Hexagonal boron nitride-guanazole-sodium hexametaphosphate flame-retardant resin coating and preparation method thereof

Abstract

The application discloses a kind of hexagonal boron nitride-guanazole-sodium hexametaphosphate fire-retardant resin coating, BNGS is combined with urea and formaldehyde as main raw material, with dioctyl phthalate DOP as plasticizer, tannic acid TA as curing agent, UF-BNGS is prepared by three-stage reaction;BNGS is by hexagonal boron nitride BN, 3,5-diamino-1,2,4-triazole GZ and sodium hexametaphosphate SHMP as bio-based flame-retardant component as raw material;The temperature of UF-BNGS decomposition mass is 5% when 228.9±1.1℃, the temperature when reaching maximum decomposition rate is 301.47±1.5℃, and the carbon residue amount at 800℃ is 39.95±0.5wt.%;Can form dense carbon residue carbon layer.The preparation method comprises the following steps: 1, preparation of BNGS flame retardant;2, preparation of modified urea-formaldehyde resin emulsion UF;As the application of wood fire-retardant coating, it has flame-retardant properties, forms continuous dense carbon residue carbon layer;Pass UL-94V-0 level test;Heat release rate HRR is 55.73±1.25kW / m 2 .

Description

Technical Field

[0001] This invention relates to the field of flame retardant materials, specifically to a hexagonal boron nitride-guanidazole-sodium hexametaphosphate flame retardant resin coating and its preparation method. Background Technology

[0002] Wood is an abundant and sustainable biomass material, widely used in various fields due to its low cost and excellent mechanical properties. However, wood is easily ignited and releases a lot of smoke, posing a great danger to people. Therefore, we need to improve the flame retardant properties of wood. There are two main methods to reduce the flame retardant properties of wood: coating wood with flame retardant coatings and impregnating wood with solutions. Wood flame retardant coatings usually use compounds containing halogens, boron, phosphorus, nitrogen, and inorganic metals (such as aluminum, magnesium, and zinc) to improve the flame retardancy of wood. For example, the inventors of this invention previously researched and published literature 1 (application number: 2024113226527. Preparation and application of urea-formaldehyde resin blended guanidineazole-phytate copper flame retardant resin coating), which uses guanidineazole, phytate, copper hydroxide, formaldehyde, and urea as raw materials to prepare a urea-formaldehyde resin blended guanidineazole-phytate-copper flame retardant resin coating through chemical reaction and physical blending. The invention aims to improve the density of the char layer in a flame-retardant matrix and reduce heat release and total heat output. Therefore, metallic copper is introduced through a complexation reaction to synthesize a guanidineazole-copper phytate flame retardant, which is then blended with urea-formaldehyde resin to form a flame-retardant coating. While this invention utilizes the catalytic degradation properties of metallic copper to promote the formation of a dense char layer, thus solving the problems of char layer density and heat release, this same property also leads to a decrease in the resin degradation temperature, resulting in reduced resin thermal stability. This problem is not only reflected in the decomposition temperature but also in the relatively low effect on improving the amount of char residue and the charring rate.

[0003] To address the issue of low charring rate, components with high thermal conductivity can be introduced to improve the charring rate, thermal stability, and thermal conductivity of the polymer matrix. For example, existing literature 2 (Improving fire safety and mechanical properties of waterborne polyurethane by montmorillonite-passivated black phosphorus[J]. Chemical Engineering Journal, 2023, 464:142683.) uses hexagonal boron nitride, chitosan, and polyvinyl alcohol as raw materials to prepare a flame retardant through magnetic stirring. When coated on the wood surface, it forms a flame-retardant film. Combustion tests show that the charring rate of this flame retardant reaches 61.3%. This technical solution introduces hexagonal boron nitride, utilizing its inherent high thermal stability and thermal conductivity to improve the thermal stability and charring rate of the flame-retardant system. The principle is that the residual char of the flame-retardant material is positively correlated with the initial charring, meaning that increasing the initial charring temperature can increase the charring rate. For the above reasons, the total heat release (THR) of this technical solution is reduced by only 7.54%. However, the smoke release rate of this technical solution not only failed to decrease, but actually increased by 55.56%. Further analysis revealed that the main reason for the smoke release was the use of polyvinyl alcohol as a film-forming material in the raw materials, which releases a large amount of smoke when burned in an open flame. This technical solution also suffers from the problem that hexagonal boron nitride, due to its chemical inertness, is difficult to disperse uniformly in aqueous solutions.

[0004] To address the issue of excessive smoke, existing technologies employ gel-type flame retardants instead of film-forming flame retardants, avoiding the use of film-forming materials such as polyvinyl alcohol. Simultaneously, to address the problems associated with hexagonal boron nitride, modification of the hexagonal boron nitride can be used to improve its dispersibility. For example, existing literature 3 (Zinc ion cross-linked sodium alginate modified hexagonal boron nitride to enhance the flame retardant properties of composite coatings[J]. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2022, 647:129200) first modifies hexagonal boron nitride by loading water-soluble polyethyleneimine onto hexagonal boron nitride nanosheets through Lewis acid-base interaction and ultrasonic treatment. Then, sodium alginate is added to prepare a gel-type flame retardant. The flame retardant obtained by this technical solution can achieve a char residue rate of 31.7%, and the smoke density rating (SDR) is reduced from 63.5% to 41.2%, a reduction of 35.12%. This technical solution avoids the use of raw materials that produce large amounts of smoke. However, because the resulting material is a gel, it directly leads to two technical problems: 1. The modified hexagonal boron nitride still exists in the form of nanoparticles and cannot be uniformly dispersed in the gel; 2. The char residue layer formed during combustion inevitably contains a small number of pores and even cracks.

[0005] One method to address the dispersibility of hexagonal boron nitride (BN) is to improve its dispersibility by modifying it with an organic solvent. For example, existing literature 4 (Thermal exfoliation of hexagonal boronnitride for effective enhancements on thermal stability, flame retardancy and smoke suppression of epoxy resin nanocomposites via sol-gel process[J]. Journal of Materials Chemistry A, 2016, 4(19): 7330-40) first modifies BN to hydroxylated BNO using a heat treatment method. Then, acetone is used as a solvent to improve the dispersibility of BNO. Simultaneously, epoxy resin EP is modified with (propyltriethoxysilane) to obtain silane-modified epoxy resin MEP. Finally, BNO, MEP, and dibutyltin dilaurate are combined to prepare a flame retardant. In this study, BNO and MEP are covalently bonded through functional groups represented by hydroxyl groups, which improves dispersibility and stability. The technical effect achieved a reduction of PHRR and THR by 53.1% and 32.6% respectively, and a reduction of total smoke emission by 23.13%. However, the char residue was only 22.4%. The reason for this is that, due to the low carbon content of BNO itself, it is impossible to directly increase the char residue. Therefore, using BNO alone as a flame retardant additive results in a low char residue. Summary of the Invention

[0006] The purpose of this invention is to provide a hexagonal boron nitride-guanidazole-sodium hexametaphosphate flame retardant resin coating and its preparation method.

[0007] To address the issues of existing flame retardants based on hexagonal boron nitride requiring activation treatment and increased char residue, this problem is solved by compounding hexagonal boron nitride (BN) with 3,5-diamino-1,2,4-triazole (GZ) and sodium hexametaphosphate (SHMP). Specifically, guanidinazole (GZ) is used as a surface amination agent and nitrogen source, while SHMP serves as a physical crosslinking agent, phosphorylation agent, and acid source. Combined with ultrasonic treatment, the dispersibility of BN is improved, ultimately enhancing the flame retardant performance of the flame-retardant resin coating.

[0008] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0009] A hexagonal boron nitride-guanidine azole-sodium hexametaphosphate flame retardant resin coating, UF-BNGS, is prepared by combining hexagonal boron nitride-guanidine azole-sodium hexametaphosphate flame retardant BNGS with urea and formaldehyde as the main raw materials, using dioctyl phthalate (DOP) as a plasticizer and tannic acid (TA) as a curing agent, through a four-stage reaction.

[0010] The BNGS is prepared by chemical reaction using hexagonal boron nitride (BN), 3,5-diamino-1,2,4-triazole (GZ), and sodium hexametaphosphate (SHMP) as bio-based flame retardant components.

[0011] The resulting BNGS contains BN, PNC, POP, P=O, -NH2, and OH;

[0012] The temperature at which the UF-BNGS decomposes to 5% by mass is 228.90±1.10℃, the temperature at which the maximum decomposition rate is reached is 301.47±1.50℃, and the amount of char residue at 800.00℃ is 39.95±0.50wt.%.

[0013] When the amount of BNGS added is 2 wt.%, a dense residual carbon layer is formed.

[0014] A method for preparing a hexagonal boron nitride-guanidazole-sodium hexametaphosphate flame-retardant resin coating includes the following steps:

[0015] Step 1, Preparation of hexagonal boron nitride-guanidazole-sodium hexametaphosphate flame retardant: First, hexagonal boron nitride (BN) is placed in water and ultrasonically dispersed under certain conditions to obtain a BN solution. Then, guanidazole (GZ) is placed in the BN solution and stirred in a water bath under certain conditions to obtain an amino-functionalized BN-GZ solution. After that, sodium hexametaphosphate (SHMP) is placed in the BN-GZ solution and stirred under certain conditions to obtain a BNGS solution. After the reaction is complete, the obtained product is filtered, washed, dried, and ground into powder to obtain the hexagonal boron nitride-guanidazole-sodium hexametaphosphate flame retardant BNGS.

[0016] In step 1, the mass ratio of BN, GZ and SHMP is 1:1:2;

[0017] In step 1, the ultrasound conditions are that the ultrasound time is 1 hour;

[0018] In step 1, the conditions for water bath stirring are: water bath temperature of 60-70℃, stirring speed of 400-500rpm, and stirring time of 1-1.5h.

[0019] In step 1, the conditions for the stirring reaction are: reaction temperature of 90°C and reaction time of 3 hours.

[0020] In step 1, the washing is completed when the pH of the washing solution is 6-7; the drying is completed when the drying temperature is 80℃ and the drying time is 24h.

[0021] Step 2, Preparation of hexagonal boron nitride-guanidazole-sodium hexametaphosphate flame retardant resin coating: First, sodium hydroxide solution is added to formaldehyde solution to adjust the pH value of the solution to obtain solution A. Then, under certain conditions, urea, BNGS and other raw materials are added in four stages to prepare urea-formaldehyde resin blended hexagonal boron nitride-guanidazole-sodium hexametaphosphate flame retardant resin coating UF-BNGS.

[0022] In step 2, the mass ratio of the total amount of BNGS, formaldehyde and urea added in step 1 is 2:100:57.

[0023] In step 2, the conditions for preparing solution A are as follows: the pH value of the solution is adjusted to 8.0-8.5;

[0024] In step 2, the conditions for adding urea are: stirring speed of 400-500 rpm and reaction temperature of 90℃.

[0025] In step 2, the four stages of adding urea are as follows:

[0026] Step 2.1 involves adding the first stage of urea while maintaining a certain temperature. After the addition is complete, stirring is continued for a certain period of time.

[0027] In step 2.1, the amount of urea added is 64.9% of the total urea, the temperature in step 2.1 is 90℃, and the stirring time is 30 minutes.

[0028] Step 2.2 involves first adding acetic acid solution to adjust the pH value of the solution while maintaining a certain temperature, and then adding urea in the second stage. After the addition is complete, stirring is continued for a certain period of time until the reaction endpoint is reached.

[0029] In step 2.2, the amount of urea added is 21.6% of the total amount of urea, the pH of the solution is adjusted to 4.5-5.0, the temperature in step 2.2 is 90℃, and the stirring time is 15min.

[0030] The endpoint of the second stage reaction is determined by dropping a drop of the solution into water at 30°C; the solution will solidify and not disperse in the water.

[0031] Step 2.3 involves first adjusting the pH value by adding sodium hydroxide solution while maintaining a certain temperature, then adding urea from the third stage. After the addition is complete, the mixture is stirred until it becomes viscous to obtain UF.

[0032] In step 2.3, the amount of urea added is 13.3% of the total amount of urea, the pH of the solution is adjusted to 7.5-8.0, the temperature in step 2.2 is 90℃ when adjusting the pH, and 70℃ after the pH is adjusted, and the stirring time is 30-40min.

[0033] Step 2.4 involves adding BNGS to UF and stirring it under certain conditions to obtain UF-BNGS.

[0034] In step 2.4, the stirring rate of BNGS is 400 rpm and the stirring temperature is room temperature.

[0035] A hexagonal boron nitride-guanidazole-sodium hexametaphosphate flame-retardant resin coating, when used as a flame-retardant coating for wood, exhibits flame-retardant properties and forms a continuous, dense char layer after combustion. It passes the UL-94 V-0 rating test in the UL-94 rating test; and in the cone calorimetry test, its heat release rate (HRR) is 55.73 ± 1.25 kW / m³. 2 .

[0036] The technical effects of the hexagonal boron nitride-guanidazole-sodium hexametaphosphate flame-retardant resin coating obtained by this invention have been tested as follows:

[0037] According to TG test results, the temperature at which UF-BNGS-2 decomposes to a mass of 5% is 228.90±1.10℃, the temperature at which the maximum decomposition rate is reached is 301.47±1.50℃, and the char residue at 800.00℃ is 39.95±0.50wt.%. Coating with UF-BNGS-2 can improve the char residue rate of the material and produce a more stable char residue layer in the high-temperature region.

[0038] Further SEM testing was conducted on the expanded char layer formed on the surface of the NW coated with UF-BNGS-2 flame-retardant coating after combustion. UF-BNGS-2 can form a dense char layer with almost no pores. The test results indicate that UF-BNGS-2 can form a high-quality residual char layer after combustion, effectively isolating oxygen and heat, thereby improving the flame-retardant performance of the NW.

[0039] Vertical burning tests showed that applying UF-BNGS-2 flame retardant coating enabled NW to pass the UL-94V-0 rating.

[0040] Limiting oxygen index (LOI) tests show that applying UF-BNGS-2 flame retardant coating can improve its limiting oxygen index, reaching 34.0%.

[0041] The results of cone calorimetry testing show that the heat release rate of wood coated with UF-BNGS-2 flame retardant coating is 55.73±1.25%, which can significantly reduce the heat release rate of NW.

[0042] Therefore, the present invention has the following advantages over the prior art:

[0043] 1. The bio-based flame retardant resin coating of the present invention improves the flame retardant performance while increasing the residual char content of the matrix by using hexagonal boron nitride. Sodium hexametaphosphate decomposes into pyrophosphate upon heating, which not only promotes the carbonization of the matrix but also increases the formation of coke and improves the residual char content.

[0044] 2. This invention improves the activity of hexagonal boron nitride by amination treatment and phosphorylation treatment by introducing sodium hexametaphosphate as a physical crosslinking agent;

[0045] 3. All raw materials involved in this invention are commercially available and are low-cost raw materials, which meet the application requirements for large-scale production. Attached Figure Description

[0046] Figure 1 The FTIR plot of Example 1;

[0047] Figure 2 The FTIR plots are those of Example 1 and Comparative Example 2;

[0048] Figure 3 The TG plots are for Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4;

[0049] Figure 4 This is a SEM image of Example 1;

[0050] Figure 5 The images show vertical combustion test results for Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4.

[0051] Figure 6 HRR plots for Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4;

[0052] Figure 7 This is the SEM image of Comparative Example 1;

[0053] Figure 8 This is the SEM image of Comparative Example 2;

[0054] Figure 9 This is the SEM image of Comparative Example 3;

[0055] Figure 10 This is the SEM image of Comparative Example 4;

[0056] Figure 11This is the SEM image of Comparative Example 5. Detailed Implementation

[0057] The present invention will be further described in detail through embodiments and with reference to the accompanying drawings, but this is not intended to limit the scope of the invention.

[0058] Example 1

[0059] A method for preparing a hexagonal boron nitride-guanidazole-sodium hexametaphosphate flame-retardant resin coating includes the following steps:

[0060] Step 1: Preparation of hexagonal boron nitride-guanidazole-sodium hexametaphosphate flame retardant BNGS. First, 2g of hexagonal boron nitride (BN) was placed in 150mL of water and ultrasonically dispersed for 1 hour to obtain a BN solution. Then, 9.71g of guanidazole (GZ) was placed in the BN solution and stirred in a water bath at 70℃, 400rpm, and for 1 hour to obtain an amino-functionalized BN-GZ solution. Next, 10g of sodium hexametaphosphate (SHMP) was placed in the BN-GZ solution and stirred at 90℃ for 3 hours to obtain a BNGS solution. After the reaction was completed, the resulting product was filtered, washed, dried, and ground into powder to obtain the hexagonal boron nitride-guanidazole-sodium hexametaphosphate flame retardant, abbreviated as BNGS.

[0061] The washing is completed under the following conditions: the pH of the washing solution is 6-7; the drying is completed under the following conditions: the drying temperature is 80℃ and the drying time is 24 hours.

[0062] To confirm the composition of BNGS, i.e., successful synthesis, an FTIR test was performed. The test results are as follows: Figure 1 As shown, BNGS contains characteristic peaks for -NH, P=O, PNC / BN, and POP. The -NH characteristic peak is attributed to GZ, the P=O and POP characteristic peaks are attributed to SHMP, PNC is attributed to a mixture of GZ and SHMP, and BN is attributed to BN and amino-functionalized BN. The test results indicate that the BNGS flame retardant was successfully synthesized.

[0063] Step 2, preparation of the hexagonal boron nitride-guanidazole-sodium hexametaphosphate flame retardant resin coating UF-BNGS: First, 20 wt.% sodium hydroxide solution was added to 100 g of 37 wt.% formaldehyde solution to adjust the pH of the solution to 8.0-8.5, obtaining solution A. Then, under the conditions of stirring speed of 400 rpm and reaction temperature of 90℃, the BNGS obtained in step 1, urea, and other raw materials were added in four stages.

[0064] The amount of BNGS added is 2 wt.% of UF, specifically 2 g, and the total amount of urea added is 57%, specifically 57 g.

[0065] This allows for the preparation of a flame-retardant resin coating made from a blend of urea-formaldehyde resin and boron nitride-guanidazole-sodium hexametaphosphate, abbreviated as UF-BNGS-2.

[0066] The four stages are as follows:

[0067] Step 2.1 involves adding 37g of the first-stage urea while maintaining a temperature of 90℃. After the addition is complete, continue stirring for 30 minutes.

[0068] Step 2.2 involves maintaining a temperature of 90℃, first adding 20wt.% acetic acid solution to adjust the pH of the solution to 4.5-5.0, then adding 12.4g of second-stage urea. After the addition is complete, continue stirring for 15 minutes until the reaction endpoint is reached.

[0069] The endpoint of the second stage reaction is determined by dropping a drop of the solution into water at 30°C; the solution will solidify and not disperse in the water.

[0070] Step 2.3 involves first maintaining a temperature of 90℃, adding 20wt.% sodium hydroxide solution to adjust the pH to 7.5-8.0, then adding 7.6g of urea from the third stage. After the addition is complete, the temperature is adjusted, and the mixture is stirred at 70℃ for 30 minutes to obtain UF.

[0071] Step 2.4 involves adding 2g of BNGS to UF and stirring at room temperature with a stirring speed of 400 rpm for 30 minutes to obtain UF-BNGS. Specifically, the UF-BNGS-2 mixed emulsion obtained in Example 1 is named UF-BNGS-2.

[0072] Since subsequent tests need to be conducted after UF-BNGS-2 has cured, a specific curing method is provided. The curing method is as follows: First, under the conditions of a stirring rate of 400 rpm and a stirring time of 30 min, dioctyl phthalate (DOP), tannic acid (TA), and UF-BNGS-2 are mixed in a mass ratio of 0.1:0.1:10, i.e., 1g of DOP and 1g of TA are added to 100g of UF-BNGS-2 to obtain the UF-BNGS-2 flame-retardant resin coating. Then, depending on the experimental requirements, the UF-BNGS-2 flame-retardant resin coating is placed in a mold for direct curing or coated onto the wood surface for 72 h to obtain the BNGS-based flame-retardant resin coating. Since there is no need for differentiation, the cured material is still simply referred to as UF-BNGS-2.

[0073] The specific method for coating the wood surface is as follows: apply UF-BNGS-2 evenly to the wood surface with a coating thickness of 0.3 mm, and then dry it for 24 hours after coating.

[0074] To confirm the composition of UF-BNGS-2, i.e., successful synthesis, FTIR testing was performed. The FTIR test results are as follows: Figure 2 As shown, UF-BNGS-2 contains characteristic peaks of -OH, P=O, OPC, PO-ph, BN, and BOC. Among them, the characteristic peak of -NH2 belongs to GZ, the characteristic peaks of P=O, PO-ph, and OPC belong to SHMP, and BN and BOC belong to BN. The test results show that the UF-BNGS-2 flame retardant coating is composed of GZ, SHMP, and BN, that is, UF-BNGS-2 was successfully synthesized.

[0075] To demonstrate the technical effectiveness of UF-BNGS-2 as a flame-retardant coating for wood, a TG test was conducted. The test results are as follows: Figure 3 As shown in Table 1, the temperature at which UF-BNGS decomposes to a mass of 5% is 228.90±1.10℃, the temperature at which the maximum decomposition rate is reached is 301.47±1.50℃, and the char residue at 800.00℃ is 39.95±0.50wt.%.

[0076] Table 1 Summary of TG Test Results

[0077]

[0078] To further demonstrate the microstructure of the residual carbon layer, SEM was performed on the surface of UF-BNGS-2 after TG testing. The test results are as follows: Figure 4 As shown, UF-BNGS-2 can form a dense char layer with almost no pores, which can be simply referred to as a dense structure. Test results show that UF-BNGS-2 can form a high-quality char layer after combustion, which can effectively isolate oxygen and heat, thereby improving the flame retardant properties of wood.

[0079] To further demonstrate the flame retardancy of UF-BNGS-2, vertical burning tests and limiting oxygen index tests were conducted.

[0080] Vertical burning test results are as follows Figure 5 As shown in Table 2, the open flame time after the first ignition of UF-BNGS-2 is 1.0s, and the open flame and flameless burning time after the second ignition is 1.7s, with no dripping, indicating that UF-BNGS-2 has passed the UL-94 V-0 rating.

[0081] The limiting oxygen index test results are shown in Table 2. The limiting oxygen index of UF-BNGS-2 is 34.0%.

[0082] Table 2 Results of Vertical Combustion Test and Oxygen Index Test

[0083]

[0084] To further quantify the flame retardancy of UF-BNGS-2, a cone calorimetry test was conducted. The test results are as follows: Figure 6 As shown, the heat release rate (HRR) of UF-BNGS-2 is 55.73 kW / m². 2 .

[0085] To demonstrate the effect of UF-BNGS-2 on the flame retardant properties of wood, Comparative Example 1, uncoated wood, was provided as a base reference, and Comparative Example 2, pure urea-formaldehyde resin UF without the addition of BNGS-2 flame retardant, was provided.

[0086] Comparative Example 1

[0087] A type of wood that is not coated with flame retardant, abbreviated as NW.

[0088] To demonstrate the microstructure of the residual char layer, SEM analysis was performed on the NW after complete combustion. The test results are as follows: Figure 7 As shown, the char layer after NW combustion is almost completely broken, referred to as a broken structure. Compared with Example 1, it can be seen that coating with UF-BNGS-2 can form a dense residual char layer, thus improving flame retardant performance.

[0089] To further demonstrate the flame retardancy of NW, vertical burning tests and limiting oxygen index tests were conducted.

[0090] Vertical burning test results are as follows Figure 5 As shown in Table 2, if the open flame time after the first ignition of the NW is greater than 60 seconds and there is dripping, it indicates that the NW has not passed the UL-94 V-0 rating. A comparison with Example 1 shows that coating the NW with UF-BNGS-2 can enable it to pass the UL-94 rating test.

[0091] The limiting oxygen index test results are shown in Table 2. The limiting oxygen index of NW is 20.3%. Compared with Example 1, it can be seen that coating with UF-BNGS-2 can increase the limiting oxygen index from 20.0% to 34.0%.

[0092] To further quantify the flame retardancy of NW, a cone calorimeter test was conducted. The test results are as follows: Figure 6 As shown, the HRR of NW is 232.22 kW / m². 2Compared with Example 1, it can be seen that coating with UF-BNGS-2 can reduce the HRR by 76.00%, that is, significantly reduce the heat release rate, thereby significantly improving flame retardancy.

[0093] Comparative Example 2

[0094] A method for preparing pure urea-formaldehyde resin UF without adding BNGS flame retardant is disclosed. Unless otherwise specified, the steps are the same as in Example 1, except that step 1 is not required, and in step 2, step 2.2, BNGS is not added to obtain pure urea-formaldehyde resin UF without adding BNGS flame retardant, which is referred to as UF.

[0095] To demonstrate the technical effectiveness of UF as a flame-retardant coating for wood, a TG test was conducted. The test results are as follows: Figure 3 As shown in Table 1, the temperature at which UF decomposes to a mass of 5% is 204.2℃, the temperature at which the maximum decomposition rate is reached is 300.32℃, and the char residue at 800℃ is 10.00 wt.%. Compared with Example 1, it can be seen that the addition of UF-BNGS can increase the char residue from 10.00 wt.% to 39.94 wt.%, an increase of 74.96%, that is, the addition of UF-BNGS-2 can significantly increase the char residue.

[0096] To further demonstrate the microstructure of the residual carbon layer, SEM was performed on the UF surface after TG testing. The test results are as follows: Figure 8 As shown, the char layer formed after UF combustion exhibits severe fragmentation, i.e., a fractured structure.

[0097] Compared with Comparative Example 1, it can be seen that although coating with UF can slightly reduce the degree of breakage of the residual char layer and slightly improve the flame retardancy, the resulting residual char layer is not substantially changed compared with NW, and it is still a broken structure.

[0098] Compared with Example 1, it can be seen that adding BNGS-2 flame retardant can transform the char residue layer from a broken structure to a dense structure.

[0099] To further demonstrate the flame retardancy of UF, vertical burning tests and limiting oxygen index tests were conducted.

[0100] Vertical burning test results are as follows Figure 5 As shown in Table 2, the open flame time after the first ignition of UF is 14.2s, and the open flame and flameless burning time after the second ignition is 16.6s. There are no drips, which indicates that UF has passed the UL-94V-1 rating.

[0101] Compared with Comparative Example 1, it can be seen that coating with UF can improve the NW rating from no rating to UL-94V-1 rating, that is, coating with UF can improve flame retardancy.

[0102] Compared with Example 1, it can be seen that adding BNGS flame retardant can improve the UL-94 rating from V-1 to V-0.

[0103] The limiting oxygen index test results are shown in Table 2. The limiting oxygen index of UF is 27.8%.

[0104] Compared with Comparative Example 1, it can be seen that coating with UF can increase the limiting oxygen index from 20.0% to 27.8%, that is, coating with UF can improve flame retardancy;

[0105] Compared with Example 1, it can be seen that adding BNGS flame retardant can increase the limiting oxygen index from 27.8% to 34.0%.

[0106] To further quantify the flame retardancy of NW, a cone calorimeter test was conducted. The test results are as follows: Figure 6 As shown, the HRR of UF reaches 87.22 kW / m². 2 ,

[0107] Compared with Comparative Example 1, it can be seen that the HRR reduction achieved by coating with UF is 62.44%, which means that the heat release rate is reduced and the flame retardancy is improved.

[0108] Compared with Example 1, the addition of BNGS-2 flame retardant can further reduce the HRR by 36.10%.

[0109] As can be seen from Examples 1, 1, and 2, the reason why coating with UF improves flame retardancy is that UF itself has higher flame retardancy than pure wood. However, adding UF alone can only obtain a very low amount of char residue, and the formed char residue layer is in a broken state, i.e., of poor quality, which leads to the inability to effectively improve flame retardancy. On the other hand, adding BNGS flame retardant can significantly increase the amount of char residue and form a dense char residue layer at the same time, thus achieving a significant improvement in flame retardancy.

[0110] To demonstrate the effect of SHMP on the flame retardant properties of BNGS, i.e. its role in the technical solution, Comparative Example 3 is provided, a hexagonal boron nitride-guanidazole coating prepared without the addition of SHMP.

[0111] Comparative Example 3

[0112] A hexagonal boron nitride-guanidazole coating prepared without the addition of SHMP is described below. Unless otherwise specified, the steps are the same as in Example 1, except that sodium hexametaphosphate is not added in step 1, and the resulting material is referred to as BNG. In step 2, BNG is used instead of BNGS, that is, 2g of BNG is added, and the resulting material is referred to as UF-BNG.

[0113] To demonstrate the technical effectiveness of UF-BNG as a flame-retardant coating for wood, a TG test was conducted. The test results are as follows: Figure 9 As shown in Table 1, the temperature at which UF-BNG decomposes to a mass of 5% is 235.38 ± 0.20 °C, the temperature at which the maximum decomposition rate is reached is 341.28 ± 0.80 °C, and the char residue at 800 °C is 26.84 ± 1.01 wt.%. Compared with Example 1, it can be seen that the addition of sodium hexametaphosphate (SHMP) can significantly increase the char residue. This is because SHMP contains phosphate groups, which can promote the carbonization of UF-BNG by forming pyrophosphates when heated, thereby increasing the char residue.

[0114] To demonstrate the effect of BNGS addition amount on flame retardant properties, Comparative Examples 4 and 5 were provided, with BNGS addition amounts of 1 wt.% and 3 wt.% of UF, respectively, of hexagonal boron nitride-guanidazole-sodium hexametaphosphate flame retardant.

[0115] Comparative Example 4

[0116] A flame-retardant resin coating of hexagonal boron nitride-guanidazole-sodium hexametaphosphate with a BNGS addition amount of 1 wt.% is described. Unless otherwise specified, the steps are the same as those in Example 1, except that in step 2.4, the BNGS addition amount is 1 wt.%, specifically 1 g of BNGS is added. The flame retardant obtained in step 1 is abbreviated as BNGS-1, and the material obtained in step 2.4 is abbreviated as UF-BNGS-1.

[0117] To demonstrate the technical effectiveness of UF-BNGS-1 as a flame-retardant coating for wood, a TG test was conducted. The test results are as follows: Figure 3 As shown in Table 1, the temperature at which UF-BNGS decomposes to a mass of 5% is 204.80±1.20℃, the temperature at which the maximum decomposition rate is reached is 300.48±0.98℃, and the char residue at 800℃ is 26.88±2.01wt.%.

[0118] Compared with Comparative Example 2, it can be seen that even with a small amount of BNGS added, the residual carbon content of UF can be effectively increased by 62.80%.

[0119] Compared with Example 1, when the BNGS addition amount reaches 2 wt.%, the residual char content is significantly increased further, with an increase of 32.70%.

[0120] Test results show that the amount of BNGS added can significantly affect the amount of char residue.

[0121] To further demonstrate the microstructure of the residual carbon layer, SEM was performed on the surface of UF-BNGS-1 after TG testing. The test results are as follows: Figure 10As shown, the residual carbon layer formed by UF-BNGS-1 has many pores, meaning that a dense residual carbon layer cannot be formed.

[0122] Compared with Comparative Example 2, it can be seen that when the amount of BNGS added is small, it can only transform the residual carbon layer from a broken structure to a porous structure.

[0123] Compared with Example 1, it can be seen that when the amount of BNGS added reaches 2 wt.%, the residual carbon layer can be transformed from a porous structure to a dense structure, that is, the quality of the residual carbon layer is improved.

[0124] Test results show that the working principle of BNGS flame retardant is to fill the char layer with a broken structure formed by NW combustion through its own carbonization process, thereby forming a dense residual char layer. When the amount of BNGS added is small, it cannot fill the char layer sufficiently and can only transform the broken structure into a porous structure. Therefore, it cannot form a dense residual char layer, which means it cannot effectively improve the flame retardant performance.

[0125] To further demonstrate the flame retardancy of UF-BNGS-1, vertical burning tests and limiting oxygen index tests were conducted.

[0126] Vertical burning test results are as follows Figure 5 As shown in Table 2, the open flame time after the first ignition of UF-BNGS-1 is 1.2s, and the open flame and flameless burning time after the second ignition is 3.3s, with no dripping, indicating that UF-BNGS-1 has passed the UL-94V-0 rating.

[0127] Compared with Comparative Example 1, it can be seen that coating with UF-BNGS-1 can improve the NW rating from no rating to UL-94V-0 rating, that is, coating with UF-BNGS-1 can significantly improve flame retardancy.

[0128] Compared with Comparative Example 2, it can be seen that adding a small amount of BNGS to the coating can improve the UL-94 rating of UF from V-1 to V-0. That is, even when the amount of BNGS added is small, it can effectively improve the UL-94 rating and have a substantial impact.

[0129] Compared with Example 1, it can be seen that both UF-BNGS-2 and UF-BNGS-1 coatings can pass the UL-94 rating test, which indicates that the amount of flame retardant BNGS added has no substantial impact on the UL-94 rating.

[0130] The limiting oxygen index test results are shown in Table 2. The limiting oxygen index of UF-BNGS-1 is 32.0%.

[0131] Compared with Comparative Example 1, it can be seen that coating with UF-BNGS-1 can effectively improve the limiting oxygen index of NW by 36.56%.

[0132] Compared with Comparative Example 2, it can be seen that even with a small amount of BNGS added, the limiting oxygen index of UF can be further increased by 13.13%.

[0133] Compared with Example 1, it can be seen that the effect of increasing the amount of BNGS on improving the limiting oxygen index is negligible, which means that the amount of BNGS added has no substantial effect on the limiting oxygen index.

[0134] To further quantify the flame retardancy of UF-BNGS-1, a cone calorimeter test was conducted. The test results are as follows: Figure 6 As shown, the HRR of UF-BNGS-1 reaches 58.00 kW / m². 2 .

[0135] Compared with Comparative Example 1, it can be seen that coating with UF-BNGS-1 can effectively reduce the HRR of NW by 75.02%.

[0136] Compared with Comparative Example 2, it can be seen that even with a small amount of BNGS added, the HRR of UF can be significantly reduced further, with a reduction of 33.50%.

[0137] Compared with Example 1, it can be seen that when the amount of BNGS added is increased, the HRR actually increases slightly, by 4.07%.

[0138] Comparative Example 4 shows that even a small amount of UF-BNGS coating can significantly improve the flame retardant properties of NW, namely, greatly increasing the char residue, UL-94 rating and limiting oxygen index, and reducing HRR. However, when the amount of BNGS added is small, it is not possible to effectively form a dense char residue layer.

[0139] Comparative Example 5

[0140] A flame-retardant resin coating of hexagonal boron nitride-guanidazole-sodium hexametaphosphate with a BNGS addition amount of 3 wt.% is described. Unless otherwise specified, the steps are the same as those in Example 1, except that in step 2.4, the BNGS addition amount is 3 wt.%, specifically 3 g of BNGS is added. The flame retardant obtained in step 1 is abbreviated as BNGS-3, and the material obtained in step 2.4 is abbreviated as UF-BNGS-3.

[0141] To demonstrate the technical effectiveness of UF-BNGS-3 as a flame-retardant coating for wood, a TG test was conducted. The test results are as follows: Figure 3 As shown in Table 1, the decomposition temperature of UF-BNGS when 5% decomposition occurs is 192.10℃. The temperature at which the maximum decomposition rate is reached is 295.81℃, and the char residue at 800.00% is 17.72 wt.%.

[0142] Compared with Comparative Example 2, it can be seen that when the amount of BNGS added is higher, it can also effectively increase the carbon residue of UF, with an increase of 43.57%.

[0143] Compared with Example 1, it can be seen that when the amount of BNGS added reaches 3 wt.%, that is, when it is excessive, the amount of residual char is significantly reduced, with a reduction of 55.64%.

[0144] Test results show that the amount of BNGS added can significantly affect the amount of char residue.

[0145] To further demonstrate the microstructure of the residual carbon layer, SEM was performed on the surface of UF-BNGS-3 after TG testing. The test results are as follows: Figure 11 As shown, the residual carbon layer formed by UF-BNGS-3 has many pores, meaning that a dense residual carbon layer cannot be formed.

[0146] Compared with Comparative Example 2, it can be seen that when the amount of BNGS added is high, it can only transform the residual carbon layer from a broken structure to a porous structure.

[0147] Compared with Example 1, it can be seen that when the amount of BNGS added reaches 3 wt.%, that is, when it is excessive, the original dense structure of the residual carbon layer is transformed back into a porous structure.

[0148] Test results show that when the amount of BNGS added is excessive, the overfilling of BNGS will instead form protrusions on the coating surface, creating new defects. This will prevent the formation of a dense char layer and thus fail to effectively improve the flame retardant performance.

[0149] To further demonstrate the flame retardancy of UF-BNGS-3, vertical burning tests and limiting oxygen index tests were conducted.

[0150] Vertical burning test results are as follows Figure 5 As shown in Table 2, the open flame time after the first ignition of UF-BNGS-3 is 1.1s, and the open flame and flameless burning time after the second ignition is 15.0s, with no dripping, indicating that UF-BNGS-3 has passed the UL-94V-0 rating.

[0151] Compared with Comparative Example 1, it can be seen that coating with UF-BNGS-3 can improve the NW rating from no rating to UL-94V-0 rating, that is, coating with UF-BNGS-3 can significantly improve flame retardancy.

[0152] Compared with Comparative Example 2, it can be seen that the addition of excessive BNGS can also improve the UL-94 rating of UF from V-1 to V-0. That is, when the amount of BNGS added is excessive, it can also effectively improve the UL-94 rating and have a substantial impact.

[0153] Compared with Example 1, it can be seen that both UF-BNGS-2 and UF-BNGS-3 coatings can pass the UL-94 rating test, which indicates that the amount of flame retardant BNGS added has no substantial impact on the UL-94 rating.

[0154] The limiting oxygen index test results are shown in Table 2. The limiting oxygen index of UF-BNGS-3 is 27.5%.

[0155] Compared with Comparative Example 1, it can be seen that coating with UF-BNGS-3 can effectively improve the limiting oxygen index of NW by 26.18%.

[0156] Compared with Comparative Example 2, it can be seen that when the amount of BNGS is excessive, it will actually reduce the limiting oxygen index of UF by 1.09%.

[0157] Compared with Example 1, it can be seen that further increasing the amount of BNGS, i.e., when the amount of BNGS added is excessive, the limiting oxygen index decreases significantly, by 18.64%. This indicates that excessive BNGS has a substantial impact on the limiting oxygen index.

[0158] Based on the SEM test results, it can be seen that adding excessive BNGS causes protrusions on the coating surface, creating new defects. This prevents the formation of a dense residual carbon layer, which in turn fails to prevent heat and combustible gases from entering the substrate, ultimately leading to a decrease in the limiting oxygen index.

[0159] To further quantify the flame retardancy of UF-BNGS-3, a cone calorimeter test was conducted. The test results are as follows: Figure 6 As shown, the HRR of UF-BNGS-3 reaches 90.03 kW / m². 2 .

[0160] Compared with Comparative Example 1, it can be seen that coating with UF-BNGS-3 can effectively reduce the HRR of NW by 61.23%.

[0161] Compared with Comparative Example 2, it can be seen that when the amount of BNGS added is high, the effect on reducing HRR is almost negligible;

[0162] Compared with Example 1, it can be seen that when the amount of BNGS added is further increased, that is, when the amount of BNGS added is excessive, the HRR actually increases significantly, with an increase of 56.5%.

[0163] Combining the SEM test results and the limiting oxygen index, the HRR test results also support the aforementioned conclusion, that is, when the amount of BNGS added is too large, it will reduce the flame retardant performance.

[0164] The following conclusions can be drawn from Example 1, Comparative Example 4, and Comparative Example 5:

[0165] 1. Applying UF-BNGS-2 flame-retardant resin coating can achieve good flame-retardant properties;

[0166] 2. The amount of BNGS added has no substantial impact on the UL-94 rating;

[0167] 3. Adding a small amount of BNGS can further improve the flame retardant performance, but adding too much BNGS will reduce the flame retardant performance. The reason is that BNGS, as a filler, works by adding an appropriate amount of BNGS to effectively fill the defects of the surface flame retardant coating, while adding too much BNGS will cause the coating surface to have protrusions, resulting in more defects.

[0168] 4. The amount of BNGS added has a significant impact on the quality of the char layer formed after combustion, HRR and char residue. The reason is that the role of UF-BNGS-2 in the technical solution is to promote the formation of a dense structure in the char layer, significantly increase the char residue, reduce HRR, and thus improve the flame retardant performance.

Claims

1. A method for preparing a hexagonal boron nitride-guanidazole-sodium hexametaphosphate flame-retardant resin coating, characterized in that, Includes the following steps: Step 1, Preparation of hexagonal boron nitride-guanidazole-sodium hexametaphosphate flame retardant: First, hexagonal boron nitride (BN) is ultrasonically dispersed in water to obtain a BN solution. Then, guanidazole (GZ) is placed in the BN solution and stirred in a water bath to obtain an amino-functionalized BN-GZ solution. After that, sodium hexametaphosphate (SHMP) is placed in the BN-GZ solution and stirred to react. After the reaction is complete, the obtained product is filtered, washed, dried, and ground into powder to obtain hexagonal boron nitride-guanidazole-sodium hexametaphosphate flame retardant BNGS. Step 2, preparation of UF-BNGS: First, sodium hydroxide solution is added to formaldehyde solution to adjust the pH value of the solution to obtain solution A. Then, urea, BNGS and other raw materials are added according to steps 2.1, 2.2, 2.3 and 2.4 to prepare UF-BNGS. Step 2.1 involves first adding the first stage of urea, and then continuing to stir after the addition is complete. Step 2.2 involves first adding acetic acid solution to adjust the pH value of the solution, then adding the second-stage urea. After the addition is complete, continue stirring until the reaction endpoint is reached. The endpoint of the reaction is determined by the following criterion: when a drop of the solution is added to water at 30°C, the solution solidifies in the water without dispersing. Step 2.3 involves adding sodium hydroxide solution to adjust the pH value, then adding urea from the third stage, and stirring until viscous to obtain UF. Step 2.4 involves adding BNGS to UF and stirring to obtain UF-BNGS; Step 3: Under the conditions of stirring speed of 400 rpm and stirring time of 30 min, DOP, TA and UF-BNGS are added to UF-BNGS in a mass ratio of 0.1:0.1:10 to obtain the coating.

2. The preparation method according to claim 1, characterized in that: In step 1, the mass ratio of BN, GZ and SHMP is 1:1:2; In step 1, the ultrasound conditions are as follows: the ultrasound time is 1 hour. In step 1, the conditions for water bath stirring are: water bath temperature of 60-70℃, stirring speed of 400-500 rpm, and stirring time of 1-1.5 h. In step 1, the conditions for the stirring reaction are: reaction temperature of 90°C and reaction time of 3 h. In step 1, the washing is completed when the pH of the washing solution is 6-7; the drying is completed when the drying temperature is 80℃ and the drying time is 24 h.

3. The preparation method according to claim 1, characterized in that: In step 2, the mass ratio of the total amount of BNGS, formaldehyde solution and urea added in step 1 is 2:100:

57. In step 2, the conditions for preparing solution A are that the pH value of the solution is adjusted to 8.0-8.

5.

4. The preparation method according to claim 1, characterized in that: In step 2.1, the amount of urea added is 64.9% of the total amount of urea, the temperature in step 2.1 is 90℃, and the stirring time is 30 min. In step 2.2, the amount of urea added is 21.8% of the total amount of urea, the pH of the solution is adjusted to 4.5-5.0, the temperature in step 2.2 is 90 ℃, and the stirring time is 15 min. In step 2.3, the amount of urea added is 13.3% of the total amount of urea, the pH of the solution is adjusted to 7.5-8.0, the temperature in step 2.3 is 90 ℃ when adjusting the pH, and 70 ℃ after the pH is adjusted, and the stirring time is 30-40 min. In step 2.4, the stirring rate of BNGS is 400 rpm and the stirring temperature is room temperature.

5. The preparation method according to claim 1, characterized in that: The obtained hexagonal boron nitride-guanidazole-sodium hexametaphosphate flame retardant resin coating had a decomposition mass of 5% at a temperature of 228.90±1.10℃, a maximum decomposition rate at a temperature of 301.47±1.50℃, and a carbon residue of 39.95±0.50wt. at 800.00℃.

6. The preparation method according to claim 1, characterized in that: When the obtained hexagonal boron nitride-guanidazole-sodium hexametaphosphate flame retardant resin coating is used as a flame retardant coating for wood, it has flame retardant properties and forms a continuous and dense char layer after combustion; in the UL-94 rating test, it passed the UL-94 V-0 rating test.

7. The preparation method according to claim 1, characterized in that: When the obtained hexagonal boron nitride-guanidazole-sodium hexametaphosphate flame-retardant resin coating is used as a flame-retardant coating for wood, the heat release rate (HRR) in the cone calorimetry test is 55.73 ± 1.25 kW / m². 2 .

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