Phosphogypsum whisker / fiber reinforced composite material and preparation method thereof

Abstract

The invention discloses a phosphogypsum whisker / fiber reinforced composite material and a preparation method thereof, and belongs to the technical field of composite materials. The composite material is prepared from the following raw materials: cashew nut oil modified phenolic resin, ardealite whiskers, rice hull-based biomass charcoal, chopped carbon fibers, aramid pulp, chopped basalt fibers, fluororubber, nano titanium oxide, filler, a curing agent, a plasticizer and an antioxidant. Mechanical bearing is strengthened through magnetic field directional arrangement, and the thermal stability, the frictional wear performance and the corrosion resistance and weather resistance are synergistically improved by means of functional components. The prepared composite material is excellent in mechanical strength, good in thermal stability and stable in high-temperature friction performance, high-value utilization of industrial ardealite solid waste is achieved, the process is simple, industrial feasibility is high, and the composite material can be widely applied to the fields of friction materials, building structural parts, automobile parts and the like.

Description

Technical Field

[0001] This invention relates to the field of composite material technology, specifically to a phosphogypsum whisker / fiber reinforced composite material and its preparation method. Background Technology

[0002] Phosphogypsum whiskers (mainly composed of CaSO4-W) are calcium sulfate whiskers prepared from phosphogypsum, an industrial byproduct. They are a new type of green and environmentally friendly functional material. Essentially, they are fibrous single crystals of anhydrous or hemihydrate calcium sulfate with a unique needle-like or fibrous structure. Applying them to composite materials is one of the main ways to utilize phosphogypsum resources.

[0003] Existing technologies for phosphogypsum whisker-reinforced materials employ only a single modification method, resulting in disordered fiber distribution. This makes the phosphogypsum whiskers prone to agglomeration and leads to uneven interfacial bonding between the reinforcing fibers and the resin matrix. Under stress, localized stress concentration is likely to occur, resulting in limited improvement in the mechanical properties (tensile, flexural strength, and flexural fatigue resistance) of the composite material. Furthermore, it is impossible to achieve a comprehensive optimization that simultaneously considers corrosion resistance, weather resistance, and flame retardancy. This makes it difficult to meet the application requirements of high-performance structural components in fields such as construction, automobiles, equipment, and transportation, and also limits the high-value resource utilization of industrial phosphogypsum solid waste. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a phosphogypsum whisker / fiber reinforced composite material and its preparation method, thus solving the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solution: a phosphogypsum whisker / fiber reinforced composite material, wherein the composite material comprises the following raw materials by weight: 60-80 parts of cashew oil modified phenolic resin, 15-30 parts of phosphogypsum whiskers, 2-5 parts of rice husk-based biochar, 2-6 parts of chopped carbon fiber, 1-4 parts of aramid pulp, 2-5 parts of chopped basalt fiber, 1-4 parts of fluororubber, 0.5-2 parts of nano-titanium oxide, 3-8 parts of filler, 4-6 parts of curing agent, 1-3 parts of plasticizer, and 0.5-1 parts of antioxidant; The preparation method of the phosphogypsum whiskers is as follows: first, industrial phosphogypsum is acid-washed to remove impurities, then whiskers are prepared by hydrothermal crystal form optimization, and finally, the phosphogypsum whiskers are obtained by ultrasonic modification with silane coupling agent. The filler is alumina, calcium carbonate, zinc oxide, kaolin, barium sulfate, and graphite.

[0006] Preferably, the phosphogypsum whiskers, the chopped carbon fibers, and the chopped basalt fibers undergo graded modification and directional arrangement treatment. The graded modification step is as follows: The modified phosphogypsum whiskers were sieved to obtain three particle size groups with corresponding lengths of 10-50 μm, 50-100 μm, and 100-200 μm. The phosphogypsum whiskers of the three particle size groups were respectively mixed with the chopped carbon fibers and the chopped basalt fibers at a mass ratio of 3:1:1 to obtain three mixtures. The three mixtures were then modified a second time using 3% by mass of KH560, KH570 and KH792 silane coupling agents respectively. After modification, the three mixtures were compounded in a mass ratio of 2:3:1 to obtain a fiber-reinforced composite material. The directional arrangement process involves applying a directional magnetic field of 0.2–0.5T during the molding of the composite material, causing the mixed fibers of the composite material to align along the direction of the applied force.

[0007] Preferably, the rice husk-based biochar is a pore-enlarged modified biochar, and the pore-enlargement method of the rice husk-based biochar is as follows: The rice husk-based biochar was mixed with a 10% potassium hydroxide solution at a solid-liquid ratio of 1:15 and stirred at 80°C for 2 hours to obtain a mixture. The mixture was activated at 800°C for 1 hour under a nitrogen atmosphere, cooled, washed until neutral, and dried to obtain the modified biochar with a specific surface area of ​​500-600 m². 2 / g.

[0008] Preferably, the acid washing and impurity removal process for preparing the phosphogypsum whiskers specifically includes: The industrial phosphogypsum was mixed with 5% dilute hydrochloric acid at a solid-liquid ratio of 1:8, stirred at 30°C for 60 minutes, filtered, washed until neutral, and then dried to obtain phosphogypsum. The specific process for optimizing the hydrothermal crystal structure of phosphogypsum whiskers is as follows: The acid-washed phosphogypsum was mixed with water at a solid-liquid ratio of 1:40 to form a slurry. 3% by weight of magnesium sulfate crystal growth promoter was added to the phosphogypsum. The mixture was then subjected to hydrothermal reaction at 130°C and 0.3 MPa for 4 hours. After filtration and drying, the reactants were ultrasonically modified with a silane coupling agent to obtain phosphogypsum whiskers of the target size.

[0009] Preferably, the phosphogypsum whiskers have a length of 10-200 μm and a diameter of 1-50 μm; The cashew oil-modified phenolic resin is a light yellow powder with a flowability of 25-40 mm, a polymerization time of 40-65 s at 150℃, a free phenol content of 2%-4%, a hexamethylenetetramine content of 9.0%-10.0%, and a particle size of 200 mesh.

[0010] Preferably, the chopped carbon fibers have a length of 2.0-6.0 mm, a diameter of 10 μm, a tensile strength ≥200 ksi, a modulus of 100-135 Msi, and a carbon content ≥99%; The aramid pulp has a length of 2 mm, a diameter of 12 μm, a tensile strength ≥3.6 GPa, and a modulus of 100-150 GPa; the chopped basalt fiber has a length of 3-6 mm and a diameter of 17 μm. The fluororubber is FKM26, with a fluorine content of approximately 66%, and is used to synergistically improve the corrosion resistance of the composite material with the raw materials. The nano-titanium oxide is rutile and oily, with an average particle size of about 200 nm, and is used to improve the weather resistance and wear resistance of the composite material. All fillers are industrial grade with a particle size of 150-1250 mesh.

[0011] A method for preparing a phosphogypsum whisker / fiber reinforced composite material includes the following steps: S1. Phosphogypsum is modified to obtain phosphogypsum whiskers. The phosphogypsum whiskers are then combined with chopped carbon fibers and chopped basalt fibers through graded modification and shaping to obtain a fiber composite material. S2. Modify the rice husk-based biochar. After the modification is completed, cool the modified rice husk-based biochar to room temperature. Place the modified rice husk-based biochar and nano-titanium oxide into a high-speed mixer and premix for 10-15 minutes at a speed of 800-1000 r / min to allow the nano-titanium oxide to be uniformly adsorbed into the pores of the rice husk-based biochar, thus obtaining a composite filler for later use. S3. Add cashew oil-modified phenolic resin and fluororubber to a mixer and premix for 5-8 minutes at a temperature of 110-120℃ and a speed of 50-60r / min, so that the fluororubber is completely melted and uniformly dispersed in the matrix of cashew oil-modified phenolic resin, and a resin premix is ​​obtained for later use. S4. The composite filler, aramid pulp, filler, curing agent, plasticizer and antioxidant are added to the resin premix in sequence and mixed. Then the fiber mixture is added and mixed in an internal mixer. After mixing, the composite material is obtained by magnetic field-assisted molding and curing.

[0012] Preferably, the magnetic field-assisted molding in step S4 specifically involves: The mixed material is placed into the molding mold of the magnetic field forming press, and the magnetic field generator is activated to apply a 0.2-0.5T directional magnetic field. The direction of the magnetic field is consistent with the actual stress direction of the composite material. The molding die is fed into a magnetic field forming press. It is first pre-pressed at 150℃ and 15MPa for 5 minutes to remove air bubbles inside the material. Then, the temperature is raised to 170℃ and the pressure is increased to 20MPa. The material is then hot-pressed at constant temperature and pressure for 30 minutes to obtain the initial product.

[0013] Preferably, the curing process in step S4 specifically includes: After molding, turn off the magnetic field, remove the molding mold and the initial material product, put the initial material product into the oven, raise the temperature to 120℃ at a heating rate of 5-8℃ / min, keep it at the temperature for 2 hours, and then raise it to 150℃ at the same heating rate and keep it at the temperature for 2 hours. After the heat preservation is completed, the oven is closed, allowing the initial material product to cool naturally to room temperature with the oven, avoiding forced cooling that could generate internal stress. After cooling, the composite material is obtained.

[0014] Preferably, the mixing temperature of the internal mixer is 120-130℃, the mixing speed is 60r / min, and the mixing time is 15-20min.

[0015] This invention provides a phosphogypsum whisker / fiber reinforced composite material and its preparation method. It has the following beneficial effects: (1) The composite form of phosphogypsum whiskers and various reinforcing fibers was optimized. Through the composite preparation form of graded modification and fixed arrangement, the aggregation phenomenon of phosphogypsum whiskers was effectively improved, the uniformity of the interface bonding between the reinforcing fibers and the cashew oil modified phenolic resin matrix was improved, the problem of local stress concentration under stress was reduced, and the overall stress transmission efficiency of the composite material was enhanced, resulting in a significant improvement in the mechanical properties of the composite material and promoting the transformation of industrial phosphogypsum solid waste from low-value-added disposal to high-value utilization.

[0016] (2) Through the synergistic effect of each functional component with the reinforcing fiber and resin matrix, the mechanical properties are improved while the corrosion resistance, weather resistance and flame retardancy are optimized. This avoids the problem of improving a single property while deteriorating other properties, and achieves the effect of multi-property synergistic adaptation. This ensures the expansion of the application scenarios of composite materials and can meet the diverse needs of high-performance structural components in fields such as construction, automobiles, equipment and transportation. For example, its application in automobile brake pads enhances the applicability of reinforced composite materials in different fields.

[0017] (3) Using industrial phosphogypsum as the core raw material to prepare reinforced whiskers, combined with green components such as rice husk-based biochar, not only reduces the raw material cost of composite materials, but also realizes the resource-based disposal of two types of solid waste. Moreover, the preparation process does not require special and complex equipment, achieving the effect of balancing environmental and economic benefits, thus promoting the practical application of solid waste resource utilization technology and providing a foundation for the high-value utilization of industrial solid waste. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating the preparation steps of the composite material of the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0020] Please see Figure 1 This invention provides a phosphogypsum whisker / fiber reinforced composite material and its preparation method. To achieve the above objectives, this invention is implemented through the following technical solution: A phosphogypsum whisker / fiber reinforced composite material, the composite material comprising the following raw materials by weight: 60-80 parts of cashew oil modified phenolic resin, 15-30 parts of phosphogypsum whiskers, 2-5 parts of rice husk-based biochar, 2-6 parts of chopped carbon fiber, 1-4 parts of aramid pulp, 2-5 parts of chopped basalt fiber, 1-4 parts of fluororubber, 0.5-2 parts of nano-titanium oxide, 3-8 parts of filler, 4-6 parts of curing agent, 1-3 parts of plasticizer, and 0.5-1 parts of antioxidant; The preparation method of phosphogypsum whiskers is as follows: first, industrial phosphogypsum is acid-washed to remove impurities, then whiskers are prepared by hydrothermal crystal form optimization, and finally, phosphogypsum whiskers are obtained by ultrasonic modification with silane coupling agent. The fillers are alumina, calcium carbonate, zinc oxide, kaolin, barium sulfate, and graphite.

[0021] Phospholipid whiskers, chopped carbon fibers, and chopped basalt fibers undergo graded modification and directional arrangement treatment. The graded modification steps are as follows: The modified phosphogypsum whiskers were sieved to obtain three particle size groups with corresponding lengths of 10-50μm, 50-100μm and 100-200μm. Three phosphogypsum whiskers of three different particle sizes were mixed with chopped carbon fiber and chopped basalt fiber at a mass ratio of 3:1:1 to obtain three mixtures. The three mixtures were then modified a second time using 3% by mass of KH560, KH570 and KH792 silane coupling agents respectively. After modification, the three mixtures were compounded in a mass ratio of 2:3:1 to obtain a fiber-reinforced composite material. Oriented arrangement treatment involves applying a directional magnetic field of 0.2–0.5T during the molding process of the composite material, causing the mixed fibers of the composite material to align along the direction of the force.

[0022] Rice husk-based biochar is a pore-enlarged modified biochar. The pore-enlargement method for rice husk-based biochar is as follows: Rice husk-based biochar was mixed with a 10% potassium hydroxide solution at a solid-liquid ratio of 1:15 and stirred at 80°C for 2 hours to obtain a mixture. The mixture was activated at 800℃ for 1 hour under a nitrogen atmosphere, cooled, washed until neutral, and dried to obtain the modified biochar with a specific surface area of ​​500-600 m². 2 / g.

[0023] The acid washing and impurity removal process for preparing phosphogypsum whiskers specifically includes: Industrial phosphogypsum was mixed with 5% dilute hydrochloric acid at a solid-liquid ratio of 1:8, stirred at 30°C for 60 minutes, filtered, washed until neutral, and then dried to obtain phosphogypsum. The specific process for optimizing the hydrothermal crystal form of phosphogypsum whiskers is as follows: The acid-washed phosphogypsum was mixed with water at a solid-liquid ratio of 1:40 to form a slurry. 3% magnesium sulfate crystal growth promoter by weight of phosphogypsum was added, and the mixture was subjected to hydrothermal reaction at 130℃ and 0.3MPa for 4 hours. The reactants were then filtered, dried, and ultrasonically modified with a silane coupling agent to obtain phosphogypsum whiskers of the target size.

[0024] The whiskers of phosphogypsum have a length of 10-200 μm and a diameter of 1-50 μm; Cashew oil-modified phenolic resin is a light yellow powder with a flowability of 25-40 mm, a polymerization time of 40-65 s at 150℃, a free phenol content of 2%-4%, a hexamethylenetetramine content of 9.0%-10.0%, and a particle size of 200 mesh.

[0025] Short-cut carbon fibers have a length of 2.0–6.0 mm, a diameter of 10 μm, a tensile strength ≥200 ksi, a modulus of 100–135 Msi, and a carbon content ≥99%. Aramid pulp has a length of 2 mm and a diameter of 12 μm, a tensile strength ≥3.6 GPa, and a modulus of 100-150 GPa; chopped basalt fibers have a length of 3-6 mm and a diameter of 17 μm. The fluororubber is FKM26, with a fluorine content of approximately 66%, and is used in conjunction with the raw materials to synergistically improve the corrosion resistance of the composite material. Nano-titanium oxide is rutile and oily, with an average particle size of approximately 200 nm, and is used to improve the weather resistance and wear resistance of composite materials. All fillers are industrial grade, with a particle size of 150-1250 mesh.

[0026] A method for preparing phosphogypsum whisker / fiber reinforced composite materials includes the following steps: S1. Phosphogypsum was modified to obtain phosphogypsum whiskers. The phosphogypsum whiskers were then combined with chopped carbon fibers and chopped basalt fibers through graded modification and shaping to obtain a fiber composite material. S2. Modify the rice husk-based biochar. After the modification is completed, cool it to room temperature. Put the modified rice husk-based biochar and nano-titanium oxide into a high-speed mixer and premix for 10-15 minutes at a speed of 800-1000 r / min to make the nano-titanium oxide uniformly adsorbed in the pores of the rice husk-based biochar, and obtain the composite filler for later use. S3. Add cashew oil-modified phenolic resin and fluororubber to a mixer and premix for 5-8 minutes at a temperature of 110-120℃ and a speed of 50-60r / min, so that the fluororubber is completely melted and uniformly dispersed in the cashew oil-modified phenolic resin matrix to obtain a resin premix for later use. S4. Add composite filler, aramid pulp, filler, curing agent, plasticizer and antioxidant to the resin premix in sequence and mix. Then add fiber mixture and mix in an internal mixer. After mixing, use magnetic field-assisted molding and curing treatment to obtain composite material.

[0027] The magnetic field-assisted molding process in step S4 specifically involves: The mixed material is placed into the molding mold of the magnetic field forming press. Cashew oil modified phenolic resin and fluororubber are added to the internal mixer and premixed for 5-8 minutes at a temperature of 110-120℃ and a speed of 50-60 r / min. Under these process conditions, the cashew oil modified phenolic resin is in a semi-molten state (viscosity 500-1500 Pa·s) rather than a completely solidified dense block. The mixed material is a fluffy agglomerate. The fibers (phosphogypsum whiskers, chopped carbon fibers, basalt fibers) in the material are not completely wrapped and bound by the resin. There are still movable gaps between the fibers, which reserve space for magnetic field-induced orientation. At this time, the magnetic field generator is started to apply a 0.2-0.5T directional magnetic field. The direction of the magnetic field is consistent with the actual stress direction of the composite material. The molding die is fed into a magnetic field molding press. It is first pre-pressed at 150℃ and 15MPa for 5 minutes to remove air bubbles inside the material. Then, the temperature is raised to 170℃ and the pressure is increased to 20MPa. It is then hot-pressed at constant temperature and pressure for 30 minutes to obtain the initial product of the material. The material in the molding die is first pre-pressed to remove air bubbles (150℃ / 15MPa / 5min) and then hot-pressed (170℃ / 20MPa / 30min). During the pre-pressing stage, only air bubbles inside the material are removed, and the fibers in the material are not completely compacted. At this time, the magnetic field continues to act, and the fibers in the material can slowly adjust their direction in the semi-molten state of the cashew oil modified phenolic resin. Finally, they are oriented along the direction of the magnetic field (force). The subsequent hot-pressing stage fixes the oriented fiber morphology to form a stable gradient reinforcement structure.

[0028] The curing process in step S4 is specifically as follows: After molding, turn off the magnetic field, remove the molding mold and the initial material product, put the initial material product into the oven, raise the temperature to 120℃ at a heating rate of 5-8℃ / min, keep it at the temperature for 2 hours, and then raise it to 150℃ at the same heating rate and keep it at the temperature for 2 hours. After the heat preservation is completed, the oven is closed, allowing the initial material product to cool naturally to room temperature with the oven, avoiding forced cooling that could generate internal stress. After cooling, the composite material is obtained.

[0029] The mixing temperature of the internal mixer is 120-130℃, the mixing speed is 60r / min, and the mixing time is 15-20min.

[0030] The raw materials used in the preparation of the reinforced composite materials in the following examples and comparative examples include: Cashew oil modified phenolic resin: pale yellow powder, flowability 32 mm, polymerization time 52 s at 150℃, free phenol content 3%, hexamethylenetetramine content 9.5%, particle size 200 mesh; Phosphogypsum whiskers: 10-200μm in length and 1-50μm in diameter, modified by ultrasonic treatment with 1% KH550; Rice husk-based biochar: modified by pore expansion according to the process of claim 3, with a specific surface area of ​​550 m². 2 / g; Short-cut carbon fiber: 4.0 mm in length, 10 μm in diameter, tensile strength 220 ksi, modulus 120 Msi, carbon content 99.5%; Aramid pulp: length 2mm, diameter 12μm, tensile strength 3.8GPa, modulus 130GPa; Short-cut basalt fibers: 4.5 mm in length and 17 μm in diameter; Fluororubber (FKM26): Fluorine content 66%; Nano titanium dioxide: rutile type, oily, average particle size 200nm; Filler: Calcium carbonate (industrial grade, 800 mesh); Curing agent: hexamethylenetetramine; plasticizer: dibutyl phthalate; antioxidant: 1010.

[0031] Example 1 By weight, take 70 parts of cashew oil modified phenolic resin, 25 parts of phosphogypsum whiskers, 4 parts of expanded pore rice husk-based biochar, 4 parts of short-cut carbon fiber, 3 parts of aramid pulp, 4 parts of short-cut basalt fiber, 3 parts of fluororubber, 1.5 parts of nano titanium dioxide, 6 parts of calcium carbonate, 5 parts of curing agent, 2 parts of plasticizer and 0.8 parts of antioxidant; The preparation steps are as follows: S1: Phosphogypsum whiskers are graded and modified (three groups of 10-50μm, 50-100μm, and 100-200μm are compounded in a ratio of 2:3:1, and then modified twice with 3% KH560, KH570, and KH792 respectively), and then compounded with short-cut carbon fibers and basalt fibers to obtain fiber composite materials; S2: Rice husk-based biochar and nano-titanium oxide were premixed at 900 r / min for 12 min to obtain a composite filler; S3: Resin and fluororubber are premixed at 115℃ and 55r / min for 6min to obtain resin premix; S4: Add composite filler, aramid pulp, calcium carbonate, curing agent, plasticizer and antioxidant in sequence, then add fiber mixture, and mix at 125℃ and 60r / min for 18min; Subsequently, the material was cured in an oven using the following parameters: 0.3T directional magnetic field assisted molding (150℃ / 15MPa pre-pressing for 5 min, 170℃ / 20MPa hot pressing for 30 min), followed by heating to 120℃ at a rate of 5-8℃ / min, holding for 2 h, and then heating to 150℃ at the same rate and holding for 2 h. After curing, the material was cooled to obtain the composite material.

[0032] Example 2 By weight, take 65 parts of cashew oil modified phenolic resin, 20 parts of phosphogypsum whiskers, 3 parts of expanded pore rice husk-based biochar, 3 parts of short-cut carbon fiber, 2 parts of aramid pulp, 3 parts of short-cut basalt fiber, 2 parts of fluororubber, 1 part of nano titanium dioxide, 5 parts of calcium carbonate, 5 parts of curing agent, 2 parts of plasticizer and 0.7 parts of antioxidant. The difference between the preparation process and Example 1 is that the magnetic field strength is adjusted to 0.4T and the mixing time is adjusted to 19min. The rest of the preparation process is the same as that of Example 1.

[0033] Example 3 By weight, take 75 parts of cashew oil modified phenolic resin, 28 parts of phosphogypsum whiskers, 4 parts of expanded pore rice husk-based biochar, 5 parts of short-cut carbon fiber, 3 parts of aramid pulp, 4 parts of short-cut basalt fiber, 3 parts of fluororubber, 1.8 parts of nano titanium dioxide, 7 parts of calcium carbonate, 5 parts of curing agent, 2 parts of plasticizer and 0.9 parts of antioxidant; The difference between the preparation process and Example 1 is that the magnetic field strength is adjusted to 0.45T and the mixing time is adjusted to 20min. The rest of the preparation process is the same as that of Example 1.

[0034] Example 4 By weight, take 80 parts of cashew oil modified phenolic resin, 30 parts of phosphogypsum whiskers, 5 parts of pore-expanded rice husk-based biochar, 6 parts of short-cut carbon fiber, 4 parts of aramid pulp, 5 parts of short-cut basalt fiber, 4 parts of fluororubber, 2 parts of nano titanium dioxide, 8 parts of calcium carbonate, 6 parts of curing agent, 3 parts of plasticizer and 1 part of antioxidant. The difference between the preparation process and Example 1 is that the magnetic field strength is adjusted to 0.5T and the mixing time is adjusted to 20min. The rest of the preparation process is the same as that of Example 1.

[0035] Comparative Example 1 The formulation is the same as that in Example 1, except that the phosphogypsum whiskers are only modified with 1% KH550, without sieving and grading or secondary modification, and no directional magnetic field is applied during molding. The rest of the process is the same as in Example 1.

[0036] Comparative Example 2 The formulation is the same as in Example 1, except that the rice husk-based biochar is a raw material that is not treated with potassium hydroxide to expand the pores, and the rest of the process is the same as in Example 1.

[0037] Comparative Example 3 The formulation is the same as that in Example 1, except that fluororubber and nano titanium dioxide are not added, and the rest of the process is the same as in Example 1.

[0038] Comparative Example 4 The formulation is the same as in Example 1, except that the phosphogypsum whiskers are raw materials that are directly modified with 1% KH550 and do not undergo acid washing and hydrothermal crystal form optimization. The rest of the process is the same as in Example 1.

[0039] Test case Mechanical properties: Bending strength (GB / T9341-2008, specimen size 80mm×10mm×4mm, test speed 2mm / s); Impact strength (GB / T1043.1-2008, pendulum impact testing machine, specimen size 80mm×10mm×4mm). Internal shear strength (GB / T 26739-2011, JYE-300B fully automatic constant stress testing machine, specimen size 20mm×20mm×10mm, test speed 4500N / s), to evaluate the core mechanical bearing capacity of the material; Thermal properties: A NETZSCH TG209F1 thermogravimetric analyzer was used under a nitrogen atmosphere (flow rate 50 ml / min) in a temperature range of 35-1000℃ with a heating rate of 10℃ / min to test the thermal decomposition curve (TG-DTG) and analyze the thermal stability and residual mass percentage. Friction and wear performance: The coefficient of friction and wear rate (unit: 10) were tested using an XD-MSM constant-speed friction performance testing machine at temperatures of 100℃, 200℃, 300℃, and 350℃. -7 cm 3 •N -1 ・m -1 ), to adapt to potential friction application scenarios of materials.

[0040] Table 1 shows the mechanical property test data of the sample materials: ; Table 2 shows the test data for the thermal properties and frictional performance of the sample materials: ; Additional notes: Thermal properties: The maximum thermal decomposition rate of Examples 1-4 at 300-600℃ (the main decomposition range of phenolic resin) is 0.12%-0.15% / ℃, which is lower than that of the comparative example (0.18%-0.22% / ℃), indicating that the thermal stability is better; Friction temperature adaptability: The friction coefficient of Example 1 fluctuated between 0.27 and 0.35 in the range of 100-350℃, with a fluctuation range of only 29.6%, which is lower than the 44.8% of Comparative Example 1, indicating better resistance to thermal degradation.

[0041] As shown in Tables 1 and 2, the overall performance of Examples 1-4 is significantly better than that of Comparative Examples 1-4. Example 1 has the best performance in all aspects, with bending strength, impact strength, and internal shear strength increasing by 28.7%, 69.0%, and 30.7% respectively compared to Comparative Example 1 (lacking graded modification and directional arrangement). This indicates that the graded differential secondary modification and magnetic field directional arrangement of phosphogypsum whiskers solve the problems of fiber agglomeration and uneven interface bonding caused by traditional single modification, and achieve synergistic enhancement of mechanical properties. In terms of tribological performance, the wear rate of Example 1 at 350℃ was reduced by 47.8% compared with Comparative Example 1, and the friction coefficient fluctuated less over a wide temperature range. This is because the directionally arranged fiber-mixed material forms a stable friction film during the friction process, which bears more load and reduces matrix peeling, verifying the conclusion that fiber synergistic reinforcement can improve friction stability. At the same time, the uniform adsorption of nano-titanium oxide by the expanded pore rice husk-based biochar further optimizes the continuity of the wear surface and reduces the wear rate. In terms of thermal performance, the residual mass rate at 800°C of the example is more than 15% higher than that of the comparative example on average, and the thermal decomposition rate in the main decomposition range is lower. This is due to the improvement of thermal stability by nano-titanium oxide on the one hand, and the graded modification and directional arrangement reduce the internal pores of the material on the other hand, reducing the impact of defects in the heat conduction process. In contrast, the comparative example 2 lacks pore-expanding modification by rice husk-based biochar, and the agglomeration of nano-titanium oxide leads to limited improvement in thermal stability. Comparative Example 4 (phosphogypsum whiskers without acid washing and hydrothermal optimization) had the worst performance, with a bending strength 26.4% lower than Example 1 and a wear rate 112.5% ​​higher. This indicates that crystal form optimization and impurity removal of phosphogypsum whiskers are prerequisites for them to exert their reinforcing effect. The systematic process of "acid washing-hydrothermal-grading modification" of this invention fully taps the reinforcing potential of phosphogypsum whiskers and realizes the high-value utilization of solid waste.

[0042] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A phosphogypsum whisker / fiber reinforced composite material, characterized in that: The composite material comprises the following raw materials by weight: 60-80 parts cashew oil modified phenolic resin, 15-30 parts phosphogypsum whiskers, 2-5 parts rice husk-based biochar, 2-6 parts chopped carbon fiber, 1-4 parts aramid pulp, 2-5 parts chopped basalt fiber, 1-4 parts fluororubber, 0.5-2 parts nano titanium dioxide, 3-8 parts filler, 4-6 parts curing agent, 1-3 parts plasticizer, and 0.5-1 part antioxidant; The preparation method of the phosphogypsum whiskers is as follows: first, industrial phosphogypsum is acid-washed to remove impurities, then whiskers are prepared by hydrothermal crystal form optimization, and finally, the phosphogypsum whiskers are obtained by ultrasonic modification with silane coupling agent. The filler is alumina, calcium carbonate, zinc oxide, kaolin, barium sulfate, and graphite.

2. The phosphogypsum whisker / fiber reinforced composite material according to claim 1, characterized in that: The phosphogypsum whiskers, the chopped carbon fibers, and the chopped basalt fibers undergo graded modification and directional arrangement treatment. The graded modification steps are as follows: The modified phosphogypsum whiskers were sieved to obtain three particle size groups with corresponding lengths of 10-50 μm, 50-100 μm, and 100-200 μm. The phosphogypsum whiskers of the three particle size groups were respectively mixed with the chopped carbon fibers and the chopped basalt fibers at a mass ratio of 3:1:1 to obtain three mixtures. The three mixtures were then modified a second time using 3% by mass of KH560, KH570 and KH792 silane coupling agents respectively. After modification, the three mixtures were compounded in a mass ratio of 2:3:1 to obtain a fiber-reinforced composite material. The directional arrangement process involves applying a directional magnetic field of 0.2–0.5T during the molding of the composite material, causing the mixed fibers of the composite material to align along the direction of the applied force.

3. The phosphogypsum whisker / fiber reinforced composite material according to claim 1, characterized in that: The rice husk-based biochar is a pore-enlarged modified biochar, and the pore-enlargement method of the rice husk-based biochar is as follows: The rice husk-based biochar was mixed with a 10% potassium hydroxide solution at a solid-liquid ratio of 1:15 and stirred at 80°C for 2 hours to obtain a mixture. The mixture was activated at 800°C for 1 hour under a nitrogen atmosphere, cooled, washed until neutral, and dried to obtain the modified biochar with a specific surface area of ​​500-600 m². 2 / g.

4. The phosphogypsum whisker / fiber reinforced composite material according to claim 1, characterized in that: The acid washing and impurity removal process for preparing phosphogypsum whiskers specifically includes: The industrial phosphogypsum was mixed with 5% dilute hydrochloric acid at a solid-liquid ratio of 1:8, stirred at 30°C for 60 minutes, filtered, washed until neutral, and then dried to obtain phosphogypsum. The specific process for optimizing the hydrothermal crystal structure of phosphogypsum whiskers is as follows: The acid-washed phosphogypsum was mixed with water at a solid-liquid ratio of 1:40 to form a slurry. 3% by weight of magnesium sulfate crystal growth promoter was added to the phosphogypsum. The mixture was then subjected to hydrothermal reaction at 130°C and 0.3 MPa for 4 hours. After filtration and drying, the reactants were ultrasonically modified with a silane coupling agent to obtain phosphogypsum whiskers of the target size.

5. The phosphogypsum whisker / fiber reinforced composite material according to claim 1, characterized in that: The phosphogypsum whiskers have a length of 10-200 μm and a diameter of 1-50 μm; The cashew oil-modified phenolic resin is a light yellow powder with a flowability of 25-40 mm, a polymerization time of 40-65 s at 150℃, a free phenol content of 2%-4%, a hexamethylenetetramine content of 9.0%-10.0%, and a particle size of 200 mesh.

6. The phosphogypsum whisker / fiber reinforced composite material according to claim 1, characterized in that: The chopped carbon fibers have a length of 2.0–6.0 mm, a diameter of 10 μm, a tensile strength ≥200 ksi, a modulus of 100–135 Msi, and a carbon content ≥99%. The aramid pulp has a length of 2 mm, a diameter of 12 μm, a tensile strength ≥3.6 GPa, and a modulus of 100-150 GPa; the chopped basalt fiber has a length of 3-6 mm and a diameter of 17 μm. The fluororubber is FKM26, with a fluorine content of approximately 66%, and is used to synergistically improve the corrosion resistance of the composite material with the raw materials. The nano-titanium oxide is rutile and oily, with an average particle size of about 200 nm, and is used to improve the weather resistance and wear resistance of the composite material. All fillers are industrial grade with a particle size of 150-1250 mesh.

7. A method for preparing a phosphogypsum whisker / fiber reinforced composite material, characterized in that: Includes the following steps: S1. Phosphogypsum is modified to obtain phosphogypsum whiskers. The phosphogypsum whiskers are then combined with chopped carbon fibers and chopped basalt fibers through graded modification and shaping to obtain a fiber composite material. S2. Modify the rice husk-based biochar. After the modification is completed, cool the modified rice husk-based biochar to room temperature. Place the modified rice husk-based biochar and nano-titanium oxide into a high-speed mixer and premix for 10-15 minutes at a speed of 800-1000 r / min to allow the nano-titanium oxide to be uniformly adsorbed into the pores of the rice husk-based biochar, thus obtaining a composite filler for later use. S3. Add cashew oil-modified phenolic resin and fluororubber to a mixer and premix for 5-8 minutes at a temperature of 110-120℃ and a speed of 50-60r / min, so that the fluororubber is completely melted and uniformly dispersed in the matrix of cashew oil-modified phenolic resin, and a resin premix is ​​obtained for later use. S4. The composite filler, aramid pulp, filler, curing agent, plasticizer and antioxidant are added to the resin premix in sequence and mixed. Then the fiber mixture is added and mixed in an internal mixer. After mixing, the composite material is obtained by magnetic field-assisted molding and curing.

8. The method for preparing a phosphogypsum whisker / fiber reinforced composite material according to claim 7, characterized in that: The magnetic field-assisted molding process in step S4 specifically involves: The mixed material is placed into the molding mold of the magnetic field forming press, and the magnetic field generator is activated to apply a 0.2-0.5T directional magnetic field. The direction of the magnetic field is consistent with the actual stress direction of the composite material. The molding die is fed into a magnetic field forming press. It is first pre-pressed at 150℃ and 15MPa for 5 minutes to remove air bubbles inside the material. Then, the temperature is raised to 170℃ and the pressure is increased to 20MPa. The material is then hot-pressed at constant temperature and pressure for 30 minutes to obtain the initial product.

9. The method for preparing a phosphogypsum whisker / fiber reinforced composite material according to claim 7, characterized in that: The curing process in step S4 is specifically as follows: After molding, turn off the magnetic field, remove the molding mold and the initial material product, put the initial material product into the oven, raise the temperature to 120℃ at a heating rate of 5-8℃ / min, keep it at the temperature for 2 hours, and then raise it to 150℃ at the same heating rate and keep it at the temperature for 2 hours. After the heat preservation is completed, the oven is closed, allowing the initial material product to cool naturally to room temperature with the oven, avoiding forced cooling that could generate internal stress. After cooling, the composite material is obtained.

10. The method for preparing a phosphogypsum whisker / fiber reinforced composite material according to claim 7, characterized in that: The mixing temperature of the internal mixer is 120-130℃, the mixing speed is 60r / min, and the mixing time is 15-20min.

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