A method for preparing a light-curable flame-retardant transparent coating based on linear polyphosphazene and its application in wood products

Abstract

The present invention discloses a method for preparing a photocurable flame-retardant transparent coating based on linear polyphosphazene and its application in wood products. The present invention adjusts the molar ratio of flame-retardant group DOPO derivatives and monoalcohol / phenol with photocurable double bonds, synthesizes a series of polyphosphazene resins with linear polydichlorophosphazene through substitution reaction, and studies the influence of the ratio of monoalcohol / phenol with double bonds to DOPO derivatives on the state of the resin, photocurability, transparency, carbonization and compatibility with epoxy acrylic resin. The present invention improves the transparency and flame retardancy of the coating by regulating the functional groups, prolongs the ignition time of the coating, and also reduces the peak value of the heat release rate and the total heat release of the coating. This flame retardant modification technology is beneficial to prolong the protection time of the coating on wood, hinder heat transfer, and realize efficient and long-lasting flame retardancy of wood.

Description

Technical Field

[0001] The invention relates to a preparation method of a linear polyphosphazene-based light-curable flame-retardant transparent coating and application thereof in wooden products, belonging to the technical field of wood flame retardancy. Background Art

[0002] Wood is a renewable, environmentally friendly, non-toxic natural polymer material with unique aesthetic properties, high strength, superior processing performance and low cost. However, wood is very hard. If it is used as furniture and is directly exposed to the outside without protection, it is easy to be scratched or worn. At the same time, the stability of wood is easily affected by air humidity. Unprotected wood is prone to deformation due to the infiltration of external moisture and the evaporation of internal moisture. Third, logs are directly exposed to the air and are easily corroded and oxidized and discolored, losing their fresh wood color. Therefore, it is necessary to use coatings to protect wood. At present, traditional wood coatings include polyurethane, acrylic resin, epoxy resin, etc. However, the high flammability of resins greatly limits their application on wood. Therefore, it is very necessary to improve the flame retardant properties of wood product coatings.

[0003] Phosphorus / nitrogen-containing photocurable coatings have attracted extensive attention in recent years due to their flame retardancy in both the condensed phase and the gas phase. In the condensed phase, phosphorus-containing flame retardants significantly hinder the transfer of heat and combustible debris between the underlying polymer and the combustion zone by promoting the formation of charcoal as a physical barrier against heat and mass. In the gas phase, phosphorus-containing flame retardants decompose at high temperatures, releasing many phosphorus-containing free radicals that can capture highly active H and HO radicals, thereby improving flame retardancy. Nitrogen-containing groups decompose during combustion to release inert nitrogen-containing gases, which strengthen the gas phase mechanism by diluting the concentration of oxygen and fuel. Therefore, by rationally designing the chemical structure of photocurable coatings and regulating the flame retardant mechanism of phosphorus / nitrogen-containing photocurable resins, it is expected to develop flame-retardant and transparent wood coatings.

[0004] Linear polyphosphazene compounds are a class of compounds whose main chains are composed of alternating phosphorus atoms and nitrogen atoms. The skeleton structure of phosphorus and nitrogen and the organic side groups attached to the phosphorus atoms give phosphazene compounds unique physical and chemical properties. Therefore, polyphosphazenes have become the most promising class of materials and are used to develop halogen-free, high-performance linear polyphosphazene photocurable flame retardant coatings. However, although the tunability of the side groups of linear polydichlorophosphazene gives polyphosphazene materials rich properties, there is currently little research on regulating polyphosphazenes substituted with different functional groups, especially for wood coatings. Summary of the invention

[0005] The present invention aims to solve the high flammability of epoxy acrylic wood coatings and explore the influence of linear polyphosphazene side group regulation on flame retardancy, transparency, photocurability and charring. A preparation method of a photocurable flame retardant transparent coating based on linear polyphosphazene and its application in wood products are proposed. The technical problem to be solved by the present invention is to construct a transparent flame retardant photocurable linear polyphosphazene coating on the wood surface without destroying the natural aesthetic texture of the wood surface.

[0006] The present invention synthesizes an intrinsic flame-retardant linear polyphosphazene resin with excellent flame-retardant properties through molecular design and structural regulation. The effect of the regulation of the side groups on the viscosity, photocurability, charring property and compatibility with epoxy acrylic resin of the polyphosphazene resin is explored.

[0007] The method for preparing the linear polyphosphazene-based light-curable flame-retardant transparent coating comprises mixing epoxy acrylic resin, intrinsic flame-retardant linear polyphosphazene resin, diluent and photoinitiator according to a proportion, and stirring until the system is a uniform transparent solution.

[0008] Calculated by weight, the added amount of each component is: 50-80 parts of epoxy acrylic resin, 20-40 parts of linear polyphosphazene resin, 15-20 parts of diluent, and 3-5 parts of photoinitiator.

[0009] The photoinitiator is one of 2-hydroxy-2-methyl-1-phenyl-1-propanone (photoinitiator 1173) and 1-hydroxycyclohexyl phenyl ketone (photoinitiator 184).

[0010] The diluent is selected from one or more of hydroxyethyl methacrylate, n-butyl acrylate, isooctyl acrylate, isodecyl acrylate, lauryl acrylate, styrene, and vinyl acetate.

[0011] The linear polyphosphazene resin is prepared by a method comprising the following steps:

[0012] Step 1: Synthesize linear polydichlorophosphazene (PDCP) by solution polymerization. Add 30g hexachlorocyclotriphosphazene, 0.3g aminosulfonic acid, 0.03g calcium sulfate dihydrate and 30mL 1,2,4-trichlorobenzene into a 50mL three-necked flask, heat to 210°C in a nitrogen atmosphere and react for 3-4 hours; stop the reaction when the viscosity of the system increases, precipitate PDCP with petroleum ether, and dissolve the obtained PDCP in tetrahydrofuran for later use.

[0013] Step 2: Rapid preparation of DOPO-based derivatives in one step by addition reaction. DOPO (162.00 g, 0.75 mol) and 200 mL of benzene were mixed, heated to 70°C under nitrogen protection, and 27 g of paraformaldehyde was added to the system in batches within 4 hours; after the addition was completed, the mixture was stirred at 70°C for 8 hours; after the reaction was completed, the mixture was filtered while hot, and the obtained solid was vacuum dried at 80°C for 8 hours to obtain DOPOOH, 181 g, with a product yield of 98.0%.

[0014] Step 3: The DOPOOH prepared in step 2 is mixed with a monoalcohol / phenol containing a double bond in tetrahydrofuran, and reacted with the PDCP prepared in step 1 at 50-80° C. for 24 hours in the presence of an acid binding agent; after the reaction, the impurity salt is filtered out, the filtered solution is precipitated with a solvent, and the product is washed with water for 3-5 times, and vacuum dried for 24 hours to obtain a linear polyphosphazene resin.

[0015] The monoalcohol / phenol is selected from one of hydroxyethyl acrylate, eugenol, and 2-ethyleneoxyethanol. The molar ratio of DOPOOH to the monoalcohol / phenol is 3:1 to 1:3, and the molar ratio of PDCP to DOPOOH and the monoalcohol / phenol is 1.5:1.

[0016] The acid binding agent is selected from one of triethylamine, N,N-diisopropylethylamine, pyridine, potassium carbonate and potassium hydroxide.

[0017] The solvent is selected from one of n-hexane, n-heptane and petroleum ether.

[0018] The application method of the light-curable flame-retardant transparent coating based on linear polyphosphazene of the present invention is to coat the coating at a temperature of 5 g / dm 3 Apply to the wood surface and leave at room temperature for 30 minutes to allow the coating to level, then use a 1000W UV curing lamp to irradiate at a distance of 30cm for 3 minutes.

[0019] The present invention synthesizes a series of polyphosphazene resins by regulating the molar ratio of flame retardant group DOPO derivatives and monoalcohol / phenol with photocurable double bonds, and synthesizes the monoalcohol / phenol with linear polydichlorophosphazene through substitution reaction, and studies the influence of the ratio of monoalcohol / phenol with double bonds to DOPO derivatives on the state, photocurability, transparency, carbonization and compatibility with epoxy acrylic resin of the resin. The results show that as the ratio increases, the viscosity of the resin decreases, the photocurability increases, the compatibility with epoxy acrylic resin improves, and the transparency is better. By changing the ratio of polyphosphazene resin to epoxy acrylic resin, different ultraviolet curing solutions are prepared, and evenly coated on the surface of wood, and finally co-cured under ultraviolet light to form a transparent flame retardant coating. The present invention proposes the preparation and application of a photocurable flame retardant transparent wood coating based on linear polyphosphazene, and improves the transparency, compatibility with epoxy acrylic resin and photocurability of the coating by regulating the functional group. The synthesized resin A2 is co-cured with epoxy acrylic resin to form a wood coating, which prolongs the ignition time of the coating and reduces the peak heat release rate and total heat release of the coating. This flame retardant modification technology is conducive to prolonging the protection time of the coating on the wood, hindering heat transfer, and achieving efficient and long-lasting flame retardancy of the wood.

[0020] Compared with the existing technology, the beneficial effects of the present invention are embodied in:

[0021] 1. The present invention successfully prepared an intrinsically flame-retardant and transparent linear polyphosphazene photocurable resin through molecular design and structural regulation; and studied the effects of linear polyphosphazene photocurable resins with different side group ratios on viscosity, photocurability, transparency, charring and compatibility with epoxy acrylic resin.

[0022] 2. The intrinsic flame-retardant and transparent linear polyphosphazene photocurable resin prepared by the present invention has the characteristics of good compatibility with epoxy acrylic resin, low viscosity, photocurability, good charring, etc., and can be applied to the fire protection of wood and other surfaces. The preparation process of the present invention is simple and widely used. At the same time, the curing speed is fast, which can effectively improve production efficiency and save energy; the linear polyphosphazene photocurable coating of the present invention can be combined with epoxy acrylic resin to prepare a halogen-free, low-smoke, low-toxic, transparent and excellent flame-retardant coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is the synthesis route and structural formula of the linear polyphosphazene photocurable resin A2 in Example 1.

[0024] Figure 2 is the NMR spectrum of the reactive phosphorus-containing flame retardant in Example 1. 31 PNMR;(cd)DOPO 1 HNMR and 31PNMR; (ef)DOPOOH 1 H NMR and 31 PNMR; (gh)PDCPDX(A2) 1 HNMR and 31 PNMR.

[0025] Figure 3 These are the states and colors of the polyphosphazene products with different proportions of side groups in Example 1.

[0026] Figure 4 The transparency test of the coating in Example 1: (left) untreated wood, (right) EA-5.0.

[0027] Figure 5 1 and 2 are the heat release rate curve (a), total heat release curve (b) and thermal gravimetric curve (c) of the cone calorimetry test of the coating in Example 1.

[0028] Figure 6 The thermal stability of (a) PDCPDX (A2) in Example 1, (b) the TGA curve and DTG curve (c) of the thermal stability of the coating in Example 1. DETAILED DESCRIPTION

[0029] In order to further illustrate the technical solution of the present invention, the preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention. Based on the examples in the present invention, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention.

[0030] The raw materials and tests in Examples 1-7 were funded by the National Key R&D Program (No. 2022YFC3003100).

[0031] Embodiment 1:

[0032] (1) Synthesize linear polydichlorophosphazene (PDCP) by solution polymerization. Put 30g hexachlorocyclotriphosphazene, 0.3g aminosulfonic acid, 0.03g calcium sulfate dihydrate and 30ml 1,2,4-trichlorobenzene into a 150mL three-necked flask equipped with two gas guides and a condenser. Pass nitrogen, raise the temperature to 210°C within a certain period of time, remove nitrogen, and react at this temperature for 3-4 hours. When the viscosity of the system increases, stop the reaction, precipitate PDCP with petroleum ether, and dissolve the obtained PDCP in tetrahydrofuran for later use.

[0033] (2) DOPO-based derivatives were prepared quickly and efficiently in one step by addition reaction. DOPO (162.00 g, 0.75 mol) and 200 mL of benzene were placed in a three-necked flask equipped with a thermometer, a magnetic stirrer and a spherical condenser. Under nitrogen protection, the system temperature was slowly raised to 70°C, and 27 g of paraformaldehyde was added to the three-necked flask in batches over 4 hours. After the addition was completed, the reaction was further stirred at 70°C for 8 hours. After the reaction was completed, the mixture was filtered while hot, and the obtained solid was vacuum dried at 80°C for 8 hours. Finally, 181 g of product was obtained with a product yield of 98.0%, and the product was named DOPOOH.

[0034] (3) The DOPOOH synthesized in the second step and eugenol are put into a three-necked flask at a molar ratio of 3:1, 1:1, and 1:3, and reacted with PDCP at 50-80°C for 24 hours in the presence of triethylamine, an acidifying agent, using tetrahydrofuran as solvent (the molar ratio of acidifying agent: PDCP is 1.2:1, and the molar ratio of PDCP to (DOPOOH and monoalcohol / phenol) is 1.5:1). The solution after the reaction is filtered to remove impurity salts, the filtered solution is precipitated with a solvent, and the product is washed with water for 3-5 times, and finally the obtained product is dried in a vacuum oven for 24 hours. The synthesized resin products are named A1, A2 and A3 respectively. The states and colors of the three synthesized resins are shown in Figure 3 As the number of benzene ring groups of A1, A2, and A3 decreases, the viscosity of the polymer decreases continuously.

[0035] Embodiment 2:

[0036] (1) Synthesis of linear polydichlorophosphazene (PDCP) by solution polymerization. 30 g of hexachlorocyclotriphosphazene, 0.3 g of aminosulfonic acid, 0.03 g of calcium sulfate dihydrate and 30 ml of 1,2,4-trichlorobenzene were placed in a 150 ml three-necked flask equipped with two gas guides and a condenser. Nitrogen was introduced, the temperature was raised to 210°C within a certain period of time, the nitrogen was removed, and the reaction was carried out at this temperature for 3-4 hours. When the viscosity of the system increased, the reaction was stopped, PDCP was precipitated with petroleum ether, and the resulting product was dissolved in tetrahydrofuran for later use.

[0037] (2) DOPO-based derivatives were prepared quickly and efficiently in one step by addition reaction. DOPO (162.00 g, 0.75 mol) and 200 ml of benzene were placed in a three-necked flask equipped with a thermometer, a magnetic stirrer and a spherical condenser. Under nitrogen protection, the system temperature was slowly raised to 70°C, and 27 g of paraformaldehyde was added to the three-necked flask in batches over 4 hours. After the addition was completed, the reaction was further stirred at 70°C for 8 hours. After the reaction was completed, the mixture was filtered while hot, and the obtained solid was vacuum dried at 80°C for 8 hours. Finally, 181 g of product was obtained with a product yield of 98.0%, and the product was named DOPOOH.

[0038] (3) The DOPOOH synthesized in the second step and hydroxyethyl acrylate were added into a three-necked flask at a molar ratio of 3:1, 1:1, and 1:3, and reacted with PDCP at 50-80°C for 24 hours in the presence of an acidifying agent using tetrahydrofuran as a solvent. The solution after the reaction was filtered to remove impurity salts, the filtered solution was precipitated with a solvent, and the product was washed with water for 3-5 times, and finally the obtained product was dried in a vacuum oven for 24 hours. The synthesized resin products were named B1, B2, and B3, respectively.

[0039] Example 3: Photocurability of polyphosphazene resins with different side group ratios in Example 1

[0040] The detailed test method and formula for the photocurable ability of the polyphosphazene resin with different proportions of side groups in Example 1 are shown in Table 1. The specific operation is as follows: the oligomer epoxy acrylic resin, the intrinsic flame retardant polyphosphazene resins A1, A2 and A3 synthesized in Example 1, the diluent hydroxyethyl acrylate and the photoinitiator 1173 are placed in a beaker according to the ingredient list 1. At room temperature, stir on a magnetic stirrer until the system is uniform and transparent. Use a 1000W ultraviolet curing lamp to irradiate, the irradiation distance is 30cm, and the time is 3min. Grind the obtained cured product, use a Soxhlet extractor to extract with ethanol for 24h, and determine the gel content of the cured resin by the weight change of the sample after extraction. With the increase of double bond content, the photocurable ability of the polyphosphazene resin increases.

[0041] Example 4: Compatibility of polyphosphazene resin with different side group ratios in Example 1 and epoxy acrylic resin

[0042] The detailed test method and formula of the compatibility of the polyphosphazene resin with different side group ratios and the epoxy acrylic resin in Example 1 are shown in Table 2. The specific operation is as follows: 25g of oligomer epoxy acrylic resin is taken, and A1, A2, and A3 are added respectively, and the epoxy acrylic resin is dissolved in the epoxy acrylic resin at room temperature by means of stirring and ultrasound, and the dissolved product is left to stand for a week, the state of the mixture is observed, and the precipitate after filtration is weighed. Table 2 shows that as the double bond content increases, the compatibility of the polyphosphazene resin and the epoxy acrylic resin increases.

[0043] Example 5: Preparation and application of a light-curable flame-retardant transparent wood coating based on linear polyphosphazene

[0044] The detailed preparation method of the light-curable flame-retardant transparent coating based on linear polyphosphazene is as follows: First, the oligomer epoxy acrylic resin, the intrinsic flame-retardant polyphosphazene resin A2 synthesized in Example 1, the diluent hydroxyethyl acrylate and the photoinitiator 1173 are placed in a beaker according to the ingredient table 1. At room temperature, stir on a magnetic stirrer until the system is uniform, transparent and has a viscosity suitable for coating.3 Apply to the wood surface and leave at room temperature for 30 minutes to allow the coating to level out. Use a 1000W UV curing lamp to irradiate at a distance of 30cm for 3 minutes. Use electronic photos to record the transparency of the coating. Figure 4 It can be seen that the coated wood has good transparency and the wood surface is more glossy.

[0045] Example 6: Flame retardant properties of a photocurable flame retardant transparent coating based on linear polyphosphazene and its application

[0046] The sample was prepared according to the method shown in Example 5, stirred and mixed evenly, and then applied on a piece of wood with a size of 100 mm*100 mm*4 mm at a rate of 5 g / dm 3 Apply to the wood surface and leave at room temperature for 30 minutes to allow the coating to level out. Use a 1000W UV curing lamp to irradiate at a distance of 30cm for 3 minutes. Use a cone calorimeter to test the flame retardant properties of the coating. Figure 5 The results show that the coating with epoxy acrylic resin has a very high heat release rate, with the highest heat release reaching 438KJ / m 2 With the co-curing of A2, the heat release rate of the coating continued to decrease. The heat release rate of EA-12.5 was 50.3% lower than that of EA-0. At the same time, the total heat release rate was also reduced by 58.4%, and the carbon residue rate at 800 °C was increased by 28.5%.

[0047] Example 7: Preparation and application of thermal stability of light-curable flame-retardant transparent wood coating based on linear polyphosphazene

[0048] The sample was prepared according to the method shown in Example 5. After being stirred and mixed evenly, it was coated on a glass plate and left for 5 minutes to fully level. A 1000W UV curing lamp was used to irradiate the sample at a distance of 30 cm for 3 minutes. The coating was ground into powder and the thermal stability of the coating was tested using a thermogravimetric analyzer. Figure 6 As shown, the carbon residue rate of the photocurable resin A2 synthesized in Case 1 is 28.7% at 800°C. At the same time, the carbon residue rate of the wood coating increases with the introduction of PDCPDX (A2), and the maximum thermal decomposition temperature is advanced with the introduction of A2.

[0049] Table 1. Photocuring ability of polyphosphazenes with different side group ratios

[0050]

[0051] Table 2. Compatibility of polyphosphazene with different side group ratios and epoxy acrylic resin

[0052]

[0053] Table 3. Example 3 UV-curable coating formulation

[0054]

Claims

1. A method for preparing a photocurable flame-retardant transparent coating based on linear polyphosphazene, characterized in that: Epoxy acrylic resin, intrinsically flame-retardant linear polyphosphazene resin, diluent and photoinitiator are mixed according to the proportion, and stirred until the system is a uniform transparent solution; the addition amount of each component is: 50-80 parts of epoxy acrylic resin, 20-40 parts of intrinsically flame-retardant linear polyphosphazene resin, 15-20 parts of diluent, and 3-5 parts of photoinitiator in parts by mass; The intrinsically flame-retardant linear polyphosphazene resin is prepared by a method comprising the following steps: Step 1: adding hexachlorocyclotriphosphazene, aminosulfonic acid, calcium sulfate dihydrate and 1,2,4-trichlorobenzene into a reactor, heating to 210° C. in a nitrogen atmosphere for reaction for 3-4 hours; stopping the reaction when the viscosity of the system increases, precipitating the synthesized linear polydichlorophosphazene with petroleum ether, and dissolving it in tetrahydrofuran for later use; Step 2: DOPO and benzene are mixed, and the temperature is raised to 70°C under nitrogen protection, and paraformaldehyde is added to the system in batches within 4 hours; after the addition is completed, the mixture is stirred and reacted at 70°C; after the reaction is completed, the mixture is filtered while hot, and the obtained solid is vacuum dried at 80°C to obtain DOPOOH; Step 3: The DOPOOH prepared in step 2 and the monoalcohol / phenol containing a double bond are mixed in tetrahydrofuran, and reacted with the linear polydichlorophosphazene prepared in step 1 at 50-80° C. in the presence of an acid binding agent; after the reaction is completed, the impurity salt is filtered out, the filtered solution is precipitated with a solvent, and the product is washed with water and vacuum dried to obtain an intrinsically flame-retardant linear polyphosphazene resin.

2. The preparation method according to claim 1, characterized in that: The photoinitiator is one of 2-hydroxy-2-methyl-1-phenyl-1-propanone and 1-hydroxycyclohexyl phenyl ketone.

3. The preparation method according to claim 1, characterized in that: The diluent is selected from one or more of hydroxyethyl methacrylate, n-butyl acrylate, isooctyl acrylate, isodecyl acrylate, lauryl acrylate, styrene, and vinyl acetate.

4. The preparation method according to claim 1, characterized in that: The monoalcohol / phenol containing a double bond is selected from one of hydroxyethyl acrylate, eugenol and 2-ethyleneoxyethanol.

5. The preparation method according to claim 1, characterized in that: The molar ratio of DOPOOH to the monoalcohol / phenol containing a double bond is 3:1 to 1:3; the molar ratio of the linear polydichlorophosphazene to the total molar ratio of DOPOOH and the monoalcohol / phenol containing a double bond is 1.5:

1.

6. The preparation method according to claim 1, characterized in that: The solvent used for precipitation is selected from one of n-hexane, n-heptane and petroleum ether.

7. Application of the photocurable flame retardant transparent coating prepared by the preparation method according to any one of claims 1 to 6 in wood products, characterized in that: The coating was mixed at 5 g / dm 3 Apply to the wood surface and leave at room temperature for 30 minutes to allow the coating to level, then use a 1000W UV curing lamp to irradiate at a distance of 30cm for 3 minutes.

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