A method for pre-treating a composite fibrous structural material

Abstract

This application relates to the field of fiber material technology and provides a pretreatment method for composite fiber structural materials. The pretreatment method includes the following steps: S100, performing surface cleaning pretreatment on the composite fiber structural material to obtain pre-cleaned fibers; S200, adding the pre-cleaned fibers to a surface treatment solution for selective surface swelling and roughening treatment to obtain intermediate fibers; S300, performing termination treatment and washing treatment on the intermediate fibers to obtain pretreated composite fibers. This application improves the surface roughness and surface activity of the fibers by selectively swelling and roughening the composite fiber structural material, combined with termination treatment and washing treatment, while maintaining the basic integrity of the fiber's main structure, thus providing more favorable surface conditions for subsequent interfacial bonding and composite processing.

Description

Technical Field

[0001] This invention relates to the field of fiber materials technology, and more specifically, to a pretreatment method for composite fiber structural materials. Background Technology

[0002] Composite fiber structural materials refer to fiber materials formed by combining two or more components along the fiber's axial, radial, or cross-sectional direction. Common types include core-sheath composite fibers, matrix-fiber composite fibers, and hollow composite fibers. These fiber materials can integrate the performance characteristics of different components, exhibiting advantages in strength, toughness, specific surface area, interfacial properties, and functional designability. Therefore, they have broad application prospects in fiber-reinforced materials, filtration and separation materials, paper-based composite materials, and functional textile materials.

[0003] In practical applications of composite fiber structural materials, it is often necessary to pretreat the fiber surface before subsequent compounding, bonding, impregnation, finishing or forming to remove residual oil, oligomers or impurities on the surface, and improve the roughness, wettability and interfacial reactivity of the fiber surface, thereby improving the interfacial bonding ability between the fiber and the matrix material.

[0004] In existing technologies, commonly used pretreatment methods include water washing, organic solvent cleaning, alkali treatment, oxidation treatment, plasma treatment, and solvent swelling treatment. While these methods can improve the surface condition of fibers to some extent, they still suffer from insufficient adaptability for fiber materials with multiphase composite structures. This is because composite fiber structures typically exhibit uneven component distribution, complex interface structures, and significant differences in response to different treatment media. For example, the sheath and core layers of core-sheath composite fibers differ in chemical composition and swelling behavior; the continuous and dispersed phases of matrix-fiber composite fibers do not exhibit consistent chemical resistance and structural stability; and hollow composite fibers are more sensitive to outer layer erosion and cavity retention. In such cases, if conventional pretreatment methods with strong effects or lack of selectivity are used, excessive erosion of the fiber structure can easily occur while improving surface activity, leading to problems such as over-erosion of the fiber surface, damage to the core or matrix phase, interface delamination, hollow structure collapse, and decreased mechanical properties, thereby affecting the stability of subsequent processing and the final material properties.

[0005] Therefore, there is an urgent need for a pretreatment method for composite fiber structural materials that can balance surface modification effects with structural retention performance. Summary of the Invention

[0006] The problem addressed by this invention is how to provide a pretreatment method for composite fiber structural materials.

[0007] To address the above problems, this invention provides a pretreatment method for composite fiber structural materials, the pretreatment method comprising the following steps: S100. The composite fiber structure material is subjected to surface cleaning pretreatment to obtain pre-cleaned fibers. S200: Add the pre-cleaned fibers to the surface treatment solution for selective surface swelling and roughening treatment to obtain intermediate fibers; S300: The intermediate fibers are terminated and washed to obtain pretreated composite fibers.

[0008] In the above technical solution, in S100, the composite fiber structural material includes at least one of core-sheath type composite fiber, matrix-fiber type composite fiber, and hollow composite fiber; and / or the length of the composite fiber structural material is 1~12mm and the fineness is 0.3~6dtex.

[0009] In the above technical solution, in S100, the cleaning solution for surface cleaning pretreatment includes at least one of deionized water, aqueous ethanol solution, or aqueous isopropanol solution; and the temperature of surface cleaning pretreatment is 20~60℃, and the cleaning time is 5~30min.

[0010] In the above technical solution, in S200, the surface treatment liquid includes, by weight: 70-92 parts water, 5-20 parts eutectic activation component, 0.05-2 parts sodium carbonate, and 0.02-1 parts polyvinylpyrrolidone.

[0011] In the above technical solution, the eutectic activation components include choline chloride and glycerol.

[0012] In the above technical solution, the molar ratio of choline chloride to glycerol is 1:(2~4).

[0013] In the above technical solution, in S200, the selective surface swelling and roughening treatment includes a pre-wetting stage and a surface swelling and roughening stage; wherein, the temperature of the pre-wetting stage is 20~40℃; and the temperature of the surface swelling and roughening stage is 50~80℃.

[0014] In the above technical solution, in S200, the liquid-solid ratio of the surface treatment liquid to the pre-cleaned fiber is (10~60):1.

[0015] In the above technical solution, in S300, the termination treatment includes at least one of cooling quenching, weak acid neutralization treatment, and deionized water washing.

[0016] In the above technical solution, the weak acid neutralization treatment uses at least one of acetic acid solution, citric acid solution, and lactic acid solution, the mass fraction of the weak acid neutralization solution is 0.01~1%, and the solution is washed until the pH of the filtrate is 6.0~7.5.

[0017] Beneficial effects (1) This application combines surface cleaning pretreatment, selective surface swelling and roughening treatment, termination treatment and washing treatment to limit the treatment effect to the surface of the composite fiber structure material. This can improve the surface roughness and surface activity of the fiber while maintaining the integrity of the main fiber structure as much as possible. (2) This application can reduce the risk of fiber damage, structural destruction and performance degradation caused by excessive treatment or lack of selectivity in conventional pretreatment, thereby better balancing surface modification effect and structural retention performance. (3) The pretreated composite fibers obtained in this application have a more favorable surface state, which helps to improve their interfacial bonding effect and processing adaptability in subsequent composite, bonding, impregnation, finishing or forming processes. Detailed Implementation

[0018] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, a detailed description of specific embodiments of the present invention will be provided below.

[0019] Unless otherwise specified, all reagents and raw materials used in this invention are commercially available. Experimental methods in the following examples that do not specify particular conditions should be performed according to conventional methods and conditions, or as selected in the product instructions.

[0020] This invention aims to provide a pretreatment method for composite fiber structural materials, addressing the problem that existing composite fiber structural materials often struggle to simultaneously achieve surface modification effects and maintain the performance of the main structure during pretreatment. The pretreatment method includes the following steps: S100. The composite fiber structure material is subjected to surface cleaning pretreatment to obtain pre-cleaned fibers. S200: Add the pre-cleaned fibers to the surface treatment solution for selective surface swelling and roughening treatment to obtain intermediate fibers; S300: The intermediate fibers are terminated and washed to obtain pretreated composite fibers.

[0021] In S100, the surface cleaning pretreatment of composite fiber structural materials primarily aims to remove residual spinning oils, processing aids, oligomers, free small molecules, and adsorbed impurities from the fiber surface, reducing the interference of the surface contamination layer on the mass transfer and uniformity of the subsequent surface treatment solution. During the preparation, cutting, transportation, and storage of composite fiber structural materials, a certain amount of organic low-molecular-weight substances and exogenous contaminants usually remain on the fiber surface. These substances tend to cover the fiber surface or accumulate in the micropores, micro-depressions, and near the phase interface of the fiber surface, thus hindering the contact and wetting of the actual fiber surface by the subsequent surface treatment solution. When surface swelling and roughening treatment is performed directly without cleaning, the surface treatment solution often reacts first with the residual contamination layer, failing to act uniformly and stably on the surface structure of the composite fiber. This easily leads to both insufficient and excessive local treatment, ultimately resulting in uneven roughening effects and even inducing the expansion of interface defects. Therefore, surface cleaning pretreatment using S100 can, on the one hand, expose the true surface of the composite fiber, improving the contact efficiency and wetting uniformity of the subsequent surface treatment liquid on the fiber surface; on the other hand, it can reduce the shielding effect of surface residues on the selective action of different components at the interface, allowing the subsequent selective surface swelling and roughening treatment to act more concentratedly on the target surface area, thereby improving the controllability, uniformity and repeatability of the entire pretreatment process.

[0022] Furthermore, the composite fiber structural material includes at least one of core-sheath composite fibers, matrix-fiber composite fibers, and hollow composite fibers. In core-sheath composite fibers, the sheath layer is located on the outside of the fiber and directly determines the fiber's contact behavior with the external medium. The pretreatment method of this application can preferentially improve the surface state of the sheath layer, enhancing the fiber's surface activity and interfacial compatibility without significantly damaging the core layer's load-bearing structure. In matrix-fiber composite fibers, the matrix phase and fibrillary phase typically differ in structural density and chemical responsiveness. The pretreatment method of this application facilitates controlled activation and coarsening of the outer matrix region while reducing the risk of damage to the internal fibrillary continuous structure. In hollow composite fibers, the outer layer and hollow cavity are coupled. Conventional strong treatment methods easily cause outer layer instability and further induce cavity deformation or collapse. However, this application, through a combination of pre-cleaning and post-termination, helps to limit the effect to the outer layer region, thereby improving surface properties while maintaining the integrity of the hollow structure. The length of the composite fiber structural material is controlled between 1 and 12 mm, and the fineness is controlled between 0.3 and 6 dtex. When the length is too short, although the fibers are easy to disperse during the treatment process, the effective structural characteristics of the unit fiber are not prominent, and the structural advantages of the surface modification after treatment are not easily reflected. Moreover, it is not conducive to the reinforcing and interfacial bonding effects of the composite fibers in subsequent applications. When the length is too long, the fibers are more prone to entanglement, bridging, and local accumulation in liquid phase treatment, making it difficult for the cleaning and surface treatment solutions to contact the fiber surface evenly, thus reducing the consistency of pretreatment. When the fineness is too small, the fiber surface layer is relatively thinner, the treatment window is narrower, and slight improper handling may cause the surface treatment to extend inward. When the fineness is too large, the specific surface area is relatively reduced, which is not conducive to reflecting the efficiency of surface treatment in improving surface activity and roughness.

[0023] Furthermore, the cleaning solution for surface cleaning pretreatment includes at least one of deionized water, aqueous ethanol solution, or aqueous isopropanol solution. Using deionized water as the cleaning medium effectively removes water-soluble residues, inorganic salts, and loosely adsorbed impurities adhering to the fiber surface, and reduces the impact of foreign ions on the stability of the subsequent surface treatment solution. Using aqueous ethanol solution or aqueous isopropanol solution as the cleaning medium maintains a certain polarity and wetting ability, while enhancing the dissolution and desorption of organic residues, oily components, and oligomers on the fiber surface, thereby improving the removal effect on the contamination layer on the composite fiber surface. The surface cleaning pretreatment temperature is 20~60℃, which is beneficial to improve the dissolution rate and migration rate of residues in the cleaning solution without causing significant thermal deformation of the composite fiber structure or premature instability of the component interfaces, thus enhancing the mass transfer efficiency of the cleaning process. The cleaning time is 5~30 min, which is beneficial to ensure sufficient removal of surface residues while avoiding excessive soaking time that could lead to excessive fiber absorption, excessive structural swelling, or reduced treatment efficiency. The surface cleaning pretreatment can be carried out by stirring, oscillating, or circulating rinsing, which helps to improve the effectiveness of the surface cleaning pretreatment. This allows the composite fibers to have a cleaner, more uniform, and more easily wetted surface state before entering the S200, thus providing good preconditions for the subsequent selective surface swelling and roughening treatment.

[0024] In S200, pre-cleaned fibers are added to a surface treatment solution for selective surface swelling and roughening treatment. This is further divided into two consecutive stages: a pre-wetting stage and a surface swelling and roughening stage. This allows the surface treatment solution to preferentially, uniformly, and controllably act on the outer surface area of ​​the composite fibers, rather than forming an excessively strong effect in a localized location at the initial contact, thus avoiding problems such as localized over-etching, uneven treatment, or excessive penetration.

[0025] For composite fiber structural materials, the surface, internal phases, and phase interfaces typically differ in chemical composition, amorphous region content, molecular chain mobility, and media responsiveness. If a one-step surface treatment is performed directly at a high temperature, the surface treatment solution may preferentially penetrate and act on certain areas in the initial stage of contact with the fibers due to localized high concentrations, uneven wetting, and different fiber stacking states. This results in some areas being undertreated and others overtreated, ultimately hindering the achievement of controlled surface coarsening and preservation of the main structure.

[0026] Therefore, this application employs a two-stage process to ensure that the surface treatment solution is uniformly distributed on the fiber surface and in the micro-defect region, reducing the possibility of localized sudden strong effects. The roughening effect preferentially occurs in the amorphous region, defect region, or more responsive phase of the fiber surface, rather than indiscriminately extending into the deeper layers of the fiber. This allows the entire surface treatment process to balance treatment effectiveness with structural preservation, improving process stability and repeatability.

[0027] Preferably, the temperature of the pre-impregnation stage is 20~40℃, allowing the surface treatment solution to fully wet the composite fiber surface under relatively mild temperature conditions, and gradually penetrate into the micropores, microcracks, adjacent regions of the phase interface, and amorphous regions of the fiber surface, thereby completing the uniform introduction and distribution reforming of the treatment solution on the fiber surface. Furthermore, at 20~40℃, the aqueous phase, low eutectic activation components, sodium carbonate, and polyvinylpyrrolidone in the surface treatment solution can undergo initial contact, adsorption, and interfacial penetration with the fiber surface without significantly triggering strong swelling. At this time, the treatment solution can replace residual adsorbed air and loose adhering layers on the fiber surface, transforming the fiber surface from a relatively dry or locally repellent state to a uniformly wetted state; allowing the effective components in the treatment solution to preferentially enter the accessible areas of the fiber surface, rather than instantaneously diffusing to a deep depth under highly activated conditions; and forming a mild pre-plasticizing and pre-relaxation effect on the amorphous regions and adjacent regions of the phase interface, making the coarsening effect in the subsequent heating stage more uniform.

[0028] Preferably, after pre-impregnation, raising the system temperature to 50-80°C allows the synergistic effect of the eutectic activating component, sodium carbonate, and aqueous phase in the surface treatment solution to be fully utilized. This promotes controlled chain relaxation, local swelling, surface micro-etching, and micro-coarsening in the responsive regions of the composite fiber surface. Under elevated temperature conditions, the mass transfer efficiency and component activity of the surface treatment solution are both improved. The eutectic activating component can reduce the molecular chain binding degree of the amorphous regions or more responsive phases of the fiber surface through hydrogen bond rearrangement, polar environment regulation, and local plasticization, making it easier for controlled swelling to occur. Sodium carbonate provides a mild alkaline environment, which can further promote mild activation of weakly bonded regions, defect regions, or unstable regions on the surface. The aqueous phase plays a role in heat transfer, mass transfer, dilution, and buffering, keeping the above activation processes within a mild and controlled range. As a result, the fiber surface can gradually form microscale undulations, micro-depressions, micropores, or roughened interfaces, thereby increasing the effective surface contact area and surface activity.

[0029] Furthermore, the liquid-to-solid ratio of the surface treatment liquid to the pre-cleaned fibers is (10~60):1. Controlling the liquid-to-solid ratio within this range helps ensure sufficient coating, uniform contact, and stable mass transfer of the surface treatment liquid onto the fibers, thereby improving the consistency of the surface treatment process. In liquid-phase treatment of composite fibers, if the liquid-to-solid ratio is too low, the amount of treatment liquid per unit mass of fiber will be insufficient. This makes it easier for fibers to accumulate locally, become entangled, and block each other, making it difficult for the surface treatment liquid to fully penetrate the surface areas of all fibers, leading to local concentration gradients and uneven treatment. Especially in two-stage treatment, if the liquid volume is insufficient, the pre-wetting stage cannot fully exert its uniform introduction effect, and the surface swelling and coarsening stage cannot maintain stable and balanced mass transfer conditions. On the other hand, if the liquid-to-solid ratio is too high, although it is beneficial for fiber dispersion, it will reduce the effective amount of fiber processed per unit equipment volume, increasing the process load and liquid circulation costs, and is also detrimental to process economy. In addition, excessive liquid volume may also lead to a decrease in the system's heat utilization efficiency, prolonging the heating and cooling processes, which is not conducive to the rhythm control of the two-stage treatment.

[0030] Furthermore, the surface treatment solution of this application comprises, by weight: 70-92 parts water, 5-20 parts eutectic activating component, 0.05-2 parts sodium carbonate, and 0.02-1 parts polyvinylpyrrolidone. This forms a synergistic treatment system with water as the continuous phase, the eutectic activating component as the core of surface activation, sodium carbonate as a mild regulating component, and polyvinylpyrrolidone as the interface regulating component. This ensures that the surface treatment solution possesses sufficient surface activation capacity without causing severe damage to the composite fiber structure as strong alkali or strong solvent systems. Sodium carbonate provides a moderately alkaline environment for the surface treatment solution, promoting activation and relaxation of more responsive areas on the fiber surface, making surface swelling and roughening easier to occur. Simultaneously, sodium carbonate can also help remove some saponifiable or weakly bound organic matter that may still remain on the surface, improving the cleanliness and consistency of the surface treatment. Polyvinylpyrrolidone (PVP) has good water solubility and interfacial affinity, which can improve the spreading and wetting behavior of the surface treatment liquid on the composite fiber surface and enhance the uniformity of the pre-wetting stage. In addition, PPVP can help stabilize desorbed substances and trace surface debris in liquid phase treatment, reducing the probability of their redeposition on the fiber surface, thereby maintaining the cleanliness and openness of the treated surface. Furthermore, PPVP can also buffer against localized excessive action, making the surface roughening process more stable and reducing localized sudden over-etching phenomena.

[0031] It is worth noting that the eutectic activating component can induce mild chain segment relaxation and localized plasticization in the amorphous, weakly bonded, defective, or more responsive phases of the composite fiber surface by constructing a special polar and hydrogen-bonding environment. This makes the surface region more susceptible to controlled swelling and microscopic coarsening during subsequent heating. Compared to simply using strong organic solvents or high-concentration alkaline solutions, the eutectic activating component's effect is more inclined towards mild surface activation and selective intervention. This treatment method is more suitable for composite fibers, which are composed of multiphase structures and exhibit different responses to different media. By introducing the eutectic activating component, the responsiveness of the surface treatment solution to the fiber surface can be enhanced without easily causing deep-seated damage. Controlling the eutectic activating component to 5-20 parts helps it provide sufficient activation capacity to the surface treatment solution without being excessive. If the content is too low, the surface activation effect is insufficient, and the coarsening effect is limited; if the content is too high, the treatment system may be too strong, increasing the risk of uncontrolled treatment depth and damage to the main structure.

[0032] Preferably, the eutectic activating component includes choline chloride and glycerol. Choline chloride, as a hydrogen bond acceptor, has strong polarity and good ionic characteristics, and can form a stable hydrogen bond network with glycerol containing multiple hydroxyl groups; glycerol, as a hydrogen bond donor, has a multi-hydroxyl structure, good hydrophilicity, and mild plasticizing ability. The combination of these two components creates a surface treatment environment that possesses a certain degree of activation without being overly aggressive, making it particularly suitable for the process system of this application that emphasizes "mild selective surface treatment."

[0033] Furthermore, the molar ratio of choline chloride to glycerol is 1:(2~4), which helps maintain the balance between polarity, viscosity, fluidity, and hydrogen bond network strength in the eutectic activation system. If the glycerol ratio is too low, there will be insufficient hydrogen bond donors in the system, which is not conducive to the formation of a stable and uniform eutectic activation environment, and the fluidity and wettability of the system will also be affected. If the glycerol ratio is too high, the proportion of free glycerol will increase, which may weaken the integrity of the eutectic activation structure, making the system more inclined to ordinary plasticization and wetting, while reducing the controlled activation ability of the fiber surface.

[0034] In practical implementation, the preparation of the surface treatment solution includes the following steps: S201. Add choline chloride and glycerol to a reaction vessel at a molar ratio of 1:(2~4) and stir and mix at 60~90℃ until a eutectic activation mother liquor is formed. S202. Add water to the eutectic activation mother liquor and continue stirring to form an aqueous phase system. S203. Add sodium carbonate to the aqueous phase system and stir until the sodium carbonate is completely dissolved; finally, add polyvinylpyrrolidone and continue stirring until all components are mixed evenly to obtain the surface treatment solution.

[0035] S300 includes termination and washing processes. S300 promptly terminates the selective surface swelling and roughening treatment in S200, removing residual treatment media, desorption products, and migratable small molecules from the fiber surface, thus fixing the already formed surface roughening state and preventing further penetration of the treatment into the fiber. The termination process includes at least one of cooling quenching, weak acid neutralization, and deionized water washing. Cooling quenching helps suppress the diffusion and continued action of the surface treatment solution by rapidly lowering the system temperature; weak acid neutralization helps neutralize the residual alkaline environment, terminating the surface activation process under alkaline conditions; and deionized water washing helps remove residual eutectic activation components, salts, and desorption fragments, improving the cleanliness and stability of the fiber surface after treatment.

[0036] Preferably, the weak acid neutralization treatment uses at least one of acetic acid solution, citric acid solution, and lactic acid solution, wherein the mass fraction of the weak acid neutralizing solution is 0.01-1%, and the solution is washed until the pH of the filtrate is 6.0-7.5. Acetic acid, citric acid, and lactic acid are all organic weak acids with good water solubility, mild acidity, and high process compatibility, which can effectively neutralize residual alkalinity while reducing the risk of secondary disturbance to the surface and main structure of the composite fiber. Controlling the mass fraction of the weak acid neutralizing solution at 0.01-1% is beneficial for balancing neutralization efficiency and the mildness of the final treatment; controlling the washing endpoint at a filtrate pH of 6.0-7.5 is beneficial for keeping the pretreated composite fiber in a near-neutral stable state, thereby improving the retention of the surface roughened structure and the adaptability to subsequent processing.

[0037] This application has undergone multiple experiments, and some of the test results are presented here for reference to further describe the invention in detail. The following is a detailed description in conjunction with specific embodiments. Example 1

[0038] This embodiment provides a pretreatment method for composite fiber structural materials, the pretreatment method including the following steps: S100. Take 100g of core-sheath composite fiber (core layer is polyethylene terephthalate, sheath layer is copolyester; fiber length is 1mm, fineness is 0.3dtex), add it to 2000g of deionized water, wash it at 20℃ by mechanical stirring for 5min, filter it, and obtain pre-cleaned fiber. S200. Add the pre-cleaned fiber to the surface treatment solution, control the liquid-solid ratio of the surface treatment solution to the pre-cleaned fiber to be 10:1, pre-wet at 20°C for 10 min, then raise the temperature to 50°C at about 2°C / min, perform surface swelling and roughening treatment for 10 min, filter after treatment to obtain intermediate fiber. S300: Immediately add the intermediate fiber to 10℃ deionized water for cooling and quenching for 2 minutes, then transfer it to a 0.01% acetic acid aqueous solution for weak acid neutralization treatment for 5 minutes, then wash with deionized water until the pH of the filtrate is 6.0, and dry to obtain the pretreated composite fiber. The surface treatment solution includes the following preparation steps: S201. Add choline chloride and glycerol to the reaction vessel at a molar ratio of 1:2, and stir at 60°C for 30 minutes until a transparent and homogeneous eutectic activation mother liquor is formed. S202. Add 92 parts of water to 7.75 parts of eutectic activation mother liquor and continue stirring to form a homogeneous aqueous phase system; S203. Add 0.05 parts of sodium carbonate to the aqueous phase system and stir until the sodium carbonate is completely dissolved; then add 0.02 parts of polyvinylpyrrolidone and continue stirring until all components are mixed evenly to obtain the surface treatment solution. Example 2

[0039] This embodiment provides a pretreatment method for composite fiber structural materials, the pretreatment method including the following steps: S100. Take 100g of matrix-fiber composite fiber (continuous matrix phase is copolyester, fibril phase is polyester microfiber; fiber length is 6mm, fineness is 2.0dtex), add it to 2000g of 50% ethanol aqueous solution, and clean it for 15min at 40℃ using a shaking cleaning method. Filter to obtain pre-cleaned fiber. S200. Add the pre-cleaned fiber to the surface treatment solution, control the liquid-solid ratio to 30:1, pre-wet at 30℃ for 15 minutes, then heat to 65℃ for surface swelling and roughening treatment for 20 minutes, filter to obtain the intermediate fiber. S300: The intermediate fiber is first neutralized in a 0.1% citric acid aqueous solution for 5 minutes, then washed with deionized water until the pH of the filtrate is 6.8, and dried to obtain the pretreated composite fiber. The surface treatment solution is the same as in Example 1, except that in S201, choline chloride and glycerol are added to the reaction vessel at a molar ratio of 1:3 and stirred at 75°C for 40 min to obtain a eutectic activation mother liquor. In S202, 82 parts of water were added to 17.3 parts of eutectic activation component; In S203, 0.5 parts sodium carbonate and 0.2 parts polyvinylpyrrolidone are added to obtain a surface treatment solution. Example 3

[0040] This embodiment provides a pretreatment method for composite fiber structural materials, the pretreatment method including the following steps: S100. Take 100g of hollow composite fiber (outer layer is copolyester, inner layer is polyester, hollow structure extends along fiber axis; fiber length is 12mm, fineness is 6dtex), add it to 2500g of isopropanol aqueous solution with a volume fraction of 70%, wash it for 30min at 60℃ using a circulating rinsing method, filter it, and obtain pre-cleaned fiber. S200. Add the pre-cleaned fiber to the surface treatment solution, control the liquid-solid ratio to 60:1, pre-impregnate at 40℃ for 20 minutes, then raise the temperature to 80℃ for surface swelling and roughening treatment for 30 minutes, filter, and obtain the intermediate fiber. S300. The intermediate fiber is first placed in deionized water for cooling and quenching for 3 minutes, then transferred to a 1% lactic acid aqueous solution for neutralization treatment for 8 minutes, and then washed with deionized water until the pH of the filtrate is 7.5. After drying, the pretreated composite fiber is obtained. The surface treatment solution is the same as in Example 1, except that in S201, choline chloride and glycerol are added to the reaction vessel at a molar ratio of 1:4 and stirred at 90°C for 50 min to obtain a eutectic activation mother liquor. In S202, 70 parts of water are added to 27 parts of eutectic activation component; In S203, 2 parts sodium carbonate and 1 part polyvinylpyrrolidone are added to obtain a surface treatment solution. Example 4

[0041] This embodiment provides a pretreatment method for composite fiber structural materials, the pretreatment method including the following steps: S100, same as in Example 1; S200: Add the pre-cleaned fibers to the surface treatment solution, and control the liquid-solid ratio to be 20:1. The rest is the same as in Example 1. S300: The intermediate fiber is placed in 10℃ deionized water for 2 minutes and then washed with deionized water until the pH of the filtrate is 7.0. After drying, the pretreated composite fiber is obtained. The surface treatment solution is the same as in Example 1, except that in S201, choline chloride and glycerol are added to the reaction vessel at a molar ratio of 1:3 and stirred at 80°C for 50 min to obtain a eutectic activation mother liquor. In S202, 85 parts of water were added to 14.6 parts of the eutectic activation component; In S203, 0.3 parts sodium carbonate and 0.1 parts polyvinylpyrrolidone are added to obtain a surface treatment solution. Example 5

[0042] This embodiment provides a pretreatment method for composite fiber structural materials, the pretreatment method including the following steps: S100, same as in Example 2; S200: Add the pre-cleaned fibers to the surface treatment solution, and control the liquid-solid ratio to be 25:1. The rest is the same as in Example 2. S300: The intermediate fibers were treated in a 0.3% (w / w) acetic acid aqueous solution for 6 min, followed by washing with deionized water until the pH of the filtrate reached 6.5. After drying, the pretreated composite fibers were obtained. The surface treatment solution is the same as in Example 2.

[0043] Comparative Example 1 This comparative example provides a pretreatment method for composite fiber structural materials. The pretreatment method is the same as in Example 2, except that in S100, no surface cleaning pretreatment is performed. Instead, 100g of matrix-fiber composite fiber is taken and directly subjected to S200 surface swelling and roughening treatment and S300 termination treatment.

[0044] Comparative Example 2 This comparative example provides a pretreatment method for composite fiber structural materials. The pretreatment method is the same as in Example 2, except that the surface treatment liquid is changed to include 82 parts water, 0.5 parts sodium carbonate and 0.2 parts polyvinylpyrrolidone by weight, that is, no eutectic activation component is added.

[0045] Comparative Example 3 This comparative example provides a pretreatment method for composite fiber structural materials. The pretreatment method is the same as in Example 2, except that the surface treatment liquid is changed to include 82 parts water, 17.3 parts eutectic activating component and 0.2 parts polyvinylpyrrolidone by weight, i.e., sodium carbonate is not added.

[0046] Comparative Example 4 This comparative example provides a pretreatment method for a composite fiber structural material. The pretreatment method is the same as in Example 2, except that the surface treatment liquid is changed to include 82 parts water, 17.3 parts eutectic activating component and 0.5 parts sodium carbonate by weight, i.e., polyvinylpyrrolidone is not added.

[0047] Comparative Example 5 This comparative example provides a pretreatment method for composite fiber structural materials. The pretreatment method is the same as in Example 2, except that in S200, the pre-cleaned fibers are directly added to a surface treatment solution at 65°C for 20 minutes, i.e., no pre-wetting stage is set.

[0048] Performance testing The composite fiber structural materials obtained in Examples 1-5 and Comparative Examples 1-5, as well as the untreated blank group, were tested using the following test methods. The results are shown in Table 1. Fiber surface roughness: Take the treated fiber sample, lay it flat and fix it on the sample stage, and use an atomic force microscope to test the fiber surface morphology; 20 fibers are randomly selected from each group of samples, and the average surface roughness Ra is taken; Fiber surface wettability: The treated fibers were made into thin fiber sheets, and their static water contact angles were tested at 25°C using a contact angle meter; each group of samples was tested in parallel 5 times, and the average value was taken; Main structure retention of fiber: Take fibers before and after treatment and conduct single fiber strength tests. 30 fibers are tested in each group of samples, and calculate the breaking strength retention rate. Subsequent interfacial bonding performance: pretreated fibers were added to paper-based composite pulp or resin matrix to prepare composite strips, and the internal bonding strength was measured; Table 1 As shown in Table 1, the pretreated composite fibers obtained in Examples 1-5 all exhibited good comprehensive effects in terms of fiber surface roughness, surface wettability and subsequent interfacial bonding performance, and maintained a high degree of fiber main structure integrity while improving surface performance.

[0049] In summary, this application, through the synergistic combination of surface cleaning pretreatment, a specific surface treatment liquid system, two-stage selective surface swelling and roughening treatment, and termination and washing treatments, effectively improves the surface roughness and wettability of composite fiber structural materials, enhances their subsequent interfacial bonding performance, and simultaneously maintains the integrity of the fiber's main structure, thus achieving a balance between surface modification effects and structural retention performance. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of this invention; therefore, the scope of protection of this invention should be determined by the scope defined in the claims.

Claims

1. A pretreatment method for composite fiber structural materials, characterized in that, The preprocessing method includes the following steps: S100. The composite fiber structure material is subjected to surface cleaning pretreatment to obtain pre-cleaned fibers. S200: The pre-cleaned fibers are added to a surface treatment solution for selective surface swelling and roughening treatment to obtain intermediate fibers; S300. The intermediate fiber is subjected to termination treatment and washing treatment to obtain pretreated composite fiber.

2. The pretreatment method according to claim 1, characterized in that, In S100, The composite fiber structural material includes at least one of core-sheath type composite fiber, matrix-fiber type composite fiber, and hollow composite fiber; and / or The composite fiber structure material has a length of 1~12mm and a fineness of 0.3~6dtex.

3. The pretreatment method according to claim 1, characterized in that, In S100, the cleaning solution for the surface cleaning pretreatment includes at least one of deionized water, aqueous ethanol solution, or aqueous isopropanol solution; and the temperature of the surface cleaning pretreatment is 20~60℃, and the cleaning time is 5~30min.

4. The pretreatment method according to claim 1, characterized in that, In S200, the surface treatment liquid comprises, by weight: 70-92 parts water, 5-20 parts eutectic activation component, 0.05-2 parts sodium carbonate, and 0.02-1 parts polyvinylpyrrolidone.

5. The pretreatment method according to claim 4, characterized in that, The eutectic activating components include choline chloride and glycerol.

6. The pretreatment method according to claim 5, characterized in that, The molar ratio of the choline chloride to the glycerol is 1:(2~4).

7. The pretreatment method according to claim 1, characterized in that, In S200, the selective surface swelling and roughening treatment includes a pre-wetting stage and a surface swelling and roughening stage; The temperature of the pre-impregnation stage is 20~40℃; the temperature of the surface swelling and roughening stage is 50~80℃.

8. The pretreatment method according to claim 1, characterized in that, In S200, the liquid-solid ratio of the surface treatment liquid to the pre-cleaned fiber is (10~60):

1.

9. The pretreatment method according to claim 1, characterized in that, In S300, the termination process includes at least one of cooling quenching, weak acid neutralization treatment, and deionized water washing.

10. The pretreatment method according to claim 9, characterized in that, The weak acid neutralization treatment uses at least one of acetic acid solution, citric acid solution, and lactic acid solution, wherein the mass fraction of the weak acid neutralizing solution is 0.01~1%, and the solution is washed until the pH of the filtrate is 6.0~7.5.

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