A modified organic fiber material and a method for preparing and using the same

Abstract

The application discloses a modified organic fiber material and a preparation method and application thereof.The modified organic fiber material comprises an organic fiber and a calcium silicate hydrate layer on the surface of the organic fiber.The modified organic fiber material has the calcium silicate hydrate layer on the surface, can form a chemical compatible interface layer with a cement hydration product, significantly improves the interface bonding force between the fiber and the cement matrix, and improves the interface bonding performance of the fiber / cement matrix.The modified organic fiber material is used in a fiber reinforced cement-based composite material, improves the fiber pull-out strength, makes the fiber not easy to be pulled out and not easy to slip, has a good fiber reinforcing effect, significantly improves the crack resistance of the cement-based composite material, has good durability of the composite material, and can meet the reliability and industrial application requirements of the high-performance cement-based composite material under long-term service conditions.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a modified organic fiber material, its preparation method, and its application. Background Technology

[0002] High-performance fiber-reinforced cementitious composites are widely used in bridges, tunnels, marine engineering, and other infrastructure projects due to their excellent crack resistance and toughness. Polymer fibers are a common building fiber material; however, traditional hydrophobic polymer fibers, such as polypropylene, polyethylene, or nylon fibers, suffer from weak interfacial bonding with the cement matrix, are prone to pull-out, and are susceptible to slippage, which limits the full realization of the fiber reinforcement effect. Summary of the Invention

[0003] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a modified organic fiber material, wherein the fiber surface has hydrated calcium silicate, which enhances the interfacial bonding force between the fiber and the cement matrix. When used in conjunction with cement, the fiber is not easily pulled out or slips, and the fiber reinforcement effect is good.

[0004] The present invention also proposes a method for preparing modified organic fiber materials.

[0005] The present invention also proposes a cement-based composite material.

[0006] In a first aspect, the present invention provides a modified organic fiber material comprising organic fibers and a hydrated calcium silicate layer located on the surface of the organic fibers.

[0007] The modified organic fiber material according to embodiments of the present invention has at least the following beneficial effects: The modified organic fiber material in this invention contains a hydrated calcium silicate layer (CSH coating) on ​​its surface. The CSH coating can form a chemically compatible interface layer with cement hydration products, significantly improving the interfacial bonding force between the fiber and the cement matrix, thus enhancing the fiber / cement matrix interfacial bonding performance. Using the modified organic fiber material in fiber-reinforced cement-based composites improves fiber pull-out strength, making the fibers less prone to pull-out and slippage, resulting in good fiber reinforcement and significantly improving the crack resistance of cement-based composites. This meets the reliability and industrial application requirements of high-performance cement-based composites under long-term service conditions.

[0008] In some embodiments of the present invention, the length of the organic fiber is 1 mm to 5 cm, such as 3 mm to 3 cm.

[0009] In some embodiments of the present invention, the diameter of the organic fiber is 10 μm to 3 mm.

[0010] In some embodiments of the present invention, the diameter of the organic fiber is 30~200μm.

[0011] In some embodiments of the present invention, the aspect ratio of the organic fiber is (50~2000):1, such as (100~1000):1.

[0012] In some embodiments of the present invention, the organic fiber includes at least one of polypropylene, polyethylene, nylon, aramid, or polyethylene terephthalate.

[0013] In some embodiments of the present invention, the organic fiber includes at least one of polypropylene fiber (PP fiber), polyethylene fiber (PE fiber), nylon fiber, aramid fiber or polyethylene terephthalate fiber (PET fiber).

[0014] In some embodiments of the present invention, the hydrated calcium silicate layer comprises xCaO·ySiO2·zH2O.

[0015] In some embodiments of the present invention, x / y is 0.3~2 and z / y is 0.5~5.

[0016] In some embodiments of the present invention, the thickness of the hydrated calcium silicate layer is 10 nm to 10 µm.

[0017] In some embodiments of the present invention, the thickness of the hydrated calcium silicate layer is 50~2000 nm.

[0018] A second aspect of the present invention provides a method for preparing a modified organic fiber material, comprising the following steps: S1, surface hydrophilic activation treatment of organic fibers; S2 uses an electrolyte containing calcium and silicon sources to perform electrochemical deposition on activated organic fibers, depositing a hydrated calcium silicate layer in situ on the surface of the organic fibers.

[0019] The method for preparing modified organic fiber materials according to embodiments of the present invention has at least the following beneficial effects: This invention introduces hydrophilic groups into the surface of organic fibers through surface hydrophilic activation treatment, creating active sites on the fiber surface that promote inorganic bonding. This significantly improves the deposition of CSH (calcium silicate hydrate) on the fiber surface under electrochemical processes, resulting in a significant increase in interfacial bonding strength. In some embodiments of this invention, the hydrophilic groups include hydroxyl groups. Furthermore, this invention uses electrochemically induced deposition of CSH on the surface of organic fibers to form a chemically continuous, dense inorganic interfacial layer that is chemically compatible with cement hydration products. This significantly improves the interfacial bonding performance between the fiber and the cement matrix, and significantly enhances the mechanical properties and long-term durability of the composite material. Using modified organic fiber materials in fiber-reinforced cement-based composites improves fiber pull-out strength, making the fibers less prone to pull-out and slippage, resulting in good fiber reinforcement. This significantly improves the crack resistance and durability of cement-based composites, meeting the reliability and industrial application requirements of high-performance cement-based composites under long-term service conditions. Simultaneously, the preparation method of this invention combines process simplicity and industrial feasibility, representing a low-energy-consumption and highly controllable material preparation method.

[0020] In some embodiments of the present invention, the organic fiber before surface activation treatment is a hydrophobic polymeric organic fiber. Optionally, the organic fiber includes at least one of polypropylene, polyethylene, nylon, aramid, or polyethylene terephthalate. Optionally, the organic fiber includes at least one of polypropylene fiber (PP fiber), polyethylene fiber (PE fiber), nylon fiber, aramid fiber, and polyethylene terephthalate fiber (PET fiber).

[0021] In some embodiments of the present invention, the length of the organic fiber is 1 mm to 5 cm, such as 3 mm to 3 cm.

[0022] In some embodiments of the present invention, the diameter of the organic fiber is 10 μm to 3 mm, and may be 30 to 200 μm.

[0023] In some embodiments of the present invention, the aspect ratio of the organic fiber is (50~2000):1, such as (100~1000):1.

[0024] In some embodiments of the present invention, in step S1, the organic fibers are subjected to surface hydrophilic activation treatment using a wet chemical oxidation method.

[0025] In some embodiments of the present invention, step S1 includes the following steps: mixing organic fibers with an aqueous solution of an inorganic acid, reacting the mixture to obtain activated organic fibers. Optionally, the inorganic acid includes at least one of sulfuric acid or nitric acid.

[0026] In some embodiments of the present invention, in step S1, the mass ratio of organic fiber to inorganic acid aqueous solution is (0.01~0.5):1.

[0027] In some embodiments of the present invention, step S1 includes the following steps: placing the organic fiber in an aqueous sulfuric acid solution with a sulfuric acid mass fraction of 10-80%, reacting at 30-80°C for 1-12 hours, filtering, washing with water, and drying to obtain activated organic fiber. Optionally, after the reaction, the fiber is filtered with water, washed multiple times, and then dried at 50-105°C to obtain activated organic fiber.

[0028] Through the above embodiments, the surface activation treatment in this invention is a mild activation completed under low temperature and short time conditions. Combined with a specific acid concentration, it not only allows the organic fiber to better maintain its complete structure, but also allows the formation of active sites on the fiber surface that can promote the combination of inorganic substances. This can significantly improve the deposition of CSH coating on the fiber surface under electrochemical processes and bring about a significant improvement in interfacial bonding strength.

[0029] In some embodiments of the present invention, step S2 includes the following steps: placing the activated organic fiber in an electrolyte containing a calcium source and a silicon source, applying an electric field, and depositing a hydrated calcium silicate layer in situ on the surface of the organic fiber.

[0030] In some embodiments of the present invention, the applied electric field in step S2 is a DC electric field.

[0031] In some embodiments of the present invention, in step S2, the electrochemical deposition is performed under constant current density or constant potential conditions.

[0032] In some embodiments of the present invention, in step S2, the constant current density is 0.1~100 mA / cm². 2 The constant potential is 0.5~30V.

[0033] In some embodiments of the present invention, in step S2, the deposition time of the electrochemical deposition is 1 to 600 min.

[0034] In some preferred embodiments of the present invention, in step S2, the deposition time of the electrochemical deposition is 120~240 min.

[0035] In some embodiments of the present invention, the concentration of the calcium source in the electrolyte is 0.1~5 mol / L, calculated as calcium atoms.

[0036] In some embodiments of the present invention, the concentration of the silicon source in the electrolyte is 0.1~2.5 mol / L, based on silicon atoms.

[0037] In some embodiments of the present invention, the ratio of the molar amount of calcium atoms in the calcium source to the molar amount of silicon atoms in the silicon source is (0.1~2.0):1.

[0038] In some embodiments of the present invention, the calcium source includes at least one of calcium oxide, calcium hydroxide, or calcium salt.

[0039] In some embodiments of the present invention, the calcium salt includes at least one of calcium carbonate, calcium nitrate, or calcium chloride.

[0040] In some embodiments of the present invention, the silicon source is a water-soluble silicate.

[0041] In some embodiments of the present invention, the silicon source includes at least one of anhydrous sodium silicate or hydrated sodium silicate.

[0042] In some embodiments of the present invention, the temperature of the electrolyte is 20~90°C during the electrochemical deposition process.

[0043] In some embodiments of the present invention, the pH of the electrolyte is 8 to 13 during the electrochemical deposition process.

[0044] The thickness of the hydrated calcium silicate layer is adjustable, for example, by adjusting conditions such as the ion concentration in the electrolyte, the current density, and the deposition time. In some embodiments of the present invention, the thickness of the hydrated calcium silicate layer is 10 nm to 10 µm.

[0045] In some embodiments of the present invention, in step S2, an electrochemical deposition apparatus is used to electrochemically deposit the activated organic fibers. The electrochemical deposition apparatus includes a power source, an anode chamber, and a cathode chamber. The anode chamber and cathode chamber are respectively provided with an anode and a cathode connected to the power source. The anode chamber contains an electrolyte I containing a calcium source, and the cathode chamber contains the activated organic fibers and an electrolyte II containing a silicon source. The anode and cathode are respectively connected to the positive and negative terminals of the power source. Both the positive and negative terminals can be platinum.

[0046] In some embodiments of the present invention, the anode chamber and the cathode chamber are connected by a membrane layer having a microporous structure. Optionally, the membrane layer comprises filter paper.

[0047] In some embodiments of the present invention, the average pore size of the micropores is less than 200 μm, such as 80~120 μm.

[0048] In some embodiments of the present invention, electrolyte I comprises solvent I and a calcium source, and electrolyte II comprises solvent II and a silicon source. In some embodiments of the present invention, solvent I comprises water, and solvent II comprises water.

[0049] In some embodiments of the present invention, the initial concentration of the calcium source in electrolyte I, based on calcium atoms, is 0.1~5 mol / L. The initial concentration refers to the concentration of the calcium source before electrochemical deposition occurs.

[0050] In some embodiments of the present invention, the initial concentration of the silicon source in electrolyte II, based on silicon atoms, is 0.1~2.5 mol / L. The initial concentration refers to the concentration of the silicon source before electrochemical deposition occurs.

[0051] In some embodiments of the present invention, based on the mass of the unactivated organic fiber, the initial molar amount of silicon atoms in the silicon source in the cathode chamber to the mass of the organic fiber is (0.01~3 mol):5 g.

[0052] In some embodiments of the present invention, based on the mass of the unactivated organic fiber, the initial molar amount of calcium atoms in the calcium source in the anode chamber to the mass of the organic fiber is (0.01~3 mol):5 g.

[0053] The method for preparing the modified organic fiber material of the present invention has many beneficial effects, such as: 1) The CSH coating on the surface of the modified organic fiber material can be chemically compatible with the cement matrix, significantly improve the interfacial bonding force between the fiber and the cement matrix, increase the fiber pull-out strength, and significantly improve the crack resistance of the cement-based composite material. 2) Enhanced durability of the obtained modified organic fiber material: without an organic coupling agent layer, the CSH coating is stable in alkaline and humid environments for a long time; 3) Simple process and low energy consumption: low temperature, wet electrochemical deposition, avoiding high temperature, vacuum or complex equipment; 4) High controllability: The coating thickness, uniformity, and microstructure can be controlled by adjusting electrochemical parameters and ion donors; 5) Great industrialization potential: The process is applicable to continuous production, with cost advantages and environmental friendliness.

[0054] In a third aspect, the present invention provides a cement-based composite material comprising the aforementioned modified organic fiber material.

[0055] In some embodiments of the present invention, the cement-based composite material further includes cement.

[0056] Through the above embodiments, modified organic fibers with CSH coatings are combined with cement-based materials. The CSH coatings and cement hydration products form a chemically compatible interface layer, thereby enhancing the fiber / matrix bonding force and the mechanical properties of the composite material.

[0057] In some embodiments of the present invention, the modified organic fiber material in the cement-based composite material has a mass fraction of 0.02-0.3%, such as 0.05-0.3%.

[0058] In some embodiments of the present invention, the cement-based composite material further includes one or more of aggregates, gelling materials, chemical admixtures, or functional components. Optionally, the aggregates include one or more of natural river sand, manufactured sand, quartz sand, fly ash sand, crushed stone, pebbles, ceramsite, and expanded perlite. The gelling materials include one or more of fly ash, slag powder, silica fume, metakaolin, or gypsum. The chemical admixtures include one or more of water-reducing agents, setting regulators, air-entraining agents, water-retaining agents, or expanding agents. The functional components include one or more of conductive components, thermal insulation components, or corrosion-resistant components. Attached Figure Description

[0059] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein: Figure 1 This is a schematic diagram of the electrochemical device in Embodiment 1 of the present invention; Figure 2 These are scanning electron microscope images of the unmodified PP fiber, the surface-activated PP fiber, and the modified organic fiber material in Example 1 of the present invention. Figure 3 The figures show the interfacial shear strength test results of fiber-reinforced cement-based composite materials prepared using unmodified PP fibers, surface-activated PP fibers, and modified organic fiber materials, respectively, as described in Example 1 of this invention. Figure 4 The figures show the interfacial shear strength test results of fiber-reinforced cementitious composite materials prepared using the modified organic fiber materials obtained in Examples 1-4 of this invention, respectively. Figure 5 The figures show the flexural strength test results of fiber-reinforced cement-based composite materials prepared using unmodified PP fibers, surface-activated PP fibers, and modified organic fiber materials, respectively, as described in Example 1 of this invention. Detailed Implementation

[0060] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0061] Unless otherwise specified, the experimental methods used in the following examples and comparative examples are generally performed under conventional conditions in the art or as recommended by the manufacturer; the raw materials and reagents used are all commercially available from the conventional market unless otherwise specified.

[0062] Example 1 This embodiment discloses a modified organic fiber material, the preparation process of which includes the following steps: (I) Activation of organic fibers by wet chemical method: 5g of polypropylene (PP) fiber (length 18mm, diameter 50μm, aspect ratio 360) was immersed in 100mL of sulfuric acid aqueous solution (the mass fraction of sulfuric acid in the sulfuric acid aqueous solution was 30%) and reacted at 60℃ for 6 hours. After filtration with sufficient deionized water and washing multiple times, the obtained solid material was dried at 80℃ to obtain the modified PP fiber activated by wet chemical method, denoted as PPs.

[0063] (II) Place 5g of modified PP fiber in a container as follows: Figure 1 The reactor shown contains: a calcium hydroxide suspension (composed of 3.7 g calcium hydroxide and 100 mL deionized water) on the left side and a sodium silicate aqueous solution (0.5 mol / L) on the right side. A 100-micron pore size filter paper is placed between the left and right sides to prevent backflow. The left side is designated as the anode chamber, and the right side as the cathode chamber. Platinum sheets are used as electrode elements in both chambers, and a constant current density of 50 mA / cm² is set. 2 Electrochemical deposition was performed for 180 minutes at a reaction temperature of 30°C, with the pH on the right side of the reactor controlled at 11.5. The resulting solid was then filtered with sufficient deionized water, washed multiple times, and dried under a nitrogen atmosphere at 80°C to obtain CSH-coated modified PP fibers. This resulted in a hydrated calcium silicate layer (CSH coating, chemical formula CaO·SiO2·2H2O) forming on the surface of the modified PP fibers, with a coating thickness of 600–800 nm, denoted as PPcsh.

[0064] This embodiment also discloses a cement-based composite material, including the modified organic fiber material prepared in this embodiment and cement.

[0065] Example 2 This embodiment discloses a modified organic fiber material, which differs from Example 1 in that: the deposition time in step (II) is 60 min, the coating composition is the same as in Example 1, and the coating thickness is 50 nm to 200 nm.

[0066] This embodiment also discloses a cement-based composite material, including the modified organic fiber material prepared in this embodiment and cement.

[0067] Example 3 This embodiment discloses a modified organic fiber material, which differs from Example 1 in that: the deposition time in step (II) is 120 min, the coating composition is the same as in Example 1, and the coating thickness is 250~450 nm.

[0068] This embodiment also discloses a cement-based composite material, including the modified organic fiber material prepared in this embodiment and cement.

[0069] Example 4 This embodiment discloses a modified organic fiber material, which differs from Example 1 only in that: the deposition time in step (II) is 240 min, the coating composition is the same as in Example 1, and the coating thickness is 1100~1500 nm.

[0070] This embodiment also discloses a cement-based composite material, including the modified organic fiber material prepared in this embodiment and cement.

[0071] Test case This experimental example tested the performance of the organic fiber material in the examples, including: (1) The microstructure of the unmodified raw PP fibers, the PPs fibers activated by wet chemical methods, and the modified PPcsh fibers with CSH coating obtained by electrochemical deposition in Example 1 were tested. The surface morphology of the fibers was observed and photographed using a scanning electron microscope. The test results are as follows: Figure 2 As shown, (a) is the test result diagram of the original PP fiber, (b) is the test result diagram of the PPs fiber, and (c) is the test result diagram of the modified PPcsh fiber.

[0072] Depend on Figure 2 It can be seen that the surfaces of wet chemically activated PPs and unmodified PP fibers are indistinguishable, both being relatively smooth. However, the surface of the modified PPcsh fiber is uniformly coated with a layer of irregularly shaped material, which is verified to be CSH (hydrated calcium silicate). This result proves that a layer of CSH can be uniformly coated on the surface of organic fibers by electrochemical deposition.

[0073] (2) To test the interfacial interaction performance between different fibers and the cement matrix, fiber-reinforced cement-based composite materials were prepared using the various organic fibers to be tested. The organic fibers to be tested included: unmodified virgin PP fibers from Example 1, PPs fibers activated by wet chemical methods from Example 1, and modified organic fiber materials (PPcsh) obtained in Examples 1-4. The preparation steps included: The cement matrix was prepared by mixing ordinary Portland cement (PO42.5) and deionized water at a mass ratio of 2:1. The mixture was stirred at approximately 500 rpm for 3 minutes in a mixer to ensure uniform dispersion. The slurry was then poured into a rectangular mold measuring 2cm × 2cm × 2mm and gently compacted to eliminate any air bubbles. During this process, individual organic fiber materials (here, individual fibers used for subsequent monofilament pull-out tests) were embedded into the cement matrix as reinforcing phases. Each fiber was inserted vertically into the center of the slurry, ensuring consistent embedding depth and good alignment of the fiber axis with the applied load direction. After slurry pouring and organic fiber embedding, the resulting samples were placed at 25°C for 24 hours for initial hardening. They were then demolded and cured under standard conditions of 20°C and relative humidity greater than 95% for 27 days to obtain a series of fully hardened fiber-reinforced cement-based composite materials.

[0074] The obtained series of fiber-reinforced cementitious composite materials were subjected to single-filament pull-out tests. The test method included using an electronic servo universal tensile testing machine equipped with a high-sensitivity 10N force sensor. Before the test, the fixture was precisely adjusted to ensure that the fibers in the composite material were completely aligned with the tensile direction. The loading rate was set to 0.5 mm / min, and the load-displacement curves were continuously recorded. At least six valid samples were tested for each type of fiber-reinforced cementitious composite material, excluding samples with non-interface-controlled failure due to early fiber breakage, defects, etc. The interfacial shear strength was calculated from the maximum load during the pull-out process, based on the fiber diameter and actual embedding length. The results were averaged and the standard deviation was calculated to ensure data reliability. Test results: 1) The interfacial shear strength test results of fiber-reinforced cementitious composite materials prepared using unmodified PP fibers, wet chemically activated PPs, and modified organic fiber material PPcsh from Example 1 are shown in the figure below. Figure 3 As shown, compared with the interfacial shear strength of fiber-reinforced cementitious composites prepared from original unmodified PP fibers, the interfacial shear strength of fiber-reinforced cementitious composites prepared from wet chemically activated PPs and CSH-coated PPcsh is increased by 30.3% and 81.8%, respectively.

[0075] It is evident that this invention, by depositing a CSH coating on the surface of pre-activated PP fibers using an electrochemical method, can significantly improve the interfacial shear strength between the fibers and the cement matrix. The performance improvement stems primarily from two synergistic effects: First, CSH and the cement matrix possess excellent physicochemical compatibility. During cement hydration, the CSH coating on the fiber surface can continuously bond with the newly formed CSH phase in the matrix, thereby establishing a stable inorganic phase interface. Second, CSH can form hydrogen bonds with the surface active groups (such as hydroxyl groups) of the PP fibers after wet chemical pre-activation treatment. Compared to the almost unreacted interface between the original hydrophobic PP fibers and the cement matrix, this invention significantly improves the adhesion quality between the fibers and the coating. Therefore, by constructing a continuous CSH coating on the fiber surface, an effective "bridging effect" can be formed between the fibers and the matrix: on the one hand, it enhances the interaction between CSH and the fibers; on the other hand, it promotes the formation of a stable chemical bond between the fibers and the cement matrix. The aforementioned dual enhancement mechanism leads to a significant improvement in interfacial shear strength. Experimental results show that the system of the present invention can achieve a significant improvement in interfacial strength compared to unmodified fibers, proving that the CSH coating has an outstanding effect in improving the interfacial interaction of PP fibers.

[0076] 2) The interfacial shear strength test results of fiber-reinforced cementitious composite materials prepared using the modified organic fiber materials obtained in Examples 1-4 of this invention are as follows: Figure 4 As shown in the figure. The results show that when the deposition time is below 180 min, the interfacial shear strength increases with the increase of deposition time; when the deposition time is 180 min, the interfacial shear strength is higher than the corresponding test results for deposition times of 60 min and 120 min, with an average interfacial shear strength of 1.20 ± 0.04 MPa, which is 26.3% higher than the sample with a deposition time of 60 min. Compared with the fiber-reinforced cement-based composite material obtained with a deposition time of 180 min, the interfacial shear strength of the fiber-reinforced cement-based composite material obtained with a deposition time of 240 min is slightly lower. The reasons include: the deposition time of 240 min is relatively longer than that of 180 min. Since the deposited CSH forms a certain thickness, it will affect its subsequent composite with the cement matrix, ultimately resulting in a slightly worse improvement in the interfacial interaction.

[0077] (3) To test the flexural strength of cement-based materials after different fibers are combined with the cement matrix, fiber-reinforced cement-based composite materials were prepared using various organic fibers to be tested. The organic fibers to be tested included: unmodified raw PP fibers from Example 1, PPs fibers activated by wet chemical methods from Example 1, and the modified organic fiber material (PPcsh) obtained in Example 1. The preparation steps included: The cement matrix was prepared by mixing ordinary Portland cement (PO42.5) and deionized water at a mass ratio of 2:1. The mixture was stirred at approximately 500 rpm for 3 minutes in a mixer to ensure uniform dispersion. Then, the tested organic fiber materials were added as reinforcing phases, with a fiber mass fraction of 0.05%. The mixture was then stirred at approximately 500 rpm for 3 minutes. The resulting slurry was poured into a rectangular mold measuring 4 cm × 4 cm × 16 mm and gently compacted to eliminate air bubbles. The resulting samples were placed at 25°C for 24 hours to allow for initial hardening. They were then demolded and cured under standard conditions of 20°C and relative humidity greater than 95% for 27 days to obtain a series of fully hardened fiber-reinforced cementitious composite materials.

[0078] The obtained series of fiber-reinforced cementitious composite materials were subjected to three-point bending tests using an electronic servo universal tensile testing machine. The loading rate was set to 0.5 mm / min, and the load-displacement curves were continuously recorded. At least three valid samples were tested for each type of fiber-reinforced cementitious composite material. The bending strength was calculated from the maximum load during loading, based on the composite sample size and a clamp span of 10 cm. The results were averaged and the standard deviation was calculated to ensure data reliability. Test results: The flexural strength test results of fiber-reinforced cementitious composite materials prepared using unmodified PP fibers, wet chemically activated PPs, and modified organic fiber material PPcsh from Example 1 are shown in the figure below. Figure 5 As shown, compared with the flexural strength (4.84 MPa) of the fiber-reinforced cementitious composite material prepared from the original unmodified PP fibers, the flexural strength of the fiber-reinforced cementitious composite material prepared by wet chemically activated PPs and CSH-coated PPcsh is increased by 16.5% and 56.2%, respectively, reaching 5.64 MPa and 7.56 MPa.

[0079] It is evident that this invention, through electrochemical deposition of a CSH coating on the surface of pre-activated PP fibers, can significantly improve the flexural strength of fiber-reinforced cementitious composites. The performance improvement is primarily due to two synergistic effects: the interaction between CSH and the fibers, and the formation of a stable chemical bond between the fibers and the cement matrix. This dual reinforcement mechanism leads to a significant increase in flexural strength. Experimental results demonstrate that the system of this invention achieves a marked improvement in flexural strength compared to unmodified fibers, proving that the CSH coating has a prominent effect on improving the flexural properties of PP fiber-reinforced composites.

[0080] In summary, this invention proposes a method for in-situ constructing a calcium silicate hydrate (CSH) coating on low-activity, hydrophobic polymer fibers (such as polypropylene fibers) to improve the bonding performance between the fiber and the cement matrix. The method first pre-activates the polymer fiber surface through chemical oxidation to introduce hydrophilic groups and increase surface energy. Then, the fiber is placed in an electrolyte system containing calcium ions and a silicon source, and a uniform and dense CSH layer is formed in-situ deposited on the fiber surface through electrochemical induction. The resulting coating exhibits good compatibility with cement hydration products and can establish continuous chemical bonding and mechanical interlocking structures at the interface, thereby significantly improving fiber pull-out energy and interfacial shear strength. This method does not require the use of silane coupling agents, is simple, environmentally friendly, and highly controllable, and is suitable for the large-scale processing of different types of hydrophobic polymer fibers, providing a novel interface control approach for high-performance, long-life fiber-reinforced cementitious materials.

[0081] Unless otherwise specified, the term "about" in this invention actually means that the error is allowed to be within ±2%, for example, about 100 is actually 100 ± 2% × 100.

[0082] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments, and various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A modified organic fiber material, characterized in that, It includes organic fibers and a layer of hydrated calcium silicate on the surface of the organic fibers.

2. The modified organic fiber material according to claim 1, characterized in that, The organic fiber has a length of 1 mm to 5 cm; and / or, the organic fiber has a diameter of 10 μm to 3 mm; and / or, the organic fiber has an aspect ratio of (50 to 2000):1; and / or, the organic fiber includes at least one of polypropylene, polyethylene, nylon, aramid, or polyethylene terephthalate.

3. The modified organic fiber material according to claim 1, characterized in that, The hydrated calcium silicate layer comprises xCaO·ySiO2·zH2O; and / or, the thickness of the hydrated calcium silicate layer is 10nm~10µm; Preferably, x / y is 0.3~2 and z / y is 0.5~5.

4. A method for preparing a modified organic fiber material, characterized in that, Includes the following steps: S1, surface hydrophilic activation treatment of organic fibers; S2 uses an electrolyte containing calcium and silicon sources to perform electrochemical deposition on activated organic fibers, depositing a hydrated calcium silicate layer in situ on the surface of the organic fibers.

5. The method for preparing the modified organic fiber material according to claim 4, characterized in that, In step S1, the organic fibers are subjected to surface hydrophilic activation treatment using a wet chemical oxidation method; Preferably, step S1 includes the following steps: mixing organic fibers with an inorganic acid aqueous solution and reacting to obtain activated organic fibers; Preferably, in step S1, the mass ratio of organic fiber to inorganic acid aqueous solution is (0.01~0.5):1; and / or, step S1 includes the following steps: placing the organic fiber in an aqueous solution of sulfuric acid with a mass fraction of 10~80%, reacting at 30~80°C for 1~12 hours, filtering, washing with water, and drying to obtain activated organic fiber.

6. The method for preparing the modified organic fiber material according to claim 4, characterized in that, Step S2 includes the following steps: placing the activated organic fiber in an electrolyte containing calcium and silicon sources, applying an electric field, and depositing a hydrated calcium silicate layer in situ on the surface of the organic fiber. Preferably, in step S2, the applied electric field is a DC electric field; Preferably, in step S2, the electrochemical deposition is performed under constant current density or constant potential conditions; Preferably, in step S2, the constant current density is 0.1~100 mA / cm². 2 The constant potential is 0.5~30V; and / or the deposition time of the electrochemical deposition is 1~600min; Preferably, the deposition time for the electrochemical deposition is 120~240 min.

7. The method for preparing the modified organic fiber material according to claim 4, characterized in that, In the electrolyte, the concentration of the calcium source, calculated as calcium atoms, is 0.1~5 mol / L; and / or, in the electrolyte, the concentration of the silicon source, calculated as silicon atoms, is 0.1~2.5 mol / L; and / or, the ratio of the molar amount of calcium atoms in the calcium source to the molar amount of silicon atoms in the silicon source is (0.1~2.0):

1.

8. The method for preparing the modified organic fiber material according to claim 4, characterized in that, The calcium source includes at least one of calcium oxide, calcium hydroxide, or calcium salt; and / or, the silicon source is a water-soluble silicate; Preferably, the calcium salt includes at least one of calcium carbonate, calcium nitrate, or calcium chloride; and / or, the silicon source includes at least one of anhydrous sodium silicate or hydrated sodium silicate.

9. The method for preparing the modified organic fiber material according to claim 4, characterized in that, During electrochemical deposition, the temperature of the electrolyte is 20–90°C; and / or, during electrochemical deposition, the pH of the electrolyte is 8–13.

10. A cement-based composite material, characterized in that, This includes the modified organic fiber material according to any one of claims 1 to 3 or the modified organic fiber material prepared by the preparation method according to any one of claims 4 to 9.

Images