Method for detecting metal ion content of polyvinyl alcohol

Abstract

A method for detecting metal ion content in polyvinyl alcohol (PVA), belonging to the field of PVA metal ion content detection, includes the following steps: Step 1: Prepare an aqueous solution of PVA and an aqueous solution of sodium acetate; Step 2: Take several portions of the PVA aqueous solution and accurately add sodium acetate aqueous solution to prepare PVA aqueous solutions with different sodium ion contents; Step 3: Adjust the temperature of the PVA aqueous solutions with different sodium ion contents to a specified temperature, and sequentially use a conductivity meter to detect the conductivity and record the conductivity values; Step 4: Construct a linear regression equation based on the conductivity values ​​obtained in Step 3 and the corresponding sodium ion contents, thereby obtaining the sodium ion content in the corresponding PVA by detecting the conductivity. This invention is simple to operate, requires no high-temperature treatment, is highly safe, and can continuously prepare multiple PVA sample aqueous solutions for detection, effectively improving detection efficiency.

Description

Technical Field

[0001] This invention belongs to the field of polyvinyl alcohol metal ion content detection, specifically a method for detecting polyvinyl alcohol metal ion content. Background Technology

[0002] Polyvinyl alcohol (PVA) is a widely used water-soluble polymer. Due to its excellent adhesion, film-forming properties, and stability, it is widely applied in various fields. Currently, the most common production method for PVA is the reaction of polyvinyl acetate with sodium hydroxide. However, the PVA obtained after this reaction contains a certain amount of sodium acetate. Because of the impurities generated during the reaction of sodium acetate, sodium ions from sodium acetate account for the majority of the metallic impurities in PVA, leaving very low levels of other metallic impurities. Therefore, in PVA testing, it is generally accepted that the sodium ion content represents the metallic impurity content of PVA.

[0003] Currently, the grayscale method is mostly used to detect metallic impurities in polyvinyl alcohol. However, the grayscale method requires high-temperature calcination, which takes a long time and consumes energy and poses certain safety hazards. In addition, sodium ions are calcined at high temperatures to obtain sodium oxide, which is unstable and readily absorbs moisture and carbon dioxide from the ambient air to react chemically. If not handled properly, it can lead to a large error in the final weighed result of the impurity content, thus affecting the accuracy of the detection of metallic impurities in polyvinyl alcohol. Summary of the Invention

[0004] This invention provides a method for detecting the metal ion content of polyvinyl alcohol, thereby overcoming the deficiencies in the prior art.

[0005] This invention is achieved through the following technical solution: A method for detecting metal ion content in polyvinyl alcohol includes the following steps: Step 1: Prepare aqueous solutions of polyvinyl alcohol and sodium acetate; Step 2: Take several portions of polyvinyl alcohol aqueous solution and precisely add sodium acetate aqueous solution to prepare polyvinyl alcohol aqueous solutions with different sodium ion contents; Step 3: Adjust the temperature of polyvinyl alcohol aqueous solutions with different sodium ion contents to the specified temperature, and use a conductivity meter to detect the conductivity and record the conductivity values ​​in sequence. Step 4: Construct a linear regression equation based on the conductivity value obtained in Step 3 and the corresponding sodium ion content, and then obtain the sodium ion content in the corresponding polyvinyl alcohol by detecting the conductivity.

[0006] In the polyvinyl alcohol metal ion content detection method described above, the concentrations of both the polyvinyl alcohol aqueous solution and the sodium acetate aqueous solution in step one are 4%.

[0007] The method for detecting metal ion content in polyvinyl alcohol as described above involves preparing the polyvinyl alcohol aqueous solution as follows: Weigh the polyvinyl alcohol and add it to a specified volume of deionized water. Stir at a speed of 200-500 rad / min for 10 minutes, then heat to 95°C at a rate of 1°C / min. Maintain this temperature for 60 minutes while stirring at 200-500 rad / min. Check if the solution is completely dissolved. If not, continue stirring and maintaining the temperature until complete dissolution. During the dissolution process, pay attention to water loss and replenish water promptly. After complete dissolution, stop heating and allow the solution to cool naturally to room temperature.

[0008] In the polyvinyl alcohol (PVA) metal ion content detection method described above, the PVA aqueous solution is prepared by adding a specified volume of deionized water to PVA and weighing it. After dissolution, the solution is cooled to room temperature and weighed again. The difference in mass between the two is calculated and the corresponding mass of deionized water is added to avoid errors in the concentration of the PVA aqueous solution.

[0009] In the polyvinyl alcohol metal ion content detection method described above, the sodium ion content in the polyvinyl alcohol aqueous solutions with different sodium ion contents prepared in step two is ≤0.5% (polyvinyl alcohol content + sodium acetate content).

[0010] In the polyvinyl alcohol metal ion content detection method described above, step two involves preparing at least six polyvinyl alcohol aqueous solutions with different sodium ion contents.

[0011] In the polyvinyl alcohol metal ion content detection method described above, the specified temperature in step three is 20-30℃.

[0012] In the polyvinyl alcohol metal ion content detection method described above, the error range between the detection temperature and the specified temperature of the polyvinyl alcohol aqueous solution with different sodium ion contents in step three is ±0.3℃.

[0013] In the polyvinyl alcohol metal ion content detection method described above, the conductivity value and the corresponding sodium ion concentration obtained in step four are used to construct a linear regression equation as y = 12.71 + 490*x, where y is the solution conductivity and x is the sodium ion content in the polyvinyl alcohol.

[0014] As described above, in the method for detecting metal ion content in polyvinyl alcohol, the R-squared value of the linear regression equation is... 2 =0.996.

[0015] The advantages of this invention are: by establishing the relationship between the conductivity of a polyvinyl alcohol sample aqueous solution and the sodium ion content, this invention allows for the calculation of the sodium ion content in the polyvinyl alcohol sample, which is the content of metallic impurities, simply by preparing the polyvinyl alcohol sample into an aqueous solution and measuring its conductivity. Furthermore, this invention is simple to operate, requires no high-temperature treatment, is highly safe, and allows for the continuous preparation of multiple polyvinyl alcohol sample aqueous solutions for detection, effectively improving detection efficiency. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of different concentrations of polyvinyl alcohol aqueous solutions selected for the verification test of this invention; Figure 2 This is a schematic diagram showing the conductivity test results of a 12% polyvinyl alcohol aqueous solution used in the verification test of this invention. Figure 3 This is a line graph showing the relationship between conductivity and concentration in the concentration selection for the verification test of this invention; Figure 4 This is a line graph showing the relationship between conductivity and temperature during the temperature selection for the verification test of this invention. Figure 5 This is a schematic diagram of the weighing of polyvinyl alcohol in the preparation of the polyvinyl alcohol aqueous solution according to the present invention; Figure 6 This is a schematic diagram of weighing deionized water in the preparation of the polyvinyl alcohol aqueous solution of the present invention. Figure 7 This is a schematic diagram of the feeding process for preparing the polyvinyl alcohol aqueous solution of the present invention; Figure 8 This is a schematic diagram showing the weighing process of preparing the polyvinyl alcohol aqueous solution of the present invention before dissolution, with a beaker attached. Figure 9 This is a schematic diagram of the heating and stirring process for preparing the polyvinyl alcohol aqueous solution according to the present invention. Figure 10 This is a schematic diagram illustrating the preparation, stirring, and dissolution of a polyvinyl alcohol aqueous solution according to the present invention. Figure 11 This is a schematic diagram showing the dissolution and weighing of the polyvinyl alcohol aqueous solution prepared according to the present invention, with a beaker attached. Figure 12 This is a schematic diagram illustrating the water replenishment process for preparing the polyvinyl alcohol aqueous solution according to the present invention. Figure 13 This is a schematic diagram of the weighing of sodium acetate prepared from the sodium acetate aqueous solution of the present invention; Figure 14 This is a schematic diagram of weighing deionized water in the preparation of sodium acetate aqueous solution according to the present invention. Figure 15 This is a schematic diagram illustrating the feeding and dissolution process for preparing the sodium acetate aqueous solution according to the present invention; Figure 16 This is a schematic diagram of the sodium acetate aqueous solution addition operation of the present invention; Figure 17 This is a schematic diagram illustrating the construction of the linear regression equation of this invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] A method for detecting metal ion content in polyvinyl alcohol includes the following steps: Step 1: Prepare aqueous solutions of polyvinyl alcohol and sodium acetate; Step 2: Take several portions of polyvinyl alcohol aqueous solution and precisely add sodium acetate aqueous solution to prepare polyvinyl alcohol aqueous solutions with different sodium ion contents; Step 3: Adjust the temperature of polyvinyl alcohol aqueous solutions with different sodium ion contents to the specified temperature, and use a conductivity meter to detect the conductivity and record the conductivity values ​​in sequence. Step 4: Construct a linear regression equation based on the conductivity value obtained in Step 3 and the corresponding sodium ion content, and then obtain the sodium ion content in the corresponding polyvinyl alcohol by detecting the conductivity.

[0020] Specifically, in step one of this embodiment, the concentrations of both the polyvinyl alcohol aqueous solution and the sodium acetate aqueous solution are 4%.

[0021] Specifically, the preparation of the polyvinyl alcohol aqueous solution described in this embodiment is as follows: the weighed polyvinyl alcohol is added to a specified volume of deionized water, stirred at a speed of 200-500 rad / min for 10 min, then heated to 95°C at a heating rate of 1°C / min, and then kept at a stirring speed of 200-500 rad / min for 60 min. Check whether it is completely dissolved. If it is not completely dissolved, continue to keep warm and stir until it is completely dissolved. During the dissolution process, pay attention to the loss of water and add water in time. After it is completely dissolved, stop heating and let it cool naturally to room temperature.

[0022] More specifically, in the polyvinyl alcohol aqueous solution described in this embodiment, polyvinyl alcohol is added to a specified volume of deionized water and weighed. After dissolution, it is cooled to room temperature and weighed again. The mass difference between the two is calculated and the corresponding mass of deionized water is added to avoid errors in the concentration of the polyvinyl alcohol aqueous solution.

[0023] More specifically, in step two of this embodiment, the sodium ion content in the polyvinyl alcohol aqueous solutions with different sodium ion contents is ≤0.5% (polyvinyl alcohol content + sodium acetate content).

[0024] More specifically, in step two of this embodiment, at least six polyvinyl alcohol aqueous solutions with different sodium ion contents are prepared.

[0025] Furthermore, the specified temperature in step three of this embodiment is 20-30℃.

[0026] Furthermore, in step three of this embodiment, the detection temperature of polyvinyl alcohol aqueous solutions with different sodium ion contents has an error range of ±0.3℃ compared to the specified temperature.

[0027] Furthermore, in step four of this embodiment, the conductivity value and the corresponding sodium ion concentration are used to construct a linear regression equation as y = 12.71 + 490*x, where y is the solution conductivity and x is the sodium ion content in polyvinyl alcohol.

[0028] Furthermore, the R-squared of the linear regression equation described in this embodiment... 2 =0.996.

[0029] Verification test 1. Concentration selection Prepare polyvinyl alcohol aqueous solutions of different concentrations (e.g.) Figure 1 As shown), the conductivity was measured using a conductivity meter at a temperature of 21±0.3℃ (the conductivity measurement results for a concentration of 12% are shown in the figure). Figure 2 As shown in the table), the final test results are shown in Table 1 and... Figure 3 As shown.

[0030]

[0031] Table 1 Depend on Figure 1-3As shown in Table 1 and through actual preparation and observation, the viscosity increases significantly when the concentration is greater than 5%, and the difficulty of complete dissolution also increases. The concentration-conductivity curve shows a significant change when the concentration is greater than 5%, thus affecting the accuracy of the conductivity test results. Furthermore, the sodium ion content decreases when the concentration is below 4%. While low concentrations facilitate dissolution, the lower ion content can lead to larger errors during detection, affecting the accuracy of subsequent data. Therefore, a concentration of 4% was chosen as the concentration of the polyvinyl alcohol aqueous solution for polyvinyl alcohol detection. This concentration not only dissolves easily but also has a low detection error, ensuring detection efficiency.

[0032] 2. Detection Temperature Selection A 4% polyvinyl alcohol aqueous solution was prepared, and its conductivity was measured using a conductivity meter at different temperatures. The results are shown in Table 2. Figure 4 As shown.

[0033]

[0034] Table 2 From Table 2 and Figure 4 The data shows that the conductivity changes tend to be stable at 20-30℃. Therefore, even if there is a large temperature error within this temperature range, it will not lead to a large error in the final measured conductivity, thus ensuring the accuracy of the conductivity test results.

[0035] 3. Establish the relationship between the conductivity and sodium ion content of polyvinyl alcohol aqueous solution. Step 1: Prepare a 4% polyvinyl alcohol aqueous solution and a 4% sodium acetate aqueous solution; like Figures 5-12 As shown, the preparation procedure for the polyvinyl alcohol aqueous solution is as follows: Weigh 12g of polyvinyl alcohol and add it to 288ml of deionized water. Weigh 451g of the solution with a beaker. Stir at 400rad / min for 10min. Then heat the solution to 95℃ at a heating rate of 1℃ / min. Then keep the solution at 400rad / min for 60min until it is completely dissolved. Stop heating and let it cool naturally to room temperature. Then add deionized water until the weight of the solution with the beaker is 451g and stir evenly. like Figures 13-15 As shown, the preparation procedure for the sodium acetate aqueous solution is as follows: weigh 8g of sodium acetate and add it to 192ml of deionized water. Stir at 200rad / min for 10min at room temperature until completely dissolved and set aside. Step 2: Accurately add six portions of polyvinyl alcohol aqueous solution to sodium acetate aqueous solution to prepare polyvinyl alcohol aqueous solutions with different sodium ion contents (the sodium acetate aqueous solution addition procedure is as follows). Figure 16As shown, six polyvinyl alcohol aqueous solutions with different sodium ion contents were prepared, namely 0.046%, 0.1%, 0.2%, 0.3%, 0.4%, and 0.5%, respectively. Nine samples were prepared for each concentration of polyvinyl alcohol aqueous solution. Step 3: Adjust the temperature of polyvinyl alcohol aqueous solutions with different sodium ion contents to 25±0.5℃, and use a conductivity meter to detect the conductivity and record the conductivity values. The results are shown in Table 3.

[0036]

[0037] Table 3 Step 4: Based on the conductivity value obtained in Step 3 and the corresponding sodium ion concentration, construct a linear regression equation: y = 12.71 + 490*x (e.g., ...). Figure 17 As shown in the figure, where y is the solution conductivity, x is the sodium ion content in polyvinyl alcohol, and R0 is the linear regression equation. 2 =0.996, thus the sodium ion concentration in polyvinyl alcohol can be obtained by detecting the conductivity.

[0038] The coefficient of determination R of the linear regression equation constructed in this invention 2 The value reached 0.996, indicating that there is a very high linear correlation between the conductivity of polyvinyl alcohol aqueous solution and the sodium ion content, and the equation fitting accuracy is fully capable of meeting the detection requirements.

[0039] Compared to traditional ash content detection methods, this invention eliminates the need for high-temperature calcination, simplifies the operation process, and offers a high safety factor. It also eliminates the need for expensive large-scale detection equipment such as atomic absorption spectrometers and ion chromatographs, requiring only a conventional conductivity meter to complete the detection, thus reducing testing costs. Furthermore, this invention allows for batch processing of samples, with single-sample testing time shorter than traditional methods and large-scale instrument methods, improving detection efficiency. It is highly suitable for rapid batch sampling in polyvinyl alcohol production processes, meeting the needs of daily production quality control.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for detecting the metal ion content of polyvinyl alcohol, characterized in that: Includes the following steps: Step 1: Prepare aqueous solutions of polyvinyl alcohol and sodium acetate; Step 2: Take several portions of polyvinyl alcohol aqueous solution and precisely add sodium acetate aqueous solution to prepare polyvinyl alcohol aqueous solutions with different sodium ion contents; Step 3: Adjust the temperature of polyvinyl alcohol aqueous solutions with different sodium ion contents to the specified temperature, and use a conductivity meter to detect the conductivity and record the conductivity values ​​in sequence. Step 4: Construct a linear regression equation based on the conductivity value obtained in Step 3 and the corresponding sodium ion content, and then obtain the sodium ion content in the corresponding polyvinyl alcohol by detecting the conductivity.

2. The method for detecting metal ion content in polyvinyl alcohol according to claim 1, characterized in that: In step one, the concentrations of both the polyvinyl alcohol aqueous solution and the sodium acetate aqueous solution are 4%.

3. The method for detecting metal ion content in polyvinyl alcohol according to claim 1, characterized in that: The preparation procedure for the polyvinyl alcohol aqueous solution is as follows: add the weighed polyvinyl alcohol to the specified volume of deionized water, stir at a speed of 200-500 rad / min for 10 min, then heat to 95°C at a heating rate of 1°C / min, and then keep warm at a stirring speed of 200-500 rad / min for 60 min. Check whether it is completely dissolved. If it is not completely dissolved, continue to keep warm and stir until it is completely dissolved. After it is completely dissolved, stop heating and let it cool naturally to room temperature.

4. The method for detecting metal ion content in polyvinyl alcohol according to claim 3, characterized in that: When preparing the polyvinyl alcohol aqueous solution, polyvinyl alcohol is added to a specified volume of deionized water and weighed. After dissolution, it is cooled to room temperature and weighed again. The difference in mass between the two is calculated and the corresponding mass of deionized water is added to avoid errors in the concentration of the polyvinyl alcohol aqueous solution.

5. The method for detecting metal ion content in polyvinyl alcohol according to claim 1, characterized in that: The sodium ion content in the polyvinyl alcohol aqueous solutions with different sodium ion contents prepared in step two is ≤0.5% (polyvinyl alcohol content + sodium acetate content).

6. The method for detecting metal ion content in polyvinyl alcohol according to claim 1, characterized in that: In step two, at least six aqueous solutions of polyvinyl alcohol with different sodium ion contents are prepared.

7. The method for detecting metal ion content in polyvinyl alcohol according to claim 1, characterized in that: The specified temperature in step three is 20-30℃.

8. The method for detecting metal ion content in polyvinyl alcohol according to claim 1, characterized in that: In step three, the detection temperature of polyvinyl alcohol aqueous solutions with different sodium ion contents has an error range of ±0.3℃ compared to the specified temperature.

9. The method for detecting metal ion content in polyvinyl alcohol according to claim 1, characterized in that: In step four, the conductivity value and the corresponding sodium ion concentration are used to construct a linear regression equation as y = 12.71 + 490*x, where y is the solution conductivity and x is the sodium ion content in polyvinyl alcohol.

10. The method for detecting metal ion content in polyvinyl alcohol according to claim 9, characterized in that: The R-squared value of the linear regression equation is... 2 =0.996.

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