Preparation method of nano sepiolite fiber, composite coating, preparation method and application of composite coating

Abstract

The invention discloses a preparation method of nano sepiolite fibers, which comprises the following steps: acidizing sepiolite by a hydrothermal synthesis method to enable the interior of the sepiolite to have mutually communicated holes, and loading SiO2 particles on the surface of the sepiolite to prepare the nano sepiolite fibers; the sepiolite is modified, the specific surface area of the sepiolite is increased, the sepiolite is used for the steel structure water-based acrylic acid anti-corrosion coating in the inland wharf environment, good compatibility with water-based acrylic acid emulsion is achieved, and the tensile strength and the erosion resistance of the coating can be improved.

Description

Technical Field

[0001] The present invention relates to the field of coatings, and in particular to a preparation method of nano-sepiolite fibers, a composite coating, a preparation method and applications thereof. Background Art

[0002] Water-based acrylic emulsions are formed by emulsion polymerization of vinyl monomers, primarily acrylate monomers. Various additives, such as emulsifiers, stabilizers, and pH adjusters, are added during the polymerization process, resulting in a complex system. Paint films produced with water-based acrylic emulsions exhibit excellent weather resistance, are less susceptible to yellowing, have high hardness, and possess a high gloss. While fillers can enhance the coating's erosion resistance, water- and sand-erosion resistance at high flow rates remains insufficient. Furthermore, water- and sand-erosion wear primarily results from the cutting action of the water flow and the irregular solid particles it carries on the coating surface, gradually reducing the coating thickness and ultimately losing its protective effectiveness. Sepiolite, a green and environmentally friendly one-dimensional nanomaterial, possesses excellent adsorption capacity, thermal stability, and chemical inertness. Its fibrous structure and properties make it an ideal nanoreinforcement material. Modified and incorporated into water-based acrylic coatings, it can enhance the coating's water resistance and corrosion resistance, resulting in superior corrosion protection. Currently, most research on modified sepiolite for use in marine anti-corrosion coatings focuses on electrochemical corrosion, simulating marine corrosion. However, research on the protective mechanisms and effectiveness of protective coatings for steel structures on inland river terminals in China remains insufficient. Due to issues such as shallow overburden and deepwater construction, the substructure of frame terminals on Chinese inland rivers, especially those on the upper Yangtze River, primarily utilizes concrete-filled steel tubular rock piles. Steel structures are predominantly used in the lower pile foundations and lower longitudinal and transverse bracing. The anti-corrosion design of steel structures on inland rivers in China primarily refers to the Anti-Corrosion Code for Steel Structures in Seaport Projects, primarily relying on coating protection. Field investigations of the corrosion protection of hydraulic steel components at large terminals such as Chongqing Guoyuan Port revealed that after approximately one year of water erosion, the anti-corrosion coatings on these components degraded extensively, exposing the steel structure to corrosion and reducing its strength, directly impacting the operational performance of inland hydraulic steel components. The rapid erosion of anti-corrosion coatings by high-velocity (>1 m / s) sand-laden water in inland rivers presents a significant challenge in port engineering maintenance. According to statistics, China suffers direct economic losses of hundreds of billions of yuan annually due to metal corrosion, accounting for 1% to 4% of GDP. Aquatic corrosion accounts for over 33% of this total. Consequently, the corrosion protection of hydraulic steel components in inland ports is becoming increasingly important. Because marine and inland waterways differ in their corrosion mechanisms, coatings designed for marine environments present significant incompatibilities when used in inland waterways. Consequently, the erosion resistance of anti-corrosion coatings for steel structures in inland waterway port environments remains an unresolved issue.

[0003] Therefore, it is necessary to solve the problem of anti-erosion performance of anti-corrosion coatings for steel structures in inland river terminal environments. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a preparation method of nano-sepiolite fiber, a composite coating, a preparation method and its application, by modifying the sepiolite to improve its performance so that it can improve the erosion resistance of the anti-corrosion coating when used in steel structure anti-corrosion coatings in inland wharf environments.

[0005] The preparation method of the nano-sepiolite fiber of the present invention comprises the following steps: acidifying sepiolite by hydrothermal synthesis to form interconnected pores inside the sepiolite, and loading SiO2 particles on the surface of the sepiolite to obtain the nano-sepiolite fiber;

[0006] Furthermore, the method comprises the following steps: dispersing sepiolite in an acidic solution, then performing a hydrothermal treatment, and finally washing the hydrothermal product and freeze-drying the product to obtain nano sepiolite fibers;

[0007] Furthermore, the acidic solution is a SiCl4 solution, and the hydrothermal temperature is 150-250°C;

[0008] Furthermore, the hydrothermal product is washed with water until it becomes neutral.

[0009] The present invention also discloses a nano-sepiolite fiber reinforced water-based acrylic composite coating, wherein the nano-sepiolite fiber is added to a water-based acrylic coating base material to prepare the composite coating;

[0010] Furthermore, the dosage of the nano-sepiolite fiber is 0.1-0.9wt%;

[0011] Furthermore, the nano-sepiolite has interconnected mesopores of 15-30 nm; the linear dimension of the nano-sepiolite fiber is 7-75 nm;

[0012] Furthermore, the diameter of the SiO2 particles loaded on the surface of the nano-sepiolite fiber is 1 to 5 nm, and the SiO2 particles are uniformly attached to the surface of the sepiolite fiber or aggregated on the fiber surface to form nano-spheres of 100 to 300 nm.

[0013] The invention also discloses a preparation method of a nano-sepiolite fiber reinforced water-based acrylic composite coating, comprising the following steps: dispersing nano-sepiolite fibers in deionized water, ultrasonically treating the nano-sepiolite fibers to obtain a nano-sepiolite dispersion, and uniformly mixing the nano-sepiolite dispersion with a water-based acrylic coating base.

[0014] The nano-sepiolite fiber reinforced water-based acrylic composite coating of the present invention is used for corrosion protection of steel structures.

[0015] The beneficial effects of the present invention are as follows: the preparation method, composite coating, preparation method and application of the nano-sepiolite fiber of the present invention increase the specific surface area of ​​the sepiolite by modifying the sepiolite, and use it in a water-based acrylic anti-corrosion coating for steel structures in an inland wharf environment. The coating has good compatibility with a water-based acrylic emulsion and can improve the tensile strength and erosion resistance of the coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0017] Figure 1 Figure 2 is the morphology change of sepiolite before and after modification, where a~c are the morphologies of natural sepiolite, and d~f are the morphologies of modified sepiolite;

[0018] Figure 2 This is the EDS diagram of sepiolite;

[0019] Figure 3 This is the AFM image of sepiolite;

[0020] Figure 4 The infrared absorption spectra of sepiolite before and after hydrothermal treatment;

[0021] Figure 5 X-ray diffraction patterns of sepiolite before and after hydrothermal treatment; (a) sepiolite ore; (b) AM-SEP;

[0022] Figure 6 X-ray electron spectra of sepiolite before and after hydrothermal treatment; (a) full peak map; (b) Si and O scan map;

[0023] Figure 7 N2 adsorption-desorption isotherms and pore distribution diagram of sepiolite before and after hydrothermal treatment;

[0024] Figure 8 are the pore structure parameters of sepiolite before and after hydrothermal treatment;

[0025] Figure 9 is the tensile stress-strain curve of AM-SEP / WBAC composite coating;

[0026] Figure 10 are the tensile strength and elongation at break of the AM-SEP / WBAC composite coating;

[0027] Figure 11 The water-sand erosion mass wear change of the composite coating;

[0028] Figure 12 These are digital photos of the composite coating after erosion at different times. DETAILED DESCRIPTION

[0029] The preparation method of the nano-sepiolite fiber of this embodiment uses sepiolite to undergo an acidification treatment via a hydrothermal synthesis method to impart interconnected pores to the sepiolite, and then loads SiO2 particles on the surface of the sepiolite to produce the nano-sepiolite fiber. While the hydrothermal treatment can promote the exfoliation and nano-crystallization of the sepiolite, the loading of SiO2 particles on the surface of the sepiolite fiber improves the dispersibility of the nano-sepiolite fiber. Nano-sepiolite is prone to agglomeration due to its large specific surface area and high surface energy. The SiO2 particles form a coating or bridging network on the surface, which can slow down the agglomeration trend and improve its dispersion stability in aqueous systems. The introduction of SiO2 also creates more hydroxyl active sites, increasing the specific surface area and reaction sites, boosting the surface activity of the material and facilitating subsequent functionalization or forming a stronger physical / chemical bond with the resin. Furthermore, an inorganic shell of a certain thickness can be formed on the sepiolite surface through methods such as sol-gel, enhancing the fiber's acid and alkali resistance and thermal stability, and improving the material's stability and durability in complex environments. Moreover, SiO2 itself has good mechanical reinforcement and barrier properties. When superimposed with the fiber structure of sepiolite, it is conducive to constructing a "skeleton + particle" composite microstructure, synergistically improving the overall performance of the composite system. When nano-sepiolite fibers loaded with SiO2 particles are used in coatings, they have the following advantages: 1. They can improve the mechanical properties of the coating: SiO2 particles have high hardness and rigidity, and together with sepiolite, can significantly improve the scratch resistance, hardness, and impact resistance of the coating. 2. They can enhance the shielding effect of the coating: The composite structure can construct multiple "maze effects", improving the barrier properties of the coating against gas, water vapor, and corrosive ions, and enhancing its corrosion resistance and aging resistance. 3. They can improve compatibility with acrylic emulsions: sepiolite with SiO2 particles on its surface can more easily react with the carboxyl / hydroxyl groups in the emulsion or form hydrogen bonds, thereby improving the bonding force between the filler and the matrix and preventing interfacial debonding.

[0030] In the present embodiment, the method comprises the following steps: sepiolite is dispersed in an acidic solution, then subjected to hydrothermal treatment, and finally the hydrothermal product is washed and freeze-dried to obtain nano sepiolite fibers. Before the operation, the sepiolite needs to be further purified for better results. The specific operation steps are: sepiolite is dispersed in deionized water and sheared for a certain period of time at 3000 rad / min (or other rotating speeds), then allowed to settle, the supernatant is filtered, and the crude purified sepiolite is obtained by drying. The purified sepiolite is then utilized to prepare nano sepiolite fibers. Freeze-drying can improve the dispersibility of sepiolite. Because sepiolite nanofibers mainly exist in the form of crystal bundles, the crystal bundles often combine to form aggregates, which makes it difficult to effectively display its nanometer characteristics.

[0031] Natural sepiolite exists as fiber bundles containing flaky particles. Short fibers and flaky aggregates are attached to the surface of long fiber bundles, resulting in a smooth, flat surface. After hydrothermal treatment, sepiolite appears as individual fibers, and the fiber length remains at the micrometer scale. Acid treatment effectively removes impurities from the sepiolite, fully deagglomerating the fiber bundles and reducing their average diameter without affecting their length. Furthermore, acid treatment penetrates the internal pores of the sepiolite, thereby increasing its specific surface area.

[0032] In this embodiment, the acidic solution is SiCl4 solution, and the hydrothermal temperature is 150-250°C; strong acid will promote the depolymerization between the sepiolite fiber bundles, thereby increasing its specific surface area. Preferably, SiCl4 solution is used. After hydrolysis, SiCl4 solution generates hydrochloric acid and orthosilicic acid. Hydrochloric acid, as a strong acid, is used to replace the Mg in the internal structure of sepiolite. 2+ The Si-O-Mg-O-Si bond is converted into two Si-OH bonds, penetrating the pores within the sepiolite, thereby increasing its specific surface area. Orthosilicic acid is adsorbed on the surface of the sepiolite to form heterogeneous nuclei, and condenses into SiO2 particles at hydrothermal temperatures.

[0033] In this embodiment, the hydrothermal product is washed with water until it becomes neutral to remove unreacted acidic substances in the product.

[0034] The present embodiment also discloses a nano-sepiolite fiber-reinforced water-based acrylic composite coating, in which the nano-sepiolite fiber is added to a water-based acrylic coating base material to prepare the composite coating; the water-based acrylic coating base material refers to a coating with a water-based acrylic emulsion as the main raw material, which also includes other necessary raw materials for preparing the water-based acrylic coating, which is a prior art and will not be described in detail herein. The present invention is to add nano-sepiolite fiber as a filler to the water-based acrylic coating, which has good binding properties with the water-based acrylic emulsion and can form a stable three-dimensional structure, thereby increasing the cohesive strength of the coating, thereby achieving the purpose of improving the tensile strength and erosion resistance of the coating. Because the nano-sepiolite fiber has interconnected holes inside and the fiber surface is loaded with SiO2 particles, the mechanical properties of the coating can be improved, the shielding effect of the enhanced coating can be enhanced, and the compatibility with the acrylic emulsion can be improved. The specific mechanism of action is as described above.

[0035] In this embodiment, the dosage of the nano-sepiolite fibers is 0.1-0.9 wt %; only a relatively small amount is needed to enhance the tensile strength and erosion resistance of the coating.

[0036] In this embodiment, the nano-sepiolite has interconnected mesopores of 15-30 nm; the nano-sepiolite fibers have a linear size of 7-75 nm. The pore size distribution of raw sepiolite is primarily concentrated in mesopores of around 5 nm, which are not interconnected. In contrast, the nano-sepiolite of the present invention has interconnected and larger pores, enhancing its adsorption performance. Furthermore, while raw sepiolite has micron-scale lengths, the sepiolite of the present invention has nanoscale dimensions (7-75 nm), a result of the depolymerization of sepiolite fibers.

[0037] In this embodiment, the SiO2 particles loaded on the surface of the nano-sepiolite fibers have a diameter of 1 to 5 nm. The SiO2 particles are uniformly attached to the surface of the sepiolite fibers or aggregated on the fiber surface to form nanospheres of 100 to 300 nm, having a higher specific surface area.

[0038] This embodiment also discloses a method for preparing a nano-sepiolite fiber-reinforced water-based acrylic composite coating, comprising the following steps: dispersing nano-sepiolite fibers in deionized water and ultrasonically treating the water to obtain a nano-sepiolite dispersion; and uniformly mixing the nano-sepiolite dispersion with a water-based acrylic coating base.

[0039] Example 1

[0040] Preparation of nano-sepiolite (AM-SEP)

[0041] SEP (40 g) was dispersed in deionized water (800 mL) at 3000 rad / min, sheared for 30 min, and allowed to settle for 12 h. The supernatant was filtered and dried to obtain crude purified sepiolite, which was labeled as g-SEP.

[0042] Prepare different concentrations of SiCl4 solution (0.1mol / L, 0.3mol / L, 0.5mol / L, 0.7mol / L, 1mol / L), take g-SEP (1g) and disperse it in the SiCl4 solution. Stir magnetically for 30 minutes to ensure that the sepiolite is evenly dispersed. Then pour the suspension into a tetrafluoroethylene-lined container, seal it, and hydroheat it at 200℃ for 8 hours. After hydrothermal treatment, the product is washed with water several times until the pH is about 7. The resulting product is redispersed in water and freeze-dried to obtain nano-sepiolite, which is recorded as AM-SEP. Y (Representing SiCl4 solutions with different concentrations).

[0043] AM-SEP Y The nano-sepiolite dispersion was dispersed in deionized water and ultrasonicated for 30 minutes to obtain a nano-sepiolite dispersion. The nano-sepiolite dispersion was then added to a water-based acrylic base material and stirred to obtain a sepiolite / water-based acrylic composite coating.

[0044] Performance testing:

[0045] The sepiolite / waterborne acrylic acid composite coating was drop-coated on a substrate of a certain size, and the film thickness was controlled. The coating was cured at room temperature for 7 days to obtain a sepiolite / waterborne acrylic acid composite coating (AM-SEP / WBAC). The prepared AM-SEP / WBAC had different AM-SEP contents of 0.1wt%, 0.3wt%, 0.5wt%, 0.7wt%, and 0.9wt% (the modified AM-SEP X mass fraction of WBAC), recorded as WBAC sep-Z (Z represents different nano-sepiolite fiber dosages).

[0046] 1. Effect of hydrothermal acidification treatment on the morphology of nano-sepiolite

[0047] Morphological changes of sepiolite before and after hydrothermal treatment Figure 1 As shown. Figure 1 (a-c) It can be observed that natural sepiolite exists in the form of fiber bundles with flake particles. Short fibers and flake aggregates are attached to the surface of long fiber bundles, and the fiber surface presents a smooth plane. In contrast, Figure 1 (d-f) show that the sepiolite after hydrothermal treatment is in the form of single fibers, and the fiber length still maintains its micrometer scale. This shows that after acid treatment, the impurities in the sepiolite are effectively removed, so that the sepiolite fiber bundles are fully depolymerized and the average diameter becomes smaller, but the fiber length is not affected. In addition, the acid treatment reduces the Mg content in the internal structure of the sepiolite. 2+ The protons replace the Si-O-Mg-O-Si bond, transforming it into two Si-OH bonds, which penetrate the internal pores of the sepiolite, thereby increasing its specific surface area. Figure 1 (g) to (i), a large number of particles with a diameter of only about 1 to 5 nanometers were found on the fiber surface, evenly attached to the surface of the sepiolite fiber or agglomerated into nanospheres ranging from 100 to 300 nm. This indicates that hydrochloric acid and orthosilicic acid are generated after the hydrolysis of SiCl4 solution. Hydrochloric acid, as a strong acid, is used to replace the Mg in the internal structure of sepiolite. 2 + , while orthosilicic acid is adsorbed on the surface of sepiolite to form heterogeneous nuclei and condense into SiO2 particles at 200℃.

[0048] Changes in elemental composition of sepiolite before and after hydrothermal treatment Figure 2 As shown in (a-f). With the increase of SiCl4 dosage, the amount of orthosilicic acid after hydrolysis increases, and thus the number of SiO2 particles on the surface of sepiolite gradually increases. In addition, the distribution of Mg element in sepiolite after hydrothermal treatment decreases (darker) with the increase of SiCl4 dosage, while the distribution of Si and O elements gradually increases (brighter). More noteworthy is that AM-SEP 0.1 Although the Mg / Si atomic ratio parameter of the Mg / Si matrix has been reduced from the original 1.17 to 0.68, there are still a lot of Mg2+ , indicating that a small amount of SiCl4 cannot completely convert Mg 2+ Complete replacement. With the increase of SiCl4 dosage, the Mg / Si atomic ratio parameter decreases to 0, indicating that only in the presence of a large number of protons, through high temperature, high pressure and other methods to make the protons move quickly can the metal ions in the deep layer of sepiolite be completely replaced. At the same time, by analyzing the elemental composition of sepiolite, it was verified that the amount of SiCl4 had an effect on the Mg content of sepiolite. 2+ The impact of removal rate.

[0049] 2. Effect of hydrothermal treatment on the size of nano-sepiolite

[0050] Atomic force microscopy (AFM) was used to characterize the size of the sepiolite samples after hydrothermal treatment in order to further analyze their morphology and structural changes. Figure 3 AFM images show that after hydrothermal treatment, the overall length of the sepiolite remains in the micrometer range, indicating that its basic skeletal structure did not undergo significant fracture during the hydrothermal process. However, there are some differences in the height changes between different regions. The height change of L1 is approximately 7nm, indicating that the degree of exfoliation is relatively limited. In contrast, the height change of L2 is more significant, reaching 40nm and 75nm, respectively, indicating that a large degree of exfoliation or structural reorganization may have occurred in this localized area. The height change of L3 is approximately 8nm, remaining within a relatively small range.

[0051] These results indicate that while hydrothermal treatment promotes the exfoliation and nanocrystallization of sepiolite, the exfoliation process is incomplete in some areas, and a certain layered structure remains. However, the height of most treated sepiolite is less than 100 nm, demonstrating that hydrothermal treatment is an effective method for the preparation of nanoscale sepiolite.

[0052] 3. Infrared spectrum (FTIR) of sepiolite after hydrothermal treatment

[0053] The Fourier transform infrared spectra (FTIR) of sepiolite before and after hydrothermal treatment are shown in Figure 1. Figure 4 As shown, 3688cm -1 The absorption peak at 683 cm corresponds to the stretching vibration of Mg-OH in sepiolite. -1 The peak at 3433cm corresponds to the bending vibration of Mg-OH. -1 The broad absorption peak at 1653 cm -1 The absorption peak at 1100 cm represents the antisymmetric stretching and bending vibration of -OH. -1 ~900cm -1 The various absorption peaks in the range correspond to the stretching vibration and bending vibration of Si-O-Si tetrahedron in sepiolite. In addition, 1436cm -1The peak at 895 cm represents CO vibration. -1 It is a symmetrical deformation of -CO, which indicates that impurities such as calcite still exist in the crudely purified sepiolite.

[0054] The infrared spectrum of acidified sepiolite changes from 1075 cm -1 , 1211cm -1 , 970cm -1 and 800cm -1 The absorption peaks at 1068 cm -1 With 800cm -1 Represents the asymmetric stretching vibration and bending vibration of Si-O-Si. At 970cm -1 The weak peak near the surface corresponds to the absorption peak of Si-OH stretching vibration. The peak intensity is not very high, indicating that the sample surface contains only a small amount of -OH. A broad shoulder peak at 1211cm-1 is a typical feature after acid treatment. 2+ The position originally occupied by H in the sepiolite structure is removed. + Replacement, and H + The relative molecular weight and volume are the smallest, H + The introduction of increases the degree of freedom of the silicon-oxygen bond in the silicon-oxygen tetrahedron, causing the angle of the silicon-oxygen bond in the tetrahedron to change. The appearance of this shoulder peak and the change of the silicon-oxygen bond vibration mode verify the effect of acid treatment on the structure of sepiolite, proving that acid treatment can 2+ Removed from the crystal structure of sepiolite. But AM-SEP 0.1 At 3688cm -1 There is still a weak absorption peak, indicating that there is still a small amount of Mg inside 2+ , which proves that the concentration of SiCl4 solution has an effect on Mg 2+ The removal rate has a great impact.

[0055] 3. X-ray diffraction results of sepiolite after hydrothermal acidification treatment:

[0056] g-SEP and AM-SEP X The X-ray diffraction pattern of Figure 5As shown. According to the comparison with the PDF card (JCPDS No. 26-1226), the 2θ value of the diffraction peak of the (110) plane of sepiolite should be 7.24°. However, since the sepiolite deposits in Hebei Province, China are eluvial-hydrothermal deposits with low purity, imperfect crystallization, and large inter-plane spacing, the diffraction angle shifts to the left to 5.70°, the reflection intensity weakens, and the half-peak width increases. In addition, reflections at 2θ = 23.6°, 26.5°, 27.8°, and 34.9° are observed, corresponding to the (231), (080), (331), and (530) crystal planes, respectively. These peaks are completely consistent with those of Sepiolite (Sep, JCPDS No. 26-1226) in the PDF card, representing the typical crystal plane structure of sepiolite. In addition, the reflections at 2θ=26.6°, 29.4°, and 30.9° represent the presence of quartz, calcite, dolomite and other impurities in the sepiolite. In contrast, the reflections of quartz, calcite, dolomite and other impurities disappear first, indicating that these impurities are effectively stripped or dissolved during the acidification process. The reflection intensity of the highly crystalline sepiolite samples is greatly reduced after being acidified and stripped by SiCl4 solutions of different concentrations. This indicates that the crystallinity of the samples treated with acid is significantly reduced, especially the Mg in the sepiolite. 2+ After being replaced, the structure of sepiolite has changed significantly. And the Mg in sepiolite 2+ After being removed, a single layer of SiO2 is formed. These SiO2 layers are amorphous and lack an ordered structure. As the water evaporates, these single layers of SiO2 will delaminate, and the gaps between the layers will gradually decrease, resulting in a significant hump in the XRD pattern of the sample between 19° and 30°, showing the characteristics of amorphous SiO2. [ In addition, AM-SEP 0.1 There are still strong reflection peaks at (110), (231), (080), (331), and (530). These peaks represent the typical crystal characteristics of sepiolite, indicating that the structure of sepiolite treated at this concentration has not been completely destroyed and there are still a lot of Mg in it. 2+ This indicates that in a lower concentration of SiCl4 solution, Mg 2+ The removal effect of MgCl4 solution is limited, and the structure and crystallinity of sepiolite are still maintained to a certain extent. In contrast, as the concentration of SiCl4 solution increases, only the reflection peak representing amorphous SiO2 (JCPDS No.29-0085) appears in the XRD spectrum of each sample, and there is almost no visible characteristic reflection peak of sepiolite. This phenomenon shows that as the concentration of SiCl4 solution increases, the Mg in sepiolite 2+ The crystalline structure of sepiolite is completely destroyed and converted into amorphous SiO2. This further illustrates the effect of SiCl4 solution concentration on the Mg content in sepiolite. 2+The removal rate of Mg 2+ The removal rate increases with the increase of SiCl4 solution concentration, which is consistent with the previous EDS element distribution test results.

[0057] 4. X-ray electron spectrum of sepiolite:

[0058] Although the sample morphology, functional groups and crystallinity were analyzed in detail in the early stage, it is still necessary to analyze the sample elements to verify the Mg content in sepiolite. 2+ Completely removed. Figure 6 (a) It can be observed that the samples after acidification generally contain a large amount of Si and O elements, but AM-SEP 0.1 With AM-SEP 0.3 The Auger spectrum of Mg element appears in the binding energy range of 400~280, indicating that there is still a small amount of Mg in the sample. 2+ Not completely removed. In contrast, AM-SEP 0.5 , AM-SEP 0.7 , AM-SEP 1.0 No Mg element was found in sepiolite, indicating that Mg in these samples 2+ has been effectively removed.

[0059] Further fine scanning results of O and Si elements are shown in Figure 6(b). Each sample has typical O-Si peaks at 531.08eV and 101.78eV, representing the main components of sepiolite. 0.1 In addition to the typical O-Si peak, there is also an O-Mg peak at 529.68 eV representing sepiolite, which further indicates that the sample still contains some Mg ions that have been completely removed. 0.3 Mg element appears in the full peak, but it does not appear in the O element fine scan. The analysis suggests that residual Mg 2+ The content is too low to show obvious signal. XPS analysis further verified that Mg 2+ The removal of Mg in sepiolite in different acidification treatment samples 2+ The removal efficiency provides an important experimental basis.

[0060] 5. Nano-sepiolite specific surface area (BET)

[0061] Strong acid will promote the deagglomeration between sepiolite fiber bundles and thus increase their specific surface area, such as Figure 7 The N2 adsorption-desorption isotherms and pore distribution diagrams of sepiolite before and after hydrothermal treatment are shown. o) is low at low relative pressures, while the adsorption capacity increases dramatically at higher relative pressures and exhibits a distinct hysteresis loop, consistent with a Type IV adsorption isotherm, indicating the presence of a large number of mesopores within the sepiolite. Furthermore, the hysteresis loop of the raw sepiolite exhibits an H3 type, while that of the hydrothermally treated sepiolite exhibits an H4 type hysteresis loop, indicating that the SiO2 generated by the hydrolysis of the introduced SiCl4 forms a new pore structure on the sepiolite surface. It is also noteworthy that increasing the amount of SiCl4 increases the amount of hydrolyzed SiO2, thereby increasing the adsorption capacity of the sepiolite. Furthermore, the pore size distribution of the raw sepiolite is primarily concentrated in mesopores of approximately 5 nm, but after hydrothermal modification, this increases to mesopores of approximately 20 nm, indicating that the hydrochloric acid released by the hydrolysis of SiCl4 enters the sepiolite interior and effectively penetrates the internal pores of the sepiolite.

[0062] from Figure 8 It can be observed that with the increase of SiCl4 dosage, the specific surface area of ​​sepiolite shows an upward trend, from the original 19.08m 2 ·g -1 Increased to 238.19m 2 ·g -1 But it still hasn't reached the theoretical 900m 2 ·g -1 Combined with SEM analysis, it was discovered that some of the nano-SiO2 produced by the hydrolysis of SiCl4 condensed on the sepiolite surface, blocking some channels and causing the formation of internally enclosed pores. Notably, the pore volume and pore diameter of the sepiolite also increased with increasing SiCl4 dosage, increasing by approximately 70 times and 7 times, respectively, compared to the initial values.

[0063] 6. Tensile strength of AM-SEP / WBAC composite coating prepared by adding treated sepiolite to waterborne acrylic paint:

[0064] Figure 9 The effects of different sepiolite content on the tensile properties of the coating are shown. Figure 10 WBAC SEP-Z The tensile strength and elongation at break values ​​of the coating. It can be observed that when the sepiolite content is 1-3‰, the tensile strength of the coating is only slightly improved. As the sepiolite content continues to increase to 5‰, the coating reaches the maximum tensile strength (1.21MPa). When further sepiolite is added, the tensile strength of the coating shows a downward trend. This shows that when a small amount of sepiolite is added, the sepiolite cannot form physical crosslinks in the coating, resulting in only a small increase in the tensile strength of the coating. However, too much sepiolite will cause it to partially agglomerate inside the coating, weakening the coating performance. Compared with WBAC SEP-0 The tensile strength of the coating increased by 2.8%, 14%, 32%, 8.6% and 5.2% respectively with the increase of sepiolite content.

[0065] It is worth noting that with the increase of sepiolite dosage, the elongation at break of the coating shows a trend of first increasing and then decreasing. This indicates that the addition of sepiolite increases the stiffness of the coating and thus affects its elongation at break. SEP-0 The tensile strength of the coating and the elongation at break of the coating increased by 9.0%, 16.0%, 26.8%, 18.4% and 1.2% with the increase of sepiolite content, indicating that the introduction of an appropriate amount of sepiolite can effectively increase the cohesive strength of the coating.

[0066] 7. Erosion resistance of AM-SEP / WBAC composite coating

[0067] After a certain period of water and sand erosion, the coating quality loss is as follows: Figure 10 WBAC SEP-0 The sample maintained its high mass loss (up to 0.11g) during the entire erosion process, while the erosion mass loss of the composite coating after adding nano-sepiolite was reduced. This shows that nano-sepiolite effectively increases the cohesion of the coating, thereby improving the coating's resistance to water and sand erosion. Secondly, the softer acrylic resin on the surface of the coating is consumed, resulting in a higher mass loss of all coatings in the first 3 minutes of erosion. Under further erosion, inorganic skeletons such as sepiolite are exposed on the surface, effectively reducing the mass loss of the coating. It is worth noting that different sepiolite dosages also have a certain effect on the erosion resistance of the coating, among which WBAC SEP-0.1 and WBAC SEP-0.3 The mass loss of the coating showed a downward trend in the first 6 minutes of erosion, but after 9 minutes of erosion, its mass loss increased to 0.08g and 0.06g respectively. This shows that a small amount of sepiolite in the coating has a small coverage, which can improve the erosion resistance of the coating in a short period of time. However, as time goes by, a large amount of sepiolite is consumed, causing the coating to return to its initial cohesive strength and the erosion resistance to decrease. In contrast, more sepiolite interacts with the film-forming material to form a stable three-dimensional network inside the coating, making WBAC SEP-0.5 、WBAC SEP-0.7 and WBAC SEP-0.9 The mass loss of the composite coating is basically constant at 0.04g after 9 minutes of erosion.

[0068] In addition, digital photos of the composite coating after erosion at different times ( Figure 12 ) It can be observed that the coating without sepiolite showed damage after 9 minutes of erosion, indicating that its erosion resistance is low. In contrast, the coating with sepiolite did not change much in appearance, indicating that sepiolite effectively enhanced the coating's erosion resistance.

[0069] In summary, nano-SiO2-loaded nano-sepiolite fibers were prepared in one step by a hydrothermal method and introduced into a water-based acrylic coating to prepare a composite coating, which has the following advantages:

[0070] (1) First, different concentrations of SiCl4 solution were mixed with sepiolite, and then the nano-SiO2 loaded nano-sepiolite fibers were obtained by hydrothermal treatment at 200℃ for 8h (of course, when the hydrothermal temperature was 150-250℃ or other hydrothermal temperatures were used, the treatment time was different, and the obtained nano-sepiolite fibers could achieve the purpose of the present invention). Through morphological characterization, it was found that the 1-2nm nano-SiO2 hydrolyzed from SiCl4 was heterogeneously nucleated under hydrothermal conditions and evenly distributed on the surface of sepiolite. Secondly, through AFM testing, it was found that the hydrothermal method could make the diameter of sepiolite reach the nanoscale (7-75nm) without destroying the micron-scale length of sepiolite, indicating that SiCl4 helps the depolymerization of sepiolite fibers. In addition, the effect of SiCl4 solution concentration on the internal Mg content of sepiolite was verified by microscopic means such as FTIR and XPS. 2+ The removal rate of Mg 2+ The higher the removal rate, the lower the Mg content in sepiolite when the concentration of SiCl4 solution reaches 1.0 mol / L. 2+ In addition, the specific surface area of ​​sepiolite after SiCl4 solution treatment is greatly improved, AM-SEP 1.0 The maximum specific surface area can reach 238.19m 2 ·g -1 , with a pore volume of up to 0.778 cm 3 ·g -1 , pore diameter 21.11nm.

[0071] (2) Waterborne composite coatings were prepared by adding different amounts of sepiolite to waterborne acrylic base materials. The tensile test showed that when the sepiolite content was 0.5%, the coating had the maximum tensile strength (1.21MPa) and maximum elongation at break (111.8), which was significantly higher than that of WBAC. SEP-0 , increased by about 32% and 26.8% respectively. The analysis shows that the higher specific surface area of ​​sepiolite enables it to combine well with water-based acrylic emulsion, forming a stable three-dimensional structure and thus improving the cohesive strength of the coating. And through erosion testing, it was found that when the sepiolite content exceeded 0.5%, the mass loss of the coating after 9 minutes of erosion was basically constant at 0.04g, which is lower than that of WBAC. SEP-0 , which was reduced by about 63.6%. Therefore, the tensile and erosion tests verified that sepiolite can effectively improve the cohesive strength of the coating, thereby improving the erosion resistance, providing a new green protective material for the dock steel structure protection system.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for preparing nano-sepiolite fiber, characterized by: The nanometer sepiolite fiber is prepared by acidification treatment of sepiolite by hydrothermal synthesis method so that the sepiolite has interconnected pores inside and SiO2 particles are loaded on the surface of the sepiolite.

2. The method for preparing nano-sepiolite fibers according to claim 1, wherein: The following steps are involved: The sepiolite is dispersed in an acidic solution and then subjected to a hydrothermal treatment. Finally, the hydrothermal product is washed with water and then freeze-dried to obtain nano sepiolite fibers.

3. The method for preparing nano-sepiolite fibers according to claim 2, wherein: The acidic solution is SiCl4 solution, and the hydrothermal temperature is 150-250°C.

4. The method for preparing nano-sepiolite fibers according to claim 2, wherein: The hydrothermal product was washed with water until neutral.

5. A composite coating of water-based acrylic acid reinforced with the nano-sepiolite fiber according to claim 1, characterized in that: Nano-sepiolite fibers were added to water-based acrylic paint base to prepare composite paint.

6. The nano-sepiolite fiber reinforced water-based acrylic composite coating according to claim 5, characterized in that: The dosage of the nano-sepiolite fiber is 0.1-0.9 wt%.

7. The method for preparing nano-sepiolite fibers according to claim 5, wherein: The nano-sepiolite has mutually interpenetrating mesopores of 15-30 nm, and the linear dimension of the nano-sepiolite fiber is 7-75 nm.

8. The nano-sepiolite-enhanced water-based acrylic composite coating according to claim 5, characterized in that: The diameter of the SiO2 particles loaded on the surface of the nano-sepiolite fiber is 1-5 nm. The SiO2 particles are uniformly attached to the surface of the sepiolite fiber or aggregated on the fiber surface to form nano-spheres of 100-300 nm.

9. The method for preparing the nano-sepiolite fiber-reinforced water-based acrylic composite coating according to claim 5, wherein: The following steps are involved: The nano-sepiolite fibers are dispersed in deionized water and ultrasonically treated to obtain a nano-sepiolite dispersion liquid, and the nano-sepiolite dispersion liquid is uniformly mixed with a water-based acrylic paint base material.

10. The use of the nano-sepiolite fiber reinforced water-based acrylic composite coating according to claim 5, characterized in that: Nano-sepiolite fiber reinforced water-based acrylic composite coating is used for corrosion protection of steel structures.

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