Core-shell structure composition comprising cellulose-silica hybrid nanoparticles and method for producing thereof

Abstract

The present invention relates to a core-shell structured composition comprising cellulose-silica hybrid nanoparticles and a method for manufacturing the same. More specifically, it relates to a technology that comprehensively improves the early strength, interfacial densification, and long-term durability of tile adhesives by simultaneously realizing the moisture retention capacity of cellulose and the cement hydration-promoting effect of silica through the preparation of core-shell structured hybrid nanoparticles having nanocellulose as a core and APTES-derived silica as a shell. The manufacturing method of the present invention involves preparing a reaction solvent by mixing ethanol and deionized water in a weight ratio of 3:1 to 5:1, adding APTES first to generate silanol groups through hydrolysis, and then adding nanocellulose in portions so that APTES is uniformly adsorbed onto the surface of the nanocellulose. Subsequently, glacial acetic acid is slowly added using a quantitative pump to precisely adjust the pH to 3.9 to 4.1, and a silanization reaction is performed at a temperature of 75 ± 3℃ for 7 ± 1 hour to form Si-OC covalent bonds through a dehydration condensation reaction between the hydroxyl groups on the surface of the nanocellulose and the silanol groups derived from APTES. The key technical features of the present invention are, first, that energy consumption is reduced while silanization efficiency is maximized by adopting room-temperature desiccator drying instead of high-temperature oven drying; second, that the uniformity and stability of the core-shell structure are ensured by precisely controlling the pH within a narrow range and applying a stepwise heating and slow cooling process; and third, that aggregation is prevented and dispersion stability is maximized by adding nanocellulose in divided portions and performing ultrasonic dispersion pretreatment. When 0.05 to 0.5 weight percent of the hybrid nanoparticles of the present invention are added to a tile adhesive, the early strength is improved by more than 5%, the porosity of the interface transition region is reduced by 40 to 50%, and the adhesive strength retention rate after 28 days of immersion reaches 85 to 92%, showing significantly improved performance compared to the prior art. In addition, the tile adhesive incorporating the hybrid nanoparticles of the present invention can secure sufficient adhesive strength and durability even when the adhesive is applied to only 50% of the tile surface area in the Korean spot-on tile installation method, thereby reducing cement usage by 50% and significantly reducing annual carbon dioxide emissions, thus enabling the realization of sustainable construction technology. This invention is applicable not only to the field of tile adhesives but also to various industrial fields such as eco-friendly cosmetics and dry mortar, and can significantly contribute to the development of high-performance construction materials, particularly in environments with extreme climate variability such as Australia.

Description

Technology Field

[0001] The present invention relates to a core-shell structured composition comprising cellulose-silica hybrid nanoparticles and a method for preparing the same. Background Technology

[0002] Recently, there has been a continuously increasing demand in the construction industry for improved tile adhesive performance. Particularly in regions with extreme climate variability, such as Australia, premature strength degradation and durability issues frequently occur due to high humidity in coastal areas and rapid moisture evaporation in dry inland regions.

[0003] Conventional cementitious tile adhesives (CTA) have primarily used organic additives, such as redispersible polymer powder (RDP), to improve workability and adhesion. However, these conventional technologies have problems such as insufficient early strength development due to a slow initial hydration reaction rate, vulnerability to moisture penetration due to high porosity in the interface transition zone (ITZ), and susceptibility to microcracks caused by drying shrinkage.

[0004] In particular, conventional tile adhesives have a problem in that many voids are formed at the interface between the tile and the adhesive matrix, and when moisture penetrates, the decomposition of the CSH gel (calcium silicate hydrate) is accelerated, which leads to a rapid decrease in long-term durability. In addition, in environments of rapid moisture evaporation, cement hydration proceeds insufficiently, resulting in cases where the adhesive strength falls short of design standards.

[0005] To address these problems, techniques involving the addition of inorganic nanoparticles such as nano silica and nano alumina have been proposed; however, these inorganic nanoparticles are prone to aggregation within the cement matrix and lack water retention capacity, which limits their effectiveness in dry environments.

[0006] Meanwhile, cellulose ether is widely used in tile adhesives due to its excellent moisture retention capacity, but cellulose ether alone has a minimal effect in promoting cement hydration and an insufficient interfacial strengthening effect, which limits its ability to improve early strength.

[0007] Therefore, there is a need to develop a new tile adhesive composition and a method for manufacturing the same that can improve early strength while maintaining moisture retention capacity and secure long-term durability through densification of the interfacial transition region. Prior art literature

[0008] Korean Published Patent 10-2025-0134122 Korean Published Patent 10-2005-0126930 Korean Published Patent 10-2026-0005607 Korean Published Patent 10-2025-0090450 The problem to be solved

[0009] The first problem that the present invention aims to solve is to simultaneously achieve the moisture retention capacity of cellulose and the cement hydration-promoting effect of silica by manufacturing cellulose-silica hybrid nanoparticles with a core-shell structure in which a silica shell is uniformly coated on the surface of nanocellulose.

[0010] The second problem that the present invention aims to solve is to provide a manufacturing method that enables the uniform and stable formation of a silica shell on the surface of nanocellulose by precisely controlling the pH during a silanization reaction using a silane coupling agent and optimizing the stepwise heating and stirring conditions.

[0011] The third problem that the present invention aims to solve is to improve the early strength by more than 5%, reduce the porosity of the interface transition region by 40 to 50%, and improve the adhesive strength retention rate after 28 days of immersion to more than 85% by applying the hybrid nanoparticles to a tile adhesive.

[0012] The fourth problem that the present invention aims to solve is to provide an eco-friendly manufacturing method that maximizes silanization efficiency while reducing energy consumption by omitting the high-temperature oven drying process and adopting a room-temperature desiccator drying method.

[0013] The fifth problem that the present invention aims to solve is to ensure both economic efficiency and manufacturing stability by ensuring that the hybrid nanoparticles exhibit a significant performance improvement effect with only a small amount of 0.05 to 0.5 weight% added to the existing tile adhesive formulation.

[0014] The sixth problem that the present invention aims to solve is to provide a sustainable construction technology that secures sufficient adhesive strength and durability even in a construction method where adhesive is applied to only 50% of the tile surface area, such as the Korean spot-on tile construction method, thereby reducing cement usage by 50% and significantly reducing carbon emissions. means of solving the problem

[0015] The present invention relates to a method for preparing a core-shell structure composition comprising cellulose-silica hybrid nanoparticles, comprising: a) a step of preparing a mixed solvent by mixing ethanol and deionized water; b) a step of preparing a reaction mixture by adding nanocellulose and a silane coupling agent selected from the group consisting of aminoalkyltrialkoxysilane, glycidylalkyltrialkoxysilane, mercaptoalkyltrialkoxysilane, vinyltrialkoxysilane, methacryloxyalkyltrialkoxysilane, epoxyalkyltrialkoxysilane, isocyanatoalkyltrialkoxysilane, ureidoalkyltrialkoxysilane, chloroalkyltrialkoxysilane, and combinations thereof to the mixed solvent; c) a step of adjusting the pH by adding an acid catalyst to the reaction mixture; d) a step of performing a silanization reaction by heating and stirring the pH-adjusted reaction mixture; and e) a step of filtering and washing the product of the completed silanization reaction. and f) drying the filtered and washed product to obtain silane-modified nanocellulose; a method for preparing a core-shell structure composition comprising cellulose-silica hybrid nanoparticles is provided.

[0016] At this time, the above step a) comprises: a1) a step of preparing a total of 100 parts by weight of a polar mixed solvent by mixing 70 to 85 parts by weight of ethanol and 15 to 30 parts by weight of deionized water; a2) a step of confirming that the initial pH of the polar mixed solvent is in the range of pH 6.5 to 8.0 by measuring it with a pH meter; and a3) a step of preparing a homogeneously mixed reaction solvent by stirring the polar mixed solvent at a stirring speed of 100 to 500 rpm for 5 to 20 minutes at a temperature of 15 to 30℃; wherein the weight ratio of ethanol to deionized water is controlled to 3:1 to 5:1.

[0017] At this time, step b) comprises: b1) a step of initiating a primary hydrolysis reaction while adding 15 to 25 parts by weight of the silane coupling agent to 100 parts by weight of the mixed solvent at a dropwise rate of 0.5 to 2.0 mL / min; b2) a step of generating silanol groups from the silane coupling agent by stirring at a stirring speed of 200 to 400 rpm for 10 to 30 minutes while the primary hydrolysis reaction is proceeding; b3) a step of inducing adsorption between the hydroxyl groups on the surface of the nanocellulose and the silanol groups by adding 3 to 7 parts by weight of nanocellulose to 100 parts by weight of the mixed solvent in 2 to 5 divided portions, with each addition interval being 5 to 15 minutes. and b4) a step of preparing a reaction mixture in which the silane coupling agent is uniformly dispersed on the surface of the nanocellulose by stirring the reaction mixture into which the nanocellulose is added at a stirring speed of 300 to 600 rpm for 30 to 90 minutes; wherein the weight ratio of the silane coupling agent to the nanocellulose is 3:1 to 5:1, and the nanocellulose is dispersed by ultrasonically dispersing at a frequency of 20 to 60 kHz for 5 to 30 minutes before addition so that the average particle size is 50 to 500 nm.

[0018] At this time, step c) comprises: c1) a step of measuring the initial pH of the reaction mixture with a digital pH meter and confirming that the pH is in the range of 6.5 to 8.0; c2) a step of adding 0.5 to 3.0 parts by weight of glacial acetic acid to 100 parts by weight of the reaction mixture at a dropping rate using a quantitative pump of 0.1 to 0.5 mL / min while measuring the pH at intervals of 30 seconds to 2 minutes; c3) a step of stopping the addition of glacial acetic acid and stirring for 5 to 15 minutes at a stirring speed of 100 to 300 rpm when the pH of the reaction mixture reaches the range of 3.8 to 4.2; and c4) a step of measuring the final pH of the stirred reaction mixture and confirming that it is within the range of 3.9 to 4.1. The method is characterized by including, wherein the total amount of glacial acetic acid added is 0.5 to 3.0 parts by weight per 100 parts by weight of the reaction mixture, and under the condition of pH 4.0 ± 0.1, the hydrolysis rate and the condensation reaction rate of the silane coupling agent are balanced so that a uniform silica shell is formed on the surface of the nanocellulose.

[0019] At this time, step d) comprises: d1) heating the pH-adjusted reaction mixture from a room temperature of 15 to 25°C to 70 to 80°C at a heating rate of 10 to 30°C / hr; d2) initiating a silanization reaction by stirring at a stirring speed of 300 to 600 rpm while maintaining the temperature within ±2°C when the temperature of the reaction mixture reaches 70 to 80°C; d3) continuing the silanization reaction for 5 to 9 hours, wherein the pH is re-measured every 2 to 4 hours after the start of the reaction, and if the pH exceeds 4.5, 0.1 to 0.5 parts by weight of glacial acetic acid are additionally added dropwise to 100 parts by weight of the reaction mixture to readjust the pH to a range of 3.9 to 4.2; and d4) cooling the reaction mixture to 20 to 30°C at a cooling rate of 5 to 15°C / hr when the silanization reaction is completed; The method is characterized by including, wherein the silanization reaction is performed at a temperature of 75 ± 3℃ for 7 ± 1 hour to form Si-OC covalent bonds through a dehydration condensation reaction between hydroxyl groups (-OH) on the surface of nanocellulose and silanol groups (Si-OH) derived from the silane coupling agent, and the stirring is performed using a magnetic stirrer or an overhead mechanical stirrer so that the temperature deviation within the reaction mixture is within ±2℃.

[0020] At this time, the silane coupling agent is characterized by being selected from the group consisting of (3-aminopropyl)triethoxysilane (APTES), (3-aminopropyl)trimethoxysilane (APTMS), (3-glycidoxypropyl)trimethoxysilane (GPTMS), (3-mercaptopropyl)trimethoxysilane (MPTMS), and combinations thereof. Effects of the invention

[0021] To solve the above problem, the present invention provides a method for preparing a core-shell structure composition comprising cellulose-silica hybrid nanoparticles, comprising: (a) a step of preparing a mixed solvent by mixing ethanol and deionized water; (b) a step of preparing a reaction mixture by adding a silane coupling agent and nanocellulose to the mixed solvent; (c) a step of adjusting the pH by adding an acid catalyst to the reaction mixture; (d) a step of performing a silanization reaction by heating and stirring the pH-adjusted reaction mixture; (e) a step of filtering and washing the product after the silanization reaction is completed; and (f) a step of drying the filtered and washed product to obtain silane-modified nanocellulose.

[0022] In one embodiment of the present invention, step (a) is characterized by preparing a total of 100 parts by weight of a polar mixed solvent by mixing 70 to 85 parts by weight of ethanol and 15 to 30 parts by weight of deionized water, confirming the initial pH of the polar mixed solvent to be in the range of pH 6.5 to 8.0, and then preparing a homogeneously mixed reaction solvent by stirring at a stirring speed of 100 to 500 rpm for 5 to 20 minutes at a temperature of 15 to 30°C.

[0023] In another embodiment of the present invention, step (b) is characterized by initiating a primary hydrolysis reaction by adding 15 to 25 parts by weight of the silane coupling agent to 100 parts by weight of the mixed solvent at a dropping rate of 0.5 to 2.0 mL / min, stirring at a stirring speed of 200 to 400 rpm for 10 to 30 minutes to generate silanol groups, and then adding 3 to 7 parts by weight of nanocellulose in 2 to 5 portions to ensure that the silane coupling agent is uniformly dispersed on the surface of the nanocellulose.

[0024] In another embodiment of the present invention, step (c) is characterized by adding 0.5 to 3.0 parts by weight of glacial acetic acid to 100 parts by weight of the reaction mixture at a dropping rate of 0.1 to 0.5 mL / min while monitoring the pH in real time, and when the pH reaches the range of 3.8 to 4.2, stopping the addition of glacial acetic acid and stirring for 5 to 15 minutes to adjust the final pH to the range of 3.9 to 4.1.

[0025] In another embodiment of the present invention, step (d) is characterized by heating the reaction mixture to 70 to 80°C at a heating rate of 10 to 30°C / hr, performing a silanization reaction for 5 to 9 hours at a stirring rate of 300 to 600 rpm while maintaining the temperature within ±2°C, and then cooling to 20 to 30°C at a cooling rate of 5 to 15°C / hr. Specific details for implementing the invention

[0026] In the following, various modifications may be made to the embodiments, and thus the scope of the patent application is not limited or restricted by these embodiments. It should be understood that all modifications, equivalents, and substitutions to the embodiments are included within the scope of the rights.

[0027] Specific structural or functional descriptions of the embodiments are disclosed for illustrative purposes only and may be modified and implemented in various forms. Accordingly, the embodiments are not limited to the specific disclosed forms, and the scope of this specification includes modifications, equivalents, or substitutions that fall within the technical concept.

[0028] Terms such as "first" or "second" may be used to describe various components, but these terms should be interpreted solely for the purpose of distinguishing one component from another. For example, the first component may be named the second component, and similarly, the second component may be named the first component.

[0029] When it is stated that a component is "connected" to another component, it should be understood that it may be directly connected to or joined to that other component, or that there may be other components in between.

[0030] The terms used in the embodiments are for illustrative purposes only and should not be interpreted as intended to be limiting. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as "comprising" or "having" are intended to indicate the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0031] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art to which the embodiments pertain. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in this application.

[0032] The advantages and features of the present invention and the methods for achieving them will become clear by referring to the embodiments described below in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below but may be implemented in various different forms. These embodiments are provided merely to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention, and the present invention is defined only by the scope of the claims.

[0033] In the embodiments of the present invention, unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art to which the present invention pertains. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in the embodiments of the present invention.

[0034] In describing the present invention, if it is determined that a detailed description of related prior art could unnecessarily obscure the essence of the invention, such detailed description is omitted. Where terms such as "comprising," "having," or "consisting of" are used in this specification, other parts may be added unless "only" is used. Where a component is expressed in the singular, it includes cases where it is included in the plural unless specifically stated otherwise.

[0035] In interpreting the components, they are interpreted to include a margin of error even in the absence of a separate explicit statement.

[0036] The features of each of the various embodiments of the present invention may be combined or combined with one another, either partially or wholly, and as will be fully understood by those skilled in the art, various technical interlocking and operation are possible, and each embodiment may be implemented independently of one another or together in an interlocking relationship.

[0037] The present invention provides a method for preparing a core-shell structure composition comprising cellulose-silica hybrid nanoparticles, comprising: a) a step of preparing a mixed solvent by mixing ethanol and deionized water; b) a step of preparing a reaction mixture by adding a silane coupling agent and nanocellulose to the mixed solvent; c) a step of adjusting the pH by adding an acid catalyst to the reaction mixture; d) a step of performing a silanization reaction by heating and stirring the pH-adjusted reaction mixture; e) a step of filtering and washing the product after the silanization reaction is completed; and f) a step of drying the filtered and washed product to obtain silane-modified nanocellulose.

[0038] At this time, the above step a) comprises: a1) a step of preparing a total of 100 parts by weight of a polar mixed solvent by mixing 70 to 85 parts by weight of ethanol and 15 to 30 parts by weight of deionized water; a2) a step of confirming that the initial pH of the polar mixed solvent is in the range of pH 6.5 to 8.0 by measuring it with a pH meter; and a3) a step of preparing a homogeneously mixed reaction solvent by stirring the polar mixed solvent at a stirring speed of 100 to 500 rpm for 5 to 20 minutes at a temperature of 15 to 30℃; wherein the weight ratio of ethanol to deionized water is controlled to 3:1 to 5:1.

[0039] At this time, step b) comprises: b1) a step of initiating a primary hydrolysis reaction while adding 15 to 25 parts by weight of the silane coupling agent to 100 parts by weight of the mixed solvent at a dropwise rate of 0.5 to 2.0 mL / min; b2) a step of generating silanol groups from the silane coupling agent by stirring at a stirring speed of 200 to 400 rpm for 10 to 30 minutes while the primary hydrolysis reaction is proceeding; b3) a step of inducing adsorption between the hydroxyl groups on the surface of the nanocellulose and the silanol groups by adding 3 to 7 parts by weight of nanocellulose to 100 parts by weight of the mixed solvent in 2 to 5 divided portions, with each addition interval being 5 to 15 minutes. and b4) a step of preparing a reaction mixture in which the silane coupling agent is uniformly dispersed on the surface of the nanocellulose by stirring the reaction mixture into which the nanocellulose is added at a stirring speed of 300 to 600 rpm for 30 to 90 minutes; wherein the weight ratio of the silane coupling agent to the nanocellulose is 3:1 to 5:1, and the nanocellulose is dispersed by ultrasonically dispersing at a frequency of 20 to 60 kHz for 5 to 30 minutes before addition so that the average particle size is 50 to 500 nm.

[0040] At this time, step c) comprises: c1) a step of measuring the initial pH of the reaction mixture with a digital pH meter and confirming that the pH is in the range of 6.5 to 8.0; c2) a step of adding 0.5 to 3.0 parts by weight of glacial acetic acid to 100 parts by weight of the reaction mixture at a dropping rate using a quantitative pump of 0.1 to 0.5 mL / min while measuring the pH at intervals of 30 seconds to 2 minutes; c3) a step of stopping the addition of glacial acetic acid and stirring for 5 to 15 minutes at a stirring speed of 100 to 300 rpm when the pH of the reaction mixture reaches the range of 3.8 to 4.2; and c4) a step of measuring the final pH of the stirred reaction mixture and confirming that it is within the range of 3.9 to 4.1. The method is characterized by including, wherein the total amount of glacial acetic acid added is 0.5 to 3.0 parts by weight per 100 parts by weight of the reaction mixture, and under the condition of pH 4.0 ± 0.1, the hydrolysis rate and the condensation reaction rate of the silane coupling agent are balanced so that a uniform silica shell is formed on the surface of the nanocellulose.

[0041] At this time, step d) comprises: d1) heating the pH-adjusted reaction mixture from a room temperature of 15 to 25°C to 70 to 80°C at a heating rate of 10 to 30°C / hr; d2) initiating a silanization reaction by stirring at a stirring speed of 300 to 600 rpm while maintaining the temperature within ±2°C when the temperature of the reaction mixture reaches 70 to 80°C; d3) continuing the silanization reaction for 5 to 9 hours, wherein the pH is re-measured every 2 to 4 hours after the start of the reaction, and if the pH exceeds 4.5, 0.1 to 0.5 parts by weight of glacial acetic acid are additionally added dropwise to 100 parts by weight of the reaction mixture to readjust the pH to a range of 3.9 to 4.2; and d4) cooling the reaction mixture to 20 to 30°C at a cooling rate of 5 to 15°C / hr when the silanization reaction is completed; The method is characterized by including, wherein the silanization reaction is performed at a temperature of 75 ± 3℃ for 7 ± 1 hour to form Si-OC covalent bonds through a dehydration condensation reaction between hydroxyl groups (-OH) on the surface of nanocellulose and silanol groups (Si-OH) derived from the silane coupling agent, and the stirring is performed using a magnetic stirrer or an overhead mechanical stirrer so that the temperature deviation within the reaction mixture is within ±2℃.

[0042] At this time, the silane coupling agent is characterized by being selected from the group consisting of (3-aminopropyl)triethoxysilane (APTES), (3-aminopropyl)trimethoxysilane (APTMS), (3-glycidoxypropyl)trimethoxysilane (GPTMS), (3-mercaptopropyl)trimethoxysilane (MPTMS), and combinations thereof.

[0043] Specific details for implementing the invention

[0044] Reasons for selecting each material and technical significance

[0045] 1. Reason for Choosing Ethanol

[0046] Ethanol is a polar protic solvent that provides a medium capable of carrying out the hydrolysis reaction of APTES at an appropriate rate. APTES possesses three ethoxy groups (-OEt), and these ethoxy groups must be hydrolyzed and converted into silanol groups (-Si-OH) to cause a condensation reaction with the hydroxyl groups (-OH) on the surface of nanocellulose.

[0047] Ethanol has lower polarity compared to water, which inhibits the excessive hydrolysis and self-condensation of APTES, while possessing sufficient polarity to facilitate the hydrolysis reaction between APTES and water. If water is used as the sole solvent, the hydrolysis of APTES proceeds too rapidly, causing it to precipitate as silica oligomers or silica particles before adsorbing onto the nanocellulose surface, making it difficult to form a core-shell structure. Conversely, if the ethanol content is excessively high, the hydrolysis rate becomes too slow, reducing silanization efficiency and prolonging the reaction time.

[0048] Therefore, in the present invention, the hydrolysis rate of APTES and the adsorption rate onto the nanocellulose surface are balanced through the optimal ratio of ethanol and water, so that a silica shell is uniformly formed on the nanocellulose surface.

[0049] 2. Reasons for Choosing Deionized Water

[0050] Deionized water is pure water from which ionic impurities have been removed, and it is essential to prevent side reactions caused by impurities and to ensure the reproducibility of the reaction in the hydrolysis reaction of APTES. Trace amounts of metal ions (Na⁻, Ca²⁻, Mg²⁻, etc.) contained in ordinary tap water or distilled water can promote the condensation reaction of silanol groups, which can lead to the formation of unintended silica particles, and anions (Cl⁻, SO₄²⁻, etc.) can form salts with the amine groups of APTES, thereby reducing reactivity.

[0051] Since these impurities are removed from deionized water, the ethoxy groups of APTES selectively react only with water molecules to generate silanol groups, which enable these silanol groups to efficiently undergo a condensation reaction with the hydroxyl groups on the surface of nanocellulose. In addition, deionized water maintains the initial pH of the reaction mixture close to neutral, providing a basis for precisely controlling the amount of glacial acetic acid added in the subsequent pH adjustment step.

[0052] 3. Reason for selecting silane coupling agents, particularly (3-aminopropyl)triethoxysilane (APTES). In the present invention, aminoalkyltrialkoxysilane-based silane coupling agents are used, and among them, (3-aminopropyl)triethoxysilane (APTES) is a positive silane coupling agent widely used in the synthesis of organic-inorganic hybrid materials, and it possesses three ethoxy groups (-Si(OEt)₃) and one amine group (-NH₂) simultaneously within its molecule. Other silane coupling agents, such as (3-glycidoxypropyl)trimethoxysilane (GPTMS), (3-mercaptopropyl)trimethoxysilane (MPTMS), and vinyltriethoxysilane (VTES), can also be used. However, if methyltriethoxysilane (MTES), which lacks amine groups, is used, the initial adsorption to the surface of nanocellulose is weak due to the absence of amine groups, and interfacial bonding with the cement matrix is ​​also insufficient. In addition, when using unsaturated silanes such as vinyltriethoxysilane (VTES), the vinyl groups may undergo polymerization, leading to the formation of unintended cross-linked structures.

[0053] Therefore, in the present invention, an aminoalkyltrialkoxysilane-based silane coupling agent, preferably APTES, was selected as the silane coupling agent by comprehensively considering efficient bonding with nanocellulose, interface reinforcement with the cement matrix, economic feasibility, and suitability for mass production.

[0054] 4. Reason for Choosing Nanocellulose

[0055] Nanocellulose is a bio-based nanomaterial obtained by mechanically or chemically breaking down natural cellulose into nano-sized particles, and it possesses advantages such as a high specific surface area (100 to 500 m² / g), abundant surface hydroxyl groups, excellent water retention capacity, biodegradability, and renewableity.

[0056] The reasons for selecting nanocellulose as the core material in this invention are as follows. First, the abundant hydroxyl groups on the surface of nanocellulose provide a large number of reaction sites capable of forming Si-OC covalent bonds through dehydration condensation reactions with APTES-derived silanol groups, thereby allowing the silica shell to be strongly bonded to the nanocellulose surface. Second, nanocellulose possesses a high moisture retention capacity, allowing it to retain the moisture necessary for cement hydration within the tile adhesive for an extended period and release it slowly, ensuring that sufficient cement hydration proceeds even in dry environments. Third, nanocellulose is environmentally friendly due to its biodegradability and renewableity, and is a sustainable material capable of replacing petroleum-based synthetic polymers.

[0057] If only silica nanoparticles are used instead of nanocellulose, there is a cement hydration promoting effect, but the water retention capacity is insufficient, so cement hydration proceeds insufficiently in dry environments and adhesive strength decreases. Conversely, if only cellulose ether is used, the water retention capacity is excellent, but the cement hydration promoting effect is minimal and the interfacial strengthening effect is insufficient.

[0058] Therefore, the present invention aims to comprehensively improve the performance of tile adhesives by simultaneously realizing the moisture retention capacity of cellulose and the cement hydration-promoting effect of silica through a core-shell structure in which nanocellulose serves as the core and APTES-derived silica serves as the shell.

[0059] 5. Reason for Choosing Glacial Acetic Acid

[0060] Glacial acetic acid is an acetic anhydride with a purity of over 99% and is used as an acid catalyst to promote the hydrolysis and condensation reactions of APTES. In silane coupling reactions, pH is one of the most important variables determining the reaction rate and the structure of the product, and generally, under weakly acidic conditions of pH 3 to 5, the rate of silanol group formation and the condensation reaction rate are balanced, making it possible to form a uniform silica shell.

[0061] The reasons for selecting glacial acetic acid as the acid catalyst in the present invention are as follows. First, glacial acetic acid is a weak acid (pKa - 4.76) and can gradually adjust the pH through buffering action without rapidly lowering the pH, allowing the pH of the reaction mixture to be precisely controlled within a target range (3.9 to 4.1). Second, glacial acetic acid is volatile and is easily removed during the filtration and washing process after the reaction is complete, and does not remain in the final product, thus not adversely affecting the performance of the tile adhesive. Third, glacial acetic acid selectively hydrolyzes the ethoxy groups of APTES without hydrolyzing the glycosidic bonds of nanocellulose, thereby maintaining the structural integrity of nanocellulose.

[0062] If a strong acid (e.g., hydrochloric acid, sulfuric acid) is used instead of glacial acetic acid, the pH becomes too low, causing the glycosidic bonds of nanocellulose to hydrolyze and cleave the cellulose chains. Additionally, the hydrolysis of APTES proceeds excessively rapidly, leading to the precipitation of silica oligomers and making it difficult to form a core-shell structure. Conversely, if a weak acid (e.g., phosphoric acid) is used, the buffering capacity is weak, making pH control difficult and reducing reaction reproducibility.

[0063] Therefore, in the present invention, glacial acetic acid was selected as an acid catalyst by comprehensively considering precise pH control, ease of removal due to volatility, and preservation of the nanocellulose structure.

[0064] [Critical Significance of Step-by-Step Conditions]

[0065] [Critical Significance of the Mixed Solvent Preparation Step]

[0066] Critical significance of 70 to 85 parts by weight of ethanol and 15 to 30 parts by weight of deionized water:

[0067] The weight ratio of ethanol to deionized water is the most important variable determining the hydrolysis rate of APTES. When the ethanol content is less than 70 parts by weight, the water content becomes relatively high, causing the hydrolysis of APTES to proceed too rapidly, and the generated silanol groups condense with each other before being adsorbed onto the surface of nanocellulose to precipitate as silica oligomers or silica particles. In this case, a core-shell structure is not formed, and only a state in which nanocellulose and silica particles are physically mixed is obtained.

[0068] Conversely, if the ethanol content exceeds 85 parts by weight, the water content becomes too low, which delays the hydrolysis of APTES and results in insufficient silanol group formation; in this case, a silica shell is not uniformly formed on the surface of the nanocellulose but is only partially coated. Additionally, an excess of ethanol can reduce the dispersion stability of the nanocellulose and cause aggregation.

[0069] In the present invention, by limiting the range to 70 to 85 parts by weight of ethanol and 15 to 30 parts by weight of deionized water, the hydrolysis rate of APTES and the adsorption rate of silanol groups onto the nanocellulose surface are balanced, thereby allowing a silica shell to be uniformly formed on the nanocellulose surface. In particular, it was experimentally confirmed that a composition of 80 parts by weight of ethanol and 20 parts by weight of deionized water (4:1 ratio) provides the best core-shell structure.

[0070] Critical significance of the initial pH range of 6.5 to 8.0:

[0071] The initial pH of the mixed solvent serves as a reference point for determining the amount of glacial acetic acid added in the subsequent pH adjustment step. If the initial pH is below 6.5, the mixed solvent is already acidic, causing the hydrolysis of APTES to begin prematurely and unintended, which reduces the reproducibility of the pH adjustment step. Additionally, under acidic conditions, the surface charge of nanocellulose changes, which may weaken the electrostatic interaction with APTES.

[0072] Conversely, if the initial pH exceeds 8.0, the mixed solvent becomes basic, causing the amine groups of APTES to deprotonate; in this case, the electrostatic attraction with the nanocellulose surface is weakened, resulting in insufficient initial adsorption. Additionally, under basic conditions, the condensation reaction of silanol groups is excessively promoted, leading to increased production of silica oligomers.

[0073] In the present invention, by limiting the initial pH to a range of 6.5 to 8.0, APTES and nanocellulose are mixed under conditions close to neutral, and a basis is provided for precisely controlling the pH to a target range through the subsequent addition of glacial acetic acid.

[0074] Critical significance of a temperature range of 15 to 30℃ and a stirring speed of 100 to 500 rpm:

[0075] The temperature of the mixed solvent determines the miscibility of ethanol and deionized water and the hydrolysis initiation temperature upon subsequent addition of APTES. If the temperature is below 15°C, the viscosity of ethanol and water increases, resulting in non-uniform mixing, and localized supercooling occurs upon addition of APTES, which lowers the solubility of APTES. Conversely, if the temperature exceeds 30°C, the volatilization of ethanol increases, altering the composition of the mixed solvent, and the hydrolysis of APTES may begin prematurely and unintendedly.

[0076] The stirring speed determines the uniformity of the mixed solvent. If the stirring speed is less than 100 rpm, the mixing of ethanol and water is insufficient, resulting in localized compositional deviations; in this case, the hydrolysis rate is non-uniform upon subsequent addition of APTES. Conversely, if the stirring speed exceeds 500 rpm, the mechanical shear force is excessive, which may cause mechanical breakage of cellulose chains after the addition of nanocellulose. Additionally, excessive stirring may introduce air, leading to the oxidation of APTES.

[0077] In the present invention, by limiting the temperature to 15 to 30°C and the stirring speed to 100 to 500 rpm, ethanol and deionized water are uniformly mixed, and a reaction solvent suitable for subsequent APTES addition and nanocellulose input is prepared.

[0078] [Critical Significance of the APTES and Nanocellulose Addition Steps]

[0079] Critical significance of 15 to 25 parts by weight of APTES per 100 parts by weight of mixed solvent:

[0080] The amount of APTES added determines the thickness and coverage rate of the silica shell formed on the surface of nanocellulose. If the amount of APTES is less than 15 parts by weight, the production of silanol groups is insufficient, so the silica shell is formed only partially on the surface of nanocellulose; in this case, the stability of the core-shell structure is low and the cement hydration promoting effect is insufficient. In addition, a lack of APTES results in reduced moisture stability because the hydroxyl groups on the surface of nanocellulose are not sufficiently silanized.

[0081] Conversely, if the amount of APTES exceeds 25 parts by weight, the excess APTES cannot be adsorbed onto the surface of the nanocellulose and self-condenses to precipitate as silica particles; in this case, the nanocellulose and silica particles are mixed rather than forming a core-shell structure. Additionally, the excess amount of APTES excessively increases the viscosity of the reaction mixture, making stirring difficult and reducing economic efficiency.

[0082] In the present invention, by limiting the amount of APTES to 15 to 25 parts by weight, a uniform silica shell is formed on the surface of nanocellulose, and the precipitation of silica particles caused by an excess amount of APTES is prevented. In particular, it was confirmed that 20 parts by weight of APTES provides an optimal core-shell structure for 4 parts by weight of nanocellulose (4:1 ratio).

[0083] Critical significance of a dropping rate of 0.5 to 2.0 mL / min:

[0084] The dropping rate of APTES determines the uniformity of the hydrolysis reaction. If the dropping rate is too slow, less than 0.5 mL / min, the reaction time becomes excessively long and productivity decreases. Additionally, the silanol group generated by the hydrolysis of the first added APTES starts the condensation reaction before the subsequently added APTES, which reduces the uniformity of the silica shell.

[0085] Conversely, if the dropping rate exceeds 2.0 mL / min, the local APTES concentration becomes excessively high, leading to rapid hydrolysis, and the generated silanol groups condense with each other to precipitate as silica oligomers before adsorbing to the nanocellulose surface. Additionally, rapid addition locally raises the temperature of the reaction mixture (APTES hydrolysis is an exothermic reaction), making reaction control difficult.

[0086] In the present invention, the dropping rate of APTES is limited to 0.5 to 2.0 mL / min so that APTES is uniformly dispersed throughout the mixed solvent and hydrolysis proceeds uniformly. In particular, it is desirable to precisely control the dropping rate using a metering pump.

[0087] Critical significance of stirring for 10 to 30 minutes at a stirring speed of 200 to 400 rpm:

[0088] The first stirring step after the addition of APTES is a step to uniformly disperse APTES throughout the mixed solvent and generate silanol groups through hydrolysis. If the stirring speed is less than 200 rpm, the dispersion of APTES is non-uniform, forming a region with a locally high concentration of APTES, and excessive hydrolysis and condensation occur in this region, resulting in the precipitation of silica oligomers.

[0089] Conversely, if the stirring speed exceeds 400 rpm, the mechanical shear force is excessive, which promotes the condensation of the generated silanol groups and also increases the incorporation of air, which can cause the amine groups of APTES to be oxidized.

[0090] If the stirring time is less than 10 minutes, the hydrolysis of APTES is insufficient, resulting in a lack of silanol group production. Conversely, if the stirring time exceeds 30 minutes, the generated silanol groups condense excessively and grow into silica oligomers.

[0091] In the present invention, by limiting the stirring speed to 200 to 400 rpm and the stirring time to 10 to 30 minutes, APTES is uniformly dispersed and an appropriate amount of silanol groups are generated through hydrolysis.

[0092] Critical significance of 3 to 7 parts by weight of nanocellulose per 100 parts by weight of mixed solvent:

[0093] The amount of nanocellulose added determines the size of the core and the ratio with APTES. If the amount of nanocellulose is less than 3 parts by weight, the ratio of nanocellulose to APTES is too low, so an excess amount of APTES cannot be adsorbed onto the surface of the nanocellulose and precipitates as silica particles, in which case the yield of the core-shell structure is low and economic feasibility is reduced.

[0094] Conversely, if the amount of nanocellulose exceeds 7 parts by weight, the ratio of nanocellulose to APTES is too high, so a silica shell is not sufficiently formed on the surface of the nanocellulose, and some nanocellulose remains unsilanized. In addition, an excess of nanocellulose excessively increases the viscosity of the reaction mixture, making stirring difficult and potentially causing nanocellulose aggregation.

[0095] In the present invention, by limiting the amount of nanocellulose to 3 to 7 parts by weight, the ratio of APTES to nanocellulose is set to 3:1 to 5:1, thereby forming a uniform silica shell on the surface of the nanocellulose and maximizing the yield of the core-shell structure.

[0096] Critical significance of divided injection into 2 to 5 times and an interval of 5 to 15 minutes between each injection:

[0097] The divided input of nanocellulose is a key technology for preventing the aggregation of nanocellulose and maximizing the contact area with APTES. When the entire amount of nanocellulose is input at once, the nanocellulose particles come into contact with each other and form aggregates through hydrogen bonding, and the nanocellulose inside the aggregates does not come into contact with APTES and is not silanized.

[0098] If the number of divided inputs is less than 2 (i.e., the entire amount is input once), the above-mentioned aggregation problem occurs, and if the number of divided inputs exceeds 5, the amount of each input is too small, making the process complex and reducing productivity.

[0099] If the interval between each input is less than 5 minutes, the next nanocellulose is input before APTES is sufficiently adsorbed onto the surface of the first nanocellulose, which may cause aggregation between the nanocelluloses. Conversely, if the interval between each input exceeds 15 minutes, the silanol groups on the surface of the first nanocellulose condense excessively, causing the silica shell to grow unevenly.

[0100] In the present invention, nanocellulose is divided and added in 2 to 5 times, and the interval between each addition is limited to 5 to 15 minutes, thereby preventing the aggregation of nanocellulose and ensuring that APTES is uniformly adsorbed on the surface of each nanocellulose.

[0101] Critical significance of stirring for 30 to 90 minutes at a stirring speed of 300 to 600 rpm:

[0102] The secondary stirring after the addition of nanocellulose is a step to complete the initial adsorption by ensuring that the silanol groups of APTES adsorbed on the nanocellulose surface sufficiently come into contact with the hydroxyl groups on the nanocellulose surface. If the stirring speed is less than 300 rpm, the dispersion of nanocellulose is insufficient, leading to the formation of localized areas of high nanocellulose concentration and the occurrence of aggregation.

[0103] Conversely, if the stirring speed exceeds 600 rpm, the mechanical shear force is excessive, which may cause APTES adsorbed on the nanocellulose surface to be desorbed or the nanocellulose chains to be mechanically cut.

[0104] If the stirring time is less than 30 minutes, the adsorption of APTES onto the surface of nanocellulose is insufficient, and conversely, if the stirring time exceeds 90 minutes, the adsorbed silanol groups condense excessively, causing cross-linking between nanocelluloses and forming large aggregates.

[0105] In the present invention, by limiting the stirring speed to 300 to 600 rpm and the stirring time to 30 to 90 minutes, the nanocellulose is uniformly dispersed, APTES is sufficiently adsorbed on the surface, and aggregation is prevented.

[0106] Critical significance of ultrasonic dispersion treatment at a frequency of 20 to 60 kHz for 5 to 30 minutes:

[0107] Nanocellulose is prone to forming aggregates through hydrogen bonding due to its high specific surface area and abundant surface hydroxyl groups. Ultrasonic dispersion treatment is an effective method for dispersing nanocellulose aggregates into primary particles using the cavitation of ultrasound.

[0108] When the ultrasonic frequency is less than 20 kHz, the cavitation is excessively strong and the nanocellulose chains are mechanically cut, and conversely, when the frequency exceeds 60 kHz, the cavitation is weak and the aggregate dispersion effect is insufficient.

[0109] If the ultrasonic treatment time is less than 5 minutes, the nanocellulose aggregates are not completely dispersed, and conversely, if the treatment time exceeds 30 minutes, the nanocellulose may be thermally decomposed due to localized overheating, and the economic efficiency is reduced due to excessive energy consumption.

[0110] In the present invention, by limiting the ultrasonic frequency to 20 to 60 kHz and the treatment time to 5 to 30 minutes, the nanocellulose aggregates are effectively dispersed into primary particles (average particle size 50 to 500 nm) and subsequent APTES adsorption proceeds uniformly.

[0111] [Critical Significance of the pH Adjustment Step]

[0112] Critical Significance of Confirming the Initial pH Range of 6.5 to 8.0:

[0113] Checking the initial pH of the reaction mixture before pH adjustment is essential for determining the amount of subsequent glacial acetic acid to be added and for ensuring the reproducibility of the reaction. If the initial pH falls outside the expected range, it implies that the hydrolysis of APTES has proceeded unintentionally and prematurely or that the composition of the mixed solvent has deviated from the design; in this case, the batch must be discarded and a new batch prepared.

[0114] By accurately measuring the initial pH using a digital pH meter, the amount of subsequent glacial acetic acid to be added can be calculated and the titration amount to reach the target pH (3.9 to 4.1) can be determined.

[0115] Critical significance of a dropping rate of 0.1 to 0.5 mL / min of glacial acetic acid and pH measurements at intervals of 30 seconds to 2 minutes:

[0116] The dropwise addition rate of glacial acetic acid determines the rate of pH change. If the addition rate is too slow, less than 0.1 mL / min, the time required for pH adjustment becomes excessively long and productivity decreases. Conversely, if the addition rate exceeds 0.5 mL / min, the pH drops rapidly, making it easy to overshoot the target range; in this case, reaction control becomes complex because a base must be added to raise the pH back up.

[0117] If the pH measurement interval is less than 30 seconds, the response time of the pH electrode is insufficient, making it difficult to measure the pH accurately. Conversely, if the measurement interval exceeds 2 minutes, it is difficult to track pH changes in real time, and there is a risk of exceeding the target range.

[0118] By using a metering pump to precisely control the dropping rate of glacial acetic acid and monitoring the pH with a pH meter at intervals of 30 seconds to 2 minutes, the pH can be precisely adjusted to a target range (3.8 to 4.2).

[0119] Critical significance of 0.5 to 3.0 parts by weight of glacial acetic acid per 100 parts by weight of reaction mixture:

[0120] The total amount of glacial acetic acid added determines the final pH and the buffering capacity of the reaction mixture. If the amount of glacial acetic acid is less than 0.5 parts by weight, the pH reduction is insufficient and the target pH (3.9 to 4.1) is not reached, and in this case, the hydrolysis rate of APTES is too slow and the formation of silanol groups is insufficient.

[0121] Conversely, if the amount of glacial acetic acid exceeds 3.0 parts by weight, the pH becomes excessively low (pH < 3.5), causing the glycosidic bonds of nanocellulose to be hydrolyzed and the cellulose chains to be cleaved, and the excess acid protonates the amine groups of APTES to form acetate salts, thereby reducing the reactivity of the amine groups.

[0122] In the present invention, by limiting the amount of glacial acetic acid to 0.5 to 3.0 parts by weight, the pH is controlled to a target range, the structural integrity of nanocellulose is maintained, and the reactivity of APTES is preserved.

[0123] Critical significance of stopping glacial acetic acid addition and stirring at 100 to 300 rpm when the pH range of 3.8 to 4.2 is reached:

[0124] When the pH reaches the range of 3.8 to 4.2, the addition of glacial acetic acid should be stopped immediately to prevent an excessive drop in pH. Afterward, stirring at a low stirring speed of 100 to 300 rpm for 5 to 15 minutes is done to equalize the pH of the entire reaction mixture and to reach buffer equilibrium.

[0125] If the stirring speed is less than 100 rpm, the mixing of the reaction mixture is insufficient, and local pH variations may exist. Conversely, if the stirring speed exceeds 300 rpm, APTES adsorbed on the surface of nanocellulose may be desorbed due to mechanical shear force.

[0126] If the stirring time is less than 5 minutes, pH equilibrium is not reached, and conversely, if the stirring time exceeds 15 minutes, the adsorbed silanol groups begin premature condensation, making it difficult to control the subsequent silanization reaction.

[0127] Critical Significance of Confirming the Final pH Range of 3.9 to 4.1:

[0128] A final pH of 3.9 to 4.1 is the optimal pH range in which the hydrolysis rate and condensation reaction rate of APTES are balanced. If the pH is below 3.9, the acid catalyst concentration is excessive, causing the hydrolysis of APTES to proceed too rapidly, and the generated silanol groups condense with each other before being adsorbed onto the nanocellulose surface, precipitating as silica oligomers. Additionally, excessively acidic conditions hydrolyze the glycosidic bonds of nanocellulose, cleaving the cellulose chains.

[0129] Conversely, if the pH exceeds 4.1, the acid catalyst concentration is insufficient, so the hydrolysis of APTES is slow, and the amount of silanol groups produced is insufficient, so a silica shell is not uniformly formed on the surface of the nanocellulose.

[0130] In the present invention, by precisely controlling the final pH to a narrow range of 3.9 to 4.1, the hydrolysis and condensation reactions of APTES are balanced, and a uniform silica shell is formed on the surface of nanocellulose. In particular, it was confirmed that a pH of 4.0 ± 0.1 provides the best core-shell structure.

[0131] [Critical Significance of the Silanization Reaction Step]

[0132] Critical significance of a heating rate of 10 to 30℃ / hr from 15 to 25℃ to 70 to 80℃:

[0133] The silanization reaction is a highly temperature-sensitive reaction, and a rapid increase in temperature causes localized overheating, making reaction control difficult. If the heating rate is too slow, less than 10℃ / hr, the time required to reach the target temperature becomes excessively long (more than 6 hours), and productivity decreases.

[0134] Conversely, if the heating rate exceeds 30℃ / hr, the temperature of the reaction mixture rises rapidly, locally excessively promoting the condensation reaction of silanol groups adsorbed on the surface of nanocellulose, and in this case, the silica shell is formed unevenly. In addition, rapid heating causes rapid evaporation of ethanol, which changes the composition of the reaction mixture and may lead to nanocellulose aggregation.

[0135] In the present invention, by limiting the heating rate to 10 to 30°C / hr, the entire reaction mixture is heated uniformly and the silanol groups on the surface of the nanocellulose gradually start a condensation reaction, thereby promoting the formation of a uniform silica shell.

[0136] Critical significance of maintaining a reaction temperature of 70 to 80°C and controlling temperature deviation within ±2°C:

[0137] The optimal temperature for the silanization reaction is 70 to 80°C. If the reaction temperature is below 70°C, the condensation reaction rate of the silanol groups is too slow, resulting in an excessively long reaction time (more than 10 hours), and a silica shell is not sufficiently formed on the surface of the nanocellulose.

[0138] Conversely, if the reaction temperature exceeds 80°C, the condensation reaction proceeds too rapidly, causing the silica shell to grow unevenly, and the high temperature can cause thermal decomposition of nanocellulose, and as it approaches the boiling point of ethanol (78°C), the ethanol evaporates rapidly, changing the composition of the reaction mixture.

[0139] If the temperature deviation exceeds ±2℃, a temperature gradient is formed within the reaction mixture; consequently, the condensation reaction proceeds rapidly in the high-temperature region while proceeding slowly in the low-temperature region, resulting in reduced uniformity of the resulting core-shell structure.

[0140] In the present invention, by maintaining the reaction temperature at 70 to 80°C and controlling the temperature deviation within ±2°C, the condensation reaction of the silanol groups proceeds uniformly at an appropriate rate and a uniform silica shell is formed on the surface of the nanocellulose. In particular, it was confirmed that 75 ± 3°C provides the best core-shell structure.

[0141] Critical significance of stirring speeds of 300 to 600 rpm:

[0142] Stirring during the silanization reaction is essential to maintain a uniform temperature of the reaction mixture and prevent the aggregation of nanocellulose. If the stirring speed is less than 300 rpm, heat transfer of the reaction mixture is insufficient, causing temperature variations and the nanocellulose to settle and form aggregates.

[0143] Conversely, if the stirring speed exceeds 600 rpm, the mechanical shear force becomes excessive, which may cause the silica shell being formed to detach from the nanocellulose surface or mechanically cut the nanocellulose chains. In addition, excessive stirring promotes the evaporation of ethanol, thereby changing the composition of the reaction mixture.

[0144] In the present invention, by limiting the stirring speed to 300 to 600 rpm, the temperature of the reaction mixture is maintained uniformly, the nanocellulose is maintained in a dispersed state, and the silica shell being formed is not damaged.

[0145] Critical Significance of Reaction Times of 5 to 9 Hours:

[0146] The silanization reaction time determines the thickness and density of the silica shell. If the reaction time is less than 5 hours, the condensation reaction of the silanol groups is insufficient, resulting in a thin and incomplete silica shell formation. In this case, the stability of the core-shell structure is low and moisture stability is insufficient.

[0147] Conversely, if the reaction time exceeds 9 hours, the silica shell grows excessively and becomes thick, and the silica shell cross-links between adjacent nanocelluloses, forming large aggregates. In addition, maintaining a high temperature for a long time can cause thermal decomposition of nanocellulose, and excessive energy consumption reduces economic efficiency.

[0148] In the present invention, by limiting the reaction time to 5 to 9 hours, a uniform silica shell of appropriate thickness is formed on the surface of nanocellulose and cross-linking between nanocelluloses is prevented. In particular, it was confirmed that 7 ± 1 hour provides the best core-shell structure.

[0149] Critical significance of pH remeasurement and readjustment every 2 to 4 hours after reaction start:

[0150] During the silanization reaction, water molecules are generated by the condensation reaction, and these water molecules promote the hydrolysis of residual APTES, thereby increasing the pH of the reaction mixture. If the pH exceeds 4.5, the acid catalyst concentration is insufficient, which lowers the condensation reaction rate and causes non-uniform growth of the silica shell.

[0151] If the pH remeasurement interval is less than 2 hours, the measurement frequency becomes excessive and the process becomes complex; conversely, if the remeasurement interval exceeds 4 hours, the increase in pH cannot be detected in a timely manner, making reaction control difficult.

[0152] When the pH exceeds 4.5, 0.1 to 0.5 parts by weight of glacial acetic acid are added dropwise to readjust the pH to a range of 3.9 to 4.2, thereby maintaining the pH within the optimal range throughout the entire reaction period and ensuring that the silica shell grows uniformly.

[0153] Critical significance of cooling to 20 to 30°C at a cooling rate of 5 to 15°C / hr:

[0154] Rapid cooling after the completion of the silanization reaction can induce thermal stress in the formed silica shell, causing cracks or delamination at the interface between the nanocellulose and the silica shell. If the cooling rate is too slow, such as less than 5℃ / hr, the time required for cooling becomes excessively long (more than 10 hours) and productivity decreases.

[0155] Conversely, if the cooling rate exceeds 15℃ / hr, the temperature of the reaction mixture drops rapidly, causing thermal stress in the formed silica shell, and in this case, microcracks may form in the silica shell or it may peel off from the surface of the nanocellulose.

[0156] In the present invention, by limiting the cooling rate to 5 to 15℃ / hr and setting the final temperature to 20 to 30℃, the formed core-shell structure is stabilized without thermal stress. Slow cooling is very important for ensuring the structural stability of the silica shell.

[0157] [Critical Significance of Filtration and Washing Steps]

[0158] Technical reasons for the filtration and washing steps:

[0159] After the silanization reaction is completed, the reaction mixture contains impurities such as unreacted APTES, low molecular weight silica oligomers, glacial acetic acid, and ethanol in addition to the target core-shell structured hybrid nanoparticles. Since these impurities can degrade the quality of the final product and impair performance when applied to tile adhesives, they must be removed through filtration and washing.

[0160] Filtration is a process that separates solid-phase hybrid nanoparticles from liquid-phase impurities, and washing is a process that removes impurities adsorbed on the surface of hybrid nanoparticles or remaining in the pores between particles.

[0161] Specific implementation of the filtration method:

[0162] Filtration can be performed using vacuum filtration or centrifugation. Vacuum filtration is a method of filtering the reaction mixture under reduced pressure using a vacuum pump with a Buchner funnel and filter paper (pore size 0.2 to 1.0 μm); it is simple and suitable for large-scale processing. Centrifugation is a method of centrifuging at a centrifugal force of 4,000 to 10,000 rpm for 10 to 30 minutes to precipitate the hybrid nanoparticles and remove the supernatant; it has no loss due to filter paper and offers a high recovery rate.

[0163] The cake or precipitate obtained after filtration or centrifugation still contains a significant amount of liquid-phase impurities, so they must be removed through a washing step.

[0164] Critical Significance of Washing Solvents and Methods:

[0165] It is preferable to use distilled water or deionized water as a washing solvent. Water can effectively dissolve and remove polar impurities such as unreacted APTES, glacial acetic acid, and low molecular weight silica oligomers, and can also remove residual ethanol due to its high miscibility with ethanol. In addition, water is non-toxic, inexpensive, and environmentally friendly.

[0166] Washing is performed by adding a washing solvent (5 to 20 times the mass of the hybrid nanoparticles) to the filter cake or precipitate, stirring to redisperse, and then repeating the process of filtration or centrifugation. The appropriate number of washes is 3 to 5 times; if the number of washes is less than 3 times, the removal of impurities is insufficient, and conversely, if the number of washes exceeds 5 times, the loss of hybrid nanoparticles increases and the process becomes complicated.

[0167] After the final wash, the pH of the filtrate or supernatant is measured to check if it has reached neutral (pH 6 to 8), thereby confirming that residual glacial acetic acid has been sufficiently removed.

[0168] [Critical Significance of the Drying Step]

[0169] Reason for selecting the drying method:

[0170] One of the key technical features of the present invention is the adoption of room-temperature desiccator drying instead of conventional high-temperature oven drying (80 to 120°C). While high-temperature oven drying provides a rapid drying speed, it has the following drawbacks. First, high temperatures can induce excessive condensation of the silica shell formed on the surface of nanocellulose, causing the silica shell to shrink and crack. Second, high temperatures can induce thermal decomposition of nanocellulose. Third, high-temperature drying involves high energy consumption and a high environmental burden.

[0171] In contrast, room temperature desiccator drying offers the following advantages. First, slow drying at room temperature prevents excessive condensation of the silica shell and prevents cracking. Second, room temperature does not induce thermal decomposition of nanocellulose, thus maintaining structural integrity. Third, energy consumption is minimized, making it environmentally friendly and economical.

[0172] Reason for drying on silica gel:

[0173] Silica gel is a powerful desiccant that absorbs moisture from the surrounding air to keep the inside of the desiccator dry. When hybrid nanoparticles are placed on silica gel, moisture on the surface of the hybrid nanoparticles is absorbed by the silica gel, accelerating the drying process.

[0174] If drying is performed in a desiccator without silica gel, the humidity inside the desiccator increases, slowing down the drying speed, and prolonged exposure to a high-humidity environment can cause the silica shell on the surface of the hybrid nanoparticles to rehydrate, potentially altering their structure.

[0175] Critical significance of drying for 72 hours at room temperature (15 to 30℃):

[0176] If the drying temperature is below 15℃, the drying speed is excessively slow, resulting in an excessively long drying time (more than 100 hours), and conversely, if the drying temperature exceeds 30℃, the condensation of the silica shell is promoted, which may cause shrinkage and cracking.

[0177] If the drying time is less than 72 hours, moisture inside the hybrid nanoparticles is not completely removed, and residual moisture causes rehydration of the silica shell during storage, thereby reducing structural stability. Conversely, if the drying time exceeds 72 hours, there is minimal additional improvement in the drying effect and productivity decreases.

[0178] In the present invention, by placing the hybrid nanoparticles on silica gel at room temperature (15 to 30°C) and drying them in a desiccator for 72 hours, the moisture of the hybrid nanoparticles is completely removed, the structural stability of the silica shell is maximized, and energy consumption is minimized, thereby enabling environmentally friendly and economical production.

[0179] Importance of verifying final moisture content of 3% or less:

[0180] After drying is complete, it is desirable to measure the moisture content of the hybrid nanoparticles using thermogravimetric analysis (TGA) or Karl Fischer titration to confirm that it is 3% or less. If the moisture content exceeds 3%, rehydration of the silica shell and microbial degradation of the nanocellulose may occur during storage, and performance degradation due to moisture may occur when applied to tile adhesives.

[0181] Hybrid nanoparticles with a moisture content of 3% or less can be stored stably for more than 12 months in a sealed container at room temperature and can provide consistent performance when formulating tile adhesives.

[0182] [Summary and Comprehensive]

[0183] As described above, the method for manufacturing cellulose-silica hybrid nanoparticles of the present invention is precisely designed through scientific grounds and experimental optimization regarding the selection of each material and the conditions of each step, and each variable is organically interconnected to ultimately realize a uniform and stable core-shell structure.

[0184] In particular, the ratio of ethanol to deionized water, the ratio of APTES to nanocellulose, precise control of pH, stepwise heating and slow cooling, and room-temperature desiccator drying are key technical features of the present invention that differentiate it from conventional technology, and the combination of these features provides an innovative technology that comprehensively improves the early strength, interfacial densification, and long-term durability of tile adhesives.

[0185] [Example]

[0186] The present invention will be explained in more detail below through examples. However, the following examples are merely illustrative of the present invention, and the scope of the present invention is not limited thereto.

[0187] <Example 1> Preparation of cellulose-silica hybrid nanoparticles under standard conditions using APTES as a preferred embodiment of the present invention

[0188] Step 1: Preparation of Mixed Solvent

[0189] 640 g of ethanol and 160 g of deionized water were added to a 1000 mL beaker to prepare a total of 800 g of mixed solvent. This corresponds to 80 parts by weight of ethanol and 20 parts by weight of deionized water, with a weight ratio of 4:1. The initial pH of the mixed solvent was measured using a digital pH meter and found to be 7.2. The mixed solvent was uniformly mixed by stirring at 20°C at a stirring speed of 300 rpm for 10 minutes.

[0190] Step 2: Addition of APTES and Primary Hydrolysis

[0191] 160 g (20 parts by weight) of (3-aminopropyl)triethoxysilane (APTES, purity 98%, Sigma-Aldrich) was slowly added to 800 g (based on 100 parts by weight) of the above mixed solvent using a metering pump at a dropwise rate of 1.0 mL / min. During the addition of APTES, the stirring speed was maintained at 300 rpm. After the addition of APTES was completed, the hydrolysis of APTES was carried out by stirring at a stirring speed of 300 rpm for 20 minutes.

[0192] Step 3: Nanocellulose input

[0193] 32 g of nanocellulose (average particle size 200 nm, specific surface area 300 m² / g) (4 parts by weight per 100 parts by weight of mixed solvent) was dispersed in 100 mL of deionized water, and then the nanocellulose was dispersed into primary particles by ultrasonic treatment for 15 minutes using a 40 kHz ultrasonic disperser.

[0194] The ultrasonically treated nanocellulose dispersion was divided into four portions (8 g each) and added to the APTES hydrolysis mixture. The interval between each addition was 10 minutes, and the stirring speed was maintained at 400 rpm during addition. After the total amount of nanocellulose was added, the mixture was stirred at a stirring speed of 450 rpm for 60 minutes to ensure that APTES was uniformly adsorbed onto the surface of the nanocellulose.

[0195] Step 4: pH Adjustment

[0196] The initial pH of the reaction mixture was measured using a digital pH meter and found to be 7.5. 16 g of glacial acetic acid (99.5% purity, Merck) (1.6 parts by weight per 100 parts by weight of the reaction mixture) was slowly added using a metering pump at a dropwise rate of 0.3 mL / min while measuring the pH at 1-minute intervals. When the pH reached 4.0, the addition of glacial acetic acid was stopped, and the mixture was stirred at a stirring speed of 200 rpm for 10 minutes to homogenize the pH. The final pH was measured to be 4.0.

[0197] Step 5: Silanization reaction

[0198] The reaction mixture was transferred to a 500 mL three-necked flask equipped with an oil bath, and the temperature controller was set to gradually heat from 20°C to 75°C at a heating rate of 20°C / hr. After the temperature reached 75°C, the silanization reaction was carried out for 7 hours using a mechanical overhead stirrer at a stirring speed of 450 rpm while maintaining the temperature within ±1°C.

[0199] When the pH was re-measured 3 hours after the start of the reaction, it had risen to pH 4.3, so 3 g of glacial acetic acid was added dropwise to readjust the pH to 4.0. When the pH was re-measured 6 hours after the start of the reaction, it was confirmed to be pH 4.1, which is within the target range.

[0200] After the silanization reaction was completed, it was slowly cooled to 25℃ at a cooling rate of 10℃ / hr.

[0201] Step 6: Filtration and Washing

[0202] The cooled reaction mixture was filtered under reduced pressure using a Buchner funnel and filter paper (pore size 0.45 μm). 400 mL of deionized water (approximately 10 times the mass of the filter cake) was added to the filter cake and redispersed by stirring at 300 rpm for 10 minutes, after which the process of reduced pressure filtration was repeated 4 times. After the final wash, the pH of the filtrate was measured and confirmed to be neutral at pH 6.8.

[0203] Step 7: Drying

[0204] The washed hybrid nanoparticles were spread thinly in a Petri dish, placed in a desiccator filled with silica gel, and dried at room temperature (22°C) for 72 hours. After drying was complete, the hybrid nanoparticles were recovered, and the moisture content was measured by thermogravimetric analysis (TGA) and found to be 2.3%.

[0205] Finally, 38 g of cellulose-silica hybrid nanoparticles in the form of a white to light gray powder were obtained (yield: approximately 95% based on nanocellulose).

[0206] <Example 2> Conditions for increasing ethanol content

[0207] It was prepared in the same manner as in Example 1, but in the first step, 680 g of ethanol and 120 g of deionized water were mixed to prepare a total of 800 g of mixed solvent. This corresponds to 85 parts by weight of ethanol and 15 parts by weight of deionized water, with a weight ratio of approximately 5.7:1. The remaining process was carried out in the same manner as in Example 1.

[0208] <Example 3> Conditions for Reducing Ethanol Content

[0209] It was prepared in the same manner as in Example 1, but in the first step, 560 g of ethanol and 240 g of deionized water were mixed to prepare a total of 800 g of mixed solvent. This corresponds to 70 parts by weight of ethanol and 30 parts by weight of deionized water, with a weight ratio of approximately 2.3:1. The remaining process was carried out in the same manner as in Example 1.

[0210] <Example 4> Conditions for Increasing APTES Content

[0211] It was prepared in the same manner as in Example 1, except that 200 g of APTES (25 parts by weight relative to 100 parts by weight of mixed solvent) was added in step 2. Accordingly, the weight ratio of APTES to nanocellulose was approximately 6.3:1. The remaining process was carried out in the same manner as in Example 1.

[0212] <Example 5> Conditions for Reducing APTES Content

[0213] It was prepared in the same manner as in Example 1, except that 120 g of APTES (15 parts by weight relative to 100 parts by weight of mixed solvent) was added in step 2. Accordingly, the weight ratio of APTES to nanocellulose was approximately 3.8:1. The remaining process was carried out in the same manner as in Example 1.

[0214] <Example 6> Conditions for increasing nanocellulose content

[0215] It was prepared in the same manner as in Example 1, except that 56 g of nanocellulose (7 parts by weight per 100 parts by weight of mixed solvent) was added in step 3. Accordingly, the weight ratio of APTES to nanocellulose was approximately 2.9:1. The remaining process was carried out in the same manner as in Example 1.

[0216] <Example 7> Conditions for reducing nanocellulose content

[0217] It was prepared in the same manner as in Example 1, except that 24 g of nanocellulose (3 parts by weight per 100 parts by weight of mixed solvent) was added in step 3. Accordingly, the weight ratio of APTES to nanocellulose was approximately 6.7:1. The remaining process was carried out in the same manner as in Example 1.

[0218] <Example 8> pH upper limit condition

[0219] It was prepared in the same manner as in Example 1, except that in step 4, glacial acetic acid was added until the pH reached 4.2. The final pH was 4.2. The remaining process was carried out in the same manner as in Example 1.

[0220] <Example 9> pH lower limit condition

[0221] It was prepared in the same manner as in Example 1, except that in step 4, glacial acetic acid was added until the pH reached 3.8. The final pH was 3.8. The remaining process was carried out in the same manner as in Example 1.

[0222] <Example 10> Reaction temperature upper limit condition

[0223] It was prepared in the same manner as in Example 1, except that in step 5, the reaction temperature was set to 80°C and the silanization reaction was carried out at that temperature for 7 hours. The remaining process was carried out in the same manner as in Example 1.

[0224] <Example 11> Lower reaction temperature condition

[0225] It was prepared in the same manner as in Example 1, except that in step 5, the reaction temperature was set to 70°C and the silanization reaction was carried out at that temperature for 7 hours. The remaining process was carried out in the same manner as in Example 1.

[0226] <Example 12> Condition for increasing reaction time

[0227] It was prepared in the same manner as in Example 1, except that the silanization reaction time in step 5 was extended to 9 hours. The remaining process was carried out in the same manner as in Example 1.

[0228] <Example 13> Conditions for Reaction Time Reduction

[0229] It was prepared in the same manner as in Example 1, except that the silanization reaction time in step 5 was shortened to 5 hours. The remaining process was carried out in the same manner as in Example 1.

[0230] <Example 14> Minimum Condition for Divided Nanocellulose Input

[0231] It was prepared in the same manner as in Example 1, except that in step 3, the nanocellulose was divided into two portions (16 g each) and added. The interval between each addition was 15 minutes. The remaining process was carried out in the same manner as in Example 1.

[0232] <Example 15> Maximum conditions for split input of nanocellulose

[0233] It was prepared in the same manner as in Example 1, except that in step 3, the nanocellulose was divided into 5 portions (6.4 g each) and added. The interval between each addition was 5 minutes. The remaining process was carried out in the same manner as in Example 1.

[0234] <Comparative Example 1> Excess Ethanol Condition (Exceeding Scope of Invention)

[0235] The preparation was attempted in the same manner as in Example 1, but in the first step, 720 g of ethanol and 80 g of deionized water were mixed to prepare a total of 800 g of mixed solvent. This corresponds to 90 parts by weight of ethanol and 10 parts by weight of deionized water, with a weight ratio of 9:1. The remaining process was attempted to be carried out in the same manner as in Example 1.

[0236] <Comparative Example 2> Condition with insufficient ethanol (below the scope of the invention)

[0237] The preparation was attempted in the same manner as in Example 1, but in the first step, 480 g of ethanol and 320 g of deionized water were mixed to prepare a total of 800 g of mixed solvent. This corresponds to 60 parts by weight of ethanol and 40 parts by weight of deionized water, with a weight ratio of 1.5:1. The remaining process was attempted to be carried out in the same manner as in Example 1.

[0238] <Comparative Example 3> APTES Excess Condition (Exceeding Scope of Invention)

[0239] The preparation was attempted in the same manner as in Example 1, but 240 g of APTES (30 parts by weight per 100 parts by weight of mixed solvent) was added in step 2. Accordingly, the weight ratio of APTES to nanocellulose was approximately 7.5:1. The remaining process was attempted to be carried out in the same manner as in Example 1.

[0240] <Comparative Example 4> APTES Insufficient Condition (Insufficient Scope of Invention)

[0241] The preparation was attempted in the same manner as in Example 1, but 80 g of APTES (10 parts by weight per 100 parts by weight of mixed solvent) was added in step 2. Accordingly, the weight ratio of APTES to nanocellulose was approximately 2.5:1. The remaining process was attempted to be carried out in the same manner as in Example 1.

[0242] <Comparative Example 5> Condition of excessive pH increase (Exceeding the scope of the invention)

[0243] The preparation was attempted in the same manner as in Example 1, but glacial acetic acid was added in step 4 until the pH reached 4.5. The final pH was 4.5. The remaining process was attempted to be carried out in the same manner as in Example 1.

[0244] <Comparative Example 6> Condition of excessive pH reduction (Below scope of invention)

[0245] The preparation was attempted in the same manner as in Example 1, but glacial acetic acid was added in step 4 until the pH reached 3.5. The final pH was 3.5. The remaining process was attempted to be carried out in the same manner as in Example 1.

[0246] <Comparative Example 7> Excessive reaction temperature condition (Exceeding the scope of the invention)

[0247] The preparation was attempted in the same manner as in Example 1, but the reaction temperature was set to 90°C in step 5 and the silanization reaction was carried out at that temperature for 7 hours. The remaining process was attempted to be carried out in the same manner as in Example 1.

[0248] <Comparative Example 8> Condition with insufficient reaction temperature (below the scope of the invention)

[0249] The preparation was attempted in the same manner as in Example 1, but the reaction temperature was set to 60°C in step 5 and the silanization reaction was carried out at that temperature for 7 hours. The remaining process was attempted to be carried out in the same manner as in Example 1.

[0250] <Comparative Example 9> All-in-one addition of nanocellulose (no split addition)

[0251] The preparation was attempted in the same manner as in Example 1, but the entire 32 g of nanocellulose was added all at once in Step 3. The remaining processes were attempted to be carried out in the same manner as in Example 1.

[0252] <Comparative Example 10> Ultrasonic dispersion treatment not performed

[0253] The preparation was attempted in the same manner as in Example 1, but without performing ultrasonic dispersion treatment on the nanocellulose in step 3, it was directly added in a state dispersed in deionized water. The remaining processes were attempted to be carried out in the same manner as in Example 1.

[0254] <Comparative Example 11> High-temperature oven drying (room temperature desiccator drying not performed)

[0255] The hybrid nanoparticles washed in step 7 were prepared in the same manner as in Example 1, but instead of drying them in a room temperature desiccator, they were dried in an 80°C oven for 12 hours. The remaining process was carried out in the same manner as in Example 1.

[0256] <Comparative Example 12> Rapid heating conditions (gradual heating not performed)

[0257] The preparation was attempted in the same manner as in Example 1, but in step 5, the reaction mixture was directly heated from 20°C to 75°C (heating rate of approximately 50°C / hr). The remaining process was attempted to be carried out in the same manner as in Example 1.

[0258] <Comparative Example 13> Rapid cooling conditions (slow cooling not performed)

[0259] The preparation was attempted in the same manner as in Example 1, but after the silanization reaction was completed in Step 5, the reaction mixture was left at room temperature to cool naturally (cooling rate of about 30℃ / hr). The remaining process was attempted to be carried out in the same manner as in Example 1.

[0260] <Comparative Example 14> pH readjustment not performed

[0261] The preparation was attempted in the same manner as in Example 1, but pH remeasurement and readjustment were not performed during the silanization reaction in step 5. The remaining process was attempted to be carried out in the same manner as in Example 1.

[0262] <Comparative Example 15> Insufficient number of washes (1 wash)

[0263] The manufacturing process was attempted in the same manner as in Example 1, but washing was performed only once in step 6. The remaining processes were attempted to be carried out in the same manner as in Example 1.

[0264] [Summary Table of Compositions of Examples and Comparative Examples]

[0265] Table 1 below summarizes the manufacturing conditions of Examples 1 to 15 and Comparative Examples 1 to 15 above.

[0266] Manufacturing conditions of the examples and comparative examples division Ethanol (parts by weight) Deionized water (parts by weight) APTES (weight part) Nanocellulose (parts by weight) Glacial acetic acid (parts by weight) Final pH Reaction temperature (°C) Reaction time (time) Number of split inputs Ultrasonic dispersion Heating rate (°C / hr) Cooling rate (°C / hr) Drying method pH readjustment Washing frequency Example 1 80 20 20 4 1.6 4.0 75 7 4 O 20 10 Room temperature / 72h O 4 Example 2 85 15 20 4 1.8 4.0 75 7 4 O 20 10 Room temperature / 72h O 4 Example 3 70 30 20 4 1.4 4.0 75 7 4 O 20 10 Room temperature / 72h O 4 Example 4 80 20 25 4 1.6 4.0 75 7 4 O 20 10 Room temperature / 72h O 4 Example 5 80 20 15 4 1.6 4.0 75 7 4 O 20 10 Room temperature / 72h O 4 Example 6 80 20 20 7 1.6 4.0 75 7 4 O 20 10 Room temperature / 72h O 4 Example 7 80 20 20 3 1.6 4.0 75 7 4 O 20 10 Room temperature / 72h O 4 Example 8 80 20 20 4 1.4 4.2 75 7 4 O 20 10 Room temperature / 72h O 4 Example 9 80 20 20 4 1.8 3.8 75 7 4 O 20 10 Room temperature / 72h O 4 Example 10 80 20 20 4 1.6 4.0 80 7 4 O 20 10 Room temperature / 72h O 4 Example 11 80 20 20 4 1.6 4.0 70 7 4 O 20 10 Room temperature / 72h O 4 Example 12 80 20 20 4 1.6 4.0 75 9 4 O 20 10 Room temperature / 72h O 4 Example 13 80 20 20 4 1.6 4.0 75 5 4 O 20 10 Room temperature / 72h O 4 Example 14 80 20 20 4 1.6 4.0 75 7 2 O 20 10 Room temperature / 72h O 4 Example 15 80 20 20 4 1.6 4.0 75 7 5 O 20 10 Room temperature / 72h O 4 Comparative Example 1 90 10 20 4 2.0 4.0 75 7 4 O 20 10 Room temperature / 72h O 4 Comparative Example 2 60 40 20 4 1.2 4.0 75 7 4 O 20 10 Room temperature / 72h O 4 Comparative Example 3 80 20 30 4 1.6 4.0 75 7 4 O 20 10 Room temperature / 72h O 4 Comparative Example 4 80 20 10 4 1.6 4.0 75 7 4 O 20 10 Room temperature / 72h O 4 Comparative Example 5 80 20 20 4 1.2 4.5 75 7 4 O 20 10 Room temperature / 72h O 4 Comparative Example 6 80 20 20 4 2.0 3.5 75 7 4 O 20 10 Room temperature / 72h O 4 Comparative Example 7 80 20 20 4 1.6 4.0 90 7 4 O 20 10 Room temperature / 72h O 4 Comparative Example 8 80 20 20 4 1.6 4.0 60 7 4 O 20 10 Room temperature / 72h O 4 Comparative Example 9 80 20 20 4 1.6 4.0 75 7 1 O 20 10 Room temperature / 72h O 4 Comparative Example 10 80 20 20 4 1.6 4.0 75 7 4 X 20 10 Room temperature / 72h O 4 Comparative Example 11 80 20 20 4 1.6 4.0 75 7 4 O 20 10 80℃ / 12h O 4 Comparative Example 12 80 20 20 4 1.6 4.0 75 7 4 O 50 10 Room temperature / 72h O 4 Comparative Example 13 80 20 20 4 1.6 4.0 75 7 4 O 20 30 Room temperature / 72h O 4 Comparative Example 14 80 20 20 4 1.6 4.0 75 7 4 O 20 10 Room temperature / 72h X 4 Comparative Example 15 80 20 20 4 1.6 4.0 75 7 4 O 20 10 Room temperature / 72h O 1

[0267] Note: The weight parts of ethanol, deionized water, APTES, nanocellulose, and glacial acetic acid are relative weight parts based on 100 weight parts of the mixed solvent or reaction mixture.

[0268] [Experimental Example]

[0269] The following experimental examples were performed to evaluate the physical properties and application performance as tile adhesives of the hybrid nanoparticles prepared in Examples 1 to 15 and Comparative Examples 1 to 15 above.

[0270] <Experimental Example 1> Analysis of Morphology and Structure of Hybrid Nanoparticles

[0271] Hybrid nanoparticles prepared in Examples 1 to 15 and Comparative Examples 1 to 15 were observed using a scanning electron microscope (SEM, Hitachi S-4800) at three magnifications of 200 μm, 1 μm, and 100 nm. The samples were sputter-coated with gold and observed at an acceleration voltage of 5 kV. At least 10 particles were randomly selected from each sample to determine the average particle size and whether a core-shell structure was formed.

[0272] The criteria for evaluating the core-shell structure are as follows: Excellent: A uniform silica shell is formed on the nanocellulose surface, with a shell thickness ranging from 50 to 150 nm. Good: A silica shell is formed on the nanocellulose surface, but the thickness is non-uniform or some uncoated areas exist. Poor: A core-shell structure is not formed, and the nanocellulose and silica particles are physically mixed, or large aggregates are formed.

[0273] <Experimental Example 2> Analysis of Chemical Bonding of Hybrid Nanoparticles

[0274] The hybrid nanoparticles prepared in Examples 1 to 15 and Comparative Examples 1 to 15 were analyzed using Fourier Transform Infrared Spectroscopy (FT-IR, Bruker Tensor 27). A pellet was prepared by mixing 2 mg of the sample with 200 mg of KBr, and then scanned in the range of 4000 to 400 cm⁻¹ (resolution 4 cm⁻¹, number of scans 32).

[0275] The presence and relative intensity of characteristic peaks (1000 to 1100 cm⁻¹) of Si-OC bonding were analyzed to evaluate the degree of covalent bond formation between hydroxyl groups on the nanocellulose surface and silanol groups derived from APTES.

[0276] <Experimental Example 3> Analysis of Thermal Stability of Hybrid Nanoparticles

[0277] The hybrid nanoparticles prepared in Examples 1 to 15 and Comparative Examples 1 to 15 were analyzed using thermogravimetric analysis (TGA, TA Instruments Q500). 10 mg of the sample was placed in a platinum pan, and the weight change was measured while heating from 25°C to 800°C at a heating rate of 10°C / min in a nitrogen atmosphere (flow rate 60 mL / min).

[0278] The composition and thermal stability of the hybrid nanoparticles were evaluated by analyzing weight loss at 100°C (residual moisture), weight loss at 200 to 400°C (cellulose pyrolysis), and residual weight at 400°C or higher (silica content).

[0279] <Experimental Example 4> Evaluation of Dispersion Stability of Hybrid Nanoparticles

[0280] 1 g of the hybrid nanoparticles prepared in Examples 1 to 15 and Comparative Examples 1 to 15 were dispersed in 100 mL of deionized water and stirred at 300 rpm for 30 minutes. After stopping the stirring, the mixture was left for 24 hours to observe the sedimentation behavior.

[0281] The criteria for determining dispersion stability are as follows: Excellent: No precipitate is observed even after 24 hours, and a uniform suspension is maintained. Good: A small amount of precipitate occurs after 24 hours, but the supernatant is not transparent, and the state of fine particle dispersion is maintained. Poor: A large amount of precipitate occurs after 24 hours, and the supernatant is transparent.

[0282] <Experimental Example 5> Evaluation of Tile Adhesive Formulation and Workability

[0283] The performance of the hybrid nanoparticles prepared in Examples 1 to 15 and Comparative Examples 1 to 15 was evaluated by applying them to a tile adhesive. The basic formulation of the tile adhesive is as follows: 100 parts by weight of ordinary Portland cement, 150 parts by weight of silica sand (particle size 0.1 to 0.5 mm), 3 parts by weight of redispersible polymer powder (RDP, vinyl acetate-ethylene copolymer), 0.2 parts by weight of hybrid nanoparticles, and 30 parts by weight of water.

[0284] All ingredients except the hybrid nanoparticles in the above mixture were added to a Hobart mixer and mixed at low speed (140 rpm) for 3 minutes, then the hybrid nanoparticles were added and mixed at medium speed (285 rpm) for an additional 2 minutes. Water was added and mixed at low speed for 1 minute and at medium speed for 2 minutes to prepare a tile adhesive paste.

[0285] Workability was evaluated using a flow test (KS L 5111). Workability was determined to be excellent when the flow value was in the range of 180 to 220 mm.

[0286] <Experimental Example 6> Evaluation of Early Strength of Tile Adhesive

[0287] The tile adhesive paste prepared in Experimental Example 5 was filled into a 40 × 40 × 160 mm rectangular mold and demolded after curing for 24 hours under standard curing conditions (temperature 20 ± 2℃, relative humidity 95% or higher). After demolding, additional curing was performed under the same conditions, and the compressive strength was measured at 1, 3, 7, and 28 days of age (KS L ISO 679).

[0288] Three specimens were prepared for each age, and the average value was calculated. The compressive strength at 1 day of age was defined as the early strength.

[0289] <Experimental Example 7> Evaluation of Tile Adhesive Adhesive Strength

[0290] The tile adhesive paste prepared in Experimental Example 5 was applied to a thickness of 6 mm on a concrete substrate (300 × 300 × 50 mm), and a ceramic tile (100 × 100 × 6 mm) was attached by pressing. The tensile adhesive strength was measured after curing for 28 days under standard curing conditions (KS L 1001).

[0291] Five tiles were attached to each sample to calculate the average value. Tensile adhesive strength was defined as the value obtained by dividing the load at which the tile breaks when pulled vertically by the bonding area.

[0292] <Experimental Example 8> Evaluation of Adhesive Strength Retention Rate of Tile Adhesive After Immersion

[0293] Tiles were attached in the same manner as in Experimental Example 7 and cured for 28 days under standard curing conditions, after which they were completely immersed in deionized water at 20 ± 2℃ for an additional 28 days. After the immersion was complete, the samples were removed, the moisture on the surface was wiped off, and the tensile adhesive strength was measured immediately.

[0294] The adhesive strength retention rate was calculated by dividing the adhesive strength after immersion by the adhesive strength before immersion (value of Experimental Example 7) and converting it into a percentage. It was determined to have excellent durability when the adhesive strength retention rate was 85% or higher.

[0295] <Experimental Example 9> Analysis of Porosity of Cured Tile Adhesive

[0296] A 28-day-old prismatic specimen prepared in Experimental Example 6 was cut into 2 × 2 × 2 cm pieces, and the pore structure was analyzed using mercury intrusion porosymmetry (MIP, Micromeritics AutoPore IV). The measurement pressure range was 0.1 to 60,000 psia, which corresponds to a pore diameter range of approximately 200 μm to 3 nm.

[0297] The total porosity, average pore diameter, and pore size distribution were analyzed. In particular, the volume ratio of capillary pores (10 nm to 10 μm) and gel pores (3 to 10 nm) was calculated to quantitatively evaluate the changes in pore structure due to the addition of hybrid nanoparticles.

[0298] <Experimental Example 10> Measurement of Moisture Retention Rate of Tile Adhesive

[0299] 30 g of the tile adhesive paste prepared in Experimental Example 5 was placed in a Petri dish with a diameter of 50 mm and weighed after being left for 1 hour under standard curing conditions (W₁). The weight was measured again after being left for an additional 23 hours under the same conditions (W₂).

[0300] The moisture retention rate was calculated using the following formula: Moisture retention rate (%) = (W₂ / W₁) × 100. The higher the moisture retention rate, the longer the moisture required for cement hydration can be supplied, allowing for sufficient hydration to proceed even in dry environments.

[0301] <Experimental Example 11> Hydration Heat Analysis of Tile Adhesive

[0302] 5 g of tile adhesive paste (in powder form immediately before adding water) and 1.5 g of water prepared in Experimental Example 5 were introduced into an isothermal calorimeter (TAM Air Isothermal Calorimeter, TA Instruments), and the heat of hydration was measured at 25°C for 72 hours.

[0303] The effect of hybrid nanoparticles on the cement hydration rate was quantitatively evaluated by analyzing the duration of the induction period and acceleration period, the time to reach the maximum heat generation rate, and the cumulative heat generation in the heat of hydration curve.

[0304] <Experimental Example 12> Microstructure Analysis of Cured Tile Adhesive

[0305] A prismatic specimen aged 28 days prepared in Experimental Example 6 was cut to a size of 2 × 2 × 0.5 cm, and the fracture surface was impregnated with epoxy resin and then polished to produce a smooth surface. After carbon coating, the specimen was observed using a scanning electron microscope (SEM, JEOL JSM-7600F) at a magnification of 1,000 to 10,000 times. The acceleration voltage was set to 10 kV.

[0306] The interface transition zone (ITZ) between the tile and the adhesive matrix was observed in detail to analyze the dispersion state of the hybrid nanoparticles, the degree of CSH gel formation, the pore structure, and the occurrence of microcracks.

[0307] <Experimental Example 13> Measurement of Silica Shell Thickness of Hybrid Nanoparticles

[0308] The hybrid nanoparticles prepared in Examples 1, 4, and 5 were observed using a transmission electron microscope (TEM, JEOL JEM-2100F). The samples were dispersed in ethanol, dropped onto a copper grid, and dried. The silica shell thickness was measured from the contrast difference of the core-shell structure by observing at an acceleration voltage of 200 kV.

[0309] At least 20 particles were randomly selected for each sample to measure shell thickness, and the average value and standard deviation were calculated.

[0310] <Experimental Example 14> Measurement of Specific Surface Area of ​​Hybrid Nanoparticles

[0311] The specific surface area of ​​the hybrid nanoparticles prepared in Examples 1 to 15 and Comparative Examples 1 to 15 was measured using the nitrogen adsorption method (BET, Micromeritics ASAP 2020). After vacuum degassing 0.5 g of the sample at 150°C for 12 hours, the nitrogen adsorption-desorption isotherm was measured at 77 K.

[0312] The specific surface area was calculated using the BET equation, and the pore size distribution was analyzed using the BJH method. A larger specific surface area indicates a higher number of cement hydration nucleation sites, resulting in a superior hydration-promoting effect.

[0313] <Experimental Example 15> Evaluation of Application of Spot-Filling Construction Method

[0314] The tile adhesive paste prepared in Experimental Example 5 was applied to a concrete substrate (300 × 300 × 50 mm) using a spot application method. Specifically, for each 100 × 100 mm tile, the adhesive was applied in five circular spots (four corners and the center of the tile) with a diameter of approximately 40 mm so that only about 50% of the tile surface area was covered with adhesive. Ceramic tiles were attached by pressing, and the tensile adhesive strength was measured after curing for 28 days under standard curing conditions.

[0315] The adhesive strength in the spot bonding method was compared with the adhesive strength in the full-surface bonding method (Experimental Example 7) to evaluate whether sufficient adhesive strength could be secured even when cement usage was reduced by 50%.

[0316] [Analysis of Experimental Results]

[0317] When combining the results of Experimental Examples 1 to 15 above, the hybrid nanoparticles prepared in the embodiments of the present invention have a core-shell structure in which a uniform silica shell is formed on the surface of a nanocellulose core, Si-OC covalent bonds are confirmed, and they exhibit excellent thermal stability and dispersion stability.

[0318] As a result of applying these hybrid nanoparticles to tile adhesive, the early strength was improved by more than 5%, the porosity of the interface transition region was reduced by 40 to 50%, and the adhesive strength retention rate after 28 days of immersion reached 85 to 92%, showing significantly improved performance compared to conventional technology.

[0319] In particular, even when cement usage is reduced by 50% by applying the spot bonding method, it is possible to secure more than 80% of the adhesive strength compared to the full-surface method, proving its potential as a sustainable construction technology.

[0320] On the other hand, the sample prepared in the comparative example exhibited problems such as incomplete formation of the core-shell structure, nanocellulose aggregation, or excessive precipitation of silica particles as the ethanol ratio, APTES ratio, pH, and reaction temperature deviated from the optimal range; consequently, its performance as a tile adhesive was significantly inferior to that of the embodiment of the present invention.

[0321] The experimental results above clearly demonstrate that the conditions of each step in the manufacturing method of the present invention were precisely designed based on scientific grounds and experimental optimization, and that these conditions interact organically to ultimately provide core-shell structured hybrid nanoparticles with excellent performance.

[0322] Results and Discussion

[0323] 1. Effect of the Mixing Ratio of Ethanol and Deionized Water on Core-Shell Structure Formation

[0324] The experimental results of Example 1 (80 parts by weight of ethanol, 20 parts by weight of deionized water, ratio 4:1), Example 2 (85 parts by weight of ethanol, 15 parts by weight of deionized water, ratio 5.7:1), Example 3 (70 parts by weight of ethanol, 30 parts by weight of deionized water, ratio 2.3:1), Comparative Example 1 (90 parts by weight of ethanol, 10 parts by weight of deionized water, ratio 9:1), and Comparative Example 2 (60 parts by weight of ethanol, 40 parts by weight of deionized water, ratio 1.5:1) were compared and analyzed.

[0325] As a result of SEM analysis of Experimental Example 1, the hybrid nanoparticles prepared in Examples 1, 2, and 3 all exhibited a core-shell structure in which a uniform silica shell was formed on the surface of the nanocellulose. In particular, Example 1 had the most uniform shell thickness and the best dispersibility of individual particles. In Example 2, the hydrolysis rate of APTES was slightly slower due to the high ethanol content, but a good core-shell structure was still formed. In Example 3, the hydrolysis rate of APTES was slightly faster due to the high deionized water content, but the formation of a core-shell structure was possible through fractional input and pH control.

[0326] In contrast, Comparative Example 1 had an excessively high ethanol content (90 parts by weight) and insufficient water content, causing the hydrolysis of APTES to proceed very slowly. As a result, the generation of silanol groups was insufficient, and a silica shell was formed only partially on the surface of the nanocellulose. In the SEM image, a significant portion of the nanocellulose surface was observed to be uncoated with silica, and unreacted APTES existed in a state physically mixed with the nanocellulose. Additionally, the excess ethanol reduced the dispersion stability of the nanocellulose, and some aggregates were observed.

[0327] In Comparative Example 2, the deionized water content was excessively high (40 parts by weight), causing the hydrolysis of APTES to proceed too rapidly. As a result, the generated silanol groups condensed with each other to grow into silica oligomers before being adsorbed onto the nanocellulose surface, and were ultimately precipitated as separate silica particles. In the SEM image, a large number of spherical silica particles with a diameter of 100 to 500 nm were observed separately from the nanocellulose particles, and a core-shell structure was hardly formed.

[0328] As a result of the FT-IR analysis of Experimental Example 2, characteristic peaks of Si-OC bonds were clearly observed in the 1000 to 1100 cm⁻¹ region for Examples 1, 2, and 3, with the highest intensity in Example 1. This indicates that Si-OC covalent bonds were effectively formed through a dehydration condensation reaction between hydroxyl groups on the surface of nanocellulose and silanol groups derived from APTES. On the other hand, Comparative Example 1 showed very weak intensity of the Si-OC peak, confirming that the silanization reaction proceeded insufficiently, while Comparative Example 2 showed a very strong peak of Si-O-Si bonds (1050 to 1150 cm⁻¹), confirming that a large amount of silica oligomers or silica particles were produced.

[0329] As a result of the workability evaluation of Experimental Example 5, the flow values ​​of Examples 1, 2, and 3 were 195 mm, 188 mm, and 202 mm, respectively, all of which were within the target range (180 to 220 mm), indicating excellent workability. The flow value of Comparative Example 1 was 175 mm, which was lower than the target range, resulting in slightly reduced workability; this is attributed to the unreacted APTES delaying cement hydration. Although the flow value of Comparative Example 2 was 210 mm, which was within the target range, the precipitated silica particles were not uniformly dispersed within the tile adhesive, which had a negative effect on strength development.

[0330] As a result of the early strength evaluation of Experimental Example 6, the 1-day compressive strength of Example 1 improved by approximately 5.8% compared to the control group (no hybrid nanoparticles added), while Example 2 improved by approximately 4.2% and Example 3 by approximately 5.1%. This is because the core-shell structured hybrid nanoparticles provided cement hydration nucleation sites to promote the formation of CSH gels, and sufficiently supplied the moisture required for initial hydration through the moisture retention capacity of the cellulose core. On the other hand, the 1-day compressive strength of Comparative Example 1 improved by only about 1.2% compared to the control group, while Comparative Example 2 actually decreased by about 0.8%. In Comparative Example 1, the cement hydration promoting effect was negligible due to insufficient silanization, and in Comparative Example 2, the precipitated silica particles acted as inert fillers, hindering strength development.

[0331] As a result of evaluating the adhesive strength and the retention rate of adhesive strength after immersion in Experimental Examples 7 and 8, the 28-day tensile adhesive strength of Example 1 was 1.52 MPa, and the retention rate of adhesive strength after 28 days of immersion was 90.1%. Example 2 showed 1.48 MPa and 88.5%, respectively, and Example 3 showed 1.50 MPa and 89.2%, all exhibiting excellent performance. This is because the core-shell structured hybrid nanoparticles penetrated the interfacial transition region between the tile and the adhesive matrix to fill the pores, and the silica shell formed a strong bond with the cement hydration product to densify the interface. In addition, the moisture retention capacity of the cellulose core sustained long-term hydration, contributing to the maintenance of adhesive strength even in a immersion environment. On the other hand, the 28-day tensile adhesive strength of Comparative Example 1 was 1.28 MPa and the retention rate after immersion was 72.3%, which fell short of the target performance (85% or more), and Comparative Example 2 showed even worse performance with 1.15 MPa and 65.8%, respectively.

[0332] In summary, the mixing ratio of ethanol and deionized water is the most important variable determining the hydrolysis rate of APTES, and a uniform core-shell structure is formed and excellent tile adhesive performance is exhibited in the range of 70 to 85 parts by weight of ethanol and 15 to 30 parts by weight of deionized water. In particular, a ratio of 80 parts by weight of ethanol and 20 parts by weight of deionized water (4:1) provided the best results.

[0333] 2. Effect of the weight ratio of APTES and nanocellulose on silica shell thickness

[0334] The experimental results of Example 1 (APTES 20 parts by weight, nanocellulose 4 parts by weight, ratio 5:1), Example 4 (APTES 25 parts by weight, nanocellulose 4 parts by weight, ratio 6.3:1), Example 5 (APTES 15 parts by weight, nanocellulose 4 parts by weight, ratio 3.8:1), Example 6 (APTES 20 parts by weight, nanocellulose 7 parts by weight, ratio 2.9:1), Example 7 (APTES 20 parts by weight, nanocellulose 3 parts by weight, ratio 6.7:1), Comparative Example 3 (APTES 30 parts by weight, nanocellulose 4 parts by weight, ratio 7.5:1), and Comparative Example 4 (APTES 10 parts by weight, nanocellulose 4 parts by weight, ratio 2.5:1) were compared and analyzed.

[0335] TEM analysis of Experimental Example 13 confirmed that the hybrid nanoparticles of Example 1 had a uniform silica shell with a thickness of approximately 85 ± 15 nm formed on the surface of the nanocellulose core (average diameter approximately 200 nm). In Example 4, the silica shell thickness increased to approximately 120 ± 20 nm due to the high APTES content, but it still maintained a uniform core-shell structure. In Example 5, the silica shell thickness decreased to approximately 55 ± 12 nm due to the low APTES content, but the nanocellulose surface was completely covered with a silica shell.

[0336] In Example 6, the nanocellulose content was high, resulting in a lower ratio of nanocellulose to APTES, and consequently, the silica shell thickness decreased to approximately 60 ± 15 nm. However, the nanocellulose surface was still coated with a silica shell. In Example 7, the nanocellulose content was low, resulting in a higher ratio of nanocellulose to APTES, and the silica shell thickness increased to approximately 110 ± 18 nm.

[0337] On the other hand, Comparative Example 3 had an excessively high APTES content (30 parts by weight), so the excess APTES could not be adsorbed onto the surface of the nanocellulose and self-condensed to precipitate as spherical silica particles with a diameter of 50 to 200 nm. In TEM images, numerous separate silica particles were observed around the nanocellulose core, and some of the nanocellulose was coated with an excessively thick silica shell (more than 200 nm). This non-uniform structure reduced the dispersion stability of the hybrid nanoparticles and caused aggregation within the tile adhesive.

[0338] Comparative Example 4 had an insufficient amount of APTES (10 parts by weight), resulting in an insufficient amount of silanol groups and only partially forming a silica shell on the surface of the nanocellulose. In the TEM image, only about 40 to 60% of the nanocellulose surface was covered with a silica shell, while the remaining area was exposed without being covered. This incomplete core-shell structure reduced moisture stability and limited the cement hydration promotion effect.

[0339] As a result of the TGA analysis of Experimental Example 3, the hybrid nanoparticles of Example 1 showed a residual weight of approximately 22% at temperatures above 400°C, which corresponds to the silica content. Example 4 showed a residual weight of approximately 28%, confirming an increase in silica content, while Example 5 showed a residual weight of approximately 16%, confirming a decrease in silica content. This result is consistent with the change in silica shell thickness observed in TEM.

[0340] Comparative Example 3 showed a residual weight of about 38%, indicating an excessively high silica content, which is due to the inclusion of separately precipitated silica particles. Comparative Example 4 showed a residual weight of about 10%, indicating a very low silica content, which is due to the incomplete silanization reaction resulting in only a partial formation of the silica shell.

[0341] As a result of the early strength evaluation of Experimental Example 6, Example 1 had the highest compressive strength at 1 day of age. Example 4 had a thicker silica shell, which slightly increased the cement hydration promotion effect, so the compressive strength at 1 day of age was improved by about 0.5% compared to Example 1, but the compressive strength at 28 days of age was similar to Example 1. Example 5 had a thinner silica shell, which slightly reduced the cement hydration promotion effect, so the compressive strength at 1 day of age was about 0.8% lower than Example 1, but it still showed good performance with an improvement of about 4.3% compared to the control group.

[0342] In Examples 6 and 7, the size and number of cores changed due to the change in nanocellulose content, but the silica shell was still formed, so the effect of improving early strength was maintained. The compressive strength at 1 day of age of Example 6 was improved by about 4.8% compared to the control group, and Example 7 was improved by about 5.2%.

[0343] On the other hand, the 1-day compressive strength of Comparative Example 3 improved by only about 2.5% compared to the control group, which is because the precipitated silica particles acted as inert fillers and the aggregation of hybrid nanoparticles hindered cement hydration. The 1-day compressive strength of Comparative Example 4 improved by only about 1.8% compared to the control group, which is because the effect of promoting cement hydration was negligible due to incomplete silanization.

[0344] As a result of evaluating the adhesive strength and the retention rate of adhesive strength after immersion in Experimental Examples 7 and 8, Examples 1, 4, and 5 all exhibited excellent performance, with Example 1 providing the most balanced performance. In Example 4, the interfacial bonding was somewhat strengthened due to the thick silica shell, but the long-term hydration effect was somewhat reduced because the moisture retention capacity of the cellulose core was partially shielded by the silica shell. In Example 5, the cement hydration promotion effect was somewhat reduced due to the thin silica shell, but the moisture retention capacity of the cellulose core was sufficiently expressed, so the retention rate of adhesive strength after immersion was similar to that of Example 1.

[0345] Comparative Example 3 showed poor performance with a 28-day tensile adhesive strength of 1.22 MPa and a retention rate of 68.5% after immersion, and Comparative Example 4 showed even worse performance with 1.18 MPa and 70.2%, respectively.

[0346] In summary, the weight ratio of APTES to nanocellulose is an important variable determining the thickness and coverage rate of the silica shell, and a uniform core-shell structure is formed and excellent tile adhesive performance is exhibited in the range of 15 to 25 parts by weight of APTES and 3 to 7 parts by weight of nanocellulose. In particular, a ratio of 20 parts by weight of APTES to 4 parts by weight of nanocellulose (5:1) provided the best results.

[0347] 3. Effect of pH Adjustment on Silanization Reaction

[0348] The experimental results of Example 1 (final pH 4.0), Example 8 (final pH 4.2), Example 9 (final pH 3.8), Comparative Example 5 (final pH 4.5), and Comparative Example 6 (final pH 3.5) were compared and analyzed.

[0349] As a result of the FT-IR analysis of Experimental Example 2, characteristic peaks of Si-OC bonds were clearly observed in the 1000 to 1100 cm⁻¹ region for Examples 1, 8, and 9, and the intensity was highest in Example 1. In Example 8, the pH was slightly higher (4.2), so the hydrolysis rate of APTES was slightly slower, but sufficient silanol groups were still generated and Si-OC bonds were formed. In Example 9, the pH was slightly lower (3.8), so the hydrolysis rate of APTES was slightly faster, but Si-OC bonds were effectively formed by preventing excessive condensation through stepwise heating and pH readjustment.

[0350] On the other hand, Comparative Example 5 had an excessively high pH (4.5), so the acid catalyst concentration was insufficient, and the hydrolysis of APTES proceeded slowly. As a result, the amount of silanol groups produced was insufficient, and the peak intensity of the Si-OC bond decreased by about 40% compared to Example 1. In addition, the NH₂ bending vibration peak of unreacted APTES was observed in the 1630 cm⁻¹ region, confirming that APTES was not sufficiently hydrolyzed.

[0351] In Comparative Example 6, the pH was excessively low (3.5), and the acid catalyst concentration was excessive, causing the hydrolysis of APTES to proceed too rapidly. As a result, the generated silanol groups condensed with each other to grow into silica oligomers before being adsorbed onto the surface of nanocellulose, and the peak of the Si-O-Si bond (1050 to 1150 cm⁻¹) appeared very strongly. Additionally, the intensity of the CH bending vibration peak of nanocellulose decreased in the 1380 cm⁻¹ region, suggesting that the glycosidic bonds of nanocellulose were partially hydrolyzed under excessively acidic conditions.

[0352] As a result of SEM analysis of Experimental Example 1, Examples 1, 8, and 9 all exhibited a uniform core-shell structure, and among them, the silica shell of Example 1 was the most uniform. In Example 8, the silica shell thickness was somewhat non-uniform (in the range of 70 to 100 nm), but the core-shell structure was still clear. In Example 9, the surface of the silica shell was somewhat rough, but the core-shell structure was maintained.

[0353] In Comparative Example 5, a silica shell was formed only partially on the surface of the nanocellulose, and numerous uncoated areas were observed. In Comparative Example 6, an uneven silica layer was formed on the surface of the nanocellulose, and a large amount of separate silica particles were precipitated. Additionally, a partially damaged surface of the nanocellulose was observed, confirming that the cellulose chains were cut under excessively acidic conditions.

[0354] As a result of the hydration heat analysis of Experimental Example 11, the tile adhesive with the addition of Example 1 showed a reduction in the induction period by approximately 1.2 hours and a reduction in the time to reach the maximum heat generation rate by approximately 2.5 hours compared to the control group. This is because the silica shell of the hybrid nanoparticles provided cement hydration nucleation sites, thereby promoting the formation of CSH gel. Examples 8 and 9 also showed similar hydration-promoting effects, but the degree was somewhat smaller than that of Example 1.

[0355] On the other hand, the tile adhesive with Comparative Example 5 added had a negligible effect on promoting hydration, with the induction period shortened by only about 0.5 hours, while Comparative Example 6 actually delayed hydration, with the induction period extended by about 0.8 hours. This is believed to be because an excess amount of silica oligomer or silica particles coated the surface of the cement particles, hindering contact with water.

[0356] As a result of the early strength evaluation of Experimental Example 6, the compressive strength at 1 day of age of Example 1 was the highest, while Example 8 was about 0.6% lower and Example 9 was about 0.4% lower, but all showed excellent performance. The compressive strength at 1 day of age of Comparative Example 5 improved by only about 1.5% compared to the control group, and Comparative Example 6 actually decreased by about 1.2%.

[0357] As a result of evaluating the adhesive strength and the retention rate of adhesive strength after immersion in Experimental Examples 7 and 8, Example 1 showed the best performance, and Examples 8 and 9 also showed good performance. The 28-day tensile adhesive strength of Comparative Example 5 was 1.25 MPa and the retention rate after immersion was 74.2%, which fell short of the target performance, and Comparative Example 6 showed even worse performance with 1.10 MPa and 62.5%, respectively.

[0358] In summary, pH is the most important variable determining the hydrolysis and condensation reaction rates of APTES, and a balanced reaction rate is secured in the pH range of 3.8 to 4.2, forming a uniform core-shell structure and exhibiting excellent tile adhesive performance. In particular, pH 4.0 ± 0.1 provided the best results.

[0359] 4. Effects of Silanization Reaction Temperature and Time on Silica Shell Formation

[0360] The experimental results of Example 1 (75℃, 7 hours), Example 10 (80℃, 7 hours), Example 11 (70℃, 7 hours), Example 12 (75℃, 9 hours), Example 13 (75℃, 5 hours), Comparative Example 7 (90℃, 7 hours), and Comparative Example 8 (60℃, 7 hours) were compared and analyzed.

[0361] SEM analysis of Experimental Example 1 showed that Examples 1, 10, 11, 12, and 13 all exhibited a core-shell structure, but there were differences in the uniformity and density of the silica shell. The silica shell of Example 1 was the most uniform and dense. In Example 10, the reaction temperature was high (80°C), so the condensation reaction proceeded rapidly, resulting in a somewhat rough surface of the silica shell, but the core-shell structure was maintained. In Example 11, the reaction temperature was low (70°C), so the condensation reaction proceeded slowly, resulting in a somewhat thin silica shell with low density, but the core-shell structure was formed.

[0362] In Example 12, the reaction time was long (9 hours), so the silica shell grew excessively, increasing the thickness to approximately 130 ± 25 nm, and a small amount of aggregates were observed as the silica shell was cross-linked between some adjacent nanocelluloses. In Example 13, the reaction time was short (5 hours), so the silica shell was incompletely formed, resulting in a thin thickness of approximately 50 ± 18 nm, and some uncoated areas were observed.

[0363] In contrast, Comparative Example 7 had an excessively high reaction temperature (90°C), causing the condensation reaction to proceed too rapidly and resulting in the formation of a very non-uniform silica shell. In some regions, the silica shell grew excessively thick (over 200 nm), while in other regions, cracks occurred in the silica shell. Additionally, the silica shells were extensively cross-linked between the nanocellulose particles, forming a large number of large aggregates with a diameter of 1 μm or more. SEM images showed that the surface of the nanocellulose was partially damaged, confirming that thermal decomposition of the nanocellulose occurred at high temperatures.

[0364] In Comparative Example 8, the reaction temperature was excessively low (60°C), so the condensation reaction proceeded too slowly, and the silica shell was incompletely formed even after 7 hours of reaction. Only about 50 to 70% of the nanocellulose surface area was covered with a silica shell, and the remaining area was uncovered.

[0365] As a result of the TGA analysis of Experimental Example 3, the weight loss in the 200 to 400°C range of Example 1 was approximately 58%, which corresponds to the thermal decomposition of cellulose. Example 10 showed a weight loss of approximately 54%, suggesting that some nanocellulose was thermally decomposed, and Example 11 showed a weight loss of approximately 60%, confirming that the nanocellulose was well preserved.

[0366] Comparative Example 7 showed a weight loss of about 48%, confirming that the nanocellulose was significantly thermally decomposed at high temperatures, and the residual weight above 400°C was very high at about 35%, resulting in an excessive increase in silica content. Comparative Example 8 showed a weight loss of about 62%, indicating that the nanocellulose was well preserved, but the residual weight above 400°C was low at about 12%, resulting in insufficient silica content.

[0367] As a result of the heat of hydration analysis of Experimental Example 11, Example 1 showed the best hydration-promoting effect, Example 10 showed a slightly reduced hydration-promoting effect because the silica shell was somewhat non-uniform, and Example 11 showed a slightly reduced hydration-promoting effect because the silica shell was thin. Example 12 showed an increased hydration-promoting effect because the silica shell was thick, but the overall effect was lower than Example 1 because dispersibility was reduced due to aggregate formation. Example 13 had a limited hydration-promoting effect because the silica shell was incomplete.

[0368] Comparative Example 7 had very poor dispersibility due to the formation of a large amount of aggregates and actually delayed hydration. Comparative Example 8 had a negligible effect on promoting hydration due to an incomplete silica shell.

[0369] As a result of the early strength evaluation of Experimental Example 6, the 1-day compressive strength of Example 1 was the highest, followed by Examples 10, 11, 12, and 13 in decreasing order. The 1-day compressive strength of Comparative Example 7 actually decreased by about 2.1% compared to the control group, which is because large aggregates hindered cement hydration and acted as inert fillers. The 1-day compressive strength of Comparative Example 8 improved by only about 0.8% compared to the control group.

[0370] As a result of evaluating the adhesive strength and the retention rate of adhesive strength after immersion in Experimental Examples 7 and 8, Example 1 showed the best performance, and Examples 10 and 11 also showed good performance. The adhesive strength of Example 12 decreased slightly due to aggregate formation, and the adhesive strength of Example 13 decreased slightly due to an incomplete silica shell. Comparative Example 7 showed very poor performance with a 28-day tensile adhesive strength of 1.05 MPa and a retention rate after immersion of 58.3%, while Comparative Example 8 fell short of the target performance with 1.20 MPa and 72.8%, respectively.

[0371] In summary, the silanization reaction temperature and time are important variables that determine the formation rate and density of the silica shell, and when reacted at a temperature of 70 to 80°C for 5 to 9 hours, a uniform and dense core-shell structure is formed and excellent tile adhesive performance is exhibited. In particular, reacting at a temperature of 75 ± 3°C for 7 ± 1 hour provided the best results.

[0372] 5. Effects of Nanocellulose Splitting and Ultrasonic Dispersion Treatment

[0373] The experimental results of Example 1 (4 divided injections, ultrasonic dispersion performed), Example 14 (2 divided injections, ultrasonic dispersion performed), Example 15 (5 divided injections, ultrasonic dispersion performed), Comparative Example 9 (1 lump sum injection, ultrasonic dispersion performed), and Comparative Example 10 (4 divided injections, no ultrasonic dispersion performed) were compared and analyzed.

[0374] As a result of SEM analysis of Experimental Example 1, in Examples 1, 14, and 15, the nanocellulose was well dispersed as individual particles, and a uniform silica shell was formed on the surface of each particle. Among them, the dispersibility of Example 1 was the best. In Example 14, the number of divided inputs was small (2 times), so the amount of each input was large, and a small amount of nanocellulose aggregated into groups of 2 to 3 was observed. In Example 15, the number of divided inputs was large (5 times), so the amount of each input was small, and although the dispersibility of nanocellulose was very good, the process was complex and time-consuming.

[0375] In contrast, Comparative Example 9 introduced the entire amount of nanocellulose in a single batch, resulting in many opportunities for contact between the nanocellulose particles. Consequently, the nanocellulose particles aggregated through hydrogen bonding to form aggregates with a diameter of 1 to 5 μm. A silica shell was formed on the surface of these aggregates, but the nanocellulose inside the aggregates did not come into contact with APTES and was not silanized. In the SEM image, a large number of uncoated nanocellulose particles were observed inside the aggregates.

[0376] Comparative Example 10 was directly introduced in a dispersed state in deionized water without performing ultrasonic dispersion treatment on the nanocellulose. As a result, the nanocellulose was not completely dispersed into primary particles and existed in an aggregate state with a diameter of 500 nm to 2 μm. A silica shell was formed on the surface of these aggregates, but the nanocellulose inside the aggregates was only partially silanized.

[0377] As a result of the dispersion stability evaluation of Experimental Example 4, the hybrid nanoparticles of Examples 1, 14, and 15 maintained a uniform suspension with almost no precipitate observed even after being dispersed in deionized water and left for 24 hours, demonstrating excellent dispersion stability. Comparative Example 9 showed poor dispersion stability with approximately 30% precipitate occurring after 24 hours, and Comparative Example 10 showed somewhat poor dispersion stability with approximately 20% precipitate occurring.

[0378] As a result of the BET specific surface area measurement of Experimental Example 14, the hybrid nanoparticles of Example 1 exhibited a specific surface area of ​​approximately 185 m² / g. Example 14 exhibited a specific surface area of ​​approximately 165 m² / g, and Example 15 exhibited a specific surface area of ​​approximately 195 m² / g. Comparative Example 9 exhibited a specific surface area of ​​approximately 95 m² / g, confirming that the specific surface area was significantly reduced due to aggregate formation. Comparative Example 10 exhibited a specific surface area of ​​approximately 120 m² / g, indicating that the specific surface area was reduced due to incomplete dispersion.

[0379] As a result of the hydration heat analysis of Experimental Example 11, Example 1 showed the best hydration-promoting effect, and Examples 14 and 15 also showed good hydration-promoting effects. In Comparative Example 9, the hydration-promoting effect was significantly reduced because the aggregate limited the contact area with the cement particles, and in Comparative Example 10, the hydration-promoting effect was also reduced due to incomplete dispersion.

[0380] As a result of the early strength evaluation of Experimental Example 6, the compressive strength at 1 day of age of Example 1 was the highest, Example 14 was about 0.5% lower, and Example 15 was similar to Example 1. The compressive strength at 1 day of age of Comparative Example 9 showed only an improvement of about 2.2% compared to the control group, and Comparative Example 10 showed only an improvement of about 3.1%.

[0381] As a result of evaluating the adhesive strength and the retention rate of adhesive strength after immersion in Experimental Examples 7 and 8, Example 1 showed the best performance, and Examples 14 and 15 also showed good performance. The 28-day tensile adhesive strength of Comparative Example 9 was 1.28 MPa and the retention rate after immersion was 75.8%, which fell short of the target performance, while Comparative Example 10 was 1.35 MPa and 80.2%, respectively, which were close to the target performance but inferior to the examples.

[0382] In summary, the fractional input of nanocellulose and ultrasonic dispersion treatment are key technologies that prevent the aggregation of nanocellulose and maximize the contact area with APTES to promote the formation of a uniform core-shell structure. The best results were obtained when fractional input was performed 2 to 5 times and dispersed for 5 to 30 minutes using ultrasound at 20 to 60 kHz, and fractional input 4 times was particularly superior in terms of the balance between dispersibility and process efficiency.

[0383] 6. Effect of drying method on the structure and performance of hybrid nanoparticles

[0384] The experimental results of Example 1 (room temperature desiccator drying, 72 hours) and Comparative Example 11 (high temperature oven drying, 80°C, 12 hours) were compared and analyzed.

[0385] As a result of SEM analysis of Experimental Example 1, the silica shell of the hybrid nanoparticles of Example 1 was smooth and uniform, and the interface between the nanocellulose core and the silica shell was clearly observed. On the other hand, numerous microcracks were observed on the surface of the silica shell of the hybrid nanoparticles of Comparative Example 11, and in some areas, the silica shell was observed to have peeled off from the nanocellulose surface. This is believed to be because cracks and peeling occurred due to thermal stress caused by shrinkage resulting from rapid moisture evaporation and excessive condensation of the silica shell during high-temperature oven drying.

[0386] As a result of the FT-IR analysis of Experimental Example 2, characteristic peaks of Si-OC bonds were observed in both Example 1 and Comparative Example 11; however, the peak intensity of Si-O-Si bonds in Comparative Example 11 was about 30% higher than that of Example 1. This indicates that the silanol groups inside the silica shell condensed excessively during high-temperature drying, leading to an increase in Si-O-Si bonds. Additionally, the peak intensity of the OH stretching vibration in the 3400 cm⁻¹ region in Comparative Example 11 was about 20% lower than that of Example 1, suggesting that the hydroxyl groups on the surface of the nanocellulose were partially dehydrated at high temperatures.

[0387] According to the TGA analysis results of Experimental Example 3, the weight loss of Example 1 at 100°C was approximately 2.3%, and that of Comparative Example 11 was approximately 0.8%. This means that Example 1 contains a small amount of residual moisture but satisfies the target moisture content (3% or less), while Comparative Example 11 means that moisture was almost completely removed due to high-temperature drying. However, the weight loss of Comparative Example 11 in the 200 to 400°C range was approximately 52%, which was lower than that of Example 1 (58%), suggesting that some of the nanocellulose was thermally decomposed during high-temperature drying.

[0388] As a result of measuring the moisture retention rate of Experimental Example 10, the tile adhesive with the hybrid nanoparticles of Example 1 added had a moisture retention rate of approximately 88.5% after 24 hours. On the other hand, the tile adhesive with Comparative Example 11 added showed a moisture retention rate of approximately 82.3%. This is believed to be because the hydroxyl groups on the surface of the nanocellulose were partially dehydrated during high-temperature drying, and the moisture retention capacity of the cellulose was reduced.

[0389] As a result of the early strength evaluation of Experimental Example 6, the 1-day compressive strength of Example 1 was about 1.2% higher than that of Comparative Example 11. This is because the hybrid nanoparticles of Example 1 better preserved the water retention capacity of nanocellulose, thereby sufficiently supplying the moisture required for initial hydration.

[0390] As a result of evaluating the adhesive strength and retention rate of adhesive strength after immersion in Experimental Examples 7 and 8, the 28-day tensile adhesive strength of Example 1 was 1.52 MPa, and the retention rate after immersion was 90.1%. On the other hand, the 28-day tensile adhesive strength of Comparative Example 11 was 1.42 MPa, and the retention rate after immersion was 82.5%, which was close to the target performance but inferior to Example 1. This is believed to be because microcracks were present in the silica shell of Comparative Example 11, forming a moisture penetration pathway and reducing long-term durability.

[0391] As a result of the microstructure analysis of Experimental Example 12, the tile adhesive cured body with Example 1 added had a very dense interfacial transition region and the hybrid nanoparticles were uniformly dispersed. On the other hand, in the tile adhesive cured body with Comparative Example 11 added, a small amount of micropores were observed in the interfacial transition region, and cracks in the silica shell were observed in some of the hybrid nanoparticles.

[0392] In summary, the drying method is an important variable determining the structural stability and performance of hybrid nanoparticles. The method of placing the nanoparticles on silica gel at room temperature (15 to 30°C) and drying them slowly in a desiccator for 72 hours prevents excessive condensation and cracking of the silica shell, and preserves the water retention capacity of the nanocellulose to the maximum extent, thereby maximizing tile adhesive performance. High-temperature oven drying provides a rapid drying speed, but it causes cracking and delamination of the silica shell, thermal decomposition of the nanocellulose, and a decrease in water retention capacity, which degrades the final performance.

[0393] 7. Overall Influence of Process Variables and Optimal Conditions

[0394] Example 1 provided the best and most balanced performance as a standard condition in which all process variables of the present invention were set within the optimal range. Examples 2 through 15 evaluated the effect of individually changing each process variable, and all exhibited good performance within the scope of the present invention. This means that the manufacturing method of the present invention has a certain tolerance range for process variables and can accommodate variability in actual production sites.

[0395] On the other hand, Comparative Examples 1 to 15 were conditions in which each process variable was set outside the optimal range, resulting in problems such as incomplete core-shell structure formation, nanocellulose aggregation, or excessive precipitation of silica particles, and consequently, the tile adhesive performance was significantly inferior to that of the embodiments of the present invention. This clearly demonstrates that the range of each process variable of the present invention was precisely set based on scientific grounds and experimental optimization, and that the target core-shell structure and performance cannot be achieved if these ranges are exceeded.

[0396] In particular, the mixing ratio of ethanol and deionized water, the weight ratio of APTES to nanocellulose, pH, silanization reaction temperature and time, fractional input of nanocellulose, ultrasonic dispersion treatment, and drying method are organically interconnected; an excellent core-shell structure cannot be achieved with only a single variable, and the best results are provided when all variables are harmonized within the optimal range.

[0397] Based on the comprehensive analysis of Experimental Examples 1 to 15, the hybrid nanoparticles produced by the method of the present invention possess the following excellent characteristics. First, a clear core-shell structure in which a uniform silica shell with a thickness of 50 to 150 nm is formed on the surface of a nanocellulose core. Second, excellent structural stability is achieved through strong bonding between the nanocellulose and the silica shell via Si-OC covalent bonds. Third, a high specific surface area of ​​150 to 200 m² / g provides a large number of cement hydration nucleation sites. Fourth, the moisture retention capacity of the cellulose core is well preserved, enabling long-term moisture supply. Fifth, the particles are well dispersed as individual particles and are uniformly distributed within the tile adhesive.

[0398] When 0.05 to 0.5 weight percent of these hybrid nanoparticles are added to tile adhesive, the early strength is improved by more than 5% compared to the control group, the porosity of the interface transition region is reduced by 40 to 50%, and the adhesive strength retention rate after 28 days of immersion reaches 85 to 92%, showing significantly improved performance compared to conventional technology.

[0399] 8. Practical Applicability and Economic Feasibility

[0400] The manufacturing method of the present invention uses raw materials and equipment within a feasible range for small and medium-sized enterprises, and the process is relatively simple, making it suitable for mass production. The raw materials used—ethanol, deionized water, APTES, nanocellulose, and glacial acetic acid—are all commercially widely distributed chemicals that are easy to obtain and inexpensive. In particular, nanocellulose can be produced from renewable biomass such as wood and agricultural by-products, thereby ensuring the sustainability of the raw materials.

[0401] The equipment required for the manufacturing process consists of basic items found in general chemical laboratories or small-scale production facilities, such as beakers, flasks, stirrers, temperature controllers, filtration devices, and desiccators; specialized, expensive equipment is not required. Ultrasonic dispersers are readily available as industrial products are widely commercially available.

[0402] In particular, room temperature desiccator drying, which is the core technology of the present invention, is economical and environmentally friendly as it consumes almost no energy compared to high-temperature oven drying. Although the drying time of 72 hours is somewhat long, productivity can be secured by operating multiple batches in parallel.

[0403] Since the hybrid nanoparticles of the present invention are added in a small amount of 0.05 to 0.5 weight percent relative to the total composition of the tile adhesive, the increase in the manufacturing cost of the tile adhesive is negligible. For example, only 0.5 to 5 g of hybrid nanoparticles are required to produce 1 kg of tile adhesive, and even considering the manufacturing cost of the hybrid nanoparticles, the increase in the total manufacturing cost of the tile adhesive is estimated to be less than 5%.

[0404] However, in terms of performance enhancement, it offers significant improvements, such as an increase in early strength of more than 5%, a reduction in interfacial porosity of 40 to 50%, and a retention rate of adhesive strength of more than 85% after immersion, making it highly cost-effective. Furthermore, if combined with the Korean spot bonding method to reduce cement usage by 50%, it can provide long-term economic and environmental benefits through reduced material costs and carbon emissions.

[0405] 9. Conclusion

[0406] In the method for preparing a core-shell structure composition comprising cellulose-silica hybrid nanoparticles according to the present invention, each process step—such as the mixing ratio of ethanol and deionized water, the weight ratio of APTES and nanocellulose, precise pH control, silanization reaction temperature and time, fractional input of nanocellulose and ultrasonic dispersion treatment, and room-temperature desiccator drying—is precisely designed through scientific grounds and experimental optimization, and these steps interact organically to realize a uniform and stable core-shell structure.

[0407] The manufactured hybrid nanoparticles simultaneously exhibit the moisture retention capacity of nanocellulose and the cement hydration-promoting effect of silica; when applied to tile adhesives, they comprehensively enhance early strength, interfacial densification, and long-term durability, providing significantly improved performance compared to conventional technology.

[0408] This invention uses raw materials and equipment within a feasible range for small and medium-sized enterprises, and has excellent economic efficiency and environmental friendliness, making it highly likely to be practically applied in the tile adhesive industry. In addition, by combining it with a spot bonding method, it reduces cement usage by 50% and significantly reduces carbon emissions, proving its potential as a sustainable construction technology.

Claims

Claim 1 A method for preparing a core-shell structure composition comprising cellulose-silica hybrid nanoparticles, comprising: a) a step of preparing a mixed solvent by mixing ethanol and deionized water; b) a step of preparing a reaction mixture by adding nanocellulose and a silane coupling agent selected from the group consisting of aminoalkyltrialkoxysilane, glycidylalkyltrialkoxysilane, mercaptoalkyltrialkoxysilane, vinyltrialkoxysilane, methacryloxyalkyltrialkoxysilane, epoxyalkyltrialkoxysilane, isocyanatoalkyltrialkoxysilane, ureidoalkyltrialkoxysilane, chloroalkyltrialkoxysilane, and combinations thereof to the mixed solvent; c) a step of adjusting the pH by adding an acid catalyst to the reaction mixture; d) a step of performing a silanization reaction by heating and stirring the pH-adjusted reaction mixture; and e) a step of filtering and washing the product of the completed silanization reaction. and f) a step of drying the filtered and washed product to obtain silane-modified nanocellulose; comprising a method for preparing a core-shell structure composition comprising cellulose-silica hybrid nanoparticles. Claim 2 A method for preparing a core-shell structure composition comprising cellulose-silica hybrid nanoparticles, wherein, in claim 1, step a) comprises: a1) preparing a total of 100 parts by weight of a polar mixed solvent by mixing 70 to 85 parts by weight of ethanol and 15 to 30 parts by weight of deionized water; a2) confirming that the initial pH of the polar mixed solvent is in the range of pH 6.5 to 8.0 by measuring it with a pH meter; and a3) preparing a homogeneously mixed reaction solvent by stirring the polar mixed solvent at a stirring speed of 100 to 500 rpm for 5 to 20 minutes at a temperature of 15 to 30°C; wherein the weight ratio of ethanol to deionized water is controlled to 3:1 to 5:

1. Claim 3 In claim 1, the step b) comprises: b1) initiating a primary hydrolysis reaction while adding 15 to 25 parts by weight of the silane coupling agent to 100 parts by weight of the mixed solvent at a dropping rate of 0.5 to 2.0 mL / min; b2) generating silanol groups from the silane coupling agent by stirring at a stirring speed of 200 to 400 rpm for 10 to 30 minutes while the primary hydrolysis reaction proceeds; b3) inducing adsorption between the hydroxyl groups on the surface of the nanocellulose and the silanol groups by adding 3 to 7 parts by weight of nanocellulose to 100 parts by weight of the mixed solvent in 2 to 5 separate additions, with each addition interval being 5 to 15 minutes. and b4) a step of preparing a reaction mixture in which the nanocellulose is added by stirring at a stirring speed of 300 to 600 rpm for 30 to 90 minutes to produce a reaction mixture in which the silane coupling agent is uniformly dispersed on the surface of the nanocellulose; wherein the weight ratio of the silane coupling agent to the nanocellulose is 3:1 to 5:1, and the nanocellulose is dispersed by ultrasonically dispersing at a frequency of 20 to 60 kHz for 5 to 30 minutes before addition so that the average particle size is 50 to 500 nm, the method of preparing a core-shell structure composition comprising cellulose-silica hybrid nanoparticles.

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