A three-step pretreatment method for enhancing the performance of graphene fibers

Abstract

The application belongs to the technical field of high-performance fiber preparation and textile processing, and discloses a three-step pretreatment method for enhancing the performance of graphene fibers, which comprises the following steps: in the first step, graphene fibers are preliminarily twisted; in the second step, the preliminarily twisted graphene fibers are sized by using an impregnation method; and in the third step, the sized graphene fibers are re-twisted; the porosity of the preliminarily twisted graphene fibers is 20%-60%, and the pore diameter is greater than 500 nm; the emulsion particle size of the sizing agent is 10-200 nm, the viscosity of the sizing agent is not higher than 50 mPa·s, and the contact angle between the sizing agent and the graphene fibers is not higher than 60°; and the porosity of the re-twisted graphene fibers is 5%-30%. The three-step pretreatment system can completely solve the contradiction between the brittleness and easy breakage of graphene fibers and the surface wrinkle and difficult penetration.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-performance fiber preparation and textile processing, and relates to a three-step pretreatment method for enhancing the performance of graphene fibers. BACKGROUND

[0002] Graphene fibers, as a new type of macroscopic carbonyl fiber assembled by two-dimensional graphene nanosheets, have shown great application prospects in the fields of flexible wearable electronic devices, smart fabrics and functional composites due to their excellent electrical conductivity, thermal conductivity and high specific strength. In order to realize the engineering application of graphene fibers, it is necessary to process them into two-dimensional or three-dimensional fabrics through knitting, weaving or special weaving process. However, before high-strength weaving processing, the original yarn must be sized and twisted to improve the fiber bundle characteristics, repair its surface defects, and enhance the wear resistance of the fiber bundle.

[0003] However, the existing general fiber (such as traditional chemical fiber, pitch-based carbon fiber or glass fiber, etc.) pretreatment technology is not suitable for graphene fibers, mainly due to the following difficult-to-overcome technical bottlenecks:

[0004] (1) The unique surface morphology of graphene fibers causes fluid resistance breakage. Unlike traditional carbon fibers with smooth surfaces, on the one hand, the surface of graphene fibers is covered with micro-creases and irregular grooves, which increases the specific surface area of the fibers; on the other hand, the single fiber density in graphene fibers is extremely low. During the traditional sizing process in the sizing tank, the high specific surface area and rough structure cause the fiber bundle to be subjected to great fluid dynamic resistance in the sizing agent. If the fiber bundle is in an untwisted or extremely low twisted state, the loose single fibers are prone to "floating" and separation under the action of viscous resistance of the sizing agent, resulting in uneven tension on the single fibers, and further causing breakage, flying and winding of the fibers in the sizing tank.

[0005] (2) Contradiction between brittle material and traditional twisting process. In order to resist fluid resistance and improve the bundling property, the existing technology usually adopts a twisting process. However, graphene fibers have the characteristics of high modulus and low elongation, and the interlayer shear strength is low. The traditional twisting process often pursues high tightness, and the high twist factor and twist angle will cause excessive torsional shear stress on the fibers, resulting in structural damage or even breakage of the fibers before entering the sizing tank. In addition, the excessively high pre-twist degree will block the pore channels on the surface of the fiber bundle, hinder the penetration of the sizing agent into the interior of the fiber bundle, and form a "skin-core" distribution, which cannot protect the inner fibers.

[0006] (3) Incompatibility between slurry micro-parameters and fiber pore structure. There are a large number of nanometer to micrometer pores formed by the stacking of graphene sheets inside the graphene fiber bundle. Existing industrial-grade sizing agent emulsions usually focus on macroscopic viscosity and solid content, while ignoring the compatibility between emulsion particle size and fiber bundle micro-pore. When the emulsion particle size is larger than the fiber gap, the "filter cake effect" occurs, causing the sizing to accumulate on the surface of the fiber bundle, not only causing uneven sizing, but also causing hair and fly silk due to the peeling of the hard and brittle layer on the surface during subsequent weaving.

[0007] In summary, how to balance the contradiction between "twisting and bundling to reduce fluid resistance" and "maintaining pores to facilitate penetration" for the unique properties of graphene fibers "brittle, thin, and surface wrinkles", and solve the problem of slurry micro-permeability, is a key problem to be solved for the preparation of high-performance graphene fiber fabrics.

[0008] The patent with the authorization announcement number CN119877184B discloses a preparation method of carbon nanofiber reinforced carbon material fiber fabric. The carbon material fiber tows after preliminary twisting are fixed on an electrostatic spinning nanoyarn machine, and carbon nanofiber membranes are formed by electrostatic spinning and subsequent operations to protect the carbon nanofibers. The preliminary twisting refers to a twist of 5-13 tpm. However, this technology attempts to solve the bundling problem through external physical wrapping, but fails to fundamentally solve the problem of the penetration of sizing agents into the interior of graphene tows and the construction of a stable and dense structure through secondary twisting (re-twisting).

[0009] The patent application with the application publication number CN120989798A discloses a twist-free / weak-twist yarn production process independent of water-soluble vinylon filaments. The single yarn is subjected to warping and sizing treatment (using sizing materials such as starch and wax flakes), the sizing is used to enhance the strength of the single yarn, and then the sizing single yarn is fed into a double-twisting machine to apply reverse twist to untwist, and finally the finished product is obtained through weaving and desizing treatment. However, this patent, although it produces "loose and soft" twist-free yarns (twist factor 0-50) through the process of "sizing first, then untwisting", the sizing agent is difficult to penetrate into the deep core of the fiber bundle, and can only adhere to the surface. Once the subsequent "untwisting" operation is performed, the fiber bundle without sizing adhesion in the core is easily loose without twist protection, which cannot meet the use requirements in high-frequency friction environment.

[0010] The patent application with the application publication number CN109898204A discloses a composite yarn preparation technology based on a ring spinning system. The core process of this scheme is to control the tension of the filament by using the friction field generated by the rolling of the filament in the groove. Finally, through the twisting action at the front nip, the short fibers are wrapped on the surface of the filament to form a core-spun yarn or a wrapped yarn structure. Although this method uses twisting to form a wrapped structure, the filament is in a "suspended" or "zero draft" state, lacking an active radial compression mechanism for the filament bundle itself (such as complex twisting densification), making it difficult to produce high-performance yarns of a single material with high density and high surface quality.

[0011] The patent application with the application publication number CN107366052A discloses a preparation technology that integrates nanofiber spinning, orientation, and twisting. The core of this scheme is to use a negative pressure fiber collection drum with spiral grooves and air holes on the surface. The drum is driven by a motor to rotate at high speed and form a negative pressure airflow inside, inducing electrospinning jets to gather in the grooves and highly orient along the groove direction, forming continuous nanofiber bundles. Then, a twisting winding device is used to pull the fiber bundle from the drum for twisting, thereby producing continuously oriented nanofiber yarns. However, this scheme relies solely on mechanical twisting force to compact the fibers, which is difficult to eliminate internal micro voids for graphene fibers with loose structure or large surface wrinkles in dry or semi-dry state, and cannot achieve the high-density locking effect of "wet complex twisting". The bulk density and wear resistance of the yarn are limited.

[0012] The patent application with the application publication number CN120844253A discloses an online steam setting technology for high-twist yarns. This scheme adopts a "single-strand" processing approach, which is characterized by using two oppositely arranged rubbing elements to clamp and move the yarn in the same direction. During the rubbing process, the hollow piercing needles on the surface of the rubbing elements pierce into the yarn to perform deep steam injection, while the external steam injection is used to achieve internal and external penetration. After treatment, the device also uses a repair section with soft silica gel protrusions to touch and repair the pinholes on the yarn, aiming to improve the steam treatment efficiency and solve the penetration problem caused by high twist. However, this method forcibly uses "piercing needles" to pierce into the yarn, which will directly cut the filaments for high-performance fibers composed of continuous filaments, causing irreversible mechanical damage and significantly reducing the overall tensile strength of the yarn. The subsequent "touch repair" can only improve the appearance smoothness and cannot restore the mechanical properties of the broken filaments. At the same time, for new fibers with dense structure, high modulus, and brittleness, this aggressive treatment method of "destroying first and then repairing" is not suitable and can easily cause the collapse of the yarn structure.

[0013] The patent application with the application publication number CN121047012A discloses a preparation technology of an aramid and cotton fiber blended wear-resistant yarn. The scheme mixes 70wt% aramid and 30wt% cotton fiber, and after the traditional opening, carding, drawing and roving processes, a single yarn with a twist of 900-950tpm is prepared in the spinning process. Subsequently, the process of two single yarns with the same direction and the opposite direction of the strand is adopted to form the strand. However, the scheme focuses on the macro blended ratio and the twist parameter, and does not involve the dynamic regulation of the micro porosity of the fiber bundle. It cannot actively adapt the slurry particle size by "preliminary twisting pre-pore" like the present application, and it is difficult to prepare a high-performance pure component fiber yarn with integrated structure and function.

[0014] Therefore, it is necessary to provide a three-step pretreatment method for enhancing the performance of graphene fibers to solve the above problems, which has very important significance. SUMMARY

[0015] The present application aims to solve the problems existing in the prior art and provide a three-step pretreatment method for enhancing the performance of graphene fibers.

[0016] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0017] A three-step pretreatment method for enhancing the performance of graphene fibers, the first step is to preliminarily twist the graphene fibers, the second step is to use the dipping method to use the sizing agent to size the preliminarily twisted graphene fibers, and the third step is to re-twist the sized graphene fibers;

[0018] The porosity of the preliminarily twisted graphene fibers is 20%-60%, and the pore size is >500nm;

[0019] The average particle size of the sizing agent emulsion is 10-200nm, which is much smaller than the pore size of the preliminarily twisted graphene fibers, so that the "filter cake effect" and surface blockage are eliminated, the viscosity of the sizing agent is not higher than 50mPa·s, and the contact angle between the sizing agent and the graphene fibers is not higher than 60°;

[0020] The porosity of the re-twisted graphene fibers is 5%-30%.

[0021] The present application establishes a three-step pretreatment method of "preliminary twisting stable porosity-sizing agent micro-penetration-re-twisting densification" for graphene fibers, and the role of each step is specifically described as follows:

[0022] The first step is to construct a "preliminary twisting" structure suitable for the penetration of sizing agent into brittle fibers.

[0023] In view of the characteristics of single-fiber thinness, large surface wrinkles and high brittleness in the graphene fiber, the application adopts a "preliminary twisting" pretreatment process, introduces a small amount of transverse restraint force, and makes the fiber bundle pass through the liquid surface in the form of "whole" rather than "single fiber", effectively sharing the fluid resistance, while maintaining the interlayer spacing between the fibers. The porosity of the graphene fiber after preliminary twisting is controlled to be 20%-60%, which can not only provide the minimum critical cohesive force required to resist the fluid resistance of the sizing agent, prevent single-fiber "floating" breakage, but also reserve an open "micro-fluid channel" for the subsequent sizing agent to enter.

[0024] The second step is a non-destructive penetration sizing system based on the "pore-particle matching criterion".

[0025] In order to overcome the high hysteresis resistance caused by the surface wrinkles of the graphene fiber, the application limits the matching relationship between the micro-rheological parameters of the sizing agent and the pore structure of the graphene fiber after preliminary twisting. According to the Washburn penetration equation, the penetration rate of liquid in porous medium is proportional to the pore size and inversely proportional to the viscosity. By limiting the emulsion particle size of the sizing agent to be much smaller than the pore size of the graphene fiber after preliminary twisting, the application avoids the "bridging" and blocking of polymer particles on the surface of the fiber bundle; in combination with low viscosity and suitable contact angle, the sizing agent can mainly rely on capillary force (rather than destructive mechanical extrusion force) to spontaneously fill into the wrinkle depth and single-fiber gap of the graphene fiber, realizing the "wicking effect".

[0026] The third step is a "re-twisting" densification and stress balancing technology.

[0027] After the sizing agent is fully penetrated and the sizing film is in a semi-cured or cured state, the "re-twisting" process is implemented. The sizing agent that penetrates into the interior is uniformly spread into a continuous interfacial film under the radial pressure generated by re-twisting. Re-twisting not only expels excess air and solvent, but also uses the geometric interlocking principle to convert the originally loose and brittle fiber bundle into a high-strength composite yarn with consistent skin and core, greatly improving the wear threshold. The porosity of the graphene fiber after re-twisting is controlled to be 5%-30%, which not only locks the internal sizing agent distribution, but also eliminates internal stress through twist matching, giving the brittle graphene fiber sufficient structural integrity to withstand high-frequency weaving friction.

[0028] As a preferred technical solution:

[0029] The three-step pretreatment method for enhancing the performance of graphene fibers as described above, the twist of the preliminary twisting is 5-30 tpm, and the twist back angle is 2°-15°. The combination of the parameters can make the porosity of the graphene fibers after the preliminary twisting be 20%-60%, and the pore size be >500 nm. The twist of the preliminary twisting is obviously lower than the twist (>60 tpm) when the twisting is performed for the purpose of bundling in the traditional way. The combination of the parameters adopted by the present application can make the fiber bundle pass through the liquid surface in the form of "whole", effectively share the fluid resistance, and maintain the high porosity of 20%-60%, which reserves the open "micro-fluid channel" for the subsequent slurry to enter, and prevents the pore closure caused by excessive twisting.

[0030] The three-step pretreatment method for enhancing the performance of graphene fibers as described above, the viscosity of the sizing agent is not less than 5 mPa·s, and the contact angle between the sizing agent and the graphene fibers is not less than 20°.

[0031] The three-step pretreatment method for enhancing the performance of graphene fibers as described above, the sizing agent is one or more of water-based sizing agent and organic-based sizing agent.

[0032] The three-step pretreatment method for enhancing the performance of graphene fibers as described above, the preparation process of the sizing agent is as follows: first, the soft segment polymer dispersion is added to the solvent, and stirred uniformly at low speed, then the wetting agent and the penetrating agent are added in sequence, the stirring speed is adjusted to stir until completely dissolved, finally the defoaming agent is added, and the defoaming is performed at low speed, and the sizing agent is obtained after filtration; wherein the solvent is deionized water or an organic solvent, and the mass ratio of the soft segment polymer dispersion, the solvent, the wetting agent, the penetrating agent, and the defoaming agent is 2-50 : 20-90 : 2-10 : 1-10 : 5-10; the soft segment polymer dispersion is polyether type polyurethane, polycaprolactone type polyurethane, polycarbonate type polyurethane, polyurea type polyurethane, or polyester type polyurethane.

[0033] The three-step pretreatment method for enhancing the performance of graphene fibers as described above, the twist of the re-twisting is 80-150 tpm, and the twist back angle is 30°-70°. The combination of the parameters can make the porosity of the graphene fibers after the re-twisting be 5%-30%.

[0034] The three-step pretreatment method for enhancing the performance of graphene fibers as described above, the specific steps are as follows:

[0035] (a) The graphene fibers are pulled into the twister under the slow shearing of the bidirectional rotating rollers, and are subjected to the preliminary twisting. The graphene fibers after the preliminary twisting remain in the twisted form without loosening;

[0036] (b) The graphene fiber after the primary twisting is slowly pulled into the sizing agent in the sizing tank for impregnation, and then is pulled into the dryer for drying, and the brittleness of the sized graphene fiber is obviously reduced, and the flexibility is increased;

[0037] (c) The sized graphene fiber is pulled into the re-twisting device for re-twisting.

[0038] The three-step pretreatment method for enhancing the performance of graphene fiber as described above, in step (b), the temperature for impregnation is 20-45°C, and the time is 20-100 min; the temperature for drying is 60-120°C, and the time is 5-20 min; and the transverse spread of the graphene fiber after the primary twisting in the sizing tank is reduced by 50%-90% compared with that of the graphene fiber without twisting.

[0039] The three-step pretreatment method for enhancing the performance of graphene fiber as described above, the specification of the graphene fiber is 50-800 tex / 1000-3000 F (i.e. the linear density of the graphene fiber is 50-800 tex, and 1000-3000 filaments are composed); after the three-step pretreatment, the lint amount of the graphene fiber is reduced by 80%-98%, the tensile strength is increased by 10%-50%, the wear life is increased by 50-100 times, and the bending strength is increased by 30%-80%.

[0040] Advantages:

[0041] (1) The present application establishes a gradient three-step pretreatment system of "primary twisting-microscopic penetration-re-twisting", the brittle graphene fiber is given the lowest critical cohesive force to resist the fluid resistance of the sizing agent by "primary twisting", so as to prevent the filament from floating and breaking in the sizing tank, then the lossless penetration is realized by "pore-particle size matching", so as to avoid the brittle damage caused by mechanical extrusion, finally the structure is densified and the stress is balanced by "re-twisting", so as to lock the internal sizing agent, and the contradiction between "brittleness and easy breaking" and "surface wrinkle and difficult penetration" of the graphene fiber is completely solved through this processing system, and the conventional process of "direct sizing" or "sizing after strong twisting" of the traditional fiber is broken.

[0042] (2) The present application effectively overcomes the problem of fluid resistance breaking caused by surface wrinkles, eliminates the "skin-core" defect, and improves the bundling; compared with the traditional high-twist sizing process, the present application realizes the full penetration of the sizing agent on the cross section of the filament bundle by using the particle size matching and weak-twist pores, and the internal filament bundle after re-twisting is free of "dry spots" or "white core", the adhesion between the fibers is uniform, and the splitting of the raw yarn in the subsequent weaving is effectively prevented.

[0043] (3) The graphene filament after the "weak twist-permeation-repeated twisting" treatment has a down quantity decrease of 80-98%, a tensile strength increase of 10-50%, a wear life increase of 50-100 times, and a bending resistance increase of 30-80%, thereby significantly improving the braiding property and mechanical property. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 The flow chart of the three-step pretreatment method for enhancing the performance of graphene fiber of the present application;

[0045] Figure 2 The SEM image of the graphene fiber after the initial twisting in Example 3 of the present application;

[0046] Figure 3 The tensile strength comparison chart of the graphene fiber before and after the three-step pretreatment in Examples 1-5 of the present application;

[0047] In the figure, 1 is a roller, 2 is a twister, 3 is a sizing tank, 4 is a dryer, and 5 is a repeated twister. DETAILED DESCRIPTION

[0048] The present application will be further described in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and not to limit the scope of the present application. In addition, it should be understood that those skilled in the art can make various modifications or changes to the present application after reading the content taught by the present application, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

[0049] To ensure the performance of the substances used in each example and comparative example is fully disclosed, the manufacturer and brand of the substance are specified, and other products from other manufacturers and brands that meet the definition of the present application are also feasible.

[0050] The test methods of the relevant performance indicators in each of the following examples and comparative examples are as follows:

[0051] Viscosity: The sizing agent in each example and comparative example is used as a sample, and then the viscosity of the sample is tested according to the standard GB / T 10247-2008 "Viscosity Measurement Method".

[0052] Twist: Tested according to GB / T 2543.1-2015 "Textiles-Determination of Yarn Twist-Part 1: Direct Counting Method".

[0053] Twist back angle: Tested according to FZ / T 01086-2020 "Textiles-Determination of Yarn Hairiness-Projection Counting Method".

[0054] Porosity: The graphene fibers in each example and comparative example were respectively taken as a sample, and then the porosity of the sample was tested according to the standard GB / T 21650.1-2008 "Pore Size Distribution and Permeability of Solid Materials by Mercury and Gas Adsorption Methods - Part 1: Mercury Porosimetry".

[0055] Lateral spread rate: the untwisted and the primary twisted graphene fibers in each example and comparative example were respectively taken as a sample, the bundle width of the sample in dry state was measured using an optical microscope under the condition of applying a specified tension of 3 N, then the sample was introduced into a transparent tank containing a sizing agent, the same tension was maintained, and the sample was completely immersed and reached a stable state (soaked for 60 s), the filament bundle morphology was photographed by a high-definition camera perpendicular to the liquid surface, and finally the maximum lateral width of the filament bundle in the liquid (i.e. the distance between the outermost two filaments) was measured by using the image processing software ImageJ, 10 different positions were measured for each group of samples, and the average value was taken; wherein the lateral spread rate = (W1-W0) / W0 x 100%, in the formula, W0 is the initial bundle width before the sample enters the tank, and W1 is the maximum lateral width of the filament bundle in the sizing tank.

[0056] Fuzzing amount: the graphene fibers in each example and comparative example were respectively taken as a sample, and then the fuzzing amount of the sample was determined according to the standard GB / T 41956-2022 "Determination of Fuzzing Amount of Carbon Fiber Tows", the unit was mg / kg (the number of milligrams of fluff produced per kilogram of fiber).

[0057] Tensile strength: tested according to GB / T 3362-2017 "Test Method for Tensile Properties of Carbon Fiber Multifilament" (the glue solution used during testing was prepared according to A.3.3 in the standard).

[0058] Wear life: tested according to ASTM D3108-2001 "Standard Test Method for Coefficient of Friction Between Yarns and Solid Materials".

[0059] Bending strength: according to the standard GB / T 3362-2017, a 500 mm sample was wound on a multifilament frame, immersed in a resin glue solution at 25°C (prepared according to A.3.3 in the standard GB / T 3362-2017) for 5 min, and placed in a 120°C electric heating air drying oven for curing to obtain a sample composite sample; the bending strength of the sample (unit: MPa) was tested according to the standard GB / T 1449-2005 "Test Method for Bending Properties of Fiber Reinforced Plastics".

[0060] Example 1

[0061] A three-step pretreatment method for enhancing the performance of graphene fibers, the process is as shown in Figure 1 , and the steps are as follows:

[0062] (1) Prepare a sizing agent;

[0063] First, the polyether polyurethane (manufacturer is Korschn, brand is Impranil DL 1380) is added into deionized water and stirred uniformly in a dispersing machine, then the polyether modified siloxane (manufacturer is BYK-Chemie GmbH, Germany, brand is BYK-346) and isomeric alcohol polyoxyethylene ether (manufacturer is BASF SE, brand is Lutensol TO 7) are added in sequence and stirred to dissolve completely under the condition of 3000 rpm and 30℃, finally the mineral oil defoaming agent (manufacturer is BYK-Chemie GmbH, Germany, brand is BYK-024) is added and stirred to defoam, after filtration, the sizing agent is obtained; wherein the mass ratio of polyether polyurethane, deionized water, polyether modified siloxane, isomeric alcohol polyoxyethylene ether and mineral oil defoaming agent is 2:60:6:5:7.5;

[0064] The average particle size of the obtained sizing agent emulsion is 10 nm, and the viscosity of the sizing agent is 5 mPa·s;

[0065] (2) The graphene fiber with a specification of 50 tex / 1000F is sheared by a bidirectional rotating roller 1 and is drawn into a primary twister 2 for primary twisting; wherein the shearing speed of the roller 1 is 0.2 m / min, the twist degree of the primary twisting is 5 tpm, and the twist back angle is 2°;

[0066] The porosity of the graphene fiber after the primary twisting is 60%, and the average pore size is 800 nm;

[0067] (3) The graphene fiber after the primary twisting is dipped into the sizing agent in a sizing tank 3 for 20 min at 20°C and is dried in a dryer 4 for 5 min at 60°C; wherein the contact angle between the sizing agent and the graphene fiber is 20°;

[0068] Compared with the graphene fiber without twisting (the transverse spread rate in the sizing tank is 90%), the transverse spread rate of the graphene fiber after the primary twisting in the sizing tank is reduced by 50%;

[0069] (4) The graphene fiber after the sizing is drawn into a secondary twister 5 for secondary twisting; wherein the twist degree of the secondary twisting is 80 tpm, and the twist back angle is 30°; the porosity of the graphene fiber after the secondary twisting is 30%.

[0070] Before the three-step pretreatment, the lint amount of the graphene fiber is 350 mg / kg, the tensile strength is 200 MPa, the wear life is 10 times, and the bending strength is 50 MPa;

[0071] After the three-step pretreatment, the lint amount of the graphene fiber is reduced by 85%, the tensile strength is increased by 10%, the wear life is increased by 100 times, and the bending strength is increased by 30%.

[0072] Comparative Example 1

[0073] A three-step pretreatment method for enhancing the performance of graphene fibers, which is basically the same as Example 1, except that in step (1), when preparing the sizing agent, the mass ratio of polyether polyurethane, deionized water, polyether modified siloxane, isomeric alcohol polyoxyethylene ether, and mineral oil defoaming agent is 10:88:0.5:0.5:1 (significantly reducing the amount of wetting agent and penetrating agent), the stirring speed of the disperser during the dissolution process is 500 rpm, the stirring and dissolution temperature is 10°C, and the emulsion particle size of the obtained sizing agent is 275 nm; the sizing agent used in step (3) is prepared according to this comparative example.

[0074] After three-step pretreatment, the lint amount of graphene fibers decreases by 30%, the tensile strength increases by 5%, the wear life increases by 30 times, and the bending strength increases by 8%.

[0075] Comparing Comparative Example 1 and Example 1, it can be seen that the graphene fibers after three-step pretreatment in this comparative example have some aggregated sizing agent components on the surface, and the lint improvement is not obvious. The sizing agent is difficult to enter the inside of the fiber bundle, ultimately leading to lower improvement in tensile strength, wear resistance, and bending strength. This is because the emulsion particle size of the sizing agent (>250 nm) is much larger than the effective pore size of the graphene fibers after preliminary twisting. According to the filtration principle of porous media, when the particle size is too large, the latex particles on the surface of the fiber produce a serious "filter cake effect" and "bridge phenomenon", blocking the micro-pore inlet and preventing the sizing agent from penetrating into the fiber bundle to fill the gap between the filaments. This results in the sizing agent only floating on the surface to form a fragile shell, which not only fails to enhance the interlayer bonding force of the fiber inside, but also easily peels off in friction due to the surface accumulation layer, resulting in an increase in lint and limited improvement in wear resistance, tensile strength, and bending strength.

[0076] Comparative Example 2

[0077] A three-step pretreatment method for enhancing the performance of graphene fibers, which is basically the same as Example 1, except that in step (2), the twist of the preliminary twisting is reduced to 2 tpm, and the roller shear speed is reduced to 0.05 m / min, so that the porosity of the graphene fibers after preliminary twisting is 75%; the graphene fibers after preliminary twisting used in step (3) are prepared according to this comparative example.

[0078] After three-step pretreatment, the lint amount of graphene fibers decreases by 10%, the tensile strength decreases by 5%, the wear life increases by 10 times, and the bending strength does not significantly increase.

[0079] Comparative Example 2 and Example 1 can be compared, the graphene fiber of the present comparative example after three-step pretreatment has loose structure and serious breakage, which is because the initial twisting is insufficient, resulting in too high porosity, and the fiber bundle lacks the necessary cohesion. In this case, when the sizing is pulled, the loose filaments cannot share the tension cooperatively, resulting in a large number of forced breakage; and due to the lack of basic structural support, the sizing film after drying cannot effectively collect the loose fiber bundle, resulting in poor final mechanical properties, and the improvement effect is poor compared with the untreated graphene fiber.

[0080] Comparative Example 3

[0081] A three-step pretreatment method for enhancing the performance of graphene fiber, which is basically the same as Example 1, except that the twist of the re-twist in step (4) is reduced to 40 tpm, so that the porosity of the graphene fiber after re-twist is 45%.

[0082] Compared with the graphene fiber before three-step pretreatment, the fuzz amount of the graphene fiber after three-step pretreatment decreases by 25%, the tensile strength decreases by 8%, the wear life decreases by 10 times, and the bending strength increases by 25%.

[0083] Comparative Example 3 and Example 1 can be compared, the graphene fiber of the present comparative example after three-step pretreatment has loose structure and serious breakage, which is because the initial twisting is insufficient, resulting in too high porosity, and the fiber bundle lacks the necessary cohesion. In this case, when the sizing is pulled, the loose filaments cannot share the tension cooperatively, resulting in a large number of forced breakage; and due to the lack of basic structural support, the sizing film after drying cannot effectively collect the loose fiber bundle, resulting in poor final mechanical properties, and the improvement effect is poor compared with the untreated graphene fiber.

[0084] Example 2

[0085] A three-step pretreatment method for enhancing the performance of graphene fiber, the steps are as follows:

[0086] (1) preparing a sizing agent;

[0087] Firstly, polycaprolactone polyurethane (manufacturer is Lubrizol, brand is Pearlstick 45-60 / 25) is added into dimethylformamide and stirred uniformly in a dispersion machine, then acetylenic diol surfactant (manufacturer is Wincrete Industrial Group, brand is Surfynol 104BC) and fatty alcohol polyoxyethylene ether (manufacturer is Dow Chemical, brand is Tergitol 15-S-9) are added in sequence and stirred to dissolve completely under the condition of 3000 rpm and 45℃, finally polyether modified polysiloxane (manufacturer is Wincrete Special Chemical (Shanghai) Co., Ltd., brand is Degussa TEGO Foamex N) is added and stirred to defoam, after filtration, the sizing agent is obtained; wherein the mass ratio of polycaprolactone polyurethane, dimethylformamide, acetylenic diol surfactant, fatty alcohol polyoxyethylene ether and polyether modified polysiloxane is 30:20:10:10:10;

[0088] The average particle size of the obtained sizing agent emulsion is 105 nm, and the viscosity of the sizing agent is 28 mPa·s;

[0089] (2) The graphene fiber with a specification of 300 tex / 2000F is subjected to preliminary twisting in a twister under the shearing of a bidirectional rotating roller, wherein the shearing speed of the roller is 3 m / min, and the twist degree of the preliminary twisting is 20 tpm and the twist back angle is 10°;

[0090] The porosity of the graphene fiber after the preliminary twisting is 40%, and the average pore size is 650 nm;

[0091] (3) The graphene fiber after the preliminary twisting is dipped in the sizing agent in a sizing tank for 60 min at 30°C, and then is dried in a dryer at 90°C for 12 min; wherein the contact angle between the sizing agent and the graphene fiber is 40°;

[0092] Compared with the graphene fiber without twisting (the transverse spread rate in the sizing tank is 75%), the transverse spread rate of the graphene fiber after the preliminary twisting in the sizing tank is reduced by 70%;

[0093] (4) The graphene fiber after the sizing is subjected to re-twisting in a re-twister, wherein the twist degree of the re-twisting is 115 tpm and the twist back angle is 50°; the porosity of the graphene fiber after the re-twisting is 15%.

[0094] Before the three-step pretreatment, the lint amount of the graphene fiber is 200 mg / kg, the tensile strength is 350 MPa, the wear life is 25 times, and the bending strength is 115 MPa;

[0095] After the three-step pretreatment, the lint amount of the graphene fiber is reduced by 92%, the tensile strength is increased by 30%, the wear life is increased by 250 times, and the bending strength is increased by 55%.

[0096] Example 3

[0097] A three-step pre-treatment method for enhancing the performance of graphene fibers, the steps are as follows:

[0098] (1) preparing a sizing agent;

[0099] First, polycarbonate polyurethane (manufacturer: Meishenew Material Co., Ltd., brand: C85) is added to tetrahydrofuran and stirred uniformly in a dispersing machine, then glycerol (manufacturer: Chemical Reagent Co., Ltd. of China National Pharmaceutical Group, specification: analytical pure AR, CAS: 56-81-5) and propylene carbonate (manufacturer: Chemical Reagent Co., Ltd. of China National Pharmaceutical Group, specification: analytical pure AR) are added in sequence, and stirring is carried out at a speed of 1000 rpm and a temperature of 45°C until complete dissolution, finally silicone resin (manufacturer: Shin-Etsu Chemical Co., Ltd., brand: X-22-819) is added and stirred to remove bubbles, and after filtration, the sizing agent is obtained; wherein the mass ratio of polycarbonate polyurethane, tetrahydrofuran, glycerol, propylene carbonate and silicone resin is 50:70:5:4:7;

[0100] The average particle size of the obtained sizing agent emulsion is 200 nm, and the viscosity of the sizing agent is 50 mPa·s;

[0101] (2) The graphene fiber with a specification of 400 tex / 3000F is pulled to the primary twister under the shearing of the bidirectional rotating roller, and primary twisting is carried out; wherein the roller shearing speed is 6 m / min, the twist degree of primary twisting is 30 tpm, and the twist back angle is 15°;

[0102] The porosity of the graphene fiber after primary twisting (the SEM thereof is shown in Figure 2 ) is 20%, and the average pore size is 500 nm;

[0103] (3) The graphene fiber after primary twisting is immersed in the sizing agent in the sizing tank at 45°C for 100 min, and then is pulled to the dryer for drying at 120°C for 20 min; wherein the contact angle between the sizing agent and the graphene fiber is 60°;

[0104] Compared with the graphene fiber without twisting (the transverse spread rate thereof in the sizing tank is 60%), the transverse spread rate of the graphene fiber after primary twisting in the sizing tank is reduced by 90%;

[0105] (4) The sized graphene fiber is pulled to the secondary twister for secondary twisting; wherein the twist degree of secondary twisting is 150 tpm, and the twist back angle is 70°; the porosity of the graphene fiber after secondary twisting is 5%.

[0106] Before the three-step pre-treatment, the linting amount of the graphene fiber is 150 mg / kg, the tensile strength is 500 MPa, the wear life is 40 times, and the bending strength is 180 MPa;

[0107] After the three-step pre-treatment, the linting amount of the graphene fiber decreases by 98%, the tensile strength increases by 50%, the wear life increases by 400 times, and the bending strength increases by 80%.

[0108] Comparative Example 4

[0109] A three-step pre-treatment method for enhancing the performance of graphene fibers, which is basically the same as Example 3, except that in step (1), the mass ratio of polycarbonate polyurethane, tetrahydrofuran, glycerol, propylene carbonate, and silicone resin is 50:30:5:4:7, i.e., the solid content of the soft segment polymer dispersion (polycarbonate polyurethane) is increased, so that the viscosity of the obtained sizing agent is 85 mPa·s; and the sizing agent used in step (3) is prepared according to this comparative example.

[0110] After the three-step pre-treatment, the linting amount of the graphene fiber decreases by 30%, the tensile strength increases by 8%, the wear life increases by 40 times, and the bending strength increases by 15%.

[0111] Comparing Comparative Example 4 with Example 3, it can be seen that the linting amount of the graphene fiber after the three-step pre-treatment of this comparative example increases, and the tensile strength, wear frequency, and bending strength are less improved, because the penetration rate of a fluid in a porous medium is inversely proportional to the viscosity of the fluid (Darcy's law), and the excessively high viscosity makes the sizing agent flow resistance too large in a very short impregnation time, so it cannot enter the deep layer of the fiber bundle under the action of capillary force, resulting in poor internal wetting of the graphene fiber, only the skin layer containing the sizing agent, forming a typical skin-core structure, which makes the fiber hard on the outside and soft on the inside, and the stress is not uniformly transmitted between the inside and outside layers when stressed, so it is easy to delaminate and break, thus the enhancement effect is significantly lower than that of the low-viscosity example.

[0112] Comparative Example 5

[0113] A three-step pre-treatment method for enhancing the performance of graphene fibers, which is basically the same as Example 3, except that in step (1), no wetting agent (acetylenic diol surfactant) and penetrating agent (fatty alcohol polyoxyethylene ether) are added, only the solvent is used to dilute the polymer, and the viscosity of the obtained sizing agent is 45 mPa·s; and in step (3), the sizing agent used for sizing is prepared according to this comparative example, and the contact angle between the sizing agent and the graphene fiber is 85°.

[0114] After the three-step pre-treatment, the linting amount of the graphene fiber decreases by 15%, the tensile strength increases by 3%, the wear life increases by 20 times, and the bending strength increases by 5%.

[0115] Comparative Example 5 and Example 3, the hairiness of the graphene fiber after three-step pretreatment increases, the tensile strength, wear resistance and bending strength increase slightly, and obvious "shrinkage" phenomenon appears on the surface and the hair is not laid down. This is because the contact angle is too large, resulting in poor wettability. According to the Washburn penetration equation, the contact angle close to 90° makes the capillary adsorption force ineffective or even repulsive effect, which hinders the spontaneous penetration of the sizing agent into the pores or effective wrapping of the single wire, resulting in invalid sizing, so the performance is almost not improved.

[0116] Comparative Example 6

[0117] A three-step pretreatment method for enhancing the performance of graphene fiber, which is basically the same as Example 3, except that in step (2), the twist of the preliminary twisting is increased to 50 tpm, and the porosity of the graphene fiber after preliminary twisting is 10%, and in step (3), the graphene fiber after preliminary twisting is prepared by this comparative example.

[0118] After three-step pretreatment, the hairiness of the graphene fiber decreases by 40%, the tensile strength increases by 15%, and the bending strength increases by 20%.

[0119] Comparing Comparative Example 6 and Example 3, the hairiness of the graphene fiber after three-step pretreatment increases, and the tensile strength and bending strength increase slightly. This is because the preliminary twisting is too much, resulting in too low porosity, and the low porosity also closes the micro-penetration channel of the sizing agent. When sizing, the sizing agent can only adhere to the surface to form a sheath layer of skin-core structure, resulting in lack of sizing inside the fiber, and the internal unsized single wire slips and cannot bear the whole force when stressed, limiting the strengthening effect.

[0120] Comparative Example 7

[0121] A three-step pretreatment method for enhancing the performance of graphene fiber, which is basically the same as Example 3, except that in step (4), the twist of the re-twisting is increased to 250 tpm, and the porosity of the graphene fiber after re-twisting is 2%.

[0122] Compared with the graphene fiber before three-step pretreatment, the tensile strength of the graphene fiber after three-step pretreatment decreases by 10%, the wear life increases by 130 times, and the bending strength decreases by 20%.

[0123] Comparative Example 7 and Example 3, the wear resistance of the graphene fiber after three-step pretreatment in the present comparative example is increased, but the tensile strength and bending strength are less improved, and the surface is smooth and wear-resistant, but brittle fracture easily occurs, because excessive overtwisting leads to a great residual torsional stress and damages the microstructure of the fiber; in addition, excessive compression changes the elastic connection of the pulp layer into a rigid inclusion without buffer, resulting in great brittleness of the fiber during stretching or bending, and thus damaging the mechanical properties.

[0124] Example 4

[0125] A three-step pretreatment method for enhancing the performance of graphene fiber, the steps are as follows:

[0126] (1) preparing a sizing agent;

[0127] First, polyurea type polyurethane (manufacturer: Wanhua Chemical, brand: WANNATE 6085) is added to dimethylacetamide and stirred uniformly in a disperser, then polyether modified siloxane (manufacturer: YPC Industrial Group, brand: TEGO Wet 270) and sodium diisooctyl sulfosuccinate (manufacturer: Solvay Group, brand: Aerosol OT-75) are added in sequence, and stirred until completely dissolved at a speed of 1000 rpm and a temperature of 60°C, and finally non-silicon defoaming agent (manufacturer: BASF SE, brand: FoamStar SI 2210) is added and stirred to remove bubbles, and after filtration, the sizing agent is obtained; wherein the mass ratio of polyurea type polyurethane, dimethylacetamide, polyether modified siloxane, sodium diisooctyl sulfosuccinate and non-silicon defoaming agent is 25:50:8:7:8;

[0128] The average particle size of the obtained sizing agent emulsion is 50 nm, and the viscosity of the sizing agent is 15 mPa·s;

[0129] (2) The graphene fiber with a specification of 800 tex / 1000 F is drawn to the twister under the shearing of the rotating roller, and then subjected to preliminary twisting; wherein the shearing speed of the roller is 1.5 m / min, the preliminary twisting degree is 10 tpm, and the twist back angle is 5°;

[0130] The porosity of the graphene fiber after preliminary twisting is 50%, and the average pore size is 700 nm;

[0131] (3) The graphene fiber after preliminary twisting is dipped in the sizing agent in the sizing tank at 25°C for 40 min, and then dried in a dryer at 80°C for 8 min; wherein the contact angle between the sizing agent and the graphene fiber is 30°;

[0132] The graphene fiber after the preliminary twisting has a transverse spread rate in the sizing tank reduced by 60% compared to the graphene fiber without twisting (the transverse spread rate in the sizing tank is 85%);

[0133] (4) The graphene fiber after the sizing is drawn into a re-twisting device for re-twisting; wherein the twist of the re-twisting is 100 tpm, and the twist back angle is 40°; the porosity of the graphene fiber after the re-twisting is 25%.

[0134] Before the three-step pretreatment, the lint amount of the graphene fiber is 300 mg / kg, the tensile strength is 250 MPa, the wear life is 15 times, and the bending strength is 70 MPa;

[0135] After the three-step pretreatment, the lint amount of the graphene fiber is reduced by 88%, the tensile strength is increased by 20%, the wear life is increased by 350 times, and the bending strength is increased by 40%.

[0136] Embodiment 5

[0137] A three-step pretreatment method for enhancing the performance of graphene fiber, the steps are as follows:

[0138] (1) preparing a sizing agent;

[0139] First, the polyester polyurethane (manufacturer: Wacker, brand: Dispercoll U 54) is added into dimethyl sulfoxide and stirred uniformly in a disperser, then glycerol (manufacturer: Chemical Reagent Co., Ltd. of China National Pharmaceutical Group, specification: analytical pure AR, CAS: 56-81-5) and propylene carbonate (manufacturer: Chemical Reagent Co., Ltd. of China National Pharmaceutical Group, specification: analytical pure AR) are sequentially added, and stirring is performed until complete dissolution under the conditions of a rotation speed of 2000 rpm and a temperature of 30°C, and finally the silicone resin (silicone resin, manufacturer: Dow Chemical, brand: DOWSIL 65) is added and stirred to remove bubbles, and after filtration, the sizing agent is obtained; wherein the mass ratio of the polyester polyurethane, dimethyl sulfoxide, glycerol, propylene carbonate, and silicone resin is 45:90:2:1:5;

[0140] The average particle size of the obtained sizing agent emulsion is 150 nm, and the viscosity of the sizing agent is 40 mPa·s;

[0141] (2) The graphene fiber with a specification of 600 tex / 3000F is drawn into a twisting device for preliminary twisting under the shearing of a bidirectional rotating roller; wherein the roller shearing speed is 5 m / min, the twist of the preliminary twisting is 25 tpm, and the twist back angle is 12°;

[0142] The porosity of the graphene fiber after the preliminary twisting is 30%, and the average pore size is 550 nm;

[0143] (3) the preliminarily twisted graphene fiber is drawn into the sizing agent in the sizing tank, immersed at 40°C for 80 min, and then drawn into the dryer to be dried at 100°C for 15 min; wherein the contact angle between the sizing agent and the graphene fiber is 50°;

[0144] Compared with the untwisted graphene fiber (the transverse spread rate in the sizing tank is 65%), the transverse spread rate of the preliminarily twisted graphene fiber in the sizing tank is reduced by 80%;

[0145] (4) the sized graphene fiber is drawn into the re-twisting device to be re-twisted; wherein the twist of the re-twisting is 135 tpm, and the twist back angle is 60°; the porosity of the re-twisted graphene fiber is 10%.

[0146] Before the three-step pretreatment, the lint amount of the graphene fiber is 400 mg / kg, the tensile strength is 450 MPa, the wear life is 35 times, and the bending strength is 160 MPa;

[0147] After the three-step pretreatment, the lint amount of the graphene fiber is reduced by 80%, the tensile strength is increased by 40%, the wear life is increased by 200 times, and the bending strength is increased by 70%.

[0148] The tensile strength of the graphene fiber tows before and after the three-step pretreatment in Examples 1-5 is compared, and the comparison result is shown in Figure 3 As can be seen from the figure, the mechanical properties of the graphene fiber tows are improved after the treatment by the method of the present application.

Claims

1. A three-step pretreatment method for enhancing the properties of graphene fibers, characterized in that, The first step is to initially twist the graphene fiber; the second step is to use an impregnation method to sizing the initially twisted graphene fiber with a sizing agent; and the third step is to re-twist the sizing graphene fiber. The initial twist is 5-30 tpm, and the twist angle is 2°-15°. The porosity of the pre-twisted graphene fibers is 20%-60%, and the pore size is >500nm; The preparation process of the sizing agent is as follows: First, the soft segment polymer dispersion is added to the solvent and stirred evenly. Then, the wetting agent and penetrant are added in sequence and stirred until completely dissolved. Finally, the defoamer is added and stirred to remove bubbles. After filtration, the sizing agent is obtained. The soft segment polymer dispersion is polyether polyurethane, polycaprolactone polyurethane, polycarbonate polyurethane, polyurea polyurethane, or polyester polyurethane. The average particle size of the sizing agent emulsion is 10-200 nm, the viscosity of the sizing agent is 5-50 mPa·s, and the contact angle between the sizing agent and the graphene fiber is 20°-60°. The twist of the additional twist is 80-150 tpm, and the twist angle is 30°-70°; The porosity of the twisted graphene fibers is 5%-30%; The specifications of graphene fiber are 50-800tex / 1000-3000F; after three-step pretreatment, the fuzzing of graphene fiber is reduced by 80%-98%, the tensile strength is increased by 10%-50%, the wear resistance life is increased by 50-100 cycles, and the bending strength is increased by 30%-80%.

2. The three-step pretreatment method for enhancing the properties of graphene fibers according to claim 1, characterized in that, The specific steps are as follows: (a) Graphene fibers are drawn into a twister for initial twisting under bidirectional rotating roller shearing; (b) After initial twisting, the graphene fibers are drawn into the sizing agent in the sizing tank for impregnation, and then drawn into the dryer for drying. (c) The sized graphene fibers are drawn into a retwisting machine for retwisting.

3. The three-step pretreatment method for enhancing the properties of graphene fibers according to claim 2, characterized in that, In step (b), the impregnation temperature is 20-45°C and the time is 20-100 min; the drying temperature is 60-120°C and the time is 5-20 min; compared with untwisted graphene fibers, the transverse widening rate of the pre-twisted graphene fibers in the sizing tank is reduced by 50%-90%.

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