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

Abstract

The invention discloses a superfine high-strength meta-position aramid fiber and a preparation method thereof, and the superfine high-strength meta-position aramid fiber is obtained by adjusting the type of a wet spinning coagulating bath and reducing the temperature of the coagulating bath to realize super-stretching. Ethyl acetate and dimethylacetamide are used as a coagulating bath, and meanwhile, the temperature of the coagulating bath is reduced, so that the coagulating speed of the fiber in the coagulating bath is slowed down, the intermolecular force of the fiber is stronger, a more stable network gel state is formed, and very excellent stretchability is achieved. The meta-position aramid fiber prepared by the method has the advantages that the diameter is as small as 1.43 mu m, the tensile rate can reach 8000 times, the breaking strength reaches 1332 MPa, and the elongation at break is more than 20%.

Description

Technical Field

[0001] The invention belongs to the technical field of aramid fibers, and in particular relates to an ultrafine high-strength meta-aramid fiber and a preparation method thereof. Background Art

[0002] Meta-aramid fiber (usually poly(m-phenylene isophthalamide), PMIA for short, trade name such as Nomex) is a type of high-performance synthetic fiber with excellent heat resistance, flame retardancy and mechanical strength. This type of material performs well in high temperature environments, is not easy to burn, and does not melt or drip even when burning, so it is widely used in protective clothing, thermal insulation materials, electrical insulation and other fields.

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

[0004] First, metaphenylenediamine and isophthalic acid or their derivatives are polymerized in an appropriate solvent to form a high molecular weight poly(metaphenylene isophthalamide) solution. The resulting polymer solution is then made into fibers through wet spinning or dry-jet wet spinning. During wet spinning, the polymer solution is squeezed out of the pores into a thin stream and enters the coagulation bath to solidify and form; dry-jet wet spinning combines the speed advantage of dry spinning with the easy-to-operate characteristics of wet spinning, allowing the polymer solution to partially solidify in a gas environment before entering the coagulation bath to fully solidify.

[0005] However, the existing wet spinning technology has some limitations. Since water is a strong and inferior solvent for meta-aramid fibers, the fibers will coagulate quickly after entering the coagulation bath, which not only affects the subsequent stretching operation, but also makes it difficult to obtain ultrafine fibers when using a spinneret with a larger aperture. If ultrafine fibers are to be produced, a spinneret with a smaller aperture is required, but this will significantly increase the difficulty and cost of production.

[0006] In addition, the current stretching bath only provides a stretching ratio of 2 to 10 times, which is insufficient when pursuing higher performance fibers. Therefore, in order 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 value of the coagulation bath, or developing new solvent systems to improve fiber quality and reduce production costs. Summary of the invention

[0007] Aiming at the problem that the meta-aramid fiber in the prior art coagulates too quickly in the coagulation bath, resulting in poor stretching effect and failure to obtain ultrafine fibers, the present invention provides an ultrafine high-strength meta-aramid fiber and a preparation method thereof.

[0008] The present invention uses ethyl acetate and dimethylacetamide as a coagulation bath and reduces the temperature of the coagulation bath at the same time, so that the coagulation speed of the fiber in the coagulation bath is slowed down, and the intermolecular force of the fiber is stronger, forming a more stable network gel state with very excellent stretchability, thereby preparing ultrafine meta-aramid fibers.

[0009] One of the technical solutions of the present invention is to provide a method for preparing ultra-fine high-strength meta-aramid fiber. Specifically, the following steps are included: preparing a meta-aramid spinning solution with a solid content of 15%-25%, wherein the solvent is dimethylacetamide (DMAC); after the spinning solution is degassed, the spinneret is extended into a coagulation bath, wherein the coagulation bath is a mixed solution of ethyl acetate and DMAC solution with a volume ratio of 80:20-75:25; then the fiber is pulled into a stretching bath for stretching, followed by drying and heat treatment; the stretching bath includes a normal temperature stretching bath and a 70-90°C hot water stretching bath; the stretching rate in the normal temperature stretching bath is 1-2 times, and the stretching rate in the hot water stretching bath is 1-2 times.

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

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

[0012] Furthermore, the spinning speed is 10-40ul / h.

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

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

[0015] Under the coagulation bath and temperature conditions, the meta-aramid fiber exhibits a very excellent gel state and has very excellent stretchability in the coagulation bath. Especially under lower coagulation bath temperature conditions, the intermolecular forces such as hydrogen bonds and van der Waals forces between the primary fiber molecules are enhanced, and it has a stronger gel network structure, which can further improve the tensile properties of the primary fiber, and its stretching ratio can reach 8000 times.

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

[0017] The diameter of the produced fiber is only 1.43-2.94 um, the strength reaches 1.3 GPa, and the elongation at break is 20%-40%.

[0018] The beneficial effects of the present invention are: 1) The coagulation bath is selected to use a good solvent for meta-aramid to reduce the double diffusion rate of the fiber in the coagulation bath, so that the nascent fiber presents a gel state with excellent tensile properties in the coagulation bath, thereby achieving super-stretching.

[0019] 2) The diameter of the fiber after ultra-stretching is very fine, so ultra-fine fibers can be produced.

[0020] 3) Because the fiber is super stretched, the molecular orientation is high, the internal defects are few, and it has very excellent mechanical properties.

[0021] 4) Due to the small fiber diameter, only lower temperature heat treatment is required, which results in lower energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the process of the preparation method of the present invention.

[0023] Figure 2 The scanning electron microscope images of Examples 1-4 are shown. DETAILED DESCRIPTION

[0024] The following examples are used to further illustrate the present invention, and their purpose is to illustrate the present invention and should not be construed as limiting the scope of the present invention. Unless otherwise specified, all parts by weight and weight percentages are used below.

[0025] The raw materials used in the present invention, unless otherwise specified, are conventional commercially available products; the methods used in the present invention, unless otherwise specified, are conventional methods in the art.

[0026] The embodiments of the present invention are further described below with reference to a plurality of embodiments.

[0027] It should be clear that the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0028] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0029] The solid content mentioned below refers to the mass content; The percentages described below are by volume unless otherwise specified.

[0030] The normal temperature water bath and hot water bath described below contain deionized water.

[0031] Example 1 Prepare meta-aramid spinning solution with a solid content of 15%, and wet spinning after degassing. The injection pump speed is set to 40ul / h, the spinneret diameter is 0.38mm, the coagulation bath is 80%EA+20%DMAC, and the temperature is 3℃. After the nascent fiber comes out of the spinneret, it enters the coagulation bath and is pulled to roller 1. The roller speed is set to 24m / min; then the fiber enters the room temperature water bath with a stretching ratio of 1; then enters the 90℃ hot water bath with a stretching ratio of 1; after the hot water wash, it enters the tubular furnace for continuous drying at a temperature of 80℃; then enters the tubular furnace for heat treatment at a heat treatment temperature of 300℃; after heat treatment, the fiber is collected with a collection roller. The meta-aramid fiber prepared by this method has a diameter of 1.43um, a stretching ratio of 8826 times, a breaking strength of 737MPa, and an elongation at break of 30%.

[0032] Example 2 Prepare meta-aramid spinning solution with a solid content of 25%, and wet spinning after degassing. The injection pump speed is set to 10ul / h, the spinneret diameter is 0.5mm, the coagulation bath is 80%EA+20%DMAC, and the temperature is 30℃. After the nascent fiber comes out of the spinneret, it enters the coagulation bath and is pulled to roller 1. The roller speed is set to 2m / min; then the fiber enters the room temperature water bath with a stretching ratio of 2 times; then enters the 70℃ hot water bath with a stretching ratio of 2 times; after hot water washing, it enters the tubular furnace for continuous drying at a temperature of 80℃; then enters the tubular furnace for heat treatment at a heat treatment temperature of 280℃; after heat treatment, the fiber is collected with a collection roller. The meta-aramid fiber prepared by this method has a diameter of 5.9um, a stretching ratio of 1795 times, a breaking strength of 620MPa, and an elongation at break of 20%.

[0033] Example 3 Prepare meta-aramid spinning solution with a solid content of 15%, and wet spinning after degassing. The injection pump speed is set to 10ul / h, the spinneret diameter is 0.5mm, the coagulation bath is 80%EA+20%DMAC, and the temperature is 30℃. After the nascent fiber comes out of the spinneret, it enters the coagulation bath and is pulled to roller 1. The roller speed is set to 5m / min; then the fiber enters the room temperature water bath with a stretching ratio of 2 times; then enters the 90℃ hot water bath with a stretching ratio of 2 times; after the hot water wash, it enters the tubular furnace for continuous drying at a temperature of 100℃; then enters the tubular furnace for heat treatment at a heat treatment temperature of 300℃; after heat treatment, the fiber is collected with a collection roller. The meta-aramid fiber prepared by this method has a diameter of 2.9um, a stretching ratio of 3715 times, a breaking strength of 1073MPa, and an elongation at break of 40%.

[0034] Example 4 Prepare meta-aramid spinning solution with a solid content of 25%, and wet spinning after degassing. The injection pump speed is set to 10ul / h, the spinneret diameter is 0.5mm, the coagulation bath is 75%EA+25%DMAC, and the temperature is -30℃. After the nascent fiber comes out of the spinneret, it enters the coagulation bath and is pulled to roller 1. The roller speed is set to 8m / min; then the fiber enters the room temperature water bath with a stretching ratio of 2 times; then enters the 90℃ hot water bath with a stretching ratio of 2 times; after the hot water wash, it enters the tubular furnace for continuous drying at a temperature of 100℃; then enters the tubular furnace for heat treatment at a heat treatment temperature of 300℃; after heat treatment, the fiber is collected with a collection roller. The meta-aramid fiber prepared by this method has a diameter of 2.8um, a stretching ratio of 3840 times, a breaking strength of 1332MPa, and an elongation at break of 20%.

[0035] Comparative Example 1 Prepare meta-aramid spinning solution with a solid content of 15%, and wet spinning after degassing. The injection pump speed is set to 40ul / m, the spinneret diameter is 0.38mm, the coagulation bath is 100%EA, and the temperature is 30℃. After the nascent fiber comes out of the spinneret, it enters the coagulation bath and is pulled to roller 1. The roller speed is set to 0.1m / min; then the fiber enters the room temperature water bath with a stretching ratio of 5 times; then enters the 90℃ hot water bath with a stretching ratio of 3 times; after the hot water wash, it enters the tubular furnace for continuous drying at a temperature of 80℃; then enters the tubular furnace for heat treatment at a heat treatment temperature of 300℃; after heat treatment, the fiber is collected with a collection roller. The meta-aramid fiber prepared by this method has a diameter of 36.8um, a stretching ratio of 16 times, a breaking strength of 120MPa, and an elongation at break of 60%.

[0036] Comparative Example 2 Meta-aramid spinning solution was prepared with a solid content of 25%, and wet spinning was performed after degassing. The injection pump speed was set to 10ul / h, the spinneret diameter was 0.38mm, the coagulation bath was 60%EA+40%DMAC, the temperature was 30℃, and the spinning solution could not be formed into filaments after coming out of the spinneret.

[0037] Comparative Example 3 Prepare meta-aramid spinning solution with a solid content of 15%, and wet spinning after degassing. The injection pump speed is set to 10ul / h, the spinneret diameter is 0.5mm, the coagulation bath is 80%EA+20%DMAC, and the temperature is 30℃. After the nascent fiber comes out of the spinneret, it enters the coagulation bath and is pulled to roller 1. The roller speed is set to 5m / min; then the fiber enters the room temperature water bath with a stretching ratio of 2 times; then enters the 90℃ hot water bath with a stretching ratio of 2 times; after hot water washing, it enters the tubular furnace for continuous drying at a temperature of 100℃; then enters the tubular furnace for heat treatment at a heat treatment temperature of 350℃; after heat treatment, the fiber is collected with a collection roller. The meta-aramid fiber prepared by this method has a diameter of 4.2um, a stretching ratio of 1776 times, a breaking strength of 400MPa, and an elongation at break of 20%.

[0038] The above embodiments describe in detail the structure, features and effects of the present invention. The above are only preferred embodiments of the present invention. Any changes made in accordance with the concept of the present invention, or modifications to equivalent embodiments with equivalent changes, which do not exceed the scope covered by the specification, should be within the protection scope of the present invention.

Claims

1. A method for preparing ultrafine high-strength meta-aramid fiber, characterized in that: The method comprises the following steps: preparing a meta-aramid spinning solution with a solid content of 15%-25%, wherein the solvent is dimethylacetamide; after the spinning solution is degassed, the spinning tube is extended into a coagulation bath for spinning, wherein the coagulation bath is a mixed solution of ethyl acetate and DMAC solution with a volume ratio of 80:20-75:25; then the spinning solution is pulled into a stretching bath for stretching, and then dried and heat-treated; the stretching bath comprises a normal temperature stretching bath and a hot water stretching bath at 70-90°C; the stretching rate in the normal 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 coagulation bath temperature is -30-30°C.

3. The preparation method according to claim 1, characterized in that: The aperture of the spinneret is 0.38-0.5 mm.

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

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

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

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

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