Method for evaluating pre-oxidation reaction result of polyacrylonitrile fiber

Abstract

The invention provides an evaluation method for a pre-oxidation reaction result of polyacrylonitrile fibers, and belongs to the technical field of carbon fiber manufacturing. The evaluation method for the pre-oxidation reaction result of the polyacrylonitrile fiber comprises the following steps: S1, providing a polyacrylonitrile precursor before pre-oxidation treatment and a pre-oxidation fiber after pre-oxidation treatment, and marking the polyacrylonitrile precursor and the pre-oxidation fiber as PANF and OF; s2, respectively testing cyclization reaction heat of PANF and OF in an inert gas atmosphere by adopting a differential scanning calorimeter, and respectively recording the cyclization reaction heat as Q1PANF and Q1OF; s3, under the same test condition, respectively testing the first total reaction heat of the PANF and the first total reaction heat of the OF in the air atmosphere by adopting a differential scanning calorimeter, and respectively recording the first total reaction heat as Q2PANF and Q2OF; s4, the oxidation reaction degree is obtained through calculation according to a formula I. The evaluation method can comprehensively evaluate the pre-oxidation reaction result of the polyacrylonitrile fibers, and therefore production, research and development of the polyacrylonitrile-based carbon fibers can be better guided.

Description

Technical Field

[0001] The present application relates to the technical field of carbon fiber manufacturing, and in particular to a method for evaluating the results of a pre-oxidation reaction of polyacrylonitrile fibers. Background Art

[0002] The industrial production process of polyacrylonitrile-based carbon fibers (PAN-CF) generally includes the polymerization of acrylonitrile to prepare a PAN spinning solution, the spinning of the solution to prepare PAN precursor fibers, the removal of impurities from the precursor fibers through pre-oxidation, low-temperature carbonization, and high-temperature carbonization to prepare carbon filaments, and the preparation of finished carbon fibers through surface treatment and sizing. The pre-oxidation process, accompanied by a dramatic evolution of the PAN molecular chain structure from linear to trapezoidal, is a key process in determining the mechanical properties of carbon fibers. Therefore, the results of the PAN fiber pre-oxidation reaction are particularly important for the production and development of PAN-CF. Currently, evaluating the results of the pre-oxidation reaction using the cyclization reaction degree index is a common method. However, this evaluation method suffers from the problem of overly one-sided 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, which can more 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 embodiment of the present application is implemented as follows: In a first aspect, an embodiment of the present application provides a method for evaluating the results of a pre-oxidation reaction of polyacrylonitrile fiber, comprising the following steps: S1 provides polyacrylonitrile precursor before pre-oxidation treatment and pre-oxidized fiber after pre-oxidation treatment, which are respectively recorded as PANF and OF; S2 uses differential scanning calorimetry to measure the cyclization reaction heat of PANF and OF under inert gas atmosphere, which are respectively recorded as Q 1PANF and Q 1OF ; S3 Under the same test conditions, the first total reaction heat of PANF and OF was measured in air atmosphere by differential scanning calorimetry, respectively, and recorded as Q 2PANF and Q 2OF ; S4 calculates the degree of oxidation reaction according to formula I: .

[0005] The inventors have found that in the pre-oxidation reaction process of polyacrylonitrile fiber, the oxidation reaction usually dominates. Specifically, the proportion of the oxidation reaction is about 2 to 3 times that of the cyclization reaction. Therefore, the existing technology uses the cyclization reaction degree index to evaluate the pre-oxidation reaction results, which has the problem of overly one-sided conclusions. In this application, a more representative oxidation reaction degree is innovatively used as an evaluation index for the pre-oxidation reaction results, and a specific test method for the oxidation reaction degree is provided. Specifically, the cyclization reaction heat of PANF and OF is first tested separately, and then the total reaction heat of the two is tested separately. Then, the specific oxidation reaction degree is calculated according to the above formula; the core principle is: cyclization reaction heat + oxidation reaction heat = total reaction heat. Based on this, Q 2PANF -Q 1PANF represents the heat of oxidation reaction of polyacrylonitrile precursor (i.e. the initial heat of oxidation reaction of polyacrylonitrile precursor), Q 2OF -Q 1OF represents the oxidation reaction heat of the pre-oxidized fiber (i.e., the oxidation reaction heat of the residual polyacrylonitrile precursor), (Q 2PANF -Q 1PANF )-(Q 2OF -Q 1OF ) represents the oxidation reaction heat that has occurred in the polyacrylonitrile precursor during the pre-oxidation reaction. The oxidation reaction degree in the pre-oxidation reaction process can be calculated through the oxidation reaction heat that has occurred in the polyacrylonitrile precursor and the initial oxidation reaction heat of the polyacrylonitrile precursor, so as to more comprehensively evaluate the pre-oxidation reaction results of the polyacrylonitrile fiber, so as to better guide the production and research and development of polyacrylonitrile-based carbon fibers.

[0006] In some optional embodiments, in the step of testing the heat of cyclization reaction and the first total reaction heat by differential scanning calorimetry, the starting temperature of the heating section is 20-40°C, the ending temperature is 400-500°C, or / and the heating rate is 5-20°C / min.

[0007] In the above technical solution, for polyacrylonitrile, the starting temperature, ending temperature and heating rate of the heating section are respectively limited to the above ranges to provide more suitable testing conditions, which can test and obtain more accurate results of the degree of oxidation reaction, thereby more accurately evaluating the pre-oxidation reaction results of polyacrylonitrile fiber.

[0008] In some optional embodiments, in the step of measuring the cyclization reaction heat and the first total reaction heat by differential scanning calorimetry, the sample amount is 4-6 mg and the gas flow rate is 60-80 mL / min.

[0009] 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 respectively limited to the above ranges to provide suitable testing conditions, which helps polyacrylonitrile to react fully and efficiently, thereby being able to test and obtain more accurate results of the degree of oxidation reaction, and further more accurately evaluate the pre-oxidation reaction results of polyacrylonitrile fiber.

[0010] In some optional embodiments, the test is repeated to obtain multiple oxidation reaction degree values, and 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, and the average value is used as the final test result of the oxidation reaction degree.

[0011] In the above technical solution, multiple oxidation reaction degree values ​​obtained from the test are screened and averaged, so as to obtain a more representative oxidation reaction degree result, thereby more realistically reflecting the pre-oxidation reaction result of the polyacrylonitrile fiber.

[0012] In some optional embodiments, the temperature section in the test conditions of step S3 is a temperature rising section; step S5 includes: using a differential scanning calorimeter to measure the second total reaction heat of OF in an air atmosphere, recorded as Q 3OF The temperature sections in the test conditions of step S5 include a first heating section, a first holding section, a first cooling section, and a second heating section in sequence; wherein the treatment temperature of the first holding section is 300-350°C, and the conditions of the second heating section in step S5 are consistent with the conditions of the heating section in step S3; step S6 includes: using a differential scanning calorimeter to test the third total reaction heat of OF in an air atmosphere, recorded as Q 4OF The difference between the test conditions of step S6 and step S5 is that the treatment time of the first holding section in step S6 is T2, the treatment time of the first holding section in step S5 is T1, and T2=2T1; S7 calculates the degree of homogenization of the oxidation reaction according to formula II: .

[0013] In the above technical solution, on the basis of step S3, steps S5 to S7 are further performed according to the above process, wherein Q 2OF -Q 3OF represents the heat of oxidation reaction of the fiber in the first half of the first holding period. The treatment temperature of the first holding period is set within the above range in order to make the cyclization reaction basically complete at this stage, which helps to reduce the interference of the heat of cyclization reaction on the heat of oxidation reaction, thereby making Q 2OF -Q 3OF Closer to the actual heat difference of the oxidation reaction at this stage, so as to improve the test accuracy of the degree of homogenization; Q 3OF -Q4OF It represents the oxidation reaction heat of the fiber in the second half of the first insulation section. Setting T2 to 2T1 is to make the reaction time of the first half and the second half of the first insulation section the same. The degree of homogenization of the oxidation reaction can be calculated through the oxidation reaction heat in two adjacent reaction stages and at the same time, and then the uniformity of the oxidation reaction in the pre-oxidation process can be evaluated more accurately. 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, thereby building a more comprehensive evaluation system for the pre-oxidation process.

[0014] In some optional embodiments, in step S5, the treatment time of the first insulation section is 2 to 10 minutes.

[0015] In the above technical solution, the treatment time of the first insulation stage is limited to the above range to provide a suitable reaction time. The suitable reaction 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 is closer to the actual heat difference of the oxidation reaction at this stage, thereby more effectively improving the test accuracy of the degree of homogenization.

[0016] In some optional implementation schemes, in step S5, the heating rate of the first heating section is 40-60°C / min.

[0017] In the above technical solution, the heating rate of the first heating section is limited to the above range, which can make the temperature section reach the first insulation section as soon as possible, so that the heat difference mainly comes from the first insulation section, which helps to improve the test accuracy of the degree of homogenization.

[0018] In some optional embodiments, in step S5, a second heat preservation section is further included between the first temperature reduction section and the second temperature increase section.

[0019] In the above technical solution, a second insulation section is added between the first cooling section and the second heating section to make the temperature of the entire material relatively stable before the second heating section, so that the starting temperature condition of the second heating section is closer to the starting temperature condition in step S3, thereby helping to improve the test accuracy of the degree of homogenization.

[0020] In some optional implementation schemes, the treatment time of the second insulation section is 3 to 5 minutes.

[0021] In the above technical solution, the processing time of the second insulation section is limited to the above range to provide an appropriate insulation time, so that the starting temperature condition of the second heating section is closer to the starting temperature condition in step S3, which is more conducive to improving the test accuracy of the degree of homogenization.

[0022] In some optional embodiments, the test is repeated to obtain multiple homogenization degree values, and then the maximum and minimum values ​​among the multiple homogenization degree values ​​are removed and the average value of the remaining multiple homogenization degree values ​​is calculated, and the average value is used as the final test result of the homogenization degree.

[0023] In the above technical solution, multiple homogenization degree values ​​obtained from the test are screened and averaged, so that a more representative homogenization degree result can be obtained, thereby more realistically reflecting the pre-oxidation reaction result of the polyacrylonitrile fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0025] Figure 1 A process flow chart of a method for evaluating the results of a pre-oxidation reaction of polyacrylonitrile fiber provided in an embodiment of the present application; Figure 2 Temperature program curve diagrams for Program 1 and Program 2 provided in the embodiments of this application; Figure 3 This is a comparison of the DSC curves of PANF and OF obtained through Procedure 1 provided in Example 1 of the present application; Figure 4 This is a comparison of the DSC curves of PANF and OF provided in Example 1 of the present application obtained through Procedure 2; Figure 5 Temperature program curve diagrams for Program 3 and Program 4 provided in the embodiments of this application; Figure 6 This is a comparison chart of the DSC curves obtained by procedures three and four for the OF provided in Example 1 of the present application. DETAILED DESCRIPTION

[0026] To make the purpose, technical solutions and advantages of the examples of the present application clearer, the technical solutions in the examples of the present application will be described clearly and completely below. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0027] It should be noted that “and / or” in this application, such as “Feature 1 and / or Feature 2”, refers to three situations: “Feature 1” alone, “Feature 2” alone, or “Feature 1” plus “Feature 2”.

[0028] In addition, in the description of this application, unless otherwise specified, the "multiple" in "one or more" means two or more; the range of "value a~value b" includes the two end values ​​"a" and "b", and the "unit of measurement" in "value a~value b+unit of measurement" represents the "unit of measurement" of both "value a" and "value b".

[0029] At present, technicians mainly use the cyclization reaction degree indicator to evaluate the results of the pre-oxidation reaction. However, this evaluation method has the problem of overly one-sided conclusions. The inventors' research found that the problem with the current evaluation method's lack of representativeness is that the main reactions that occur during the pre-oxidation of PAN fibers are cyclization, dehydrogenation, and oxidation reactions from the outer layer to the inner layer, forming a conjugated cyclized structure, an oxygen-containing structure, and a skin-core heterogeneous structure; among them, the dehydrogenation reaction is an endothermic reaction, while the cyclization reaction and oxidation reaction are both exothermic reactions (the specific heat release can be directly obtained through DSC testing). Moreover, during the pre-oxidation process, the proportion of the oxidation reaction is approximately 2 to 3 times that of the cyclization reaction, occupying a dominant position, that is, the proportion of the cyclization reaction is very small. Based on this, the inventors innovatively used the more representative oxidation reaction degree 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.

[0030] The following is a detailed description of a method for evaluating the pre-oxidation reaction results of polyacrylonitrile fiber according to an embodiment of the present application.

[0031] In a first aspect, an embodiment of the present application provides a method for evaluating the results of a pre-oxidation reaction of polyacrylonitrile fiber, comprising the following steps: S1 provides polyacrylonitrile precursor before pre-oxidation treatment and pre-oxidized fiber after pre-oxidation treatment, which are respectively recorded as PANF and OF; S2 uses differential scanning calorimetry to measure the cyclization reaction heat of PANF and OF under inert gas atmosphere, which are respectively recorded as Q 1PANF and Q 1OF ; S3 Under the same test conditions, the first total reaction heat of PANF and OF was measured in air atmosphere by differential scanning calorimetry, respectively, and recorded as Q 2PANF and Q 2OF ; S4 calculates the degree of oxidation reaction according to formula I: .

[0032] In this application, a more representative degree of oxidation reaction is innovatively used as an evaluation index for the pre-oxidation reaction result, and a specific test method for the degree of oxidation reaction is provided. Specifically, the cyclization reaction heat of PANF and OF is first measured separately, and then the total reaction heat of the two is measured separately. Then, the specific degree of oxidation reaction is conveniently calculated according to the above formula; the core principle is: cyclization reaction heat + oxidation reaction heat = total reaction heat. Based on this, Q 2PANF -Q 1PANF represents the heat of oxidation reaction of polyacrylonitrile precursor (i.e. the initial heat of oxidation reaction of polyacrylonitrile precursor), Q 2OF -Q 1OF represents the oxidation reaction heat of the pre-oxidized fiber (i.e., the oxidation reaction heat of the residual polyacrylonitrile precursor), (Q 2PANF -Q 1PANF )-(Q 2OF -Q 1OF ) represents the oxidation reaction heat that has occurred in the polyacrylonitrile precursor during the pre-oxidation reaction. The oxidation reaction degree in the pre-oxidation reaction process can be calculated through the oxidation reaction heat that has occurred in the polyacrylonitrile precursor and the initial oxidation reaction heat of the polyacrylonitrile precursor, so as to more comprehensively evaluate the pre-oxidation reaction results of the polyacrylonitrile fiber, so as to better guide the production and research and development of polyacrylonitrile-based carbon fibers.

[0033] It should be noted that, through the Q 1PANF and Q 1OF , the degree of cyclization reaction can also be directly calculated. The specific formula is:

[0034] As an example, in the step of testing the heat of cyclization reaction and the first total reaction heat by differential scanning calorimetry, the starting temperature of the heating section is 20-40°C (for example, but not limited to, the starting temperature is any one of 20°C, 25°C, 30°C, 35°C and 40°C, or a range between any two of them), the ending temperature is 400-500°C (for example, but not limited to, the ending temperature is any one of 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, 460°C, 470°C, 480°C, 490°C and 500°C, or a range between any two of them), or / and, the heating rate is 5-20°C / min, for example, but not limited to, the heating rate is any one of 5°C / min, 8°C / min, 10°C / min, 12°C / min, 14°C / min, 16°C / min, 18°C / min and 20°C / min, or a range between any two of them.

[0035] In this embodiment, for polyacrylonitrile, the starting temperature, ending temperature and heating rate of the heating section are respectively limited to the above ranges to provide more suitable testing conditions, which can test and obtain more accurate results of the degree of oxidation reaction, thereby more accurately evaluating the pre-oxidation reaction results of polyacrylonitrile fiber.

[0036] As an example, in the step of testing the heat of cyclization reaction and the first total reaction heat by differential scanning calorimetry, the sample amount is 4-6 mg (for example, but not limited to, the sample amount is any one of 4 mg, 4.5 mg, 5 mg, 5.5 mg and 6 mg, or a range between any two of them), and the gas flow rate is 60-80 mL / min, for example, but not limited to, the gas flow rate is any one of 60 mL / min, 65 mL / min, 70 mL / min, 75 mL / min and 80 mL / min, or a range between any two of them.

[0037] 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 being able to test and obtain more accurate results of the degree of oxidation reaction, and further more accurately evaluate the pre-oxidation reaction results of polyacrylonitrile fiber.

[0038] As an example, the test is repeated to obtain multiple oxidation reaction degree values, and 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, and the average value is used as the final test result of the oxidation reaction degree.

[0039] In this embodiment, a plurality of oxidation reaction degree values ​​obtained by the test are screened and averaged, so that a more representative oxidation reaction degree result can be obtained, thereby more realistically reflecting the pre-oxidation reaction result of the polyacrylonitrile fiber.

[0040] In other possible implementations, a single oxidation reaction degree value obtained from the test may also be directly used as the final test result.

[0041] It should be noted that, at present, there is still a lack of test indicators that can characterize the uniformity of the oxidation reaction type in the pre-oxidation reaction process.

[0042] Based on this, the inventors further discovered that the degree of homogenization of the oxidation reaction can be calculated by the heat of the oxidation reaction in two adjacent reaction stages and at the same time, and thus the uniformity of the oxidation reaction during the pre-oxidation process can be more accurately evaluated. The following is an explanation of the specific test steps.

[0043] As an example, the temperature section in the test condition of step S3 is a temperature rising section; step S5 includes: using a differential scanning calorimeter to test the second total reaction heat of OF in an air atmosphere, recorded as Q 3OF ; The temperature sections in the test conditions of step S5 include a first heating section, a first holding section, a first cooling section and a second heating section performed in sequence; wherein the treatment temperature of the first holding section is 300-350°C (for example, but not limited to, the treatment temperature is any one of 300°C, 310°C, 320°C, 330°C, 340°C and 350°C or a range between any two thereof), and the conditions of the second heating section in step S5 are consistent with the conditions of the heating section in step S3; step S6 comprises: using a differential scanning calorimeter to test the third total reaction heat of OF in an air atmosphere, recorded as Q 4OF The difference between the test conditions of step S6 and step S5 is that the treatment time of the first holding section in step S6 is T2, the treatment time of the first holding section in step S5 is T1, and T2=2T1; S7 calculates the degree of homogenization of the oxidation reaction according to formula II: .

[0044] It should be noted that in steps S5 to S6 , relevant parameters such as sample volume and gas flow rate can refer to step S3 .

[0045] In this embodiment, based on step S3, steps S5 to S7 are further performed according to the above process, wherein Q 2OF -Q 3OF represents the heat of oxidation reaction of the fiber in the first half of the first holding period. The treatment temperature of the first holding period is set within the above range in order to make the cyclization reaction basically complete at this stage, which helps to reduce the interference of the heat of cyclization reaction on the heat of oxidation reaction, thereby making Q 2OF -Q 3OF Closer to the actual heat difference of the oxidation reaction at this stage, so as to improve the test accuracy of the degree of homogenization; Q 3OF -Q 4OF It represents the oxidation reaction heat of the fiber in the second half of the first insulation section. Setting T2 to 2T1 is to make the reaction time of the first half and the second half of the first insulation section the same. The degree of homogenization of the oxidation reaction can be calculated through the oxidation reaction heat in two adjacent reaction stages and at the same time, and then the uniformity of the oxidation reaction in the pre-oxidation process can be evaluated more accurately. 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, thereby building a more comprehensive evaluation system for the pre-oxidation process.

[0046] As an example, in step S5, the processing time of the first insulation section is 2 to 10 minutes, for example, but not limited to, the processing time is any one of 2 minutes, 3 minutes, 4 minutes, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes and 10 minutes, or a range between any two of them.

[0047] In this embodiment, the treatment time of the first insulation stage is limited to the above range to provide a suitable reaction time. The suitable reaction 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 is closer to the actual heat difference of the oxidation reaction at this stage, thereby more effectively improving the test accuracy of the degree of homogenization.

[0048] As an example, in step S5, the heating rate of the first heating section is 40~60℃ / min, for example, but not limited to, the heating rate is any one of 40℃ / min, 45℃ / min, 50℃ / min, 55℃ / min and 60℃ / min, or a range between any two of them.

[0049] In this embodiment, the heating rate of the first heating section is limited to the above range, so that the temperature section can reach the first insulation section as soon as possible, so that the heat difference mainly comes from the first insulation section, which helps to improve the test accuracy of the degree of homogenization.

[0050] As an example, in step S5, the cooling rate of the first cooling section is 40~60℃ / min, for example, but not limited to, the cooling rate is any one of 40℃ / min, 45℃ / min, 50℃ / min, 55℃ / min and 60℃ / min, or a range value between any two of them.

[0051] As an example, in step S5, a second heat preservation section is further included between the first temperature reduction section and the second temperature increase section.

[0052] In this embodiment, a second insulation 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 is carried out, thereby making the starting temperature condition of the second heating section closer to the starting temperature condition in step S3, thereby helping to improve the test accuracy of the degree of homogenization.

[0053] As an example, the processing time of the second insulation section is 3 to 5 minutes, for example but not limited to, the processing time is any one of 3 minutes, 3.5 minutes, 4 minutes, 4.5 minutes and 5 minutes, or a range between any two of them.

[0054] In this embodiment, the processing time of the second insulation section is limited to the above range to provide an appropriate insulation time, so that the starting temperature condition of the second heating section is closer to the starting temperature condition in step S3, which is more conducive to improving the test accuracy of the degree of homogenization.

[0055] As an example, the test is repeated to obtain multiple homogenization degree values, and then the maximum and minimum values ​​among the multiple homogenization degree values ​​are removed and the average value of the remaining multiple homogenization degree values ​​is calculated, and the average value is used as the final test result of the homogenization degree.

[0056] In this embodiment, multiple homogenization degree values ​​obtained from the test are screened and averaged, so as to obtain a more representative homogenization degree result, thereby more realistically reflecting the pre-oxidation reaction result of the polyacrylonitrile fiber.

[0057] In other possible implementations, a single homogenization degree value obtained from the test may also be directly used as the final test result.

[0058] In summary, the evaluation method provided in the embodiment of the present application can use DSC to simultaneously test the three indicators of the cyclization reaction degree, oxidation reaction degree and homogenization degree of the oxidation reaction of polyacrylonitrile fiber during the pre-oxidation process, so as to achieve efficient and accurate monitoring of the pre-oxidation process of polyacrylonitrile fiber, which plays an important guiding role in the production and research and development of PAN-CF.

[0059] The features and performance of the present application are further described in detail below with reference to the embodiments.

[0060] Example 1 The present invention provides a method for evaluating the pre-oxidation reaction results of polyacrylonitrile fiber, including the following steps. The specific process flow chart can be found in Figure 1 : The 0.67 dtex polyacrylonitrile precursor and the pre-oxidized fibers after pre-oxidation treatment were divided into PANF and OF.

[0061] 4 mg of PANF and OF were respectively taken and tested for the cyclization heat of PANF and OF according to Procedure 1 under a nitrogen atmosphere with a purity of ≥99.999% and a gas flow rate of 60 mL / min. 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 Figure 3 Then, the data processing unit of DSC was used to obtain the cyclization reaction heat of PANF and OF, which were recorded as Q 1PANF and Q 1OF .

[0062] 4 mg of PANF and OF were taken respectively and the first total reaction heat of PANF and OF was measured according to procedure 2 in an air atmosphere with a gas flow rate of 60 mL / min. 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 Figure 4 Then, the first total reaction heat of PANF and OF was obtained by using the data processing unit of DSC, which was recorded as Q 2PANF and Q 2OF .

[0063] Take 4 mg of OF and test the second total heat of reaction of OF in an air atmosphere with a gas flow rate of 60 mL / min according to procedure 3; the details of procedure 3 can be found in Figure 5 (Specific temperature sections include: ① first heating section, 30~300℃, heating rate 50℃ / min; ② first heat preservation section, 300℃, 5 min; ③ first cooling section, 300~30℃, cooling rate 50℃ / min; ④ second heat preservation section, 30℃, 3 min; ⑤ second heating section, 30~450℃, heating rate 10℃ / min). The data curve obtained by the test can be found in Figure 6 Then, the DSC built-in data processing unit is used to obtain the second total reaction heat of OF, which is recorded as Q 3OF .

[0064] Take 4 mg of OF and test the third total heat of reaction of OF in an air atmosphere with a gas flow rate of 60 mL / min according to Procedure 4. Figure 5 (Specific temperature sections include: ① first heating section, 30~300℃, heating rate 50℃ / min; ② first heat preservation section, 300℃, 10 min; ③ first cooling section, 300~30℃, cooling rate 50℃ / min; ④ second heat preservation section, 30℃, 3 min; ⑤ second heating section, 30~450℃, heating rate 10℃ / min). The test data curve can be found in Figure 6 , and then the third total reaction heat of OF is obtained by using the data processing unit of DSC, which is recorded as Q 4OF .

[0065] Q 1PANF and Q 1OF Substitute the following formula to obtain the degree of cyclization reaction:

[0066] Q 1PANF , Q 1OF , Q 2PANF and Q 2OFSubstitute the following formula to obtain the degree of oxidation reaction:

[0067] Q 2OF , Q 3OF and Q 4OF Substitute the following formula to obtain the degree of homogenization:

[0068] Repeat the above steps to obtain 5 parallel results for each test indicator and record them in Table 1.

[0069] Table 1

[0070] According to Table 1, the final calculation results are: the final result of the cyclization reaction degree is 68.61%=(69.46+67.26+69.10) / 3×100%, the final result of the oxidation reaction degree is 58.35%=(56.20+58.87+59.97) / 3×100%, and the final result of the homogenization degree is 28.38%=(28.02+26.75+30.37) / 3×100%.

[0071] Example 2 The embodiment of the present application provides a method for evaluating the pre-oxidation reaction results of polyacrylonitrile fiber, which differs from Example 1 only in that: 1.10 dtex polyacrylonitrile precursor and pre-oxidized fiber after pre-oxidation treatment are divided into PANF and OF, and the corresponding results are recorded in Table 2.

[0072] Table 2

[0073] According to Table 2, the final calculation results are: the final result of the cyclization reaction degree is 62.40%=(63.69+62.36+61.14) / 3×100%, the final result of the oxidation reaction degree is 51.75%=(52.02+50.13+53.11) / 3×100%, and the final result of the homogenization degree is 11.26%=(12.36+11.78+9.64) / 3×100%.

[0074] It can be seen from the tabular data of Example 1 and Example 2 that the heat of the oxidation reaction is significantly higher than the heat of the cyclization reaction, indicating that the oxidation reaction dominates the pre-oxidation process; in addition, it can be seen from the results of Example 1 and Example 2 that the pre-oxidized fiber prepared from 0.67 dtex precursor has a higher degree of cyclization reaction, oxidation reaction and homogenization than that prepared from 1.10 dtex precursor, especially a significantly higher degree of homogenization, which indicates that precursor refinement is an important direction for improving the mechanical properties of carbon fibers.

[0075] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

Claims

1. A method for evaluating the results of a pre-oxidation reaction of polyacrylonitrile fiber, characterized in that: The following steps are involved: S1 provides polyacrylonitrile precursor before pre-oxidation treatment and pre-oxidized fiber after pre-oxidation treatment, which are denoted as PANF and OF; S2 The cyclization reaction heats of PANF and OF were measured by differential scanning calorimetry under an inert atmosphere and were recorded as Q 1PANF and Q 1OF ; S3 Under the same test conditions, the first total reaction heat of PANF and OF was measured by differential scanning calorimetry in air atmosphere, respectively, and recorded as Q 2PANF and Q 2OF ; S4 Calculate the degree of oxidation reaction according to formula I: 。 2. The evaluation method according to claim 1, wherein: In the step of measuring the cyclization reaction heat and the first total reaction heat by differential scanning calorimetry, the starting temperature of the heating section is 20-40°C, the ending temperature is 400-500°C, or / and, the heating rate is 5-20°C / min.

3. The evaluation method according to claim 2, wherein In the step of measuring the cyclization reaction heat and the first total reaction heat using a differential scanning calorimeter, 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 Repeat the test to obtain multiple oxidation reaction degree values, then remove the maximum and minimum values ​​among the multiple oxidation reaction degree values ​​and calculate the average value of the remaining multiple oxidation reaction degree values, and use the average value as the final test result of the oxidation reaction degree.

5. The evaluation method according to any one of claims 1 to 3, characterized in that The temperature section in the test condition of step S3 is a temperature rising section; Step S5 includes: using a differential scanning calorimeter to measure the second total reaction heat of OF in an air atmosphere, which is recorded as Q 3OF The temperature sections in the test conditions of step S5 include a first heating section, a first holding section, a first cooling section, and a second heating section, which are performed in sequence; wherein the processing temperature of the first holding section is 300-350°C, and the conditions of the second heating section in step S5 are consistent with the conditions of the heating section in step S3; Step S6 includes: using a differential scanning calorimeter to measure the third total reaction heat of OF in an air atmosphere, recorded as Q 4OF ; The difference between the test conditions of step S6 and step S5 is that the processing time of the first holding section in step S6 is T2, the processing time of the first holding section in step S5 is T1, T2=2T1; S7 The degree of homogenization of the oxidation reaction is calculated according to formula II: 。 6. The evaluation method according to claim 5, wherein: In step S5, the treatment time of the first insulation stage is 2 to 10 minutes.

7. The evaluation method according to claim 5, wherein: In step S5, the heating rate of the first heating stage is 40-60°C / min.

8. The evaluation method according to claim 5, wherein: In step S5, a second heat preservation section is included between the first temperature reduction section and the second temperature increase section.

9. The evaluation method according to claim 8, wherein The treatment time of the second insulation section is 3~5 minutes.

10. The evaluation method according to claim 1, wherein: Repeat the test to obtain multiple homogenization degree values, then remove the maximum and minimum values ​​from the multiple homogenization degree values ​​and calculate the average value of the remaining multiple homogenization degree values, and use the average value as the final test result of the homogenization degree.

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