Building expansion joint sealing composite material and preparation method and application thereof

Abstract

The invention relates to the technical field of building expansion joint sealing composite materials, in particular to a building expansion joint sealing composite material and a preparation method and application thereof. The preparation method comprises the following steps: mixing an epoxy resin precursor containing disulfide bonds and polyurethane containing disulfide bonds to obtain a polyurethane-epoxy resin matrix with an interpenetrating network structure; a Na source, an Nb source, a Ba source, a Ti source, a Sn source, a Sr source and a Zr source are mixed to prepare the sodium niobate leadless piezoelectric ceramic with piezoelectric performance. The preparation method comprises the following steps: modifying sodium niobate lead-free piezoelectric ceramic by adopting dopamine hydrochloride to obtain polydopamine modified sodium niobate lead-free piezoelectric ceramic; and mixing the polydopamine modified sodium niobate lead-free piezoelectric ceramic, the polyurethane-epoxy resin matrix and the aminated carbon nanotube, and curing to obtain the building expansion joint sealing composite material. The building expansion joint sealing composite material has excellent mechanical properties and bonding strength, has good damping performance in a wide temperature range, and solves the problems in the prior art.

Description

Technical Field

[0001] This invention relates to the field of building expansion joint sealing composite materials, specifically to a building expansion joint sealing composite material, its preparation method, and its application. Background Technology

[0002] Expansion joints are specially designed gaps in building and bridge structures to provide space for expansion and contraction during temperature fluctuations or foundation settlement, thereby preventing structural damage and extending their service life. Expansion joints are crucial for ensuring the functional integrity and structural safety of building structures during long-term use. However, despite their vital role, expansion joints are also vulnerable to damage, often starting with the sealant. The main forms of sealant failure are breakage and peeling from the inner wall of the expansion joint. This results in the sealant losing its waterproofing function, allowing rainwater and snowmelt to penetrate the building, damaging the structure and ultimately reducing its load-bearing capacity. Therefore, researching and developing building expansion joint sealants with high damping performance to address the problem of sealant failure under long-term heavy loads and noise vibrations has become a hot research topic in the field of building expansion joints.

[0003] Although sealing materials prepared by traditional methods have good sealing performance and economy, their damping performance is poor, and they still suffer serious damage under long-term heavy load and noise and vibration conditions. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a building expansion joint sealing composite material, its preparation method, and its application. The invention first obtains a polyurethane-epoxy resin matrix with an interpenetrating network structure by covalently bonding a polyurethane containing disulfide bonds and an epoxy resin precursor containing disulfide bonds; then, it prepares a material with the chemical formula (0.9-x)NaNbO3-0.1Ba(Ti 0.7 Sn 0.3Sodium niobate lead-free piezoelectric ceramics with piezoelectric properties (O3-xSrZrO3) were obtained, and their surfaces were modified by encapsulating polydopamine to obtain polydopamine-modified sodium niobate lead-free piezoelectric ceramics. Finally, polydopamine-modified sodium niobate lead-free piezoelectric ceramics, polyurethane-epoxy resin matrix and aminated carbon nanotubes were mixed and cured to obtain building expansion joint sealing composite material. This invention, by incorporating polydopamine-modified sodium niobate lead-free piezoelectric ceramics, endows the building expansion joint sealing composite material with excellent piezoelectric properties, enabling it to generate charge under external stress and thus directly utilize building vibration energy. Aminated carbon nanotubes, acting as a medium for electro-thermal conversion, form a conductive network within the building expansion joint sealing composite material, converting the charge generated by the polydopamine-modified sodium niobate lead-free piezoelectric ceramics under stress into heat energy. Together with the internal friction between the polydopamine-modified sodium niobate lead-free piezoelectric ceramics and the matrix, and the internal friction among the polydopamine-modified sodium niobate lead-free piezoelectric ceramics themselves, the combined effect of these three factors effectively converts mechanical energy into heat energy for dissipation. This endows the expansion joint sealing material with excellent damping properties, allowing it to have a wide operating temperature range while also possessing good vibration and noise reduction performance, effectively reducing damage to expansion joints under long-term heavy loads and noise vibration conditions.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first objective of this invention is to provide a method for preparing a building expansion joint sealing composite material, comprising the following steps: S1. An epoxy resin precursor containing disulfide bonds and a polyurethane containing disulfide bonds are mixed so that the molecular chains of the epoxy resin precursor and the polyurethane interpenetrate at the nanoscale, resulting in a polyurethane-epoxy resin matrix with an interpenetrating network structure.

[0006] S2. Combine the Na, Nb, Ba, Ti, Sn, Sr, and Zr sources according to the chemical formula (0.9-x)NaNbO3-0.1Ba(Ti) 0.7 Sn 0.3 O3-xSrZrO3 is mixed and pre-calcined to obtain pre-calcined powder; wherein x is selected from 0, 0.15, 0.20 or 0.25; the pre-calcined powder is ball-milled and then polarized to make the internal electric domains of the pre-calcined powder oriented to obtain sodium niobate lead-free piezoelectric ceramic with piezoelectric properties.

[0007] S3. Disperse sodium niobate lead-free piezoelectric ceramics in an aqueous solution of tris(hydroxymethyl)aminomethane buffer to obtain a sodium niobate lead-free piezoelectric ceramic dispersion. Then, disperse dopamine hydrochloride in the sodium niobate lead-free piezoelectric ceramic dispersion for modification. During the modification process, dopamine hydrochloride is oxidized under weakly alkaline conditions and self-polymerizes to form polydopamine. The catechol groups of polydopamine react with the hydroxyl groups on the surface of the sodium niobate lead-free piezoelectric ceramic to form hydrogen, which causes polydopamine to deposit and bind to the surface of the sodium niobate lead-free piezoelectric ceramic to form a coating layer, thus obtaining polydopamine-modified sodium niobate lead-free piezoelectric ceramics.

[0008] In the modification process, sodium niobate lead-free piezoelectric ceramic is added and stirred first, followed by the addition and stirring of dopamine hydrochloride. This is primarily because sodium niobate lead-free piezoelectric ceramic powder is prone to agglomeration. If directly mixed with dopamine hydrochloride, the dopamine hydrochloride will preferentially coat the surface of the agglomerates, forming an "outer shell" that hinders the dispersion of internal particles. However, stirring the sodium niobate lead-free piezoelectric ceramic separately allows for the full decomposition of agglomerates through mechanical shear force, exposing more active sites. Simultaneously, during stirring, water molecules can adsorb onto the surface of the sodium niobate lead-free piezoelectric ceramic to form hydroxyl groups, providing anchoring sites for the subsequent oxidative self-polymerization of dopamine hydrochloride. Furthermore, since dopamine hydrochloride undergoes oxidative self-polymerization in alkaline buffer to form polydopamine, if mixed simultaneously with sodium niobate lead-free piezoelectric ceramic, the dopamine hydrochloride will preferentially self-polymerize in solution to form free polydopamine particles rather than coating the ceramic.

[0009] Compared to other alkaline buffers, tris(hydroxymethyl)aminomethane buffer has a wide pH adaptability, low metal interference, and dynamic stability mechanism, making it the preferred choice for polydopamine-modified piezoelectric ceramics. The optimal pH for dopamine oxidative polymerization is 8.5 ± 0.2. Compared to other alkaline buffers, tris(hydroxymethyl)aminomethane buffer has a buffering efficiency of over 90% in the pH range of 7.5 to 9.0. In addition, tris(hydroxymethyl)aminomethane buffer does not contain strong coordinating groups, effectively avoiding the formation of precipitates by reacting with metal ions on the surface of sodium niobate lead-free piezoelectric ceramics.

[0010] S4. After mixing polydopamine-modified sodium niobate lead-free piezoelectric ceramic, polyurethane-epoxy resin matrix and aminated carbon nanotubes, the mixture is placed in a mold for curing. During the curing process, the amino groups on the surface of the polydopamine-modified sodium niobate lead-free piezoelectric ceramic and the amino groups in the aminated carbon nanotubes form hydrogen bonds with the -C=O groups in the polyurethane-epoxy resin matrix, and at the same time, they undergo ring-opening reactions with the epoxy groups to form hydroxyl covalent bonds, thus obtaining a building expansion joint sealing composite material.

[0011] Preferably, the mass ratio of polyurethane to epoxy resin precursor is 57~63:37~43.

[0012] Preferably, the mass ratio of sodium niobate lead-free piezoelectric ceramic to dopamine hydrochloride is 2~3:1.

[0013] Preferably, the mass ratio of polydopamine-modified sodium niobate lead-free piezoelectric ceramic, polyurethane-epoxy resin matrix and aminated carbon nanotubes is 20~80:100:0.5.

[0014] Preferably, the pre-calcination treatment conditions are: calcination at 900℃~950℃ for 4h~6h in an air atmosphere.

[0015] Preferably, the polarization treatment conditions are: polarization at room temperature and under a DC electric field of 1kV / mm to 3kV / mm for 10 min to 30 min.

[0016] The preferred modification conditions are: stirring at room temperature for 6 to 12 hours.

[0017] Preferably, the curing process is as follows: first, degas at 60°C for 4 to 6 hours until all air bubbles are eliminated, and then let stand at 80°C to 100°C for 48 to 72 hours.

[0018] Preferably, the particle size of the pre-sintered powder after ball milling is 0.062 mm to 0.125 mm. When the particle size of the pre-sintered powder is too small, its high surface activity easily causes powder agglomeration, which is not conducive to the full polarization of the pre-sintered powder, resulting in insufficient overall piezoelectric properties of the composite material. When the particle size of the pre-sintered powder is too large, it leads to poor compatibility between the polydopamine-modified sodium niobate lead-free piezoelectric ceramic and the polyurethane-epoxy resin matrix. The excessively large polydopamine-modified sodium niobate lead-free piezoelectric ceramic will become a stress concentration point, which is prone to causing microcracks or debonding at the interface of the polydopamine-modified sodium niobate lead-free piezoelectric ceramic / polyurethane-epoxy resin matrix under dynamic load, reducing the mechanical properties and reliability of the building expansion joint sealing composite material. Controlling the particle size of the pre-sintered powder after ball milling to 0.062 mm to 0.125 mm can achieve better piezoelectricity while ensuring the mechanical properties of the building expansion joint sealing composite material.

[0019] Preferably, the Na source is selected from Na2CO3 with a purity ≥99.8%; the Nb source is selected from Nb2O5 with a purity ≥99.5%; the Ba source is selected from BaCO3 with a purity ≥99%; the Ti source is selected from TiO2 with a purity ≥98%; the Sn source is selected from SnO2 with a purity ≥99.5%; the Sr source is selected from SrCO3 with a purity ≥99%; and the Zr source is selected from ZrO2 with a purity ≥99%.

[0020] Preferably, in the aqueous solution of tris(hydroxymethyl)aminomethane buffer, the volume ratio of tris(hydroxymethyl)aminomethane buffer to water is 1:3-4. Since the polymerization of polydopamine requires hydroxyl groups, if the water content is too high, the pH value in the later stages of the reaction is easily out of control and drops below 7.5, leading to polymerization termination. If the water content is too low, the high concentration of Cl in the solution... -It will corrode the grain boundaries of piezoelectric ceramics; among them, the pH value of the tris(hydroxymethyl)aminomethane buffer is 8.5, and the concentration of the tris(hydroxymethyl)aminomethane buffer is 0.1 mol / L.

[0021] Preferably, the epoxy resin precursor containing disulfide bonds is prepared according to the following steps: Epoxy resin and 2,2'-diaminodiphenyl disulfide were mixed and subjected to a ring-opening addition reaction. During the ring-opening addition reaction, the primary amine group (-NH2) in 2,2'-diaminodiphenyl disulfide first acts as a nucleophile, attacking the epoxy group of the epoxy resin, causing the three-membered ring of the epoxy resin to open. After ring opening, the nitrogen atom of the amine group forms a new CN bond with the carbon atom of the epoxy group (at this time, the primary amine is converted into a secondary amine). At the same time, the oxygen atom of the epoxy group accepts a proton to generate a hydroxyl group. The generated secondary amine then continues to attack another epoxy group (the secondary amine is converted into a tertiary amine and generates another hydroxyl group). Through this ring-opening addition reaction, the epoxy group is consumed, CN bonds and hydroxyl groups are generated, and finally a three-dimensional cross-linked network is formed between molecules to obtain an epoxy resin precursor containing disulfide bonds. The molar ratio of the epoxy group in the epoxy resin to the amino group in 2,2'-diaminodiphenyl disulfide is 1.8~2.0:1.

[0022] Preferably, the conditions for the ring-opening addition reaction are: stirring at 120℃~130℃ for 4h~6h in a nitrogen atmosphere.

[0023] Preferably, the polyurethane containing disulfide bonds is prepared according to the following steps: A polyurethane prepolymer and 2,2'-diaminodiphenyl disulfide are mixed and subjected to a chain extension reaction. The isocyanate groups in the polyurethane prepolymer undergo an addition reaction with the amino groups in the 2,2'-diaminodiphenyl disulfide to form urea bonds, thereby extending the polyurethane chain and obtaining a polyurethane containing disulfide bonds. The molar ratio of the isocyanate groups in the polyurethane prepolymer to the amino groups in the 2,2'-diaminodiphenyl disulfide is 3:1.9~2.

[0024] Preferably, the chain extension reaction is carried out under a nitrogen atmosphere at 100℃~120℃ for 4h~6h with stirring.

[0025] Preferably, the epoxy resin is a bisphenol A type epoxy resin, more preferably an E51 bisphenol A type epoxy resin. Compared with other types of epoxy resins, bisphenol A type epoxy resin has the following significant characteristics: First, it has high strength and high rigidity, which can withstand large external loads and helps to improve the mechanical properties of building expansion joint sealing composite materials; Second, it has good chemical corrosion resistance and can remain stable in acid, alkali and some organic solvent environments, which better meets the application requirements of building expansion joint sealing composite materials; Third, it has low viscosity, which is easy to process and mold, and can achieve good composite with reinforcing materials such as glass fiber, exhibiting excellent adhesion, high temperature resistance and excellent mechanical properties in practical applications.

[0026] A second objective of this invention is to provide a building expansion joint sealing composite material prepared by the above-described method.

[0027] A third objective of this invention is to provide the application of the above-mentioned building expansion joint sealing composite material in the preparation of sealing materials.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention provides a method for preparing a building expansion joint sealing composite material, comprising mixing an epoxy resin precursor containing disulfide bonds and a polyurethane containing disulfide bonds to obtain a polyurethane-epoxy resin matrix with an interpenetrating network structure; and mixing Na, Nb, Ba, Ti, Sn, Sr, and Zr sources according to the chemical formula (0.9-x)NaNbO3-0.1Ba(Ti 0.7 Sn 0.3O3-xSrZrO3 was mixed and pre-calcined to obtain pre-calcined powder; where x is selected from 0 to 0.25. The pre-calcined powder was ball-milled and then polarized to obtain sodium niobate lead-free piezoelectric ceramics with piezoelectric properties. The sodium niobate lead-free piezoelectric ceramics were dispersed in an aqueous solution of tris(hydroxymethyl)aminomethane buffer to obtain a sodium niobate lead-free piezoelectric ceramic dispersion. Subsequently, dopamine hydrochloride was dispersed in the sodium niobate lead-free piezoelectric ceramic dispersion, and modified with dopamine hydrochloride as a modifier, so that polydopamine was deposited and combined with sodium niobate. A coating layer is formed on the surface of a lead-free piezoelectric ceramic to obtain a polydopamine-modified sodium niobate lead-free piezoelectric ceramic. The polydopamine-modified sodium niobate lead-free piezoelectric ceramic, a polyurethane-epoxy resin matrix, and aminated carbon nanotubes are mixed and cured. During curing, the amino groups on the surface of the polydopamine-modified sodium niobate lead-free piezoelectric ceramic and the amino groups in the aminated carbon nanotubes form hydrogen bonds with the -C=O groups in the polyurethane-epoxy resin matrix, and simultaneously undergo ring-opening reactions with epoxy groups to form hydroxyl covalent bonds, resulting in a building expansion joint sealing composite material. This invention introduces polydopamine-modified sodium niobate lead-free piezoelectric ceramic into a polyurethane-epoxy matrix, simultaneously constructing a piezoelectric-conductive synergistic network, endowing the building expansion joint sealing composite material with excellent damping function. When external vibration and mechanical energy are applied, a triple energy dissipation mechanism occurs within the building expansion joint sealing composite material: first, internal friction between polydopamine-modified sodium niobate lead-free piezoelectric ceramic particles; second, internal friction between the polydopamine-modified sodium niobate lead-free piezoelectric ceramic particles and the polyurethane-epoxy resin matrix; and third, the piezoelectric effect of the polydopamine-modified sodium niobate lead-free piezoelectric ceramic particles and the resulting charge migration in the conductive path, thereby dissipating mechanical energy as Joule heat. The synergistic effect of these mechanisms enables the building expansion joint sealing composite material to achieve efficient vibration and noise reduction over a wide temperature range, significantly reducing damage to the expansion joint structure under long-term heavy loads and noise vibration conditions, overcoming the shortcomings of existing technologies.

[0029] 2. This invention uses polyurethane prepolymer and 2,2'-diaminodiphenyl disulfide as raw materials to prepare polyurethane. Using 2,2'-diaminodiphenyl disulfide as a chain extender, reversible dynamic covalent disulfide bonds are successfully introduced, endowing the polyurethane with self-healing properties. The polyurethane prepolymer exhibits outstanding hydrolysis resistance and good elasticity, enabling it to better adapt to the operating environment of expansion joints. It can also undergo significant deformation under external forces and quickly return to its original shape after the external force is removed.

[0030] 3. This invention, through structural design, obtains a polyurethane-epoxy resin matrix with an interpenetrating network structure. In this interpenetrating network structure, different polymers have their own unique glass transition temperatures (T0). gThis difference causes a shift and widening of the glass transition region of the material. Based on this characteristic, the polyurethane-epoxy resin matrix of the present invention can operate efficiently over a wider temperature range, converting the mechanical energy generated by vibration into heat energy, thereby significantly reducing the negative impacts of various harmful vibrations and noises. This advantage gives the building expansion joint sealing composite material of the present invention a wider range of applications, enabling it to perform excellently in a variety of complex environments.

[0031] 4. This invention directly prepares a sodium niobate-based solid solution system (0.9-x)NaNbO3-0.1Ba(Ti) using carbonates (Na2CO3 (≥99.8%), BaCO3 (≥99%), SrCO3 (≥99%)) and oxides (Nb2O5 (≥99.5%), TiO2 (≥98%), SnO2 (≥99.5%), and ZrO2 (≥99%). 0.7 Sn 0.3 The sodium niobate lead-free piezoelectric ceramic prepared by O3-xSrZrO3 exists at a quasi-isomorphic phase boundary at room temperature, exhibiting a coexistence of orthorhombic, tetragonal, and pseudocubic phases. On one hand, in perovskite ceramics, the pseudocubic phase possesses a triple-tilted structure, which optimizes the lattice symmetry of the phase structure. This increased lattice symmetry favors the formation of relaxor ferroelectric nanodomains. Therefore, the appearance of the pseudocubic phase transforms the sodium niobate lead-free piezoelectric ceramic from a high-content ferroelectric macrodomain to a coexistence of ferroelectric macrodomains and relaxor ferroelectric nanodomains. This multiphase coexistence and the presence of relaxor ferroelectric nanodomains are beneficial to the dielectric constant ε. r The increase in ferroelectric macrodomains is beneficial to the remanent polarization P. r The value is increased because the piezoelectric properties of sodium niobate lead-free piezoelectric ceramics are related to ε. r ×P r The values ​​are positively correlated, thus sodium niobate lead-free piezoelectric ceramics exhibit excellent piezoelectric properties. On the other hand, multiphase coexistence and the introduction of relaxor ferroelectric nanodomains into ferroelectric macrodomains can obtain more switchable non-180° domain walls, which can effectively reduce the Gibbs free energy barrier and improve the piezoelectric properties of sodium niobate lead-free piezoelectric ceramics at room temperature.

[0032] 5. The building expansion joint sealing composite material of the present invention has good damping performance, with a maximum damping loss factor of 0.78~1.05; it also has good mechanical and adhesive properties, with a bonding strength with cement mortar of 5.73MPa~7.36MPa at room temperature. It is highly practical, simple to prepare, and easy to mass-produce in a routine manner. This is because the polyurethane-epoxy resin matrix with an interpenetrating network structure serves as the matrix, ensuring good damping performance of the building expansion joint sealing composite material over a wide temperature range while also possessing good mechanical properties and deformability; the polydopamine-modified sodium niobate lead-free piezoelectric ceramic optimizes the compatibility between the ceramic filler and the polyurethane-epoxy resin matrix, while promoting ring-opening of the epoxy resin and increasing the crosslinking density of the matrix resin, resulting in better mechanical and adhesive properties of the building expansion joint sealing composite material.

[0033] 6. The polyurethane prepolymer of the present invention is prepared by reacting 4,4-diphenylmethane diisocyanate with a polyether polyol with a molecular weight of 2000 g / mol. The 4,4-diphenylmethane diisocyanate and the polyether polyol are inexpensive, have a simple process, good chemical stability of ether bonds, and are resistant to hydrolysis. The overall cost advantage is obvious, making it suitable for large-scale application in the field of building expansion and sealing. The molecular weight of polyether polyols determines the ratio of soft to hard segments, which in turn controls mechanical and damping properties: if the molecular weight is too low (e.g., 1000 g / mol), the proportion of hard segments increases, resulting in increased rigidity but insufficient elasticity; if the molecular weight is too high (e.g., above 3000 g / mol), the soft segments become excessively enriched, leading to a decrease in strength; a polyether polyol with a molecular weight of 2000 g / mol can achieve a balance between high damping and mechanical properties while ensuring the stability of the crosslinked network through sufficient chain segment mobility; the molar ratio of hydroxyl to isocyanate groups is 1:3, which takes into account the requirements of subsequent chain extension, self-repair, and damping. When the ratio is lower than 1:2, there are insufficient isocyanate groups, hindering chain extension; when it is higher than 1:4, free isocyanate is prone to side reactions with epoxy groups, initiating phase separation and narrowing the effective damping temperature range. Attached Figure Description

[0034] Figure 1 The images show the XRD patterns of the building expansion joint sealing composite materials of Examples 1 to 4 of the present invention.

[0035] Figure 2 The infrared spectra of the building expansion joint sealing composite materials of Examples 1 to 4 of the present invention are shown.

[0036] Figure 3 The graph shows the loss factor of the building expansion joint sealing composite material of Examples 1 to 4 of the present invention as a function of temperature.

[0037] Figure 4 The stress-strain curves are for the building expansion joint sealing composite materials of Examples 1 to 4 of the present invention.

[0038] Figure 5 The diagram shows the bonding strength of the building expansion joint sealing composite material in Examples 1 to 4 of the present invention.

[0039] Figure 6 The dielectric temperature spectra of the sodium niobate lead-free piezoelectric ceramic prepared in Example 3 before and after polarization are shown. Among them, (a) is before polarization and (b) is after polarization. Detailed Implementation

[0040] The technical solution of the present invention will be clearly and completely described below with reference to the data in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0041] It should be noted that the technical terms used in this invention are only for describing specific embodiments and are not intended to limit the scope of protection of this invention. Unless otherwise specified, 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. Among them, high-purity aminated carbon nanotubes were purchased from Shenzhen Suiheng Graphene Technology, with a purity >99%; the epoxy resin is bisphenol A type epoxy resin, model E51; the polyurethane prepolymer was purchased from Jiatong Plastic Raw Materials Business Department, and is obtained by reacting 4,4-diphenylmethane diisocyanate with polyether polyol, wherein the molar ratio of the hydroxyl groups of the polyether polyol to the isocyanate groups of 4,4-diphenylmethane diisocyanate is 1:3, the molecular weight of the polyether polyol is 2000, and in the polyurethane prepolymers of Examples 1 to 4 of this invention, only isocyanate is present without hydroxyl groups.

[0042] In the existing technology, although the sealing materials prepared by traditional methods have good sealing performance and economy, their insufficient damping performance becomes increasingly prominent when dealing with complex working conditions such as long-term heavy load and noise and vibration. This leads to serious damage to the sealing materials under the above conditions, and they cannot effectively meet the performance requirements of building expansion joints in actual use.

[0043] To address the problems of the existing technology, this invention mixes a polyurethane-epoxy resin matrix with polydopamine-modified sodium niobate lead-free piezoelectric ceramics and aminated carbon nanotubes. This mixing optimizes the compatibility between the polydopamine-modified sodium niobate lead-free piezoelectric ceramics and the polyurethane-epoxy resin matrix, while promoting ring-opening of the epoxy resin and increasing the crosslinking density of the polyurethane-epoxy resin matrix, resulting in better mechanical and adhesive properties of the building expansion joint sealing composite material. Furthermore, the composite of the polyurethane-epoxy resin matrix, polydopamine-modified sodium niobate lead-free piezoelectric ceramics, and aminated carbon nanotubes yields a building expansion joint sealing composite material with excellent damping properties.

[0044] Piezoelectric materials, as an important system of smart materials, can convert mechanical energy generated by vibration loads into electrical energy. This invention provides polydopamine-modified sodium niobate lead-free piezoelectric ceramics and their preparation method. The polydopamine-modified sodium niobate lead-free piezoelectric ceramics convert mechanical energy generated in building structures into electrical energy. This electrical energy is then combined with a polyurethane-epoxy resin matrix with an interpenetrating network structure and aminated carbon nanotubes to obtain a building expansion joint sealing composite material. Through the construction of its internal conductive network, the building expansion joint sealing composite material achieves the conversion of electrical energy into heat energy, thereby promoting the dissipation of mechanical energy as heat. This plays a crucial role in improving the damping performance of expansion joint sealing materials. Furthermore, the preparation method of the polydopamine-modified sodium niobate lead-free piezoelectric ceramics of this invention is simple, reproducible, and has a high yield, and it exhibits excellent room-temperature piezoelectric properties.

[0045] To enable those skilled in the art to more clearly understand the technical solution of the present invention, the following will provide a detailed description in conjunction with specific embodiments: Example 1 A method for preparing a building expansion joint sealing composite material includes the following steps: S1. Under a nitrogen atmosphere, E51 bisphenol A type epoxy resin and 2,2'-diaminodiphenyl disulfide were weighed at a molar ratio of epoxy group to amino group of 1.9:1. The mixture was heated to 120°C in a four-necked flask and stirred at 800 r / min for 5 h to obtain a viscous solution, which is the epoxy resin precursor containing disulfide bonds, referred to as epoxy resin precursor.

[0046] S2. Under a nitrogen atmosphere, the polyurethane prepolymer and 2,2'-diaminodiphenyl disulfide were mixed according to a molar ratio of 3:1.9 between the isocyanate groups in the polyurethane prepolymer and the amino groups in 2,2'-diaminodiphenyl disulfide, and stirred at 700 r / min for 4 h at 120 °C to obtain polyurethane.

[0047] S3. The polyurethane from step S2 and the epoxy resin precursor from step S1 are mixed at a mass ratio of 63:37. Then, under a nitrogen atmosphere, the mixture is mechanically stirred at 120°C and a rate of 800 r / min for 2 h to obtain a polyurethane-epoxy resin matrix with an interpenetrating network structure, denoted as polyurethane-epoxy resin matrix.

[0048] S4, based on the molecular formula 0.90NaNbO3-0.1Ba(Ti 0.7 Sn 0.3 To determine the stoichiometric ratio of O3, weigh out Na2CO3, Nb2O5, BaCO3, SnO2, and TiO2, mix them thoroughly, add agate balls and anhydrous ethanol, and ball mill for 10 hours. After ball milling, separate the agate balls, dry them at 60℃ for 24 hours, and pass them through a 120-mesh sieve to obtain the raw material mixture. The ratio of the raw material mixture, agate balls, and anhydrous ethanol is 0.30 g: 1 g: 0.50 mL.

[0049] The raw material mixture was pre-calcined at 950℃ for 4 hours, and then naturally cooled to room temperature to obtain the first pre-calcined powder. Agate balls and anhydrous ethanol were added to the first pre-calcined powder, and the mixture was ball-milled for 8 hours. After ball milling, the agate balls were separated and dried at 70℃ for 8 hours. The powder was then passed through a 120-mesh sieve to obtain the second pre-calcined powder with a particle size of 0.125 mm. The ratio of the first pre-calcined powder, agate balls and anhydrous ethanol was 0.25 g: 1 g: 0.35 mL.

[0050] The second pre-calcined powder was polarized at room temperature and under a DC electric field of 2kV / mm for 20 minutes to obtain sodium niobate lead-free piezoelectric ceramic with piezoelectric properties, denoted as sodium niobate lead-free piezoelectric ceramic.

[0051] S5. The sodium niobate lead-free piezoelectric ceramic from step S4 was placed in a mixed solution prepared with 0.1 mol / L Tris buffer and deionized water, and stirred continuously for 6 hours. Then, dopamine hydrochloride was added to the mixed system, and stirring was continued for 8 hours to obtain a suspension. Finally, the suspension was centrifuged, dried, ground, and sieved sequentially to obtain polydopamine-modified sodium niobate lead-free piezoelectric ceramic. The mass-volume ratio of sodium niobate lead-free piezoelectric ceramic, Tris buffer, deionized water, and dopamine hydrochloride was 3 g: 100 mL: 300 mL: 1 g.

[0052] S6. The polydopamine-modified sodium niobate lead-free piezoelectric ceramic and aminated carbon nanotubes from step S5 are added together to the polyurethane-epoxy resin matrix from step S3, and mechanically stirred at 800 r / min for 6 h at 100 °C to obtain a uniformly mixed black viscous liquid; wherein, the mass ratio of polydopamine-modified sodium niobate lead-free piezoelectric ceramic, polyurethane-epoxy resin matrix and aminated carbon nanotubes is 20:100:0.5.

[0053] Casting: The black viscous liquid from step S6 is poured into a preheated polytetrafluoroethylene mold to obtain a polyurethane-epoxy resin-piezoelectric composite casting with dimensions of 160×20×1mm.

[0054] Curing: The polyurethane-epoxy resin-piezoelectric composite casting was placed in a vacuum oven to degas and completely eliminate air bubbles. Then, it was cured in the vacuum oven at a heating rate of 3℃ / min to 80℃ for 72h to obtain the building expansion joint sealing composite material.

[0055] Example 2 A method for preparing a building expansion joint sealing composite material includes the following steps: S1. Under a nitrogen atmosphere, E51 bisphenol A type epoxy resin and 2,2'-diaminodiphenyl disulfide were weighed at a molar ratio of epoxy group to amino group of 1.8:1. The mixture was heated to 130°C in a four-necked flask and mechanically stirred at a rate of 700 r / min for 4 h to obtain a viscous solution, which is the epoxy resin precursor containing disulfide bonds, referred to as epoxy resin precursor.

[0056] S2. Under a nitrogen atmosphere, the polyurethane prepolymer and 2,2'-diaminodiphenyl disulfide are mixed according to a molar ratio of 3:1.95 between the isocyanate groups in the polyurethane prepolymer and the amino groups in 2,2'-diaminodiphenyl disulfide, and stirred at 800 r / min for 5 h at 100 °C to obtain polyurethane.

[0057] S3. The polyurethane from step S2 and the epoxy resin precursor from step S1 are mixed at a mass ratio of 60:40. Then, under a nitrogen atmosphere, the mixture is mechanically stirred at 125°C and a speed of 600 r / min for 5 h to obtain a polyurethane-epoxy resin matrix with an interpenetrating network structure, denoted as polyurethane-epoxy resin matrix.

[0058] S4, based on the molecular formula 0.75NaNbO3-0.1Ba(Ti 0.7 Sn 0.3 To determine the stoichiometric ratio of O3-0.15SrZrO3, weigh out Na2CO3, Nb2O5, BaCO3, SnO2, SrCO3, ZrO2, and TiO2, mix them thoroughly, add agate balls and anhydrous ethanol, and ball mill for 12 hours. After ball milling, separate the agate balls, dry them at 70℃ for 20 hours, and pass them through a 120-mesh sieve to obtain the raw material mixture. The ratio of the raw material mixture, agate balls, and anhydrous ethanol is 0.25g:1g:0.45mL.

[0059] The raw material mixture was pre-calcined at 900℃ for 6 hours, and then naturally cooled to room temperature to obtain the first pre-calcined powder. Agate balls and anhydrous ethanol were added to the first pre-calcined powder, and the mixture was ball-milled for 10 hours. After ball milling, the agate balls were separated and dried at 60℃ for 10 hours. The powder was then passed through a 250-mesh sieve to obtain the second pre-calcined powder with a particle size of 0.062 mm. The ratio of the first pre-calcined powder, agate balls and anhydrous ethanol was 0.20 g: 1 g: 0.30 mL. The second pre-calcined powder was polarized at room temperature and under a DC electric field of 3 kV / mm for 10 min to obtain sodium niobate lead-free piezoelectric ceramic with piezoelectric properties, denoted as sodium niobate lead-free piezoelectric ceramic.

[0060] S5. The sodium niobate lead-free piezoelectric ceramic from step S4 was placed in a mixed solution prepared with 0.1 mol / L Tris buffer and deionized water, and stirred continuously for 12 h. Then, dopamine hydrochloride was added to the mixed system, and stirring was continued for 10 h to obtain a suspension. Finally, the suspension was centrifuged, dried, ground, and sieved sequentially to obtain polydopamine-modified sodium niobate lead-free piezoelectric ceramic. The mass-volume ratio of sodium niobate lead-free piezoelectric ceramic, Tris buffer, deionized water, and dopamine hydrochloride was 2.5 g: 100 mL: 350 mL: 1 g.

[0061] S6. The polydopamine-modified sodium niobate lead-free piezoelectric ceramic and aminated carbon nanotubes from step S5 are added together to the polyurethane-epoxy resin matrix from step S3, and mechanically stirred at 600 r / min for 4 h at 90 °C to obtain a uniformly mixed black viscous liquid; wherein, the mass ratio of polydopamine-modified sodium niobate lead-free piezoelectric ceramic, polyurethane-epoxy resin matrix and aminated carbon nanotubes is 40:100:0.5.

[0062] Casting: The black viscous liquid from step S6 is poured into a preheated polytetrafluoroethylene mold to obtain a polyurethane-epoxy resin-piezoelectric composite casting with dimensions of 160×20×1mm.

[0063] Curing: The polyurethane-epoxy resin-piezoelectric composite casting was placed in a vacuum oven to degas and completely eliminate air bubbles. Then, it was cured in the vacuum oven at a heating rate of 5℃ / min to 95℃ for 60h to obtain the building expansion joint sealing composite material.

[0064] Example 3 A method for preparing a building expansion joint sealing composite material includes the following steps: S1. Under a nitrogen atmosphere, E51 bisphenol A type epoxy resin and 2,2'-diaminodiphenyl disulfide were weighed according to a molar ratio of epoxy group to amino group of 1.92:1. The mixture was heated to 120°C in a four-necked flask and stirred at 600 r / min for 6 h to obtain a viscous solution, which is the epoxy resin precursor containing disulfide bonds, referred to as epoxy resin precursor.

[0065] S2. Under a nitrogen atmosphere, the polyurethane prepolymer and 2,2'-diaminodiphenyl disulfide are mixed according to a molar ratio of 3:2 between the isocyanate groups in the polyurethane prepolymer and the amino groups in 2,2'-diaminodiphenyl disulfide, and stirred at 110°C and 600 r / min for 6 h to obtain polyurethane.

[0066] S3. The polyurethane from step S2 and the epoxy resin precursor from step S1 are mixed at a mass ratio of 57:43. Then, under a nitrogen atmosphere, the mixture is mechanically stirred at 120°C and a rate of 800 r / min for 4 h to obtain a polyurethane-epoxy resin matrix with an interpenetrating network structure, denoted as polyurethane-epoxy resin matrix.

[0067] S4, based on the molecular formula 0.70NaNbO3-0.1Ba(Ti 0.7 Sn 0.3 To determine the stoichiometric ratio of O3-0.20SrZrO3, weigh out Na2CO3, Nb2O5, BaCO3, SnO2, SrCO3, ZrO2, and TiO2, mix them thoroughly, add agate balls and anhydrous ethanol, and ball mill for 12 hours. After ball milling, separate the agate balls, dry them at 60℃ for 18 hours, and pass them through a 120-mesh sieve to obtain the raw material mixture. The ratio of the raw material mixture, agate balls, and anhydrous ethanol is 0.35g:1g:0.55mL.

[0068] The raw material mixture was pre-calcined at 920℃ for 6 hours, and then naturally cooled to room temperature to obtain the first pre-calcined powder. Agate balls and anhydrous ethanol were added to the first pre-calcined powder, and the mixture was ball-milled for 8 hours. After ball milling, the agate balls were separated and dried at 70℃ for 8 hours. The powder was then passed through a 200-mesh sieve to obtain the second pre-calcined powder with a particle size of 0.074 mm. The ratio of the first pre-calcined powder, agate balls and anhydrous ethanol was 0.30 g: 1 g: 0.50 mL.

[0069] The second pre-calcined powder was polarized at room temperature and under a DC electric field of 1 kV / mm for 30 min to obtain sodium niobate lead-free piezoelectric ceramic with piezoelectric properties, denoted as sodium niobate lead-free piezoelectric ceramic.

[0070] S5. The sodium niobate lead-free piezoelectric ceramic from step S4 was placed in a mixed solution prepared with 0.1 mol / L Tris buffer and deionized water and stirred continuously for 8 hours. Then, dopamine hydrochloride was added to the mixed system and stirred for another 6 hours to obtain a suspension. Finally, the suspension was centrifuged, dried, ground, and sieved sequentially to obtain polydopamine-modified sodium niobate lead-free piezoelectric ceramic. The mass-volume ratio of sodium niobate lead-free piezoelectric ceramic, Tris buffer, deionized water, and dopamine hydrochloride was 2 g: 100 mL: 400 mL: 1 g.

[0071] S6. The polydopamine-modified sodium niobate lead-free piezoelectric ceramic and aminated carbon nanotubes from step S5 are added together to the polyurethane-epoxy resin matrix from step S3, and mechanically stirred at 600 r / min for 2 h at 95 °C to obtain a uniformly mixed black viscous liquid; wherein, the mass ratio of polydopamine-modified sodium niobate lead-free piezoelectric ceramic, polyurethane-epoxy resin matrix and aminated carbon nanotubes is 60:100:0.5.

[0072] Casting: The black viscous liquid from step S6 is poured into a preheated polytetrafluoroethylene mold to obtain a polyurethane-epoxy resin-piezoelectric composite casting with dimensions of 160×20×1mm.

[0073] Curing: The polyurethane-epoxy resin-piezoelectric composite casting was placed in a vacuum oven to degas and completely eliminate air bubbles. Then, it was cured in the vacuum oven at a heating rate of 4℃ / min to 90℃ for 70h to obtain the building expansion joint sealing composite material.

[0074] Example 4 A method for preparing a building expansion joint sealing composite material includes the following steps: S1. Under a nitrogen atmosphere, E51 bisphenol A type epoxy resin and 2,2'-diaminodiphenyl disulfide are weighed at a molar ratio of epoxy group to amino group of 2:1. The mixture is heated to 130°C in a four-necked flask and stirred at 600 r / min for 4 h to obtain a viscous solution, which is the epoxy resin precursor containing disulfide bonds, referred to as epoxy resin precursor.

[0075] S2. Under a nitrogen atmosphere, the polyurethane prepolymer and 2,2'-diaminodiphenyl disulfide are mixed according to a molar ratio of 3:2 between the isocyanate groups in the polyurethane prepolymer and the amino groups in 2,2'-diaminodiphenyl disulfide, and stirred at 700 r / min for 6 h at 105 °C to obtain polyurethane.

[0076] S3. The polyurethane from step S2 and the epoxy resin precursor from step S1 are mixed at a mass ratio of 62:38. Then, under a nitrogen atmosphere, the mixture is mechanically stirred at 110°C and a rate of 700 r / min for 2 h to obtain a polyurethane-epoxy resin matrix with an interpenetrating network structure, denoted as polyurethane-epoxy resin matrix.

[0077] S4, based on the molecular formula 0.65NaNbO3-0.1Ba(Ti 0.7 Sn 0.3 To determine the stoichiometric ratio of O3-0.25SrZrO3, weigh out Na2CO3, Nb2O5, BaCO3, SnO2, SrCO3, ZrO2, and TiO2, mix them thoroughly, add agate balls and anhydrous ethanol, and ball mill for 10 hours. After ball milling, separate the agate balls, dry them at 60℃ for 24 hours, and pass them through a 120-mesh sieve to obtain the raw material mixture. The ratio of the raw material mixture, agate balls, and anhydrous ethanol is 0.32g:1g:0.52mL.

[0078] The raw material mixture was pre-calcined at 930℃ for 5 hours, and then naturally cooled to room temperature to obtain the first pre-calcined powder. Agate balls and anhydrous ethanol were added to the first pre-calcined powder, and the mixture was ball-milled for 10 hours. After ball milling, the agate balls were separated and dried at 70℃ for 8 hours. The powder was then passed through a 150-mesh sieve to obtain the second pre-calcined powder with a particle size of 0.104 mm. The ratio of the first pre-calcined powder, agate balls and anhydrous ethanol was 0.28 g: 1 g: 0.45 mL.

[0079] The second pre-calcined powder was polarized at room temperature and under a DC electric field of 3kV / mm for 20 minutes to obtain sodium niobate lead-free piezoelectric ceramic with piezoelectric properties, denoted as sodium niobate lead-free piezoelectric ceramic.

[0080] S5. Place the sodium niobate lead-free piezoelectric ceramic from step S4 into a mixed solution prepared with 0.1 mol / L Tris buffer and deionized water, and stir continuously for 12 h; then add dopamine hydrochloride to the mixed system and continue stirring for 12 h to obtain a suspension; finally, centrifuge, dry, grind and sieve the suspension sequentially to obtain polydopamine-modified sodium niobate lead-free piezoelectric ceramic; wherein, the mass-volume ratio of sodium niobate lead-free piezoelectric ceramic, Tris buffer, deionized water and dopamine hydrochloride is 3 g: 100 mL: 300 mL: 1 g.

[0081] S6. The polydopamine-modified sodium niobate lead-free piezoelectric ceramic and aminated carbon nanotubes from step S5 are added together to the polyurethane-epoxy resin matrix from step S3, and mechanically stirred at 800 r / min for 6 h at 100 °C to obtain a uniformly mixed black viscous liquid; wherein, the mass ratio of polydopamine-modified sodium niobate lead-free piezoelectric ceramic, polyurethane-epoxy resin matrix and aminated carbon nanotubes is 80:100:0.5.

[0082] Casting: The black viscous liquid from step S6 is poured into a preheated polytetrafluoroethylene mold to obtain a polyurethane-epoxy resin-piezoelectric composite casting with dimensions of 160×20×1mm.

[0083] Curing: The polyurethane-epoxy resin-piezoelectric composite casting was placed in a vacuum oven to degas and completely eliminate air bubbles. Then, it was cured in the vacuum oven at a heating rate of 6℃ / min to 100℃ for 48 hours to obtain the building expansion joint sealing composite material.

[0084] observe Figure 1 The XRD spectra of the building expansion joint sealing composite materials prepared in Examples 1 to 4 all showed sharp crystalline peaks and broad amorphous peaks. These sharp crystalline peaks are mainly attributed to the highly crystalline polydopamine-modified sodium niobate lead-free piezoelectric ceramic, indicating that the polydopamine-modified sodium niobate lead-free piezoelectric ceramic is uniformly distributed in the polyurethane-epoxy resin matrix and forms a stable and homogeneous system.

[0085] Depend on Figure 2 It was found that the building expansion joint sealing composite materials prepared in Examples 1 to 4 all had almost the same infrared spectrum, indicating that the polyurethane-epoxy resin matrix with interpenetrating network structure had been successfully constructed.

[0086] Depend on Figure 3The results show that the building expansion joint sealing composite materials prepared in Examples 1-4 consistently exhibit excellent damping performance across the entire temperature range, with the loss factor (tanδ) increasing to 1.05 and the effective damping temperature range (tanδ>0.3) widening to 39.8°C~97.8°C. This is mainly because polydopamine-modified sodium niobate lead-free piezoelectric ceramics are added to the polyurethane-epoxy resin matrix, directly endowing the composite material with piezoelectric properties. When external vibration mechanical energy is applied, the internal friction between the piezoelectric ceramics and the matrix, the internal friction between the piezoelectric ceramics themselves, and the charge generated by the piezoelectric effect of the piezoelectric ceramics are all converted into heat energy through the conductive network. The combined effect of these three factors effectively dissipates the mechanical energy into heat energy, giving the material excellent damping performance. This allows the sealing material to have a wide operating temperature range while also possessing good vibration reduction and noise reduction performance, effectively reducing the damage to expansion joints under long-term heavy loads and noise vibration conditions.

[0087] Depend on Figure 4 The building expansion joint sealing composite materials prepared in Examples 1-4 all exhibited excellent mechanical properties. All samples demonstrated good mechanical properties and elongation at break, which may be related to the covalent and hydrogen bonds formed between the polyurethane-epoxy resin matrix and polydopamine. This enhanced the interfacial compatibility between the ceramic filler and the matrix, improving the material's mechanical properties. Simultaneously, the toughness of the composite material was comprehensively optimized through particle bridging, shear yielding, and crack pinning effects. The fracture strength and elongation at break of Examples 1-4 reached 10.0 MPa, 10.8 MPa, 10.1 MPa, and 8.1 MPa, and 201.6%, 241.8%, 292.4%, and 207.6%, respectively.

[0088] Depend on Figure 5The results show that the building expansion joint sealing composite materials prepared in Examples 1-4 all exhibit excellent adhesion to the inner wall of the expansion joint. When an appropriate amount of polydopamine-modified sodium niobate lead-free piezoelectric ceramic is incorporated into the polyurethane-epoxy resin matrix, the good compatibility between the polydopamine-modified sodium niobate lead-free piezoelectric ceramic and the polyurethane-epoxy resin matrix, along with the reinforcing effect of the polydopamine-modified sodium niobate lead-free piezoelectric ceramic at weak points prone to interfacial tensile failure and spalling, improves the interfacial interaction between the building expansion joint sealing composite material and the steel plate, cement mortar, and asphalt mixture, resulting in a continuous increase in interfacial bond strength. The bond strengths of the building expansion joint sealing composite materials in Examples 1, 2, 3, and 4 to cement mortar are 7.02 MPa, 7.36 MPa, 7.12 MPa, and 5.73 MPa, respectively. This result indicates that when the content of polydopamine-modified sodium niobate lead-free piezoelectric ceramics reaches 80%, the excess polydopamine-modified sodium niobate lead-free piezoelectric ceramics will coat more polydopamine, resulting in a significant reduction in the polydopamine content at the interface and effectively reducing the shrinkage of the bonding area. Simultaneously, the agglomeration of polydopamine-modified sodium niobate lead-free piezoelectric ceramics induces localized stress concentration, significantly weakening the interfacial load-bearing capacity. Even so, the resulting bond strength is still higher than that of the unmodified matrix polymer, and both damping performance and interfacial adhesion performance are effectively improved.

[0089] via Figure 6 It was found that the depolarization temperature of sodium niobate lead-free piezoelectric ceramics can reach 105℃~115℃. Within the curing and service temperature range of expansion joint sealing materials, sodium niobate lead-free piezoelectric ceramics will not lose their piezoelectric properties due to depolarization.

[0090] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range, as well as any value between the two endpoints, can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this invention.

Claims

1. A method for preparing a building expansion joint sealing composite material, characterized in that, Includes the following steps: An epoxy resin precursor containing disulfide bonds and a polyurethane containing disulfide bonds are mixed to obtain a polyurethane-epoxy resin matrix with an interpenetrating network structure. The Na, Nb, Ba, Ti, Sn, Sr, and Zr sources were combined according to the chemical formula (0.9-x)NaNbO3-0.1Ba(Ti) 0.7 Sn 0.3 O3-xSrZrO3 is mixed and pre-calcined to obtain pre-calcined powder; wherein x is selected from 0~0.25; the pre-calcined powder is ball-milled and then polarized to obtain sodium niobate lead-free piezoelectric ceramic with piezoelectric properties; Sodium niobate lead-free piezoelectric ceramics were dispersed in an aqueous solution of tris(hydroxymethyl)aminomethane buffer to obtain a sodium niobate lead-free piezoelectric ceramic dispersion. Subsequently, dopamine hydrochloride was dispersed in the sodium niobate lead-free piezoelectric ceramic dispersion for modification, so that polydopamine was deposited and bound to the surface of the sodium niobate lead-free piezoelectric ceramic to form a coating layer, thus obtaining polydopamine-modified sodium niobate lead-free piezoelectric ceramics. Polydopamine-modified sodium niobate lead-free piezoelectric ceramic, polyurethane-epoxy resin matrix, and aminated carbon nanotubes were mixed and cured. During the curing process, the amino groups on the surface of the polydopamine-modified sodium niobate lead-free piezoelectric ceramic and the amino groups in the aminated carbon nanotubes formed hydrogen bonds with the -C=O groups in the polyurethane-epoxy resin matrix, and simultaneously underwent ring-opening reactions with the epoxy groups to form hydroxyl covalent bonds, thus obtaining a building expansion joint sealing composite material.

2. The method for preparing the building expansion joint sealing composite material according to claim 1, characterized in that, The mass ratio of polyurethane to epoxy resin precursor is 57~63:37~43.

3. The method for preparing the building expansion joint sealing composite material according to claim 1, characterized in that, The mass ratio of sodium niobate lead-free piezoelectric ceramic to dopamine hydrochloride is 2~3:

1.

4. The method for preparing the building expansion joint sealing composite material according to claim 1, characterized in that, The mass ratio of polydopamine-modified sodium niobate lead-free piezoelectric ceramic, polyurethane-epoxy resin matrix and aminated carbon nanotubes is 20~80:100:0.

5.

5. The method for preparing the building expansion joint sealing composite material according to claim 1, characterized in that, The pre-calcination conditions are: calcination at 900℃~950℃ for 4h~6h in air atmosphere.

6. The method for preparing the building expansion joint sealing composite material according to claim 1, characterized in that, The polarization conditions are: polarization at room temperature and under a DC electric field of 1kV / mm to 3kV / mm for 10 to 30 minutes.

7. The method for preparing the building expansion joint sealing composite material according to claim 1, characterized in that, The curing process is as follows: first, degas at 60℃ for 4 to 6 hours until all air bubbles are eliminated, and then let stand at 80℃ to 100℃ for 48 to 72 hours.

8. The method for preparing the building expansion joint sealing composite material according to claim 1, characterized in that, An epoxy resin precursor containing disulfide bonds is prepared according to the following steps: An epoxy resin and 2,2'-diaminodiphenyl disulfide are mixed and subjected to a ring-opening addition reaction to obtain an epoxy resin precursor containing disulfide bonds; wherein the molar ratio of the epoxy group in the epoxy resin to the amino group in the 2,2'-diaminodiphenyl disulfide is 1.8~2.0:

1. Polyurethane containing disulfide bonds is prepared according to the following steps: A polyurethane prepolymer and 2,2'-diaminodiphenyl disulfide are mixed and subjected to a chain extension reaction to obtain a polyurethane containing disulfide bonds; wherein the molar ratio of isocyanate groups in the polyurethane prepolymer to amino groups in the 2,2'-diaminodiphenyl disulfide is 3:1.9~2.

9. A composite material for sealing building expansion joints, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the building expansion joint sealing composite material of claim 9 in the preparation of sealing materials.

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