CN110865047A - Method for detecting molecular weight of acrylonitrile-itaconic acid copolymer precursor - Google Patents
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- 239000002243 precursor Substances 0.000 title claims abstract description 69
- 229920001577 copolymer Polymers 0.000 title claims abstract description 66
- 238000000034 method Methods 0.000 title claims abstract description 44
- 238000002329 infrared spectrum Methods 0.000 claims abstract description 40
- 238000009499 grossing Methods 0.000 claims description 8
- 230000004069 differentiation Effects 0.000 claims description 6
- 230000009466 transformation Effects 0.000 claims description 6
- 229910000530 Gallium indium arsenide Inorganic materials 0.000 claims description 5
- 229910001634 calcium fluoride Inorganic materials 0.000 claims description 5
- 238000001228 spectrum Methods 0.000 claims description 4
- 229920000049 Carbon (fiber) Polymers 0.000 abstract description 10
- 239000004917 carbon fiber Substances 0.000 abstract description 10
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 abstract description 10
- 238000001514 detection method Methods 0.000 abstract description 5
- 238000004458 analytical method Methods 0.000 abstract description 3
- 239000003153 chemical reaction reagent Substances 0.000 abstract description 3
- 238000005227 gel permeation chromatography Methods 0.000 description 8
- 238000005259 measurement Methods 0.000 description 8
- 230000000694 effects Effects 0.000 description 3
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- 238000012360 testing method Methods 0.000 description 3
- 238000012795 verification Methods 0.000 description 3
- 239000002904 solvent Substances 0.000 description 2
- 241000208125 Nicotiana Species 0.000 description 1
- 235000002637 Nicotiana tabacum Nutrition 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
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- 238000010586 diagram Methods 0.000 description 1
- 238000003912 environmental pollution Methods 0.000 description 1
- 235000013305 food Nutrition 0.000 description 1
- 235000019198 oils Nutrition 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 238000009987 spinning Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
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- G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
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Abstract
The invention belongs to the field of carbon fiber precursor detection, and particularly relates to a method for detecting the molecular weight of an acrylonitrile-itaconic acid copolymer precursor, which comprises the steps of collecting the near infrared spectrum of the acrylonitrile-itaconic acid copolymer precursor with known molecular weight under a specific condition, carrying out specific treatment on the collected near infrared spectrum, establishing a correlation model of the molecular weight of the acrylonitrile-itaconic acid copolymer precursor and the near infrared spectrum under specific parameters by using chemometrics software and adopting a partial least square method, collecting the near infrared spectrum of the acrylonitrile-itaconic acid copolymer precursor to be detected under the same condition, substituting the near infrared spectrum of the acrylonitrile-itaconic acid copolymer precursor to be detected into the correlation model, and rapidly calculating the molecular weight of the acrylonitrile-itaconic acid copolymer precursor to be detected by the correlation model, the method does not need any chemical reagent to pretreat the sample, and is environment-friendly, efficient, high in sample analysis speed, free of sample damage and good in repeatability.
Description
Technical Field
The invention belongs to the field of carbon fiber precursor detection, and particularly relates to a method for detecting the molecular weight of an acrylonitrile-itaconic acid copolymer precursor.
Background
Carbon fiber has a series of excellent characteristics of high specific modulus, high specific strength, high temperature resistance, fatigue resistance, corrosion resistance, creep resistance, electric conduction, heat transfer and the like, and is widely applied to the fields of aviation, aerospace, automobiles, chemical industry, energy, traffic, buildings, electronics and the like.
Acrylonitrile-itaconic acid copolymer precursor is the most common and important precursor for producing carbon fiber, and its performance directly determines the quality of the final carbon fiber. Among the parameters affecting the precursor acrylonitrile-itaconic acid copolymer, molecular weight is one of the most important indicators. Generally, the greater the molecular weight, the higher the ultimate carbon fiber strength and modulus; however, when the molecular weight exceeds a certain range, the strength of the carbon fiber is rather reduced as the molecular weight is higher, because the viscosity of the spinning solution is higher, and fine-denier precursor is less likely to be obtained as the viscosity is higher, thereby reducing the strength of the final carbon fiber. Therefore, the method for accurately measuring the molecular weight of the acrylonitrile-itaconic acid copolymer precursor has very important significance for the preparation and the use of the precursor.
The existing method for measuring the molecular weight of the acrylonitrile-itaconic acid copolymer precursor is mainly through a permeation gel chromatography (GPC), the method needs to measure and average for multiple times to obtain a relatively ideal measurement result, the repeatability of the method is not ideal, in addition, the method needs to dissolve the acrylonitrile-itaconic acid copolymer precursor into a specific solvent, and a series of defects of long sample pretreatment time, long detection time, environmental pollution caused by the solvent, damage to the health of operators, difficulty in realizing on-line measurement and the like exist, so that the establishment of the method for measuring the molecular weight of the acrylonitrile-itaconic acid copolymer precursor, which is rapid, lossless and good in repeatability, has very important significance for promoting the progress of the carbon fiber industry.
The near infrared spectrum technology is successfully applied to a plurality of fields such as food, tobacco, oil products and the like, but the application of the near infrared spectrum technology to the determination of the molecular weight of the acrylonitrile-itaconic acid copolymer is only reported, and particularly for the acrylonitrile-itaconic acid copolymer serving as a carbon fiber precursor, because the molecular weight of the acrylonitrile-itaconic acid copolymer is usually higher (usually more than 10 ten thousand), when the molecular weight of the acrylonitrile-itaconic acid copolymer precursor with the high molecular weight is determined by the near infrared spectrum technology, the accuracy and the good repeatability can be ensured, and the problem is well recognized.
Disclosure of Invention
The invention provides a method for detecting molecular weight of an acrylonitrile-itaconic acid copolymer precursor, which aims at the blank of the prior art, and comprises the steps of collecting a near infrared spectrum of an acrylonitrile-itaconic acid copolymer precursor with a known molecular weight under a specific condition, carrying out specific treatment on the collected near infrared spectrum, establishing a correlation model of the molecular weight of the acrylonitrile-itaconic acid copolymer precursor and the near infrared spectrum under specific parameters by using chemometrics software and adopting a partial least square method, collecting the near infrared spectrum of the acrylonitrile-itaconic acid copolymer precursor to be detected under the same condition, substituting the near infrared spectrum of the acrylonitrile-itaconic acid copolymer precursor to be detected into the correlation model, rapidly calculating the molecular weight of the acrylonitrile-itaconic acid copolymer precursor to be detected by the correlation model, and carrying out pretreatment on a sample without using any chemical reagent, the method is environment-friendly and efficient, and has the advantages of high sample analysis speed, no damage to samples and good repeatability.
The specific technical scheme of the invention is as follows:
a method for detecting the molecular weight of an acrylonitrile-itaconic acid copolymer precursor comprises the following steps:
(1) using a detector with an InGaAs 26 μm and a CaF2The near infrared spectrometer of the beam splitter adopts a diffuse reflection integrating sphere mode to acquire the near infrared spectrum of the acrylonitrile-itaconic acid copolymer precursor with known molecular weight; miningThe collection conditions are as follows: scanning the background and then scanning the sample, wherein the background scanning times are 16-512 times, the sample scanning times are 8-256 times, the background scanning times are 2 times of the sample scanning times, and the resolution ratio is 2-16 cm-1Gain is 2-4X, no attenuator is used, and the spectrum scanning range is 4000cm-1～10000cm-15 times per sample of known molecular weight;
(2) sequentially carrying out first-order differentiation, 3-11-point Norris Derivativ smoothing and standard canonical transformation (SNV) on the collected near infrared spectrum to obtain a spectrogram;
(3) using chemometric software using Partial Least Squares (PLS) at 4000cm-1～9000cm-1Under the wave number range, the main factor number is 6-8, and a correlation model of the molecular weight of an acrylonitrile-itaconic acid copolymer precursor and a near infrared spectrum is established;
(4) acquiring the near infrared spectrum of the acrylonitrile-itaconic acid copolymer precursor to be detected at least once by using a near infrared spectrometer according to the same conditions;
(5) and substituting the near infrared spectrum of the precursor of the acrylonitrile-itaconic acid copolymer to be detected into the correlation model, and calculating the molecular weight of the precursor of the acrylonitrile-itaconic acid copolymer to be detected through the correlation model.
The wave number range in the step (3) is preferably 5600cm-1～6100cm-1And 5000cm-1～5400cm-1And 4000cm-1～5200cm-1A wave number range;
furthermore, the number of background scans in the step (1) is preferably 64-128, and the number of sample scans is preferably 32-64; the resolution is preferably 8cm-1(ii) a The gain is preferably 2X;
preferably, 5 points are adopted for Norris Derivativ smoothing in the step (2);
the number of the main factors in the step (3) is preferably 7;
the number of times of collection in the step (3) is at least one, but the method of taking an average value by multiple times of collection can also be adopted, and the effect is generally better at the moment.
The optimal parameters can better improve the accuracy of the detection result and are the optimal detection parameters obtained after the inventor searches for the optimal parameters for a long time.
In summary, the method obtains the correlation model, the molecular weight of the acrylonitrile-itaconic acid copolymer precursor to be detected can be rapidly calculated by using the correlation model, the sample is not required to be pretreated by using any chemical reagent, and the method is environment-friendly, high in efficiency, high in sample analysis speed, free of sample damage and good in repeatability.
Drawings
FIG. 1 is a diagram showing the collected near infrared spectrum of a precursor of acrylonitrile-itaconic acid copolymer with known molecular weight,
FIG. 2 is a spectrum obtained by first-order differentiation, 5-point Norris Derivativ smoothing and standard canonical transformation of the near infrared spectrum collected in FIG. 1;
fig. 3 shows the test effect of the method on the calibration set sample (○) and the verification set sample (+), wherein the abscissa is the actual molecular weight value, and the ordinate is the molecular weight test value of the method, which shows that the method has good test effect on both the calibration set sample and the verification set sample, the correlation coefficient is above 0.99, and the root mean square of the prediction error (RMSEC) of the calibration set and the root mean square of the prediction error (RMSEP) of the verification set are both less than 0.03.
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 the molecular weight of an acrylonitrile-itaconic acid copolymer precursor comprises the following steps:
1. using a detector with an InGaAs 26 μm and a CaF2The near infrared spectrometer of the beam splitter adopts a diffuse reflection integrating sphere mode to collect the near infrared spectrums of 8 types of acrylonitrile-itaconic acid copolymer precursors with known molecular weights; 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 32 times, and the resolution is 8cm-1Gain of 2X, no attenuator, spectral scan range of 4000cm-1～10000cm-1Each sample was collected 5 times and the resulting spectra are shown in figure 1.
2. The acquired near infrared spectrum is subjected to first order differentiation, 5-point Norris Derivativ smoothing and standard canonical transformation (SNV) in sequence, and the obtained spectrogram is shown in figure 2.
3. Using chemometric software TQ Analyst using Partial Least Squares (PLS) at 5600cm-1～6100cm-1Adding 5000cm-1～5400cm-1Adding 4000cm-1～5200cm-1In the wave number range, the main factor number is 7, a correlation model of the molecular weight of the precursor of the acrylonitrile-itaconic acid copolymer and the near infrared spectrum is established, the correlation between the real value of the molecular weight of the precursor of the acrylonitrile-itaconic acid copolymer and the predicted value of the model is shown in figure 3, the abscissa in the figure is the real value of the molecular weight of the precursor of the acrylonitrile-itaconic acid copolymer, and the ordinate is the predicted value of the model.
4. Acquiring a near infrared spectrum of an acrylonitrile-itaconic acid copolymer precursor to be detected by using a near infrared spectrometer according to the same conditions;
5. and substituting the near infrared spectrum of the precursor of the acrylonitrile-itaconic acid copolymer to be detected into the correlation model, and rapidly calculating the molecular weight of the precursor of the acrylonitrile-itaconic acid copolymer to be detected by the correlation model.
6. GPC measurement is carried out on the acrylonitrile-itaconic acid copolymer precursor to be measured, repeatability (calculated by relative standard deviation RSD of 7 times of measurement) is calculated, the comparison with the method result of the invention is shown in attached table 1, and the absolute difference value of the two methods is 0.1 multiplied by 105The relative values are below 25%, and the consistency is good; meanwhile, the repeatability of the method is below 1 percent, and the repeatability of the GPC method is above 3 percent.
TABLE 1
Example 2
A method for detecting the molecular weight of an acrylonitrile-itaconic acid copolymer precursor comprises the following steps:
1. using a detector with InGaAs 2.6 μm and CaF2The near infrared spectrometer of the beam splitter adopts a diffuse reflection integrating sphere mode to collect the near infrared spectrums of 8 types of acrylonitrile-itaconic acid copolymer precursors with known molecular weights; the collection conditions are as follows: scanning the background and then scanning the sample, wherein the background scanning times are 16, the sample scanning times are 8, and the resolution is 2cm-1Gain of 3X, no attenuator, spectral scan range of 4000cm-1-10000cm-1Each sample was collected 5 times.
2. And sequentially carrying out first-order differentiation, 11-point Norris Derivativ smoothing and standard regular transformation (SNv) on the acquired near infrared spectrum to obtain a spectrogram.
3. Using the chemometric software Unscamblebler, Partial Least Squares (PLS) at 5000cm-1-9000cm-1In the wave number range, the main factor number is 8, and a correlation model of the molecular weight of the acrylonitrile-itaconic acid copolymer precursor and the near infrared spectrum is established.
4. Acquiring a near infrared spectrum of an acrylonitrile-itaconic acid copolymer precursor to be detected by using a near infrared spectrometer according to the same conditions;
5. and substituting the near infrared spectrum of the precursor of the acrylonitrile-itaconic acid copolymer to be detected into the correlation model, and rapidly calculating the molecular weight of the precursor of the acrylonitrile-itaconic acid copolymer to be detected by the correlation model.
6. GPC measurement is carried out on the acrylonitrile-itaconic acid copolymer precursor to be measured, repeatability (calculated by relative standard deviation RSD of 7 times of measurement) is calculated, and the comparison with the method result of the invention is shown in attached table 2, and the absolute difference value of the two methods is 0.05 multiplied by 105The relative values are all below 3%, and the consistency is good; meanwhile, the repeatability of the method is below 0.7 percent, and the repeatability of the GPC method is above 3 percent.
TABLE 2
Example 3
A method for detecting the molecular weight of an acrylonitrile-itaconic acid copolymer precursor comprises the following steps:
1. using a detector with InGaAs 2.6 μm and CaF2The near infrared spectrometer of the beam splitter adopts a diffuse reflection integrating sphere mode to collect the near infrared spectrums of 8 types of acrylonitrile-itaconic acid copolymer precursors with known molecular weights; 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 16cm-1Gain of 4X, no attenuator, spectral scan range of 4000cm-1-10000cm-1Each sample was collected 5 times.
2. And sequentially carrying out first-order differentiation, 3-point Norris Derivativ smoothing and standard regular transformation (sNV) on the acquired near infrared spectrum to obtain a spectrogram.
3. Using the chemometric software Unscamblebler, Partial Least Squares (PLS) at 5600cm-1-6100cm-1Adding 5000cm-1-5400cm-1Adding 4000cm-1-5200cm-1In the wave number range, the main factor number is 6, and a correlation model of the molecular weight of the acrylonitrile-itaconic acid copolymer precursor and the near infrared spectrum is established.
4. Acquiring a near infrared spectrum of an acrylonitrile-itaconic acid copolymer precursor to be detected by using a near infrared spectrometer according to the same conditions;
5. and substituting the near infrared spectrum of the precursor of the acrylonitrile-itaconic acid copolymer to be detected into the correlation model, and rapidly calculating the molecular weight of the precursor of the acrylonitrile-itaconic acid copolymer to be detected by the correlation model.
6. GPC measurement is carried out on the acrylonitrile-itaconic acid copolymer precursor to be measured, repeatability (calculated by relative standard deviation RSD of 7 times of measurement) is calculated, and the comparison with the method result of the invention is shown in attached table 3, and the absolute difference value of the two methods is 0.2 multiplied by 105The relative values are all below 3%, and the consistency is good; meanwhile, the repeatability of the method is below 1.5 percent,the GPC method is more than 4.5 percent, and the method has outstanding repeatability and high accuracy.
TABLE 3
Claims (5)
1. A method for detecting the molecular weight of an acrylonitrile-itaconic acid copolymer precursor is characterized by comprising the following steps: the method comprises the following steps:
(1) using a detector with InGaAs 2.6 μm and CaF2The near infrared spectrometer of the beam splitter adopts a diffuse reflection integrating sphere mode to acquire the near infrared spectrum of the acrylonitrile-itaconic acid copolymer precursor with known molecular weight; the collection conditions are as follows: scanning the background and then scanning the sample, wherein the background scanning times are 16-512 times, the sample scanning times are 8-256 times, the background scanning times are 2 times of the sample scanning times, and the resolution ratio is 2-16 cm-1Gain is 2-4X, no attenuator is used, and the spectrum scanning range is 4000cm-1～10000cm-15 times per sample of known molecular weight;
(2) sequentially carrying out first-order differentiation, 3-11 point Norris Derivativ smoothing and standard regular transformation on the collected near infrared spectrum to obtain a spectrogram;
(3) using chemometric software using partial least squares at 4000cm-1～9000cm-1Under the wave number range, the main factor number is 6-8, and a correlation model of the molecular weight of an acrylonitrile-itaconic acid copolymer precursor and a near infrared spectrum is established;
(4) acquiring the near infrared spectrum of the acrylonitrile-itaconic acid copolymer precursor to be detected at least once by using a near infrared spectrometer according to the same conditions;
(5) and substituting the near infrared spectrum of the precursor of the acrylonitrile-itaconic acid copolymer to be detected into the correlation model, and calculating the molecular weight of the precursor of the acrylonitrile-itaconic acid copolymer to be detected through the correlation model.
2. The method for detecting the molecular weight of the precursor of the acrylonitrile-itaconic acid copolymer as claimed in claim 1, wherein:
the wave number range in the step (3) is 5600cm-1～6100cm-1And 5000cm-1～5400cm-1And 4000cm-1～5200cm-1Wave number range.
3. The method for detecting the molecular weight of the precursor of the acrylonitrile-itaconic acid copolymer as claimed in claim 1, wherein: in the step (1), the number of background scanning times is 64-128, and the number of sample scanning times is 32-64; resolution of 8cm-1(ii) a The gain is 2X.
4. The method for detecting the molecular weight of the precursor of the acrylonitrile-itaconic acid copolymer as claimed in claim 1, wherein: and 5 points are adopted for Norris Derivativ smoothing in the step (2).
5. The method for detecting the molecular weight of the precursor of the acrylonitrile-itaconic acid copolymer as claimed in claim 1, wherein: and (3) adopting 7 as the number of the main factors.
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