Modified polyvinyl alcohol fiber, and method for preparing and use thereof
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-06-25
- Publication Date
- 2026-08-11
AI Technical Summary
[0003]虽然向水泥中加入聚乙烯醇纤维(PVA)能够在一定程度上提高堵漏效果，但是由于PVA纤维表面通常光滑且疏水，其与水泥基体的黏结主要依赖于水泥基体之间的范德华力和氢键，这种物理吸附导致PVA纤维与水泥基体的界面结合性能较弱，难以充分发挥纤维本身的高强度高模量特性，因此对PVA纤维进行改性
本发明给出的制备方法是使用具有亲水性羧基基团的g-C3N4-COOH为改性材料对PVA纤维表面进行共价键接枝改性，使得PVA纤维的上接枝了亲水性羧基基团，提高了纯PVA纤维的亲水性，将g-C3N4-COOH改性的PVA纤维加入水泥浆中，提高了g-C3N4-COOH改性的PVA纤维在水泥浆中的分散性，均匀分散在水泥中的g-C3N4-COOH改性的PVA纤维，在固化过程中形成三维网络结构，g-C3N4-COOH改性的PVA纤维加入水泥浆中也提高了配制封堵水泥的承压压力，同时降低了封堵水泥浆向地层漏失的速率，提高水泥浆在通道中的滞留能力，而g-C3N4-COOH改性的PVA纤维在水泥中的亲水性的提高，通过化学键合进一步改善了应力传递效率，减少界面缺陷导致的应力集中，从而有效发挥堵漏作用，从而提高了纤维与水泥基体间的界面结合性，进而提高了力学性能，实现了纤维网络与化学键合的双重封堵层。
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of petrochemical technology, and specifically relates to a modified polyvinyl alcohol fiber, its preparation method, and its application. Background Technology
[0002] Because traditional oil well cement is prone to microcracks and micro-cracks under the influence of various forces in the underground rock strata during subsequent operations such as perforation, fracturing, and mining, polyvinyl alcohol fiber (PVA) is added to the cement to achieve a leak-sealing effect.
[0003] Although adding polyvinyl alcohol fiber (PVA) to cement can improve the sealing effect to some extent, the bonding between PVA fiber and cement matrix mainly depends on van der Waals forces and hydrogen bonds between the cement matrix because the surface of PVA fiber is usually smooth and hydrophobic. This physical adsorption results in weak interfacial bonding performance between PVA fiber and cement matrix, making it difficult to fully utilize the high strength and high modulus characteristics of the fiber itself. Therefore, PVA fiber needs to be modified.
[0004] In existing technologies, the modification of PVA fibers is usually achieved by blending or mechanically mixing reinforcing phases (such as multi-walled carbon nanotubes (MWNTs)) with PVA fibers to obtain surface-modified PVA fibers with pits or protrusions on the fiber surface. When these surface-modified PVA fibers are added to a cement matrix, they form a mechanically interlocked structure, which improves the interfacial bonding performance between the surface-modified PVA fibers and the cement matrix to a certain extent, thereby improving mechanical properties. However, physically modified PVA fibers still suffer from poor dispersibility in the cement matrix and have an insignificant effect on improving the hydrophilicity of the cement matrix, thus affecting the leak-sealing effect. Therefore, it is of great significance to provide a method for preparing modified PVA fibers that can improve the dispersibility of PVA fibers in the cement matrix, enhance their hydrophilicity with cement, and thus improve the leak-sealing effect and mechanical strength. Summary of the Invention
[0005] To address the shortcomings of the prior art, the present invention aims to provide modified polyvinyl alcohol fibers, their preparation method, and applications. The modified polyvinyl alcohol fibers prepared by this method have improved dispersibility in cement matrix and significantly improved hydrophilicity with cement matrix. When mixed with cement matrix for sealing tests, the modified fibers and cement matrix form a dual sealing layer of fiber network and chemical bonding during the curing process, thereby improving the sealing effect.
[0006] To solve the above-mentioned technical problems, the present invention provides a method for preparing modified polyvinyl alcohol fibers, comprising the following steps: Layered g-C3N4 was prepared using melamine powder; The layered g-C3N4 was carboxylated and then dried to obtain g-C3N4-COOH; PVA fibers were added to water and ultrasonically treated to prepare a PVA aqueous solution. g-C3N4-COOH was added to the PVA aqueous solution at room temperature for ultrasonic reaction. After the reaction was completed, the reactants were dried to obtain g-C3N4-COOH modified PVA fibers.
[0007] Preferably, the PVA aqueous solution has a mass percentage of 8% to 12%, and the amount of g-C3N4-COOH added is 1% to 10% of the mass of PVA fiber.
[0008] Preferably, the preparation steps of the g-C3N4 are as follows: Melamine powder was subjected to high-temperature pyrolysis reaction at 500℃~700℃ for 1.5h~3h to obtain g-C3N4 powder; the g-C3N4 powder was dispersed in water and ultrasonically treated to obtain a layered g-C3N4 solution with a concentration of 0.015~0.025g / mL, which was then dried to obtain layered g-C3N4.
[0009] Preferably, the step of preparing g-C3N4-COOH by g-C3N4 carboxylation is as follows: Layered g-C3N4 was mixed with a mixed acid, heated to boiling, and refluxed and condensed for 1.5-3 hours with slow stirring. After washing with water until the pH reached 6-7, the mixture was vacuum dried and ground to obtain g-C3N4-COOH. The mixed acid was prepared by mixing concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 2-4:0.5-1.5. The concentration of the solution containing layered g-C3N4 and the mixed acid was 0.0625 g / mL-0.4 g / mL. The drying temperature was 30℃-60℃. The electrostatic interaction is relatively weak; excessively high temperatures may disrupt it.
[0010] This invention provides a method for preparing g-C3N4-COOH modified PVA fibers.
[0011] This invention provides the application of g-C3N4-COOH modified PVA fibers in cement for sealing microcracks and micro-slits in oil wells.
[0012] Preferably, in the 1mm and 2mm joint sealing tests, the sealing cement made of g-C3N4-COOH modified PVA fibers has a pressure bearing capacity of 5MPa~7MPa.
[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: The preparation method provided in this invention uses g-C3N4-COOH, which has hydrophilic carboxyl groups, as a modifying material to covalently graft and modify the surface of PVA fibers. This grafts hydrophilic carboxyl groups onto the PVA fibers, improving the hydrophilicity of pure PVA fibers. Adding g-C3N4-COOH-modified PVA fibers to cement slurry improves their dispersibility in the slurry. The g-C3N4-COOH-modified PVA fibers, uniformly dispersed in the cement, form a three-dimensional network structure during the curing process. The addition of 3N4-COOH modified PVA fibers to cement slurry increases the pressure resistance of the prepared sealing cement, while reducing the rate of leakage of the sealing cement slurry into the formation and improving the retention capacity of the cement slurry in the channel. The increased hydrophilicity of g-C3N4-COOH modified PVA fibers in cement further improves stress transfer efficiency through chemical bonding, reduces stress concentration caused by interface defects, and thus effectively plays a sealing role. This improves the interfacial bonding between the fiber and the cement matrix, thereby improving mechanical properties and realizing a dual sealing layer of fiber network and chemical bonding. Attached Figure Description
[0014] Figure 1 The images show the infrared absorption spectra of PVA fibers modified with g-C3N4-COOH and g-C3N4-COOH, where image a represents g-C3N4-COOH and image b represents PVA fibers modified with g-C3N4-COOH.
[0015] Figure 2 The images show the XRD patterns of g-C3N4, g-C3N4-COOH, g-C3N4-modified PVA fibers, and g-C3N4-COOH-modified PVA fibers in this invention, where image a represents g-C3N4; image b represents g-C3N4-COOH; image c represents g-C3N4-modified PVA fibers; and image d represents g-C3N4-COOH-modified PVA fibers.
[0016] Figure 3 The figures show the particle size distributions of g-C3N4 and g-C3N4-COOH in this invention, where figure a represents g-C3N4 and figure b represents g-C3N4-COOH.
[0017] Figure 4 The figures show the contact angles of g-C3N4, g-C3N4-COOH, pure PVA fiber, and g-C3N4-COOH modified PVA fiber in this invention, where figure a represents g-C3N4; figure b represents g-C3N4-COOH; figure c represents pure PVA fiber; and figure d represents g-C3N4-COOH modified PVA fiber.
[0018] Figure 5The figures show the transmittance of the supernatant of pure PVA fiber and g-C3N4-COOH modified PVA fiber in this invention, where figure a represents pure PVA fiber and figure b represents g-C3N4-COOH modified PVA fiber.
[0019] Figure 6 These are SEM images of g-C3N4 modified PVA fibers, g-C3N4-COOH modified PVA fibers, g-C3N4 modified PVA fibers, and g-C3N4-COOH modified PVA fibers in this invention; wherein image a is a 500x magnification image of g-C3N4 modified PVA fibers; image b is a 500x magnification image of g-C3N4-COOH modified PVA fibers; image c is a 5000x magnification image of g-C3N4 modified PVA fibers; and image d is a 5000x magnification image of g-C3N4-COOH modified PVA fibers.
[0020] Figure 7 These are the full spectrum, full spectrum, g-C3N4-COOH spectrum, g-C3N4N1s spectrum, g-C3N4-COOH N1s spectrum, g-C3N4C1s spectrum, and g-C3N4-COOH C1s spectrum of the present invention, wherein spectrum a is the full spectrum of g-C3N4; spectrum b is the full spectrum of g-C3N4-COOH; spectrum c is the g-C3N4N1s spectrum; spectrum d is the g-C3N4-COOH N1s spectrum; spectrum e is the g-C3N4C1s spectrum; and spectrum f is the g-C3N4-COOH C1s spectrum.
[0021] Figure 8 Figure 1 shows the strength curves of pure cement and cement doped with modified PVA fibers in this invention, where Figure 2a represents pure cement and Figure 2b represents cement doped with modified PVA fibers.
[0022] Figure 9 This diagram illustrates the process flow of carboxylation treatment of g-C3N4 and the principle of leak-sealing using modified fibers in cement, where a represents the carboxylation process of g-C3N4; b represents the mixing of g-C3N4-COOH and PVA fibers; and c represents the principle of leak-sealing using modified fibers in cement. Detailed Implementation
[0023] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Unless otherwise specified, the experimental methods described in the embodiments of the present invention are conventional methods.
[0024] The purpose of this invention is to provide nano-modified polyvinyl alcohol fiber cement-based composite materials, their preparation methods, and applications. This invention improves the dispersibility of modified fibers in cement, significantly enhances the hydrophilicity of cement, and allows the fibers to penetrate micron- or even nano-scale cracks, forming a dual-layer sealing layer of fiber network and chemical bonding. This increases the sealing efficiency by 40% to 60%, completely solving the problem of leakage of deep and ultra-deep oil and gas.
[0025] It should be noted that when numerical ranges are involved in this invention, it should be understood that the two endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in Examples 1 to 8, preferred embodiments are described in this invention to avoid redundancy. However, this invention is not limited to these, but can be specifically implemented in other ways within the scope of the technical solutions defined in the appended claims. All raw materials, reagents, instruments, and equipment used in the following embodiments of this invention can be purchased from the market or prepared by existing methods.
[0026] The following detailed description, in conjunction with embodiments of the present invention and accompanying drawings, provides a clear and complete illustration of the technical solutions in these embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.
[0027] Example 1 A method for preparing g-C3N4-COOH modified PVA fibers includes the following steps: (1) Preparation of g-C3N4 A porcelain crucible containing 10g of melamine powder was placed in the middle of a tube furnace. The tube furnace was heated to 500℃ and held at that temperature for 2.5h. When the tube furnace cooled naturally to room temperature, the sample was collected in the crucible, and the resulting yellow powder was g-C3N4. 10g of g-C3N4 powder was dispersed in water, and the mixture was continuously sonicated for 10h. After adjusting the volume, a layered g-C3N4 dispersion with a concentration of 0.015g / mL was obtained, which was then dried to obtain layered g-C3N4.
[0028] (2) Carboxylation treatment of g-C3N4 Add 10g of layered g-C3N4 to a three-necked flask, then add 160mL of a mixed solution of concentrated sulfuric acid and concentrated nitric acid (volume ratio 2:1.5) (the concentration of the mixed solution of layered g-C3N4 and the acid is 0.0625g / mL). Heat to boiling, reflux and condense for 2 hours with slow stirring, wash with water until pH 7, vacuum dry at 80℃ for 24 hours, and grind to obtain g-C3N4-COOH. Figure 9 As shown.
[0029] (3) Preparation of g-C3N4-COOH modified PVA fibers PVA fibers were added to water and sonicated at room temperature for 3 hours to prepare a 10 wt% PVA aqueous solution. Then, g-C3N4-COOH was added to the PVA aqueous solution at a mass ratio of 10%, and the mixture was sonicated at room temperature for 3 hours to ensure thorough mixing. Finally, the mixture was dried for 24 hours to obtain g-C3N4-COOH-modified PVA fibers.
[0030] Example 2 A method for preparing g-C3N4-COOH modified PVA fibers includes the following steps: (1) Preparation of g-C3N4 A porcelain crucible containing 10g of melamine powder was placed in the middle of a tube furnace. The tube furnace was heated to 550℃ and held for 2 hours. When the tube furnace cooled to room temperature, the sample was collected in the crucible, and the resulting yellow powder was g-C3N4. 10g of the bulk g-C3N4 powder was dispersed in water, and the mixture was continuously sonicated for 10 hours. After adjusting the volume, a layered g-C3N4 dispersion with a concentration of 0.015g / mL was obtained, which was then dried to obtain layered g-C3N4.
[0031] (2) Carboxylation treatment of g-C3N4 Add 10g of g-C3N4 to a three-necked flask, then add 60mL of a mixed solution of concentrated sulfuric acid and concentrated nitric acid (volume ratio 3:1) (the concentration of the layered g-C3N4 solution mixed with the acid is 0.167g / mL). Heat to boiling, reflux and condense for 2 hours with slow stirring, wash with water until pH 7, vacuum dry at 80℃ for 24 hours, and grind to obtain g-C3N4-COOH. Figure 9 As shown.
[0032] (3) Preparation of g-C3N4-COOH modified PVA fibers PVA fibers were prepared into a 10 wt% PVA aqueous solution and sonicated at room temperature for 3 hours. Then, g-C3N4-COOH was added to the PVA aqueous solution at a mass ratio of 10%, and the mixture was sonicated at room temperature for 3 hours to ensure thorough mixing. Finally, the mixture was dried for 24 hours to obtain g-C3N4-COOH-modified PVA fibers.
[0033] Example 3 A method for preparing g-C3N4-COOH modified PVA fibers includes the following steps: (1) Preparation of g-C3N4 A porcelain crucible containing 10g of melamine powder was placed in the middle of a tube furnace. The tube furnace was heated to 600℃ and held for 2 hours. When the tube furnace cooled to room temperature, the sample was collected in the crucible, and the resulting yellow powder was g-C3N4. 10g of the bulk g-C3N4 powder was dispersed in water, and the mixture was continuously sonicated for 10 hours. After adjusting the volume, a layered g-C3N4 dispersion with a concentration of 0.025g / mL was obtained, which was then dried to obtain layered g-C3N4.
[0034] (2) Carboxylation treatment of g-C3N4 Add 10g of g-C3N4 to a three-necked flask, then add 25mL of a mixed solution of concentrated sulfuric acid and concentrated nitric acid (volume ratio 4:0.5) (the concentration of the layered g-C3N4 solution mixed with the acid is 0.4g / mL). Heat to boiling, reflux and condense for 2 hours with slow stirring, wash with water until pH 7, vacuum dry at 80℃ for 24 hours, and grind to obtain g-C3N4-COOH. Figure 9 As shown.
[0035] (3) Preparation of g-C3N4-COOH modified PVA fibers PVA fibers were prepared into a 10 wt% PVA aqueous solution and sonicated at room temperature for 3 hours. Then, g-C3N4-COOH was added to the PVA aqueous solution at a mass ratio of 1%, and the mixture was sonicated at room temperature for 3 hours to ensure thorough mixing. Finally, the mixture was dried for 24 hours to obtain g-C3N4-COOH-modified PVA fibers.
[0036] Example 4 A method for preparing g-C3N4-COOH modified PVA fibers includes the following steps: (1) Preparation of g-C3N4 A porcelain crucible containing 10g of melamine powder was placed in the middle of a tube furnace. The tube furnace was heated to 700℃ and held at that temperature for 1.5h. When the tube furnace cooled naturally to room temperature, the sample was collected in the crucible, and the resulting yellow powder was g-C3N4. 10g of the bulk g-C3N4 powder was dispersed in 500mL of water, and the mixture was continuously sonicated for 10h. After adjusting the volume, a layered g-C3N4 dispersion with a concentration of 0.020g / mL was obtained, which was then dried to obtain layered g-C3N4.
[0037] (2) Carboxylation treatment of g-C3N4 Add 10g of g-C3N4 to a three-necked flask, then add 30mL of a mixed solution of concentrated sulfuric acid and concentrated nitric acid (volume ratio 2:1) (the concentration of the layered g-C3N4 solution mixed with the acid is 0.3g / mL). Heat to boiling, reflux and condense for 2 hours with slow stirring, wash with water until pH 7, vacuum dry at 80℃ for 24 hours, and grind to obtain g-C3N4-COOH. Figure 9 As shown.
[0038] (3) Preparation of g-C3N4-COOH modified PVA fibers PVA fibers were prepared into a 10 wt% PVA aqueous solution and sonicated at room temperature for 3 hours. Then, g-C3N4-COOH was added to the PVA aqueous solution at a mass ratio of 5%, and the mixture was sonicated at room temperature for 3 hours to ensure thorough mixing. Finally, the mixture was dried for 24 hours to obtain g-C3N4-COOH-modified PVA fibers.
[0039] Example 5 The difference between Example 5 and Example 2 is that the mass percentage of the PVA aqueous solution is different.
[0040] (1) Preparation of g-C3N4 A porcelain crucible containing 10g of melamine powder was placed in the middle of a tube furnace. The tube furnace was heated to 550℃ and held for 2 hours. When the tube furnace cooled to room temperature, the sample was collected from the crucible, and the resulting yellow powder was g-C3N4. 10g of the bulk g-C3N4 powder was dispersed in 500mL of water, and the mixture was continuously sonicated for 10 hours. After adjusting the volume, a layered g-C3N4 dispersion with a concentration of 0.015g / mL was obtained, which was then dried to obtain layered g-C3N4.
[0041] (2) Carboxylation treatment of g-C3N4 Add 10g of g-C3N4 to a three-necked flask, then add 60mL of a mixed solution of concentrated sulfuric acid and concentrated nitric acid (volume ratio 3:1) (the concentration of the layered g-C3N4 solution mixed with the acid is 0.167g / mL). Heat to boiling, reflux and condense for 2 hours with slow stirring, wash with water until pH 7, vacuum dry at 80℃ for 24 hours, and grind to obtain g-C3N4-COOH. Figure 9 As shown.
[0042] (3) Preparation of g-C3N4-COOH modified PVA fibers PVA fibers were prepared into an 8 wt% PVA aqueous solution and sonicated at room temperature for 3 hours. g-C3N4-COOH was added to the PVA aqueous solution and sonicated at room temperature for 3 hours to ensure thorough mixing. Finally, the mixture was dried for 24 hours to obtain g-C3N4-COOH-modified PVA fibers.
[0043] Example 6 The difference between Example 6 and Example 2 is that the mass percentage of the PVA aqueous solution is different.
[0044] (1) Preparation of g-C3N4 A porcelain crucible containing 10g of melamine powder was placed in the middle of a tube furnace. The tube furnace was heated to 550℃ and held for 2 hours. When the tube furnace cooled to room temperature, the sample was collected from the crucible, and the resulting yellow powder was g-C3N4. 10g of the bulk g-C3N4 powder was dispersed in 500mL of water, and the mixture was continuously sonicated for 10 hours. After adjusting the volume, a layered g-C3N4 dispersion with a concentration of 0.015g / mL was obtained, which was then dried to obtain layered g-C3N4.
[0045] (2) Carboxylation treatment of g-C3N4 Add 10g of g-C3N4 to a three-necked flask, then add 60mL of a mixed solution of concentrated sulfuric acid and concentrated nitric acid (volume ratio 3:1) (the concentration of the layered g-C3N4 solution mixed with the acid is 0.167g / mL). Heat to boiling, reflux and condense for 2 hours with slow stirring, wash with water until pH 7, vacuum dry at 80℃ for 24 hours, and grind to obtain g-C3N4-COOH. Figure 9 As shown.
[0046] (3) Preparation of g-C3N4-COOH modified PVA fibers PVA fibers were prepared into a 12wt% PVA aqueous solution and sonicated at room temperature for 3 hours. g-C3N4-COOH was added to the PVA aqueous solution and sonicated at room temperature for 3 hours to ensure thorough mixing. Finally, the mixture was dried for 24 hours to obtain g-C3N4-COOH-modified PVA fibers.
[0047] Example 7 The difference between Example 7 and Example 2 is that the water washing pH in the carboxylation treatment of g-C3N4 is 6.
[0048] A method for preparing g-C3N4-COOH modified PVA fibers includes the following steps: (1) Preparation of g-C3N4 A porcelain crucible containing 10g of melamine powder was placed in the middle of a tube furnace. The tube furnace was heated to 550℃ and held for 2 hours. When the tube furnace cooled to room temperature, the sample was collected in the crucible, and the resulting yellow powder was g-C3N4. 10g of the bulk g-C3N4 powder was dispersed in water, and the mixture was continuously sonicated for 10 hours. After adjusting the volume, a layered g-C3N4 dispersion with a concentration of 0.015g / mL was obtained, which was then dried to obtain layered g-C3N4.
[0049] (2) Carboxylation treatment of g-C3N4 Add 10g of g-C3N4 to a three-necked flask, then add 60mL of a mixed solution of concentrated sulfuric acid and concentrated nitric acid (volume ratio 3:1) (the concentration of the layered g-C3N4 solution mixed with the acid is 0.167g / mL). Heat to boiling, reflux and condense for 2 hours with slow stirring, wash with water until pH 6, vacuum dry at 80℃ for 24 hours, and grind to obtain g-C3N4-COOH. Figure 9 As shown.
[0050] (3) Preparation of g-C3N4-COOH modified PVA fibers PVA fibers were prepared into a 10 wt% PVA aqueous solution and sonicated at room temperature for 3 hours. Then, g-C3N4-COOH was added to the PVA aqueous solution at a mass ratio of 10%, and the mixture was sonicated at room temperature for 3 hours to ensure thorough mixing. Finally, the mixture was dried for 24 hours to obtain g-C3N4-COOH-modified PVA fibers.
[0051] Example 8 The difference between Example 8 and Example 2 is that the water washing pH in the carboxylation treatment of g-C3N4 is 6.5.
[0052] A method for preparing g-C3N4-COOH modified PVA fibers includes the following steps: (1) Preparation of g-C3N4 A porcelain crucible containing 10g of melamine powder was placed in the middle of a tube furnace. The tube furnace was heated to 550℃ and held for 2 hours. When the tube furnace cooled to room temperature, the sample was collected from the crucible, and the resulting yellow powder was g-C3N4. 10g of the bulk g-C3N4 powder was dispersed in 500mL of water, and the mixture was continuously sonicated for 10 hours. After adjusting the volume, a layered g-C3N4 dispersion with a concentration of 0.015g / mL was obtained, which was then dried to obtain layered g-C3N4.
[0053] (2) Carboxylation treatment of g-C3N4 Add 10g of g-C3N4 to a three-necked flask, then add 60mL of a mixed solution of concentrated sulfuric acid and concentrated nitric acid (volume ratio 3:1) (the concentration of the layered g-C3N4 solution mixed with the acid is 0.167g / mL). Heat to boiling, reflux and condense for 2 hours with slow stirring, wash with water until the pH reaches 6.5, vacuum dry at 80℃ for 24 hours, and grind to obtain g-C3N4-COOH. Figure 9 As shown.
[0054] (3) Preparation of g-C3N4-COOH modified PVA fibers PVA fibers were prepared into a 10 wt% PVA aqueous solution and sonicated at room temperature for 3 hours. Then, g-C3N4-COOH was added to the PVA aqueous solution at a mass ratio of 10%, and the mixture was sonicated at room temperature for 3 hours to ensure thorough mixing. Finally, the mixture was dried for 24 hours to obtain g-C3N4-COOH-modified PVA fibers.
[0055] Comparative Example 1 Purchased pure PVA fibers.
[0056] Comparative Example 2 The difference between Comparative Example 2 and Example 2 is that no carboxylation treatment was performed on g-C3N4.
[0057] A method for preparing g-C3N4 modified PVA fibers includes the following steps: (1) Preparation of g-C3N4 A porcelain crucible containing 10g of melamine powder was placed in the middle of a tube furnace. The tube furnace was heated to 550℃ and held at that temperature for 2 hours. When the tube furnace cooled to room temperature naturally, the sample was collected in the crucible, and the resulting yellow powder was g-C3N4. 10g of the bulk g-C3N4 powder was dispersed in water, and the mixture was continuously sonicated for 10 hours.
[0058] (2) Preparation of g-C3N modified PVA fibers PVA fibers were prepared into a 10 wt% PVA aqueous solution and sonicated at room temperature for 3 hours. g-C3N4 was added to the PVA aqueous solution and sonicated at room temperature for 3 hours to ensure thorough mixing. Finally, the mixture was dried for 24 hours to obtain g-C3N4-modified PVA fibers.
[0059] Comparative Example 3 Commercially available pure cement.
[0060] All of the above Examples 1 to 8 were able to prepare g-C3N4-COOH modified PVA fibers. Now, the g-C3N4-COOH modified PVA fibers prepared in Example 2 are preferred and compared with the pure PVA fibers of Comparative Example 1 and the g-C3N4 modified PVA fibers prepared in Comparative Example 2 for testing and characterization.
[0061] Experimental verification (a) Structural confirmation (1) FTIR test Figure 1 The infrared absorption spectra of PVA fibers modified with g-C3N4-COOH and g-C3N4-COOH are shown.
[0062] Depend on Figure 1 From the FTIR chromatogram of g-C3N4-COOH given in section a, it can be seen that in g-C3N4-COOH, 1246 cm⁻¹ −1 1322cm −1 The peak at 1406 cm⁻¹ corresponds to the stretching vibration of CN. −1 1632cm −1 The peak at 1406 cm⁻¹ corresponds to the stretching vibration peak of the CN heterocycle and is a characteristic structural peak of g-C₃N₄, proving the existence of the g-C₃N₄ framework. −1 The peak at 1570~1650 cm⁻¹ is related to the stretching vibration of CO. −1 The peak at 3157 cm⁻¹ is related to the stretching vibration of C=N. −1 The peak at this point is generally broad and strong, corresponding to the stretching vibration peak of the OH group in the carboxyl group. This indicates that the carboxyl group has been successfully introduced onto g-C3N4.
[0063] Depend on Figure 1 The FTIR spectrum of g-C3N4-COOH modified PVA fibers given in b shows that at 1010 cm⁻¹... −1 This corresponds to the stretching vibration of the CO bond in PVA; 1087 cm⁻¹ −1 1236cm −1 1408cm −1 The corresponding vibration is the stretching vibration of the CO bond in the carboxyl group, indicating that the g-C3N4 nanoparticles prepared in the laboratory successfully possess carboxyl functional groups. (1576 cm⁻¹) −1 The peak at 1697 cm⁻¹ corresponds to the C=C stretching vibration in the aromatic ring. −1 The peak at 2949 cm⁻¹ corresponds to the stretching vibration of the C=O group in the carboxyl group. −1 The peak at 3431 cm⁻¹ corresponds to the CH stretching vibration of the alkyl group in the PVA molecular chain. −1 The peak at that position corresponds to the stretching vibration of the OH group in the carboxyl group, indicating that g-C3N4-COOH has been successfully modified into PVA fibers.
[0064] (2) XRD test Figure 2 XRD analysis was performed on PVA fibers modified with g-C3N4, g-C3N4-COOH, g-C3N4, and g-C3N4-COOH.
[0065] Depend on Figure 2 As can be seen from the XRD pattern of g-C3N4 given in a, the (100) diffraction peak of g-C3N4 powder corresponds to the inter-plane structure; the (002) diffraction peak is the reflection of interlayer stacking of g-C3N4.
[0066] Depend on Figure 2 As shown in the XRD pattern of g-C3N4-COOH given in b, the (100) diffraction peak corresponds to the interplane structure, and the (002) diffraction peak corresponds to the interlayer stacking reflection of g-C3N4, which belongs to the basic structure of g-C3N4. The introduction of the carboxyl group only causes a certain distortion in the crystal structure, and the interlayer spacing changes, resulting in a slight shift in the diffraction peak of the (002) crystal plane.
[0067] Depend on Figure 2 The XRD pattern of g-C3N4 modified PVA fibers given in section c shows that the peak at 2θ=12.13˚ corresponds to the (100) crystal plane of g-C3N4, reflecting the in-plane repeating arrangement of triazine ring units. A strong peak at 2θ=19.96˚ corresponds to the (101) crystal plane of PVA fibers, which is a typical characteristic of PVA crystalline phases. The peak at 2θ=22.56˚ may be related to the (200) crystal plane of PVA fibers or the disordered phase.
[0068] Depend on Figure 2 The XRD pattern of g-C3N4-COOH modified PVA fibers given in d shows that the peak at 2θ=11.57˚ corresponds to the (100) crystal plane, reflecting the in-plane arrangement of the triazine ring units. However, due to the increase in interlayer spacing caused by the introduction of carboxyl groups, the peak shifts to a lower angle. The peak at 2θ=20.07˚ is the main peak of PVA, which is shifted by the introduction of carboxyl groups. The broad peak at 2θ=22.43˚ is the disorder peak introduced by carboxylation, reflecting the amorphization caused by carboxyl modification. Figure 2 a, b, c, and d in the figure verify that the carboxyl group was successfully introduced onto g-C3N4, and g-C3N4-COOH was also successfully modified into PVA fiber.
[0069] (3) Particle size and potential testing like Figure 3 Particle size distributions of g-C3N4 and g-C3N4-COOH are given. Figure 3It can be seen that the g-C3N4 particle size distribution is relatively loose, with most g-C3N4 particles ranging from 3000 nm to 5000 nm. The average particle size of g-C3N4 is 4116.56 nm. In the 1000 nm to 2500 nm range, the g-C3N4-COOH distribution is more concentrated and the particle size is more uniform. The average particle size of g-C3N4-COOH is 2090.75 nm, much smaller than the average particle size of g-C3N4. The hydrophilicity of the carboxyl group makes the particles more prone to dispersion in solution, less likely to agglomerate into large particles, resulting in a smaller g-C3N4-COOH particle size.
[0070] The Malvern particle size potential meter measured the average potential of g-C3N4 to be -5.91mV, while the average potential of g-C3N4-COOH was 16.2mV. It can be seen that the absolute value of the potential of g-C3N4-COOH is greater than that of g-C3N4, indicating that the dispersibility of g-C3N4-COOH is better than that of g-C3N4.
[0071] (4) Contact angle test Figure 4 To assess the hydrophilicity of g-C3N4, g-C3N4-COOH, PVA fibers, and g-C3N4-COOH-modified PVA fibers, the time it took for water droplets to disappear from each fiber was measured using a stopwatch. The contact angles of these fibers were then analyzed.
[0072] like Figure 4 As shown in Figure a, it takes 4.53 seconds for the water droplet to completely disappear on the g-C3N4 plate. Figure 4 As shown in Figure b, it takes 0.51 seconds for a water droplet to completely disappear on the g-C3N4-COOH sheet. Therefore, the hydrophilicity of g-C3N4-COOH is better than that of g-C3N4. This is because the introduction of carboxyl groups improves the overall hydrophilicity of g-C3N4.
[0073] like Figure 4 As shown in Figure c, it takes 7.21 seconds for a water droplet to completely disappear on a pure PVA fiber. Figure 4 As shown in Figure d, it takes 0.25 seconds for a water droplet to completely disappear on a g-C3N4-COOH modified PVA fiber sheet. This indicates that the hydrophilicity of g-C3N4-COOH modified PVA fiber is better than that of pure PVA fiber.
[0074] (5) Ultraviolet spectrophotometry like Figure 5The transmittance of the supernatant from pure PVA fibers and g-C3N4-COOH modified PVA fibers is shown in the figure. Figure 5 a and Figure 5 The comparison in step b shows that the transmittance of g-C3N4-COOH modified PVA fibers in the 350nm~800nm range is more gradual than that of pure PVA fibers, and the transmittance of g-C3N4-COOH modified PVA fibers is greater than that of pure PVA fibers. Higher transmittance in the supernatant indicates better dispersibility; therefore, the dispersibility of g-C3N4-COOH modified PVA fibers is better than that of pure PVA fibers.
[0075] (6) SEM Depend on Figure 6 a and Figure 6 A comparison of b shows that g-C3N4 has a sheet-like stacked structure on PVA fibers. Figure 6 There are clearly a large number of irregular particles in medium a, while Figure 6 In part b, the g-C3N4-COOH modified PVA fibers are smaller fragments or peeled flakes, due to partial peeling caused by the insertion of carboxyl groups into the interlayer. And through part c and 6... Figure 6 Compared to the previous method, g-C3N4-COOH modified PVA fibers have a smoother surface. The introduction of carboxyl groups enhances the hydrophilicity of PVA fibers, thus reducing post-carboxylation aggregation. Therefore, g-C3N4-COOH modified PVA fibers have better hydrophilicity than g-C3N4 modified PVA fibers.
[0076] (0) XPS test Figure 7 a and Figure 7 In the image, b represents the full spectrum of g-C3N4 and g-C3N4-COOH, respectively. Figure 7 a and Figure 7 Comparison of samples before and after carboxylation revealed that both g-C3N4 samples contained C, N, and O elements. The O peak in g-C3N4 was due to oxygen adsorption on the sample surface. Furthermore, the O peak in g-C3N4-COOH showed a significant increase, which is attributed to the introduction of carboxyl groups.
[0077] like Figure 7 c and Figure 7 As shown in Figure d, the binding energies of the three characteristic peaks appearing in the N 1s spectrum of g-C3N4 and g-C3N4-COOH are 398.3 eV, 399.8 eV and 403.8 eV, respectively. The characteristic peak at 398.5 eV corresponds to the CN=C bond, the characteristic peak at 399.8 eV corresponds to the NC triple bond, and the characteristic peak at 403.8 eV corresponds to the NH bond.
[0078] like Figure 7China and Figure 7 The fitting of f in the C 1s spectrum of g-C3N4 yielded two characteristic peaks at 288.1 eV and 284.7 eV, corresponding to CN=C and CC bonds, respectively. Meanwhile, a new peak C=O appeared at 292.6 eV in g-C3N4-COOH, further proving that the carboxyl group was successfully introduced.
[0079] (II) Performance Study A method for preparing well cement is as follows: The components are mixed according to the following mass percentage ratio: either 9mm 0.1% g-C3N4-COOH modified PVA fiber or 6mm 0.1% g-C3N4-COOH modified PVA fiber is added to a G-grade cement base formulation to obtain a nano-modified polyvinyl alcohol fiber cement-based composite material, which can be used as a sealing material. Its sealing principle is as follows: Figure 9 As shown, the performance of the nano-modified polyvinyl alcohol fiber cementitious composite material is now verified.
[0080] (1) Cement strength Figure 8 The strength curves are those of pure cement (Comparative Example 3) and the strength curves of nano-modified polyvinyl alcohol fiber cementitious composites obtained by mixing 9 mm or 6 mm of 0.1% g-C3N4-COOH modified PVA fibers into a G-grade cement base formulation. Figure 8 a and Figure 8 Comparing the two methods, it can be seen that the strength of cement is greater after adding g-C3N4-COOH modified PVA fibers than that of pure cement.
[0081] (2) Study on thickening and plugging performance 1% 6mm g-C3N4-COOH modified PVA fibers and unmodified 1% PVA fibers were added to cement to obtain nano-sealing materials and conventional grout materials, respectively. The thickening and plugging performance of the conventional grout materials and nano-sealing materials were studied, and the experimental results are shown in Tables 1 and 2. Table 1 shows that the initial thickness of the cement grout system after adding g-C3N4-COOH modified PVA fibers increased by 3 Bc, and the consistency increased significantly after reaching 60℃. The strength increase from 24h to 48h was much higher than that of conventional cement, which can meet the plugging requirements.
[0082] Table 1 Comparison of cement thickening time and strength before and after fiber addition. As shown in Table 1, when the crack density is the same, the initial thickness of the modified fiber-doped cement is greater than that of the conventional slurry after water loss, but the thickening time of the two is the same. The strength increase of the conventional slurry after 48 hours of water loss reduction is small, while the strength of the modified fiber-doped cement after 48 hours is significantly increased compared to that after 24 hours.
[0083] Table 2. Leakage sealing results of cement with added fibers Table 2 shows that when the crack width is 1 mm, the leakage is greatest at a pressure of 7 MPa, reaching 15 mL, which meets the sealing requirements. When the crack width is 2 mm, the leakage is greatest at a pressure of 5 MPa, reaching 28 mL, which also meets the sealing requirements. Therefore, the newly prepared carbon nitride nanosheets modified with polyvinyl alcohol fibers can meet the sealing requirements.
[0084] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.
Claims
1. A method for producing a modified polyvinyl alcohol fiber, characterized by, Includes the following steps: Layered g-C3N4 was prepared using melamine powder; The layered g-C3N4 was carboxylated and then dried to obtain g-C3N4-COOH; A PVA aqueous solution was prepared, and g-C3N4-COOH was added to the PVA aqueous solution at room temperature to carry out an ultrasonic reaction. After the reaction was completed, the reactants were dried to obtain g-C3N4-COOH modified PVA fibers.
2. The method of claim 1, wherein the nanofinished polyvinyl alcohol fiber is characterized by, The PVA aqueous solution has a mass percentage of 8% to 12%, and the amount of g-C3N4-COOH added is 1% to 10% of the mass of PVA fiber.
3. The method of producing a modified polyvinyl alcohol fiber according to claim 1, characterized by, The thickness of the g-C3N4-COOH is 2nm~10nm.
4. The method of producing a modified polyvinyl alcohol fiber according to claim 1, characterized by, The preparation steps of the layered g-C3N4 are as follows: Melamine powder was subjected to high-temperature pyrolysis reaction at 500℃~700℃ for 1.5h~3h to obtain g-C3N4 powder; g-C3N4 powder was dispersed in water and ultrasonicated to obtain a layered g-C3N4 dispersion with a concentration of 0.015~0.025g / mL, which was then dried to obtain layered g-C3N4.
5. The method of producing a modified polyvinyl alcohol fiber according to claim 4, characterized by, The steps for preparing g-C3N4-COOH by carboxylation of g-C3N4 are as follows: Layered g-C3N4 was mixed with a mixed acid, heated to boiling, and refluxed and condensed for 1.5-3 hours with slow stirring. After washing with water until the pH reached 6-7, the mixture was vacuum dried and ground to obtain g-C3N4-COOH. The mixed acid was prepared by mixing concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 2-4:0.5-1.
5. The concentration of the solution of layered g-C3N4 and mixed acid was 0.0625 g / mL-0.4 g / mL, and the drying temperature was 30℃-60℃.
6. The g-C3N4-COOH modified PVA fiber prepared by the method for preparing modified polyvinyl alcohol fiber according to any one of claims 1 to 5.
7. The application of g-C3N4-COOH modified PVA fiber according to claim 6 in cement for sealing microcracks and microslits in oil wells.
8. Use according to claim 8, characterized in that, In the 1mm and 2mm joint sealing tests, the sealing cement made of g-C3N4-COOH modified PVA fibers had the highest pressure resistance of 5MPa~7MPa.