CN112881334A - Method for detecting itaconic acid content in poly (acrylonitrile-itaconic acid) - Google Patents
Method for detecting itaconic acid content in poly (acrylonitrile-itaconic acid) Download PDFInfo
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- SWUMLOXBPGDJOR-UHFFFAOYSA-N 2-methylidenebutanedioic acid;prop-2-enenitrile Chemical compound C=CC#N.OC(=O)CC(=C)C(O)=O SWUMLOXBPGDJOR-UHFFFAOYSA-N 0.000 title claims abstract description 85
- JAHNSTQSQJOJLO-UHFFFAOYSA-N 2-(3-fluorophenyl)-1h-imidazole Chemical compound FC1=CC=CC(C=2NC=CN=2)=C1 JAHNSTQSQJOJLO-UHFFFAOYSA-N 0.000 title claims abstract description 79
- LVHBHZANLOWSRM-UHFFFAOYSA-N methylenebutanedioic acid Natural products OC(=O)CC(=C)C(O)=O LVHBHZANLOWSRM-UHFFFAOYSA-N 0.000 title claims abstract description 78
- 238000000034 method Methods 0.000 title claims abstract description 61
- 238000002329 infrared spectrum Methods 0.000 claims abstract description 39
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims abstract description 25
- 229910052760 oxygen Inorganic materials 0.000 claims abstract description 25
- 239000001301 oxygen Substances 0.000 claims abstract description 25
- 239000000126 substance Substances 0.000 claims abstract description 19
- 238000009499 grossing Methods 0.000 claims description 8
- 238000012937 correction Methods 0.000 claims description 6
- 230000004069 differentiation Effects 0.000 claims description 6
- 230000003595 spectral effect Effects 0.000 claims description 6
- 125000000744 organoheteryl group Chemical group 0.000 claims description 2
- 238000005259 measurement Methods 0.000 abstract description 7
- 238000001514 detection method Methods 0.000 abstract description 4
- 229920000642 polymer Polymers 0.000 abstract 1
- 229920002239 polyacrylonitrile Polymers 0.000 description 14
- 238000012360 testing method Methods 0.000 description 9
- 229920000049 Carbon (fiber) Polymers 0.000 description 5
- 239000004917 carbon fiber Substances 0.000 description 5
- 238000004458 analytical method Methods 0.000 description 4
- 238000012935 Averaging Methods 0.000 description 3
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- 239000003153 chemical reaction reagent Substances 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- VGTPCRGMBIAPIM-UHFFFAOYSA-M sodium thiocyanate Chemical compound [Na+].[S-]C#N VGTPCRGMBIAPIM-UHFFFAOYSA-M 0.000 description 3
- 229920002994 synthetic fiber Polymers 0.000 description 3
- 239000012209 synthetic fiber Substances 0.000 description 3
- NLHHRLWOUZZQLW-UHFFFAOYSA-N Acrylonitrile Chemical compound C=CC#N NLHHRLWOUZZQLW-UHFFFAOYSA-N 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- IOLCXVTUBQKXJR-UHFFFAOYSA-M potassium bromide Chemical compound [K+].[Br-] IOLCXVTUBQKXJR-UHFFFAOYSA-M 0.000 description 2
- 230000006641 stabilisation Effects 0.000 description 2
- 238000011105 stabilization Methods 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 238000003763 carbonization Methods 0.000 description 1
- 125000003178 carboxy group Chemical group [H]OC(*)=O 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 229920001577 copolymer Polymers 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 239000003814 drug Substances 0.000 description 1
- 230000003631 expected effect Effects 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 229920002521 macromolecule Polymers 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 1
- 238000003333 near-infrared imaging Methods 0.000 description 1
- 230000003472 neutralizing effect Effects 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 239000002243 precursor Substances 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 238000004445 quantitative analysis Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 238000012795 verification Methods 0.000 description 1
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- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
- G01N21/359—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using near infrared light
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Abstract
The invention belongs to the field of polymer detection, and relates to a method for detecting itaconic acid content in poly (acrylonitrile-itaconic acid), which uses an organic element analyzer to determine oxygen content in poly (acrylonitrile-itaconic acid) standard products with different itaconic acid contents, calculating the content of itaconic acid in the poly (acrylonitrile-itaconic acid) standard according to the molecular formula of itaconic acid through oxygen content, collecting the near infrared spectrum of the poly (acrylonitrile-itaconic acid) standard under specific conditions, and carrying out specific treatment on the collected near infrared spectrum, establishing a correlation model of the itaconic acid content in the poly (acrylonitrile-itaconic acid) standard substance and the near infrared spectrum by using chemometrics software and adopting a partial least square method under specific parameters, and collecting a near infrared spectrogram of a poly (acrylonitrile-itaconic acid) sample to be detected and substituting the near infrared spectrogram into the correlation model to quickly calculate the itaconic acid content. The method has the advantages of rapidness, no damage, high accuracy, good repeatability, good stability, capability of realizing on-line measurement and the like.
Description
Technical Field
The invention belongs to the field of itaconic acid content detection, and particularly relates to a method for detecting itaconic acid content in poly (acrylonitrile-itaconic acid).
Background
Polyacrylonitrile is one of the most common and important materials for preparing carbon fibers, and the properties of polyacrylonitrile directly affect the quality of carbon fibers. Itaconic acid is generally added into polyacrylonitrile for preparing carbon fibers, and because a molecular structure of a single acrylonitrile homopolymer has no side chain and a large number of-CN groups exist on a main chain, the acting force between polyacrylonitrile macromolecules is too strong, so that the pre-oxidation and carbonization periods are very long, heat release in a thermal stabilization process is violent and uncontrollable, the processability is very poor, the production cost is high, and the strength and other properties of the final carbon fibers are not ideal. Itaconic acid contains two carboxyl groups, and can effectively improve the processing performance of polyacrylonitrile and relieve the heat release effect in the thermal stabilization process by copolymerizing with acrylonitrile, and becomes one of the most common comonomers in the production of polyacrylonitrile. The itaconic acid content in the poly (acrylonitrile-itaconic acid) has great influence on the performance of the final carbon fiber, the itaconic acid content is too low to achieve the expected effect, and the carbon yield and the mechanical property are reduced if the itaconic acid content is too high, so that the establishment of a proper method for measuring the itaconic acid content in the poly (acrylonitrile-itaconic acid) has great significance for the production and subsequent application of the poly (acrylonitrile-itaconic acid).
The existing method for measuring the content of itaconic acid in poly (acrylonitrile-itaconic acid) mainly comprises a chemical method and an infrared method: (1) analysis of the composition of copolymerized acrylonitrile precursors (Xuzhong, synthetic fiber industry, 3 rd year 1979, pp.35-36) discloses a chemical method for determining the content of itaconic acid in poly (acrylonitrile-itaconic acid) by dissolving poly (acrylonitrile-itaconic acid) in NaSCN solution, which is a basic principle that itaconic acid lowers the pH of NaSCN solution, and neutralizing itaconic acid with standard NaOH solution to restore the pH of NaSCN solution to the original pHStarting the pH value, and further calculating the content of itaconic acid; (2) infrared quantitative analysis of itaconic acid in acrylonitrile copolymer (Shanghai synthetic fiber research institute, synthetic fiber, 1978, 4 th, 20-23 pages) discloses a method for measuring itaconic acid content in poly (acrylonitrile-itaconic acid) by infrared method, which comprises mixing acrylonitrile homopolymer and itaconic acid at different ratio to prepare standard substance, tabletting 2mg sample and potassium bromide, measuring infrared spectrogram, and measuring by 2252cm-1And 1700cm-1And determining the content of itaconic acid in the poly (acrylonitrile-itaconic acid) to be detected according to the difference of the ratios of the absorption peaks.
The two methods have the advantages of simple principle and obvious defects, including poor test repeatability, the need of using chemical reagents, long analysis time, the need of damaging samples, incapability of realizing online measurement, inapplicability to high molecular weight (weight average molecular weight is more than 300000) polyacrylonitrile samples (because the high molecular weight polyacrylonitrile cannot be completely dissolved in a specific solvent, and the high molecular weight polyacrylonitrile cannot be fully and uniformly mixed with itaconic acid to obtain a standard product required by an infrared method), and the like.
The near infrared spectrum analysis technology has been used in the fields of food, medicine, chemicals and the like, but the application of the near infrared spectrum analysis technology in the determination of the itaconic acid content in polyacrylonitrile is only reported, and particularly, the problems that the determination of the itaconic acid content in high molecular weight polyacrylonitrile, more particularly, the determination of the itaconic acid content in ultra-high molecular weight (weight average molecular weight is more than 1000000) polyacrylonitrile, the repeatability of a test result is good, the stability of a near infrared method is poor and the like are ensured are well-known.
Disclosure of Invention
The invention provides a method for detecting itaconic acid content in poly (acrylonitrile-itaconic acid) aiming at the blank of the prior art, which comprises the steps of measuring oxygen content in poly (acrylonitrile-itaconic acid) standard products with different itaconic acid contents by using an organic element analyzer, calculating the itaconic acid content in the poly (acrylonitrile-itaconic acid) standard products according to the itaconic acid molecular formula through the oxygen content, collecting near infrared spectrums of the poly (acrylonitrile-itaconic acid) standard products under specific conditions, carrying out specific treatment on the collected near infrared spectrums, establishing a correlation model of the itaconic acid content in the poly (acrylonitrile-itaconic acid) standard products and the near infrared spectrums under specific parameters by using a chemometrics software and adopting a partial least square method, collecting the near infrared spectrums of at least one time poly (acrylonitrile-itaconic acid) samples to be detected by using the same conditions, the method has the advantages of being fast, lossless, high in accuracy, good in repeatability and stability, free of using any chemical reagent and capable of achieving on-line measurement.
The specific technical scheme of the invention is as follows:
a method for detecting itaconic acid content in poly (acrylonitrile-itaconic acid) comprises the following steps:
(1) determining oxygen content in poly (acrylonitrile-itaconic acid) standards having different itaconic acid contents using an organoelement analyzer;
(2) calculating the content of itaconic acid in the poly (acrylonitrile-itaconic acid) standard according to the molecular formula of the itaconic acid through the oxygen content;
(3) collecting the near infrared spectrum of the poly (acrylonitrile-itaconic acid) standard substance by using a near infrared spectrometer in a diffuse reflection integrating sphere mode;
the collection conditions are as follows: scanning a background and then scanning a sample, wherein the background scanning times are 64-512 times, the sample scanning times are 128-256 times, and the resolution is 4-16 cm-1Gain of 1-2X, no attenuator, and spectral scanning range of 4000cm-1～10000cm-1Each sample was collected 5 times;
(4) sequentially carrying out second-order differentiation, 5-9-point Savitzky Golay smoothing and Multivariate Scattering Correction (MSC) on the collected near infrared spectrum;
(5) using chemometric software using Partial Least Squares (PLS) at 4000cm-1～8000cm-1In the wave number range, the main factor number is 3-5, and a correlation model of the itaconic acid content and the near infrared spectrum in the poly (acrylonitrile-itaconic acid) is established;
(6) collecting the near infrared spectrum of the poly (acrylonitrile-itaconic acid) to be detected for at least 1 time by using a near infrared spectrometer according to the same conditions;
(7) substituting the near infrared spectrum of the poly (acrylonitrile-itaconic acid) to be detected into the correlation model, wherein the correlation model can quickly calculate the content of itaconic acid in the poly (acrylonitrile-itaconic acid) to be detected;
the weight average molecular weight of the poly (acrylonitrile-itaconic acid) to be detected is 50000-1200000.
Furthermore, the oxygen content of the poly (acrylonitrile-itaconic acid) standard with different itaconic acid contents in the step (1) is in a range of 0.68-11.10%;
the spectral scanning wave number range in the step (3) is preferably 5200cm-1～5800cm-1Adding 6700cm-1～7400cm-1Plus 4200cm-1～4600cm-1；
The background scanning frequency in the step (3) is preferably 256-512, and the sample scanning frequency is preferably 256; the resolution is preferably 8cm-1(ii) a The gain is preferably 1X;
in the step (3), each sample is collected for 5 times to obtain five final near-infrared spectrum diagrams, and the acquisition of each final near-infrared spectrum diagram requires at least one collection time, and can also be performed by adopting a mode of collecting and averaging for multiple times, so that the effect is generally better.
The Savitzky Golay smoothing in the step (4) preferably adopts 7 points;
the number of the main factors in the step (5) is preferably 4;
more preferably, the poly (acrylonitrile-itaconic acid) to be detected has a weight average molecular weight of 1000000-1200000.
The optimal parameters can better improve the accuracy, repeatability and stability of the detection result, and are the optimal detection parameters obtained by the inventor after long-term exploration.
In conclusion, by adopting the method, the correlation model of the itaconic acid content and the near infrared spectrum in the poly (acrylonitrile-itaconic acid) standard substance is obtained, the itaconic acid content in the poly (acrylonitrile-itaconic acid) to be detected can be rapidly calculated by utilizing the correlation model, and the method has the advantages of rapidness, no damage, high accuracy, good repeatability, good stability, no need of using any chemical reagent and capability of realizing on-line measurement.
Drawings
FIG. 1 is a spectrogram obtained by performing second order differentiation, 7-point Savitzky Golay smoothing and multivariate scattering correction on an acquired near infrared spectrum;
FIG. 2 shows the test effect of the method on the calibration set sample (. smallcircle.) and the verification set sample (+), wherein the abscissa in the figure is the actual value of the itaconic acid content, which is obtained by conversion of the oxygen content measured by the organic element analyzer, and the ordinate is the calculated value of the itaconic acid content of the method.
Detailed Description
The present invention is further illustrated below with reference to examples, which will enable those skilled in the art to more fully understand the present invention, but which are not intended to limit the invention in any way;
example 1:
a method for detecting itaconic acid content in poly (acrylonitrile-itaconic acid) comprises the following steps:
1. an organic element analyzer is used for measuring the oxygen content in 8 poly (acrylonitrile-itaconic acid) standard products with different itaconic acid contents, wherein the oxygen content is between 0.68 and 5.24 percent, and the specific steps are as follows:
| |
1# | 2# | 3# | 4# | 5# | 6# | 7# | 8# |
| Oxygen content | 0.68％ | 1.27％ | 1.84％ | 2.74％ | 3.14％ | 3.91％ | 4.46％ | 5.24％ |
2. The content of itaconic acid in the poly (acrylonitrile-itaconic acid) standard substance is calculated according to the molecular formula of itaconic acid through the oxygen content, and is between 1.38 and 10.65 percent.
3. Collecting the near infrared spectra of the 8 poly (acrylonitrile-itaconic acid) standard substances by using a near infrared spectrometer in a diffuse reflection integrating sphere mode; the collection conditions are as follows: scanning the background and then scanning the sample, wherein the background scanning times are 64 times, the sample scanning times are 256 times, and the resolution is 16cm-1Gain of 2X, no attenuator, spectral scan range of 4000cm-1～10000cm-1And each sample is collected for 5 times, and the spectrogram of each sample is obtained by collecting 3 times and taking an average value.
4. The collected near infrared spectrum is subjected to second order differentiation, 5-point Savitzky Golay smoothing and Multivariate Scattering Correction (MSC) in sequence, and the obtained spectrogram is shown in the attached figure 1.
5. The Partial Least Squares (PLS) at 5200cm using the chemometric software TQ Analyst-1～5800cm-1Adding 6700cm-1～7400cm-1Plus 4200cm-1～4600cm-1In the wave number range, the main factor number is 3, a correlation model of the itaconic acid content in the poly (acrylonitrile-itaconic acid) and the near infrared spectrum is established, the correlation between the actual value of the itaconic acid content in the poly (acrylonitrile-itaconic acid) and the calculated value of the model is shown in an attached figure 2, the abscissa in the figure is the actual value of the itaconic acid content in the poly (acrylonitrile-itaconic acid), and the ordinate is the calculated value of the model, so that the linear relation of the established correlation model is obvious, and the calculation precision of the model is high.
6. And (3) acquiring the near infrared spectrum of the poly (acrylonitrile-itaconic acid) to be detected for 1 time by using a near infrared spectrometer according to the same conditions.
7. And substituting the near infrared spectrum of the poly (acrylonitrile-itaconic acid) to be detected into the correlation model, and quickly calculating the content of the itaconic acid in the poly (acrylonitrile-itaconic acid) to be detected by the correlation model.
8. The poly (acrylonitrile-itaconic acid) to be measured is respectively measured by an infrared method and a chemical method, the repeatability (calculated by relative standard deviation RSD of 5 times of measurement) is calculated, and the comparison with the method result of the invention is shown in the attached table 1, and the table shows that the repeatability of the method of the invention is below 3.9 percent, is superior to 6.9 to 8.4 percent of that of the infrared method and 9.9 to 15.5 percent of that of the chemical method, and the repeatability of the method of the invention is outstanding.
9. The model is used for the determination of the same sample again after two months, the difference value between the test average value and the test average value before two months is not more than 0.2 percent in the last two columns of the table 1, and the repeatability is still below 4 percent, which shows that the method has outstanding stability.
10. The weight average molecular weight of the poly (acrylonitrile-itaconic acid) related to the embodiment is 50000-100000.
TABLE 1
Example 2
A method for detecting itaconic acid content in poly (acrylonitrile-itaconic acid) comprises the following steps:
1. an organic element analyzer is used for measuring the oxygen content in 12 poly (acrylonitrile-itaconic acid) standard products with different itaconic acid contents, wherein the oxygen content is between 5.08% and 11.10%, and the specific steps are as follows:
| |
1# | 2# | 3# | 4# | 5# | 6# |
| Oxygen content | 5.08％ | 5.63％ | 6.38％ | 6.73％ | 7.13％ | 7.54 |
| Sample number | ||||||
| 7# | 8# | 9# | 10# | 11# | 12# | |
| Oxygen content | 8.01％ | 8.62％ | 9.36％ | 9.94％ | 10.73％ | 11.10％ |
2. The content of itaconic acid in the poly (acrylonitrile-itaconic acid) standard substance is calculated according to the molecular formula of itaconic acid through the oxygen content, and is between 10.33 and 22.56 percent.
3. Collecting the near infrared spectra of the 12 poly (acrylonitrile-itaconic acid) standard substances by using a near infrared spectrometer in a diffuse reflection integrating sphere mode; the collection conditions are as follows: scanning the background and then scanning the sample, wherein the background scanning times are 128 times, the sample scanning times are 128 times, and the resolution is 4cm-1Gain of 1X, no attenuator, and spectral scan range of 4000cm-1～10000cm-1And each sample is collected for 5 times, and the spectrogram of each sample is obtained by collecting 5 times and taking an average value.
4. And sequentially carrying out second-order differentiation, 9-point Savi tzky Golay smoothing and Multivariate Scattering Correction (MSC) on the collected near infrared spectrum.
5. Using the chemometric software Unscamblebler, the partial least squares method (PLS) was used at 4000cm-1～8000cm-1In the wave number range, the main factor number is 5, and a correlation model of the itaconic acid content in the poly (acrylonitrile-itaconic acid) and the near infrared spectrum is established.
6. And (3) acquiring the near infrared spectrum of the poly (acrylonitrile-itaconic acid) to be detected by using a near infrared spectrometer according to the same conditions, and averaging the acquired near infrared spectrum.
7. And substituting the near infrared spectrum of the poly (acrylonitrile-itaconic acid) to be detected into the correlation model, and quickly calculating the content of the itaconic acid in the poly (acrylonitrile-itaconic acid) to be detected by the correlation model.
8. The poly (acrylonitrile-itaconic acid) to be measured is respectively measured by an infrared method and a chemical method, the repeatability (calculated by relative standard deviation RSD of 5 times of measurement) is calculated, and the comparison with the method result of the invention is shown in the attached table 2, and the table shows that the repeatability of the method of the invention is below 5.2 percent and is superior to 6.8 to 7.4 percent of that of the infrared method and 9.3 to 11.5 percent of that of the chemical method, and the repeatability of the method of the invention is outstanding.
9. The model is used for the determination of the same sample again after two months, the difference value between the test average value and the test average value before two months is not more than 0.4 percent in the last two columns of the table 2, and the repeatability is still below 5.6 percent, which shows that the method has outstanding stability.
10. The weight average molecular weight of the poly (acrylonitrile-itaconic acid) is 800000-1000000.
TABLE 2
Example 3
A method for detecting itaconic acid content in poly (acrylonitrile-itaconic acid) comprises the following steps:
1. an organic element analyzer is used for measuring the oxygen content in 9 poly (acrylonitrile-itaconic acid) standard products with different itaconic acid contents, wherein the oxygen content is between 3.04% and 8.55%, and the oxygen content is as follows:
| |
1# | 2# | 3# | 4# | 5# | 6# | 7# | 8# | 9# |
| Oxygen content | 3.04％ | 3.71％ | 4.48％ | 5.02％ | 5.74％ | 6.54％ | 7.22％ | 7.84％ | 8.55％ |
2. The content of itaconic acid in the poly (acrylonitrile-itaconic acid) standard substance is calculated according to the molecular formula of itaconic acid through the oxygen content, and is between 6.18 and 17.38 percent.
3. Collecting the near infrared spectrum of the 9 poly (acrylonitrile-itaconic acid) standard products by using a near infrared spectrometer in a diffuse reflection integrating sphere mode; the collection conditions are as follows: scanning the background and then scanning the sample, wherein the background scanning times are 512 times, the sample scanning times are 256 times, and the resolution is 8cm-1Gain of 1X, no attenuator, and spectral scan range of 4000cm-1～10000cm-1And each sample is collected for 5 times, and the spectrogram of each sample is obtained by collecting for 1 time.
4. And sequentially carrying out second-order differentiation, 7-point Savitzky Golay smoothing and Multivariate Scattering Correction (MSC) on the collected near infrared spectrum.
5. The Partial Least Squares (PLS) at 5200cm using the chemometric software TQ Analyst-1～5800cm-1Adding 6700cm-1～7400cm-1Plus 4200cm-1～4600cm-1In the wave number range, the main factor number is 4, and a correlation model of the itaconic acid content in the poly (acrylonitrile-itaconic acid) and the near infrared spectrum is established.
6. And (3) acquiring the near infrared spectrum of the poly (acrylonitrile-itaconic acid) to be detected by using a near infrared spectrometer according to the same conditions for 2 times, and averaging.
7. And substituting the near infrared spectrum of the poly (acrylonitrile-itaconic acid) to be detected into the correlation model, and quickly calculating the content of the itaconic acid in the poly (acrylonitrile-itaconic acid) to be detected by the correlation model.
8. The poly (acrylonitrile-itaconic acid) to be measured is respectively measured by an infrared method and a chemical method, the repeatability (calculated by relative standard deviation RSD of 5 times of measurement) is calculated, and the comparison with the method result of the invention is shown in the attached table 3, and the table shows that the repeatability of the method of the invention is below 3.5 percent, is superior to 6.8 to 7.8 percent of the infrared method and 9.7 to 14.2 percent of the chemical method, and the repeatability of the method of the invention is outstanding.
9. The model is used for the determination of the same sample again after two months, the difference value between the test average value and the test average value before two months is not more than 0.3 percent in the last two columns of the table 3, and the repeatability is still below 3.5 percent, which shows that the method has outstanding stability.
10. The weight average molecular weight of the poly (acrylonitrile-itaconic acid) is 1000000-1200000.
TABLE 3
Claims (7)
1. A method for detecting itaconic acid content in poly (acrylonitrile-itaconic acid) is characterized in that: the method comprises the following steps:
(1) determining oxygen content in poly (acrylonitrile-itaconic acid) standards having different itaconic acid contents using an organoelement analyzer;
(2) calculating the content of itaconic acid in the poly (acrylonitrile-itaconic acid) standard according to the molecular formula of the itaconic acid through the oxygen content;
(3) collecting the near infrared spectrum of the poly (acrylonitrile-itaconic acid) standard substance by using a near infrared spectrometer in a diffuse reflection integrating sphere mode;
the collection conditions are as follows: scanning a background and then scanning a sample, wherein the background scanning times are 64-512 times, the sample scanning times are 128-256 times, and the resolution is 4-16 cm-1Gain of 1-2X, no attenuator, and spectral scanning range of 4000cm-1～10000cm-1Each sample was collected 5 times;
(4) sequentially carrying out second-order differentiation, 5-9-point Savitzky Golay smoothing and multivariate scattering correction on the collected near infrared spectrum;
(5) using chemometric software using partial least squares at 4000cm-1～8000cm-1In the wave number range, the main factor number is 3-5, and a correlation model of the itaconic acid content and the near infrared spectrum in the poly (acrylonitrile-itaconic acid) is established;
(6) collecting the near infrared spectrum of the poly (acrylonitrile-itaconic acid) to be detected for at least 1 time by using a near infrared spectrometer according to the same conditions;
(7) substituting the near infrared spectrum of the poly (acrylonitrile-itaconic acid) to be detected into the correlation model, wherein the correlation model can quickly calculate the content of itaconic acid in the poly (acrylonitrile-itaconic acid) to be detected;
the weight average molecular weight of the poly (acrylonitrile-itaconic acid) to be detected is 50000-1200000.
2. The method for detecting itaconic acid content in poly (acrylonitrile-itaconic acid) as claimed in claim 1, wherein: the wave number range in the step (5) adopts 5200cm-1～5800cm-1Adding 6700cm-1～7400cm-1Plus 4200cm-1～4600cm-1Wave number range.
3. Root of herbaceous plantThe method for detecting itaconic acid content in poly (acrylonitrile-itaconic acid) as defined in claim 1, wherein: in the step (3), the scanning times of the background are 256-512 times, and the scanning times of the sample are 256 times; resolution of 8cm-1(ii) a The gain is 1X.
4. The method for detecting itaconic acid content in poly (acrylonitrile-itaconic acid) as claimed in claim 1, wherein: and (4) adopting 7 points for Savitzky Golay smoothing in the step (4).
5. The method for detecting itaconic acid content in poly (acrylonitrile-itaconic acid) as claimed in claim 1, wherein: and 4 is adopted as the number of the main factors in the step (5).
6. The method for detecting itaconic acid content in poly (acrylonitrile-itaconic acid) as claimed in claim 1, wherein: the poly (acrylonitrile-itaconic acid) has a weight average molecular weight of 1000000-1200000.
7. The method for detecting itaconic acid content in poly (acrylonitrile-itaconic acid) as claimed in claim 1, wherein: the oxygen content range of the poly (acrylonitrile-itaconic acid) standard products with different itaconic acid contents in the step (1) is 0.68-11.10%.
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