Recycled aramid pulp with mechanical force induced brooming and preparation method thereof

Abstract

The invention relates to the technical field of aramid fiber recycling, high-performance fiber modification and functional fiber reinforced materials, in particular to recycled aramid pulp with mechanical force induced brooming and a preparation method of the recycled aramid pulp. The preparation method comprises the steps of physical screening, chemical stripping pretreatment, thread rolling, pulping, pulping mechanical force coupling, stepped heating drying and opener secondary delinting, and the prepared high-quality aramid pulp is applied to the fields of automobile friction materials, high-performance sealing products and special rubber composite materials. The problems that traditional recycled fibers are poor in dispersity, insufficient in specific surface area and weak in matrix interface bonding can be effectively solved.

Description

Technical Field

[0001] The invention relates to the technical fields of aramid fiber recycling, high-performance fiber modification and functionalized fiber reinforcement materials, and in particular to a mechanical force-induced broomed recycled aramid pulp and a preparation method thereof. Background Art

[0002] As a high-performance material, aramid pulp fiber combines high strength, high modulus, excellent heat and wear resistance, and chemical stability. It is widely used in key sectors such as aerospace, defense, automotive manufacturing, and industrial sealing. In aerospace, it is used to manufacture high-performance aircraft brake components and specialty rubber. In the automotive sector, it significantly improves the wear resistance of clutch panels and tires. In industrial sealing, the addition of this fiber effectively enhances the material's heat and corrosion resistance, ensuring stable equipment operation.

[0003] For a long time, the development of recycled aramid fibers for the production of high-quality aramid pulp fibers and key preparation methods has been of great importance, and is related to the iterative upgrade of products in specific application areas. CN119265991A provides a method for preparing para-aramid pulp with high specific surface area and excellent morphology through a simple precipitation and shearing process, significantly improving its tear resistance in reinforcing materials such as aramid paper. CN119287550A provides a method for preparing meta-aramid nano-pulp based on electrospinning, hot pressing slicing, and refining processes. This method is simple and low-cost, and can produce nano-pulp with high specific surface area and stable dimensions, significantly improving the strength of aramid paper and composite materials.

[0004] However, the surge in the use of aramid products has generated a significant amount of waste aramid fiber precursor. Currently, efficient and high-value recycling technologies for this waste aramid fiber precursor are insufficient. Currently, the efficient and high-value recycling technology system for this high-value but difficult-to-process waste resource is still relatively weak. Landfill or simple incineration are still the primary disposal methods, resulting in a significant waste of high-quality aramid resources and contradicting the current concepts of a circular economy and sustainable development. Furthermore, it fails to fully tap the potential economic value of waste aramid as a raw material for reintegration into the industrial chain. Summary of the Invention

[0005] In view of the problems in the prior art of poor dispersibility, insufficient specific surface area and weak interface bonding with the matrix of traditional recycled fibers in existing processes, the present invention provides a mechanically induced broomed recycled aramid pulp and a preparation method thereof.

[0006] The present invention is achieved through the following technical solutions: A method for preparing recycled aramid pulp by mechanical force induced brooming, comprising the following steps: Step 1: Physically screening and chemically stripping the waste aramid fiber raw material to obtain pretreated fiber A; Step 2: Cut the pretreated fiber A and perform mechanical coupling treatments of thread rolling, beating and alkali solution-assisted refining in sequence to obtain a mechanical force-induced broomed mixed pulp B; Step 3: The mechanically broomed mixed pulp B is subjected to multi-stage centrifugal washing, and then subjected to a stepwise temperature-raising drying process to obtain a dry aramid pulp C; Step 4: De-linting the dried aramid pulp C to prepare recycled aramid pulp D.

[0007] Preferably, in step 1, two-stage sieves are used for physical screening, the aperture of the first-stage sieve is 10-20 mm, and the aperture of the second-stage sieve is 2-5 mm.

[0008] Preferably, in step 1, the raw material after physical screening is immersed in an alkaline solution system for chemical stripping for 40 to 60 minutes and then cut to obtain pretreated fiber A; wherein the alkaline solution system includes a sodium hydroxide solution with a concentration of 5 wt% to 15 wt% and a hydrogen peroxide solution with a volume ratio of 3:1 to 5:1.

[0009] Preferably, in step 2, the pretreated fiber A is cut to a length of 4 to 12 mm; during the rolling process, the linear speed of the rolling machine is 3 to 6 m / min, the pressure is 0.3 to 0.5 MPa, a rolling roller with a fine serrated surface is used, and the feed rate is 25 to 35 kg / min.

[0010] Preferably, in step 2, during beating, the beating concentration is 12% to 18%, the time is 2 to 5 hours, the pressure is 0.6 to 0.8 MPa, and during refining, the refining power is 2 to 8 kW, the refining time is 1 to 13 hours, and the pressure is 500 to 800 Pa.

[0011] Preferably, in step 2, the alkaline solution is a sodium hydroxide or potassium hydroxide solution with a concentration of 2-10 wt% and a pH value of 8-9; during mixing, the volume ratio of the slurry to the alkaline solution is (10:2)-(10:6).

[0012] Preferably, in step 3, the multi-stage centrifugal cleaning is a three-stage gradient centrifugal cleaning process, the centrifugal speed of each time is in the range of 3000-6000 r / min, and increases gradually; the cleaning time of each time is in the range of 10-30 minutes, and decreases gradually; the total processing time of the three centrifugal steps is controlled within 30-90 minutes, and the moisture content of the aramid pulp fiber after cleaning is 12%-18%.

[0013] Preferably, in step 3, gradient drying adopts a programmed temperature control mode, and in the first stage, the temperature is raised to 50-70°C at a heating rate of 2-5°C / min and kept constant at this temperature for 30-50 minutes; in the second stage, the temperature is raised to 80-100°C at a heating rate of 1-3°C / min and kept constant at this temperature for 20-40 minutes; drying is carried out under a vacuum degree of 0.06-0.12 MPa, and after drying, the temperature is naturally lowered to below 20°C to obtain the dried aramid pulp C.

[0014] Preferably, in step 4, a double-toothed roller high-efficiency opening machine is used for depilation, and the feed rate is 15 to 25 kg / min.

[0015] Aramid pulp prepared by a method for preparing recycled aramid pulp through mechanical force induced brooming.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a method for preparing recycled aramid pulp with mechanical force induced brooming, which effectively solves the problems of incomplete impurity removal, difficulty in precise control of filament separation and brooming, and high energy consumption in drying in the existing process through key process steps and precise parameter control such as physical screening-chemical stripping pretreatment, thread rolling-beating-refining mechanical force coupling, step-by-step temperature drying and secondary depilation by an opener. It can realize the technical upgrade from waste aramid fiber to high-performance aramid pulp, thereby overcoming the problems of poor dispersibility, insufficient specific surface area and weak interface bonding with the matrix of traditional recycled fiber. First, the overall preparation method of the present invention is efficient, controllable and optimizes resource utilization. It systematically solves key problems such as incomplete impurity removal, difficulty in precise control of fiber separation and brooming, and high energy consumption in drying. Physical screening (multi-level screens 10~20mm / 2~5mm) and chemical stripping (5 wt%~15wt% NaOH + 1~3wt% H2O2) synergistically and efficiently remove impurities and stickies.

[0017] Secondly, the present invention utilizes a mechanically coupled process of "rolling-beating-refining" to improve the dispersibility, specific surface area, and interfacial bonding strength of recycled aramid pulp with the substrate, overcoming the core drawbacks of conventional recycled fibers, such as poor dispersibility, insufficient specific surface area, and weak interfacial bonding. A specially designed fine-toothed rolling roller (at a linear speed of 3-6 m / min and a pressure of 0.3-0.5 MPa) is used for the initial depilling of the fibers, guiding their longitudinal tearing. This is then combined with an optimized concentration of alkali solution (2 wt%-10 wt% NaOH or KOH, pH 8-9) for auxiliary refining (power of 2-8 kW, time of 1-13 hours, pressure of 500-800 Pa). This synergistic beating action (at a concentration of 12%-18%, time of 2-5 hours, and pressure of 0.6-0.8 MPa) ensures maximum longitudinal fiber fibrillation and minimizes damage, significantly reducing fiber agglomeration and increasing the specific surface area, thereby providing more binding sites and strengthening the interfacial bonding strength with the substrate.

[0018] Third, three-stage gradient centrifugal cleaning (speed increasing from 3000 to 5000 r / min, time decreasing from 10 to 20 minutes, filter screen 100 to 200 mesh / 300 to 400 mesh / 500 to 600 mesh) effectively removes residual impurity particles of different particle sizes and densities (such as incompletely reacted chemicals, tiny colloid particles, inorganic fillers, etc.) by gradually increasing the speed and filter screen accuracy, ensuring thorough cleaning while reducing fiber loss.

[0019] Fourth, step-by-step vacuum drying (2-5°C / min to 50-70°C constant temperature for 30-50 minutes, 1-3°C / min to 80-100°C constant temperature for 20-40 minutes, vacuum 0.06-0.08MPa) to prevent agglomeration and brittleness and maintain a fluffy structure; Fifth, the double-toothed roller opener for depilation (feeding 15-25 kg / min) can further loosen the slight aggregates that may be formed during the drying process, ensuring that the final pulp is uniform and stable, and the entire process is efficient and controllable.

[0020] In summary, this invention converts waste raw materials into high-performance pulp, achieving efficient and high-value conversion of waste aramid fibers, with significant economic and environmental benefits. Direct application in automotive friction materials, high-performance sealing products, and specialty rubber composites can improve performance and reduce costs. The entire set of experimentally optimized process parameters effectively reduces energy consumption and pollution while ensuring quality and efficiency, meeting the requirements of a circular economy and sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a flow chart of a method for preparing recycled aramid pulp by mechanical force induced brooming according to the present invention; 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 will be further described in detail below with reference to specific embodiments, which are intended to explain the present invention rather than to limit it.

[0023] The present invention discloses a method for preparing recycled aramid pulp by mechanical force induction brooming, referring to Figure 1 , including the following steps: Step 1: pass through an XFS-100 multi-stage screening machine (first-stage sieve aperture 10-20 mm, second-stage sieve aperture 2-5 mm), and then immerse in an alkaline solution system, wherein the alkaline solution system is a sodium hydroxide solution with a concentration of 5-15wt% and a hydrogen peroxide solution with a volume ratio of 3:1-5:1, and react for 40-60 minutes to obtain pretreated fiber A.

[0024] Step 2: The pretreated fiber A is cut into 4-12 mm lengths and then mechanically broomed using a CMF-300 brooming and rolling machine. The line speed is set at 3-6 m / min, the pressure is 0.3-0.5 MPa, and the feed rate is 25-35 kg / min. A rolling roller with a fine serrated surface is used to induce longitudinal fiber tearing, which can reduce transverse cutting. After rolling, it is transferred to a ZDG-200HC beating machine with a concentration of 12%-18% for 2-5 hours; the pressure is 0.6-0.8 MPa. The pulp is refined using an FZ-102 disc refiner with alkali solution injection to assist refining. The refining power is 2-8 kW, the refining time is 1-3 hours, and the pressure is 500-800 Pa. The alkaline solution is a sodium hydroxide or potassium hydroxide solution with a concentration of 2-10 wt% and a pH value of 8-9; during mixing, the volume ratio of the slurry to the alkaline solution is 10:2-10:6, and a mixed slurry B is obtained after refining.

[0025] Step 3: The mixed pulp B is centrifuged and washed three times in sequence. The centrifugal speed of each time is in the range of 3000-6000 r / min and increases gradually. The washing time of each time is in the range of 10-30 minutes and decreases gradually. The total processing time of the three centrifugal steps is controlled within 30-90 minutes. The moisture content of the aramid pulp fiber after washing is 12%-18%.

[0026] First cleaning: centrifugal speed is 3000-4000r / min, feed rate is 15-25L / min, filter mesh size is 100-200 mesh, and cleaning time is 16-30min; Second cleaning: centrifugal speed is 4000-5000r / min, feed rate is 10-15L / min, filter mesh size is 300-400 mesh, and cleaning time is 13-27min; The third cleaning: the centrifugal speed is 5000-6000 r / min, the feed rate is 5-8 L / min, the filter mesh size is 500-600 mesh, and the cleaning time is 10-24 min.

[0027] After each washing, the pulp is replaced with deionized water (water-to-material volume ratio 3:1-5:1), and finally aramid pulp fiber with a moisture content of 12%-18% is obtained; The water-containing aramid pulp fiber is then subjected to gradient drying under vacuum conditions: The first stage: heating to 50-70°C at a rate of 2-5°C / min and maintaining the temperature for 30-50 minutes; The second stage: heating to 80-100°C at a rate of 1-3°C / min and maintaining the temperature for 20-40 minutes; The vacuum degree is 0.06-0.12 MPa, and after drying, the dried aramid pulp C is obtained by cooling to 20° C. at a natural cooling rate.

[0028] In step 4, the dried aramid pulp C is subjected to a secondary de-linting treatment by an opener, wherein the opener adopts a FLO-80 double-toothed roller high-efficiency opener with a feed rate of 15 to 25 kg / min, and finally high-quality aramid pulp D is prepared.

[0029] The present invention discloses a method for preparing recycled aramid pulp with mechanical force induction brooming, comprising physical screening-chemical stripping pretreatment, thread rolling-beating-refining mechanical force coupling, step-by-step temperature drying, and secondary de-linting with an opener. The prepared recycled aramid pulp with mechanical force induction brooming is used in the fields of automotive friction materials, high-performance sealing products, and special rubber composite materials, effectively overcoming the problems of poor dispersibility, insufficient specific surface area, and weak interfacial bonding with the matrix of traditional recycled fibers. In addition, the multi-stage vibrating screening machine, thread rolling machine, beater, refiner, centrifuge, opener, etc. used in the preparation method proposed by the present invention are all conventional equipment. The process links conform to the concepts of circular economy and sustainable development, laying a good foundation for industrialization and scale-up, and having a high market competitive advantage.

[0030] Example 1 Step 1: remove impurities through an XFS-100 multi-stage screening machine (first-stage sieve hole 10 mm, second-stage sieve hole 2 mm), and then immerse in an alkaline solution system, which is a 5wt% sodium hydroxide solution and a 1wt% hydrogen peroxide solution in a volume ratio of 3:1, and react for 40 minutes to obtain pretreated fiber A.

[0031] Step 2: Pretreated fiber A was cut to 4 mm in length and then mechanically broomed using a CMF-300 brooming machine at a line speed of 3 m / min, a pressure of 0.3 MPa, and a feed rate of 25 kg / min. After spinning, the fibers were transferred to a ZDG-200HC beater at a concentration of 12% for 2 hours. The fibers were then refined using an FZ-102 disc refiner with alkali solution at a power of 2 kW, a refining time of 1 hour, and a pressure of 500 Pa. The alkaline solution consisted of a 2 wt% sodium hydroxide or potassium hydroxide solution with a pH of 8. The volume ratio of the pulp to the alkaline solution was 10:2. After refining, mixed pulp B was obtained.

[0032] Step 3: Centrifuge the mixed slurry B three times in sequence: First cleaning: centrifugal speed is 3000r / min, feed rate is 15L / min, filter mesh size is 100 mesh, and cleaning time is 16min; Second cleaning: centrifugal speed is 4000r / min, feed rate is 10L / min, filter mesh size is 300 mesh, and cleaning time is 13min; The third cleaning: the centrifugal speed is 5000r / min, the feed rate is 5L / min, the filter mesh size is 500 mesh, and the cleaning time is 10min.

[0033] After each washing, the water content was replaced with deionized water (water-to-material volume ratio 3:1), and finally aramid pulp fiber with a moisture content of 12% was obtained.

[0034] The water-containing aramid pulp fiber is then subjected to gradient drying under vacuum conditions: The first stage: heating to 50°C at a rate of 2°C / min and maintaining the temperature for 30 min; The second stage: heating to 80°C at a rate of 1°C / min and maintaining the temperature for 20 min; The vacuum degree is 0.06 MPa, and after drying, the dried aramid pulp C is obtained by cooling to 20° C. at a natural cooling rate.

[0035] Step 4: The dried aramid pulp C is subjected to a secondary de-linting treatment by an opener, wherein the opener adopts a FLO-80 double-toothed roller high-efficiency opener with a feed rate of 15 kg / min, and finally high-quality aramid pulp D is prepared.

[0036] The aramid pulp prepared in Example 1 has excellent performance: beating degree 47.5°SR, specific surface area 11.7 m 2 / g, bifurcation density 120 branches / mm, moisture content 4.2%, thermal decomposition temperature 550℃. Its high specific surface area, rich bifurcation structure and excellent adhesion enable it to significantly improve product grades when used in special paper, friction plates and sealing gaskets.

[0037] Reference Figure 2 , a dense and uniform bifurcation structure is formed on the fiber surface, showing typical longitudinal tearing characteristics, while the fiber surface roughness is significantly improved, and there is no obvious transverse cutting mark. Figure 3 It can be seen that the fiber branches are multi-level forked. These branches can increase the interweaving points between fibers and the contact area with the matrix material, thereby greatly improving the specific surface area.

[0038] Example 2 Step 1: remove impurities through an XFS-100 multi-stage screening machine (first-stage sieve hole 20 mm, second-stage sieve hole 5 mm), and then immerse in an alkaline solution system, which is a 15wt% sodium hydroxide solution and a 3wt% hydrogen peroxide solution in a volume ratio of 5:1, and react for 60 minutes to obtain pretreated fiber A.

[0039] Step 2: The pretreated fiber A was cut into 12 mm lengths and then mechanically broomed using a CMF-300 brooming and rolling machine with a line speed of 6 m / min, a pressure of 0.5 MPa, and a feed rate of 35 kg / min. After rolling, it was transferred to a ZDG-200HC beater with a concentration of 18%, a time of 5 hours, and a pressure of 0.8 MPa. During refining, an FZ-102 disc refiner was used to inject alkali solution to assist refining. The refining power was 8 kW, the refining time was 3 hours, and the pressure was 800 Pa. The alkaline solution was a 10 wt% sodium hydroxide or potassium hydroxide solution with a pH of 9. During mixing, the volume ratio of the slurry to the alkaline solution was 10:6, and after refining, a mixed slurry B was obtained.

[0040] Step 3: Centrifuge the mixed slurry B three times in sequence: First cleaning: centrifugal speed is 4000r / min, feed rate is 25L / min, filter mesh size is 200 mesh, and cleaning time is 30min; Second cleaning: centrifugal speed is 5000r / min, feed rate is 15L / min, filter mesh size is 400 mesh, and cleaning time is 27min; The third cleaning: the centrifugal speed is 6000r / min, the feed rate is 8L / min, the filter mesh size is 600 mesh, and the cleaning time is 24min.

[0041] After each washing, the water content was replaced with deionized water (water-to-material volume ratio 5:1), and finally aramid pulp fiber with a moisture content of 18% was obtained.

[0042] The water-containing aramid pulp fiber is then subjected to gradient drying under vacuum conditions: The first stage: heating to 70°C at a rate of 5°C / min and maintaining the temperature for 50 min; The second stage: heating to 100°C at a rate of 3°C / min and maintaining the temperature for 40 min; The vacuum degree is 0.12 MPa, and after drying, the dried aramid pulp C is obtained by cooling to 20° C. at a natural cooling rate.

[0043] Step 4: In step 4, the dried aramid pulp C is subjected to a secondary de-linting treatment by an opener, wherein the opener adopts a FLO-80 model double-toothed roller high-efficiency opener with a feed rate of 25 kg / min, and finally high-quality aramid pulp D is prepared.

[0044] The aramid pulp prepared in Example 2 has excellent performance: beating degree 48.5°SR, specific surface area 13.2 m 2 / g, branching density 130 branches / mm, moisture content 5.2%, thermal decomposition temperature 530℃.

[0045] Example 3 Step 1: remove impurities through an XFS-100 multi-stage screening machine (first-stage sieve hole 15 mm, second-stage sieve hole 4 mm), and then immerse in an alkaline solution system, which is a 10wt% sodium hydroxide solution and a 2wt% hydrogen peroxide solution in a volume ratio of 4:1, and react for 50 minutes to obtain pretreated fiber A.

[0046] Step 2: Pretreated fiber A was cut to 8 mm in length and then mechanically broomed using a CMF-300 brooming and rolling machine at a line speed of 5 m / min, a pressure of 0.4 MPa, and a feed rate of 30 kg / min. After rolling, the fibers were transferred to a ZDG-200HC beater at a concentration of 15%, a time of 4 hours, and a pressure of 0.7 MPa. Refining was performed using an FZ-102 disc refiner with alkaline solution injection, at a power of 5 kW, a time of 2 hours, and a pressure of 600 Pa. The alkaline solution was a 6 wt% sodium hydroxide or potassium hydroxide solution with a pH of 8. During mixing, the volume ratio of the pulp to the alkaline solution was 10:4. After refining, mixed pulp B was obtained.

[0047] Step 3: Centrifuge the mixed slurry B three times in sequence: First cleaning: centrifugal speed is 3500r / min, feed rate is 20L / min, filter mesh size is 150 mesh, and cleaning time is 23min; Second cleaning: centrifugal speed is 4500r / min, feed rate is 13L / min, filter mesh size is 350 mesh, and cleaning time is 20min; The third cleaning: the centrifugal speed is 5500r / min, the feed rate is 6L / min, the filter mesh size is 550 mesh, and the cleaning time is 17min.

[0048] After each washing, the water content was replaced with deionized water (water-to-material volume ratio 4:1), and finally aramid pulp fiber with a moisture content of 15% was obtained.

[0049] The water-containing aramid pulp fiber is then subjected to gradient drying under vacuum conditions: The first stage: heating to 60°C at a rate of 3°C / min and maintaining the temperature for 40 min; The second stage: heating to 90°C at a rate of 2°C / min and maintaining the temperature for 30 min; The vacuum degree is 0.09 MPa, and after drying, the dried aramid pulp C is obtained by cooling to 20° C. at a natural cooling rate.

[0050] Step 4: The dried aramid pulp C is subjected to a secondary de-linting treatment by an opener, wherein the opener adopts a FLO-80 model double-toothed roller high-efficiency opener with a feed rate of 20 kg / min, and finally high-quality aramid pulp D is prepared.

[0051] The aramid pulp prepared in Example 3 has excellent performance: beating degree 46.7°SR, specific surface area 10.7 m 2 / g, branching density 126 branches / mm, moisture content 4.6%, thermal decomposition temperature 460℃.

[0052] Example 4 Step 1: remove impurities through an XFS-100 multi-stage screening machine (first-stage sieve hole 13 mm, second-stage sieve hole 4 mm), and then immerse in an alkaline solution system, which consists of a 6wt% sodium hydroxide solution and a 3wt% hydrogen peroxide solution in a volume ratio of 3:1, and react for 46 minutes to obtain pretreated fiber A.

[0053] Step 2: The pretreated fiber A was cut into 4 mm lengths and then mechanically broomed using a CMF-300 brooming and rolling machine with a line speed of 5 m / min, a pressure of 0.3 MPa, and a feed rate of 28 kg / min. After rolling, it was transferred to a ZDG-200HC beater with a concentration of 14%, a time of 4 hours, and a pressure of 0.6 MPa. During refining, an FZ-102 disc refiner was used to inject alkali solution to assist refining. The refining power was 2 kW, the refining time was 1 hour, and the pressure was 600 Pa. The alkaline solution was a 5 wt% sodium hydroxide or potassium hydroxide solution with a pH of 9. During mixing, the volume ratio of the pulp to the alkaline solution was 10:5. After refining, a mixed pulp B was obtained.

[0054] Step 3: Centrifuge the mixed slurry B three times in sequence: First cleaning: centrifugal speed is 3200r / min, feed rate is 16L / min, filter mesh size is 160 mesh, and cleaning time is 26min; Second cleaning: centrifugal speed is 4200r / min, feed rate is 11L / min, filter mesh size is 360 mesh, and cleaning time is 23min; The third cleaning: the centrifugal speed is 5200r / min, the feed rate is 6L / min, the filter mesh size is 560 mesh, and the cleaning time is 20min.

[0055] After each washing, the water content was replaced with deionized water (water-to-material volume ratio 5:1), and finally aramid pulp fiber with a moisture content of 16% was obtained.

[0056] The water-containing aramid pulp fiber is then subjected to gradient drying under vacuum conditions: Stage 1: Heating at a rate of 4°C / min to 50°C and maintaining the temperature for 36 minutes; The second stage: heating to 80°C at a rate of 2°C / min and maintaining the temperature for 26 min; The vacuum degree is 0.06 MPa, and after drying, the dried aramid pulp C is obtained by cooling to 20° C. at a natural cooling rate.

[0057] Step 4: The dried aramid pulp C is subjected to secondary depilation treatment by an opener, wherein the opener adopts a FLO-80 double-toothed roller high-efficiency opener with a feed rate of 16 kg / min, and finally high-quality aramid pulp D is prepared. The aramid pulp prepared in Example 1 has excellent performance: beating degree is 48.5°SR, specific surface area is 12.6 m 2 / g, the branching density is 110 branches / mm, the moisture content is 6.2%, and the thermal decomposition temperature is 520℃.

[0058] Example 5 Step 1: remove impurities through an XFS-100 multi-stage screening machine (first-stage sieve hole 18 mm, second-stage sieve hole 4 mm), and then immerse in an alkaline solution system, which is an 8wt% sodium hydroxide solution and a 2wt% hydrogen peroxide solution in a volume ratio of 4:1, and react for 48 minutes to obtain pretreated fiber A.

[0059] Step 2: The pretreated fiber A was cut into 8mm lengths and then mechanically broomed using a CMF-300 brooming and rolling machine with a line speed of 4m / min, a pressure of 0.4MPa, and a feed rate of 28kg / min. After rolling, it was transferred to a ZDG-200HC beater at a concentration of 18%, a time of 4h, and a pressure of 0.8MPa. During refining, an FZ-102 disc refiner was used to inject alkali solution to assist refining. The refining power was 2kW, the refining time was 1h, and the pressure was 800Pa. The alkaline solution was an 8wt% sodium hydroxide or potassium hydroxide solution with a pH of 8. During mixing, the volume ratio of the pulp to the alkaline solution was 10:4. After refining, a mixed pulp B was obtained.

[0060] Step 3, centrifugation washing the mixed slurry B three times in sequence; First cleaning: centrifugal speed is 3800r / min, feed rate is 18L / min, filter mesh size is 180 mesh, and cleaning time is 18min; Second cleaning: centrifugal speed is 4800r / min, feed rate is 13L / min, filter mesh size is 380 mesh, and cleaning time is 15min; The third cleaning: the centrifugal speed is 5800r / min, the feed rate is 8L / min, the filter mesh size is 380 mesh, and the cleaning time is 12min.

[0061] After each washing, the water content was replaced with deionized water (water-to-material volume ratio 4:1), and finally aramid pulp fiber with a moisture content of 18% was obtained.

[0062] The water-containing aramid pulp fiber is then subjected to gradient drying under vacuum conditions: Stage 1: Heating at a rate of 4°C / min to 58°C and maintaining the temperature for 38 minutes; The second stage: heating to 88°C at a rate of 2°C / min and maintaining the temperature for 28 min; The vacuum degree is 0.08 MPa, and after drying, the dried aramid pulp C is obtained by cooling to 20° C. at a natural cooling rate.

[0063] Step 4: The dried aramid pulp C is subjected to a secondary de-fluffing treatment by an opener, wherein the opener adopts a FLO-80 double-toothed roller high-efficiency opener with a feed rate of 18 kg / min, and finally high-quality aramid pulp D is prepared.

[0064] The aramid pulp prepared in Example 5 has excellent performance: beating degree 48.5°SR, specific surface area 12.8 m 2 / g, branching density 110 branches / mm, moisture content 3.8%, thermal decomposition temperature 540℃.

[0065] The present invention also discloses aramid pulp prepared by a method for preparing recycled aramid pulp through mechanical force induced brooming. The aramid pulp has a high specific surface area, rich bifurcation structure and excellent gripping force, and can be applied to special paper, friction plates, and sealing gaskets, significantly improving the grade of the products.

[0066] The above description is merely 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 replacements, and these modifications and replacements are also within the scope of protection covered by the claims.

Claims

1. A method for preparing recycled aramid pulp by mechanical force induced brooming, characterized in that: The following steps are involved: Step 1: Physically screening and chemically stripping the waste aramid fiber raw material to obtain pretreated fiber A; Step 2: After the pretreated fiber A is cut, it is subjected to mechanical coupling treatments of thread rolling, beating and alkali solution-assisted refining in sequence to obtain a mechanical force-induced brooming mixed pulp B; Step 3: The mechanically broomed mixed pulp B is subjected to multi-stage centrifugal washing, and then subjected to a stepwise temperature-raising drying process to obtain a dry aramid pulp C; Step 4: De-linting the dried aramid pulp C to prepare recycled aramid pulp D.

2. The method for preparing recycled aramid pulp by mechanical force induced brooming according to claim 1, characterized in that: In step 1, two-stage sieves are used for physical screening, the aperture of the first-stage sieve is 10-20 mm, and the aperture of the second-stage sieve is 2-5 mm.

3. The method for preparing recycled aramid pulp by mechanical force induced brooming according to claim 1, characterized in that: In step 1, the physically screened raw material is immersed in an alkaline solution system for chemical stripping for 40 to 60 minutes to obtain pretreated fiber A; wherein the alkaline solution system includes a sodium hydroxide solution with a concentration of 5 wt% to 15 wt% and a hydrogen peroxide solution with a volume ratio of 1 wt% to 3 wt% and a volume ratio of 3:1 to 5:

1.

4. The method for preparing recycled aramid pulp by mechanical force induced brooming according to claim 1, characterized in that: In step 2, the pretreated fiber A is cut into a length of 4 to 12 mm; during the thread rolling, the linear speed of the thread rolling machine is 3 to 6 m / min, the pressure is 0.3 to 0.5 MPa, a thread rolling roller with a fine serrated surface is used, and the feed rate is 25 to 35 kg / min.

5. The method for preparing recycled aramid pulp by mechanical force induced brooming according to claim 1, characterized in that: In step 2, during beating, the beating concentration is 12% to 18%, the time is 2 to 5 hours, and the pressure is 0.6 to 0.8 MPa; During refining, the refining power is 2 to 8 kW, the refining time is 1 to 13 h, and the pressure is 500 to 800 Pa.

6. The method for preparing recycled aramid pulp by mechanical force induced brooming 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 2 to 10 wt% and a pH value of 8 to 9; during mixing, the volume ratio of the slurry to the alkaline solution is (10:2) to (10:6).

7. The method for preparing recycled aramid pulp by mechanical force induced brooming according to claim 1, characterized in that: In step 3, the multi-stage centrifugal cleaning is a three-stage gradient centrifugal cleaning process, and the centrifugal speed of each time is in the range of 3000-6000 r / min and increases gradually; the cleaning time of each time is in the range of 10-30 minutes and decreases gradually; the total processing time of the three centrifugal steps is controlled within 30-90 minutes, and the moisture content of the aramid pulp fiber after cleaning is 12%-18%.

8. The method for preparing recycled aramid pulp by mechanical force induced brooming according to claim 1, characterized in that: In step 3, gradient drying adopts programmed temperature control mode; In the first stage, the temperature is raised to 50-70°C at a rate of 2-5°C / min and kept constant for 30-50 minutes; In the second stage, the temperature is raised to 80-100°C at a rate of 1-3°C / min and kept constant for 20-40 minutes; The drying is carried out under a vacuum degree of 0.06 to 0.12 MPa. After the drying is completed, the temperature is naturally lowered to below 20° C. to obtain the dried aramid pulp C.

9. The method for preparing recycled aramid pulp by mechanical force induced brooming according to claim 1, characterized in that: In step 4, a double-toothed roller high-efficiency opening machine is used for depilation, and the feed rate is 15 to 25 kg / min.

10. Aramid pulp prepared by the method for preparing recycled aramid pulp by mechanical force induced brooming according to any one of claims 1 to 9.

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