A double-layer composite sealing and protecting material for iron cultural relics protection

Abstract

The application relates to a high polymer material, in particular to a double-layer composite sealing and protecting material for iron cultural relics, which comprises a bottom sealing and protecting layer and a surface layer composite sealing and protecting layer; the bottom sealing and protecting layer is a silane solution containing an inhibitor, and the surface layer composite sealing and protecting layer is modified hexagonal boron nitride / silicone-terminated modified water-based polyurethane (h-BN / WPU-Si); the application is scientific and reasonable, raw materials are rich, green and environment-friendly, and easy to produce and prepare; the double-layer sealing and protecting material can be applied to the protection field of iron cultural relics, plays a role in isolating external harmful substances, makes the iron cultural relics have excellent water resistance and corrosion resistance, and meanwhile does not affect the appearance of the iron cultural relics, thereby providing a new idea for the surface sealing and protecting of the iron cultural relics.

Description

TECHNICAL FIELD

[0001] The present application relates to high molecular materials, in particular to a double-layer composite protective material for iron cultural relics. BACKGROUND

[0002] The use of iron cultural relics promoted the development of agriculture, handicraft and commerce, thus making human society step into the advanced iron cultural relics era. However, the quantity of iron cultural relics commonly seen by ordinary people is far less than that of bronze cultural relics, which is because in the natural environment, iron is relatively active and has poor chemical stability compared with copper, lead and other metals, thus being easily corroded, and the quantity of the remaining iron cultural relics is not much. Therefore, different methods are adopted for scientific protection of the unearthed iron cultural relics according to the situation, generally including cleaning, rust removal, desalination, corrosion inhibition and other methods, but finally a protective layer is coated on the surface to prevent the iron cultural relics from being further corroded by harmful substances in the environment such as water and acidic gas. Due to the special requirements of iron cultural relics protection, the protective film formed on the surface of the iron cultural relics should be colorless and transparent, the coating material should have strong adhesion, can prevent the corrosion of the external environment, and the processing technology should be simple, etc. Therefore, the research work of cultural relics protection is important and arduous, and it is necessary to solve the technical problem of researching a double-layer composite protective material for iron cultural relics. SUMMARY

[0003] In view of the above situation, in order to overcome the defects of the prior art, the purpose of the present application is to provide a double-layer composite protective material for iron cultural relics, which can not only play a role in isolating external harmful substances, but also make the iron cultural relics have excellent water resistance and corrosion resistance, and at the same time will not affect the appearance of the iron cultural relics.

[0004] The technical solution solved by the present application is a double-layer composite protective material for iron cultural relics, comprising a bottom protective layer and a surface composite protective layer; the bottom protective layer is a silane solution containing corrosion inhibitor, and the surface composite protective layer is modified hexagonal boron nitride / siloxane end-capped modified waterborne polyurethane (h-BN / WPU-Si).

[0005] The silane solution containing corrosion inhibitor is prepared by the following method:

[0006] γ-aminopropyltriethoxysilane (KH550): ethanol: deionized water is stirred at 25℃ for 8h at a volume ratio of 5:20:75, and then 2wt% phytic acid is dissolved in the above solution to obtain the silane solution containing corrosion inhibitor;

[0007] The modified hexagonal boron nitride / siloxane end-capped modified waterborne polyurethane (h-BN / WPU-Si) is prepared by the following method:

[0008] 1) Preparation of hydroxylated siloxane (KP):

[0009] Under nitrogen protection and magnetic stirring, equal-molar γ-aminopropyl triethoxysilane (KH550) and propylene carbonate (PC) were added into a flask, the temperature was raised to 40-100°C, and the reaction was carried out for 4-12 hours. The content of primary amino group in the molecular structure of the reactant γ-aminopropyl triethoxysilane was determined by the salicylaldehyde-sodium methoxide method to monitor the reaction of the reactant KH550. The infrared was used to monitor the characteristic absorption peak of C=O at 1800 cm-1 of the reactant propylene carbonate every hour. When the characteristic absorption peak of C=O disappeared, the reaction was terminated to obtain the product, which was recorded as KP;

[0010] 2) Preparation of the siloxane-terminated modified waterborne polyurethane emulsion (WPU-Si):

[0011] First, polycarbonate diol (PCDL-1000) and castor oil (CO) were vacuumed to remove water at 110-130°C for 2-3 hours, dimethylol propionic acid (DMPA) was dried at 80-100°C for 2 hours, and acetone was dehydrated in 4A molecular sieves for one week. Isophorone diisocyanate (IPDI), polycarbonate diol (PCDL-1000), and castor oil (CO) and 1-2 drops of catalyst dibutyltin dilaurate (DBTDL) were added into a three-necked flask equipped with a reflux condenser and a mechanical stirrer. The reaction was carried out at 70-90°C for 2-3 hours. Then, the hydrophilic chain extender dimethylol propionic acid (DMPA) was added, and the temperature was reduced to 60-90°C for 1.5-3 hours. Subsequently, 1,4-butanediol (BDO) was added to make the molar ratio of NCO:OH 1.1-1.5, and the reaction was carried out for 1-2 hours. The temperature was reduced to 50-60°C, and KP was added. Acetone was added drop by drop. When the temperature of the system was reduced to 30-40°C, the neutralizer triethylamine (TEA) in an amount equal to that of DMPA was directly added into the flask. The carboxyl groups in the reaction system were neutralized by stirring for 30-50 minutes. Then, deionized water was added into the reaction system for high-speed emulsification, so that the total mass of the reactants accounted for 30% of the total mass of the emulsion. Finally, the WPU-Si emulsion with a siloxane content of 0-5% and a solid content of 30 wt% was obtained by removing acetone from the system under reduced pressure and vacuum. The emulsion was recorded as WPU-Si.

[0012] The molar ratio of isocyanate group (NCO) in isophorone diisocyanate (IPDI) to hydroxyl group (OH) in polycarbonate diol (PCDL-1000) and castor oil (CO) was 2-4 (wherein the molar ratio of hydroxyl groups in PCDL-1000 and CO was 7:3).

[0013] The mass of acetone added was 40% of the total mass of the reactants to reduce the viscosity and facilitate stirring and reaction.

[0014] The hydrophilic chain extender dimethylol propionic acid (DMPA) is added in an amount such that its mass fraction is 4.5-6.5wt%, the mass fraction of the hydrophilic chain extender dimethylol propionic acid (DMPA) to the mass of the total reactants;

[0015] The KP is added in an amount such that its mass fraction is 0-5wt%, the mass fraction of the KP to the mass of the total reactants;

[0016] 3) Preparation of modified hexagonal boron nitride (h-BN)

[0017] The h-BN powder is weighed and dissolved in isopropyl alcohol and added to a single-necked round-bottom flask, stirred at 60°C for 24h, treated with a low-power ultrasonic cleaning machine for 20h, and then placed at room temperature for 48h, followed by centrifugation at 3000r / min for 15min. The h-BN nanoparticles with good dispersibility form a suspension in the upper layer of the centrifuge tube. Two-thirds of the volume of the upper layer suspension is taken out with a dropper to obtain the h-BN suspension. The h-BN suspension is then centrifuged at high speed, and the supernatant is discarded. The h-BN nanosheets with fewer layers are obtained after drying at 60°C for 12h. The h-BN nanosheets are dissolved in a 5mol / L NaOH solution, heated and stirred at 120°C for 24h to obtain a hydroxylated h-BN mixture. The mixture is filtered, washed with deionized water until neutral, and dried in an oven at 80°C to obtain hydroxylated h-BN nanosheets. Then, the hydroxylated h-BN nanosheets, deionized water, KH550, and ethanol are mixed in a beaker, ultrasonically treated for 60min, and stirred at 60°C for 8h. The solution is then centrifuged for 10min, washed with ethanol and deionized water to remove excess KH550, and freeze-dried for 24h to obtain modified hexagonal boron nitride (h-BN) nanosheets.

[0018] The weight / volume ratio of the h-BN powder, isopropyl alcohol, hydroxylated h-BN nanosheets, deionized water, KH550, and ethanol is 2-3:100:0.5:4:10-20:30-50, where the weight is measured in grams and the volume is measured in milliliters.

[0019] 4) Hexagonal boron nitride / silicone-terminated modified waterborne polyurethane (h-BN / WPU-Si) composite material

[0020] The modified h-BN is added to the WPU-Si and ultrasonically dispersed for 30min, so that the mass fraction of the modified h-BN is 0-1wt%, to obtain the h-BN / WPU-Si composite material.

[0021] The silane solution containing corrosion inhibitor in the bottom layer sealing material can not only firmly cover the metal surface, so that the corrosion resistance of the silane film is significantly improved, but also can increase the adhesion of the organic coating on the surface of the ironware. The h-BN / WPU-Si can enhance the mechanical properties, thermal stability, water resistance and corrosion resistance of the waterborne polyurethane coating by simultaneously introducing the hydroxylated siloxane and the modified nanoparticles. The application is scientific and reasonable, the raw materials are abundant, green and environment-friendly, and easy to produce and prepare. The double-layer sealing can be applied to the protection field of iron cultural relics, plays a role in isolating external harmful substances, makes the iron cultural relics have excellent water resistance and corrosion resistance, and at the same time does not affect the appearance of the iron cultural relics, thereby providing a new idea for the surface sealing of the iron cultural relics. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 It is a reaction mechanism diagram of the hydroxylated siloxane (KP) of the application;

[0023] Figure 2 It is a reaction mechanism diagram of the siloxane end-capped modified waterborne polyurethane (WPU-Si) of the application. DETAILED DESCRIPTION

[0024] The specific embodiments of the application are described in detail below in combination with examples and specific cases, and it should be understood that these examples are used to illustrate the application and do not limit the scope of the application.

[0025] Example 1

[0026] A double-layer composite sealing material for iron cultural relic protection, comprising a bottom sealing layer and a surface composite sealing layer; the bottom sealing layer is a silane solution containing corrosion inhibitor, and the surface composite sealing layer is a modified hexagonal boron nitride / siloxane end-capped modified waterborne polyurethane (h-BN / WPU-Si);

[0027] The silane solution containing corrosion inhibitor is prepared by the following method:

[0028] The γ-aminopropyl triethoxysilane (KH550):ethanol:deionized water is stirred at 25℃ for 8h at a volume ratio of 5:20:75, and then 2wt% phytic acid is dissolved in the above solution to obtain the silane solution containing corrosion inhibitor;

[0029] The modified hexagonal boron nitride / siloxane end-capped modified waterborne polyurethane (h-BN / WPU-Si) is prepared by the following method:

[0030] 1) Preparation of hydroxylated siloxane (KP):

[0031] Under nitrogen protection and magnetic stirring, equal-molar γ-aminopropyl triethoxysilane (KH550) and propylene carbonate (PC) were added into a flask, the temperature was raised to 40-100°C, and the reaction was carried out for 4-12 hours. The content of primary amino group in the molecular structure of the reactant γ-aminopropyl triethoxysilane was determined by the salicylaldehyde-sodium methoxide method to monitor the reaction of the reactant KH550. The characteristic absorption peak of C=O at 1800 cm-1 of the reactant propylene carbonate was monitored by infrared every hour. When the characteristic absorption peak of C=O disappeared, the reaction was terminated to obtain the product, which was recorded as KP.

[0032] 2) Preparation of a siloxane-terminated modified waterborne polyurethane emulsion (WPU-Si):

[0033] First, polycarbonate diol (PCDL-1000) and castor oil (CO) were vacuumed to remove water at 110-130°C for 2-3 hours, dimethylol propionic acid (DMPA) was dried at 80-100°C for 2 hours, and acetone was dehydrated in 4A molecular sieves for one week. Isophorone diisocyanate (IPDI), polycarbonate diol (PCDL-1000), and castor oil (CO) and 1-2 drops of catalyst dibutyltin dilaurate (DBTDL) were added into a three-necked flask equipped with a reflux condenser and a mechanical stirrer. The reaction was carried out at 70-90°C for 2-3 hours. Then, the hydrophilic chain extender dimethylol propionic acid (DMPA) was added, and the temperature was reduced to 60-90°C for 1.5-3 hours. Subsequently, 1,4-butanediol (BDO) was added to make the molar ratio of NCO:OH 1.1-1.5, and the reaction was carried out for 1-2 hours. The temperature was reduced to 50-60°C, and KP was added. The mass ratio of KP to the total mass of the reactants was 1 wt%. Acetone was added dropwise. When the temperature of the system was reduced to 30-40°C, the neutralizer triethylamine (TEA) in an amount equal to that of DMPA was directly added into the flask. The system was stirred for 30-50 minutes to neutralize the carboxyl groups in the reaction system. Then, deionized water was added into the reaction system to carry out high-speed emulsification. The total mass of the reactants accounted for 30% of the total mass of the emulsion. Finally, the acetone in the system was removed by vacuum extraction under reduced pressure to obtain a WPU-Si emulsion with a siloxane content of 1% and a solid content of 30 wt%, which was recorded as WPU-Si1.

[0034] The molar ratio of isocyanate groups (NCO) in isophorone diisocyanate (IPDI) to hydroxyl groups (OH) in polycarbonate diol (PCDL-1000) and castor oil (CO) was 2-4 (wherein the molar ratio of hydroxyl groups in PCDL-1000 to CO was 7:3).

[0035] The mass of acetone added was 40% of the total mass of the reactants to reduce the viscosity and facilitate stirring and reaction.

[0036] The amount of the hydrophilic chain extender dimethylolpropionic acid (DMPA) added is such that its mass fraction is 4.5 to 6.5 wt%, and its mass fraction is the mass of the hydrophilic chain extender dimethylolpropionic acid (DMPA) to the mass of the total reactants;

[0037] The amount of BDO is calculated by determining the final amount of NCO:OH. If the final NCO:OH = 1.2, the required amount of OH is calculated by determining the amount of NCO in isophorone diisocyanate. This is the total amount of OH in reactants PCDL, CO, DMPA, and BDO. Subtracting the amount of OH contained in PCDL, CO, and DMPA gives the amount of OH in BDO, thus allowing the calculation of the amount of BDO.

[0038] 3) Preparation of modified hexagonal boron nitride (h-BN)

[0039] Weigh 2-3g of h-BN powder and dissolve it in 100ml of isopropanol. Add the solution to a single-necked round-bottom flask and stir at 60℃ for 24 hours. After ultrasonic treatment with a low-power ultrasonic cleaner for 20 hours, place it at room temperature for 48 hours. Then, centrifuge at 3000r / min for 15 minutes. The well-dispersed h-BN nanoparticles form a suspension in the upper layer of the centrifuge tube. Use a dropper to take 2 / 3 of the volume of the upper suspension to obtain the h-BN suspension. Then, centrifuge the h-BN suspension at high speed and discard the supernatant. After drying the clear liquid at 60℃ for 12 h, h-BN nanosheets with fewer layers were obtained. The obtained h-BN nanosheets were dissolved in 5 mol / L NaOH solution and heated and stirred at 120℃ for 24 h to hydroxylate the h-BN mixture. The mixture was filtered, washed with deionized water until neutral, and dried in an oven at 80℃ to obtain hydroxylated h-BN nanosheets. Then, 0.5 g of hydroxylated h-BN nanosheets, 4 g of deionized water, 10-20 g of KH550 and 30-50 g of ethanol were mixed in a beaker, sonicated for 60 min, stirred at 60℃ for 8 h, and then centrifuged for 10 min. Excess KH550 was removed by washing with ethanol and deionized water, and the mixture was freeze-dried for 24 h to obtain modified hexagonal boron nitride (h-BN) nanosheets.

[0040] 4) Hexagonal boron nitride / siloxane-terminated modified waterborne polyurethane (h-BN / WPU-Si) composite material

[0041] Modified h-BN was added to WPU-Si1 and ultrasonically dispersed for 30 min to obtain an h-BN / WPU-Si composite material with a mass fraction of 0.2 wt%.

[0042] Example 2:

[0043] The difference between the present example and example 1 is that the amount of KP added is 2wt% of the mass of KP to the mass of the total reactants, obtaining a WPU-Si emulsion with a siloxane content of 2% and a solid content of 30wt%, denoted as WPU-Si2, adding modified h-BN to WPU-Si2 and ultrasonic dispersion for 30min, so that the mass fraction of modified h-BN is 0.4wt%, obtaining an h-BN / WPU-Si composite material.

[0044] Example 3: The difference between the present example and example 1 is that the amount of KP added is 5wt% of the mass of KP to the mass of the total reactants, obtaining a WPU-Si emulsion with a siloxane content of 5% and a solid content of 30wt%, denoted as WPU-Si5, adding modified h-BN to WPU-Si5 and ultrasonic dispersion for 30min, so that the mass fraction of modified h-BN is 0.6wt%, obtaining an h-BN / WPU-Si composite material.

[0045] The double-layer composite protective material for iron cultural relics prepared by the present application, the material of the bottom protective layer is a silane solution containing corrosion inhibitor, and the material of the surface protective layer is a modified h-BN / WPU-Si composite protective material. The silane solution containing corrosion inhibitor not only firmly covers the surface of the iron, but also significantly improves the corrosion resistance of the silane film and increases the adhesion of the organic coating on the surface of the iron. The h-BN / WPU-Si composite protective material uses environmentally friendly bio-based castor oil as polyol and crosslinking agent. The branched castor oil will introduce a crosslinked structure into the final coating, resulting in a denser coating. In addition, because the hydroxylated siloxane has a low surface energy, it is end-capped with polyurethane, so that the hydrophobic groups migrate to the surface of the film during the coating process, reducing the surface tension of the coating and improving the hydrophobicity. The contact angle of the coating gradually increases. At the same time, the Si-OH groups in the siloxane hydrolyze to form Si-O-Si crosslinking structure, further improving the crosslinking density of the coating, making the coating surface more dense and not easy to penetrate water molecules, thereby improving the hydrophobicity. Hexagonal boron nitride is a two-dimensional nanoparticle with good impermeability, excellent barrier properties, oxidation resistance and chemical inertness. By modifying hexagonal boron nitride with amino siloxane, particle agglomeration can be avoided, and the compatibility of hexagonal boron nitride with waterborne polyurethane can be improved, further enhancing the water resistance and corrosion resistance of the protective material. The introduction of hydroxylated siloxane and modified nanoparticles can enhance the mechanical properties, thermal stability, water resistance and corrosion resistance of the waterborne polyurethane coating.

[0046] In specific use of the present application, the cleaned ironware is first soaked in the bottom layer sealing protective liquid for 10 min, and then placed in a 100 DEG C oven for 30 min to obtain a bottom layer sealing protective coating; then the surface layer sealing protective liquid is uniformly coated on the surface of the ironware with a fine brush, the surface layer sealing protective coating is first naturally dried at room temperature for 24-48 h, and then dried in a 50-70 DEG C oven for 12-24 h to obtain a double-layer iron cultural relic sealing protective coating. In order to verify the use effect of the present application, the products of the embodiments of the present application and the unmodified waterborne polyurethane are treated on tinplate pieces by the above method, and the pencil hardness, adhesion, contact angle and corrosion resistance of the substrate before and after treatment are tested, and the results are shown in Table 1. Among them, the pencil hardness is tested according to GB / T6739-2006 Pencil Method for Testing Film Hardness of Paint and Varnish; the adhesion is evaluated according to GB / T 9286-2021 Scratch Test for Paint and Varnish to evaluate the adhesion between the coating and the metal substrate; the macroscopic corrosion resistance is tested according to GBT1771-2007 Determination of Neutral Salt Fog Resistance of Paint and Varnish; and the microscopic corrosion resistance is evaluated by electrochemical test.

[0047] The test index results of the double-layer composite sealing protective materials prepared by the methods of embodiments 1, 2 and 3 of the present application are compared in Table 1.

[0048] Table 1:

[0049]

[0050] The double-layer sealing protection adopted in the present application can not only firmly cover the metal surface with the silane solution containing corrosion inhibitor in the bottom layer sealing protective material, so that the corrosion resistance of the silane film is significantly improved, but also can increase the adhesion of the organic coating on the surface of the ironware. The h-BN / WPU-Si can enhance the mechanical properties, thermal stability, water resistance and corrosion resistance of the waterborne polyurethane coating by simultaneously introducing hydroxylated siloxane and modified nanoparticles. The present application is scientific and reasonable, the raw materials are abundant, green and environmentally friendly, and easy to produce and prepare. The double-layer sealing protection can be applied to the protection field of iron cultural relics, plays a role in isolating external harmful substances, makes the iron cultural relics have excellent water resistance and corrosion resistance, and at the same time does not affect the appearance of the iron cultural relics, providing a new idea for the surface sealing protection of iron cultural relics.

Claims

1. A double-layer composite sealing material for the preservation of iron cultural relics, comprising a bottom sealing layer and a top composite sealing layer; characterized in that: The bottom protective layer is a silane solution containing corrosion inhibitor, and the top composite protective layer is a modified hexagonal boron nitride / siloxane end-capped waterborne polyurethane (h-BN / WPU-Si) composite material. The silane solution containing the corrosion inhibitor is prepared by the following method: γ-aminopropyltriethoxysilane (KH550):ethanol:deionized water were hydrolyzed at 25°C for 8 hours with stirring at a volume ratio of 5:20:

75. Then, 2wt% phytic acid was dissolved in the above solution to obtain a silane solution containing corrosion inhibitor. Modified hexagonal boron nitride / siloxane-terminated waterborne polyurethane (h-BN / WPU-Si) was prepared by the following method: 1) Preparation of hydroxylated siloxanes (KP): Under nitrogen protection and magnetic stirring, equimolar amounts of γ-aminopropyltriethoxysilane (KH550) and propylene carbonate (PC) were added to a flask. The temperature was adjusted to 40-100℃, and the reaction was allowed to proceed for 4-12 h. The content of primary amino groups in the molecular structure of γ-aminopropyltriethoxysilane (KH550) was determined using the salicylaldehyde-sodium methoxide method to monitor the reaction status. Every hour, the characteristic absorption peak of C=O at 1800 cm⁻¹ of propylene carbonate was monitored using infrared spectroscopy. The reaction was terminated when the characteristic absorption peak of C=O disappeared, yielding the product, denoted as hydroxylated siloxane (KP). 2) Preparation of siloxane-terminated modified waterborne polyurethane emulsion (WPU-Si): First, polycarbonate diol (PCDL-1000) and castor oil (CO) were dehydrated under vacuum at 110-130°C for 2-3 hours. Dimethylolpropionic acid (DMPA) was dried at 80-100°C for 2 hours. Acetone was dehydrated in a 4A molecular sieve for one week. Isophorone diisocyanate (IPDI), PCDL-1000, castor oil (CO), and 1-2 drops of dibutyltin dilaurate (DBTDL) catalyst were added to a three-necked flask equipped with a reflux condenser and a mechanical stirrer. The mixture was reacted in an oil bath at 70-90°C for 2-3 hours. Next, the hydrophilic chain extender dimethylolpropionic acid (DMPA) was added, and the temperature was lowered to 60-90°C for 1.5-3 hours. Then, 1,4-butanediol (BDO) was added to achieve a final NCO:OH molar ratio of 1.1-1.5, and the reaction was continued for 1-2 hours. Finally, the temperature was lowered to 50-60°C. At ℃, hydroxylated siloxane (KP) was added, followed by dropwise addition of acetone. When the system temperature dropped to 30–40 ℃, triethylamine (TEA), an equimolar amount of neutralizing agent equal to that of dimethylolpropionic acid (DMPA), was weighed and added directly to the flask. The mixture was stirred for 30–50 min to neutralize the carboxyl groups in the reaction system. Then, deionized water was added to the reaction system at room temperature for high-speed emulsification, so that the total mass of the reactants accounted for 30% of the total mass of the emulsion. Finally, after removing the acetone from the system by vacuum decompression, a siloxane-terminated modified waterborne polyurethane emulsion (WPU-Si) with a solid content of 30 wt% was obtained. The isocyanate group (NCO) in the isophorone diisocyanate (IPDI) has a molar ratio of 2 to 4 with the hydroxyl group (OH) in polycarbonate diol PCDL-1000 and castor oil (CO), wherein the molar ratio of polycarbonate diol PCDL-1000 to the hydroxyl group in castor oil (CO) is 7:

3. The amount of the hydrophilic chain extender dimethylolpropionic acid (DMPA) added is such that its mass fraction is 4.5 to 6.5 wt%, and its mass fraction is the mass of the hydrophilic chain extender dimethylolpropionic acid (DMPA) to the mass of the total reactants; The amount of hydroxylated siloxane (KP) added is such that its mass fraction is 1-5 wt%, and its mass fraction is the mass of hydroxylated siloxane (KP) to the mass of the total reactants. 3) Preparation of modified hexagonal boron nitride Weigh 2–3 g of h-BN powder and dissolve it in 100 ml of isopropanol. Add the solution to a single-necked round-bottom flask and stir at 60 °C for 24 h. After ultrasonic treatment with a low-power ultrasonic cleaner for 20 h, place the flask at room temperature for 48 h. Then, centrifuge at 3000 r / min for 15 min. The well-dispersed h-BN nanoparticles form a suspension in the upper layer of the centrifuge tube. Take 2 / 3 of the upper suspension volume with a dropper to obtain the h-BN suspension. Centrifuge the h-BN suspension at high speed, discard the supernatant, and dry at 60 °C for 12 h to obtain h-BN nanosheets with fewer layers. Dissolve the obtained h-BN nanosheets in 5 mol / L NaOH solution and heat and stir at 120 °C for 24 h to hydroxylate the h-BN mixture. Filter the mixture, wash with deionized water until neutral, and dry in an oven at 80 °C to obtain hydroxylated h-BN nanosheets. Then, mix 0.5 g of the hydroxylated h-BN nanosheets in a beaker. 4 g of hydroxylated h-BN nanosheets, 4 g of deionized water, 10–20 g of KH550 and 30–50 g of ethanol were ultrasonically treated for 60 min, stirred at 60 °C for 8 h, centrifuged for 10 min, rinsed with ethanol and deionized water to remove excess KH550, and freeze-dried for 24 h to obtain modified hexagonal boron nitride nanosheets. 4) Modified hexagonal boron nitride / siloxane-terminated waterborne polyurethane (h-BN / WPU-Si) composite material Modified hexagonal boron nitride nanosheets were added to WPU-Si and ultrasonically dispersed for 30 min to obtain a mass fraction of 0.2-1 wt% of modified hexagonal boron nitride nanosheets, thus obtaining a modified hexagonal boron nitride / siloxane-terminated waterborne polyurethane (h-BN / WPU-Si) composite material.

2. The double-layer composite sealing material for the protection of iron cultural relics according to claim 1, characterized in that: The amount of hydroxylated siloxane (KP) added was 1 wt% of the total reactants, resulting in a WPU-Si emulsion with a solid content of 30 wt%, denoted as WPU-Si1. Modified hexagonal boron nitride nanosheets were added to WPU-Si1 and ultrasonically dispersed for 30 min, so that the mass fraction of modified hexagonal boron nitride nanosheets was 0.2 wt%, thus obtaining a modified hexagonal boron nitride / siloxane-terminated waterborne polyurethane (h-BN / WPU-Si) composite material.

3. The double-layer composite sealing material for the protection of iron cultural relics according to claim 1, characterized in that: The amount of hydroxylated siloxane (KP) added was 2 wt% of the total reactants, resulting in a WPU-Si emulsion with a solid content of 30 wt%, denoted as WPU-Si2. Modified hexagonal boron nitride nanosheets were added to WPU-Si2 and ultrasonically dispersed for 30 min, so that the mass fraction of modified hexagonal boron nitride nanosheets was 0.4 wt%, thus obtaining a modified hexagonal boron nitride / siloxane-terminated waterborne polyurethane (h-BN / WPU-Si) composite material.

4. The double-layer composite sealing material for the protection of iron cultural relics according to claim 1, characterized in that: The amount of hydroxylated siloxane (KP) added was 5 wt% of the total reactants, resulting in a WPU-Si emulsion with a solid content of 30 wt%, denoted as WPU-Si5. Modified hexagonal boron nitride nanosheets were added to WPU-Si5 and ultrasonically dispersed for 30 min, so that the mass fraction of modified hexagonal boron nitride nanosheets was 0.6 wt%, thus obtaining a modified hexagonal boron nitride / siloxane-terminated waterborne polyurethane (h-BN / WPU-Si) composite material.

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