A bio-based flame-retardant coating based on pgl and a preparation method and application thereof

Abstract

This invention discloses a PGL-based bio-based flame-retardant coating, using urea and formaldehyde as main raw materials, silane coupling agent KH550 as an additive, phytic acid-guanidazole-lignin composite polymer PGL as a bio-based flame retardant, and ammonium chloride as a curing agent. The decomposition temperature at 5% by mass is 231.9±5℃, and the temperature at which the maximum decomposition rate is reached is 284.5±5℃. The char residue at 800℃ is 35.3±2 wt.%. The preparation method includes the following steps: 1. Preparation of phytic acid-guanidazole-lignin composite polymer PGL; 2. Preparation of modified urea-formaldehyde resin emulsion (MUF); 3. Preparation of the PGL-based bio-based flame-retardant coating PGL / MUF. 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 residue after combustion is continuous and dense; the limiting oxygen index is 36.5±1%; and the maximum heat release rate is 19.19±1.29kW / m³. 2 The total heat release is 1.20 ± 0.05 MJ / m³. 2 The fire growth index is 0.27 ± 0.05 kW / m². 2 / s.

Description

Technical Field

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

[0002] As a resource-rich, green, renewable, and highly processable material, wood is widely used in construction, furniture, and other fields, and is closely related to people's lives. However, wood itself is flammable, and fires caused by wood combustion are common. Therefore, it is necessary to modify wood to be flame-retardant, improve its flame-retardant properties, and reduce its fire hazard.

[0003] For example, existing literature 1 ("Innovative Polyelectrolyte Treatment to Flame-Retard Wood" [J]. Polymers (Basel) 2021 13(17)) significantly improves the flame retardant properties of wood by depositing polyethyleneimine and sodium phytate polyelectrolyte on the wood surface. However, the problem with this technical solution is that due to insufficient adhesion of the flame retardant to the surface, it will fall off during long-term use, resulting in a decrease in the flame retardant properties of the wood.

[0004] To address the aforementioned technical issues, flame retardants can be incorporated into wood coatings to prepare flame-retardant wood coatings. Wood coatings exhibit good adhesion to wood surfaces. Incorporating flame retardants into wood coatings and then applying them to the wood not only improves adhesion but also enhances the flame-retardant properties of the wood. For example, existing literature 2 (Epoxy-modified silicone resin based N / P / Si synergistic flame-retardant coating for wood surface [J]. Progress in Organic Coatings 170(2022)106953) describes the condensation of dimethyldiethoxysiloxane with 3-glycidoxypropyltrimethoxysilane (KH-560) to form an epoxy-modified silicone (SiR) coating, which is then cured with a nitrogen-phosphorus flame retardant (PTDP). The cured coating significantly improves the flame-retardant properties of the wood. However, this technical solution has a drawback: non-bio-based flame retardants such as PTDP may accumulate in the environment due to poor biocompatibility during long-term use, causing environmental damage.

[0005] To address the aforementioned technical challenges, biodegradable and environmentally friendly bio-based materials are typically selected during the preparation of flame retardants. For instance, existing literature 3 ("Synthesis of bio-based flame-retardant epoxy co-curing agent and application in wood surface coating" [J]. Progress in Organic Coatings 167(2022)106848) synthesized a novel bio-based flame-retardant co-curing agent (PDD) through the reaction of protocatechuic aldehyde (PH), 4,4′-diaminodiphenyl ether (DDE), and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). After infiltrating PDD and 4,4′-diaminodiphenylmethane (DDM) as co-curing agents into a commercial epoxy resin, a flame-retardant epoxy coating for wood was obtained, achieving a limiting oxygen index of 32.6% for the coated wood. The problem with this technical solution is that the content of the bio-based flame retardant PDD in the flame-retardant coating exceeds 20 wt.%, significantly increasing the cost of using this flame retardant.

[0006] To achieve the same flame-retardant effect while reducing the amount of flame retardant added, in the inventors' previous work, existing literature 4 ("A Flame-Retardant Coating Based on PA-MEL Flame-Retardant Curing Agent and Its Preparation Method and Application" CN117887324A) used phytic acid-melamine polyelectrolyte PM as a bio-based flame-retardant curing agent for sodium lignosulfonate modified urea-formaldehyde resin. This achieved both flame-retardant and curing effects in the coating, with PM added at only 2 wt.%, enabling the wood coated with the flame-retardant coating to achieve a UL-94V-0 rating and a limiting oxygen index of 32.1%. Subsequent research revealed that the carbon content of the flame-retardant curing agent in this technical solution was insufficient, resulting in a low limiting oxygen index value. In other words, there is room for further improvement in the limiting oxygen index. Summary of the Invention

[0007] The purpose of this invention is to provide a PGL-based bio-based flame-retardant coating, its preparation method, and its application. Addressing the problems of existing technologies, this invention first utilizes the Mannich reaction and supramolecular self-assembly technology to prepare a bio-based flame retardant, phytic acid-guanidine azole-lignin composite polymer (PGL), containing high-carbon lignin groups. This PGL is then used as the bio-based flame-retardant component and infiltrated into urea-formaldehyde resin modified with silane coupling agent KH550 to prepare a bio-based flame-retardant coating. The bio-based flame-retardant coating is then applied to wood to improve its flame-retardant properties. Specifically, the invention uses urea-formaldehyde resin as the matrix, silane coupling agent KH550 as an additive, phytic acid-guanidine azole-lignin composite polymer (PGL) as the bio-based flame-retardant component, and ammonium chloride as a curing agent to achieve the following technical effects:

[0008] 1. The addition of silane coupling agent KH550 optimizes the molecular structure of urea-formaldehyde resin, thereby enhancing the compatibility between the urea-formaldehyde resin matrix and the additives. Furthermore, the presence of silicon helps improve the flame retardant properties of the material.

[0009] 2. Add PGL bio-based flame retardant with high carbon lignin groups as a bio-based flame retardant component in urea-formaldehyde resin coatings to improve the flame retardant performance of the coatings. Simultaneously, enhance the bio-friendliness of the material and avoid environmental harm.

[0010] 3. Adding commercially available ammonium chloride as a curing agent enables the coating to cure effectively.

[0011] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0012] A bio-based flame-retardant coating based on PGL uses urea and formaldehyde as main raw materials, silane coupling agent KH550 as an additive, phytic acid-guanidazole-lignin composite polymer PGL as the bio-based flame-retardant component, and ammonium chloride as a curing agent. The temperature at which the decomposition mass is 5% is 231.9±5℃, and the temperature at which the maximum decomposition rate is reached is 284.5±5℃. The char residue at 800℃ is 35.3±2wt.%.

[0013] A method for preparing a PGL-based bio-based flame retardant coating includes the following steps:

[0014] Step 1, Preparation of phytic acid-guanidine azole-lignin composite polymer PGL: Under certain conditions, the raw materials formaldehyde solution, guanidine azole GZ, lignin LIG and phytic acid PA solution are stirred and reacted to prepare phytic acid-guanidine azole-lignin composite polymer PGL.

[0015] In step 1, the stirring reaction for preparing PGL consists of two steps.

[0016] Step 1.1 is as follows: First, add the first-stage formaldehyde solution to deionized water to obtain solution A. Then, add GZ to solution A to obtain solution B. After the addition is complete, stir the reaction under certain conditions to obtain solution C.

[0017] Step 1.2 involves first adding LIG to solution C obtained in step 1.1 to obtain solution D. Then, adding a 37 wt.% formaldehyde solution to solution D to obtain solution E. Next, adding a 70 wt.% PA solution to solution E to obtain solution F. Then, under certain conditions, stirring solution F is subjected to a reaction. After the reaction is complete, the resulting product is filtered, repeatedly washed with deionized water, and then the filter residue is dried and ground to obtain the PA-GZ-LIG composite polymer, abbreviated as PGL.

[0018] In step 1, the mass ratio of the total formaldehyde solution, deionized water, GZ, LIG, and PA solution is 17.6:300:13.2:8.7:21.

[0019] In step 1, the mass ratio of the first-stage formaldehyde solution to the second-stage formaldehyde solution is 6.6:11.

[0020] In step 1, the stirring reaction conditions for preparing PGL are: stirring temperature of 80℃ and stirring speed of 400 rpm.

[0021] In step 1.1, the stirring conditions are: stirring time is 1 hour;

[0022] During the stirring process in step 1.1, the change of solution B from clear to turbid and then back to clear indicates that step 1.1 is complete.

[0023] In step 1.2, the stirring conditions are: stirring time is 5 hours;

[0024] In step 1.2, the washing conditions are as follows: the pH value of the washing solution is between 4.0 and 5.0; the drying temperature is 60-80℃; and the drying time is 24-48h.

[0025] Step 2, preparation of modified urea-formaldehyde resin emulsion MUF: First, a 20 wt.% sodium hydroxide solution is added to a 37 wt.% formaldehyde solution to adjust the pH value of the solution, resulting in solution G. Then, under certain conditions, solution G is heated. Finally, raw materials urea, silane coupling agent KH550, PGL obtained in step 1, acetic acid solution, and sodium hydroxide solution are added to solution G and stirred to react, thus preparing modified urea-formaldehyde resin emulsion MUF.

[0026] In step 2, the stirring reaction for preparing MUF consists of three steps.

[0027] Step 2.1 involves, under certain temperature conditions, firstly, adding the first-stage urea to solution G to obtain solution H, then adding the silane coupling agent KH550 to solution H, and continuing to stir under certain conditions to obtain solution I.

[0028] Step 2.2 involves, under certain temperature conditions, firstly, adding a 20 wt.% acetic acid solution to solution I to adjust the pH value, resulting in solution J; then, adding the second-stage urea to solution J to obtain solution K; finally, adding the PGL obtained in step 1 to solution K; and continuing stirring under certain conditions until the reaction endpoint is reached, resulting in solution L.

[0029] Step 2.3 involves, under certain temperature conditions, firstly, adding a 20 wt.% sodium hydroxide solution to solution L to adjust the pH value, thus obtaining solution M; then, adding the third-stage urea to solution M, adjusting the temperature, and stirring solution M under certain conditions to obtain MUF.

[0030] In step 2, the total mass of formaldehyde solution, urea, KH550, and PGL are in the mass ratio of 100:57:5.7:2.85.

[0031] The formaldehyde solution is adjusted to pH 8.0-8.5 by adding sodium hydroxide solution.

[0032] In step 2, the heating conditions for solution G are as follows: heating to 90°C with a stirring speed of 400 rpm.

[0033] In step 2, the urea addition amounts in the three stages meet the mass ratio of 37:12.4:7.6;

[0034] The conditions for step 2.1 are: maintain the temperature at 90°C, and after the addition is complete, continue stirring for 30 minutes.

[0035] The conditions for step 2.2 are as follows: maintain the temperature at 90℃, add acetic acid solution to adjust the pH of the solution to 4.5-5.0, and after the PGL is added, stir for 10-15 minutes to ensure that the reaction reaches the endpoint.

[0036] In step 2.2, the endpoint of the reaction is determined when, at a water temperature of 30°C, solution L becomes an insoluble colloidal state after being dropped into water.

[0037] The conditions for step 2.3 are as follows: maintain the temperature at 90°C, add sodium hydroxide solution to adjust the pH of the solution to 7.5-8.0, and after the urea is added, the stirring conditions are: stirring temperature at 70°C and stirring time at 30 min.

[0038] Step 3: Preparation of PGL-based bio-based flame retardant coating PGL / MUF. MUF and ammonium chloride are added to the MUF obtained in Step 2 to obtain solution N. Then, under certain conditions, the mixture is stirred to ensure uniform mixing of all components, thus obtaining the PGL-based bio-based flame retardant coating, abbreviated as PGL / MUF.

[0039] In step 3, the mass ratio of MUF to ammonium chloride is 100:1;

[0040] The mechanical stirring conditions after the ammonium chloride is added are as follows: stirring speed of 500-600 rpm and stirring time of 1-1.5 h.

[0041] A PGL-based bio-based flame-retardant coating is applied as a flame-retardant coating for wood. It exhibits flame-retardant properties; wood coated with this coating passes the UL-94 V-0 rating test; the char layer formed on the surface of the coated wood after combustion shows a continuous and dense structure with no observable pores; the limiting oxygen index (LOI) of the coated wood is 36.5 ± 1%; and the maximum heat release rate in the cone calorimetry test is 19.19 ± 1.29 kW / m³. 2 The total heat release is 1.20 ± 0.05 MJ / m³. 2 The fire growth index is 0.27 ± 0.05 kW / m². 2 / s.

[0042] The technical effects of the PGL-based bio-based flame-retardant coating obtained in this invention have been verified as follows:

[0043] The TG test results show that the bio-based flame-retardant coating obtained in this invention decomposes at a mass of 5% at a temperature of 231.9±5℃, and reaches its maximum decomposition rate at a temperature of 284.5±5℃; the char residue at 800℃ is 35.3±2 wt.%. Using the bio-based flame retardant PGL can increase the initial decomposition temperature and the temperature at which the maximum decomposition rate is reached, thus improving thermal stability, and also significantly increasing the char residue. However, increasing the amount of PGL causes the temperature at which the flame-retardant coating reaches its maximum decomposition rate to first rise and then fall; therefore, the amount of PGL added must be appropriate.

[0044] Further SEM testing of the expanded char layer formed on the surface of wood coated with the flame-retardant coating after combustion revealed that the char layer formed on the surface of wood coated with the bio-based flame-retardant coating of this invention exhibits continuous and dense properties, with no pores observed. The flame-retardant coating improves the quality of the char layer after wood combustion. Using the bio-based flame retardant PGL can improve the quality of the char layer after wood coated with the flame-retardant coating, enhance the char layer's ability to isolate oxygen and heat, and thus improve flame-retardant performance.

[0045] Vertical burning tests showed that the wood coated with the bio-based flame-retardant coating obtained in this invention achieved a UL-94 V-0 rating. Applying a flame-retardant coating can improve the UL-94 rating of wood. Using the bio-based flame retardant PGL can further improve the UL-94 rating of wood coated with the flame-retardant coating.

[0046] The limiting oxygen index (LOI) test results show that the LIO of wood coated with the bio-based flame-retardant coating obtained in this invention is 36.5 ± 1%. Coating with flame-retardant coating can increase the LIO of wood. Using the bio-based flame retardant PGL can significantly improve the LIO of wood coated with the flame-retardant coating.

[0047] The cone calorimeter test results show that the maximum heat release rate of the wood coated with the bio-based flame-retardant coating obtained in this invention is 19.19 ± 1.29 kW / m². 2 The total heat release is 1.20 ± 0.05 MJ / m³. 2 The fire growth index is 0.27 ± 0.05 kW / m². 2 / s. Applying flame-retardant coatings can reduce the maximum heat release rate, total heat release, and fire growth index of wood. Using the bio-based flame retardant PGL can significantly reduce the maximum heat release rate, total heat release, and fire growth index of wood coated with flame-retardant coatings, resulting in a lower fire hazard.

[0048] Therefore, the PGL-based bio-based flame retardant coating of the present invention has the following advantages over the prior art:

[0049] 1. The bio-based flame retardant coating prepared by this invention significantly improves the flame retardant effect on wood, and the wood coated with the flame retardant coating has excellent flame retardant properties.

[0050] 2. The bio-based flame retardant PGL prepared by this invention has a high carbon content lignin group, which is more effective in improving the limiting oxygen index.

[0051] 3. The bio-based flame retardant PGL used in this invention can significantly improve flame retardant performance with a low addition amount, while being more environmentally friendly. Attached Figure Description

[0052] Figure 1 The FT-IR image of phytic acid-guanidazole-lignin PGL prepared in Example 1;

[0053] Figure 2 The FT-IR images are of Example 1, Comparative Example 2, and Comparative Example 3.

[0054] Figure 3 The TG graphs are for Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, and Example 2.

[0055] Figure 4 The images shown are SEM images of the char residue layers after combustion of Examples 1, 1, 2, and 3. Figure 4 a is comparative example 1. Figure 4 b is comparative example 2. Figure 4 c is comparative example 3. Figure 4 d represents Example 1;

[0056] Figure 5 The figures shown are vertical combustion test diagrams for Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, and Example 2. Figure 5 'a' represents the period before the vertical combustion test. Figure 5 b represents the result after the vertical combustion test.

[0057] Figure 6 The cone calorimetry test diagrams are for Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, and Example 2. Detailed Implementation

[0058] 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.

[0059] Example 1

[0060] A method for preparing a PGL-based bio-based flame retardant coating includes the following steps:

[0061] Step 1, Preparation of phytic acid-guanidine azole-lignin composite polymer PGL: Under the conditions of stirring temperature of 80℃ and stirring speed of 400rpm, the raw materials formaldehyde solution, guanidine azole GZ, lignin LIG and phytic acid PA solution are stirred and reacted to prepare phytic acid-guanidine azole-lignin composite polymer PGL.

[0062] In step 1, the stirring reaction for preparing PGL consists of two steps.

[0063] Step 1.1 involves first adding 6.6g of a 37wt.% formaldehyde solution to 300g of deionized water to obtain solution A. Then, 13.2g of GZ is added to solution A to obtain solution B. After the addition is complete, the mixture is stirred for 1 hour to obtain solution C.

[0064] During the stirring process in step 1.1, the change of solution B from clear to turbid and then back to clear indicates that step 1.1 is complete.

[0065] Step 1.2 involves first adding 8.7g of LIG to solution C obtained in step 1.1 to obtain solution D. Then, adding 11g of formaldehyde solution with a mass fraction of 37wt.% to solution D to obtain solution E. Next, adding 21g of PA solution with a mass fraction of 70wt.% to solution E to obtain solution F. Then, stirring solution F for 5 hours is carried out. After the stirring reaction is completed, the obtained product is filtered, washed with deionized water until the pH value is in the range of 4.0-5.0, dried at 80℃ for 24 hours, and then ground to obtain PA-GZ-LIG composite polymer, abbreviated as PGL.

[0066] To confirm the composition of PGL, i.e., successful synthesis, FT-IR testing was performed. Simultaneously, the starting material LIG was also tested using FT-IR for comparison. The test results are as follows: Figure 1 As shown, PGL simultaneously contains characteristic peaks of LIG, GZ, and PA. Test results indicate that PGL was successfully synthesized.

[0067] Step 2, preparation of modified urea-formaldehyde resin emulsion MUF: First, a 20 wt.% sodium hydroxide solution is added to 100 g of a 37 wt.% formaldehyde solution to adjust the pH of the solution to 8.0-8.5, obtaining solution G. Then, solution G is heated to 90°C under a stirring speed of 400 rpm. Finally, raw materials urea, silane coupling agent KH550, PGL obtained in step 1, acetic acid solution, and sodium hydroxide solution are added to solution G for stirring and reaction to prepare modified urea-formaldehyde resin emulsion MUF.

[0068] In step 2, the stirring reaction for preparing MUF consists of three steps.

[0069] Step 2.1 involves maintaining a temperature of 90°C, firstly, adding 37g of urea to solution G to obtain solution H, then adding 5.7g of silane coupling agent KH550 to solution H, and continuing to stir for 30 minutes to obtain solution I.

[0070] Step 2.2 involves maintaining a temperature of 90°C, firstly, adding a 20 wt.% acetic acid solution to solution I to adjust the pH to 4.5-5.0, resulting in solution J. Then, adding 12.4 g of urea to solution J, resulting in solution K. Finally, adding 2.85 g of PGL obtained in step 1 to solution K, and stirring for 10 min until the reaction endpoint is reached, resulting in solution L.

[0071] In step 2.2, the endpoint of the reaction is determined when, at a water temperature of 30°C, solution L becomes an insoluble colloidal state after being dropped into water.

[0072] Step 2.3 involves maintaining a temperature of 90°C, firstly, adding a 20 wt.% sodium hydroxide solution to solution L to adjust the pH to 7.5-8.0, thus obtaining solution M. Then, adding 7.6 g of urea to solution M, adjusting the temperature, and stirring solution M at 70°C for 30 min to obtain MUF.

[0073] Step 3, Preparation of PGL-based bio-based flame retardant coating PGL / MUF: First, ammonium chloride is used as a curing agent. At a mass ratio of MUF to ammonium chloride of 100:1, 1g of ammonium chloride is added to 100g of MUF obtained in Step 2 to obtain solution N. Then, solution N is stirred at a stirring speed of 500rpm for 1h to obtain the PGL-based bio-based flame retardant coating PGL / MUF, abbreviated as PGL / MUF. Specifically, the PGL / MUF obtained in Example 1 is abbreviated as PGL / MUF-5.

[0074] To confirm the composition of PGL / MUF-5, i.e., successful synthesis, FT-IR testing was performed. Simultaneously, the results were compared with MUF-0 without PGL addition using FT-IR testing. The test results are as follows: Figure 2 As shown, PGL / MUF-5 contains characteristic peaks of both MUF-0 and PGL. The test results demonstrate the successful synthesis of PGL and MUF, i.e., the successful preparation of PGL / MUF-5.

[0075] To demonstrate the thermal stability of PGL / MUF-5, a TG test was conducted. The test results are as follows: Figure 3 As shown in Table 1, the temperature at which PGL / MUF-5 decomposes to a mass of 5% is 231.9℃, the temperature at which the maximum decomposition rate is reached is 284.5℃, and the char residue at 800℃ is 35.3 wt.%. The test results indicate that the high decomposition temperature demonstrates that PGL / MUF-5 possesses high thermal stability, and it also exhibits a high char residue.

[0076] Table 1. Thermogravimetric test results

[0077]

[0078]

[0079] To demonstrate the technical effectiveness of PGL / MUF as a flame-retardant coating for wood, flame-retardant wood PGL / MUF / W was prepared by coating PGL / MUF onto the wood surface and then conducting flame-retardant tests. The specific preparation method for PGL / MUF / W was as follows: a coating density of 0.1 g / cm³ was used. 2 PGL / MUF is coated onto the surface of wood. After coating, it is dried for 24 hours to obtain PGL / MUF / W. Specifically, the PGL / MUF / W prepared based on Example 1 PGL / MUF-5 is named PGL / MUF / W-5.

[0080] Based on TG testing, PGL / MUF-5 exhibits a high char residue. To further demonstrate the impact of this high char residue on flame retardant performance, SEM testing was performed on the expanded char layer formed on the surface of PGL / MUF / W-5 after combustion. The test results are as follows: Figure 4 As shown in Figure d, the expanded char layer formed after burning flame-retardant wood coated with PGL / MUF-5 exhibits continuous and dense properties, with almost no pores. The test results demonstrate that the expanded char layer of PGL / MUF / W-5 is of excellent quality, effectively isolating oxygen and heat on the wood surface, thereby improving the flame-retardant properties of the wood.

[0081] To further demonstrate the flame-retardant properties of PGL / MUF / W-5, vertical burning tests and limiting oxygen index tests were conducted. The test results are as follows: Figure 5 As shown in Table 2, PGL / MUF / W-5 passed the UL-94V-0 rating test; furthermore, PGL / MUF / W-5 has a limiting oxygen index as high as 36.5%. The test results demonstrate that PGL / MUF / W-5 exhibits excellent flame retardant properties.

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

[0083]

[0084] To further demonstrate the flame-retardant performance of PGL / MUF / W-5 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 PGL / MUF / W-5 to reach its maximum heat release rate is 71 s, and the maximum heat release rate is 19.19 kW / m³. 2 The total heat release is 1.20 MJ / m³. 2The fire growth index is 0.27 kW / m³. 2 / s. Test results show that the low fire growth index indicates that PGL / MUF / W-5 has a low fire hazard, meaning that PGL / MUF / W-5 has excellent flame retardant properties.

[0085] Table 3 Results of cone calorimetry test

[0086]

[0087] To demonstrate the effect of flame-retardant coating PGL / MUF on the flame-retardant properties of wood, Comparative Example 1 is provided, consisting of pure wood without PGL / MUF coating.

[0088] Comparative Example 1

[0089] Pure wood without PGL / MUF coating is simply referred to as pure wood.

[0090] SEM test results of the char layer after complete combustion of pure wood are as follows: Figure 4 As shown in Figure a, the charcoal layer of pure wood is completely broken, containing many fragmented fibrous structures. Compared with Example 1, it can be seen that coating with PGL / MUF-5 makes the expanded charcoal layer formed on the wood surface continuous and dense, with few and small pores, that is, the quality of the charcoal layer is greatly improved.

[0091] 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, in the vertical burning test, pure wood failed the UL-94 rating test, with a limiting oxygen index of 19.7%. Compared with Example 1, coating with PGL / MUF-5 improved the UL-94 rating of the wood from failing the test to V-0, and significantly increased the limiting oxygen index from 19.7% to 36.5%, an increase of 185.3%. The test results demonstrate that PGL / MUF-5 significantly improves the flame retardant properties of PGL / MUF / W.

[0092] The results of the cone calorimetry test on pure wood are as follows: Figure 6 As shown in Table 3, in the cone calorimetry test, the time for pure wood to reach the maximum heat release rate was 110 s, and the maximum heat release rate was 263.9 kW / m². 2 The total heat release is 18.68 MJ / m³. 2 The fire growth index is 2.40 kW / m³. 2 / s. Compared with Example 1, coating with PGL / MUF-5 shortened the time for flame-retardant wood to reach its maximum heat release rate by 39s, reduced the maximum heat release rate by 92.73%, reduced the total heat release by 93.58%, and reduced the fire growth index by 88.75%. The test results show that coating with PGL / MUF-5 significantly improves the flame-retardant performance of flame-retardant wood under real combustion conditions and significantly reduces the fire hazard.

[0093] To demonstrate the effect of bio-based flame retardant PGL on the performance of flame-retardant coatings PGL / MUF and flame-retardant wood PGL / MUF / W, Comparative Example 2 is provided, showing flame-retardant coatings without the addition of bio-based flame retardant PGL.

[0094] Comparative Example 2

[0095] A method for preparing a conventional flame-retardant coating without adding bio-based flame retardant PGL is described. Unless otherwise specified, the steps are the same as in Example 1, except that step 1 is not required, and in step 2.2, bio-based flame retardant PGL is not added. The resulting conventional flame-retardant coating is named MUF-0, and the resulting conventional flame-retardant wood is named MUF / W-0.

[0096] The TG test results of MUF-0 are as follows: Figure 3 As shown in Table 1, the temperature at which MUF-0 decomposes to a mass of 5% is 177.7℃, the temperature at which the maximum decomposition rate is reached is 283.4℃, and the char residue at 800℃ is 18.1 wt.%.

[0097] Compared with Example 1, it can be seen that adding bio-based flame retardant PGL can increase the temperature at which the decomposition mass is 5% by 54.2°C, increase the temperature at which the maximum decomposition rate is reached by 1.1°C, and increase the char residue at 800°C by 17.2 wt.%. This proves that using bio-based flame retardant PGL can improve the thermal stability of PGL / MUF, and at the same time, can also significantly increase the char residue of PGL / MUF.

[0098] SEM test results of the expanded char layer formed on the surface after combustion of MUF / W-0 are as follows: Figure 4 As shown in b, the expanded carbon residue layer of MUF / W-0 has many wrinkles and large pores.

[0099] Compared with Comparative Example 1, it can be seen that applying conventional flame retardant coatings can form a continuous expanding char layer on the surface of wood when it burns, thereby protecting the wood. However, the char layer formed has large pores and cannot provide effective protection for the wood.

[0100] Compared with Example 1, it can be seen that adding bio-based flame retardant PGL can make the expanded char layer of flame-retardant wood more continuous and dense, and without producing pores.

[0101] Test results show that using the bio-based flame retardant PGL can improve the quality of the expanded char layer of PGL / MUF / W, thereby improving its flame retardant performance.

[0102] The results of the vertical combustion test and limiting oxygen index test of MUF / W-0 are as follows: Figure 5 As shown in Table 2, in the vertical burning test, MUF / W-0 passed the UL-94V-1 rating test with a limiting oxygen index of 29.1%.

[0103] Compared with Comparative Example 1, it can be seen that applying conventional flame retardant coatings can only improve the UL-94 rating of wood from failing the test to V-1, but cannot reach the V-0 rating, thus increasing the limiting oxygen index by 9.4%.

[0104] Compared with Example 1, it can be seen that using the bio-based flame retardant PGL can improve the UL-94 rating of flame-retardant wood from V-1 to V-0, and increase the limiting oxygen index by 7.4%. The test results show that using the bio-based flame retardant PGL can improve the UL-94 rating and significantly increase the limiting oxygen index, thereby greatly improving the flame retardant performance.

[0105] The cone calorimetry test results of MUF / W-0 are as follows: Figure 6 As shown in Table 3, in the cone calorimetry test, the time for MUF / W-0 to reach the maximum heat release rate was 88 s, and the maximum heat release rate was 55.58 kW / m². 2 The total heat release is 4.27 MJ / m³. 2 The fire growth index is 0.63 kW / m³. 2 / s.

[0106] Compared with Comparative Example 1, it can be seen that applying a conventional flame-retardant coating with a V-1 rating shortened the time for wood to reach its maximum heat release rate by 22 seconds, reduced the maximum heat release rate by 78.94%, reduced the total heat release by 77.14%, and reduced the fire growth index by 73.75%. However, its maximum heat release rate, total heat release, and fire growth index still cannot meet the application requirements.

[0107] Compared with Example 1, the use of bio-based flame retardant PGL can shorten the time for flame-retardant wood to reach its maximum heat release rate by 17 seconds, reduce the maximum heat release rate by 65.47%, reduce the total heat release by 71.89%, and reduce the fire growth index by 57.14%. The test results show that the use of bio-based flame retardant PGL can significantly improve the flame-retardant performance of flame-retardant wood under real combustion conditions and significantly reduce the fire hazard.

[0108] To further demonstrate the improvement of the performance of bio-based flame retardant PGL on flame retardant coatings PGL / MUF and flame retardant wood PGL / MUF / W, Comparative Example 3 is provided, showing flame retardant coatings with added commercial flame retardant triphenyl phosphate (TPP).

[0109] Comparative Example 3

[0110] A method for preparing a flame-retardant coating with added commercial flame retardant triphenyl phosphate (TPP) is described. Unless otherwise specified, the steps are the same as in Example 1, except that in step 2.2, the commercial flame retardant TPP is added instead of the bio-based flame retardant PGL. The resulting flame-retardant coating is named TPP / MUF, and the further obtained flame-retardant wood is named TPP / MUF / W.

[0111] The TG test results of TPP / MUF are as follows: Figure 3 As shown in Table 1, the temperature at which TPP / MUF decomposes to 5% by mass is 114.2℃, the temperature at which the maximum decomposition rate is reached is 279.8℃, and the char residue at 800℃ is 27.7 wt.%.

[0112] Compared with Comparative Example 2, it can be seen that adding the commercial flame retardant TPP can increase the carbon residue of the coating at 800℃ by 9.6 wt.%, but the temperature at which it decomposes to 5% decreases by 63.5℃, and the temperature at which it reaches the maximum decomposition rate decreases by 3.6℃, ​​that is, the thermal stability decreases.

[0113] Compared with Example 1, it can be seen that using the bio-based flame retardant PGL can increase the temperature at which the decomposition mass is 5% by 117.7°C, increase the temperature at which the maximum decomposition rate is reached by 4.7°C, and increase the char residue at 800°C by 7.6 wt.%. This proves that using the bio-based flame retardant PGL can improve the thermal stability of PGL / MUF, and at the same time, can also significantly increase the char residue of PGL / MUF.

[0114] SEM test results of the expanded char layer formed on the surface of TPP / MUF / W after combustion are as follows: Figure 4 As shown in c, the expanded carbon residue layer of TPP / MUF / W has many wrinkles and some cracks.

[0115] Compared with Comparative Example 2, it can be seen that adding the commercial flame retardant TPP can make the expanded char layer of flame-retardant wood denser, but wrinkles and cracks still exist, meaning it cannot form an effective protection for the wood.

[0116] Compared with Example 1, it can be seen that using the bio-based flame retardant PGL can make the expanded char layer of flame-retardant wood more continuous and dense, without producing pores. Test results show that using the bio-based flame retardant PGL can improve the quality of the expanded char layer of PGL / MUF / W, thereby improving the flame retardant performance.

[0117] The results of the vertical combustion test and limiting oxygen index test for TPP / MUF / W are as follows: Figure 5 As shown in Table 2, in the vertical combustion test, TPP / MUF / W passed the UL-94V-1 rating test with a limiting oxygen index of 34.2%.

[0118] Compared with Comparative Example 2, it can be seen that although adding the commercial flame retardant TPP can increase the limiting oxygen index of flame-retardant wood by 5.1%, it does not change the UL-94 rating of flame-retardant wood.

[0119] Compared with Example 1, it can be seen that using the bio-based flame retardant PGL can improve the UL-94 rating of flame-retardant wood from V-1 to V-0, and increase the limiting oxygen index by 2.3%. The test results show that using the bio-based flame retardant PGL can improve the UL-94 rating and the limiting oxygen index, thereby improving the flame retardant performance.

[0120] The cone calorimetry test results of TPP / MUF / W are as follows: Figure 6 As shown in Table 3, in the cone calorimetry test, the time for TPP / MUF / W to reach the maximum heat release rate was 93 s, and the maximum heat release rate was 53.31 kW / m². 2 The total heat release is 1.58 MJ / m³. 2 The fire growth index is 0.59 kW / m³. 2 / s.

[0121] Compared with Comparative Example 2, the addition of the commercial flame retardant TPP can reduce the maximum heat release rate of flame-retardant wood by 4.08%, the total heat release by 62.99%, and the fire growth index by 6.35%. However, the time to reach the maximum heat release rate increases by 5 seconds, and the decrease in the maximum heat release rate and the fire growth index is relatively small.

[0122] Compared with Example 1, the use of bio-based flame retardant PGL can shorten the time for flame-retardant wood to reach its maximum heat release rate by 22 seconds, reduce the maximum heat release rate by 64%, reduce the total heat release by 24%, and reduce the fire growth index by 54.24%. The test results show that the use of bio-based flame retardant PGL can significantly improve the flame-retardant performance of flame-retardant wood under real combustion conditions and significantly reduce the fire hazard.

[0123] To demonstrate the effect of the amount of bio-based flame retardant PGL added on the performance of flame retardant coatings PGL / MUF and flame retardant wood PGL / MUF / W, Comparative Example 4 and Example 2 are provided, with flame retardant coatings having a PGL addition amount of 1 wt.% and 3 wt.% of the total urea, respectively.

[0124] Comparative Example 4

[0125] A method for preparing PGL / MUF with a PGL addition amount of 1 wt.% of the total urea is described. Unless otherwise specified, the steps are the same as in Example 1, except that in the second stage of step 2, the PGL addition amount is 1 wt.% of the total urea, i.e., 0.57 g PGL. The resulting flame-retardant coating is named PGL / MUF-1, and the further obtained flame-retardant wood is named PGL / MUF / W-1.

[0126] The TG test results of PGL / MUF-1 are as follows: Figure 3 As shown in Table 1, the temperature at which PGL / MUF-1 decomposes to 5% by mass is 186.8℃, the temperature at which the maximum decomposition rate is reached is 284.3℃, and the char residue at 800℃ is 23.2 wt.%.

[0127] Compared with Comparative Example 2, it can be seen that when the amount of PGL added is 1 wt.%, the temperature at which the coating decomposes to 5% mass can be increased by 9.1℃, that is, the effect on the temperature at which the maximum decomposition rate is reached is not significant, and the amount of residual carbon at 800℃ is increased by 5.1 wt.%, which slightly improves the thermal stability.

[0128] Compared with Example 1, increasing the amount of bio-based flame retardant PGL can increase the temperature at which the decomposition mass is 5% by 29.8°C, while the increase in temperature at which the maximum decomposition rate is reached has little effect, and the char residue at 800°C increases by 12.1 wt.%. The test results show that increasing the amount of bio-based flame retardant PGL can improve the thermal stability of PGL / MUF, and at the same time, can significantly increase the char residue of PGL / MUF.

[0129] The vertical combustion test and limiting oxygen index test results of PGL / MUF / W-1 are as follows: Figure 5 As shown in Table 2, in the vertical combustion test, PGL / MUF / W-1 passed the UL-94V-1 rating test with a limiting oxygen index of 31.6%.

[0130] Compared with Comparative Example 2, it can be seen that when the amount of PGL added is 1 wt.%, the limiting oxygen index of flame-retardant wood can be increased by 2.5%, but the UL-94 rating of flame-retardant wood is not changed.

[0131] Compared with Example 1, it can be seen that increasing the amount of bio-based flame retardant PGL can improve the UL-94 rating of flame-retardant wood from V-1 to V-0, and increase the limiting oxygen index by 4.9%. The test results show that increasing the amount of bio-based flame retardant PGL can improve the UL-94 rating and the limiting oxygen index, thereby improving the flame retardant performance.

[0132] The cone calorimetry test results of PGL / MUF / W-1 are as follows: Figure 6As shown in Table 3, in the cone calorimetry test, the time for PGL / MUF / W-1 to reach the maximum heat release rate was 78 s, and the maximum heat release rate was 51.19 kW / m³. 2 The total heat release is 3.04 MJ / m³. 2 The fire growth index is 0.65 kW / m³. 2 / s.

[0133] Compared with Comparative Example 2, it can be seen that when the addition amount of PGL is 1 wt.%, the time for flame-retardant wood to reach the maximum heat release rate is shortened by 10 seconds, the maximum heat release rate decreases by 7.89%, and the total heat release decreases by 28.81%. However, the fire growth index increases by 3.17%.

[0134] Compared with Example 1, increasing the amount of bio-based flame retardant PGL shortens the time for flame-retardant wood to reach its maximum heat release rate by 7 seconds, reduces the maximum heat release rate by 62.5%, decreases the total heat release by 60.53%, and reduces the fire growth index by 58.46%. Test results show that increasing the amount of bio-based flame retardant PGL significantly improves the flame-retardant performance of flame-retardant wood under real-world combustion conditions and significantly reduces the fire hazard.

[0135] Example 2

[0136] A method for preparing PGL / MUF with a PGL addition amount of 3 wt.% of the total urea is described. Unless otherwise specified, the steps are the same as in Example 1, except that in the second stage of step 2, the PGL addition amount is 3 wt.% of the total urea, i.e., 1.71 g PGL. The resulting flame-retardant coating is named PGL / MUF-3, and the further obtained flame-retardant wood is named PGL / MUF / W-3.

[0137] The TG test results of PGL / MUF-3 are as follows: Figure 3 As shown in Table 1, the temperature at which PGL / MUF-3 decomposes to a mass of 5% is 216.6℃, the temperature at which the maximum decomposition rate is reached is 288.1℃, and the char residue at 800℃ is 28.2 wt.%.

[0138] Compared with Example 1, it can be seen that further increasing the amount of bio-based flame retardant PGL can increase the temperature at 5% decomposition mass by 15.3°C, decrease the temperature at the maximum decomposition rate by 3.6°C, and increase the char residue at 800°C by 12.1 wt.%. This proves that increasing the amount of bio-based flame retardant PGL can increase the initial decomposition temperature of PGL / MUF, decrease the temperature at the maximum decomposition rate, and significantly increase the char residue of PGL / MUF.

[0139] The vertical combustion test and limiting oxygen index test results of PGL / MUF / W-3 are as follows: Figure 5 As shown in Table 2, in the vertical burning test, PGL / MUF / W-3 passed the UL-94V-1 rating test with a limiting oxygen index of 34.8%.

[0140] Compared with Example 1, it can be seen that further increasing the amount of bio-based flame retardant PGL can improve the UL-94 rating of flame-retardant wood from V-1 to V-0, and increase the limiting oxygen index by 1.7%. The test results show that increasing the amount of bio-based flame retardant PGL can improve the UL-94 rating and the limiting oxygen index, thereby improving the flame retardant performance.

[0141] The cone calorimetry test results of PGL / MUF / W-3 are as follows: Figure 6 As shown in Table 3, in the cone calorimetry test, the time for PGL / MUF / W-1 to reach the maximum heat release rate was 73 s, and the maximum heat release rate was 41.55 kW / m³. 2 The total heat release is 2.32 MJ / m³. 2 The fire growth index is 0.57 kW / m³. 2 / s.

[0142] Compared with Example 1, further increasing the amount of bio-based flame retardant PGL can shorten the time for flame-retardant wood to reach its maximum heat release rate by 2 seconds, reduce the maximum heat release rate by 53.81%, reduce the total heat release by 48.28%, and reduce the fire growth index by 52.63%. Test results show that increasing the amount of bio-based flame retardant PGL can significantly improve the flame-retardant performance of flame-retardant wood under real combustion conditions and significantly reduce the fire hazard.

[0143] To demonstrate the technical effect of adding 3 wt.% PGL, Example 2 was compared with Comparative Example 3. When the amount of PGL added was 3 wt.%, the flame retardant performance of the resulting PGL / MUF / W-3 was better than that of the TPP / MUF / W obtained when the amount of commercial flame retardant TPP added was 5 wt.% of the total amount of urea. That is, the test results show that PGL is better than commercial flame retardant TPP in improving flame retardant performance.

[0144] By comparing Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, Example 1, and Example 2, the following conclusions can be drawn:

[0145] 1. Wood coated with flame-retardant paint has significantly improved flame-retardant properties compared to uncoated wood, and its fire growth index is also significantly reduced under actual combustion conditions. Flame-retardant paint can effectively improve the flammable characteristics of wood, giving it high flame-retardant properties.

[0146] 2. Using PGL as a bio-based flame retardant can effectively improve the flame retardant performance of PGL / MUF. As the PGL content increases, the flame retardant performance of PGL / MUF / W also increases significantly. However, increasing the amount of PGL will cause the temperature at which the flame retardant coating reaches its maximum decomposition rate to rise first and then fall. Therefore, the amount of PGL added should be appropriate.

[0147] 3. Compared with the commercial flame retardant triphenyl phosphate (TPP), PGL has a better effect on improving the flame retardant performance of flame retardant coatings. When the amount of PGL added is 3 wt.%, the flame retardant effect of PGL / MUF / W-3 is comparable to that of TPP / MUF / W when the amount added is 5 wt.%.

Claims

1. A method for preparing a PGL-based bio-based flame-retardant coating, characterized in that... Includes the following steps: Step 1, Preparation of phytic acid-guanidine azole-lignin composite polymer PGL: Formaldehyde solution, guanidine azole GZ, lignin LIG and phytic acid PA solution are stirred and reacted to prepare phytic acid-guanidine azole-lignin composite polymer PGL; The stirring reaction in step 1 consists of two steps. Step 1.1 is as follows: First, add the formaldehyde solution from the first stage to deionized water to obtain solution A. Then, add GZ to solution A to obtain solution B. After the addition is complete, stir the reaction to obtain solution C. Step 1.2 involves first adding LIG to solution C obtained in step 1.1 to obtain solution D. Then, adding the formaldehyde solution from the second stage to solution D to obtain solution E. Next, adding a PA solution with a mass fraction of 70 wt.% to solution E to obtain solution F. Then, stirring solution F to react. After the stirring reaction is complete, the obtained product is filtered, washed repeatedly with deionized water, and then the filter residue is dried and ground to obtain phytic acid-guanidazole-lignin composite polymer PGL. Step 2, preparation of modified urea-formaldehyde resin emulsion MUF: First, sodium hydroxide solution is added to formaldehyde solution to adjust the pH value of the solution to obtain solution G. Then, solution G is heated. Finally, urea, silane coupling agent KH550, PGL obtained in step 1, acetic acid solution, and sodium hydroxide solution are added to solution G for stirring and reaction to prepare modified urea-formaldehyde resin emulsion MUF. The stirring reaction in step 2 consists of three steps. Step 2.1 involves, under certain temperature conditions, firstly, adding the first-stage urea to solution G to obtain solution H, then adding the silane coupling agent KH550 to solution H and continuing stirring to obtain solution I; Step 2.2 involves, under certain temperature conditions, firstly, adding acetic acid solution to solution I to adjust the pH value of the solution to obtain solution J; then, adding urea from the second stage to solution J to obtain solution K; finally, adding PGL obtained in step 1 to solution K and continuing to stir until the reaction endpoint is reached to obtain solution L. Step 2.3 involves, under certain temperature conditions, firstly, adding sodium hydroxide solution to solution L to adjust the pH value of the solution, obtaining solution M; then, adding urea from the third stage to solution M, adjusting the temperature, and stirring solution M to obtain MUF. Step 3, preparation of PGL-based bio-based flame retardant coating: MUF and ammonium chloride are added to the MUF obtained in Step 2 to obtain solution N. Then, the mixture is stirred to ensure uniform mixing of all components, thus obtaining the PGL-based bio-based flame retardant coating. In both steps 1 and 2, the mass fraction of the formaldehyde solution is 37 wt.%. In step 2, the mass fraction of the sodium hydroxide solution is 20 wt.%. In step 2.2, the acetic acid solution has a mass fraction of 20 wt.%.

2. The preparation method according to claim 1, characterized in that: In step 1, the mass ratio of the total mass of formaldehyde solution, GZ, deionized water, LIG, and PA is 17.6:13.2:300:8.7:

21. In step 1, the formaldehyde solution added in the two stages meets the mass ratio of 6.6:11; In step 2, the total mass of formaldehyde solution, urea, KH550, and PGL are in the mass ratio of 100:57:5.7:2.

85. In step 2, the amount of urea added in the three stages meets the mass ratio of 37:12.4:7.6; In step 3, the mass ratio of MUF to ammonium chloride is 100:

1.

3. The preparation method according to claim 1, characterized in that: The stirring reaction conditions in step 1 are: stirring temperature of 80 ℃ and stirring speed of 400 rpm; In step 1.1, the stirring reaction time is 1 hour; In the stirring reaction of step 1.1, the change of solution B from clear to turbid and then from turbid to clear indicates that step 1.1 is complete. In step 1.2, the stirring reaction time is 5 hours. In step 1.2, the washing conditions are as follows: the pH value of the washing solution is between 4.0 and 5.0; the drying temperature is 60-80 ℃; and the drying time is 24-48 h.

4. The preparation method according to claim 1, characterized in that: In step 2, sodium hydroxide solution is added to adjust the pH of the formaldehyde solution to 8.0-8.

5. In step 2, the heating of solution G refers to heating it to 90 °C while stirring at a speed of 400 rpm. The temperature condition in step 2.1 is 90 ℃. After the silane coupling agent KH550 is added, stirring is continued for 30 min. The temperature condition in step 2.2 is 90 ℃. Acetic acid solution is added to adjust the pH of the solution to 4.5-5.

0. After the PGL is added, the stirring time is 10-15 min to ensure that the reaction reaches the endpoint. In step 2.2, the endpoint of the reaction is determined when, at a water temperature of 30°C, solution L becomes an insoluble colloidal state after being dropped into water. In step 2.3, the temperature is 90 ℃, sodium hydroxide solution is added to adjust the pH of the solution to 7.5-8.0, and after the urea is added, the stirring conditions are: stirring temperature 70 ℃ and stirring time 30 min.

5. The preparation method according to claim 1, characterized in that: In step 3, the stirring conditions after the ammonium chloride is added are: stirring speed of 500-600 rpm and stirring time of 1-1.5 h.

6. The preparation method according to claim 2, characterized in that: When the obtained PGL-based bio-based flame retardant coating is used as a flame retardant coating for wood, it has flame retardant properties. Wood coated with the flame retardant coating passed the UL-94 V-0 rating test in the UL-94 rating test. The expanded char layer formed on the surface of the wood coated with the flame retardant coating after burning exhibits continuous and dense properties.

7. The preparation method according to claim 2, characterized in that: When the obtained PGL-based bio-based flame retardant coating is used as a flame retardant coating for wood, the limiting oxygen index of the wood coated with the flame retardant coating is 36.5±1% in the limiting oxygen index test.

8. The preparation method according to claim 2, characterized in that: When the obtained PGL-based bio-based flame-retardant coating is used as a flame-retardant coating for wood, the maximum heat release rate of the wood coated with the flame-retardant coating in the cone calorimetry test is 19.19 ± 1.29 kW / m². 2 The total heat release is 1.20 ± 0.05 MJ / m³. 2 The fire growth index is 0.27 ± 0.05 kW / m³. 2 / s.

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