Composite nano material and method for measuring content of combined acrylonitrile in polymerization process of butyronitrile latex

Abstract

The invention provides a composite nano-material and a method for determining the content of bound acrylonitrile in a butyronitrile latex polymerization process. The method comprises the following steps: pretreating a butyronitrile latex sample by adopting the composite nano material, then collecting a Raman spectrum of the butyronitrile latex, carrying out data pretreatment, extracting a characteristic peak, and calculating to obtain the content of bound acrylonitrile in the butyronitrile latex. The method can be used for rapidly, accurately and nondestructively measuring the content of the combined acrylonitrile in the polymerization process of the butyronitrile latex.

Description

Technical Field

[0001] This invention belongs to the field of rubber analysis and testing technology, specifically relating to a composite nanomaterial and a method for determining the content of acrylonitrile bound during the polymerization of nitrile rubber latex. Background Technology

[0002] The raw materials for nitrile rubber (NBR) are mainly acrylonitrile and butadiene monomers. By quantitatively controlling the ratio of these two monomers and the emulsion polymerization conditions, NBRs with different properties and applications can be obtained. Due to its excellent oil and solvent resistance, NBR is widely used in the automotive industry, aerospace, petrochemicals, construction machinery, tire manufacturing, seals, and rubber products. Seals and fittings made of NBR are widely used in key components such as automotive engines, hydraulic systems, and fuel lines for sealing and transmitting various liquid media.

[0003] The oil resistance of nitrile rubber (NBR) is mainly attributed to the introduction of acrylonitrile monomers, while the introduction of butadiene monomers imparts elasticity and processability to NBR. The content of acrylonitrile monomers has a significant impact on the properties of NBR; a higher content of acrylonitrile monomers results in excellent oil resistance but reduces its impact strength and processability. In practical applications, the performance of NBR can be optimized by adjusting the acrylonitrile content to meet different needs. Therefore, real-time online monitoring of the NBR latex polymerization process and determining the acrylonitrile content at different polymerization stages are crucial.

[0004] Currently, most methods for detecting bound acrylonitrile content in nitrile rubber are offline methods, targeting the final product. These methods include gas chromatography (GC), liquid chromatography (LC), infrared spectroscopy, nuclear magnetic resonance (NMR), ultraviolet-visible spectroscopy (UV-Vis), combustion analysis, and the Kjeldahl method. Gas chromatography is a commonly used method. Its principle is to volatilize bound and residual acrylonitrile in the sample into gases, which are then separated and detected by gas chromatography. This method is fast and accurate, but requires sophisticated equipment and specialized skills, and is complex to operate. Liquid chromatography is also frequently used to analyze the bound and residual acrylonitrile content in nitrile rubber. Its principle is to dissolve the sample and then separate and detect the two components using liquid chromatography. This method reduces sample pretreatment time and complexity, but requires the selection of appropriate reagents to dissolve the sample. Infrared spectroscopy determines the content of bound and residual acrylonitrile by detecting the absorbed, scattered, and reflected infrared signals in the sample. This method is simple to operate and has low instrument costs, but the analytical results may be interfered with by samples containing many mixtures and impurities.

[0005] Most of the analytical techniques mentioned above are slow (≥30 min) and cannot be directly applied to the real-time detection of the polymerization process. Therefore, it is necessary to find a more effective method to supplement the shortcomings in the online detection of nitrile latex polymerization. Raman spectroscopy is a non-destructive, non-contact analytical method with the following advantages and characteristics: High sensitivity: Raman spectroscopy can detect trace amounts of substances in a sample, typically at the milligram to nanogram level. This high sensitivity allows it to analyze low concentrations of compounds or detect specific components in complex mixtures; it requires little or no sample preparation: compared to other analytical methods, Raman spectroscopy typically requires no sample pretreatment or has simpler sample preparation, and does not require additional reagents, which helps reduce analysis time and improve analytical efficiency; it has high selectivity: Raman spectroscopy has high selectivity for the analysis of substances, and can identify and distinguish substances in a sample through specific Raman spectra, even distinguishing substances with similar structures but different chemical properties; it is non-destructive and non-contact: Raman spectroscopy is a non-destructive technique because it only requires irradiating the sample with a laser and measuring the scattering spectrum, without causing physical or chemical changes to the sample. It is also a non-contact technique because the sample does not need to directly contact the laser or instrument; and it provides rapid analysis: Raman spectroscopy typically has a fast measurement speed, completing sample scanning and analysis within seconds to minutes, suitable for high-throughput real-time monitoring and rapid analysis needs. However, the presence of fluorescence background can severely affect the detection effect of Raman spectroscopy when detecting some complex samples. Therefore, developing effective fluorescence background subtraction techniques is of great significance for improving the imaging quality of Raman spectroscopy.

[0006] The main techniques for reducing fluorescence background during Raman spectroscopy testing include: 1. Using laser excitation of specific wavelengths: Selecting an appropriate wavelength of laser as the excitation source can reduce the generation of certain types of fluorescence, thereby reducing background interference. 2. Time-resolved techniques: Utilizing the temporal differences between Raman and fluorescence signals, rapid gating techniques are used to select a specific time window for signal collection, reducing fluorescence interference. 3. Background subtraction algorithms: Mathematical methods are used to process the Raman spectrum, such as direct difference spectroscopy or adaptive noise cancellation, to subtract the background signal from the Raman spectrum. 4. Sample preparation: Chemical or physical methods, such as adding antifluorescent agents or prolonged bleaching, can reduce the fluorescence background of the sample itself. 5. Surface-enhanced Raman spectroscopy (SERS): SERS technology enhances the Raman signal through the surface plasmon resonance effect of metal nanostructures, thereby improving the signal-to-noise ratio and reducing background interference. 6. Digital colloidal enhanced Raman spectroscopy (dCERS): dCERS technology uses single-molecule counting for digital colloidal enhancement, successfully achieving reliable quantitative detection of ultra-low concentration target molecules, helping to reduce background interference and improve detection sensitivity. Optimizing spectral acquisition parameters: By adjusting spectral acquisition parameters, such as integration time, laser power, and spectral resolution, the signal-to-noise ratio can be optimized, reducing the impact of background noise. However, when measuring nitrile latex, the complex matrix system of nitrile latex generates strong background fluorescence interference during Raman spectroscopy acquisition, which poses a significant challenge to the determination of latex propylene content.

[0007] CN103487461A discloses a rapid analytical method for the bound acrylonitrile content in nitrile rubber (NBR): Two 2-3 mg NBR samples are accurately weighed. The weighed NBR samples are wrapped in a tin boat sample cell. The NBR samples wrapped in the tin boat sample cell are placed in the sample pan of an elemental analyzer, and the two NBR samples are tested sequentially to obtain the nitrogen content of the NBR samples. During the determination, the oxidation tube temperature is 910-950℃, the reduction tube temperature is 480-500℃, and the oxygenation time is 40-60 s. Then, the bound acrylonitrile content of the NBR samples is estimated from the total nitrogen content. However, the total nitrogen content in this method does not solely refer to the nitrogen content in acrylonitrile; it also includes the contribution of nitrogen-containing additives in the NBR. Therefore, the measured content is significantly higher than the actual content, resulting in low accuracy.

[0008] CN104655582B discloses an infrared spectroscopy method for determining the content of bound acrylonitrile in nitrile rubber: The method involves extracting the added oil and antioxidant from the nitrile rubber sample using an alcohol solvent, drying it, weighing 0.1g-0.4g of the dried sample, and placing it in a 20mL sample bottle; adding 10mL-20mL of a ketone solvent to the sample bottle, and shaking the bottle to completely dissolve the sample; uniformly coating the sample solution onto a potassium bromide sheet, evaporating the ketone solvent from the potassium bromide sheet to obtain a sample film; placing the film in an infrared spectrometer; and then... (The text abruptly ends here, so the translation stops as well.) -1 -4000cm -1 Within the specified range, the background spectrum of the blank potassium bromide tablet was measured; at 400 cm⁻¹ -1 -4000cm -1 Within the specified range, the sample spectrum was obtained by measuring the potassium bromide film coated with the film; the infrared spectrum of the test sample was obtained by subtracting the background spectrum from the sample spectrum; the infrared spectrum of the test sample was measured at 2196-2281 cm⁻¹. -1 The area of ​​the internal absorption peak is used as the absorption area of ​​the bound acrylonitrile to calculate the acrylonitrile content. However, this method uses a mixture of samples, which is susceptible to spectral interference from impurities and additives, resulting in poor accuracy and reproducibility.

[0009] CN105067608A discloses a method for determining the bound acrylonitrile content in nitrile rubber: A pre-extracted nitrile rubber sample (m1) is placed in a tube furnace, sealed, and purged with nitrogen. The furnace is heated to 400±10℃, and the pyrolysis products are collected. The pyrolysis products are weighed to a constant weight (m2). A pyrolysis product (m3) is dissolved in dilute sulfuric acid and placed in an iodine flask. 2-3 drops of a mixture of alizarin and thymolphthalein indicator are added. The sample is titrated with a 0.1 mol / L sodium hydroxide standard solution until a pale blue color is obtained. 10 mL of a 126 g / L sodium sulfite solution is added, and the solution turns blue-purple. The solution is shaken well, the flask is sealed, and the mixture is left to stand. After 5 minutes, titrate with 0.1 mol / L sulfuric acid standard solution until pale yellow, consuming V1 of the sulfuric acid standard solution. Take the same volume of dilute sulfuric acid solution and place it in an iodine flask, add 2-3 drops of alizarin and thymolphthalein mixed indicator, and titrate the sample with 0.1 mol / L sodium hydroxide standard solution until pale blue. Add 10 mL of 126 g / L sodium sulfite solution, the solution turns blue-purple, shake well, stopper the flask, seal it, and let it stand for 5 minutes. Then titrate with 0.1 mol / L sulfuric acid standard solution until pale yellow, consuming V0 of the sulfuric acid standard solution. Finally, calculate the bound acrylonitrile content based on the experimental results. However, this method is complex and time-consuming, requires high technical skills, and the reagents used are not environmentally friendly.

[0010] The industry standard SH / T 1157-2012, "Determination of Bound Acrylonitrile Content in Raw Rubber Acrylonitrile-Butadiene Rubber (NBR)," is used to determine the bound acrylonitrile content in raw rubber or latex. Nitrogen in the sample is converted to nitrogen oxides in a high-purity oxygen environment. These nitrogen oxides are then reduced to nitrogen gas under the action of a catalyst. The generated carbon dioxide and water vapor are removed by adsorption or other separation methods, and the nitrogen content is detected using a thermal conductivity detector (TCD). The mass fraction of nitrogen is then obtained, and the bound acrylonitrile content in the sample is calculated. However, while the main source of nitrogen in the sample using this method is nitrogen from acrylonitrile, a portion also comes from other additives.

[0011] The industry standard SH / T 1503-2014, "Determination of Bound Acrylonitrile Content in Nitrile Latex," describes a method for determining the bound acrylonitrile content in latex. First, the latex is coagulated with anhydrous ethanol. After drying the coagulated material, it is digested with sulfuric acid in the presence of a catalyst, converting the nitrogen in the acrylonitrile into ammonium bisulfate. Then, excess sodium hydroxide solution is added, and the mixture is distilled. The distilled ammonia is absorbed with boric acid solution, and finally, the solution is titrated with a standard sulfuric acid titration solution. The bound acrylonitrile content is calculated based on the titration results. However, this method has several drawbacks. First, the catalyst contains highly toxic components, posing a safety hazard to operators. Second, the procedure is complex and time-consuming. Summary of the Invention

[0012] To address the aforementioned problems, this invention provides a composite nanomaterial and a method for determining the content of bound acrylonitrile during the polymerization of nitrile rubber latex. This method can rapidly, accurately, and non-destructively determine the content of bound acrylonitrile during the polymerization of nitrile rubber latex.

[0013] To achieve the above objectives, the present invention provides a composite nanomaterial, which is prepared by the following steps:

[0014] (1) Ce(NO3)3·6H2O was subjected to a hydrothermal reaction with polyvinylpyrrolidone (PVP), and after the reaction was completed, it was cooled and dried to obtain the first intermediate product.

[0015] (2) The first intermediate product is reacted with dopamine. After the reaction is completed, the precipitate is subjected to anaerobic carbonization treatment to obtain carbonized material.

[0016] (3) The carbonized material is reacted with chloroauric acid to obtain the composite nanomaterial.

[0017] According to a specific embodiment of the present invention, preferably, the preparation method of the composite nanomaterial includes the following steps:

[0018] (1) Mix Ce(NO3)3·6H2O, PVP and water, and adjust the pH to 8-11 to obtain a mixed solution;

[0019] (2) The mixture obtained in step (1) is reacted at 60-200℃ for 8-16h, cooled and dried, dispersed in dopamine solution, reacted at 40-90℃ for 1-4h, the precipitate is collected, dried and subjected to anaerobic carbonization treatment to obtain carbonized material.

[0020] (3) The carbonized material obtained in step (2) is mixed with water, chloroauric acid is added, and the mixture is reacted at 30-80℃ for 0.1-0.5h. Sodium citrate is added to reduce chloroauric acid to prepare gold nanoparticles. The mixture is reacted at 80-120℃ for 1-4h. After cooling, the composite nanomaterial (CeO2 / NC / Au) is obtained.

[0021] According to a specific embodiment of the present invention, preferably, the mass ratio of Ce(NO3)3·6H2O, PVP, dopamine, and gold chlorate is 1:(0.01-1):(0.0001-0.5):(0.001-0.5), more preferably 1:0.2:0.001:0.2.

[0022] According to a specific embodiment of the present invention, preferably, the dopamine solution is a Tris-HCl buffer solution with pH=8.5 containing dopamine.

[0023] According to a specific embodiment of the present invention, preferably, the conditions for the oxygen-free carbonization treatment are: reaction at 600-800°C for 4-8 hours in a tube furnace under an inert atmosphere, more preferably reaction at 600°C for 4 hours.

[0024] This invention also provides the application of the above-mentioned composite nanomaterials in reducing fluorescence interference in Raman spectroscopy detection.

[0025] The present invention also provides a method for determining the content of acrylonitrile bound during the polymerization of nitrile latex, which includes the following steps:

[0026] (1) Sample pretreatment: Take nitrile latex, add a reaction terminator to terminate the reaction, and then add the above-mentioned composite nanomaterials to obtain the sample to be tested;

[0027] (2) The sample to be tested is detected by Raman spectroscopy to obtain the Raman characteristic peak of bound acrylonitrile in the sample to be tested. The content of bound acrylonitrile in nitrile latex is calculated by combining the Raman spectroscopy quantitative model.

[0028] According to a specific embodiment of the present invention, preferably, the amount of the composite nanomaterial added is 0.1-5 wt%, more preferably 1-3 wt%, calculated based on 100% of the mass of nitrile latex.

[0029] According to a specific embodiment of the present invention, preferably, the reaction terminating agent includes one or more of benzoic acid, p-hydroxybenzoic acid, succinic acid, hydroquinone, dimercaptodiphenylamine, diphenylamine, 2-mercaptoethanol, and mercaptoacetic acid.

[0030] According to a specific embodiment of the present invention, preferably, the amount of the reaction terminator added is 0.1-1% of the mass of nitrile latex, more preferably 0.2-0.6%.

[0031] According to a specific embodiment of the present invention, preferably, the time for terminating the reaction is 1-10 min, more preferably 2-8 min.

[0032] According to a specific embodiment of the present invention, preferably, the detection conditions of the Raman spectroscopy satisfy one or two of the following conditions:

[0033] (1) The wavelength of the excitation source is 457nm, 532nm, 633nm, 785nm or 1064nm, more preferably 532nm, 785nm or 1064nm;

[0034] (2) The laser power is 0.1-10mW, more preferably 0.5-5mW.

[0035] According to a specific embodiment of the present invention, preferably, the Raman spectroscopy quantitative model is determined by Raman spectroscopy combined with gas chromatography.

[0036] According to a specific embodiment of the present invention, preferably, the method for determining the acrylonitrile content bound during the polymerization of nitrile latex includes the following steps:

[0037] (1) Sample pretreatment: Take nitrile latex, add a reaction terminator to terminate the reaction, and then add the above-mentioned composite nanomaterials to obtain the sample to be tested;

[0038] (2) The sample to be tested is detected by Raman spectroscopy to obtain a Raman spectrum;

[0039] (3) Perform background correction and noise filtering on the Raman spectrum;

[0040] (4) Obtain the Raman characteristic peaks of acrylonitrile bound in the sample to be tested;

[0041] (5) Based on the intensity of the Raman characteristic peak of bound acrylonitrile, and combined with the Raman spectroscopy quantitative model, the content of bound acrylonitrile in nitrile latex was calculated.

[0042] According to a specific embodiment of the present invention, preferably, the method for determining the acrylonitrile content during the polymerization of nitrile latex includes the following specific steps:

[0043] (1) Sample pretreatment: Collect samples of nitrile latex at different polymerization reaction stages, add a certain amount of reaction terminator and react for a certain time, then add a certain amount of CeO2 / NC / Au composite nanomaterials to form a uniform dispersion system and obtain nitrile latex samples to be tested.

[0044] (2) Raman spectroscopy determination: Place the nitrile latex sample to be tested obtained in step (1) on the sample stage of the Raman spectrometer, and select an appropriate laser wavelength, power and number of repeated acquisitions for measurement; more preferably, the number of repeated acquisitions is 1-20 times;

[0045] (3) Raman spectrum processing: The acquired nitrile latex Raman spectrum was corrected for background and filtered for noise using the instrument’s built-in software or exported data files and Origin software.

[0046] (4) Characteristic peak extraction: Analyze the Raman spectrum and extract the characteristic peaks related to the binding of acrylonitrile;

[0047] (5) Calculation of acrylonitrile content: Based on the intensity of the extracted characteristic peaks, the quantitative model of Raman spectroscopy is determined by gas chromatography, and the content of bound acrylonitrile in nitrile latex is calculated.

[0048] The method for determining the bound acrylonitrile content during the polymerization of nitrile butadiene latex in this invention involves first pretreating the nitrile butadiene latex sample with composite nanomaterials, then acquiring the Raman spectrum of the nitrile butadiene latex and performing data preprocessing and characteristic peak extraction, and finally calculating the bound acrylonitrile content based on the intensity and position of the characteristic peaks. This invention has the following beneficial effects:

[0049] 1. This invention addresses the issue of fluorescence background interference during latex determination by preparing composite nanomaterials that can reduce fluorescence background. This effectively reduces background fluorescence during Raman spectroscopy acquisition, thereby improving the accuracy of spectral quantification.

[0050] 2. This invention uses Raman spectroscopy to determine the content of bound acrylonitrile in nitrile latex. Compared with traditional analytical methods, it omits complex reagent processing and sample pretreatment steps, reduces the use of chemical reagents, and is environmentally friendly.

[0051] 3. This invention enables real-time and rapid detection of acrylonitrile bound during the polymerization of nitrile latex. It is simple to operate, with a single measurement time of about 20 minutes. It can quickly determine the content of acrylonitrile bound at different polymerization stages, laying the foundation for further online detection and analysis of the polymerization reaction.

[0052] 4. The Raman spectroscopy used in this invention enables non-contact measurement and will not cause any damage to the sample. Attached Figure Description

[0053] Figure 1 The image shows the Raman spectrum of the nitrile latex from Example 1.

[0054] Figure 2 This is the Raman spectrum of the nitrile peak region in the nitrile latex of Example 1.

[0055] Figure 3 This is the Raman spectrum of the double bond peak region in the nitrile latex of Example 1.

[0056] Figure 4 The image shows the Raman spectrum of nitrile latex in Comparative Example 1 without the addition of composite nanomaterials.

[0057] Figure 5 The image shows the Raman spectrum of nitrile latex in Comparative Example 1 when composite nanomaterials were added. Detailed Implementation

[0058] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0059] The preparation process of the nitrile latex used below is as follows:

[0060] 1. Raw materials:

[0061] Butadiene: with a purity of over 99%, it is the main monomer.

[0062] Acrylonitrile: purity above 99%, is a comonomer.

[0063] Emulsifier: Sodium dodecyl sulfate, used at approximately 3% of the total monomer content.

[0064] Initiator: Potassium persulfate, used at 0.3% of the total monomer amount.

[0065] Molecular weight regulator: n-dodecyl mercaptan, used in an amount of approximately 0.2% of the total monomer.

[0066] Deionized water: used as a reaction medium, the amount of which is determined according to the required latex concentration.

[0067] 2. Polymerization process:

[0068] (1) Add deionized water to the polymerization reactor, start stirring, add emulsifier in sequence, stir evenly, and then heat to 35°C.

[0069] (2) Mix butadiene, acrylonitrile and molecular weight regulator in a certain proportion, and then gradually add them to the reaction vessel. At the same time, start adding initiator solution, control the dropping rate, and make the reaction complete the monomer dropping process within 4-6 hours. The reaction temperature is maintained at 50℃.

[0070] (3) After the monomer is added, continue to keep the reaction at a constant temperature for 12 hours to ensure that the monomer reacts fully.

[0071] (4) After the reaction is complete, cool down to below 30°C and add an appropriate amount of terminator (such as hydroquinone) to terminate the reaction.

[0072] Example 1

[0073] To more accurately analyze the samples and obtain reliable results, this embodiment designed relevant experiments to determine the reaction termination conditions, and optimized the amount of terminator and the reaction time. The specific experimental steps and results are as follows:

[0074] 1. Samples and reagents are shown in Tables 1 and 2;

[0075] Table 1 Samples

[0076] Sample Name Sampling time Nitrile latex 3 3 hours after the start of the polymerization reaction

[0077] Table 2 Reagents

[0078] Reagent Name purity Drug source hydroquinone Chromatographic purity Aladdin

[0079] 2. Experimental Procedure

[0080] (1) Sample pretreatment: First, nitrile latex sample 3 was selected, and hydroquinone was added in three batches at 0.1%, 0.5%, and 1% of the mass of nitrile latex sample 3, respectively. After shaking and reacting for 1 min, 5 min, and 10 min, 0.1 wt% of CeO2 / NC / Au composite nanomaterials were added. After being dispersed evenly, the nitrile latex sample to be tested was obtained, and the next step of Raman spectroscopy acquisition was carried out.

[0081] The preparation method of CeO2 / NC / Au composite nanomaterials is as follows: Dissolve 1g Ce(NO3)3·6H2O in 50ml deionized water, stir with a magnetic stirrer until completely dissolved, and then add 0.01g... PVP was added to the solution and stirred until completely dissolved. pH adjustment: Sodium hydroxide was slowly added to the solution to adjust the pH to 10 to promote the precipitation of CeO2. The mixture was then transferred to a 100mL reactor with a polytetrafluoroethylene liner. The reactor was placed in a temperature-controlled oven and the temperature was set to 180℃ for 12 hours. After natural cooling, the mixture was collected by centrifugation, dried, and dispersed in 50mL of Tris-HCl buffer solution (pH 8.5) containing 0.1mg / mL dopamine. The mixture was stirred at 60℃ for 3 hours, and the precipitate was collected by centrifugation. After drying, the precipitate was subjected to anaerobic carbonization at 600℃ for 4 hours in a tube furnace. The carbonized material was then uniformly dispersed in water, and 0.01g of chloroauric acid was added. After stirring at 60℃ for 30 minutes, 5mL of 1wt% sodium citrate was added. The mixture was then heated under reflux at 100℃ for 1 hour. After natural cooling, the final composite nanomaterial was collected by centrifugation and dried for later use.

[0082] (2) Raman spectroscopy determination: The above-mentioned nitrile latex sample was placed on the sample stage of the Raman spectrometer for measurement. The laser power was 2mW, the selected area laser wavelength was 1064nm, and the spectral data were collected 10 times. Finally, the average spectrum of the 10 spectra was selected as the Raman spectrum of the nitrile latex.

[0083] (3) Raman Spectrum Processing: After obtaining the Raman spectra of the nitrile latex samples, the spectra were processed using the SpecLiteRM V2.0 analysis software included with the EPD-1064M online Raman spectrometer to perform background correction and noise filtering, thereby improving the signal-to-noise ratio. The Raman peak intensities of different samples were compared, such as... Figure 1 As shown, Figure 1 The five chromatograms in the table correspond to experiments 1, 3, 5, 7, and 9 from top to bottom.

[0084] (4) Characteristic Peak Extraction: Acrylonitrile exists in various forms in nitrile latex, and each form may have unique Raman peaks. Therefore, it is necessary to carefully analyze the Raman spectrum and extract the characteristic peaks related to the bound acrylonitrile. The changes related to acrylonitrile are mainly divided into the nitrile group region (2200 cm⁻¹). -1 ~2260cm -1 ,like Figure 2 As shown, the chromatograms correspond to the cyano region chromatograms of experiments 1, 4, 5, and 9 in Table 3, respectively, and the double bond region (1580 cm⁻¹). -1 ~1700cm -1 ,like Figure 3As shown, the chromatograms correspond to the double bond regions of experiments 1, 4, 5, and 9 in Table 3, respectively. As the polymerization reaction proceeds, the double bond peaks of the samples exhibit a very regular change, reaching 1600 cm⁻¹. -1 The double bond will drop rapidly, 1630cm -1 and 1660cm -1 The double bond will rise. A characteristic peak will appear in the nitrile group peak region, starting from 2230 cm⁻¹. -1 Towards 2236cm -1 The peak intensity also changes to some extent with the change in wavenumber shift.

[0085] (5) Calculation based on acrylonitrile content: Based on the extracted characteristic peak (1580 cm⁻¹) -1 ~1700cm -1 2200cm -1 ~2260cm -1 The intensity of the light was determined by combining the method of SH / T1503-2014 "Determination of bound acrylonitrile content in nitrile latex", and the quantitative model of Raman light was determined. Finally, the content of bound acrylonitrile in nitrile latex was calculated, and the results are shown in Table 3.

[0086] Table 3. Acrylonitrile content in latex under different pretreatment conditions

[0087]

[0088]

[0089] As shown in Table 3, when the amount of reaction terminator is low, the reaction is not completely terminated, and the error between the three parallel determinations is large. When the amount of reaction terminator increases, although the reaction is completely terminated, the resulting spectral interference is large, so the error between the three parallel determinations is also large. When the amount of reaction terminator is moderate, the error of the determination results is small. In order to ensure the timeliness of the determination results, the preferred experimental conditions for the pretreatment of nitrile latex samples in this embodiment were finally determined: that is, adding 0.5% hydroquinone and shaking the mixture for 5 min.

[0090] Example 2

[0091] In this embodiment, to obtain accurate Raman spectra, appropriate laser wavelengths and powers were selected. The laser wavelength was chosen to maximize the excitation of chemical bond vibrations in the nitrile rubber latex while avoiding overheating of the sample. The laser power was also chosen to ensure the acquisition of the optimal Raman spectral signal without damaging the sample. Therefore, this embodiment selected different laser wavelengths and powers to test the Raman spectra of the same latex, and calculated the bound acrylonitrile content of each latex based on the spectra. The specific operating steps and results are as follows:

[0092] 1. Samples and reagents are shown in Tables 4 and 5.

[0093] Table 4 Samples

[0094] Sample Name Sampling time Nitrile latex 1 2 hours after the start of the polymerization reaction

[0095] Table 5 Reagents

[0096] Reagent Name purity Drug source 2-Mercaptoethanol (MEKO) Chromatographic purity Aladdin

[0097] 2. Experimental Procedure

[0098] (1) Sample pretreatment: First, nitrile latex sample 1 was selected, 3 ml of 2-mercaptoethanol (MEKO) was added, and after shaking and reacting for 5 min, 1 wt% of CeO2 / NC / Au composite nanomaterials of nitrile latex sample 1 were added. After being dispersed evenly, nitrile latex sample to be tested was obtained, and Raman spectroscopy acquisition was carried out in the next step.

[0099] The preparation method of CeO2 / NC / Au composite nanomaterials is as follows: Dissolve 1g of Ce(NO3)3·6H2O in 50ml of deionized water, stir with a magnetic stirrer until completely dissolved, and then add 0.2g of... PVP was added to the solution and stirred until completely dissolved. pH adjustment: Sodium hydroxide was slowly added to the solution to adjust the pH to 10 to promote CeO2 precipitation. The mixture was then transferred to a 100mL reactor with a PTFE liner. The reactor was placed in a temperature-controlled oven at 180℃ for 12 hours. After natural cooling, the precipitate was collected by centrifugation, dried, and dispersed in 50mL of Tris-HCl buffer (pH 8.5) containing 0.01mg / mL dopamine. The mixture was stirred at 50℃ for three hours, and the precipitate was collected by centrifugation. After drying, the precipitate was subjected to anaerobic carbonization at 700℃ for 2 hours in a tube furnace. The carbonized material was then uniformly dispersed in water, and 0.2g of chloroauric acid was added. After stirring at 60℃ for 20 minutes, 5mL of 1wt% sodium citrate was added. The mixture was then heated under reflux at 120℃ for one hour. After natural cooling, the final composite nanomaterial was collected by centrifugation, dried, and ready for further Raman spectroscopy.

[0100] (2) Raman spectroscopy determination: The above-mentioned nitrile latex sample was placed on the sample stage of the Raman spectrometer for measurement. The laser power was set to 0.1mW, 2mW and 10mW, and the laser wavelength was set to 532nm, 785nm and 1064nm, respectively. The spectral data were collected 10 times, and the average spectrum of the 10 spectra was finally selected as the Raman spectrum of the nitrile latex.

[0101] (3) The Raman spectrum processing, characteristic peak extraction and acrylonitrile content calculation were the same as in Example 1, and the results are shown in Table 6.

[0102] Table 6. Content of bound acrylonitrile in latex under different laser powers and wavelengths.

[0103]

[0104] The bound acrylonitrile content of nitrile latex 1 was determined using the method in the industry standard SH / T 1503-2014 "Determination of Bound Acrylonitrile Content in Nitrile Latex" (see Table 9), and compared with the values ​​obtained from Raman spectroscopy under different conditions. Table 6 shows that when the excitation wavelengths for Raman spectroscopy were 532 nm and 785 nm, the fluorescence background interference was significant, affecting the accuracy of spectral quantification and causing errors compared to the standard method. However, at 1064 nm, the fluorescence background was weaker, consistent with the standard measurement values. Therefore, 1064 nm was chosen as the excitation wavelength for Raman spectroscopy acquisition. To obtain Raman spectra with higher intensity, Raman spectra were acquired at different laser powers. At 0.1 mW, the spectral signal was too weak; at 10 mW, the latex slowly changed color, failing to reflect the true spectral signal within the latex system; and at 2 mW, the spectral signal intensity was significant. Therefore, the optimal experimental conditions for Raman spectroscopy acquisition of nitrile latex were selected: laser power of 2 mW and laser wavelength of 1064 nm.

[0105] Example 3

[0106] This embodiment evaluates the accuracy of the method established in this invention for determining the bound acrylonitrile content in nitrile rubber latex. Nitrile rubber latex was collected at different time points during the polymerization process, and its bound acrylonitrile content was measured. Finally, the test results were compared with industry standard methods. The specific steps are as follows:

[0107] 1. Samples and reagents are shown in Tables 7 and 8;

[0108] Table 7 Samples

[0109] Sample Name Sampling time Nitrile latex 1 2 hours after the start of the polymerization reaction Nitrile latex 2 2.5 hours after the polymerization reaction begins Nitrile latex 3 3 hours after the start of the polymerization reaction Nitrile latex 4 3.5 hours after the polymerization reaction begins Nitrile latex 5 4 hours after the start of the polymerization reaction

[0110] Table 8 Reagents

[0111] Reagent Name purity Drug source p-hydroxybenzoic acid 95.2％ Jiang Weng Reagent

[0112] 2. Experimental Procedure

[0113] (1) Sample pretreatment: Take out the collected nitrile latex sample and put it into a 100ml conical flask. Add 2ml of p-hydroxybenzoic acid solution and shake well. After reacting for 5min, add 5wt% of CeO2 / NC / Au composite nanomaterials based on the mass of the nitrile latex sample. After it is evenly dispersed, the nitrile latex sample to be tested is obtained and Raman spectroscopy acquisition is carried out in the next step.

[0114] The preparation method of CeO2 / NC / Au composite nanomaterials is as follows: Dissolve 1g Ce(NO3)3·6H2O in 50ml deionized water, stir with a magnetic stirrer until completely dissolved, and then add 0.5g... PVP was added to the solution and stirred until completely dissolved. pH adjustment: Sodium hydroxide was slowly added to the solution to adjust the pH to 10 to promote the precipitation of CeO2. The mixture was then transferred to a 100mL reactor with a polytetrafluoroethylene liner. The reactor was placed in a temperature-controlled oven and the temperature was set to 180℃ for 12 hours. After natural cooling, the mixture was collected by centrifugation, dried, and dispersed in 50mL of Tris-HCl buffer solution (pH 8.5) containing 0.1mg / mL dopamine. The mixture was stirred at 80℃ for 3 hours, and the precipitate was collected by centrifugation. After drying, the precipitate was subjected to anaerobic carbonization at 700℃ for 4 hours in a tube furnace. The carbonized material was then uniformly dispersed in water, and 0.3g of chloroauric acid was added. After stirring at 60℃ for 30 minutes, 5mL of 1wt% sodium citrate was added. The mixture was then heated under reflux at 110℃ for 1 hour. After natural cooling, the final composite nanomaterial was collected by centrifugation and dried for later use.

[0115] (2) Raman spectroscopy determination: The above-mentioned nitrile latex sample was placed on the sample stage of the Raman spectrometer for measurement. The laser power was 2mW, the selected area laser wavelength was 1064nm, and the spectral data were collected 10 times. Finally, the average spectrum of the 10 spectra was selected as the Raman spectrum of the nitrile latex.

[0116] (3) The Raman spectrum processing, characteristic peak extraction and acrylonitrile content calculation steps are the same as in Example 1, and the results are shown in Table 9.

[0117] (4) The method in SH / T 1503-2014 "Determination of Bound Acrylonitrile Content in Nitrile Latex" was used to determine the bound acrylonitrile content in different nitrile latex samples. First, approximately 5g of nitrile latex was gradually added to a beaker containing 150mL of anhydrous ethanol. After the latex coagulated for 5 minutes, the coagulated material was filtered. The coagulated material was then poured back into the beaker with 100mL of anhydrous ethanol and stirred for 5 minutes. After filtration again, the coagulated material was dried in an oven at 100℃ for 2 hours, removed, and cooled in a desiccator for later use. An appropriate amount of the coagulated material, accurate to 0.0001g, was weighed and placed at the bottom of a dry Kjeldahl flask. 6.5g of a mixed catalyst (selenium powder, copper sulfate, and potassium sulfate) and 20mL of sulfuric acid were added. An appropriate amount of distilled water was added. The Kjeldahl flask was tilted and placed on a hot plate in a fume hood. The heating was gradually increased, maintaining a gentle boil until the solution became clear. Heating continued for 60 minutes to ensure complete digestion of the sample. Then, distilled water was added to bring the liquid volume in the Kjeldahl flask to 250 mL to 300 mL, and 0.5 g of zinc powder was added. The flask was then fitted with a rubber stopper equipped with a droplet trap and a separatory funnel, and a spherical condenser was attached. A 2% boric acid solution and 3 drops of a mixed methyl red and methylene blue indicator were added to the absorption bottle, and the lower end of the condenser tube was immersed in the absorption liquid. 100 mL of 40% sodium hydroxide solution was added to the Kjeldahl flask through the separatory funnel. After rinsing with a small amount of distilled water, the separatory funnel was stopped, and then 50 mL of distilled water was added to the funnel. The mixture was heated and distilled at a constant distillation rate, collecting approximately 200 mL of the distillate. The distillate was titrated with a standard sulfuric acid solution until the indicator color changed from bright green to pale purple. The content of bound acrylonitrile was calculated based on the volume of standard sulfuric acid solution consumed in the titration, expressed as a mass fraction. This result was compared with the determination results of the method of the present invention to demonstrate the accuracy of the method of the present invention. The results are shown in Table 9.

[0118] Table 9. Content of bound acrylonitrile in latex determined by Raman spectroscopy and industry standard method.

[0119]

[0120]

[0121] As can be seen from the comparison of the acrylonitrile content data in Table 9, the Raman spectroscopy method provided by this invention is comparable to the Kjeldahl nitrogen determination method used in industry standards for the determination of bound acrylonitrile content in nitrile latex. Furthermore, compared to traditional methods, the method provided by this invention has other advantages such as: simple operation, fast measurement speed, and the ability to achieve rapid online detection; it does not require the use of toxic or harmful chemical reagents, making it environmentally friendly.

[0122] Comparative Example 1

[0123] In this comparative example, the Raman chromatograms of nitrile latex (8 hours after the start of polymerization) were collected using the same determination method as in Example 1. The difference is that this comparative example examined the detection results with and without the addition of composite nanomaterials. Figure 4 The results are without the addition of composite nanomaterials. It is evident that the fluorescence background is too large to acquire an effective Raman spectrum, making it impossible to calculate the bound acrylonitrile content. When composite nanomaterials are added, the fluorescence background significantly disappears (see...). Figure 5 Therefore, the composite nanomaterial of this invention has the effect of reducing fluorescence interference, which is beneficial for the determination of acrylonitrile content.

[0124] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. A composite nanomaterial, which is prepared by the following steps: (1) Ce(NO3)3·6H2O was subjected to a hydrothermal reaction with polyvinylpyrrolidone. After the reaction was completed, the product was cooled and dried to obtain the first intermediate product. (2) The first intermediate product is reacted with dopamine. After the reaction is completed, the precipitate is subjected to anaerobic carbonization treatment to obtain carbonized material. (3) The carbonized material is reacted with chloroauric acid to obtain the composite nanomaterial.

2. The composite nanomaterial according to claim 1, wherein, The preparation method of the composite nanomaterial includes the following steps: (1) Mix Ce(NO3)3·6H2O, polyvinylpyrrolidone and water, and adjust the pH to 8-11 to obtain a mixture; (2) The mixture obtained in step (1) is reacted at 60-200℃ for 8-16h, cooled and dried, dispersed in dopamine solution, reacted at 40-90℃ for 1-4h, the precipitate is collected, dried and subjected to anaerobic carbonization treatment to obtain carbonized material. (3) The carbonized material obtained in step (2) is mixed with water, chloroauric acid is added, and the mixture is reacted at 30-80℃ for 0.1-0.5h. Sodium citrate is added, and the mixture is reacted at 80-120℃ for 1-4h. After cooling, the composite nanomaterial is obtained.

3. The composite nanomaterial according to claim 1 or 2, wherein, The mass ratio of Ce(NO3)3·6H2O, polyvinylpyrrolidone, dopamine, and gold chlorate is 1:(0.01-1):(0.0001-0.5):(0.001-0.5).

4. The composite nanomaterial according to claim 1 or 2, wherein, The conditions for the oxygen-free carbonization treatment are: reaction at 600-800℃ for 4-8 hours in a tube furnace under an inert atmosphere.

5. The application of the composite nanomaterial according to any one of claims 1-4 in reducing fluorescence interference in Raman spectroscopy detection.

6. A method for determining the content of acrylonitrile bound during the polymerization of nitrile latex, comprising the following steps: (1) Sample pretreatment: Take nitrile latex, add a reaction terminator to terminate the reaction, and then add the composite nanomaterial according to any one of claims 1-4 to obtain the sample to be tested; (2) The sample to be tested is detected by Raman spectroscopy to obtain the Raman characteristic peak of bound acrylonitrile in the sample to be tested. The content of bound acrylonitrile in nitrile latex is calculated by combining the Raman spectroscopy quantitative model.

7. The method according to claim 6, wherein, Based on the mass of nitrile latex as 100%, the amount of the composite nanomaterial added is 0.1-5 wt%. And / or, the reaction terminating agent includes one or more of benzoic acid, p-hydroxybenzoic acid, succinic acid, hydroquinone, dimercaptodiphenylamine, diphenylamine, 2-mercaptoethanol, and mercaptoacetic acid; And / or, the amount of the reaction terminator added is 0.1-1% of the mass of the nitrile latex; And / or, the time for terminating the reaction is 1-10 min.

8. The method according to claim 6, wherein, The detection conditions for the Raman spectroscopy meet one or two of the following conditions: (1) The excitation light source wavelength is 457nm, 532nm, 633nm, 785nm or 1064nm; (2) The laser power is 0.1-10mW.

9. The method according to claim 6, wherein, The quantitative model of Raman spectroscopy was determined by combining Raman spectroscopy with gas chromatography.

10. The method according to claim 6, wherein, The method for determining the acrylonitrile content bound during the polymerization of nitrile latex includes the following steps: (1) Sample pretreatment: Take nitrile latex, add a reaction terminator to terminate the reaction, and then add the composite nanomaterial according to any one of claims 1-4 to obtain the sample to be tested; (2) The sample to be tested is detected by Raman spectroscopy to obtain a Raman spectrum; (3) Perform background correction and noise filtering on the Raman spectrum; (4) Obtain the Raman characteristic peaks of acrylonitrile bound in the sample to be tested; (5) Based on the intensity of the Raman characteristic peak of bound acrylonitrile, and combined with the Raman spectroscopy quantitative model, the content of bound acrylonitrile in nitrile latex was calculated.

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