Quantitative analysis method for residual saponification value

Abstract

The invention discloses a quantitative analysis method of a residual saponification value, which is applied to polytetramethylene ether glycol, according to the method, quantitative analysis is carried out by using an infrared spectrometer, the infrared absorption wave number of an ester group functional group in a to-be-detected product is determined, and the content of the ester group functional group in the to-be-detected product is in a linear relationship with the residual saponification value of the to-be-detected product. And drawing a working curve representing a linear relationship between the residual saponification value and the response value of the standard substance at the infrared absorption wave number, then detecting the response value of the to-be-detected substance at the infrared absorption wave number, and finally calculating based on the response value of the to-be-detected substance at the infrared absorption wave number and the working curve, thereby obtaining the residual saponification value of the to-be-detected substance. According to the method, quantitative analysis of the residual saponification value of the polytetramethylene ether glycol is realized, the analysis time is short, and the analysis process is simple and safe.

Description

Technical Field

[0001] This invention relates to the field of analytical testing technology, and in particular to a quantitative analysis method for residual saponification value. Background Technology

[0002] Polytetramethylene ether glycol, also known as polytetrahydrofuran (PTMEG), has the chemical formula (C4H8O). n PTMEG, where n represents the number of polymers with different molecular weights, is a very important polymer material. It is a linear polyether diol with primary hydroxyl-terminated groups, a white waxy solid at room temperature, and melts into a transparent, colorless liquid when the temperature exceeds room temperature. It is readily soluble in alcohols, esters, ketones, aromatics, and chlorinated hydrocarbons, but insoluble in aliphatic hydrocarbons and water. PTMEG is a homopolymer obtained by cationic ring-opening polymerization of monomer THF (tetrahydrofuran) in the presence of a catalyst. PTMEG is mainly used as a soft segment in block polyurethanes or block polyether polyesters.

[0003] Residual saponification value is one of the important indicators in the PTMEG production process and also a factor affecting the quality of downstream spandex production. The traditional method for analyzing residual saponification value is to manually titrate the ester functional groups in PTMEG and then calculate the residual saponification value using a calculation formula. This process uses volatile and toxic substances such as isopropanol. The determination method takes nearly 3 hours, the analysis process is cumbersome and complex, there are many factors affecting the accuracy of the determination, resulting in serious delays in process adjustment. In addition, the substances volatilized during the titration process are detrimental to the health of the analysts. Summary of the Invention

[0004] To address the aforementioned problems, the present invention aims to provide a quantitative analysis method for residual saponification value, thereby solving the problems of long analysis time, complex analysis process, and potential hazards to analysts from volatile substances released during the analysis in existing quantitative analysis methods for residual saponification value of polytetramethylene ether glycol. The technical solution is as follows:

[0005] On the one hand, a quantitative analysis method for residual saponification value is provided, applied to polytetramethylene ether glycol, and quantitative analysis is performed using an infrared spectrometer. The method includes the following steps:

[0006] Step 1) Determine the infrared absorption wavenumber of the ester functional group in the sample to be tested; the content of the ester functional group in the sample to be tested is linearly related to the residual saponification value of the sample to be tested;

[0007] Step 2) Plot the working curve; the working curve represents the linear relationship between the remaining saponification value and the response value of the standard at the infrared absorption wavenumber;

[0008] Step 3) Detect the response value of the sample to be tested at the infrared absorption wavenumber;

[0009] Step 4) Calculate the remaining saponification value of the test sample based on the response value of the test sample at the infrared absorption wavenumber and the working curve.

[0010] In one exemplary implementation, step 1) further includes the following steps:

[0011] The infrared absorption spectra of the polytetramethylene ether diester sample and the polytetramethylene ether diol sample were analyzed to determine the infrared absorption wavenumbers of the ester functional groups in the test sample.

[0012] In one exemplary embodiment, the infrared absorption wavenumber is 1750 cm⁻¹. -1 ~1710cm -1 Inside.

[0013] In one exemplary implementation, step 2) includes the following steps:

[0014] Standards with different residual saponification values ​​were prepared using polytetramethylene ether diester samples with known saponification values ​​and polytetramethylene ether glycol samples with known residual saponification values.

[0015] Working curves were plotted based on the response values ​​of the standards with different residual saponification values ​​at the infrared absorption wavenumber and the different residual saponification values.

[0016] In one exemplary embodiment, the working curve operates in the range of 0.03–0.4 mg (KOH) / g.

[0017] In one exemplary implementation, the method includes:

[0018] Calcium fluoride windows were used as windows for infrared spectroscopy testing.

[0019] In one exemplary embodiment, when using an infrared spectrometer for quantitative analysis, a high-energy mid-infrared light source is selected as the light source.

[0020] In one exemplary implementation, the method includes:

[0021] When performing quantitative analysis using an infrared spectrometer, the wavenumber scan range is 2500 cm⁻¹. -1 -1500cm -1 .

[0022] This invention discloses a quantitative analysis method for residual saponification value, applied to polytetramethylene ether glycol (PTG). Quantitative analysis is performed using an infrared spectrometer. The method determines the infrared absorption wavenumber of the ester functional groups in the sample, where the content of these ester functional groups is linearly related to the residual saponification value. A working curve characterizing the linear relationship between the residual saponification value and the response value of a standard at the infrared absorption wavenumber is plotted. The response value of the sample at the infrared absorption wavenumber is then detected, and the residual saponification value is calculated based on the response value and the working curve. This invention achieves quantitative analysis of the residual saponification value of PTG, with a short analysis time, simple process, and safety. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the present invention, the accompanying drawings used in the description of the embodiments or prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0024] Figure 1 This is a flowchart of a quantitative analysis of residual saponification value provided by an embodiment of the present invention;

[0025] Figure 2 This is an infrared spectrum of a standard with different residual saponification values ​​provided in an embodiment of the present invention;

[0026] Figure 3 This is a working curve fitting graph provided in an embodiment of the present invention. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] This application provides a method for quantitative analysis of residual saponification value, applied to polytetramethylene ether glycol, using an infrared spectrometer for quantitative analysis. For detailed steps, please refer to [link to specific steps]. Figure 1 , Figure 1 The flowchart illustrates a quantitative analysis method for residual saponification value, which includes the following steps:

[0029] Step 1) Determine the infrared absorption wavenumber of the ester functional group in the sample to be tested; the content of the ester functional group in the sample to be tested is linearly related to the residual saponification value of the sample to be tested.

[0030] Specifically, this method uses a Fourier transform infrared spectrometer for detection. Unlike dispersive infrared spectroscopy, it is based on the principle of Fourier transforming the interferometric infrared light. It mainly consists of an infrared light source, aperture, interferometer (beam splitter, moving mirror, fixed mirror), sample chamber, detector, various infrared reflectors, laser, control circuit board, and power supply. It can perform qualitative and quantitative analysis of samples and is widely used in pharmaceuticals, chemicals, geology, petroleum, coal, environmental protection, customs, gem identification, and forensic identification.

[0031] The sample to be tested refers to polytetramethylene ether glycol.

[0032] Step 2) Plot the working curve; the working curve represents the linear relationship between the remaining saponification value and the response value of the standard at the infrared absorption wavenumber.

[0033] Specifically, standard samples with different residual saponification values ​​are prepared, and these standard samples with different residual saponification values ​​are tested using a Fourier transform infrared spectrometer to obtain the response values ​​of these standard samples with different residual saponification values ​​at the infrared absorption wavenumber. Then, a working curve is plotted based on the magnitude of the residual saponification value and the response values ​​of these standard samples with different residual saponification values ​​at the infrared absorption wavenumber.

[0034] Step 3) Detect the response value of the sample at the infrared absorption wavenumber.

[0035] Using a Fourier transform infrared spectrometer with the same detection parameters as in step 1), the response value of the sample at the infrared absorption wavenumber was detected.

[0036] Step 4) Calculate the remaining saponification value of the sample based on the response value of the sample at the infrared absorption wavenumber and the working curve.

[0037] Specifically, based on the response value of the sample to be tested at the infrared absorption wavenumber detected in step 3), the result is substituted into the working curve for calculation, and the remaining saponification value is the remaining saponification value of the sample to be tested.

[0038] In this embodiment of the application, step 1) further includes the following steps:

[0039] The infrared absorption spectra of polytetramethylene ether diester and polytetramethylene ether glycol samples were analyzed to determine the infrared absorption wavenumbers of the ester functional groups in the test samples.

[0040] Specifically, by adding a small amount of polytetramethylene ether diester sample to a polytetramethylene ether glycol sample and measuring its infrared absorption spectrum, the infrared absorption wavenumber of the ester functional groups in the polytetramethylene ether diester can be determined as the infrared absorption wavenumber of the ester functional groups in the sample to be tested.

[0041] In this embodiment, the infrared absorption wavenumber is 1750 cm⁻¹. -1 ~1710cm -1 Inside.

[0042] Specifically, the response value is at 1750cm. -1 ~1710cm -1 The peak area is obtained by integrating within the range.

[0043] In this embodiment of the application, step 2) includes the following steps:

[0044] Standards with different residual saponification values ​​were prepared using polytetramethylene ether diester samples with known saponification values ​​and polytetramethylene ether glycol samples with known residual saponification values.

[0045] Working curves were plotted based on the response values ​​of standards with different residual saponification values ​​at infrared absorption wavenumbers and different residual saponification values.

[0046] Specifically, the polytetramethylene ether diester sample with a known saponification value and the polytetramethylene ether glycol sample with a known remaining saponification value can be determined by manual titration to determine the saponification value of the polytetramethylene ether diester sample and the remaining saponification value of the polytetramethylene ether glycol sample. For specific infrared absorption spectra of standards with different remaining saponification values, please refer to [link to relevant documentation]. Figure 2 .

[0047] In this embodiment of the application, the working range of the working curve is 0.03 to 0.4 mg (KOH) / g.

[0048] Specifically, the residual saponification value of polytetramethylene ether glycol can be quantitatively analyzed within the range of 0.03–0.4 mg (KOH) / g.

[0049] In this embodiment of the application, the method includes:

[0050] Calcium fluoride windows were used as windows for infrared spectroscopy testing.

[0051] Specifically, the type of window for infrared spectroscopy testing can be selected according to actual needs, with calcium fluoride windows being the preferred choice. This application embodiment considers that when using potassium bromide windows, the windows readily absorb moisture from the air, forming a water film on the surface, thus affecting the transmittance of infrared light and potentially causing deliquescence and fogging, impacting spectral quality. Potassium bromide windows also have low hardness and are soft, making them easily scratched and worn, requiring replacement approximately every 2-3 months. In contrast, calcium fluoride windows have better chemical stability and higher hardness than potassium bromide windows, making them less prone to scratches and wear. Under normal use and operation, they maintain surface smoothness and optical performance better, resulting in a longer service life. They also have lower hygroscopicity, are less affected by moisture in the air, and do not experience deliquescence or fogging like potassium bromide windows, thus maintaining more stable optical performance and reducing the requirements for experimental humidity. Without human-caused damage, they can be used for one year or more.

[0052] In this embodiment of the application, the method includes:

[0053] When using an infrared spectrometer for quantitative analysis, a high-energy mid-infrared light source should be selected.

[0054] In this embodiment of the application, the method includes:

[0055] When performing quantitative analysis using an infrared spectrometer, the wavenumber scan range is 2500 cm⁻¹. -1 -1500cm -1 .

[0056] Specifically, at 2500cm -1 -1500cm -1 It includes the infrared absorption wavenumber range of ester groups.

[0057] The technical solution of this application will be described below with reference to specific embodiments. This application uses an Agilent Cary 630FTIR sensor, a DTGS detector, a high-energy mid-infrared light source, and a transmission sample chamber sampling accessory for sample analysis, eliminating the need for pellet compression. The scanning range is 2500 cm⁻¹. -1 -1500cm -1 A polytetramethylene ether diester sample with a known saponification value of 61.73 mg (KOH) / g and a polytetramethylene ether glycol sample with a known residual saponification value of 0.03 mg (KOH) / g were used to prepare standards with different residual saponification values: 0.03, 0.1, 0.2, 0.3, and 0.4 mg (KOH) / g. The following formula can be used as a reference when preparing standards with different residual saponification values:

[0058]

[0059] Taking the preparation of a 0.1 g mg(KOH) / g residual saponification value standard as an example: RN0 represents the residual saponification value of the standard; m1 is a polytetramethylene ether diester sample with a known saponification value, RN1 is a polytetramethylene ether diester sample with a known saponification value of 61.73 mg(KOH) / g; m2 is a polytetramethylene ether glycol sample with a known residual saponification value, RN2 is a polytetramethylene ether glycol sample with a known residual saponification value of 0.03 mg(KOH) / g. Weigh 0.11 g of the polytetramethylene ether diester sample with a known saponification value and 100 g of the polytetramethylene ether glycol sample with a known residual saponification value, mix them evenly at 40℃, and thus obtain the 0.1 mg(KOH) / g residual saponification value standard.

[0060] Example 1

[0061] A method for analyzing the residual saponification value of polytetramethylene ether glycol using Fourier transform infrared spectroscopy was established.

[0062] Establish the working curve; please refer to the fitting graph of this working curve. Figure 3 The working curve relationship is: Y = 0.1118x + 0.0304, R 2 =0.9994; Y is the concentration content, x is the response value (at 1750cm²). -1 ~1710cm -1 The peak area obtained by integrating within the range); after simultaneous measurement of the unknown sample with manual analysis, the following data were obtained (Table 1). It can be seen that the maximum difference between instrumental analysis and manual analysis is within 0.01.

[0063] The analysis time is much shorter than that of manual analysis, the instrument analysis is simple to operate, and it does not involve contact with toxic substances.

[0064] Table 1. Simultaneous analysis of backtesting data from 16 samples and the time taken

[0065]

[0066] The method of analyzing the residual saponification value of polytetramethylene ether glycol using Fourier transform infrared spectroscopy was used to establish curves in the later stage. A large number of samples on the production line were tracked and analyzed, and the results were obtained simultaneously with manual analysis. The data are shown in Table 2. It can be seen that the maximum difference between instrumental analysis and manual analysis is 0.01 mg (KOH) / g. The method of using Fourier transform infrared spectroscopy to replace manual analysis is mature and reliable.

[0067] Table 2. Comparative Data on PTMEG Residual Saponification Value Verification Analysis

[0068]

[0069]

[0070]

[0071]

[0072] As can be seen from the above technical solutions of the embodiments of the present invention, the present invention discloses a quantitative analysis method for residual saponification value, applied to polytetramethylene ether glycol. Quantitative analysis is performed using an infrared spectrometer. The infrared absorption wavenumber of the ester functional groups in the sample is determined, wherein the content of the ester functional groups in the sample is linearly related to the residual saponification value of the sample. A working curve characterizing the linear relationship between the residual saponification value and the response value of the standard at the infrared absorption wavenumber is plotted. Then, the response value of the sample at the infrared absorption wavenumber is detected, and the residual saponification value of the sample is calculated based on the response value of the sample at the infrared absorption wavenumber and the working curve. The present invention achieves quantitative analysis of the residual saponification value of polytetramethylene ether glycol, with short analysis time, simple analysis process, and safety.

[0073] The foregoing description has fully disclosed the specific embodiments of the present invention. It should be noted that any modifications made to the specific embodiments of the present invention by those skilled in the art do not depart from the scope of the claims. Accordingly, the scope of the claims is not limited to the foregoing specific embodiments.

Claims

1. A quantitative analysis method for residual saponification value, applied to polytetramethylene ether glycol, characterized in that, Quantitative analysis using an infrared spectrometer includes the following steps: Step 1) Determine the infrared absorption wavenumber of the ester functional group in the sample to be tested; the content of the ester functional group in the sample to be tested is linearly related to the residual saponification value of the sample to be tested; Step 2) Plot the working curve; the working curve represents the linear relationship between the remaining saponification value and the response value of the standard at the infrared absorption wavenumber; Step 3) Detect the response value of the sample to be tested at the infrared absorption wavenumber; Step 4) Calculate the remaining saponification value of the test sample based on the response value of the test sample at the infrared absorption wavenumber and the working curve.

2. The quantitative analysis method for residual saponification value according to claim 1, characterized in that, Step 1) also includes the following steps: The infrared absorption spectra of the polytetramethylene ether diester sample and the polytetramethylene ether diol sample were analyzed to determine the infrared absorption wavenumbers of the ester functional groups in the test sample.

3. The quantitative analysis method for residual saponification value according to any one of claims 1 or 2, characterized in that, The infrared absorption wavenumber is 1750 cm⁻¹ -1 ~1710cm -1 Inside.

4. The quantitative analysis method for residual saponification value according to any one of claims 1 or 2, characterized in that, Step 2) includes the following steps: Standards with different residual saponification values ​​were prepared using polytetramethylene ether diester samples with known saponification values ​​and polytetramethylene ether glycol samples with known residual saponification values. Working curves were plotted based on the response values ​​of the standards with different residual saponification values ​​at the infrared absorption wavenumber and the different residual saponification values.

5. The quantitative analysis method for residual saponification value according to claim 1, characterized in that, The working range of the working curve is 0.03–0.4 mg (KOH) / g.

6. The quantitative analysis method for residual saponification value according to claim 1, characterized in that, The method includes: Calcium fluoride windows were used as windows for infrared spectroscopy testing.

7. The quantitative analysis method for residual saponification value according to claim 1, characterized in that, The method includes: When using an infrared spectrometer for quantitative analysis, a high-energy mid-infrared light source should be selected.

8. The quantitative analysis method for residual saponification value according to claim 1, characterized in that, The method includes: When performing quantitative analysis using an infrared spectrometer, the wavenumber scan range is 2500 cm⁻¹. -1 -1500cm -1 .

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