A bio-based ammonium polyphosphate-based flame retardant coating, and a preparation method and application thereof

Abstract

This invention discloses a bio-based flame-retardant coating based on ammonium polyphosphate. It uses chitosan / lignin / ammonium polyphosphate bio-based flame retardant CS / LS / APP (CLA) as the flame retardant, urea, formaldehyde, and melamine as resin raw materials, dioctyl phthalate (DOP) as a plasticizer, and tannic acid as a curing agent. The preparation method includes the following steps: 1. Preparation of chitosan / lignin / ammonium polyphosphate bio-based flame retardant CLA; 2. Preparation of melamine-urea-formaldehyde resin emulsion MUF; 3. Preparation of the ammonium polyphosphate-based bio-based flame-retardant coating MUF / CLA. When used as a flame-retardant coating for wood, it exhibits flame-retardant properties and passes the UL-94 V-0 rating test; the char layer formed after complete combustion is continuous and dense; the limiting oxygen index is 32.6 ± 0.06%; and the maximum heat release rate is 42.83 ± 1.51 kW / m³. 2 The total heat release is 2.62 ± 1.25 MJ / m³. 2 The fire growth index was 0.37 ± 0.02 kW / m³. 2 ·s.

Description

Technical Field

[0001] This invention relates to the field of flame retardant materials, specifically to a bio-based flame retardant coating based on ammonium polyphosphate, its preparation method, and its application. Background Technology

[0002] Wood is a commonly used renewable natural polymer material, characterized by abundant raw materials and low cost. However, its flammable nature necessitates the construction of a flame-retardant layer on its surface to meet application requirements. Lignin, as a common biomass material, possesses numerous phenolic hydroxyl groups, forming a protective char layer during combustion and reducing the polymer's flammability. Therefore, it can be used to prepare bio-based flame retardants. For example, existing literature 1 ("Hexachlorocyclotriphosphazene functionalized lignin as a sustainable and effective flame retardant for epoxy resins[J]". Industrial Crops and Products, 2022, 187: 115543.) uses hexachlorocyclotriphosphazene to modify lignin as an additive to improve the flame retardancy of epoxy resins. This technical solution requires the addition of 20 wt.% functionalized lignin to achieve a limiting oxygen index of 28.2% and a UL-94V-0 rating in vertical burning tests for the epoxy resin composite material. The main problems with this technical solution are twofold: 1. The additive contains chlorine, which is a halogenated flame retardant. This releases harmful hydrogen chloride gas during combustion, causing environmental pollution. 2. The excessive amount of flame retardant added leads to high production costs and large processing costs.

[0003] To address the issues of halogen content and excessive addition in the aforementioned flame retardants, bio-based flame retardants can be prepared by introducing biomass containing nitrogen (N) and phosphorus (P) elements. For example, existing literature 2 ("Flame retardant polypropylene with a single molecule intumescent flame retardant based on chitosan[J]". Materials Today Communications, 2022, 33: 104689.) describes the use of in-situ polymerization to coat chitosan and ammonium polyphosphate with melamine-formaldehyde resin for modifying polypropylene. The chitosan single-molecule intumescent flame retardant inhibits the thermal degradation of polypropylene and promotes the formation of a carbon layer. Although this technical solution achieves a halogen-free bio-based flame retardant and improves thermal stability, the limiting oxygen index is only 25.7%, and the vertical burning performance only reaches the UL-94V-1 rating. This is because the gas generated by the gas source cannot expand effectively, resulting in the inability to form a dense carbon layer. Consequently, the carbon layer structure formed by chitosan is easily destroyed, meaning a stable carbon layer cannot be formed.

[0004] To improve the density of the residual char layer and increase the limiting oxygen index, thereby enhancing the integrity and flame retardant properties of the char layer, the inventors' research group previously conducted work, specifically document 3 ("A Flame Retardant Coating Based on PA-MEL Flame Retardant Curing Agent and Its Preparation Method and Application" CN202410058920.2), which used phytic acid-melamine polyelectrolyte PM as a bio-based flame retardant curing agent for sodium lignosulfonate modified urea-formaldehyde resin. With an addition amount of only 2 wt.% of PM, a continuous and dense residual char layer was obtained, and the limiting oxygen index of the wood after coating with the flame retardant coating reached 32.1%, while the UL-94 rating reached V-0.

[0005] In addition, another previous work by the inventors' research group, existing literature 4 ("A Flame Retardant Resin Coating Blended with Guanidazole-Phytic Acid-Copper and Its Preparation Method and Application", CN202411322652.7), uses guanidazole, phytic acid and copper as bio-based flame retardants to blend with urea-formaldehyde resin for wood flame retardancy. When the addition amount is only 1wt.%, the residual char layer is continuous and dense. After coating with flame retardant coating, the wood reaches UL-94V-0 rating and LOI reaches 32.0%.

[0006] Both of the above technical solutions use phytic acid, a bio-based flame retardant, as the phosphorus source. Although phytic acid has the advantages of being environmentally friendly and non-toxic, such flame retardants based on phytic acid have the problem of low decomposition temperature. Furthermore, phytic acid is a soluble weak acid. On the one hand, due to its solubility, its flame retardant effect is reduced in humid and hot environments. On the other hand, its acidity has a corrosive effect on wood and other components. In addition, although the existing literature 4 uses copper as a catalyst to degrade resin, which can form a dense char layer and improve the flame retardant performance of the material, there are still problems with heavy metal pollution and recycling after disposal. Summary of the Invention

[0007] The purpose of this invention is to provide a bio-based flame-retardant coating based on ammonium polyphosphate, its preparation method, and its application. Addressing the problems of existing technologies, this invention prepares a bio-based flame-retardant coating by introducing chitosan, lignin, and ammonium polyphosphate as the main raw materials.

[0008] in,

[0009] Ammonium polyphosphate is used as an acid source, which works synergistically with carbon and gas sources to promote the dehydration and carbonization of the material, form a dense carbon layer, and improve the limiting oxygen index, thereby enhancing the flame retardant effect of the material while reducing raw material costs.

[0010] Chitosan was used as a carbon and nitrogen source, and dehydrated and condensed with the chain polymer ammonium polyphosphate as a phosphorus source under acidic conditions.

[0011] The molecular structure of urea-formaldehyde resin is modified with melamine to improve the resin's aging resistance, enhance its bonding performance, and improve its adhesion to wood. In addition, melamine also improves the thermal stability of urea-formaldehyde resin and produces a stable carbon layer and releases non-flammable nitrogen gas during high-temperature decomposition, thus slowing down the combustion rate.

[0012] Tannic acid is used as a curing agent to maintain the original color of the wood and reduce resin cracking;

[0013] Dioctyl phthalate (DOP) is used as a plasticizer to improve the mechanical properties of the flame retardant.

[0014] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0015] A bio-based flame retardant coating based on ammonium polyphosphate is prepared using chitosan / lignin / ammonium polyphosphate bio-based flame retardant CS / LS / APP (CLA) as the flame retardant, urea, formaldehyde and melamine as resin raw materials, dioctyl phthalate (DOP) as plasticizer and tannic acid as curing agent.

[0016] The CLA is prepared from lignin (LS), chitosan (CS), and ammonium polyphosphate (APP), and CLA contains -NH2, OH, P=O, and PO4 groups. --CONH2;

[0017] The temperature at which the CLA decomposed to 5% was 228.63±5℃, and the temperature at which the maximum decomposition rate was reached was 295.4±5℃; the char residue at 800℃ was 24.29±2wt.%.

[0018] A method for preparing a bio-based flame-retardant coating based on ammonium polyphosphate includes the following steps:

[0019] Step 1, preparation of chitosan / lignin / ammonium polyphosphate bio-based flame retardant CLA: First, lignin (LS), chitosan (CS), and ammonium polyphosphate (APP) are prepared in a certain mass ratio to form LS solution, CS solution, and APP solution respectively. Then, under certain dropping conditions, the LS solution is added dropwise to the CS solution to react and obtain an LS / CS mixed solution. Finally, under the same dropping conditions, the APP solution is added dropwise to the LS / CS mixed solution to react and obtain the chitosan / lignin / ammonium polyphosphate bio-based flame retardant CS / LS / APP, abbreviated as CLA.

[0020] In step 1, the mass ratio of LS, CS and APP is 2:2:1;

[0021] In step 1, the LS solution is prepared by dissolving LS in deionized water under the following conditions: the dissolution temperature is 30℃, the dissolution stirring speed is 400-450rpm, and the dissolution stirring time is 30min.

[0022] In step 1, the CS solution is prepared by dissolving CS in lactic acid solution under the following conditions: the dissolution temperature is 45℃, the dissolution stirring speed is 400-450rpm, and the dissolution stirring time is 120min, thereby obtaining the CS solution.

[0023] In step 1, the APP solution is prepared by dissolving APP in deionized water under the following conditions: the dissolution temperature is 80℃, the dissolution stirring speed is 400-450rpm, and the dissolution stirring time is 120min, thereby obtaining the APP solution.

[0024] In step 1, the dropping conditions are as follows: dropping temperature is 45℃, dropping stirring speed is 600-650rpm, dropping stirring time is 1h, and dropping acceleration rate is 0.5 drops / s.

[0025] Step 2, Preparation of melamine-urea-formaldehyde resin emulsion MUF: First, sodium hydroxide solution is added to the formaldehyde solution to adjust the pH to 8.0-8.5. Then, the temperature is raised to 90℃ while stirring at 400-450 rpm. Afterwards, raw materials are added in three stages to prepare the melamine-urea-formaldehyde resin emulsion MUF, abbreviated as MUF.

[0026] In step 2, the mass ratio of the total amount of CLA, formaldehyde, melamine (MEL), and urea added in step 1 is 2:100:1.14:57.

[0027] In step 2, the ratio of urea added in the three stages is 37:12.4:7.6;

[0028] The three specific stages are as follows:

[0029] Phase 2.1 involves maintaining a temperature of 90℃, first adding the first-stage urea, then adding melamine (MEL), and continuing to stir for 30 minutes after the addition is complete.

[0030] In stage 2.2, while maintaining a temperature of 90℃, lactic acid solution is first added to adjust the pH of the solution to 4.5-5.0, and then urea is added in the second stage. After the addition is complete, stirring is continued for 10 minutes until the reaction reaches the endpoint.

[0031] The endpoint of the reaction in stage 2.2 is determined by the following criterion: when a drop of solution is added to water at 30°C, the added solution solidifies in the water without dispersing.

[0032] Stage 2.3 involves first adding sodium hydroxide solution at a temperature of 90℃ to adjust the pH of the solution to 7.5-8.0, then adding urea in the third stage. After the addition is complete, the temperature is adjusted, and the mixture is stirred at a temperature of 70℃ for 30 minutes to obtain MUF.

[0033] Step 3: Preparation of the ammonium polyphosphate-based bio-based flame retardant coating MUF / CLA. MUF, dioctyl phthalate (DOP), tannic acid (TA), and CLA obtained in Step 1 are mixed in a certain mass ratio. DOP, TA, and CLA are added to the MUF obtained in Step 2. After the addition is complete, mechanical stirring is performed under certain conditions to ensure uniform mixing of all components, thus obtaining the ammonium polyphosphate-based bio-based flame retardant coating MUF / CLA, abbreviated as MUF / CLA.

[0034] In step 3, the mass ratio of MUF, DOP, TA and CLA obtained in step 1 is 100:1:1:2;

[0035] In step 3, the mechanical stirring conditions are: stirring speed of 600-650 rpm and stirring time of 2 hours.

[0036] Bio-based flame-retardant coatings based on ammonium polyphosphate exhibit flame-retardant properties when used as wood flame-retardant coatings, passing the UL-94V-0 rating test. The char layer formed after complete combustion is continuous and dense; the limiting oxygen index is 32.6±0.06%; and the maximum heat release rate is 42.83±1.51kW / m³. 2 The total heat release is 2.62 ± 1.25 MJ / m³. 2 The fire growth index was 0.37 ± 0.02 kW / m³. 2 ·s.

[0037] The technical effects achieved by this invention have been verified as follows:

[0038] The TG test results show that when MUF / CLA is used as a bio-based flame retardant coating, the temperature at which MUF / CLA decomposes to 5% by mass is 228.63℃, the temperature at which the maximum decomposition rate is reached is 295.4℃, and the residual char content at 800℃ is 24.29 wt.%. Coating with MUF / CLA can increase the residual char content of the material and form a more stable char layer in high-temperature regions.

[0039] Further SEM testing was conducted on the expanded char layer formed on the surface of NW coated with MUF / CLA flame-retardant paint after combustion. After complete combustion, MUF / CLA formed a complete and dense char layer without expansion. The test results indicate that the dense char layer of MUF / CLA can effectively isolate combustible gases and heat release, thus improving the flame-retardant properties of wood.

[0040] The vertical burning test and the limiting oxygen index test show that W / MUF / CLA has passed the UL-94V-0 rating test.

[0041] Limiting oxygen index (LOI) tests show that W / MUF / CLA flame-retardant coatings can improve its LOI, reaching 32.6%.

[0042] Cone calorimetry analysis showed that the time to reach the maximum heat release rate was 113 seconds, and the maximum heat release rate was 42.83 kW / m³. 2 The total heat release is 2.62 MJ / m³. 2 .

[0043] Therefore, the present invention has the following advantages over the prior art:

[0044] 1. The bio-based flame retardant CLA used in this invention promotes char layer formation and prevents the release of combustible gases and heat, thereby improving flame retardant performance;

[0045] 2. The bio-based flame retardant CLA used in this invention produces less than 30% residual carbon from thermal decomposition, but it can still effectively inhibit combustion, thereby improving flame retardant performance.

[0046] 3. This invention uses renewable biomass materials lignin and chitosan, which are biodegradable and have low environmental impact. The combined use of ammonium polyphosphate and lignin can produce a synergistic effect and improve the flame retardant properties of the material. Attached Figure Description

[0047] Figure 1 The FTIR plot of Example 1;

[0048] Figure 2 The FTIR plots are those of Example 1 and Comparative Example 1.

[0049] Figure 3 The TG plots are for Comparative Example 1, Comparative Example 2, Example 1, Example 2, and Comparative Example 3.

[0050] Figure 4 The images show SEM images of the char residue layers after combustion of the reference example, comparative example 1, comparative example 2, example 1, example 2, and comparative example 3. Figure 4 'a' is a parameter. Figure 4 b is comparative example 1. Figure 4 c is comparative example 2. Figure 4 d represents Figure 1 of Example 1, and 4e represents Figure 2 of Example 2. Figure 4 f is comparative example 4;

[0051] Figure 5 The figures show vertical combustion test diagrams for the reference example, comparative example 1, comparative example 2, example 2, example 1, and comparative example 3. Figure 5 'a' represents the period before the vertical combustion test. Figure 5 b represents the result after the vertical combustion test;

[0052] Figure 6 The cone calorimetry test diagrams are for the reference example, comparative example 1, comparative example 2, example 2, example 1, and comparative example 3. Detailed Implementation

[0053] 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.

[0054] Example 1

[0055] A method for preparing a bio-based flame-retardant coating based on ammonium polyphosphate includes the following steps:

[0056] Step 1, preparation of chitosan / lignin / ammonium polyphosphate bio-based flame retardant CLA: First, lignin (LS), chitosan (CS), and ammonium polyphosphate (APP) are prepared in a mass ratio of 2:2:1 to form LS, CS, and APP solutions respectively. Then, under certain dropping conditions, the LS solution is added dropwise to the CS solution to obtain an LS / CS mixed solution. Finally, under the same dropping conditions, the APP solution is added dropwise to the LS / CS mixed solution to obtain the chitosan / lignin / ammonium polyphosphate bio-based flame retardant CS / LS / APP, abbreviated as CLA.

[0057] The LS solution is prepared by dissolving 2.1g of lignin LS in 10mL of deionized water under the conditions of a dissolution temperature of 30℃, a dissolution stirring speed of 400rpm, and a dissolution stirring time of 30min to obtain the LS solution.

[0058] The CS solution is prepared by dissolving 2.0 g of chitosan CS in 20 mL of 3% lactic acid solution under the conditions of a dissolution temperature of 45℃, a dissolution stirring speed of 400 rpm, and a dissolution stirring time of 120 min, thereby obtaining the CS solution.

[0059] The APP solution is prepared by dissolving 1.0 g of ammonium polyphosphate (APP) in 10 mL of deionized water under the conditions of a dissolution temperature of 80°C, a stirring speed of 400 rpm, and a stirring time of 120 min, and then stirring to obtain the APP solution.

[0060] The dropping conditions are as follows: dropping temperature is 45℃, dropping stirring speed is 600 rpm, dropping stirring time is 1 hour, and dropping acceleration rate is 0.5 drops / s;

[0061] To confirm the composition of CLA, i.e., successful synthesis, FTIR testing was performed; simultaneously, for comparison, the raw materials CS, LS, and APP were also subjected to FTIR testing. The test results are as follows: Figure 1 As shown,

[0062] CS exhibits characteristic peaks for -OH and -NH2 functional groups;

[0063] LS exhibits characteristic peaks for -OH and -NH2 functional groups;

[0064] APP exhibits characteristic peaks of P=O and PO;

[0065] CLA exhibits a characteristic peak of -CONH2;

[0066] Test results show that the characteristic peak of -CONH2 in CLA is formed by the condensation reaction of the amino group of chitosan and the phenolic hydroxyl group of lignin under acidic heating conditions to generate amide.

[0067] Step 2, Preparation of melamine-urea-formaldehyde resin emulsion MUF: First, add 20 wt.% sodium hydroxide solution to 100g of 37wt.% formaldehyde solution to adjust the pH of the solution to 8.0-8.5. Then, heat to 90℃ while stirring at 400rpm. Afterwards, add raw materials in three stages to prepare melamine-urea-formaldehyde resin emulsion MUF, abbreviated as MUF.

[0068] The three specific stages are as follows:

[0069] In stage 2.1, while maintaining a temperature of 90℃, first add 37g of the first-stage urea, then add 1.14g of melamine (MEL). After the addition is complete, continue stirring for 30 minutes.

[0070] In stage 2.2, while maintaining a temperature of 90℃, 10wt.% lactic acid solution was first added to adjust the pH of the solution to 4.5-5.0, and then 12.4g of urea for the second stage was added. After the addition was completed, stirring was continued for 10 minutes until the reaction reached the endpoint.

[0071] The endpoint of the reaction in stage 2.2 is determined by the following criterion: when a drop of solution is added to water at 30°C, the added solution solidifies in the water without dispersing.

[0072] In stage 2.3, while maintaining a temperature of 90℃, 20wt.% sodium hydroxide solution is first added to adjust the pH of the solution to 7.5-8.0, and then 7.6g of third-stage urea is added. After the addition is complete, the temperature is adjusted, and the mixture is stirred at a stirring temperature of 70℃ for 30 minutes to obtain MUF.

[0073] Step 3: Preparation of the ammonium polyphosphate-based bio-based flame retardant coating MUF / CLA. The mass ratio of MUF, dioctyl phthalate (DOP), tannic acid (TA), and CLA obtained in Step 1 is 100:1:1:2. 1g of DOP, 1g of TA, and 2g of CLA are added to the MUF obtained in Step 2. After addition, mechanical stirring is performed at 600 rpm for 2 hours to ensure uniform mixing of all components, thus obtaining the ammonium polyphosphate-based bio-based flame retardant coating MUF / CLA, abbreviated as MUF / CLA. Specifically, the MUF / CLA obtained in Example 1 is MUF / CLA-2.

[0074] To confirm the composition of MUF / CLA-2, FTIR testing was performed. The test results are as follows: Figure 2As shown, MUF / CLA-2 exhibits characteristic peaks for -OH, -NH2, P=O, PO, and -CONH2, as well as a characteristic peak for -CHO. The test results indicate that MUF and CLA are the main components in MUF / CLA-1.

[0075] To demonstrate the thermal stability of MUF / CLA-2, a TG test was conducted, and the results are as follows: Figure 3 As shown in Table 1, the temperature at which MUF / CLA-2 decomposes to 5% by mass is 228.63℃, the temperature at which the maximum decomposition rate is reached is 295.4℃, and the char residue at 800℃ is 24.29 wt.%. The test results indicate that MUF / CLA-2 possesses high thermal stability and a relatively high char residue.

[0076] Table 1. Thermogravimetric test results

[0077]

[0078] To demonstrate the technical effectiveness of MUF / CLA-2 as a flame-retardant coating for wood, flame-retardant wood (W / MUF / CLA-2) was prepared by coating MUF / CLA-2 onto the surface of wood and then subjected to flame-retardant testing. The specific preparation method for W / MUF / CLA-2 was as follows: a coating thickness of 0.3 mm and a coating density of 0.1 g / cm³. 2 MUF / CLA-2 is coated onto the surface of the wood, and after coating, it is dried for 24 hours to obtain W / MUF / CLA-2.

[0079] To verify the quality of the char residue layer after complete combustion of MUF / CLA-2, SEM testing was performed on the char residue layer. The test results are as follows: Figure 4 As shown in Figure c, after complete combustion, the flame-retardant wood coated with MUF / CLA-2 forms a complete and dense char layer without expansion. The test results indicate that the dense char layer of MUF / CLA-2 effectively isolates combustible gases and heat release, improving the flame-retardant properties of the wood.

[0080] To further demonstrate the flame-retardant properties of W / MUF / CLA-2, vertical burning tests and limiting oxygen index tests were conducted. The test results are as follows: Figure 5 As shown in Table 2, W / MUF / CLA-2 passed the UL-94V-0 rating test; furthermore, W / MUF / CLA-2 has a limiting oxygen index as high as 32.6%. The test results demonstrate that W / MUF / CLA-2 exhibits excellent flame retardant properties.

[0081] Table 2 Results of Vertical Combustion Test and Oxygen Index Test

[0082]

[0083] To further demonstrate the flame-retardant performance of W / MUF / CLA-2 under real-world combustion conditions, a cone calorimeter test was conducted. The test results are as follows: Figure 6 As shown in Table 3, the time for W / MUF / CLA-2 to reach its maximum heat release rate is 113 s, and the maximum heat release rate is 42.83 kW / m². 2 The total heat release is 2.62 MJ / m³. 2 The fire growth index is 0.37 kW / m³. 2 Test results show that W / MUF / CLA-2 has excellent flame retardant properties.

[0084] Table 3 Results of cone calorimetry test

[0085]

[0086] To demonstrate the effect of the bio-based flame retardant CLA on performance, Comparative Example 1 is provided, a flame-retardant coating without the addition of the bio-based flame retardant CLA; at the same time, a reference example is provided, pure wood without any coating as a base reference.

[0087] Parameter

[0088] A type of wood that is not coated with MUF / CLA, often simply called pure wood.

[0089] SEM test results of residual char layer of pure wood are as follows: Figure 4 As shown in Figure a, the charcoal layer structure in the pure wood is completely destroyed, and a large number of broken cellulose and hemicellulose structures are clearly visible. After burning and fracturing, the interior of the pure wood contains a neatly arranged pore structure. Compared with Example 1, it can be seen that coating with MUF / CLA-1 causes the expanded charcoal layer generated on the wood surface to form a complete and dense charcoal layer, and there is no expansion phenomenon. That is, the quality of the charcoal layer is greatly improved.

[0090] The results of the vertical burning test and limiting oxygen index test of pure wood are as follows: Figure 5 As shown in Table 2, pure wood failed the UL-94 rating test; furthermore, the limiting oxygen index (LOI) of pure wood was 20.0%. Compared to Example 1, coating with MUF / CLA-1 improved the UL-94 rating to V-0, significantly increasing the LIO from 20.0% to 32.5%, an improvement of 62.5%. The test results demonstrate that MUF / CLA-1 can significantly improve the flame retardant properties of pure wood.

[0091] The results of the cone calorimetry test on pure wood are as follows: Figure 6 As shown in Table 3, the time for the maximum heat release rate of pure wood is 138 s, the maximum heat release rate is 212.49 kW / m², and the total heat release is 11.35 MJ / m². 2The fire growth index is 1.54 kW / m³. 2 Compared with Example 1, coating with MUF / CLA-2 shortened the time for flame-retardant wood to reach its maximum heat release rate by 25 seconds, reduced the maximum heat release rate by 79.84%, reduced the total heat release by 76.91%, and reduced the fire growth index by 75.97%. The test results demonstrate that MUF / CLA-2 significantly improves flame retardancy and reduces fire hazard.

[0092] Comparative Example 1

[0093] A conventional coating without the addition of bio-based flame retardant CLA, i.e., a method for preparing conventional coating, is described below. Unless otherwise specified, the steps are the same as in Example 1, except that: in step 3, the bio-based flame retardant CLA is not added. The resulting conventional coating is named MUF, and the further obtained conventional flame-retardant wood is named W / MUF.

[0094] MUF's TG test results are as follows Figure 3 As shown in Table 1, the temperature at which MUF decomposes to a mass of 5% is 190.79℃, the temperature at which the maximum decomposition rate is reached is 301.3℃, and the char residue at 800℃ is 12.5 wt.%.

[0095] Compared with Example 1, it can be seen that adding bio-based flame retardant CLA can significantly increase the temperature at which the decomposition mass is 5% and significantly increase the char residue at 800°C. The increase in temperature at which the decomposition mass is 5% is 37.84°C and the increase in char residue at 800°C is 11.79 wt.%. However, it actually decreases the temperature at which the maximum decomposition rate is reached by 5.9°C. Therefore, the test results show that adding CLA can significantly improve the flame retardant performance.

[0096] The SEM test results of the residual carbon layer of W / MUF are as follows: Figure 4 As shown in b, after complete combustion of W / MUF, a large number of bubbles of varying sizes are formed on the surface of the residual char layer.

[0097] Compared with reference example 1, it can be seen that although the conventional coating MUF can form an expanded carbon layer on the surface of the wood, the surface of the residual carbon layer has many pores and cannot effectively protect the wood. This proves that MUF has no substantial impact on the quality of the residual carbon layer.

[0098] Compared with Example 1, it can be seen that adding the bio-based flame retardant CLA can transform the original porous structure of the residual char layer into a continuous and dense residual char layer, and there are no pores, which can significantly change the morphology and structure of the residual char layer.

[0099] Test results show that using the bio-based flame retardant CLA can improve the quality of the expanded char layer of W / MUF / CLA, thereby improving the flame retardant performance.

[0100] The results of the vertical combustion test and limiting oxygen index test of W / MUF are as follows: Figure 5 As shown in Table 2, W / MUF passed the UL-94V-1 level test; and the limiting oxygen index of W / MUF is 29.0%.

[0101] Compared with reference ratio 1, it can be seen that applying conventional coating MUF can only improve the UL-94 rating of wood from failing the test to V-1, but cannot reach V-0. At the same time, it can increase the limiting oxygen index by 9.0%.

[0102] Compared with Example 1, it can be seen that the use of bio-based flame retardant CLA can further improve the UL-94 rating of flame-retardant wood from V-1 to V-0, and can further increase the limiting oxygen index by 3.5%.

[0103] Test results show that using the bio-based flame retardant CLA can improve the UL-94 rating and significantly increase the limiting oxygen index, thereby greatly improving flame retardant performance.

[0104] The cone calorimetry test results of W / MUF are as follows: Figure 6 As shown in Table 3, the time for the maximum heat release rate of W / MUF is 113 s, the maximum heat release rate is 60.56 kW / m², and the total heat release is 4.47 MJ / m². 2 The fire growth index is 0.53 kW / m³. 2 ·s.

[0105] Compared with reference ratio 1, it can be seen that using conventional coating MUF can shorten the time for flame-retardant wood to reach the maximum heat release rate by 25 seconds, reduce the maximum heat release rate by 71.49%, reduce the total heat release by 60.61%, and reduce the fire growth index by 65.58%.

[0106] Compared with Example 1, it can be seen that using conventional coating MUF can shorten the time for flame-retardant wood to reach the maximum heat release rate by 25 seconds, reduce the maximum heat release rate by 29.27%, reduce the total heat release by 41.38%, and reduce the fire growth index by 30.18%.

[0107] Test results show that the use of bio-based flame retardant CLA can significantly improve the flame retardant performance of fire-retardant wood under real combustion conditions and greatly reduce the fire hazard.

[0108] To further demonstrate the impact of each component in the bio-based flame retardant CLA on performance, i.e. the role of APP in the technical solution, Comparative Example 2 is provided, showing a bio-based flame retardant and flame-retardant coating prepared without the addition of APP.

[0109] Comparative Example 2

[0110] A method for preparing a bio-based flame retardant coating CL without adding APP is described. Unless otherwise specified, the steps are the same as in Example 1, except that: in step 3, APP is not added, the bio-based flame retardant obtained in step 1 is named CL, the flame retardant coating obtained in step 3 is named MUF / CL, and the flame retardant wood obtained further is named W / MUF / CL.

[0111] The TG test results of MUF / CL are as follows: Figure 3 As shown in Table 1, the temperature at which MUF / CL decomposes to a mass of 5% is 183.9℃, the temperature at which the maximum decomposition rate is reached is 301.3℃, and the char residue at 800℃ is 12.0 wt.%.

[0112] Compared with Comparative Example 1, it can be seen that although adding CL can slightly increase the temperature at which the maximum decomposition rate is reached by only 1.8℃, it also simultaneously reduces the temperature and residual carbon content at a decomposition mass of 5%, by 6.89℃ and 0.5wt.%, respectively. Therefore, the test results show that adding CL alone actually leads to a decrease in the flame retardant properties of MUF.

[0113] Compared with Example 1, it can be seen that although adding APP will reduce the temperature at the maximum decomposition rate by 7.9°C, it can significantly increase the temperature and residual carbon content when the decomposition mass is 5%. The temperature increase when the decomposition mass is 5% reaches 44.73°C, and the residual carbon content increases by 12.19 wt.%, which is 102.41%. Therefore, the test results show that adding APP can significantly improve the flame retardant performance.

[0114] The SEM test results of the residual carbon layer of W / MUF / CL are as follows: Figure 4 As shown in c, after complete combustion of W / MUF / CL, although a continuous char layer can be formed, there are still pores on the surface of the char layer, and there are expanding bubbles, which is called an expanded char layer.

[0115] Compared with reference example 1, it can be seen that although coating with MUF / CL can form a continuous char layer on the wood surface, there are expansion bubbles and pores on the surface of the char layer, which cannot effectively protect the wood. This proves that MUF / CL has no substantial impact on the quality of the char layer.

[0116] Compared with Comparative Example 1, it can be seen that adding CL can slightly reduce the expansion bubbles and pores of the char layer, that is, slightly improve the flame retardancy. However, it has no substantial change in the formation of the char layer with MUF, which proves that CL has no substantial effect on the quality of the char layer.

[0117] Compared with Example 1, it can be seen that adding APP can significantly change the morphology and structure of the residual carbon layer, transforming the original cracks and pores into a dense state, and there is no expansion phenomenon;

[0118] Test results show that adding bio-based flame retardant APP can significantly change the morphology and structure of the char layer. This is because APP is dehydrated under high temperature conditions to generate polyphosphoric acid or metaphosphoric acid, which then reacts with the hydroxyl groups in CL to form a complete and dense carbon layer. This improves the quality of the expanded char layer of W / MUF / CL, thereby enhancing the flame retardant performance.

[0119] The results of the W / MUF / CL vertical combustion test and limiting oxygen index test are as follows: Figure 5 As shown in Table 2, W / MUF / CL passed the UL-94V-1 level test, and the limiting oxygen index of W / MUF / CL is 29.5%.

[0120] Compared with reference ratio 1, it can be seen that coating with MUF / CL can only improve the UL-94 rating of wood from failing the test to V-1 rating, but cannot reach V-0 rating. At the same time, it can increase the limiting oxygen index by 9.5%.

[0121] Compared with Comparative Example 1, it can be seen that adding CL has no substantial impact on the UL-94 rating, which remains at the V-1 level. Furthermore, it also has no substantial impact on the limiting oxygen index, increasing it by only 0.5%, indicating that adding CL has no substantial impact on flame retardant performance.

[0122] Compared with Example 1, it can be seen that adding the bio-based flame retardant APP can improve the UL-94 rating of flame-retardant wood from V-1 to V-0, and can further increase the limiting oxygen index by a significant 3.1%.

[0123] Test results show that adding CL alone has no substantial impact on flame retardant performance. Only by adding APP at the same time can there be a substantial impact on the UL-94 rating and limiting oxygen index. This proves that the role of APP in the technical solution is to significantly improve flame retardant performance.

[0124] The cone calorimetry test results of W / MUF / CL are as follows: Figure 6 As shown in Table 3, the time for W / MUF / CL to reach the maximum heat release rate is 96 s, and the maximum heat release rate is 57.6 kW / m². 2 The total heat release is 5.15 MJ / m³. 2 The fire growth index is 0.6 kW / m³. 2 ·s.

[0125] Compared with reference example 1, it can be seen that coating with MUF / CL can shorten the time for flame-retardant wood to reach the maximum heat release rate by 38s, significantly reduce the maximum heat release rate by 64.05%, reduce the total heat release by 60.44%, and reduce the fire growth index by 50.64%.

[0126] Compared with Comparative Example 1, it can be seen that adding CL can shorten the time for flame-retardant wood to reach the maximum heat release rate by 17 seconds, increase the maximum heat release rate by 4.88%, increase the total heat release by 15.2%, and increase the fire growth index by 13.2%. That is, adding CL has no substantial impact on flame-retardant performance under real combustion conditions.

[0127] Compared with Example 1, it can be seen that although adding APP increases the time for flame-retardant wood to reach the maximum heat release rate by 17 seconds, it can reduce the maximum heat release rate by 25.64%, the total heat release by 49.12%, and the fire growth index by 38.33%.

[0128] Test results show that adding the bio-based flame retardant CLA can significantly improve the flame retardant performance of wood under real combustion conditions and significantly reduce the fire hazard.

[0129] To demonstrate the effect of CLA addition on performance, Comparative Examples 3 and 4 are provided, with CLA additions of 1 wt.% and 3 wt.% of the total MUF, respectively, and are referred to as flame retardant coatings prepared with CLA additions of 2 wt.% and 3 wt.%.

[0130] Example 2

[0131] A method for preparing MUF / CLA with an addition amount of 1 wt.% is described below. Unless otherwise specified, the steps are the same as in Example 1, except that in step 3, the addition amount of CLA is 1 wt.%, specifically 1 g of CLA is added. The resulting flame-retardant coating is named MUF / CLA-1, and the further obtained flame-retardant wood is named W / MUF / CLA-1.

[0132] The TG test results of MUF / CLA-1 are as follows: Figure 3 As shown in Table 1, the temperature at which MUF / CLA-1 decomposes to 5% by mass is 235.64℃, the temperature at which the maximum decomposition rate is reached is 281.5℃, and the char residue at 800℃ is 19.64 wt.%.

[0133] Compared with Comparative Example 1, it can be seen that adding a small amount of CLA can also significantly increase the temperature at a decomposition mass of 5%, by 44.85℃, increase the temperature at which the mass loss rate is maximum by 19.8℃, and increase the residual carbon content by 7.14 wt.%. Therefore, the test results show that even adding a small amount of CLA can significantly improve thermal stability and residual carbon content.

[0134] Compared with Example 1, it can be seen that although increasing the amount of CLA can increase the temperature at which the decomposition mass is 5% by 7.01°C, the temperature at which the mass loss rate is the largest decreases by 13.9°C, and the amount of char residue at 800°C decreases by 4.06 wt.%.

[0135] Therefore, the test results show that increasing the amount of CLA added can improve thermal stability and residual carbon content.

[0136] The SEM test results of the residual carbon layer of MUF / CLA-1 are as follows: Figure 4 As shown in e, after complete combustion of W / MUF / CLA-1, a complete and dense char residue layer is formed.

[0137] Compared with reference example 1, it can be seen that adding a small amount of CLA can also transform the original porous structure of the residual carbon layer into a continuous and dense residual carbon layer, thus significantly improving the quality of the residual carbon layer.

[0138] Compared with Comparative Example 1, it can be seen that adding a small amount of CLA can also transform the original bubbly carbon layer into a continuous and dense bubbly carbon layer.

[0139] Compared with Example 1, it can be seen that increasing the amount of CLA added has no substantial impact on the residual carbon layer, that is, it remains continuous and dense.

[0140] Test results show that, within the specified range, the amount of CLA added has no substantial impact on the quality of the residual carbon layer.

[0141] The results of the vertical combustion test and limiting oxygen index test of W / MUF / CLA-1 are as follows: Figure 5 As shown in Table 2, it passed the UL-94V-0 rating test in the vertical burning test; and the limiting oxygen index of W / MUF / CLA-1 is 31.5%.

[0142] Compared with reference ratio 1, it can be seen that adding a small amount of CLA can also improve the UL-94 grade of wood from failing the test to V-0 grade, and at the same time, it can significantly increase the limiting oxygen index by 11.5%.

[0143] Compared with Comparative Example 1, it can be seen that adding a small amount of CLA can also improve the UL-94 grade of wood from V-1 to V-0, and at the same time, it can increase the limiting oxygen index by 2.5%.

[0144] Compared with Example 1, it can be seen that although increasing the amount of CLA added cannot change the UL-94 rating of flame-retardant wood, it can increase the limiting oxygen index by 1.1%.

[0145] The results of the W / MUF / CLA-1 cone calorimetry test are as follows: Figure 6As shown in Table 3, the time for the maximum heat release rate of W / MUF / CLA-1 is 100 s, and the maximum heat release rate is 44.72 kW / m². 2 The total heat release is 2.35 MJ / m³. 2 The fire growth index is 0.44 kW / m³. 2 ·s.

[0146] Compared with reference ratio 1, it can be seen that adding a small amount of CLA can also shorten the time for flame-retardant wood to reach the maximum heat release rate by 38s, significantly reduce the maximum heat release rate by 78.95%, reduce the total heat release by 79.29%, and reduce the fire growth index by 71.42%.

[0147] Compared with Comparative Example 1, adding a small amount of CLA can also shorten the time for flame-retardant wood to reach its maximum heat release rate by 13 seconds, reduce the maximum heat release rate by 26.15%, reduce the total heat release by 47.42%, and reduce the fire growth index by 16.98%.

[0148] Compared with Example 1, it can be seen that although increasing the amount of CLA can reduce the time for flame-retardant wood to reach the maximum heat release rate by 13 seconds, decrease the total heat release by 10.30%, and increase the fire growth index by 18.91%, it can increase the maximum heat release rate by 4.41%.

[0149] Test results show that increasing the amount of CLA added can further improve the flame retardant properties of wood under real combustion conditions.

[0150] Comparative Example 3

[0151] A method for preparing MUF / CLA with an addition amount of 3g is described. Unless otherwise specified, the steps are the same as in Example 1, except that in step 3, the CLA addition amount is 3wt.%, specifically 3g of CLA is added. The resulting flame-retardant coating is named MUF / CLA-3, and the further obtained flame-retardant wood is named W / MUF / CLA-3.

[0152] The TG test results of MUF / CLA-3 are as follows: Figure 3 As shown in Table 1, the temperature at which MUF / CLA-3 decomposes to a mass of 5% is 211.74℃, the temperature at which the maximum decomposition rate is reached is 307.1℃, and the char residue at 800℃ is 22.71 wt.%.

[0153] Compared with Comparative Example 1, it can be seen that adding excess CLA can also increase the temperature at 5% decomposition mass by 20.95℃, increase the temperature at which the mass loss rate is maximum by 5.8℃, and increase the residual carbon content by 10.21 wt.%. Therefore, the test results show that adding excess CLA can improve thermal stability and residual carbon content.

[0154] Compared with Example 1, it can be seen that although adding excessive CLA can further increase the temperature at which the mass loss rate is maximized by 11.7°C, it significantly reduces the temperature at which the decomposition mass is 5% and the char residue at 800°C. The temperature at which the decomposition mass is 5% decreases by 16.89°C, and the char residue at 800°C decreases by 1.58 wt.%. Therefore, the test results show that adding excessive CLA not only fails to further improve the flame retardant properties but also reduces them.

[0155] The SEM test results of the residual carbon layer of W / MUF / CLA-3 are as follows: Figure 4 As shown in f, although a continuous char layer can be formed after W / MUF / CLA-3 is completely burned, there are still pores on the surface of the char layer.

[0156] Compared with reference ratio 1, it can be seen that adding excessive CLA can form a continuous char layer on the wood surface. However, cracks appear on the surface and a large number of holes of different sizes are formed, which proves that adding excessive CLA can still improve the quality of the char layer.

[0157] Compared with Comparative Example 1, it can be seen that adding excessive CLA can also reduce the expansion and bubble phenomenon of residual char layer and improve flame retardant performance.

[0158] Compared with Example 1, it can be seen that adding excessive CLA actually forms pores of varying sizes on the continuous and dense residual carbon layer.

[0159] Test results show that adding excessive CLA will create new defects after combustion, causing the dense char residue layer to have a porous structure, resulting in a decrease in flame retardant performance.

[0160] The results of the vertical combustion test and limiting oxygen index test of W / MUF / CLA-3 are as follows: Figure 5 As shown in Table 2, it passed the UL-94V-1 rating test in the vertical burning test, with a limiting oxygen index of 30.0%.

[0161] Compared with reference ratio 1, it can be seen that adding excessive CLA improves the UL-94 grade of wood from failing the test to V-1 grade, and at the same time, it can significantly increase the limiting oxygen index by 10.0%.

[0162] Compared with Comparative Example 1, it can be seen that adding excessive CLA does not improve the UL-94 rating of flame-retardant wood, but it can increase the limiting oxygen index by 1.0%.

[0163] Compared with Example 1, it can be seen that adding excessive CLA actually reduced the UL-94 rating of flame-retardant wood from V-0 to V-0, and also reduced the limiting oxygen index by 2.6%.

[0164] Further comparison with Example 2 shows that while adding excessive CLA can increase the limiting oxygen index, the UL-94 rating actually decreases. Combined with SEM test results, it is clear that adding an appropriate amount of CLA is necessary to form a continuous and dense char layer, i.e., a high-quality char layer. This also demonstrates that the limiting oxygen index is not the sole criterion for judging flame retardant performance.

[0165] The results of the W / MUF / CLA-3 cone calorimetry test are as follows: Figure 6 As shown in Table 3, the time for the maximum heat release rate of W / MUF / CLA-3 is 82 s, and the maximum heat release rate is 55.04 kW / m³. 2 The total heat release is 3.42m³. 2 The fire growth index is 0.67 kW / m³. 2 ·s.

[0166] Compared with reference ratio 1, it can be seen that adding excessive CLA shortens the time for flame-retardant wood to reach the maximum heat release rate by 56, significantly reduces the maximum heat release rate by 74.09%, reduces the total heat release by 69.86%, and reduces the fire growth index by 56.49%.

[0167] Compared with Comparative Example 1, it can be seen that adding excessive CLA shortens the time for flame-retardant wood to reach the maximum heat release rate by 31 seconds, reduces the maximum heat release rate by 9.11%, reduces the total heat release by 23.48%, and increases the fire growth index by 26.41%. That is, adding MUF / CLA-3 can slightly improve the flame-retardant performance of wood in real combustion conditions, but it increases the fire growth index.

[0168] Compared with Example 1, it can be seen that although adding excessive CLA reduces the time for flame-retardant wood to reach the maximum heat release rate by 31 seconds, increases the total heat release by 30.53%, and increases the fire growth index by 81.08%, the maximum heat release rate increases by 12.21%.

[0169] Test results show that adding excessive CLA can improve the flame retardant properties of wood under real burning conditions, but it also increases the maximum heat release rate, meaning that the amount of CLA added should not be too much.

[0170] By comparing Example 1, Example 2, and Comparative Example 3, it can be seen that:

[0171] 1. Wood coated with MUF / CLA has significantly improved flame retardant properties compared to uncoated pure wood. Flame retardant coatings can effectively improve the flammability of wood, giving it flame retardant properties.

[0172] 2. Adding an appropriate amount of CLA as a bio-based flame retardant can effectively improve the thermal stability, limiting oxygen index, UL-94 rating, and flame retardant performance of W / MUF. As its content increases, the thermal stability of W / MUF also increases. However, adding excessive CLA will lead to a decrease in char residue, limiting oxygen index, and UL-94 rating.

Claims

1. A method for preparing a bio-based flame-retardant coating based on ammonium polyphosphate, characterized in that, The flame retardant CLA, a bio-based flame retardant derived from chitosan / lignin / ammonium polyphosphate, is prepared using urea, formaldehyde, and melamine as resin raw materials, dioctyl phthalate (DOP) as a plasticizer, and tannic acid as a curing agent. CLA is derived from lignin (LS), chitosan (CS), and ammonium polyphosphate (APP), and contains -NH2, OH, P=O, and PO groups. - -CONH2 includes the following steps: Step 1, preparation of chitosan / lignin / ammonium polyphosphate bio-based flame retardant CLA: First, LS solution, CS solution and APP solution are prepared by using lignin LS, chitosan CS and ammonium polyphosphate APP respectively. Then, the LS solution is added dropwise to the CS solution to react and obtain an LS / CS mixed solution. Finally, under the same dropping conditions, the APP solution is added dropwise to the LS / CS mixed solution to react and obtain the chitosan / lignin / ammonium polyphosphate bio-based flame retardant CLA. Step 2, Preparation of melamine-urea-formaldehyde resin emulsion (MUF): First, sodium hydroxide solution is added to the formaldehyde solution to adjust the pH to 8.0-8.

5. Then, the temperature is raised to 90℃ while stirring at 400-450 rpm. Afterwards, raw materials are added in three stages to prepare the melamine-urea-formaldehyde resin emulsion (MUF). Step 2 consists of three stages. Phase 2.1 involves adding the first-stage urea at a temperature of 90℃, followed by the addition of melamine (MEL). After the addition is complete, stirring is continued for 30 minutes. In stage 2.2, while maintaining a temperature of 90℃, lactic acid solution is first added to adjust the pH of the solution to 4.5-5.0, and then urea is added in the second stage. After the addition is complete, stirring is continued for 10 minutes until the reaction reaches the endpoint. The endpoint of the reaction in stage 2.2 is determined by the following: when a drop of solution is added to water at 30°C, the solution will solidify in the water without dispersing. Stage 2.3 involves first adding sodium hydroxide solution at a temperature of 90℃ to adjust the pH of the solution to 7.5-8.0, then adding urea in the third stage. After the addition is complete, the temperature is adjusted, and the mixture is stirred at a temperature of 70℃ for 30 minutes to obtain MUF. Step 3: Preparation of bio-based flame retardant coating MUF / CLA based on ammonium polyphosphate. Dioctyl phthalate (DOP), tannic acid (TA), and the CLA obtained in Step 1 are added to the MUF obtained in Step 2. After the addition is complete, mechanical stirring is performed to mix the components evenly, thus obtaining the bio-based flame retardant coating MUF / CLA based on ammonium polyphosphate.

2. The preparation method according to claim 1, characterized in that: In step 1, the mass ratio of LS, CS and APP is 2:2:

1.

3. The preparation method according to claim 1, characterized in that: In step 1, the LS solution is prepared by dissolving LS in deionized water under the following conditions: the dissolution temperature is 30℃, the dissolution stirring speed is 400-450 rpm, and the dissolution stirring time is 30 min, thereby obtaining the LS solution. In step 1, the CS solution is prepared by dissolving CS in lactic acid solution under the following conditions: the dissolution temperature is 45℃, the dissolution stirring speed is 400-450rpm, and the dissolution stirring time is 120min, thereby obtaining the CS solution. In step 1, the APP solution is prepared by dissolving APP in deionized water under the following conditions: the dissolution temperature is 80℃, the dissolution stirring speed is 400-450rpm, and the dissolution stirring time is 120min, to obtain the APP solution. In step 1, the dropping conditions are as follows: dropping temperature is 45℃, dropping stirring speed is 600-650 rpm, dropping stirring time is 1 h, and dropping acceleration rate is 0.5 drops / s.

4. The preparation method according to claim 1, characterized in that: In step 2, the mass ratio of the total amount of formaldehyde solution, melamine (MEL), and urea added is 100:1.14:

57. In step 2, the ratio of urea added in the three stages is 37:12.4:7.

6.

5. The preparation method according to claim 1, characterized in that: In step 3, the mass ratio of MUF, DOP, TA and CLA obtained in step 1 is 100:1:1:2; In step 3, the mechanical stirring conditions are: stirring speed of 600-650 rpm and stirring time of 2 h.

6. The preparation method according to claim 5, characterized in that: The temperature at which the MUF / CLA decomposed to a mass of 5% was 228.63±5℃, and the temperature at which the maximum decomposition rate was reached was 295.4±5℃; the char residue at 800℃ was 24.29±2wt.%.

7. The preparation method according to claim 5, characterized in that: When the resulting ammonium polyphosphate-based bio-based flame retardant coating is used as a flame retardant coating for wood, it exhibits flame retardant properties and passes the UL-94 V-0 rating test; the residual char layer formed after complete combustion is continuous and dense.

8. The preparation method according to claim 5, characterized in that: When the resulting ammonium polyphosphate-based bio-based flame-retardant coating is used as a flame-retardant coating for wood, the limiting oxygen index is 32.6 ± 0.06%; the maximum heat release rate is 42.83 ± 1.51 kW / m³. 2 The total heat release is 2.62 ± 1.25 MJ / m³. 2 The fire growth index was 0.37 ± 0.02 kW / m³. 2 •s.

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