Capsaicin derivative modified epoxy resin fluorescent coating as well as preparation method and application thereof

Abstract

The invention discloses a capsaicin derivative modified epoxy resin fluorescent coating which is prepared by taking a capsaicin amide derivative as a functional curing agent and taking a polyether amine curing agent and epoxy resin as raw materials through heating and curing. The fluorescent coating shows enhanced mechanical properties and adhesive force, emits bright indigo fluorescent light under excitation of 365 nm ultraviolet light, and has an early self-warning function on metal corrosion. The fluorescent coating has a wide application prospect in intelligent anti-corrosion monitoring in the fields of major infrastructures, ships, chemical equipment and the like.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to capsaicin derivative-modified epoxy resin fluorescent coatings, their preparation methods, and applications. Background Technology

[0002] Epoxy resin coatings have become an indispensable key material in the field of metal protection due to their excellent adhesion, superior mechanical strength, good chemical corrosion resistance, and reliable substrate protection performance. However, traditional epoxy coatings are mostly passive protection and cannot provide early warning of early corrosion of the metal under the coating or minor damage to the coating itself. This may lead to untimely maintenance, resulting in serious safety accidents and economic losses.

[0003] Developing intelligent coatings with self-sensing and self-reporting capabilities is a crucial direction for overcoming the bottlenecks of traditional protective technologies. Among numerous detection methods, fluorescence detection has attracted widespread attention due to its unique advantages such as ultra-high sensitivity, rapid response, high spatial resolution, and intuitive signal visualization. Currently, most studies employ physical blending to introduce commercially available fluorescent dyes or nano-fluorescent materials into the coating matrix. However, this simple blending strategy has several inherent drawbacks: poor compatibility between the fluorescent component and the polymer matrix, leading to phase separation, migration, and aggregation, resulting in fluorescence quenching and performance inhomogeneity; the introduction of exogenous fluorescent components often negatively impacts the mechanical integrity, durability, and interfacial adhesion of the coating. Furthermore, the recognition ability and specificity of physically embedded fluorescent molecules for specific corrosion factors are often insufficient to meet the requirements of practical engineering monitoring. Therefore, developing epoxy resin fluorescent coatings with both stable fluorescence performance and excellent mechanical properties holds broad application prospects. Summary of the Invention

[0004] The purpose of this invention is to overcome the technical defects of existing physically blended fluorescent coatings, such as poor fluorescence stability, impaired mechanical properties, and insufficient specificity in response to corrosion factors, and to provide a coating that combines stable fluorescence performance, excellent mechanical properties, and resistance to Fe. 3+ Capsaicin derivative-modified epoxy resin fluorescent coating achieves high selectivity and high sensitivity fluorescence response.

[0005] According to a first aspect of the present invention, a capsaicin derivative modified epoxy resin fluorescent coating is provided, wherein the raw materials are composed of epoxy resin, polyetheramine curing agent and capsaicin amide derivative; The structural formula of the capsaicin amide derivative is shown below: .

[0006] The capsaicin derivative-modified epoxy resin fluorescent coating of this invention uses capsaicin amide derivative (BSPC) as a raw material. BSPC serves not only as a functional monofunctional curing agent but also as a fluorescent source and reacts with the metal corrosion product Fe. 3+ Specific coordination occurs, producing a significant fluorescence quenching effect, thus endowing the coating with an early warning function against metal corrosion. Simultaneously, the capsaicinamide derivative possesses a rigid benzene ring structure, enhancing the coating's tensile strength, modulus, and surface hardness, while its polar groups improve adhesion.

[0007] In some embodiments, the molar number of amino groups in the capsaicinamide derivative accounts for 1%-4% of the total molar number of amino groups in the capsaicinamide derivative and the polyetheramine curing agent. In some embodiments, the molar number of amino groups in the capsaicinamide derivative accounts for 3% of the total molar number of amino groups in the capsaicinamide derivative and the polyetheramine curing agent. If the percentage of the molar number of amino groups in the capsaicinamide derivative relative to the total molar number of amino groups in the capsaicinamide derivative and the polyetheramine curing agent is low, the mechanical properties, thermomechanical properties, thermal stability, and fluorescence properties will be insufficient; if it is high, it will weaken the network structure. By systematically controlling the molar number of amino groups in the capsaicinamide derivative in the raw material, the optimized design of the coating crosslinking network structure is achieved.

[0008] In some embodiments, the polyetheramine curing agent is a polyetheramine with an average molecular weight of 200-600. The polar functional groups (phenolic hydroxyl groups, amide groups) contained in BSPC have good affinity with the ether bonds and amine groups in the molecular chain of the polyetheramine curing agent. Preferably, the polyetheramine curing agent is a polyetheramine with an average molecular weight of 400-430, such as polyetheramine D400. Capsaicinamide derivatives have good solubility in polyetheramine D400.

[0009] In some embodiments, the polyetheramine curing agent may also be a polyetheramine with an average molecular weight of 230 or 440. For example, the polyetheramine curing agent may also be a difunctional linear polyetheramine D230 (molecular weight of about 230) or a trifunctional branched polyetheramine T403 (molecular weight of about 440).

[0010] In some embodiments, the epoxy resin is a bisphenol A type epoxy resin. The epoxy value of the bisphenol A type epoxy resin is 0.44 eq / 100g.

[0011] In some embodiments, the molar ratio of the epoxy group of the epoxy resin to the amino hydrogen in the raw material is 1:0.5~2, wherein the molar number of amino hydrogen in the raw material is the sum of the molar number of amino hydrogen in the polyether amine curing agent and the capsaicinamide derivative.

[0012] According to a second aspect of the present invention, a method for preparing a capsaicin derivative-modified epoxy resin fluorescent coating is provided, comprising the following steps: S1. Dissolve capsaicin amide derivatives in polyether amine curing agents to obtain mixed curing agents; S2. Add epoxy resin to the mixed curing agent to obtain a resin mixture; S3. Cure the resin mixture at 75-85℃ for 2.5-3.5 hours to obtain the final product.

[0013] If capsaicinamide derivatives are only blended with epoxy resin as physical fillers, the lack of chemical bonding between the fluorescent component and the resin matrix inevitably leads to problems such as poor compatibility, easy migration, and aggregation-induced quenching. Through the preparation method of this invention, capsaicinamide derivatives participate in the epoxy-amine curing reaction as functional monofunctional curing agents, embedding themselves into the epoxy network through covalent bonds. This fundamentally solves the inherent defects of physical blending (easy migration and quenching of the fluorescent component), achieving long-term stability of fluorescence performance.

[0014] In some embodiments, step S2 further includes stirring and sonicating the resin mixture. Specifically, the resin mixture is stirred for 10-15 minutes, and then sonicated for 10-15 minutes. Stirring ensures thorough mixing of the resin mixture, and sonication thoroughly removes air bubbles from the resin mixture.

[0015] According to a third aspect of the present invention, the application of capsaicin derivative-modified epoxy resin fluorescent coating in the preparation of protective materials for metal substrates is provided.

[0016] In some implementations, the metal substrate contains iron.

[0017] Specifically, capsaicin derivative-modified epoxy resin fluorescent coatings can be applied to the surface of metal substrates. When the coating is damaged, the capsaicin amide derivative acts as a fluorescent source and reacts with the metal corrosion product Fe. 3+ Specific coordination occurs, meaning the carbonyl oxygen atom (C=O) of the amide group in the capsaicin amide derivative and the phenolic hydroxyl oxygen atom (-OH) in the ortho position on the benzene ring are spatially positioned to interact with a Fe. 3+ The ions form a stable six-membered chelate ring, producing a significant fluorescence quenching effect, thereby achieving early warning of metal corrosion and protection of the metal substrate.

[0018] In some embodiments, when capsaicin derivative-modified epoxy resin fluorescent coating is used as a protective material for a metal substrate, fluorescence quenching occurs in the material area when the fluorescent coating is damaged.

[0019] According to a fourth aspect of the present invention, the application of capsaicin derivative-modified epoxy resin fluorescent coatings in the preparation of smart anti-corrosion materials or corrosion monitoring sensor systems is provided.

[0020] In some implementations, capsaicin derivative-modified epoxy resin fluorescent coatings are used as protective materials for metal substrates, intelligent anti-corrosion materials, or corrosion monitoring sensor systems in fields such as steel structures, ships, and chemical equipment.

[0021] In some implementations, the steel structure can be a bridge, a transmission tower, or a building. Specifically, the building can be a stadium.

[0022] The beneficial effects of this invention are as follows: (1) The raw materials of the present invention do not contain any other organic solvents except for polyetheramine curing agents, which meets the requirements of green chemical industry.

[0023] (2) The preparation method of the present invention introduces capsaicin amide derivatives into epoxy resin coatings in a covalently bonded manner, which not only fundamentally solves the problem of easy migration and quenching of fluorescent components, but also enhances the tensile strength, modulus and surface hardness of the coating by the rigid benzene ring structure of capsaicin amide derivatives, and improves the adhesion.

[0024] (3) The capsaicin derivative of the present invention has a positive effect on Fe 3+ Exhibiting highly selective fluorescence response, the capsaicin derivative-modified epoxy resin fluorescent coating, when subjected to mechanical damage or localized failure that triggers corrosion of the underlying metal, generates Fe during the corrosion process. 3+ It exhibits highly selective coordination with the characteristic functional groups of BSPC molecules in the coating, leading to significant quenching of the fluorescence signal in the damaged area. This significant change in fluorescence signal can be detected by simple equipment, enabling rapid and intuitive location and early warning of corrosion initiation. This provides an innovative technical means for intelligent corrosion prevention and structural health monitoring in major infrastructure, shipbuilding and marine engineering, and chemical equipment, and has broad prospects in the field of intelligent corrosion prevention. Attached Figure Description

[0025] Figure 1 The above are the FT-IR images of SAM, BAE, and BSPC of this invention; Figure 2 (a) is the BSPC of the present invention. 1 H NMR spectrum; Figure 2 (b) is the BSPC of the present invention. 13 C-NMR spectrum; Figure 3 This is the HRMS diagram of the BSPC of this invention; Figure 4 The stress-strain curves for EP-0, EP-1, EP-2, EP-3 and EP-4 of this invention are shown. Figure 5 (a) is the energy storage modulus-temperature curve of EP-0, EP-1, EP-2, EP-3 and EP-4 of the present invention; Figure 5 (b) are the loss factor-temperature curves of EP-0, EP-1, EP-2, EP-3 and EP-4 of the present invention; Figure 6 (a) TGA curves of EP-0, EP-1, EP-2, EP-3 and EP-4 of the present invention; Figure 6 (b) are the DTG curves of EP-0, EP-1, EP-2, EP-3 and EP-4 of the present invention; Figure 7 For DMF solutions loaded with BSPC, the effects of different concentrations of Fe 3+ Colorimetric and fluorescence responses; Figure 8 (a) A comparison of the appearance of the present invention EP-0, EP-1, EP-2, EP-3 and EP-4 under natural light and ultraviolet light; Figure 8 (b) shows the fluorescence emission spectra of EP-1, EP-2, EP-3 and EP-4; Figure 9 The fluorescence response diagrams show the type A scratch of the EP-3 scratch-through coating of the present invention and the type B scratch that scratches through the coating and exposes the metal substrate. Detailed Implementation

[0026] The present invention will now be described in further detail with reference to the accompanying drawings, but the embodiments of the present invention are not limited thereto. The raw materials and reagents involved in the following embodiments are all commercially available.

[0027] The Friedel-Crafts alkylation reaction of the capsaicin amide derivative of the present invention is synthesized via the following route: .

[0028] Salicylic acid amide (SAM) and N-hydroxymethylbenzamide (BAE) were reacted at 35°C for 72 hours under concentrated sulfuric acid catalysis. The amino group of SAM reacted with the hydroxyl group of BAE to form an amide reaction, yielding a capsaicin amide derivative (BSPC). The product was a white solid.

[0029] The preparation method includes the following steps: 0.1 mol SAM and 0.12 mol BAE were dissolved in 100 mL of anhydrous ethanol. While stirring, 10 mL of concentrated sulfuric acid was added through a constant-pressure dropping funnel at a dropping rate of 1-3 drops / second. The mixture was then reacted at 35 °C for 72 hours. After the reaction was complete, the solid was collected by suction filtration and repeatedly washed with deionized water until the filtrate was neutral, yielding the crude product. The crude product was recrystallized three times using anhydrous ethanol as a solvent to obtain a white, pure solid, namely the target compound N-(2-hydroxy-3-amide benzyl)benzamide (BSPC). The product was dried at 60 °C and then stored in a sealed container.

[0030] The BSPC is characterized as follows.

[0031] 1. Fourier transform infrared spectroscopy The FT-IR spectra of the relevant samples were recorded using a Thermo Fisher Nicolet iS10 Fourier transform infrared (FTIR) spectrometer, with a measurement range of 4000–400 cm⁻¹. -1 The number of scans was 32. The solid material samples were prepared by grinding and mixing with potassium bromide, followed by tableting using a tablet press.

[0032] 2. Nuclear Magnetic Resonance Spectroscopy The sample 1 H-NMR and 13 C-NMR was acquired on a Bruker AVANCE 400 nuclear magnetic resonance spectrometer in Germany, using deuterated dimethyl sulfoxide (DMSO) as solvent and tetramethylsilane (TMS, δ=0) as internal reference. The number of scans was 64, the operating temperature was 25°C, and the frequency was 400 MHz.

[0033] 3. High-resolution mass spectrometry High-resolution mass spectrometry (HRMS) analysis was performed on capsaicin derivative monomers using a high-resolution mass spectrometer with methanol as solvent, ESI as ion source, and positive ion mode as the test mode.

[0034] Fourier transform infrared (FT-IR) spectroscopy characterization was performed on SAM, BAE, and BSPC, and the results are as follows: Figure 1 As shown. From Figure 1 It can be seen that at 3351 cm -1 The strong, broad absorption peak at 3296 cm⁻¹ is attributed to the stretching vibration of the phenolic hydroxyl group (-OH) in the molecule, while the peak at 3296 cm⁻¹ is attributed to this vibration. -1 The absorption peak at 3000-3100 cm⁻¹ corresponds to the stretching vibration of the NH group in the amide group. The presence of aromatic structures is indicated by the peak at 3000-3100 cm⁻¹. -1 The weak peak of aromatic CH stretching vibration within the range, and 1597 cm⁻¹ -1 With 1485 cm -1 The absorption peaks at 1633 cm⁻¹, attributed to the stretching vibrations of the benzene ring skeleton, further confirm this. -1 The strong peak at 1528 cm⁻¹ clearly indicates the stretching vibration of the amide carbonyl group (C=O). -1 The absorption at the NH4+ position originates from the in-plane bending vibration of NH4+. The positions of all characteristic peaks are in perfect agreement with the expected structure of the target product N-(2-hydroxy-3-amide benzyl)benzamide (BSPC), providing preliminary evidence of the successful synthesis of this compound.

[0035] 1H NMR spectrum of BSPC ( 1H-NMR, carbon nuclear magnetic resonance (NMR) 13 Characterization by C-NMR, the results are as follows Figure 2 As shown. From Figure 2 It can be seen that, 1 In the 1H NMR spectrum, the phenolic hydroxyl proton signal was stable at δ 12.22 ppm, indicating that it did not participate in bonding during the reaction, consistent with the selectivity of the Friedel-Crafts alkylation reaction. Multiple broad peaks at δ 9.33, 9.18, and 9.05 ppm correspond to NH protons on the two amide groups (-CONH-), respectively. The multiplets in the δ 6.88–7.95 ppm range are attributed to all aromatic ring protons (Ar-H). Most importantly, a new characteristic singlet was observed at δ 4.89 ppm, clearly attributed to the newly generated benzylmethylene (-Ar-CH2-N-) proton from the Friedel-Crafts alkylation reaction, providing direct evidence of the target reaction occurring. 13 In the C10 NMR spectrum, the signals at δ 168.70, 167.21, and 159.69 correspond to the carbonyl carbon of benzamide, the carbonyl carbon of salicylamide, and the aromatic carbon adjacent to the phenolic hydroxyl group, respectively. The multiple signals in the range of δ 116.23–134.26 correspond to the carbon atoms of all aromatic rings in the molecule. In particular, the characteristic peak at δ 45.25 clearly belongs to the newly generated benzylmethylene carbon (-Ar-CH2-N-), which corroborates the corresponding proton signal (δ 4.89) in the proton spectrum. In summary, the synergistic appearance of the benzyl proton signal (δ 4.89) in the proton spectrum and the benzyl carbon signal (δ 45.25) in the C10 spectrum further confirms the successful synthesis of the target product BSPC.

[0036] To accurately determine the molecular weight of the target compound BSPC, high-resolution mass spectrometry (HRMS) was used for analysis, and the results are as follows: Figure 3 As shown. Compared to conventional mass spectrometry, HRMS provides higher mass precision, thus enabling more accurate identification of the molecular weight of compounds. The capsaicin derivative BSPC (C 15 H 14 The molecular weight of N₂O₃ is 270.1, consistent with theoretical calculations. The spectrum shows two main characteristic ion peaks, with a strong signal peak observed at m / z 293.0871, corresponding to the adduct [M+Na] formed by the molecule and sodium ions. + The signal peak at m / z 271.1052 corresponds to the protonated form of the molecule [M+H]. + The two key ion peaks are highly consistent with the expected addition behavior of the target compound BSPC, confirming that the obtained white pure substance is the target molecule.

[0037] The capsaicin derivative modified epoxy resin fluorescent coating is prepared by bisphenol A type epoxy resin (E-44), polyetheramine D400 and capsaicin amide derivative (BSPC) through an epoxy-amine curing reaction.

[0038] It should be noted that the raw materials used in this invention include commercially available bisphenol A type E-44 epoxy resin, with an epoxy value of 0.44 eq / 100g. Polyetheramine D400 is calculated and added based on its functionality of approximately 2 and average molecular weight of approximately 400 g / mol. The stoichiometric ratio of polyetheramine D400, the amino hydrogen (hydrogen on -NH2) of BSPC, and the epoxy group of E-44 epoxy resin is 1:0.5~2. Due to steric hindrance or electronic effects in its molecular structure, only one amino hydrogen atom can effectively participate in the epoxy reaction.

[0039] Example 1 This embodiment provides a method for preparing a capsaicin derivative-modified epoxy resin fluorescent coating, including the following steps: Using 100g of epoxy resin E-44 as a reference, accurately weigh 87.12g of polyetheramine D400 and 1.19g of BSPC. Dissolve BSPC in polyetheramine D400 and stir at room temperature for 2 hours until completely dissolved. Then add 100g of epoxy resin, first magnetically stir for 10 minutes, then ultrasonically degas for 10 minutes. Pour the resulting mixture into a polytetrafluoroethylene mold and cure in an oven at 80℃ for 3 hours. The prepared sample is labeled EP-1.

[0040] In this embodiment, the number of amino moles in BSPC accounts for 1% of the total number of amino moles in BSPC and polyetheramine D400.

[0041] Example 2 This embodiment provides a method for preparing a capsaicin derivative-modified epoxy resin fluorescent coating, including the following steps: Using 100g of epoxy resin E-44 as a reference, accurately weigh 86.24g of polyetheramine D400 and 2.38g of BSPC. Dissolve BSPC in polyetheramine D400 and stir at room temperature for 2 hours until completely dissolved. Then add 100g of epoxy resin, stir magnetically for 10 minutes, and then ultrasonically degas for 10 minutes. Pour the resulting mixture into a polytetrafluoroethylene mold and cure in an oven at 80℃ for 3 hours. Label the prepared sample as EP-2.

[0042] In this embodiment, the molar number of amino groups in BSPC accounts for 2% of the total molar number of amino groups in BSPC and polyetheramine D400.

[0043] Example 3 This embodiment provides a method for preparing a capsaicin derivative-modified epoxy resin fluorescent coating, including the following steps: Using 100g of epoxy resin E-44 as a reference, accurately weigh 85.36g of polyetheramine D400 and 3.57g of BSPC. Dissolve BSPC in polyetheramine D400 and stir at room temperature for 2 hours until completely dissolved. Then add 100g of epoxy resin, first magnetically stir for 10 minutes, then ultrasonically degas for 10 minutes. Pour the resulting mixture into a polytetrafluoroethylene mold and cure in an oven at 80℃ for 3 hours. The prepared sample is labeled EP-3.

[0044] In this embodiment, the molar number of amino groups in BSPC accounts for 3% of the total molar number of amino groups in BSPC and polyetheramine D400.

[0045] Example 4 This embodiment provides a method for preparing a capsaicin derivative-modified epoxy resin fluorescent coating, including the following steps: Using 100g of epoxy resin E-44 as a reference, accurately weigh 84.48g of polyetheramine D400 and 4.76g of BSPC. Dissolve BSPC in polyetheramine D400 and stir at room temperature for 2 hours until completely dissolved. Then add 100g of epoxy resin, stir magnetically for 10 minutes, and then ultrasonically degas for 10 minutes. Pour the resulting mixture into a polytetrafluoroethylene mold and cure in an oven at 80℃ for 3 hours. The prepared sample is labeled EP-4.

[0046] In this embodiment, the molar number of amino groups in BSPC accounts for 4% of the total molar number of amino groups in BSPC and polyetheramine D400.

[0047] Comparative Example 1 This comparative example provides a method for preparing an epoxy resin fluorescent coating, which differs from Example 1 in that BSPC is not added. The prepared sample is labeled EP-0.

[0048] II. Testing Methods The samples prepared in Examples 1-4 and Comparative Example 1 were subjected to the following experiments.

[0049] 1. Tensile property test The mechanical properties of the samples were tested using a Shenzhen Sansi Zongheng UTM 4204 electronic universal testing machine according to the GB / T 1040.2-2006 standard. To ensure accuracy, each sample was tested in parallel five times and the average value was taken.

[0050] 2. Dynamic thermomechanical analysis A DMA 242E dynamic thermomechanical analyzer from Netzsch GmbH, Germany, was used to test cuboid samples measuring 80 mm × 60 mm × 1 mm in double cantilever mode. The test temperature range was -20 to 120 °C, the heating rate was 10 K / min, and a 1 Hz sinusoidal alternating load was applied. The glass transition temperature of the cured coating was determined by the peak value of the tanδ curve.

[0051] 3. Thermogravimetric analysis Thermogravimetric analysis (TGA) of the samples was performed using a Netzsch TG209F1 Libra thermogravimetric analyzer. The thermal stability of the samples was determined within the temperature range of 35℃ to 900℃, with a heating rate of 10℃·min. -1 The flow rate under a nitrogen atmosphere was 20 mL / min. -1 .

[0052] 4. Fluorescence performance test The fluorescence emission spectrum of the cured film was measured using a fluorescence spectrophotometer with an excitation wavelength of 350 nm and a scanning range of 365-500 nm to evaluate the fluorescence properties of BSPC in the coating. Each sample was measured at least three times. Simultaneously, a standard solution of BSPC was prepared by dissolving it in DMF, and different concentrations of Fe were added to further refine the solution. 3+ The solution was subjected to observation of color and fluorescence changes under natural light and 365 nm ultraviolet light, respectively, to qualitatively characterize the effect of BSPC on Fe. 3+ Its specific recognition and response behavior.

[0053] 5. Scratch corrosion test The fluorescence self-reporting behavior of the coating after damage was evaluated using an artificial scratch method. Two types of scratches were prepared on the surface of the cured coating using a sharp blade: type A scratches that penetrated only the coating and type B scratches that penetrated the coating and exposed the metal substrate. The scratched samples were immersed in a 3.5 wt% NaCl solution, removed at predetermined time points, and the changes in fluorescence color and intensity of the scratched areas were observed and recorded under a 365 nm UV lamp to analyze the intelligent response of the coating to different damage types.

[0054] 6. Adhesion test The adhesion strength between the samples and the Q235 steel substrate was measured using a pull-out adhesion tester. Five aluminum ingots (diameter: 20 mm) were glued to different locations of each coating using epoxy resin adhesive. The adhesion strength was measured by a pull-out test, in which the ingots were pulled off the substrate at a pull-out rate of 0.2 MPa / s. Finally, the measurements from five different areas were taken to obtain an average value as the result.

[0055] 7. Pencil Hardness Test The pencil hardness of the coating was tested according to GB / T 6739-1996. The highest pencil hardness rating that the sample surface could withstand without permanent damage was used as the hardness evaluation index. To ensure data reliability, a triple-replication verification mechanism was adopted, with three parallel samples in each group. 8. Gel content test The acetone extraction method was used. First, the mass of the resin film sample (denoted as m1) was accurately weighed and placed in a clean container. Sufficient acetone was added to completely submerge the sample, and it was left to soak at room temperature for 48 hours to allow the uncrosslinked soluble resin to fully dissolve. After soaking, the insoluble matter was separated by filtration and washed repeatedly with fresh acetone to remove residual soluble components. The washed insoluble matter was dried in a 60℃ vacuum oven to constant weight, cooled, and then weighed (denoted as m2). The gelation rate was calculated using the formula GC(%) = (m2 / m1)×100%. Each sample was tested in triplicate, and the average value was used to evaluate the degree of resin crosslinking.

[0056] 9. Swelling rate test Accurately weigh the initial mass of the cured film sample (denoted as m0) at room temperature, and then immerse it in water, ethanol, and toluene for 48 h each. Remove the sample, blot off excess solvent from the surface with filter paper, and record the equilibrium mass m1. The swelling ratio (SR) is calculated using the formula SR(%) = [(m1-m0) / m0] × 100%. Each sample is tested in triplicate, and the average value is used to evaluate the solvent resistance of the coating.

[0057] 10. Acid and alkali resistance test The test was conducted according to GB / T 9274-1988 (Method A). A suitable amount of the cured film was taken at room temperature and immersed in 10 wt% sodium hydroxide and 0 wt% hydrochloric acid aqueous solutions for 48 h, respectively. The morphology of the samples was observed and recorded; changes in the sample were recorded as "change," and samples that maintained their intact morphology were recorded as "no change."

[0058] III. Results Analysis 1. Mechanical property analysis The tensile properties of a series of samples were systematically evaluated using an electronic universal testing machine. The stress-strain curves of the samples prepared in Examples 1-4 and Comparative Example 1 are shown below. Figure 4As shown in Table 1, the results indicate that the introduction of BSPC significantly affects the mechanical behavior of the epoxy resin. Compared with unmodified EP-0, EP-3 exhibits the best overall mechanical properties when the molar number of amino groups in BSPC is 3% of the total molar number of amino groups in the raw material. Its tensile strength increases to 65.84±2.97 MPa, an increase of approximately 53.5% compared to EP-0 (42.90±2.61 MPa); simultaneously, the Young's modulus increases to 955.75±7.11 MPa, an increase of approximately 33%, while the elongation at break also increases from 6.85% to 7.62%. This performance optimization is attributed to the dual role of BSPC molecules in the epoxy crosslinking network. On the one hand, its rigid benzene ring structure can act as a reinforcing unit, effectively bearing and transferring stress; on the other hand, its monofunctional characteristics and potential amide group hydrogen bond physical crosslinking improve the material's deformability while moderately adjusting the chemical crosslinking density. However, when the molar number of amino groups in BSPC was 4% of the total molar number of amino groups in the raw material, both the tensile strength and modulus of EP-4 decreased. This indicates that excessive BSPC exacerbates its chain termination effect, and the resulting network dilution and weakening become dominant, thus offsetting the reinforcing effect provided by the rigid structure.

[0059] Table 1 Tensile property test results

[0060] 2. Dynamic Thermomechanical Properties (DMA) Analysis Based on a systematic study using dynamic thermomechanical analysis (DMA), the regulatory effect of BSPC on the thermodynamic behavior of epoxy resin curing systems was clearly revealed, and the results are as follows: Figure 5 As shown in Table 2, the relevant data indicate that the introduction of BSPC affects the dynamic mechanical properties of the material at multiple levels. With the BSPC content increasing from 0 to 3 mol%, the storage modulus (E') of the cured system at 25°C shows a continuous upward trend, increasing from 2540.4 MPa for EP-0 to 2898.7 MPa for EP-3, an increase of approximately 14%. This phenomenon indicates that the stiffness of the material in the glassy state is significantly enhanced with the addition of BSPC. Simultaneously, the glass transition temperature (Tg) of the system... g The storage modulus also gradually increased from 56.5℃ in EP-0 to 59.2℃ in EP-3, indicating that the rigid benzene ring structure in BSPC effectively restricts the movement of polymer chain segments. However, in the high-elasticity region above Tg 30℃, the storage modulus of all BSPC-modified samples was lower than that of the unmodified system EP-0, and showed a monotonically decreasing trend with increasing BSPC content. The modulus of EP-0 in this region was 7.32 MPa, while that of EP-3 decreased to 6.27 MPa, and that of EP-4 further decreased to 6.02 MPa. The crosslinking density (ν) calculated according to rubber elasticity theory... eThe concentration of EP-0 also showed a regular decrease, from 816.36 mol·m⁻¹. -3 It decreased to 667.29 mol·m⁻¹ of EP-4. -3 This provides direct evidence for the dilution effect of the crosslinking network caused by BSPC as a monofunctional reactant. Notably, when the BSPC content increased to 4 mol%, although the crosslinking density continued to decrease, the storage modulus and Tg of the system at 25 °C both declined, from 2898.7 MPa and 59.2 °C for EP-3 to 2602.4 MPa and 58.7 °C for EP-4, respectively. This indicates that excessive BSPC has allowed its chain termination-induced network weakening effect to dominate, reducing the contribution of rigid units to the enhancement of material stiffness and thermal stability.

[0061] Table 2 Dynamic thermomechanical properties and crosslinking density

[0062] 3. Thermal stability analysis The thermal stability of EP-0 to EP-4 samples was systematically studied using thermogravimetric analysis (TGA). The TGA and DTG curves of the samples are shown below. Figure 6 As shown, the relationship between residual carbon content and degradation temperature (T) 10% T 50% The relevant data are shown in Table 3. In the DTG curves, all samples exhibited a single characteristic decomposition peak, indicating that their thermal degradation process was a single-stage process. This phenomenon proves that the introduction of BSPC did not change the inherent thermal decomposition pathway of epoxy resin; the thermal degradation of the cured film was mainly attributed to the thermal decomposition of the epoxy crosslinking network backbone. In the TGA curves, all samples showed similar thermal decomposition behavior, with their 10% thermogravimetric temperature concentrated in the range of 355-361℃, their 50% thermogravimetric temperature stable between 385-386℃, and their residual carbon rate ranging from 6.55% to 7.84%. With the introduction of BSPC, the thermal stability parameters showed slight fluctuations but remained generally stable. The slight decrease in thermal decomposition temperature may be related to the moderate decrease in crosslinking density caused by the monofunctionality of BSPC molecules, but its rigid benzene ring structure compensated for this effect to some extent, allowing the overall thermal stability to be maintained. The initial decomposition temperature of all samples was higher than 355℃, proving that this series of materials possesses good thermal stability and can meet the heat resistance requirements of most practical applications.

[0063] Table 3. Thermal decomposition results of different fluorescent coatings

[0064] 4. Comprehensive Performance Analysis of Coating The gelation rate, swelling behavior, and general properties of capsaicin derivative-modified epoxy resin fluorescent coatings were systematically evaluated, and the relevant results are listed in Tables 4 and 5. The gelation rate test results showed that the gelation rate of all samples was higher than 95.6%, indicating that the resin had been fully cured and a complete three-dimensional network had been formed. With the increase of BSPC content, the gelation rate gradually decreased from 97.85% for EP-0 to 95.62% for EP-4. This decreasing trend is consistent with the role of BSPC as a monofunctional reactant in the cured system; its introduction moderately reduced the chemical crosslinking density of the system, which is consistent with the crosslinking density change observed in dynamic thermomechanical analysis. These results demonstrate that the capsaicin derivative-modified epoxy resin fluorescent coatings formed a complete three-dimensional network after curing, with BSPC, as a reactive component, firmly fixed within it and unable to migrate.

[0065] Swelling behavior analysis further confirmed the aforementioned structural changes. As shown in Table 5, the swelling ratio of the coating increased with increasing BSPC content in water, ethanol, and toluene, especially in toluene, from 7.88% in EP-0 to 10.02% in EP-4. The increase in swelling ratio was correlated with the decrease in gelation rate, indicating that the introduction of BSPC, while maintaining the overall network integrity, moderately increased the molecular chain movement space and free volume due to its long-chain structure, the introduction of polar functional groups, and the dilution at crosslinking points, thereby promoting solvent penetration. Nevertheless, the swelling ratio of all samples remained at a low level of less than 10% in each solvent, demonstrating that the coating still possesses good solvent resistance.

[0066] The general properties of the coating, such as adhesion and hardness, are shown in Table 3.5. Adhesion test results show that as the BSPC content increases from 0 to 4 mol%, the adhesion of the coating on the iron substrate significantly increases from 1.84 MPa to 2.40 MPa, an increase of 30.4%. This enhancement is mainly attributed to the strong interfacial interaction between the abundant polar groups (phenolic hydroxyl and amide groups) in the BSPC molecule and the substrate surface. Simultaneously, all BSPC-modified samples achieved a pencil hardness of 4H, higher than the unmodified EP-0 (3H), demonstrating the effective enhancement of the coating surface stiffness by the rigid benzene ring structure in the BSPC molecule. Regarding chemical resistance, all samples remained "unchanged" after immersion in 10 wt% HCl and NaOH solutions for 48 hours, indicating that the introduction of BSPC optimized the mechanical and interfacial properties of the coating without compromising the inherent excellent acid and alkali corrosion resistance of the epoxy resin matrix. This balance between moderately adjusting the crosslinking density and significantly enhancing interfacial properties fully demonstrates the unique value of BSPC as a multifunctional modifier, providing a new technical approach for developing high-performance epoxy resin coatings.

[0067] Table 4. Gel ratio and swelling ratio of different fluorescent coatings

[0068] Table 5. Test results of acid and alkali resistance, adhesion and pencil hardness of different fluorescent coatings.

[0069] 5. Research on fluorescence properties and intelligent monitoring function 5.1 Solution fluorescence of BSPC and Fe 3+ Identification Through systematic solvent screening, DMF was determined to be the optimal solvent, exhibiting good solubility for BSPC and low autofluorescence background. In DMF solution, BSPC exhibits unique Fe... 3+ Response characteristics. From Figure 7 It can be seen that under natural light, as Fe... 3+ As the concentration increases, the solution gradually changes from colorless to a distinct purple. This significant color change originates from the carbonyl oxygen atom (C=O) of the amide group in the BSPC molecule and the oxygen atom (-OH) of the ortho-phenolic hydroxyl group, along with Fe. 3+ The resulting coordinating coordination leads to the formation of a stable six-membered chelate ring complex, causing intramolecular electron cloud density rearrangement and conjugation system expansion, and initiating significant metal-ligand charge transfer (MLCT), thus red-shifting the molecule's absorption spectrum into the visible region. Under 365 nm UV irradiation, the DMF solution of BSPC exhibits bright indigo fluorescence, primarily due to electronic transitions generated by the rigid conjugated system constructed by the benzene ring, hydroxyl group, and amide group in its molecular structure. When Fe is introduced... 3+ Afterwards, a significant fluorescence quenching phenomenon can be observed, the mechanism of which includes both dynamic and static pathways: Fe 3+ As a strong oxidant, BSPC-Fe captures excited-state electrons through photoinduced electron transfer (PET) to form a non-radiative transition channel; simultaneously, BSPC-Fe 3+ The formation of the complex alters the ground-state electronic structure, leading to the deactivation of the excited state. This dual-mode colorimetric and fluorescence response confirms that BSPC acts as a Fe... 3+ The application potential of probes.

[0070] 5.2 Fluorescence properties and intelligent monitoring function of BSPC in epoxy coatings Introducing BSPC into the epoxy resin system effectively preserved its fluorescence properties and further developed it into a smart self-reporting function. Figure 8 (a) It can be seen that under 365 nm UV light irradiation, all BSPC-containing coatings exhibited obvious blue fluorescence, proving that BSPC maintained its fluorescent activity during the curing process. From Figure 8(b) It can be seen that the fluorescence intensity of the cured coating increases with the increase of BSPC content, and the EP-4 sample exhibits the strongest fluorescence emission. This indicates that BSPC successfully maintains its fluorescence activity during the curing process of epoxy resin and exists stably in the crosslinking network in the form of chemical bonds. This phenomenon is due to the hydrogen bonding in the crosslinking network stabilizing the molecular configuration of BSPC and reducing the energy loss of nonradiative transitions. To further evaluate the intelligent monitoring capability of the coating, we designed a scratch test for EP-3, and the results are as follows: Figure 9 As shown, in a 3.5 wt% NaCl solution, different types of damage exhibit distinctly different fluorescence response characteristics. Type A scratches, which only penetrate the surface coating, show enhanced fluorescence due to light scattering caused by BSPC molecule exposure and increased surface roughness; while Type B scratches, which penetrate to the metal substrate, show enhanced fluorescence due to the penetration of the corrosive medium into the Fe... 3+ Release occurs through the characteristic functional groups (carbonyl oxygen and ortho-phenolic hydroxyl oxygen) in the BSPC molecule and Fe. 3+ The specific chelation coordination effect leads to complete fluorescence quenching. This differentiated fluorescence response mechanism enables the coating to distinguish between surface damage and deep corrosion in real time and intuitively, providing a reliable guarantee for realizing the self-reporting function of intelligent anti-corrosion coatings. Figure 9 It can be seen that the scratch penetrating the metal substrate began to exhibit fluorescence quenching in the area after 3 hours, and complete quenching of the area was clearly observed after 5 hours. In contrast, the coating not exposed to the metal substrate showed fluorescence enhancement from 0 to 5 hours after the scratch appeared, demonstrating the potential of capsaicin derivative-modified epoxy resin fluorescent coating as a protective material for metal substrates. Specifically, the coating exhibits fluorescence enhancement when used as a protective material; however, when the coating is damaged and the metal substrate is exposed to the environment, the metal substrate corrodes and produces Fe... 3+ It coordinates with the characteristic functional groups of the coating, causing fluorescence quenching in the surface region of the coating, thereby achieving self-warning of corrosion of the metal substrate.

[0071] The capsaicin derivative-modified epoxy resin fluorescent coating of this invention exhibits excellent mechanical properties. Young's modulus reflects the stiffness of a material against elastic deformation; the Young's modulus of EP-3 is approximately 33% higher than that of the unmodified system. Elongation at break characterizes the toughness of the material, i.e., its ability to undergo plastic deformation; this value for EP-3 also increased from 6.85% to 7.62%. Surface hardness is good, with all modified samples reaching 4H, superior to the 3H of the control sample. These synergistic improvements in properties stem from the dual effect of the BSPC molecule. Its rigid benzene ring structure acts as a reinforcing unit, enhancing the coating stiffness and surface scratch resistance. Simultaneously, the introduction of BSPC as a monofunctional curing agent moderately regulates the crosslinking density, and its amide groups can form reversible hydrogen bond physical crosslinks in the network. These dynamic interaction points can absorb energy through dissociation and recombination under stress, thereby enhancing both rigidity and toughness.

[0072] In summary, this invention successfully developed a novel epoxy resin fluorescent coating based on the chemical modification of the capsaicin derivative BSPC. By introducing BSPC as a multifunctional curing agent into the classic epoxy-amine curing system, and through systematic optimization determining its optimal addition amount to be 3 mol%, a high-performance coating material integrating excellent mechanical properties, stable and durable fluorescence characteristics, and intelligent corrosion early warning function was successfully prepared. Particularly noteworthy is the excellent solubility of BSPC in polyetheramine D400, which eliminates the need for any organic solvents during the entire preparation process, demonstrating the environmental friendliness and economy of the process. This coating preparation process is stable and reliable, exhibiting outstanding performance and demonstrating enormous application potential and significant market value in cutting-edge fields such as intelligent corrosion protection for critical infrastructure and long-term structural health monitoring.

[0073] The above descriptions are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A capsaicin derivative-modified epoxy resin fluorescent coating, characterized in that, The raw material consists of epoxy resin, polyetheramine curing agent, and capsaicinamide derivative; the amino group molar number of the capsaicinamide derivative accounts for 1%-4% of the total amino group molar number of the capsaicinamide derivative and the polyetheramine curing agent; wherein, the structural formula of the capsaicinamide derivative is shown below: 。 2. The capsaicin derivative-modified epoxy resin fluorescent coating according to claim 1, characterized in that, The molar ratio of the epoxy group in the epoxy resin to the amino hydrogen in the raw material is 1:0.5~2, and the molar number of amino hydrogen in the raw material is the sum of the molar numbers of amino hydrogen in the polyether amine curing agent and the capsaicin amide derivative.

3. The capsaicin derivative-modified epoxy resin fluorescent coating according to claim 1, characterized in that, The polyetheramine curing agent is a polyetheramine with an average molecular weight of 200-600.

4. The capsaicin derivative-modified epoxy resin fluorescent coating according to claim 1, characterized in that, The epoxy resin is a bisphenol A type epoxy resin.

5. The method for preparing the capsaicin derivative modified epoxy resin fluorescent coating according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Dissolve capsaicin amide derivatives in polyether amine curing agents to obtain mixed curing agents; S2. Add epoxy resin to the mixed curing agent to obtain a resin mixture; S3. Cure the resin mixture at 75-85℃ for 2.5-3.5 hours to obtain the final product.

6. The preparation method according to claim 5, characterized in that, Step S2 also includes stirring and ultrasonic treatment of the resin mixture.

7. The application of the capsaicin derivative modified epoxy resin fluorescent coating according to any one of claims 1-4 in the preparation of protective materials for metal substrates.

8. The application according to claim 7, characterized in that, The metal substrate contains iron.

9. The application of the capsaicin derivative modified epoxy resin fluorescent coating according to any one of claims 1-4 in the preparation of intelligent anti-corrosion materials or corrosion monitoring sensor systems.

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