Preparation method of porous calcium carbonate microspheres and application thereof in paper-based archive self-cleaning

Abstract

The present application relates to inorganic nanometer material preparation and cultural relic protection technical field, disclose the preparation method and application of porous calcium carbonate microspheres in paper archives self-cleaning, including the following steps: S1, respectively, prepare sodium dodecyl sulfate solution and polyvinyl pyrrolidone solution;S2, polyvinyl pyrrolidone solution and calcium chloride solution are mixed, stirring is uniform, first mixed solution is obtained;Sodium dodecyl sulfate solution and sodium carbonate solution are mixed, stirring is uniform, second mixed solution is obtained;S3, the first mixed solution and the second mixed solution are mixed, after reaction is completed, centrifugation, washing, drying, porous calcium carbonate microspheres are obtained.The technical scheme for preparing porous calcium carbonate microspheres by adopting PVP and SDS double template system, the technical effect of improving the specific surface area of material, rich pore structure, providing sufficient reaction site and micron roughness is achieved, the deficiency of insufficient reaction site and rough structure difficult to construct is solved.

Description

Technical Field

[0001] This invention relates to the field of inorganic nanomaterial preparation and cultural relic preservation technology, specifically to a method for preparing porous calcium carbonate microspheres and their application in the self-cleaning of paper archives. Background Technology

[0002] Paper archives, rare ancient books, and other paper artifacts are important carriers of human civilization, possessing irreplaceable and extremely precious historical and cultural value. However, during long-term preservation, they are highly susceptible to environmental factors (such as humidity, pollutants, and microorganisms), leading to dust accumulation, mold growth, acid corrosion, and yellowing on their surfaces, resulting in blurred writing, reduced material mechanical strength, and irreversible damage. Imparting superhydrophobic and self-cleaning capabilities to paper archives, enabling them to effectively resist moisture, liquid stains, and particulate contaminants, is of great significance for achieving long-term preventative protection.

[0003] In recent years, superhydrophobic self-cleaning technology based on the biomimetic lotus leaf effect has provided a new approach to solving the above problems. At present, research on superhydrophobic treatment of paper materials is mainly divided into two categories: one is to construct micro-nano rough structures using exogenous nanomaterials (such as SiO2, TiO2, ZnO) and perform hydrophobic modification; the other is to use natural materials with good compatibility with paper (such as cellulose, calcium carbonate) for functional design.

[0004] Calcium carbonate has good compatibility with paper cellulose and is a traditional paper filler, making its application in the preservation of paper artifacts considered to have potential advantages. However, existing technologies mostly focus on using ordinary nanoparticles or simply modified calcium carbonate, which suffer from problems such as limited specific surface area and insufficient active sites leading to low self-cleaning efficiency. Other superhydrophobic technologies, such as SiO2 / PDMS-based coatings, while each with its own characteristics, are also limited in their application in the preservation of paper archives due to poor compatibility with paper, weak adhesion that makes them easy to fall off, or the potential to damage paper fibers and significantly alter the appearance and feel of the paper. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing porous calcium carbonate microspheres and their application in self-cleaning of paper archives, solving the problems of insufficient reaction sites and difficulty in constructing a coarse structure in the technical solution of ordinary calcium carbonate particles.

[0006] To achieve the above objectives, the present invention provides the following technical solution: The preparation method of porous calcium carbonate microspheres and their application in self-cleaning of paper archives includes the following steps: Sodium dodecyl sulfate solution and polyvinylpyrrolidone solution were prepared separately. The polyvinylpyrrolidone solution was mixed with calcium chloride solution to obtain a first mixture. The sodium dodecyl sulfate solution was mixed with sodium carbonate solution to obtain a second mixture. The two mixtures were mixed evenly and reacted at a constant temperature. After centrifugation, washing and drying, porous calcium carbonate microspheres were obtained. The prepared porous calcium carbonate microspheres were dispersed with stearic acid in anhydrous ethanol and stirred at a constant temperature to carry out the esterification reaction. After the reaction was completed, the microspheres were separated, washed and dried to obtain hydrophobically modified porous calcium carbonate microspheres. Hydrophobically modified porous calcium carbonate microspheres and beeswax were co-dispersed in anhydrous ethanol and ultrasonically treated to obtain a uniform and stable self-cleaning spray liquid for paper archives. The coating liquid was evenly sprayed onto the surface of the paper archive and dried under constant temperature and humidity conditions to form a superhydrophobic self-cleaning protective coating. After drying, the water contact angle and roll-off angle of the paper archive surface were measured, and the water resistance, abrasion resistance and durability were determined to evaluate the self-cleaning protection effect.

[0007] By adopting the above technical solution, high specific surface area porous calcium carbonate microspheres are prepared using a dual-template approach. After hydrophobic modification by chemical bonding with stearic acid and compounding with beeswax to construct a micro-nano rough structure, combined with a gentle spraying and drying process, the surface of paper archives achieves superhydrophobic self-cleaning function. At the same time, environmentally friendly raw materials are used throughout the process, without damaging the paper or the writing. Therefore, a stable, durable, green and safe paper archive protection effect is obtained, effectively solving the problems of poor compatibility of existing protective materials, easy peeling of hydrophobic layers, and easy damage to cultural relics.

[0008] Preferably, the concentration of sodium dodecyl sulfate solution is 2 g / L to 8 g / L, the concentration of polyvinylpyrrolidone solution is 6 g / L to 12 g / L, the concentrations of calcium chloride solution and sodium carbonate solution are both 0.1 mol / L to 0.5 mol / L, the reaction temperature is 25℃ to 60℃, and the reaction time is 6 h to 12 h.

[0009] By adopting the above technical solution, the nucleation and growth of calcium carbonate can be precisely controlled by using a dual-template system of sodium dodecyl sulfate and polyvinylpyrrolidone, forming a porous microsphere structure. Under suitable reactant concentrations and reaction temperatures, the microspheres are guaranteed to have abundant pores, large specific surface area, and uniform morphology. Therefore, porous calcium carbonate microspheres with regular structure and sufficient active sites are obtained, providing a stable substrate for subsequent hydrophobic modification.

[0010] Preferably, the first mixture and the second mixture are stirred for 10 minutes in advance to mix them evenly. After centrifugation, they are washed with water and ethanol in sequence, and the drying temperature is from room temperature to 60°C.

[0011] By adopting the above technical solution, the reactants can be in uniform contact due to sufficient premixing, avoiding excessive local concentration that could lead to particle agglomeration; the alternating washing with water and ethanol can remove unreacted ions and residual template agents; and the gentle drying can maintain the microsphere pore structure from collapsing. Therefore, high-purity, structurally intact porous calcium carbonate microspheres are obtained, improving the subsequent modification effect.

[0012] Preferably, the mass ratio of porous calcium carbonate microspheres to stearic acid is 1:0.02~0.08, the reaction temperature is 60℃~100℃, the reaction time is 30min~90min, and the dispersion medium is anhydrous ethanol.

[0013] By adopting the above technical solution, stearic acid in an appropriate ratio can fully undergo esterification with the hydroxyl groups on the surface of the microspheres to form covalent bonds; a suitable reaction temperature can ensure complete reaction without damaging the microsphere structure; and anhydrous ethanol can provide a uniform reaction environment and avoid side reactions. Therefore, modified microspheres with a strong hydrophobic layer and low surface energy are obtained, significantly improving the stability of the coating.

[0014] Preferably, after the reaction is completed, centrifugation is performed, followed by washing with anhydrous ethanol 2-3 times in sequence, and drying to obtain hydrophobically modified porous calcium carbonate microspheres.

[0015] By adopting the above technical solution, the product can be collected quickly by centrifugation, unreacted stearic acid can be removed by ethanol washing, and thorough drying can avoid residual solvent from affecting the stability of the subsequent spraying solution. Therefore, clean and well-dispersed modified microspheres are obtained, ensuring the uniformity and stability of the spraying solution.

[0016] Preferably, the mass ratio of hydrophobically modified porous calcium carbonate microspheres to beeswax is 1:0.1~5, the dispersion medium is anhydrous ethanol, and the ultrasonic time is 10min~30min.

[0017] By adopting the above technical solutions, beeswax can synergistically construct a micro-nano composite rough structure with modified microspheres, thereby enhancing the superhydrophobic effect; a suitable ratio can balance roughness and coating adhesion; and ultrasonic treatment can ensure that the material is fully dispersed and does not agglomerate. Therefore, a uniform, stable, and film-forming superhydrophobic spray liquid with excellent film-forming properties can be obtained.

[0018] Preferably, the prepared spraying liquid is sealed and allowed to stand without layering or sedimentation before being used for spraying paper archives.

[0019] By adopting the above technical solution, static testing can ensure stable dispersion of the spray liquid, avoiding stratification that leads to uneven coating thickness; a stable spray liquid can form a continuous and uniform protective film; therefore, a protective coating with uniform film formation and consistent performance is obtained, ensuring stable self-cleaning effect.

[0020] Preferably, the spraying method is uniform spraying, the drying temperature is 20℃~24℃, the relative humidity is 30%~52%, and the drying time is 24h~48h.

[0021] By adopting the above technical solution, the mild temperature and humidity environment can ensure that the coating dries slowly and forms, avoiding cracks and peeling caused by rapid drying; suitable humidity can prevent the paper from absorbing moisture and deforming, and the writing from bleeding; sufficient drying time can ensure that the coating is completely cured; therefore, a protective coating that is firmly bonded to the paper and does not damage the cultural relics is obtained.

[0022] Preferably, the distance between the nozzle and the paper document should be kept uniform during spraying, and the amount of spraying in a single spray should be such that the surface is wet but not waterlogged.

[0023] By adopting the above technical solution, uniform spraying can avoid localized excessive thickness that alters the appearance and feel of the paper; the absence of liquid accumulation can prevent liquid penetration that damages paper fibers and writing; therefore, a protective coating of moderate thickness with no significant changes in appearance is obtained, meeting the requirements of reversibility and aesthetics in the protection of paper archives.

[0024] Preferably, after treatment, the water contact angle of the paper archive surface is not less than 150° and the roll-off angle is not more than 10°. After 50 water washes or rubbing with a 500g weight, the contact angle is still not less than 145° and the roll-off angle is not more than 15°.

[0025] By adopting the above technical solutions, the superhydrophobic interface enables water droplets to roll and self-clean, effectively removing dust and contaminants; the excellent water resistance and abrasion resistance ensure stable long-term protection; thus, a long-lasting, durable paper archive protection system with outstanding self-cleaning effect is obtained.

[0026] Performance testing includes contact angle and roll-off angle tests, water washability tests, abrasion resistance tests, finger touch tests, and water droplet impact tests. The testing environment is normal temperature and pressure, with an air humidity of 40% to 60%.

[0027] By adopting the above technical solutions, multi-dimensional performance testing can comprehensively evaluate the hydrophobicity, durability, and stability of the coating; the standard testing environment can ensure accurate and comparable results; therefore, scientific and reliable protective effect evaluation data can be obtained, providing support for the application and optimization of the method.

[0028] This invention provides a method for preparing porous calcium carbonate microspheres and their application in the self-cleaning of paper archives. It has the following beneficial effects: 1. The present invention uses a PVP and SDS dual-template system to prepare porous calcium carbonate microspheres, which achieves the technical effects of increasing the specific surface area of ​​the material, enriching the pore structure, providing sufficient reaction sites and micron-level roughness. Compared with the existing technology that uses ordinary calcium carbonate particles, it solves the shortcomings of insufficient reaction sites and difficulty in constructing rough structure.

[0029] 2. The present invention achieves the technical effect of strengthening the bonding strength of the hydrophobic layer and improving the stability of the coating by using the esterification chemical bonding modification of stearic acid and the hydroxyl groups on the surface of porous calcium carbonate. Compared with the existing technology of physical blending hydrophobic modification, it solves the shortcomings of the hydrophobic layer being easy to fall off and having poor water washing and friction resistance.

[0030] 3. The present invention achieves the technical effect of optimizing the surface hydrophobic state and enhancing the self-cleaning effect by using beeswax and hydrophobically modified microspheres to synergistically construct a micro-nano composite rough structure. Compared with the existing single-material film-forming technology, it solves the problems of limited hydrophobic effect and weak self-cleaning ability.

[0031] 4. This invention achieves the technical effect of safe and non-toxic, without changing the appearance and feel of the paper, and without damaging the writing by adopting green and environmentally friendly raw materials and mild processes for the preservation of paper archives. Compared with the existing technical solutions that use non-environmentally friendly reagents or strong processes, this invention solves the shortcomings of existing technologies that have safety hazards, are easy to damage paper and writing, and do not meet the requirements for the preservation of cultural relics.

[0032] 5. This invention achieves the technical effect of improving the long-term stability of the coating and maintaining a durable superhydrophobic state by adopting a coating construction technology solution that combines stable covalent bond bonding with micro-nano structure synergistic support. Compared with the existing physical hybrid coating technology solution, it solves the shortcomings of poor durability and inability to achieve long-term stable protection. Attached Figure Description

[0033] Figure 1 Scanning electron microscope image of porous calcium carbonate microspheres prepared in Example 1 of the present invention; Figure 2 This is a SEM image of the hydrophobically modified porous calcium carbonate microspheres of the present invention. Figure 3 A comparison diagram of the contact angles of the untreated paper, the beeswax-treated paper, the modified porous calcium carbonate-treated paper, and the treated paper of the present invention. Figure 4 This is a photograph of the self-cleaning process of paper processing according to the present invention (the contaminants are sand and methylene blue). Detailed Implementation

[0034] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] PVP stands for polyvinylpyrrolidone; SDS stands for sodium dodecyl sulfate.

[0036] Please see the appendix Figure 1 - Appendix Figure 4 The present invention is further described below with reference to the following embodiments: Example 1: Preparation of porous calcium carbonate microspheres: 0.5 g PVP was dissolved in 50 mL of water to obtain solution 1; 0.3 g SDS was dissolved in 50 mL of water to obtain solution 2; 1.11 g anhydrous calcium chloride was dissolved in 100 mL of water to obtain solution 3; 1.06 g anhydrous sodium carbonate was dissolved in 100 mL of water to obtain solution 4. Solution 1 was added to solution 3 and stirred to obtain the first mixture; solution 2 was added to solution 4 and stirred to obtain the second mixture. The first mixture and the second mixture were mixed and reacted at room temperature for 8 h. After centrifugation, washing, and drying, porous calcium carbonate microspheres were obtained.

[0037] Hydrophobic modification: 1g of porous calcium carbonate microspheres and 0.06g of stearic acid were added to 30g of anhydrous ethanol and reacted in a water bath at 90℃ for 1h. After centrifugation, washing and drying, hydrophobic modified microspheres were obtained.

[0038] Preparation of composite spraying liquid: Modified microspheres and beeswax are dispersed in anhydrous ethanol at a mass ratio of 1:1 and ultrasonicated for 15 min to obtain the spraying liquid.

[0039] Application: Apply the coating liquid evenly to the paper surface and dry for 24 hours at a temperature of 23±1℃ and a relative humidity of 50±2%. The tested contact angle is 103.2° and the roll-off angle is 32.4°.

[0040] Example 2, Preparation of porous calcium carbonate microspheres: 0.2 g PVP was dissolved in 50 mL of water to obtain solution 1; 0.1 g SDS was dissolved in 50 mL of water to obtain solution 2; 0.37 g anhydrous calcium chloride was dissolved in 100 mL of water to obtain solution 3; 0.35 g anhydrous sodium carbonate was dissolved in 100 mL of water to obtain solution 4. Solution 1 was added to solution 3 and stirred to obtain the first mixture; solution 2 was added to solution 4 and stirred to obtain the second mixture. The first mixture and the second mixture were mixed and reacted at 25 °C for 12 h. After centrifugation, washing, and drying, porous calcium carbonate microspheres were obtained.

[0041] Hydrophobic modification: 1g of porous calcium carbonate microspheres and 0.02g of stearic acid were added to 30g of anhydrous ethanol and reacted in a water bath at 60℃ for 90min. After centrifugation, washing and drying, hydrophobic modified microspheres were obtained.

[0042] Preparation of composite spraying liquid: Modified microspheres and beeswax are dispersed in anhydrous ethanol at a mass ratio of 0.1:1 and sonicated for 10 min to obtain the spraying liquid.

[0043] Application: Spray the coating liquid evenly onto the paper surface and dry it at 20℃ and 30% relative humidity for 48 hours.

[0044] Example 3, Preparation of porous calcium carbonate microspheres: 0.6 g PVP was dissolved in 50 mL of water to obtain solution 1; 0.4 g SDS was dissolved in 50 mL of water to obtain solution 2; 1.85 g anhydrous calcium chloride was dissolved in 100 mL of water to obtain solution 3; 1.77 g anhydrous sodium carbonate was dissolved in 100 mL of water to obtain solution 4. Solution 1 was added to solution 3 and stirred to obtain the first mixture; solution 2 was added to solution 4 and stirred to obtain the second mixture. The first mixture and the second mixture were mixed and reacted at 60 °C for 6 h. After centrifugation, washing, and drying, porous calcium carbonate microspheres were obtained.

[0045] Hydrophobic modification: 1g of porous calcium carbonate microspheres and 0.08g of stearic acid were added to 30g of anhydrous ethanol and reacted in a water bath at 100℃ for 30min. After centrifugation, washing and drying, hydrophobic modified microspheres were obtained.

[0046] Preparation of composite spraying liquid: Modified microspheres and beeswax were dispersed in anhydrous ethanol at a mass ratio of 5:1 and sonicated for 30 min to obtain the spraying liquid.

[0047] Application: Spray the coating liquid evenly onto the paper surface and dry it at 24℃ and 52% relative humidity for 24 hours.

[0048] Example 4 differs from Example 1 in that the modified microspheres and beeswax were prepared in a mass ratio of 2:1 in the composite spraying liquid preparation, while the rest were the same. The results are shown in Table 1.

[0049] Example 5 differs from Example 1 in that the modified microspheres and beeswax were prepared in a mass ratio of 3:1 in the composite spraying liquid preparation, while the rest were the same. The results are shown in Table 1.

[0050] Example 6 differs from Example 1 in that the modified microspheres and beeswax were prepared in a mass ratio of 4:1 in the composite spraying liquid preparation, while the rest were the same. The results are shown in Table 1.

[0051] Comparative Example 1 differs from Example 1 in that the modified microspheres and beeswax were prepared in a mass ratio of 5:1 in the composite spraying liquid preparation, while the rest remained the same. The results are shown in Table 1. Comparative Example 2 used the same porous calcium carbonate microspheres as in Example 1, without stearic acid modification, and directly dispersed them with beeswax in anhydrous ethanol at a mass ratio of 1:1. The mixture was then sprayed onto the surface of paper, and the contact angle was tested after drying. The initial contact angle was only 115.2°, the roll-off angle was 35.6°, and the contact angle dropped to below 90° after 10 touches, indicating that the physical mixed hydrophobic layer had poor stability.

[0052] Comparative Example 3 uses only stearic acid-modified porous calcium carbonate microspheres, without beeswax compounding, dispersed in anhydrous ethanol, and after spraying and drying, the contact angle is 128.5°, the roll-off angle is 25.8°, and the surface roughness of the coating is insufficient, resulting in poor self-cleaning effect.

[0053] Test Example 1, Durability Test: Paper was treated with the spray liquid prepared in Comparative Example 1, and the contact angle and roll-off angle were tested before and after finger touch and before and after water droplet impact.

[0054] Finger-touch test: A gloved finger was placed in full contact with the sample surface under a certain pressure, and the hydrophobicity of the sample surface was recorded after each press to further evaluate the stability of the coating. The results showed that after 60 finger touches, the contact angle still reached 150.3° and the roll-off angle was 10.2°.

[0055] Water droplet impact test: In the water droplet impact test, the sample is placed below the experimental device at a 45° angle and a distance of 30 cm, and is allowed to fall freely at a frequency of 2 drops / second to impact the sample surface. After 500 water droplets impact, the contact angle is 149.5° and the roll-off angle is 11.8°.

[0056] Table 1. Experimental Results

[0057] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing porous calcium carbonate microspheres, characterized in that, Includes the following steps: S1, prepare sodium dodecyl sulfate solution and polyvinylpyrrolidone solution respectively; S2, Mix the polyvinylpyrrolidone solution with the calcium chloride solution and stir until homogeneous to obtain the first mixture; Sodium dodecyl sulfate solution and sodium carbonate solution were mixed and stirred until homogeneous to obtain a second mixture; S3. The first mixture and the second mixture are mixed and reacted at 25℃~60℃ for 6h~12h. After the reaction is completed, the mixture is centrifuged, washed and dried to obtain porous calcium carbonate microspheres.

2. The method for preparing porous calcium carbonate microspheres according to claim 1, characterized in that, In S1, the concentration of sodium dodecyl sulfate solution is 2 g / L-8 g / L, and the concentration of polyvinylpyrrolidone solution is 6 g / L-12 g / L.

3. The method for preparing porous calcium carbonate microspheres according to claim 1, characterized in that, The concentration of the anhydrous sodium carbonate solution in S2 is 0.1 mol / L-0.5 mol / L, and the concentration of the anhydrous calcium chloride solution is 0.1 mol / L-0.5 mol / L.

4. The method for preparing porous calcium carbonate microspheres according to claim 1, characterized in that, In S3, the reaction temperature is 25℃-60℃ and the reaction time is 6h-12h.

5. A method for preparing hydrophobically modified porous calcium carbonate microspheres, characterized in that, The porous calcium carbonate microspheres prepared by the method according to any one of claims 1 to 4 are obtained by dispersing the porous calcium carbonate microspheres and stearic acid in anhydrous ethanol at a mass ratio of 1:0.02 to 0.08, reacting at 60°C to 100°C for 30 min to 90 min, and then separating, washing and drying to obtain hydrophobically modified porous calcium carbonate microspheres.

6. The preparation method according to claim 5, characterized in that, The stearic acid and porous calcium carbonate microspheres form a chemical bond through an esterification reaction.

7. A superhydrophobic composite coating spray liquid for self-cleaning paper archives, characterized in that, It includes the hydrophobic modified porous calcium carbonate microspheres as described in claim 5 or 6, beeswax, and anhydrous ethanol, wherein the mass ratio of the hydrophobic modified porous calcium carbonate microspheres to beeswax is 5 to 1:0.

1.

8. The spraying liquid according to claim 7, characterized in that, The beeswax and hydrophobically modified porous calcium carbonate microspheres together construct a micro-nano composite rough structure.

9. The application of the spraying liquid according to claim 7 or 8 in the self-cleaning of paper archives, characterized in that, The coating liquid is evenly sprayed onto the surface of the paper archive and dried for 24 to 48 hours at a temperature of 20°C to 24°C and a relative humidity of 30% to 52% to form a superhydrophobic self-cleaning coating.

10. The application according to claim 9, characterized in that, After treatment, the water contact angle of the paper archive surface is ≥150° and the roll-off angle is ≤10°. After 50 water washes or rubbing with a 500g weight, the contact angle is still ≥145° and the roll-off angle is ≤15°.

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