Polyacrylonitrile-based large-tow carbon fiber and preparation method thereof

Abstract

The present invention relates to a method for preparing polyacrylonitrile-based large-tow carbon fibers, which solves the problems existing in the prior art, such as concentrated heat release during the pre-oxidation process, easy fiber breakage, aggregation of carbon fiber products, poor widening effect, and difficulty in application. The specific steps are as follows: using a pre-oxidation furnace to perform pre-oxidation treatment on polyacrylonitrile fibers in four temperature zones, and controlling the tow width of the pre-oxidized fibers by draft matching to obtain pre-oxidized fibers; using a low-temperature carbonization furnace to perform low-temperature carbonization treatment in three temperature zones, and then using a high-temperature carbonization furnace to perform high-temperature carbonization treatment in three temperature zones to obtain polyacrylonitrile-based large-tow carbon fibers. In the continuous fiber preparation process, by matching the temperature, draft ratio, and residence time of pre-oxidation, low-temperature carbonization, and high-temperature carbonization, and controlling the wire width of the fibers, the continuous preparation of large-tow carbon fibers is achieved, which effectively solves the above problems and can be used in the industrial production of the preparation process of polyacrylonitrile-based large-tow carbon fibers.

Description

Technical Field

[0001] The present invention belongs to the field of carbon fibers, and in particular relates to a polyacrylonitrile-based large-tow carbon fiber and a preparation method thereof. Background Art

[0002] Carbon fiber refers to inorganic polymer fibers composed of polymer precursors or carbon allotropes with a carbon content of at least 92%. It is a typical high-performance fiber. Its advantages include high specific strength, high specific modulus, high-temperature resistance, corrosion resistance, creep resistance, electrical conductivity, and low specific gravity. These advantages have led to its widespread application in automobiles, aircraft, rail transportation, wind power generation, sports equipment, and other fields. Carbon fiber is categorized by its precursor into polyacrylonitrile-based, pitch-based, and viscose-based fibers, with the majority of commercially available fibers being polyacrylonitrile-based.

[0003] Carbon fibers are categorized as large and small tows, with those with a density of 48K or greater considered large-tow. Small-tow carbon fibers are primarily used in defense and military applications, while large-tow carbon fibers are more commonly used in the industrial sector due to their low cost. However, the production and application of large-tow fibers present numerous technical challenges, primarily: During the pre-oxidation of large-tow precursor fibers, the heat of reaction is concentrated, making it difficult to dissipate, making it susceptible to melt and stranding, breakage, and even spontaneous combustion. Large-tow carbon fibers also suffer from poor aggregation and spreading, leading to poor resin wettability and uneven distribution of the carbon fibers and resin, which can easily cause defects. This compromises the strength and rigidity of the carbon fibers and composite materials, resulting in unstable product performance. Therefore, mitigating the concentrated heat release during the pre-oxidation of large-tow precursor fibers and controlling the tow width are essential. Currently, methods for controlling this heat are to reduce the starting temperature of the precursor pre-oxidation using comonomers or to adjust the pre-oxidation atmosphere (CN111647973A). Large-tow carbon fibers are also widened and flattened (CN107904738A) to prevent product defects.

[0004] Although existing technical solutions can increase the pre-oxidation speed, reduce heat release or optimize the pre-oxidation structure, they only stay at the research of small-tow fiber precursors or are difficult to apply on a large scale; further widening treatment of large-tow carbon fibers increases costs and impairs performance. Summary of the Invention

[0005] In order to solve the problems in the prior art of concentrated heat release during the pre-oxidation process, easy fiber breakage, and aggregation, poor widening effect, and difficulty in application of carbon fiber products, the present invention provides a preparation method of polyacrylonitrile pre-oxidized fiber, which has the characteristics of moderate heat release during the pre-oxidation process, difficult fiber breakage, and excellent performance of the final product.

[0006] One of the objects of the present invention is to provide a method for preparing polyacrylonitrile-based large-tow carbon fibers, comprising subjecting polyacrylonitrile fiber precursors to pre-oxidation treatment, low-temperature carbonization, and high-temperature carbonization to obtain the polyacrylonitrile large-tow carbon fibers, wherein, in millimeters, the tow width during the pre-oxidation process is 0.0003 to 0.0007 times the number of polyacrylonitrile fiber precursors, preferably 0.0004 to 0.0006 times.

[0007] In the above preparation method,

[0008] The number of the polyacrylonitrile fiber precursors is 48,000 to 600,000, preferably 48,000 to 360,000;

[0009] The moisture content of the polyacrylonitrile fiber precursor is less than or equal to 7wt%, preferably less than or equal to 5wt%;

[0010] The fineness of the polyacrylonitrile fiber precursor is 0.2 to 3.0 dtex, preferably 0.5 to 2.5 dtex.

[0011] In the above preparation method, the pre-oxidation treatment is set in four temperature zones:

[0012] The temperatures of the four pre-oxidation temperature zones are 160-220°C, 180-240°C, 200-260°C, and 210-280°C, respectively, and the temperatures of the four temperature zones are set incrementally. Preferably, the temperatures of the four temperature zones are 180-200°C, 200-220°C, 220-240°C, and 230-260°C, respectively;

[0013] The pre-oxidation residence time in each pre-oxidation temperature zone is 10 to 30 minutes, preferably 15 to 25 minutes;

[0014] The drafting ratios of the four pre-oxidation temperature zones are 0.5-3.5%, -2.5--0.5%, -2.5--0.5%, and -2.5--0.5%, respectively. Preferably, the drafting ratios of the four temperature zones are 1-3%, -2--1%, -2--1%, and -2--1%, respectively.

[0015] In the above preparation method, the low-temperature carbonization is set in three temperature zones:

[0016] The temperatures of the three temperature zones of low-temperature carbonization are 300-600°C, 400-700°C, and 600-900°C, respectively, and the temperatures of the three temperature zones are set incrementally. Preferably, the temperatures of the three temperature zones are 350-550°C, 450-650°C, and 650-850°C, respectively;

[0017] The residence time of each temperature zone of the low-temperature carbonization is 1 to 20 minutes, preferably 2 to 10 minutes;

[0018] The draft ratio of each temperature zone of the low-temperature carbonization is 0.5-10%, preferably 2-7%.

[0019] In the above preparation method, the high temperature carbonization is set in three temperature zones:

[0020] The temperatures of the three temperature zones of high-temperature carbonization are 900-1300°C, 1100-1400°C, and 1200-1600°C, respectively, and the temperatures of the three temperature zones are set incrementally. Preferably, the temperatures of the three temperature zones are 1000-1250°C, 1200-1350°C, and 1300-1500°C, respectively;

[0021] The residence time of each temperature zone of the high temperature carbonization is 1 to 20 minutes, preferably 2 to 10 minutes;

[0022] The draft ratio of each temperature zone of the high-temperature carbonization is -5.0 to -0.5%, preferably -3.5 to -1.5%.

[0023] A second object of the present invention is to provide a polyacrylonitrile-based large-tow carbon fiber prepared by the above-mentioned preparation method.

[0024] The polyacrylonitrile-based large-tow carbon fiber obtained by the above preparation method has a tensile strength of ≥3.5 GPa and a tensile modulus of ≥230 GPa.

[0025] The tow width W of the polyacrylonitrile fiber precursor is related to the number of fibers N. In the present invention, by controlling the relationship between the tow width and the number of fibers during the pre-oxidation process, the tow width satisfies the tow width W (mm) = (0.0003-0.0007) × N, preferably W (mm) = (0.0004-0.0006) × N, and matches the pre-oxidation temperature, draft ratio, and residence time. By controlling the tow within a suitable width range, the fibers of the large tow have good heat dissipation during the intense oxidation reaction, and the individual fibers are not easily adhered to each other, thereby avoiding problems such as smoke and breakage of the tow caused by local excessive temperature. At the same time, the temperature, draft ratio, and residence time of low-temperature carbonization and high-temperature carbonization are matched to achieve continuous preparation of large-tow carbon fibers.

[0026] By adopting the technical solution of the present invention, a pre-oxidation furnace is used to perform pre-oxidation treatment on polyacrylonitrile fiber in four temperature zones, and the tow width of the pre-oxidized fiber is controlled by stretching matching to obtain pre-oxidized fiber; a low-temperature carbonization furnace is used to perform low-temperature carbonization treatment in three temperature zones, and then a high-temperature carbonization furnace is used to perform high-temperature carbonization treatment in three temperature zones to obtain polyacrylonitrile-based large-tow carbon fiber, the tensile strength of the large-tow carbon fiber is greater than 3.5GPa, and the tensile modulus is greater than 230GPa, achieving good technical effects.

[0027] The present invention achieves continuous preparation of large-tow carbon fibers by matching the temperatures, draft ratios, and residence times of pre-oxidation, low-temperature carbonization, and high-temperature carbonization to control the fiber wire width. The invention can be used in the industrial production of the preparation process of large-tow carbon fibers based on polyacrylonitrile. DETAILED DESCRIPTION

[0028] The present invention will be described in detail below with reference to specific embodiments. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and are not to be construed as limiting the scope of protection of the present invention. Non-essential improvements and adjustments made by those skilled in the art to the present invention based on the contents of the present invention still fall within the scope of protection of the present invention.

[0029] The test instruments and test conditions used in the examples are as follows:

[0030] The tensile strength and tensile modulus of carbon fiber are tested according to GB / T 3362-2017.

[0031] [Example 1]

[0032] 48K polyacrylonitrile fiber (fineness 1.5 dtex, moisture content 2%) was pre-oxidized in an air atmosphere in a four-zone pre-oxidation furnace. The pre-oxidation temperatures in the four zones were 190°C, 210°C, 230°C, and 245°C, and the draft ratios were 2%, -1.5%, -1.5%, and -1.5%, respectively. The residence time in each zone was 15 min, and the fiber width was 24 mm.

[0033] The pre-oxidized fibers were subjected to a three-zone low-temperature carbonization treatment in a low-temperature carbonization furnace under a nitrogen atmosphere. The temperatures of each zone were 450°C, 550°C, and 750°C, respectively. The fiber draft ratio was 4.5%, and the fiber residence time was 3 minutes.

[0034] The low carbon fiber was subjected to a high-temperature carbonization treatment in three temperature zones using a high-temperature carbonization furnace under a nitrogen atmosphere. The temperatures of the high-temperature carbonization treatment in each temperature zone were 1100°C, 1250°C, and 1400°C, respectively. The fiber draft ratio was -3.0%, and the fiber residence time was 3 minutes. The large-tow carbon fiber was prepared. The obtained carbon fiber had a tensile strength of 3.9 GPa and a tensile modulus of 251 GPa.

[0035] [Example 2]

[0036] 48K polyacrylonitrile fiber (fineness 1.5 dtex, moisture content 2%) was pre-oxidized in an air atmosphere in a four-zone pre-oxidation furnace. The pre-oxidation temperatures in the four zones were 190°C, 210°C, 230°C, and 245°C, and the draft ratios were 2.5%, -1.0%, -1.0%, and -1.0%, respectively. The residence time in each zone was 15 min, and the fiber width was 20 mm.

[0037] The pre-oxidized fibers were subjected to a three-zone low-temperature carbonization treatment in a low-temperature carbonization furnace under a nitrogen atmosphere. The temperatures of each zone were 450°C, 550°C, and 750°C, respectively. The fiber draft ratio was 4.5%, and the fiber residence time was 3 minutes.

[0038] The low carbon fiber was subjected to a high-temperature carbonization treatment in three temperature zones using a high-temperature carbonization furnace under a nitrogen atmosphere. The temperatures of the high-temperature carbonization treatment in each temperature zone were 1100°C, 1250°C, and 1400°C, respectively. The fiber draft ratio was -3.0%, and the fiber residence time was 3 minutes. The large-tow carbon fiber was prepared. The obtained carbon fiber had a tensile strength of 3.8 GPa and a tensile modulus of 243 GPa.

[0039] [Example 3]

[0040] 120K polyacrylonitrile fiber (fineness 1.5 dtex, moisture content 2%) was pre-oxidized in an air atmosphere in a four-zone pre-oxidation furnace. The pre-oxidation temperatures in the four zones were 190°C, 210°C, 230°C, and 245°C, and the draft ratios were 2%, -1.5%, -1.5%, and -1.5%, respectively. The residence time in each zone was 15 min, and the fiber width was 60 mm.

[0041] The pre-oxidized fibers were subjected to a three-zone low-temperature carbonization treatment in a low-temperature carbonization furnace under a nitrogen atmosphere. The temperatures of each zone were 450°C, 550°C, and 750°C, respectively. The fiber draft ratio was 4.5%, and the fiber residence time was 3 minutes.

[0042] The low carbon fiber was subjected to a three-zone high-temperature carbonization treatment in a high-temperature carbonization furnace under a nitrogen atmosphere. The temperatures of the high-temperature carbonization treatment in each zone were 1100°C, 1250°C, and 1400°C, respectively. The fiber draft ratio was -3.0%, and the fiber residence time was 3 minutes. The large-tow carbon fiber was prepared. The obtained carbon fiber had a tensile strength of 3.6 GPa and a tensile modulus of 233 GPa.

[0043] [Example 4]

[0044] 48K polyacrylonitrile fiber (fineness 1.5 dtex, moisture content 2%) was pre-oxidized in an air atmosphere in a four-zone pre-oxidation furnace. The pre-oxidation temperatures in the four zones were 180°C, 200°C, 240°C, and 260°C, and the draft ratios were 2%, -1.5%, -2%, and -2%, respectively. The residence time in each zone was 15 min, and the fiber width was 24 mm.

[0045] The pre-oxidized fibers were subjected to a three-zone low-temperature carbonization treatment in a low-temperature carbonization furnace under a nitrogen atmosphere. The temperatures of each zone were 450°C, 550°C, and 750°C, respectively. The fiber draft ratio was 4.5%, and the fiber residence time was 3 minutes.

[0046] The low carbon fibers were subjected to a three-zone high-temperature carbonization treatment in a high-temperature carbonization furnace under a nitrogen atmosphere. The temperatures for the high-temperature carbonization treatment in each zone were 1100°C, 1250°C, and 1400°C, respectively. The fiber draft ratio was -3.0%, and the fiber residence time was 3 minutes. The large-tow carbon fibers were prepared. The obtained carbon fibers had a tensile strength of 3.7 GPa and a tensile modulus of 244 GPa.

[0047] [Example 5]

[0048] 48K polyacrylonitrile fiber (fineness 1.5 dtex, moisture content 2%) was pre-oxidized in an air atmosphere in a four-zone pre-oxidation furnace. The pre-oxidation temperatures in the four zones were 190°C, 210°C, 230°C, and 245°C, and the draft ratios were 2%, -1.5%, -1.5%, and -1.5%, respectively. The residence time in each zone was 15 min, and the fiber width was 24 mm.

[0049] The pre-oxidized fibers were subjected to a three-zone low-temperature carbonization treatment in a low-temperature carbonization furnace under a nitrogen atmosphere. The temperatures of each zone were 450°C, 550°C, and 800°C, respectively. The fiber draft ratio was 4.5%, and the fiber residence time was 3 minutes.

[0050] The low carbon fiber was subjected to a high-temperature carbonization treatment in three temperature zones using a high-temperature carbonization furnace under a nitrogen atmosphere. The temperatures of the high-temperature carbonization treatment in each temperature zone were 1200°C, 1350°C, and 1450°C, respectively. The fiber draft ratio was -3.0%, and the fiber residence time was 3 minutes. The large-tow carbon fiber was prepared. The obtained carbon fiber had a tensile strength of 3.6 GPa and a tensile modulus of 258 GPa.

[0051] [Comparative Example 1]

[0052] 48K polyacrylonitrile fiber (fineness 1.5 dtex, moisture content 2%) was pre-oxidized in an air atmosphere in a four-zone pre-oxidation furnace. The pre-oxidation temperatures in the four zones were 190°C, 210°C, 230°C, and 245°C, and the draft ratios were 4%, -1.5%, -1.5%, and -1.5%, respectively. The residence time in each zone was 15 min, and the fiber width was 9 mm.

[0053] The pre-oxidized fibers were subjected to a three-zone low-temperature carbonization treatment in a low-temperature carbonization furnace under a nitrogen atmosphere. The temperatures of each zone were 450°C, 550°C, and 750°C, respectively. The fiber draft ratio was 4.5%, and the fiber residence time was 3 minutes.

[0054] The low carbon fiber was subjected to a three-zone high-temperature carbonization treatment in a high-temperature carbonization furnace under a nitrogen atmosphere. The temperatures of the high-temperature carbonization treatment in each zone were 1100°C, 1250°C, and 1400°C, respectively. The fiber draft ratio was -3.0%, and the fiber residence time was 3 minutes. The large-tow carbon fiber was prepared. The obtained carbon fiber had a tensile strength of 2.3 GPa and a tensile modulus of 217 GPa.

[0055] [Comparative Example 2]

[0056] 48K polyacrylonitrile fiber (fineness 1.5 dtex, moisture content 2%) was pre-oxidized in an air atmosphere in a four-zone pre-oxidation furnace. The pre-oxidation temperatures in the four zones were 190°C, 210°C, 230°C, and 245°C, and the draft ratios were 3%, -3%, 0.5%, and -3%, respectively. The residence time in each zone was 15 min, and the fiber width was 35 mm.

[0057] The pre-oxidized fibers were subjected to a three-zone low-temperature carbonization treatment in a low-temperature carbonization furnace under a nitrogen atmosphere. The temperatures of each zone were 450°C, 550°C, and 750°C, respectively. The fiber draft ratio was 4.5%, and the fiber residence time was 3 minutes.

[0058] The low carbon fibers were subjected to a three-zone high-temperature carbonization treatment in a high-temperature carbonization furnace under a nitrogen atmosphere. The temperatures for the high-temperature carbonization treatment in each zone were 1100°C, 1250°C, and 1400°C, respectively. The fiber draft ratio was -3.0%, and the fiber residence time was 3 minutes. The large-tow carbon fibers were prepared. The obtained carbon fibers had a tensile strength of 2.1 GPa and a tensile modulus of 223 GPa.

[0059] [Comparative Example 3]

[0060] 48K polyacrylonitrile fiber (fineness 1.5 dtex, moisture content 2%) was pre-oxidized in an air atmosphere in a four-zone pre-oxidation furnace. The pre-oxidation temperatures in the four zones were 160°C, 170°C, 190°C, and 230°C, and the draft ratios were 4%, -2%, -1.5%, and -1.5%, respectively. The residence time in each zone was 15 min, and the fiber width was 24 mm.

[0061] The pre-oxidized fibers were subjected to a three-zone low-temperature carbonization treatment in a low-temperature carbonization furnace under a nitrogen atmosphere. The temperatures of each zone were 400°C, 500°C, and 700°C, respectively. The fiber draft ratio was 4.5%, and the fiber residence time was 3 minutes.

[0062] The low carbon fibers were subjected to a three-zone high-temperature carbonization treatment in a high-temperature carbonization furnace under a nitrogen atmosphere. The temperatures for the high-temperature carbonization treatment in each zone were 1000°C, 1150°C, and 1300°C, respectively. The fiber draft ratio was -3.0%, and the fiber residence time was 3 minutes. The large-tow carbon fibers were prepared. The obtained carbon fibers had a tensile strength of 2.3 GPa and a tensile modulus of 210 GPa.

[0063] Obviously, the technical solution of the present invention can slow down the concentrated heat release in the pre-oxidation process, avoid the problem of melt breakage caused by concentrated heat release, and the final product has a better widening effect, which is convenient for subsequent applications. It has great technical advantages and can be used in the industrial production of polyacrylonitrile-based large-tow carbon fiber preparation process.

Claims

1. A method for preparing polyacrylonitrile-based large-tow carbon fibers, comprising subjecting polyacrylonitrile fiber precursors to pre-oxidation, low-temperature carbonization, and high-temperature carbonization to obtain the polyacrylonitrile large-tow carbon fibers, wherein: In millimeters, the width of the filament bundle during the pre-oxidation process is 0.0003 to 0.0007 times the number of polyacrylonitrile fiber strands; the pre-oxidation treatment is set with four temperature zones, and the temperatures of the four pre-oxidation temperature zones are 160 to 220°C, 180 to 240°C, 200 to 260°C, and 210 to 280°C, respectively, and the temperatures of the four temperature zones are set incrementally. The pre-oxidation residence time of each pre-oxidation temperature zone is 10 to 30 minutes, and the draft ratios of the four pre-oxidation temperature zones are 0.5 to 3.5%, -2.5 to -0.5%, -2.5 to -0.5%, and -2.5 to -0.5%, respectively.

2. The preparation method according to claim 1, characterized in that In millimeters, the width of the filament bundle during the pre-oxidation treatment is 0.0004 to 0.0006 times the number of polyacrylonitrile fiber strands.

3. The preparation method according to claim 1, characterized in that The number of the polyacrylonitrile fiber precursors is 48,000 to 600,000; and / or, The moisture content of the polyacrylonitrile fiber precursor is less than or equal to 7 wt %; and / or, The fineness of the polyacrylonitrile fiber precursor is 0.2-3.0 dtex.

4. The preparation method according to claim 3, characterized in that The number of the polyacrylonitrile fiber precursors is 48,000 to 360,000; and / or, The moisture content of the polyacrylonitrile fiber precursor is less than or equal to 5wt%; and / or, The fineness of the polyacrylonitrile fiber precursor is 0.5-2.5 dtex.

5. The preparation method according to claim 1, characterized in that The temperatures of the four pre-oxidation temperature zones are 180-200° C., 200-220° C., 220-240° C., and 230-260° C., respectively, and the temperatures of the four temperature zones are set in increasing order; and / or, The pre-oxidation residence time in each pre-oxidation temperature zone is 15 to 25 minutes; and / or, The drafting ratios of the four pre-oxidation temperature zones are respectively 1-3%, -2--1%, -2--1%, and -2--1%.

6. The preparation method according to claim 1, characterized in that The low-temperature carbonization is set in three temperature zones.

7. The preparation method according to claim 6, characterized in that The temperatures of the three temperature zones of low-temperature carbonization are 300-600° C., 400-700° C., and 600-900° C., respectively, and the temperatures of the three temperature zones are set in increasing order; and / or, The residence time of each temperature zone of the low-temperature carbonization is 1 to 20 minutes; and / or, The draft ratio of each temperature zone of the low-temperature carbonization is 0.5-10%.

8. The preparation method according to claim 7, characterized in that The temperatures of the three temperature zones of low-temperature carbonization are 50-550°C, 450-650°C, and 650-850°C, respectively, and the temperatures of the three temperature zones are set in increasing order; and / or, The residence time of each temperature zone of the low-temperature carbonization is 2 to 10 minutes; and / or, The draft ratio of each temperature zone of the low-temperature carbonization is 2-7%.

9. The preparation method according to claim 1, characterized in that The high temperature carbonization is set in three temperature zones.

10. The preparation method according to claim 9, characterized in that The temperatures of the three temperature zones of high-temperature carbonization are 900-1300° C., 1100-1400° C., and 1200-1600° C., respectively, and the temperatures of the three temperature zones are set in increasing order; and / or, The residence time of each temperature zone of the high temperature carbonization is 1 to 20 minutes; and / or, The draft ratio of each temperature zone of the high temperature carbonization is -5.0 to -0.5%.

11. The preparation method according to claim 10, characterized in that: The temperatures of the three temperature zones of high-temperature carbonization are 1000-1250° C., 1200-1350° C., and 1300-1500° C., respectively, and the temperatures of the three temperature zones are set in increasing order; and / or, The residence time of each temperature zone of the high temperature carbonization is 2 to 10 minutes; and / or, The draft ratio of each temperature zone of the high temperature carbonization is -3.5 to -1.5%.

12. A polyacrylonitrile-based large-tow carbon fiber prepared by the preparation method according to any one of claims 1 to 11.

13. The polyacrylonitrile-based large-tow carbon fiber according to claim 12, characterized in that: The tensile strength of the carbon fiber is ≥3.5 GPa, and the tensile modulus is ≥230 GPa.