Aramid pulp with bionic plant branch fractal structure and preparation process thereof

Abstract

The invention relates to the technical field of preparation of aramid fibers, differential fibers and bionic structure materials, in particular to aramid pulp with a bionic plant branch fractal structure and a preparation process of the aramid pulp, and the preparation process comprises the steps of thread rolling-pulping circulation, alkali liquor assisted pulping, three-stage centrifugal cleaning and gradient drying. The prepared aramid pulp with the bionic plant branch fractal structure is applied to the fields of automobile friction materials, chemical sealing gaskets and special toughened rubber, and can effectively solve the problems that the interface bonding strength of a traditional fiber reinforced material and a base material is low and the reinforcing effect is limited; the aramid pulp with the bionic plant branch fractal structure has a unique structure and excellent performance, and the preparation process of the aramid pulp is provided.

Description

Technical Field

[0001] The invention relates to the technical field of aramid fiber, differential fiber and bionic structural material preparation, in particular to aramid pulp with a bionic plant branch fractal structure and a preparation process thereof. Background Art

[0002] As a material with excellent performance, aramid pulp fiber has high strength, high modulus, excellent temperature resistance, wear resistance and chemical stability, and plays an important role in many key fields such as aerospace, national defense, automobile manufacturing, and industrial sealing. In the aerospace field, aramid pulp can be used to manufacture high-performance brake components and special rubber for aircraft; in the automotive industry, aramid pulp can significantly improve the wear resistance of clutch panels and tires; in the field of industrial sealing, the introduction of aramid pulp can effectively improve temperature resistance and corrosion resistance, and ensure stable operation of equipment.

[0003] For a long time, the development of high-quality and specially structured aramid pulp fibers and key preparation processes has been very important, and it is related to the iterative upgrade of products in subdivided application fields. CN117264269A uses nano-aramid fiber filaments to make a sheet-like three-dimensional stacked aramid nanofiber insulation material; CN119287550A discloses aramid nano pulp with a delicate shape and stable dimensions, which is used in the field of aramid paper and high-performance reinforced composite materials; CN119019982A discloses a high-wear-resistant friction material for electromagnetic brakes and its preparation process, the raw materials contain adhesives, reinforcing materials, and fillers, which can reduce wear and stabilize the friction coefficient.

[0004] However, industrial applications still lack aramid pulp with special structure and excellent performance to meet the high requirements for enhanced fiber grip and interface bonding in the fields of friction and sealing. The main reason is that in the process of existing technology, it is difficult to achieve precise control of the aramid fiber fibrillation process, and its morphology is difficult to effectively regulate according to actual needs, and the energy consumption in the drying process is too high. These problems seriously restrict the preparation and application of aramid pulp with excellent performance, resulting in the inability to meet the high requirements of industrial applications. Summary of the invention

[0005] In view of the problems in the prior art that aramid fiber fibrillation is difficult to accurately control, the morphology is difficult to regulate, and the drying energy consumption is high in the existing process, the present invention provides an aramid pulp with a bionic plant branch fractal structure and a preparation process thereof.

[0006] The present invention is achieved through the following technical solutions: A process for preparing aramid pulp with a bionic plant branch fractal structure comprises the following steps: Step 1: After the pretreated waste aramid fiber raw material is cut, it is subjected to a spinning and beating cycle to obtain a fiber slurry A; Step 2: mixing the fiber slurry A with an alkaline solution, and then grinding to obtain a mixed slurry B; Step 3: performing multi-stage centrifugal washing on the mixed pulp B in sequence to obtain aramid pulp fiber C; Step 4: The aramid pulp fiber C is subjected to gradient drying by controlling the temperature and time to prepare aramid pulp D having a bionic plant branch morphology.

[0007] Preferably, in step 1, the waste aramid fiber raw material is cut to a length of 3 to 5 mm; during thread rolling, the linear speed of the thread rolling machine is 1.5 to 2.5 m / min, and the pressure is 0.1 to 0.3 MPa; a thread rolling roller with a spiral groove texture on the surface is used, and the feed rate is 20 to 30 kg / h.

[0008] Preferably, in step 1, during pulping, the pulping concentration is 3% to 6%, the time is 3 to 5 hours, and the pressure is 0.2 to 0.4 MPa. Preferably, in step 2, during refining, the refining power is 4-6 kW, the refining time is 0.5-1.5 h, and the pressure is 700-800 Pa.

[0009] Preferably, in step 2, the alkaline solution is a sodium hydroxide or potassium hydroxide solution with a concentration of 0.5% to 2.0% and a pH value of 8 to 9; during mixing, the volume ratio of the slurry to the alkali solution is 10:3 to 10:5.

[0010] Preferably, in step 3, the multi-stage centrifugal cleaning is a three-stage gradient centrifugal cleaning process, the centrifugal speed is in the range of 3000-5000r / min, and increases gradually; each cleaning time is in the range of 10-20min, and decreases gradually; a 100-200 mesh filter is used for the first centrifugation, and a 300-500 mesh filter is used for the second and third centrifugations; the total processing time of the three centrifugation steps is controlled within 30-60min.

[0011] Preferably, in step 3, during the first centrifugation, the slurry feed rate is 15 to 25 L / min; during the second centrifugation, the slurry feed rate is 10 to 15 L / min; during the third centrifugation, the slurry feed rate is 5 to 8 L / min; After each centrifugal washing, the washing liquid is replaced by deionized water, and the volume ratio of deionized water to pulp is 3:1-5:1; after three-stage centrifugal washing, the moisture content of the aramid pulp fiber C is 12%-18%.

[0012] Preferably, in step 4, the gradient drying adopts a programmed temperature control mode, and in the first stage, the temperature is increased to 50-70°C at a heating rate of 2-5°C / min and kept constant for 30-50 minutes; in the second stage, the temperature is increased to 80-100°C at a heating rate of 1-3°C / min and kept constant for 20-40 minutes.

[0013] Preferably, the drying is carried out under a vacuum degree of 0.06-0.08 MPa, and after the drying is completed, the material is discharged after the temperature is naturally lowered to below 20°C.

[0014] The invention discloses aramid pulp prepared by using an aramid pulp preparation process having a bionic plant branch fractal structure.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The aramid pulp preparation process with the bionic plant branch morphology prepared by the present invention endows the aramid pulp with more excellent performance, such as higher gripping force, stronger adsorption and better dispersibility, by biomimetic unique fractal structure of plant branches in nature. At the same time, the present invention solves the problems of incomplete impurity removal, difficult precise control of fiber separation and high drying energy consumption in the existing process by optimizing the preparation process, realizes the technical upgrade from waste aramid fiber to high-performance aramid pulp, and effectively solves many problems existing in traditional aramid pulp and preparation process. Its main advantages are as follows: First, through a series of processes such as thread rolling-beating cycle, alkali solution-assisted refining, multi-stage centrifugal cleaning, gradient drying, and precise parameter control, an innovative breakthrough in the structure of aramid pulp was achieved, and the prepared aramid pulp has a bionic plant branch fractal structure. This bionic plant branch fractal structure can be more evenly dispersed in the dispersion and better combined with the matrix material. The unique bionic plant branch morphology gives aramid pulp new performance characteristics, such as increasing the specific surface area of ​​the pulp, so that it can provide more reaction sites and adsorption space in the application.

[0016] Secondly, the bionic structure enhances the mechanical properties of pulp. Its dendritic fractal structure can effectively disperse stress when subjected to force, improving the strength and toughness of pulp. According to tests, compared with traditional aramid pulp, the tensile strength is increased by 20%-30%, and the elongation at break is increased by 5%-25%. In the preparation of high-performance composite materials, it can significantly enhance the comprehensive mechanical properties of composite materials, reduce material damage caused by external forces, and make the application of composite materials in aerospace, automobile manufacturing and other fields more reliable and safe.

[0017] Furthermore, from the perspective of preparation process, the preparation process of the present invention also solves the key problem in the treatment of waste aramid fibers. Through the thread rolling and beating cycle operation after pretreatment, the fiber can be more efficiently separated and broomed. Compared with the traditional process, the fiber dispersion is more uniform and the morphology is more regular, which lays a solid foundation for the subsequent preparation of high-quality aramid pulp. In the alkali solution treatment and grinding steps, the precisely controlled process parameters ensure the precise regulation of the fiber surface and internal structure, which not only effectively removes impurities, but also optimizes the surface activity of the fiber and enhances the bonding force between the fibers.

[0018] Furthermore, multiple centrifugal washing processes can more thoroughly remove residual alkali solution and impurities by precisely controlling the centrifugal speed and washing time, so that the obtained pulp raw material has higher purity, greatly reducing the negative impact of impurities on the performance of the final product.

[0019] Furthermore, the two-stage gradient drying process is based on the characteristics of pulp in different drying stages. In the first stage, the slow heating at a lower temperature (2-5°C / min) promotes the gradual evaporation of water on the surface of pulp fibers, avoiding fiber shrinkage or structural collapse caused by rapid water loss. The constant temperature stage further stabilizes the hydrogen bonding between fibers, initially forming a loose porous network structure, laying the foundation for subsequent drying. In the second stage, the temperature is increased (1-3°C / min) to accelerate the removal of internal moisture, while the boiling point is reduced by vacuum conditions (0.06-0.08MPa) to reduce the damage of thermal stress to the fractal structure of fibers. The constant temperature stage promotes the complete removal of residual moisture inside the fibers, optimizes the orientation of the fibers through thermal relaxation, reasonably controls the temperature and time, and achieves fluffy drying, so that the final prepared aramid pulp has good structural stability and excellent performance.

[0020] Furthermore, the present invention optimizes the process parameters of each step after a large number of experiments and long-term research, such as the selection range of aramid fiber raw materials, the specific parameters of thread rolling and beating, the concentration and treatment time of the alkaline solution, the number and conditions of centrifugal cleaning, and the temperature and time gradient of the drying stage. These optimized parameters not only improve the production efficiency and product quality of aramid pulp, but also reduce production costs, reduce energy consumption and environmental pollution, and achieve efficient utilization of resources and sustainable development of the industry. This all-round innovation and optimization makes the present invention have a significant competitive advantage in the field of aramid pulp, and can effectively promote the technological progress and product upgrades of related industries. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is the process flow chart of aramid pulp with fractal structure of bionic plant branches; Figure 2 is a SEM image of the surface of the aramid pulp obtained in Example 1; Figure 3 This is an optical micrograph of the fractal structure of the aramid pulp obtained in Example 1. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below in conjunction with specific embodiments, which are intended to explain the present invention rather than to limit it.

[0023] The present invention discloses a process for preparing aramid pulp with a bionic plant branch fractal structure. Figure 1 , including the following steps: Step 1: pre-treat the waste aramid fiber, including removing impurities and cutting to a length of 3-5 mm. Then, a TMF250 thread rolling machine is used for thread rolling, with a line speed of 1.5-2.5 m / min, a pressure of 0.1-0.3 MPa, and a feed rate of 20-30 kg / h; the surface of the thread rolling roller is a spiral groove texture to enhance the fiber thread rolling effect.

[0024] After rolling, the fibers are transferred to a KDH100-XT pulping machine with a pulping concentration of 3% to 6% for 3 to 5 hours to obtain fiber pulp A.

[0025] Step 2: Mix the fiber slurry A with 0.5% to 2.0% sodium hydroxide or potassium hydroxide solution with a pH value of 8 to 9 at a volume ratio of 10:3 to 10:5, and inject into the FZ-102 disc refiner; The refining power is set to 4-6 kW, the refining time is set to 0.5-1.5 h, and the pressure is set to 700-800 Pa to obtain a mixed slurry B.

[0026] Step 3, subjecting the mixed slurry B to three-stage centrifugal washing in sequence: First stage: centrifugal speed 3000~4000r / min, feed rate 15~25L / min, filter mesh size 100~200 mesh, cleaning 16~20min; Second stage: centrifugal speed 3500-4500r / min, feed rate 10-15L / min, filter mesh size 300-500 mesh, cleaning 13-17min; The third stage: centrifugal speed 4000 ~ 5000r / min, feed rate 5 ~ 8 L / min, filter aperture 300 ~ 500 mesh, cleaning 10 ~ 14min.

[0027] After each stage of cleaning, the fiber is replaced with deionized water (water-to-material volume ratio 3:1-5:1), and finally aramid pulp fiber C with a moisture content of 12%-18% is obtained.

[0028] Step 4: Gradient drying of the aramid pulp fiber C under vacuum conditions: The first stage: the temperature is raised to 50-70°C at a rate of 2-5°C / min and kept at a constant temperature for 30-50 minutes; The second stage: heating to 80-100°C at a rate of 1-3°C / min and keeping the temperature constant for 20-40min; Among them, the vacuum degree is 0.06-0.08MPa, and after drying, the material is cooled to below 20°C at a natural cooling rate and then discharged.

[0029] The invention discloses a process for preparing aramid pulp with a bionic plant branch fractal structure, comprising a thread rolling-beating cycle, alkali solution-assisted pulping, three-stage centrifugal cleaning, and gradient drying. The prepared aramid pulp with a bionic plant branch fractal structure is applied to the fields of automotive friction materials, chemical sealing gaskets, and special toughened rubber, and can effectively overcome the problems of low interface bonding strength and limited reinforcement effect between traditional fiber-reinforced materials and matrix materials. In addition, the thread rolling machine, pulping machine, pulping machine, centrifuge, etc. used in the preparation process proposed by the invention are all conventional equipment, and the process links are environmentally friendly, which lays a good foundation for industrialization and scale-up, and has a high market competitive advantage.

[0030] Example 1 Step 1: pre-treat the waste aramid fiber, including removing impurities and cutting to a length of 5 mm. Then, a TMF250 type thread rolling machine is used for thread rolling, and the line speed is set to 2.5 m / min, the pressure is 0.3 MPa, and the feed rate is 30 kg / h; the surface of the thread rolling roller is a spiral groove texture to enhance the fiber separation effect; after thread rolling, it is transferred to a KDH100-XT pulping machine, and the pulping concentration is 6% for 5 hours to obtain fiber slurry A.

[0031] Step 2: Mix fiber slurry A with 2.0% sodium hydroxide in a volume ratio of 10:5, the pH value of the sodium hydroxide solution is 9, and inject it into a FZ-102 disc refiner; set the refining power to 6kW, the refining time to 1.5h, and the pressure to 800pa to obtain mixed slurry B.

[0032] Step 3, subjecting the mixed slurry B to three-stage centrifugal washing in sequence: First stage: centrifugal speed 4000r / min, feed rate 25L / min, filter mesh size 150 mesh, cleaning 20min; Second stage: centrifugal speed 4500r / min, feed rate 15L / min, filter mesh size 400 mesh, cleaning 17min; The third stage: centrifugal speed 5000r / min, feed rate 8L / min, filter aperture 500 mesh, cleaning 14min.

[0033] After each stage of cleaning, the fiber was replaced with deionized water (water-to-material volume ratio 5:1), and finally aramid pulp fiber C with a moisture content of 18% was obtained.

[0034] Step 4: Gradient drying of the aramid pulp fiber C under a vacuum degree of 0.08 MPa: The first stage: the temperature was raised to 70°C at a rate of 5°C / min and kept constant for 50 min; The second stage: the temperature was raised to 100°C at a rate of 3°C / min and kept constant for 40 minutes; After drying, cool to below 40°C at a natural cooling rate and then discharge.

[0035] The aramid pulp prepared by the process of Example 1 has excellent performance, with a beating degree of 48°SR, a specific surface area of ​​14.5 m² / g, a bifurcation density of up to 120 branches / mm, a moisture content of only 5.2%, and a thermal decomposition temperature of 520°C. It has the characteristics of large specific surface area, rich fractal structure, and excellent grip, and can be used for special rubber, friction materials, and sealing gaskets to improve product grades.

[0036] Reference Figure 2 The pulp surface presents a typical bionic tree fractal structure, with dense and uniform fiber bifurcation, which verifies the precise regulation of fiber surface morphology by the spinning-beating cycle and alkali solution refining. The SEM image shows that the fiber surface roughness has increased significantly, indicating an increase in specific surface area. Figure 3 The three-dimensional fractal network structure of aramid pulp is intuitively displayed through optical microscopy technology. The fiber branches in the figure are multi-level forked, which is highly similar to the shape of plant branches, proving that the present invention has successfully achieved the design goal of bionic structure.

[0037] Example 2 Step 1: pre-treat the waste aramid fiber, including removing impurities and cutting to a length of 3 mm. Then, a TMF250 type thread rolling machine is used for thread rolling, and the line speed is set to 1.5 m / min, the pressure is 0.1 MPa, and the feed rate is 20 kg / h; the surface of the thread rolling roller is a spiral groove texture to enhance the fiber separation effect; after thread rolling, it is transferred to a KDH100-XT pulping machine, and the pulping concentration is 3% for 3 hours to obtain fiber slurry A.

[0038] Step 2: Mix fiber slurry A with 0.5% potassium hydroxide solution in a volume ratio of 10:3, the pH value of the potassium hydroxide solution is 8, and inject it into the FZ-102 disc refiner; set the refining power to 4kW, the refining time to 0.5h, and the pressure to 700pa to obtain mixed slurry B.

[0039] Step 3, subjecting the mixed slurry B to three-stage centrifugal washing in sequence: First stage: centrifugal speed 3000r / min, feed rate 15L / min, filter aperture 150 mesh, cleaning 16min; Second stage: centrifugal speed 3500r / min, feed rate 10L / min, filter aperture 400 mesh, cleaning 13min; The third stage: centrifugal speed 4000r / min, feed rate 5L / min, filter aperture 500 mesh, cleaning 10min.

[0040] After each stage of cleaning, it was replaced with deionized water (water-to-material volume ratio 3:1), and finally aramid pulp fiber C was obtained with a moisture content of 13%.

[0041] Step 4: Gradient drying of the aramid pulp fiber C under a vacuum degree of 0.06 MPa: The first stage: the temperature was raised to 50°C at a rate of 2°C / min and kept constant for 30 minutes; The second stage: the temperature was raised to 80°C at a rate of 1°C / min and kept at this temperature for 20 minutes; After drying, cool to below 20°C at a natural cooling rate and then discharge.

[0042] The aramid pulp prepared by the process of Example 2 has excellent performance, with a beating degree of 45°SR, a specific surface area of ​​12.3 m² / g, a bifurcation density of up to 110 branches / mm, a moisture content of only 5.2%, and a thermal decomposition temperature of 510°C. It has the characteristics of large specific surface area, rich fractal structure, and excellent grip, and can be used for special rubber, friction materials, and sealing gaskets to improve product grades.

[0043] Example 3 Step 1: pre-treat the waste aramid fiber, including removing impurities and cutting to a length of 4 mm. Then, a TMF250 type thread rolling machine is used for thread rolling, with a line speed of 2 m / min, a pressure of 0.2 MPa, and a feed rate of 25 kg / h; the surface of the thread rolling roller is a spiral groove texture to enhance the fiber separation effect; after thread rolling, it is transferred to a KDH100-XT pulping machine with a pulping concentration of 5% and a time of 4 hours to obtain fiber slurry A.

[0044] Step 2: Mix fiber slurry A with 1.3% sodium hydroxide solution in a volume ratio of 10:4, the pH value of the sodium hydroxide solution is 8, and inject it into a FZ-102 disc refiner; set the refining power to 5 kW, the refining time to 1 h, and the pressure to 750 Pa to obtain mixed slurry B.

[0045] Step 3, subjecting the mixed slurry B to three-stage centrifugal washing in sequence: First stage: centrifugal speed 3500r / min, feed rate 20L / min, filter aperture 150 mesh, cleaning 18min; Second stage: centrifugal speed 4000r / min, feed rate 13L / min, filter aperture 400 mesh, cleaning 15min; The third stage: centrifugal speed 4500r / min, feed rate 6L / min, filter aperture 500 mesh, cleaning 12min.

[0046] After each stage of cleaning, it was replaced with deionized water (water-to-material volume ratio 4:1), and finally aramid pulp fiber C was obtained with a moisture content of 15%. Step 4: Gradient drying of the aramid pulp fiber C under a vacuum degree of 0.07 MPa: The first stage: the temperature was raised to 60°C at a rate of 4°C / min and kept constant for 40 min; The second stage: the temperature was raised to 90°C at a rate of 2°C / min and kept constant for 30 minutes; After drying, cool to below 20°C at a natural cooling rate and then discharge.

[0047] The aramid pulp prepared by the process of Example 3 has excellent performance, with a beating degree of 46°SR, a specific surface area of ​​13.2 m² / g, a bifurcation density of up to 105 branches / mm, a moisture content of only 6.2%, and a thermal decomposition temperature of 523°C. It has the characteristics of large specific surface area, rich fractal structure, and excellent grip, and can be used for special rubber, friction materials, and sealing gaskets to improve product grades.

[0048] Example 4 Step 1, pre-treat the waste aramid fiber, including removing impurities and cutting to 5 mm length. Then use TMF250 type thread rolling machine for thread rolling, the line speed is set to 1.5m / min, the pressure is 0.3MPa, and the feed rate is 20kg / h; the surface of the thread rolling roller is a spiral groove texture to enhance the fiber separation effect; after thread rolling, transfer to KDH100-XT beater, the beating concentration is 3%, the time is 5h, and fiber slurry A is obtained.

[0049] Step 2: Mix fiber slurry A with 2.0% potassium hydroxide solution in a volume ratio of 10:3, the pH value of the potassium hydroxide solution is 8, and inject it into a FZ-102 disc refiner; set the refining power to 4kW, the refining time to 1.5h, and the pressure to 700pa to obtain mixed slurry B.

[0050] Step 3, subjecting the mixed slurry B to three-stage centrifugal washing in sequence: First stage: centrifugal speed 3000r / min, feed rate 25L / min, filter aperture 150 mesh, cleaning 20min; Second stage: centrifugal speed 4500r / min, feed rate 10L / min, filter aperture 400 mesh, cleaning 13min; The third stage: centrifugal speed 5000r / min, feed rate 8L / min, filter aperture 500 mesh, cleaning 10min.

[0051] After each stage of cleaning, it was replaced with deionized water (water-to-material volume ratio 5:1), and finally aramid pulp fiber C was obtained with a moisture content of 12%.

[0052] Step 4: Gradient drying of the aramid pulp fiber C under a vacuum degree of 0.06 MPa: The first stage: the temperature was raised to 50°C at a rate of 5°C / min and kept constant for 50 min; The second stage: the temperature was raised to 100°C at a rate of 1°C / min and kept constant for 20 minutes; After drying, cool to below 20°C at a natural cooling rate and then discharge.

[0053] The aramid pulp prepared by the process of Example 4 has excellent performance, with a beating degree of 43°SR, a specific surface area of ​​11.6m² / g, a bifurcation density of up to 112 branches / mm, a moisture content of only 4.8%, and a thermal decomposition temperature of 518°C. It has the characteristics of large specific surface area, rich fractal structure, and excellent grip, and can be used for special rubber, friction materials, and sealing gaskets to improve product grades.

[0054] Example 5 Step 1: pre-treat the waste aramid fiber, including removing impurities and cutting to a length of 3 mm. Then, a TMF250 type thread rolling machine is used for thread rolling, and the line speed is set to 2.5 m / min, the pressure is 0.1 MPa, and the feed rate is 30 kg / h; the surface of the thread rolling roller is a spiral groove texture to enhance the fiber separation effect; after thread rolling, it is transferred to a KDH100-XT pulping machine, and the pulping concentration is 6% for 3 hours to obtain fiber slurry A.

[0055] Step 2: Mix fiber slurry A with 0.5% sodium hydroxide solution in a volume ratio of 10:5, the pH value of the sodium hydroxide solution is 9, and inject it into a FZ-102 disc refiner; set the refining power to 6kW, the refining time to 0.5h, and the pressure to 700pa to obtain mixed slurry B.

[0056] Step 3, subjecting the mixed slurry B to three-stage centrifugal washing in sequence: First stage: centrifugal speed 3000r / min, feed rate 25L / min, filter aperture 150 mesh, cleaning 16min; Second stage: centrifugal speed 3500r / min, feed rate 15L / min, filter aperture 400 mesh, cleaning 13min; The third stage: centrifugal speed 5000r / min, feed rate 5L / min, filter aperture 500 mesh, cleaning 10min.

[0057] After each stage of cleaning, it was replaced with deionized water (water-to-material volume ratio 3:1), and finally aramid pulp fiber C was obtained with a moisture content of 18%.

[0058] Step 4: Gradient drying of the aramid pulp fiber C under a vacuum degree of 0.08 MPa: The first stage: the temperature was raised to 70°C at a rate of 5°C / min and kept constant for 50 min; The second stage: the temperature was raised to 100°C at a rate of 3°C / min and kept constant for 40 minutes; After drying, cool to below 20°C at a natural cooling rate and then discharge.

[0059] The aramid pulp prepared by the process of Example 5 has excellent performance, with a beating degree of 49°SR, a specific surface area of ​​13.7m² / g, a bifurcation density of up to 113 branches / mm, a moisture content of only 6.4%, and a thermal decomposition temperature of 520°C. It has the characteristics of large specific surface area, rich fractal structure, and excellent grip, and can be used for special rubber, friction materials, and sealing gaskets to improve product grades.

[0060] The above description is only a preferred embodiment of the present invention and is not intended to impose any limitation on the technical solution of the present invention. Those skilled in the art should understand that, without departing from the spirit and principles of the present invention, the technical solution can also be subjected to several simple modifications and substitutions, and these modifications and substitutions are also within the scope of protection covered by the claims.

Claims

1. A process for preparing aramid pulp with a bionic plant branch fractal structure, characterized in that: The following steps are involved: Step 1: After the pretreated waste aramid fiber raw material is cut, it is subjected to a spinning and beating cycle to obtain a fiber slurry A; Step 2: mixing the fiber slurry A with an alkaline solution, and then grinding to obtain a mixed slurry B; Step 3: performing multi-stage centrifugal washing on the mixed pulp B in sequence to obtain aramid pulp fiber C; Step 4: The aramid pulp fiber C is subjected to gradient drying by controlling the temperature and time to prepare aramid pulp D having a bionic plant branch morphology.

2. The process for preparing aramid pulp having a bionic plant branch morphology according to claim 1, characterized in that: In step 1, the waste aramid fiber raw material is cut into a length of 3-5 mm; when rolling, the linear speed of the rolling machine is 1.5-2.5 m / min, and the pressure is 0.1-0.3 MPa; a rolling roller with a spiral groove texture on the surface is used, and the feed rate is 20-30 kg / h.

3. The process for preparing aramid pulp having a bionic plant branch morphology according to claim 1, characterized in that: In step 1, during pulping, the pulping concentration is 3% to 6%, the time is 3 to 5 hours, and the pressure is 0.2 to 0.4 MPa.

4. The process for preparing aramid pulp having a bionic plant branch morphology according to claim 1, characterized in that: In step 2, during refining, the refining power is 4-6 kW, the refining time is 0.5-1.5 h, and the pressure is 700-800 Pa.

5. The process for preparing aramid pulp having a bionic plant branch morphology according to claim 1, characterized in that: In step 2, the alkaline solution is a sodium hydroxide or potassium hydroxide solution with a concentration of 0.5% to 2.0% and a pH value of 8 to 9; during mixing, the volume ratio of the slurry to the alkaline solution is 10:3 to 10:

5.

6. The process for preparing aramid pulp having a bionic plant branch morphology according to claim 1, characterized in that: In step 3, the multi-stage centrifugal cleaning is a three-stage gradient centrifugal cleaning process, the centrifugal speed is in the range of 3000-5000r / min, and increases gradually; each cleaning time is in the range of 10-20min, and decreases gradually; a 100-200 mesh filter is used for the first centrifugation, and a 300-500 mesh filter is used for the second and third centrifugations; the total processing time of the three centrifugation steps is controlled within 30-60min.

7. The process for preparing aramid pulp having a bionic plant branch morphology according to claim 6, characterized in that: In step 3, during the first centrifugation, the slurry feed rate is 15 to 25 L / min; during the second centrifugation, the slurry feed rate is 10 to 15 L / min; during the third centrifugation, the slurry feed rate is 5 to 8 L / min; After each centrifugal washing, the washing liquid is replaced by deionized water, and the volume ratio of deionized water to pulp is 3:1-5:1; after three-stage centrifugal washing, the moisture content of aramid pulp fiber C is 12%-18%.

8. The process for preparing aramid pulp having a bionic plant branch morphology according to claim 1, characterized in that: In step 4, the gradient drying adopts a programmed temperature control mode. In the first stage, the temperature is increased to 50-70°C at a heating rate of 2-5°C / min and kept constant for 30-50 minutes; in the second stage, the temperature is increased to 80-100°C at a heating rate of 1-3°C / min and kept constant for 20-40 minutes.

9. The process for preparing aramid pulp having a bionic plant branch morphology according to claim 1, characterized in that: In step 4, drying is carried out under vacuum conditions of 0.06-0.08 MPa, and after drying, the material is discharged after naturally cooling to below 20°C.

10. Aramid pulp prepared by the process for preparing aramid pulp having a bionic plant branch fractal structure according to any one of claims 1 to 9.

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