A method for detecting the total content of cyclic siloxanes

Abstract

The application discloses a detection method of total cyclic siloxane content, and relates to the technical field of instrument analysis. The detection method of near infrared is used to detect the sample, and in particular, 4875cm ‑1 4921cm ‑1 As the characteristic peak, the accuracy of the detection result can be effectively ensured, the influence of linear Si-O bonds, C=C bonds and the like on the detection is reduced, the detection efficiency is greatly improved, and the real-time detection of the total cyclic siloxane content in the cyclic siloxane removal process can be met.

Description

Technical Field

[0001] This invention relates to the field of instrumental analysis technology, and more specifically, to a method for detecting the total content of cyclic siloxanes. Background Technology

[0002] Polyether silicone surfactants are widely used in various fields due to their unique physicochemical properties. Polyether silicone surfactants are copolymers synthesized from hydrogen-containing polysiloxanes and allyl polyethers through a hydrosilylation reaction. Hydrogen-containing polysiloxanes are prepared from cyclic siloxanes, hexamethyldisiloxane, and high-hydrogen silicone oils through ring-opening and equilibrium reactions. Hexamethylcyclotrisiloxane (CAS No.: 541-05-9), octamethylcyclotetrasiloxane (CAS No.: 556-67-2), decamethylcyclopentasiloxane (CAS No.: 541-02-6), and dodecylcyclohexasiloxane (CAS No.: 540-97-6) (hereinafter referred to as D3, D4, D5, and D6) are widely present in hydrogen-containing polysiloxanes and polyether silicone surfactants. Since polyether silicone surfactants are used in the preparation of polyurethane foam, cyclic siloxanes can enter the foam. Therefore, the content of D3, D4, D5, and D6 needs to be carefully monitored in many regions.

[0003] Currently, there are many methods for detecting the residues of D3, D4, D5, and D6, which can be broadly classified into: gas chromatography, headspace gas chromatography, and gas chromatography-mass spectrometry. GB / T 20436-2006 proposes a gas chromatography method for detecting mixed cyclic dimethylsiloxanes. However, this method has a narrow applicability, limited to the purity detection of pure and mixed D4, D5, and D6 products, and is not suitable for samples with complex matrices. T / CPUIA 0011-2022, a method for determining cyclic siloxanes in polyurethane flexible foam surfactants using headspace gas chromatography, presents a method with high detection sensitivity, but its detection cycle is as long as 2 hours, making real-time detection of cyclic siloxane content impossible. Patent CN110702811 proposes a gas chromatography-mass spectrometry method for determining cyclic siloxanes, but it also faces the problem of long pretreatment time and uses highly toxic and volatile solvents such as acetone, tetrahydrofuran, and acetonitrile.

[0004] With the rapid development of science and technology and the economy, as well as the improvement of people's living standards, there is increasing attention both domestically and internationally to the residual amount of cyclic siloxanes in hydrogen-containing polysiloxanes, polyether silicone surfactants, and polyurethane foams. However, there is currently no method to detect the total amount of cyclic siloxanes in the cyclic siloxane removal process in real time.

[0005] Therefore, there is an urgent need to find a method that can quickly and accurately detect the total content of cyclic siloxanes to meet the requirement of real-time detection of the total amount of cyclic siloxanes during the cyclic siloxane removal process.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a method for detecting the total content of cyclic siloxanes, which is to provide a simple, fast, stable and accurate detection method that can detect the total amount of cyclic siloxanes in real time.

[0008] This invention is implemented as follows:

[0009] In a first aspect, the present invention provides a method for detecting the total content of cyclic siloxanes, comprising: detecting the sample to be tested using near-infrared spectroscopy to obtain a characteristic peak at 4875 cm⁻¹. -1 -4921cm -1 The absorbance is obtained, and the total amount of cyclic siloxanes in the sample is calculated by substituting the absorbance into the standard curve formula.

[0010] The sample to be tested is selected from any one of hydrogen-containing polysiloxane, polyether silicone surfactant and polyurethane foam;

[0011] The standard curve formula is obtained by near-infrared detection and analysis of the standard of the sample to be tested.

[0012] In an optional implementation, the detection conditions for near-infrared detection include: a spectral acquisition range of 4000 cm⁻¹. -1 -10000cm -1 The resolution is 1cm. -1 -16cm -1 .

[0013] In an optional implementation, a DTGS-BK-7 detector is used for detection;

[0014] Preferably, the number of scans is 60-70, each sample is measured at least 3 times, the average spectrum is taken as the sample spectrum, and the reference spectrum is air.

[0015] In an optional implementation, during near-infrared detection, the heating temperature is 30℃-70℃ and the heating time is 1min-5min.

[0016] In an optional implementation, when the sample to be tested is a hydrogen-containing polysiloxane or a polyether silicone surfactant, the standard curve formula is Y = 0.94503010X + 0.06537312; when the sample to be tested is polyurethane foam, the standard curve formula is Y1 = 0.96231572X + 0.08218631.

[0017] Where X represents absorbance;

[0018] Y or Y1 represents the total content of cyclic siloxanes, with Y in wt% and Y1 in ppm.

[0019] In an optional implementation, the process of obtaining the standard curve formula includes: using a standard sample of known content to detect near-infrared spectroscopy, analyzing the obtained near-infrared spectral data using Horizon MB spectral analysis software, and determining the characteristic absorption peak of the cyclic Si-O bond to be 4875 cm⁻¹. -1 -4921cm -1 The standard curve formula is obtained by processing the spectrum obtained from near-infrared detection using the partial least squares method.

[0020] In an optional implementation, when the sample to be tested is a hydrogen-containing polysiloxane, the detection range of the total amount of cyclic siloxanes is 0.20 wt% to 6.00 wt%.

[0021] When the sample to be tested is a polyether silicone surfactant, the detection range for the total amount of cyclic siloxanes is 0.10 wt% - 3.00 wt%.

[0022] When the sample to be tested is polyurethane foam, the detection range for the total amount of cyclic siloxanes is 100ppm-300ppm.

[0023] In an optional implementation, when the sample to be tested is a hydrogen-containing polysiloxane or a polyether organosilicon surfactant, the sample to be tested is directly subjected to near-infrared detection; when the sample to be tested is polyurethane foam, the polyurethane foam is first pretreated to obtain a polyurethane foam extract, and then the polyurethane foam extract is subjected to near-infrared detection.

[0024] In an optional embodiment, the pretreatment includes: extracting cyclic siloxanes from polyurethane foam using Soxhlet extraction, followed by heat treatment to remove the solvent, with the heating temperature controlled at 55°C-70°C.

[0025] In an optional embodiment, acetone is used as the extractant when extracting cyclic siloxanes from polyurethane foam.

[0026] This invention has the following beneficial effects: it utilizes a near-infrared detection method to detect the sample, especially using 4875 cm⁻¹. -1 -4921cm -1 As a characteristic peak, it can effectively ensure the accuracy of detection results, reduce the influence of straight-chain Si-O bonds, C=C bonds, etc. on detection, and greatly improve detection efficiency, which can meet the real-time detection of the total amount of cyclic siloxanes in the cyclic siloxane removal process. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 The Fourier transform near-infrared spectrum provided by this invention;

[0029] Figure 2 The spectrum after the second derivative is provided by this invention;

[0030] Figure 3 The resulting graph of principal factor counts plotted using SECV is provided by this invention;

[0031] Figure 4 The standard curve provided for this invention. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0033] This invention provides a method for detecting the total content of cyclic siloxanes, comprising the following steps:

[0034] S1, Preprocessing

[0035] The detection method provided in this embodiment of the invention is applicable to three main types of test samples: polyether silicone surfactants or polyurethane foam.

[0036] Specifically, commercially available hydrogen-containing polysiloxanes are generally suitable for the detection method provided in the embodiments of this invention, and there are no requirements for parameters such as molecular weight. This is because hydrogen-containing polysiloxanes are polymerized from MM, D4, and high-hydrogen-content silicone oils. The molecular weight of hydrogen-containing polysiloxanes is related to the ratio, while cyclic siloxanes are only byproducts generated during the reaction process.

[0037] Specifically, polyether silicone surfactants can change the surface tension of liquids or the interfacial tension between two phases. General polyether silicone surfactants can be detected using the detection method provided in the embodiments of this invention. The main component of polyether silicone surfactants is a copolymer obtained by hydrosilylation reaction of hydrogen-containing polysiloxane and polyether polyol.

[0038] Specifically, polyurethane foam is a high molecular polymer synthesized from polyols and isocyanates as the main raw materials, with the help of various additives such as foaming agents, catalysts, and foam stabilizers (polyether silicone surfactants). It is porous, and commercially available polyurethane foam can generally be tested using the detection methods provided in the embodiments of this invention.

[0039] When the sample to be tested is a hydrogen-containing polysiloxane or a polyether organosilicon surfactant, near-infrared detection can be performed directly on the sample. However, when the sample to be tested is polyurethane foam, the polyurethane foam needs to be pretreated to obtain a polyurethane foam extract, and then the polyurethane foam extract is subjected to near-infrared detection. The method for obtaining the polyurethane foam extract is not limited.

[0040] In some embodiments, Soxhlet extraction can be used to extract cyclic siloxanes from polyurethane foam. Acetone can be chosen as the extractant. Other highly soluble solvents, such as toluene, have boiling points exceeding the extraction temperature, and excessively high extraction temperatures pose a risk of volatilization of the cyclic siloxanes. After extraction, heat treatment is performed to remove the solvent, with the heating temperature controlled at 55℃-70℃ (e.g., 55℃, 60℃, 65℃, 70℃, etc.). After solvent removal, a volume-adjusting process can be performed using an organic solvent such as n-heptane.

[0041] S2. Determine the formula for the standard curve.

[0042] The standard curve formula is obtained by near-infrared detection and analysis of the test sample's standards. Specifically, hydrogen-containing polysiloxanes, polyether silicone surfactants, and polyurethane foam extracts with known content were selected as standards, and Fourier transform near-infrared spectrometers were used for detection. The obtained near-infrared spectral data were analyzed and processed using Horizon MB spectral analysis software, and the characteristic absorption peak of the cyclic Si-O bond was determined to be 4875 cm⁻¹. -1 -4921cm -1 Then, the standard curve formula was obtained by processing the spectrum obtained from near-infrared detection using partial least squares method. The inventors determined the characteristic absorption peak to be 4875 cm⁻¹. -1 -4921cm -1 This ensures that the final standard curve formula is stable and highly accurate. At the same time, the selected wavelength range can effectively reduce the impact of other non-detectable functional groups or groups on the detection results, and will not cause environmental pollution.

[0043] Specifically, when the sample to be tested is a hydrogen-containing polysiloxane or a polyether silicone surfactant, the standard curve formula is Y = 0.94503010X + 0.06537312; where X represents absorbance; Y represents the total content of cyclic siloxanes in wt%. When the sample to be tested is polyurethane foam, the standard curve formula is Y1 = 0.96231572X + 0.08218631; where X represents absorbance; Y or Y1 represents the total content of cyclic siloxanes in wt%; Y1 is in ppm.

[0044] Once the standard curve formula is obtained, subsequent testing can be performed directly using this formula, without the need for repeated measurements.

[0045] Specifically, partial least squares (PLS) is an existing mathematical optimization technique that finds the best function fit for a set of data by minimizing the sum of squared errors. It uses the simplest method to find some absolutely unknown truth values ​​while minimizing the sum of squared errors.

[0046] In some embodiments, the detection conditions for near-infrared detection include: a spectral acquisition range of 4000 cm⁻¹. -1 -10000cm -1 The resolution is 1cm. -1 -16cm -1 The DTGS-BK-7 detector was used for detection, with 60-70 scans performed. Each sample was measured at least three times, and the average spectrum was used as the sample spectrum. The reference spectrum was air. Standardized detection conditions were established through further control of the detection conditions to improve the accuracy of subsequent test results. Specifically, the resolution was 1 cm⁻¹. -1 5cm -1 10cm -1 15cm -1 16cm -1 The number of scans can be 60, 65, 70, etc., and each sample can be tested 3 or more times.

[0047] In some embodiments, during near-infrared detection, the outer diameter of the quartz tube used is 1mm-12mm, the volume of the standard solution added to the quartz tube is 0.6mL-8.0mL, the heating temperature is 30℃-70℃, the heating time is 1min-5min, and then the tube is sealed with a stopper. Specifically, the heating temperature can be 30℃, 40℃, 50℃, 60℃, 70℃, etc., and the heating time can be 1min, 3min, 5min, etc.

[0048] S3. Detection and analysis of the sample to be tested

[0049] The characteristic peak at 4875 cm⁻¹ was obtained by near-infrared spectroscopy of the sample. -1-4921cm -1 The absorbance is obtained, and the total amount of cyclic siloxanes in the sample is calculated by substituting the absorbance into the standard curve formula.

[0050] It should be noted that the testing conditions are the same as those in S2 when performing the analysis on the sample to be tested, and will not be repeated here.

[0051] Furthermore, the detection range varies slightly depending on the sample being tested. When the sample is a hydrogen-containing polysiloxane, the detection range for the total cyclic siloxane content is 0.20 wt%–6.00 wt%; when the sample is a polyether silicone surfactant, the detection range is 0.10 wt%–3.00 wt%; and when the sample is polyurethane foam, the detection range is 100 ppm–300 ppm. When the concentration of the sample is within the above range, the method provided in this embodiment can accurately detect the total cyclic siloxane content.

[0052] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0053] It should be noted that in the following examples, hexamethylcyclotrisiloxane is represented as D3, octamethylcyclotetrasiloxane as D4, decamethylcyclopentasiloxane as D5, and dodecylcyclohexasiloxane as D6.

[0054] Example 1

[0055] The purpose of this embodiment is to determine the standard curve formula. The specific steps are as follows:

[0056] The samples, which do not contain D3, D4, D5, or D6 (specifically, polydimethyl-methylhydrosiloxane, hereinafter referred to as hydrogen-containing polysiloxane) and do not contain D4, D5, or D6, and the samples, which contain polyether silicone surfactants (specifically, polyethylene oxide-polydimethylsiloxane copolymer, hereinafter referred to as polyether silicone surfactants), are from Nanjing Meiside New Materials Co., Ltd.

[0057] Using hydrogen-containing polysiloxanes and polyether silicone surfactants that do not contain D3, D4, D5, and D6 as stock solutions, D4, D5, and D6 standards were added to prepare cyclic solutions of different concentrations. The results are shown in Table 1.

[0058] Table 1 Actual values ​​of the standard curve for the toroidal body

[0059]

[0060]

[0061] Twenty batches of cyclic solutions of different concentrations (A1-10 were prepared with hydrogen-containing polysiloxanes, and B1-10 were prepared with polyether silicone surfactants) were analyzed using Fourier transform near-infrared spectroscopy, with 64 scans and a resolution of 16 cm⁻¹. -1 Spectral acquisition range 4000cm -1 -10000cm -1 A DTGS-BK-7 detector was used. Each sample was measured three times, and the average spectrum was taken as the sample spectrum. The reference spectrum was air. The quartz tube had an outer diameter of 12 mm, and the volume of the standard solution added to the quartz tube was 8.0 mL. The heating temperature was 70℃. After the sample was added to the quartz tube, it was sealed. The near-infrared spectral data obtained after scanning are shown below. Figure 1 As shown.

[0062] Determination of characteristic spectral bands: Partial least squares (PLS) was used to process the original spectrum, and the second derivative spectrum was obtained as follows: Figure 2 As shown: The inventor determined the value at 4875cm based on spectral information. -1 -4921cm -1 Within this band, it may be possible to eliminate interference from straight-chain Si-O bonds and C=C double bonds, ultimately determining the characteristic spectral band to be 4875 cm⁻¹. -1 -4921cm -1 .

[0063] Determination of spectral preprocessing methods: Conventional methods include calibration, thickness correction, baseline correction, smoothing / differential differentiation, and point interpolation. Evaluation parameters for the near-infrared quantitative standard curve formula include the correlation coefficient (R²). 2 The standard curve is calculated using preprocessing methods such as cross-validation standard error (SECV), test value (F-Ratio), and associative hypothesis testing (F-Test). A closer R-value to 1.0000 indicates a better standard curve result; a smaller SECV indicates better standard curve regression; and a closer F-Ratio to 1.0000 and an F-Test value to 0.5000 indicate higher accuracy of the standard curve. Table 2 shows the impact of different preprocessing methods on the standard curve. When the preprocessing method is thickness correction + baseline + smoothing / differential differentiation, i.e., Gap Derivative = 2 and GapLength = 9 in Gap Derivative Options, the R-value of the standard curve... 2 =0.9444, SECV < 0.24%, F-Ratio = 1.0000, F-Test = 0.5000. Taking all factors into consideration, thickness correction + baseline + smoothing / differential differentiation is selected for spectral preprocessing.

[0064] Table 2. The Influence of Different Preprocessing Methods on the Standard Curve Formula

[0065] Preprocessing methods Best principal factor <![CDATA[R 2 Value SECV (%) F-Ratio F-test No processing 3 0.6724 1.24 0.9432 0.4627 Thickness Correction 5 0.7924 1.02 0.9624 0.4821 Baseline 3 0.8021 0.92 0.9732 0.4726 Thickness correction + baseline 4 0.9025 0.84 1.0000 0.5000

[0066] The effects of using thickness correction + baseline + smoothing differential preprocessing on the standard curve formula are shown in Table 3:

[0067] Determining the number of principal factors: Plot the number of principal factors using SECV. When the SECV value reaches its minimum and then shows a slight increase, the minimum point is the number of principal factors. The result is as follows: Figure 3 The optimal number of principal factors was determined to be 3, R 2 =0.9444, SECV < 0.24%.

[0068] Table 3 shows the impact of the thickness correction + baseline + smooth differential preprocessing method on the standard curve formula.

[0069]

[0070]

[0071] Establishing the quantitative standard curve formula: Using Horizon MB spectral analysis software, PLS is the multivariate correction method. The preprocessing method is thickness correction + baseline + smoothing. When differentiating, Gap Derivative = 2, Gap DerivativeOptions Gap length = 9, and the selected band is 4875cm. -1 -4921cm -1 With a principal factor of 3, a near-infrared standard curve formula was established for the total cyclic siloxane content in the aforementioned hydrogen-containing polysiloxanes and polyether silicone surfactants. The correlation diagram between the predicted and reference values ​​of the total cyclic siloxane content (i.e., the standard curve formula) is shown below. Figure 4 As shown. Standard curve formula for quality evaluation R. 2 >0.9000, SECV<0.24%, F-Ratio=1.0000, F-Test=0.5000, indicating that there is a good correlation between the predicted value of the total cyclic siloxane content obtained by the standard curve formula and the reference value. The standard curve formula is Y=0.94503010X+0.06537312.

[0072] Example 2

[0073] This embodiment uses the standard curve formula determined in Example 1 to test the sample. The specific steps are as follows:

[0074] Samples: Hydrogen-containing polysiloxane (A-11-20) and polyether silicone surfactant (B-11-20) were from Nanjing Meiside New Materials Co., Ltd.

[0075] The above samples were analyzed using a Fourier transform near-infrared spectrometer under the following conditions: 64 scans and a resolution of 16 cm⁻¹. -1 Spectral acquisition range 4000cm -1 -10000cm -1 The DTGS-BK-7 detector was used. Each sample was measured three times, and the average spectrum was taken as the sample spectrum. The reference spectrum was air, and the heating temperature was 70℃.

[0076] The obtained spectrum was then analyzed and processed to obtain 4875 cm⁻¹. -1 -4921cm- 1 The absorbance was measured, and then substituted into the standard curve formula to calculate the total content of cyclic siloxanes in the sample. The standard curve formula is: Y = 0.94503010X + 0.06537312. The calculation results are shown in Table 4.

[0077] Comparative Example 1

[0078] To verify that the detection method provided in this embodiment of the invention can quickly and accurately detect the total content of cyclic siloxanes in hydrogen-containing polysiloxanes, headspace gas chromatography was used to detect the sample of Example 2.

[0079] (1) Headspace conditions

[0080] Heater temperature: 100℃; Metering loop temperature: 110℃; Transfer line temperature: 120℃; Equilibrium time: 30min;

[0081] (2) Gas phase conditions

[0082] Chromatographic column: HP-5 (30m × 320μm × 0.25μm);

[0083] Column oven: initial temperature 50℃, hold for 5 min; increase to 250℃ at 15℃ / min, hold for 10 min; injection port temperature: 250℃; detector temperature: 285℃;

[0084] Reagent: n-dodecane (nC) 12 H 26 ): Purity > 99%; Octamethylcyclotetrasiloxane (D4): Purity > 98%; Decamethylcyclopentasiloxane (D5): Purity > 98%; Dodecylcyclohexasiloxane (D6): Purity > 98%.

[0085] (3) Sample preparation

[0086] Internal standard mixture: Using a pipette, transfer 200 μL of D4, D5, and D6 standards, and n-dodecane internal standard, respectively. Weigh 10 g of hydrogen-containing polysiloxane sample (excluding D4, D5, and D6) into a 50 mL round-bottom flask and record the weight of each substance. Add a rotor to the flask and rotate it at a speed of at least 200 rpm for at least 20 minutes to ensure thorough mixing and prepare the internal standard mixture.

[0087] Correction factor determination: Weigh 1.01 g to 1.02 g of the internal standard mixture into a 20 mL headspace vial, record its weight, and determine it under the above chromatographic conditions.

[0088] Sample mixture preparation: Weigh 10g of the sample to be tested into a 50mL round-bottom flask and record the weight, defined as m1; use a pipette to transfer 200µL of n-dodecane internal standard into the sample vial and record the weight, defined as m2. Add a rotor to the flask, rotating at a speed of not less than 200 rpm for a duration of not less than 20 minutes to ensure thorough mixing.

[0089] Sample testing: Weigh 1.01 g to 1.02 g of the sample mixture to be tested into a 20 mL headspace vial, accurate to 0.0001 g, and record the weight, defined as m3. Perform the determination under the above chromatographic conditions.

[0090] (4) Calculation method of D4, D5 and D6 content in sample (taking D4 as an example)

[0091] D4 relative correction factor:

[0092] The calculation formula is: f = (A 正构十二烷烃 / A D4 )×(m D4 / m 正构十二烷烃 );

[0093] In the formula,

[0094] f is the relative correction factor for D4;

[0095] A D4 The peak area of ​​D4 in the internal standard mixture;

[0096] A is the peak area of ​​the internal standard n-dodecane in the internal standard mixture;

[0097] mn-dodecane is the mass of the internal standard n-dodecane added to the internal standard mixture, expressed in grams.

[0098] m D4 The value is the mass of standard sample D4 added to the internal standard mixture, in grams.

[0099] (5) The content ω% of component D4 in the sample to be tested is calculated using the following formula:

[0100] ω%=f×(A D4 / A 正构十二烷烃 )×(m 正构十二烷烃 / m 样 )×100%;

[0101] In the formula,

[0102] f is the relative correction factor for D4;

[0103] A D4 The peak area of ​​the D4 chromatographic peak in the mixed solution to be tested;

[0104] A 正构十二烷烃 The peak area of ​​the internal standard n-dodecane in the mixed solution to be tested;

[0105] m 正构十二烷烃 m represents the mass of the internal standard n-dodecane in the mixed solution to be tested. 正构十二烷烃 =m2×m3 / (m1+m2) (unit: g);

[0106] m 样 m is the mass of the sample to be tested. 样 =m1×m3 / (m1+m2), unit: g.

[0107] Note: The relative correction factors and content determination methods for cyclic D5 and D6 are the same as those described above. The total content of cyclic siloxanes is the sum of the contents of components D4, D5, and D5.

[0108] Table 4. Near-infrared spectral predicted values ​​and headspace gas chromatography detected values.

[0109]

[0110] In the table above, A-11 to A-20 represent hydrogen-containing polysiloxanes, and B-11 to B-20 represent polyether silicone surfactants. According to the table, the absolute deviation between the predicted value obtained by the detection method for the total cyclic siloxane content in hydrogen-containing polysiloxanes provided in this embodiment and the reference value obtained by headspace gas chromatography is -0.12% to 0.31%. The absolute deviation between the predicted value obtained by the detection method for the total cyclic siloxane content in polyether silicone surfactants provided in this embodiment and the reference value obtained by headspace gas chromatography is -0.11% to 0.14%. This indicates that the detection method provided in this embodiment is low-cost, fast, and simple to operate, enabling rapid and non-destructive detection of the total cyclic siloxane content in hydrogen-containing polysiloxanes and polyether silicone surfactants, with high detection accuracy.

[0111] Example 3

[0112] The purpose of this embodiment is to detect the content of cyclic siloxanes in polyurethane foam.

[0113] Preparation of polyurethane foam C-1-10: Take the soft polyurethane surfactant B-11-20 from Example 2, weigh all components except A33, T-9 and TDI according to the formula in Table 5 at 22°C, mix them evenly, and prepare the composite material. Under high-speed mechanical stirring at 2100 r / min, add A33 and stir for 20s, add T-9 and stir for 20s, add TDI and stir for 7s, then pour into a small square mold, cut samples and test.

[0114] Table 5. Formulation of Flexible Polyurethane Foam:

[0115] Components Number of copies TDI(T-80) 49.97 Polyether polyol (molecular weight: 3000; functionality: 3) 100 water 3.8 Flexible polyurethane surfactant (M-6688LV) 1 Stannous octoate (T-9) 0.18 Organic amine catalyst (A33) 0.16

[0116] Pretreatment of polyurethane foam C-1-10: Cyclic siloxanes in polyurethane foam were extracted by Soxhlet extraction with acetone as the extractant. The solvent was then removed by a 60°C water bath. The extract was then diluted to 10 mL with n-heptane in a volumetric flask.

[0117] The above samples were analyzed using a Fourier transform near-infrared spectrometer under the following conditions: 64 scans and a resolution of 16 cm⁻¹. -1 Spectral acquisition range 4000cm -1 -10000cm -1 The DTGS-BK-7 detector was used. Each sample was measured three times, and the average spectrum was taken as the sample spectrum. The reference spectrum was air, and the heating temperature was 70℃.

[0118] The obtained spectrum was then analyzed and processed to obtain 4875 cm⁻¹. -1 -4921cm- 1 The absorbance was measured, and then the absorbance was substituted into the standard curve formula to calculate the total content of cyclic siloxanes in the sample. The standard curve formula is: Y1 = 0.96231572X + 0.08218631. The calculation results are shown in Table 6.

[0119] Table 6. Predicted values ​​of near-infrared spectra and theoretical values ​​of samples

[0120]

[0121] In the table above, C-1 to C-10 represent flexible polyurethane foam. According to the table, the absolute deviation between the predicted value and the theoretical value obtained by the detection method for the total content of cyclic siloxanes in flexible polyurethane foam provided in this embodiment of the invention is between -1.01ppm and 7.18ppm. This indicates that the detection method provided in this embodiment of the invention is low in cost, fast in detection, simple in operation, and can detect the total content of cyclic siloxanes in polyurethane foam.

[0122] Comparative Example 2

[0123] The difference from Example 1 is that the characteristic spectral band is selected as 8270 cm⁻¹. -1 -8580cm -1 The corresponding standard curve formulas are shown in Table 7.

[0124] Comparative Example 3

[0125] The difference from Example 1 is that the characteristic spectral band is selected as 5890 cm⁻¹. -1 -6000cm -1 The corresponding standard curve formulas are shown in Table 7.

[0126] Comparative Example 4

[0127] The difference from Example 1 is that the characteristic spectral band selected is 5819 cm⁻¹. -1 -5900cm -1 The corresponding standard curve formulas are shown in Table 7.

[0128] Comparative Example 5

[0129] The difference from Example 1 is that the characteristic spectral band is selected as 5650 cm⁻¹. -1 -5820cm -1 The corresponding standard curve formulas are shown in Table 7.

[0130] Comparative Example 6

[0131] The difference from Example 1 is that the characteristic spectral band is selected as 5500 cm⁻¹. -1 -5650cm -1 The corresponding standard curve formulas are shown in Table 7.

[0132] Comparative Example 7

[0133] The difference from Example 1 is that the characteristic spectral band is selected as 5400 cm⁻¹. -1 -5500cm -1 The corresponding standard curve formulas are shown in Table 7.

[0134] Table 7 Comparison of detection methods between the examples and comparative examples

[0135]

[0136] As shown in Table 7, compared with the bands not selected in this invention, the characteristic bands selected in this invention have good correlation and small prediction deviation, and can accurately detect the total content of cyclic siloxanes in hydrogen-containing polysiloxanes and polyether organosilicon surfactants.

[0137] In summary, the detection method provided by the embodiments of the present invention can accurately detect the total content of cyclic siloxanes in hydrogen-containing polysiloxanes, polyether silicone surfactants, and polyurethane foams. It can meet the requirements for real-time detection of the total amount of cyclic siloxanes during the cyclic siloxane removal process, and the detection time is short and will not cause environmental pollution.

[0138] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for detecting the total content of cyclic siloxanes, characterized in that, include: The characteristic peak at 4875 cm⁻¹ was obtained by near-infrared spectroscopy of the sample. -1 -4921cm -1 The absorbance is obtained, and the total amount of cyclic siloxanes in the sample is calculated by substituting the absorbance into the standard curve formula. The sample to be tested is selected from any one of hydrogen-containing polysiloxane, polyether silicone surfactant, and polyurethane foam; The standard curve formula is obtained by near-infrared detection and analysis of the standard of the sample to be tested.

2. The detection method according to claim 1, characterized in that, The detection conditions for near-infrared detection include: a spectral acquisition range of 4000 cm⁻¹. -1 -10000cm -1 The resolution is 1cm. -1 -16cm -1 .

3. The detection method according to claim 2, characterized in that, The detection was performed using a DTGS-BK-7 detector; The number of scans is 60-70, and each sample is measured at least 3 times. The average spectrum is taken as the sample spectrum, and the reference spectrum is air.

4. The detection method according to claim 3, characterized in that, During near-infrared detection, the heating temperature is 30℃-70℃, and the heating time is 1min-5min.

5. The detection method according to claim 1, characterized in that, When the sample to be tested is a hydrogen-containing polysiloxane or a polyether silicone surfactant, the standard curve formula is Y = 0.94503010X + 0.06537312; when the sample to be tested is polyurethane foam, the standard curve formula is Y1 = 0.96231572X + 0.08218631. Where X represents absorbance; Y or Y1 represents the total content of cyclic siloxanes, with Y in wt% and Y1 in ppm.

6. The detection method according to claim 5, characterized in that, The process of obtaining the standard curve formula includes: using near-infrared spectroscopy to detect a standard of the sample with a known content; analyzing the obtained near-infrared spectral data using Horizon MB spectral analysis software; and determining the characteristic absorption peak of the cyclic Si-O bond to be 4875 cm⁻¹. -1 -4921cm -1 The standard curve formula is obtained by processing the spectrum obtained from near-infrared detection using the partial least squares method.

7. The detection method according to claim 1, characterized in that, When the sample to be tested is a hydrogen-containing polysiloxane, the detection range of the total amount of cyclic siloxanes is 0.20wt%-6.00wt%; When the sample to be tested is a polyether silicone surfactant, the detection range for the total amount of cyclic siloxanes is 0.10 wt% - 3.00 wt%. When the sample to be tested is polyurethane foam, the detection range for the total amount of cyclic siloxanes is 100ppm-300ppm.

8. The detection method according to claim 7, characterized in that, When the sample to be tested is a hydrogen-containing polysiloxane or a polyether organosilicon surfactant, the sample to be tested is directly subjected to near-infrared detection; when the sample to be tested is polyurethane foam, the polyurethane foam is first pretreated to obtain a polyurethane foam extract, and then the polyurethane foam extract is subjected to near-infrared detection.

9. The detection method according to claim 8, characterized in that, The pretreatment includes: extracting cyclic siloxanes from the polyurethane foam using Soxhlet extraction, followed by heat treatment to remove the solvent, with the heating temperature controlled at 55℃-70℃.

10. The detection method according to claim 9, characterized in that, Acetone was used as the extractant for extracting the cyclic siloxanes from the polyurethane foam.

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