A PVA fiber oiling method oriented to fiber-cement material adhesion

Abstract

The application relates to the technical field of fiber reinforced cement-based composite materials, and discloses a PVA fiber oil coating method oriented by fiber-gel material adhesion, which comprises the following steps: determining a target interface adhesion performance grade between polyvinyl alcohol fibers and gel materials; according to the target interface adhesion performance grade, an oil coating liquid is prepared; dry polyvinyl alcohol fibers are immersed in the prepared oil coating liquid, and the polyvinyl alcohol fibers absorb the prepared oil coating liquid; the polyvinyl alcohol fibers absorbing the oil coating liquid are subjected to spin-drying treatment; and the spin-dried polyvinyl alcohol fibers are subjected to heat curing treatment, so that a continuous, uniform and non-peeling coating film layer is formed on the surface of the polyvinyl alcohol fibers. By establishing a five-grade adhesion performance grading system based on a single fiber tensile test and correlating the five-grade adhesion performance grading system with macroscopic tensile performance and crack behavior of concrete, the problem that adhesion performance regulation lacks systematicness and quantitative basis in the prior art is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fiber reinforced cement-based composite materials, in particular to a PVA fiber oil coating method oriented by fiber-cementitious material adhesion. BACKGROUND

[0002] Polyvinyl alcohol (PVA) fiber is a key component for preparing high-ductility cement-based composites. The macro-mechanical properties of such composites, such as tensile strain hardening capacity and multi-cracking behavior, are largely determined by the interfacial properties between PVA fiber and cement matrix. The adhesion strength, frictional properties and energy dissipation capacity of the fiber-matrix interface directly affect the stress transfer efficiency and crack propagation pattern of the composite under loading conditions.

[0003] In the prior art, in order to solve the problem of excessive adhesion between PVA fiber and cement matrix due to the rich hydroxyl groups in PVA fiber, an oil coating treatment method is usually used. The basic application is to form a physical isolation film on the surface of PVA fiber by applying a layer of oil coating agent. This film aims to weaken the excessive chemical adhesion and hydrogen bonding between the fiber and the cement hydration products. In this way, the fiber can be prevented from being directly pulled off when the matrix cracks, and it is encouraged to slide and pull out from the matrix.

[0004] However, the existing PVA fiber oil coating technology has a simple oil coating agent formula, mainly plays a lubricating role, and its target is to weaken the adhesion. However, it lacks systematic control means for grading and quantifying the adhesion strength, and the control of key process parameters such as impregnation, spin-drying and heat curing is not strict, which easily leads to uneven or poor adhesion of the fiber oil coating film, resulting in performance dispersion of single batch of fibers. Therefore, the present application provides a PVA fiber oil coating method oriented by fiber-cementitious material adhesion to solve the problems existing in the prior art. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a PVA fiber oil coating method oriented by fiber-cementitious material adhesion, which solves the problem that the interfacial adhesion performance of existing polyvinyl alcohol fiber in reinforcing cement-based composites is difficult to accurately control.

[0006] To achieve the above purpose, the present application is implemented by the following technical scheme: the present application provides a PVA fiber oil coating method oriented by fiber-cementitious material adhesion, comprising the following steps:

[0007] S1, according to the preset performance requirements of fiber reinforced concrete, determine the target interfacial bond performance level between polyvinyl alcohol fiber and cementitious material, the target interfacial bond performance level can be selected according to the required concrete performance, such as ductility, strength or crack control. The target interfacial bond performance level includes low bond levels I-II, balanced bond level III and high bond levels IV-V.

[0008] S2, according to the target interfacial bond performance level determined, select hydroxyl silicone oil, coating auxiliary silicone oil, polydimethylsiloxane, vinyl acetate-ethylene copolymer emulsion and solvent, and prepare the oil covering liquid, the mass fraction of each component in the oil covering liquid can be adjusted according to the target bond level. For example, the mass fraction of polydimethylsiloxane is 10-500 parts by mass; the mass fraction of coating auxiliary silicone oil is 5-200 parts by mass; the mass fraction of hydroxyl silicone oil is 10-200 parts by mass; the mass fraction of vinyl acetate-ethylene copolymer emulsion is 5-400 parts by mass, and the solid content of the vinyl acetate-ethylene copolymer emulsion is in the range of 30%-55%; the mass fraction of the solvent is 800-1200 parts by mass. For lower bond levels (such as levels I-II), the oil covering liquid formula can tend to use a higher proportion of polydimethylsiloxane and coating auxiliary silicone oil; for higher bond levels (such as levels IV-V), the proportion of vinyl acetate-ethylene copolymer emulsion and hydroxyl silicone oil can be increased.

[0009] S3, the polyvinyl alcohol fiber subjected to pre-drying treatment is completely immersed in the prepared oil covering liquid. During the immersion process, the temperature of the oil covering liquid is controlled in the range of 25℃ to 40℃, and the immersion time is controlled to be 25±2 minutes. The polyvinyl alcohol fiber absorbs the oil covering liquid and forms a uniform liquid film on the surface of the fiber.

[0010] S4, the polyvinyl alcohol fiber that has absorbed the oil covering liquid is subjected to spin-drying treatment. The spin-drying operation aims to remove the excess oil covering liquid on the surface of the fiber, ensure that the oil covering liquid is evenly attached to the surface of the fiber, and there is no visible liquid droplet residue on the surface. The spin-drying process can be carried out by centrifugal spin-drying, roller removal or slight vibration. The liquid absorption rate of the oil-covered polyvinyl alcohol fiber after spin-drying treatment is controlled to be between 5% and 15%.

[0011] S5, the polyvinyl alcohol fiber after spin-drying is subjected to heat curing treatment. The heat curing treatment provides controlled heat energy to promote the volatilization of the solvent in the oil covering liquid and initiate the cross-linking reaction between the oil covering components. The heat curing temperature is controlled in the range of 80℃-120℃, and the heat curing time is set to be 5-10 minutes. Through heat curing, a continuous, uniform, non-peeling and firm and stable coating film layer is formed on the surface of the polyvinyl alcohol fiber.

[0012] The application provides a PVA fiber oiling method oriented to fiber-gel material adhesion.

[0013] 1、The application solves the problem of lack of systematicness and quantitative basis in adhesion performance regulation in the prior art by establishing a five-level adhesion performance classification system based on single fiber tensile test and correlating it with the macroscopic tensile performance and crack behavior of concrete.

[0014] 2、The application forms a targeted oiling formula system by selecting a plurality of components such as hydroxyl silicone oil, polydimethylsiloxane and ethylene-vinyl acetate emulsion and adjusting the mass fraction ratio according to the target adhesion grade, ensuring the continuity, uniformity and non-peeling of the oiling film layer on the surface of the PVA fiber.

[0015] 3、The application realizes iterative optimization and closed-loop control of the interface performance by introducing single fiber tensile test to evaluate the modification effect in real time and comparing the test results with the preset grade, and adjusting the oiling formula parameters in time when deviating from the target interval. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 The method flowchart of the application. DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the specification of the application. Obviously, the described embodiments are only part of the embodiments of the application, not all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the application.

[0018] The sources and specifications of the main raw materials and reagents used in the following examples and comparative examples are as follows, and the reagents not specifically described are commercially available analytical pure or higher grade products.

[0019] Hydroxyl silicone oil: polydimethylsiloxane (containing hydroxyl), CAS number: 70131-67-8, viscosity 500 mPa·s.

[0020] Coating aid silicone oil: poly(dimethylsiloxane-3-hydroxypropyl methylsiloxane) polyoxyethylene polyoxypropylene ether, CAS No.: 68937-55-3.

[0021] Polydimethylsiloxane: CAS No.: 9006-65-9, viscosity 1000 mPa-s.

[0022] Vinyl acetate-ethylene copolymer emulsion: CAS No.: 24937-78-8, solid content 50%.

[0023] See attached Figure 1 , Example 1:

[0024] Raw material components (by mass fraction):

[0025] Polydimethylsiloxane: 400 parts;

[0026] Coating aid silicone oil: 150 parts;

[0027] Hydroxyl silicone oil: 20 parts;

[0028] Vinyl acetate-ethylene copolymer emulsion: 30 parts;

[0029] Deionized water: 1000 parts.

[0030] Preparation steps:

[0031] Oil coating liquid formula: add each component raw material to the stirring container, stir at room temperature for 30 minutes until a uniform and stable oil coating liquid is formed;

[0032] Immersion: completely immerse the PVA fiber (diameter 20 μm, length 12 mm, density 1.3 g / cm 3 ) that has been pre-dried into the oil coating liquid that has been prepared. During this immersion process, control the temperature of the oil coating liquid to maintain at 25°C. The immersion time is controlled to be 25 minutes. The PVA fiber absorbs the oil coating liquid and forms a uniform liquid film on the surface of the fiber;

[0033] Spin-drying: spin-dry the PVA fiber that has completed the immersion to remove the excess oil coating liquid on its surface. During the spin-drying process, adjust the centrifugal speed so that there is no visible liquid droplet residue on the surface of the PVA fiber, ensuring that the oil coating liquid is evenly attached to the surface of the fiber. The liquid absorption rate of the oil-coated PVA fiber after spin-drying is controlled to be 10%;

[0034] Thermal curing: perform thermal curing treatment on the PVA fiber after spin-drying. Place the oil-coated PVA fiber in a forced air drying oven, control the thermal curing temperature to be 100°C, and set the thermal curing time to be 8 minutes. Through thermal curing, a continuous and uniform coating film layer is formed on the surface of the PVA fiber without peeling.

[0035] Example 2:

[0036] Raw material components (by mass fraction):

[0037] Polydimethylsiloxane: 150;

[0038] Coating aid silicone oil: 80;

[0039] Hydroxyl silicone oil: 80;

[0040] Vinyl acetate-ethylene copolymer emulsion: 150;

[0041] Deionized water: 1000.

[0042] Preparation steps:

[0043] Oil coating liquid formula: Add each component raw material to a stirring container and stir at room temperature for 30 minutes until a uniform and stable oil coating liquid is formed;

[0044] Immersion: Completely immerse the pre-dried PVA fiber into the prepared oil coating liquid. During the immersion process, control the temperature of the oil coating liquid to maintain at 30°C. The immersion time is controlled for 25 minutes. The PVA fiber absorbs the oil coating liquid and forms a uniform liquid film on the surface of the fiber;

[0045] Spin-drying: Perform roller pressing removal treatment on the immersed PVA fiber to remove the excess oil coating liquid on its surface. During the spin-drying process, adjust the roller pressing pressure to ensure that there is no visible liquid droplet residue on the surface of the PVA fiber, and ensure that the oil coating liquid is evenly attached to the surface of the fiber. The liquid absorption rate of the oil-coated PVA fiber after spin-drying treatment is controlled at 12%;

[0046] Heat curing: Perform heat curing treatment on the spin-dried PVA fiber. Place the oil-coated PVA fiber in a forced air drying oven, control the heat curing temperature at 110°C, and set the heat curing time for 7 minutes. Through heat curing, a continuous and uniform coating film layer is formed on the surface of the PVA fiber without peeling.

[0047] Example 3:

[0048] Raw material components (by mass fraction):

[0049] Polydimethylsiloxane: 50;

[0050] Coating aid silicone oil: 10;

[0051] Hydroxyl silicone oil: 180;

[0052] Vinyl acetate-ethylene copolymer emulsion: 350;

[0053] Deionized water: 1000.

[0054] Preparation steps:

[0055] Oiling liquid formulation: Add each component raw material into a stirring container, stir for 30 minutes at room temperature until a uniform and stable oiling liquid is formed;

[0056] Immersion: The pre-dried PVA fiber is completely immersed into the prepared oiling liquid. During the immersion process, the temperature of the oiling liquid is controlled at 35°C. The immersion time is controlled for 25 minutes. The PVA fiber absorbs the oiling liquid and forms a uniform liquid film on the surface of the fiber.

[0057] Spin-drying: The PVA fiber after immersion is subjected to a slight vibration spin-drying treatment to remove the excess oiling liquid on its surface. During the spin-drying process, the vibration frequency and time are adjusted so that there is no visible liquid droplet residue on the surface of the PVA fiber, ensuring that the oiling liquid is evenly attached to the surface of the fiber. The liquid absorption rate of the oiling PVA fiber after spin-drying is controlled at 15%.

[0058] Heat curing: The PVA fiber after spin-drying is subjected to heat curing treatment. The oiling PVA fiber is placed in a forced air drying oven, the heat curing temperature is controlled at 90°C, and the heat curing time is set for 10 minutes. Through heat curing, a continuous and uniform coating film layer is formed on the surface of the PVA fiber without peeling off.

[0059] Comparative Example 1:

[0060] Compared with Example 1, the difference is that the PVA fiber is not subjected to any oiling treatment, and the rest is the same.

[0061] Comparative Example 2:

[0062] Compared with Example 1, the difference is that the mass fraction of polydimethylsiloxane in the oiling liquid is 550 parts, and the rest is the same.

[0063] Comparative Example 3:

[0064] Compared with Example 3, the difference is that the mass fraction of vinyl acetate-ethylene copolymer emulsion in the oiling liquid is 20 parts, and the rest is the same.

[0065] Comparative Example 4:

[0066] Compared with Example 2, the difference is that the temperature of the oiling liquid during the immersion process is controlled at 50°C, and the rest is the same.

[0067] Comparative Example 5:

[0068] Compared with Example 3, the difference is that the heat curing time is set for 3 minutes, and the rest is the same.

[0069] Experiment 1:

[0070] Purpose of the experiment: to evaluate the interfacial bonding performance between each PVA fiber and the cement matrix.

[0071] Experimental procedure:

[0072] The PVA monofilament fibers (including the oil-coated PVA fibers and the uncoated PVA fibers prepared in the examples and comparative examples) were embedded in the center of the cement mortar cubic specimens (size 40 mm x 40 mm x 40 mm) with a preset embedding length (e.g., 10 mm). The cement mortar matrix was divided into three types according to the preset conditions:

[0073] Matrix A: prepared with high mineral admixture content (e.g., fly ash and silica fume with a total mass fraction of more than 60%), low water-binder ratio (water / binder mass ratio of 0.25), and fine aggregate (e.g., river sand with a fineness modulus of 2.6).

[0074] Matrix B: prepared with medium water-binder ratio (water / binder mass ratio of 0.4), ordinary Portland cement, and medium sand.

[0075] Matrix C: prepared with low water-binder ratio (water / binder mass ratio of 0.30) and added with silica fume or expansive agent to improve the density and early strength performance. The prepared specimens were cured under standard curing conditions (temperature 20°C, relative humidity greater than 95%) for 28 days.

[0076] The cured fiber-embedded specimens were fixed on the grips of an electronic universal testing machine, ensuring that the fiber axis was aligned with the loading direction. The loading rate was set to 0.5 mm / min until the fiber was pulled out or broken, and the data was recorded.

[0077] The experimental results are shown in Table 1.

[0078] Table 1: Results of monofilament pull-out test

[0079]

[0080] From the single filament pull-out test results in Table 1, it can be seen that the PVA fibers prepared in Example 1 have both the maximum bond stress and the pull-out work at a lower level. This indicates that the higher proportion of dimethicone and coating auxiliary silicone oil in the oiling formulation combined with specific process parameters forms a relatively smooth and low-friction interface film layer on the fiber surface, which is beneficial for the effective slip of the fiber in the cement matrix, thereby achieving a lower interfacial bond strength. The PVA fibers prepared in Example 3 have both the maximum bond stress and the pull-out work at a higher level, which is related to the higher proportion of vinyl acetate-ethylene copolymer emulsion and hydroxyl silicone oil in the oiling formulation and the corresponding process parameters. This combination forms a more adhesive and tough film layer on the fiber surface, increasing the frictional resistance and occlusal force between the fiber and the matrix, making the fiber need to overcome greater resistance during the pulling process, showing a higher interfacial bond strength.

[0081] The test results of the comparative examples further verify the direct influence of the oiling formulation components and process parameters on the interfacial bonding performance. For example, Comparative Example 1 (PVA fibers without oiling) has a significantly lower maximum bond stress and pull-out work than all the examples due to the lack of an oiling film layer, direct contact between the fiber and the matrix, and ineffective regulation of interfacial friction and adhesion. Comparative Examples 2 and 3, compared with the examples, change the physical and chemical properties of the interfacial film layer by adjusting the proportion of specific components (such as dimethicone or vinyl acetate-ethylene copolymer emulsion). Comparative Examples 4 and 5 change the formation process or the degree of solidification of the oiling film layer by changing the immersion temperature and heat curing time, thereby affecting the uniformity, density and adhesion of the film layer, resulting in a deviation of the bonding performance from the target interval, which shows that the precise control of process parameters plays an important role in achieving the target interfacial performance. The above results all support the invention content that by regulating the oiling liquid components and oiling process parameters, a controllable interfacial film layer is constructed on the surface of the PVA fiber, and the interfacial bonding performance between the PVA fiber and the cement matrix is precisely regulated.

[0082] By selecting hydroxyl silicone oil, coating auxiliary silicone oil, dimethicone, vinyl acetate-ethylene copolymer emulsion and solvent, and formulating the oiling liquid, the quantitative regulation of the interfacial bonding performance between the PVA fiber and the cementitious material is achieved. The mass fraction of each component in the oiling liquid and the subsequent oiling process steps (immersion, spin-drying, heat curing) work together to form a coating film layer with specific physical and chemical properties on the surface of the PVA fiber. This film layer provides a controllable frictional resistance during the fiber pull-out process, affecting the energy dissipation at the interface.

[0083] Experiment 2:

[0084] Purpose of the experiment: to evaluate the influence of PVA fibers treated with different oiling on the macroscopic mechanical properties of cement-based composites.

[0085] Experimental procedure:

[0086] PVA fibers prepared in the Examples and Comparative Examples were used to prepare cementitious composite tensile specimens with a fiber volume fraction of 2.0%. The matrix composition was based on an ECC system, which included P.O 42.5 ordinary portland cement, Class I fly ash, silica fume, river sand with a fineness modulus of 2.6, water, and polycarboxylate superplasticizer. The components and fibers were mixed uniformly in a mixer and then cast into dumbbell-shaped specimen molds with a gauge length of 80 mm x 30 mm x 15 mm. The specimens were cured under standard curing conditions (temperature 20 °C, relative humidity greater than 95%) for 28 days.

[0087] The test was performed on an electronic universal testing machine. The cured dumbbell-shaped specimens were fixed at both ends in the grips of the testing machine. Displacement transducers (LVDTs) were installed on both sides of the gauge length of the specimen to measure the deformation during the tensile test. The test was displacement-controlled with a loading rate of 0.5 mm / min, and the loading was continued until the specimen was completely destroyed. During the test, the load-displacement data were recorded synchronously.

[0088] Based on the recorded load-displacement data, the following mechanical properties were calculated:

[0089] Tensile strength: determined from the peak stress in the tensile stress-strain curve.

[0090] Ultimate tensile strain: the strain value on the tensile stress-strain curve corresponding to the peak stress. At the same time, after the test was completed, the macroscopic crack distribution characteristics in the gauge length of the specimen were recorded by visual observation.

[0091] The experimental results are shown in Table 2.

[0092] Table 2: Mechanical properties of fiber-reinforced concrete

[0093]

[0094] The test data in Table 2 show that the tensile strength and ultimate tensile strain of the concrete specimens prepared with the oil-coated fibers in the different Examples exhibit regular changes. The fibers prepared in Example 1 imparted a tensile strength of 2.37 MPa and an ultimate tensile strain of 2.15% to the concrete specimens. The fibers prepared in Example 3 resulted in a tensile strength of 5.62 MPa and an ultimate tensile strain of 0.68% for the concrete specimens. The results of Example 2 were intermediate between the two.

[0095] In Example 1, the low-friction interface film layer formed by the oiling formulation results in a low bonding force between the fiber and the matrix. When the concrete cracks, the fiber can smoothly slide and pull out from the matrix, which effectively dissipates energy and promotes stress redistribution in the matrix, thereby initiating new micro-cracks. The continuous process results in high ultimate tensile strain and uniform development of multiple cracks in the macroscopic view. In Example 3, the high-adhesion interface film layer formed by the oiling formulation results in a strong bonding force between the fiber and the matrix. In this condition, the fiber can effectively bear and transfer stress, thereby improving the tensile strength of the concrete. However, due to the strong bonding force, the fiber is difficult to slide and pull out before reaching its own tensile strength, and stress is concentrated at the crack tip, resulting in fiber breakage, which limits the macroscopic deformation capacity of the material, showing low ultimate tensile strain and fewer cracks.

[0096] The PVA fiber without oiling treatment in Comparative Example 1 forms an uncontrollable interface bonding between the fiber and the matrix, which cannot effectively transfer stress or dissipate energy, resulting in cracking of the concrete specimen at a low stress level, and once the crack is formed, it rapidly expands, ultimately showing a low ultimate tensile strain of 0.19% and a low tensile strength of 1.83 MPa, exhibiting brittle fracture characteristics. The test data objectively reflect that the present application can regulate the bonding performance of the fiber-matrix interface by systematically designing the oiling liquid formulation and controlling the oiling process, thereby enabling the final fiber-reinforced concrete composite material to obtain specific tensile strength, ultimate tensile strain, and crack distribution characteristics.

[0097] Experiment 3:

[0098] Experimental purpose: Through four-point bending test, the effect of PVA fiber treated by different oiling on the bending performance of cement-based composite material is evaluated.

[0099] Experimental steps:

[0100] The PVA fibers prepared in the examples and comparative examples are used to prepare cement-based composite beam-shaped specimens at a volume fraction of 2.0%. The matrix ratio uses the ECC system, and the components are the same as those used in the uniaxial tensile test. After mixing the components and the fiber uniformly in a mixer, they are poured into a beam-shaped specimen mold with dimensions of 350 mm x 50 mm x 15 mm. After the specimen is poured and formed, it is cured under standard curing conditions (temperature 20°C, relative humidity greater than 95%) for 28 days.

[0101] The test was performed on an electronic universal testing machine, using a four-point bending loading method. The support point span of the test device was set to 300 mm, and the loading point span was set to 100 mm. A displacement sensor (LVDT) was installed at the bottom of the mid-span of the test piece to measure the deflection of the pure bending section of the beam. The test used displacement control loading, and the loading rate was set to 0.5 mm / min, and stopped when the mid-span deflection reached 3 mm. During the test, the load-deflection data was recorded synchronously.

[0102] According to the recorded load-deflection curve, the following mechanical performance indicators were calculated:

[0103] Flexural strength: calculated according to the peak load in the load-deflection curve.

[0104] Flexural toughness: calculate the area of the curve envelope under the load-deflection curve, from the starting point of loading to the point where the mid-span deflection reaches 3 mm. This area represents the energy absorbed by the test piece during bending deformation.

[0105] The experimental results are shown in Table 2.

[0106] Table 2: Mechanical performance results of fiber-reinforced concrete

[0107]

[0108] The test data in Table 3 shows that the flexural strength and flexural toughness of the beam-shaped test pieces prepared using the oil-coated fibers in different embodiments are significantly different. Among them, the flexural toughness of the test piece using the fiber of Example 1 reaches 16.2 J; the flexural strength of the test piece using the fiber of Example 3 reaches 9.15 MPa. The results of Example 2 show a combination of flexural strength and flexural toughness.

[0109] In Example 1, the low bonding interface formed by the oil coating formula allows the fiber to mainly act in the form of pull-out at the crack surface. Fiber pull-out is a continuous, long-stroke energy dissipation process that effectively suppresses the unstable propagation of cracks, allowing the material to deform significantly under bending load without losing load-carrying capacity, which is manifested macroscopically as high flexural toughness. In Example 3, the high bonding interface formed by the oil coating formula allows effective stress transfer between the fiber and the matrix. When a crack appears, the high bonding force allows the fiber to bear higher tensile stress, thereby improving the material's ability to resist cracking and failure. However, due to the excessive bonding, the fiber is broken before pull-out, limiting energy dissipation, and therefore the flexural toughness is low.

[0110] The uncoated fiber in Comparative Example 1 cannot effectively form a sustained bridging effect at the crack due to the uncontrollable interface performance between the fiber and the matrix, resulting in the beam-shaped test piece being broken after reaching a low bending strength, and the energy absorption capacity is limited, and the final bending toughness is only 2.1 J. The test data show that by adjusting the mass fraction of each component (such as polydimethylsiloxane, hydroxyl silicone oil, and vinyl acetate-ethylene copolymer emulsion) of the oil coating liquid, and combining with specific dipping, drying and heat curing processes, the physical and chemical properties of the fiber surface can be accurately constructed. This construction directly changes the interfacial bonding behavior of the fiber in the matrix, so that the macroscopic bending performance (bending strength and bending toughness) of the composite material can be controlled according to the preset target.

[0111] Although embodiments of the present application have been shown and described, it is to be understood that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for coating PVA fibers with oil based on the adhesive properties of fiber-cementing materials, characterized in that, Includes the following steps: S1. Determine the target interfacial bond performance level between polyvinyl alcohol fiber and cementitious material based on the preset performance requirements of fiber-reinforced concrete. S2. Based on the target interface adhesion performance level, select hydroxyl silicone oil, coating additive silicone oil, polydimethylsiloxane and vinyl acetate-ethylene copolymer emulsion, as well as solvent, and prepare the coating solution. S3. The dried polyvinyl alcohol fiber is impregnated in the prepared coating solution. The polyvinyl alcohol fiber absorbs the prepared coating solution and forms a uniform liquid film. S4. Spin dry the polyvinyl alcohol fibers that have absorbed the oil solution. S5. Perform heat curing treatment on the spun-dry polyvinyl alcohol fiber to form a continuous, uniform, and non-peeling coating layer on the surface of the polyvinyl alcohol fiber. In step S1, determining the target interfacial bonding performance level between polyvinyl alcohol fiber and cementitious material includes a low bonding level (Level I-II), a balanced bonding level (Level III), and a high bonding level (Level IV-V). In step S2, the coating liquid comprises the following components in parts by mass: The mass fraction range of polydimethylsiloxane is 10-500 parts by mass; The mass fraction range of silicone oil, a coating additive, is 5-200 parts by mass. The mass fraction range of hydroxyl silicone oil is 10-200 parts by mass; The mass fraction range of vinyl acetate-ethylene copolymer emulsion is 5-400 parts by mass; The solvent has a mass fraction of 800-1200 parts by mass; The vinyl acetate-ethylene copolymer emulsion is an emulsion with a solid content in the range of 30%-55%; In step S3, the process of impregnating the dried polyvinyl alcohol fibers in the prepared coating solution includes the following steps: The pre-dried polyvinyl alcohol fibers are completely immersed in the prepared coating solution. During this immersion process, the temperature of the coating solution is controlled to be maintained within the range of 25°C to 40°C. The impregnation time is controlled at 25±2 minutes. Polyvinyl alcohol fibers absorb the coating liquid and form a uniform liquid film. The liquid absorption rate of the oil-coated polyvinyl alcohol fiber after the spin-drying treatment is controlled between 5% and 15%. In step S5, the temperature of the thermosetting treatment is controlled between 80℃ and 120℃, and the thermosetting time is set to 5 minutes. 10 minutes.

2. The PVA fiber coating method based on the adhesive properties of fiber-cementing materials according to claim 1, characterized in that, In step S4, the spin-drying treatment of the polyvinyl alcohol fibers that have absorbed the oil coating includes the following steps: The impregnated polyvinyl alcohol fibers are spun dry to remove excess oil from their surface. The drying process employs centrifugal drying, roller pressing, or slight vibration to ensure that there are no visible liquid droplets remaining on the surface of the polyvinyl alcohol fiber, thus ensuring that the coating liquid adheres evenly to the fiber surface.

3. The PVA fiber coating method based on the adhesive properties of fiber-cementing materials according to claim 1, characterized in that, In step S5, the polyvinyl alcohol fiber after spin drying is subjected to heat curing treatment. By providing controlled heat energy, the solvent in the coating liquid evaporates and a cross-linking reaction is initiated between the coating components, forming a strong and stable coating film layer on the surface of the polyvinyl alcohol fiber.

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