A method for quickly determining the double bond content in polyethylene materials

Abstract

The present invention provides a method for quickly determining the double bond content in a polyethylene material, comprising the following steps: S1. Tabletting: grinding a dry alkali metal halide, and using a tabletting machine to form a thin sheet; S2. Dissolving: heating and dissolving the polyethylene material in an organic solvent to obtain a polyethylene solution; S3. Sample preparation: placing the thin sheet in a pressing tank, dripping the polyethylene solution on the thin sheet, and pressing with a metal block to obtain a sample intermediate; S4. Testing: drying the obtained sample intermediate, and testing it using a Fourier infrared spectrometer; S5. Calculation: analyzing the double bond content according to the absorption peak area in the test result. The present invention is different from the conventional sample preparation process, improves the accuracy of testing the double bond content in the polyethylene material using a Fourier infrared spectrometer, effectively avoids the occurrence of the cold analysis problem, can prepare multiple groups of samples at one time, and improves the test efficiency; at the same time, the determination method provided by the present invention has wide applicability, low requirements for instruments and equipment, and convenient and simple testing.

Description

Technical Field

[0001] The invention belongs to the field of testing technology, and in particular relates to a method for quickly determining the double bond content in a polyethylene material. Background Art

[0002] Polyethylene is a typical thermoplastic plastic. Its molecules are long-chain linear structures or branched structures. It is a typical crystalline polymer. It is an odorless, tasteless, non-toxic combustible white powder. It is widely used in industry, agriculture, medicine, construction, chemical industry, national defense and other fields. In different application fields, the choice of polyethylene materials is different. The difference in the selection is based on the difference in the performance of different polyethylenes. The key factor that determines the difference in the performance of polyethylene is the difference in the molecular chain structure of polyethylene.

[0003] In the field of hot melt adhesive bonding, it involves grafting modification of polyethylene materials, grafting maleic anhydride on polyethylene. The grafting process generally uses peroxide to initiate double bond free radical reaction. The double bond content of polyethylene in this process is particularly important. Similarly, there are similar problems in the field of cross-linked polyethylene cables. Whether using peroxide or irradiation, the extent to which the free radical reaction can proceed is related to the double bond content of the polyethylene material. In the field of packaging films, because the weather resistance of double bonds is worse than that of saturated alkane chains, the double bond content will directly affect the service life of the film during use. However, in polyethylene materials, the double bond content generally accounts for only one thousandth of the total amount of polyethylene or even less, and the analysis and characterization is extremely difficult.

[0004] Patent application number 201110078741.8 relates to a method for measuring the unsaturation of viscous solid substances using an infrared instrument, which includes placing a certain amount of at least one viscous solid substance in multiple through holes of a porous sample plate, and then pressing the sample plate in a tablet press to obtain a sample, and placing the sample plate carrying multiple samples on a special sample holder for infrared measurement on an infrared spectrometer. According to the obtained spectrum, the unsaturation of the viscous solid substance to be measured can be directly obtained by comparing it with the standard curve obtained from the standard sample with known saturation. However, this invention is more suitable for the determination of unsaturation in rubber polymers, and is not suitable for the determination of double bond content in polyethylene materials.

[0005] At present, the mainstream method for determining the double bond content in polyethylene materials is mainly through high temperature nuclear magnetic resonance 13 C, but because 13The C-NMR spectrum has high requirements for sample concentration, and the solubility of some polyethylene materials is relatively low, which makes the test process cumbersome and requires high requirements for nuclear magnetic resonance equipment. Therefore, the present application aims to provide a method for quickly determining the double bond content in polyethylene materials, which uses Fourier transform infrared spectroscopy to accurately and efficiently determine the double bond content in polyethylene materials after special treatment in the early stage. Summary of the invention

[0006] In view of the existing technical problems, the purpose of the present invention is to provide a method for quickly determining the double bond content in polyethylene materials. Different from the conventional sample preparation process, the present invention improves the accuracy of testing the double bond content in polyethylene materials using a Fourier infrared spectrometer, effectively avoids the problem of cold precipitation of samples during transfer or testing, and can prepare multiple groups of samples at one time, thereby improving the test efficiency; at the same time, the determination method provided by the present invention has wide applicability, low requirements for instruments and equipment, and convenient and simple testing, and is particularly suitable for universal application in the manufacturing industry.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] The present invention provides a method for quickly determining the double bond content in a polyethylene material, the method comprising the following steps:

[0009] S1. Tabletting: Grind the dried alkali metal halide into powder, put it into a tableting mold, and use a tablet press to press the tablets while evacuating the vacuum to make thin sheets;

[0010] S2. Dissolving: heating the polyethylene material and dissolving it in an organic solvent to obtain a polyethylene solution;

[0011] S3. Sample preparation: Place the sheet into a pressure tank, drop the polyethylene solution onto the sheet, pressurize it with a metal block to obtain a sample intermediate;

[0012] S4. Testing: The prepared sample intermediate is dried and tested using a Fourier transform infrared spectrometer;

[0013] S5. Calculation: Analyze the content of different types of carbon-carbon double bonds based on the absorption peak area in the test results.

[0014] The reaction mechanism and effects of the present invention are as follows:

[0015] 1. The entire sample preparation and testing process of the present invention is relatively innovative. In the prior art, the test methods used by Fourier infrared spectrometers for samples in different physical states mainly include attenuated total reflection method, liquid smearing method, tableting method, and melt-formed film transmission method. However, although the attenuated total reflection method can be used to judge the double bonds of some polyethylene materials, when the double bond content in the polyethylene material is low, the attenuated total reflection method cannot identify the low response peak; the liquid smearing method is also not applicable. The polyethylene material is solid. If the liquid smearing method is required, a solvent needs to be used for heating and dissolving, and cold precipitation is very likely to occur during the test, affecting the test results; the conventional tableting method is generally applicable to powder samples, while polyethylene samples are less in a micro-powder state, and even after being ground into powder by freezing, the thin sheets formed after grinding and tableting with potassium bromide have poor light transmittance and cannot obtain an ideal spectrum; the conventional melt-formed film transmission method is also not applicable to polyethylene samples with extremely low melt index or micro-crosslinking, and it is difficult to prepare a film that meets the test thickness requirements. The present invention is different from the conventional sample preparation process, improves the accuracy of testing the double bond content in polyethylene materials using a Fourier transform infrared spectrometer, and effectively avoids the cold precipitation problem of samples during transfer or testing. Multiple groups of samples can be prepared at one time, thereby improving test efficiency.

[0016] 2. The test method of the present invention has wide applicability, and is applicable to all materials except a small amount of polyethylene materials with too high average molecular weight. At the same time, the requirements for instruments and equipment are low, the test is convenient and simple, and it is particularly suitable for universal application in the manufacturing industry.

[0017] 3. The present invention controls the ratio of polyethylene material to organic solvent, so that the dissolution rate of the polyethylene material is better, the solubility is better, the test efficiency is improved, and the test accuracy is improved.

[0018] 4. The present invention controls the thickness of the blank sheet and the amount of polyethylene solution added so that the thickness of the final sheet is appropriate, thereby avoiding the problem that the instrument cannot recognize the amount of solution added is too small, and also solves the problem of poor light transmittance that may be caused, so that the instrument can accurately identify the double bonds in the polyethylene material.

[0019] 5. The present invention effectively improves the flatness of the sheet and the light transmittance by controlling the depth of the groove and the pressure applied during the groove pressing, thereby making the test results more accurate.

[0020] In some embodiments, the polyethylene material has an average molecular weight of less than 500,000.

[0021] Preferably, the average molecular weight of the polyethylene material is 100,000-400,000.

[0022] In some embodiments, the alkali metal halide in step S1 is potassium bromide, and the thickness of the sheet is 0.3-0.6 mm.

[0023] Preferably, the thickness of the sheet is 0.4-0.5 mm.

[0024] In some embodiments, the heating temperature in step S2 is 85-200°C.

[0025] Preferably, the heating temperature in step S2 is 115-145°C.

[0026] In some embodiments, the organic solvent in step S2 is one or two of benzene, toluene, xylene and decahydronaphthalene.

[0027] Preferably, the organic solvent in step S2 is toluene or xylene.

[0028] In some embodiments, the content ratio of the polyethylene material to the organic solvent in step S2 is (0.1-0.2) g: (4-5) ml.

[0029] In some embodiments, the amount of the polyethylene solution added dropwise in step S3 is 0.05-0.125 ml.

[0030] Preferably, the amount of the polyethylene solution added dropwise in step S3 is 0.075-0.1 ml.

[0031] In some embodiments, the groove depth in step S3 is 0.35-0.7 mm, and the applied pressure is 5-15N.

[0032] Preferably, the groove depth in step S3 is 0.45-0.6 mm, and the applied pressure is 6-12N.

[0033] In some embodiments, the drying time in step S4 is 0.5-10 hours, and the drying temperature is 90-205°C.

[0034] Preferably, the drying time in step S4 is 1-2.5 hours, and the drying temperature is 120-145°C.

[0035] In some embodiments, the method of testing using Fourier transform infrared spectrometer in step S4 is a transmission method.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] (1) The present invention is different from the conventional sample preparation process, improves the accuracy of testing the double bond content in polyethylene materials using a Fourier transform infrared spectrometer, and effectively avoids the problem of cold precipitation of samples during transfer or testing. Multiple groups of samples can be prepared at one time, thereby improving test efficiency.

[0038] (2) The testing method of the present invention has wide applicability, low requirements for instruments and equipment, and is convenient and simple to test, and is particularly suitable for universal application in the manufacturing industry.

[0039] (3) The present invention improves the dissolution rate and solubility of the polyethylene material and the light transmittance of the sheet by regulating the ratio of the polyethylene material to the organic solvent, the appropriate thickness of the sheet, the depth of the groove and the pressure applied during the groove pressing, thereby improving the test efficiency and the accuracy of the test. DETAILED DESCRIPTION

[0040] The present invention will be described below in conjunction with specific embodiments. It should be noted that the following embodiments are examples of the present invention and are only used to illustrate the present invention, rather than to limit the present invention. Other combinations and various modifications within the concept of the present invention may be performed without departing from the spirit or scope of the present invention.

[0041] According to the steps of the following embodiments and comparative examples, testing and calculation were performed using a Fourier transform infrared spectrometer.

[0042] The detection parameters of the Fourier transform infrared spectrometer (Thermo Fisher, IS-5) in the following examples are: (1) Spectral range: 4000-500 cm -1 ; (2) Resolution: 4.0cm -1 ; (3) Number of scans: 16 times; (4) Beam splitter: KBr; (5) Detector: DTGS detector; (6) Light source: infrared light source.

[0043] The polyethylene material is provided by REHAU Polymer (Suzhou) Co., Ltd., and the sample model is PE-SL188.

[0044] Example 1

[0045] A method for quickly determining the double bond content in a polyethylene material comprises the following steps:

[0046] S1 tableting: Take dried potassium bromide into an agate mortar and grind it into powder, put the powder into a tableting mold, and use a tablet press to press while evacuating the vacuum to form a circular sheet with a thickness of 0.4mm and a diameter of 12mm;

[0047] S2 dissolution: 0.18g of polyethylene material was heated and dissolved in 4.5ml of toluene to obtain a polyethylene solution;

[0048] S3. Sample preparation: A 0.4 mm thin sheet was placed in a groove, the groove depth was adjusted to 0.6 mm, 0.08 ml of polyethylene solution was dripped onto the sheet, and a pressure of 10 N was applied to it with a smooth metal block to obtain a sample intermediate;

[0049] S4. Testing: Dry the prepared sample intermediate at 120°C for 1.5h to remove toluene, and use a Fourier transform infrared spectrometer to perform a transmission test on the treated sample. During the measurement, first perform a blank scan of the air, then align the sample to be tested with the test area and perform an infrared spectrum scan. The infrared spectrum of the sample is the spectrum of the sample to be tested minus the air blank.

[0050] S5. Calculation: Analyze the content of different types of carbon-carbon double bonds based on the absorption peak area in the test results. Refer to the infrared spectrum curve of the known sample, perform manual baseline calibration and integration on the characteristic absorption peaks of different types of carbon-carbon double bonds and the peak area of ​​the internal standard peak in the spectrum, and obtain the content of unsaturated double bonds at different positions based on the change in peak area or peak intensity by the internal standard method.

[0051] Among them, different types of carbon-carbon double bonds include: R-CH=CH-R', R-CH=CH2, >C=CH2; the internal standard peak refers to the absorption peak of R-CH2-R'; the vibration absorption peak of R-CH=CH-R' is located at 965cm -1 The vibration absorption peak of R-CH=CH2 is located at 908cm -1 The vibration absorption peak of R-CH=CH-R' is located at 888cm -1 The vibration absorption peak of R-CH2-R' is located at 2019cm -1 .

[0052] The content of various double bonds is calculated using the Lambert-Beer law, the formula is:

[0053] A=εCL=-logI / I0

[0054] Wherein, A is the absorbance of the characteristic absorption peak of the functional group; ε is the molar absorption coefficient; C is the molar concentration of the sample, M / L; L is the thickness of the sample, cm; I0 is the incident light intensity; and I is the transmitted light coefficient.

[0055] Example 2

[0056] A method for quickly determining the double bond content in a polyethylene material comprises the following steps:

[0057] S1 tableting: Take dried potassium bromide into an agate mortar and grind it into powder, put the powder into a tableting mold, and use a tablet press to press while evacuating the vacuum to form a circular sheet with a thickness of 0.5 mm and a diameter of 12 mm;

[0058] S2 dissolution: 0.15g of polyethylene material was heated and dissolved in 4ml of decahydronaphthalene to obtain a polyethylene solution;

[0059] S3. Sample preparation: A 0.5 mm thin sheet was placed in a groove, the groove depth was adjusted to 0.65 mm, 0.08 ml of polyethylene solution was dripped onto the sheet, and a pressure of 10 N was applied to it with a smooth metal block to obtain a sample intermediate;

[0060] S4. Testing: Dry the prepared sample intermediate at 205°C for 10 hours to remove decahydronaphthalene, and perform a transmission test on the treated sample using a Fourier transform infrared spectrometer. During the measurement, first perform a blank scan of the air, then align the sample to be tested with the test area, and perform an infrared spectrum scan. The infrared spectrum of the sample is the spectrum of the sample to be tested minus the air blank;

[0061] S5. Calculation: The specific implementation method is the same as Example 1.

[0062] Example 3

[0063] A method for quickly determining the double bond content in a polyethylene material comprises the following steps:

[0064] S1. Tableting: The specific implementation method is the same as in Example 1;

[0065] S2 dissolution: 0.18g of polyethylene material was heated and dissolved in 5ml of anisole to obtain a polyethylene solution;

[0066] S3. Sample preparation: The specific implementation method is the same as Example 1.

[0067] S4. Testing: The prepared sample intermediate was dried at 160°C for 5h to remove anisole, and the treated sample was tested by transmission method using a Fourier transform infrared spectrometer. During the measurement, a blank scan of air was first performed, and then the sample to be tested was aligned with the test area and an infrared spectrum scan was performed. The infrared spectrum of the sample was the spectrum of the sample to be tested minus the air blank;

[0068] S5. Calculation: The specific implementation method is the same as Example 1.

[0069] Example 4

[0070] A method for quickly determining the double bond content in a polyethylene material, the specific implementation method is the same as that of Example 1, except that step S3. Sample preparation: a 0.4 mm thin sheet is placed in a pressing groove, the pressing groove depth is adjusted to 0.7 mm, 0.2 ml of polyethylene solution is dripped on the thin sheet, and a metal block with a smooth surface is used to apply a pressure of 12 N to obtain a sample intermediate.

[0071] Example 5

[0072] A method for quickly determining the double bond content in a polyethylene material, the specific implementation method is the same as that of Example 1, except that step S3. Sample preparation: 0.08 ml of polyethylene solution is dripped onto a thin sheet to obtain a sample intermediate.

[0073] Comparative Example 1

[0074] A method for quickly determining the double bond content in a polyethylene material comprises the following steps:

[0075] S1. Sample preparation: The polyethylene material was ground into powder by freezing, and dried potassium bromide and 0.18 g of polyethylene material were put into an agate mortar and ground into powder. The powder was placed in a tableting mold and pressed with a tablet press while vacuuming to form a circular sheet with a thickness of 0.5 mm and a diameter of 12 mm;

[0076] S2. Testing: The prepared sheet is tested by a Fourier infrared spectrometer. During the measurement, a blank scan of air is first performed, and then the sample to be tested is aligned with the test area and an infrared spectrum scan is performed. The infrared spectrum of the sample is the spectrum of the sample to be tested minus the air blank;

[0077] S3. Calculation: The specific implementation method is the same as Example 1.

[0078] Comparative Example 2

[0079] A method for quickly determining the double bond content in a polyethylene material comprises the following steps:

[0080] S1. Dissolution: 0.18 g of polyethylene material was heated and dissolved in 4.5 ml of toluene to obtain a polyethylene solution;

[0081] S2. Sample preparation: Apply 0.08 ml of polyethylene solution on a sodium chloride wafer and evenly apply it to obtain a sample to be tested;

[0082] S3. Testing: The sample to be tested is tested using a Fourier infrared spectrometer. During the measurement, a blank scan of the air is first performed, and then the sample to be tested is aligned with the test area and an infrared spectrum scan is performed. The infrared spectrum of the sample is the spectrum of the sample to be tested minus the air blank;

[0083] S4. Calculation: The specific implementation method is the same as Example 1.

[0084] Effect evaluation:

[0085] According to the above Examples 1-5 and Comparative Examples 1-2, samples were prepared according to different steps, tested using a Fourier transform infrared spectrometer, and the double bond content was calculated. The specific results are shown in Table 1.

[0086] Table 1 Content of different double bonds in polyethylene materials

[0087]

[0088] It can be seen from the results in Table 1 that the test results of Examples 1-2 of the present invention are relatively accurate (close to the results provided by the polyethylene material supplier), while the accuracy of the double bond tests of Examples 3-5 and Comparative Examples 1-2 is relatively poor.

[0089] In Example 3, anisole is used to dissolve the polyethylene material, which results in poor solubility of the polyethylene material, thereby causing the test result to be low.

[0090] In Example 4, the amount of polyethylene solution dripped onto the sheet is 0.2 ml. Excessive polyethylene solution makes the sheet too thick, affecting the transmittance, and thus the tested content of double bonds is low.

[0091] In Example 5, no pressure treatment was performed after the dropwise addition. Since the polyethylene solution had a high viscosity, the surface flatness of the obtained sheet was poor, which in turn affected the light transmittance and reduced the tested content of double bonds.

[0092] Comparative Example 1 uses the traditional tabletting method to prepare samples and measure the double bond content in the polyethylene material. Due to the poor light transmittance of the prepared thin film, the infrared spectrum data is poor, and the vibration absorption peaks at different double bonds are significantly reduced.

[0093] In Comparative Example 2, the polyethylene material was heated and dissolved and then evenly applied on a sodium chloride wafer to determine the double bond content. However, a small amount of polyethylene material was precipitated during the application process, affecting the test result, resulting in a low result.

[0094] The above is only a preferred embodiment of the present invention and does not constitute any form of limitation to the present application. Although the present application is disclosed as above in the preferred embodiment, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution.

Claims

1. A method for quickly determining the double bond content in polyethylene material, characterized in that: The following steps are involved: S1. Tabletting: Take the dried alkali metal halide and grind it into a tableting mold, and use a tablet press to press while evacuating the vacuum to make a thin sheet; S2. Dissolving: heating the polyethylene material and dissolving it in an organic solvent to obtain a polyethylene solution; S3. Sample preparation: Place the sheet into a pressure tank, drop the polyethylene solution onto the sheet, pressurize it with a metal block to obtain a sample intermediate; S4. Testing: The prepared sample intermediate is dried and tested using a Fourier transform infrared spectrometer; S5. Calculation: Analyze the content of different types of carbon-carbon double bonds based on the absorption peak area in the test results; The average molecular weight of the polyethylene material is less than 500,000; The heating temperature in step S2 is 85-200° C.; the organic solvent in step S2 is one or two of benzene, toluene, xylene and decahydronaphthalene; In the step S2, the content ratio of the polyethylene material to the organic solvent is (0.1-0.2) g: (4-5) ml; The amount of the polyethylene solution added dropwise in step S3 is 0.05-0.125 ml; The groove depth in step S3 is 0.35-0.7 mm, and the applied pressure is 5-15 N; The different types of carbon-carbon double bonds tested in step S5 include: R-CH=CH-R', R-CH=CH2, >C=CH2; the internal standard peak refers to the absorption peak of R-CH2-R'; the vibration absorption peak of R-CH=CH-R' is located at 965cm -1 The vibration absorption peak of R-CH=CH2 is located at 908cm -1 The vibration absorption peak of R-CH=CH-R' is located at 888cm -1 The vibration absorption peak of R-CH2-R' is located at 2019cm -1 .

2. The method for quickly determining the double bond content in a polyethylene material according to claim 1, characterized in that: The alkali metal halide in step S1 is potassium bromide, and the thickness of the sheet is 0.3-0.6 mm.

3. The method for quickly determining the double bond content in a polyethylene material according to claim 1, characterized in that: The drying time in step S4 is 0.5-10 h, and the drying temperature is 90-205°C.

4. The method for rapidly determining the double bond content in a polyethylene material according to claim 1, characterized in that: The method of testing in step S4 using Fourier transform infrared spectrometer is transmission method.

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