KR102662920B1 - A manufacturing method of carbon fibers from cellulose fiber or cellulose derivative fiber - Google Patents

Abstract

The present invention relates to a manufacturing method for obtaining carbon fiber by carbonizing Lyocell fiber, which involves immersing raw Lyocell fiber in a polyacrylamide (PAM) solution and then adding it to the Lyocell fiber through radiation, heating, and a cross-linking agent. It relates to a manufacturing method for obtaining carbon fibers through grafting, thermal stabilization in a certain temperature range, and then high-temperature carbonization.

Description

Carbon fiber manufacturing method using cellulose fiber or cellulose derivative fiber {A MANUFACTURING METHOD OF CARBON FIBERS FROM CELLULOSE FIBER OR CELLULOSE DERIVATIVE FIBER}

The present invention relates to a manufacturing method for obtaining carbon fiber by carbonizing cellulose-based Lyocell fiber. The raw Lyocell fiber is immersed in a polyacrylamide (PAM) solution and then formed into Lyocell fiber through radiation, heating, and a crosslinking agent. It relates to a manufacturing method of obtaining carbon fiber by grafting it onto cell fiber, heat stabilizing it in a certain temperature range, making it non-flammable, and then subjecting it to high-temperature carbonization.

Carbon fiber is widely used as a reinforcing material in advanced composite materials such as automobiles, aviation, high-quality sporting goods, and wind turbine blades. Precursors of carbon fiber are classified into polyacrylonitrile (PAN), pitch, and cellulose. Among them, PAN fiber is a precursor for high-performance carbon fiber, accounting for more than 98%. However, since PAN fibers are obtained from fossil fuels, they have major disadvantages in terms of generating a large amount of toxic gases during carbonization and disposing of them after use. In addition, PAN fiber is expensive and can vary depending on international oil price fluctuations. Therefore, research into environmentally friendly and inexpensive precursors is necessary.

Cellulose is the most abundant organic material on Earth obtained from wood or non-wood and is the oldest carbon fiber precursor, but has the disadvantage of low yield and mechanical strength. Nevertheless, research is continuing to improve the yield and mechanical strength of cellulose-based carbon fiber so that it can replace PAN-based carbon fiber due to the stable supply of raw materials, economic efficiency, and eco-friendliness.

Cellulose used as a precursor for carbon fiber is representative of rayon fiber and lyocell fiber. Rayon fiber is a regenerated fiber made by regenerating the cellulose of wood pulp, and is accompanied by complex pretreatment processes such as alkalization and xanthogen acidification, and various by-products are generated. Meanwhile, Lyocell fiber is a fiber obtained by dissolving cellulose directly in the solvent N -methylmorpholine- N -oxide (NMMO) alone or in a solution of NMMO and water, and is a fiber with a round cross-section and a long, thin shape. Because it uses relatively simple organic solvent spinning, it can be manufactured simply and in an environmentally friendly manner.

However, since cellulose such as lyocell fiber and rayon fiber have very low carbon yield and strength, pretreatment such as flame retardant treatment has been performed before conversion to carbon fiber.

Accordingly, the present invention, as an example, focused on a new manufacturing method to obtain carbon fiber using lyocell-based fiber, a type of cellulose, and improve carbon yield and strength.

Prior literature: Korean Patent Publication 10-1138291 (registered on April 13, 2012)

The purpose of the present invention is to provide a method of manufacturing carbon fiber using Lyocell fiber, which can increase the physical strength and carbonization yield of carbon fiber when manufacturing carbon fiber using cellulose.

The purpose of the present invention is to provide a carbon fiber manufacturing method including a new treatment method that can replace flame retardant treatment to obtain carbon fiber using cellulose-based lyocell.

In order to achieve the above object, the present invention

- Step of immersing cellulose-based Lyocell fibers in a graft polymer solution (S1);

- Grafting Lyocell fibers immersed in a graft polymer solution through radiation or heating (S2);

- Drying the grafted lyocell fibers (S3);

- A step (S4) of thermally stabilizing the dried Lyocell fibers in a certain temperature range to make them non-flammable; and

- A method of manufacturing carbon fiber using Lyocell fiber, including the step (S5) of carbonizing the heat-stabilized Lyocell fiber at high temperature.

The present invention involves grafting polyacrylamide onto Lyocell fibers using radiation or heating to manufacture them into carbon fibers or fabrics using cellulose-based Lyocell fibers or fabrics, followed by a heat stabilization process to simplify and speed up the process. By stabilizing the fiber within the carbon fiber, the physical strength and carbonization yield of the carbon fiber were significantly improved.

Figure 1 is a simplified diagram of a method for manufacturing lyocell-based carbon fiber according to an embodiment of the present invention.
Figure 2 is a photograph of a Lyocell-based carbon fabric manufactured according to an embodiment of the present invention.
Figure 3 is a thermogravimetric analysis (TGA) graph of Lyocell carbon fiber manufactured according to an embodiment of the present invention.
Figure 4 is a scanning electron microscope (SEM) photograph of Lyocell carbon fiber manufactured according to an embodiment of the present invention.
Figure 5 is a graph of tensile strength measurements of Lyocell carbon fiber manufactured according to an embodiment of the present invention.

In the present invention, a preferred embodiment of the carbon fiber manufacturing method using cellulose-based Lyocell fiber basically follows the following process. Here, lyocell fiber means including not only lyocell-based fiber but also fabric, and carbon fiber produced by carbonization means including carbon fabric. The method of manufacturing carbon fiber using Lyocell fiber according to the present invention shows the sequence of each step in Figure 1 and will be described with reference to this.

- Step of immersing cellulose-based Lyocell fibers in a graft polymer solution (S1);

- Grafting Lyocell fibers immersed in a graft polymer solution through radiation or heating (S2);

- Drying the grafted lyocell fibers (S3);

- A step (S4) of thermally stabilizing the dried Lyocell fibers in a certain temperature range to make them non-flammable; and

- A carbon fiber manufacturing method using Lyocell fiber, characterized in that it includes the step (S5) of carbonizing the heat-stabilized Lyocell fiber at a high temperature.

The carbon fiber manufacturing method will be described in detail through an example below.

- Step 1 (S1) is a step of immersing cellulose-based Lyocell fibers (or fabrics) in a graft polymer solution, which is a crosslinking agent. The lyocell fibers can be used as is or by using a roller, etc. Alternatively, the state in which an appropriate amount of the graft polymer solution has been removed from the fabric can be used.

The graft polymer solution includes polyacrylamide, acrylic acid derivatives, methacrylonitrile, glycidyl methacrylate, and citric acid. One or more types may be selected from the group including epichlorhydrin, polyethylimine, and glutaraldehyde, but polyacrylamide solution is preferably used and was used as an example of the present invention. The polyacrylamide solution may be 0.005% by weight to 4% by weight, but is preferably 0.05% by weight to 0.5% by weight. If it is less than 0.05% by weight, it is difficult to show the effect, and if it is more than 0.5% by weight, the viscosity increases and the carbon fibers stick together, making it difficult to separate the fibers.

- Step 2 is a step of grafting the lyocell fibers immersed in the graft polymer solution through radiation or heating as described above.

Gamma rays, electron beams, ion beams, neutron beams, ultraviolet rays, and 300 kGy is appropriate. On the other hand, when grafting by heat, it is preferable to heat it at 80°C or higher.

- Drying the grafted lyocell fibers by irradiation or heating (S3);

In the step of drying the lyocell fibers grafted with polyacrylamide, the grafted lyocell fibers can be dried by either freeze-drying in an ultra-low temperature freezer or natural, room temperature, or heat drying, but it is preferable. The best way is to freeze-dry it.

- Thermal stabilization of the dried Lyocell fiber in a certain temperature range (S4);

This is a heat treatment step for heat stabilization of the dried Lyocell fiber in a certain temperature range. The heat treatment step can be performed at 200 to 300° C. for 30 minutes to 3 hours at 1 to 10° C. per minute. Through the above steps, Lyocell acquires a molecular structure suitable for performing the carbonization process.

- It includes a step (S5) of carbonizing the heat-stabilized Lyocell fiber at high temperature.

The carbonization step is a step of carbonizing lyocell fibers or fabrics in an inert atmosphere. The carbonization process is carried out by heating to a temperature of 500 to 2500 ℃, and the temperature increase rate is 1 to 10 ℃ per minute, but the temperature is 1400 ℃ or more. It is desirable to increase the temperature to . It is desirable to slow the temperature increase rate as much as possible, but if the temperature increase rate is too slow, there is a problem of increased energy consumption.

During the manufacturing process of the above steps, the strength and carbonization yield of the lyocell-based carbon fiber are determined depending on the grafting concentration, radiation dose, and heat stabilization temperature and time.

Hereinafter, the present invention will be described in more detail through examples. However, the following examples only illustrate the present invention, and the content of the present invention is not limited to the following examples.

<Carbon fiber comparative example>

- Polyacrylamide solutions were prepared at concentrations of 0.05, 0.1, 0.5, 1, 2, and 4% by weight, Lyocell fabrics were immersed, and all were equally irradiated with an electron dose of 100 kGy to prepare five samples. In this comparative example, lyocell fabric was used to easily manufacture carbon fiber.

- Lyocell fabrics grafted with polyacrylamide by irradiation with electron beams were frozen in an ultra-low temperature freezer and then freeze-dried.

- Optionally, the dried samples were heated at 10°C per minute and then thermally stabilized at 250°C for 1 hour.

- In order to compare samples that did not undergo a thermal stabilization step with those that were thermally stabilized, each was carbonized under a nitrogen atmosphere. Preferably, raising the temperature to 1400°C at a rate of 10°C per minute helps increase the strength, but in the above experiment, the carbon fabric was manufactured by raising the temperature to 1000°C and then carbonizing it.

- And a comparative experiment was conducted on each Lyocell-based carbon fabric manufactured through this process.

<Carbon fiber comparative experiment>

TGA analysis

TGA analysis was performed to determine the carbonization rate of the fabric grafted with polyacrylamide via radiation and heat-stabilized.

As shown in the TGA analysis graph of Figure 3, when carbonizing the basic lyocell fabric without grafting, it can be seen that the weight decreases sharply at 300 ℃ and then complete weight loss occurs at 600 ℃, which is due to carbonization. This means that carbon fiber cannot be produced.

On the other hand, Lyocell fabric grafted with polyacrylamide showed an increase in carbon yield from 10% to 20% at 1000°C through irradiation (see Figure 3b).

Meanwhile, as shown in Figure 3c, it can be seen that the carbonization yield can be increased and the weight loss can be significantly alleviated by heat stabilization treatment by heat treatment. For example, as a result of TGA analysis after heat treatment at 250℃ for 1 hour, the carbonization yield increased and the weight loss was alleviated. In particular, as the polyacrylamide increased, the carbonation yield increased from 40% to 55% and the weight loss also increased at 350℃. It appeared gradually between ~650℃.

2. SEM image

Figure 4 is a photograph of the cross-section and surface of a carbon fiber obtained from a lyocell fabric in which polyacrylamide was grafted via radiation.

Through this, it was shown that the carbon fibers obtained from Lyocell fabric with less than 0.5% by weight of polyacrylamide graphed had a round, hard cross-section and a smooth surface, and that the fibers could be separated from each other, but they did not emit more than 1.0% by weight of radiation. The cross-section of the Lyocell fabric to which polyacrylamide was graphed was generally round, but the surface appeared as if the polyacrylamide was peeling off, or in the case of 2% or 4% by weight, the fibers were seen to be attached to each other. This is expected to affect the mechanical strength value of the fiber.

3. Mechanical strength

Figure 5 shows the mechanical strength of carbon fibers obtained from Lyocell fabric grafted with polyacrylamide via radiation.

The strength value of Lyocell carbon fiber grafted with less than 0.5% by weight of polyacrylamide increased as the concentration increased, and the strength value of Lyocell carbon fiber grafted with 0.5% by weight polyacrylamide showed up to 1.39 GPa. .

As shown in the SEM image, the carbon fiber of Lyocell grafted with 1.0% by weight polyacrylamide was damaged during the fiber separation process due to its slightly high viscosity, and its strength value decreased.

Meanwhile, the carbon fiber of Lyocell grafted with 2% by weight and 4% by weight polyacrylamide had high viscosity, which caused the fibers to stick together and single fiber strands could not be extracted, making strength measurement impossible.

Claims (10)

- Step (S1) of immersing cellulose fibers or cellulose derivative fibers in a graft polymer solution;
- A step (S2) of grafting cellulose fibers or cellulose derivative fibers immersed in a graft polymer solution by irradiating radiation or applying heat;
- drying the grafted cellulose fibers or cellulose derivative fibers (S3);
- Thermal stabilization of the dried cellulose fiber or cellulose derivative fiber in a certain temperature range (S4); and
- A method of producing carbon fiber using cellulose fiber or cellulose derivative fiber, comprising the step (S5) of carbonizing the heat-stabilized cellulose fiber or cellulose derivative fiber at high temperature,
The graft polymer includes polyacrylamide, acrylic acid derivatives, methacrylonitrile, glycidyl methacrylate, and citric acid. A method of producing carbon fiber using cellulose fiber or cellulose derivative fiber, characterized in that it is one or more selected from the group including epichlorhydrin, polyethylimine, and glutaraldehyde.
delete delete According to paragraph 1,
A method of producing carbon fiber using cellulose fiber or cellulose derivative fiber, characterized in that the radiation in step S2 is selected from the group consisting of gamma rays, electron beams, ion beams, neutron beams, ultraviolet rays, and X-rays.
According to paragraph 1,
A method of producing carbon fiber using cellulose fiber or cellulose derivative fiber, characterized in that the total radiation dose in step S2 is 50 to 500 kGy.
According to paragraph 1,
A method of producing carbon fiber using cellulose fiber or cellulose derivative fiber, characterized in that the grafting by heat in step S2 is heated at 80 ° C. or higher.
According to paragraph 1,
A carbon fiber manufacturing method using cellulose fiber or cellulose derivative fiber, characterized in that the drying in step S3 is any one selected from the group consisting of heat drying, natural drying, and freeze drying.
According to paragraph 1,
A carbon fiber manufacturing method using cellulose fibers or cellulose derivative fibers, characterized in that the heat treatment temperature increase rate in step S2 is 1 to 10 ° C per minute and is carried out at 200 to 300 ° C for 30 minutes to 3 hours.
According to paragraph 1,
A method of producing carbon fiber using cellulose fiber or cellulose derivative fiber, characterized in that the carbonization in step S5 is carried out at 500 to 2500 ° C. at a temperature increase rate of 1 to 10 ° C./min.
A cellulose-based carbon fiber manufactured by the carbon fiber manufacturing method according to any one of claims 1, 4 to 9.