Viscoelastic characteristic parameter-based insulation material aging resistance evaluation method

Abstract

The invention belongs to the technical field of high polymer material performance testing, and particularly relates to a viscoelastic characteristic parameter-based insulating material aging resistance evaluation method, which comprises the following steps of: measuring a change curve of viscoelastic characteristic parameters of a sample along with time by adopting a rotational rheometer, and drawing a double logarithmic diagram of the viscoelastic characteristic parameters and the time to evaluate the aging resistance of the insulating material. And determining inflection point time ta on the double logarithmic diagram by using a double tangent method, and evaluating the aging resistance of different samples by comparing the inflection point time ta of different samples. By adopting the evaluation method provided by the invention, the aging resistance is effectively evaluated through the inflection point time ta, the influence of the intrinsic difference of the material on the evaluation result is reduced, the evaluation consistency and comparability are improved, the aging resistance of the material can be directly evaluated without an accelerated aging experiment, the experiment period is effectively shortened, and the evaluation efficiency is improved. And an accurate test result can be obtained by using a small sample amount.

Description

Technical Field

[0001] This invention belongs to the technical field of polymer material performance testing, specifically relating to a method for evaluating the aging resistance of insulating materials based on viscoelastic property parameters. Background Technology

[0002] Insulating materials, especially polymer insulating materials, undergo aging during production, transportation, storage, or service due to prolonged exposure to factors such as heat, electricity, force, light, and oxygen. This aging leads to irreversible degradation of material properties and even insulation failure, ultimately affecting the safe and reliable operation of electrical equipment. Assessing and improving the aging performance of insulating materials is a current research hotspot both domestically and internationally. The aging of insulating materials is the result of multiple factors acting over a long period, often lasting several years or even decades. To shorten the testing cycle, most existing research employs accelerated aging tests. These tests simulate the long-term aging process by intensifying aging factors (such as high temperature, high pressure, and mechanical stress) within a shorter timeframe. The accelerated-aged samples are then analyzed to assess the degree of aging and, consequently, the material's aging resistance. Although accelerated aging tests can significantly shorten the testing cycle, they still generally require several days or even months, resulting in a relatively long testing period.

[0003] Currently used methods for analyzing the aging degree of insulating materials, such as infrared spectroscopy, assess the degree of oxidation by detecting changes in chemical bonds (e.g., carbonyl index). This method is only suitable for assessing the aging degree of materials with the same chemical composition. When the chemical composition of insulating materials differs, this method cannot provide a unified index for evaluating the material's aging performance. For example, regarding polyethylene and glycidyl methacrylate-grafted polyethylene, the glycidyl methacrylate-grafted polyethylene itself contains carbonyl groups, making it impossible to eliminate the intrinsic differences between the materials. Therefore, it is difficult to assess the oxidative aging degree of the two materials by comparing their carbonyl indices. Similarly, other commonly used methods, such as testing the crystallinity, elongation at break, or dielectric loss of materials, cannot eliminate the intrinsic differences between different materials.

[0004] Therefore, there is a need for a method to evaluate the aging resistance performance that has a short experimental cycle and can eliminate the intrinsic differences between different materials. Summary of the Invention

[0005] In a first aspect, this invention provides a method for evaluating the aging resistance of insulating materials based on viscoelastic property parameters, comprising the following steps:

[0006] S1. The sample was tested using a rotational rheometer to obtain the curves of the changes in the viscoelastic properties of the test sample over time, and a double logarithmic graph of the viscoelastic properties and time was plotted.

[0007] S2. Determine the inflection point time t on a double logarithmic graph using the double tangent method. a ;

[0008] S3. By comparing the inflection point time t of different samples a Size was used to evaluate the aging resistance of different samples.

[0009] In some implementations, in step S1, the sample needs to be preheated before testing. The preheating temperature is higher than the melting temperature of the sample, and the preheating time is 1-10 minutes.

[0010] In some implementations, the test temperature in step S1 is 190-210°C.

[0011] In some implementations, in step S2, the inflection point time t is determined on a double logarithmic graph using the double tangent method. a The specific method is as follows: Draw tangent lines l1 and l2 in the plateau region and rising region of the double logarithmic graph, respectively. Take the intersection point of the two tangent lines. The time corresponding to the intersection point is the inflection point time t. a .

[0012] In some implementations, in step S2, the plateau region is determined by the following method: starting from time t0, within the continuous interval [t0, t0+Δt], the fluctuation range of the viscoelastic property parameter value is <±2% A, and the interval duration Δt ≥ 60s, then [t0, t0+Δt] is defined as the plateau region; where t0 is the test start time, A is the viscoelastic property parameter value corresponding to the test start time, and Δt is the interval duration.

[0013] In some preferred embodiments, the interval duration Δt ≥ 90s.

[0014] In some implementations, the tangent l1 is obtained by linearly fitting the data points in the plateau region.

[0015] In some implementations, in step S2, the rising region is determined by the following method: the tangent slope k of each data point in the rising region is greater than 0, and the tangent slope k of each data point in the rising region is greater than the tangent slope k1 of the plateau region l1, wherein k satisfies the condition: k≥10k1.

[0016] In some implementations, in step S1, during the test, the test is stopped when the energy storage modulus value rises to twice or more the minimum energy storage modulus value in the platform area.

[0017] In some implementations, the tangent l2 is the tangent with the steepest slope in the rising region.

[0018] In some implementations, the viscoelastic property parameter includes the storage modulus.

[0019] In a second aspect, the present invention provides the application of the above method in evaluating the aging resistance of materials.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) Traditional accelerated thermal aging tests usually take several days or even several months to simulate the long-term aging process of materials under actual use conditions. The aging resistance evaluation method provided by this invention does not require accelerated aging tests and can directly evaluate the aging resistance of materials, effectively shortening the test cycle.

[0022] (2) Current methods for assessing the aging degree of insulating materials, such as elongation at break, crystallinity, and dielectric loss, cannot eliminate the intrinsic differences between different materials. The aging resistance assessment method provided by this invention uses the inflection point time t of the viscoelastic property parameter (such as storage modulus) curve. a To assess aging resistance, reduce the impact of intrinsic material differences on assessment results, and improve the consistency and comparability of assessments;

[0023] (3) The aging resistance evaluation method provided by the present invention does not require accelerated thermal aging test or complex equipment, greatly simplifies the experimental operation process, and is particularly suitable for application scenarios that require rapid evaluation in laboratory or industrial production.

[0024] (4) The aging resistance evaluation method provided by the present invention can obtain accurate test results with a small sample amount. Attached Figure Description

[0025] Figure 1 This is a schematic diagram illustrating the determination of intersection points using the double tangent method.

[0026] Figure 2 The diagram shows a double logarithmic plot of the storage modulus versus time for four types of insulation samples. Detailed Implementation

[0027] The following detailed embodiments further illustrate the content of the present invention. These embodiments do not constitute a limitation on the scope of protection of the present invention. Non-essential modifications and adjustments made by others based on the concept of the present invention still fall within the scope of protection of the present invention. The raw materials, reagents, or devices used in the embodiments are all available from conventional commercial sources or can be obtained through existing technical methods. Unless otherwise specified, the experimental or testing methods are conventional methods in the art.

[0028] Insulation Sample A: Low-density polyethylene for high-voltage cable insulation, commercially available product.

[0029] Insulation sample B: Ethylene-acrylic acid copolymer, commercially available product.

[0030] Insulation sample C: Ethylene-glycidyl methacrylate copolymer, commercially available product.

[0031] Insulation sample D: Insulation sample A was aged at 100°C for 10 days to obtain aged low-density polyethylene for high-voltage cable insulation.

[0032] This embodiment provides a method for evaluating the aging resistance of insulating materials based on viscoelastic property parameters, including the following steps:

[0033] S1. Sample preparation: Prepare the insulating sample into a thin sheet for rheological testing. The thickness of the insulating sample is 1.0 mm. The shape of the insulating sample is consistent with the shape of the parallel plate rotor of the rotating rheometer, and the diameter is 25 mm.

[0034] S2. Conduct the test: Use a rotational rheometer, select the parallel plate test system, and set the test mode to small oscillation shear mode. Place the insulating sample in the rotational rheometer, preheat at 120℃ for 5 minutes, then raise the temperature to 200℃ for testing. When the storage modulus value rises to twice the minimum storage modulus value in the plateau region (i.e., after the curve shows a clear upward trend), the test can be stopped. Obtain the curve of the viscoelastic properties of the test sample changing with time, and plot a double logarithmic graph of storage modulus versus time. Figure 2 Note: The preheating temperature needs to be 5-15℃ higher than the melting temperature of the insulation sample to ensure that the insulation sample is completely melted.

[0035] S3. Determine the plateau region and tangent l1: Select a continuous interval where the energy storage modulus fluctuation is <±2%, and the interval duration Δt≥90s. That is, starting from time t0, within the continuous interval [t0, t0+Δt], if the energy storage modulus fluctuation is <±2% A, and the interval duration Δt≥90s, then this continuous interval is the plateau region. Here, t0 is the test start time, A is the viscoelastic characteristic parameter value corresponding to the test start time, and Δt is the interval duration. Perform linear fitting on the data points of the plateau region to obtain the tangent l1.

[0036] S4. Determine the rising region and tangent l2: Select a continuous interval where the slope of the tangent line to the data points is greater than or equal to 0 and k ≥ 10k1 (k1 is the slope of tangent l1). This continuous interval is the rising region. Select the tangent line with the largest slope in the rising region to obtain tangent l2.

[0037] S5. Determine the inflection point: The intersection of tangent l1 and tangent l2 is the inflection point, and the time corresponding to the inflection point is t. a inflection point time t a The larger the value, the better the aging resistance of the insulation sample.

[0038] Figure 1 This is a schematic diagram illustrating the use of the double tangent method to determine the intersection point in this invention. Figure 2 Table 1 shows the inflection point time t for the four types of insulation samples, with the storage modulus as a function of time being a double logarithmic plot. a And the corresponding interval duration Δt.

[0039] Table 1

[0040] Insulation test specimen <![CDATA[t a / s]]> Δt / s Insulation Sample A 3566 492 Insulation sample B 1298 96 Insulation sample C 1367 90 Insulation sample D 239 192

[0041] Table 1 shows that the aging resistance of the four insulating samples is: A > C > B > D. Among them, the inflection point time t of insulating sample A is... a The inflection point time t of the insulation sample D, which has been aged at 100°C for 10 days, is 3566s. a It dropped to 239s.

[0042] To verify the effectiveness of the method provided by the present invention, the oxidation induction period (OIT), which is commonly used in the art to evaluate the aging resistance of polymer materials, was used to test the aging resistance of four insulating samples.

[0043] Test Method: The oxidation induction time (OIT) of four types of insulating samples was tested using differential scanning calorimetry (DSC). 5 mg of the insulating sample was weighed and heated from 50 °C to 200 °C at a heating rate of 10 °C / min in a N2 atmosphere. After holding at 200 °C for 5 min, the N2 atmosphere was switched to an O2 atmosphere. The flow rates of both N2 and O2 were 50 mL / min. The experiment was terminated when a clear exothermic oxidation peak appeared on the DSC curve. OIT is the time corresponding to the intersection of the tangent line at the point of maximum slope of the oxidation curve and the extension line of the horizontal segment at the tail of the oxidation curve. The longer the oxidation induction time, the better the heat-induced oxygen aging resistance of the material. Table 2 shows the oxidation induction time (OIT) data for the four types of insulating samples.

[0044] Table 2

[0045] Insulation test specimen OIT / min Insulation Sample A 5.8 Insulation sample B 3.4 Insulation sample C 4.7 Insulation sample D 1.9

[0046] Table 2 shows that the aging resistance of the four insulating samples is: A > C > B > D, consistent with the conclusions in Table 1, proving that the evaluation method provided by this invention has accuracy and reliability. Furthermore, in insulating samples A and D, the ta values ​​obtained using the evaluation method of this invention are 3566s and 239s, respectively, a difference of nearly 15 times, while the OIT values ​​obtained using the OTI method are 5.8min and 1.9min, respectively, a difference of only 3 times, showing a small difference. Therefore, the evaluation method provided by this invention has higher sensitivity when applied to the aging resistance evaluation of various materials.

[0047] In summary, the evaluation method provided by this invention can effectively eliminate the intrinsic property differences between different materials, realize the aging resistance evaluation of insulating materials with different chemical compositions, and the evaluation method of this invention does not require accelerated aging tests on the samples. The test process only takes tens of minutes or several hours, which significantly shortens the experimental cycle.

[0048] 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 evaluating the aging resistance of insulating materials based on viscoelastic property parameters, characterized in that, Includes the following steps: S1. The sample was tested using a rotational rheometer to obtain the curves of the changes in the viscoelastic properties of the sample over time, and a double logarithmic graph of the viscoelastic properties versus time was plotted. S2. Determine the inflection point time t on a double logarithmic graph using the double tangent method. a ; S3. By comparing the inflection point time t of different samples a Size was used to evaluate the aging resistance of different samples.

2. The method as described in claim 1, characterized in that, In step S1, the sample needs to be preheated before testing. The preheating temperature is higher than the melting temperature of the sample, and the preheating time is 1-10 minutes.

3. The method as described in claim 1, characterized in that, In step S1, the test temperature is 190-210℃.

4. The method as described in claim 1, characterized in that, In step S2, the inflection point time t is determined on the double logarithmic graph using the double tangent method. a The specific method is as follows: Draw tangent lines l1 and l2 in the plateau region and rising region of the double logarithmic graph, respectively. Take the intersection point of the two tangent lines. The time corresponding to the intersection point is the inflection point time t. a .

5. The method as described in claim 4, characterized in that, In step S2, the plateau region is determined by the following method: starting from time t0, within the continuous interval [t0, t0+Δt], the fluctuation range of the viscoelastic property parameter value is <±2%A, and the interval duration Δt≥60s, then [t0, t0+Δt] is defined as the plateau region; Where t0 is the test start time, A is the viscoelastic property parameter value corresponding to the test start time, and Δt is the interval duration.

6. The method as described in claim 4, characterized in that, The tangent l1 is obtained by linearly fitting the data points in the plateau region.

7. The method as described in claim 4, characterized in that, In step S2, the rising region is determined by the following method: the tangent slope k of each data point in the rising region is greater than 0, and the tangent slope k of each data point in the rising region is greater than the tangent slope k1 of the plateau region l1. The k satisfies the condition: k≥10k1.

8. The method as described in claim 4, characterized in that, The tangent l2 is the tangent with the largest slope in the ascending region.

9. The method as described in claim 1, characterized in that, The viscoelastic property parameters include the storage modulus.

10. The application of the method as described in any one of claims 1-9 in evaluating the aging resistance of materials.

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