Modification method of polyvinyl alcohol fiber

Abstract

The invention discloses a modification method of polyvinyl alcohol fibers, and belongs to the technical field of buildings. According to the invention, the polyvinyl alcohol fiber is soaked in a dopamine hydrochloride solution, so that the surface performance of the polyvinyl alcohol fiber is modified. According to the invention, dopamine is self-polymerized to generate polydopamine, and the polydopamine is attached to the surface of the polyvinyl alcohol fiber to change the surface property of the material, so that the strength and durability of the concrete can be obviously enhanced, the service life of the concrete can be prolonged, the maintenance cost of the service life cycle of the concrete structure can be reduced, and the application prospect is good.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of building, and particularly relates to a modification method of polyvinyl alcohol (PVA) fiber. BACKGROUND

[0002] Polyvinyl alcohol (PVA) fiber has become an important material for reinforcing cement-based composite materials due to its excellent tensile strength, high modulus, acid and alkali resistance, and stable chemical properties. It can significantly improve the crack resistance and impact resistance of concrete by preventing the expansion of micro-cracks, and is widely used in bridge engineering, tunnel lining, and protective engineering. However, the poor interfacial adhesion between PVA fiber and cement matrix limits its performance in composite materials.

[0003] Currently, researchers have proposed various modification methods to improve the interfacial adhesion of PVA fiber, including chemical coating, electrochemical treatment, and plasma surface treatment. These methods have improved the compatibility between the fiber and the matrix to some extent, but they are usually complex, costly, and require harsh environmental conditions. SUMMARY

[0004] The purpose of the present application is to provide a modification method of polyvinyl alcohol (PVA) fiber, which forms a polydopamine coating on the surface of the fiber, changes the physicochemical properties of the fiber surface, and improves the interfacial adhesion strength between the fiber and the cement matrix, thereby improving the mechanical properties and durability of concrete, prolonging the service life of the material, and reducing maintenance costs.

[0005] To achieve the above-mentioned purpose, the present application adopts the following technical solutions: A modification method of polyvinyl alcohol fiber, comprising the following steps: 1) Dissolve hydrochloric acid dopamine in water, then add tris(hydroxymethyl) aminomethane (TRIS) to adjust the pH of the solution to 8.4 to obtain a hydrochloric acid dopamine solution; 2) Immerse the polyvinyl alcohol fiber in the hydrochloric acid dopamine solution prepared in step 1), then take it out and wash it with deionized water; 3) Dry the washed polyvinyl alcohol fiber to constant weight, and then cool it to room temperature to obtain a modified polyvinyl alcohol fiber with high modulus and high strength.

[0006] Further, the mass ratio of hydrochloric acid dopamine to deionized water used in step 1) is 1:1000-10:1000.

[0007] Further, the time for immersion in step 2) is 6-24h.

[0008] Further, the temperature for drying in step 3) is 60℃-80℃.

[0009] Further, the obtained modified polyvinyl alcohol fiber has smooth surface, length of 12 mm, diameter of 16 microns, aspect ratio of 750, and tensile strength of greater than or equal to 1500 MPa.

[0010] The present application utilizes the self-polymerization property of dopamine molecules (DA) to form a polydopamine (PDA) coating under weak alkaline conditions, and simulates the role of adhesive proteins in nature to uniformly deposit the PDA coating on the surface of polyvinyl alcohol (PVA) fibers in a normal temperature and pressure and weak alkaline aqueous solution environment. The abundant amino and hydroxyl groups of the PDA coating can interact chemically or physically with the hydration products in the cement matrix, and induce more hydration products to deposit on the fiber surface, thereby significantly improving the interfacial bonding performance between the PVA fiber and the cement matrix, and achieving good reinforcing effect.

[0011] The present application uses dopamine hydrochloride and TRIS solution to modify and treat PVA fibers to form a polydopamine coating on the surface of the fibers, which significantly improves the interfacial activity and bonding performance of the fibers, and has the following advantages and effects: (1) significantly enhancing the interfacial bonding strength: the PDA coating can react with Ca(OH)2 and C-S-H (calcium silicate hydrate) in the cement matrix to promote the deposition of hydration products on the surface of the fiber, so that the interfacial bonding strength between the fiber and the matrix is improved by more than 80%.

[0012] (2) improving the mechanical properties of concrete: after the modified PVA fiber is incorporated into concrete, the crack resistance can be significantly improved. Experiments show that the flexural strength of the modified fiber concrete is improved by 40%-70%, and the compressive strength is improved by 20%-40%.

[0013] (3) simplifying the modification process: the method is completed at normal temperature and pressure without the need for complex equipment and high temperature environment, and the modification process is environmentally friendly and efficient.

[0014] (4) reducing production cost: since the PDA coating improves the reinforcing efficiency of the fiber, the amount of fiber incorporated in the concrete can be appropriately reduced, thereby reducing the overall material cost.

[0015] (5) improving the durability of the material: the presence of the PDA coating significantly improves the compatibility of the fiber and the matrix, effectively delays the expansion of the interfacial microcracks, and improves the long-term durability of the concrete structure.

[0016] The method proposed in the present application provides a new solution for enhancing the performance of PVA fibers in concrete. Through optimization of the modification process and significant improvement of the performance, the method can be widely applied to: 1. high-performance concrete engineering: such as bridge, tunnel lining, high-rise building and other scenes requiring high durability and high mechanical properties; 2. Special concrete materials: such as protective engineering and military engineering that require high impact resistance, crack resistance and fatigue resistance; 3. Sustainable building materials: The use of modified fibers reduces the life cycle maintenance cost of concrete and contributes to the development of green buildings. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Electron microscope images of unmodified polyvinyl alcohol fiber (a) and modified polyvinyl alcohol fiber (b) prepared in Example 2.

[0018] Figure 2 This is a comparison of the flexural strength of mortar specimens prepared using different polyvinyl alcohol fibers in the application example.

[0019] Figure 3 This is the P-δ curve of the mortar specimens prepared using different polyvinyl alcohol fibers in the application example. DETAILED DESCRIPTION

[0020] A method for modifying polyvinyl alcohol fiber, comprising the following steps: 1) Dissolve dopamine hydrochloride in water, then add tris(hydroxymethyl)aminomethane (TRIS) to adjust the pH of the solution to 8.4 to obtain a dopamine hydrochloride solution; 2) Immersing the polyvinyl alcohol fiber in the dopamine hydrochloride solution prepared in step 1) for 6-24 hours, then removing the fiber and washing it with deionized water; 3) Dry the cleaned polyvinyl alcohol fiber at 60°C-80°C to constant weight, and then cool it to room temperature to obtain high modulus and high strength modified polyvinyl alcohol fiber.

[0021] Wherein, the mass ratio of dopamine hydrochloride used in step 1) to deionized water is 1:1000-10:1000.

[0022] In order to make the contents of the present invention easier to understand, the technical solutions of the present invention are further described below in conjunction with specific implementation methods, but the present invention is not limited thereto.

[0023] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0024] Example 1 A method for modifying polyvinyl alcohol fiber comprises the following steps: 1) Dissolve 3 g of dopamine hydrochloride in 1 kg of water, then add TRIS to adjust the pH of the solution to 8.4 to obtain a dopamine hydrochloride solution; 2) immersing the polyvinyl alcohol fiber in the dopamine hydrochloride solution prepared in step 1) for 24 hours, then removing the fiber and washing it with deionized water; 3) The cleaned polyvinyl alcohol fiber is dried at 60° C. to a constant weight, and then cooled to room temperature to obtain a high modulus and high strength modified polyvinyl alcohol fiber.

[0025] The obtained polyvinyl alcohol fiber has a rough surface, a length of 12 mm, a diameter of 16 μm, an aspect ratio of 750, and a tensile strength of ≥1500 MPa.

[0026] Example 2 A method for modifying polyvinyl alcohol fiber comprises the following steps: 1) Dissolve 5 g of dopamine hydrochloride in 1 kg of water, then add TRIS to adjust the pH of the solution to 8.4 to obtain a dopamine hydrochloride solution; 2) immersing the polyvinyl alcohol fiber in the dopamine hydrochloride solution prepared in step 1) for 24 hours, then removing the fiber and washing it with deionized water; 3) The cleaned polyvinyl alcohol fiber is dried at 60° C. to a constant weight, and then cooled to room temperature to obtain a high modulus and high strength modified polyvinyl alcohol fiber.

[0027] The obtained polyvinyl alcohol fiber has a rough surface, a length of 12 mm, a diameter of 16 μm, an aspect ratio of 750, and a tensile strength of ≥1500 MPa.

[0028] Example 3 A method for modifying polyvinyl alcohol fiber comprises the following steps: 1) Dissolve 9 g of dopamine hydrochloride in 1 kg of water, then add TRIS to adjust the pH of the solution to 8.4 to obtain a dopamine hydrochloride solution; 2) immersing the polyvinyl alcohol fiber in the dopamine hydrochloride solution prepared in step 1) for 24 hours, then removing the fiber and washing it with deionized water; 3) The cleaned polyvinyl alcohol fiber is dried at 60° C. to a constant weight, and then cooled to room temperature to obtain a high modulus and high strength modified polyvinyl alcohol fiber.

[0029] The obtained polyvinyl alcohol fiber has a rough surface, a length of 12 mm, a diameter of 16 μm, an aspect ratio of 750, and a tensile strength of ≥1500 MPa.

[0030] The surface morphology of polyvinyl alcohol (PVA) fibers before and after modification was analyzed using scanning electron microscopy (SEM). Figure 1 .Depend on Figure 1 It can be seen that the surface of the modified polyvinyl alcohol (PVA) fiber is rougher, which helps to increase the adhesion of the interface.

[0031] Application Examples By weight, 400 parts of cement, 480 parts of quartz sand, 480 parts of fly ash, and 16.5 parts of modified polyvinyl alcohol fiber or unmodified polyvinyl alcohol fiber prepared in the embodiment were added to the cement mortar mixing pot in sequence and dry mixed for 3 minutes; then 5 parts of polycarboxylic acid high-efficiency water reducer were added to 264 parts of water, stirred evenly, and poured into the mixing pot, and continued stirring for 5 minutes. After that, the obtained fiber mortar was injected into a 40mm×40mm×160mm mold and placed in a constant temperature box with a humidity of 95% and a temperature of 20°C for curing.

[0032] 1. According to the Test Method for Cement Mortar Strength (ISO Method) (GB / T 17671-2021), flexural tests were conducted on mortar specimens cured for 14 days and 28 days using a 300KN universal testing machine. The results are shown in Figure 2 .

[0033] Depend on Figure 2 It can be seen that the mortar specimens prepared using unmodified PVA fibers have the lowest flexural strength, which is about 5.5 MPa at D14 and about 6.5 MPa at D28, indicating that the reinforcing effect of unmodified PVA fibers is limited. In comparison, the flexural strength of the mortar specimens prepared using the modified polyvinyl alcohol fibers of the examples is significantly improved. Among them, the flexural strength of the mortar specimens prepared using the modified polyvinyl alcohol fibers of Example 1 reaches 6.8 MPa at D14 and increases to 7.5 MPa at D28. The flexural strength of the mortar specimens prepared using the modified polyvinyl alcohol fibers of Example 2 reaches 9.5 MPa at D14 and exceeds 10.5 MPa at D28. The flexural strength of the mortar specimens prepared using the modified polyvinyl alcohol fibers of Example 3 is close to 8.5 MPa at D14 and about 9.0 MPa at D28, indicating that the modified fibers can improve the interfacial adhesion with the matrix and enhance the mechanical properties of the material. Among them, the flexural strength of the mortar specimens prepared using the modified polyvinyl alcohol fibers of Example 2 is increased by more than 60% compared with the mortar specimens prepared using the unmodified polyvinyl alcohol fibers, and its effect is the best.

[0034] 2. According to the three-point bending fracture test, the cured mortar specimens were subjected to a three-point bending test using a 250kN MTS fatigue performance testing machine. The results are shown in Figure 3 And Table 1.

[0035] Depend on Figure 3It can be seen that the mortar specimens prepared using the modified polyvinyl alcohol fibers of the examples exhibited higher flexural strength and toughness during the stress process. The peak force of the force-displacement (P-δ) curve was significantly increased, and the decline after the peak value was more gradual, indicating that the material's ductility and energy absorption capacity were enhanced. Among them, the mortar specimens prepared using unmodified polyvinyl alcohol fibers had the lowest peak force (approximately 100N) and a steep decline, indicating rapid crack propagation and poor toughness. The mortar specimens prepared using the modified polyvinyl alcohol fibers of Example 1 had an increased peak force (approximately 500N) and a slightly slower decline, indicating improved material toughness. The mortar specimens prepared using the modified polyvinyl alcohol fibers of Example 2 had the highest peak force (nearly 900N) and the slowest decline, indicating that this group of materials can maintain a higher load-bearing capacity during the crack propagation stage and exhibit the best ductility and crack resistance. The mortar specimens prepared using the modified polyvinyl alcohol fibers of Example 3 had a peak force of approximately 700N and a relatively slow decline, indicating that the modified fibers can provide good crack bridging ability and energy dissipation performance.

[0036] Table 1 shows the three-point bending mechanical calculation results of mortar specimens prepared with different polyvinyl alcohol fibers

[0037] As can be seen from Table 1, the fracture energy of the mortar specimen prepared using the modified polyvinyl alcohol fiber in Example 1 presents a maximum value (5037.81 N / m), proving that it can significantly improve the time-dependent crack toughness and greatly inhibit the crack propagation.

[0038] As can be seen from the above, the use of the modified polyvinyl alcohol fiber of the present invention can significantly improve the flexural strength, ductility and crack suppression ability of cement-based composite materials, making it have broad application prospects in high-performance concrete engineering applications.

[0039] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for modifying polyvinyl alcohol fiber, characterized in that: The following steps are involved: 1) dissolving dopamine hydrochloride in water, then adding tris(hydroxymethyl)aminomethane to adjust the pH of the solution to 8.4 to obtain a dopamine hydrochloride solution; 2) immersing the polyvinyl alcohol fiber in the dopamine hydrochloride solution prepared in step 1), then removing the fiber and washing it with deionized water; 3) Drying the cleaned polyvinyl alcohol fiber to constant weight and then cooling it to room temperature to obtain high modulus and high strength modified polyvinyl alcohol fiber.

2. The method for modifying polyvinyl alcohol fiber according to claim 1, characterized in that: The mass ratio of dopamine hydrochloride to deionized water used in step 1) is 1:1000-10:1000.

3. The method for modifying polyvinyl alcohol fiber according to claim 1, characterized in that: The immersion time in step 2) is 6-24 hours.

4. The method for modifying polyvinyl alcohol fiber according to claim 1, characterized in that: The drying temperature in step 3) is 60°C-80°C.

5. The method for modifying polyvinyl alcohol fiber according to claim 1, characterized in that: The obtained modified polyvinyl alcohol fiber has a smooth surface, an aspect ratio of 750, and a tensile strength of ≥1500 MPa.

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