P-n-si-ca based flame retardant composite coating and preparation method and application thereof

Abstract

The application belongs to the technical field of fire-retardant coating and specifically discloses a fire-retardant composite coating based on P-N-Si-Ca as well as a preparation method and application thereof. The composite coating comprises a fire-retardant composite coating based on P-N-Si-Ca, which is prepared by using P-N-Si-Ca fire retardant, urea and formaldehyde as main raw materials, 3-aminopropyl triethoxysilane and nano CaCO3 as fillers and coupling agents, and beta-cyclodextrin as a carbonization agent and a crosslinking agent, and by using water bath heating and stirring. The fire-retardant composite coating based on P-N-Si-Ca is prepared. The fire-retardant composite coating based on P-N-Si-Ca as well as the preparation method and application thereof are used to improve the fire-retardant performance of the fire-retardant urea-formaldehyde resin composite coating based on P-N-Si as wood fire-retardant coating, and the reaction condition is mild and free of dangerous chemicals.

Description

Technical Field

[0001] This invention relates to the field of flame retardant coating technology, and in particular to flame retardant composite coatings based on PN-Si-Ca, their preparation methods, and applications. Background Technology

[0002] Wood, as a natural material, is widely used in many fields such as construction, furniture, and decoration due to its excellent properties such as being lightweight, high-strength, and easy to process, making it one of the indispensable basic materials. However, the inherent flammability of wood greatly limits its further application and also brings serious safety hazards.

[0003] In fires, wood burns rapidly and produces a large amount of smoke, quickly damaging wood products and shortening their lifespan. It can also cause the fire to spread, posing a direct threat to people's lives and property. Therefore, effective flame-retardant treatment of wood is of paramount importance. Scientific flame-retardant treatment can significantly reduce the burning rate of wood, decrease smoke production, reduce the probability of fires at their source, and mitigate the severity of the damage caused by fires.

[0004] To address the flammability of wood, flame-retardant coatings can be applied to its surface. This process not only protects wood products but also promotes the rational use of resources, reducing waste caused by fires. Simultaneously, it aligns with environmental protection and sustainable development principles, minimizing fire-related pollution and providing core support for safety upgrades in construction, furniture, and other fields. However, existing flame-retardant coatings offer limited improvement in the flame-retardant properties of the substrate, failing to meet higher fire safety standards, or requiring harsh and dangerous reaction conditions while enhancing flame retardancy. Therefore, developing efficient, safe, and highly adaptable flame-retardant wood materials has become a crucial issue urgently needing to be addressed in the field of flame-retardant materials. Summary of the Invention

[0005] The purpose of this invention is to provide a flame-retardant composite coating based on PN-Si-Ca, its preparation method and application, to improve the flame-retardant performance of PN-Si flame-retardant urea-formaldehyde resin composite coating as a flame-retardant coating for wood, with mild reaction conditions and no hazardous chemicals.

[0006] To achieve the above objectives, this invention provides a flame-retardant composite coating based on PN-Si-Ca, which uses PN-Si-Ca flame retardant combined with urea and formaldehyde as the main raw materials, 3-aminopropyltriethoxysilane and nano-CaCO3 as fillers and coupling agents, and β-cyclodextrin as a char-forming agent and crosslinking agent. The flame-retardant composite coating based on PN-Si-Ca can be prepared by water bath heating and stirring.

[0007] Preferably, the PN-Si-Ca flame retardant is a compound flame retardant made of ammonium polyphosphate and diammonium hydrogen phosphate.

[0008] Preferably, the temperature at which the PN-Si-Ca flame-retardant composite coating decomposes to 5% is 198.23±0.7℃, the temperature at which the maximum decomposition rate is reached is 345.30±0.6℃, and the amount of residual carbon at 800.00℃ is 31.43±0.5wt.%.

[0009] This invention also provides a method for preparing a flame-retardant composite coating based on PN-Si-Ca, comprising the following steps:

[0010] Step 1, Preparation of PN-Si-Ca flame retardant: Ammonium polyphosphate is heated to 65℃ and stirred for 30 min, diammonium hydrogen phosphate is added and stirred for 30 min, and then stirred in a water bath to obtain an APD solution. 3-aminopropyltriethoxysilane, β-cyclodextrin and nano-CaCO3 are placed in the APD solution in sequence, and dimethyl silicone oil and polyacrylamide are added as additives. The reaction is stirred to obtain an APDKC solution. After the reaction is complete, the obtained product is freeze-dried and ground into powder to obtain the PN-Si-Ca flame retardant.

[0011] Step 2, Preparation of PN-Si-Ca flame-retardant composite coating: Sodium hydroxide solution is added to formaldehyde solution to adjust the pH value of the solution, and then nano-CaCO3 is added and stirred to obtain a suspension solution. Urea and PN-Si-Ca flame retardant are added in three stages to prepare the PN-Si-Ca flame-retardant composite coating.

[0012] Preferably, in step 1, the mass ratio of ammonium polyphosphate, diammonium hydrogen phosphate, 3-aminopropyltriethoxysilane, β-cyclodextrin, and nano-CaCO3 is 5:1:1:2:1.

[0013] Preferably, in step 1, the stirring temperature for water bath stirring is 90℃, the stirring speed is 300-600 rpm, and the water bath stirring time is 2.5 h; the stirring temperature for stirring reaction is 90℃, and the stirring speed is 300-600 rpm; the freezing temperature for freeze drying is -20℃, and the drying time is 42 h.

[0014] Preferably, in step 2, the mass ratio of the total amount of PN-Si-Ca flame retardant, formaldehyde, urea, and nano-CaCO3 added is 2:100:55:10.

[0015] Preferably, in step 2, the pH of the solution is adjusted to 8.0-8.5.

[0016] Preferably, in step 2, the conditions for adding urea are: stirring speed of 300-600 rpm and reaction temperature of 90℃.

[0017] This invention also provides the application of PN-Si-Ca based flame-retardant composite coatings for the preparation of flame-retardant coatings for wood.

[0018] The advantages and beneficial effects of the above-mentioned flame-retardant composite coating based on PN-Si-Ca, its preparation method, and its application are as follows:

[0019] 1. The bio-based flame-retardant resin coating of the present invention improves the residual char content of the matrix by adding ammonium polyphosphate, diammonium hydrogen phosphate, 3-aminopropyltriethoxysilane, β-cyclodextrin and nano-CaCO3, and significantly improves the flame-retardant performance. Among them, ammonium polyphosphate and diammonium hydrogen phosphate decompose into pyrophosphate when heated, which not only promotes the carbonization of the matrix, but also increases the formation of coke and improves the residual char content.

[0020] 2. This invention improves the compatibility of ammonium polyphosphate in urea-formaldehyde resin by using a compound of ammonium polyphosphate and diammonium hydrogen phosphate, with 3-aminopropyltriethoxysilane as a coupling agent and filler, and introducing β-cyclodextrin as a physical crosslinking agent and carbonizing agent. The addition of nano-CaCO3 to the polymer effectively reduces costs, improves the compatibility of the composite material and its bonding strength to the wood matrix, and the nano-CaCO3 decomposes under high-temperature conditions, absorbing heat and releasing CO2, effectively improving the flame-retardant properties of the composite coating.

[0021] 3. The present invention is based on the fact that the temperature at which the PN-Si-Ca flame-retardant composite coating decomposes to 5% by mass is 198.23±0.7℃, and the temperature at which the maximum decomposition rate is reached is 345.30±0.6℃. Furthermore, the char residue at 800.00℃ is 31.43±0.5wt.%. After combustion, a continuous and dense char layer is formed, and a more stable char layer is produced in the high-temperature region. In the UL-94 rating test, it passed the UL-94V-0 rating test. In the cone calorimetry test, the heat release rate (HRR) is 24.8±0.25kW / m³. 2 .

[0022] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0023] Figure 1 The FTIR plot of APDKC in Embodiment 1 of the present invention;

[0024] Figure 2 These are the FTIR images of Embodiment 1 and Comparative Example 2 of the present invention;

[0025] Figure 3These are the TG images of Embodiment 1 and Comparative Example 2 of the present invention;

[0026] Figure 4 This is a SEM image of UF-APDKC in Embodiment 1 of the present invention;

[0027] Figure 5 The images show vertical combustion test diagrams of Embodiment 1, Comparative Example 1, and Comparative Example 2 of the present invention, where (a) is before the combustion test and (b) is after the combustion test.

[0028] Figure 6 The HRR plots are for Embodiment 1, Comparative Example 1, and Comparative Example 2 of the present invention.

[0029] Figure 7 This is a SEM image of Comparative Example 1 of the present invention;

[0030] Figure 8 This is a SEM image of Comparative Example 2 of the present invention. Detailed Implementation

[0031] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0032] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0033] The following examples are not intended to limit the invention, but are only for illustration. Unless otherwise specified, the experimental methods used in the following examples are generally performed under conventional conditions. Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0034] Example 1

[0035] The flame-retardant composite coating based on PN-Si-Ca is prepared by using PN-Si-Ca flame retardant combined with urea and formaldehyde as the main raw materials, 3-aminopropyltriethoxysilane and nano-CaCO3 as fillers and coupling agents, and β-cyclodextrin as a char-forming agent and crosslinking agent. The coating can be prepared by water bath heating and stirring.

[0036] PN-Si-Ca flame retardant is a compound flame retardant made of ammonium polyphosphate and diammonium hydrogen phosphate.

[0037] The preparation method of PN-Si-Ca organic-inorganic flame-retardant composite coating includes the following steps:

[0038] Step 1, Preparation of PN-Si-Ca Flame Retardant: First, ammonium polyphosphate (APP) is heated to 65℃ and stirred for 30 min in a three-necked flask. Then, diammonium hydrogen phosphate (ADP) is added and stirred for 30 min. The mixture is then subjected to a water bath at 90℃ and a stirring speed of 300-600 rpm for 2.5 h to obtain an APD solution. Next, 3-aminopropyltriethoxysilane (KH550), β-cyclodextrin (β-CD), and nano-CaCO3 are added sequentially to the APD solution, along with dimethyl silicone oil and polyacrylamide as additives. The reaction is carried out at 90℃ and a stirring speed of 300-600 rpm to obtain an APDKC solution. After the reaction is complete, the resulting product is freeze-dried at -20℃ for 42 h and ground into powder to obtain the PN-Si-Ca flame retardant, abbreviated as APDKC. The mass ratio of APP, ADP, KH550, β-CD, and nano-CaCO3 is 5:1:1:2:1.

[0039] Step 2, Preparation of PN-Si-Ca Flame Retardant Composite Coating (UF-APDKC): Add 20wt.% sodium hydroxide solution to 100g of 37wt.% formaldehyde solution, then add 10g of nano-CaCO3. Stir at 400rpm for 10 minutes, adjust the pH of the solution to 8.0-8.5 to obtain solution A. Then, under the conditions of stirring at 400rpm and reaction temperature of 90℃, add APDKC obtained in Step 1, urea and other raw materials, wherein the amount of APDKC added is 2g and the amount of urea added is 55g; thus, the PN-Si-Ca organic-inorganic flame retardant composite coating, abbreviated as UF-APDKC, can be prepared.

[0040] Comparative Example 1

[0041] A type of wood that is not coated with flame retardant, abbreviated as NW.

[0042] Comparative Example 2

[0043] A method for preparing pure urea-formaldehyde resin UF without adding APDKC flame retardant is described below. Unless otherwise specified, the steps are the same as in Example 1, except that step 1 is not required, and in step 2, APDKC is not added to obtain pure urea-formaldehyde resin UF without adding APDKC flame retardant, which is referred to as UF.

[0044] Test Example 1

[0045] Since subsequent tests need to be conducted after UF-APDKC has cured, the UF-APDKC flame-retardant resin coating is placed in a mold and cured directly or applied to the wood surface. Curing is carried out for 72 hours to obtain an APDKC-based flame-retardant resin coating. The cured material is still simply referred to as UF-APDKC.

[0046] The specific method for coating the wood surface is as follows: apply UF-APDKC evenly to the wood surface with a coating thickness of 0.3mm, and then dry it for 24 hours after coating.

[0047] To confirm the composition of APDKC, i.e., successful synthesis, an FTIR test was performed. The test results are as follows: Figure 1 As shown, APDKC simultaneously contains -NH, PNC, Si-OC, and CO3. - and PO - Characteristic peaks, including -NH, PNC, PO-, and CO3. - The characteristic peaks were attributed to APP and ADP, while the characteristic peaks of Si-OC and CaCO3 were attributed to a mixture of KH550 and β-CD. The test results indicate that the APDKC flame retardant was successfully synthesized.

[0048] To confirm the composition of UF-APDKC, i.e., successful synthesis, FTIR testing was performed. The FTIR test results are as follows: Figure 2 As shown, UF-APDKC contains -OH, -CH2, -NH2, PNC, Si-OC, and CO3. - and PO - Characteristic peaks, among which -OH and -CH2 characteristic peaks are attributed to UF, -NH2, PNC, CaCO3, and PO - The characteristic peaks are attributed to a mixture of APP, ADP, and β-CD, while Si-OC is attributed to a mixture of KH550 and β-CD. Test results indicate that the UF-APDKC flame-retardant coating is composed of APP, ADP, KH550, β-CD, and CaCO3, meaning UF-APDKC was successfully synthesized.

[0049] To demonstrate the effectiveness of the coatings prepared in Example 1, Comparative Example 1, and Comparative Example 2 as flame-retardant coatings for wood, TG tests, vertical burning tests, and limiting oxygen index tests were conducted on the coatings of Example 1, Comparative Example 1, and Comparative Example 2, respectively. The test results are shown in Tables 1 and 2.

[0050] Test results are as follows Figure 3 As shown in Table 1, the temperature at which the decomposition mass of UF-APDKC is 5% is 198.23±0.7℃, the temperature at which the maximum decomposition rate is reached is 345.30±0.6℃, and the amount of char residue at 800.00℃ is 31.43±0.5wt.%.

[0051] Table 1 Summary of TG Test Results

[0052]

[0053] To further demonstrate the microstructure of the residual carbon layer, SEM was performed on the UF-APDKC surface after TG testing. The test results are as follows: Figure 4 As shown, UF-APDKC can form a dense char layer with almost no pores, referred to as a dense structure. Test results indicate that UF-APDKC can form a high-quality char layer after combustion, effectively isolating oxygen and heat, thereby improving the flame-retardant properties of wood.

[0054] The vertical combustion test results of UF-APDKC are as follows: Figure 5 As shown in Table 2, the open flame time of UF-APDKC after the first ignition is 1.3s, and the open flame and flameless burning time after the second ignition is 8.5s, with no dripping, indicating that UF-APDKC has passed the V-0 rating of UL-94.

[0055] The limiting oxygen index test results of UF-APDKC are shown in Table 2. The limiting oxygen index of UF-APDKC is 33.5%.

[0056] Table 2 Results of Vertical Combustion Test and Oxygen Index Test

[0057]

[0058] To further quantify the flame retardancy of UF-APDKC, cone calorimetry (HRR) testing was conducted. The test results are as follows: Figure 6 As shown, the heat release rate (HRR) of UF-APDKC is 24.8 kW / m³. 2 .

[0059] To demonstrate the effect of UF-APDKC on the flame retardant properties of wood, Comparative Example 1, wood without flame retardant coating, was used as the base reference sample and compared with Comparative Example 2, pure urea-formaldehyde resin UF without APDKC flame retardant.

[0060] SEM tests were performed on the NW in Comparative Example 1 after complete combustion. The test results are as follows: Figure 7 As shown, the char layer after NW combustion is almost completely broken, referred to as a broken structure. Compared with Example 1, it can be seen that coating with UF-APDKC can form a dense residual char layer, thus improving flame retardant performance.

[0061] Comparative Example 1: Vertical Combustion Test Results Figure 5 As shown in Table 2, if the open flame time after the first ignition of the NW is greater than 60 seconds and there is dripping, it indicates that the NW has not passed the UL-94 V-0 rating. A comparison with Example 1 shows that coating the NW with UF-APDKC can enable it to pass the UL-94 rating test.

[0062] The limiting oxygen index test results of Comparative Example 1 are shown in Table 2. The limiting oxygen index of NW is 20.3%. Compared with Example 1, it can be seen that coating with UF-APDKC can increase the limiting oxygen index from 20.0% to 33.5%.

[0063] The cone calorimetry test results of NW in Comparative Example 1 are as follows: Figure 6 As shown, the HRR of NW is 232.22 kW / m². 2 Compared with Example 1, it can be seen that coating with UF-APDKC can reduce the HRR by 89.3%, that is, significantly reduce the heat release rate, thereby significantly improving flame retardancy.

[0064] The TG test results of UF in Comparative Example 2 are as follows Figure 3 As shown in Table 1, the temperature at which UF decomposes to a mass of 5% is 204.2℃, the temperature at which the maximum decomposition rate is reached is 300.32℃, and the char residue at 800℃ is 10.00 wt.%. Compared with Example 1, it can be seen that adding UF-APDKC can increase the char residue from 10.00 wt.% to 31.43 wt.%, that is, adding UF-APDKC can significantly increase the char residue.

[0065] SEM tests were performed on the UF surface in Comparative Example 2. The test results are as follows: Figure 8 As shown, the char layer formed after combustion by UF exhibits severe fragmentation, i.e., a fragmented structure. Compared with Comparative Example 1, it can be seen that although coating with UF can slightly reduce the fragmentation of the char layer and slightly improve flame retardancy, the resulting char layer is not substantially different from that of NW, and remains a fragmented structure. Compared with Example 1, it can be seen that adding APDKC flame retardant can transform the char layer from a fragmented structure to a dense structure.

[0066] The vertical combustion test results of UF in Comparative Example 2 are as follows: Figure 5 As shown in Table 2, the open flame time after the first ignition of UF was 14.2 s, and the open flame and flameless burning time after the second ignition was 37.0 s, with no dripping, indicating that UF passed the UL-94 V-1 rating. Compared with Comparative Example 1, it can be seen that coating with UF can improve the NW rating from none to UL-94 V-1, meaning that coating with UF can improve flame retardancy; compared with Example 1, it can be seen that adding APDKC flame retardant can improve the UL-94 rating from V-1 to V-0.

[0067] The limiting oxygen index (LOI) test results of UF in Comparative Example 2 are shown in Table 2. The LIO of UF is 27.8%. Compared with Comparative Example 1, it can be seen that coating with UF can increase the LIO from 20.0% to 27.8%, that is, coating with UF can improve flame retardancy. Compared with Example 1, it can be seen that adding APDKC flame retardant can increase the LIO from 27.8% to 33.5%.

[0068] The cone calorimetry (HRR) test results of UF in Comparative Example 2 are as follows: Figure 6 As shown, the HRR of UF reaches 87.22 kW / m². 2 Compared with Comparative Example 1, it can be seen that the HRR reduction achieved by coating with UF is 62.44%, that is, reducing the heat release rate and improving flame retardancy; compared with Example 1, it can be seen that adding APDKC flame retardant can further reduce the HRR by 71.56%.

[0069] As can be seen from Examples 1, 1, and 2, the reason why coating with UF improves flame retardancy is that UF itself has higher flame retardancy than pure wood. However, adding only UF can only obtain a very low amount of char residue, and the formed char residue layer is in a broken state, i.e., of poor quality, which leads to the inability to effectively improve flame retardancy. On the other hand, adding APDKC flame retardant can significantly increase the amount of char residue and form a dense char residue layer at the same time, thus achieving a significant improvement in flame retardancy. In addition, the addition of nano CaCO3 also effectively improves flame retardancy.

[0070] The following conclusions can be drawn from Examples 1, 1, and 2: Coating with UF-APDKC flame-retardant resin can achieve good flame-retardant performance; the addition of UF-APDKC flame retardant has a substantial impact on char residue, char layer quality, and HRR. Its flame-retardant mechanism is that the addition of APDKC, along with the synergistic effects of APP, ADP, β-cyclodextrin, and nano-CaCO3, promotes the formation of char residue in the matrix, thereby increasing char residue and forming a dense char layer, reducing HRR, and thus improving flame-retardant performance.

[0071] Therefore, this invention employs the above-mentioned PN-Si-Ca flame-retardant composite coating, its preparation method, and its application to improve the flame-retardant performance of PN-Si flame-retardant urea-formaldehyde resin composite coatings as wood flame-retardant coatings. The reaction conditions are mild and free of hazardous chemicals. While increasing the char content of the matrix with ammonium polyphosphate, diammonium hydrogen phosphate, 3-aminopropyltriethoxysilane, β-cyclodextrin, and nano-CaCO3, a significant improvement in flame-retardant performance is simultaneously achieved. Specifically, the thermal decomposition of ammonium polyphosphate and diammonium hydrogen phosphate into pyrophosphate not only promotes matrix carbonization but also increases coke formation and improves the char content.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A flame-retardant composite coating based on PN-Si-Ca, characterized in that, The preparation method of the flame-retardant composite coating based on PN-Si-Ca includes the following steps: Step 1, Preparation of PN-Si-Ca flame retardant: Ammonium polyphosphate was heated to 65℃ and stirred for 30 min, diammonium hydrogen phosphate was added and stirred for 30 min, and then stirred in a water bath to obtain an APD solution. 3-aminopropyltriethoxysilane, β-cyclodextrin, and nano-CaCO3 were placed in the APD solution in sequence, and dimethyl silicone oil and polyacrylamide were added as additives. The reaction was stirred to obtain an APDKC solution. After the reaction was completed, the obtained product was freeze-dried and ground into powder to obtain the PN-Si-Ca flame retardant. The mass ratio of ammonium polyphosphate, diammonium hydrogen phosphate, 3-aminopropyltriethoxysilane, β-cyclodextrin, and nano-CaCO3 was 5:1:1:2:

1. Step 2, Preparation of PN-Si-Ca flame-retardant composite coating: Sodium hydroxide solution is added to formaldehyde solution to adjust the pH value of the solution, and then nano-CaCO3 is added and stirred to obtain a suspension solution. Urea and PN-Si-Ca flame retardant are added in three stages to prepare the PN-Si-Ca flame-retardant composite coating.

2. The flame-retardant composite coating based on PN-Si-Ca according to claim 1, characterized in that: The temperature at which the PN-Si-Ca flame-retardant composite coating decomposes to 5% by mass is 198.23±0.7℃, the temperature at which the maximum decomposition rate is reached is 345.30±0.6℃, and the residual char content at 800.00℃ is 31.43±0.5wt.%.

3. The flame-retardant composite coating based on PN-Si-Ca according to claim 1, characterized in that: In step 1, the stirring temperature for water bath stirring is 90℃, the stirring speed is 300-600 rpm, and the water bath stirring time is 2.5h; the stirring temperature for stirring reaction is 90℃, and the stirring speed is 300-600 rpm; the freezing temperature for freezing drying is -20℃, and the drying time is 42h.

4. The flame-retardant composite coating based on PN-Si-Ca according to claim 1, characterized in that: In step 2, the mass ratio of the total amount of PN-Si-Ca flame retardant, formaldehyde, urea, and nano-CaCO3 added is 2:100:55:

10.

5. The flame-retardant composite coating based on PN-Si-Ca according to claim 1, characterized in that: In step 2, the pH of the solution is adjusted to 8.0-8.

5.

6. The flame-retardant composite coating based on PN-Si-Ca according to claim 1, characterized in that: In step 2, the conditions for adding urea are: stirring speed of 300-600 rpm and reaction temperature of 90℃.

7. The application of the PN-Si-Ca-based flame-retardant composite coating according to any one of claims 1-6, characterized in that: It is used in the preparation of flame-retardant coatings for wood.

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