Rapid analysis method of high-density polyethylene structure

Abstract

The invention relates to the field of organic matter structure characterization, in particular to a rapid analysis method of a high-density polyethylene structure. Compared with a known quantitative 13C NMR spectrum with high accuracy, the method provided by the invention has the following three advantages: (1) by utilizing the method provided by the invention and a corrected branching rate calculation formula, the branching rate content test accuracy of the high-density polyethylene is equivalent to that of a quantitative carbon spectrum; (2) under the condition of the same sample concentration, the quantitative accuracy is ensured, the experimental time is greatly saved, and certain guiding significance is provided for quality monitoring in the production process and new product development; (3) the damage to instruments caused by high temperature and the demand on nitrogen consumption can be greatly reduced, and the economic value is higher; and (4) the requirements on the solubility of the sample and the sensitivity of nuclear magnetic hardware are greatly reduced, so that the method can be more widely applied to samples with poorer solubility, and the range of detection characterization objects is greatly expanded.

Description

Technical Field

[0001] The invention relates to the field of organic matter structure characterization, in particular to a rapid analysis method for high-density polyethylene structure. Background Art

[0002] High-density polyethylene (HDPE) is an important class of polymer materials, widely used in the manufacture of bottles, barrels, fuel tanks and other containers. It is characterized by a density range of 0.945 to 0.965 / cm 3 , showing very low levels of short chain branches (SCB < 1%). It is mainly prepared by copolymerization of ethylene with butene or hexene, or by isomerization reaction during ethylene polymerization. These branches form structural defects during the crystallization process, thus affecting the crystallization rate, final crystallinity, other physical properties and bulk mechanical properties. Therefore, its branching type and branching rate must be paid attention to.

[0003] At present, people mainly use high temperature quantitative 13 C NMR spectroscopy is used for such characterization and quantitative analysis. 13 CNMR spectroscopy is a method of detecting 13 One-dimensional NMR technology for C nuclei. By suppressing the NOE gain of various carbon nuclei and adjusting the sampling time interval, the signal integral area in the carbon spectrum is proportional to the number of carbons corresponding to the signal, thereby achieving a quantitative effect. 13 In C NMR spectrum, D1 (Delay) is the time to wait for the nucleus to recover equilibrium before each scan sampling. NS (number of scans) is the number of scans. SW is the spectrum width. o1p is the central chemical shift. INEPT (Insensitive Nuclei Enhanced by Polarization Transfer) is the insensitive nuclear polarization transfer technology. DEPT (Distortionless Enhancement by Polarization Transfer) is the distortionless enhancement by polarization transfer. Quantitative 13 The principle of CNMR spectroscopy is that the signal intensity and phase are different according to the different deflection angles of the hydrogen magnetization vector. When the deflection angle is 135 degrees, methyl and methine are positive peaks, methylene is a negative peak, and carbon without hydrogen does not produce a signal, so it is often used to determine the type of carbon atoms.

[0004] But quantitative 13 There are some problems with C NMR spectroscopy: (1) Detection of nuclei 13 The natural abundance of C is only 1.1%, and the sensitivity is only 1 H is about 1 / 5700, compared to 1 H NMR, 13C NMR experiments require much more sample volume and significantly increase the number of sampling times and sampling time to obtain spectra with a relatively high signal-to-noise ratio; (2) Some 13 The relaxation time of C nuclei is relatively long, and it takes a long time (about 40 seconds or more) to wait for them to recover equilibrium before each scan, which means that the same number of sampling times requires more experimental time; (3) The branching rate of HDPE is extremely low, which further increases the difficulty of scanning peaks. For example, in a report, using 500 megahertz to characterize 0.03% of branches in low-density polyethylene requires an average of more than 28 hours of experimental time and more than 2 million scans; it can be seen that the experimental time required to characterize high-density polyethylene is very long and difficult.

[0005] To solve these problems, DEPT (Distortionless Enhancement by Polarization Transfer) and INEPT technologies have attracted attention. They mainly use highly sensitive hydrogen nuclei ( 1 H) for carbon nucleus ( 13 C) energy transfer to achieve cross-polarization transfer enhancement of insensitive nuclei. It has the advantages of high sensitivity and signal enhancement, but the various signal enhancements are uneven and the enhancement degree is uncertain. It cannot be directly used for quantitative analysis. DEPT and INEPT technologies are now mainly used to identify carbon atom types. In 2017, Dow Chemical Company obtained the optimal recombination time of 2-ethylhexyl acrylate and the proportional relationship between the enhancement of various carbon signals by comparing the theoretical standard curves and experimental real curves of DEPT and INEPT, and then used it to calculate the branching rate of low-density polyethylene. Its implementation scheme is as follows: (1) Select small molecule 2-ethylhexyl acrylate for modeling, and obtain the curve of its recombination time and the enhancement degree of various carbon signals. (2) Select a suitable recombination time and calculate the signal enhancement degree at the recombination time. (3) Under similar conditions, the carbon spectrum of ethylene / 1-octene copolymer was tested, and it was found that the nuclear magnetic spectrometer equipped with a 10 mm ordinary probe could obtain a spectrum with a flat baseline, saving about 50 times the experimental time. Dow Chemical confirmed that the developed QA-INEPT is a method suitable for characterizing the structure of linear low-density polyethylene (ethylene / 1-octene copolymer). However, this method of Dow has the following disadvantages: (1) They have not been used to characterize high-density polyethylene and have not characterized polymers with extremely low branching rates; (2) The branching rates of the characterized polyolefin samples are narrow (8.8-12.7 mol%), and the characterization range is limited; (3) Although the cryogenic probe can further improve the signal-to-noise ratio and sensitivity of the spectrum and save experimental time, the spectrum obtained by the cryogenic probe has serious phase distortion; (4) It is not applicable to 5 mm probes, has low accuracy, and has a quantitative error rate of more than 20%. Currently, more than 95% of the nuclear magnetic resonance spectrometers in China are equipped with ordinary 5 mm probes, and these instruments cannot be used for quantitative characterization using this method.

[0006] It can be seen that high temperature quantitative 13 C is the most common method to characterize the branching rate of high-density polyethylene, but due to 13 The intrinsic low natural abundance and low magnetogyroscopic ratio of C nuclei are quantitatively 13 C NMR technology has the disadvantages of low sensitivity and long experimental time. At present, there are no reports of other NMR methods for characterizing the branching rate of high-density polyethylene, only some reports of other NMR methods for characterizing the branching rate of low-density polyethylene, and these other NMR methods for characterizing the branching rate of low-density polyethylene also have problems.

[0007] In addition, although the above problems can be solved by significantly improving the hardware conditions of nuclear magnetic resonance instruments, such as changing from 400MHZ instruments to 800 or 900MHZ instruments and using more sensitive probes, it will cost 10 times or even dozens of times more, and the cost will be greatly increased. Currently, there are very few users in the world who own such instruments, and they are not widely applicable. Therefore, it is particularly important for the polyolefin industry to develop a time-saving and fast method to characterize the degree of branching of HDPE using carbon cores as the detection object. Summary of the invention

[0008] In view of this, the technical problem to be solved by the present invention is to provide a rapid analysis method for the structure of high-density polyethylene. The method provided by the present invention is based on existing instruments and equipment with a high retention rate, and can save time and quickly characterize the monomer content and branching rate of high-density polyethylene, and provide accurate characterization results.

[0009] The present invention provides a rapid analysis method for high-density polyethylene structure, comprising the following steps:

[0010] S1) obtaining an INEPT spectrum of the pretreated high-density polyethylene and defining an integral interval, then attributing and integrating the peaks of the INEPT spectrum according to the integral interval, and obtaining a monomer content formula and a branching rate formula of the high-density polyethylene according to the integral interval;

[0011] When the high-density polyethylene contains only one type of branched chain, the integral interval is:

[0012] A: δ38.5~41.5ppm;

[0013] B: δ33.8~34.8ppm;

[0014] C: δ29.5~31.0ppm;

[0015] D: δ26.2~27.3ppm;

[0016] E: δ24.2~24.6ppm;

[0017] F: δ10.5~11.7ppm;

[0018] When the high-density polyethylene contains two or more branched chains, the integral interval is:

[0019] G: δ23.3~23.5ppm;

[0020] H: δ26.6~26.8ppm;

[0021] I: δ29.4~29.6ppm;

[0022] J: δ29.9~30.1ppm;

[0023] K: δ30.4~30.6ppm;

[0024] L: δ34.0~34.1ppm;

[0025] M: δ34.2~34.3ppm;

[0026] N: δ39.6~39.8ppm;

[0027] S2) correcting the monomer content formula according to the result of the attribution in step S1) to obtain a monomer content correction formula, and obtaining the monomer content of the high-density polyethylene according to the monomer content correction formula and the result of the integration in step S1);

[0028] The branching rate formula is corrected according to the result of the attribution in step S1) to obtain a branching rate correction formula, and the branching rate of the high-density polyethylene is obtained according to the branching rate correction formula and the result of the integration in step S1).

[0029] Step S1) of the present invention needs to obtain the INEPT spectrum of the pretreated high-density polyethylene. The pretreated high-density polyethylene is obtained from the high-density polyethylene, a paramagnetic agent and deuterated tetrachloroethane, specifically, 5 to 30 mg of high-density polyethylene is weighed and added to a 5 mm or 10 mm nuclear magnetic tube, and then 0.5 to 20 mg of paramagnetic agent and 0.3 to 3.0 mL of deuterated tetrachloroethane are added, and heated to fully dissolve to obtain a homogeneous polymer solution of the pretreated high-density polyethylene.

[0030] The sampling parameters for obtaining the INEPT spectrum of the present invention include: d1 = 1 ~ 10s, cnst2 = 100 ~ 200Hz, cnst8 = 100 ~ 150Hz, and these three sampling parameters are more important for the test accuracy of the method of the present invention. Further, the sampling parameters for obtaining the INEPT spectrum include: d1 = 1 ~ 10s, cnst2 = 100 ~ 200Hz, cnst8 = 100 ~ 150Hz, td = 16 ~ 64k, ns = 128 ~ 5000, ds = 4 ~ 16, sw = 50 ~ 250ppm, d3 = 0.0005 ~ 0.0015s, O1P = 10 ~ 40ppm. Preferably, d1=1-5s, cnst2=100-150Hz, cnst8=120-130Hz, td=32-64k, ns=500-2000, ds=15-16, sw=100-150ppm, d3=0.0008-0.0013s, O1P=25-35ppm. The experimental temperature for obtaining the INEPT spectrum of the present invention is 80-150°C, and the experimental time is 0.3-5h. The present invention obtains a nuclear magnetic carbon spectrum with a clear gain and high signal-to-noise by optimizing the parameters of the INEPT spectrum (d1, cnst8, etc.), and defines the interval for calculation according to the representative carbon atom chemical shift. After obtaining the INEPT spectrum, the present invention also includes baseline calibration and phase calibration of the INEPT spectrum. The peak position and baseline of the spectrum are corrected so that all signals can be accurately integrated later.

[0031] The step S1) of the present invention also requires defining the integral interval, specifically defining the integral interval according to the atomic arrangement structure in the polymer chain. When the high-density polyethylene contains only one type of branch chain, the integral interval of the present invention is:

[0032] A: δ38.5~41.5ppm;

[0033] B: δ33.8~34.8ppm;

[0034] C: δ29.5~31.0ppm;

[0035] D: δ26.2~27.3ppm;

[0036] E: δ24.2~24.6ppm;

[0037] F: δ10.5~11.7ppm;

[0038] When the high-density polyethylene contains two or more branched chains, the integral interval of the present invention is:

[0039] G: δ23.3~23.5ppm;

[0040] H: δ26.6~26.8ppm;

[0041] I: δ29.4~29.6ppm;

[0042] J: δ29.9~30.1ppm;

[0043] K: δ30.4~30.6ppm;

[0044] L: δ34.0~34.1ppm;

[0045] M: δ34.2~34.3ppm;

[0046] N: δ39.6~39.8ppm;

[0047] Preferably, the defining of the integral interval is performed under the assumption that:

[0048] Assumption 1: The weight average molecular weight of the high-density polyethylene is less than 1 million, that is, the polymer molecular weight is required to be moderate and not ultra-high density polyethylene;

[0049] Assumption 2: When the molecular weight of the polymer is small, there will be terminal end groups. If the high-density polyethylene has terminal end groups, the terminal end groups are not included in the calculation;

[0050] Assumption 3: The signal-to-noise ratio of the INEPT spectrum is high enough, specifically, the signal-to-noise ratio of the INEPT spectrum is greater than 400, and the signal-to-noise ratio of the smallest signal is greater than 10;

[0051] Assumption 4: The branch content of the high-density polyethylene is less than 1%, and there is no sequence of continuous branched chains.

[0052] Due to different gain levels, different types of carbon atoms need to be calibrated for integration. The present invention attributes the peaks of the obtained INEPT spectrum according to the integration interval to obtain an attribution result, and integrates to obtain an integration result.

[0053] The present invention obtains a monomer content formula of high-density polyethylene and a branching rate formula of high-density polyethylene according to the integral interval. The obtained monomer content formula of high-density polyethylene and the branching rate formula of high-density polyethylene are formulas before correction, as shown in formula a, formula b and formula c:

[0054] Mole fraction of butene:

[0055] B mol%={(I B -I A ) / (I B -I A +0.5I C +0.25ID -0.75I F )}×100%formula a;

[0056] Mole fraction of ethylene:

[0057] E mol% = 100% - B mol% formula b;

[0058] Branching rate of high density polyethylene:

[0059] C bb ={(5I B -5I A ) / (I B -I A +0.5I C +0.25I D -0.75I F )}×1000‰ formula c;

[0060] Wherein, B mol% represents the molar content of butene monomer in the high-density polyethylene, E mol% represents the molar content of ethylene monomer in the high-density polyethylene, and C bb represents the branching rate of the high-density polyethylene.

[0061] The present invention also needs to appropriately correct specific types of carbon core signals according to the attribution of different signals in the INEPT spectrum, that is, according to the result of the attribution described in step S1), the monomer content formula is corrected to obtain a monomer content correction formula, and according to the result of the attribution described in step S1), the branching rate formula is corrected to obtain a branching rate correction formula. Specifically, the monomer content formula is corrected by multiplying the calibration factor by comparing the experimental results of high-temperature quantitative carbon spectrum, and the branching rate formula is corrected by multiplying the calibration factor by comparing the experimental results of high-temperature quantitative carbon spectrum, so that it is suitable for the integral calculation of the INEPT spectrum, and the original sequence structure distribution formula for different types of high-density polyethylene carbon spectra is optimized to obtain the monomer content correction formula and the branching rate correction formula described in the present invention. In the present invention, the derivation of the formula for sequence distribution and the selection of the correction factor are extremely important for the calculation of the structure and branching rate of high-density polyethylene.

[0062] After obtaining the monomer content correction formula, the present invention obtains the monomer content of the high-density polyethylene according to the monomer content correction formula and the result of the integration in step S1). Specifically, when the high-density polyethylene contains only one type of branch chain, the monomer content calculation formula of the high-density polyethylene includes:

[0063] B mol%={(I B -1.30I A ) / (I B –1.30I A+0.5I C +0.25I E -0.75I F )}×100%Formula 1;

[0065] E mol% = 100% - B mol% Formula 2;

[0066] When the high-density polyethylene contains two or more branched chains, the monomer content calculation formula of the high-density polyethylene includes:

[0067] B mol% = {(0.333I H +0.167I L +0.443I N ) / (0.333I H +0.167I L +0.443I N +

[0068] 0.5I G +0.5I M +0.5I J +0.5I K -0.5I I )}×100%Formula 3;

[0069] H mol%={(0.5I G +0.5I M )} / (0.333I H +0.167I L +0.443I N +0.5I G +0.5

[0070] I M +0.5I J +0.5I K -0.5I I}×100%Formula 4;

[0071] E mol%=100%-B mol%-H mol% Formula 5;

[0072] Wherein, B mol% represents the molar content of butene monomer in the high-density polyethylene, H mol% represents the molar content of 1-hexene monomer in the high-density polyethylene, E mol% represents the molar content of ethylene monomer in the high-density polyethylene, and I A ,I B ,I C ,I E ,I F ,I G ,I H ,II ,I J ,I K ,I L ,I M and I N They represent the integrated areas of the spectral peaks in the integration intervals A, B, C, E, F, G, H, I, J, K, L, M and N respectively.

[0073] After obtaining the branching rate correction formula, the present invention obtains the branching rate of the high-density polyethylene according to the branching rate correction formula and the result of the integration in step S1). Specifically, when the high-density polyethylene contains only one type of branch chain, the branching rate calculation formula of the high-density polyethylene includes:

[0074] C bb ={(5I B –6.5I A ) / (I B –1.30I A +0.5 I C +0.25 I D -0.75 I E )}×1000‰Formula 6;

[0075] When the high-density polyethylene contains two or more branch chains, the branching rate calculation formula of the high-density polyethylene includes:

[0076] C bb ={(3.33I H +1.67I L +4.43I N +5I G +5I M ) / (0.666I H +0.333I L +0.886I N

[0077] +I G +I M +I J +I K -I I )}×1000%Formula 7;

[0078] Among them, C bb represents the branching rate of the high-density polyethylene, I A ,I B ,I C ,I D ,I E ,I G ,I H ,I I ,I J ,IK ,I L ,I M and I N They represent the integrated areas of the spectral peaks in the integration intervals A, B, C, D, E, G, H, I, J, K, L, M and N respectively.

[0079] The present invention provides a method for rapid analysis of the structure of high-density polyethylene. The method for rapid analysis of the structure of high-density polyethylene provided by the present invention is a carbon nuclear magnetic quantitative method, which is consistent with the recognized high accuracy quantitative 13 Compared with C NMR spectra, the present invention has the following three advantages: (1) Using the method of the present invention and the corrected branching rate calculation formula, the branching rate content test accuracy of high-density polyethylene is equivalent to that of quantitative carbon spectrum; (2) Under the same sample concentration conditions, while ensuring quantitative accuracy, the experimental time is greatly saved, which has certain guiding significance for production process quality monitoring and new product development; (3) The invention can greatly reduce the damage to the instrument caused by high temperature and the demand for nitrogen consumption, and has high economic value; (4) The requirements for sample solubility and sensitivity of nuclear magnetic hardware are greatly reduced, which can be more widely applied to samples with poor solubility, and the scope of detection and characterization objects is greatly expanded. BRIEF DESCRIPTION OF THE DRAWINGS

[0080] Figure 1 This is a graph showing the INEPT spectrum of high-density polyethylene of Example 1 of the present invention;

[0081] Figure 2 The second figure is the INEPT spectrum of the high-density polyethylene of Example 1 of the present invention;

[0082] Figure 3 Three figures are the INEPT spectra of high-density polyethylene of Example 1 of the present invention;

[0083] Figure 4 The conventional quantitative high-density polyethylene used for comparison in Example 1 of the present invention 13 C NMR spectra;

[0084] Figure 5 This is the INEPT spectrum of the high-density polyethylene of Example 2 of the present invention. DETAILED DESCRIPTION

[0085] The present invention discloses a method for rapid analysis of high-density polyethylene structure. Those skilled in the art can refer to the content of this article and appropriately improve the process parameters to achieve it. It is particularly important to point out that all similar substitutions and modifications are obvious to those skilled in the art, and they are all considered to be included in the present invention. The method and application of the present invention have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the method and application of this article without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention.

[0086] The process of the present invention includes: (1) sample preparation; (2) optimization of INEPT spectrum sampling and data processing parameters; (3) obtaining the branching rate formula of the sample and calculating the branching rate; (4) quantitative limit, detection limit, precision, repeatability, and stability experiments. The calculation formula of the branching rate will vary depending on the type of branched chains in the sample, and will be given separately in the examples.

[0087] The present invention will be further described below in conjunction with embodiments:

[0088] Example 1

[0089] Measuring the degree of branching of high-density polyethylene represented by ethylene / butene copolymer:

[0090] (1) Weigh 40 mg of high-density polyethylene (HDPE), represented by ethylene / butene copolymer, and add it to a 5 mm NMR tube. Then, add 10 mg of chromium acetylacetonate, inject 0.6 mL of deuterated o-dichlorobenzene, and heat to fully dissolve into a homogeneous polymer solution.

[0091] (2) Optimization of spectrum sampling and data processing parameters

[0092] (2.1) The INEPT spectrum of a certain HDPE (S1) was collected on a 400MHz instrument equipped with a common 5mm BBFO probe. The sampling parameters are as follows: td = 32k, ns = 2000, ds = 16, sw = 130ppm, d1 = 2s, cnst2 = 125Hz, d3 = 0.001 seconds, O1P = 30ppm, cnst8 = 125Hz, temperature 110 degrees, and experimental time 2.0 hours. After the sampling is completed, the spectrum is baseline calibrated and phase calibrated using the NMR spectrum analysis software to obtain the INEPT spectrum, such as Figure 1 As shown, Figure 1 This is a graph of the INEPT spectrum of the high-density polyethylene of Example 1 of the present invention.

[0093] (2.2) The INEPT spectrum of HDPE was collected on a 400 MHz instrument equipped with a common 5 mm BBFO probe, with sampling parameters d1 = 5 s and an experimental time of 3.5 hours. The spectrum was baseline calibrated and phase calibrated using NMR spectrum analysis software, such as Figure 2 As shown, Figure 2 This is the second figure of the INEPT spectrum of the high-density polyethylene of Example 1 of the present invention.

[0094] (2.3) The INEPT spectrum of HDPE was collected on a 500 MHz instrument equipped with a 5 mm prodigy cryogenic probe. The sampling parameters were as follows: td = 32 k, ns = 512, ds = 16, sw = 130 ppm, d1 = 2 s, cnst2 = 125 Hz, d3 = 0.001 sec, O1P = 30 ppm, cnst8 = 125 Hz, experimental temperature 110 °C, and experimental time 0.5 h. The spectrum was baseline calibrated and phase calibrated using NMR spectrum analysis software, such as Figure 3 As shown, Figure 3 These are three graphs showing the INEPT spectra of the high-density polyethylene of Example 1 of the present invention.

[0095] (2.4) Traditional quantitative analysis of HDPE using an instrument equipped with a 5 mm BBOF probe 13 C NMR spectrum. The acquisition parameters are as follows: d1 = 14s, cnst2 = 100Hz, td = 32k, ns = 5000, ds = 10, sw = 130ppm, O1P = 30ppm, and the experimental time is 24 hours. The spectrum is baseline calibrated and phase calibrated using the NMR spectrum analysis software, such as Figure 4 As shown, Figure 4 The conventional quantitative high-density polyethylene used for comparison in Example 1 of the present invention 13 C NMR spectrum.

[0096] (2.5) According to the traditional quantitative collection of HDPE 13 C NMR spectrum, the difference is that the test time is changed to 4 hours.

[0097] (3) Obtaining the branching rate formula and branching rate of the sample, specifically, firstly attributing the carbon spectrum signal and integrating the spectrum peak, then correcting the sequence formula, proposing the branching rate formula, and obtaining the branching rate, more specifically as follows:

[0098] (3.1) Define the integration interval based on the atomic arrangement structure in the polymer chain.

[0099] The integration interval is defined based on the following four assumptions:

[0100] Assumption 1: The polymer has a moderate molecular weight, is not ultra-high polyethylene, and has a weight-average molecular weight of less than 1 million;

[0101] Assumption 2: When the molecular weight of the polymer is small, there will be terminal end groups, which are not involved in the calculation;

[0102] Assumption 3: The signal-to-noise ratio of the spectrum is high enough;

[0103] Hypothesis 4: The branch content of high-density polyethylene is less than 1%, and there is no sequence of continuous branched chains.

[0104] The integration interval is defined as follows:

[0105] A: δ38.5~41.5ppm;

[0106] B: δ33.8~34.8ppm;

[0107] C: δ29.5~31.0ppm;

[0108] D: δ26.2~27.3ppm;

[0109] E: δ24.2~24.6ppm;

[0110] F: δ10.5~11.7ppm;

[0111] Based on the above assumptions and the defined integral interval, the formula is derived as follows:

[0112] Mole fraction of butene:

[0113] B mol%={(I B -I A ) / (I B -I A +0.5I C +0.25I D -0.75I F )}×100%Formula (I);

[0114] Mole fraction of ethylene:

[0115] E mol%=100%-B mol% Formula (II);

[0116] Branching rate of high density polyethylene:

[0117] C bb ={(5I B -5I A ) / (I B -I A +0.5I C +0.25I D -0.75I F )}×1000‰ formula

[0118] (III);

[0119] For HDPE containing only one branch chain, the molar fraction of ethylene is as shown in formula (II). According to the structural attribution of the spectrum peak and the peak characteristics of the INEPT spectrum in the present invention, the formula for calculating the molar content and branching rate of the branch chain using the INEPT spectrum is as follows:

[0120] Mole fraction of butene:

[0121] B mol%={(I B -1.30I A ) / (I B –1.30I A +0.5I C +0.25I E -0.75I F )}×100%

[0122] Formula (IV);

[0123] Branching rate of high density polyethylene:

[0124] C bb ={(5I B –6.5I A ) / (I B –1.30I A +0.5I C +0.25I D -0.75I E )}×1000‰

[0125] Formula (V);

[0126] (3.2) According to the above corrected formulas (IV) to (V), calculate Figure 1 to Figure 3 The molar content of butene in the sample and the branching rate of the sample are shown in the spectrum, and compared with the traditional quantitative carbon spectrum of the sample ( Figure 4 ) are compared with the calculation results of the previous study, and the specific values ​​are listed in Table 1.

[0127] Table 1

[0128]

[0129] As can be seen from the data in Table 1, using INEPT as the experimental method, using the modified and corrected branching rate formula, and comparing the results of the traditional quantitative carbon spectrum, the test results obtained are very different, and the experimental errors are all within an acceptable range, indicating that the present invention can achieve accurate determination of the structure of ethylene-butene copolymer high-density polyethylene. From the comparison of experimental time, it is obvious that the experimental time can be greatly saved and the characterization efficiency can be improved. Since the characterization of polyolefins is carried out under high-temperature experimental conditions, high-purity nitrogen protection is required, and there is a large loss to the probe. Therefore, saving experimental time essentially saves experimental costs.

[0130] (4) Limit of quantification, limit of detection, precision, repeatability and stability experiments.

[0131] (4.1) According to the carbon nuclear magnetic spectrum, the detection limit (LOD) is taken as the concentration when the signal-to-noise ratio S / N = 3, and the quantification limit (LOQ) is taken as the concentration when the signal-to-noise ratio S / N = 10. The standard solution of HDPE was used for the experiment, and the results showed that the LOD of this method was 2.50 mg / mL and the LOQ was 8.50 mg / mL.

[0132] (4.2) Take the same sample solution and perform INEPT spectrum test according to step (2.1) for 6 times. According to formula (V), the RSD of precision is 0.95%, indicating that the precision of this method is good.

[0133] (4.3) Six sample solutions were prepared in parallel and tested for INEPT spectrum according to step (2.1). The RSD of repeatability was calculated according to formula (V) and was 2.38%, indicating that the method had good repeatability.

[0134] (4.4) Take a HDPE sample solution and perform INEPT spectrum test at 0, 2, 4, 8, 24, 48 and 72 hours according to step (2.1). According to formula (V), the RSD of the measurement results at each time point is 0.98%, indicating that the method has good stability.

[0135] Example 2

[0136] Measuring the degree of branching of high density polyethylene represented by ethylene / butene / 1-hexene copolymer:

[0137] (1) Weigh 40 mg of high-density polyethylene (HDPE) (S2) represented by ethylene / butene / 1-hexene copolymer, add it to a 5 mm NMR tube, add an appropriate amount of paramagnetic reagent, inject 0.6 mL of deuterated o-dichlorobenzene, and heat to fully dissolve it into a homogeneous polymer solution.

[0138] (2) Optimization of spectrum sampling and data processing parameters

[0139] (2.1) NMR test was performed according to step (2.1) of Example 1, except that the experimental time was changed to 3.5 hours, and each sample was measured 3 times. The typical spectrum is shown in Figure 5 , Figure 5 This is the INEPT spectrum of the high-density polyethylene of Example 2 of the present invention.

[0140] (2.2) Perform NMR testing according to step (2.1) of Example 1, except that the probe is changed to 500 MHz, the experimental time is changed to 1.0 hour, and each sample is tested 3 times.

[0141] (2.3) Collect the traditional quantitative HDPE according to step (2.4) of Example 1 13 C NMR spectrum. The spectrum was baseline calibrated and phase calibrated using NMR spectrum analysis software.

[0142] (3) defining the integral interval according to the four assumptions of Example 1;

[0143] The integration interval is:

[0144] G: δ23.3~23.5ppm;

[0145] H: δ26.6~26.8ppm;

[0146] I: δ29.4~29.6ppm;

[0147] J: δ29.9~30.1ppm;

[0148] K: δ30.4~30.6ppm;

[0149] L: δ34.0~34.1ppm;

[0150] M: δ34.2~34.3ppm;

[0151] N: δ39.6~39.8ppm;

[0152] For HDPE containing two or more branches, the corresponding monomer content and branching rate calculation formulas can be obtained according to the corresponding attribution and spectrum correction, as shown in formulas (VI), (VII), (VIII) and (IX):

[0153] Mole fraction of butene:

[0154] B mol% = {(0.333I H +0.167I L +0.443I N ) / (0.333I H +0.167I L +0.443I N+

[0155] 0.5I G +0.5I M +0.5I J +0.5I K -0.5I I )}×100%Formula (VI);

[0156] Mole fraction of 1-hexene:

[0157] H mol%={(0.5I G +0.5I M )} / (0.333I H +0.167I L +0.443I N +0.5I G +0.5

[0158] I M +0.5I J +0.5I K -0.5I I}×100%Formula (VII);

[0159] Mole fraction of ethylene:

[0160] E mol%=100%-B mol%-H mol% formula (VIII);

[0161] Branching rate of high density polyethylene:

[0162] C bb ={(3.33I H +1.67I L +4.43I N +5I G +5I M ) / (0.666I H +0.333I L +0.886I N

[0163] +I G +I M +I J +I K -I I )}×1000%Formula (IX);

[0164] The integrated areas of the peaks of the spectra obtained in (2.1) and (2.2) of Example 2 of the present invention are also substituted into formulas (VI) to (IX) to calculate the component content and branching rate of the high-density polyethylene HDPE (S2), and compared with the calculation results of the traditional quantitative carbon spectrum of the sample, as shown in Table 2.

[0165] Table 2

[0166]

[0167] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A rapid analysis method for high-density polyethylene structure, characterized in that: The following steps are involved: S1) obtaining an INEPT spectrum of the pretreated high-density polyethylene and defining an integral interval, then attributing and integrating the peaks of the INEPT spectrum according to the integral interval, and obtaining a monomer content formula and a branching rate formula of the high-density polyethylene according to the integral interval; When the high-density polyethylene contains only one type of branched chain, the integral interval is: A: δ38.5~41.5ppm; B: δ33.8~34.8ppm; C: δ29.5~31.0ppm; D: δ26.2~27.3ppm; E: δ24.2~24.6ppm; F: δ10.5~11.7ppm; When the high-density polyethylene contains two or more branched chains, the integral interval is: G: δ23.3~23.5ppm; H: δ26.6~26.8ppm; I: δ29.4~29.6ppm; J: δ29.9~30.1ppm; K: δ30.4~30.6ppm; L: δ34.0~34.1ppm; M: δ34.2~34.3ppm; N: δ39.6~39.8ppm; S2) correcting the monomer content formula according to the result of the attribution in step S1) to obtain a monomer content correction formula, and obtaining the monomer content of the high-density polyethylene according to the monomer content correction formula and the result of the integration in step S1); The branching rate formula is corrected according to the result of the attribution in step S1) to obtain a branching rate correction formula, and the branching rate of the high-density polyethylene is obtained according to the branching rate correction formula and the result of the integration in step S1).

2. The method according to claim 1, characterized in that In step S1), the pretreated high-density polyethylene is obtained from the high-density polyethylene, a paramagnetic agent and deuterated tetrachloroethane.

3. The method according to claim 1, characterized in that In step S1), the sampling parameters of the INEPT spectrogram include: d1=1~10s, cnst2=100~200Hz, cnst8=100~150Hz.

4. The method according to claim 3, characterized in that In step S1), the sampling parameters of the INEPT spectrogram also include: td=16~64k, ns=128~5000, ds=4~16, sw=50~250ppm, d3=0.0005~0.0015s, O1P=10~40ppm.

5. The method according to claim 3, characterized in that: In step S1), the sampling parameters of the INEPT spectrogram also include: The experimental temperature is 80-150°C and the experimental time is 0.3-5h.

6. The rapid analysis method of high-density polyethylene structure according to claim 1, characterized in that: In step S1), after obtaining the INEPT spectrum, the method further includes performing baseline calibration and phase calibration on the INEPT spectrum.

7. The method according to claim 1, characterized in that In step S1), the definition of the integral interval is performed under the assumption that: Assumption 1: The weight average molecular weight of the high-density polyethylene is less than 1 million; Assumption 2: If the high-density polyethylene has terminal groups, the terminal groups are not included in the calculation; Assumption 3: The signal-to-noise ratio of the INEPT spectrum is greater than 400; Assumption 4: The branch content of the high-density polyethylene is less than 1%, and there is no sequence of continuous branched chains.

8. The method according to claim 1, characterized in that In step S2), the monomer content formula is corrected according to the result of the attribution: The monomer content formula is corrected by comparing the high temperature quantitative carbon spectrum experimental results and multiplying by a calibration factor; The branching rate formula corrected according to the attribution result is specifically: The branching rate formula was corrected by multiplying the calibration factor by comparing the high temperature quantitative carbon spectrum experimental results.

9. The method according to any one of claims 1 to 8, characterized in that: In step S2), when the high-density polyethylene contains only one type of branched chain, the monomer content calculation formula of the high-density polyethylene is include: B mol% = { ( I B - 1.30I A ) / ( I B – 1.30I A + 0.5I C + 0.25I E - 0.75I F )} × 100% Formula 1; E mol% = 100% - B mol% Formula 2; When the high-density polyethylene contains two or more branched chains, the monomer content calculation formula of the high-density polyethylene includes: B mol%={(0.333I H +0.167I L +0.443I N ) / (0.333I H +0.167I L +0.443I N + 0.5I G +0.5I M +0.5I J +0.5I K -0.5I I )}×100% Equation 3; H mol%={(0.5I G +0.5I M )} / (0.333I H +0.167I L +0.443I N +0.5I G +0.5 I M +0.5I J +0.5I K -0.5I I }×100% formula 4; E mol% = 100% - B mol% - H mol% Formula 5; Wherein, B mol% represents the molar content of butene monomer in the high-density polyethylene, H mol% represents the molar content of 1-hexene monomer in the high-density polyethylene, E mol% represents the molar content of ethylene monomer in the high-density polyethylene, and I A ,I B ,I C ,I E ,I F ,I G ,I H ,I I ,I J ,I K ,I L ,I M and I N They represent the integrated areas of the spectral peaks in the integration intervals A, B, C, E, F, G, H, I, J, K, L, M and N respectively.

10. The method according to any one of claims 1 to 8, characterized in that: In step S2), when the high-density polyethylene contains only one type of branch chain, the branching rate calculation formula of the high-density polyethylene includes: C bb = { (5I B – 6.5I A ) / (I B – 1.30I A + 0.5 I C + 0.25 I D - 0.75 I E )}×1000 ‰ Formula 6; When the high-density polyethylene contains two or more branch chains, the branching rate calculation formula of the high-density polyethylene includes: C bb = {(3.33I H + 1.67I L + 4.43I N + 5I G + 5I M ) / (0.666I H + 0.333I L + 0.886I N + I G + I M + I J + I K - I I )} × 1000% Equation 7; Among them, C bb represents the branching rate of the high-density polyethylene, I A ,I B ,I C ,I D ,I E ,I G ,I H ,I I ,I J ,I K ,I L ,I M and I N They represent the integrated areas of the spectral peaks in the integration intervals A, B, C, D, E, G, H, I, J, K, L, M and N respectively.

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