Flame-retardant and self-repairing wood epoxy coating, and preparation method and application thereof

Abstract

The application discloses a kind of fire-retardant and self-repairing wood epoxy coating and its preparation method and application, belong to epoxy resin technical field.The preparation method specifically includes the following steps: (1) vanillin, epoxy chloropropane and tetrabutylammonium bromide are uniformly mixed, reaction, cooling, dropwise addition NaOH aqueous solution, continue to react, wash, dry, precipitate, dry again, obtain biobased epoxy resin, standby;(2) methanol and hydrochloric acid are uniformly mixed, heated, condensation reflux, add gamma-aminopropyl triethoxysilane, reaction, cooling, add tetrahydrofuran, wash, vacuum drying, obtain cage polysilsesquioxane;(3) cage polysilsesquioxane is dissolved in organic solvent, add biobased epoxy resin, stir uniformly, stand, solidification, obtain.The application is constructed with imine bond epoxy resin with vanillin, realizes the self-repairing of epoxy resin and excellent flame-retardant performance.

Description

Technical Field

[0001] This invention relates to the field of epoxy resin technology, and more specifically to a flame-retardant and self-healing epoxy coating for wood, its preparation method, and its application. Background Technology

[0002] Natural wood has been used as a building material, fuel, and furniture because of its versatility, renewability, and aesthetic appeal. However, wood is flammable and poses a risk to assets and human safety.

[0003] Applying fire-retardant coatings to the surface of wood materials is a key method to improve their fire resistance. However, traditional petroleum-based epoxy resins have problems such as being non-renewable and causing environmental hazards.

[0004] Therefore, how to develop a new type of epoxy coating for wood is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a flame-retardant and self-healing epoxy coating for wood, its preparation method and application, so as to overcome the shortcomings of the prior art.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing a flame-retardant and self-healing epoxy coating for wood, specifically including the following steps:

[0008] (1) Mix vanillin, epichlorohydrin and tetrabutylammonium bromide, react, cool, add NaOH aqueous solution dropwise, continue the reaction, wash, dry, precipitate, dry again to obtain bio-based epoxy resin (VE), for later use;

[0009] (2) Mix methanol and hydrochloric acid, heat, reflux, add γ-aminopropyltriethoxysilane (KH-550), react, cool, add tetrahydrofuran, wash, and vacuum dry to obtain cage-type polysilsesquioxane (OA-POSS).

[0010] (3) Dissolve cage-type polysilsesquioxane in an organic solvent, add bio-based epoxy resin, stir evenly, let stand, and cure to obtain flame-retardant and self-healing wood epoxy coating (VE / OA-POSS).

[0011] Furthermore, in step (1) above, the mass fraction of the NaOH aqueous solution is 50 wt%; the mass ratio of vanillin, epichlorohydrin, tetrabutylammonium bromide and NaOH aqueous solution is 20:48.8:1:26.4.

[0012] The further beneficial effect of adopting the above is that vanillin is a derivative of wood lignin, which belongs to biomass raw materials. It is taken from wood and used for wood, thus realizing recycling.

[0013] Furthermore, in step (1) above, the reaction temperature is 80℃ and the time is 2h; the dropping time is 15min; the reaction continues at 16℃ for 3h.

[0014] Furthermore, in step (1) above, the washing reagent is deionized; the drying reagent is anhydrous magnesium sulfate; the precipitation reagent is petroleum ether; and the re-drying temperature is 80℃ and the time is 2h.

[0015] Furthermore, in step (2) above, the volume ratio of methanol, hydrochloric acid, γ-aminopropyltriethoxysilane and tetrahydrofuran is 100:15:15.2:200.

[0016] Furthermore, in step (2) above, the temperature is heated to 60°C; the reaction temperature is 90°C and the time is 18h; the washing reagent is anhydrous ethanol; and the vacuum drying temperature is 40°C.

[0017] Furthermore, in step (3) above, the organic solvent is methanol; the mass ratio of cage-type polysilsesquioxane, organic solvent and bio-based epoxy resin is 16:(80-160):100.

[0018] The further beneficial effect of the above method lies in constructing a thermosetting bio-based flame-retardant epoxy resin crosslinking system using bio-based epoxy resin (VE) and the curing agent cage-type polysilsesquioxane (OA-POSS). A small amount of methanol is used as a solvent, and after mixing evenly, the mixture is allowed to stand for later use. Each 100g of VE corresponds to 16g of OA-POSS (i.e., each 1g of VE requires 0.16g of OA-POSS). The volume of methanol is 5-10 times the mass of OA-POSS; for example, 16g of OA-POSS is added to 80-160mL of methanol.

[0019] Furthermore, in step (3) above, the stirring time is 30 min; the curing procedure is: 80℃ curing for 2 h, 120℃ curing for 4 h.

[0020] This invention also claims protection for a flame-retardant and self-healing epoxy coating for wood prepared by the above-described method.

[0021] This invention also claims protection for the application of a flame-retardant and self-healing epoxy coating for wood prepared by the above method in the protection of wood materials.

[0022] As can be seen from the above technical solution, compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] This invention constructs an epoxy resin containing imine bonds using vanillin, achieving self-healing and excellent flame-retardant properties of the epoxy resin. Attached Figure Description

[0024] Figure 1 The synthetic circuit diagram for VE / OA-POSS;

[0025] Figure 2 FTIR plots of VE(a) and VE / OA-POSS(b);

[0026] Figure 3 For VE 1 H NMR spectrum;

[0027] Figure 4 DSC curves of E-51 / DDM(a) and VE / OA-POSS(b) at heating rates of 5-25℃ / min, and ln(β / T) p 2 (c) and lnβ(d) with 1 / T p ×10 3 The fitted curve;

[0028] Figure 5 Three-dimensional microscopic images of the healing process of VE / OA-POSS at 65℃;

[0029] Figure 6 The TG curves (a) and DTG curves (b) for E-51 / DDM and VE / OA-POSS are shown.

[0030] Figure 7 Infrared thermal imaging of the wood surface with constant heating perpendicular to the back of the wood;

[0031] Figure 8 For simulated combustion testing of the wooden house model;

[0032] Figure 9 For E-51 / DDM and VE / OA-POSS, LOI values ​​and UL-94 ratings;

[0033] Figure 10 Real-time images of UL-94 vertical burning tests for E-51 / DDM(a) and VE / OA-POSS(b);

[0034] Figure 11 The graphs are cone calorimetric curves of epoxy resin wood coatings, including (a) HRR, (b) THR, (c) SPR, (d) TSP, (e) E-51 / DDM char graph, and (f) VE / OA-POSS char graph.

[0035] Figure 12Scanning electron microscope images of E-51 / DDM(a) and VE / OA-POSS(b) char residues after the CONE experiment, and elemental analysis of E-51 / DDM(c) and VE / OA-POSS(d) char residues after the CONE experiment;

[0036] Figure 13 Raman spectra of E-51 / DDM(a) and VE / OA-POSS(b) carbon residues after the CONE experiment;

[0037] Figure 14 X-ray electron spectroscopy (XPS) spectra of E-51 / DDM and VE / OA-POSS carbon residues after the CONE experiment are shown in the following figures: (a) XPS spectrum of E-51 / DDM carbon residue, (b) high-resolution C1s spectrum of E-51 / DDM carbon residue, (c) high-resolution N1s spectrum of E-51 / DDM carbon residue, (d) high-resolution O1s spectrum of E-51 / DDM carbon residue, (e) XPS spectrum of VE / OA-POSS carbon residue, (f) high-resolution C1s spectrum of VE / OA-POSS carbon residue, (g) high-resolution N1s spectrum of VE / OA-POSS carbon residue, (h) high-resolution O1s spectrum of VE / OA-POSS carbon residue, and (i) high-resolution Si2p spectrum of VE / OA-POSS carbon residue.

[0038] Figure 15 This is a schematic diagram of the flame-retardant mechanism of the VE / OA-POSS wood coating. Detailed Implementation

[0039] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Example 1

[0041] The preparation method of flame-retardant and self-healing epoxy coating for wood specifically includes the following steps:

[0042] (1) Preparation of bio-based epoxy resin (VE)

[0043] Vanillin, epichlorohydrin, and tetrabutylammonium bromide were added to a round-bottom flask equipped with a constant-pressure funnel and a magnetic stirrer at a mass ratio of 20:48.8:1, and reacted at 80°C for 2 hours. After cooling, 26.4 times the mass of tetrabutylammonium bromide in a 50wt% NaOH aqueous solution was added dropwise over 15 minutes, and the reaction was continued at 16°C for 3 hours. The mixture after the reaction was completed was repeatedly washed with deionized water to remove excess NaOH and water-soluble impurities. It was dried with anhydrous magnesium sulfate and precipitated with petroleum ether to remove excess epichlorohydrin and petroleum ether-soluble impurities. The precipitate was dried at 80°C for 2 hours to obtain a bio-based epoxy resin.

[0044] (2) Preparation of cage-type polysilsesquioxane (OA-POSS)

[0045] 100 mL of methanol and 15 mL of hydrochloric acid were added to a 250 mL three-necked round-bottom flask equipped with a magnetic stir bar, a dropping funnel, and a reflux condenser. The mixture was heated to 60 °C, refluxed, and then 15.2 mL of γ-aminopropyltriethoxysilane was added dropwise. The mixture was kept at 90 °C for 18 h. After cooling to room temperature, 200 mL of tetrahydrofuran was added, resulting in a white precipitate. The white precipitate was then washed with anhydrous ethanol and dried under vacuum at 40 °C to obtain cage-like polysilsesquioxane.

[0046] (3) Construction of thermosetting bio-based flame-retardant epoxy resin crosslinking system

[0047] Add 16g of cage-type polysilsesquioxane to 160mL of methanol and stir magnetically until completely dissolved to form a transparent solution. Slowly add the dissolved cage-type polysilsesquioxane solution to 100g of bio-based epoxy resin and stir mechanically for 30min until uniformly mixed. Let the mixture stand until the methanol completely evaporates, pour it into a mold, and cure at 80℃ for 2h and 120℃ for 4h to obtain a flame-retardant and self-healing wood epoxy coating.

[0048] Performance testing

[0049] 1 Introduction

[0050] In the context of green and ecological development, wood materials are highly favored due to their natural and environmentally friendly characteristics, but their flammability severely restricts their widespread application. Developing wood surface coatings with both flame-retardant and self-healing functions is of great significance for improving the safety and extending the service life of wood materials. However, traditional petroleum-based epoxy resins suffer from non-renewable and environmentally harmful issues, while vanillin, as a biomass derivative, possesses both benzene ring rigidity and abundant functional groups, making it an ideal epoxy resin precursor. The excellent performance of epoxy resins stems from their cross-linked network after curing, but this also makes them unrecyclable. Introducing reversible covalent imine bonds into the epoxy network is an effective way to solve this problem. Imine bonds are a common type of reversible covalent bond, obtained by the dehydration condensation of aldehyde and amino groups. Imine bonds not only undergo reversible exchange in multiple ways, but also do not require catalysts during bond exchange, and the activation energy is relatively low. Therefore, constructing epoxy resins containing imine bonds with vanillin to achieve self-healing and excellent flame-retardant properties has significant practical application value.

[0051] This chapter describes the preparation of vanillin-based epoxy resin VE using vanillin and epichlorohydrin as raw materials. VE was then cured with amino-cage-type polysilsesquioxane (OA-POSS) to successfully obtain a thermosetting resin VE / OA-POSS containing Schiff base bonds. Its flame-retardant effect was investigated using limiting oxygen index, vertical burning test (UL-94), cone calorimetry, and infrared thermography. The flame-retardant mechanism was revealed through microscopic characterization of char residue (SEM, EDS, and XPS) and Raman spectroscopy (LRS). The flame-retardant properties and self-healing properties of the thermosetting resin were investigated. The activation energy of different epoxy resin systems was calculated using differential scanning calorimetry (DSC) and compared with E-51 (DGEBA) / DDM. The preparation process, performance mechanism, and practical application effects were systematically studied, providing theoretical and technical support for the efficient protection of wood materials.

[0052] 2. Experimental Materials and Equipment

[0053] 2.1 Test Materials

[0054] The main experimental materials for flame-retardant and self-healing epoxy coatings for wood are shown in Table 1.

[0055] Table 1 Raw Materials and Sources

[0056]

[0057]

[0058] 2.2 Test Instruments and Equipment

[0059] The main experimental instruments and equipment for the preparation of flame-retardant and self-healing epoxy coatings for wood are shown in Table 2.

[0060] Table 2 Main Instruments and Equipment

[0061]

[0062] 3. Test methods (same as in Example 1)

[0063] 3.1 Preparation of Bio-based Epoxy Resin (VE)

[0064] The preparation principle of bio-based epoxy resin is as follows: Figure 1 As shown. Vanillin, epichlorohydrin, and tetrabutylammonium bromide were added to a round-bottom flask equipped with a constant-pressure funnel and a magnetic stirrer at a mass ratio of 20:48.8:1, and reacted at 80°C for 2 hours. After cooling, a 50 wt% NaOH aqueous solution was added dropwise over 15 minutes. The mass of the NaOH aqueous solution was 26.4 times that of the tetrabutylammonium bromide. The reaction was continued at 16°C for 3 hours. The resulting mixture was repeatedly washed with deionized water to remove excess NaOH and water-soluble impurities. The mixture was dried with anhydrous magnesium sulfate and precipitated with petroleum ether to remove excess epichlorohydrin and petroleum ether-soluble impurities. The precipitate was dried at 80°C for 2 hours to give pale yellow vitamin E, with a yield of approximately 67.2%.

[0065] 3.2 Preparation of the curing agent, cage-type polysilsesquioxane (OA-POSS)

[0066] Methanol (100 mL) and hydrochloric acid (15 mL) were added to a 250 mL three-necked round-bottom flask equipped with a magnetic stirrer, dropping funnel, and reflux condenser. The solution was heated to 60 °C, refluxed, and then γ-aminopropyltriethoxysilane (15.2 mL) was added dropwise. The mixture was kept at 90 °C for 18 h. After cooling to room temperature, 200 mL of tetrahydrofuran was added, resulting in a white precipitate. The precipitate was then washed with anhydrous ethanol and dried under vacuum at 40 °C to obtain a white OA-POSS powder with a yield of 33%.

[0067] 3.3 Construction of a thermosetting bio-based flame-retardant epoxy resin crosslinking system

[0068] Add 16g of cage-type polysilsesquioxane to 160mL of methanol and stir magnetically until completely dissolved to form a transparent solution. Slowly add the dissolved OA-POSS solution to 100g of VE resin and stir mechanically for 30min until uniformly mixed. Allow the mixture to stand until the methanol has completely evaporated. Pour into a mold and cure at 80℃ for 2h, then at 120℃ for 4h.

[0069] 3.4 Preparation of control group E-51(DGEBA) / DDM

[0070] For every 100g of E-51 (a commercial epoxy resin product containing bisphenol A diglycidyl ether, abbreviated as DGEBA), 25g of DDM is required (i.e., 0.25g of DDM is needed for every 1g of E-51). The weighed DDM is heated to a molten state at 90℃, and then slowly added to the E-51 resin. Mechanical stirring is performed for 30 minutes until the mixture is homogeneous, ensuring no unmelted DDM particles remain. The mixture is poured into a mold, pre-cured at 80℃ for 2 hours, and then cured at 120℃ for 4 hours.

[0071] 4. Characterization and Analysis

[0072] 4.1 Fourier Transform Infrared Spectroscopy (FTIR)

[0073] The structures of bio-based epoxy resin (VE) and cured resin (VE / OA-POSS) were analyzed using a WQF-510 Fourier transform infrared spectrometer. The resin was compressed into tablets with a flame retardant:potassium bromide (KBr) ratio of 1:100 and the tablets were prepared at 4000 to 400 cm⁻¹. -1 The infrared scan was performed within the range, with 32 scans and a resolution of 4.00 cm. -1 .

[0074] 4.2 Nuclear Magnetic Resonance (NMR) Test

[0075] The 1H NMR and 31NMR of bio-based epoxy resin (VE) were determined using an Ultrashied™ 400MHz nuclear magnetic resonance spectrometer. The samples were dissolved in deuterated heavy water and deuterated DMSO.

[0076] 4.3 Differential Scanning Calorimetry (DSC)

[0077] Differential scanning calorimetry (DSC214) was used to perform differential scanning calorimetry analysis on the epoxy coatings on wood (VE / OA-POSS and E-51 / DDM). The samples were heated from 60°C to 200°C at a heating rate of 10°C / min under N2 atmosphere.

[0078] 4.4 Self-healing performance

[0079] The self-healing performance analysis involved scratching wood epoxy coatings (VE / OA-POSS and E-51 / DDM) and then placing them in an oven at a specific temperature. Using a Keyence VHX-2000 ultra-depth-of-field 3D microscope system, 100mm × 100mm × 3mm samples with scratches were placed under a 3D microscope to observe the scratch repair process.

[0080] 4.5 Pencil hardness test and adhesion test

[0081] Pencil hardness testing of the wood epoxy coatings (VE / OA-POSS and E-51 / DDM) was performed using a QHQ-A pencil hardness tester (Zhejiang Airuipu Instrument Co., Ltd.) according to ASTM D3363-2005. Adhesion testing of the wood epoxy coatings (VE / OA-POSS and E-51 / DDM) was performed using a QFH-A cross-cut adhesion tester (Zhejiang Airuipu Instrument Co., Ltd.) according to ASTM D3359-09.

[0082] 4.6 Thermogravimetric Analysis (TG)

[0083] Under N2 atmosphere, 6-7 mg of wood epoxy coating (VE / OA-POSS and E-51 / DDM) was heated from 30℃ to 800℃ at a heating rate of 10℃ / min to obtain TGA and DTG curves.

[0084] 4.7 Infrared Thermal Imaging Test

[0085] By using an alcohol lamp to provide a continuous and stable heat input to the bottom of the wood epoxy coating (VE / OA-POSS and E-51 / DDM), the surface temperature changes were recorded using a handheld infrared thermometer (B256V infrared thermal imager).

[0086] 4.8 Wood Model Combustion Test

[0087] VE / OA-POSS, VAPD / EP, and the control group EP coating (500g / m²) 2 The coating was applied to a wooden house model, ignited using a butane spray gun, and the flame spread, self-extinguishing time, and charred area were recorded to compare the actual flame-retardant effect.

[0088] 4.9 Limiting Oxygen Index (LOI) Test and Vertical Burning Test (UL-94)

[0089] The limiting oxygen index (LOI) of epoxy-coated wood samples (VE / OA-POSS and E-51 / DDM) was tested according to ASTM D2863, with sample dimensions of 130 mm × 6.5 mm × 3 mm. The test data is the average of five samples. The vertical burning test was conducted according to ASTM D3801, with sample dimensions of 130 mm × 13 mm × 3 mm, to determine the UL-94 rating of the samples. The test data is the average of five samples.

[0090] 4.10 Cone Calorimetry Test

[0091] The epoxy coatings (VE / OA-POSS and E-51 / DDM) on wood were tested according to the international standard ISO 5660-1:2015, and their thermal radiation power was 50 kW / m². 2The sample size was 100mm × 100mm. To reduce the influence of external factors during the experiment, the sample was wrapped with tin foil except for the heated surface and placed in a stainless steel holder to prevent heat loss from the back of the sample. The test time was 400s. The test data included the heat release rate (HRR, kW / m³). 2 Peak heat release rate (pHRR, kW / m³) 2 Total heat release (THR, MJ / m³) 2 Smoke release rate (SPR, m) 2 / s), peak smoke release rate (m 2 / s), total smoke emissions (TSP, m 2 The data included CO2 release rate (CO2PR, g / s), peak CO2 release rate (pCO2PR, g / s), and average effective heat of combustion (mEHC, MJ / kg). In addition, the fire growth index (FGI, kW·m³) was also analyzed based on the above data. -2 ·s -1 Fire performance index (FPI, s / kW·m) -2 The calculation is performed using the flame retardant index (FRI) and the formula shown below.

[0092]

[0093] 4.11 Scanning Electron Microscopy – Elemental Analysis (SEM-EDS)

[0094] The microstructure of the samples was observed at room temperature with an accelerating voltage of 20 kV using a SIGMA HD scanning electron microscope from Zeiss AG, Germany. The elemental content of the wood epoxy coatings (VE / OA-POSS and E-51 / DDM) after cone calorimetry testing was analyzed by energy dispersive electron spectrometry.

[0095] 4.12 Raman Spectroscopy Test

[0096] Raman spectroscopy analysis of the char residue after cone calorimetry testing of wood epoxy coatings (VE / OA-POSS and E-51 / DDM) was performed using a Thermo Scientific DXR 3Xi spectrometer, with a spectral range of 500-3000 cm⁻¹.

[0097] 4.13 X-ray electron spectroscopy (XPS)

[0098] X-ray photoelectron spectroscopy (XPS) was performed using a Skal AB250XI electron spectrometer (Thermo Fisher Scientific, USA) to analyze the composition of the carbon slag. The emission current was 10 MHz and the voltage was 15 kV.

[0099] 5 Results and Discussion

[0100] 5.1 Fourier Transform Infrared Spectroscopy (FTIR)

[0101] The chemical structures of VE, vanillin, ECH, and VE / OA-POSS were characterized by FTIR. Figure 2 In (a), it can be observed that for VE, the epoxy groups belonging to ECH are at 908 cm⁻¹. -1 An absorption peak appeared at 3500-3200 cm⁻¹, while the -OH group belonging to vanillin showed an absorption peak at 3500-3200 cm⁻¹. -1 The absorption peak disappeared at that point. The results indicate that vanillin was completely converted into the epoxy monomer VE. Figure 2 In (b), it can be observed that VE is at 908 cm. -1 The absorption peak of the epoxy group disappears, while that of VE / OA-POSS is at 1640 cm⁻¹. -1 An absorption peak appeared at the C=N group. The ring-opening reaction of the epoxy group on VE with -NH2 indicates that the synthesis of VE / OA-POSS was successful. 5.2 Nuclear Magnetic Resonance Analysis (NMR)

[0102] VE 1 H NMR spectrum as follows Figure 3 As shown in the figure, the single peak at 9.8 ppm belongs to the H1 proton of the acetaldehyde group, the peaks at 7.2-7.5 ppm belong to the H2-H4 protons on the benzene ring, and the peaks at 3.3-3.6 ppm represent the H8-H10 protons of the epoxy group. These results indicate that VE was successfully prepared.

[0103] 5.3 Differential Scanning Calorimetry (DSC)

[0104] The curing kinetics of the E-51 / DDM and VE / OA-POSS systems at different heating rates were evaluated using DSC testing. Figure 4The DSC curves of E-51 / DDM and VE / OA-POSS at heating rates of 5-25℃ / min shown in (a,b) clearly show that both systems exhibit only one exothermic peak. This exothermic peak is attributed to the heat release during epoxy resin curing, indicating that the curing reaction (ring-opening reaction between epoxy groups and active hydrogen) occurs at the corresponding temperature. Furthermore, the exothermic peak temperature (Tp) gradually increases with the increase of the exothermic rate. This may be because at lower heating rates, the chemically reacting groups have more time to complete curing at lower temperatures. However, it can be seen that the Tp of VE / OA-POSS is lower than that of E-51 / DDM at the same heating rate, indicating that OA-POSS has stronger reactivity than DDM in the curing reaction. This also suggests that adding OA-POSS to the EP system can improve the curing activity of the matrix. The activation energy (Ea) represents the reactivity of EP during the curing process and is an important parameter in curing kinetics. The corresponding activation energy can be calculated using the Kissinger (Equation 1) and Ozawa (Equation 2) methods.

[0105]

[0106] Where R represents the ideal gas constant, with a value of 8.314 J / (mol K), A is the prefactor, and β is the heating rate. Specifically, it can be determined according to... Figure 4 ln(β / T) in (c) p 2 ) and 1 / T p ×10 3 and Figure 4 lnβ and 1 / T in (d) p ×10 3 The slope of the fitted curve is used to calculate the corresponding activation energy. In the Kissinger method, the E of E-51 / DDM is... a The value is 66.51 kJ / mol, while the E of VE / OA-POSS is... a The value is 58.19 kJ / mol. In the Ozawa method, the E-51 / DDM... a The value is 63.71 kJ / mol, while the E of VE / OA-POSS a The value is 45.51 kJ / mol. This indicates that OA-POSS can participate in the curing reaction and promote the crosslinking of the VE system. This phenomenon is attributed to the functional groups in OA-POSS; the active hydrogen in the secondary amine group can act as a proton donor and catalyze the ring-opening reaction of the epoxy group. Furthermore, the hydrogen bonds formed between the active hydrogen atoms in OA-POSS and the oxygen atoms in the epoxide group can increase the polarization of the epoxide ring, further promoting the ring-opening reaction of the epoxy.

[0107] 5.4 Self-healing performance analysis

[0108] To investigate the self-healing properties of the VE / OA-POSS coating, a scratch healing experiment was conducted on wood samples coated with the coating. The scratched samples were placed in a 65℃ vacuum oven, and the healing process was observed in real-time using a three-dimensional microscope. The experimental results showed that ( Figure 5 Under conditions without external force intervention, the coating exhibits remarkable self-healing efficiency: with an initial scratch width of 7550 μm, a 100% healing rate can be achieved in just 15 minutes. This is mainly attributed to the reversible reconstruction characteristics of dynamic C=N bonds in the coating. Imine bonds (C=N) break and recombine under thermal excitation conditions, prompting the polymer network structure to rearrange, thereby rapidly filling the microscopic defects in the scratch area.

[0109] 5.5 Pencil Hardness and Adhesion Analysis

[0110] The physical properties of the E-51 / DDM and VE / OA-POSS coatings are shown in Table 3. Experimental results show that the VE / OA-POSS coating achieves a pencil hardness of 6H, significantly higher than the pure EP coating (2H). This is attributed to the rigid support of the aromatic structure and the high bond energy of the Si-O bonds in the VE / OA-POSS coating, which synergistically enhance the coating's surface scratch resistance. In the adhesion test, the VE / OA-POSS coating achieves an adhesion rating of 4B. Its excellent performance can be attributed to the covalent cross-linking network formed between the abundant epoxy groups in VE and the resin matrix, effectively improving the interfacial bonding strength.

[0111] Table 3 Physical properties of E-51 / DDM and VE / OA-POSS wood coatings

[0112] Sample group Pencil hardness Adhesion E-51 / DDM 2H 3B VE / OA-POSS 6H 4B

[0113] 5.6 Thermogravimetric Analysis (TG)

[0114] Thermal stability is an essential requirement for the application of thermosetting materials. The thermal stability of modified epoxy resins under nitrogen atmosphere was analyzed using thermogravimetric analysis (TGA). Figure 6 The TGA and DTG curves of E-51 / DDM and VE / OA-POSS are shown in Table 4, with specific thermal decomposition data. The results indicate that the TGA curves of E-51 / DDM and VE / OA-POSS exhibit a two-step decomposition process under nitrogen atmosphere. Before 150℃, the main decomposition process of E-51 / DDM and VE / OA-POSS is almost unaffected, and their TGA curves are essentially identical. This is due to the thermal decomposition of the EP chain. 5％The temperatures were 277.1℃ and 189.7℃, respectively, indicating that the addition of Schiff base bonds reduced the thermal stability of the epoxy resin. For EP, the first decomposition process was attributed to the thermal decomposition of the EP chain itself, while the second process was mainly related to the further thermal oxidative decomposition of unstable coke residue at high temperatures. It was found that the char residue of VE / OA-POSS at 700℃ was higher than that of E-51 / DDM, increasing from 22.6% to 39.3%, indicating that VE epoxy resin can effectively promote its char formation performance.

[0115] Table 4 Thermal decomposition parameters of E-51 / DDM and VE / OA-POSS under nitrogen atmosphere

[0116] Sample <![CDATA[T 5％ (℃)]]> <![CDATA[T max (℃)]]> Residue at 700℃ (wt.%) E-51 / DDM 277.1 368.6 22.6 VE / OA-POSS 189.7 271.1 39.3

[0117] 5.7 Infrared Thermal Imaging Analysis

[0118] To systematically evaluate the thermal protection performance of the coatings, this study dynamically monitored the heat transfer behavior of E-51 / DDM and VE / OA-POSS wood under standard heating conditions using infrared thermal imaging technology. Figure 7 As shown, the substrate back surface temperature of the E-51 / DDM coated sample exhibits a sharp upward trend, rapidly changing from a low-temperature blue (approximately 28.2℃) to a high-temperature red (114.2℃) within 40 seconds. In contrast, the VE / OA-POSS coated sample demonstrates a significant gradual temperature rise, with a noticeably slower color gradient, directly reflecting the superior thermal insulation performance of the modified coating. In the initial stage of combustion (0-20s), the back temperature of the E-51 / DDM coated sample reaches 64.4℃, while the VE / OA-POSS coating only reaches 43.5℃, a temperature difference of 1.2 times. The experimental results indicate that VE / OA-POSS not only prolongs the thermal decomposition time of the coating but also significantly improves the fire safety of the wood substrate by constructing a multi-scale thermal insulation barrier.

[0119] 5.8 Combustion Test Analysis of Wood Model Based on Flame-Retardant Modified Epoxy Coating with Dynamic Bonds

[0120] To systematically evaluate the practical application effectiveness of flame-retardant coatings, this study quantitatively analyzed the flame-retardant performance of three wood models (EP-wood, VAPD-wood, and VE-wood) through simulated combustion experiments (e.g., Figure 8(As shown). Experimental data shows that the unmodified EP-wood model ignited rapidly after ignition, forming a bright flame within 10 seconds and exhibiting a rapid spread trend. By 130 seconds, the roof collapsed and the main structure was completely burned, indicating its extremely high flammability. In contrast, the flame-retardant modified VAPD-wood and VE-wood models showed significant flame-retardant advantages. In the test of continuous ignition with a butane torch for 10 seconds, both modified models only experienced localized combustion; when the ignition source was removed, the combustion process terminated spontaneously, forming a 33.4 cm flame in the roof area respectively. 2 and 38.86cm 2 The carbonized layer. It is worth noting that in the second ignition test, after burning for 450 seconds, the overall structure of the VAPD-wood model remained intact, while the wall structure of the VE-wood model did not collapse after burning for 380 seconds.

[0121] The improved flame-retardant properties can be attributed to the flame-retardant mechanism formed after epoxy resin modification: in the initial stage of combustion, the epoxy resin coating can undergo rapid thermal decomposition, forming a dense charred protective layer on the wood surface. This physical barrier effectively blocks heat transfer and oxygen supply, thereby inhibiting the spread of flames and ultimately achieving a significant optimization of the flame-retardant performance of the wooden model.

[0122] 5.9 Limiting Oxygen Index (LOI) Analysis and Vertical Burning Analysis (UL-94)

[0123] The flame retardant properties of wood epoxy coatings treated with different methods were tested using limiting oxygen index and vertical burning analysis. Figure 9 The limiting oxygen index (LOI) and vertical flammability rating (LHR) of the commercial epoxy resin system E-51 / DDM and the Schiff base-containing epoxy resin system VE / OA-POSS were measured. During testing, pure epoxy resin (EP) was found to be highly flammable with severe dripping, exhibiting an LOI of only 25.8% and failing the UL-94 test. Because EP / DDM is a flammable material, its combustion produces relatively little black smoke and char residue. This is attributed to the flammability of both wood and commercial epoxy resin, leading to minimal black smoke and dripping during combustion. However, the flame retardancy of the wood-based epoxy coating in the VE / OA-POSS system was significantly improved. The LOI of VE / OA-POSS increased to 33.1%. This is because the silicon element present in VE / OA-POSS promotes the char residue of EP during combustion, thereby enhancing the flame retardancy of the epoxy resin.

[0124] The combustion behavior of the commercial epoxy resin system E-51 / DDM and the Schiff base-containing epoxy resin system VE / OA-POSS during the UL-94 test was recorded and displayed. Figure 10In the first ignition, E-51 / DDM continued to burn. For VE / OA-POSS, the sample self-extinguished 18 seconds after the first ignition, released a small amount of white smoke upon the second ignition, and self-extinguished 9 seconds after being removed from the flame source. VE / OA-POSS achieved a V-0 rating.

[0125] 5.10 Cone Calorimetry (CONE)

[0126] The combustion behavior of wood-based epoxy coatings was tested using a cone calorimeter to simulate a real fire, yielding important experimental results. Table 5 shows that the ignition time of the wood-based epoxy coating containing Schiff base bonds (VE / OA-POSS) was prolonged to varying degrees, with the TTI (Time to Ignition) of the VE / OA-POSS wood-based epoxy coating being 29 seconds longer than that of the E-51 / DDM control group. Heat release rate (HRR) and total heat release (THR) are considered the most important parameters in flame research. Figure 11 In Figures (a, b) and Table 5, the pHRRs of E-51 / DDM and VE / OA-POSS were 414.50 and 265.12 kW / m³, respectively. 2 Compared to the control group E-51 / DDM, the pHRR of the wood-based epoxy coating decreased by 36.0%. HRR curve observation showed that the curve had only one peak, indicating that this stage was mainly flaming combustion, with heat release concentrated in this phase. The exothermic peak of VE / OA-POSS was reduced and delayed to varying degrees. Meanwhile, THR increased with increasing combustion time, with THRs of 30.02 and 17.72 MJ / m² for E-51 / DDM and VE / OA-POSS, respectively. 2 The VE / OA-POSS ratio was reduced by 40.9% compared to the control group E-51 / DDM.

[0127] FGI represents the flame retardancy of the composite material, while FPI represents the flashover time. Composite materials with low FGI and high FPI exhibit stronger flame retardancy and a slower flame development trend. Data in Table 5 shows that E-51 / DDM has an FGI of 4.18 and an FPI of 0.10, while VE / OA-POSS has an FGI of 2.08 (excellent) and an FPI of 0.27, indicating that the heat release of the bio-based epoxy resin coating VE / OA-POSS is delayed to varying degrees, demonstrating better fire resistance.

[0128] The generation, composition, and toxic release of smoke are another important hazard factor in real fires. For example... Figure 11Tables (c, d) and Table 5 show the smoke release rate (SPR) and total smoke release (TSP) of the E-51 / DDM and VE / OA-POSS wood-based epoxy coatings. The peak values ​​of the smoke release rate show a unimodal or bimodal trend, indicating that the wood-based epoxy coating material contains both combustible and non-combustible smoke generated during combustion. The bio-based epoxy resin VE exhibits a certain smoke suppression ability. Its pSPR and TSP decreased by 86.6% and 81.2% respectively compared to E-51 / DDM. Figure 11 Figure (e,f) shows the cone-shaped calorimetric char residue of E-51 / DDM and VE / OA-POSS. The figure shows that the commercial epoxy resin wood coating produces less char residue upon combustion, with the residue consisting of lightweight and low-content ash. In contrast, the bio-based wood epoxy coating after flame retardant treatment forms a dense char residue with high strength and resistance to damage. This indicates that the introduction of cage-like polysilsesquioxanes and imine bonds effectively promotes the char formation of the wood epoxy coating, effectively preventing the entry of heat and oxygen. Silicon can form structures such as Si-C and silicon dioxide, enhancing the stability of the expanded char layer and thus protecting the base wood from further combustion. Therefore, it can be inferred that its flame retardant mechanism conforms to the gas-phase, condensation phase mechanism, exhibiting a dense structure that acts as a physical protective layer, hindering the transfer of heat and combustibles and slowing down the ablation of the internal base material.

[0129] Table 5. Conical calorimetry test data for epoxy resin wood coatings

[0130]

[0131] 5.11 Scanning Electron Microscopy-Elemental Analysis of Residual Carbon (SEM-EDS)

[0132] The microstructure of char residue on the surface of the thermosetting resin was further analyzed using scanning electron microscopy, and the flame-retardant mechanism in the condensed phase was further explored. Figure 12 As shown in the images, E51 / DDM exhibits numerous pores and cracks, complicating the dissipation of heat and gases during combustion. In contrast, the residual char structure of VE / OA-POSS displays a continuous and dense characteristic, effectively preventing the release of combustible gases and inhibiting heat transfer to the internal matrix. ]Therefore, the dense char layer of VE / OA-POSS exhibits excellent flame-retardant properties. This may be because Schiff base bonds promote cross-linking of the char layer, and the presence of silicon in VE / OA-POSS generates substances such as Si-C and silicon dioxide, slowing down the combustion rate. The intact char layer prevents the transfer of decomposition products and heat, further protecting the underlying substrate from ignition, thus improving the fire safety of EP in practical applications. EDS results further indicate that the wood-based epoxy coating after VE / OA-POSS combustion contains C, N, O, and Si elements, which can prevent further combustion of the substrate wood material, playing a role in condensed phase analysis. 5.12 Residual Char Raman Spectroscopy Analysis

[0133] Figure 13 The Raman spectrum of the epoxy wood coating after combustion is shown. I0 in this spectrum... D / I G The ratio reflects the degree of graphitization, I D / I G A lower value indicates a more symmetrical structure. At 1350cm -1 Two independent peaks can be seen at 1600 cm⁻¹, which is related to the D band. -1 The location is related to the G band. The I of VE / OA-POSS D / I G (1.86) lower than E-51 / DDM's I D / I G (2.54) indicates that the char layer formed by VE / OA-POSS during combustion is more regular.

[0134] 5.13 X-ray electron spectroscopy (XPS) analysis of carbon residue

[0135] The elemental composition of the char residue after combustion of E-51 / DDM and VE / OA-POSS epoxy resin coatings was analyzed using XPS, such as... Figure 14 As shown. From Figure 14 As can be seen from (a,e), E-51 / DDM contains only C, O and N, while VE / OA-POSS contains Si in addition to C, O and N. Figure 14 The high-resolution XPS spectra of C1s, N1s, and O1s of E-51 / DDM are shown in Figures B and C, respectively. The C1s spectrum exhibits three main peaks at 284.8 eV (CC / CH), 285.6 eV (CO), and 289.2 eV (OC=O). The two peaks in the N1s spectrum at 399.9 and 405.6 eV are attributed to pyridine nitrogen and pyrrole nitrogen, respectively. Furthermore, the O1s peak shows signals for C=O (532.4 eV), COC / C-OH (533.4 eV), and CO (533.8 eV). Figure 14Figure 1 (fi) shows the high-resolution XPS spectra of C1s, N1s, O1s, and Si2p of VE / OA-POSS. The C1s spectrum has three main peaks at 284.8 eV (CC / CH), 285.6 eV (CO / CN), and 289.2 eV (C=O). The two peaks at 400.8 and 407.2 eV in the N1s spectrum are attributed to NH and CN, respectively. In addition, the O1s peak shows C=O (532.5 eV) and COC / C-OH (533.8 eV) signals. The Si2p spectrum consists of three peaks with binding energies of 101.7, 102.3, and 103.1 eV, corresponding to Si-C, Si-O, and silicon dioxide, respectively. All of the above indicate that VE / OA-POSS helps the epoxy resin to dehydrate and carbonize during combustion, generating a silica protective carbon layer to prevent further combustion. At the same time, the Schiff base in the VE / OA-POSS structure can promote the carbonization of the epoxy resin.

[0136] 5.14 Flame Retardant Mechanism

[0137] A schematic diagram of the flame retardant mechanism of VAPDs / EP is shown below. Figure 15 As shown, the summary is as follows:

[0138] (1) The high carbon residue of the VE / OA-POSS system is the result of the synergistic effect of Schiff base bond carbonization and siloxane-assisted carbonization. This layer, composed of strong, highly interconnected carbon, plays an effective shielding role, hindering the transfer of heat and matter.

[0139] (2) Due to the cross-linking structure formed by the Schiff base groups, the char residue in the flame-retardant epoxy resin exhibits a robust structure with increasing volume. This structure can serve as a thermally insulating protective layer during combustion because it forms a carbon layer. Furthermore, it can reduce the level of combustible gases, leading to the generation of NH3 in the gas phase, ultimately delaying the combustion process of the material.

[0140] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a flame-retardant and self-healing epoxy coating for wood, characterized in that, Specifically, the following steps are included: (1) Mix vanillin, epichlorohydrin and tetrabutylammonium bromide, react, cool, add NaOH aqueous solution dropwise, continue the reaction, wash, dry, precipitate, dry again to obtain bio-based epoxy resin for later use; The NaOH aqueous solution has a mass fraction of 50 wt%; the mass ratio of vanillin, epichlorohydrin, tetrabutylammonium bromide, and NaOH aqueous solution is 20:48.8:1:26.

4. (2) Mix methanol and hydrochloric acid, heat, reflux, add γ-aminopropyltriethoxysilane, react, cool, add tetrahydrofuran, wash, and vacuum dry to obtain cage-type polysilsesquioxane. The volume ratio of methanol, hydrochloric acid, γ-aminopropyltriethoxysilane and tetrahydrofuran is 100:15:15.2:

200. (3) Dissolve cage-type polysilsesquioxane in an organic solvent, add bio-based epoxy resin, stir evenly, let stand, and cure to obtain the flame-retardant and self-healing wood epoxy coating. The organic solvent is methanol; the mass ratio of the cage-type polysilsesquioxane, the organic solvent, and the bio-based epoxy resin is 16:(80-160):

100.

2. The method for preparing a flame-retardant and self-healing epoxy coating for wood according to claim 1, characterized in that, In step (1), the reaction temperature is 80℃ and the time is 2h; the dropping time is 15min; the temperature for the continued reaction is 16℃ and the time is 3h.

3. The method for preparing a flame-retardant and self-healing epoxy coating for wood according to claim 1, characterized in that, In step (1), the washing reagent is deionized water; the drying reagent is anhydrous magnesium sulfate; the precipitation reagent is petroleum ether; and the re-drying temperature is 80°C and the time is 2 hours.

4. The method for preparing a flame-retardant and self-healing epoxy coating for wood according to claim 1, characterized in that, In step (2), the temperature is heated to 60°C; the reaction temperature is 90°C and the time is 18h; the washing reagent is anhydrous ethanol; the vacuum drying temperature is 40°C.

5. The method for preparing a flame-retardant and self-healing epoxy coating for wood according to claim 1, characterized in that, In step (3), the stirring time is 30 min; the curing procedure is: 80℃ curing for 2 h, 120℃ curing for 4 h.

6. A flame-retardant and self-healing epoxy coating for wood prepared by the method described in any one of claims 1-5.

7. The application of a flame-retardant and self-healing epoxy coating for wood prepared by any one of claims 1-5 in the protection of wood materials.

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