Method for evaluating the results of a pre-oxidation reaction of polyacrylonitrile fibers

Abstract

The application provides an evaluation method for pre-oxidation reaction results of polyacrylonitrile fibers, and belongs to the technical field of carbon fiber manufacturing. The evaluation method for pre-oxidation reaction results of polyacrylonitrile fibers comprises the following steps: S1, providing polyacrylonitrile filaments before pre-oxidation treatment and pre-oxidized fibers after pre-oxidation treatment, which are denoted as PANF and OF; S2, respectively testing the cyclization reaction heat of PANF and OF under inert gas atmosphere by using a differential scanning calorimeter, and denoted as Q 1PANF and Q 1OF respectively; S3, respectively testing the first total reaction heat of PANF and OF under air atmosphere by using a differential scanning calorimeter under the same test conditions, and denoted as Q 2PANF and Q 2OF respectively; and S4, calculating the oxidation reaction degree according to formula I. The evaluation method can comprehensively evaluate the pre-oxidation reaction results of polyacrylonitrile fibers, thereby better guiding the production and research and development of polyacrylonitrile-based carbon fibers.

Description

Technical Field

[0001] This application relates to the field of carbon fiber manufacturing technology, and more specifically, to a method for evaluating the results of the pre-oxidation reaction of polyacrylonitrile fibers. Background Technology

[0002] The industrial production process of polyacrylonitrile-based carbon fiber (PAN-CF) generally includes acrylonitrile polymerization to prepare PAN spinning solution, spinning the solution to prepare PAN precursor fibers, removing impurities from the precursor fibers through pre-oxidation, low-temperature carbonization, and high-temperature carbonization to prepare carbon filaments, and finally, surface treatment and sizing to obtain the finished carbon fiber. Among these processes, the pre-oxidation process, accompanied by a dramatic evolution of the PAN molecular chain structure from linear to trapezoidal, is a crucial process determining the mechanical properties of carbon fiber. Therefore, the results of the PAN fiber pre-oxidation reaction are particularly important for the production and research and development of PAN-CF. Currently, evaluating the pre-oxidation reaction results using the degree of cyclization reaction is a common method; however, this evaluation method suffers from overly simplistic conclusions. Summary of the Invention

[0003] The purpose of this application is to provide a method for evaluating the pre-oxidation reaction results of polyacrylonitrile fibers. This evaluation method can comprehensively evaluate the pre-oxidation reaction results of polyacrylonitrile fibers, thereby better guiding the production and research and development of polyacrylonitrile-based carbon fibers.

[0004] The embodiments of this application are implemented as follows:

[0005] In a first aspect, embodiments of this application provide a method for evaluating the results of a pre-oxidation reaction of polyacrylonitrile fibers, comprising the following steps:

[0006] S1 provides pre-oxidized polyacrylonitrile precursor fibers and pre-oxidized fibers after pre-oxidation treatment, denoted as PANF and OF respectively; S2 uses a differential scanning calorimeter under an inert atmosphere to test the cyclization heat of PANF and OF respectively, denoted as Q. 1PANF and Q 1OF S3 Under the same test conditions, the first total heat of reaction of PANF and OF was measured separately in air atmosphere using a differential scanning calorimeter, and denoted as Q. 2PANF and Q 2OF S4 The degree of oxidation reaction is calculated according to formula I: .

[0007] The inventors discovered that in the pre-oxidation process of polyacrylonitrile fibers, oxidation usually dominates; specifically, the proportion of oxidation reaction is approximately 2 to 3 times that of cyclization reaction. Therefore, the existing technology of using the degree of cyclization reaction as an indicator to evaluate the pre-oxidation reaction result has the problem of being too one-sided. This application innovatively uses the more representative degree of oxidation reaction as an evaluation indicator for the pre-oxidation reaction result and provides a specific method for testing the degree of oxidation reaction. Specifically, the cyclization reaction heat of PANF and OF is first tested separately, and then the total reaction heat of both is tested separately. The specific degree of oxidation reaction is then easily calculated using the above formula. The core principle is: cyclization reaction heat + oxidation reaction heat = total reaction heat. Based on this, Q... 2PANF -Q 1PANF The heat of oxidation of polyacrylonitrile precursor fiber (i.e., the initial heat of oxidation of polyacrylonitrile precursor fiber), Q 2OF -Q 1OF The heat of oxidation of pre-oxidized fibers (i.e., the heat of oxidation remaining in the polyacrylonitrile precursor fiber), (Q) 2PANF -Q 1PANF )-(Q 2OF -Q 1OF The heat of oxidation of the polyacrylonitrile precursor fiber during the pre-oxidation process can be used to calculate the degree of oxidation during the pre-oxidation process by comparing the heat of oxidation of the polyacrylonitrile precursor fiber with the initial heat of oxidation. This allows for a more comprehensive evaluation of the pre-oxidation results of the polyacrylonitrile fiber, thus providing better guidance for the production and research and development of polyacrylonitrile-based carbon fibers.

[0008] In some optional implementations, in the step of testing the cyclization reaction heat and the first total reaction heat with differential scanning calorimetry, the starting temperature of the heating section is 20~40℃, the ending temperature is 400~500℃, or / and the heating rate is 5~20℃ / min.

[0009] In the above technical solution, for polyacrylonitrile, the starting temperature, ending temperature and heating rate of the heating section are limited to the above range to provide more suitable test conditions, which can test more accurate results of the degree of oxidation reaction, thereby more accurately evaluating the pre-oxidation reaction results of polyacrylonitrile fibers.

[0010] In some alternative implementations, in the step of testing the cyclization reaction heat and the first total reaction heat using differential scanning calorimetry, the sample amount is 4-6 mg and the gas flow rate is 60-80 mL / min.

[0011] In the above technical solution, in the step of testing the cyclization reaction heat and the first total reaction heat using a differential scanning calorimeter, the sample amount and gas flow rate are limited to the above ranges to provide suitable testing conditions, which helps polyacrylonitrile to react fully and efficiently, thereby enabling the test to obtain more accurate results of the oxidation reaction degree, and thus more accurately evaluate the pre-oxidation reaction results of polyacrylonitrile fibers.

[0012] In some alternative implementations, the test is repeated to obtain multiple oxidation reaction degree values. Then, the maximum and minimum values ​​among the multiple oxidation reaction degree values ​​are removed, and the average value of the remaining multiple oxidation reaction degree values ​​is calculated. The average value is used as the final test result of the oxidation reaction degree.

[0013] In the above technical solution, the multiple oxidation reaction degree values ​​obtained from the test are screened and averaged to obtain more representative oxidation reaction degree results, thus more realistically reflecting the pre-oxidation reaction results of polyacrylonitrile fibers.

[0014] In some optional implementations, the temperature range in the test conditions of step S3 is a heating range; step S5 includes: measuring the second total heat of reaction of OF in an air atmosphere using a differential scanning calorimeter, denoted as Q. 3OF The temperature range in the test conditions of step S5 includes a first heating stage, a first holding stage, a first cooling stage, and a second heating stage performed sequentially; wherein, the processing temperature of the first holding stage is 300~350℃, and the conditions of the second heating stage in step S5 are the same as those of the heating stage in step S3; step S6 includes: using a differential scanning calorimeter to test the third total reaction heat of OF in an air atmosphere, denoted as Q. 4OF The only difference between the test conditions in steps S6 and S5 is that the processing time of the first heat preservation stage in step S6 is T2, while the processing time of the first heat preservation stage in step S5 is T1, where T2 = 2T1; S7 calculates the degree of homogenization of the oxidation reaction according to formula II:

[0015] .

[0016] In the above technical solution, based on step S3, steps S5 to S7 are further performed according to the above process, wherein Q 2OF -Q 3OF The heat of oxidation of the fiber in the first half of the first heat preservation stage is represented by the temperature within the aforementioned range. Setting the processing temperature of the first heat preservation stage within this range ensures that the cyclization reaction is essentially completed at this stage, helping to reduce the interference of the cyclization heat on the oxidation heat, thereby increasing Q. 2OF -Q 3OF To more closely approximate the actual thermal difference of the oxidation reaction at this stage, thereby improving the accuracy of homogenization testing; Q3OF -Q 4OF The oxidation reaction heat of the fiber in the latter half of the first heat preservation stage is represented by T2. Setting T2 to 2T1 is to ensure that the reaction time in the first and second halves of the first heat preservation stage is the same. By using the oxidation reaction heat of two adjacent reaction stages within the same time period, the degree of homogenization of the oxidation reaction can be calculated. This allows for a more accurate evaluation of the uniformity of the oxidation reaction during the pre-oxidation process. At the same time, the degree of homogenization can also be used to evaluate the texture uniformity of the fiber obtained after pre-oxidation treatment, thus constructing a more comprehensive evaluation system for the pre-oxidation process.

[0017] In some alternative implementations, the processing time for the first heat preservation stage in step S5 is 2 to 10 minutes.

[0018] In the above technical solution, the processing time of the first heat preservation stage is limited to the aforementioned range to provide a suitable reaction time. This suitable time can more effectively reduce the interference of the cyclization reaction heat on the oxidation reaction heat during this stage, thereby ensuring that Q... 2OF -Q 3OF It more closely approximates the actual thermal difference of the oxidation reaction at this stage, thereby more effectively improving the accuracy of homogenization degree testing.

[0019] In some alternative implementations, in step S5, the heating rate of the first heating stage is 40~60℃ / min.

[0020] In the above technical solution, limiting the heating rate of the first heating stage to the above range enables the temperature stage to reach the first heat preservation stage as soon as possible, so that the heat difference mainly comes from the first heat preservation stage, which helps to improve the test accuracy of homogenization degree.

[0021] In some alternative implementations, step S5 may include a second heat preservation stage between the first cooling stage and the second heating stage.

[0022] In the above technical solution, a second heat preservation section is added between the first cooling section and the second heating section so that the temperature of the entire material is relatively stable before the second heating section, thereby making the starting temperature conditions of the second heating section closer to the starting temperature conditions in step S3, which helps to improve the test accuracy of homogenization degree.

[0023] In some alternative implementations, the second insulation stage lasts for 3 to 5 minutes.

[0024] In the above technical solution, the processing time of the second heat preservation stage is limited to the above range to provide a suitable heat preservation time, so that the starting temperature conditions of the second heating stage are closer to the starting temperature conditions in step S3, which helps to improve the test accuracy of homogenization degree.

[0025] In some alternative implementations, the test is repeated to obtain multiple homogenization values. Then, the maximum and minimum values ​​among the multiple homogenization values ​​are removed, and the average of the remaining multiple homogenization values ​​is calculated. The average value is used as the final test result of the homogenization degree.

[0026] In the above technical solution, the multiple homogenization values ​​obtained from the test are screened and averaged to obtain more representative homogenization results, thus more realistically reflecting the pre-oxidation reaction results of polyacrylonitrile fibers. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 A process flow diagram of a method for evaluating the pre-oxidation reaction results of polyacrylonitrile fibers provided in this application embodiment;

[0029] Figure 2 Temperature program curves for Program 1 and Program 2 provided in the embodiments of this application;

[0030] Figure 3 A comparison chart of DSC curves of PANF and OF obtained by procedure one in Example 1 of this application;

[0031] Figure 4 A comparison chart of DSC curves of PANF and OF obtained by procedure two in Example 1 of this application;

[0032] Figure 5 Temperature program curves for procedures three and four provided in the embodiments of this application;

[0033] Figure 6 A comparison chart of DSC curves obtained by OF through procedures three and four in Embodiment 1 of this application. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0035] It should be noted that the terms "and / or" in this application, such as "feature 1 and / or feature 2", all refer to the three cases of "feature 1" alone, "feature 2" alone, and "feature 1" plus "feature 2".

[0036] In addition, in the description of this application, unless otherwise stated, "one or more" means two or more; the range of "numerical value a to numerical value b" includes the two endpoints "a" and "b"; and "unit of measurement" in "numerical value a to numerical value b + unit of measurement" represents the "unit of measurement" of both "numerical value a" and "numerical value b".

[0037] Currently, technicians primarily evaluate the pre-oxidation reaction results using the degree of cyclization reaction as an indicator. However, this evaluation method suffers from overly simplistic conclusions. The inventors' research revealed that the current evaluation method lacks representativeness because: during the pre-oxidation of PAN fibers, cyclization, dehydrogenation, and oxidation reactions from the outer layer to the inner layer mainly occur, forming conjugated cyclized structures, oxygen-containing structures, and heterogeneous structures between the skin and core. Among these, dehydrogenation is endothermic, while cyclization and oxidation are exothermic (the specific heat release can be directly obtained through DSC testing). Furthermore, during pre-oxidation, the proportion of oxidation is approximately 2-3 times that of cyclization, making it dominant; that is, the proportion of cyclization is very small. Based on this, the inventors innovatively use the more representative degree of oxidation reaction as an evaluation indicator for the pre-oxidation reaction results, which can better guide the production and research and development of polyacrylonitrile-based carbon fibers.

[0038] The following is a detailed description of an evaluation method for the pre-oxidation reaction results of polyacrylonitrile fibers according to an embodiment of this application.

[0039] In a first aspect, embodiments of this application provide a method for evaluating the results of a pre-oxidation reaction of polyacrylonitrile fibers, comprising the following steps:

[0040] S1 provides pre-oxidized polyacrylonitrile precursor fibers and pre-oxidized fibers after pre-oxidation treatment, denoted as PANF and OF respectively; S2 uses a differential scanning calorimeter under an inert atmosphere to test the cyclization heat of PANF and OF respectively, denoted as Q. 1PANF and Q 1OF S3 Under the same test conditions, the first total heat of reaction of PANF and OF was measured separately in air atmosphere using a differential scanning calorimeter, and denoted as Q. 2PANF and Q 2OF S4 The degree of oxidation reaction is calculated according to formula I: .

[0041] This application innovatively uses the more representative degree of oxidation reaction as an evaluation index for the pre-oxidation reaction result, and provides a specific testing method for the degree of oxidation reaction. Specifically, the cyclization reaction heats of PANF and OF are first tested separately, and then the total reaction heats of the two are tested separately. The specific degree of oxidation reaction is then easily calculated using the above formula. The core principle is: cyclization reaction heat + oxidation reaction heat = total reaction heat. Based on this, Q... 2PANF -Q 1PANF The heat of oxidation of polyacrylonitrile precursor fiber (i.e., the initial heat of oxidation of polyacrylonitrile precursor fiber), Q 2OF -Q 1OF The heat of oxidation of pre-oxidized fibers (i.e., the heat of oxidation remaining in the polyacrylonitrile precursor fiber), (Q) 2PANF -Q 1PANF )-(Q 2OF -Q 1OF The heat of oxidation of the polyacrylonitrile precursor fiber during the pre-oxidation process can be used to calculate the degree of oxidation during the pre-oxidation process by comparing the heat of oxidation of the polyacrylonitrile precursor fiber with the initial heat of oxidation. This allows for a more comprehensive evaluation of the pre-oxidation results of the polyacrylonitrile fiber, thus providing better guidance for the production and research and development of polyacrylonitrile-based carbon fibers.

[0042] It should be noted that, through Q in step S2 1PANF and Q 1OF The degree of cyclization can also be calculated directly using the following formula:

[0043]

[0044] As an example, in the step of testing the cyclization reaction heat and the first total reaction heat using a differential scanning calorimeter, the starting temperature of the heating section is 20~40℃ (e.g., but not limited to any one of 20℃, 25℃, 30℃, 35℃ and 40℃ or any range between any two), the ending temperature is 400~500℃ (e.g., but not limited to any one of 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, 460℃, 470℃, 480℃, 490℃ and 500℃ or any range between any two), and / or the heating rate is 5~20℃ / min, e.g., but not limited to any one of 5℃ / min, 8℃ / min, 10℃ / min, 12℃ / min, 14℃ / min, 16℃ / min, 18℃ / min and 20℃ / min or any range between any two).

[0045] In this embodiment, for polyacrylonitrile, the starting temperature, ending temperature, and heating rate of the heating section are limited to the above-mentioned ranges to provide more suitable testing conditions, which can obtain more accurate results of the degree of oxidation reaction, thereby more accurately evaluating the pre-oxidation reaction results of polyacrylonitrile fibers.

[0046] As an example, in the differential scanning calorimeter test for the cyclization reaction heat and the first total reaction heat, the sample amount is 4 to 6 mg (e.g., but not limited to any one of 4 mg, 4.5 mg, 5 mg, 5.5 mg and 6 mg, or any range between any two), and the gas flow rate is 60 to 80 mL / min, e.g., but not limited to any one of 60 mL / min, 65 mL / min, 70 mL / min, 75 mL / min and 80 mL / min, or any range between any two).

[0047] In this embodiment, in the step of testing the cyclization reaction heat and the first total reaction heat using a differential scanning calorimeter, the sample amount and gas flow rate are respectively limited to the above-mentioned ranges to provide suitable testing conditions, which helps polyacrylonitrile to react fully and efficiently, thereby enabling the test to obtain more accurate results of the degree of oxidation reaction, and thus more accurately evaluate the pre-oxidation reaction results of polyacrylonitrile fibers.

[0048] As an example, the test is repeated to obtain multiple oxidation reaction degree values. Then, the maximum and minimum values ​​of the multiple oxidation reaction degree values ​​are removed, and the average value of the remaining multiple oxidation reaction degree values ​​is calculated. The average value is used as the final test result of the oxidation reaction degree.

[0049] In this embodiment, the multiple oxidation reaction degree values ​​obtained from the test are screened and averaged to obtain more representative oxidation reaction degree results, thereby more realistically reflecting the pre-oxidation reaction results of polyacrylonitrile fibers.

[0050] In other possible implementations, the value of a single oxidation reaction obtained from the test can be directly used as the final test result.

[0051] It should be noted that, at present, there is a lack of test indicators that can characterize the uniformity of oxidation reaction in the pre-oxidation process.

[0052] Based on this, the inventors further discovered that the degree of homogenization of the oxidation reaction can be calculated by the oxidation reaction heat of two adjacent reaction stages within the same time period, thus enabling a more accurate evaluation of the uniformity of the oxidation reaction during the pre-oxidation process. The following is an explanation of the specific test steps.

[0053] As an example, the temperature range in the test conditions of step S3 is the heating range; step S5 includes: using a differential scanning calorimeter to test the second total heat of reaction of OF in an air atmosphere, denoted as Q. 3OF The temperature range in the test conditions of step S5 includes a first heating stage, a first holding stage, a first cooling stage, and a second heating stage performed sequentially. The processing temperature of the first holding stage is 300~350℃ (e.g., but not limited to any one of 300℃, 310℃, 320℃, 330℃, 340℃, and 350℃, or a range between any two). The conditions for the second heating stage in step S5 are the same as those for the heating stage in step S3. Step S6 includes: measuring the third total heat of reaction of OF using a differential scanning calorimeter in an air atmosphere, denoted as Q. 4OF The only difference between the test conditions in steps S6 and S5 is that the processing time of the first heat preservation stage in step S6 is T2, while the processing time of the first heat preservation stage in step S5 is T1, where T2 = 2T1; S7 calculates the degree of homogenization of the oxidation reaction according to formula II:

[0054] .

[0055] It should be noted that in steps S5 and S6, the relevant parameters such as sample volume and gas flow rate can be referenced from step S3.

[0056] In this embodiment, based on step S3, steps S5 to S7 are further performed according to the above-described process, wherein Q 2OF -Q 3OF The heat of oxidation of the fiber in the first half of the first heat preservation stage is represented by the temperature within the aforementioned range. Setting the processing temperature of the first heat preservation stage within this range ensures that the cyclization reaction is essentially completed at this stage, helping to reduce the interference of the cyclization heat on the oxidation heat, thereby increasing Q. 2OF -Q 3OF To more closely approximate the actual thermal difference of the oxidation reaction at this stage, thereby improving the accuracy of homogenization testing; Q 3OF -Q 4OF The oxidation reaction heat of the fiber in the latter half of the first heat preservation stage is represented by T2. Setting T2 to 2T1 is to ensure that the reaction time in the first and second halves of the first heat preservation stage is the same. By using the oxidation reaction heat of two adjacent reaction stages within the same time period, the degree of homogenization of the oxidation reaction can be calculated. This allows for a more accurate evaluation of the uniformity of the oxidation reaction during the pre-oxidation process. At the same time, the degree of homogenization can also be used to evaluate the texture uniformity of the fiber obtained after pre-oxidation treatment, thus constructing a more comprehensive evaluation system for the pre-oxidation process.

[0057] As an example, in step S5, the processing time of the first heat preservation stage is 2 to 10 minutes, for example, but not limited to any one of the following points or any range between two processing times: 2 minutes, 3 minutes, 4 minutes, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, and 10 minutes.

[0058] In this embodiment, the processing time of the first heat preservation stage is limited to the above-mentioned range to provide a suitable reaction time. A suitable time can more effectively reduce the interference of the cyclization reaction heat on the oxidation reaction heat in this stage, so that Q... 2OF -Q 3OF It more closely approximates the actual thermal difference of the oxidation reaction at this stage, thereby more effectively improving the accuracy of homogenization degree testing.

[0059] As an example, in step S5, the heating rate of the first heating stage is 40~60℃ / min, for example, but not limited to any one of 40℃ / min, 45℃ / min, 50℃ / min, 55℃ / min and 60℃ / min or any range between two of them.

[0060] In this embodiment, limiting the heating rate of the first heating stage to the above range enables the temperature stage to reach the first heat preservation stage as quickly as possible, so that the heat difference mainly comes from the first heat preservation stage, which helps to improve the test accuracy of homogenization degree.

[0061] As an example, in step S5, the cooling rate of the first cooling stage is 40~60℃ / min, for example, but not limited to any one of 40℃ / min, 45℃ / min, 50℃ / min, 55℃ / min and 60℃ / min or any range between two of them.

[0062] As an example, in step S5, a second heat preservation section is also included between the first cooling section and the second heating section.

[0063] In this embodiment, a second heat preservation section is added between the first cooling section and the second heating section to make the temperature of the entire material more stable before the second heating section, so that the starting temperature conditions of the second heating section are closer to the starting temperature conditions in step S3, thereby helping to improve the test accuracy of homogenization degree.

[0064] As an example, the processing time of the second heat preservation stage is 3 to 5 minutes, for example, but not limited to any one of the processing times of 3 minutes, 3.5 minutes, 4 minutes, 4.5 minutes and 5 minutes or any range between two of them.

[0065] In this embodiment, the processing time of the second heat preservation stage is limited to the above range to provide a suitable heat preservation time, so that the starting temperature conditions of the second heating stage are closer to the starting temperature conditions in step S3, which helps to improve the test accuracy of homogenization degree.

[0066] As an example, the test is repeated to obtain multiple homogenization values. Then, the maximum and minimum values ​​among the multiple homogenization values ​​are removed, and the average of the remaining multiple homogenization values ​​is calculated. The average value is used as the final test result of the homogenization degree.

[0067] In this embodiment, the multiple homogenization values ​​obtained from the test are screened and averaged to obtain more representative homogenization results, thereby more realistically reflecting the pre-oxidation reaction results of polyacrylonitrile fibers.

[0068] In other possible implementations, the single homogenization value obtained from the test can be directly used as the final test result.

[0069] In summary, the evaluation method provided in this application can use DSC to simultaneously test three indicators of polyacrylonitrile fiber during the pre-oxidation process: the degree of cyclization reaction, the degree of oxidation reaction, and the degree of homogenization of the oxidation reaction. This enables efficient and accurate monitoring of the pre-oxidation process of polyacrylonitrile fiber, which has important guiding significance for the production and research and development of PAN-CF.

[0070] The features and performance of this application will be further described in detail below with reference to the embodiments.

[0071] Example 1

[0072] This application provides a method for evaluating the pre-oxidation reaction results of polyacrylonitrile fibers, including the following steps. A detailed process flow diagram can be found in [reference needed]. Figure 1 :

[0073] The 0.67 dtex polyacrylonitrile precursor fiber and the pre-oxidized fiber after pre-oxidation treatment were classified as PANF and OF.

[0074] 4 mg of PANF and OF were respectively tested under a nitrogen atmosphere with a purity ≥99.999% and a gas flow rate of 60 mL / min according to Procedure 1 to determine the cyclization reaction heat of PANF and OF; for details of Procedure 1, please refer to [link to Procedure 1]. Figure 2 (Specifically: the heating range is 30~450℃, and the heating rate is 10℃ / min). The data curve obtained from the test can be found in [reference needed]. Figure 3 Then, the cyclization reaction heats of PANF and OF were obtained using the data processing unit built into the DSC, and denoted as Q. 1PANF and Q 1OF .

[0075] 4 mg of PANF and OF were respectively tested under an air atmosphere with a gas flow rate of 60 mL / min according to Procedure 2 to determine the first total enthalpy change of PANF and OF; for details of Procedure 2, please refer to [link to Procedure 2]. Figure 2 (Specifically: the heating range is 30~450℃, and the heating rate is 10℃ / min). The data curve obtained from the test can be found in [reference needed]. Figure 4 Then, the first total heat of reaction of PANF and OF is obtained by processing the data using the data processing unit built into the DSC, and is denoted as Q. 2PANF and Q 2OF .

[0076] 4 mg of OF was tested under an air atmosphere with a gas flow rate of 60 mL / min according to procedure three; procedure three can be found in [reference needed]. Figure 5 (The specific temperature ranges include: ① First heating stage, 30~300℃, heating rate 50℃ / min; ② First holding stage, 300℃, 5 min; ③ First cooling stage, 300~30℃, cooling rate 50℃ / min; ④ Second holding stage, 30℃, 3 min; ⑤ Second heating stage, 30~450℃, heating rate 10℃ / min). The data curves obtained from the tests can be found in [reference needed]. Figure 6 Then, the second total heat of reaction of OF is obtained by processing the data using the data processing unit built into the DSC, denoted as Q. 3OF .

[0077] 4 mg of OF was tested under an air atmosphere with a gas flow rate of 60 mL / min according to procedure four; procedure four can be found in [reference needed]. Figure 5 (The specific temperature ranges include: ① First heating stage, 30~300℃, heating rate 50℃ / min; ② First holding stage, 300℃, 10 min; ③ First cooling stage, 300~30℃, cooling rate 50℃ / min; ④ Second holding stage, 30℃, 3 min; ⑤ Second heating stage, 30~450℃, heating rate 10℃ / min). The data curves obtained from the tests can be found in [reference needed]. Figure 6 Then, the third total heat of reaction of OF is obtained by processing the data using the data processing unit built into the DSC, denoted as Q. 4OF .

[0078] Q 1PANF and Q 1OF Substituting into the following formula, we can obtain the degree of cyclization:

[0079]

[0080] Q 1PANF Q 1OFQ 2PANF and Q 2OF Substituting into the following formula, we can obtain the degree of oxidation reaction:

[0081]

[0082] Q 2OF Q 3OF and Q 4OF Substituting into the following formula, we can obtain the degree of homogenization:

[0083]

[0084] Repeat the above steps to obtain 5 parallel results for each test metric, and record them in Table 1.

[0085] Table 1

[0086]

[0087] According to Table 1, the final calculations are as follows: the final result of the degree of cyclization reaction is 68.61% = (69.46 + 67.26 + 69.10) / 3 × 100%; the final result of the degree of oxidation reaction is 58.35% = (56.20 + 58.87 + 59.97) / 3 × 100%; and the final result of the degree of homogenization is 28.38% = (28.02 + 26.75 + 30.37) / 3 × 100%.

[0088] Example 2

[0089] This application provides a method for evaluating the pre-oxidation reaction results of polyacrylonitrile fibers. The only difference between this method and Example 1 is that the 1.10 dtex polyacrylonitrile precursor fiber and the pre-oxidized fiber after pre-oxidation treatment are denoted as PANF and OF, and the corresponding results are recorded in Table 2.

[0090] Table 2

[0091]

[0092] According to Table 2, the final calculations are as follows: the final result of the degree of cyclization reaction is 62.40% = (63.69 + 62.36 + 61.14) / 3 × 100%; the final result of the degree of oxidation reaction is 51.75% = (52.02 + 50.13 + 53.11) / 3 × 100%; and the final result of the degree of homogenization is 11.26% = (12.36 + 11.78 + 9.64) / 3 × 100%.

[0093] As can be seen from the table data of Examples 1 and 2, the heat of oxidation reaction is significantly higher than that of cyclization reaction, indicating that oxidation reaction dominates the pre-oxidation process. In addition, the results of Examples 1 and 2 show that the pre-oxidized fiber prepared from 0.67 dtex precursor fiber has a higher degree of cyclization reaction, oxidation reaction and homogenization than that prepared from 1.10 dtex precursor fiber, especially the degree of homogenization is significantly higher. This indicates that precursor fiber refinement is an important direction for improving the mechanical properties of carbon fibers.

[0094] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A method for evaluating the pre-oxidation reaction results of polyacrylonitrile fibers, characterized in that, Includes the following steps: S1 provides polyacrylonitrile precursor fiber before pre-oxidation treatment and pre-oxidized fiber after pre-oxidation treatment, denoted as PANF and OF respectively; S2 The cyclization heats of PANF and OF were measured using a differential scanning calorimeter under an inert atmosphere, and denoted as Q. 1PANF and Q 1OF ; S3 Under the same test conditions, the first total heat of reaction of PANF and OF were measured separately in air atmosphere using a differential scanning calorimeter, and denoted as Q. 2PANF and Q 2OF ; S4 The degree of oxidation reaction is calculated according to Formula I: （I）； The temperature range in the test conditions of step S3 is the heating range; S5: The second total heat of reaction of OF was measured using a differential scanning calorimeter in air atmosphere and denoted as Q. 3OF The temperature range in the test conditions of step S5 includes the first heating stage, the first holding stage, the first cooling stage, and the second heating stage performed sequentially; wherein, the processing temperature of the first holding stage is 300~350℃, and the conditions of the second heating stage in step S5 are the same as those of the heating stage in step S3. S6: The third total heat of reaction of OF was measured using a differential scanning calorimeter in air atmosphere and denoted as Q. 4OF The only difference between the test conditions in step S6 and step S5 is that the processing time of the first heat preservation stage in step S6 is T2, and the processing time of the first heat preservation stage in step S5 is T1, where T2 = 2T1. S7 The degree of homogenization of the oxidation reaction is calculated according to Formula II: (II)。 2. The evaluation method according to claim 1, characterized in that, In the step of testing the cyclization reaction heat and the first total reaction heat using a differential scanning calorimeter, the starting temperature of the heating section is 20~40℃, the ending temperature is 400~500℃, and / or the heating rate is 5~20℃ / min.

3. The evaluation method according to claim 2, characterized in that, In the step of testing the cyclization reaction heat and the first total reaction heat using differential scanning calorimetry, the sample amount is 4~6 mg and the gas flow rate is 60~80 mL / min.

4. The evaluation method according to any one of claims 1 to 3, characterized in that, Repeated tests were conducted to obtain multiple oxidation reaction degree values. Then, the maximum and minimum values ​​were removed from the multiple oxidation reaction degree values, and the average value of the remaining multiple oxidation reaction degree values ​​was calculated. The average value was taken as the final test result of the oxidation reaction degree.

5. The evaluation method according to claim 1, characterized in that, In step S5, the processing time for the first heat preservation stage is 2 to 10 minutes.

6. The evaluation method according to claim 1, characterized in that, In step S5, the heating rate of the first heating stage is 40~60℃ / min.

7. The evaluation method according to claim 1, characterized in that, In step S5, a second heat preservation section is also included between the first cooling section and the second heating section.

8. The evaluation method according to claim 7, characterized in that, The second insulation stage takes 3-5 minutes.

9. The evaluation method according to claim 1, characterized in that, Repeated testing yields multiple homogenization values. Then, the maximum and minimum values ​​are removed, and the average of the remaining homogenization values ​​is calculated. This average is taken as the final test result for homogenization.

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