阅读说明：本技术 一种在超临界二氧化碳环境中改性芳纶纤维提高力学性能与表面性能的方法 (Method for improving mechanical property and surface property of modified aramid fiber in supercritical carbon dioxide environment ) 是由 刘丽 马震宇 贾储源 苑成策 董继东 杜韫哲 黄玉东 于 2019-11-04 设计创作，主要内容包括：本发明公开了一种在超临界二氧化碳环境中改性芳纶纤维提高力学性能与表面性能的方法,所述方法包括如下步骤：步骤一、对芳纶纤维进行清洗、干燥处理；步骤二、将芳纶纤维和反应试剂装入密闭容器中,并使芳纶纤维保持张力并不与反应试剂接触；步骤三、通入二氧化碳气体,加热升温升压,使密闭容器内为超临界二氧化碳状态；步骤四、溶胀反应后,缓慢匀速泄压,得到改性的芳纶纤维；步骤五、对改性后的芳纶纤维进行清洗与干燥。本发明不仅实现了芳纶纤维表面的活化及纵向拉伸强度的提高,还通过纤维内部分子链间的交联反应强化了纤维皮层与芯层的结合,改善了皮芯结构,提高了纤维的横向强度,对芳纶纤维的改性及使用效能的提高具有重要意义。(The invention discloses a method for improving mechanical property and surface property of modified aramid fiber in a supercritical carbon dioxide environment, which comprises the following steps: firstly, cleaning and drying aramid fibers; step two, putting aramid fiber and a reaction reagent into a closed container, and keeping the aramid fiber in tension and not contacting the reaction reagent; introducing carbon dioxide gas, heating, raising the temperature and boosting the pressure to enable the inside of the closed container to be in a supercritical carbon dioxide state; after the swelling reaction, slowly releasing pressure at a constant speed to obtain modified aramid fibers; and step five, cleaning and drying the modified aramid fiber. The invention not only realizes the activation of the surface of the aramid fiber and the improvement of the longitudinal tensile strength, but also strengthens the combination of the fiber skin layer and the core layer through the cross-linking reaction among the molecular chains in the fiber, improves the skin-core structure, improves the transverse strength of the fiber, and has important significance for the modification of the aramid fiber and the improvement of the use efficiency.)

1. A method for improving mechanical property and surface property of modified aramid fiber in a supercritical carbon dioxide environment is characterized by comprising the following steps:

firstly, cleaning and drying aramid fibers;

step two, filling the washed and dried aramid fiber and a reaction reagent into a closed container, and controlling the mass ratio of the reaction reagent to the aramid fiber to be 1: 40-120, and keeping the aramid fiber at a tension of 2-20N and not contacting with the reaction reagent;

introducing carbon dioxide gas at the temperature of 4-25 ℃, heating and boosting the temperature to enable the inside of the closed container to be in a supercritical carbon dioxide state;

step four, slowly releasing pressure at a constant speed after swelling reaction for 10-120 min under the conditions that the temperature is 35-100 ℃ and the pressure is 7.5-12.5 MPa to obtain modified aramid fibers;

and step five, cleaning and drying the modified aramid fiber.

2. The method for improving the mechanical property and the surface property of the modified aramid fiber in the supercritical carbon dioxide environment according to claim 1, wherein in the first step, the cleaning solution is acetone, the cleaning temperature is 50-80 ℃, and the cleaning time is 24-48 hours.

3. The method for improving the mechanical property and the surface property of the modified aramid fiber in the supercritical carbon dioxide environment according to claim 1, wherein in the first step, the drying temperature is 40-70 ℃ and the drying time is 3-5 h.

4. The method for improving the mechanical property and the surface property of the aramid fiber in the supercritical carbon dioxide environment as claimed in claim 1, wherein in the second step, the fiber is Kevlar49, ArIII fiber or F12 fiber.

5. The method for improving the mechanical property and the surface property of the modified aramid fiber in the supercritical carbon dioxide environment as claimed in claim 1, wherein in the second step, the reaction reagent is 1, 2-dichloroethane or 1, 4-dichlorobutane.

6. The method for improving the mechanical property and the surface property of the modified aramid fiber in the supercritical carbon dioxide environment according to claim 1, wherein in the fourth step, the pressure is slowly released at a constant speed for 30-90 min.

7. The method for improving the mechanical property and the surface property of the modified aramid fiber in the supercritical carbon dioxide environment according to claim 1, wherein in the fifth step, the cleaning solution is acetone, the cleaning temperature is 20-40 ℃, and the cleaning time is 10-60 min.

8. The method for improving the mechanical property and the surface property of the modified aramid fiber in the supercritical carbon dioxide environment according to claim 1, wherein in the fifth step, the drying temperature is 20-70 ℃ and the drying time is 3-12 hours.

Technical Field

The invention relates to an aramid fiber modification method, in particular to a method for improving mechanical property and surface property of modified aramid fiber in a supercritical carbon dioxide environment.

Background

Aramid fiber is called aromatic polyamide fiber for short. The aramid fiber has excellent mechanical properties due to the rigid crystalline structure, high tensile strength, high modulus and excellent heat resistance. The aramid fiber reinforced epoxy resin composite material is an ideal shell material of missile and aircraft engines. The aramid fiber has wide application in various fields such as national defense and military industry, aerospace, automobiles, mooring ropes and the like.

However, due to the inherent 'sheath-core' structure of aramid fibers, the aramid fibers have the characteristics of high proportion of aromatic rings in molecular chain segments, large steric hindrance, weak acting force between molecular chains and the like, and the bonding force between the sheath and the core is weak, so that the transverse strength of the fibers is far lower than the longitudinal strength of the fibers. In addition, the aramid fiber has inert and smooth surface and poor interface compatibility with a resin matrix, which directly results in poor interface bonding performance of the composite material. Therefore, modification research on aramid fibers is needed, the bonding capacity between the fiber skin layer and the core layer is improved, the interface bonding performance between the fibers and the resin matrix is improved, the application efficiency of the aramid fibers is improved, and the application field of the aramid fibers is expanded.

Compared with the traditional physical and chemical modification methods, the supercritical fluid permeation modified reinforced fiber or other high polymer material preparation method has unique characteristics and advantages. Firstly, the supercritical fluid has both the density of liquid and the viscosity of gas, and is easy to diffuse and permeate in the fiber; secondly, the supercritical fluid has excellent dissolving power for various small molecule substances, and the increase of the solubility can be realized by changing the pressure and then changing the density of the supercritical fluid. Among many supercritical fluids, supercritical carbon dioxide is easy to achieve due to its supercritical conditions; the compound has good solubility to various nonpolar micromolecules, is chemically inert, nontoxic, tasteless and safe; high purity, low cost, easy obtaining and the like, and has an important position in the application of the supercritical fluid in the field of macromolecules.

The existing aramid fiber modification technology mainly comprises a physical modification technology, a chemical modification technology and other modification technologies. The physical modification method is mainly characterized in that the roughness of the surface of the aramid fiber is increased through a physical means (or physical action), the surface energy of the aramid fiber is improved, the surface activation is realized, and the interface bonding performance between the fiber and a resin matrix is improved. At present, the physical modification mainly comprises heat treatment, a surface coating method, ultrasonic impregnation, ultraviolet irradiation, gamma ray irradiation, plasma treatment and the like. The chemical modification has three main mechanisms: firstly, etching the surface of the fiber by utilizing a chemical reaction to increase the surface roughness of the fiber; secondly, introducing or grafting polar groups by utilizing a large number of benzene rings in a molecular chain; and thirdly, initiating hydrolysis of the amide group or carrying out hydrogen substitution reaction connected with a nitrogen atom on the amide group, and introducing a polar group, thereby improving the hydrophilicity, the interface caking property and the like of the fiber. The corresponding technologies are respectively a surface etching technology and a surface grafting technology, wherein the surface grafting technology comprises grafting on a benzene ring, chemical reaction based on an amido group, modification by a coupling agent and the like. However, the above techniques can only modify the surface of aramid fiber, and the reaction and physical action do not involve the interior of the fiber, and most of them cause the loss of the strength of the fiber bulk.

The fiber is modified under a certain tension by using the micro molecules carried by the supercritical carbon dioxide molecules, and the fiber can be simultaneously contacted with the surface and the inside of the fiber, so that the surface activation is realized, and the tensile strength of the fiber is improved. Workers have also stretched aramid fibers in supercritical carbon dioxide environments to achieve the above effects. However, the existing methods cannot well solve the problem of low transverse strength caused by the aramid fiber skin-core structure, which is a technical problem still to be solved.

Disclosure of Invention

The invention aims to provide a method for improving the mechanical property and the surface property of modified aramid fibers in a supercritical carbon dioxide environment, which not only realizes the activation of the surfaces of the aramid fibers and the improvement of the longitudinal tensile strength, but also strengthens the combination of fiber skin layers and core layers through the crosslinking reaction among partial sub-chains in the fibers, improves the skin-core structure, improves the transverse strength of the fibers and has important significance for the modification and the improvement of the use efficiency of the aramid fibers.

The purpose of the invention is realized by the following technical scheme:

a method for improving mechanical property and surface property of modified aramid fiber in a supercritical carbon dioxide environment comprises the following steps:

step one, aramid fiber is cleaned and dried, wherein: the cleaning solution is acetone, the cleaning temperature is 50-80 ℃, and the cleaning time is 24-48 h; the drying temperature is 40-70 ℃, and the drying time is 3-5 h; aims to remove sizing agent, coating and the like on the surface of a fiber product and facilitate modification treatment of fiber fibrils;

step two, putting the washed and dried aramid fiber and a reaction reagent into a closed container, and keeping the aramid fiber at a tension of 2-20N without contacting the reaction reagent, wherein: the fiber is Kevlar49, ArIII fiber or F12 fiber; the reaction reagent is 1, 2-dichloroethane or 1, 4-dichlorobutane, the used chloride and the fiber molecular chain are subjected to substitution reaction, grafted on the molecular chain, and a cross-linked structure is formed between the molecular chains; the mass ratio of the reaction reagent to the aramid fiber is 1: 40 to 120;

and step three, introducing carbon dioxide gas at the temperature of 4-25 ℃, heating, raising the temperature and boosting the pressure to enable the inside of the closed container to be in a supercritical carbon dioxide state, wherein: before the reaction kettle is sealed, sufficient carbon dioxide gas is firstly introduced to exhaust the air in the container, and the purpose of exhaust treatment is to eliminate the influence of active gases such as oxygen in the air and the like on the experiment; before introducing carbon dioxide gas, reducing the temperature in the container to 4-25 ℃ to different temperatures so as to control the amount of the carbon dioxide gas to be introduced, thereby achieving different temperature and pressure conditions through heating;

and step four, slowly releasing pressure at a constant speed after a swelling reaction is carried out for 10-120 min under the conditions that the temperature is 35-100 ℃ and the pressure is 7.5-12.5 MPa, so as to obtain the modified aramid fiber, wherein: the temperature and the pressure are important indexes for ensuring that the carbon dioxide is in a supercritical state, the carbon dioxide is in the supercritical state only when the temperature is higher than 31 ℃ and the pressure is higher than 7.29MPa, and meanwhile, the temperature and the pressure can influence the concentration and the density of a supercritical carbon dioxide fluid in a container, so that the diffusion capacity and the small molecule dissolving capacity of the supercritical carbon dioxide are influenced, and the experiment is greatly influenced; the swelling process is a part of swelling reaction, the supercritical carbon dioxide fluid swells the fiber, the carbon dioxide molecules carry reactant small molecules on the surface of the fiber or permeate into an amorphous area in the fiber, and the reactant small molecules are contacted with molecular chains to react; the slow constant-speed pressure relief means that an air outlet valve of the container is opened, so that the pressure in the container is reduced to normal pressure at a small and constant speed for 30-90 min;

step five, washing and drying the modified aramid fiber, wherein: the cleaning solution is acetone, the cleaning temperature is 20-40 ℃, and the cleaning time is 10-60 min; the drying temperature is 20-70 ℃, and the drying time is 3-12 h.

The chlorine-containing compounds 1, 2-dichloroethane and 1, 4-dichlorobutane and the aramid fiber molecular chain can perform a grafting reaction, so that the polar functional groups are provided for the fiber surface while chemical crosslinking is formed among the fiber microfibers, and the fiber surface energy can be improved. And the mechanical property of the modified fiber is tested by adjusting the magnitude of the static stretching force, the F12 fiber modified under the condition of the optimized stretching force is obtained, and the tensile strength of the F12 fiber modified under different stretching conditions is shown in figure 2. The method for modifying aramid fibers in the supercritical carbon dioxide environment by using the reactant does not appear in domestic and foreign researches, and has advancement and innovation. According to the invention, by virtue of excellent dissolution, diffusion and permeability of the supercritical carbon dioxide fluid, the reaction reagents 1, 2-dichloroethane and 1, 4-dichlorobutane are carried into the aramid fiber, and are subjected to grafting and crosslinking reaction with molecular chains on the surface and in the aramid fiber. Under the condition of external tension, the amorphous region of the fiber swelled by the supercritical carbon dioxide is crystallized and the orientation degree is improved. By the action, the mechanical property and the surface property of the fiber are obviously improved.

Compared with the prior art, the invention has the following advantages:

1. compared with unmodified aramid fiber, the mechanical property is obviously improved. Wherein, the tensile strength is improved by 6.9-36.5%, the fiber indentation diameter is reduced by 1.8-9.7%, and the transverse strength is obviously improved. The tensile strength is improved because the fiber is in a tensile state in supercritical carbon dioxide, the molecular crystallinity and the orientation degree are increased, the grain size is increased, and the crystallization is more complete. Meanwhile, the reaction reagent micromolecules react with the molecular chains, the crosslinking degree in the fiber is increased, the skin-core structure is improved, and the transverse strength is improved.

2. Compared with unmodified aramid fibers, the surface energy is increased by 3.7-20.5%. Under the swelling of the supercritical carbon dioxide, the roughness of the fiber surface is increased, and the reaction reagent micromolecules and the molecular chains on the fiber surface are subjected to graft reaction, so that polar functional groups exist on the fiber surface, and the surface energy is obviously improved.

3. The method has the advantages of economy, environmental protection, controllable reaction, short reaction time, simple separation of the solvent and the product, and the like, and has great industrial application value.

Drawings

FIG. 1 is a schematic diagram of the reaction of F12 fiber molecular chain with 1, 4-dichlorobutane;

FIG. 2 shows the tensile strength of fibers under different static drawing conditions F12.

Detailed Description

The technical solutions of the present invention are further described below with reference to the following examples, but the present invention is not limited thereto, and any modifications or equivalent substitutions may be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.