Flame retardant and flame-retardant coating for transparent wood, preparation method of flame retardant and flame-retardant coating, and fireproof transparent wood

Abstract

The invention relates to the technical field of flame-retardant coatings, and particularly discloses a flame retardant for transparent wood, a flame-retardant coating, a preparation method of the flame-retardant coating and fireproof transparent wood, the flame retardant for the transparent wood is characterized in that the structural general formula of the flame retardant is PAXY-M, the flame retardant is a water-soluble flame retardant, and an aqueous solution of the flame retardant is a transparent aqueous solution; m is selected from at least one of Ca < 2 + >, Co < 2 + >, Ni < 2 + >, Cu < 2 + > and Zn < 2 + >, and M is respectively coordinated with phytic acid and xylitol. The fireproof coating disclosed by the invention is high in light transmittance, and has good fireproof performance by connecting phytic acid xylitol with a metal system on the premise that the original appearance and touch of wood are not influenced, especially LOI and flame resistance are greatly improved, and the use safety of the transparent wood is further improved.

Description

Technical Field

[0001] This invention relates to the field of flame retardant coating technology, specifically to a flame retardant for transparent wood, a flame retardant coating and its preparation method, and fireproof transparent wood. Background Technology

[0002] With the rise of sustainable building concepts, wood has gradually become a popular material in the field of green building due to its renewable nature, low carbon emissions, and natural aesthetics. However, the inherent flammability of traditional wood severely restricts its application in high-rise buildings and fire-sensitive scenarios.

[0003] In recent years, "transparent wood" technology, through processes such as lignin removal and polymer filling, has endowed natural wood with high light transmittance while preserving its natural texture, providing an innovative direction for new building facade materials. However, the removal of lignin and hemicellulose during the wood-transparent treatment process may further weaken the wood's flame-retardant properties, leading to an increased fire hazard. Existing research mainly focuses on the mechanical enhancement or optical modulation of transparent wood, and optimizing its fire-resistant performance remains a challenge.

[0004] Currently, when fire-retardant treating transparent wood, to avoid affecting its appearance and transparency, the entire transparent wood is often immersed in a flame retardant solution before being dried. This process is time-consuming and cumbersome. Furthermore, directly using existing fire-retardant coatings cannot meet the performance requirements of transparent wood for high light transmittance and visual appeal. Summary of the Invention

[0005] To overcome the above-mentioned shortcomings, the present invention aims to provide a flame retardant for transparent wood, a flame retardant coating, a preparation method thereof, and fireproof transparent wood. The flame retardant for transparent wood of the present invention is highly effective in providing fireproofing for transparent wood. While maintaining the transparent appearance of the coating, it exhibits high flame retardant performance and a high LOI (Liquidity of Interest), meeting the fireproofing requirements for transparent wood. Furthermore, it is water-soluble, easy to use, and convenient for the processing and production of transparent wood.

[0006] One objective of this invention is to provide a flame retardant for transparent wood, having the general structural formula PAXY-M. The flame retardant is water-soluble, and its aqueous solution is a transparent aqueous solution. M is a metal salt selected from Ca... 2+ Co 2+ Ni 2+ Cu 2+ and Zn 2+At least one of the components, wherein M is coordinated with phytic acid and xylitol respectively. The flame retardant for transparent wood of the present invention successfully constructs a stable flame-retardant composite system through the coordination of metal ions with the phosphate groups in phytic acid molecules and the hydroxyl groups in xylitol. Its aqueous solution has high light transmittance, ensuring that it does not negatively affect the original appearance of the transparent wood. Furthermore, the flame retardant of the present invention is a water-soluble flame retardant, thus facilitating its use and greatly reducing the complexity and processing time of fireproofing treatment for transparent wood.

[0007] Furthermore, after phytic acid and xylitol react to obtain a water-soluble flame retardant precursor PAXY, an aqueous solution of the metal salt is added to the aqueous solution of the flame retardant precursor PAXY to react and obtain the flame retardant.

[0008] Furthermore, in the formation of PAXY, the molar ratio of phytic acid to xylitol is 1:3 to 1:9.

[0009] Furthermore, the molar ratio of phytic acid to xylitol is 1:6 to 1:9.

[0010] Furthermore, the molar ratio of phytic acid to xylitol is 1:7. PAXY prepared at this molar ratio exhibits a higher limiting oxygen index (up to 29.2%), and the resulting flame retardant precursor PAXY demonstrates better flame retardant properties.

[0011] Furthermore, the metal salt is an acetate, and the molar ratio of phytic acid, xylitol, and metal salt is 1:7:0.35 for phytic acid:xylitol:metal salt.

[0012] Furthermore, M is Zn 2+ Cu 2+ or Co 2+ At least one of them.

[0013] A second objective of this invention is to provide a flame-retardant coating comprising the aforementioned flame retardant and MUF. The flame-retardant coating of this invention is prepared using water-soluble PAXY-M and MUF, resulting in good overall transparency without affecting the appearance of transparent wood. It is also easy to apply to the surface of wood, facilitating fireproofing treatment of transparent wood. Furthermore, the flame-retardant coating of this invention is environmentally friendly, non-toxic, and highly safe to use.

[0014] A third objective of this invention is to provide a method for preparing a flame-retardant coating, comprising the following steps: PAXY preparation steps: Phytic acid and xylitol are reacted at 130℃ to obtain flame retardant precursor PAXY; PAXY-M preparation steps: After obtaining PAXY, a metal salt solution is added to the reaction system, and the mixture is reacted at 80°C and then purified. Steps for compounding with MUF: Dissolve purified PAXY-M in water, add MUF to the reaction system, and stir until transparent.

[0015] The fourth objective of this invention is to provide a fire-resistant transparent wood, which is obtained by applying the aforementioned flame-retardant coating to the surface of transparent wood and then curing it.

[0016] The present invention has the following beneficial effects: ① The fire-retardant coating of the present invention uses melamine urea-formaldehyde resin (MUF) as the base film-forming resin and phytic acid xylitol bonded metal system as the flame retardant. It has high light transmittance and, while protecting the original appearance and feel of the wood, gives it good fire-retardant performance by using phytic acid xylitol bonded metal system. In particular, the LOI is greatly improved and the flame-retardant time is also significantly increased, further improving the safety of transparent wood.

[0017] ②The flame-retardant coating prepared by this invention has good physical and chemical properties, with a surface drying time of 2 hours, a complete drying time of 5.5 hours, a coating hardness of 6H, and an adhesion strength grade of 0.

[0018] ③ The flame-retardant coating prepared by this invention has excellent flame-retardant properties. The highest T10% can reach 222.6℃, which is 43.1℃ higher than the sample coated with only MUF. The LOI is 32%, which is 73.8% higher than the 18.7% of the original wood. The flame-retardant time of the large board is 35min.

[0019] ④ The flame-retardant coating of the present invention has higher environmental performance; when applied to transparent wood, the smoke output during combustion is 95.84 m³. 2 174.62m longer than the original log 2 It reduced heat release by 45%; the peak carbon dioxide emission was 0.208%, a decrease of 21% compared to logs; and it formed a fluffy and dense charcoal layer after combustion, reaching a height of 2.5cm, further reducing heat release.

[0020] ⑤ The flame-retardant coating of the present invention utilizes the reaction product of water-soluble acetate and phytic acid xylitol to form a highly water-soluble flame-retardant system, which is convenient for preparation and application, and has excellent environmental performance. Attached Figure Description

[0021] Figure 1 The images show the appearance of flame retardants PAXY-M grafted with different metal ions. From left to right, the images show PAXY-Ca, PAXY-Co, PAXY-Ni, PAXY-Cu, and PAXY-Zn. Figure 2 This is a comparison chart of adhesion test standards; Figure 3This is a schematic diagram illustrating the operating conditions during a hardness test. Figure 4 The C1s spectrum of XPS; Figure 5 The O1s spectrum of XPS; Figure 6 The P2p spectrum of XPS; Figure 7 The Zn2p spectrum of XPS; Figure 8 This is a graph of the XPS full spectrum results; Figure 9 Thermogravimetric analysis charts for each sample; Figure 10 Thermogravimetric analysis (TGA) charts for each sample are shown. Figure 11 This is a schematic diagram of the large plate combustion experimental setup; Figure 12 A comparison of the flame resistance time of pure wood samples and wood samples coated with flame-retardant coating; Figure 13 A side view of a pure wood sample (NW) after the slab has been burned; Figure 14 A top view of a pure wood sample (NW) after the slab has been burned; Figure 15 A side view of a large wood sample board after burning, using MUF flame retardant. Figure 16 A top view of a large wood sample board after it has been burned using MUF flame retardant. Figure 17 This is a side view of a large wood sample board after burning, which was treated with MUF-PAXY flame retardant. Figure 18 A top view of a large wood sample board after burning, using MUF-PAXY flame retardant. Figure 19 A side view of a large wood sample board after burning, which was retardant using MUF-PAXY-Ca flame retardant. Figure 20 A top view of a large wood sample board after burning, using MUF-PAXY-Ca flame retardant. Figure 21 A side view of a large wood sample board after burning, which was treated with MUF-PAXY-Co flame retardant. Figure 22 A top view of a large wood sample board after burning, using MUF-PAXY-Co flame retardant. Figure 23 A side view of a large wood sample board after burning, using MUF-PAXY-Ni flame retardant. Figure 24A top view of a large wood sample board after burning, using MUF-PAXY-Ni flame retardant. Figure 25 A side view of a large wood sample board after burning, which was retardant using MUF-PAXY-Cu flame retardant. Figure 26 A top view of a large wood sample board after burning, using MUF-PAXY-Cu flame retardant. Figure 27 This is a side view of a large wood sample board after burning, which was retarded using MUF-PAXY-Zn flame retardant. Figure 28 A top view of a large wood sample board after burning, which was treated with MUF-PAXY-Zn flame retardant. Figure 29 A comparison chart of HRR release levels for each sample; Figure 30 A comparison chart of THR release levels for each sample; Figure 31 A comparison chart of TSP release levels for each sample; Figure 32 A comparison chart of CO2 release from each sample; Figure 33 A top view of the char residue on a pure wood sample after testing with a cone calorimeter; Figure 34 A side view of the char residue on a pure wood sample after testing with a cone calorimeter; Figure 35 This is a top view of the carbon residue of the CW sample after testing with a cone calorimeter. Figure 36 A side view of the carbon residue of the CW sample after testing with a cone calorimeter; Figure 37 A top view of the char residue of a MUF-PAXY-Zn flame-retardant wood sample after testing with a cone calorimeter; Figure 38 The image shows a side view of the char residue on a MUF-PAXY-Zn flame-retardant wood sample after testing with a cone calorimeter. Detailed Implementation

[0022] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0023] The source information of the raw materials used in the embodiments of the present invention is as follows: The fir wood lumber was provided by Fuyuan Timber Factory; the melamine-urea-formaldehyde resin powder was provided by Zhengzhou Hengtong Chemical Co., Ltd.; and the phytic acid (70wt%), xylitol, calcium acetate monohydrate (AR), cobalt acetate tetrahydrate (AR), nickel acetate tetrahydrate (AR), copper acetate monohydrate (AR), and zinc acetate dihydrate (AR) were provided by Shanghai Maclean Biochemical Technology Co., Ltd.

[0024] Experimental Example 1: Preparation of Flame Retardant PAXY-M 1.1 Screening of the ratio of phytic acid to xylitol: Phytic acid (hereinafter referred to as "PA") and xylitol (hereinafter referred to as "XY") in different molar ratios were placed in a three-necked flask and reacted at 130°C. In some embodiments, the reaction time could be 3 hours, 2 hours, or 4 hours, or adjusted as needed. The resulting product was then washed three times with anhydrous ethanol to remove impurities and dried in a vacuum drying oven at 80°C (the resulting product was named PAXY). The obtained PAXY was then mixed with deionized water and melamine urea-formaldehyde resin (hereinafter referred to as "MUF") powder, stirred evenly, and coated onto wood samples with a brush. After curing at room temperature, the samples were tested. The flame retardant performance testing method and standard referred to the UL94 flammability test method. The minimum amount of the flame retardant of this invention required to pass the V0 level of the UL94 test was selected as the basis for judging the flame retardant performance of each test sample. At the same time, the LOI (Limiting Oxygen Index) of each wood sample was determined. For the minimum addition amount and LOI test method for UL94 V0, please refer to Experimental Example "4.2 Analysis of Combustion Performance of Flame Retardant Coatings".

[0025] In some embodiments, the molar ratio of PA:XY is 1:3 to 1:9, for example, 1:3, 1:4, 1:5, 1:6, 1:6.2, 1:6.5, 1:7, 1:7.5, 1:7.3, 1:8, or 1:9. In other possible embodiments, it is 1:6 to 1:9.

[0026] Table 1 Comparison of minimum addition amount and LOI for UL94 V0 compliant treatment with different molar ratios of PA and XY.

[0027] As shown in Table 1, when the PA:XY molar ratio is 1:3 or 1:5, the minimum addition amount for UL94 V0 rating is 8%. When the PX:XY molar ratio is 1:7 or 1:9, the minimum addition amount for UL94 V0 rating is 7%, and the limiting oxygen index (LOI) is 29.2% and 27.6%, respectively. Therefore, when the PA:XY molar ratio is 1:7, the resulting flame retardant precursor PAXY has better flame retardant properties.

[0028] 1.2 Synthesis of PAXY-M: 0.01 mol PA (9.43 g) and 0.07 mol XY (10.757 g) were mixed in a three-necked flask and heated to 130 °C for 3 hours. Then, 0.00375 mol acetate (dissolved in 20 ml of deionized water, with cation M in the acetate, where M is Ca2+, Ca2+, and ... 2+ Co 2+ Ni 2+ Cu 2+ and Zn 2+ At least one of the following ( ), and continue the reaction at 80°C for 4 hours. To obtain a pure flame retardant, the resulting product was washed three times with anhydrous ethanol, then placed in a vacuum drying oven and dried under vacuum at 80°C. It was then ground and ready for use. The synthesized flame retardants with different metals, such as... Figure 1 As shown.

[0029] Experimental Example 2: Preparation of the wood sample to be tested: The flame retardant PAXY-M prepared in Experiment Example 1 was dissolved in 10g of water, then mixed with 10g of melamine-urea-formaldehyde resin powder, and mechanically stirred until the solution became clear and transparent, thus preparing the flame retardant coating. The flame retardant coating was then applied to the surface of the cedar wood with a brush, at a coating amount of 500g / m². 2 It cures naturally at room temperature. Meanwhile, a pure wood sample was used as a blank control, and a solution of 10g of melamine-urea-formaldehyde resin powder added to 10g of water was used as a control.

[0030] Uncoated wood samples are named "Neat Wood" (abbreviated as "NW"), wood samples coated only with melamine urea-formaldehyde resin are named "Coated Wood" (abbreviated as "CW"), and other wood samples coated with flame-retardant coatings are named "MUF-PAXY-M" (M refers to any one of Ca, Co, Ni, Cu or Zn) according to the different acetates attached to PAXY.

[0031] Table 2. Formulations of flame-retardant coatings for various wood samples.

[0032] Experiment Example 3: Performance Testing of Flame Retardant Coatings The adhesion, hardness, and light transmittance properties of each flame-retardant coating were tested using the samples prepared in Experiment Example 2.

[0033] 3.1 Adhesion Test Adhesion reflects the comprehensive performance of the physical and chemical bonding between the coating and the substrate surface. According to GB / T9286-2021 "Paints and Varnishes - Cross-cut Test", the cross-cut test can be used. Specifically, three different locations are selected on the coating surface, and six parallel cuts spaced 1 mm apart are made using a special tool. Then, cuts of the same specifications are made perpendicularly to form a 1 mm × 1 mm square grid, ensuring that the cuts penetrate the paint film to the substrate. Afterwards, loose debris is removed with a soft brush. Refer to the adhesion standard comparison chart (…). Figure 2 ) Assess the adhesion level.

[0034] Using an adhesion tester, a cross-cut adhesion tester was used to cut the samples coated with flame-retardant paint. The results were compared with the adhesion test standard chart after cutting. The obtained adhesion charts were compared with the standard charts, and the results are shown in Table 3. Table 3 shows that the adhesion rating of all flame-retardant coatings is less than 3, which meets the requirements of GB12441-2018 "Decorative Fire-Retardant Coatings".

[0035] In this experiment, the adhesion performance was tested using a QFH cross-cut adhesion tester. The adhesion test results for each coating are shown in Table 3.

[0036] Table 3 Adhesion rating of flame-retardant coatings

[0037] 3.2 Pencil Hardness Test The pencil hardness test was conducted using the QHQ-A push-type pencil hardness tester provided by Aipu Instruments.

[0038] The hardness of the coating was tested according to GB / T6739-2006 "Pencil Hardness Test Method". The specific operating procedure is as follows: The sample was placed horizontally, and a series of pencils with increasing hardness (hardness grades from softest to hardest: 6B-5B-4B-3B-2B-B-HB-FH-2H-3H-4H-5H-6H-7H-8H-9H) were used to perform a scratch test on the coating surface. The hardness value of the coating was defined as the pencil hardness grade that could just scratch the coating to the substrate. The operating conditions during the hardness test were as follows: Figure 3 As shown in Table 4, the hardness test results for each sample are as follows.

[0039] Table 4. Hardness rating test results of various flame-retardant coatings

[0040] 3.3 Transmittance Analysis of Flame-Retardant Coatings According to the national standard GB / T1721-2008 "Determination of Appearance and Transparency of Varnishes, Oils and Thinners", the transparency of coatings can be tested using two methods: visual observation and transmittance measurement. Visual inspection requires the sample coating to exhibit good transparency, with a smooth and flat surface free from cracking, discoloration, or other defects. A flame-retardant coating is applied to wood with a label bearing text. After curing at room temperature until completely dry, the clarity of the text on the label is observed from the sample surface. Experiments showed that after applying MUF coating, MUF-PAXY-Ca coating, MUF-PAXY-Co coating, MUF-PAXY-Ni coating, MUF-PAXY-Cu coating, and MUF-PAXY-Zn coating, the text on the label can be observed from the sample surface. Furthermore, the dried coating surface is smooth and intact, without deformation, agglomeration, or other defects.

[0041] 3.4 Analysis of the drying performance of flame-retardant coatings Drying time refers to the time required for a coating to cure from a liquid state to a specified state under specific environmental conditions. It is usually divided into two stages: surface drying time (referred to as "surface drying time") and actual drying time (referred to as "actual drying time"). Surface drying time indicates the time it takes for a solid film to form on the surface of the coating after application, while actual drying time refers to the total time required for the entire coating to completely cure into a continuous solid film. This parameter is generally expressed in hours or minutes.

[0042] According to the standard GB / T1728-2020 "Determination of Drying Time of Paint Film and Putty Film", the following two methods can be used to test the surface drying time: (1) Blowing cotton ball method: Place the degreased cotton ball lightly on the coating surface, and the tester blows air horizontally at a distance of 10-15cm. If the cotton ball can be blown away and there are no residual fibers on the surface, it is determined that the surface is dry. (2) Touch test: The dryness of the coating is judged by touching the surface of the coating with your fingers.

[0043] The determination of actual drying time involves multiple methods: (1) Blade method: scrape the coating with a safety blade. If there are no adhesive marks on the bottom layer and inside, it is qualified; (2) Cotton ball pressure method: The degree of curing is determined by applying pressure to a cotton ball; (3) Thick layer drying method: a special testing method for thicker coatings.

[0044] The wet coating weight of all samples of flame-retardant coatings was 500 g / m². 2The coated samples were allowed to cure naturally at room temperature. The surface drying time and complete drying time were determined using the cotton ball method and the blade method, respectively. The specific values ​​are shown in Table 5.

[0045] Table 5 Surface drying time and complete drying time of various flame-retardant coatings

[0046] As shown in Table 5, the surface drying time of all flame-retardant coatings is within 5 hours and the actual drying time is within 24 hours, which meets the relevant requirements of GB12441-2018 "Decorative Fire-retardant Coatings".

[0047] 3.5 Characterization of flame retardants To analyze the elemental types, chemical composition, and electronic valence states of flame retardants, PAXY-M (where M is Zn) was used as the reference material. 2+ Taking [example] as an example, X-ray photoelectron spectroscopy (XPS) was used to characterize and analyze the elemental composition and chemical state of the flame retardant PAXY-Zn. This invention utilizes a VG ESCALAB MKⅡ X-ray photoelectron spectrometer provided by VG Scientific Instruments Ltd., UK, to analyze the elemental chemical composition of the flame retardant. The results are as follows: Figures 4-8 As shown.

[0048] like Figures 4-8 As shown, XPS full spectrum results Figure 8 This confirms that the flame retardant is composed of four elements: C, O, P, and Zn. Peak fitting of C1s, O1s, P2p, and Zn2p was performed using Avantage software, revealing that in the Zn2p spectrum (… Figure 7 The results show a bimodal characteristic with binding energies of 1021.08 eV and 1043.94 eV, corresponding to Zn2p3 / 2 and Zn2p1 / 2, respectively. This confirms that Zn... 2+ It forms a stable coordination structure with the phytic acid-xylitol system. In the O1s spectrum ( Figure 5 The 529.82 eV peak corresponds to the CO bond, and the characteristic peak at 531.19 eV belongs to the -OH group. In the P2p spectrum ( Figure 6 The 132.24 eV peak corresponds to the PO bond, and the characteristic peak at 133.21 eV originates from the phosphate group in phytic acid. These analytical results fully demonstrate that Zn... 2+ A stable flame-retardant composite system was successfully constructed through coordination interactions with the phosphate groups and xylitol hydroxyl groups in phytic acid molecules. The characteristic binding energy data of each element provided direct evidence to verify the chemical structure of this flame retardant.

[0049] Experiment Example 4: Thermal stability and flammability test of flame-retardant coatings for transparent wood 4.1 Thermal stability test Thermal stability testing was conducted under an air or nitrogen atmosphere, at a temperature range of 30-800℃, with a heating rate of 10℃ / min, to assess the thermal stability of flame-retardant coatings. This invention utilizes a Netzsch TG209 thermogravimetric analyzer (TGA) to test the thermal stability of each flame-retardant coating.

[0050] Use a knife to scrape powder from the prepared wood sample coated with flame retardant paint, grind it into powder using an agate mortar, and test the obtained sample using a thermogravimetric analyzer with a heating range of 30-800℃ and a heating rate of 10℃ / min.

[0051] The thermal stability and thermal degradation behavior of the flame-retardant coatings were tested by thermogravimetric analysis (TG) in air. The pyrolysis images of each coating sample were examined, and the TG results are as follows: Figure 9 As shown, the thermogravimetric analysis (DTG) of micro-businesses is as follows: Figure 10 As shown in Table 6, the key pyrolysis parameters are as follows. T10% refers to the temperature at which the mass loss of the flame-retardant coating sample reaches 10%, and Tmax refers to the maximum weight loss temperature. The table shows that the T10% of MUF is 179.5℃, while the T10% of all flame-retardant coatings with added flame retardants increased; among them, MUF-PAXY-Zn was 43.1℃ higher than MUF. Furthermore, the Tmax of MUF appeared at 281.3℃, while the Tmax of all flame-retardant coatings with added flame retardants decreased to some extent; among them, MUF-PAXY-Zn was 261.2℃, because phosphoric acid promoted premature decomposition of the coating. The char residue of MUF at 600℃ was 17.7%. The char residue of the flame-retardant coatings with the addition of the flame retardant of the present invention has increased. Specifically, the char residue of MUF-PAXY-Co at 600°C is 23.3%, the char residue of MUF-PAXY-Cu at 600°C is 23.7%, and the char residue of MUF-PAXY-Zn at 600°C is 22.6%.

[0052] Table 6. Pyrolysis parameters of wood coated with flame-retardant coatings MUF and MUF-PAXY-M in air atmosphere

[0053] 4.2 Combustion Performance Analysis of Flame-Retardant Coatings 4.2.1 Vertical Combustion and Limiting Oxygen Index Test Limiting oxygen index (LOI) and vertical burning test (UL-94) are common methods for evaluating the flame retardant properties of materials.

[0054] The vertical flammability test of this invention uses a CFZ-2 vertical flammability tester manufactured by Jiangning Analytical Instruments Co., Ltd., and tests the vertical flammability rating (UL-94) of polyurethane sample materials according to the ASTM D3801-2010 test standard. The test sample size is set to 130mm × 13mm × 3mm, and the sample preparation and testing are strictly carried out in accordance with the standard requirements.

[0055] The limiting oxygen index (LOI) test of this invention uses an HC-2 oxygen index meter from Jiangning District Analytical Instrument Company. The LOI of the material is tested according to the ISO2406-2:2009 standard, with the test sample size set to 100mm × 6.5mm × 3mm. This test is used to evaluate the combustion characteristics of the material in a nitrogen-oxygen mixed gas environment and to determine the minimum oxygen concentration required to sustain combustion.

[0056] The UL-94 and LOI test results for each flame-retardant coating are shown in Table 7. Table 7 shows that both uncoated wood (NW) and wood coated only with melamine-urea-formaldehyde resin (CW) exhibited no vertical burning rating, burning intensely after the first ignition until the sample was completely burned. However, the sample coated with the flame-retardant coating MUF-PAXY extinguished quickly after two ignitions in vertical burning, achieving a V0 rating with a limiting oxygen index of 29.2%. The flame retardant precursor PAXY showed no significant improvement in the vertical burning rating after contact with metal, but a substantial improvement in the LOI. In particular, the LOI of the MUF-PAXY-Zn sample was 32.5%, a 73.8% increase compared to the 18.7% of pure wood. It is evident that the flame-retardant coating MUF-PAXY of this invention can significantly improve the flame-retardant properties of wood. Furthermore, after bonding PAXY to metal, the LOI can be further improved by compounding MUF, thereby further enhancing the fire resistance and safety of transparent wood.

[0057] Table 7. UL94 and LOI test results of pure wood (NW) and wood samples coated with flame retardant coating.

[0058] 4.2.2 Combustion Analysis of Large Plates The flame retardant properties of decorative fire-retardant coatings were tested using the large-panel burning method according to the national standard GB12441-2018. The flame retardant performance test employed a vertically fixed sample, using the outer flame of a butane spray gun (approximately 1300℃) as the heat source. During the test, the deformation of the back of the sample was continuously observed. The test was terminated when significant deformation occurred, and data such as the char layer expansion rate, expansion height, char layer density, and the duration of flame retardancy of the sample were recorded simultaneously. A schematic diagram of the experimental setup is shown below. Figure 11 .

[0059] (1) Flame resistance time Using the outer flame of a butane torch (approximately 1300℃) as the heat source, the test ended when deformation appeared on the back of the sample. The burning time of the sample at this point was recorded as the flame resistance time. Three samples were tested repeatedly, and the flame resistance time of each sample was recorded as follows: Figure 12 As shown. By Figure 12 It can be seen that the flame retardancy time of pure wood is 13 minutes. The flame retardancy time of the melamine-urea-formaldehyde resin coated samples after adding flame retardants (PAXY and its metal-attached flame retardant PAXY-M) was improved. The metal-attached flame retardant PAXY-M generally increased the flame retardancy time compared to PAXY. Specifically, MUF-PAXY-Cu and MUF-PAXY-Zn had flame retardancy times of 35.5 minutes and 35 minutes, respectively, representing increases of 173% and 169% compared to pure wood. This indicates that PAXY-Cu and PAXY-Zn flame retardants can effectively improve the flame retardant properties of wood.

[0060] (2) Morphological analysis of the large plate sample after combustion Figure 13 and Figure 14 These are side and top views of solid wood after it has been burned in a large slab. Figures 15-28 These are side and top views of fire-retardant wood after a large slab has burned. Figure 13 and Figure 14 As can be seen, pure wood is pierced by the flame of the butane torch after being burned in a large slab, and the char layer does not expand and is rather brittle. Figure 17 and Figure 18 It can be seen that after adding the flame retardant precursor PAXY, when the flame retardant coating on the sample surface is burned, a "worm-like" char layer is rapidly generated. This char layer rises rapidly, effectively resisting heat transfer and further improving the flame retardant performance of the sample. Figure 27 and Figure 28 As can be seen, after the PAXY metal was applied, the carbon layer on the sample surface was denser after the large plate combustion test, which could more effectively isolate heat and oxygen, and further improve the flame retardant performance of the sample.

[0061] 4.3 Cone Calorimeter Test Cone calorimeter (CONE) testing can further evaluate the combustion performance of materials, including ignition time (TTI), peak HRR (prominent pressure response rate) during coating combustion (PHRR), total heat release (THR), total smoke production (TSP), and peak CO2 emission. In this experimental example, the cone calorimeter (CONE) test was conducted according to ISO 5660-1:2002 standard using a cone calorimeter from Suzhou Yangyi Wolchi Testing Technology Co., Ltd. Pure wood samples, MUF flame-retardant wood samples, and MUF-PAXY-Zn flame-retardant wood samples were tested. The results are shown in Table 8. Figures 29-32 , Figures 33-38 As shown.

[0062] Figures 29-32 These are comparison charts of HRR, THR, TSP, and CO2 release of the samples. Figures 33-38 These are top and side views of the carbon residue of each sample after testing with a cone calorimeter.

[0063] Fire Risk Ratio (HRR) is a key parameter for assessing fire intensity. A higher HRR value indicates that more heat is released during combustion, thus increasing the fire risk. Figure 29 As shown in Table 8, the pure wood sample was ignited in 11 seconds, with a PHRR of 215.2 kW / m³. 2 The THR is 77.70 MJ / m³. 2 Compared to the pure wood sample, the MUF-PAXY-Zn sample coated with flame-retardant paint also rapidly reached its peak power of 213.63 kW / m³. 2 After 100 seconds, its HRR curve remained below that of the pure wood (NW) and CW curves. This indicates that the sample coated with flame-retardant paint effectively reduced heat release in the later stages of combustion. Table 8 shows that the TSP of the pure wood sample was 174.62 m³ / s. 2 The TSP of the MUF-PAXY-Zn sample is 95.84 m. 2 Compared to pure wood, smoke production was reduced by 45%, indicating that coatings with added PAXY-Zn flame retardant can effectively reduce smoke production. (See Table 8 and...) Figure 32 It can be seen that the CO2 emission curve of the sample coated with the flame-retardant coating MUF-PAXY-Zn is consistently lower than that of the pure wood sample (NW) and the sample coated with the MUF flame-retardant coating (CW). The peak CO2 emission of the pure wood sample is 0.260%, while the peak CO2 emission of MUF-PAXY-Zn is 0.208%, a decrease of 20% compared to pure wood. This indicates that the coating with added PAXY-Zn flame retardant can effectively reduce carbon dioxide emissions, while the peak CO2 emission of the wood sample using only MUF flame retardant increases instead of decreasing. Figures 33-38 As shown, pure wood leaves almost no char residue after being tested with a cone calorimeter, while the sample with added PAXY-Zn flame retardant forms a fluffy and dense char layer with a height of 2.5 cm after testing, which can further reduce heat release.

[0064] Experimental results show that coatings with added PAXY-Zn flame retardant can effectively reduce smoke production and carbon dioxide release, and can form a fluffy and dense char layer after combustion, further reducing heat release. Therefore, after preparing flame-retardant coatings by using PAXY-Zn flame retardant and compounding MUF, coating transparent wood with almost no impact on transparency while significantly improving overall flame-retardant performance can be achieved.

[0065] Table 8. Test results of cone calorimeter

[0066] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A flame retardant for transparent wood, characterized by, Its general structural formula is PAXY-M, the flame retardant is a water-soluble flame retardant, and the aqueous solution of the flame retardant is a transparent aqueous solution, wherein M is a metal salt selected from Ca. 2+ Co 2+ Ni 2+ Cu 2+ and Zn 2+ At least one of them, wherein M is coordinated with phytic acid and xylitol respectively.

2. The fire retardant for transparent wood according to claim 1, characterized by, After the reaction of phytic acid and xylitol to obtain water-soluble flame retardant precursor PAXY, the aqueous solution of the metal salt is added to the aqueous solution of the flame retardant precursor PAXY to obtain the flame retardant.

3. The fire retardant for transparent wood according to claim 2, characterized by, In the generation of PAXY, the molar ratio of phytic acid to xylitol is 1:3-1:

9.

4. The fire retardant for transparent wood according to claim 3, characterized by The molar ratio of phytic acid to xylitol is 1:6-1:

9.

5. The fire retardant for transparent wood according to claim 4, characterized by The molar ratio of phytic acid to xylitol is 1:

7.

6. The fire retardant for transparent wood according to claim 5, wherein The metal salt is acetate, and the molar ratio of phytic acid, xylitol and metal salt is 1:7:0.

35.

7. Flame retardant for transparent wood according to any one of claims 1-6, characterized in that, The M is at least one of Zn 2+ , Cu 2+ or Co 2+ .

8. A fire-retardant coating, characterized by, The flame retardant of any one of claims 1-7, further comprising MUF.

9. The process for the preparation of a flame retardant coating according to claim 8, characterized in that, The method comprises the following steps: PAXY preparation step: after the reaction of phytic acid and xylitol at 130°C, the flame retardant precursor PAXY is obtained; PAXY-M preparation step: after the preparation of PAXY, a metal salt solution is added to the reaction system, and after reaction at 80°C, purification is performed; MUF compounding step: after the purified PAXY-M is dissolved in water, MUF is added to the reaction system, and stirring is performed until transparency.

10. A fireproof transparent wood, characterized by, The transparent wood is obtained by coating the flame retardant coating of claim 8 or 9 on the surface of the transparent wood and curing. The transparent wood is obtained by coating the flame retardant coating of claim 8 or 9 on the surface of the transparent wood and curing.

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