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

Abstract

The invention discloses a flame-retardant and self-repairing wood epoxy coating as well as a preparation method and application thereof, and belongs to the technical field of epoxy resin. The preparation method specifically comprises the following steps: (1) uniformly mixing vanillin, epichlorohydrin and tetrabutylammonium bromide, reacting, cooling, dropwise adding a NaOH aqueous solution, continuously reacting, washing, drying, precipitating and drying again to obtain bio-based epoxy resin for later use; (2) uniformly mixing methanol and hydrochloric acid, heating, carrying out condensation reflux, adding gamma-aminopropyltriethoxysilane, reacting, cooling, adding tetrahydrofuran, washing and carrying out vacuum drying to obtain polyhedral oligomeric silsesquioxane; and (3) dissolving polyhedral oligomeric silsesquioxane in the organic solvent, adding the bio-based epoxy resin, uniformly stirring, standing and curing to obtain the composite material. According to the invention, vanillin is used for constructing the epoxy resin containing imine bonds, so that the self-repairing and excellent flame-retardant properties of the epoxy resin are realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of epoxy resin, more particularly to a flame-retardant and self-repairing wood epoxy coating and a preparation method and application thereof. BACKGROUND

[0002] Natural wood has been used in construction materials, fuel, and furniture making due to its versatility, renewability, and aesthetic appeal. However, wood is easily flammable, posing a risk to assets and human safety.

[0003] Coating fireproof paint on the surface of wood materials is a key means to improve their fireproof performance. However, traditional petroleum-based epoxy resins have problems such as non-renewability and environmental hazards.

[0004] Therefore, how to develop a new type of wood epoxy coating is a problem that those skilled in the art need to solve. SUMMARY

[0005] Therefore, the purpose of the present application is to provide a flame-retardant and self-repairing wood epoxy coating and a preparation method and application thereof to solve the problems in the prior art.

[0006] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0007] A preparation method of a flame-retardant and self-repairing wood epoxy coating, specifically comprising the following steps:

[0008] (1) uniformly mix vanillin, epichlorohydrin and tetrabutylammonium bromide, react, cool, add NaOH aqueous solution, continue to react, wash, dry, precipitate, dry again, to obtain a bio-based epoxy resin (VE) for standby;

[0009] (2) uniformly mix methanol and hydrochloric acid, heat, condense and reflux, add gamma-aminopropyl triethoxysilane (KH-550), react, cool, add tetrahydrofuran, wash, vacuum dry, to obtain a cage-shaped polyhedral oligomeric silsesquioxane (OA-POSS);

[0010] (3) dissolve the cage-shaped polyhedral oligomeric silsesquioxane in an organic solvent, add the bio-based epoxy resin, stir uniformly, stand, and cure to obtain the flame-retardant and self-repairing wood epoxy coating (VE / OA-POSS).

[0011] Further, in the above step (1), the mass fraction of the NaOH aqueous solution is 50wt%; 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 the above is that the vanillin is derived from a wood lignin derivative, which is a biomass raw material, taken from wood and used for wood, realizing recycling.

[0013] Further, in the above step (1), the reaction temperature is 80 DEG C, and the reaction time is 2h; the dropping time is 15min; the continued reaction temperature is 16 DEG C, and the continued reaction time is 3h.

[0014] Further, in the above step (1), the washing reagent is deionized water; the drying reagent is anhydrous magnesium sulfate; the precipitating reagent is petroleum ether; and the re-drying temperature is 80 DEG C, and the re-drying time is 2h.

[0015] Further, in the above step (2), the volume ratio of methanol, hydrochloric acid, gamma-aminopropyl triethoxysilane and tetrahydrofuran is 100:15:15.2:200.

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

[0017] Further, in the above step (3), the organic solvent is methanol; and 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 is that a bio-based epoxy resin (VE) and a curing agent cage-type polysilsesquioxane (OA-POSS) are used to construct a thermosetting bio-based flame-retardant epoxy resin crosslinking system, a small amount of methanol is used as a solvent, and after uniform mixing, the mixture is left to stand for use, 16g of OA-POSS is used for every 100g of VE (i.e. 0.16g of OA-POSS is required for every 1g of VE). The volume of methanol is 5-10 times the mass of OA-POSS, for example, 80-160mL of methanol is added to 16g of OA-POSS.

[0019] Further, in the above step (3), the stirring time is 30min; and the curing procedure is as follows: 80 DEG C for 2h, and 120 DEG C for 4h.

[0020] The application also protects a flame-retardant and self-repairing wood epoxy coating prepared by the above preparation method.

[0021] The application also protects the application of a flame-retardant and self-repairing wood epoxy coating prepared by the above preparation method in wood material protection.

[0022] According to the above technical solution, compared with the prior art, the beneficial effects of the application are as follows:

[0023] The present application realizes self-repair and excellent flame retardant performance of the epoxy resin by constructing the epoxy resin containing imine bond with vanillin. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 Synthetic scheme for VE / OA-POSS;

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

[0026] Figure 3 HNMR spectra for VE; 1

[0027] Figure 4 DSC curves for 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) versus 1 / T p × 10 3

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

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

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

[0031] Figure 8 Simulated burning test of a wooden house model;

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

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

[0034] Figure 11 Epoxy resin wood coating cone calorimeter curve diagram, wherein (a) HRR, (b) THR, (c) SPR, (d) TSP, (e) E-51 / DDM residual carbon map, (f) VE / OA-POSS residual carbon map;

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

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

[0037] Figure 14 X-ray photoelectron spectroscopy spectra of E-51 / DDM and VE / OA-POSS char residues after CONE test, wherein (a) XPS spectra of E-51 / DDM char residue, (b) high resolution C1s spectra of E-51 / DDM char residue, (c) high resolution N1s spectra of E-51 / DDM char residue, (d) high resolution O1s spectra of E-51 / DDM char residue, (e) XPS spectra of VE / OA-POSS char residue, (f) high resolution C1s spectra of VE / OA-POSS char residue, (g) high resolution N1s spectra of VE / OA-POSS char residue, (h) high resolution O1s spectra of VE / OA-POSS char residue, (i) high resolution Si2p spectra of VE / OA-POSS char residue;

[0038] Figure 15 Schematic diagram of flame retardant mechanism of VE / OA-POSS wood coating. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present application will be described below in a clear and complete manner. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without any creative work are within the scope of protection of the present application.

[0040] Embodiment 1

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

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

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

[0044] (2) Preparation of cage polyhedral oligomeric silsesquioxane (OA-POSS)

[0045] In a 250mL three-necked round-bottom flask equipped with a magnetic stirring rod, a dropping funnel and a reflux condenser, 100mL of methanol and 15mL of hydrochloric acid were added, heated to 60°C, and then 15.2mL of γ-aminopropyl triethoxysilane was added dropwise and kept at 90°C for 18h; after cooling to room temperature, 200mL of tetrahydrofuran was added to produce a white precipitate; then, the white precipitate was washed with anhydrous ethanol and vacuum dried at 40°C to obtain cage polyhedral oligomeric silsesquioxane;

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

[0047] 16g of cage polyhedral oligomeric silsesquioxane was added to 160mL of methanol and magnetically stirred until completely dissolved to form a transparent solution; the dissolved cage polyhedral oligomeric silsesquioxane solution was slowly added to 100g of bio-based epoxy resin and mechanically stirred for 30min until uniformly mixed; the mixed system was left to stand until the methanol completely evaporated, poured into a mold, and cured at 80°C for 2h and at 120°C for 4h to obtain a flame-retardant and self-repairing wood epoxy coating.

[0048] Performance test

[0049] 1 Introduction

[0050] Under the background of green ecological development, wood materials are favored due to their natural and environmental characteristics, but their flammability seriously restricts their wide application. Developing wood surface coating with both flame retardant and self-repairing functions is of great significance to improve the safety and prolong the service life of wood materials. However, traditional petroleum-based epoxy resins have problems such as non-renewable and environmental hazards, while vanillin, as a biomass derivative, has both benzene ring rigidity and rich functional groups, making it an ideal precursor of epoxy resin. The excellent performance of epoxy resin is derived from its cross-linked network after curing, but this also leads to its inability to be recycled. Introducing reversible covalent bonds, imine bonds, into the epoxy network is an effective method to solve this problem. Imine bond is a common reversible covalent bond, which can be obtained by dehydration condensation of aldehyde group and amino group. Imine bond not only has multiple ways of reversible exchange, but also does not require catalysts when exchanging, and the activation energy is relatively low. Therefore, it has important practical application value to construct epoxy resin containing imine bond with vanillin, realizing the self-repairing and excellent flame retardant performance of epoxy resin.

[0051] In this chapter, vanillin-based epoxy resin VE was prepared from vanillin and epichlorohydrin, and then cured with amino cage-like polyhedral oligomeric silsesquioxane (OA-POSS), successfully obtaining a thermosetting resin VE / OA-POSS containing Schiff base bond. The flame retardant effect was explored by limiting oxygen index, vertical burning test (UL-94), cone calorimeter test (Cone), and infrared thermal imaging. The flame retardant mechanism was revealed by residual carbon micro-characterization (SEM, EDS and XPS) and Raman spectroscopy (LRS). The flame retardant performance and self-repairing of the thermosetting resin were explored. The activation energy of different epoxy resin systems was calculated by differential scanning calorimetry (DSC), and compared with E-51 (DGEBA) / DDM. The preparation process, performance mechanism and practical application effect were systematically studied, providing theoretical and technical support for efficient protection of wood materials.

[0052] 2 Test materials and instruments and equipment

[0053] 2.1 Test materials

[0054] The main experimental raw materials of the flame-retardant and self-repairing wood epoxy coating 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-repairing wood epoxy coating are shown in Table 2.

[0060] Table 2 Main instruments and equipment

[0061]

[0062] 3 Test method (same as Example 1)

[0063] 3.1 Preparation of bio-based epoxy resin (VE)

[0064] The principle of the preparation of bio-based epoxy resin is shown in Figure 1 In a round-bottom flask equipped with a constant pressure funnel and a magnetic stirrer, vanillin, epichlorohydrin and tetrabutylammonium bromide were added in a mass ratio of 20:48.8:1, and reacted at 80°C for 2h. After cooling, 50wt% NaOH aqueous solution was added dropwise within 15min, the mass of NaOH aqueous solution was 26.4 times that of tetrabutylammonium bromide, and the reaction was continued at 16°C for 3h. The mixture after reaction was washed repeatedly with deionized water to remove excess NaOH and water-soluble impurities. Dried with anhydrous magnesium sulfate, and precipitated with petroleum ether to remove excess epichlorohydrin and petroleum ether-soluble impurities. The obtained precipitate was dried at 80°C for 2h to obtain a light yellow VE with a yield of about 67.2%.

[0065] 3.2 Preparation of cage-shaped polyhedral oligomeric silsesquioxane (OA-POSS) as curing agent

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

[0067] 3.3 Construction of thermal curing bio-based flame-retardant epoxy resin crosslinking system

[0068] 16g of cage-shaped polyhedral oligomeric silsesquioxane was added to 160mL of methanol and magnetically stirred until completely dissolved to form a transparent solution. The dissolved OA-POSS solution was slowly added to 100g of VE resin, and mechanically stirred for 30min to mix uniformly. The mixed system was left to stand until the methanol completely evaporated. Pour into a mold, cure at 80°C for 2h, and cure at 120°C for 4h.

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

[0070] Each 100 g E-51 (a model derived from commercial epoxy resin products, the composition is Bisphenol A diglycidyl ether (Bisphenol A diglycidyl ether, abbreviated as DGEBA) corresponding to 25 g DDM (i.e. 0.25 g DDM is required for each 1 g E-51). The weighed DDM is heated to a molten state at 90℃, and then slowly added to the E-51 resin. Mechanically stir for 30 min until mixed evenly, ensuring no unmelted DDM particles are left. Pour the mixed system into a mold, pre-cure at 80℃ for 2 h, and post-cure at 120℃ for 4 h.

[0071] 4 Characterization and analysis

[0072] 4.1 Fourier transform infrared spectroscopy test (FTIR)

[0073] The structure of bio-based epoxy resin (VE) and cured resin (VE / OA-POSS) was analyzed by WQF-510 type Fourier transform infrared spectrometer. The sample was pressed with flame retardant: potassium bromide (KBr) = 1:100 and scanned in the range of 4000 to 400 cm -1 . -1 .

[0074] 4.2 Nuclear magnetic resonance test (NMR)

[0075] The 1H NMR and 31P NMR of bio-based epoxy resin (VE) were determined by nuclear magnetic resonance spectrometer (UltrashiedTM 400MHZ). The sample was dissolved with deuterium heavy water and deuterium DMSO.

[0076] 4.3 Differential scanning calorimetry test (DSC)

[0077] The wood epoxy coating (VE / OA-POSS and E-51 / DDM) was subjected to differential scanning calorimetry analysis by DSC214 type instrument provided by Germany Netzsch Company. The sample was heated from 60℃ to 200℃ at a heating rate of 10℃ / min under N2 atmosphere.

[0078] 4.4 Self-repairing performance

[0079] The self-repairing performance analysis was carried out by scratching the wood epoxy coating (VE / OA-POSS and E-51 / DDM), and then placing it in an oven at a certain temperature. The 100 mm x 100 mm x 3 mm size sample with scratches was placed under the three-dimensional microscope to observe the scratch repair using VHX-2000 type ultra-depth three-dimensional microscope system provided by Keen Shis Company.

[0080] 4.5 Pencil hardness test and adhesion test

[0081] Pencil hardness test of wood epoxy coating (VE / OA-POSS and E-51 / DDM) was performed on QHQ-A Pencil Hardness Tester (Zhejiang Aipu Instrument Co., Ltd.) according to ASTM D3363-2005. Adhesion test of wood epoxy coating (VE / OA-POSS and E-51 / DDM) was performed on QFH-A Crosshatch Cutter (Zhejiang Aipu Instrument Co., Ltd.) according to ASTM D3359-09.

[0082] 4.6 Thermogravimetric analysis test (TG)

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

[0084] 4.7 Infrared thermal imaging test

[0085] A constant and stable heat input was provided at the bottom of wood epoxy coating (VE / OA-POSS and E-51 / DDM) by using an alcohol lamp, and a handheld infrared thermometer (B256V infrared thermal imager) was used to record the surface temperature changes.

[0086] 4.8 Wood model combustion test

[0087] VE / OA-POSS, VAPD / EP and control group EP coating (500 g / m 2 ) were coated on a wooden house model, ignited by a butane spray gun, and the flame spread, self-extinguishing time and charring area were recorded to compare the actual flame retardant effect.

[0088] 4.9 Limiting oxygen index test (LOI) and vertical burning test (UL-94)

[0089] According to ASTM D2863 standard, the limiting oxygen index value of wood epoxy coating (VE / OA-POSS and E-51 / DDM) sample was tested, and the sample size was 130 mm x 6.5 mm x 3 mm. The test data was the average value of 5 samples. According to ASTM D3801 standard, the sample size was 130 mm x 13 mm x 3 mm, and the UL-94 grade was determined by vertical burning test. The test data was the average value of 5 samples.

[0090] 4.10 Cone calorimeter test (Cone)

[0091] Wood epoxy coating (VE / OA-POSS and E-51 / DDM) was tested according to international standard ISO 5660-1:2015, and the heat radiation power was 50 kW / m 2, the sample size was 100 mm x 100 mm, in order to reduce the influence of external factors during the experiment, the sample was wrapped with tin paper except for the heating surface, placed in a stainless steel fixing frame to prevent heat from transferring and losing from the back of the sample, the test time was 400 s, and the test data included heat release rate (HRR, kW / m 2 ), peak heat release rate (pHRR, kW / m 2 ), total heat release (THR, MJ / m 2 ), smoke release rate (SPR, m 2 / s), peak smoke release rate (m 2 / s), total smoke release (TSP, m 2 ), CO2 release rate (CO2PR, g / s), peak CO2 release rate (pCO2PR, g / s), and average effective combustion heat (mEHC, MJ / kg). In addition, fire growth index (FGI, kW·m -2 ·s -1 ), fire performance index (FPI, s / kW·m -2 ), and flame retardant index (FRI) were calculated according to the above data, and the calculation formulas are as follows.

[0092]

[0093] 4.11 Scanning Electron Microscope-Elemental Content Test (SEM-EDS)

[0094] The microstructure of the sample was observed at room temperature and with an acceleration voltage of 20 kV by a scanning electron microscope of SIGMA HD type of Carl Zeiss Company, Germany. The elemental content of the wood epoxy coating (VE / OA-POSS and E-51 / DDM) after the cone calorimeter test was analyzed by an electron spectrometer.

[0095] 4.12 Raman Spectroscopy Test (Raman)

[0096] Raman spectroscopy analysis of the residual carbon of the wood epoxy coating (VE / OA-POSS and E-51 / DDM) after the cone calorimeter test was performed using a Thermo Scientific DXR 3Xi spectrometer, and the spectral range was 500-3000 cm-1.

[0097] 4.13 X-ray Electron Spectroscopy Test (XPS)

[0098] X-ray photoelectron spectroscopy (XPS) was measured by a Scanning Probe Microscope (SPM) of ab 250XI electron spectrometer (Thermo Fisher Scientific, USA) to analyze the composition of the carbon residue. The emission current was 10 M, 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 group belonging to ECH is at 908 cm -1 There is an absorption peak at 3500-3200 cm -1 The absorption peak disappeared at . The results showed that vanillin was completely converted into epoxy monomer VE. Figure 2 In (b), it can be observed that VE is at 908 cm -1 The absorption peak of epoxy group disappears, while the absorption peak of VE / OA-POSS at 1640 cm -1 The absorption peak of C=N group appeared at VE. The epoxy group on VE opened the ring and reacted with -NH2, indicating that VE / OA-POSS was successfully synthesized. 5.2 Nuclear Magnetic Resonance Analysis (NMR)

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

[0103] 5.3 Differential Scanning Calorimetry (DSC)

[0104] The curing kinetics of E-51 / DDM and VE / OA-POSS systems at different heating rates were evaluated by DSC tests. Figure 4The DSC curves of E-51 / DDM and VE / OA-POSS at heating rates of 5-25°C / min (a, b) clearly show that both systems exhibit only a single exothermic peak. This exothermic peak is attributed to the heat released during the epoxy resin curing process, 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 increasing exothermic rate. This may be because at a low heating rate, the reactive groups have more time to complete curing at a lower temperature. However, at the same heating rate, the Tp of VE / OA-POSS is lower than that of E-51 / DDM, indicating that OA-POSS is more reactive than DDM in the curing reaction. This also suggests that adding OA-POSS to the EP system can enhance the curing activity of the matrix. The activation energy (Ea) represents the reactivity of the 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, which is 8.314 J / (mol K), A is the pre-exponential factor, and β is the heating rate. 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 corresponding activation energy is calculated from the slope of the fitting curve. In the Kissinger method, E of E-51 / DDM a The value is 66.51 kJ / mol, while the E a The value is 58.19 kJ / mol. In the Ozawa method, the E of E-51 / DDM a The value is 63.71 kJ / mol, while the E 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 atoms in the secondary amine groups can act as proton donors and catalyze the epoxy ring-opening reaction. In addition, the hydrogen bonds formed between the active hydrogen atoms in OA-POSS and the oxygen atoms of the epoxide groups can increase the polarization of the epoxide ring, further promoting the epoxy ring-opening reaction.

[0107] 5.4 Self-repair performance analysis

[0108] To explore the self-healing properties of VE / OA-POSS coating, scratch healing experiments were conducted on the wood surface coated samples. The samples with scratches were placed in a 65°C vacuum oven, and the healing process was observed in real time using a three-dimensional microscope. The experimental results show that (Fig. 8) Figure 5 ), under the condition of no external intervention, the coating shows significant self-healing efficiency: when the initial width of the scratch is 7550 μm, only 15 min is needed to achieve 100% healing rate. This is mainly due to the reversible reconstruction characteristics of the dynamic C=N bond in the coating. The imine bond (C=N) breaks and recombines under thermal excitation, prompting the rearrangement of the polymer network structure, thereby quickly filling the micro-defects in the scratch area.

[0109] 5.5 Pencil hardness and adhesion analysis

[0110] The physical properties of E-51 / DDM and VE / OA-POSS coatings are shown in Table 3. The experimental results show that the pencil hardness of VE / OA-POSS coating reaches 6H level, which is significantly improved compared with pure EP coating (2H level), which is due to the rigid support of aromatic structure and the high bond energy characteristics of silicon-oxygen bond (Si-O) in VE / OA-POSS coating, which synergistically enhances the surface scratch resistance of the coating. In the adhesion test, the adhesion of VE / OA-POSS coating reaches 4B level, which is due to the formation of covalent cross-linked network between the rich epoxy groups in VE and the resin matrix, which effectively improves 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 Thermal gravimetric analysis (TG)

[0114] The thermal stability of thermosetting materials is an indispensable requirement in application. The thermal stability of modified epoxy resin under nitrogen atmosphere was analyzed by thermal gravimetric analysis (TGA). Figure 6 The TGA and DTG curves of E-51 / DDM and VE / OA-POSS are shown in Fig. 9, and the specific thermal decomposition data are shown in Table 4. The results show that the TGA curves of E-51 / DDM and VE / OA-POSS show a two-step decomposition process under nitrogen atmosphere. Before 150°C, the main decomposition process of E-51 / DDM and VE / OA-POSS has little effect, and their TGA curves are basically the same, which is due to the thermal decomposition process of EP chain. 5％The char yield of VE / OA-POSS at 700°C was found to be higher than that of E-51 / DDM, increasing from 22.6% to 39.3%, indicating that the addition of Schiff base bonds reduced the thermal stability of the epoxy resin. For EP, the first decomposition process is attributed to the thermal decomposition of the EP chain itself, while the second process is primarily related to the further thermal oxidative decomposition of unstable char residues at high temperatures. It can be seen that the char yield of VE / OA-POSS at 700°C is higher than that of E-51 / DDM, increasing from 22.6% to 39.3%, indicating that VE epoxy resin effectively promotes its char formation performance.

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

[0116] Sample T 5％ (°C) T max (°C) Residue at 700°C (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] In order to systematically evaluate the thermal protection performance of the coating, this study used infrared thermal imaging technology to dynamically monitor the heat transfer behavior of E-51 / DDM and VE / OA-POSS wood under standard heating conditions. Figure 7 As shown, the back surface temperature of the E-51 / DDM coating sample exhibited a rapid increase, rapidly transitioning from a low-temperature blue (approximately 28.2°C) to a high-temperature red (114.2°C) within 40 seconds. In contrast, the VE / OA-POSS coating sample exhibited a significant gradual temperature rise, with a significantly slower color gradient, directly reflecting the excellent thermal insulation properties of the modified coating. During the initial combustion phase (0-20 seconds), the back surface temperature of the E-51 / DDM coating reached 64.4°C, while that of the VE / OA-POSS coating was only 43.5°C, a temperature difference of 1.2 times. These experimental results demonstrate 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 Analysis of Combustion Tests on Wood Models Based on Flame-Retardant Modified Epoxy Coatings with Dynamic Bonds

[0120] In order to systematically evaluate the practical application effectiveness of flame retardant coatings, this study quantitatively analyzed the flame retardant properties of three wood models (EP-wood, VAPD-wood and VE-wood) through simulated combustion experiments (e.g. Figure 8EP-wood model was ignited rapidly after ignition, and bright flame was formed within 10 s with a tendency of fast spreading. The roof collapsed and the main structure was completely burned out at 130 s, indicating that it had extremely high flammability. In contrast, the VAPD-wood and VE-wood models modified by flame retardation exhibited significant flame retardant advantages. In the test of continuous ignition by butane spray gun for 10 s, only partial combustion occurred in the two modified models; after the ignition source was removed, the combustion process terminated itself, forming charred layers of 33.4 cm 2 and 38.86 cm 2 in the roof area of the VAPD-wood and VE-wood models, respectively. It is worth noting that in the second ignition test, the VAPD-wood model maintained its overall structure after 450 s of burning, while the wall structure of the VE-wood model did not collapse after 380 s of burning.

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

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

[0123] The flame retardant performance of the wooden epoxy coating treated by different methods was tested by limiting oxygen index and vertical burning analysis, Figure 9 The limiting oxygen index values and vertical burning grades of the commercial epoxy resin system E-51 / DDM and the epoxy resin system containing Schiff base bond VE / OA-POSS. During the test, it was found that pure EP was highly flammable and accompanied by serious dripping phenomenon, and its LOI value was only 25.8%, and it failed to pass the UL-94 test. Because EP / DDM is a flammable material, it produces less black smoke and less residual carbon during combustion, and the reason for this phenomenon is that wood and commercial epoxy resin are both flammable materials, resulting in the generation of a small amount of black smoke and dripping during combustion. However, the flame retardancy of the wooden epoxy coating of the VE / OA-POSS epoxy resin system has been significantly improved. The LOI value of VE / OA-POSS increased to 33.1% respectively. This is because the silicon element present in VE / OA-POSS can promote the residual carbon rate of EP during combustion, thereby improving the flame retardancy of the epoxy resin.

[0124] The combustion behavior of the commercial epoxy resin system E-51 / DDM and the epoxy resin system containing Schiff base bond VE / OA-POSS during the UL-94 test was recorded and shown in Figure 10E-51 / DDM continued to burn after the first ignition. For VE / OA-POSS, the sample self-extinguished after 18 s of the first ignition, released a small amount of white smoke at the second ignition, and self-extinguished after 9 s of leaving the heat source, VE / OA-POSS achieved V-0 rating.

[0125] 5.10 Cone Calorimetry Analysis (CONE)

[0126] The wood epoxy coating's burning behavior was tested by using a cone calorimeter to simulate real fire, and important experimental results were obtained. As shown in Table 5, the ignition time of the wood epoxy coating containing Schiff base bond (VE / OA-POSS) was prolonged to varying degrees, and the TTI time of the VE / OA-POSS wood epoxy coating was prolonged by 29 s compared with the control group E-51 / DDM. Heat release rate (HRR) and total heat release (THR) are considered to be the most important parameters in flame research. In Figure 11 In Table 5 (a, b) and Table 5, the pHRR of E-51 / DDM and VE / OA-POSS was 414.50 and 265.12 kW / m 2 , respectively, which was 36.0% lower than the pHRR of the wood epoxy coating of the control group E-51 / DDM. Observation of the HRR graph showed that its curve had only one peak value, and this stage was mainly flaming combustion, and the heat release was mainly concentrated in this stage. The exothermic peak of VE / OA-POSS was reduced and delayed to varying degrees. At the same time, the THR increased with the increase of the burning time, and the THR of E-51 / DDM and VE / OA-POSS was 30.02 and 17.72 MJ / m 2 , respectively, which was 40.9% lower than that of the control group E-51 / DDM.

[0127] FGI represents the flame retardancy of the composite material, and FPI represents the flash combustion time of the composite material. The composite material with low FGI and high FPI has stronger flame retardancy, and the flame development trend is slow. As shown in Table 5, the FGI of E-51 / DDM was 4.18, and the FPI was 0.10, respectively, while the FRI and FPI of VE / OA-POSS were 2.08 (excellent) and 0.27, respectively, indicating that the heat release of the bio-based epoxy resin coating VE / OA-POSS was delayed to varying degrees, and showed better fireproof performance.

[0128] The production, composition and toxicity release of smoke are another important dangerous factor in real fire. For example, Figure 11Figures (c, d) and Table 5 show the smoke release rate (SPR) and total smoke release (TSP) of E-51 / DDM and VE / OA-POSS wood epoxy coatings. The peaks of the smoke release rate exhibit a unimodal or bimodal trend, indicating that the combustion of wood epoxy coatings produces both combustible and non-combustible smoke. The bio-based epoxy resin VE exhibits a certain smoke suppression capability. Its pSPR and TSP decrease by 86.6% and 81.2%, respectively, compared to E-51 / DDM. Figure 11 (e, f) are schematic diagrams of cone calorimetry char residues of E-51 / DDM and VE / OA-POSS. It can be seen from the figure that the commercial epoxy resin wood coating generates less char residue during combustion, and the remainder is light in weight and low in ash content. However, after flame retardant treatment, the surface of the bio-based wood epoxy coating forms a dense char residue with high strength and not easy to be destroyed, indicating that the introduction of cage-type polysilsesquioxane and imine bonds can effectively promote the charring performance of the wood epoxy coating and effectively prevent the entry of heat and oxygen. The silicon element can form structures such as Si-C and silica, enhance the stability of the expanded char layer, and thus protect the base wood from further combustion. It can be inferred that its flame retardant mechanism conforms to the gas phase and condensation phase mechanism, presenting a dense structure, which is a physical protective layer, hindering the transfer of heat and combustibles, and slowing down the ablation of the internal base material.

[0129] Table 5 Cone calorimetry test data of epoxy resin wood coating

[0130]

[0131] 5.11 Carbon Residue Scanning Electron Microscopy-Elemental Content Analysis (SEM-EDS)

[0132] Scanning electron microscopy was used to further analyze the microstructure of carbon residue on the surface of thermosetting resin and to further explore the flame retardant mechanism in the condensed phase. Figure 12 As shown in the images, E51 / DDM exhibits a large number of pores and cracks, which complicate the dissipation of heat and gas during combustion. In contrast, the residual carbon structure of VE / OA-POSS shows continuous and dense features, which effectively prevents the release of combustible gases and blocks the transfer of heat to the internal matrix. ]. Therefore, the dense carbon layer of VE / OA-POSS has excellent flame retardant properties. The reason may be that the Schiff base bond promotes the cross-linking of the carbon layer and the presence of silicon in VE / OA-POSS generates substances such as Si-C and silicon dioxide, which slows down the combustion rate. The complete carbon layer can prevent the transfer of decomposition products and heat, further protecting the underlying matrix from being ignited by the flame, thereby improving the fire safety of EP in practical applications. EDS results further show that the wood epoxy coating after VE / OA-POSS combustion contains C, N, O, and Si elements, which can prevent further combustion of the base wood material and play a role in the condensed phase. 5.12 Raman spectroscopy analysis of residual carbon (Raman)

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

[0134] 5.13 Carbon Residue X-ray Electron Spectroscopy (XPS)

[0135] The elemental composition of the carbon residues after combustion of E-51 / DDM and VE / OA-POSS epoxy resin coatings was analyzed by XPS. Figure 14 As shown. Figure 14 As can be seen in (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 Panels (b, d) show the high-resolution XPS spectra of E-51 / DDM for C1s, N1s, and O1s, respectively. The C1s spectrum exhibits three main peaks at 284.8 eV (C-C / CH), 285.6 eV (CO), and 289.2 eV (OC=O). The two peaks at 399.9 and 405.6 eV in the N1s spectrum are attributed to pyridinic and pyrrolic 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 14High-resolution XPS spectra of C1s, N1s, O1s, and Si2p of VE / OA-POSS are shown in (f-i), respectively. The C1s spectrum has three main peaks at 284.8 eV (C-C / C-H), 285.6 eV (C-O / C-N), and 289.2 eV (C=0). The two peaks in N1s at 400.8 and 407.2 eV are attributed to N-H and C-N, respectively. In addition, the O1s peak of shows C=0 (532.5 eV) and C-O-C / C-OH (533.8 eV) signals. The spectrum of Si2p is divided into 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 dehydration and carbonization of epoxy resin during the combustion process, generating a silica protective carbon layer to prevent further combustion, while the Schiff base in the structure of VE / OA-POSS can promote the carbonization of epoxy resin.

[0136] 5.14 Flame-retardant mechanism

[0137] The schematic diagram of the flame-retardant mechanism of VAPDs / EP is shown in Figure 15 and is summarized as follows:

[0138] (1) The high char yield of the VE / OA-POSS system is the result of the carbonization of the Schiff base bond and the auxiliary carbonization of siloxane. This layer is composed of strong, highly interconnected carbon, which acts as an effective shield, hindering the transfer of heat and matter.

[0139] (2) Due to the cross-linked structure formed by the Schiff base group, the char in the flame-retardant epoxy resin shows a robust structure with increasing volume. This structure can act as a protective layer of thermal insulation during the combustion process, as it forms a carbon layer. In addition, it can reduce the level of flammable gas, leading to the production of NH3 gas phase, ultimately delaying the combustion process of the material.

[0140] The above description of disclosed embodiments enables one of ordinary skill in the art to make or use the application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended 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-repairing wood epoxy coating, characterized in that: The specific steps include: (1) vanillin, epichlorohydrin and tetrabutylammonium bromide are mixed, reacted, cooled, and a NaOH aqueous solution is added dropwise, the reaction is continued, washed, dried, precipitated, and dried again to obtain a bio-based epoxy resin for use; (2) mixing methanol and hydrochloric acid, heating, condensing and refluxing, adding γ-aminopropyltriethoxysilane, reacting, cooling, adding tetrahydrofuran, washing, and vacuum drying to obtain a cage-type polysilsesquioxane; (3) dissolving the cage-type polysilsesquioxane in an organic solvent, adding a bio-based epoxy resin, stirring evenly, standing, and curing to obtain the flame-retardant and self-repairing wood epoxy coating.

2. The method for preparing a flame retardant and self-repairing wood epoxy coating according to claim 1, characterized in that: In step (1), the mass fraction of the NaOH aqueous solution is 50 wt %; the mass ratio of the vanillin, epichlorohydrin, tetrabutylammonium bromide and the NaOH aqueous solution is 20:48.8:1:26.

4.

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

4. The method for preparing a flame retardant and self-repairing wood epoxy coating 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 h.

5. The method for preparing a flame retardant and self-repairing wood epoxy coating according to claim 1, characterized in that: In step (2), the volume ratio of methanol, hydrochloric acid, γ-aminopropyltriethoxysilane and tetrahydrofuran is 100:15:15.2:

200.

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

7. The method for preparing a flame retardant and self-repairing wood epoxy coating according to claim 1, characterized in that: In step (3), 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.

8. The method for preparing a flame retardant and self-repairing wood epoxy coating according to claim 1, characterized in that: In step (3), the stirring time is 30 minutes; the curing procedure is: curing at 80°C for 2 hours and curing at 120°C for 4 hours.

9. A flame retardant and self-repairing wood epoxy coating prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the flame-retardant and self-repairing wood epoxy coating prepared by the preparation method according to any one of claims 1 to 8 in the protection of wood materials.

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