阅读说明：本技术 一种大丝束聚丙烯腈预氧丝的制备方法 (Preparation method of large-tow polyacrylonitrile pre-oxidized fiber ) 是由 王春华 刘杰 于 2020-12-17 设计创作，主要内容包括：本发明公开了一种大丝束聚丙烯腈预氧丝的制备方法,属于有机纤维技术领域,该方法采用三步法,第一步先对聚丙烯腈纤维在空气中进行微量氧化,第二步再对微量氧化后的聚丙烯腈纤维于惰性气氛下进行高度环化,第三步在空气气氛下进行高温氧化,三步法总时间不超过30min的条件下,制备得到的纤维密度在1.34g/cm～3以上,耐热温度在265℃以上,可直接应用于低成本大丝束碳纤维、阻燃耐热纤维或者活性碳纤维的制备。(The invention discloses a preparation method of large-tow polyacrylonitrile pre-oxidized fibers, which belongs to the technical field of organic fibers and adopts a three-step method, wherein the first step is to carry out micro-oxidation on polyacrylonitrile fibers in air, the second step is to carry out high-degree cyclization on the polyacrylonitrile fibers after micro-oxidation in an inert atmosphere, the third step is to carry out high-temperature oxidation in the air atmosphere, and the fiber density obtained by the preparation method is 1.34g/cm under the condition that the total time of the three-step method is not more than 30min 3 The heat-resistant temperature is above 265 ℃, and the preparation method can be directly applied to the preparation of low-cost large-tow carbon fibers, flame-retardant heat-resistant fibers or activated carbon fibers.)

1. a preparation method of large-tow polyacrylonitrile fiber pre-oxidized fibers comprises the following steps: the large-tow polyacrylonitrile fiber is subjected to micro-oxidation, high-degree cyclization and high-degree oxidation to obtain the fiber with the density of 1.34g/cm³The heat-resisting temperature is above 265 ℃, and the total pre-oxidation time is less than or equal to 30 min.

2. The preparation method of the large-tow polyacrylonitrile fiber pre-oxidized fiber as claimed in claim 1, wherein the method comprises the following steps: the oxygen content of the micro oxidized fiber is less than or equal to 5 percent, and the cyclization degree of the highly cyclized fiber is more than or equal to 60 percent.

3. The preparation method of the large-tow polyacrylonitrile fiber pre-oxidized fiber as claimed in claim 1, wherein the method comprises the following steps: the temperature of the micro-oxidation stage is 150-245 ℃, and the time is 1-15 min.

4. The preparation method of the large-tow polyacrylonitrile fiber pre-oxidized fiber as claimed in claim 1, wherein the method comprises the following steps: the temperature of the high cyclization stage is 230-280 ℃, and the time is 0.5-15 min.

5. The preparation method of the large-tow polyacrylonitrile fiber pre-oxidized fiber as claimed in claim 1, wherein the method comprises the following steps: the temperature of the high oxidation stage is 250-280 ℃ and the time is 1-15 min.

6. The preparation method of the large-tow polyacrylonitrile fiber pre-oxidized fiber as claimed in claim 1, wherein the method comprises the following steps: in the micro-oxidation stage, the atmosphere in the furnace is air.

7. The preparation method of the large-tow polyacrylonitrile fiber pre-oxidized fiber as claimed in claim 1, wherein the method comprises the following steps: and in the high cyclization stage, the furnace atmosphere is one or more of nitrogen, carbon dioxide and rare gas.

8. The preparation method of the large-tow polyacrylonitrile fiber pre-oxidized fiber as claimed in claim 1, wherein the method comprises the following steps: the fiber K bundle is greater than or equal to 48K.

The technical field is as follows:

the invention belongs to the technical field of organic fibers, and relates to a preparation method of large-tow polyacrylonitrile pre-oxidized fibers.

Background art:

the polyacrylonitrile fiber is a precursor material for preparing carbon fiber, flame-retardant heat-resistant fiber and active carbon fiber, however, both carbon fiber, flame-retardant heat-resistant fiber and active carbon fiber need to be prepared in advance to form pre-oxidized fibers with a certain density, and the polyacrylonitrile fiber is generally pre-oxidized in air for 3-6 sections, but a heat-resistant structure in the fiber cannot be formed in a short time, and in the polyacrylonitrile fiber with a large tow, the problem that thermal oxygen exchange cannot be carried out timely and at a high flux exists, so that the polyacrylonitrile fiber generates local heat accumulation due to difficulty in mass and heat transfer, the reaction is uneven, the fiber is easy to harden and become brittle, even the accidents of filament breakage and fire are caused, and the phenomenon is more obvious when the tow is larger. In order to ensure that the polyacrylonitrile fiber of the large tows is stably, uniformly and preoxidized and a heat-resistant structure is added, the polyacrylonitrile fiber is usually subjected to stepped and long-time air preoxidation at a lower temperature for 70-140 min, and the preparation efficiency is not high.

Researchers carry out the method of firstly pre-cyclizing by inert gas and then oxidizing by air, but the method is limited by the characteristic of concentrated heat release of the large-tow polyacrylonitrile fiber, the pre-cyclization temperature is often lower, the cyclization degree of the obtained fiber is low and is generally less than 60%, the heat resistance is not high, and the density of the obtained fiber can be still obtained by pre-oxidizing by air at a low temperature of more than or equal to 30min³The pre-oxidized fiber above.

The invention content is as follows:

aiming at the defects of the prior art, the invention aims to ensure that the density of the large-tow polyacrylonitrile fiber reaches 1.34g/cm within 30min in a short time³Above, the heat-resistant temperature reaches above 265 ℃, in order to achieve the above purpose, the technical scheme of the invention is as follows:

large tow polyacrylonitrile fibers without any treatment the process comprises the following steps: the large-tow polyacrylonitrile fiber is subjected to micro-oxidation, high-degree cyclization and high-degree oxidation to obtain the fiber with the density of 1.34g/cm³The heat-resisting temperature is above 265 ℃, and the total pre-oxidation time is less than or equal to 30 min. The atmosphere of the micro-oxidation process is air, a proper amount of oxygen element is added into the fiber in the process, the activation energy of the cyclization reaction is favorably reduced, the cyclization reaction is easier to carry out, in addition, a small amount of heat-resistant cross-linking structures are formed in the stage, the PAN linear molecules can bear higher reaction temperature, the orientation and the space conformation structure of the PAN main chain are not affected, and the subsequent high-cyclization degree fiber structure is favorably generated. The atmosphere of the high cyclization process is inert gas and contains one or more of nitrogen, carbon dioxide and rare gas, and the process mainly carries out cyclization reaction, so that the cyclization degree of the fiber quickly reaches over 60 percent. The atmosphere of the high-temperature oxidation process is air, and the process mainly carries out oxidation reaction, so that the oxygen content of the fiber is greatly improved.

The method has the following advantages:

1. within 30min, obtaining the high-density and high-heat-resistance large-tow polyacrylonitrile oxidized fiber; is suitable for the subsequent preparation of large tow carbon fiber, flame-retardant heat-resistant fiber and active carbon fiber with low cost.

2. Effectively controlling the reaction process of each stage of the polyacrylonitrile fiber, and the method is simple and easy to implement and is suitable for industrial amplification.

The specific implementation mode is as follows:

for purposes of making the present invention more apparent in light of the objects, aspects and advantages thereof, the present invention is further described in connection with the following examples, it being understood that the specific examples set forth herein are intended to be illustrative only and are not intended to be limiting.

Comparative example 1: the large-tow polyacrylonitrile fiber is directly pre-oxidized by air in three temperature zones, wherein each temperature zone is 10min, the total time is 30min, and the temperature is 230 ℃, 245 ℃ and 255 ℃. The pre-oxidized filaments obtained had the following densities and heat resistance:

performance of	Density/g.cm-3	Heat resistance/. degree.C
			Numerical value	1.325	263

Comparative example 2: the large-tow polyacrylonitrile fiber is directly subjected to air pre-oxidation in three temperature zones, wherein each temperature zone is 10min, the total time is 30min, the temperature is 230 ℃, 255 ℃ and 265 ℃, and the fiber is broken in the 255 ℃ temperature zone, so that a pre-oxidized fiber sample cannot be obtained.

Example 1:

sequentially carrying out micro-oxidation, high-degree cyclization and high-temperature oxidation on the large-tow polyacrylonitrile fiber, wherein three temperature zones are respectively carried out for 10min, the total time is 30min, the temperature is respectively 190 ℃, 245 ℃ and 255 ℃, and the pre-oxidized fiber density, the heat resistance, the oxygen content in a micro-oxidation stage and the cyclization degree data in a high-degree cyclization stage are obtained as follows:

performance of	Density/g.cm-3	Heat resistance/. degree.C	Oxygen content/%)	Degree of cyclization/%)
					Numerical value	1.370	272	2.9	71

Example 2:

sequentially carrying out micro-oxidation, high-degree cyclization and high-temperature oxidation on the large-tow polyacrylonitrile fiber, wherein three temperature zones are respectively carried out for 6min, the total time is 18min, the temperature is respectively 180 ℃, 237 ℃ and 258 ℃, and the pre-oxidized fiber density, the heat resistance, the oxygen content in a micro-oxidation stage and the cyclization degree data in a high-degree cyclization stage are obtained as follows:

performance of	Density/g.cm-3	Heat resistance/. degree.C	Oxygen content/%)	Degree of cyclization/%)
					Numerical value	1.343	269	1.7％	65％

Example 3:

sequentially carrying out micro-oxidation, high-degree cyclization and high-temperature oxidation on large-tow polyacrylonitrile fibers, wherein the time of a three-temperature zone is respectively 5min, 2min and 5min, the total time is 12min, and the temperature is respectively 200 ℃, 240 ℃ and 265 ℃, and obtaining pre-oxidized fiber density, heat resistance, oxygen content in a micro-oxidation stage and cyclization degree data in a high-degree cyclization stage as follows:

performance of	Density/g.cm-3	Heat resistance/. degree.C	Oxygen content/%)	Degree of cyclization/%)
					Numerical value	1.340	268	2.0	62％

Example 4:

sequentially carrying out micro-oxidation, high-degree cyclization and high-temperature oxidation on the large-tow polyacrylonitrile fiber, wherein the time of a three-temperature zone is respectively 5min, 5min and 15min, the total time is 25min, and the temperature is respectively 230 ℃, 265 ℃ and 270 ℃, and the pre-oxidized fiber density, the heat resistance, the oxygen content in a micro-oxidation stage and the cyclization degree data in a high-degree cyclization stage are obtained as follows:

performance of	Density/g.cm-3	Heat resistance/. degree.C	Oxygen content/%)	Degree of cyclization/%)
					Numerical value	1.427	281	4.5	70％

Example 5:

sequentially carrying out micro-oxidation, high-degree cyclization and high-temperature oxidation on large-tow polyacrylonitrile fibers, wherein the time of a three-temperature zone is 5min, 5min and 10min respectively, the total time is 20min, and the temperature is 220 ℃, 260 ℃ and 265 ℃, and obtaining pre-oxidized fiber density, heat resistance, oxygen content in a micro-oxidation stage and cyclization degree data in a high-degree cyclization stage as follows:

performance of	Density/g.cm-3	Heat resistance/. degree.C	Oxygen content/%)	Degree of cyclization/%)
					Numerical value	1.380	275	3.5	68％

Note: the oxygen content data is measured by an element analyzer, the heat-resisting temperature is obtained by thermal weight loss analysis, the cyclization degree RCI is measured by infrared, and the calculation formula is as follows: