Bio-based carbon fiber and preparation method thereof

Abstract

The invention discloses a bio-based carbon fiber and a preparation method thereof. The method comprises the following steps: dipping a Lyoorace fiber in an aqueous solution containing phosphoric acid and urea; and carrying out stabilization and carbonization treatment on the impregnated fiber to obtain the carbon fiber. By adopting the method, the continuous preparation of the bio-based carbon fiber can be realized, the method has the characteristics of simplicity in process implementation, high efficiency and easiness in industrial production, and the prepared bio-based carbon fiber filament is excellent in mechanical property.

Description

Technical Field

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

[0002] Carbon fiber has the characteristics of high specific strength, high specific modulus, high temperature resistance, corrosion resistance, good electrical and thermal conductivity, etc., so it is widely used in aerospace, petroleum, chemical, textile, machinery and sports equipment. According to the source of carbon fiber raw materials, carbon fiber can usually be divided into three categories: polyacrylonitrile-based, viscose-based and asphalt-based. With the implementation of sustainable development strategies in countries around the world, the preparation of "green" carbon fiber using bio-based fibers as raw materials has gradually received attention.

[0003] Lyocell fiber is a new type of green and environmentally friendly fiber developed in the 1990s. Its molecular formula is (C6H 10 O5) n , the degree of polymerization is above 500, and it is an excellent fiber material for clothing. The fiber is obtained by wet spinning or dry-wet spinning process using a mixture of N-methylmorpholine-N-oxide (NMMO) and water as solvent to dissolve the fiber. It has the characteristics of high crystallinity and orientation, high strength, uniform structure, etc. It is a potential raw material for preparing carbon fiber. The current literature reports on the preparation of carbon fiber with Lyocell fiber basically adopts the intermittent method, which has the problems of low efficiency, low stability, and difficulty in industrial production. Summary of the invention

[0004] The present invention provides a bio-based carbon fiber and a preparation method thereof. The method can realize the continuous preparation of bio-based carbon fiber, and has the characteristics of simple process implementation, high efficiency and easy industrial production. The prepared bio-based carbon fiber filaments have excellent mechanical properties.

[0005] The first aspect of the present invention provides a method for continuously preparing bio-based carbon fibers, the method comprising: impregnating Lyocell fibers in an aqueous solution containing phosphoric acid and urea; and stabilizing and carbonizing the impregnated fibers to obtain carbon fibers.

[0006] Furthermore, the concentration of the aqueous solution containing phosphoric acid and urea is 1%-10%.

[0007] Furthermore, the mass ratio of phosphoric acid to urea in the aqueous solution containing phosphoric acid and urea is (1-4): (1-4).

[0008] Furthermore, the immersion time is 0.5 min-10 min.

[0009] Furthermore, the stabilization process includes: heat treating the impregnated fiber in air or nitrogen atmosphere by gradient temperature rising method, with the starting temperature of 160℃-200℃, the final temperature of 260℃-280℃, the temperature gradient of 10~50℃, divided into 2-6 temperature zones, and the total treatment time of 30min-180min.

[0010] Furthermore, the carbonization treatment includes low-temperature carbonization and high-temperature carbonization. The low-temperature carbonization process includes: using nitrogen as a protective gas, the oxygen content in the nitrogen is below 5 PPm, the temperature is 350°C-900°C, and the residence time is 1.5min-6min.

[0011] Furthermore, the high-temperature carbonization process includes: using nitrogen as a protective gas, the oxygen content in the nitrogen is below 3 PPm, the nitrogen dew point temperature is below -60°C, the temperature is 1000°C-1500°C, and the residence time is 1min-4min.

[0012] A second aspect of the present invention provides a bio-based carbon fiber, which is obtained by the above method.

[0013] Compared with the prior art, the present invention has at least the following beneficial effects: the present invention uses Lyocell fiber as raw material, impregnates the Lyocell fiber in an aqueous solution containing phosphoric acid and urea, and then stabilizes and carbonizes the impregnated carbon fiber to obtain carbon fiber. Through the impregnation treatment, a certain amount of phosphoric acid and urea are attached to the fiber, and the attached phosphoric acid and urea effectively promote the dehydration reaction of the fiber in the low temperature stage in the subsequent stabilization process, inhibit the formation of left-handed glucose, thereby increasing the carbonization yield during the subsequent high-temperature carbonization treatment and maintaining the fiber morphology. Therefore, the method of the present invention can realize the continuous production of bio-based carbon fiber, and has the characteristics of simple process implementation, high efficiency, and easy industrial production, and the prepared bio-based carbon fiber filament has excellent mechanical properties. DETAILED DESCRIPTION

[0014] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments, and the following examples are only descriptive, not restrictive, and cannot be used to limit the scope of protection of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0015] The first aspect of the present invention provides a method for continuously preparing bio-based carbon fibers. According to an embodiment of the present invention, the method comprises:

[0016] S1: Impregnation of Lyocell fiber in an aqueous solution containing phosphoric acid and urea

[0017] According to an embodiment of the present invention, Lyocell fibers are immersed in an aqueous solution containing phosphoric acid and urea, wherein the phosphoric acid and urea attached to the fibers reduce the activation energy of the fiber dehydration reaction during the subsequent stabilization treatment, and promote the formation of cross-linked structures within and between fiber molecules. Furthermore, the concentration of the aqueous solution containing phosphoric acid and urea is 1%-10%, and the immersion time is 0.5min-10min.

[0018] According to an embodiment of the present invention, the mass ratio of phosphoric acid to urea in the aqueous solution containing phosphoric acid and urea is (1-4): (1-4). The inventors found that if the phosphoric acid content is too high, that is, the urea content is too low, the promoting effect on the fiber dehydration reaction is not obvious; if the phosphoric acid content is too low, that is, the urea content is too high, the fiber is prone to twisting, affecting the smooth implementation of the process and the performance of the final carbon fiber. Therefore, mixing phosphoric acid and urea in the above ratio can effectively promote the dehydration reaction of the fiber during the stabilization process and promote the formation of cross-linked structures within and between fiber molecules.

[0019] S2: Stabilizing and carbonizing the impregnated fibers to obtain carbon fibers.

[0020] According to an embodiment of the present invention, the impregnated fiber is stabilized and carbonized. During the stabilization process, the fiber molecules in the fiber undergo intramolecular and intermolecular reactions under the catalysis of phosphoric acid and urea to form a multi-ring interconnected carbon ring structure. During the carbonization process, the carbon ring structure formed in the fiber undergoes a thermal cracking reaction to remove hydrogen and oxygen to form a graphite sheet of six carbon atoms, which is further converted into a turbostratic graphite structure.

[0021] According to an embodiment of the present invention, the stabilization process includes: heat treating the impregnated fiber by a gradient temperature rise method, with a starting temperature of 160°C-200°C, a final temperature of 260°C-280°C, a temperature gradient of 10 to 50°C, 2 to 6 temperature zones, and a total treatment time of 30 min to 180 min.

[0022] According to an embodiment of the present invention, the carbonization treatment includes low-temperature carbonization and high-temperature carbonization. The low-temperature carbonization process includes: using nitrogen as a protective gas, the oxygen content in the nitrogen is less than 5PPm, the temperature is 350°C-900°C, and the residence time is 1.5min-6min. In this process, the carbon ring structure formed in the fiber undergoes a thermal cracking reaction to remove hydrogen and oxygen to form a six-carbon atom graphite sheet; the high-temperature carbonization process includes: using nitrogen as a protective gas, the oxygen content in the nitrogen is less than 3PPm, the nitrogen dew point temperature is less than -60°C, the temperature is 1000°C-1500°C, and the residence time is 1min-4min. The six-carbon atom graphite sheet formed in this process further grows to form a carbon fiber with a graphite-like structure.

[0023] A second aspect of the present invention provides a bio-based carbon fiber, which is obtained by the above method.

[0024] It should be noted that the above method for continuously preparing bio-based carbon fiber is also applicable to the bio-based carbon fiber, which will not be repeated here.

[0025] The present invention will be further described below by way of examples, but the protection scope of the present invention is not limited to these embodiments. The present invention may also have other various embodiments, and those skilled in the art may make various corresponding changes and deformations according to the present invention without departing from the spirit and essence of the present invention, but these corresponding changes and deformations shall all belong to the protection scope of the claims attached to the present invention.

[0026] Example 1

[0027] 1) Impregnation pretreatment

[0028] The Lyocell fiber was pre-treated by immersion in a 2% aqueous solution containing phosphoric acid and urea (the mass ratio of phosphoric acid to urea was 2:1) for 4 minutes;

[0029] 2) Stabilization

[0030] The impregnated Lyocell was stabilized in air atmosphere by gradient temperature rise method. The stabilization temperatures were 170, 200, 230 and 260℃, with a total of 4 temperature zones. The temperature gradient of each temperature zone was 30℃. The fiber stayed at each temperature for 20 minutes, and the total residence time was 80 minutes.

[0031] 3) Low temperature carbonization

[0032] The stabilized fiber is then put into a low-temperature carbonization furnace for carbonization treatment, using high-purity nitrogen as the protective gas, the oxygen content in the nitrogen is below 3 ppm, the low-temperature carbonization temperature is 600°C, and the residence time is 2 minutes;

[0033] 4) High temperature carbonization

[0034] After leaving the low-temperature carbonization furnace, the fiber enters the high-temperature carbonization furnace for high-temperature carbonization treatment. High-purity nitrogen is used as the protective gas. The oxygen content in the nitrogen is less than 3PPm, the nitrogen dew point temperature is below -60°C, the carbonization temperature is 1200°C, and the high-temperature carbonization residence time is 1 minute.

[0035] The tensile mechanical properties of the obtained carbon fiber were tested with reference to GB / T3362-2017 "Test method for tensile properties of carbon fiber multifilaments", and the tensile strength was 0.8 GPa and the tensile modulus was 80 GPa.

[0036] Example 2

[0037] 1) Impregnation pretreatment

[0038] The Lyocell fiber was pre-treated by immersion in an aqueous solution containing phosphoric acid and urea at a concentration of 8% (the mass ratio of phosphoric acid to urea was 1:1) for 2 minutes;

[0039] 2) Stabilization treatment

[0040] The impregnated Lyocell fibers were stabilized in a nitrogen atmosphere using a gradient temperature ramp method. The temperatures were 180, 195, 210, 235, 250, and 265°C, a total of 6 temperature zones. The temperature gradient in each zone was 15°C. The fiber stayed at each temperature for 15 minutes, and the total residence time was 90 minutes.

[0041] 3) Low temperature carbonization

[0042] The stabilized fiber is then put into a low-temperature carbonization furnace for carbonization treatment. High-purity nitrogen is used as the protective gas. The oxygen content in the nitrogen is below 3 ppm. The low-temperature carbonization temperature is 800°C and the residence time is 3 minutes.

[0043] 4) High temperature carbonization

[0044] After leaving the low-temperature carbonization furnace, the fiber enters the high-temperature carbonization furnace for high-temperature carbonization treatment. High-purity nitrogen is used as the protective gas. The oxygen content in the nitrogen is less than 3PPm, the nitrogen dew point temperature is below -60°C, the carbonization temperature is 1300°C, and the high-temperature carbonization residence time is 1.5 minutes.

[0045] The tensile mechanical properties of the obtained carbon fiber were tested with reference to GB / T3362-2017 "Test method for tensile properties of carbon fiber multifilaments", and the tensile strength was 1.0 GPa and the tensile modulus was 90 GPa.

[0046] Example 3

[0047] 1) Impregnation pretreatment

[0048] The Lyocell fiber was pre-treated by immersion in a 2% aqueous solution containing phosphoric acid and urea (the mass ratio of phosphoric acid to urea was 1:2) for 8 minutes;

[0049] 2) Stabilization treatment

[0050] The impregnated Lyocell fibers were stabilized in air atmosphere by gradient temperature rise method. The stabilization temperatures were 160, 180, 200, 220, 240 and 260°C in 6 temperature zones. The temperature gradient of each temperature zone was 20°C. The fiber stayed at each temperature for 20 minutes, and the total residence time was 120 minutes.

[0051] 3) Low temperature carbonization

[0052] The stabilized fiber is then put into a low-temperature carbonization furnace for carbonization treatment, using high-purity nitrogen as the protective gas, the oxygen content in the nitrogen is below 3 ppm, the low-temperature carbonization temperature is 800°C, and the residence time is 3 minutes;

[0053] 4) High temperature carbonization

[0054] After leaving the low-temperature carbonization furnace, the fiber enters the high-temperature carbonization furnace for high-temperature carbonization treatment. High-purity nitrogen is used as the protective gas. The oxygen content in the nitrogen is less than 3PPm, the nitrogen dew point temperature is below -60°C, the carbonization temperature is 1400°C, and the high-temperature carbonization residence time is 1.5 minutes.

[0055] The tensile mechanical properties of the obtained carbon fiber were tested with reference to GB / T3362-2017 "Test method for tensile properties of carbon fiber multifilaments", and the tensile strength was 1.2 GPa and the tensile modulus was 95 GPa.

[0056] Example 4

[0057] 1) Impregnation pretreatment

[0058] The Lyocell fiber was pre-treated by immersion in a 5% aqueous solution containing phosphoric acid and urea (the mass ratio of phosphoric acid to urea was 3:1) for 4 minutes;

[0059] 2) Stabilization

[0060] The impregnated Lyocell fibers were stabilized in air atmosphere by gradient temperature rise method. The stabilization temperatures were 200, 240 and 280°C in three temperature zones. The temperature gradient of each temperature zone was 40°C. The fiber stayed at each temperature for 15 minutes, and the total residence time was 45 minutes.

[0061] 3) Low temperature carbonization

[0062] The stabilized fiber is then put into a low-temperature carbonization furnace for carbonization treatment, using high-purity nitrogen as the protective gas, with the oxygen content in the nitrogen below 3 ppm. The low-temperature carbonization temperature is 800°C, and the residence time is 4 minutes;

[0063] 4) High temperature carbonization

[0064] After leaving the low-temperature carbonization furnace, the fiber enters the high-temperature carbonization furnace for high-temperature carbonization treatment. High-purity nitrogen is used as the protective gas. The oxygen content in the nitrogen is less than 3PPm, and the nitrogen dew point temperature is below -60°C. The carbonization temperature is 1100°C, and the high-temperature carbonization residence time is 3 minutes.

[0065] The tensile mechanical properties of the obtained carbon fiber were tested with reference to GB / T3362-2017 "Test method for tensile properties of carbon fiber multifilaments", and the tensile strength was 0.58 GPa and the tensile modulus was 65 GPa.

[0066] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for continuously preparing bio-based carbon fibers, characterized in that: include: The Lyocell fiber is impregnated in an aqueous solution containing phosphoric acid and urea; The impregnated fibers are stabilized and carbonized to obtain carbon fibers.

2. The method according to claim 1, characterized in that: The concentration of the aqueous solution containing phosphoric acid and urea is 1%-10%.

3. The method according to claim 1 or 2, characterized in that: The mass ratio of phosphoric acid to urea in the aqueous solution containing phosphoric acid and urea is (1-4): (1-4).

4. The method according to claim 1, characterized in that: The immersion time is 0.5 min-10 min.

5. The method according to claim 1, characterized in that The stabilization process includes: The impregnated fiber is heat treated by a gradient temperature rise method, with a starting temperature of 160°C-200°C, a final temperature of 260°C-280°C, a temperature gradient of 10-50°C, 2-6 temperature zones, and a total treatment time of 30min-180min.

6. The method according to claim 1, characterized in that The carbonization treatment includes low-temperature carbonization and high-temperature carbonization, and the low-temperature carbonization process includes: Nitrogen is used as the protective gas, the oxygen content in the nitrogen is below 5PPm, the temperature is 350℃-900℃, and the residence time is 1.5min-6min.

7. The method according to claim 6, characterized in that The high temperature carbonization process comprises: Nitrogen is used as the protective gas, the oxygen content in the nitrogen is below 3PPm, the nitrogen dew point temperature is below -60°C, the temperature is 1000°C-1500°C, and the residence time is 1min-4min.

8. A bio-based carbon fiber, characterized in that: The method according to any one of claims 1 to 7 is used to obtain the