Ultrafine high-strength meta-aramid fiber and preparation method thereof

Abstract

The application discloses a kind of superfine high-strength meta-aramid fiber and its preparation method, by adjusting wet spinning coagulation bath type and reducing coagulation bath temperature, realize super-drawing, to obtain superfine high-strength meta-aramid fiber.Ethyl acetate and dimethylacetamide are used as coagulation bath, and the temperature of coagulation bath is reduced at the same time, so that the coagulation speed of the fiber in the coagulation bath is slower, and the intermolecular force of the fiber is stronger, forming a more stable network gel state, with very excellent stretchability.The meta-aramid fiber prepared by the method has a diameter of 1.43um, a tensile ratio of up to 8000 times, a breaking strength of 1332MPa, and an elongation at break of more than 20%.

Description

Technical Field

[0001] This invention belongs to the field of aramid fiber technology, specifically relating to an ultrafine high-strength meta-aramid fiber and its preparation method. Background Technology

[0002] Meta-aramid fibers (usually referring to poly(m-phenylene isophthalamide), abbreviated as PMIA, trade name such as Nomex) are a type of high-performance synthetic fiber with excellent heat resistance, flame retardancy, and mechanical strength. These materials perform exceptionally well in high-temperature environments, are not easily flammable, and do not melt or drip even when burning, thus finding wide application in protective clothing, thermal insulation materials, electrical insulation, and other fields.

[0003] The preparation of meta-aramid fibers generally includes two main steps: polymerization and spinning.

[0004] First, m-phenylenediamine and isophthalic acid or their derivatives are polymerized in a suitable solvent to form a high molecular weight poly(m-phenylenediamine isophthalamide) solution. The resulting polymer solution is then processed into fibers using processes such as wet spinning or dry-jet wet spinning. In wet spinning, the polymer solution is extruded from fine pores into a thin stream, which then enters a coagulation bath to solidify and take shape. Dry-jet wet spinning combines the speed advantages of dry spinning with the ease of operation of wet spinning, allowing the polymer solution to partially solidify in a gaseous environment before entering a coagulation bath for complete solidification.

[0005] However, existing wet spinning technology has some limitations. Since water is a strong but weak solvent for meta-aramid fibers, the fibers solidify rapidly after entering the coagulation bath. This not only affects subsequent stretching operations but also makes it difficult to obtain ultrafine fibers when using spinnerets with larger orifice diameters. To produce ultrafine fibers, spinnerets with smaller orifice diameters are required, but this significantly increases the difficulty and cost of production.

[0006] Furthermore, current stretching baths only offer stretch ratios of 2 to 10 times, which is insufficient for pursuing higher performance fibers. Therefore, to overcome these challenges, it is necessary to explore new coagulation bath compositions or optimize spinning process parameters, such as adjusting the composition, temperature, or pH of the coagulation bath, or to develop novel solvent systems to improve fiber quality and reduce production costs. Summary of the Invention

[0007] To address the problem that existing meta-aramid fibers solidify too quickly in the coagulation bath, resulting in poor stretching and thus preventing the production of ultrafine fibers, this invention proposes an ultrafine high-strength meta-aramid fiber and its preparation method.

[0008] This invention uses ethyl acetate and dimethylacetamide as a coagulation bath, and lowers the temperature of the coagulation bath to slow down the coagulation rate of the fiber in the coagulation bath and strengthen the intermolecular forces of the fiber, forming a more stable network gel state with excellent stretchability, thereby producing ultrafine meta-aramid fibers.

[0009] One of the technical solutions of this invention is to provide a method for preparing ultrafine high-strength meta-aramid fibers. Specifically, it includes the following steps: preparing a meta-aramid spinning solution with a solid content of 15%-25%, using dimethylacetamide (DMAC) as the solvent; after degassing the spinning solution, inserting a spinneret into a coagulation bath, which is a mixed solution of ethyl acetate and DMAC with a volume ratio of 80:20-75:25; subsequently drawing the solution into a stretching bath for stretching, followed by drying and heat treatment; the stretching bath includes a room temperature stretching bath and a hot water stretching bath at 70-90°C; the stretching rate is 1-2 times in both the room temperature stretching bath and the hot water stretching bath.

[0010] Furthermore, the temperature of the coagulation bath is -30 to 30°C.

[0011] Furthermore, the orifice diameter of the spinneret is 0.38-0.5 mm.

[0012] Furthermore, the spinneret speed is 10-40 μL / h.

[0013] Furthermore, the drying temperature is 80-100℃.

[0014] Furthermore, the heat treatment temperature is 280-300℃.

[0015] Under these coagulation bath and temperature conditions, meta-aramid exhibits an excellent gel state and excellent stretchability in the coagulation bath. Especially at lower coagulation bath temperatures, the intermolecular forces such as hydrogen bonds and van der Waals forces between nascent fiber molecules are enhanced, resulting in a stronger gel network structure. This can further improve the stretchability of nascent fibers, with a stretch ratio of up to 8000 times.

[0016] The second technical solution of the present invention is to provide an ultrafine high-strength meta-aramid fiber prepared by the above method.

[0017] The resulting fibers have a diameter of only 1.43-2.94 μm, a strength of 1.3 GPa, and an elongation at break of 20%-40%.

[0018] The beneficial effects of this invention are as follows:

[0019] 1) The coagulation bath is selected using a good solvent for meta-aramid fibers to reduce the double diffusion rate of the fibers in the coagulation bath, so that the nascent fibers exhibit a gel state with excellent tensile properties in the coagulation bath, thereby achieving super-stretching.

[0020] 2) The diameter of the fiber after super-stretching is very small, thus it can be used to make ultrafine fibers.

[0021] 3) Due to the super-stretching of the fiber, the molecular orientation is high and the internal defects are few, resulting in excellent mechanical properties.

[0022] 4) Due to the small fiber diameter, only lower temperature heat treatment is required, resulting in lower energy consumption. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the preparation method of the present invention.

[0024] Figure 2 These are scanning electron microscope images of Examples 1-4. Detailed Implementation

[0025] The following examples are provided to further illustrate the present invention and are intended to explain the invention, not to limit its scope. Unless otherwise specified, all figures are expressed in parts by weight and weight percentages.

[0026] Unless otherwise specified, the raw materials used in this invention are all conventional commercially available products; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0027] The embodiments of the present invention will be further described below with reference to several examples.

[0028] It should be understood that the described embodiments are merely some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0029] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0030] The solid content mentioned below refers to the mass content;

[0031] Unless otherwise specified, the percentages mentioned below are volume fractions.

[0032] The room temperature water and hot water used for bathing described below contain deionized water.

[0033] Example 1

[0034] A meta-aramid spinning solution with a solid content of 15% was prepared and wet-spun after degassing. The injection pump speed was set to 40 μL / h, the spinneret diameter was 0.38 mm, the coagulation bath was 80% EA + 20% DMAC, and the temperature was 3 °C. After the nascent fibers emerged from the spinneret, they entered the coagulation bath and were then drawn onto roller 1 at a speed of 24 m / min. The fibers were then washed in a room-temperature water bath with a stretch ratio of 1. Next, they were washed in a 90 °C hot water bath with a stretch ratio of 1. After the hot water wash, they were continuously dried in a tube furnace at 80 °C. Finally, they were heat-treated in a tube furnace at 300 °C. After heat treatment, the fibers were taken in using a take-up roller. The meta-aramid fibers obtained by this method had a diameter of 1.43 μm, a stretch ratio of 8826, a breaking strength of 737 MPa, and a breaking elongation of 30%.

[0035] Example 2

[0036] A meta-aramid spinning solution with a solid content of 25% was prepared and wet-spun after degassing. The injection pump speed was set to 10 μL / h, the spinneret diameter was 0.5 mm, the coagulation bath was 80% EA + 20% DMAC, and the temperature was 30 °C. After the nascent fibers emerged from the spinneret, they entered the coagulation bath and were then drawn onto roller 1 at a speed of 2 m / min. The fibers were then washed in a room-temperature water bath with a stretch ratio of 2:1. Next, they were washed in a 70 °C hot water bath with a stretch ratio of 2:1. After the hot water wash, they were continuously dried in a tube furnace at 80 °C. Finally, they were heat-treated in a tube furnace at 280 °C. After heat treatment, the fibers were taken in using a take-up roller. The meta-aramid fibers obtained by this method had a diameter of 5.9 μm, a stretch ratio of 1795:1, a breaking strength of 620 MPa, and a breaking elongation of 20%.

[0037] Example 3

[0038] A meta-aramid spinning solution with a solid content of 15% was prepared and wet-spun after degassing. The injection pump speed was set to 10 μL / h, the spinneret diameter was 0.5 mm, the coagulation bath was 80% EA + 20% DMAC, and the temperature was 30 °C. After the nascent fibers emerged from the spinneret, they entered the coagulation bath and were then drawn onto roller 1 at a speed of 5 m / min. The fibers were then washed in a room temperature water bath with a stretch ratio of 2:1. Next, they were washed in a 90 °C hot water bath with a stretch ratio of 2:1. After hot water washing, they were continuously dried in a tube furnace at 100 °C. Finally, they were heat-treated in a tube furnace at 300 °C. After heat treatment, the fibers were taken in using a take-up roller. The meta-aramid fibers obtained by this method had a diameter of 2.9 μm, a stretch ratio of 3715:1, a breaking strength of 1073 MPa, and a breaking elongation of 40%.

[0039] Example 4

[0040] A meta-aramid spinning solution with a solid content of 25% was prepared and wet-spun after degassing. The injection pump speed was set to 10 μL / h, the spinneret diameter was 0.5 mm, the coagulation bath was 75% EA + 25% DMAC, and the temperature was -30℃. After the nascent fibers emerged from the spinneret, they entered the coagulation bath and were then drawn onto roller 1 at a speed of 8 m / min. The fibers were then washed in a room temperature water bath with a stretch ratio of 2:1. Next, they were washed in a 90℃ hot water bath with a stretch ratio of 2:1. After the hot water wash, they were continuously dried in a tube furnace at 100℃. Finally, they were heat-treated in a tube furnace at 300℃. After heat treatment, the fibers were taken in using a take-up roller. The meta-aramid fibers obtained by this method had a diameter of 2.8 μm, a stretch ratio of 3840:1, a breaking strength of 1332 MPa, and a breaking elongation of 20%.

[0041] Comparative Example 1

[0042] A meta-aramid spinning solution with a solid content of 15% was prepared and wet-spun after degassing. The injection pump speed was set to 40 μL / min, the spinneret diameter to 0.38 mm, the coagulation bath to 100% EA at 30 °C, and the nascent fibers exiting the spinneret were drawn into the coagulation bath and then pulled to roller 1 at a speed of 0.1 m / min. The fibers were then washed in room temperature water with a stretch ratio of 5 times, followed by a 90 °C hot water wash with a stretch ratio of 3 times. After the hot water wash, the fibers were continuously dried in a tube furnace at 80 °C, followed by heat treatment in a tube furnace at 300 °C. After heat treatment, the fibers were taken in using a take-up roller. The meta-aramid fibers obtained by this method had a diameter of 36.8 μm, a stretch ratio of 16 times, a breaking strength of 120 MPa, and a breaking elongation of 60%.

[0043] Comparative Example 2

[0044] A meta-aramid spinning solution with a solid content of 25% was prepared and wet-spun after degassing. The injection pump speed was set to 10 μL / h, the spinneret diameter was 0.38 mm, the coagulation bath was 60% EA + 40% DMAC, and the temperature was 30 °C. The spinning solution could not form fibers after exiting the spinneret.

[0045] Comparative Example 3

[0046] A meta-aramid spinning solution with a solid content of 15% was prepared and wet-spun after degassing. The injection pump speed was set to 10 μL / h, the spinneret diameter was 0.5 mm, the coagulation bath was 80% EA + 20% DMAC, and the temperature was 30 °C. After the nascent fibers emerged from the spinneret, they entered the coagulation bath and were then drawn onto roller 1 at a speed of 5 m / min. The fibers were then washed in a room temperature water bath with a stretch ratio of 2:1. Next, they were washed in a 90 °C hot water bath with a stretch ratio of 2:1. After the hot water wash, they were continuously dried in a tube furnace at 100 °C. Finally, they were heat-treated in a tube furnace at 350 °C. After heat treatment, the fibers were taken in using a take-up roller. The meta-aramid fibers obtained by this method had a diameter of 4.2 μm, a stretch ratio of 1776:1, a breaking strength of 400 MPa, and a breaking elongation of 20%.

[0047] The above embodiments describe in detail the structure, features, and effects of the present invention. The above description is only a preferred embodiment of the present invention. Any changes made in accordance with the concept of the present invention, or equivalent embodiments modified to have equivalent changes, shall still fall within the scope of protection of the present invention if they do not exceed the scope covered by the specification.

Claims

1. A method for preparing ultrafine high-strength meta-aramid fiber, characterized in that, The process includes the following steps: preparing a meta-aramid spinning solution with a solid content of 15%-25%, using dimethylacetamide as the solvent; after degassing the spinning solution, inserting a spinneret into a coagulation bath for spinning, the coagulation bath being a mixture of ethyl acetate and DMAC solution with a volume ratio of 80:20-75:25; subsequently drawing the solution into a stretching bath for stretching, followed by drying and heat treatment; the stretching bath includes a room temperature stretching bath and a hot water stretching bath at 70-90°C; the stretching rate in the room temperature stretching bath is 1-2 times, and the stretching rate in the hot water stretching bath is 1-2 times.

2. The preparation method according to claim 1, characterized in that, The temperature of the coagulation bath is -30 to 30°C.

3. The preparation method according to claim 1, characterized in that, The spinneret has an orifice diameter of 0.38-0.5 mm.

4. The preparation method according to claim 1, characterized in that, The spinneret speed is 10-40 μL / h.

5. The preparation method according to claim 1, characterized in that, The drying temperature is 80-100℃.

6. The preparation method according to claim 1, characterized in that, The heat treatment temperature is 280-300℃.

7. An ultrafine high-strength meta-aramid fiber prepared by the preparation method described in claim 1.

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