A method for preparing a paper-based friction material from a lignin-cellulose assisted exfoliation of two-dimensional materials

Abstract

The application discloses a method for preparing paper-based friction material by means of lignin-cellulose assisted exfoliation of two-dimensional materials, which comprises the following steps: adding choline chloride and oxalic acid into wood powder, mixing and stirring at a temperature of 80-110 DEG C until a viscous liquid is formed; taking 100-150 mL of the viscous liquid obtained in step one, adding 2-5 g of sodium p-aminobenzenesulfonate, 10-20 mL of isopropyl alcohol, 10-20 mL of anhydrous ethanol and 1 g of two-dimensional material, and then sequentially performing crushing treatment and ball milling exfoliation on the mixed liquid; collecting the viscous liquid after the ball milling is completed, adding distilled water for dilution, and then performing filtration, washing, separation and molding and curing to obtain a recyclable wood-based composite material, which is a paper-based friction material with high wear resistance, excellent water stability, good flexibility, heat conductivity, recyclability and biodegradability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of material preparation, and particularly relates to a method for preparing a paper-based friction material by using a lignin-cellulose assisted exfoliation of two-dimensional materials. BACKGROUND

[0002] Wood raw materials have a huge reserve in nature and are low in price, and are potential substitutes for preparing high-strength composite materials. However, the wood powder material generated by processing is usually treated as waste, which not only wastes resources but also increases the processing cost. After the natural wood powder is treated in a deep eutectic solvent, the directional arrangement structure of lignin and cellulose can be completely opened, and after further treatment, a viscous wood pulp can be formed. Such fillers can be added to resins to prepare high-wear-resistance resin-based friction materials. Wood-based composites have gradually developed into potential substitutes for non-degradable resin-based materials, and biodegradable resin materials derived from biomass materials have great development potential.

[0003] Two-dimensional graphene as a potential lubricating material has attracted great interest in the field of tribology in recent years, and its preparation method has been the focus of research. Mechanical exfoliation is considered a promising method for large-scale manufacturing of two-dimensional graphene due to its low manufacturing cost, simple operation and ability to ensure the inherent properties of graphene. This mechanical exfoliation strategy mainly includes low-energy pure shear method, three-roll mill method and ball milling. The principle of these methods can be summarized as the process of converting stacked graphite crystals into single-layer graphene under mechanical shear stress. During the exfoliation process, the graphite layered structure is subjected to shear force, which counteracts the van der Waals force to exfoliate the graphite layers (thinning of the graphite crystal thickness), while the graphite layered crystal is broken to form smaller structures. However, due to the crushing, collision and vertical impact of the graphite sheet by the grinding balls, the covalent bonds in the planar layer are broken (planar structure is broken), and even the crystal structure is crushed into amorphous or unbalanced phases. Therefore, traditional mechanical exfoliation strategies are not suitable for preparing large-size two-dimensional graphene, especially in enhancing the mechanical properties of polymer-based composites. The reduction in grain size and the increase in specific surface area make graphene easy to agglomerate and disperse unevenly, increasing the redundant preparation steps and additional costs.

[0004] The preparation method of the modified friction material filled with lubricating material and resin generally needs various types of raw materials, most of which are not biomass materials, and may have expensive prices or complex preparation processes, such as carbon fibers or silicon carbide, but the friction material prepared by the blending modification method does not have the characteristics of recyclability. The phenolic resin and its modified products used in traditional paper-based friction materials (generally used as matrix and adhesive) belong to thermosetting resin, which has high crosslinking density and is difficult to be recycled or degraded in the natural environment, causing pollution to the natural environment after being discarded, and additional waste treatment steps consume more energy and cost, which is contrary to the low-carbon production strategy proposed by the country. SUMMARY

[0005] In view of the deficiencies of the prior art, the purpose of the present application is to provide a method for preparing a paper-based friction material by using lignin-cellulose to assist in exfoliating two-dimensional materials, which has high wear resistance, excellent water stability, good flexibility, thermal conductivity, recyclability and biodegradability.

[0006] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0007] A method for preparing a paper-based friction material by using lignin-cellulose to assist in exfoliating two-dimensional materials, comprising the following steps:

[0008] Step one: adding choline chloride and oxalic acid in wood powder according to the ratio of the sum of the mass of wood powder to choline chloride and oxalic acid being 1:(15-20), wherein the molar ratio of choline chloride to oxalic acid is 1:(1-3), and then fully stirring and dissolving at a temperature of 80-110°C until a viscous liquid is formed;

[0009] Step two: taking 100-150 mL of the viscous liquid obtained in step one, adding 2-5 g of sodium p-aminobenzenesulfonate, 10-20 mL of isopropyl alcohol, 10-20 mL of anhydrous ethanol and 1 g of two-dimensional material, and then sequentially performing crushing treatment and ball milling exfoliation on the mixture;

[0010] Step three: after the ball milling is completed, the viscous liquid is collected and diluted with distilled water according to a volume ratio of 1:(1-2), and then filtered, washed and separated, and the filter residue is taken for molding treatment, and then the water is evaporated at room temperature to obtain a recyclable wood-based composite material.

[0011] Preferably, the stirring time in step one is 2-4 hours.

[0012] Preferably, the two-dimensional material in step two includes any one of natural graphite, flake graphite, boron nitride and molybdenum disulfide.

[0013] Preferably, the breaking treatment in step two is ultrasonic oscillation breaking, and the treatment time is 30-60 min.

[0014] Preferably, the ball milling speed in step two is 500 rpm, the interval time is 20 min, and the total ball milling time is 24-36 h.

[0015] Preferably, the washing method in step three is distilled water washing for 3-5 times.

[0016] Preferably, the forming mode in step three includes any one of casting forming, hot-pressing forming, die-pressing forming, flow-casting forming, suction-filtering forming or freeze-drying forming.

[0017] Compared with the prior art, the present application has the following technical effects:

[0018] The preparation process of the paper-based friction material is similar to the wet papermaking process, the pulping step is combined with the mechanical exfoliation of graphene, which is helpful to promote the acquisition of large-size two-dimensional graphene and its dispersion in the base pulp, and the lignin has a certain plasticity, which can reduce the fragmentation of graphene under strong impact, and is helpful to obtain large-size two-dimensional graphene; further, the lignin is dissolved by DES, and the hydrogen bond induced by water molecules is recombined with the micro / nano cellulose, as a natural adhesive and matrix, while the micro / nano cellulose is used as a reinforcing fiber, and the SPABS modified graphene (SPABS@G) is used as an anti-wear additive, to form a thin film with high wear resistance, significant water stability, recyclability and low processing cost;

[0019] The wood powder waste is used to prepare the lignocellulose slurry, the lignocellulose slurry contains a large amount of cellulose, the lignin is dissolved into small molecules and combined with the hydrophilic functional groups on the surface of the micro / nano cellulose through hydrogen bonds, interacts with the micro / nano cellulose containing hydroxyl and carbonyl groups, forms a stable lignin-cellulose supramolecular structure, and the product after solidification forming obtains good mechanical properties and friction performance, excellent water stability, good flexibility, thermal conductivity, recyclability and biodegradability, and can effectively realize the high-value utilization of waste wood;

[0020] The graphite is peeled to form graphene, based on the interlayer slip effect under shear stress, a self-lubricating transfer film can be formed, which has good friction reduction and wear resistance effect, and is a good lubricating filler; in addition, the graphene can form a heat conduction network in the resin matrix, which helps to effectively transfer the friction heat and ensure the stability of the composite material during use; the sodium p-aminobenzenesulfonate in the application can effectively improve the surface performance of the two-dimensional material after peeling, so that it is easy to combine with the lignocellulose through secondary hydrogen bond, and is uniformly loaded in the dense layered structure of the lignocellulose and further improves the mechanical strength of the lignin-based composite material, which not only enhances the function, but also has high wear resistance and low wear rate;

[0021] The surface dense cross-linked structure of the lignin-based composite material prepared by the application has good hydrophobic property, and since the lignin is completely retained, based on the amphiphilicity of the lignin, the hydrophilic branched groups on the lignin are combined with the surface hydroxyl groups of the intertwined cellulose through hydrogen bond, and the hydrophobic main chain resists the invasion of water molecules, so that it is difficult for water molecules to invade the material, so it has good stability in water, and even after soaking in water for one month, it will not be deconstructed in the water stability experiment;

[0022] The raw materials used in the application are cheap, the preparation method adopts simple filtration and cleaning treatment, does not need additional impurity removal steps, and does not need to use any toxic solvent, the solvent used in the whole preparation process is green and environmentally friendly and pollution-free, the waste wood as a typical biomass green natural material has wide sources and large reserves and is green and environmentally friendly;

[0023] The resin-based composite material prepared by the application can not only be recycled by laboratory method after the product is scrapped, but also can be degraded by microorganisms in the natural environment due to the composition of lignin and cellulose, and is converted into humus and becomes a natural fertilizer for plant growth, so as to achieve the purpose of "taking from nature and returning to nature". BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 It is a TEM picture of the graphene peeled in situ in the lignin-cellulose prepared in Example 1;

[0025] Figure 2 It is a picture of the lignin-based slurry and the corresponding film prepared in Examples 1, 3 and 4;

[0026] Figure 3 It is a cross-sectional SEM morphology diagram of the lignin-based composite material prepared in Example 1;

[0027] Figure 4 It is an infrared spectrum diagram of the lignin-based composite film prepared in Example 1 and natural poplar;

[0028] Figure 5 is the friction coefficient curve of the wood-based composite film prepared in Example 1 under the condition of 2N-200rpm-300min;

[0029] Figure 6 is the stress-strain curve of the wood-based composite film under different proportions. DETAILED DESCRIPTION

[0030] The specific content of the application is further explained in detail in combination with the following examples.

[0031] Example 1

[0032] A lignin-cellulose assisted exfoliation of two-dimensional material strategy and paper-based friction material preparation method, the preparation includes the following steps:

[0033] Step 1: mix 13.96g of choline chloride, 14.65g of oxalic acid and 1.7g of poplar powder, and heat continuously at 110℃ for 2 hours until a viscous liquid is formed;

[0034] Step 2: add 10mL of anhydrous ethanol, 10mL of isopropyl alcohol, 2g of SPABS and 1g of natural graphite into 100mL of viscous liquid at the same time, disperse uniformly, then mechanically crush for 30min, and then perform ball exfoliation treatment for 24 hours;

[0035] Step 3: after the end, transfer the viscous liquid to a clean beaker, add 100mL of distilled water to the mixed solution according to the volume ratio of 1:1, then perform centrifugation, separation, and washing with distilled water for 3 times, disperse the obtained solid material in 50mL of water to form a pulp, and then perform vacuum filtration into a film and dry at room temperature.

[0036] Example 2

[0037] A lignin-cellulose assisted exfoliation of two-dimensional material strategy and paper-based friction material preparation method, the preparation includes the following steps:

[0038] Step 1: mix 15g of choline chloride, 15g of oxalic acid and 1.5g of scots pine powder, and heat continuously at 110℃ for 3 hours until a viscous liquid is formed;

[0039] Step 2: add 20mL of anhydrous ethanol, 10mL of isopropyl alcohol, 5g of SPABS and 1g of natural graphite into 150mL of viscous liquid at the same time, disperse uniformly, then mechanically crush for 60min, and then perform ball exfoliation treatment for 36 hours;

[0040] Step 3: After completion, the viscous liquid was transferred to a clean beaker, 200 mL distilled water was added to dilute the mixture, followed by centrifugation, separation and washing, the obtained solid material was dispersed in 80 mL water to make a slurry, and was vacuum filtered into a film and dried at room temperature.

[0041] Example 3

[0042] A lignin-cellulose assisted exfoliation of two-dimensional material strategy and paper-based friction material preparation method, the preparation comprises the following steps:

[0043] Step 1: 16 g of choline chloride, 20 g of oxalic acid and 1.8 g of poplar powder were mixed and heated at 110°C for 3 hours until a viscous liquid was formed;

[0044] Step 2: 10 mL of anhydrous ethanol, 10 mL of isopropyl alcohol and 3 g of SPABS and 1 g of hexagonal boron nitride (h-BN) were added to 120 mL of viscous liquid at the same time, and after uniform dispersion, mechanical crushing was carried out for 60 min, and ball exfoliation treatment was carried out for 36 hours;

[0045] Step 3: After completion, the viscous liquid was transferred to a clean beaker, 180 mL distilled water was added to dilute the mixture, followed by centrifugation, separation and washing, the obtained solid material was dispersed in 80 mL water to make a slurry, and was vacuum filtered into a film and dried at room temperature.

[0046] Example 4

[0047] A lignin-cellulose assisted exfoliation of two-dimensional material strategy and paper-based friction material preparation method, the preparation comprises the following steps:

[0048] Step 1: 15 g of choline chloride, 15 g of oxalic acid and 1.8 g of poplar powder were mixed and heated at 80°C for 4 hours until a viscous liquid was formed;

[0049] Step 2: 15 mL of anhydrous ethanol, 15 mL of isopropyl alcohol and 2 g of SPABS and 1 g of molybdenum disulfide (MoS2) were added to 120 mL of viscous liquid at the same time, and after uniform dispersion, mechanical crushing was carried out for 40 min, and ball exfoliation treatment was carried out for 30 hours;

[0050] Step 3: After completion, the viscous liquid was transferred to a clean beaker, 240 mL distilled water was added to dilute the mixture, followed by centrifugation, separation and washing, the obtained solid material was dispersed in 100 mL water to make a slurry, and was vacuum filtered into a film and dried at room temperature.

[0051] Example 5

[0052] A lignin-cellulose assisted exfoliation of two-dimensional material strategy and paper-based friction material preparation method, the preparation comprises the following steps:

[0053] Step 1: 6g of choline chloride, 19g of oxalic acid and 2.6g of poplar powder are mixed and heated at 100°C for 3 hours until a viscous liquid is formed;

[0054] Step 2: 20mL of anhydrous ethanol, 20mL of isopropyl alcohol and 4g of SPABS and 1g of flake graphite are simultaneously added to 150ml of the viscous liquid, uniformly dispersed and mechanically broken for 60min, and then subjected to ball exfoliation for 24 hours;

[0055] Step 3: After the end, 100mL of the viscous liquid is transferred to a clean beaker, 200mL of distilled water is added to the mixture for dilution, and then centrifugation, separation and washing are carried out, the obtained solid material is dispersed in 150mL of water to prepare a pulp, and a film is formed by vacuum filtration and dried at room temperature.

[0056] Please refer to Figure 1 , which is a TEM picture of graphene exfoliated in situ in lignin-cellulose prepared by example 1. It can be clearly observed that the graphene has a sheet structure, and the lateral size distribution is about several microns. The lignin-cellulose restrains it in the network, making it have a relatively complete structure.

[0057] Please refer to Figure 2 , which is a wood-based pulp and corresponding film prepared by examples 1, 3 and 4. It has excellent dispersion stability and mechanical durability, completely eliminates the anisotropic structure of natural wood, and has the characteristics of isotropy.

[0058] Please refer to Figure 3 , which is a cross-sectional SEM morphology diagram of the wood-based composite film prepared by example 1. From the diagram, it can be seen that it presents a very dense layered structure, which shows us the interlocking crosslinking structure of cellulose and lignin. Lignin and cellulose are crosslinked together by hydrogen bonds and intermolecular forces. The exfoliated sheet graphite is filled in it. When the wood-based composite film is subjected to tensile stress, the graphite and micro-nano fibers can play a certain force bearing role.

[0059] Please refer to Figure 4 , which is an infrared spectrum diagram of the wood-based composite film prepared by example 1 and natural poplar. From Figure 2 , it can be clearly seen that the peak positions of the two are basically the same, the functional group structures are basically the same, and the main components are mainly lignin-cellulose. The wood-based composite film also appears S=O bond and N-H bond due to the use of modified graphite for filling and modification.

[0060] Please refer to Figure 5The figure shows the friction coefficient curve of the wood-based composite film prepared in Example 1 under the condition of 2N-200rpm-300min, and the inset is the morphology of the wear scar under the light microscope. The wood-based composite film has a low wear rate under dry friction conditions, which is attributed to the dense surface structure and the sliding self-lubricating effect of graphite. The dense surface structure remains stable under long-term wear, and the self-lubricating effect of graphite makes the friction coefficient gradually tend to be low and stable, greatly reducing the surface friction and wear.

[0061] Please refer to Figure 6 The figure shows the stress-strain curve of the wood-based composite film under different proportions, and the optimal mass ratio range of natural graphite and wood pulp is determined to be 10% to 20%. The prepared wood-based composite film has good mechanical properties and excellent tribological properties, and can still easily bear a weight of 500g even after folding treatment.

Claims

1. A method of preparing a paper-based friction material from a lignin-cellulose assisted exfoliation of two-dimensional materials, characterized in that, The method comprises the following steps: Step one, adding choline chloride and oxalic acid into wood powder according to the ratio of 1:(15-20) of the sum of the mass of wood powder and choline chloride and oxalic acid, wherein the molar ratio of choline chloride and oxalic acid is 1:(1-3), mixing and then fully stirring and dissolving at the temperature of 80-110℃ until a viscous liquid is formed; Step two, taking 100-150 mL of the viscous liquid obtained in step one, adding 2-5 g of sodium p-aminobenzenesulfonate, 10-20 mL of isopropyl alcohol, 10-20 mL of anhydrous ethanol and 1 g of two-dimensional material, and then sequentially performing crushing treatment and ball milling peeling on the mixture; Step three, collecting the viscous liquid after the ball milling is completed, diluting the viscous liquid by adding distilled water according to the volume ratio of 1:(1-2), performing filtration, washing, separation, taking the filter residue for forming treatment, and then evaporating water at room temperature to obtain a recyclable wood-based composite material.

2. The method of claim 1, wherein the lignin-cellulose assisted exfoliation of two-dimensional materials to produce paper-based friction materials is characterized by, The stirring time in step one is 2-4 hours.

3. The method of claim 1, wherein the lignin-cellulose assisted exfoliation of two-dimensional materials to produce paper-based friction materials is characterized by, The two-dimensional material in step two includes any one of natural graphite, flake graphite, boron nitride and molybdenum disulfide.

4. The method of claim 1, wherein the lignin-cellulose assisted exfoliation of two-dimensional materials to produce paper-based friction materials is characterized by, The crushing treatment in step two is ultrasonic oscillation crushing, and the treatment time is 30-60 min.

5. The method of claim 1, wherein the lignin-cellulose assisted exfoliation of two-dimensional materials to produce paper-based friction materials is characterized by, The ball milling speed in step two is 500 rpm, the interval time is 20 min per hour, and the total ball milling time is 24-36 hours.

6. The method of claim 1, wherein the lignin-cellulose assisted exfoliation of two-dimensional materials to produce paper-based friction materials is characterized by, The washing method in step three is distilled water washing for 3-5 times.

7. The method of claim 1, wherein the lignin-cellulose assisted exfoliation of two-dimensional materials to produce paper-based friction materials is characterized by, The forming mode in step three includes any one of casting forming, hot pressing forming, mold pressing forming, flow casting forming, suction filtration forming or freeze-drying forming.

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