Method for testing crosslinking degree of crosslinked polyethylene

Abstract

The application discloses a kind of crosslinking degree of crosslinked polyethylene testing methods, it is related to the technical field of material detection.A kind of crosslinking degree of crosslinked polyethylene testing methods, comprising the following steps: (1) the screen mesh is wrapped PE-X sample is placed into extraction instrument, solvent is injected to extract, extraction atmosphere is nitrogen atmosphere, extraction temperature is 150-200 DEG C, extraction pressure is 10-15MPa, extraction time is 3-10min;After extraction, remove solvent, this is one extraction;(2) repeat one extraction multiple times after PE-X sample is extracted completely and is extracted with solvent with uncrosslinked portion, and nitrogen is used to the remaining sample is purged;Remaining sample is taken out and dried, and the crosslinking degree of crosslinked polyethylene is calculated.The testing method disclosed in the application has the advantages of easy operation, short testing time, accurate testing result and the like, effectively solves the problem that the result of PE-X crosslinking degree is obtained for a long time in actual production, realizes the timely monitoring of product quality in production process.

Description

Technical Field

[0001] This invention relates to the technical field of material testing, and more particularly to a method for testing the degree of crosslinking of crosslinked polyethylene. Background Technology

[0002] Polyethylene (PE) is one of the five major general-purpose plastics, widely used in industry, agriculture, and daily life. However, its resistance to high temperatures, creep, and environmental pressure corrosion is relatively poor. Physical or chemical cross-linking techniques can be used to form a three-dimensional network structure in PE, significantly improving its performance and greatly expanding its application range. Currently, cross-linked polyethylene (PE-X) is widely used in pipes, films, cables, and other products, and its degree of cross-linking directly affects the quality of the products. Standard methods for testing the degree of cross-linking of PE-X include GB / T18474, ISO10147, and ASTM D2765-16. These methods all employ extraction of PE-X samples using a solvent (containing antioxidants) under normal pressure. The degree of cross-linking is obtained by drying the remaining sample after extraction and calculating the ratio of the remaining sample mass to the initial sample mass. These standard methods take 6-8 hours to extract, which is time-consuming and makes it difficult to monitor product quality in a timely manner, easily leading to the production of substandard products.

[0003] To address the issue of lengthy testing times for the crosslinking degree of PE-X products, patent CN202010227628 discloses a method for testing the crosslinking degree of PE-X products. This method involves heating and breaking PE-X samples with different degrees of crosslinking, compiling the data into a database, and then matching the test data of subsequent samples with the database to obtain the crosslinking degree. However, this method requires significant resources to establish the database, and the crosslinking degree test results are affected by the accuracy of the correlation between mechanical parameters and the crosslinking degree, resulting in a large error compared to the actual crosslinking degree.

[0004] Therefore, there is an urgent need for a crosslinking degree testing method that can improve the testing efficiency of the crosslinking degree of PE-X products, while providing accurate test results that are consistent with the aforementioned standard methods and can be directly applied to determine whether actual products meet the relevant standard requirements. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for testing the crosslinking degree of crosslinked polyethylene. The testing method of this invention has advantages such as ease of operation, short testing time, and accurate test results, effectively solving the problem of long acquisition time for PE-X crosslinking degree results in actual production, and enabling timely monitoring of product quality during the production process.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides a method for testing the degree of crosslinking of crosslinked polyethylene, comprising the following steps: (1) Wrap the PE-X sample in a sieve and place it in the extractor. Inject solvent for extraction. The extraction atmosphere is nitrogen atmosphere, the extraction temperature is 150-200 ℃, the extraction pressure is 10-15 MPa, and the extraction time is 3-10 min. Remove the solvent after extraction. This is one extraction. (2) Repeat step (1) multiple times to completely extract the uncrosslinked part of the PE-X sample and remove it along with the solvent. Then, purge the remaining sample with nitrogen. Finally, take out the remaining sample and dry it. Calculate the degree of crosslinking of the crosslinked polyethylene. Degree of crosslinking = (weight of the remaining PE-X sample after extraction / weight of the PE-X sample before extraction) × 100%.

[0007] Preferably, the purging time in step (2) is 1-3 min.

[0008] Preferably, the nitrogen pressure during purging in step (2) is 0.6-0.8 MPa.

[0009] If the purging time is too long, it will not only fail to further improve the drying effect, but will also prolong the extraction time and reduce the testing efficiency. If the purging time is too short or the nitrogen pressure is too low, the drying effect of nitrogen purging cannot be fully utilized. If the nitrogen pressure is too high, it can easily affect the quality of the sample. Therefore, this invention, by controlling the nitrogen purging time and the nitrogen pressure during purging, helps to improve the testing efficiency and ensure that the quality of the sample does not decrease.

[0010] After extraction is completed, the extraction instrument is purged with nitrogen to remove most of the residual solvent on the remaining sample, thereby shortening the drying time and further reducing the testing time.

[0011] Preferably, a nitrogen atmosphere is maintained during the extraction process in step (1).

[0012] This invention controls the extraction process to a nitrogen atmosphere, which can prevent the sample from undergoing oxidative degradation, eliminates the need for antioxidants, simplifies the operation process, reduces experimental costs, and is more environmentally friendly.

[0013] Preferably, the solvent in step (1) includes at least one of xylene and decahydronaphthalene.

[0014] Preferably, the extraction temperature in step (1) is 160-180℃, specifically it can be any one or a range of two of 160℃, 165℃, 170℃, 175℃, and 180℃.

[0015] Preferably, the extraction pressure in step (1) is 12-14 MPa.

[0016] Preferably, the extraction time in step (1) is 3-5 min, specifically any one or a range of two of the following: 3 min, 3.2 min, 3.5 min, 3.8 min, 4 min, 4.2 min, 4.5 min, 4.6 min, and 5 min.

[0017] Preferably, the thickness of the PE-X sample in step (1) is 0.1-0.2 mm.

[0018] Preferably, the mass of the PE-X sample in step (1) is 0.2-0.3 g.

[0019] If the sample thickness or mass is too large, a longer extraction temperature, time, or number of extractions is required, which can easily lead to a decrease in extraction efficiency. If the sample thickness or mass is too small, it can easily lead to an increase in test result errors and a decrease in the accuracy of the test results. Therefore, this invention improves the accuracy and efficiency of testing by controlling the thickness and mass of the sample.

[0020] Preferably, the material of the screen in step (1) includes stainless steel or aluminum.

[0021] Preferably, the aperture of the sieve in step (1) is 100-150 μm.

[0022] More preferably, the aperture of the screen is any one or a combination of 100μm, 110μm, 120μm, 130μm, 140μm, and 150μm.

[0023] If the sieve aperture is too large, some small samples may easily flow out and be lost during the extraction process; if the sieve aperture is too small, the sample may easily clog the sieve aperture during the extraction process, reducing the extraction efficiency. Therefore, this invention improves the testing efficiency by controlling the sieve aperture.

[0024] Preferably, the extraction in step (2) is repeated 3-10 times.

[0025] Preferably, the drying time in step (2) is 1-2 h.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The PE-X sample described in this invention has its solvent boiling point increased by applying pressure during extraction. Simultaneously, the pressure promotes faster solvent penetration and dissolution of the sample, thus improving extraction efficiency. Furthermore, by controlling the extraction temperature, this invention helps to improve extraction efficiency and ensure sample quality. Therefore, using the method described in this invention to test PE-X samples with any degree of crosslinking, the entire extraction process can be completed within 2.5 hours. For some PE-X samples with a higher degree of crosslinking, the number of extractions and the extraction time per extraction can be reduced, thereby shortening the total extraction time.

[0027] 2. The extraction principle of this invention is similar to the standard method of GB / T18474, thus ensuring that the test results are accurate and consistent with those obtained by the standard method. Detailed Implementation

[0028] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments, but the scope of protection and implementation of the present invention are not limited thereto.

[0029] Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0030] Example 1 This embodiment discloses a method for testing the degree of crosslinking of crosslinked polyethylene, including the following steps: (1) Weigh 0.3 g of PE-X sample with a crosslinking degree of 79.8%. The PE-X sample is a pipe with a thickness of 0.1 mm. Wrap and seal the PE-X sample with a stainless steel sieve with a size of 80 mm × 40 mm, a weight of 1.80 g, and a pore size of 100 μm. Place the PE-X sample into the extraction cell of the extractor. The extraction atmosphere is nitrogen atmosphere, the extraction temperature is 160 °C, the extraction pressure is 10 MPa, and xylene is injected. After the PE-X sample is extracted under high temperature and high pressure for 5 min, the xylene is discharged. This is the first extraction.

[0031] (2) After three cycles of extraction, the uncrosslinked part of the sample was completely extracted and discharged with the solvent. Then, the remaining sample was purged with nitrogen for 1 min at a nitrogen pressure of 0.8 MPa. Finally, the remaining sample was dried for 1 h and the weight of the remaining sample was calculated to be 0.2385 g. The degree of crosslinking was 0.2385 / 0.3×100%=79.5%, which is 0.3% different from the result of 79.8% tested according to GB / T18474.

[0032] Example 2 This embodiment discloses a method for testing the degree of crosslinking of crosslinked polyethylene, including the following steps: (1) Weigh 0.3 g of PE-X sample with a crosslinking degree of 31.8%. The PE-X sample is a pipe with a thickness of 0.1 mm. Wrap it with an aluminum sieve with a size of 80 mm × 40 mm, a weight of 1.80 g, and a pore size of 100 μm and seal it. Place it together in the extraction cell of the extractor. The extraction atmosphere is nitrogen atmosphere, the extraction temperature is 160 °C, the extraction pressure is 10 MPa, and decahydronaphthalene is injected. After the sample is extracted under high temperature and high pressure for 3 min, the decahydronaphthalene is discharged. This is the first extraction.

[0033] (2) After 6 cycles of extraction, the uncrosslinked part of the sample was completely extracted and discharged with the solvent. Then, the remaining sample was purged with nitrogen for 3 min at a nitrogen pressure of 0.6 MPa. Finally, the remaining sample was dried for 1 h and the weight of the remaining sample was calculated to be 0.093 g. The degree of crosslinking was 0.093 / 0.3×100%=31.0%, which is 0.8% different from the result of 31.8% tested according to GB / T 18474.

[0034] Example 3 This embodiment discloses a method for testing the degree of crosslinking of crosslinked polyethylene, including the following steps: (1) Weigh 0.3 g of PE-X sample with a crosslinking degree of 31.8%. The PE-X sample is a pipe with a thickness of 0.1 mm. Wrap it with a stainless steel sieve with a size of 80 mm × 40 mm, a weight of 1.80 g, and a pore size of 100 μm and seal it. Place it together in the extraction cell of the extractor. The extraction atmosphere is nitrogen atmosphere, the extraction temperature is 180 °C, the extraction pressure is 15 MPa, xylene is injected, and the sample is extracted under high temperature and high pressure for 3 min. Then the xylene is discharged. This is the first extraction.

[0035] (2) After 6 cycles of extraction, the uncrosslinked part of the sample was completely extracted and discharged with the solvent. Then, the remaining sample was purged with nitrogen for 3 min at a nitrogen pressure of 0.6 MPa. Finally, the remaining sample was dried for 1 h and the weight of the remaining sample was calculated to be 0.0963 g. The degree of crosslinking was 0.0963 / 0.3×100%=32.1%, which is 0.3% different from the result of 31.8% tested according to GB / T18474.

[0036] Example 4 This embodiment discloses a method for testing the degree of crosslinking of crosslinked polyethylene, including the following steps: (1) Weigh 0.3 g of PE-X sample with a crosslinking degree of 31.8%. The PE-X sample is a pipe with a thickness of 0.1 mm. Wrap it with a stainless steel sieve with a size of 80 mm × 40 mm, a weight of 1.80 g, and a pore size of 100 μm and seal it. Place it together in the extraction cell of the extractor. The extraction atmosphere is nitrogen atmosphere, the extraction temperature is 180 °C, the extraction pressure is 15 MPa, xylene is injected, and the sample is extracted under high temperature and high pressure for 3 min. Then the xylene is discharged. This is the first extraction.

[0037] (2) After 6 cycles of extraction, the uncrosslinked part of the sample was completely extracted and discharged with the solvent. Then, the remaining sample was purged with nitrogen for 3 minutes at a nitrogen pressure of 0.3 MPa. Finally, the remaining sample was dried for 1 hour and the weight of the remaining sample was calculated to be 0.0933 g. The degree of crosslinking was 0.0933 / 0.3×100%=31.1%, which is 0.7% different from the result of 31.8% tested according to GB / T18474.

[0038] Example 5 This embodiment discloses a method for testing the degree of crosslinking of crosslinked polyethylene, including the following steps: (1) Weigh 0.3 g of PE-X sample with a crosslinking degree of 50.3%. The PE-X sample is a pipe with a thickness of 0.1 mm. Wrap and seal it with a stainless steel sieve with a size of 80 mm × 40 mm, a weight of 1.80 g, and a pore size of 100 μm. Place it together in the extraction cell of the extractor. The extraction atmosphere is nitrogen atmosphere, the extraction temperature is 180 °C, the extraction pressure is 10 MPa, and decahydronaphthalene is injected. After the sample is extracted under high temperature and high pressure for 5 min, the decahydronaphthalene is discharged. This is the first extraction.

[0039] (2) After five cycles of extraction, the uncrosslinked portion of the sample was completely extracted and discharged along with the solvent. Then, the remaining sample was purged with nitrogen for 1 minute at a nitrogen pressure of 0.6 MPa. Finally, the remaining sample was dried for 1 hour and the weight of the remaining sample was calculated to be 0.1464 g. The degree of crosslinking was 0.1464 / 0.3×100%=48.8%, which is 1.5% different from the result of 50.3% tested according to GB / T18474.

[0040] Example 6 This embodiment discloses a method for testing the degree of crosslinking of crosslinked polyethylene, including the following steps: (1) Weigh 0.3 g of PE-X sample with a crosslinking degree of 50.3%. The PE-X sample is a pipe with a thickness of 0.1 mm. Wrap and seal it with a stainless steel sieve with a size of 80 mm × 40 mm, a weight of 1.80 g, and a pore size of 100 μm. Place it together in the extraction cell of the extractor. The extraction atmosphere is nitrogen atmosphere, the extraction temperature is 180 °C, the extraction pressure is 10 MPa, and decahydronaphthalene is injected. After the sample is extracted under high temperature and high pressure for 5 min, the decahydronaphthalene is discharged. This is the first extraction.

[0041] (2) After five cycles of extraction, the uncrosslinked portion of the sample was completely extracted and discharged along with the solvent. Then, the remaining sample was purged with nitrogen for 3 minutes at a nitrogen pressure of 0.6 MPa. Finally, the remaining sample was dried for 1 hour and the weight of the remaining sample was calculated to be 0.0992 g. The degree of crosslinking was 0.0992 / 0.2×100%=49.6%, which is 0.7% different from the result of 50.3% tested according to GB / T18474.

[0042] Example 7 This embodiment discloses a method for testing the degree of crosslinking of crosslinked polyethylene, including the following steps: (1) Weigh 0.2 g of PE-X sample with a crosslinking degree of 50.3%. The PE-X sample is a pipe with a thickness of 0.1 mm. Wrap it with a stainless steel sieve with a size of 80 mm × 40 mm, a weight of 1.80 g, and a pore size of 100 μm and seal it. Place it together in the extraction cell of the extractor. The extraction atmosphere is nitrogen atmosphere, the extraction temperature is 180 °C, the extraction pressure is 10 MPa, and decahydronaphthalene is injected. After the sample is extracted under high temperature and high pressure for 5 min, the decahydronaphthalene is discharged. This is the first extraction.

[0043] (2) After three cycles of extraction, the uncrosslinked portion of the sample was completely extracted and discharged along with the solvent. Then, the remaining sample was purged with nitrogen for 3 minutes at a nitrogen pressure of 0.6 MPa. Finally, the remaining sample was dried for 1 hour and the weight of the remaining sample was calculated to be 0.0964 g. The degree of crosslinking was 0.0964 / 0.2×100%=48.2%, which is 2.1% different from the result of 50.3% tested according to GB / T18474.

[0044] Example 8 The difference from Example 1 is that the PE-X sample was subjected to cyclic extraction twice in step (2).

[0045] In this embodiment, the weight of the remaining sample was calculated to be 0.2562g, and its degree of crosslinking was 0.2562 / 0.3×100%=85.4%, which is 5.6% different from the test result of 79.8% according to GB / T 18474.

[0046] Comparative Example 1 The difference from Example 1 is that the extraction temperature in step (1) is 140°C and the extraction time is 20 min.

[0047] The crosslinking degree obtained in this comparative example was 92.6%, which differs by 12.8% from the 79.8% test result according to GB / T 18474.

[0048] Comparing Comparative Example 1 with Example 1, it can be seen that when the extraction temperature is too low, the PE-X sample cannot be extracted well, resulting in a longer extraction time and a decrease in extraction efficiency.

[0049] Comparative Example 2 The difference from Example 1 is that the extraction temperature in step (1) is 210°C and the extraction time is 5 min.

[0050] The crosslinking degree obtained in this comparative example was 68.7%, which differs from the 79.8% test result according to GB / T 18474 by 11.1%.

[0051] Comparing Comparative Example 2 with Example 1, it can be seen that if the extraction temperature is too high, the sample will degrade during the extraction process, and the quality will be affected.

[0052] Comparative Example 3 The difference from Example 1 is that the extraction pressure in step (1) is 5 MPa and the extraction time is 10 min.

[0053] The crosslinking degree obtained in this comparative example was 86.7%, which differs by 6.9% from the 79.8% test result according to GB / T 18474.

[0054] Comparing Comparative Example 3 with Example 1, it can be seen that when the extraction pressure is too low, the extraction time becomes longer and the extraction efficiency decreases.

[0055] Comparative Example 4 The difference from Example 1 is that the extraction pressure in step (1) is 20 MPa and the extraction time is 5 min.

[0056] The crosslinking degree obtained in this comparative example was 73.1%, which differs by 6.7% from the 79.8% test result according to GB / T 18474.

[0057] Comparing Comparative Example 4 with Example 1, it can be seen that if the extraction pressure is too high, the sample will degrade during the extraction process, and the quality will be affected.

[0058] Comparative Example 5 The difference from Example 1 is that the extraction time in step (1) is 1 min.

[0059] The crosslinking degree obtained in this comparative example was 94.6%, which differs by 14.8% from the 79.8% test result according to GB / T 18474.

[0060] Comparing Comparative Example 5 with Example 1, it can be seen that the extraction time is too short to completely extract the sample, resulting in an overestimation of the measured value.

[0061] Comparative Example 6 The difference from Example 1 is that the extraction time in step (1) is 15 min.

[0062] The crosslinking degree obtained in this comparative example was 76.1%, which differs from the 79.8% test result according to GB / T 18474 by 3.7%.

[0063] Comparing Comparative Example 6 with Example 1, it can be seen that an excessively long extraction time leads to reduced efficiency, wasted solvent, and the emission of large amounts of organic solvents, increasing costs and waste pollution. Furthermore, it can cause material degradation and affect the quality of the sample.

[0064] Comparative Example 7 The difference from Example 1 is that nitrogen is not used to purge the remaining sample in step (2), and the total drying time is 3 hours, which is far less efficient than Example 1.

[0065] In summary, this invention improves testing efficiency and accuracy by controlling the extraction temperature to 150-200 ℃, the pressure to 10-15 MPa, and the extraction time to 3-10 min per extraction, and by purging the remaining sample with nitrogen after extraction. This effectively solves the problem of long acquisition time for PE-X crosslinking degree results in actual production, and better enables timely monitoring of product quality during the production process.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for testing the degree of crosslinking of crosslinked polyethylene, characterized in that, Includes the following steps: (1) Wrap the PE-X sample in a sieve and place it in the extractor. Inject solvent for extraction. The extraction atmosphere is nitrogen atmosphere, the extraction temperature is 150-200 ℃, the extraction pressure is 10-15 MPa, and the extraction time is 3-10 min. Remove the solvent after extraction. This is one extraction. (2) Repeat step (1) multiple times to completely extract the uncrosslinked part of the PE-X sample and remove it along with the solvent. Then, purge the remaining sample with nitrogen. Finally, take out the remaining sample and dry it. Calculate the degree of crosslinking of the crosslinked polyethylene. Degree of crosslinking = (weight of the remaining PE-X sample after extraction / weight of the PE-X sample before extraction) × 100%.

2. The method for testing the degree of crosslinking of crosslinked polyethylene as described in claim 1, characterized in that, The purging time in step (2) is 1-3 min.

3. The method for testing the degree of crosslinking of crosslinked polyethylene as described in claim 1, characterized in that, The nitrogen pressure during purging in step (2) is 0.6-0.8 MPa.

4. The method for testing the degree of crosslinking of crosslinked polyethylene as described in claim 1, characterized in that, The solvent in step (1) includes at least one of xylene and decahydronaphthalene.

5. The method for testing the degree of crosslinking of crosslinked polyethylene as described in claim 1, characterized in that, In step (1), the extraction temperature is 160-180℃ and the extraction time is 3-5 min.

6. The method for testing the degree of crosslinking of crosslinked polyethylene as described in claim 1, characterized in that, The thickness of the PE-X sample in step (1) is 0.1-0.2 mm.

7. The method for testing the degree of crosslinking of crosslinked polyethylene as described in claim 1, characterized in that, The material of the screen in step (1) includes stainless steel or aluminum.

8. The method for testing the degree of crosslinking of crosslinked polyethylene as described in claim 1, characterized in that, The aperture of the sieve in step (1) is 100-150 μm.

9. The method for testing the degree of crosslinking of crosslinked polyethylene as described in claim 1, characterized in that, In step (2), the extraction is repeated 3-10 times.

10. The method for testing the degree of crosslinking of crosslinked polyethylene as described in claim 1, characterized in that, The drying time in step (2) is 1-2 h.