A method of beating pretreatment of aramid fibers

Abstract

The application discloses a kind of aramid fiber beating pretreatment method, belong to aramid pulp preparation technical field.The application utilizes CaCl2 solution to aramid fiber pretreatment, obtains CaCl2 modified aramid fiber, then again through silane coupling agent ethanol solution treatment obtains pretreated aramid short fiber.The application utilizes CaCl2 solution to treat aramid fiber, both to aramid fiber has etching effect, improves specific surface area, while complexed Ca 2+ , weaken the hydrogen bond interaction between aramid molecules, thereby reducing beating time and energy consumption.CaCl2 solution to aramid fiber treatment both removes most of the oil agent on the surface of aramid fiber, and also plays a swelling effect on the fiber, saves the step of soaking the fiber before beating.After surface grafting by silane coupling agent, the active sites of aramid fiber are increased, so that the aramid pulp obtained by beating is more easily compounded with rubber matrix.

Description

Technical Field

[0001] This invention relates to the field of aramid pulp preparation technology, and in particular to a method for aramid fiber pulping pretreatment. Background Technology

[0002] Aramid fiber is a high-performance synthetic fiber made of poly(p-phenylene terephthalamide) fiber, characterized by high modulus and high strength. Aramid pulp, on the other hand, is a pulp-like form of aramid obtained by pulping aramid fibers. Aramid pulp possesses excellent fire resistance, abrasion resistance, and chemical corrosion resistance, and can be compounded with rubber, epoxy resins, etc., to impart excellent fire-resistant, abrasion-resistant, and corrosion-resistant properties.

[0003] Before preparing aramid pulp, aramid fibers are typically cleaned to remove or reduce the amount of oil added during the aramid fiber preparation process, making it easier to prepare aramid pulp through beating. The numerous hydrogen bonds between aramid molecules make it difficult for aramid fibers to entangle during beating, requiring longer beating times and higher energy consumption to achieve this. Furthermore, two inherent problems with aramid pulp limit its large-scale application in most matrices: firstly, aramid pulp has a large specific surface area and is composed of ultrafine fibrils, making it prone to entanglement and difficult to disperse in polymer matrices; secondly, aramid pulp has highly oriented crystalline regions with very few amorphous regions and a loose structure, making it difficult for amide groups to react, resulting in strong chemical inertness and poor adhesion to the matrix. Therefore, pretreatment of aramid fibers is necessary to reduce hydrogen bonding forces, making the fibers easier to entangle and improving their dispersibility and interfacial bonding properties in the matrix.

[0004] In recent years, researchers at home and abroad have mainly modified aramid pulp by increasing the surface roughness of the fiber or adding surface-active groups to improve the dispersibility of aramid fiber pulp and its interfacial bonding ability with the matrix.

[0005] Chinese patent document CN103088627A discloses a method for treating the surface of aramid fibers. The method involves ultrasonically cleaning aramid short fibers in an ethanol solution for 2 hours, followed by drying. Then, the fibers are treated with a high-concentration (20-50%) CaCl2, LiCl, or ZnCl2 solution at 80-100℃ for 15-180 minutes, rinsed with water, and dried. This improves the interfacial adhesion and dispersibility between the aramid short fibers and materials such as rubber. While this method enhances the bonding between aramid short fibers and rubber materials, its application in industrial or large-scale production is limited by drawbacks such as insufficient stability of ultrasonic equipment during long-term operation, high initial investment costs, and high energy consumption. Furthermore, this method utilizes chloride aqueous solutions to modify the aramid fibers. This modification method has poor etching and chloride complexation effects on the aramid fibers, and it only increases the surface roughness of the aramid fibers without introducing other functional groups. Therefore, the modification effect is not significant for subsequent pulping or composite with rubber matrices. Summary of the Invention

[0006] The purpose of this invention is to provide a method for pre-treating aramid fiber pulping. This method utilizes CaCl2 solution to pre-treat aramid fibers, which can remove oil from the fiber surface and reduce hydrogen bonding between aramid molecules, making the aramid fibers easier to spin into fibers. Simultaneously, silane coupling agents can be grafted to increase the surface-active groups of the aramid pulp, thereby enhancing its interfacial bonding ability in matrix composites and solving the problems of difficult and time-consuming aramid pulping.

[0007] To achieve the objective of this invention, a technical solution for a method of pulping pretreatment of aramid fibers is provided, comprising the following steps: (1) Cut the aramid fiber into short aramid fibers of 1-5 mm; (2) The aramid short fibers were immersed in a CaCl2 solution with a concentration of 1-6wt% for water bath heating treatment, washed and dried to obtain CaCl2 modified aramid short fibers. (3) The CaCl2 modified aramid short fibers were immersed in a 15-25wt% silane coupling agent alcohol solution for water bath heating treatment, washed and dried to obtain pretreated aramid short fibers.

[0008] Furthermore, in step (2), the solvent in the CaCl2 solution is one of water, methanol, or ethanol; the water bath heating conditions are: temperature 65-100℃, time 3-5h; the cleaning is 3-5 times with pure water; the drying temperature is 60-80℃, time 0.5-2h.

[0009] Furthermore, in step (3), the water bath heating conditions are as follows: the temperature is 60-100℃ and the time is 2-4h; the silane coupling agent is one of KH550, KH560, and KH570; the cleaning is done by washing with pure water 3-5 times; the drying temperature is 60-80℃ and the time is 0.5-2h.

[0010] Compared with the prior art, the present invention has the following beneficial effects: (1) The technical solution of the present invention uses a CaCl2 solution of a specific concentration (1-6wt%) to treat aramid short fibers under heating conditions (65-100℃), thereby achieving the purpose of removing the oil on the fiber surface and swelling the fiber in a single step, thus eliminating the need for separate cleaning and soaking steps required before traditional pulping and simplifying the pretreatment process.

[0011] (2) The technical solution of the present invention involves heating aramid fibers with CaCl2 solution for a long time (3-5 hours) to reduce the Ca content. 2+ By complexing with aramid fibers, the hydrogen bonding forces between aramid molecules are effectively weakened, reducing beating time. This makes it easier for aramid fibers to separate and fuzz during subsequent beating, further reducing beating time and energy consumption. Under similar conditions of aramid pulp specific surface area and beating degree, the time consumed is significantly reduced by 76% compared with the existing NaOH pretreatment method, and the corresponding energy consumption is also significantly reduced.

[0012] (3) The technical solution of this invention, by using CaCl2 treatment followed by a secondary treatment with an ethanol solution of silane coupling agent, provides more active groups for the composite material, which is more conducive to the bonding of aramid pulp with the matrix (such as rubber), and effectively improves the performance of the composite material. Compared with the prior art CN103088627A, using CaCl2 ethanol solution as a reagent to modify aramid short fibers results in a more obvious etching effect and CaCl2 complexation effect, and can also remove the oil from the surface of the aramid short fibers, eliminating the need for separate cleaning of the oil. In addition, the complexation effect of CaCl2 is unstable, and it is very easy to detach and dissolve in water during the subsequent pulping process. After modifying the aramid short fibers with CaCl2 with a silane coupling agent, the stability of CaCl2 can be enhanced, and more active groups can be provided, which is beneficial to the subsequent composite of aramid pulp with the rubber and other matrices. Attached Figure Description

[0013] Figure 1 SEM image of untreated aramid short fibers; Figure 2 SEM image of aramid short fibers modified with CaCl2 ethanol solution; Figure 3 This is a SEM image of the pretreated aramid short fibers. Detailed Implementation

[0014] In the description of this invention, it should be noted that, unless otherwise specified in the embodiments, the conditions shall be performed according to conventional conditions or conditions recommended by the manufacturer.

[0015] The technical solutions provided by the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] Example 1: (1) Aramid fibers were cut into 3mm short aramid fibers; (2) Prepare 300 ml of 5 wt% CaCl2 ethanol solution, immerse 5 g of aramid short fiber in it, heat it in a water bath at 80°C for 4 h, then rinse it repeatedly with pure water 5 times to remove residual CaCl2 and ethanol, and dry it in an oven at 80°C for 2 h to obtain CaCl2 modified aramid short fiber. (3) Prepare 300 ml of 20 wt% KH550 ethanol solution, immerse the CaCl2 modified aramid short fiber in it, heat it in a water bath at 80°C for 4 h, then rinse it repeatedly with pure water 5 times to remove residual KH550 and ethanol, and dry it in an oven at 80°C for 2 h to obtain pretreated aramid short fiber.

[0017] Example 2: (1) Aramid fibers were cut into short fibers of 3 mm; (2) Prepare 300 ml of 4 wt% CaCl2 methanol solution, immerse 5 g of aramid short fiber in it, heat it in a water bath at 65°C for 3 h, then rinse it repeatedly with pure water 3 times to remove residual CaCl2 and methanol, and dry it in an oven at 60°C for 0.5 h to obtain CaCl2 modified aramid short fiber. (3) Prepare 300 ml of 20 wt% KH550 methanol solution, immerse the CaCl2 modified aramid short fiber in it, heat it in a water bath at 60°C for 2 h, then rinse it repeatedly with pure water 3 times to remove residual KH550 and methanol, and dry it in an oven at 60°C for 0.5 h to obtain pretreated aramid short fiber.

[0018] Example 3: (1) Aramid fibers were cut into short fibers of 3 mm; (2) Prepare 300 ml of 6 wt% CaCl2 aqueous solution, immerse 5 g of aramid short fiber in it, heat it in a water bath at 100℃ for 5 h, then rinse it repeatedly with pure water 3 times to remove residual CaCl2, and dry it in an oven at 70℃ for 2 h to obtain CaCl2 modified aramid short fiber. (3) Prepare 300 ml of 25 wt% KH570 ethanol solution, immerse the CaCl2 modified aramid short fiber in it, heat it in a water bath at 100 ℃ for 4 h, then rinse it repeatedly with pure water 3 times to remove the residual KH570, and dry it in an oven at 70 ℃ for 2 h to obtain the pretreated aramid short fiber.

[0019] Example 4: (1) Aramid fibers were cut into short fibers of 3 mm; (2) Prepare 300 ml of 1 wt% CaCl2 ethanol solution, immerse 5 g of aramid short fiber in it, heat it in a water bath at 70°C for 5 h, then rinse it repeatedly with pure water 4 times to remove residual CaCl2 and ethanol, and dry it in an oven at 60°C for 1 h to obtain CaCl2 modified aramid short fiber. (3) Prepare 300 ml of 15 wt% KH560 ethanol solution, immerse 5 g of CaCl2 modified aramid short fiber in it, heat it in a water bath at 70°C for 3 h, then rinse it repeatedly with pure water 4 times to remove residual KH560 and ethanol, and dry it in an oven at 60°C for 1 h to obtain pretreated aramid short fiber.

[0020] Comparative Example 1: The difference between this comparative example and Example 1 is that the concentration of calcium chloride in step (2) is 10wt%, and the remaining steps and process parameters are the same as in Example 1.

[0021] Comparative Example 2: The difference between this comparative example and Example 1 is that the concentration of calcium chloride in step (2) is 0.1 wt%, and the other steps and process parameters are the same as in Example 1.

[0022] Comparative Example 3: The difference between this comparative example and Example 1 is that the water bath heating time in step (2) is 1 hour, while the other steps and process parameters are the same as in Example 1.

[0023] Comparative Example 4: The difference between this comparative example and Example 1 is that the water bath heating temperature in step (2) is 40°C, and the remaining steps and process parameters are the same as in Example 1.

[0024] Comparative Example 5: The difference between this comparative example and Example 1 is that the concentration of KH550 in step (3) is 5wt%, and the other steps and process parameters are the same as in Example 1.

[0025] Comparative Example 6: As described in patent CN103088627A, aramid filaments were cut into 3mm segments, placed in a beaker, ultrasonically cleaned with ethanol for 2 hours, and then dried; then treated with 20%wt CaCl2 aqueous solution at 100℃ for 180 minutes, and then removed, cleaned and dried to obtain pretreated aramid short fibers.

[0026] The pretreated aramid staple fibers from the above embodiments and comparative examples were subjected to pulping treatment (using a trough pulper). The specific process is as follows: (1) Place the pretreated aramid short fibers into a pulper and loosen them for 0.5 h; (2) The blade spacing of the beater was set to 3 mm, and its fiber length distribution, specific surface area and beating degree were characterized.

[0027] The performance parameters of the aramid pulp prepared in all examples and comparative examples are shown in Table 1.

[0028] The elemental contents of untreated aramid staple fibers and pretreated aramid staple fibers obtained by this invention are shown in Table 2.

[0029]

[0030] As can be seen from the comparison of parameters in Table 1, the aramid pulp prepared by this invention, compared with existing methods (NaOH pretreatment), achieves a similar specific surface area and freeness while requiring significantly less time (76%), and correspondingly, significantly less energy consumption. According to the textile industry standard FZ / T51015-2018, the specific physical properties and index requirements for para-aramid pulp are: fiber length (0.5-1.5 mm), specific surface area (≥4 m² / m³), and freeness. 2 ·g -1 ), Shore beating degree (20-55°SR).

[0031] The aramid pulp prepared in Comparative Example 1 had a length of only 0.453 mm, which is lower than the standard and not conducive to the normal use of aramid pulp. This is because excessive CaCl2 concentration will severely damage the structure of short aramid fibers, making them prone to breakage during pulping. Furthermore, more fine fibers will be generated during pulping, and excessive fine fibers will easily fill mesopores and mesopores, leading to a decrease in specific surface area, which is not conducive to subsequent compounding with rubber and other matrices. The aramid pulp prepared in Comparative Example 2 had a similar length to that in Example 1 after 400 minutes of pulping, but its specific surface area and freeness were both lower. This indicates that insufficient CaCl2 has a weak etching effect on aramid fibers, and the number of hydrogen bonds replaced by calcium chloride complexation is also less. The hydrogen bond force between aramid fibers is still relatively large, and the performance parameters of the prepared aramid pulp are comparable to those of the untreated pulp. The pulps prepared in Comparative Examples 3, 4, and 5 have similar performance, with moderate fiber length, but their specific surface area and freeness are both low, and the pulping time is longer. Examples 3 and 4 show that both short processing time and low processing temperature affect the modification effect of aramid staple fibers. The main reason is that too short a time leads to poor ethanol etching effect and only a small amount of calcium chloride complexation, with hydrogen bonds not being replaced. There are still many hydrogen bond connections between fibers, making fiber separation difficult. On the other hand, if the processing temperature is too low, the ethanol does not reach its boiling point. Compared with Example 1, the lack of the impact force of bubble rupture during ethanol boiling significantly reduces the modification effect of ethanol and calcium chloride on aramid fibers. More hydrogen bonds are retained, resulting in poor fiber separation. Compared with Example 1, Comparative Example 5 added less silane coupling agent. The small amount of silane coupling agent is insufficient to bind with aramid fibers and complexed calcium chloride. The calcium chloride complexed on the aramid fibers is unstable and easily replaced by hydrogen bonds, resulting in a large binding force between fibers and making fiber separation difficult. Comparative Example 6, which involves pretreating aramid staple fibers according to the method described in CN103088627A, showed a worse effect compared to Example 1. This indicates that the CaCl2 aqueous solution had a poor etching effect on the aramid staple fibers, and the ethanol ultrasonic cleaning stage only removed the oil on the surface of the aramid staple fibers, resulting in an insignificant etching effect.

[0032] Compared to Example 3, Comparative Example 6, which requires ultrasonic equipment and three times the amount of CaCl2 (the raw material used in Example 3), achieved the same results as Example 3. This demonstrates that the technical solution of this application represents a significant advancement. This application eliminates the need for energy-intensive ultrasonic equipment for pretreatment, significantly saving energy; simultaneously, it greatly reduces the amount of raw materials used, thereby achieving cost reduction, efficiency improvement, and increased production efficiency. Table 2 shows the complexing effect of CaCl2 and the grafting effect of KH550. XPS characterization results show that Ca, Cl, and Si elements appeared on the surface of the aramid fiber after surface modification, indicating successful complexation of calcium chloride and successful grafting of the silane coupling agent. Ca mainly connects to the carbonyl groups of aramid structural monomers, promoting the NH bond to break away from the hydrogen bond and weakening the hydrogen bond force between aramid fiber molecules. At the same time, calcium ions also increase the frictional force, making the aramid fibers easier to separate and fuzz during pulping. The presence of Si indicates that the silane coupling agent has been successfully grafted. The silane coupling agent not only stabilizes the complexation effect of calcium chloride, but also provides more active sites on the surface of aramid fibers, which is beneficial to the subsequent bonding of aramid pulp with matrices such as rubber.

[0033] Figure 1 , 2 Figures 3 and 4 are SEM images of untreated aramid fibers, aramid fibers modified with CaCl2 ethanol solution, and pretreated short aramid fibers, respectively. Figure 1 The surface of untreated aramid short fibers is very smooth, which makes it difficult to separate them into fibers during the pulping process. The method of the present invention increases the roughness of the fibers by etching them with CaCl2 ethanol solution, and promotes the separation of aramid fibers by introducing some functional groups to weaken the hydrogen bonding between fibers. Figure 2 The image shows the state of aramid fibers after being treated with a CaCl2 ethanol solution at high temperature. This treatment method has a significant etching effect on the surface of aramid fibers, with many obvious grooves appearing on the fiber surface, and some fibers have separated. This may be because the water bath temperature exceeds the boiling point of ethanol, and bubbles are continuously generated and burst during the vaporization of ethanol. The mechanical force generated in this process causes the aramid fibers to separate. Figure 3 This indicates that after treatment, the hydrogen bonding between aramid fibers is further reduced, and as the mechanical force generated by ethanol vaporization continues to act on the aramid fibers, the degree of aramid fibrillation is further improved.

[0034] In summary, the aramid fiber pulping pretreatment method provided by this invention significantly improves the reduction of aramid fiber pulping energy consumption and pulping time, and also improves the subsequent bonding effect with matrices such as rubber.

[0035] The specific embodiments described above provide a further detailed explanation of the present invention; however, these descriptions should not be construed as limiting the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for pre-treatment of aramid fibers by pulping, characterized in that, Includes the following steps: (1) Cut the aramid fiber into short aramid fibers of 1-5 mm; (2) The aramid short fibers were immersed in a CaCl2 solution with a concentration of 1-6wt% for water bath heating treatment, washed and dried to obtain CaCl2 modified aramid short fibers. (3) The CaCl2 modified aramid short fibers were immersed in a 15-25wt% silane coupling agent alcohol solution for water bath heating treatment, washed and dried to obtain pretreated aramid short fibers.

2. The method for pulping and pretreatment of aramid fibers according to claim 1, characterized in that, In step (2), the solvent for the CaCl2 solution is one of water, methanol, or ethanol.

3. The method for pre-treatment of aramid fibers by pulping according to claim 1, characterized in that, In step (2), the water bath heating conditions are: temperature 65-100℃, time 3-5h.

4. The method for pulping and pretreatment of aramid fibers according to claim 1, characterized in that, In step (2), the cleaning is performed by washing with pure water 3-5 times; the drying temperature is 60-80℃ and the time is 0.5-2h.

5. The method for pulping and pretreatment of aramid fibers according to claim 1, characterized in that, In step (3), the water bath heating conditions are: temperature 60-100℃, time 2-4h.

6. The method for pulping and pretreatment of aramid fibers according to claim 1, characterized in that, In step (3), the silane coupling agent is one of KH550, KH560, and KH570.

7. The method for pulping and pretreatment of aramid fibers according to claim 1, characterized in that, In step (3), the cleaning is performed by washing with pure water 3-5 times; the drying temperature is 60-80℃ and the time is 0.5-2h.

Images