Preparation method of high-performance brake pad based on recycled carbon fiber / aramid pulp composite system

Abstract

The invention discloses a high-performance brake pad preparation method based on a recycled carbon fiber / aramid pulp composite system. According to the method, pretreated recycled carbon fibers and aramid pulp are used as main reinforcing matrixes, interlocking and synergistic toughening of the two fibers on a microstructure are achieved through reasonable matching and uniform mixing, and a continuous high-strength composite matrix is formed by introducing thermosetting resin. And then a hot press molding process is adopted, and the brake pad which is compact in structure and stable in performance is obtained through pressure maintaining cooling and machining. By means of the method, efficient recycling of the waste carbon fibers is achieved, the mechanical property and friction stability of the material are improved through the fibration characteristic of the aramid pulp, and therefore the problems that a traditional brake pad is large in noise and poor in durability are effectively solved, and the method has the environment-friendly and engineering application value.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of friction materials, in particular to a preparation method of high-performance brake pad based on recycled carbon fiber / aramid pulp composite system, which is especially suitable for automobile, rail transportation and industrial machinery braking systems. BACKGROUND

[0002] Traditional brake pads widely use semi-metallic or ceramic-based composite materials, but these material systems have obvious technical limitations, which seriously restrict the further improvement of braking performance. Semi-metallic materials use iron, copper and other metal powders as the main reinforcing phase, with a density of 5–7 g / cm 3 , resulting in heavy weight and high rotational inertia of the braking components, which not only increases the energy consumption of the whole vehicle, but also accelerates the wear of the suspension system. More importantly, the metal matrix is prone to induce high-frequency vibration during high-speed braking, producing brake noise exceeding 75 dB(A), which seriously affects the driving comfort. Although ceramic-based materials exhibit excellent friction stability at high temperature, their intrinsic brittleness leads to insufficient impact resistance, and the cost of raw material preparation and sintering processing is more than 50% higher than that of semi-metallic materials, which restricts their large-scale commercial application. Most importantly, both types of materials exhibit significant thermal decay effect during continuous braking, with a decrease in friction coefficient of 20–30%, and a corresponding increase in braking distance of 15–20%, which directly threatens the safety of driving. In addition, the traditional mixing process is difficult to achieve ideal dispersion of the reinforcing phase, and local aggregation or composition segregation leads to uneven material structure, resulting in a fluctuation amplitude of wear rate exceeding 10%, and the product consistency and reliability are difficult to meet the requirements of high-end braking systems.

[0003] Carbon fiber is a lightweight (density about 1.8 g / cm 3 ), high-strength and high-temperature-resistant functional material, which can be used stably at 2,000–3,000℃ under inert atmosphere. It is considered as a potential alternative to traditional materials due to its excellent mechanical properties and thermal stability. However, the existing preparation technology of carbon fiber brake pads still faces many challenges:

[0004] Chinese patent CN102206482A discloses a preparation method of carbon fiber brake pad, which belongs to the technical field of automobile braking system. The invention aims to solve the problems of insufficient thermal conductivity and poor high-temperature braking stability of traditional non-asbestos organic (NAO) automobile brake pads, and proposes to prepare brake pads using carbon fiber (35–55%), phenolic resin (15–35%) and powder filler (20–40%) as raw materials. Although this scheme improves the thermal conductivity to some extent, the obtained brake pad still has problems such as insufficient braking efficiency, poor impact resistance, poor friction coefficient stability and high wear rate, which makes it difficult to meet the application requirements of high-performance braking conditions.

[0005] Chinese patent CN108662050A discloses a kind of carbon fiber brake pad material with porous structure and its preparation method, belongs to the field of automobile industry.The invention uses CF-CNTs composite fiber and filler as matrix, cashew oil modified phenolic resin as binder, and obtains porous structure material by introducing pore forming agent and dry hot pressing forming process.The fillers used include graphite, TiO2, Al2O3, iron, nitrile rubber, Sb2S3, BaSO4, mica and vermiculite.The scheme effectively improves the heat dissipation and noise reduction performance of brake pad through porous structure, but also brings the problems of mechanical strength decline, insufficient wear resistance, poor high temperature stability, poor process controllability, hygroscopicity and disintegration, etc., which is difficult to guarantee the safety and durability of brake pad for a long time.

[0006] Based on the above problems, it is urgent to develop a kind of carbon fiber brake pad preparation technology with environmental protection, low cost and stable performance, through fiber modification, interface optimization and process innovation, to realize the balance of lightweight, heat resistance and friction performance, to meet the demand of automobile, rail transportation and industrial braking system for high performance brake material, and to promote the development of green transportation and circular economy. SUMMARY

[0007] The purpose of the present application is: in view of the problems or deficiencies of the prior art, the present application provides a kind of high performance brake pad preparation method based on recycled carbon fiber / aramid pulp composite system, through fiber pretreatment and modification, material uniform dispersion and hot pressing process optimization, to ensure that brake pad has the advantages of compact overall structure, stable friction performance and excellent heat resistance.

[0008] In order to achieve the above purpose, the present application provides a kind of high performance brake pad preparation method based on recycled carbon fiber / aramid pulp composite system, which comprises the following steps:

[0009] S1: pretreatment of recycled carbon fiber, pretreatment and surface modification of aramid pulp to improve the interface bonding performance;

[0010] S2: bisphenol A type epoxy resin is uniformly mixed with methyl nadic anhydride curing agent and N,N-dimethyl benzylamine (BDMA) accelerator to obtain liquid resin mixture; for forming continuous high strength composite matrix;

[0011] S3: the recycled carbon fiber, aramid pulp and liquid resin mixture obtained in step 1 are weighed according to the mass fraction ratio of 40-90:10-50:100, and stirred uniformly;

[0012] S4: the mixture obtained in step S3 is placed in a mold, and after hot pressing, pressure holding and cooling and mechanical processing, the brake pad is prepared.

[0013] Preferably, the recycled carbon fiber in step S1 is an epoxy resin-based carbon fiber reinforced composite material, and the pretreatment of the recycled carbon fiber comprises: cutting the recycled carbon fiber to 1-5 mm, then soaking in an organic solvent for soaking treatment, and then washing, drying to obtain the pretreated recycled carbon fiber.

[0014] Preferably, the organic solvent used in the soaking treatment is ethanol and / or acetone.

[0015] Preferably, the recycled carbon fiber is derived from wind power blade epoxy resin-based carbon fiber reinforced composite (CFRP) waste, and the original length is 10-15 mm.

[0016] Preferably, the pretreatment of aramid pulp in step S1 comprises: soaking the aramid pulp in an organic solvent, and then ultrasonic treatment, and then washing, drying to obtain the pretreated aramid pulp.

[0017] Preferably, the organic solvent used in the pretreatment is ethanol and / or acetone.

[0018] Preferably, the modification treatment of aramid pulp in step S1 comprises: dispersing the pretreated aramid pulp in an organic solvent to obtain a dispersion liquid, adding ammonia water (NH3·H2O) and a silane modifier to the dispersion liquid, heating and stirring to react, and then filtering, washing, drying and grinding in sequence to obtain the modified aramid pulp.

[0019] Preferably, the silane modifier is at least one selected from the group consisting of methyltrimethoxysilane (TMOS), tetraethyl orthosilicate (TEOS) and tetrapropyl orthosilicate (TPOS).

[0020] Preferably, the organic solvent used in the modification treatment is ethanol and / or acetone.

[0021] Preferably, the mass ratio of the bisphenol A type epoxy resin to the methyl nadic anhydride curing agent and N,N-dimethylbenzylamine in step S2 is 100:80-100:0.5-2.

[0022] Preferably, the process conditions of the hot pressing forming are: pressure 10-25 MPa, temperature 120-150℃, and pressure holding time 60-360 min.

[0023] Compared with the prior art, the present application has the following beneficial effects:

[0024] The present application uses recycled carbon fiber and aramid pulp to replace traditional semi-metallic or ceramic materials, which can significantly reduce the density (about 1.5-1.75 g / cm 3), and excellent heat resistance and mechanical strength are maintained. Through fiber pretreatment and modification, the dispersibility and interfacial bonding are improved, and a continuous high-strength composite matrix is formed by introducing a thermosetting resin, so that the overall strength of the material is increased by more than 20%. Simulation of the braking condition shows that the friction coefficient of the brake pad prepared by the application remains stable in the range of 100-350℃, the fluctuation is less than 0.05, the wear rate is reduced by about 25% compared with traditional materials, and the noise is lower than 70dB(A), which shows excellent stability and reliability. At the same time, the method is simple in process, easy to industrialize, and realizes the high-value utilization of recycled carbon fibers, which has good environmental protection and economic benefits. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 Figure 1 is a scanning electron microscope picture of the fracture of the sample prepared in Example 1 at different magnifications, wherein (a) the scale is 100 μm; (b) the scale is 50 μm; (c) the scale is 20 μm; (d) the scale is 10 μm.

[0026] Figure 2 Figure 2 is a scanning electron microscope picture of the fracture of the sample prepared in Example 2 at different magnifications, wherein (a) the scale is 100 μm; (b) the scale is 50 μm; (c) the scale is 20 μm; (d) the scale is 10 μm. DETAILED DESCRIPTION

[0027] In order to make the application more obvious and easy to understand, the preferred embodiments are described in detail below with the help of the drawings.

[0028] The experimental methods not specified in the following examples are usually carried out according to the conventional conditions or according to the conditions recommended by the manufacturers. Unless otherwise specified, they are all conventional materials, reagents, methods and instruments in the art, which can be obtained by commercial channels by those skilled in the art.

[0029] Among them, the specific implementation scheme friction performance test: refer to GB / T 5763-2018 national standard for detection.

[0030] Example 1

[0031] A preparation method of a high-performance brake pad based on a recycled carbon fiber / aramid pulp composite system, comprising the following steps:

[0032] (a) The recycled carbon fiber with an original length of about 10-15 mm is obtained by solvent recovery from the waste epoxy resin-based CFRP of wind turbine blades. The length is controlled at 2-5 mm by cutting and screening through a high-speed pulverizer. Then, it is soaked in ethanol at room temperature for 18 h, ultrasonically rinsed with deionized water for 4 times, and dried to constant weight in a vacuum oven at 60℃, to obtain pretreated recycled carbon fiber.

[0033] (b) Aramid pulp (Rulin (Jiangsu) New Material Co., Ltd., 14 Aramid pulp) was first treated with ultrasound in acetone at 25°C for 4h, washed with water to neutral, and then dried at 80°C under vacuum. Subsequently, it was placed in a three-necked flask, ethanol was added, and it was dispersed by mechanical stirring at 300 rpm for 2h. Ammonia water (NH3·H2O) and tetraethyl orthosilicate (TEOS) were added, and the reaction was continued at 30°C for 2h. After filtration, it was washed with water and dried at 80°C under vacuum. Finally, it was ground in a planetary ball mill at a speed of 400 rpm for 45 min, and the obtained modified aramid pulp was discharged for standby use.

[0034] (c) Bisphenol A type epoxy resin (E51, 100 parts) was mixed with methyl nadic anhydride (MNA, 90 parts), and 1 part of N,N-dimethylbenzylamine (BDMA) was added as a promoter. The obtained liquid resin mixture was stirred uniformly for standby use.

[0035] (d) 90 parts of pretreated recycled carbon fiber, 0 parts of modified aramid pulp, and 100 parts of liquid resin mixture were taken. The recycled carbon fiber was dry-mixed at 1500 rpm for 10 min. The liquid resin mixture was added, and mixed at 800 rpm for 15 min until complete wetting.

[0036] (e) The premixed material was loaded into a mold and placed in a hot press, and cured according to the following procedure: first, preheating at 120°C and 5 MPa for 10 min; then, increasing the pressure to 15 MPa at 120°C and maintaining for 120 min; then, increasing the temperature uniformly to 150°C at a pressure of 15 MPa, and maintaining for 240 min; after the end of the program, maintaining the pressure and cooling to room temperature, demolding, and finally machining into standard samples, Figure 1 are scanning electron microscope pictures of the fracture of the sample prepared in this example at different magnifications, from which it can be seen that the structure of the sample is dense. Figure 1

[0037] Example 2

[0038] The difference between this example and Example 1 is only that in step (d), 81 parts of pretreated recycled carbon fiber, 9 parts of modified aramid pulp, and 100 parts of liquid resin mixture were taken.

[0039] The rest of the operations are the same as described in Example 1.

[0040] Figure 2 are scanning electron microscope pictures of the fracture of the sample prepared in this example at different magnifications, from which it can be seen that the structure of the sample is dense. Figure 2

[0041] Example 3

[0042] The difference between this example and Example 1 is only that in step (d), 72 parts of pretreated recycled carbon fiber, 18 parts of modified aramid pulp, and 100 parts of liquid resin mixture were taken.​​

[0043] The remaining operations are the same as described in Example 1.

[0044] Example 4

[0045] The difference between this example and Example 1 is that in step (d), 63 parts of pretreated recycled carbon fiber, 27 parts of modified aramid pulp, and 100 parts of liquid resin mixture are taken.

[0046] The remaining operations are the same as described in Example 1.

[0047] Example 5

[0048] The difference between this example and Example 1 is that in step (d), 54 parts of pretreated recycled carbon fiber, 36 parts of modified aramid pulp, and 100 parts of liquid resin mixture are taken.

[0049] The remaining operations are the same as described in Example 1.

[0050] Example 6

[0051] The difference between this example and Example 1 is that in step (d), 45 parts of pretreated recycled carbon fiber, 45 parts of modified aramid pulp, and 100 parts of liquid resin mixture are taken.

[0052] The remaining operations are the same as described in Example 1.

[0053] Comparative Example 1

[0054] The difference between this example and Example 3 is that in step (d), 72 parts of pretreated recycled carbon fiber, 18 parts of modified aramid pulp, and 35 parts of phenolic resin (model 2123) are taken. In step (e), the premix is loaded into the mold and placed in the hot press, and cured according to the following program: first preheat at 120°C, 5MPa for 10 minutes; then at 120°C, the pressure is increased to 15MPa and maintained for 30 minutes; then at 15MPa, the temperature is uniformly increased to 150°C, and the pressure is maintained for 60 minutes; after the program is completed, the pressure is maintained and cooled to room temperature, then demolded, and finally machined into standard samples.

[0055] The remaining operations are the same as described in Example 1.

[0056] Comparative Example 2

[0057] The difference between this example and Example 3 is that in step (d), 63 parts of pretreated recycled carbon fiber, 27 parts of modified aramid pulp, and 35 parts of phenolic resin (model 2123) are taken.

[0058] The remaining operations are the same as described in Example 1.

[0059] Table 1 Test Results

[0060] Friction coefficient μ Wear amount (10 -7 mm 3 (N-m) Example 1 0.32 2.8 Example 2 0.37 2.6 Example 3 0.38 2.4 Example 4 0.39 2.3 Example 5 0.40 2.1 Example 6 0.41 2.0 Comparative Example 1 0.31 3.5 Comparative Example 2 0.33 3.3

[0061] The experiments of Comparative Example 1 and Examples 2-6 show that the introduction of aramid pulp is a key factor for significantly improving the performance of the recycled carbon fiber brake pad, and the introduction of aramid pulp can improve the friction coefficient while giving good wear performance, wherein the performance of Examples 5 and 6 is optimal after the ratio of aramid pulp is increased, and the brake pad prepared under the ratio of Examples 5 and 6 shows stable friction performance, optimal wear resistance and good toughness. The experimental results of Comparative Example 3 and Comparative Examples 1-2 show that if the liquid resin mixture (bisphenol A type epoxy resin) therein is changed to phenolic resin, the friction coefficient decreases, and the wear amount decreases. The present application provides a fully verified formula design and process optimization scheme, and provides a reliable technical path and industrial application basis for the high-value utilization of recycled carbon fibers.

[0062] The above is only a preferred embodiment of the present application, and is not a limitation on the form and substance of the present application. It should be noted that those skilled in the art can make some improvements and supplements without departing from the present application, and these improvements and supplements should also be considered as the protection scope of the present application.

Claims

1. A method for preparing high-performance brake pads based on a recycled carbon fiber / aramid pulp composite system, characterized in that, The method includes the following steps: S1: Pre-treat recycled carbon fibers and pre-treat and surface-modify aramid pulp to improve interfacial bonding performance; S2: Bisphenol A type epoxy resin is mixed evenly with methyl nadic anhydride curing agent and N,N-dimethylbenzylamine accelerator to obtain a liquid resin mixture; S3: Weigh the recycled carbon fiber, aramid pulp and resin mixture obtained in step 1 in a mass ratio of 40-90:10-50:100 and stir evenly; S4: The mixture obtained in step S3 is placed in a mold, and after hot pressing, pressure holding and cooling and machining, a high-performance brake pad is obtained.

2. The preparation method according to claim 1, characterized in that, The recycled carbon fiber in step S1 is an epoxy resin-based carbon fiber reinforced composite material. The pretreatment step of the recycled carbon fiber includes: cutting the recycled carbon fiber to 1-5 mm, then immersing it in an organic solvent for soaking treatment, and obtaining the pretreated recycled carbon fiber after washing and drying.

3. The preparation method according to claim 2, characterized in that, The recycled carbon fiber is derived from waste epoxy resin-based carbon fiber reinforced composite materials from wind turbine blades, with an original length of 10-15 mm.

4. The preparation method according to claim 1, characterized in that, The pretreatment of aramid pulp in step S1 includes: immersing the aramid pulp in an organic solvent, subjecting it to ultrasonic treatment, and then washing and drying it to obtain the pretreated aramid pulp.

5. The preparation method according to claim 4, characterized in that, The modification treatment of aramid pulp in step S1 includes: dispersing the pretreated aramid pulp in an organic solvent to obtain a dispersion, adding ammonia and silane modifier to the dispersion, heating and stirring to react, and after the reaction is completed, filtering, washing, drying and grinding are performed sequentially to obtain modified aramid pulp.

6. The preparation method according to claim 5, characterized in that, The silane modifier is selected from at least one of methyl orthosilicate, tetraethyl orthosilicate, and tetrapropyl orthosilicate.

7. The preparation method according to claim 1, characterized in that: In step S2, the mass ratio of bisphenol A epoxy resin to methyl nadic anhydride curing agent and N,N-dimethylbenzylamine is 100:80-100:0.5-2.

8. The preparation method according to claim 1, characterized in that, The hot pressing process conditions are: pressure 10-25MPa, temperature 120-150℃, and holding time 60-360min.

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