A method for detecting hindered phenol antioxidants in PVC heat stabilizers

Abstract

The present invention belongs to the technical field of analytical chemistry, and specifically relates to a method for detecting hindered phenol antioxidants in PVC heat stabilizers. The method comprises the following steps: S1, uniformly mixing a PVC heat stabilizer sample with a non-cyclic fatty ether to form a solution with a mass percentage of not less than 5% of the PVC heat stabilizer sample; S2, heating the solution obtained in S1 at 100-150°C for a period of time. If the solution contains hindered phenol antioxidants, the color of the solution turns yellow. Compared with the prior art, the present invention can determine the content of hindered phenol antioxidants in the stabilizer through simple processing. In the process, the amount of organic solvent used is small, resources are saved, the operation method is convenient and fast, and batch processing is easy to achieve; the sample pretreatment process is simple, and only the reactants need to be simply mixed and heated, which takes a short time and is highly efficient. After adding the solvent, the target object in the stabilizer can be quickly colored without excessive manpower and material resources.

Description

Technical Field

[0001] The invention belongs to the technical field of analytical chemistry, and in particular relates to a method for detecting a hindered phenol antioxidant in a PVC heat stabilizer. Background Art

[0002] Polyvinyl chloride (PVC) is one of the five general-purpose plastics. During storage, processing and use, it is prone to oxidation under the influence of external conditions such as strong light, high temperature or metal ions, causing degradation or cross-linking of the molecular chain, changes in the molecular structure, and ultimately leading to surface defects in the material, poor performance, and loss of use value.

[0003] In order to delay or inhibit the oxidation of materials, a general and effective method is to add a small amount of antioxidant to the heat stabilizer of PVC. Among them, hindered phenol antioxidants are often added. Hindered phenol antioxidants are free radical terminators for the initial oxidation process of PVC. They are compounds with substituted groups on one or both sides of the -OH on the benzene ring. Electron-repelling groups such as methyl and tert-butyl are introduced at the ortho and para positions of -OH. Since the hydroxyl group is restricted by spatial barriers, the hydrogen atom (H) can easily fall off from the original molecular structure, thereby achieving the effect of donating protons and combining with the peroxyl radicals (ROO-), alkyl radicals, hydroxyl radicals, etc. generated during the oxidation process of PVC materials to form a relatively stable compound, causing it to lose its original activity, terminating the oxidation reaction, thereby inhibiting the oxidative degradation of PVC.

[0004] Therefore, in PVC heat stabilizers, the content of hindered phenolic antioxidants is crucial to the performance of heat stabilizers and PVC materials.

[0005] At present, there are standards and patents describing the detection methods of general antioxidants, but there are few qualitative or quantitative test methods for hindered phenolic antioxidants in PVC stabilizers. Most of the existing conventional test methods use high-end instruments and equipment, such as gas chromatography-mass spectrometry, high-performance liquid chromatography, etc. Although they can identify hindered phenolic antioxidants and determine their content, there are also many problems in actual operation.

[0006] For example, the sample preparation process is complicated, requires special equipment and technology, and is time-consuming, which is unrealistic in large-scale production. Secondly, due to the influence of factors such as instruments and operators, existing methods can often only provide qualitative information, and quantitative results may vary greatly, which is not conducive to accurate control of product quality.

[0007] Therefore, how to obtain a simpler, faster and more accurate method for detecting the content of hindered phenol antioxidants in heat stabilizers is a problem that needs to be solved at present. Summary of the invention

[0008] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for detecting hindered phenol antioxidants in PVC heat stabilizers. While identifying whether this type of antioxidant is present, its content is also determined. The purpose is to solve the problems of complex sample preparation, large differences in quantitative results, and complex operations in the existing testing methods.

[0009] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for detecting hindered phenol antioxidants in PVC heat stabilizers, comprising the following steps:

[0010] S1. The PVC heat stabilizer sample and the non-cyclic fatty ether are uniformly mixed to form a solution with a mass percentage of the PVC heat stabilizer sample of not less than 5%;

[0011] S2. Heat the solution obtained in S1 at 100-150°C for a period of time. If it contains hindered phenol antioxidant, the solution will turn yellow.

[0012] In a preferred embodiment, the detection method further comprises step S3, establishing a standard curve of hindered phenol antioxidant content and chromaticity value, measuring the chromaticity value of the solution obtained in S2 by a colorimeter, and determining the content of hindered phenol antioxidant in the PVC heat stabilizer sample.

[0013] Furthermore, the non-cyclic aliphatic ether includes diethylene glycol butyl ether or diethylene glycol methyl ether; and the PVC heat stabilizer is a liquid PVC heat stabilizer.

[0014] In a preferred embodiment, step S3 is specifically:

[0015] S31, dissolving a hindered phenol antioxidant standard product in a non-cyclic fatty ether to obtain a diluent;

[0016] S32, dispersing the diluent in non-cyclic aliphatic ethers of different masses, heating at 100-150° C. for a period of time to obtain standard solutions of different concentrations;

[0017] S33, weigh and record the PVC heat stabilizer sample, disperse it in a non-cyclic fatty ether, heat it at 100-150°C for a period of time, and obtain a sample solution to be tested;

[0018] S34. Use a colorimeter to measure the color value data of the standard product and the sample solution to be tested, draw a standard curve with the concentration of the standard product as the horizontal axis and the measured color value data as the vertical axis, and then obtain the content of the hindered phenol antioxidant in the PVC heat stabilizer through the standard curve and the color value of the sample solution to be tested.

[0019] Furthermore, in step S2, the period of time is 1 to 3 hours.

[0020] In a preferred embodiment, in step S1, a solution containing 5% to 30% by mass of the PVC heat stabilizer sample is formed.

[0021] Preferably, in step S3, the standard substance to be tested and the sample solution are made to be non-turbid, and when the colorimetric value is detected, it is ensured that the standard substance to be tested and the sample solution are free of bubbles.

[0022] In a preferred embodiment, during quantification, the same hindered phenol antioxidant standard is taken to establish a standard working curve.

[0023] Further, the content (%) of the hindered phenol antioxidant is calculated according to formula (1):

[0024] (1)

[0025] Where:

[0026] C: Mass content of hindered phenol antioxidant in the sample solution to be tested, %;

[0027] C0: The mass content of stabilizer in the sample solution to be tested, %;

[0028] W: Mass content of hindered phenol antioxidant in PVC heat stabilizer sample, %.

[0029] Another object of the present invention is to provide a method for detecting a hindered phenol antioxidant, comprising the following steps:

[0030] S1. The antioxidant sample and the non-cyclic fatty ether are uniformly mixed to form a solution in which the mass percentage of the antioxidant sample is not less than 0.25%;

[0031] S2. Heat the solution obtained in S1 at 100-150°C for a period of time. If it contains hindered phenol antioxidant, the solution will turn yellow.

[0032] In a preferred embodiment, the detection method further comprises step S3, establishing a standard curve of hindered phenol antioxidant content and chromaticity value, measuring the color value of the solution obtained in S2 by a colorimeter, and determining the content of hindered phenol antioxidant in the antioxidant sample.

[0033] Furthermore, the non-cyclic aliphatic ether includes diethylene glycol butyl ether or diethylene glycol methyl ether. If other ethers other than non-cyclic aliphatic ether are used, the solution color cannot be turned yellow through the above steps, and thus the detection of hindered phenol antioxidants cannot be completed.

[0034] In the detection of hindered phenol antioxidants in PVC heat stabilizers or the detection of antioxidant samples, in step S1, considering the solubility of the sample, the stabilizer sample is preferably a liquid PVC heat stabilizer; considering the interference of color change, the stabilizer sample is a commonly used PVC heat stabilizer, and the components generally include: metal organic acid soap, solvent oil, phosphite, antioxidant, acid absorber, lubricant, auxiliary stabilizer, etc. In step S2, the color-changing solution is saved for subsequent color value testing; regarding heating temperature and heating time, the lower the heating temperature, the longer the time required. In step S3, in step S3, if the sample is turbid, filtration, centrifugation, heating, ultrasonic treatment or other suitable methods are required to remove turbidity, and ensure that no bubbles are generated in the sample during the test. Optionally, in step S3, the test conditions for the colorimeter to measure the standard and sample solutions are: light source lamp: halogen tungsten lamp; wavelength range: 320-1100 nanometers; scanning speed: 8 nanometers / second; photometric accuracy: 0~0.5Abs; measurement mode: Gardner colorimetric value.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] Acyclic fatty ethers catalyze and promote the free radical reaction of hindered phenol antioxidants to form colored quinones.

[0037] The content of hindered phenol antioxidant in the stabilizer can be determined by simple processing. In this process, less organic solvent is used, resources are saved, the operation method is convenient and fast, and batch processing is easy to achieve;

[0038] The sample pretreatment process is simple, and only the reactants need to be simply mixed and heated. It takes a short time and is highly efficient. After adding the solvent, the target substance in the stabilizer can be quickly colored without excessive manpower and material resources.

[0039] The detection method of the present invention has high accuracy. The existence and specific chemical structure of the hindered phenol antioxidant in the PVC heat stabilizer can be accurately identified by gas chromatography-mass spectrometry or high performance liquid chromatography. When a batch of products of a specific stabilizer is confirmed to contain the hindered phenol antioxidant through the detection method of the present invention and the accurate identification of the gas chromatography-mass spectrometry or high performance liquid chromatography, other batches of products of the stabilizer can be subjected to batch detection and processing of whether the hindered phenol antioxidant is contained and the specific content through the detection method of the present invention, which is low in cost and high in efficiency; and can be used for the control of product quality after production. In addition, in the process of producing stabilizer products, when the type of antioxidant raw materials that can be used is unclear, the detection method of the present invention can be used to determine whether the antioxidant raw materials are hindered phenol antioxidants. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1A comparison of the color changes produced by the standard product in Example 1 of the present invention, numbered 1-5 from left to right;

[0041] Figure 2 This is a spectrum detected by gas chromatography-mass spectrometry in Example 1 of the present invention, in which a characteristic peak of antioxidant 1076 is detected at a retention time of 18.78 min, with the horizontal axis being retention time (min) and the vertical axis being the response signal of the detector;

[0042] Figure 3 This is a color comparison diagram of Comparative Example 1 (left, diphenyl isooctyl phosphite sample) and Comparative Example 2 (right) of the present invention;

[0043] Figure 4 This is the spectrum detected by gas chromatography-mass spectrometry in Comparative Example 2 of the present invention, and no characteristic peak of the hindered phenol antioxidant was detected. DETAILED DESCRIPTION

[0044] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments and drawings. It should be understood that the following embodiments are only used to explain the present invention and are not used to limit the present invention.

[0045] The implementation steps of the specific determination method adopted in the following examples are:

[0046] (1) Sample processing

[0047] Accurately weigh 2g of PVC heat stabilizer sample and mix it evenly with 10g of diethylene glycol butyl ether or diethylene glycol methyl ether, and heat the sample solution at a constant temperature of 120℃ for 2h. If it contains hindered phenol antioxidants, the solution color will obviously turn yellow. Save the color-changing solution for the colorimeter to determine the content of hindered phenol antioxidants;

[0048] (2) Quantification by external standard method

[0049] Take the same hindered phenol antioxidant standard and disperse it in diethylene glycol butyl ether or diethylene glycol methyl ether, record it as diluent. Take the diluent, add different masses of diethylene glycol butyl ether or diethylene glycol methyl ether, prepare 5 standard solutions of different concentrations, numbered 1, 2, 3, 4, 5, the mass fraction of hindered phenol antioxidant standard in the standard solution is about 0.5%, 1%, 2%, 4%, 5%, heat at a constant temperature of 120℃ for 2h, the standard solution turns yellow (as the standard solution to be tested); measure the chromaticity values ​​of the 5 standard solutions to be tested respectively; draw the standard working curve y=ax+b with the mass fraction as the horizontal coordinate and the chromaticity value as the vertical coordinate.

[0050] Take the solution that turns yellow in (1) (i.e. the sample solution to be tested), numbered 6, and the mass content of the stabilizer in the sample solution to be tested is recorded as C0 (since no substance evaporates when the sample solution is heated at a constant temperature, C0 is also the ratio of the mass of the added PVC heat stabilizer sample to the total mass of the PVC heat stabilizer sample and diethylene glycol butyl ether). Substitute the chromaticity value obtained after the sample solution to be tested with a colorimeter into the standard working curve to calculate the concentration C of the hindered phenol antioxidant in the sample solution to be tested.

[0051] The content (%) of hindered phenol antioxidant is calculated according to the following formula (1):

[0052] (1)

[0053] Where:

[0054] C: Mass content of hindered phenol antioxidant in the sample solution to be tested, %;

[0055] C0: The mass content of stabilizer in the sample solution to be tested, %;

[0056] W: Mass content of hindered phenol antioxidant in PVC heat stabilizer sample, %.

[0057] This test method uses the average of three parallel determinations as the final determination result, and the relative standard deviation of the parallel determination results is less than 10%.

[0058] Example 1 Determination of the content of hindered phenol antioxidant in PVC heat stabilizer

[0059] (1) Sample processing

[0060] The PVC liquid heat stabilizer produced by ADEKA of Japan was selected. It was known that the ingredients contained hindered phenol antioxidant 1076, with a content of about 5.8% (mass fraction), and the main component was β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate octadecyl ester. Weigh 2g of the stabilizer sample and mix it evenly with 10g of diethylene glycol butyl ether. After heating at a constant temperature of 120℃ for 2h, the color of the solution turned yellow significantly, indicating that it contained hindered phenol antioxidants. The color-changing solution was saved for the colorimeter to determine the content of hindered phenol antioxidants.

[0061] (2) Quantification by external standard method

[0062] Take the antioxidant 1076 standard and disperse it in diethylene glycol butyl ether, which is recorded as the diluent. Take the diluent and add different masses of diethylene glycol butyl ether to prepare 5 standard solutions with different concentrations, numbered 1, 2, 3, 4, and 5. The mass fractions of the antioxidant 1076 standard are 0.4887%, 0.9061%, 1.8041%, 3.5375%, and 4.9688%, respectively. Heat at a constant temperature of 120℃ for 2h, and the standard solution turns yellow (as the standard solution to be tested); measure the chromaticity values ​​of the 5 standard solutions to be tested respectively; use the mass fraction as the horizontal axis and the chromaticity value as the vertical axis to draw the standard working curve y=ax+b. Take the sample solution to be tested that turns yellow in (1), numbered 6, and the mass content of the stabilizer in the sample solution to be tested is recorded as C0. The sample solution to be tested is tested using a HACH LICO 620 colorimeter, and the obtained chromaticity value is substituted into the standard working curve to calculate the concentration C of the hindered phenol antioxidant in the sample solution to be tested, such as Figure 1 And as shown in Table 1.

[0063]

[0064] Table 1 Calculation of hindered phenol antioxidant content in stabilizer samples

[0065] At the same time, according to the national standard method "GBT-33078-2016", the PVC heat stabilizer samples were analyzed using gas chromatography-mass spectrometry. The results are as follows: Figure 2 As shown, it is confirmed that it contains antioxidant 1076. Therefore, according to the measurement results, this method can be used to detect the hindered phenol antioxidant in the PVC heat stabilizer, and the difference between the measured value and the actual value is small, so this method can be used for measurement.

[0066] Example 2

[0067] The PVC liquid heat stabilizer produced by Jiangsu Alliance was selected. It is known that the ingredients contain hindered phenolic antioxidant 1010, with a content of about 4.5%. The main component is pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate. Weigh 2g of the stabilizer sample and mix it evenly with 10g of diethylene glycol methyl ether. After heating at a constant temperature of 120℃ for 2h, the color of the solution turns yellow obviously, indicating that it contains hindered phenolic antioxidants. The color-changing solution is stored for the colorimeter to determine the content of hindered phenolic antioxidants. The standard working curve is established with the hindered phenolic antioxidant 1010 standard product, and the measured content is 4.35%, which is close to the known content of hindered phenolic antioxidants in the PVC liquid heat stabilizer.

[0068] Example 3

[0069] The PVC liquid heat stabilizer produced by BAERLOCHER in Germany was selected. It is known that the ingredients contain hindered phenolic antioxidant 2246, with a content of about 4.2%. The main component is 2,2'-methylenebis (6-tert-butyl-4-methylphenol). Weigh 2g of the stabilizer sample and mix it evenly with 10g of diethylene glycol butyl ether. After heating at a constant temperature of 120℃ for 2h, the color of the solution obviously turns yellow, indicating that it contains hindered phenolic antioxidants. The color-changing solution is stored for the colorimeter to determine the content of hindered phenolic antioxidants. The standard working curve is established with the hindered phenolic antioxidant 2246 standard product, and the measured content is 4.29%, which is close to the known content of hindered phenolic antioxidants in the PVC liquid heat stabilizer.

[0070] Comparative Example 1 Color Change Test of Non-Hindered Phenolic Antioxidants

[0071] Several commonly used non-hindered phenol antioxidants were selected for testing, including phosphite antioxidants (tris(2,4-di-tert-butylphenyl) phosphite, dioctadecyl pentaerythritol diphosphite, diphenyl isooctyl phosphite) and isocyanurate ring antioxidants (tris(4-tert-butyl-3-hydroxy-2,6-xylyl) isocyanurate). 2g of antioxidant sample was weighed and evenly mixed with 10g of diethylene glycol butyl ether, and heated at a constant temperature of 120℃ for 2h. The color of the solution did not change significantly, indicating that non-hindered phenol antioxidants did not yellow.

[0072] Comparative Example 2 Color Change Test of PVC Stabilizer without Hindered Phenol Antioxidant

[0073] We selected the PVC liquid heat stabilizer produced by KDCHEM in South Korea, and the antioxidant used was a non-hindered phenol phosphite antioxidant. We used gas chromatography-mass spectrometry to analyze the components. The results are as follows: Figure 4 Weigh 2g of the heat stabilizer sample and mix it evenly with 10g of diethylene glycol butyl ether, and heat it at a constant temperature of 120℃ for 2h. The color of the solution does not change significantly ( Figure 3 ), indicating that PVC stabilizers without hindered phenolic antioxidants do not undergo yellowing.

[0074] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any form, and any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A method for detecting hindered phenol antioxidants in PVC heat stabilizers, characterized in that: The steps include: S1. The PVC heat stabilizer sample and the non-cyclic fatty ether are uniformly mixed to form a solution with a mass percentage of the PVC heat stabilizer sample of not less than 5%; S2, heating the solution obtained in S1 at 100-150°C for a period of time. If it contains hindered phenol antioxidant, the solution will turn yellow; The non-cyclic aliphatic ether includes diethylene glycol butyl ether or diethylene glycol methyl ether; the PVC heat stabilizer is a liquid PVC heat stabilizer.

2. The method for detecting hindered phenol antioxidants in a PVC heat stabilizer according to claim 1, characterized in that: The method further includes step S3, establishing a standard curve between the content of hindered phenol antioxidant and the chromaticity value, measuring the chromaticity value of the solution obtained in S2 by a colorimeter, and determining the content of hindered phenol antioxidant in the PVC heat stabilizer sample.

3. The method for detecting hindered phenol antioxidant in a PVC heat stabilizer according to claim 2, characterized in that: Step S3 is specifically as follows: S31, dissolving a hindered phenol antioxidant standard product in a non-cyclic fatty ether to obtain a diluent; S32, dispersing the diluent in non-cyclic aliphatic ethers of different masses, heating at 100-150° C. for a period of time to obtain standard solutions of different concentrations; S33, weigh and record the weight of a PVC heat stabilizer sample, disperse it in a non-cyclic fatty ether, and heat it at 100-150° C. for a period of time to obtain a sample solution to be tested; S34. Use a colorimeter to measure the chromaticity value data of the standard product and the sample solution to be tested, draw a standard curve with the concentration of the standard product as the horizontal axis and the measured chromaticity value data as the vertical axis, and then obtain the content of the hindered phenol antioxidant in the PVC heat stabilizer through the standard curve and the chromaticity value of the sample solution to be tested.

4. The method for detecting hindered phenol antioxidants in a PVC heat stabilizer according to claim 1, characterized in that: In step S2, the period of time is 1 to 3 hours.

5. The method for detecting hindered phenol antioxidant in a PVC heat stabilizer according to claim 1, characterized in that: In step S1, a solution containing 5% to 30% by mass of the PVC heat stabilizer sample is formed.

6. The method for detecting hindered phenol antioxidants in a PVC heat stabilizer according to claim 3, characterized in that: In step S3, the standard substance to be tested and the sample solution are made to be non-turbid, and when the colorimetric value is detected, it is ensured that the standard substance to be tested and the sample solution are free of bubbles.

7. The method for detecting hindered phenol antioxidants in a PVC heat stabilizer according to claim 3, characterized in that: During quantification, take the same hindered phenol antioxidant standard and establish a standard working curve.

8. The method for detecting hindered phenol antioxidants in a PVC heat stabilizer according to claim 3, characterized in that: The content (%) of hindered phenol antioxidant is calculated according to formula (1): Where: C: the mass content of hindered phenol antioxidant in the sample solution to be tested, %; C0: the mass content of stabilizer in the sample solution to be tested, %; W: Mass content of hindered phenol antioxidant in PVC heat stabilizer sample, %.

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