Qualitative and quantitative method for antioxidant in polyolefin plastic

Abstract

The invention relates to the field of separation and detection methods for additives in high-molecular polymers, and provides a qualitative and quantitative method for antioxidants in polyolefin plastics, which comprises the following steps: S1, preparation of an extraction agent: mixing tetrahydrofuran and methanol to prepare the extraction agent; s2, extracting an antioxidant, namely pressing polyolefin plastic into slices, crushing, adding an extracting agent, stirring, adding a microwave accelerant, carrying out microwave extraction, and collecting an extracting solution; s3, qualitative analysis: adding tetrahydrofuran into the extract liquor for constant volume, filtering, carrying out gas chromatography-mass spectrometry to obtain a mass spectrum, and determining the type of the antioxidant; and S4, quantitative analysis: preparing a standard solution of the antioxidant, determining by using gas chromatography-mass spectrometry, and comparing a working curve with a standard curve to obtain the content of the antioxidant in the polyolefin plastic. The qualitative and quantitative method for the antioxidant in the polyolefin plastic, provided by the invention, has the characteristics of simplicity in operation, safety, economy, high efficiency and high accuracy of a test result.

Description

Technical Field

[0001] The invention relates to the field of separation and detection methods for additives in high molecular polymers, and in particular to a qualitative and quantitative method for antioxidants in polyolefin plastics. Background Art

[0002] Polyolefin plastics are sensitive to oxygen during manufacturing, processing, storage and application. Oxygen can penetrate into plastic films and react with most polymers, causing degradation or cross-linking of the materials. The role of plastic antioxidants is to capture active free radicals, generate inactive free radicals, or decompose polymer hydroperoxides produced during the oxidation process to terminate the chain reaction, thereby delaying the oxidation process of the polymer.

[0003] In addition, during the processing of polyolefin materials, such as polypropylene, the processing temperature is high. If antioxidants are not added, thermal degradation will occur, resulting in an increase in the melt index. Antioxidants can effectively prevent thermal oxidation degradation of polymer materials during long-term aging, and are also a highly efficient processing stabilizer. The use of antioxidants can significantly improve the light stability of products, prevent discoloration caused by light and heat, improve processing stability, and obtain polymer products with better performance. Therefore, adding antioxidants can effectively protect polyolefin plastics, extend their service life, and maintain their performance and quality.

[0004] As the market share competition of plastic products becomes increasingly fierce, the requirements for product quality become more stringent, and the content of antioxidants in polyolefins will directly affect the antioxidant properties of the products. At the same time, in the development of new products and special materials, it is also necessary to analyze the types of antioxidants in foreign samples and determine their content. However, there is currently no relevant standard detection method to regulate the qualitative and quantitative methods of antioxidants in polyolefin plastics. The amount of antioxidant added to polyolefin products is relatively low, and a large amount of organic solvents are required to effectively separate them from the matrix material to prevent interference from the matrix material. The process is complicated and requires the consumption of more organic solvents. From the perspective of safety, economy and environmental protection, there is room for improvement.

[0005] Patent CN 108120787B discloses a qualitative and quantitative method for antioxidants in polyolefins, comprising the following steps: taking a sample to be tested, pressing it into thin slices, and crushing it; adding an organic solvent and stirring and dissolving it at 60-90°C for 3-8 hours; adjusting the system temperature to 60-70°C, adding a substitution reagent and a catalyst under stirring to react for 2-5 hours, cooling to 25°C, filtering, adjusting the pH value of the filtrate, and separating an organic phase; concentrating and fixing the separated organic phase, and quantitatively analyzing it. This method has a good separation effect for antioxidants in polyolefins, and the test results are accurate. However, this method requires 3-8 hours for organic solvent dissolution, and 2-5 hours for adding a substitution reagent and a catalyst to react, which is time-consuming and energy-intensive. In addition, the extraction step requires the addition of a substitution reagent and a catalyst, and the operation process is relatively complicated.

[0006] Therefore, there is an urgent need in the market for a method for qualitative and quantitative analysis of antioxidants in polyolefin plastics that is simple to operate, safe, economical, efficient, and has high test result accuracy. Summary of the invention

[0007] In view of the problems existing in the prior art, the present invention develops a method for qualitative and quantitative analysis of antioxidants in polyolefin plastics. The antioxidants are extracted from polyolefins by microwave extraction, and the antioxidants in the polyolefin materials are accurately qualitatively and quantitatively analyzed by gas chromatography-mass spectrometry. A microwave accelerator is designed and added during the microwave extraction process. The method has the advantages of simple operation, safety, economy, high efficiency and high accuracy of test results.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0009] The present invention provides a method for qualitative and quantitative determination of antioxidants in polyolefin plastics, comprising the following steps:

[0010] S1. Preparation of extractant: tetrahydrofuran and methanol are mixed and stirred to obtain an extractant for standby use;

[0011] S2, extraction of antioxidant: press the polyolefin plastic into thin slices, crush it, add the extractant of step S1, stir for 1-2h, add microwave accelerator, perform microwave extraction, and collect the extract for later use;

[0012] S3, qualitative analysis: add tetrahydrofuran to the extract of step S2 to make up the volume to obtain a test solution, filter it, and perform gas chromatography-mass spectrometry to obtain a mass spectrum to determine the type of antioxidant;

[0013] S4, quantitative analysis: prepare a standard solution of antioxidant, measure it by gas chromatography-mass spectrometry, and make a standard curve of antioxidant. After comparing the working curve obtained by the test solution in step S3 with the standard curve, the content of antioxidant in polyolefin plastic is obtained.

[0014] In some embodiments of the present invention, the volume ratio of tetrahydrofuran to methanol in step S1 is 1:(9-11).

[0015] Preferably, the volume ratio of tetrahydrofuran to methanol in step S1 is 1:10.

[0016] In some embodiments of the present invention, the ratio of the polyolefin plastic to the extractant in step S2 is 1 g: (8-12) ml.

[0017] Preferably, in step S2, the ratio of the polyolefin plastic to the extractant is 1 g:10 ml.

[0018] In some embodiments of the present invention, the mass ratio of the polyolefin plastic to the microwave accelerator in step S2 is 1:(0.1-0.3).

[0019] Preferably, in step S2, the mass ratio of the polyolefin plastic to the microwave accelerator is 1:0.2.

[0020] In some embodiments of the present invention, the method for preparing the microwave accelerator in step S2 comprises the following steps:

[0021] (1) Propanol and glycerol are mixed, stirred, and ferric nitrate nonahydrate and cobalt acetate are added, stirred, and placed in a reaction kettle, and allowed to stand at 170-190° C. for 9-11 hours under vacuum, cooled to room temperature, centrifuged, washed, dried, and calcined to obtain cobalt ferrite for use;

[0022] (2) Add the modified carbon nanotubes, polyphenylene vinylene and KH570 to anhydrous ethanol, perform ultrasound treatment, add the cobalt ferrite of step (1), stir, stir at 170-190° C. for 5-7 h, cool to room temperature, centrifuge, and freeze-dry to obtain a microwave accelerator.

[0023] In some embodiments of the present invention, in step (1), the mass ratio of ferric nitrate nonahydrate to cobalt acetate is 1:(0.2-0.4).

[0024] Preferably, in step (1), the mass ratio of ferric nitrate nonahydrate to cobalt acetate is 1:0.33.

[0025] In some embodiments of the present invention, in step (2), the mass ratio of cobalt ferrite, modified carbon nanotubes and polyphenylene vinylene is 1:(0.1-0.15):(0.1-0.15).

[0026] Preferably, in step (2), the mass ratio of cobalt ferrite, modified carbon nanotubes and polyphenylene vinylene is 1:0.125:0.125.

[0027] In some embodiments of the present invention, the method for preparing modified carbon nanotubes in step (2) comprises the following steps:

[0028] 1) Mix ferric nitrate nonahydrate and ammonium molybdate tetrahydrate, stir to obtain a liquid for use, mix vermiculite and deionized water, sonicate, soak at 95-105° C. for 5.5-6.5 hours, add the liquid while stirring, soak at 95-105° C. for 11-13 hours, filter, dry, and calcine to obtain a catalyst for use;

[0029] 2) placing the catalyst and melamine in step 1) in a reaction vessel, introducing hydrogen at 60-80 sccm for 5-10 min, then reacting in a hydrogen atmosphere of 25-35 sccm at 700-900° C. for 20-25 min, and cooling to room temperature to obtain modified carbon nanotubes.

[0030] Wherein, in the step 1), the mass ratio of vermiculite, ferric nitrate nonahydrate and ammonium molybdate tetrahydrate is 1:(0.1-0.3):(0.02-0.03).

[0031] In some embodiments of the present invention, in step 2), the mass ratio of melamine to catalyst is 1:(0.2-0.3).

[0032] Preferably, in step 2), the mass ratio of melamine to catalyst is 1:0.25.

[0033] The present application uses microwave extraction to extract antioxidants from polyolefins, and uses gas chromatography-mass spectrometry to accurately qualitatively and quantitatively analyze the antioxidants in the polyolefin materials. The present application has the advantages of simple operation, high efficiency, solvent saving, low pollution, high extraction rate and high extraction accuracy. The applicant uses tetrahydrofuran and methanol in a specific ratio to form an extractant from the perspectives of polarity, solubility, instrument usability and usage restrictions, avoids the use of halogenated hydrocarbon reagents such as chloroform, and controls the radiation power and reaction temperature of the microwave, so that the extraction method has high safety, economy and environmental protection.

[0034] In order to further improve the extraction efficiency and effect of antioxidant extraction in polyolefins and reduce the energy consumption and cost in the extraction process, the applicant synthesized a new type of microwave promoter based on ferrite. Ferrite is widely used as a microwave promoter due to its good frequency characteristics, large magnetic permeability, small relative dielectric constant, good antioxidant properties, and environmental protection and low cost. However, monovalent ferrite has defects such as narrow absorption bandwidth and poor impedance matching, which limits its application.

[0035] On the one hand, the applicant uses ferric nitrate nonahydrate and cobalt acetate as raw materials, propanol and glycerol as a mixed solvent, and controls the reaction temperature and calcination temperature to prepare cobalt ferrite, so that the cobalt ferrite has a hollow, rough surface and open-pore morphology, and the cobalt ferrite has the characteristics of low density and large specific surface area, thereby improving the microwave absorption performance of a single ferrite; on the other hand, the applicant composites the cobalt ferrite with modified carbon nanotubes and polyphenylene vinylene. The introduction of carbon nanotubes can effectively improve the impedance ratio mismatch problem of a single ferrite. As a conductive polymer, polyphenylene vinylene can effectively improve the microwave absorption performance of a microwave accelerator. And the compounding of polyphenylene acetylene can also improve the dispersibility of carbon nanotubes to a certain extent. Furthermore, the modified carbon nanotubes provided by the applicant are based on layered compounds, and the iron / molybdenum active metals are evenly dispersed between the vermiculite layers to obtain a catalyst. Melamine is used as a carbon source and a nitrogen source, and the hydrogen introduction rate and the reaction temperature are controlled to synthesize nitrogen-doped modified carbon nanotubes. Compared with ordinary carbon nanotubes, the modified carbon nanotubes have the characteristics of uniform length and diameter and orderly arrangement, so that the carbon nanotubes have good dispersibility and increase the specific surface area of ​​the microwave accelerator, thereby improving the extraction efficiency of the antioxidant and the accuracy of the test results.

[0036] In some embodiments of the present invention, the power of the microwave extraction in step S2 is 550-650 W, the temperature is 75-95° C., and the reaction time is 18-25 min.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] (1) The present invention develops a method for qualitative and quantitative analysis of antioxidants in polyolefin plastics, which uses microwave extraction to extract antioxidants from polyolefins, and uses gas chromatography-mass spectrometry to accurately qualitatively and quantitatively analyze the antioxidants in polyolefin materials. In addition, a microwave accelerator is designed and added during the microwave extraction process. The method has the advantages of simple operation, safety, economy, high efficiency, and high accuracy of test results.

[0039] (2) The present invention synthesizes a new type of microwave accelerator based on ferrite. First, ferric nitrate nonahydrate and cobalt acetate are used as raw materials, propanol and glycerol are used as mixed solvents, and the reaction temperature and calcination temperature are controlled to prepare cobalt ferrite. The cobalt ferrite is then compounded with modified carbon nanotubes and polyphenylene vinylene to improve the microwave absorption performance of the ferrite, thereby improving the extraction efficiency and the accuracy of the test results.

[0040] (3) The present invention uses layered compounds as a substrate, evenly disperses iron / molybdenum active metals between vermiculite layers to obtain a catalyst, and uses melamine as a carbon source and a nitrogen source, controls the hydrogen introduction rate and the reaction temperature, and synthesizes nitrogen-doped modified carbon nanotubes, so that the modified carbon nanotubes have high dispersibility and a large specific surface area, thereby promoting the effect of the microwave accelerator. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0042] Figure 1-1 , Figure 1-2 and Figure 1-3 They are respectively gas chromatography-mass spectrometry spectra of the qualitative determination method of antioxidant 1135, antioxidant 1222 and antioxidant 2246 in Example 1;

[0043] Figure 2-1 , Figure 2-2 and Figure 2-3 They are gas chromatography-mass spectrometry spectra of the quantitative determination method of antioxidant 1135, antioxidant 1222 and antioxidant 2246 in Example 1 respectively. DETAILED DESCRIPTION

[0044] 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, but not 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.

[0045] In the following examples, except for the microwave accelerator and the modified carbon nanotubes, the other compound monomers and related reagents used can be purchased from the market, wherein the polyolefin plastic is linear low-density polyethylene; the CAS number of polyphenylene vinylene is 25038-69-1.

[0046] Preparation Example 1

[0047] The synthesis method of microwave accelerator A comprises the following steps:

[0048] (1) 120 ml of propanol and 28 ml of glycerol were mixed, stirred for 15 min, 3 g of ferric nitrate nonahydrate and 1 g of cobalt acetate were added, stirred for 30 min, placed in a Teflon autoclave, allowed to stand at 180° C. for 10 h under vacuum, cooled to room temperature, centrifuged, washed alternately with anhydrous ethanol and deionized water 3 times, dried at 60° C. for 24 h, and calcined at 650° C. for 2 h to obtain cobalt ferrite for use;

[0049] (2) 0.5 g of modified carbon nanotube A, 0.5 g of polyphenylene vinylene and 2 g of KH570 were added to 30 ml of anhydrous ethanol, and ultrasonicated for 30 min. 4 g of cobalt ferrite prepared in step (1) was added, and stirred for 1 h. The mixture was stirred at 180 ° C for 6 h, cooled to room temperature, centrifuged, and freeze-dried at -50 ° C for 24 h to obtain microwave accelerator A.

[0050] Preparation Example 2

[0051] The specific implementation manner of microwave accelerator B is the same as that of microwave accelerator A, except that in step (1), the mass of cobalt acetate is replaced with 0.4 g.

[0052] Preparation Example 3

[0053] The specific implementation manner of microwave accelerator C is the same as that of microwave accelerator A, except that in step (2), the mass of modified carbon nanotube A is replaced with 0.32 g.

[0054] Preparation Example 4

[0055] The specific implementation manner of microwave accelerator D is the same as that of microwave accelerator A, except that in step (2), the mass of polyphenylene vinylene is replaced with 0.32 g.

[0056] Preparation Example 5

[0057] The specific implementation manner of microwave accelerator E is the same as that of microwave accelerator A, except that in step (2), modified carbon nanotube A is replaced by modified carbon nanotube B.

[0058] Preparation Example 6

[0059] The specific implementation manner of microwave accelerator F is the same as that of microwave accelerator A, except that in step (2), the modified carbon nanotube A is replaced by carbon nanotubes.

[0060] Preparation Example 7

[0061] The synthesis method of modified carbon nanotube A comprises the following steps:

[0062] 1) 4 g of ferric nitrate nonahydrate and 0.5 g of ammonium molybdate tetrahydrate were mixed and stirred for 30 min to obtain a liquid for standby use, 20 g of vermiculite and 200 ml of deionized water were mixed, ultrasonicated for 20 min, soaked at 100° C. for 6 h, added with liquid while stirring, soaked at 100° C. for 12 h, filtered, dried at 100° C. for 12 h, and calcined at 800° C. for 2 h to obtain a catalyst for standby use;

[0063] 2) 5 g of the catalyst prepared in step 1) and 20 g of melamine were placed in a reaction vessel, hydrogen was introduced at 70 sccm from the melamine side for 10 min, and then the reaction was carried out in a hydrogen atmosphere of 30 sccm and 800°C for 25 min, and then cooled to room temperature to obtain modified carbon nanotubes A.

[0064] Preparation Example 8

[0065] The specific implementation method of modified carbon nanotube B is the same as that of modified carbon nanotube A, except that in step 2), the mass of the catalyst is replaced with 3.6 g.

[0066] Example 1

[0067] A method for qualitative and quantitative determination of antioxidants in polyolefin plastics comprises the following steps:

[0068] S1. Preparation of extractant: Mix 2 ml of tetrahydrofuran and 20 ml of methanol, stir for 5 min, and obtain an extractant for standby use;

[0069] S2, extraction of antioxidants: 1g of linear low-density polyethylene containing 0.3wt% antioxidant 1135, 0.3wt% antioxidant 1222, and 0.3wt% antioxidant 2246 was pressed into thin sheets and crushed to an average particle size of 2.5mm, 10ml of the extractant of step S1 was added, stirred for 1.5h, 0.2g of microwave accelerator A was added, microwave extraction was carried out at a microwave power of 600W and 80°C for 20min, and the extract was collected for later use;

[0070] S3, qualitative analysis: tetrahydrofuran was added to the extract of step S2 to make up the volume (dilution factor 50 times) to obtain a test solution, which was filtered and subjected to gas chromatography-mass spectrometry to obtain a mass spectrum as shown in FIG1 , to determine the type of antioxidant;

[0071] S4, quantitative analysis: prepare a standard solution of antioxidant, measure it by gas chromatography-mass spectrometry, and make a standard curve of antioxidant. Compare the working curve obtained by the test solution in step S3 with the standard curve to obtain the content of antioxidant in polyolefin plastic, as shown in Figure 2.

[0072] The instrument and test parameters for gas chromatography-mass spectrometry are as follows:

[0073] The instrument is Shimadzu QP2010SE;

[0074] The chromatographic column is SH-5MS, 30m*0.25mm*0.25um;

[0075] The mobile phase was tetrahydrofuran + methanol (chromatographic grade);

[0076] Injection volume: 1 μL;

[0077] Column box temperature: 125°C;

[0078] Inlet temperature: 300°C;

[0079] Column box temperature program: start at 125°C, hold for 3 min; increase the temperature to 280°C at 15°C / min, hold for 4 min; increase the temperature to 320°C at 30°C / min, hold for 39 min;

[0080] Column flow rate: 1.2 mL / min;

[0081] Split ratio: 5:1;

[0082] Ion source temperature: 230°C;

[0083] Interface temperature: 280℃;

[0084] Solvent delay: 3min;

[0085] Scanning ion range: m / z 28-800.

[0086] Test results: The content of antioxidant 1135, the content of antioxidant 1222, and the content of antioxidant 2246 obtained by the above test method were 0.00322 g, 0.00339 g, and 0.00298 g, respectively.

[0087] Example 2

[0088] A method for qualitative and quantitative determination of antioxidants in polyolefin plastics comprises the following steps:

[0089] S1. Preparation of extractant: Mix 2 ml of tetrahydrofuran and 18 ml of methanol, stir for 5 min, and obtain an extractant for standby use;

[0090] S2, extraction of antioxidants: 1g of linear low-density polyethylene containing 0.3wt% antioxidant 1135, 0.3wt% antioxidant 1222, and 0.3wt% antioxidant 2246 was pressed into thin sheets and crushed to an average particle size of 2.5mm, 8ml of the extractant in step S1 was added, stirred for 1h, 0.1g of microwave accelerator A was added, microwave extraction was carried out at a microwave power of 550W and 75°C for 25min, and the extract was collected for later use;

[0091] S3, qualitative analysis: add tetrahydrofuran to the extract of step S2 to make up the volume (dilution factor 50 times) to obtain a test solution, filter it, and perform gas chromatography-mass spectrometry to obtain a mass spectrum to determine the type of antioxidant;

[0092] S4, quantitative analysis: prepare a standard solution of antioxidant, measure it by gas chromatography-mass spectrometry, and make a standard curve of antioxidant. Compare the working curve obtained by the test solution in step S3 with the standard curve to obtain the content of antioxidant in polyolefin plastic.

[0093] The instrument and test for gas chromatography-mass spectrometry are the same as those in Example 1.

[0094] Test results: The content of antioxidant 1135, the content of antioxidant 1222, and the content of antioxidant 2246 obtained by the above test method were 0.00320 g, 0.00337 g, and 0.00295 g, respectively.

[0095] Example 3

[0096] A method for qualitative and quantitative determination of antioxidants in polyolefin plastics comprises the following steps:

[0097] S1. Preparation of extractant: Mix 2 ml of tetrahydrofuran and 22 ml of methanol, stir for 5 min, and obtain an extractant for standby use;

[0098] S2, extraction of antioxidants: 1g of linear low-density polyethylene containing 0.3wt% antioxidant 1135, 0.3wt% antioxidant 1222, and 0.3wt% antioxidant 2246 was pressed into thin sheets and crushed to an average particle size of 2.5mm, 12ml of the extractant of step S1 was added, stirred for 2h, 0.3g of microwave accelerator A was added, microwave extraction was carried out at a microwave power of 650W and 95°C for 18min, and the extract was collected for later use;

[0099] S3, qualitative analysis: add tetrahydrofuran to the extract of step S2 to make up the volume (dilution factor 50 times) to obtain a test solution, filter it, and perform gas chromatography-mass spectrometry to obtain a mass spectrum to determine the type of antioxidant;

[0100] S4, quantitative analysis: prepare a standard solution of antioxidant, measure it by gas chromatography-mass spectrometry, and make a standard curve of antioxidant. Compare the working curve obtained by the test solution in step S3 with the standard curve to obtain the content of antioxidant in polyolefin plastic.

[0101] The instrument and test for gas chromatography-mass spectrometry are the same as those in Example 1.

[0102] Test results: The content of antioxidant 1135, the content of antioxidant 1222, and the content of antioxidant 2246 obtained by the above test method were 0.00324 g, 0.00340 g, and 0.00296 g, respectively.

[0103] Example 4

[0104] This embodiment provides a method for qualitative and quantitative analysis of antioxidants in polyolefin plastics. The specific implementation method is the same as that of Example 1, except that microwave accelerator B replaces microwave accelerator A in equal amounts.

[0105] Test results: Through the above test method, the content of antioxidant 1135 was 0.00200g, the content of antioxidant 1222 was 0.00210g, and the content of antioxidant 2246 was 0.00215g.

[0106] Example 5

[0107] This embodiment provides a method for qualitative and quantitative analysis of antioxidants in polyolefin plastics. The specific implementation method is the same as that of Example 1, except that microwave accelerator C replaces microwave accelerator A in equal amounts.

[0108] Test results: Through the above test method, the content of antioxidant 1135 was 0.00250g, the content of antioxidant 1222 was 0.00240g, and the content of antioxidant 2246 was 0.00243g.

[0109] Example 6

[0110] This embodiment provides a method for qualitative and quantitative analysis of antioxidants in polyolefin plastics. The specific implementation method is the same as that of Example 1, except that microwave accelerator D replaces microwave accelerator A in equal amounts.

[0111] Test results: The content of antioxidant 1135, the content of antioxidant 1222, and the content of antioxidant 2246 obtained by the above test method were 0.00243 g, 0.00251 g, and 0.00246 g, respectively.

[0112] Example 7

[0113] This embodiment provides a method for qualitative and quantitative analysis of antioxidants in polyolefin plastics. The specific implementation method is the same as that of Example 1, except that microwave accelerator E replaces microwave accelerator A in equal amounts.

[0114] Test results: The content of antioxidant 1135 obtained by the above test method is 0.00240g, the content of antioxidant 1222 is 0.00235g, and the content of antioxidant 2246 is 0.00237g.

[0115] Example 8

[0116] This embodiment provides a method for qualitative and quantitative analysis of antioxidants in polyolefin plastics. The specific implementation method is the same as that of Example 1, except that microwave accelerator F replaces microwave accelerator A in equal amounts.

[0117] Test results: Through the above test method, the content of antioxidant 1135 was 0.00238g, the content of antioxidant 1222 was 0.00232g, and the content of antioxidant 2246 was 0.00231g.

[0118] Example 9

[0119] This embodiment provides a method for qualitative and quantitative analysis of antioxidants in polyolefin plastics. The specific implementation method is the same as that of Example 1, except that microwave accelerator A is not added.

[0120] Test results: The content of antioxidant 1135, the content of antioxidant 1222, and the content of antioxidant 2246 obtained by the above test method were 0.00197 g, 0.00195 g, and 0.00190 g, respectively.

[0121] From the above data, it can be seen that the qualitative results of the three antioxidants in polyolefins in Examples 1-3 of the present invention are accurate and the quantitative results are almost consistent with the theoretical values, that is, the accuracy of the tests is relatively high. Among them, Examples 4-8 changed the addition ratio of the key components during the synthesis of the microwave accelerator, which reduced the ferrite's absorbing performance and the dispersibility and specific surface area of ​​the modified carbon nanotubes, resulting in the microwave accelerator being unable to play an ideal promoting role, and then resulting in a large deviation between the quantitative results of the antioxidant and the theoretical value, that is, the accuracy was significantly reduced; Example 9 was without adding microwave accelerator A, and the test found that the accuracy of the quantitative test of the antioxidant showed poor results.

[0122] The above implementation modes are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the content of the present invention and implement it, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for qualitative and quantitative determination of antioxidants in polyolefin plastics, characterized in that: The following steps are involved: S1. Preparation of extractant: tetrahydrofuran and methanol are mixed and stirred to obtain an extractant for standby use; S2, extraction of antioxidant: press the polyolefin plastic into thin slices, crush it, add the extractant of step S1, stir for 1-2h, add microwave accelerator, perform microwave extraction, and collect the extract for later use; S3, qualitative analysis: add tetrahydrofuran to the extract of step S2 to make up the volume to obtain a test solution, filter it, and perform gas chromatography-mass spectrometry to obtain a mass spectrum to determine the type of antioxidant; S4, quantitative analysis: prepare a standard solution of antioxidant, measure it by gas chromatography-mass spectrometry, and make a standard curve of antioxidant. After comparing the working curve obtained by the test solution in step S3 with the standard curve, the content of antioxidant in polyolefin plastic is obtained.

2. The method for qualitative and quantitative determination of antioxidants in polyolefin plastics according to claim 1, characterized in that: The volume ratio of tetrahydrofuran to methanol in step S1 is 1:(9-11).

3. The method for qualitative and quantitative determination of antioxidants in polyolefin plastics according to claim 1, characterized in that: The ratio of the polyolefin plastic to the extractant in step S2 is 1 g: (8-12) ml.

4. The method for qualitative and quantitative determination of antioxidants in polyolefin plastics according to claim 1, characterized in that: The mass ratio of the polyolefin plastic to the microwave accelerator in step S2 is 1:(0.1-0.3).

5. The method for qualitative and quantitative determination of antioxidants in polyolefin plastics according to claim 1, characterized in that: The preparation method of the microwave accelerator in step S2 comprises the following steps: (1) Propanol and glycerol are mixed, stirred, and ferric nitrate nonahydrate and cobalt acetate are added, stirred, and placed in a reaction kettle, and allowed to stand at 170-190° C. for 9-11 hours under vacuum, cooled to room temperature, centrifuged, washed, dried, and calcined to obtain cobalt ferrite for use; (2) Add the modified carbon nanotubes, polyphenylene vinylene and KH570 to anhydrous ethanol, perform ultrasound treatment, add the cobalt ferrite of step (1), stir, stir at 170-190° C. for 5-7 h, cool to room temperature, centrifuge, and freeze-dry to obtain a microwave accelerator.

6. The method for qualitative and quantitative determination of antioxidants in polyolefin plastics according to claim 5, characterized in that: In the step (1), the mass ratio of ferric nitrate nonahydrate to cobalt acetate is 1:(0.2-0.4).

7. The method for qualitative and quantitative determination of antioxidants in polyolefin plastics according to claim 5, characterized in that: In the step (2), the mass ratio of cobalt ferrite, modified carbon nanotubes and polyphenylene vinylene is 1:(0.1-0.15):(0.1-0.15).

8. The method for qualitative and quantitative determination of antioxidants in polyolefin plastics according to claim 5, characterized in that: The method for preparing the modified carbon nanotubes in step (2) comprises the following steps: 1) Mix ferric nitrate nonahydrate and ammonium molybdate tetrahydrate, stir to obtain a liquid for use, mix vermiculite and deionized water, sonicate, soak at 95-105° C. for 5.5-6.5 hours, add the liquid while stirring, soak at 95-105° C. for 11-13 hours, filter, dry, and calcine to obtain a catalyst for use; 2) placing the catalyst and melamine in step 1) in a reaction vessel, introducing hydrogen at 60-80 sccm for 5-10 min, then reacting in a hydrogen atmosphere of 25-35 sccm at 700-900° C. for 20-25 min, and cooling to room temperature to obtain modified carbon nanotubes.

9. The method for qualitative and quantitative determination of antioxidants in polyolefin plastics according to claim 8, characterized in that: In the step 2), the mass ratio of melamine to catalyst is 1:(0.2-0.3).

10. The method for qualitative and quantitative determination of antioxidants in polyolefin plastics according to claim 1, characterized in that: The power of the microwave extraction in step S2 is 550-650W, the temperature is 75-95°C, and the reaction time is 18-25min.

Images