Detection method of trace emulsifier in fluorinated polymer emulsion

Abstract

The present invention belongs to the field of fluorine chemical industry, and particularly relates to a method for detecting trace emulsifiers in fluorine-containing polymer emulsions. The present invention provides a method for detecting trace emulsifiers in fluorine-containing polymer emulsions, wherein different extraction methods are used to extract fluorine-containing emulsifiers from fluorine-containing polymer emulsions, and the extracted fluorine-containing emulsifiers are qualitatively and quantitatively detected by liquid chromatography-mass spectrometry, and the extraction effects of different extraction methods are obtained, and ultrasonic extraction is the best, followed by freezing extraction; the present invention can not only extract and detect fluorine-containing emulsifiers in fluorine-containing polymer emulsion stock solution, but also extract and detect emulsifiers in fluorine-containing polymer emulsions treated with ion exchange resins or other methods, and ensures high accuracy; the concentration of fluorine-containing emulsifiers therein can be accurately determined by using a minimum amount of fluorine-containing polymer emulsion or a minimum amount of extraction solvent, thereby achieving the technical effect of reducing economic costs.

Description

Technical Field

[0001] The invention belongs to the field of fluorine chemical industry, and particularly relates to a method for detecting trace emulsifiers in fluorine-containing polymer emulsions. Background Art

[0002] Fluoropolymer emulsion can be condensed and dried to obtain fluoropolymer powder, and can also be concentrated and added with other additives to obtain fluoropolymer aqueous dispersion, which can be used in various coating and impregnation products.

[0003] Per- and polyfluoroalkyl compounds (PFAS) are key emulsifiers in the production of fluoropolymers, which can prevent the polymerization reaction from being hindered by chain transfer in aqueous media. Among the many PFAS, perfluorooctane sulfonic acid and perfluorooctanoic acid are the two most common types, which are widely used in the production of fluoropolymers. However, their chemical properties are stable and difficult to degrade, they are highly bioaccumulative, and potentially toxic, posing a serious threat to the ecological environment and human health. They have been listed as persistent organic pollutants (POPs) in the Stockholm International Convention, and their use is banned or strictly controlled. Therefore, this strict ban has promoted the development and use of alternatives, resulting in a large number of different types of fluorinated alternatives being frequently detected in the environment. Some toxicological data have shown that the toxicity of some fluorinated emulsifier alternatives is comparable to or even higher than that of perfluorooctane sulfonic acid and perfluorooctanoic acid, with longer bioaccumulation and half-life in the body, and are becoming a new threat in the field of environmental health.

[0004] At present, there are methods for removing emulsifiers from fluorinated polymer emulsions, such as ion exchange resin method and membrane treatment method, and then recovering the fluorinated emulsifiers by elution, etc. However, the fluorinated emulsifiers removed are most of the free emulsifiers in the emulsion, and there is still a lack of an accurate quantitative method for the total amount of fluorinated emulsifiers in the emulsion (including residual free emulsifiers and emulsifiers participating in the formation of latex particles). Therefore, how to measure the residual amount of emulsifiers in fluorinated polymer emulsions after ion exchange resin or membrane treatment has become an urgent problem to be solved, which is of great significance for the preparation of fluorinated polymer emulsion products that meet national quality standards and listing standards. Summary of the invention

[0005] In order to solve the problem that it is difficult to determine the content of trace emulsifier in fluorine-containing polymer emulsion in the prior art, the present invention provides a method for detecting trace emulsifier in fluorine-containing polymer emulsion, adopts different extraction methods to extract fluorine-containing emulsifier from fluorine-containing polymer emulsion, and performs qualitative and quantitative detection of the extracted fluorine-containing emulsifier by liquid chromatography-mass spectrometry, which has the effects of high accuracy and good reproducibility.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] The method for detecting trace emulsifier in fluorine-containing polymer emulsion is characterized by comprising the following steps:

[0008] (1) adding an extraction solvent to a fluorine-containing polymer emulsion, and performing ultrasound at an ultrasound frequency of 28-40 kHz and an extraction temperature of 20-50° C., and obtaining a treated liquid after ultrasound for 1-4 hours;

[0009] Alternatively, the fluorine-containing polymer emulsion is subjected to freezing treatment at a freezing temperature of -20 to 5°C for a freezing time of 1 to 4 hours, and then vacuum dried, and an extraction solvent is added to the obtained solid, and the solid is allowed to stand to obtain an upper treatment liquid;

[0010] (2) Filtering the treated liquid in step (1) to obtain a test liquid, and detecting the concentration of the emulsifier in the test liquid.

[0011] Preferably, the extraction solvent in step (1) is methanol or water.

[0012] Preferably, the fluorine-containing polymer emulsion is a raw fluorine-containing polymer emulsion or a treated fluorine-containing polymer emulsion.

[0013] Preferably, the concentration of the trace amount of fluorinated emulsifier in the fluorinated polymer emulsion is 30-800 ppm.

[0014] Preferably, the fluorinated polymer emulsion in step (1) comprises, by mass fraction, 39.5-40% fluorinated polymer, 60-60.5% water, and 0.1-0.2% fluorinated emulsifier; further preferably, the fluorinated polymer emulsion in step (1) comprises, by mass fraction, 39.5-40% fluorinated polymer, 60-60.5% water, and 0.01-0.05‰ fluorinated emulsifier.

[0015] Preferably, the fluorine-containing polymer in step (1) is at least one of polytetrafluoroethylene, modified polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, propylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and polyvinylidene fluoride.

[0016] Preferably, the emulsifier is a fluorinated carboxylic acid or salt containing 1 to 3 etheric oxygen atoms and 5 to 9 carbon atoms. More preferably, the emulsifier is at least one of fluoroether acid and its salt, fluoroether carbonate and its salt, and perfluoropolyether carboxylic acid and its salt.

[0017] Preferably, the amount of the fluorinated polymer emulsion used in step (1) is 1 to 50 g. Further preferably, the amount of the fluorinated polymer emulsion extracted by ultrasound is 1 to 20 g; the amount of the fluorinated polymer emulsion extracted by freeze is 1 to 20 g; most preferably, the amount of the fluorinated emulsifier emulsion extracted by ultrasound and freeze is 1 g.

[0018] Preferably, in step (1), the ratio of the fluorinated polymer emulsion to the extraction solvent is 1 g: (2.5-3.5) mL, and further preferably, the ratio of the fluorinated polymer emulsion to the extraction solvent is 1 g: 3 mL.

[0019] Preferably, the freezing treatment temperature in step (1) is -20°C.

[0020] Preferably, in step (1), the ultrasonic extraction time is 2 hours, and the freezing treatment time is 1 hour.

[0021] Preferably, the filtering method in step (2) is filtering using a 0.22-0.45 μm microporous filter membrane.

[0022] Preferably, the detection method of step (2) is to use a liquid chromatography-mass spectrometer to detect the test liquid.

[0023] One or more technical solutions provided by the embodiments of the present invention have at least the following technical effects:

[0024] 1. The method for detecting trace emulsifiers in fluorinated polymer emulsions of the present invention is to extract the emulsifiers in the fluorinated polymer emulsions by different extraction methods, and the extraction effects of the different extraction methods are as follows: ultrasonic extraction>freezing extraction>centrifugal extraction;

[0025] 2. The present invention can effectively extract and qualitatively and quantitatively detect the emulsifier with high accuracy, and can accurately determine the concentration of the fluorinated emulsifier therein by using a minimum amount of fluorinated polymer emulsion or a minimum amount of extraction solvent, thereby achieving the technical effect of reducing economic costs;

[0026] 3. The present invention can not only extract and detect the fluorinated emulsifier in the original fluorinated polymer emulsion, but also extract and detect the emulsifier in the fluorinated polymer emulsion after being treated with ion exchange resin or other methods, thereby realizing the extraction and detection of trace fluorinated emulsifiers and ensuring a high degree of accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the standard curve of fluoroether carbonate;

[0028] Figure 2 This is the total ion current diagram of 100ppm fluoroether carbonate standard solution;

[0029] Figure 3 Total ion chromatogram extracted by ultrasonic extraction for emulsion 1;

[0030] Figure 4 This is the total ion current diagram of 100ppm perfluoropolyether carboxylic acid standard solution;

[0031] Figure 5Total ion current chromatogram of ultrasonic extraction of emulsion 2. DETAILED DESCRIPTION

[0032] The present invention will be further described below with reference to specific embodiments, but is not limited thereto.

[0033] It should be noted that the experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents, materials and equipment described are all commercially available unless otherwise specified.

[0034] The fluorinated polymer emulsions in all the embodiments and comparative examples include fluorinated polymers, water and fluorinated emulsifiers, and the fluorinated emulsifiers include fluoroether acids and their salts, fluoroether carbonates and their salts, and perfluoropolyether carboxylic acids and their salts. The emulsifier concentration in the original fluorinated polymer emulsion is about 800 ppm, and the emulsifier concentration in the fluorinated polymer emulsion after treatment with the ion exchange resin is about 50 ppm.

[0035] Examples 1-8

[0036] The detection method of emulsifier in fluorine-containing polymer emulsion is ultrasonic extraction, comprising the following steps:

[0037] (1) Extraction of emulsifier: Add the untreated fluorinated polymer emulsion or the fluorinated polymer emulsion treated with ion exchange resin into a clean glass bottle with a lid, and add a certain amount of methanol thereto. Perform ultrasound at a certain temperature and frequency. After a period of time, take the supernatant and filter the supernatant with a 0.22 μm organic microporous filter membrane to obtain the test solution. The specific conditions are shown in Table 1.

[0038] (2) Preparation of standard solutions: Take pure fluorinated emulsifier and use water as solvent to prepare standard solutions of 1, 2, 5, 10, 100, 500, and 1000 ppm.

[0039] (3) On-machine testing:

[0040] Liquid chromatography conditions were as follows: mobile phase was methanol and water (initial volume ratio: water: methanol = 9:1), gradient elution (0-0.5 min to maintain the initial ratio; 0.5-3 min methanol ratio increased to 90%; 3-4 min methanol ratio decreased to 10%; 4-5 min to maintain the initial ratio); flow rate 0.4 mL / min; chromatographic column was C18 column (2.1 mm × 50 mm, 1.7 μm); column temperature was 30 ° C; injection volume was 1 μL. Mass spectrometry conditions: ionization mode was ESI, negative ion scanning, mode was MS SCAN.

[0041] After the instrument is stable, inject a blank sample first, and then inject the standard solution from low to high concentration in sequence, and draw a standard curve based on peak area-concentration to obtain the standard curve: y=2460.4x+143606, R 2 =0.99 (y is the peak area, x is the concentration). A blank sample was injected, and then a test solution was injected to obtain the peak area, which was then inserted into the standard curve to obtain the corresponding concentration, and then multiplied by the dilution factor to obtain the final concentration of the fluorinated emulsifier. The results are shown in Table 1. Among them, the fluorinated polymer in the fluorinated polymer emulsion 1 treated with ion exchange resin and the emulsion stock solution 1 is polytetrafluoroethylene, and the fluorinated emulsifier is fluoroether carbonic acid, and the fluorinated polymer in the fluorinated polymer emulsion 2 treated with ion exchange resin is polytetrafluoroethylene, and the fluorinated emulsifier is perfluoropolyether carboxylic acid.

[0042] Table 1. Ultrasonic extraction conditions and detection concentration results of trace emulsifiers in fluoropolymer emulsions

[0043]

[0044]

[0045] Embodiment 9, 10

[0046] The method for detecting trace emulsifiers in fluoropolymer emulsions is a method of extracting by freezing treatment, comprising the following steps:

[0047] Take the untreated fluorinated polymer emulsion 1 or the fluorinated polymer emulsion 1 treated with ion exchange resin, add it to a conical bottle with a lid, put it in a refrigerator at -20°C for 1 hour, put it in a vacuum dryer in a frozen state to remove water, and re-dissolve the obtained solid in methanol. After standing, take the supernatant, filter the supernatant with a 0.22μm organic microporous filter membrane to obtain the test solution.

[0048] The steps of preparing the standard solution and testing on the machine were the same as those in Example 1, and the concentration of the fluorinated emulsifier was as shown in Table 2.

[0049] Table 2. Freezing treatment conditions and detection concentration results of trace emulsifiers in fluoropolymer emulsions

[0050]

[0051] Comparative Examples 1-5

[0052] The detection method of trace emulsifier in fluorinated polymer emulsion is ultrasonic extraction, comprising the following steps:

[0053] (1) Extraction of emulsifier: Add the untreated fluorinated polymer emulsion or the fluorinated polymer emulsion treated with ion exchange resin into a clean glass bottle with a cover, and add a certain amount of methanol or water thereto. Perform ultrasound at a certain temperature and frequency. After a period of time, take the supernatant and filter the supernatant with a 0.22 μm organic microporous filter membrane to obtain the test solution. The specific conditions are shown in the table below.

[0054] The steps of preparing the standard solution and testing on the machine were the same as those in Example 1, and the concentration of the fluorinated emulsifier was as shown in Table 3.

[0055] Table 3. Ultrasonic extraction conditions and detection concentration results of trace emulsifiers in fluoropolymer emulsions

[0056]

[0057] Comparative Examples 6 and 7

[0058] The detection method of trace emulsifier in fluorinated polymer emulsion is centrifugal extraction, comprising the following steps:

[0059] Extraction of fluorinated emulsifier: Take the untreated fluorinated polymer emulsion 1 or the fluorinated polymer emulsion 1 treated with ion exchange resin and put them into plastic centrifuge tubes respectively, set the speed and centrifugation time, and centrifuge twice. After centrifugation, take the supernatant and filter the supernatant with a 0.22μm organic microporous filter membrane to obtain the test solution.

[0060] The steps of preparing the standard solution and testing on the machine were the same as those in Example 1, and the concentration of the fluorinated emulsifier was as shown in Table 4.

[0061] Table 4. Centrifugal extraction conditions and detection concentration results of trace emulsifiers in fluoropolymer emulsions

[0062]

[0063]

[0064] Comparative Examples 8 and 9

[0065] The detection method of trace emulsifier in fluorinated polymer emulsion is to extract directly after adding demulsifier, including the following steps:

[0066] Extraction of fluorinated emulsifier: Take the untreated fluorinated polymer emulsion 1 or the fluorinated polymer emulsion 1 treated with ion exchange resin and add it into a glass test tube, then add demulsifier ammonia water to directly demulsify, take the upper clear liquid after solid-liquid separation, filter the upper clear liquid with a 0.22μm organic microporous filter membrane to obtain the test solution.

[0067] The steps of preparing the standard solution and testing on the machine were the same as those in Example 1, and the concentration of the fluorinated emulsifier was as shown in Table 5.

[0068] Table 5. Extraction conditions of ammonia demulsification and test results of fluorinated emulsifier concentration

[0069]

[0070] Comparative Example 10

[0071] The detection method of trace emulsifier in fluoropolymer emulsion is Soxhlet extraction, which includes the following steps:

[0072] Take the untreated fluorinated polymer emulsion stock solution 1 and add it into a conical flask with a lid, then add methanol to break the emulsion, separate the solid and liquid, put it into a Soxhlet extraction device for reflux, the reflux temperature is 90°C, and the reflux time is 6h; after the reflux is completed, take the supernatant liquid, filter the supernatant liquid with a 0.22μm organic microporous filter membrane to obtain the test solution.

[0073] The steps of preparing the standard solution and testing on the machine were the same as those in Example 1, and the concentration of the fluorinated emulsifier was as shown in Table 6.

[0074] Table 6. Soxhlet extraction and fluorinated emulsifier concentration test results

[0075]

[0076]

[0077] The results in Table 1-6 show that ultrasonic extraction has the following advantages: it can not only extract fluorinated emulsifiers from fluorinated polymer emulsion stock solution, but also efficiently extract trace emulsifiers from fluorinated polymer emulsion treated with ion exchange resin; the amount of fluorinated polymer sample used is small, and 1g of fluorinated polymer emulsion and 3mL of methanol can be used for effective extraction and detection; the extraction effect is the best, the detection concentration of fluorinated emulsifier is the highest, and the detection accuracy rate is over 90%; this method is also applicable to the extraction and detection of other types of fluorinated emulsifiers, and the detection range is wider; efficient extraction can also be completed at room temperature, achieving the technical effect of reducing economic costs.

[0078] The reason why ultrasonic treatment has good effect: a large number of tiny bubbles are formed inside the emulsion during ultrasound. Under ultrasonic radiation, the tiny bubbles continue to vibrate with the sound waves, producing ultrasonic cavitation effect, causing sharp pressure changes at the bubble interface and gaps, forming microjets, strengthening the stirring and diffusion effect, destroying the stability of the emulsion, and allowing the extraction solvent to fully contact all the emulsifiers in the emulsion, resulting in excellent extraction effect.

[0079] However, it is worth noting that when the temperature exceeds 50°C, the fluorinated emulsifier begins to decompose, so a higher extraction temperature is not conducive to the extraction of the fluorinated emulsifier; at the same time, when the ultrasonic time is less than 2h, the extraction effect is poor, which may be due to the fact that the agglomerated polymer macromolecular chains are not fully stretched out, and there is no obvious difference in the extraction effect after the ultrasonic time exceeds 2h; to achieve a better ultrasonic extraction effect, the ultrasonic frequency and the ultrasonic time are inversely proportional to a certain extent, that is, the higher the ultrasonic frequency, the shorter the ultrasonic time required, and when the ultrasonic time is at least 2h, the ultrasonic frequency should not be lower than 28kHz, and when the frequency exceeds a certain range, the detection effect will also deteriorate. This is because the polymer chain degrades under higher ultrasonic energy to produce molecular chain fragments that constitute impurities, which will interfere with the detection accuracy.

[0080] The extraction of fluorinated polymer emulsion by freezing treatment can also be used to extract trace fluorinated emulsifiers in fluorinated polymer emulsions. The extraction principle is: during freezing treatment, since the emulsion contains water, as the temperature decreases, the fluorinated emulsifier and water will form ice crystals, and the ice crystals will continue to grow, generating interfacial forces, thereby separating the emulsifier from the polymer particles. Under the action of vacuum drying, water is continuously sublimated and removed while the emulsifier remains on the surface of the polymer particles. The obtained polymer is dissolved in methanol, and most of the emulsifier can be extracted.

[0081] Although Soxhlet extraction can extract the fluorinated emulsifier in the fluorinated polymer emulsion, the high reflux temperature can easily cause the fluorinated emulsifier to decompose, thus causing the measured result to be low.

[0082] It is difficult to detect trace amounts of fluorinated emulsifiers in fluorinated polymer emulsions demulsified by centrifugation, indicating that trace amounts of fluorinated emulsifiers may be adsorbed or wrapped by the fluorinated polymer during centrifugation and are not easily dispersed in the supernatant. Therefore, they are not suitable for the extraction of trace amounts of fluorinated emulsifiers in fluorinated polymer emulsions.

[0083] Adding other demulsifiers to demulsify the fluorinated polymer emulsion will add interfering components to the emulsion, which is not conducive to the detection of the fluorinated emulsifier. At the same time, using this demulsification method for demulsification and LC-MS detection, the concentration of the detected fluorinated emulsifier is low and the effect is poor. It is not suitable for the detection of trace fluorinated emulsifiers in fluorinated polymer emulsions.

Claims

1. A method for detecting trace emulsifiers in fluorinated polymer emulsions, characterized in that: The following steps are involved: (1) adding an extraction solvent to a fluorine-containing polymer emulsion, and performing ultrasonic treatment at an ultrasonic frequency of 28-40 kHz and an extraction temperature of 20-50° C. to obtain a treated liquid after 2-4 hours of ultrasonic treatment; Alternatively, the fluorine-containing polymer emulsion is subjected to freezing treatment at a freezing temperature of -20 to 5°C for a freezing time of 1 to 4 hours, and then vacuum dried, and an extraction solvent is added to the obtained solid, and the solid is allowed to stand to obtain an upper treatment liquid; (2) filtering the treated liquid in step (1) to obtain a test liquid, and detecting the concentration of the emulsifier in the test liquid; The extraction solvent in step (1) is methanol; The fluorine-containing polymer in step (1) is at least one of polytetrafluoroethylene, modified polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, propylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and polyvinylidene fluoride; The emulsifier is at least one of fluoroether acid and its salt, fluoroether carbonate and its salt, perfluoropolyether carboxylic acid and its salt; The filtration method in step (2) is to filter using a 0.22-0.45 µm microporous membrane; The detection method of step (2) is to use a liquid chromatography-mass spectrometer to detect the test liquid, and the detection method is that the mobile phase is methanol and water, the initial volume ratio is: water: methanol = 9:1, gradient elution, 0-0.5min maintain the initial ratio; 0.5-3min methanol ratio increases to 90%; 3-4min methanol ratio decreases to 10%; 4-5min maintain the initial ratio; flow rate 0.4mL / min; chromatographic column is C18 column, 2.1mm×50mm, 1.7µm; column temperature is 30℃; injection volume is 1µL; mass spectrometry conditions: ionization mode is ESI, negative ion scanning, mode is MS SCAN; After the instrument is stable, first inject a blank sample, and then inject the standard solutions from low to high concentrations, and draw a standard curve with peak area-concentration to obtain the standard curve: y=2460.4x+143606, R2=0.99, y is the peak area, x is the concentration; inject a blank sample, and then inject a treated test solution to obtain the peak area, substitute it into the standard curve to obtain the corresponding concentration, and then multiply it by the dilution factor to obtain the final concentration of the fluorinated emulsifier.

2. The detection method according to claim 1, characterized in that: The concentration of the trace emulsifier in the fluorine-containing polymer emulsion is 30-800 ppm.

3. The detection method according to claim 1, characterized in that: The fluorine-containing polymer emulsion in step (1) comprises, by mass fraction, 39.5-40% of fluorine-containing polymer, 60-60.5% of water, and 0.1-0.2% of fluorine-containing emulsifier.

4. The detection method according to claim 1, characterized in that: The fluorine-containing polymer emulsion in step (1) comprises, by mass fraction, 39.5-40% of fluorine-containing polymer, 60-60.5% of water, and 0.01-0.05‰ of fluorine-containing emulsifier.

5. The detection method according to claim 1, characterized in that: The amount of fluorine-containing polymer emulsion used in step (1) is 1-50 g.

6. The detection method according to claim 1, characterized in that: In step (1), the amount of the fluorinated polymer emulsion extracted by ultrasonication is 1-20 g; the amount of the fluorinated polymer emulsion extracted by freezing is 1-20 g.

7. The detection method according to claim 1, characterized in that: In step (1), the ratio of the fluorinated polymer emulsion to the extraction solvent is 1 g: (2.5-3.5) mL.

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