A flame-retardant coating based on PG flame-retardant curing agent, its preparation method and application

Abstract

This invention discloses a flame-retardant coating based on PG flame-retardant curing agent, using urea and formaldehyde as raw materials, KH550 as an additive, dioctyl phthalate (DOP) as a plasticizer, and phytic acid-guanidine azole (PG) as a bio-based flame-retardant curing agent. The PG is prepared by ionic reaction of phytic acid and guanidine azole under aqueous conditions. The decomposition temperature is 160-200℃ when the mass is 5%, and the temperature at which the maximum decomposition rate is reached is 290-300℃. The char residue at 800℃ is 10-22 wt.%. The preparation method includes the following steps: 1. Preparation of phytic acid-guanidine azole flame-retardant curing agent PA-GZ, abbreviated as PG; 2. Preparation of modified urea-formaldehyde resin emulsion KUF; 3. Preparation of flame-retardant coating KUF-PG based on PG flame-retardant curing agent. When used as a flame-retardant coating for wood, it exhibits flame-retardant properties, with a limiting oxygen index of 29-33%, and passes the UL-94V-0 test, forming a dense char layer after complete combustion.

Description

Technical Field

[0001] This invention relates to the field of flame retardant materials, specifically to a flame retardant coating based on PG flame retardant curing agent, its preparation method, and its application. Background Technology

[0002] Wood is a common and widely used resource; however, it is flammable, thus requiring improved flame-retardant properties. The basic principle of wood flame retardancy is to coat the wood surface with a flame-retardant coating, isolating the wood from fire to achieve flame retardancy. Based on this principle, flame-retardant coatings are prepared by directly adding flame retardants to the coating to improve its flame-retardant performance. For example, existing literature 1 (Epoxy-modified silicone resin based N / P / Sisynergistic flame-retardant coating for wood surface [J]. Progress in Organic Coatings 170(2022)106953) describes a method to significantly improve the flame-retardant properties of wood by condensing dimethyldiethoxysiloxane with 3-glycidoxypropyltrimethoxysilane KH-560 to form an epoxy-modified silicon SiR coating, followed by curing the resin with a nitrogen- and phosphorus-containing flame retardant PTDP. However, the problem with this technical solution is that PTDP is a non-bio-based flame retardant, and therefore cannot be degraded in the environment, which leads to the accumulation of PTDP in the environment during long-term use and causes environmental pollution.

[0003] To solve the above-mentioned technical problems, a biomass-based flame retardant with degradable properties—phytic acid-based flame retardant—can be used. For example, existing literature 2 ("Sustainable, high-performance, flame-retardant waterborne wood coatings via phytic acid based green curing agent for melamine-urea-formaldehyde resin" [J]. Progress in Organic Coatings 162(2022)106597) prepared a phytic acid ammonium bicarbonate by controlling the molar ratio of phytic acid to urea, and used the phytic acid ammonium bicarbonate as a flame-retardant curing agent to cure melamine-urea-formaldehyde resin to obtain a flame-retardant coating. After the flame-retardant coating was applied to the wood surface, the flame-retardant wood passed the UL-94V-0 rating, and the limiting oxygen index was as high as 42.4%. However, the technical problem with this solution is that the content of the curing agent used is more than 10 wt.%, while the amount of conventional curing agent used is only 1-2 wt.%. Obviously, the curing function of the flame-retardant curing agent in this solution cannot achieve the effect of conventional curing agents. This problem directly led to a significant increase in the raw material cost of flame retardant curing agents.

[0004] To achieve the same flame-retardant effect while reducing the amount of flame retardant added, in the previous work of the inventors' research group, existing literature 3 (Zou Yongjin, Wei An, Xiang Cuili et al. A bio-based flame-retardant coating based on PGL and its preparation method and application: China, Patent No. CN118580739 A) uses urea and formaldehyde as the main raw materials, silane coupling agent KH550 as an auxiliary agent, phytic acid-guanidine azole-lignin composite polymer PGL as a bio-based flame retardant, and ammonium chloride as a curing agent to prepare a flame-retardant coating, which is then applied to the surface of wood to improve the flame-retardant performance of the wood. This technical solution requires only 1 wt% of ammonium chloride as the curing agent to achieve the curing effect. However, although this technical solution uses a small amount of biomass-based curing agent, it still requires the additional addition of conventional curing agent ammonium chloride. The reason is that using the biomass-based curing agent alone cannot achieve the same curing effect as conventional curing agents; that is, although it partially achieves the technical effect of reducing the amount of curing agent used, it cannot completely solve the aforementioned technical problem.

[0005] Therefore, the existing technology has the following technical problems: when using bio-based flame retardants alone as curing agents, and when the amount added is small, it is impossible to achieve the same curing effect as conventional curing agents. Summary of the Invention

[0006] The purpose of this invention is to provide a flame-retardant coating based on PG flame-retardant curing agent, its preparation method, and its application. Addressing the problems of existing technologies, this invention utilizes the ionic reaction between phytic acid and guanidine PG to prepare phytic acid-guanidine PG, which is then used as a flame-retardant curing agent to cure modified urea-formaldehyde resin to prepare bio-based flame-retardant coatings. This also solves the problem of high curing agent usage. KH550 is an additive, dioctyl phthalate (DOP) is a plasticizer, and phytic acid-guanidine PG is a bio-based flame-retardant curing agent. The technical principle involved is as follows:

[0007] 1. KH550, as an additive, plays a role in regulating the molecular structure of urea-formaldehyde resin and improving the compatibility of urea-formaldehyde resin with curing agents and plasticizers. In addition, since the silicon atoms in KH550 can form covalent bonds with the oxygen atoms in the ethoxy group, it can improve thermal stability, promote char formation during combustion, improve the quality of the char layer, and ultimately play a role in heat insulation and flame retardancy.

[0008] 2. As a flame retardant, PG contains a large number of phosphate and ammonium ions. Therefore, during combustion, the phosphorus element in the phytate ions can promote the dehydration of the matrix to form a protective char layer, while the nitrogen element in the ammonium ions produces non-combustible gas during combustion, diluting the oxygen in the air. The two work together to improve the flame retardant performance of the matrix.

[0009] 3. As a curing agent, PG content is positively correlated with curing speed. Therefore, in order to avoid the flame retardant coating from cracking due to excessive curing speed, DOP is added to improve the mechanical properties of the flame retardant coating and avoid the problem of cracking due to excessive curing speed.

[0010] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0011] A flame-retardant coating based on PG flame-retardant curing agent, using urea and formaldehyde as raw materials, KH550 as an additive, dioctyl phthalate (DOP) as a plasticizer, and phytic acid-guanidine PG as a bio-based flame-retardant curing agent, wherein the PG is prepared by ionic reaction of phytic acid and guanidine PG under aqueous solution conditions.

[0012] The temperature at which 5% of the mass is decomposed is 160-200℃, and the temperature at which the maximum decomposition rate is reached is 290-300℃; the char residue at 800℃ is 10-22 wt.%.

[0013] A method for preparing a flame-retardant coating based on PG flame-retardant curing agent includes the following steps:

[0014] Step 1, Preparation of phytic acid guanidine azole flame retardant curing agent: First, under certain conditions, guanidine azole GZ is dissolved in deionized water to obtain GZ solution. At the same time, phytic acid PA solution is dissolved in deionized water to obtain PA solution. Then, under certain conditions, PA solution is added dropwise to GZ solution to react fully. After the reaction is complete, rotary evaporation is performed under certain conditions. After rotary evaporation is complete, the obtained crystals are ground to obtain phytic acid guanidine azole flame retardant curing agent PA-GZ, abbreviated as PG.

[0015] In step 1, the molar ratio of GZ to PA is 7:1.

[0016] In step 1, the conditions for preparing the GZ solution are: dissolution temperature of 20-30℃, dissolution stirring speed of 500-600 rpm, and dissolution stirring time of 25-35 min.

[0017] In step 1, the conditions for dripping are: dripping temperature of 20-30℃, dripping stirring speed of 500-600 rpm, dripping stirring time of 40-60 min, and dripping acceleration rate of 0.5 drops / s;

[0018] In step 1, the conditions for rotary evaporation are: rotary evaporation temperature of 70-80℃ and rotary evaporation time of 2.5-3h.

[0019] Step 2, preparation of modified urea-formaldehyde resin emulsion: First, sodium hydroxide solution is added to formaldehyde solution to adjust the pH value of the solution. Then, under certain conditions, the initial reaction conditions are prepared. After that, urea, silane coupling agent KH550 and other raw materials are added in three stages to prepare modified urea-formaldehyde resin emulsion KUF, abbreviated as KUF.

[0020] In step 2, the total mass ratio of formaldehyde solution, urea, and KH550 is 100:56.9:2.85.

[0021] In step 2, the pH of the solution is adjusted to 8.0-8.5; the initial reaction conditions are: stirring speed of 400-500 rpm and heating to 90°C.

[0022] The three stages in step 2 are as follows:

[0023] Stage 2.1 involves adding urea first, then KH550, while maintaining a temperature of 90℃. After the addition is complete, stirring is continued for 30 minutes.

[0024] In stage 2.2, while maintaining a temperature of 90℃, acetic acid solution is first added to adjust the pH of the solution to 4.5-5.0, and then urea is added. After the addition is complete, stirring is continued for 10 minutes until the reaction reaches the endpoint.

[0025] 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.

[0026] Stage 2.3 involves maintaining a temperature of 90℃, first adding sodium hydroxide solution to adjust the pH of the solution to 7.5-8.0, then adding urea. 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 KUF.

[0027] In the three stages, the urea addition amount in the three stages meets the mass ratio of 37:12.3:7.6;

[0028] Step 3: Preparation of flame-retardant coating based on PG flame-retardant curing agent. The KUF obtained in Step 2, dioctyl phthalate (DOP), and PG obtained in Step 1 are mixed in a specific mass ratio. DOP and PG are added to the KUF. After addition, mechanical stirring is performed under certain conditions to ensure uniform mixing of all components. Sodium hydroxide is added dropwise to adjust the pH of the resulting solution to 4-5, thus obtaining the flame-retardant coating based on PG flame-retardant curing agent, abbreviated as KUF-PG.

[0029] In step 3, the mass ratio of KUF, DOP, and PG is 100:1:2.5;

[0030] In step 3, the mechanical stirring conditions are as follows: stirring speed is 500-600 rpm, and stirring time is 30 min.

[0031] When flame-retardant coatings based on PG flame-retardant curing agents are used as flame-retardant coatings for wood, they exhibit flame-retardant properties, with a limiting oxygen index of 29-33%. They pass the UL-94V-0 test and form a dense char layer after complete combustion.

[0032] The technical effects of the green bio-based wood flame-retardant coating obtained by this invention have been tested as follows:

[0033] The DSC test results show that the flame-retardant coating has only one peak in its DSC curve, indicating that the curing behavior of the flame-retardant coating is simple and that it can be cured at a relatively low temperature.

[0034] The results of the TG test show that although the residual carbon content is low when using PG as a curing agent, the temperature at which the decomposition mass is 5% increases significantly with the increase of PG content. Furthermore, the temperature at which the maximum decomposition rate is reached is not significantly affected, indicating that it has high thermal stability.

[0035] To further demonstrate why flame-retardant coatings still exhibit good flame-retardant properties even with low char content, SEM testing was conducted on the char layer after complete combustion of wood coated with the flame-retardant coating. The test results showed that using PG as a curing agent can improve the quality of the char layer after combustion of wood coated with the flame-retardant coating. The char layer formed after complete combustion is continuous and dense, and there are no pores. This dense char layer effectively isolates oxygen and heat, thereby improving the flame-retardant properties of the wood.

[0036] Vertical burning tests showed that applying flame-retardant coatings improves the UL-94 rating of wood. Wood coated with flame-retardant coatings using PG as a curing agent passed the UL-94 V-0 rating test; furthermore, the limiting oxygen index was as high as 29-33%, demonstrating excellent flame-retardant properties.

[0037] Therefore, the green bio-based wood flame-retardant coating of the present invention has the following advantages over the prior art:

[0038] 1. The bio-based flame-retardant coating obtained by this invention can significantly improve the flame-retardant properties of wood;

[0039] 2. The biomass raw materials used in this invention have the advantages of being renewable, widely available, and environmentally friendly;

[0040] 3. This invention can completely avoid the use of conventional curing agents, and the amount added is less than that of conventional curing agents, thus reducing production costs. Attached Figure Description

[0041] Figure 1 The FTIR plots of PG, PA, and GZ in Example 1 are shown.

[0042] Figure 2 FTIR plots of PG, Example 1, Example 2, Example 3, Comparative Example 2, and Comparative Example 3;

[0043] Figure 3 The following are DSC diagrams of Examples 1, 3, 2, 3, and 2: Comparative Example;

[0044] Figure 4 The following are TG plots of Examples 1, 3, 2, Comparative Example 3, and Comparative Example 2;

[0045] Figure 5 The images shown are SEM images of the char residue layers after combustion in Comparative Examples 2, 3, and 1. Figure 5 a is comparative example 2. Figure 5 b is comparative example 3. Figure 5 c represents Example 1;

[0046] Figure 6The figures shown are vertical combustion test diagrams for Comparative Example 1, Comparative Example 2, Comparative Example 3, Example 2, Example 3, and Example 1. Figure 6 'a' represents the period before the vertical combustion test. Figure 6 b represents the result after the vertical combustion test. Detailed Implementation

[0047] 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.

[0048] Example 1

[0049] A method for preparing a flame-retardant coating based on PG flame-retardant curing agent includes the following steps:

[0050] Step 1, Preparation of phytic acid guanidine azole flame retardant curing agent: First, under the conditions of a dissolution temperature of 25℃, a dissolution stirring speed of 500 rpm, and a dissolution stirring time of 30 min, 13.5 g of guanidine azole GZ was dissolved in 100 mL of deionized water to obtain a GZ solution. At the same time, 15 mL of 70 wt.% phytic acid PA solution was dissolved in 50 mL of deionized water to obtain a PA solution. Then, under the conditions of a dropping temperature of 25℃, a dropping stirring speed of 500 rpm, a dropping stirring time of 1 h, and a dropping rate of 0.5 drops / s, the PA solution was added dropwise to the GZ solution to allow for a complete reaction. After the reaction was completed, rotary evaporation was carried out at a temperature of 70℃ for a time of 3 h. After the rotary evaporation was completed, the resulting crystals were ground to obtain the phytic acid guanidine azole flame retardant curing agent PA-GZ, abbreviated as PG.

[0051] To confirm the composition of PG, i.e., successful synthesis, an FTIR test was performed, and the test results are as follows. Figure 1 As shown, PG contains characteristic peaks of both PA and GZ. Test results indicate that PG was successfully synthesized.

[0052] Step 2, preparation of modified urea-formaldehyde resin emulsion: 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 to complete the preparation of initial reaction conditions. Afterwards, add 56.9g of urea, 2.85g of silane coupling agent KH550, and other raw materials in three stages to prepare modified urea-formaldehyde resin emulsion KUF, abbreviated as KUF. The three stages are as follows...

[0053] In stage 2.1, while maintaining a temperature of 90℃, first add 37g of urea, then add 2.85g of KH550. After the addition is complete, continue stirring for 30 minutes.

[0054] In stage 2.2, while maintaining a temperature of 90℃, 20wt.% acetic acid solution was first added to adjust the pH of the solution to 4.5-5.0, and then 12.3g of urea was added. After the addition was completed, stirring was continued for 10 minutes until the reaction reached the endpoint.

[0055] 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.

[0056] Stage 2.3 involves maintaining a temperature of 90℃, first adding 20wt.% sodium hydroxide solution to adjust the pH of the solution to 7.5-8.0, then adding 7.6g of urea. 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 KUF.

[0057] Step 3: Preparation of flame-retardant coating based on PG flame-retardant curing agent. Using the mass ratio of KUF obtained in Step 2, dioctyl phthalate (DOP), and PG obtained in Step 1 as 100:1:2.5, add 1g of DOP and 2.5g of PG to 100g of KUF. After addition, mechanically stir at 600rpm for 30min to ensure uniform mixing of all components. Adjust the pH of the resulting solution to 4-5 by adding sodium hydroxide dropwise. This yields the flame-retardant coating based on PG flame-retardant curing agent, abbreviated as KUF-PG. Specifically, the KUF-PG prepared in Example 1 is abbreviated as KUF-PG-2.5.

[0058] To confirm the composition of KUF-PG-2.5, FTIR testing was performed. The test results are as follows: Figure 2 As shown, KUF-PG-2.5 simultaneously contains characteristic peaks of urea-formaldehyde resin UF, KH550, phytic acid PA, and guanidine azole GZ. The test results indicate that PG and KH550 reacted with the urea-formaldehyde resin emulsion.

[0059] To demonstrate the curing properties of KUF-PG-2.5, DSC testing was conducted. The test results are as follows: Figure 3 As shown, the DSC curve of KUF-PG-2.5 has exactly one peak, with a peak temperature of 98.5℃. The test results indicate that the curing behavior of the flame-retardant coating KUF-PG-2.5 is simple and can be cured at a relatively low temperature.

[0060] To demonstrate the thermal stability of KUF-PG-2.5, a TG test was conducted. The test results are as follows: Figure 4As shown in Table 1, the decomposition temperature of KUF-PG-2.5 at a mass of 5% is 195.3℃, the temperature at which the maximum decomposition rate is reached is 294.8℃, and the char residue at 800℃ is 21.9 wt.%. The test results indicate that although the char residue of KUF-PG-2.5 is low, only 21.9%, the decomposition temperature at a mass of 5% increases significantly with increasing PG content, and the temperature at which the maximum decomposition rate is reached is not significantly affected, demonstrating high thermal stability.

[0061] Table 1. Thermogravimetric test results

[0062]

[0063] To further demonstrate the technical effectiveness of KUF-PG as a flame-retardant coating for wood, specifically to prove why KUF-PG-2.5 still exhibits good flame-retardant properties despite its low char content, flame-retardant wood W-KUF-PG was prepared by coating KUF-PG onto the wood surface and subjected to flame-retardant testing. The specific preparation method for W-KUF-PG is as follows: KUF-PG is coated onto the wood surface with a thickness of 0.3 mm. After coating, it is dried for 24 hours to obtain W-KUF-PG. Specifically, the W-KUF-PG prepared based on KUF-PG-2.5 in Example 1 is named W-KUF-PG-2.5.

[0064] SEM analysis was performed on the char layer remaining after complete combustion of W-KUF-PG-2.5. The test results are as follows: Figure 5 As shown in Figure c, the char layer formed after complete combustion of W-KUF-PG-2.5 is continuous and dense, and there are no pores. Test results indicate that W-KUF-PG-2.5 prepared using PG as a curing agent can form a dense char layer, effectively isolating oxygen and heat, and improving the flame-retardant properties of wood.

[0065] To further demonstrate the flame-retardant properties of W-KUF-PG-2.5, vertical burning tests and limiting oxygen index tests were conducted. The test results are as follows: Figure 6 As shown in Table 2, W-KUF-PG-2.5 passed the UL-94V-0 rating test; furthermore, W-KUF-PG-2.5 has a limiting oxygen index as high as 32.7%. The test results indicate that W-KUF-PG-2.5 has excellent flame retardant properties.

[0066] Table 2 Results of Vertical Combustion Test and Oxygen Index Test

[0067]

[0068] As is generally known in the art, char residue is positively correlated with flame retardant performance; that is, the higher the char residue, the better the flame retardant performance. Therefore, based on this common knowledge, a general method for those skilled in the art to improve flame retardant performance is to increase the char residue. Simultaneously, the char residue is used as an important criterion to determine whether further research should be conducted; that is, the char residue is used to preliminarily determine whether the flame retardant performance has good potential.

[0069] To demonstrate the relationship between char residue and flame retardant performance, we further compared it with existing references. The specific performance is shown in Table 3.

[0070] Table 3. Carbon residue of different flame-retardant coatings and their impact on flame-retardant performance.

[0071]

[0072] Reference 1 (Zou Yongjin, Wei An, Xiang Cuili, et al. A bio-based flame retardant coating based on PGL and its preparation method and application: China, Patent No. CN118580739 A)

[0073] Reference 2 (Zou Yongjin, Wei An, Xiang Cuili, et al. A smoke-suppressing and flame-retardant liquid based on KH550 and its preparation method and application: China, application number 2024115890936)

[0074] According to Reference 1, when the residual carbon content is higher than that of this invention, reaching 23.2 wt%, although the limiting oxygen index is not substantially different from that of this invention, reaching 31.6%, the UL-94 rating is only V-1. By comparison, it can be seen that when the residual carbon content of KUF-PG-2.5 obtained by this invention is significantly lower than that of the reference, it not only obtains a limiting oxygen index that is not substantially different from that of the reference, but also achieves a UL-94 rating of V-0.

[0075] Further comparison with Reference 1 shows that when the carbon residue is increased to 35.3, the UL-94 rating can be improved from V-1 to V-0. This also proves that the KUF-PG-2.5 obtained by this invention can achieve the same technical effect as the reference when the carbon residue is low.

[0076] In similar work, when the carbon residue in Reference 2 reached 34.67 wt%, the UL-94 rating was V-0;

[0077] Based on the above comparison and combined with the results of TG and SEM tests, it can be seen that the reason for the high flame retardant performance is that the char layer formed after the complete combustion of W-KUF-PG-2.5 has a continuous and dense nature, and there are no pores. It can effectively isolate oxygen and heat, thereby improving the flame retardant performance of wood. This proves that the KUF-PG-2.5 obtained by this invention has a better quality char layer than the prior art.

[0078] To demonstrate the effect of flame-retardant coating KUF-PG-2.5 on the flame-retardant properties of wood, Comparative Example 1 is provided, consisting of pure wood without KUF-PG coating.

[0079] Comparative Example 1

[0080] A type of pure wood that is not coated with KUF-PG, simply referred to as pure wood.

[0081] The results of the vertical burning test and limiting oxygen index test of pure wood are as follows: Figure 6 As shown in Table 2,

[0082] The solid wood failed the UL-94 rating test. A comparison with Example 1 shows that coating with KUF-PG-2.5 allows the solid wood to pass the UL-94 rating test.

[0083] The limiting oxygen index (LOI) of pure wood is 20.5%. Compared with Example 1, coating with KUF-PG-2.5 can increase the LIO from 20.5% to 32.7%, an increase of 159.5%.

[0084] As can be seen from Comparative Example 1 and Example 1, coating with KUF-PG-2.5 can improve the UL-94 rating by increasing the limiting oxygen index, that is, improve the flame retardant performance.

[0085] To demonstrate the effect of flame retardant curing agent PG on the performance of flame retardant coating KUF-PG and flame retardant wood W-KUF-PG, Comparative Example 2 is provided, which is a flame retardant coating prepared by using conventional tannic acid as a curing agent instead of PG.

[0086] Comparative Example 2

[0087] A method for preparing a flame-retardant coating based on tannic acid curing agent, unless otherwise specified, is the same as in Example 1, except that step 1 is not required, and in step 3, tannic acid TA is used instead of PG to obtain a flame-retardant coating based on tannic acid curing agent, abbreviated as KUF-TA, and the resulting flame-retardant wood is named W-KUF-TA.

[0088] KUF-TA DSC test results as follows Figure 3 As shown, the DSC curve of KUF-TA has only one peak, with a peak temperature of 108.2℃. Comparing with Example 1, the curing curves of KUF-PG-2.5 and KUF-TA exhibit consistent behavior; however, using PG as a curing agent lowers the curing temperature. The test results indicate that using PG as a curing agent does not affect the curing behavior of KUF-PG, but rather the curing temperature.

[0089] KUF-TA TG test results are as follows Figure 4As shown in Table 1, the temperature at which KUF-TA decomposes to 5% by mass is 181.3℃, the temperature at which the maximum decomposition rate is reached is 298.7℃, and the char residue at 800℃ is 12.5 wt.%. Compared with Example 1, using PG as a curing agent can increase the temperature at which the decomposition to 5% by mass by 14℃, slightly decrease the temperature at which the maximum decomposition rate is reached by 4.4℃, and increase the char residue at 800℃ by 9.4 wt.%. The test results show that using PG as a curing agent can significantly improve the thermal stability and char residue of KUF-PG, while the negative impact on the maximum decomposition rate temperature is negligible.

[0090] SEM test results of the residual char layer after complete combustion of W-KUF-TA are as follows: Figure 5 As shown in Figure a, the residual char layer not only has numerous pits but also large pores. Compared with Example 1, it can be seen that using PG as a curing agent transforms the residual char layer from one with pits and pores to a continuous, dense layer without pores. Test results indicate that using PG as a curing agent can significantly improve the quality of the residual char layer and enhance its flame-retardant properties.

[0091] The results of the vertical combustion test and limiting oxygen index test of W-KUF-TA are as follows: Figure 6 As shown in Table 2, W-KUF-TA passed the UL-94V-1 level test; and the limiting oxygen index of W-KUF-TA is 31.5%.

[0092] Compared with Comparative Example 1, it can be seen that using TA as a curing agent can improve the UL-94 rating of pure wood from failing to passing to V-1 rating; and it can significantly increase the limiting oxygen index from 20.5% to 31.5%.

[0093] Compared with Example 1, it can be seen that using PG as a curing agent can improve the UL-94 rating of pure wood from V-1 to V-0; and can slightly increase the limiting oxygen index from 31.5% to 32.7%.

[0094] Test results show that although using PG as a curing agent has a negligible effect on improving the limiting oxygen index, it can directly improve the UL-94 rating.

[0095] Based on the results of SEM and TG tests, it can be seen that the flame retardant process of adding flame retardant curing agent PG during combustion does not originate from the release of non-combustible gases, but rather directly prevents the further combustion of W-KUF-PG-2.5 by increasing the amount of char residue and forming a dense and smooth char residue layer during combustion, thereby improving the UL-94 rating and enhancing the flame retardant performance.

[0096] As can be seen from Comparative Example 2 and Example 1, the effect of increasing the limiting oxygen index mainly comes from KUF, while the role of flame retardant curing agent PG is to increase the amount of char residue and form a dense and smooth char residue layer.

[0097] To demonstrate the effect of PG addition on the performance of flame-retardant coating KUF-PG and flame-retardant wood W-KUF-PG, Comparative Example 3, Example 2 and Example 3 are provided with flame-retardant coatings having PG addition amounts of 1 wt.%, 1.5 wt.%, and 2 wt.%, respectively.

[0098] Comparative Example 3

[0099] A method for preparing KUF-PG with a PG addition amount of 1 wt.% is described below. Unless otherwise specified, the steps are the same as those in Example 1, except that in step 3, the PG addition amount is 1 wt.%, that is, the PG addition amount is 1 g. The resulting flame retardant coating is named KUF-PG-1, and the further obtained flame retardant wood is named W-KUF-PG-1.

[0100] The DSC test results of KUF-PG-1 are as follows: Figure 3 As shown, the DSC curve of KUF-PG-1 has only one peak, with a peak temperature of 107.5℃. Compared with Example 1, the curing curves of KUF-PG-2.5 and KUF-PG-1 exhibit consistent behavior; however, increasing the amount of PG added leads to a decrease in curing temperature. The test results indicate that the amount of PG added does not affect the curing behavior of KUF-PG, but it does affect its curing temperature.

[0101] The TG test results of KUF-PG-1 are as follows: Figure 4 As shown in Table 1, the temperature at which KUF-PG-1 decomposes at a mass of 5% is 157.6℃, the temperature at which the maximum decomposition rate is reached is 300.3℃, and the char residue at 800℃ is 1.3 wt.%. The test results indicate that the addition of a small amount of PG has a negligible effect on the temperature at the maximum decomposition rate, but a significant effect on the temperature and char residue at a mass of 5%.

[0102] Compared with Comparative Example 2, it can be seen that the effect of using a small amount of PG to replace TA on the maximum decomposition rate temperature is negligible, but it will significantly reduce the temperature and char residue when the decomposition mass is 5%. That is, when a small amount of PG is added, the flame retardant performance is significantly worse than that of TA.

[0103] Compared with Example 1, it can be seen that although increasing the amount of PG added has a negligible effect on the temperature at the maximum decomposition rate, it can significantly increase the temperature and char residue at a decomposition mass of 5%.

[0104] Based on the above analysis, it can be concluded that the amount of PG added has no substantial effect on the maximum decomposition rate temperature. However, it has a significant effect on the temperature and char residue at a decomposition mass of 5%. Specifically, increasing the amount of PG added can significantly improve the temperature and char residue at a decomposition mass of 5%.

[0105] SEM test results of the residual char layer after complete combustion of W-KUF-PG-1 are as follows: Figure 5 As shown in b, although the residual carbon layer does not have pits, it still has a small number of pores;

[0106] Compared with Comparative Example 2, it can be seen that only a small amount of PG is needed to replace TA, which can achieve a pit-free char layer after complete combustion, and at the same time, significantly reduce porosity.

[0107] Compared with Example 1, it can be seen that increasing the PG content can completely prevent the formation of pores in the residual carbon layer.

[0108] Test results show that adding a small amount of PG can effectively improve the quality of the residual carbon layer. However, when the amount added is small, the residual carbon content is extremely low, resulting in a small number of pores in the formed residual carbon layer.

[0109] The results of the vertical combustion test and limiting oxygen index test of W-KUF-PG-1 are as follows: Figure 6 As shown in Table 2, W-KUF-PG-1 passed the UL-94V-1 rating test; and the limiting oxygen index of W-KUF-PG-1 is 28.8%.

[0110] Compared with Comparative Example 1, it can be seen that using a small amount of PG as a curing agent can improve the UL-94 rating of pure wood from failing to passing to V-1 rating, and can significantly improve the limiting oxygen index from 20.5% to 28.8%.

[0111] Compared with Comparative Example 2, it can be seen that adding a small amount of PG has no substantial impact on the UL-94 rating; however, the limiting oxygen index actually decreased from 31.5% to 28.8%.

[0112] Compared with Example 1, it can be seen that increasing the amount of PG added can improve the UL-94 rating from V-1 to V-0 and increase the limiting oxygen index from 28.8% to 32.7%.

[0113] Test results show that adding a small amount of PG as a curing agent can achieve the same flame retardant effect as adding TA. However, when the amount added is small, the residual char content is only 1.3 wt.%, which makes it impossible to effectively improve the limiting oxygen index. Further combined with the SEM test results, it can be seen that the reason for passing the UL-94V-1 level test is that even if a small amount of PG is used to replace TA, the quality of the residual char layer can be effectively improved. Therefore, increasing the amount of PG added can further improve the flame retardant performance.

[0114] Example 2

[0115] A method for preparing KUF-PG with a PG addition amount of 1.5 wt.% is described below. Unless otherwise specified, the steps are the same as in Example 1, except that in step 3, the PG addition amount is 1.5 wt.%, that is, the PG addition amount is 1.5 g. The resulting bio-based flame retardant coating is named KUF-PG-1.5, and the further obtained flame retardant wood is named W-KUF-PG-1.5.

[0116] The DSC test results of KUF-PG-1.5 are as follows: Figure 3 As shown, the DSC curve of KUF-PG-1.5 has only one peak, with a peak temperature of 106.7℃. The conclusion is not substantially different from that of Comparative Example 3, that is, the amount of PG added does not affect the curing behavior of KUF-PG, but it does affect its curing temperature.

[0117] The TG test results for KUF-PG-1.5 are as follows: Figure 4 As shown in Table 1, the temperature at which KUF-PG-1.5 decomposes at a mass of 5% is 188.5℃, and the temperature at which the maximum decomposition rate is reached is 289.4℃. Furthermore, the char residue at 800℃ is 7.6 wt.%. The conclusions are not substantially different from those of Comparative Example 3, meaning that the amount of PG added has no substantial effect on the maximum decomposition rate temperature, but it has a significant effect on the temperature and char residue at a decomposition mass of 5%. Increasing the amount of PG added can significantly improve both the temperature and char residue at a decomposition mass of 5%. Moreover, when the amount of PG added reaches 1.5 wt.%, the temperature at a decomposition mass of 5% achieves the same flame-retardant effect as when TA is added.

[0118] The results of the vertical combustion test and limiting oxygen index test for W-KUF-PG-1.5 are as follows: Figure 6 As shown in Table 2, W-KUF-PG-1.5 passed the UL-94V-0 rating test; and the limiting oxygen index of W-KUF-PG-1.5 is 29.9%.

[0119] Compared with Comparative Example 1, it can be seen that using PG with an addition amount of 1.5wt% as a curing agent can improve the UL-94 rating of pure wood from failing to pass to V-0 rating, and can significantly improve the limiting oxygen index from 20.5% to 29.9%.

[0120] Compared with Comparative Example 2, when the amount of PG added was 1.5 wt%, the UL-94 rating improved from V-1 to V-0, but the limiting oxygen index decreased from 31.5% to 29.9%.

[0121] Compared with Comparative Example 3, when the amount of PG added was 1.5 wt%, the UL-94 rating improved from V-1 to V-0, and the limiting oxygen index improved from 28.8% to 29.9%.

[0122] Compared with Example 1, it can be seen that although increasing the amount of PG added has no substantial impact on the UL-94 rating, it can further increase the limiting oxygen index from 29.9% to 32.7%.

[0123] Test results show that increasing the PG content can further improve the flame retardant performance.

[0124] Example 3

[0125] A method for preparing KUF-PG with a PG addition amount of 2wt.% is described below. Unless otherwise specified, the steps are the same as those in Example 1, except that in step 3, the PG addition amount is 2wt.%, that is, the PG addition amount is 2g. The resulting bio-based flame retardant coating is named KUF-PG-2, and the further obtained flame retardant wood is named W-KUF-PG-2.

[0126] The DSC test results of KUF-PG-2 are as follows: Figure 3 As shown, the DSC curve of KUF-PG-2 has only one peak, with a peak temperature of 103.3℃. The conclusions obtained are not substantially different from those of Comparative Example 3 and Example 2, that is, the amount of PG added does not affect the curing behavior of KUF-PG, but it does affect its curing temperature.

[0127] The TG test results of KUF-PG-2 are as follows: Figure 4As shown in Table 1, the temperature at which KUF-PG-2 decomposes at a mass of 5% is 190.1℃, the temperature at which the maximum decomposition rate is reached is 302.7℃, and the char residue at 800℃ is 11.7 wt.%. The conclusions are not substantially different from those of Comparative Example 3 and Example 2, meaning that the amount of PG added has no substantial effect on the maximum decomposition rate temperature, but it has a significant effect on the temperature and char residue at a mass of 5%. Increasing the amount of PG added can significantly improve both the temperature and char residue at a mass of 5%. Furthermore, when the amount of PG added reaches 2 wt.%, the char residue achieves the same effect as adding TA, and the temperature at a mass of 5% is higher than that of TA, demonstrating that the flame-retardant effect of PG is superior to that of TA.

[0128] The results of the vertical combustion test and limiting oxygen index test of W-KUF-PG-2 are as follows: Figure 6 As shown in Table 2, W-KUF-PG-2 passed the UL-94V-0 rating test; and the limiting oxygen index of W-KUF-PG-2 is 32.1%.

[0129] Compared with Comparative Example 1, it can be seen that using PG with an addition amount of 2wt% as a curing agent can improve the UL-94 rating of pure wood from failing to V-0 rating, and can significantly improve the limiting oxygen index from 20.5% to 32.1%.

[0130] Compared with Comparative Examples 2 and 3, when the amount of PG added was 2 wt%, the UL-94 rating improved from V-1 to V-0, and the limiting oxygen index increased from 31.5% and 28.8% to 32.1%, respectively.

[0131] Compared with Example 1, it can be seen that further increasing the amount of PG added, although it has no substantial impact on the UL-94 rating, can further increase the limiting oxygen index from 32.1% to 32.7%.

[0132] Test results show that increasing the PG content can further improve the flame retardant performance.

[0133] The following conclusions can be drawn from Example 1, Comparative Example 3, Example 2, and Example 3:

[0134] 1. Increasing the content of curing agent PG in flame retardant coatings can effectively increase the residual char content and the temperature at which the decomposition mass is 5%. Moreover, as the content of curing agent PG increases, the temperature at which the maximum decomposition rate is reached is not significantly affected, indicating high thermal stability.

[0135] 2. Increasing the content of curing agent PG in flame-retardant coatings can improve flame-retardant performance, raising the UL-94 rating from V-1 to V-0, and at the same time, increasing the limiting oxygen index of wood.

[0136] 3. As the content of PG curing agent in flame retardant coating increases, the flame retardant performance of PGUFW will also improve. However, the increase in its content will cause the curing speed of PGUF to be too fast, resulting in cracks in the flame retardant coating during the curing process. Therefore, the amount of PG added should not be too much.

Claims

1. A method for preparing a flame-retardant coating based on PG flame-retardant curing agent, characterized in that... Includes the following steps: Step 1, Preparation of phytic acid guanidine azole flame retardant curing agent: First, guanidine azole GZ is dissolved in deionized water to obtain GZ solution. At the same time, phytic acid PA solution is dissolved in deionized water to obtain solution A. Then, solution A is added dropwise to GZ solution to react fully. After the reaction is complete, rotary evaporation is performed. After rotary evaporation is complete, the obtained crystals are ground to obtain phytic acid guanidine azole flame retardant curing agent PA-GZ, abbreviated as PG. Step 2, preparation of modified urea-formaldehyde resin emulsion: First, sodium hydroxide solution is added to formaldehyde solution to adjust the pH value of the solution. Then, the initial reaction conditions are prepared. After that, urea, silane coupling agent KH550 and other raw materials are added in three stages to prepare modified urea-formaldehyde resin emulsion KUF, abbreviated as KUF. The three stages in step 2 are as follows: Stage 2.1 involves adding urea first, then KH550, while maintaining a temperature of 90℃, and stirring for 30 minutes after the addition is complete. In stage 2.2, while maintaining a temperature of 90℃, acetic acid solution was first added to adjust the pH of the solution to 4.5-5.0, and then urea was added. After the addition was completed, the mixture was stirred for 10 minutes until the reaction reached its endpoint. The endpoint of the reaction in stage 2.2 is determined by the following: when a drop of the solution is added to water at 30°C, the solution will solidify and not disperse in the water. Stage 2.3 involves maintaining a temperature of 90℃, first adding sodium hydroxide solution to adjust the pH of the solution to 7.5-8.0, then adding urea. After the addition is complete, the temperature is adjusted, and the mixture is stirred at 70℃ for 30 minutes to obtain KUF. Step 3: Preparation of flame-retardant coating based on PG flame-retardant curing agent. Dioctyl phthalate (DOP) and PG obtained in Step 1 are added to the KUF obtained in Step 2. After the addition is complete, mechanical stirring is performed to mix the components evenly. Sodium hydroxide is added dropwise to adjust the pH of the solution to 4-5, thus obtaining the flame-retardant coating based on PG flame-retardant curing agent.

2. The preparation method according to claim 1, characterized in that: In step 1, the molar ratio of GZ to PA is 7:

1. In step 2, the total mass ratio of formaldehyde solution, urea, and KH550 is 100:56.9:2.

85. In step 3, the mass ratio of KUF, DOP, and PG is 100:1:2.

5.

3. The preparation method according to claim 1, characterized in that: In step 1, the conditions for preparing the GZ solution are: a dissolution temperature of 20-30℃, a stirring speed of 500-600 rpm, and a stirring time of 25-35 min. In step 1, the conditions for dripping are: dripping temperature of 20-30℃, dripping stirring speed of 500-600 rpm, dripping stirring time of 40-60 min, and dripping acceleration rate of 0.5 drops / s; In step 1, the conditions for rotary evaporation are: rotary evaporation temperature of 70-80 ℃ and rotary evaporation time of 2.5-3 h.

4. The preparation method according to claim 1, wherein: In step 2, the pH of the solution is adjusted to 8.0-8.5; the initial reaction conditions are: stirring speed of 400-500 rpm and heating to 90℃.

5. The preparation method according to claim 1, characterized in that: In the three stages, the amount of urea added in each stage meets the mass ratio of 37:12.3:7.

6.

6. The preparation method according to claim 1, characterized in that: In step 3, the mechanical stirring conditions are: stirring speed of 500-600 rpm and stirring time of 30 min.

7. The preparation method according to claim 1, characterized in that: The obtained flame-retardant coating based on PG flame retardant curing agent decomposes at a temperature of 160-200℃ when the mass is 5%, and reaches the maximum decomposition rate at a temperature of 290-300℃; the residual char at 800℃ is 10-22 wt.%.

8. The preparation method according to claim 1, characterized in that: When the resulting flame-retardant coating based on PG flame-retardant curing agent is used as a flame-retardant coating for wood, it has flame-retardant properties, a limiting oxygen index of 29-33%, passes the UL-94 V-0 test, and forms a dense char layer after complete combustion.

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