Flame-retardant coating based on PG flame-retardant curing agent as well as preparation method and application of flame-retardant coating

Abstract

The invention discloses a flame-retardant coating based on a PG flame-retardant curing agent, which takes urea and formaldehyde as raw materials, KH550 as an auxiliary agent, dioctyl phthalate (DOP) as a plasticizer and phytic acid-guanazole PG as a bio-based flame-retardant curing agent, and the PG is prepared by taking phytic acid and guanazole as raw materials and carrying out ionic reaction under the condition of an aqueous solution; the temperature is 160-200 DEG C when the decomposition mass is 5%, and the temperature is 290-300 DEG C when the maximum decomposition rate is reached; and the carbon residue amount at 800 DEG C is 10-22 wt.%. The preparation method comprises the following steps: 1, preparing a guanidazole phytate flame-retardant curing agent PA-GZ (PG for short); 2, preparing a modified urea-formaldehyde resin emulsion KUF; and 3, preparing the flame-retardant coating KUF-PG based on the PG flame-retardant curing agent. When being used as a wood flame-retardant coating, the flame-retardant coating has a flame-retardant property, the limit oxygen index is 29-33%, and a dense carbon residue layer is formed after complete combustion according to a UL-94V-0 test.

Description

Technical Field

[0001] The present invention relates to the field of flame retardant materials, and in particular to a flame retardant coating based on a PG flame retardant curing agent, and a preparation method and application thereof. Background Art

[0002] Wood is a common resource and is widely used. However, it is flammable. Therefore, it is necessary to improve the flame retardant properties of wood. The basic principle of wood flame retardancy is to apply a flame retardant coating on the surface of the wood to isolate the wood from the fire and achieve the purpose of flame retardancy. Based on the above principle, the preparation method of the flame retardant coating is to directly add a flame retardant to the coating to achieve the purpose of improving the flame retardant properties. For example, the existing document 1 (Epoxy-modified silicone resin based N / P / Sisynergistic flame-retardant coating for wood surface [J]. Progress in Organic Coatings 170 (2022) 106953) condenses dimethyl diethoxysiloxane with 3-glycidyloxypropyltrimethoxysilane KH-560 to form an epoxy-modified silicone SiR coating, and cures the resin with a nitrogen-phosphorus flame retardant PTDP to obtain a technical effect of greatly improving the flame retardant properties of wood. However, the problem with this technical solution is that PTDP is a non-biobased flame retardant and therefore cannot be degraded in the environment, which results in the accumulation of PTDP in the environment during long-term use, causing environmental pollution.

[0003] In order to solve the above technical problems, it can be solved by using a biomass-based flame retardant with degradable properties-phytic acid-based flame retardant. For example, existing document 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) prepares an ammonium phytate by controlling the ratio of the amount of phytic acid to urea, and uses the ammonium phytate as a flame retardant curing agent to cure melamine-urea-formaldehyde resin to obtain a flame retardant coating. After the flame retardant coating is applied to the wood surface, the flame retardant wood passes the UL-94V-0 grade, and the limiting oxygen index is as high as 42.4%. However, the technical problem of the technical solution is that the content of the curing agent used reaches more than 10wt.%, while the amount of conventional curing agent used is only 1-2wt.%. Obviously, the curing function of the flame retardant curing agent in the technical solution cannot achieve the effect of the conventional curing agent. This problem directly leads to a substantial increase in the raw material cost of the flame retardant curing agent.

[0004] In order to achieve the same flame retardant effect while reducing the amount of flame retardant added, in the preliminary work of the inventor's research group, the existing document 3 (Zou Yongjin, Wei An, Xiang Cuili, etc. 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-guanazole-lignin composite polymer PGL as a bio-based flame retardant, and ammonium chloride as a curing agent to prepare a flame retardant coating and apply it to the wood surface, thereby improving the flame retardant properties of wood. The amount of curing agent ammonium chloride required for this technical solution is only 1wt% to achieve the curing effect. However, although the amount of biomass-based curing agent used in this technical solution is less, it is still necessary to add conventional curing agent ammonium chloride. The reason is that the use of this biomass-based curing agent alone can also not obtain the same curing effect as the conventional curing agent, that is, although the technical effect of reducing the amount of curing agent is partially achieved, it is also impossible to completely solve the aforementioned technical problems.

[0005] Therefore, the technical problem existing in the current prior art is that when bio-based flame retardants are used alone as curing agents, or when the amount added is small, the same curing effect as that of conventional curing agents cannot be achieved. Summary of the invention

[0006] The purpose of the present invention is to provide a flame retardant coating based on PG flame retardant curing agent, and its preparation method and application. In view of the problems existing in the prior art, phytic acid-guanazole PG is prepared by utilizing the ion reaction between phytic acid and guanazole, and the bio-based flame retardant coating is prepared by curing modified urea-formaldehyde resin as a flame retardant curing agent, while solving the problem of high curing agent usage, wherein KH550 is an auxiliary agent, dioctyl phthalate DOP is a plasticizer, and phytic acid-guanazole PG is a bio-based flame retardant curing agent. The technical principles involved are:

[0007] 1. As an auxiliary agent, KH550 plays a role in adjusting the molecular structure of urea-formaldehyde resin and improving the compatibility of urea-formaldehyde resin with curing agent and plasticizer; 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 carbonization during combustion, improve the quality of the carbon layer, and ultimately play a role in heat insulation and flame retardancy;

[0008] 2. PG as a flame retardant has a large number of phosphate ions and ammonium ions. Therefore, during the combustion process, the phosphorus element in the phytate ions can promote the dehydration of the matrix to form a protective carbon layer, and the nitrogen element in the ammonium ions produces non-flammable gas during the combustion process to dilute the oxygen in the air. The two synergistically improve the flame retardant properties of the matrix;

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

[0010] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is:

[0011] A flame retardant coating based on PG flame retardant curing agent, with urea and formaldehyde as raw materials, KH550 as an auxiliary agent, dioctyl phthalate DOP as a plasticizer, and phytic acid-guanazole PG as a bio-based flame retardant curing agent, wherein the PG is prepared by ion reaction under aqueous solution conditions using phytic acid and guanazole as raw materials;

[0012] The temperature when the decomposition mass is 5% is 160-200°C, and the temperature when the maximum decomposition rate is reached is 290-300°C; the residual carbon content at 800°C is 10-22wt.%.

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

[0014] Step 1, preparation of phytic acid guanazole flame retardant curing agent, first, under certain conditions, guanazole GZ is dissolved in deionized water to obtain a GZ solution, and at the same time, a phytic acid PA solution is dissolved in deionized water to obtain a PA solution, and then, under certain conditions, the PA solution is added dropwise to the GZ solution to fully react, and after the reaction is completed, rotary evaporation is performed under certain conditions, and after the rotary evaporation is completed, the obtained crystals are ground to obtain a phytic acid guanazole flame retardant curing agent PA-GZ, referred to as PG;

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

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

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

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

[0019] Step 2, preparation of modified urea-formaldehyde resin emulsion, first, adding sodium hydroxide solution to formaldehyde solution to adjust the pH value of the solution, then, under certain conditions, completing the preparation of initial reaction conditions, and then, adding urea, silane coupling agent KH550 and other raw materials in three stages to prepare modified urea-formaldehyde resin emulsion KUF, referred to as KUF;

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

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

[0022] The three stages in step 2 are:

[0023] Stage 2.1 is to add urea first and then KH550 while maintaining the temperature at 90°C. After the addition is completed, stirring is continued for 30 minutes.

[0024] Stage 2.2 is to add acetic acid solution at 90°C to adjust the pH value of the solution to 4.5-5.0, and then add urea. After the addition is completed, the stirring time is 10 minutes and the stirring is continued until the reaction reaches the end point.

[0025] The judgment mark of the reaction end point of the stage 2.2 is that a drop of the solution is dropped into 30°C water, and the dropped solution condenses in the water without dispersing;

[0026] Stage 2.3 is to add sodium hydroxide solution at 90°C to adjust the pH value of the solution to 7.5-8.0, and then add urea. After the addition is completed, adjust the temperature and stir at 70°C for 30 minutes to obtain KUF.

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

[0028] Step 3, preparation of a flame retardant coating based on a PG flame retardant curing agent, with the KUF obtained in step 2, dioctyl phthalate DOP and the PG obtained in step 1 satisfying a certain mass ratio, adding DOP and PG to KUF, after the addition is completed, mechanical stirring is performed under certain conditions to mix the components evenly, and sodium hydroxide is added dropwise to the obtained solution to adjust the pH value of the solution to 4-5, so as to obtain a flame retardant coating based on a PG flame retardant curing agent, referred to as KUF-PG.

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

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

[0031] When the flame retardant coating based on PG flame retardant curing agent is used as a wood flame retardant coating, it has flame retardant properties, a limiting oxygen index of 29-33%, passes the UL-94V-0 test, and forms a dense residual carbon layer after complete combustion.

[0032] The technical effects of the green bio-based wood flame retardant coating obtained by the present invention are as follows:

[0033] The DSC test results show that the DSC curve of the flame retardant coating has only one peak, the curing behavior of the flame retardant coating is single, and the curing can be completed at a lower temperature.

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

[0035] In order to further prove why flame retardant coatings still have good flame retardant properties when the residual carbon content is low, SEM tests were carried out on the residual carbon layer of wood coated with flame retardant coatings after complete combustion. The test results show that using PG as a curing agent can improve the quality of the residual carbon layer of wood coated with flame retardant coatings after combustion. The residual carbon layer formed after complete combustion has a continuous and dense property, and there is no hole phenomenon, which can form a dense residual carbon layer, thereby effectively isolating oxygen and heat, and improving the flame retardant properties of wood.

[0036] The results of the vertical burning test show that applying flame retardant coating can improve the UL-94 grade of wood. The wood coated with flame retardant coating using PG as a curing agent passed the UL-94 V-0 grade test; and the limiting oxygen index was as high as 29-33%. Excellent flame retardant performance.

[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 the present invention can significantly improve the flame retardant properties of wood;

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

[0040] 3. The present invention can completely avoid the use of conventional curing agents, and the added amount is less than that of conventional curing agents, which reduces production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 FTIR images of PG, PA and GZ in Example 1;

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

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

[0044] Figure 4 TG diagrams of Example 1, Example 3, Example 2, Comparative Example 3, and Comparative Example 2;

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

[0046] Figure 6It is a vertical combustion test diagram of Comparative Example 1, Comparative Example 2, Comparative Example 3, Example 2, Example 3, and Example 1, wherein Figure 6 a is before vertical burning test, Figure 6 b is after vertical burning test. DETAILED DESCRIPTION

[0047] The present invention is further described in detail through embodiments and in conjunction with the accompanying drawings, but the present invention is not limited thereto.

[0048] Example 1

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

[0050] Step 1, preparation of phytic acid guanazole flame retardant curing agent, first, under the conditions of dissolution temperature of 25°C, dissolution stirring speed of 500rpm, and dissolution stirring time of 30min, 13.5g guanazole GZ is placed in 100mL deionized water and dissolved to obtain GZ solution, and at the same time, 15mL 70wt.% phytic acid PA solution is dissolved in 50mL deionized water to obtain PA solution, and then, under the conditions of dropping temperature of 25°C, dropping stirring speed of 500rpm, dropping stirring time of 1h, and dropping rate of 0.5 drops / s, the PA solution is added dropwise to the GZ solution for sufficient reaction, after the reaction is completed, rotary evaporation is performed at a rotary evaporation temperature of 70°C and a rotary evaporation time of 3h, and after the rotary evaporation is completed, the obtained crystals are ground to obtain phytic acid guanazole flame retardant curing agent PA-GZ, referred to as PG;

[0051] In order to prove the composition of PG, i.e., successful synthesis, FTIR test was performed, and the test results are as follows Figure 1 As shown, PG contains characteristic peaks of both PA and GZ. The test results show that PG was successfully synthesized.

[0052] Step 2, preparation of modified urea-formaldehyde resin emulsion, first, add 20wt.% sodium hydroxide solution to 100g 37wt.% formaldehyde solution, adjust the pH value of the solution to 8.0-8.5, then, heat to 90°C under a stirring speed of 400rpm to complete the preparation of initial reaction conditions, then add 56.9g urea, 2.85g silane coupling agent KH550 and other raw materials in three stages to prepare modified urea-formaldehyde resin emulsion KUF, referred to as KUF, the specific three stages are,

[0053] Stage 2.1 is to add 37 g urea and then 2.85 g KH550 while maintaining the temperature at 90°C. After the addition is completed, stirring is continued for 30 min.

[0054] Stage 2.2 is to add 20 wt.% acetic acid solution at 90°C, adjust the pH value of the solution to 4.5-5.0, and then add 12.3 g urea. After the addition is completed, continue stirring for 10 minutes until the reaction reaches the end point;

[0055] The judgment mark of the reaction end point of the stage 2.2 is that a drop of the solution is dropped into 30°C water, and the dropped solution condenses in the water without dispersing;

[0056] Stage 2.3 is to add 20 wt.% sodium hydroxide solution while maintaining the temperature at 90°C, adjust the pH value of the solution to 7.5-8.0, and then add 7.6 g of urea. After the addition is completed, adjust the temperature and stir at a stirring temperature of 70°C for 30 minutes to obtain KUF.

[0057] Step 3, preparation of a flame retardant coating based on a PG flame retardant curing agent, with the mass ratio of KUF obtained in step 2, dioctyl phthalate DOP and PG obtained in step 1 being 100:1:2.5, adding 1g DOP and 2.5g PG to 100g KUF, after the addition is completed, mechanical stirring is performed at a stirring speed of 600rpm and a stirring time of 30min to mix the components evenly, and sodium hydroxide is added dropwise to the obtained solution to adjust the pH value of the solution to 4-5, so as to obtain a flame retardant coating based on a PG flame retardant curing agent, referred to as KUF-PG, and the KUF-PG prepared in specific example 1 is referred to as KUF-PG-2.5.

[0058] In order to prove the composition of KUF-PG-2.5, FTIR test was carried out. The test results are as follows Figure 2 As shown in the figure, KUF-PG-2.5 contains characteristic peaks of urea-formaldehyde resin UF, KH550, phytic acid PA and guanazole GZ. The test results show that PG and KH550 react with urea-formaldehyde resin emulsion.

[0059] In order to prove the curing characteristics of KUF-PG-2.5, DSC test was carried out. The test results are as follows Figure 3 As shown, the DSC curve of KUF-PG-2.5 has only one peak, and the peak temperature is 98.5°C. The test results show that the curing behavior of the flame retardant coating of KUF-PG-2.5 is single, and the curing can be completed at a lower temperature.

[0060] In order to prove the thermal stability of KUF-PG-2.5, TG test was carried out. The test results are as follows Figure 4As shown in Table 1, the temperature at which the decomposition mass of KUF-PG-2.5 is 5% is 195.3°C, the temperature at which the maximum decomposition rate is reached is 294.8°C, and the residual carbon content at 800°C is 21.9wt.%. The test results show that although the residual carbon content of KUF-PG-2.5 is low, only 21.9%, the temperature at which the decomposition mass is 5% increases significantly with the increase of PG content, and the temperature at which the maximum decomposition rate is reached is not greatly affected, that is, it has high thermal stability.

[0061] Table 1 Thermogravimetric test results

[0062]

[0063] In order to further prove the technical effect of KUF-PG as a flame retardant coating for wood, that is, to prove why KUF-PG-2.5 still has good flame retardant properties when the residual carbon content is low, KUF-PG is coated on the surface of wood to prepare flame retardant wood W-KUF-PG for flame retardant testing. The specific preparation method of W-KUF-PG is to coat KUF-PG on the surface of wood with a coating thickness of 0.3 mm, and after coating, dry it under the condition of a drying time of 24 hours to obtain W-KUF-PG. The W-KUF-PG prepared based on KUF-PG-2.5 in Example 1 is named W-KUF-PG-2.5.

[0064] The SEM test was performed on the residual carbon layer after the complete combustion of W-KUF-PG-2.5. The test results are as follows Figure 5 As shown in Figure c, the residual carbon layer formed after the complete combustion of W-KUF-PG-2.5 has a continuous and dense nature, and there is no hole phenomenon. The test results show that W-KUF-PG-2.5 prepared using PG as a curing agent can form a dense residual carbon layer, thereby effectively isolating oxygen and heat and improving the flame retardant properties of wood.

[0065] In order to further prove the flame retardant performance of W-KUF-PG-2.5, vertical burning test and limiting oxygen index test were carried out. The test results are as follows Figure 6 As shown in Table 2, W-KUF-PG-2.5 passed the UL-94V-0 grade test; and the limiting oxygen index of W-KUF-PG-2.5 is as high as 32.7%. The test results show that W-KUF-PG-2.5 has excellent flame retardant properties.

[0066] Table 2 Vertical combustion test and oxygen index test results

[0067]

[0068] According to the common knowledge in the art, the amount of carbon residue is positively correlated with the flame retardant performance, that is, the higher the amount of carbon residue, the better the flame retardant performance obtained. Therefore, based on this common knowledge, the general method for those skilled in the art to improve the flame retardant performance is to increase the amount of carbon residue. At the same time, the amount of carbon residue is used as an important basis for determining whether to conduct subsequent research, that is, to preliminarily judge whether the flame retardant performance has good potential by the amount of carbon residue.

[0069] In order to prove the relationship between the residual carbon content and the flame retardant performance, further comparison was made with existing references. The specific performance is shown in Table 3.

[0070] Table 3 Carbon residue of different flame retardant coatings and their influence on flame retardant properties

[0071]

[0072] Reference 1 (Zou Yongjin, Wei An, Xiang Cuili, etc. A bio-based flame retardant coating based on PGL and its preparation method and application: China, patent number CN118580739 A)

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

[0074] According to reference 1, when the carbon residue is higher than that of the present invention and reaches 23.2wt%, although the limiting oxygen index is no different from that of the present invention and reaches 31.6%, the UL-94 grade is only V-1; by comparison, it can be seen that when the carbon residue of KUF-PG-2.5 obtained by the present invention is significantly lower than that of the reference, not only the limiting oxygen index is no different from that of the reference, but also the UL-94 grade reaches V-0;

[0075] Further comparison with reference 1 shows that when the carbon residue is increased to 35.3, the UL-94 grade can be increased from V-1 to V-0, which also proves that the KUF-PG-2.5 obtained by the present 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] Through the above comparison, combined with the TG test and SEM test results, it can be seen that the reason for the high flame retardant performance is that the residual charcoal layer formed after the complete combustion of W-KUF-PG-2.5 has a continuous and dense property, and there is no hole phenomenon, which can effectively isolate oxygen and heat, thereby improving the flame retardant performance of the wood, that is, it proves that the KUF-PG-2.5 obtained by the present invention has a better residual charcoal layer quality than the prior art.

[0078] In order to demonstrate the effect of the flame retardant coating KUF-PG-2.5 on the flame retardant properties of wood, a comparative example 1 is provided, which is pure wood without coating of KUF-PG.

[0079] Comparative Example 1

[0080] A pure wood not coated with KUF-PG, referred to as pure wood.

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

[0082] Pure wood did not pass the UL-94 rating test. Compared with Example 1, coating KUF-PG-2.5 can make pure wood pass the UL-94 rating test;

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

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

[0085] In order 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, in which conventional tannic acid is used as a curing agent instead of PG as a curing agent to prepare a flame retardant coating.

[0086] Comparative Example 2

[0087] A method for preparing a flame retardant coating based on a tannic acid curing agent, wherein the steps not specifically stated are the same as those 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 a tannic acid curing agent, referred to as KUF-TA, and the flame retardant wood obtained is further named W-KUF-TA.

[0088] The DSC test results of KUF-TA are as follows Figure 3 As shown, the DSC curve of KUF-TA has only one peak, and the peak temperature is 108.2°C. Compared with Example 1, it can be seen that the curing curve behaviors of KUF-PG-2.5 and KUF-TA are consistent, but PG as a curing agent reduces the curing temperature. The test results show that using PG as a curing agent does not affect the curing behavior of KUF-PG, but affects the curing temperature.

[0089] The TG test results of KUF-TA are as follows Figure 4As shown in Table 1, the temperature at which the decomposition mass of KUF-TA is 5% is 181.3°C, the temperature at which the maximum decomposition rate is reached is 298.7°C, and the residual carbon amount at 800°C is 12.5wt.%. Compared with Example 1, the use of PG as a curing agent can increase the temperature at which the decomposition mass is 5% by 14°C, slightly reduce the temperature at which the maximum decomposition rate is reached by 4.4°C, and increase the residual carbon amount at 800°C by 9.4wt.%. The test results show that the use of PG as a curing agent can significantly improve the thermal stability and residual carbon amount of KUF-PG, and at the same time, the negative impact on the maximum decomposition rate temperature is negligible.

[0090] The SEM test results of the residual carbon layer after the complete combustion of W-KUF-TA are as follows: Figure 5 As shown in a, the residual carbon layer not only has many pits, but also has large holes. Compared with Example 1, it can be seen that the use of PG as a curing agent can transform the residual carbon layer from a situation with pits and holes to a continuous and dense situation without holes. The test results show that the use of PG as a curing agent can significantly improve the quality of the residual carbon layer and improve the flame retardant performance.

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

[0092] Compared with Comparative Example 1, it can be seen that using TA as a curing agent can improve the UL-94 grade of pure wood from failing to pass to V-1 grade; and 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 grade of pure wood from V-1 to V-0; and can slightly increase the limiting oxygen index from 31.5% to 32.7%;

[0094] The test results show that although the effect of using PG as a curing agent on improving the limiting oxygen index is negligible, it can directly improve the UL-94 grade.

[0095] Combining the SEM and TG test results, it can be seen that the flame retardant process of adding flame retardant curing agent PG during the combustion process does not come from the release of non-combustible gas, but directly prevents further combustion of W-KUF-PG-2.5 by increasing the amount of residual carbon during the combustion process and forming a dense and smooth residual carbon layer, thereby improving the UL-94 grade and flame retardant performance.

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

[0097] In order to demonstrate the effect of the amount of PG added on the performance of the flame retardant coating KUF-PG and the flame retardant wood W-KUF-PG, comparative example 3, example 2 and example 3 are provided, and the amount of PG added in the flame retardant coating is 1wt.%, 1.5wt.% and 2wt.%, respectively.

[0098] Comparative Example 3

[0099] A method for preparing KUF-PG with a PG addition amount of 1 wt.%, wherein the steps not specifically stated are the same as those in Example 1, except that: in step 3, the addition amount of PG is 1 wt.%, that is, the addition amount of PG is 1 g, and the obtained flame retardant coating is named KUF-PG-1, and the obtained flame retardant wood is further 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, and the peak temperature is 107.5°C. Compared with Example 1, the curing curve behaviors of KUF-PG-2.5 and KUF-PG-1 are consistent, but increasing the amount of PG added will cause the curing temperature to decrease. The test results show that the amount of PG added will not affect the curing behavior of KUF-PG, but will 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 to 5% by mass is 157.6°C, the temperature at which the maximum decomposition rate is reached is 300.3°C, and the residual carbon content at 800°C is 1.3wt.%. The test results show that the addition of a small amount of PG has a negligible effect on the temperature at the maximum decomposition rate, but has a significant effect on the temperature and residual carbon content at a decomposition mass of 5%.

[0102] Compared with Comparative Example 2, it can be seen that the use of a small amount of PG instead of TA has a negligible effect on the maximum decomposition rate temperature, but it will greatly reduce the temperature and residual carbon amount when the decomposition mass is 5%. That is, when a small amount of PG is added, the flame retardant performance is significantly inferior to that of TA.

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

[0104] Based on the above analysis results, it can be seen that the addition amount of PG has no substantial effect on the maximum decomposition rate temperature, but has a significant effect on the temperature and residual carbon amount when the decomposition mass is 5%. Specifically, increasing the addition amount of PG can significantly increase the temperature and residual carbon amount when the decomposition mass is 5%.

[0105] The SEM test results of the residual carbon layer after the complete combustion of W-KUF-PG-1 are as follows Figure 5 As shown in b, although there are no pits in the residual carbon layer, there are still a few holes;

[0106] Compared with Comparative Example 2, it can be seen that only a small amount of PG is needed to replace TA to achieve a carbon layer without pits after complete combustion, and at the same time, the holes are significantly reduced;

[0107] Compared with Example 1, it can be seen that increasing the PG content can prevent the residual carbon layer from forming holes.

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

[0109] The vertical combustion test and limiting oxygen index test results of W-KUF-PG-1 are as follows Figure 6 As shown in Table 2, W-KUF-PG-1 passed the UL-94V-1 grade test; and the limiting oxygen index of W-KUF-PG-1 was 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 grade of pure wood from failing to pass to V-1 grade, 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 when a small amount of PG is added, there is no substantial effect on the UL-94 grade, but the limiting oxygen index is reduced from 31.5% to 28.8%;

[0112] Compared with Example 1, increasing the amount of PG added can improve the UL-94 grade from V-1 to V-0, and the limiting oxygen index from 28.8% to 32.7%;

[0113] The 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 carbon amount is only 1.3wt.%, 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 grade test is that even if a small amount of PG is used instead of TA, the quality of the residual carbon layer can be effectively improved. Therefore, after increasing the amount of PG added, the flame retardant performance can be further improved.

[0114] Example 2

[0115] A method for preparing KUF-PG with a PG addition amount of 1.5wt.%, wherein the steps not specifically stated are the same as those in Example 1, except that: in step 3, the addition amount of PG is 1.5wt.%, that is, the addition amount of PG is 1.5g, and the obtained 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, and the peak temperature is 106.7° C. The conclusion obtained is not substantially different from that of Comparative Example 3, that is, the addition amount of PG will not affect the curing behavior of KUF-PG, but will affect its curing temperature.

[0117] The TG test results of KUF-PG-1.5 are as follows Figure 4 As shown in Table 1, the temperature at which the decomposition mass of KUF-PG-1.5 is 5% is 188.5°C, the temperature at which the maximum decomposition rate is reached is 289.4°C, and the amount of residual carbon at 800°C is 7.6wt.%. The conclusion obtained is not substantially different from that of Comparative Example 3, that is, the amount of PG added has no substantial effect on the maximum decomposition rate temperature, but has a significant effect on the temperature and residual carbon when the decomposition mass is 5%. Increasing the amount of PG added can significantly increase the temperature and residual carbon when the decomposition mass is 5%. In addition, when the amount of PG added reaches 1.5wt.%, the temperature at which the decomposition mass is 5% can achieve the same flame retardant effect as adding TA.

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

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

[0120] Compared with Comparative Example 2, when the addition amount of PG is 1.5wt%, the UL-94 grade is improved from V-1 to V-0, but the limiting oxygen index is reduced from 31.5% to 29.9%;

[0121] Compared with Comparative Example 3, when the addition amount of PG is 1.5wt%, the UL-94 grade is increased from V-1 to V-0, and the limiting oxygen index is increased 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 effect on the UL-94 grade, it can further increase the limiting oxygen index from 29.9% to 32.7%;

[0123] The test results show that increasing the PG content can further improve the flame retardant properties.

[0124] Example 3

[0125] A method for preparing KUF-PG with a PG addition amount of 2 wt.%, wherein the steps not specifically stated are the same as those in Example 1, except that: in step 3, the addition amount of PG is 2 wt.%, that is, the addition amount of PG is 2 g, and the obtained 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, and the peak temperature is 103.3° C. The conclusion obtained is not substantially different from that of Comparative Example 3 and Example 2, that is, the addition amount of PG will not affect the curing behavior of KUF-PG, but will 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 the decomposition mass of KUF-PG-2 is 5% is 190.1°C, the temperature at which the maximum decomposition rate is reached is 302.7°C, and the amount of residual carbon at 800°C is 11.7wt.%. The conclusion obtained is not substantially different from that of Comparative Example 3 and Example 2, that is, the amount of PG added has no substantial effect on the maximum decomposition rate temperature, but has a significant effect on the temperature and residual carbon when the decomposition mass is 5%. Increasing the amount of PG added can significantly increase the temperature and residual carbon when the decomposition mass is 5%. In addition, when the amount of PG added reaches 2wt.%, the residual carbon can achieve the same effect as adding TA, and the temperature at the decomposition mass of 5% is higher than TA, which proves that the flame retardant effect of PG is better than TA.

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

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

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

[0131] Compared with Example 1, further increasing the amount of PG added has no substantial effect on the UL-94 grade, but can further increase the limiting oxygen index from 32.1% to 32.7%;

[0132] The test results show that increasing the PG content can further improve the flame retardant properties.

[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 carbon content of flame retardant coatings and the temperature at which the decomposition mass reaches 5%. With the increase of the content of curing agent PG, the temperature at which the maximum decomposition rate is reached is not greatly affected, that is, it has high thermal stability;

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

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

Claims

1. A flame retardant coating based on PG flame retardant curing agent, characterized in that: The invention uses urea and formaldehyde as raw materials, KH550 as an auxiliary agent, dioctyl phthalate DOP as a plasticizer, and phytic acid-guanazole PG as a bio-based flame retardant curing agent. The PG uses phytic acid and guanazole as raw materials and is prepared by ion reaction under aqueous solution conditions.

2. The flame retardant coating based on PG flame retardant curing agent according to claim 1, characterized in that: The temperature when the decomposition mass is 5% is 160-200°C, and the temperature when the maximum decomposition rate is reached is 290-300°C; the residual carbon content at 800°C is 10-22wt.%.

3. A method for preparing a flame retardant coating based on a PG flame retardant curing agent, characterized in that The following steps are involved: Step 1, preparation of phytic acid guanazole flame retardant curing agent, first, under certain conditions, guanazole GZ is dissolved in deionized water to obtain a GZ solution, and at the same time, a phytic acid PA solution is dissolved in deionized water to obtain a PA solution, and then, under certain conditions, the PA solution is added dropwise to the GZ solution to fully react, and after the reaction is completed, rotary evaporation is performed under certain conditions, and after the rotary evaporation is completed, the obtained crystals are ground to obtain a phytic acid guanazole flame retardant curing agent PA-GZ, referred to as PG; Step 2, preparation of modified urea-formaldehyde resin emulsion, first, adding sodium hydroxide solution to formaldehyde solution to adjust the pH value of the solution, then, under certain conditions, completing the preparation of initial reaction conditions, and then, adding urea, silane coupling agent KH550 and other raw materials in three stages to prepare modified urea-formaldehyde resin emulsion KUF, referred to as KUF; Step 3, preparation of a flame retardant coating based on a PG flame retardant curing agent, with the KUF obtained in step 2, dioctyl phthalate DOP and the PG obtained in step 1 satisfying a certain mass ratio, adding DOP and PG to KUF, after the addition is completed, mechanical stirring is performed under certain conditions to mix the components evenly, and sodium hydroxide is added dropwise to the obtained solution to adjust the pH value of the solution to 4-5, so as to obtain a flame retardant coating based on a PG flame retardant curing agent, referred to as KUF-PG.

4. The preparation method according to claim 3, characterized in that: In the step 1, the molar ratio of GZ to PA is 7:1; In step 2, the mass ratio of the total mass of the formaldehyde solution, urea and KH550 is 100:56.9:2.85; In the step 3, the mass ratio of KUF, DOP and PG is 100:1:2.

5.

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

6. The preparation method according to claim 3, characterized in that: In step 2, the pH value of the solution is adjusted to 8.0-8.5; the initial reaction conditions are that the temperature is raised to 90° C. under the condition of stirring speed of 400-500 rpm.

7. The preparation method according to claim 3, characterized in that: The three stages in step 2 are: Stage 2.1 is to add urea first and then KH550 while maintaining the temperature at 90°C. After the addition is completed, stirring is continued for 30 minutes. Stage 2.2 is to add acetic acid solution at 90°C to adjust the pH value of the solution to 4.5-5.0, and then add urea. After the addition is completed, the stirring time is 10 minutes and the stirring is continued until the reaction reaches the end point. The judgment mark of the reaction end point of the stage 2.2 is that a drop of the solution is dropped into 30°C water, and the dropped solution condenses in the water without dispersing; Stage 2.3 is to add sodium hydroxide solution at 90°C to adjust the pH value of the solution to 7.5-8.0, and then add urea. After the addition is completed, adjust the temperature and stir at 70°C for 30 minutes to obtain KUF. In the three stages, the urea addition amounts in the three stages satisfy a mass ratio of 37:12.3:7.

6.

8. The preparation method according to claim 3, characterized in that: In the step 3, the mechanical stirring speed is 500-600 rpm and the stirring time is 30 min.

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

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