necessary to detect the content of ethylene-vinyl acetate copolymer in water, it is necessary to use Fourier transform infrared spectroscopy, Raman spectroscopy or hyperspectral imaging and other technologies to distinguish between polyurethane and ethylene-vinyl acetate copolymer in water. The detection cycle is long and the detection cost is high. Summary of the Invention

[0005] In order to improve the problems of long detection period and high detection cost when detecting ethylene-vinyl acetate copolymer in water, the present application provides a method for detecting ethylene-vinyl acetate copolymer in water.

[0006] The present application provides a method for detecting ethylene-vinyl acetate copolymer in water using the following technical solution:

[0007] A method for detecting ethylene-vinyl acetate copolymer in water comprises the following steps:

[0008] The following steps are involved:

[0009] S1. Pretreatment: Filter water sample;

[0010] S2. Separation of ethylene - vinyl acetate copolymer and polyurethane: 50 parts by volume of the filtered water sample was added with a flotation agent and a sorting agent, stirred and allowed to stand, and the upper portion of the liquid contained ethylene - vinyl acetate copolymer separation liquid;

[0011] S3 digestion: The digester is mixed with the separation solution containing ethylene-vinyl acetate copolymer and heated to obtain a detection solution;

[0012] S4. Detection: Filter the test solution, dry the filter membrane, and count the ethylene-vinyl acetate copolymer on the dried filter membrane to obtain the abundance of ethylene-vinyl acetate copolymer in the water sample.

[0013] By adopting the above technical solution, impurities such as aquatic plants in the water sample are filtered out, and then ethylene-vinyl acetate copolymer and polyurethane are sorted by flotation agents and sorting agents to obtain a separated liquid of ethylene-vinyl acetate copolymer. The organic matter in the separated liquid is digested by a digester to avoid as much as possible the interference of the organic matter in the water with the detection of ethylene-vinyl acetate copolymer. The detection liquid is filtered and the ethylene-vinyl acetate copolymer attached to the filter membrane is counted to obtain the number of ethylene-vinyl acetate copolymer in the water sample. There is no need to perform additional qualitative detection of the sample type by methods such as Fourier transform infrared spectrometry on the sample, thereby improving the detection efficiency of ethylene-vinyl acetate copolymer in water and reducing the detection cost of ethylene-vinyl acetate copolymer in water.

[0014] Optionally, step S2 includes the following steps:

[0015] S21. Initial separation: Divide the sorting agent into N parts, mix one part of the sorting agent, the filtered water sample and the flotation agent, let it stand, and take the upper part of the liquid as the initial liquid containing ethylene-vinyl acetate copolymer, and the remaining liquid below is the first liquid separation;

[0016] S22. Secondary separation: Add water to the first liquid separation to make up to 50 parts by volume to obtain a supplementary liquid, mix the second portion of the sorting agent with the supplementary liquid, stir, and let it stand. After standing, the upper portion of the supplementary liquid is added to the initial liquid separation, and the remaining liquid below is the second liquid separation;

[0017] S23. Repeat sorting: Repeat step S22 (N-2) times to obtain a separated liquid containing ethylene-vinyl acetate copolymer.

[0018] Furthermore, in step S21, N can be any integer from 3 to 5.

[0019] Furthermore, in step S21, the volume fractions of the first liquid separation are 10-20.

[0020] By employing the above technical solution, the separation agent is divided into N portions, facilitating multiple extractions of ethylene-vinyl acetate copolymer from the secondary fractions, thereby improving the recovery rate of ethylene-vinyl acetate copolymer. Furthermore, by controlling the volume of the secondary fractions, polyurethane from the secondary fractions is minimized from being separated into the separated liquid, thereby improving the accuracy of ethylene-vinyl acetate copolymer detection.

[0021] Optionally, in step S2, the separation agent is 5 parts by volume

[0022] Furthermore, in step S2, the sorting agent includes one or more of ethyl acetate, ethyl formate, ethanol and methanol.

[0023] Furthermore, the separating agent is composed of ethyl acetate and ethanol in a volume ratio of (2-4): (1-3).

[0024] Furthermore, the volume ratio of the ethyl acetate to the ethanol is (2.5-3.5):(1.5-2.5).

[0025] By adopting the above technical solution, polyurethane and ethylene-vinyl acetate copolymer are separated in a flotation agent through the synergistic effect of ethyl acetate and ethanol, thereby reducing the content of polyurethane in the separation agent and improving the separation effect of polyurethane and ethylene-vinyl acetate copolymer, thereby facilitating the determination of the amount of ethylene-vinyl acetate copolymer in the sample. On the one hand, there is no need to perform additional qualitative detection of the sample type using methods such as Fourier transform infrared spectroscopy, thereby improving the detection efficiency of ethylene-vinyl acetate copolymer in water and reducing the detection cost of ethylene-vinyl acetate copolymer in water. On the other hand, the recovery rate of ethylene-vinyl acetate copolymer is improved.

[0026] Optionally, in step S2, the flotation agent is sodium chloride or zinc chloride, and the mass volume ratio of the flotation agent to the filtered water sample is (10-20) g:50 ml.

[0027] By adopting the above technical solution, impurities in the water sample are further separated by a flotation agent, which avoids the impurity particles in the water sample from being mixed in the ethylene-vinyl acetate copolymer as much as possible, thereby improving the accuracy of detecting the amount of ethylene-vinyl acetate copolymer.

[0028] Optionally, in step S3, the digester is selected from one of hydrogen peroxide, nitric acid solution or potassium hydroxide solution.

[0029] By adopting the above technical solution, the organic matter in the separation liquid is digested by a digester, thereby avoiding the interference of the organic matter on the detection of ethylene-ethyl acetate vinyl ester as much as possible, thereby improving the accuracy of the detection of ethylene-ethyl acetate vinyl ester.

[0030] In summary, this application includes at least one of the following beneficial technical effects:

[0031] 1. Impurities such as aquatic plants in the water sample are filtered out, and then ethylene-vinyl acetate copolymer and polyurethane are separated by flotation agents and sorting agents to obtain a separated solution of ethylene-vinyl acetate copolymer. Organic matter in the separated solution is digested by a digester to minimize interference of organic matter in the water with the detection of ethylene-vinyl acetate. The detection solution is filtered and the ethylene-vinyl acetate copolymer attached to the filter membrane is counted to obtain the amount of ethylene-vinyl acetate copolymer in the water sample. No additional qualitative detection of the sample type by methods such as Fourier transform infrared spectroscopy is required, thereby improving the detection efficiency of ethylene-vinyl acetate copolymer in water and reducing the detection cost of ethylene-vinyl acetate copolymer in water.

[0032] 2. By dividing the sorting agent into N portions, multiple extractions of ethylene-vinyl acetate copolymer from the secondary fractions are facilitated, thereby improving the recovery rate of ethylene-vinyl acetate copolymer. Furthermore, by controlling the volume of the secondary fractions, polyurethane from the secondary fractions is minimized from being separated into the separation liquid, thereby improving the accuracy of ethylene-vinyl acetate copolymer detection. 3. Through the synergistic effect of ethyl acetate and ethanol, polyurethane and ethylene-vinyl acetate copolymer are separated within the flotation agent, reducing the polyurethane content in the sorting agent and improving the separation efficiency of polyurethane and ethylene-vinyl acetate copolymer, thereby facilitating the determination of the amount of ethylene-vinyl acetate copolymer in the sample. This eliminates the need for additional qualitative analysis of the sample using methods such as Fourier transform infrared spectroscopy, thereby improving the detection efficiency of ethylene-vinyl acetate copolymer in water and reducing the detection cost of ethylene-vinyl acetate copolymer in water. Furthermore, it improves the recovery rate of ethylene-vinyl acetate copolymer. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a flow chart of the detection method of the present invention.

[0034] Figure 2 It is a flow chart of step S2 in the detection method of the present invention. DETAILED DESCRIPTION

[0035] The present application is described in further detail below in conjunction with the accompanying drawings and Examples. The following examples are merely intended to illustrate the present invention and are not to be construed as limiting the scope of the present invention. In the following examples, if specific conditions are not specified, the methods used are conventional methods well known in the art, and the consumable materials and reagents used are commercially available, unless otherwise specified. Unless otherwise indicated, the professional and scientific terms used herein have the same meaning as those familiar to those skilled in the art. In addition, any method or material similar or equivalent to the described content may also be applied to the present invention.

[0036] Examples 1-8

[0037] The amounts of flotation agents and separators used in Examples 1-8 are shown in Table 1.

[0038] Examples 1-8 of the present application disclose a method for detecting ethylene-vinyl acetate copolymer in water. The method for detecting ethylene-vinyl acetate copolymer in water comprises the following steps:

[0039] For water sample preparation, a standard water sample without plastic is taken, and the polyurethane particles and ethylene-vinyl acetate copolymer particles are evenly mixed and added to the standard water sample to obtain a water sample, wherein each 50 ml sample contains 200 polyurethane particles and 200 ethylene-vinyl acetate copolymer particles, and the particle size range of the polyurethane particles and the ethylene-vinyl acetate copolymer particles are both 30 μm-40 μm.

[0040] For pretreatment, 50 ml of the sample was taken and filtered through a suction filtration bottle and a stainless steel filter membrane to obtain a filtered water sample, wherein the stainless steel filter membrane was a 50 mm × 50 μm stainless steel filter membrane;

[0041] Separation of ethylene-vinyl acetate copolymer and polyurethane, initial separation: take 50ml of filtered water sample and put it into the first beaker, add flotation agent to the first beaker and stir to dissolve it, divide the flotation agent into 4 parts, add one part of the flotation agent to the first beaker, place the first beaker on a magnetic stirrer, stir for 20 minutes, let it stand for 2 hours, take the upper part of the liquid as the initial separation liquid containing ethylene-vinyl acetate copolymer and put it into the second beaker, and the remaining liquid in the first beaker is the first separation liquid, and the volume of the second separation liquid is 15ml;

[0042] Second separation, add pure water to the first separation in the first beaker until the volume of the liquid in the first beaker is 50ml, then add the second separation agent to the first beaker, place the beaker on a magnetic stirrer, stir for 20min, let it stand for 2h, add the upper part of the liquid in the first beaker to the second beaker until the remaining liquid in the first beaker is the second separation, with a volume of 15ml; repeat the separation: add pure water to the first beaker again until the volume of the liquid in the first beaker is 50ml, then add the third separation agent to the first beaker, place the beaker on a magnetic stirrer, Stir for 20 minutes, let stand for 2 hours, add the upper portion of the liquid in the first beaker to the second beaker until the remaining liquid volume in the first beaker is 15 ml. Then add pure water to the first beaker until the liquid volume in the first beaker is 50 ml. Then add the third portion of the separator to the first beaker. Place the beaker on a magnetic stirrer and stir for 20 minutes. Let stand for 2 hours, and add the upper portion of the liquid in the first beaker to the second beaker until the remaining liquid volume in the first beaker is 15 ml. The liquid in the second beaker is the separated liquid containing ethylene-vinyl acetate copolymer. The volume of the first and second separations is the same.

[0043] Digestion: Add 200 ml of 35% hydrogen peroxide as a digester to the second beaker, heat the liquid in the second beaker to 70 degrees Celsius, and continue digestion for 1 day to remove organic matter in the separation liquid to obtain the test liquid;

[0044] For detection, the test liquid is filtered to obtain a filter membrane with ethylene-vinyl acetate copolymer attached, the filter membrane is dried at 70 degrees Celsius, and the dried filter membrane is placed under a stereo microscope, and the ethylene-vinyl acetate copolymer particles are counted by visual inspection. The filter membranes are all 50 mm × 20 μm glass fiber filter membranes.

[0045] Table 1 Components and dosages of flotation agents and separators used in Examples 1-9

[0046]

[0047] Examples 9-10

[0048] The components and dosages of the flotation agents and separators in Examples 9-10 are consistent with those in Example 2. The difference between the preparation methods and Example 2 is that the separators are divided into different portions, as shown in Table 2 below.

[0049] Table 2 Number of equal portions of the sorting agent N

[0050] Example N 2 4 9 3 10 5

[0051] Examples 11-12

[0052] The components and dosages of the flotation agents and separators in Examples 11-12 are consistent with those in Example 2. The difference between the preparation methods and Example 2 is that the volumes of the secondary separations are different, as shown in Table 3 below.

[0053] Table 3 Volume of Liquid Separation

[0054]

[0055]

[0056] Comparative Example 1

[0057] The difference between Comparative Example 1 and Example 2 is that the separating agent used in Comparative Example 1 does not contain ethyl acetate.

[0058] Comparative Example 2

[0059] The difference between Comparative Example 2 and Example 2 is that the sorting agent used in Comparative Example 2 does not contain ethanol.

[0060] Comparative Example 3

[0061] The difference between Comparative Example 3 and Example 2 is that Comparative Example 3 does not use a sorting agent.

[0062] Comparative Example 4

[0063] The difference between Comparative Example 4 and Example 2 is that: Comparative Example 4 does not perform the secondary selection and repeated sorting steps.

[0064] Abundance detection

[0065] The abundance of the filter membranes attached with ethylene-vinyl acetate copolymer obtained in Examples 1-12 and Comparative Examples 1-4 was detected, and the accuracy of ethylene-vinyl acetate copolymer detection and the recovery rate of ethylene-vinyl acetate copolymer particles were calculated. The results are shown in Table 4.

[0066] The particles on the filter membrane are mixed with potassium bromide and pressed into potassium bromide wafers. The samples are sent to a Fourier transform infrared spectrometer for detection. The obtained spectrum is compared with the polymer database. When the matching degree with ethylene-vinyl acetate copolymer is greater than 70%, it can be identified as ethylene-vinyl acetate copolymer particles. When the matching degree with polyurethane is greater than 70%, it can be identified as polyurethane particles.

[0067] Accuracy (%) = ethylene-vinyl acetate copolymer abundance / (ethylene-vinyl acetate copolymer abundance+polyurethane abundance)×100%.

[0068] Recovery rate (%) = abundance of ethylene-vinyl acetate copolymer / (5×20 particles / g)×100%.

[0069] Table 4 Abundance of ethylene-vinyl acetate copolymer and polyurethane, accuracy of ethylene-vinyl acetate copolymer detection and recovery rate of ethylene-vinyl acetate copolymer particles

[0070]

[0071]

[0072] The following is a detailed description of this application in conjunction with the experimental data provided in Tables 1-4.

[0073] Examples 1-3 investigated the effect of the volume ratio of sodium chloride, ethanol, and ethyl acetate on the separation of ethylene-vinyl acetate copolymer and polyurethane using sodium chloride as a flotation agent and ethanol and ethyl acetate as a separating agent. Fourier transform infrared spectroscopy (FTIR) analysis of samples obtained using the detection method of Example 2 revealed the highest abundance of ethylene-vinyl acetate copolymer and the lowest abundance of polyurethane, achieving the highest accuracy. This demonstrates that, using the detection method of this application, water samples can be analyzed for ethylene-vinyl acetate copolymer abundance with an accuracy of up to 99% simply by observing them under a stereomicroscope, eliminating the need for additional qualitative analysis of sample type using methods such as FTIR spectroscopy. This improves the efficiency of ethylene-vinyl acetate copolymer detection in water and reduces the cost of ethylene-vinyl acetate copolymer detection in water. Furthermore, the recovery rate of ethylene-vinyl acetate copolymer in samples obtained using the detection method of Example 2 reached 98.5%. Overall, Example 2 is a preferred embodiment.

[0074] Using Example 2 as a comparison, Examples 4 and 5 investigated the effects of different sorting agents on the separation of ethylene-vinyl acetate copolymer and polyurethane. The accuracy of ethylene-vinyl acetate copolymer detected using the detection methods of Examples 4 and 5 exceeded 92.2%. This indicates that the sorting agents composed of ethyl acetate and methanol and the sorting agent composed of ethanol and ethyl formate are more effective in separating ethylene-vinyl acetate copolymer and polyurethane, while the sorting agent composed of ethyl acetate and ethanol has the best separation effect. Furthermore, the ethylene-vinyl acetate copolymer recovery rate obtained in Examples 4 and 5 also reached approximately 90%.

[0075] Using Example 2 as a control, Examples 6 and 7 investigated the effects of different volume ratios of ethanol and ethyl acetate on the separation of ethylene-vinyl acetate copolymer and polyurethane. The accuracy of ethylene-vinyl acetate copolymer detected using the detection methods of Examples 6 and 7 was approximately 96%, demonstrating good separation efficiency. Furthermore, the recovery rate of ethylene-vinyl acetate copolymer obtained using the detection methods of Examples 6 and 7 was over 94%. Overall, Example 2 was considered the preferred embodiment.

[0076] Using Example 2 as a control, Example 8 investigated the effects of different flotation agents on the separation of ethylene-vinyl acetate copolymer and polyurethane. The accuracy of ethylene-vinyl acetate copolymer measured by the detection method in Example 8 was above 90%, indicating good separation effect. Compared with Example 2, it can be seen that sodium chloride is better than zinc chloride.

[0077] Using Example 2 as a comparison, Examples 9 and 10 adjusted the number of equally divided flotation agents. The accuracy of the measured ethylene-vinyl acetate copolymer was above 94%. However, the recovery rate of ethylene-vinyl acetate copolymer obtained in Example 9 was 86%, while the accuracy of ethylene-vinyl acetate copolymer obtained in Example 10 was lower than that of Example 9. This is because the secondary fractions were separated multiple times, increasing the amount of polyurethane separated and resulting in an increased error. Taking all factors into consideration, Example 2 is the preferred example.

[0078] With Example 2 as a control, Example 11 and Example 12 adjusted the volume of the remaining secondary liquid in the first beaker. The accuracy of ethylene-vinyl acetate copolymer in Example 11 and Example 12 was above 93.2%, showing good sorting effect. Among them, the accuracy of ethylene-vinyl acetate copolymer measured in Example 11 was lower than that in Example 2. The reason was that the volume of the secondary liquid was small, resulting in part of the polyurethane being extracted into the separation liquid at the same time. The accuracy of ethylene-vinyl acetate copolymer in Example 12 was as high as 98.4%, but the recovery rate of ethylene-vinyl acetate copolymer obtained was lower than that in Example 2. The reason was that due to the large volume of the remaining secondary liquid, part of the ethylene-vinyl acetate copolymer remained in the secondary liquid, resulting in a low recovery rate of ethylene-vinyl acetate copolymer, which resulted in a low abundance of ethylene-vinyl acetate copolymer in the measured water sample. Taking all factors into consideration, Example 2 is a preferred embodiment.

[0079] Furthermore, a comparison of Example 2 with Comparative Example 1 reveals that the accuracy of ethylene-vinyl acetate copolymer detection significantly decreases when ethyl acetate is not used in the sorting agent, indicating that ethyl acetate can improve the accuracy of ethylene-vinyl acetate copolymer detection when separating ethylene-vinyl acetate copolymer and polyurethane in water. Similarly, a comparison of Example 2 with Comparative Example 2 reveals that the accuracy of ethylene-vinyl acetate copolymer detection significantly decreases when ethanol is not used in the sorting agent, indicating that ethanol can improve the accuracy of ethylene-vinyl acetate copolymer detection when separating ethylene-vinyl acetate copolymer and polyurethane in water.

[0080] Furthermore, a comparison between Example 2 and Comparative Examples 1-3 reveals that when no sorting agent is used, the resulting ethylene-vinyl acetate copolymer particles and polyurethane particles have a near 1:1 ratio, with no sorting effect on the ethylene-vinyl acetate copolymer particles and polyurethane particles. Furthermore, the difference between the accuracy of Example 2 and that of Comparative Document 3 is significantly greater than the sum of the difference between the accuracy of Comparative Example 1 and Comparative Example 3 and the difference between the accuracy of Comparative Example 2 and Comparative Example 3. This indicates that when ethyl acetate and ethanol are used as sorting agents, the ethyl acetate and ethanol synergistically improve the accuracy of ethylene-vinyl acetate copolymer detection.

[0081] In addition, compared with Comparative Example 4, in Example 2, when the secondary selection is not performed, the recovery rate of ethylene-vinyl acetate copolymer is as low as 81.5%, and the accuracy rate of ethylene-vinyl acetate copolymer is 91.6%. It can be seen that the secondary selection operation improves the recovery rate of ethylene-vinyl acetate copolymer while also improving the accuracy rate of ethylene-vinyl acetate copolymer to a certain extent.

[0082] The above are all preferred embodiments of the present application, and are not intended to limit the scope of protection of the present application. Therefore, any equivalent changes made based on the structure, shape, and principle of the present application should be included in the scope of protection of the present application.

Claims

1. A method for detecting ethylene-vinyl acetate copolymer in water, characterized in that: The following steps are involved: S1. Pretreatment: Filter water sample; S2. Separation of ethylene - vinyl acetate copolymer and polyurethane: flotation agent and sorting agent were added to the filtered 50 ml water sample and stirred and allowed to stand. The upper portion of the liquid contained ethylene - vinyl acetate copolymer separation liquid; S3 digestion: The digester is mixed with the separation solution containing ethylene-vinyl acetate copolymer and heated to obtain a detection solution; S4. Detection: Filter the test solution, dry the filter membrane, and count the ethylene-vinyl acetate copolymer on the dried filter membrane to determine the abundance of ethylene-vinyl acetate copolymer in the water sample; Step S2 includes the following steps: S21. Initial separation: Divide the sorting agent into N parts, mix one part of the sorting agent, the filtered water sample and the flotation agent, let it stand, and take the upper part of the liquid as the initial liquid containing ethylene-vinyl acetate copolymer, and the remaining liquid below is the first liquid separation; S22. Secondary separation: Add water to the first separation to make up to 50 ml to obtain a supplementary solution, mix the second portion of the sorting agent with the supplementary solution, stir, and let it stand. After standing, the upper portion of the supplementary solution is added to the initial separation, and the remaining liquid below is the second separation; S23 repeated sorting: repeat step S22 (N-2) times to obtain a separated liquid containing ethylene-vinyl acetate copolymer; In said S2, the sorting agent includes one or more of ethyl acetate, ethyl formate, ethanol and methanol; In said S2, the flotation agent is sodium chloride or zinc chloride, and the mass volume ratio of the flotation agent to the filtered water sample is (10-20) g:50 ml; In S3, the digester is selected from one of hydrogen peroxide, nitric acid solution or potassium hydroxide solution.

2. The method for detecting ethylene-vinyl acetate copolymer in water according to claim 1, wherein: In the above S21, N can be any integer from 3 to 5.

3. The method for detecting ethylene-vinyl acetate copolymer in water according to claim 1, wherein: The separator is composed of ethyl acetate and ethanol in a volume ratio of (2-4): (1-3).

4. The method for detecting ethylene-vinyl acetate copolymer in water according to claim 3, wherein: The volume ratio of the ethyl acetate to the ethanol is (2.5-3.5): (1.5-2.5).

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