A method for evaluating the heat aging state of a thermoset elastomer

Abstract

The application discloses a kind of thermoset elastomer thermal aging state evaluation method, comprising the following steps: S1, elastomer is treated with heat aging;S2, the maximum elongation of aging sample and positron annihilation lifetime spectrum are tested, and the free volume of aging sample is obtained by analyzing positron annihilation lifetime spectrum;S3, least square method is used to linearly fit the maximum elongation of aging sample and free volume, and the fitting equation of maximum elongation and free volume of elastomer in the process of thermal aging treatment is established;S4, in the actual thermal aging test of the same kind of elastomer, the fitting equation is used, and the maximum elongation of elastomer is calculated by determining the free volume of elastomer, and the thermal aging state of elastomer is evaluated.The application establishes the correlation between the maximum elongation of elastomer and free volume, realizes the thermal aging state of elastomer by free volume, realizes in-situ detection of thermal aging performance, and has high accuracy.

Description

Technical Field

[0001] This invention belongs to the field of composite solid propellant manufacturing, specifically relating to a method for evaluating the thermal aging state of thermosetting elastomers. Background Technology

[0002] 3,3-bis(azidomethyloxybutylene) and tetrahydrofuran copolyether (PBT)-based thermosetting polyurethane plasticized with BDNPF / A (1:1 mass ratio) is an ideal matrix material for low-smoke, low-sensitivity, and low-signature-signature composite solid propellants in the aerospace field. Composite solid propellants undergo long-term cave storage during their service life. During this period, PBT-based propellants inevitably age under the influence of ambient temperature, primarily due to the oxidizing small molecule components produced by the decomposition of nitro plasticizers. This causes degradation of the binder matrix network structure, resulting in structural defects such as cracks and pores, macroscopically manifesting as deterioration of mechanical properties. When the propellant is in operation, this poses a significant safety risk. Therefore, accurate real-time assessment of the aging status of the PBT elastic matrix during storage is of great importance.

[0003] Current research on the storage aging performance of elastomers used in composite solid propellants typically involves conducting accelerated thermal aging experiments at high temperatures, combined with mechanical property tests, to obtain the changes in mechanical properties over aging time. Empirical models and the Arrenhnius formula are then used to infer the changes in mechanical properties under actual storage temperature conditions, and the aging state of the elastomer is evaluated based on these mechanical properties. However, because the mechanical property test samples are large and the tests are destructive, the materials cannot be reused. This method often suffers from problems such as high raw material consumption, significant individual variability, and poor repeatability. Summary of the Invention

[0004] The problem this invention aims to solve is to provide a method for evaluating the thermal aging state of thermosetting elastomers. Based on positron annihilation lifetime spectroscopy, the method obtains the correlation between the maximum elongation and free volume of the elastomer through linear fitting, and uses the free volume of the polymer as the characteristic parameter of elastomer aging. This solves the problems of difficult in-situ detection, high raw material consumption, large individual differences, and low accuracy in the study of elastomer thermal aging performance.

[0005] The present invention includes a method for evaluating the thermal aging state of thermosetting elastomers, comprising the following steps:

[0006] S1. Perform heat aging treatment on the elastomer;

[0007] S2. Test the maximum elongation and positron annihilation lifetime spectrum of the aged sample obtained in step S1, and obtain the free volume of the aged sample by analyzing the positron annihilation lifetime spectrum.

[0008] S3. The least squares method is used to linearly fit the maximum elongation and free volume of the aged sample in step S2, and the fitting equation of the maximum elongation and free volume of the elastomer during the thermal aging process is established.

[0009] S4. In the actual thermal aging test of the same type of elastomer, the maximum elongation of the elastomer is estimated by measuring the free volume of the elastomer using the fitting equation established in step S3, and the thermal aging state of the elastomer is evaluated.

[0010] Furthermore, in step S2, the aged sample includes a first test sample for positron annihilation lifetime spectrum testing and a second test sample for maximum elongation testing, with the first and second test samples taken at the same sampling interval.

[0011] Furthermore, the number of the first test samples is 2 to 3, and the positron annihilation lifetime spectrum is taken out according to the sampling cycle.

[0012] Furthermore, in step S2, each time a sample is taken, the number of second test samples is ≥5, and the maximum elongation of the second test sample is obtained by performing a uniaxial tensile test.

[0013] Furthermore, in step S3, the linear correlation coefficient R of the fitted equation is greater than 90%.

[0014] Furthermore, step S4 specifically involves: during the actual thermal aging test, after taking out the test sample of the same elastomer for positron annihilation lifetime spectrum testing, putting it back to continue the thermal aging test, obtaining the free volume of the same test sample at different times in the thermal aging test, and using the fitting equation in step S3 to calculate the corresponding elongation rate, thereby evaluating its aging state.

[0015] Furthermore, the elastomer is a polyether polyurethane whose main aging mechanism is the oxidative crosslinking of the polymer backbone.

[0016] Furthermore, the elastomer is a PBT elastomer, and in step S2, the aging sample is sampled at a certain sampling cycle, which is 20 days / time to 40 days / time.

[0017] Furthermore, in step S1, the temperature of the thermal aging treatment is 40℃~80℃.

[0018] Furthermore, the fitting equation established in step S3 is as follows:

[0019] y = 1088.95x - 11336.99 (1)

[0020] Where y is the maximum elongation and x is the free volume;

[0021] Linear correlation R of the fitted equation2 =0.91, where R is the linear correlation coefficient.

[0022] The beneficial effects of this invention are:

[0023] This invention studies the evolution of the microstructure and the trend of changes in the macroscopic mechanical properties of elastomers during thermal aging tests. It selects free volume data and maximum elongation data that both show a decreasing trend in thermal aging tests, studies the linear correlation between the free volume and maximum elongation of the elastomer, establishes a fitting equation, and thus establishes the connection between free volume and thermal aging state, realizing the characterization of the aging state of the elastomer using free volume.

[0024] This invention first sets up a thermal aging treatment for the aged samples and tests the free volume and maximum elongation data of the aged samples. A fitting equation is established for the free volume and maximum elongation of the elastomer material under study. Then, during the actual thermal aging test of the elastomer material, using the fitting equation, only the free volume needs to be obtained by testing its positron annihilation lifetime spectrum to obtain the current thermal aging state of the elastomer. Compared to destructive mechanical property testing, which damages the sample with each test and prevents subsequent tests, free volume testing does not damage the sample. After the test, the same sample can be used to continue the thermal aging test, ensuring that the test data are the free volumes of the same sample at different thermal aging times. This achieves in-situ detection of the elastomer in the thermal aging state, reduces experimental errors caused by individual sample differences, and improves the accuracy of thermal aging performance research results. Simultaneously, after determining the linear relationship, subsequent tests on the same elastomer material are all non-destructive tests, and the sample size is small, requiring only two sheet-like samples of the same size for positron annihilation lifetime spectrum testing, which can reduce raw material consumption.

[0025] This invention can be used in the field of thermosetting polyurethane aging performance research, and is applicable to the research of thermal aging performance of polyurethane elastomers for composite solid propellants. Attached Figure Description

[0026] Appendix Figure 1 This is a flowchart of an embodiment of the present invention for evaluating the thermal aging state of an elastomer;

[0027] Appendix Figure 2 The images show the PBT elastomer samples before and after aging at 70°C for 180 days in Example 1.

[0028] Appendix Figure 3 The above are positron annihilation lifetime spectra of PBT elastomers aged at 70°C for different times in Example 1.

[0029] Appendix Figure 4 This describes the evolution of the free volume of the PBT elastomer during the thermal aging process in Example 1.

[0030] Appendix Figure 5The evolution of the maximum elongation of PBT elastomer during the thermal aging process in Example 1 is shown.

[0031] Appendix Figure 6 This is a linear fit of the free volume and maximum elongation of the PBT elastomer during the thermal aging process in Example 1. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. Furthermore, the technical solutions of the various embodiments of this invention can be combined with each other, but only on the basis of being achievable by one of ordinary skill in the art. When a combination of technical solutions is contradictory or impossible to implement, such a combination should be considered non-existent and not within the scope of protection claimed by this invention.

[0034] As attached Figure 1 As shown, this embodiment of the invention provides a method for evaluating the thermal aging state of thermosetting elastomers, including the following steps:

[0035] S1. Conduct a thermal aging test on the elastomer;

[0036] S2. During the processing in step S1, an aged sample is obtained, the maximum elongation and positron annihilation lifetime spectrum of the aged sample are tested, and the free volume of the aged sample is obtained by analyzing the positron annihilation lifetime spectrum.

[0037] S3. The least squares method is used to linearly fit the maximum elongation and free volume of the aged sample in step S2, and the fitting equation between the maximum elongation and free volume of the sample is established.

[0038] S4. In the actual thermal aging test of the same type of elastomer, the maximum elongation of the elastomer is estimated by measuring the free volume of the elastomer using the fitting equation established in step S3, and the thermal aging state of the elastomer is evaluated.

[0039] This invention studies the evolution of the microstructure and the trend of changes in the macroscopic mechanical properties of elastomers during thermal aging tests. It selects free volume data and maximum elongation data that both show a decreasing trend in thermal aging tests, studies the linear correlation between the free volume and maximum elongation of the elastomer, establishes a fitting equation, and thus establishes the connection between free volume and thermal aging state, so as to realize the characterization of the aging state of the elastomer by free volume.

[0040] In this embodiment of the invention, the thermal aging treatment of the aged sample is first set up, and the free volume data and maximum elongation data of the aged sample are tested. A fitting equation for the free volume and maximum elongation of the elastomer material to be studied is established. Then, in the actual thermal aging test of the elastomer material, the fitting equation is used to obtain the free volume by testing its positron annihilation lifetime spectrum, so that the current thermal aging state of the elastomer can be obtained. Compared with the use of destructive mechanical property testing, which causes the sample to be damaged during each test and cannot continue the subsequent test, the free volume test does not damage the sample. After the test, the same sample can be used to continue the thermal aging test to ensure that the test data are the free volume of the same sample at different thermal aging times. This realizes the in-situ detection of the elastomer in the thermal aging state, reduces the test error caused by individual sample differences, and improves the accuracy of the thermal aging performance research results. At the same time, after the linear relationship is determined, the subsequent tests of the same elastomer material are all non-destructive tests, and the sample amount is small. Only two sheet-like samples of the same size are required for positron annihilation lifetime spectrum testing, which can reduce the consumption of raw materials.

[0041] The embodiments of the present invention can be used in the field of thermosetting polyurethane aging performance research, and are applicable to the research on the thermal aging performance of polyurethane elastomers for composite solid propellants.

[0042] In step S2, due to the differences in sample size required for testing and the destructive nature of the maximum elongation test, the aged samples include a first test sample for positron annihilation lifetime spectrum testing and a second test sample for maximum elongation testing. The first and second test samples are taken simultaneously at a certain sampling cycle to ensure that the aging states of the samples used in the positron annihilation lifetime spectrum test and the maximum elongation test are similar, thereby reducing data errors and improving the accuracy of the finally established fitting equation. The sampling cycle is set or adjusted according to the aging resistance characteristics of different elastomer materials. Elastomer materials with drastic performance changes in the thermal aging test require a smaller sampling cycle. Increasing the sampling frequency reduces errors and improves the accuracy of the finally established linear fitting equation.

[0043] Since positron annihilation lifetime spectroscopy can be performed non-destructively, after the first test sample is taken out according to the sampling cycle and the positron annihilation lifetime spectrum is tested, the first test sample is put back for subsequent thermal aging treatment. The free volume of each first test sample is measured during the entire thermal aging process, and the evolution law of the free volume measured in situ is used to improve the accuracy of the established fitting equation. Moreover, non-destructive testing can reduce the consumption of raw materials. The number of first test samples is set to 2 to 3 for parallel experiments to reduce test errors. Since the parallelism of the positron annihilation lifetime spectrum test used in this embodiment of the invention is good, the number of first test samples does not need to be too large. At the same time, in order to ensure complete encapsulation of the positron source in the positron annihilation lifetime spectrum test, the size of the first test sample is greater than 10mm × 10mm and the thickness is ≥2mm.

[0044] In step S2, each time sampling is performed, the number of second test samples is ≥5. The maximum elongation of the second test sample is obtained by performing a uniaxial tensile test. Generally, elastomers are considered to be materials with uniform overall composition. However, in reality, due to the influence of preparation methods or process errors, there may be some areas of non-uniform composition in different parts of the elastomer. This leads to inconsistent states of different parts of the elastomer during the heat aging test. Since the maximum elongation test is destructive, the second test sample used each time is not the same. Therefore, there may be individual differences in the second test sample for each test. Thus, ensuring a large number of second test samples to set up parallel experiments can minimize data deviations caused by individual differences and improve the accuracy of the finally established fitting equation.

[0045] In step S2, the free volume of the sample is obtained by analyzing the positron annihilation lifetime spectrum. This includes: using discrete analysis methods to resolve the positron annihilation lifetime spectrum to obtain lifetime component information. Specifically, the positron annihilation lifetime component information, including lifetime length and corresponding intensity, is obtained by interpreting the spectrum using the PATFIT program. Lifetime components of different lengths reflect the annihilation process of positrons in different characteristic structures, while the intensity reflects the content of the corresponding characteristic structure. The positron annihilation lifetime components of the polymer are typically determined by τ based on lifetime length. lThe system consists of three components: τ1 (0.1ns–0.2ns), τ2 (0.3ns–0.6ns), and τ3 (1ns–20ns), corresponding to the self-annihilation lifetime of p-Ps and positrons, the annihilation lifetime of positrons in the captured state, and the annihilation lifetime of o-Ps, respectively. The o-Ps annihilation lifetime and intensity are related to the free volume. The system detects the annihilation lifetime of positrons after implantation into the elastomer by capturing electrons in different structures such as lattice, defects, and pores, and obtains the positron annihilation lifetime component information using the PATFIT program. Using the o-Ps annihilation lifetime component τ3 (1ns–20ns), combined with the Tao-Eldrup model, the internal porosity information and free volume fraction of the PBT elastomer can be obtained. The Tao-Eldrup model provides a spherical potential well and gives a semi-empirical equation relating the o-Ps lifetime to the average radius R of the spherical aperture.

[0046]

[0047] Assuming the micropores in the material have a spherical geometry, the free volume fraction (FFV) of the material can be obtained from the radius calculated based on the average lifetime and the corresponding relative strength.

[0048]

[0049] In equations (2) and (3), τ3 is the o-Ps pick-up annihilation lifetime; I is the lifetime intensity; ΔR is the electron layer thickness parameter, usually taken as 0.1656 nm; and C is the material-related constant, usually taken as 0.5 ns.

[0050] When the test sample (such as PBT elastomer) contains a large number of strongly electronegative groups (redox potential < -0.9Ev, such as nitro, quinones, and acid anhydrides), the formation of electron octane is greatly suppressed, and there is almost no signal of the long lifetime component τ3 in the positron annihilation lifetime spectrum. In this case, the signal of the positron trapped state annihilation lifetime is used to calculate the free volume. In this case, τ3 in the Tao-Eldrup model can be replaced by τ2, and the values ​​of ΔR and C are adjusted accordingly to 0.3823 nm and 0.26 ns.

[0051] The aging state of elastomers is usually assessed by evaluating the degree of mechanical property degradation. This invention's embodiments reveal that the main aging mechanism of PBT-based polyether polyurethane is the oxidative crosslinking of the polymer backbone. The main characteristic of macroscopic mechanical property degradation during aging is a decrease in maximum elongation. Simultaneously, the microstructure of the elastomer exhibits a decrease in free volume. This invention uses the maximum elongation level as the assessment data for the thermal aging state of the elastomer. Furthermore, based on the similar trends in both microscopic and macroscopic changes, the specific correlation between the microscopic free volume and the macroscopic maximum elongation of the elastomer is studied, establishing a link between free volume and thermal aging state. The linear correlation coefficient R of the fitted equation is greater than 90%, ultimately achieving the characterization of the aging state using the microscopic free volume data of the elastomer.

[0052] Specifically, step S4 involves taking out a test sample of the same elastomer during the actual thermal aging test, performing a positron annihilation lifetime spectrum test, and then putting it back to continue the thermal aging test. This allows the test sample to be obtained at different times during the thermal aging test, thus avoiding damage to the test sample during mechanical property testing and achieving in-situ measurement of the thermal aging state of the elastomer.

[0053] The elastomers include polyether polyurethanes whose main aging mechanism is the oxidative crosslinking of the polymer backbone; further, the elastomers are PBT elastomers. PBT elastomers are essentially crosslinked polymers formed by a curing reaction of isocyanate curing agents, hydroxyl-terminated binder prepolymers, crosslinking agents, and chain extenders. The microscopic crosslinking network is the basic structure that determines its mechanical properties; the more complete the crosslinking network, the better the mechanical properties. Simultaneously, the free volume of the elastomer reflects the degree to which the crosslinking structure restricts the movement of the polymer molecular chains; the denser and more complete the network, the smaller the free volume. Therefore, the change in free volume during thermal aging can describe the evolution of the integrity of the crosslinking network structure, and the integrity of the crosslinking network structure further determines the mechanical properties of the elastomer. Furthermore, the elastomer is a PBT-based polyurethane elastomer plasticized with BDNPF / A. During thermal aging, BDNPF / A uniformly dispersed in the network structure will also undergo a certain degree of decomposition, producing oxidizing NO. x Small molecules, NO x Further, it attacks the PBT polyether backbone, causing oxidative crosslinking between molecular chains. The aforementioned aging effect introduces new crosslinking points into the polymer network structure, making the crosslinked network denser, while macroscopically it shows a decrease in elongation. Therefore, the free volume and the maximum elongation show a good linear correlation.

[0054] In step S2, aging samples are sampled at a certain sampling cycle. When the elastomer is PBT elastomer, the sampling cycle in step S2 is 20 days / time to 40 days / time. By setting the sampling frequency, sufficient sample data is ensured.

[0055] In step S1, the temperature of the heat aging treatment is set according to the actual heat aging test temperature of different elastomer materials. The recommended temperature for the heat aging test of PBT elastomer used in this embodiment is 40℃~80℃ (within this temperature range, the heat aging mechanism of the elastomer does not change, and the heat aging test temperature of energetic materials may cause danger if it is too high).

[0056] The fitting equation established in step S3 is as follows:

[0057] y = 1088.95x - 11336.99 (1)

[0058] In equation (1), y is the maximum elongation and x is the free volume; the linear correlation coefficient R of the fitted equation is... 2 =0.91, where R is the linear correlation coefficient; the fitting equation of the present invention has high accuracy in assessing the thermal aging state of PBT-based polyurethane elastomers plasticized with BDNPF / A.

[0059] Example 1:

[0060] S1. A series of PBT elastomer aging samples were vacuum-sealed in aluminum foil bags and placed in a water-insulated constant temperature incubator. The aging temperature (controlled with an accuracy of ±1℃) was set to 70℃ for heat aging treatment. The appearance of the elastomers before aging and after 180 days of aging is shown in the attached figure. Figure 2 As shown;

[0061] S2. During the aging process, the sampling cycle is 30 days per sampling cycle;

[0062] Each time, a sheet sample with dimensions of approximately 50mm × 50mm × 2mm was taken as the second test sample. After the obtained second test sample was placed in a glass desiccator and allowed to cool naturally for 48 hours, the uniaxial tensile properties of the PBT elastomer were tested using a Guangdong Kejian KJ-1066A-T universal mechanical testing machine. The test conditions were: 20℃, 100mm·min -1 Five parallel experiments were set up for each sampling, and the arithmetic mean was taken as the final result to obtain the maximum elongation variation law of PBT elastomer during thermal aging, as shown in the attached figure. Figure 3 As shown;

[0063] Three sets of 15mm×15mm×2mm sheet samples (2 sheets / set) were set up as the first test sample. The second test sample was taken out simultaneously with each sampling. The positron annihilation lifetime spectrum of the PBT elastomer first test sample was tested using the fast-fast coincidence system from Ortec, USA. The positron source (… 22Na (~10 μCi) was wrapped between two pieces of the first test sample to form a sandwich-like structure, then sealed with aluminum foil and placed in a vacuum test chamber. The test chamber was then tested until the vacuum level reached 1 × 10⁻⁶. -5 After Torr, lifetime spectra are collected, with a total count of 1 × 10⁻⁶ for a single lifetime spectrum. 6 The original positron annihilation lifetime spectrum was analyzed using the PATFIT program to obtain lifetime component information. The continuous spectrum of the positron annihilation lifetime distribution was then obtained using the MELT program, as shown in the attached diagram. Figure 4 As shown in the figure, the free volume of the matrix was calculated using the Tao-Eldrup model, and the evolution law of free volume during the aging process of PBT elastomer was obtained, as shown in the attached figure. Figure 5 As shown;

[0064] S3. The least squares method was used to linearly fit the free volume data and maximum elongation during the aging process of PBT elastomer, and a fitting equation for the maximum elongation and free volume of PBT elastomer was established, as shown in the appendix. Figure 6 As shown;

[0065] S4. In the actual thermal aging test of the same PBT elastomer, the fitting equation between the free volume and the maximum elongation of the material established in step S3 is used to estimate the maximum elongation of the elastomer by measuring the free volume of the elastomer, and to evaluate the thermal aging state of the elastomer.

[0066] Based on the results of this example, as shown in the attached document... Figure 3 and 5 As shown in the attached figure, the elongation and free volume of PBT elastomer both show a decreasing trend during the thermal aging process. Figure 6 As shown, the free volume and the maximum elongation exhibit a good linear correlation (R>90%), indicating that by measuring the free volume of the PBT elastomer during thermal aging, the elongation level of the PBT elastomer can be calculated by fitting the equation, thereby evaluating the aging state of the elastomer.

[0067] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0068] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

[0069] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

Claims

1. A method for assessing the thermal aging state of thermosetting elastomers, characterized in that, Includes the following steps: S1. Perform heat aging treatment on the elastomer; S2. Test the maximum elongation and positron annihilation lifetime spectrum of the aged sample obtained during the processing in step S1, and obtain the free volume of the aged sample by analyzing the positron annihilation lifetime spectrum. S3. The least squares method is used to linearly fit the maximum elongation and free volume of the aged sample in step S2 to establish the fitting equation of the maximum elongation and free volume of the elastomer during the thermal aging process. S4. In the actual thermal aging test of the same type of elastomer, the maximum elongation of the elastomer is estimated by measuring the free volume of the elastomer using the fitting equation established in step S3, and the thermal aging state of the elastomer is evaluated.

2. The method for assessing the thermal aging state of thermosetting elastomers as described in claim 1, characterized in that, In step S2, the aged sample includes a first test sample for positron annihilation lifetime spectrum testing and a second test sample for maximum elongation testing, and the first and second test samples are taken at the same sampling period.

3. The method for assessing the thermal aging state of thermosetting elastomers as described in claim 2, characterized in that, The number of the first test samples is 2 to 3, and the positron annihilation lifetime spectrum is taken out according to the sampling cycle.

4. The method for assessing the thermal aging state of thermosetting elastomers as described in claim 2, characterized in that, In step S2, each time a sample is taken, the number of the second test sample is ≥5, and the maximum elongation of the second test sample is obtained by performing a uniaxial tensile test.

5. The method for assessing the thermal aging state of thermosetting elastomers as described in any one of claims 1 to 4, characterized in that, In step S3, the linear correlation coefficient R of the fitted equation is greater than 90%.

6. The method for assessing the thermal aging state of thermosetting elastomers as described in any one of claims 1 to 4, characterized in that, Step S4 specifically involves: during the actual thermal aging test, after taking out the test sample of the same elastomer for positron annihilation lifetime spectrum testing, putting it back to continue the thermal aging test, and obtaining the thermal aging state of the same test sample at different times in the thermal aging test.

7. The method for assessing the thermal aging state of thermosetting elastomers as described in any one of claims 1 to 4, characterized in that, The elastomer is a polyether polyurethane whose main aging mechanism is the oxidative crosslinking of the polymer backbone.

8. The method for assessing the thermal aging state of thermosetting elastomers as described in claim 7, characterized in that, The elastomer is a PBT elastomer. In step S2, aging samples are sampled at a certain sampling cycle, which is 20 days / time to 40 days / time.

9. The method for assessing the thermal aging state of thermosetting elastomers as described in claim 8, characterized in that, In step S1, the temperature of the thermal aging treatment is 40℃~80℃.

10. The method for assessing the thermal aging state of thermosetting elastomers as described in claim 8, characterized in that, in The fitting equation established in step S3 is as follows: y = 1088.95x - 11336.99 (1) Where y is the maximum elongation and x is the free volume; The linear correlation R of the fitted equation 2 =0.91, where R is the linear correlation coefficient.

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