A post-addition nanocellulose reinforcing additive for latex paint coatings, methods of making and using the same

Abstract

The application provides a post-added nanocellulose reinforcing additive for latex paint, a preparation method and a use method thereof, and comprises the following steps: mixing butane tetracarboxylic acid, sodium hypophosphite and a nanocellulose solution, stirring and heating to obtain an esterified nanocellulose solution; adding a silane coupling agent solution to the esterified nanocellulose solution to obtain a modified nanocellulose solution; dispersing nanosilica in anhydrous ethanol to obtain a silica dispersion liquid; adding the silane coupling agent solution to the silica dispersion liquid, stirring and heating to react to obtain modified silica powder; dispersing the modified silica powder in anhydrous ethanol to obtain a modified silica dispersion liquid; adding a compound emulsifier solution to the modified silica dispersion liquid to shear and emulsify, to obtain a modified silica emulsion; adding a compatilizer to the modified nanocellulose solution, and dropping in the modified silica emulsion; and finally adjusting the viscosity.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, and relates to a post-addition nanocellulose reinforcing agent for latex paint coatings, its preparation method and application method. Background Technology

[0002] Nanocellulose, a bio-based nanomaterial extracted from natural cellulose, exhibits great application potential in the field of high-performance composite materials due to its excellent properties such as high specific surface area, high mechanical strength, biodegradability, and good biocompatibility. Introducing nanocellulose as a reinforcing phase into waterborne latex paints is considered an ideal technical approach to improve the mechanical properties, abrasion resistance, and durability of the paint film. However, in the process of practical application and promotion, the inherent physicochemical properties of nanocellulose also bring significant technical challenges.

[0003] The surface of cellulose nanofibers is rich in hydroxyl groups, which makes it easy for hydrogen bonds to form between particles, resulting in severe agglomeration. This tendency to agglomerate makes it difficult to achieve uniform dispersion of cellulose nanofibers in high-solids, high-viscosity latex paint systems. Uneven dispersion not only significantly reduces its reinforcing effect but may also lead to defects in the paint film, affecting its final appearance and performance. Furthermore, due to their larger aspect ratio, cellulose nanofibers are even more difficult to disperse uniformly than cellulose nanocrystals.

[0004] Therefore, how to overcome the challenges of uniform dispersion and long-term stabilization of nanocellulose in latex paint systems while ensuring environmental friendliness and process simplicity, and how to fully realize its enhancing function in the paint film, has become a key issue that urgently needs to be addressed in this technical field. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a post-addition nanocellulose reinforcing agent for latex paint coatings, its preparation method and application method.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a post-added nanocellulose reinforcing agent for latex paint coatings, the preparation method comprising:

[0008] (I) Butanetetracarboxylic acid, sodium hypophosphite and nanocellulose solution are mixed, stirred and heated to carry out esterification reaction. After the reaction is completed, the mixture is dialyzed to obtain esterified nanocellulose solution. Under heating and stirring conditions, silane coupling agent solution is added to esterified nanocellulose solution to carry out reaction. After the reaction is completed, the mixture is dialyzed to obtain modified nanocellulose solution.

[0009] (II) Disperse nano-silica in anhydrous ethanol to obtain a silica dispersion; add silane coupling agent to an aqueous ethanol solution, mix and stir to hydrolyze, and obtain a silane coupling agent solution; add the silane coupling agent solution to the silica dispersion, mix, stir and heat to react, and after the reaction is completed, obtain modified silica powder by centrifugation, washing and drying.

[0010] (III) The modified silica powder is dispersed in anhydrous ethanol to obtain a modified silica dispersion; the compound emulsifier is mixed with deionized water to obtain a compound emulsifier solution; under stirring conditions, the compound emulsifier solution is added to the modified silica dispersion, and then shear emulsification is performed to obtain a modified silica emulsion; under heating and stirring conditions, a compatibilizer solution is added to the modified nanocellulose solution, and then the modified silica emulsion is added dropwise, and finally deionized water is added to adjust the viscosity to obtain the nanocellulose reinforcing agent.

[0011] This invention first modifies nanocellulose through esterification and silanization, while simultaneously treating nano-silica with silanization for hydrophobicity. Then, it combines the two using a compound emulsifier and compatibilizer to prepare a stable and dispersed water-based reinforcing agent. The reinforcing agent prepared by this invention effectively solves the technical problems of easy agglomeration of nanocellulose and poor compatibility with latex paint. It can be directly added to finished latex paint with simple mixing, ultimately significantly improving the hardness, adhesion, scrub resistance, and coating area of ​​the latex paint film while maintaining a good appearance.

[0012] Nanocellulose, as a bio-based nanomaterial, possesses characteristics such as high specific surface area, high mechanical strength, and biodegradability. However, its surface is rich in hydroxyl groups, making it prone to aggregation due to hydrogen bonding, which hinders its uniform dispersion in latex paint and limits its reinforcing effect. This invention first significantly improves the interfacial compatibility of nanocellulose by subjecting it to esterification and silane coupling agent treatment. The esterification reaction introduces carboxylic acid groups, increasing the negative charge on the nanocellulose surface and generating electrostatic repulsion, thus inhibiting nanocellulose aggregation and improving its dispersion stability in water-based latex paint. Simultaneously, it provides more and stronger chemical grafting sites for subsequent silane coupling agents, ensuring that silane molecules can be effectively and stably grafted onto the cellulose molecular chain. Subsequently, aminosilane coupling agents were used to modify the esterified cellulose nanoparticles. The amino functional groups on the aminosilane coupling agent molecular chain can form strong covalent amide bonds with the carboxyl groups on the surface of the esterified cellulose nanoparticles, thereby constructing an organosilicon layer on the surface of the cellulose nanoparticles through strong covalent bonding. This not only further enhances the steric hindrance effect but also improves the interfacial compatibility with organic components in latex paint. Through esterification and silane modification, the cellulose nanoparticles are transformed from hydrophilic to amphiphilic, making them easier to disperse uniformly in high-viscosity latex paints.

[0013] Silica, as an inorganic nanoparticle, possesses high hardness, wear resistance, and stability. However, when used alone, it exhibits poor compatibility with the organic components in latex paint and is prone to agglomeration. This invention modifies silica using a silane coupling agent, which binds to the silica surface via siloxane bonds, introducing hydrophobic organosilicon segments. This ultimately forms a hydrophobic organosilicon coating layer on the silica surface, transforming the surface of the nano-silica from hydrophilic to hydrophobic, significantly reducing the risk of silica agglomeration. Furthermore, since the modified nanocellulose surface is also modified with a silane coupling agent, the surface characteristics of the modified silica and modified nanocellulose are similar, which is beneficial for improving the interfacial compatibility between the two.

[0014] This invention employs an emulsification process to integrate modified nanocellulose and modified silica into a stable reinforcing agent. The emulsifier is a compound of Span 60 and Tween 60. The hydrophobic Span 60 can firmly anchor its hydrophobic segments to the surface of the hydrophobically modified silica particles, while the hydrophilic Tween 60 molecules extend their long chains into the aqueous phase. During shear emulsification, Span 60 and Tween 60 are co-adsorbed at the oil-water interface, forming a dense and high-strength composite interfacial film. This interfacial film can significantly reduce interfacial tension. Through the strong steric hindrance generated by the long chains of Tween 60 in the aqueous phase, the agglomeration of emulsion droplets is effectively prevented, thereby achieving emulsification and stable dispersion of modified silica particles, ultimately forming a stable and dispersed O / W type modified silica emulsion. Subsequently, polyethylene glycol 6000, a compatibilizer, and modified silica emulsion were sequentially added to the modified nanocellulose solution. Polyethylene glycol 6000 primarily acts as a molecular bridge; its long molecular chains' ether bonds can adsorb onto the surface of the modified nanocellulose via hydrogen bonding with the hydroxyl and silane groups on the surface. Its hydrophobic segments can embed into the emulsifier layer on the surface of the modified silica emulsion droplets, ensuring stable composite formation. After composite formation, the modified nanocellulose and modified silica exhibit a synergistic effect. During latex paint film formation, the modified nanocellulose, with its high aspect ratio filamentous structure, can form a three-dimensional network structure in the paint film, providing skeletal support. Modified silica fills the network gaps, providing rigidity reinforcement. This structure not only improves the hardness of the paint film but also enhances its adhesion and washability by dispersing stress. In addition, modified nanocellulose and modified silica have high interfacial compatibility due to their similar surface groups, and can be stably dispersed in latex paint for a long time, avoiding agglomeration during storage and ensuring the durability of the reinforcing effect.

[0015] Adding the reinforcing additives provided by this invention can significantly improve the hardness, adhesion, and scrub resistance of latex paint films, while also significantly increasing the coating area. Regarding hardness and adhesion, the nanocellulose modified with the silane coupling agent KH550 has similar chemical properties and functional groups on its surface grafted organosilicon segments to the silica surface, which is also modified with KH550. The two are tightly bound together by silane bridging bonds and intermolecular forces. The modified nanocellulose, with its high aspect ratio, constructs a continuous three-dimensional network structure in the paint film, serving as a tough supporting framework to bear and disperse stress. Meanwhile, the rigid modified nano-silica particles are uniformly dispersed and anchored within the three-dimensional network structure, effectively hindering the slippage of polymer molecular chains and the propagation of cracks. Simultaneously, the modified nano-silica particles can uniformly fill the gaps in the three-dimensional network structure, making the paint film denser and reducing internal stress, thereby synergistically improving the hardness and adhesion of the paint film. Regarding washability, the high-hardness modified silica directly resists surface abrasion, while the three-dimensional network structure formed by modified nanocellulose provides support, preventing the modified silica particles from falling off during abrasion and ensuring the durability of the abrasion resistance. In terms of increasing the coating area, the reinforcing additive prepared in this invention can increase the coating area of ​​latex paint. This is because the silane-modified nanocellulose forms a stable three-dimensional network structure in the paint film, giving the latex paint excellent shear-dilution characteristics. This allows the viscosity to drop rapidly under shear force during application, making it easy to spread into a uniform thin coating. After application, the viscosity recovers, effectively preventing sagging, allowing a larger area of ​​wall surface to be coated with a unit mass of latex paint.

[0016] The reinforcing agent prepared by this invention is added post-processedly, meaning it is directly added to commercially available finished latex paint. After thorough mixing, it can be sprayed onto the wall. Compared to the "pre-addition" method during latex paint preparation, the "post-addition" method used in this invention avoids the degradation and aggregation of nanocellulose under the high temperature and pressure environment of emulsion polymerization, ensuring the reliability of the reinforcing effect. During use, it only requires low-speed stirring to achieve uniform dispersion, making the operation simple. The addition amount is low and does not significantly alter the rheological properties of the latex paint. It is suitable for various types of latex paints, such as acrylic and styrene-acrylic latex paints.

[0017] As a preferred technical solution of the present invention, in step (I), the mass fraction of the nanocellulose solution is 0.5~1.5wt%, for example, it can be 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1.0wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt% or 1.5wt%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0018] In some optional instances, the mass ratio of the nanocellulose solution to the butanetetracarboxylic acid is 100:(10~15), for example, it can be 100:10, 100:10.5, 100:11, 100:11.5, 100:12, 100:12.5, 100:13, 100:13.5, 100:14, 100:14.5 or 100:15, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0019] This invention specifically limits the mass ratio of nanocellulose solution to butanetetracarboxylic acid to 100:(10~15). Within this range, the amount of butanetetracarboxylic acid is sufficient to cover the active hydroxyl groups on the surface of nanocellulose. Under the action of the catalyst sodium hypophosphite, the carboxyl groups and hydroxyl groups form ester bonds, thereby introducing carboxyl groups onto the nanocellulose molecular chain. The newly introduced carboxyl groups can not only generate electrostatic repulsion by increasing the surface negative charge, effectively inhibiting the aggregation of nanocellulose caused by hydrogen bonding and improving its dispersion stability in the aqueous phase, but also provide sufficient grafting active sites for subsequent silane coupling agent modification.

[0020] When the amount of butanetetracarboxylic acid is below the lower limit defined in this invention, the degree of esterification on the surface of nanocellulose is low, resulting in insufficient number of carboxyl groups grafted onto the surface of nanocellulose. This leads to low electrostatic repulsion and easy aggregation in water due to hydrogen bonding, thus failing to fully exert the reinforcing effect of nanocellulose. Furthermore, due to the insufficient number of carboxyl groups, the number of active reaction sites available for grafting with the silane coupling agent KH550 is insufficient, affecting the grafting density and strength of the silane coupling agent on the surface of nanocellulose.

[0021] When the amount of butanetetracarboxylic acid exceeds the upper limit of the range defined in this invention, the excess butanetetracarboxylic acid will not only react with the hydroxyl groups on the surface of a single nanocellulose, but also the four carboxyl functional groups on its molecular chain will react with the hydroxyl groups on different nanocellulose at the same time, thereby causing different nanocellulose molecules to connect and agglomerate into larger aggregates, affecting its mechanical reinforcement effect and making it difficult to redisperse in subsequent operations.

[0022] In some optional instances, the mass of the sodium hypophosphite is 20 to 30 wt% of the mass of the butanetetracarboxylic acid, for example, it may be 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, 26 wt%, 27 wt%, 28 wt%, 29 wt%, or 30 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0023] In some alternative examples, the reaction temperature of the esterification reaction is 60 to 80°C, for example, 60°C, 62°C, 64°C, 66°C, 68°C, 70°C, 72°C, 74°C, 76°C, 78°C or 80°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0024] In some alternative examples, the reaction time of the esterification reaction is 8 to 10 hours, for example, 8.0 hours, 8.2 hours, 8.4 hours, 8.6 hours, 8.8 hours, 9.0 hours, 9.2 hours, 9.4 hours, 9.6 hours, 9.8 hours, or 10.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0025] In some optional instances, the dialysis bag used for the dialysis has a molecular weight cutoff of 10,000 to 15,000 Da, such as 10,000 Da, 10,500 Da, 11,000 Da, 11,500 Da, 12,000 Da, 12,500 Da, 13,000 Da, 13,500 Da, 14,000 Da, 14,500 Da, or 15,000 Da, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0026] In some optional instances, the dialysis time is 24 to 48 hours, for example, 24 hours, 26 hours, 28 hours, 30 hours, 32 hours, 34 hours, 36 hours, 38 hours, 40 hours, 42 hours, 44 hours, 46 hours, or 48 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0027] As a preferred embodiment of the present invention, in step (I), the silane coupling agent solution is added to the esterified nanocellulose solution at a heating temperature of 50-60°C and a stirring speed of 300-500 rpm. After all the solution is added, stirring and heating are continued for 2-3 hours. The heating temperature can be 50°C, 51°C, 52°C, 53°C, 54°C, 55°C, 56°C, 57°C, 58°C, 59°C, or 60°C, and the stirring speed can be 300 rpm or 320 rpm. The stirring and heating time can be 2.0h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h, or 3.0h, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0028] In some alternative examples, the silane coupling agent solution consists of a silane coupling agent and an aqueous ethanol solution.

[0029] In some optional examples, the silane coupling agent is KH550.

[0030] In some optional instances, the mass fraction of the silane coupling agent in the silane coupling agent solution is 5 to 10 wt%, for example, it can be 5.0 wt%, 5.5 wt%, 6.0 wt%, 6.5 wt%, 7.0 wt%, 7.5 wt%, 8.0 wt%, 8.5 wt%, 9.0 wt%, 9.5 wt%, or 10.0 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0031] In some optional examples, the mass ratio of the esterified cellulose nanoparticle solution to the silane coupling agent in the silane coupling agent solution is 100:(3~5), for example, it can be 100:3.0, 100:3.2, 100:3.4, 100:3.6, 100:3.8, 100:4.0, 100:4.2, 100:4.4, 100:4.6, 100:4.8 or 100:5.0, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0032] This invention specifically specifies that the mass ratio of the silane coupling agent in the nanocellulose solution to the silane coupling agent solution is 100:(3~5). After butanetetracarboxylic acid esterification, carboxyl groups are introduced onto the surface of the nanocellulose. These carboxyl groups can undergo a condensation reaction with the silanol groups generated after the hydrolysis of KH550, forming strong covalent bonds. Within the specified ratio range, the amount of KH550 is sufficient to cover the active sites on the surface of the nanocellulose, allowing a certain density of organosilicon segments to be grafted onto its surface. This grafting of organosilicon segments significantly enhances the hydrophobicity of the nanocellulose and improves its compatibility with the organic polymer matrix in latex paints.

[0033] When the amount of silane coupling agent is below the lower limit defined in this invention, KH550 molecules cannot effectively cover the active sites on the surface of nanocellulose, resulting in a low grafting density of organosilicon segments, insufficient hydrophobic modification of the nanocellulose surface, and ineffective improvement of compatibility with the organic polymer matrix in latex paint. Furthermore, due to the limited number of silane molecules grafted onto the nanocellulose surface, the number of chemical bridging points between the modified nanocellulose and modified silica is insufficient, affecting the interfacial bonding between them.

[0034] When the amount of silane coupling agent exceeds the upper limit defined in this invention, the excess KH550 in the esterified nanocellulose solution will not only react with the surface of the nanocellulose but also undergo its own hydrolysis and condensation. The silane coupling agent molecules will interconnect to form oligomers. These oligomers can only adhere to the surface of the nanocellulose through physical action and cannot be covalently grafted onto the nanocellulose. This bonding is weak and will detach in subsequent processes. Furthermore, the oligomers adhering to the surface of the nanocellulose will form an excessively thick coating layer, leading to larger aggregates and affecting the dispersibility of the nanocellulose.

[0035] In some optional instances, the dialysis bag used for the dialysis has a molecular weight cutoff of 10,000 to 15,000 Da, such as 10,000 Da, 10,500 Da, 11,000 Da, 11,500 Da, 12,000 Da, 12,500 Da, 13,000 Da, 13,500 Da, 14,000 Da, 14,500 Da, or 15,000 Da, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0036] In some optional instances, the dialysis time is 24 to 48 hours, for example, 24 hours, 26 hours, 28 hours, 30 hours, 32 hours, 34 hours, 36 hours, 38 hours, 40 hours, 42 hours, 44 hours, 46 hours, or 48 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0037] As a preferred technical solution of the present invention, in step (II), the nano-silica is added to the anhydrous ethanol for ultrasonic dispersion to obtain the silica dispersion.

[0038] In some optional instances, the mass of the nano-silica is 5 to 10 wt% of the mass of the anhydrous ethanol, for example, it can be 5.0 wt%, 5.5 wt%, 6.0 wt%, 6.5 wt%, 7.0 wt%, 7.5 wt%, 8.0 wt%, 8.5 wt%, 9.0 wt%, 9.5 wt%, or 10.0 wt%, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0039] In some optional instances, the ultrasonic power of the ultrasonic dispersion is 300 to 500 W, for example, it can be 300 W, 320 W, 340 W, 360 W, 380 W, 400 W, 420 W, 440 W, 460 W, 480 W or 500 W, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0040] In some optional instances, the ultrasonic dispersion time is 30 to 40 minutes, for example, 30 minutes, 31 minutes, 32 minutes, 33 minutes, 34 minutes, 35 minutes, 36 minutes, 37 minutes, 38 minutes, 39 minutes or 40 minutes, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0041] In some optional instances, the volume ratio of the silane coupling agent to the aqueous ethanol solution is 1:(30~40), for example, it can be 1:30, 1:31, 1:32, 1:33, 1:34, 1:35, 1:36, 1:37, 1:38, 1:39 or 1:40, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0042] In some optional examples, the silane coupling agent is KH550.

[0043] In some optional instances, the mixing and hydrolysis time is 40 to 50 minutes, for example, 40 minutes, 41 minutes, 42 minutes, 43 minutes, 44 minutes, 45 minutes, 46 minutes, 47 minutes, 48 ​​minutes, 49 minutes or 50 minutes, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0044] As a preferred technical solution of the present invention, in step (II), the mass ratio of nano-silica in the silica dispersion to silane coupling agent in the silane coupling agent solution is 1:(0.2~0.3), for example, it can be 1:0.2, 1:0.21, 1:0.22, 1:0.23, 1:0.24, 1:0.25, 1:0.26, 1:0.27, 1:0.28, 1:0.29 or 1:0.3, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0045] This invention specifically specifies that the mass ratio of nano-silica in the silica dispersion to the silane coupling agent in the silane coupling agent solution is 1:(0.2~0.3). The nano-silica surface is rich in hydroxyl groups, exhibiting high reactivity. The terminal silanol groups (-Si-OH) of the hydrolyzed silane coupling agent KH550 undergo a condensation reaction with the silanol groups (-Si-OH) on the silica surface, removing one water molecule and forming a stable siloxane bond. Ultimately, a relatively dense organosilane molecular layer is formed on the nano-silica surface, transforming the nano-silica from hydrophilic to hydrophobic, greatly improving its compatibility with the organic polymer matrix in latex paint. Furthermore, the nano-silica modified with the silane coupling agent has similar chemical properties to the nano-cellulose nanomaterials modified with the same silane coupling agent, enabling them to achieve good interfacial bonding through the interaction between silane segments, ensuring stable dispersion of the modified nano-cellulose and modified silica in latex paint.

[0046] When the amount of silane coupling agent is lower than the lower limit of the range defined in this invention, the silane coupling agent KH550 is difficult to cover all active silanol sites on the surface of silica particles, resulting in a low grafting density of KH550 and insufficient hydrophobicity on the surface of nano-silica, which limits the improvement of its compatibility with the organic polymer matrix in latex paint. In addition, due to insufficient hydrophobic modification, nano-silica is prone to agglomeration in the aqueous phase, affecting its dispersion stability in the final reinforcing additive.

[0047] When the amount of silane coupling agent exceeds the upper limit defined in this invention, excess KH550 easily undergoes self-hydrolysis and condensation to form oligomers. These oligomers are adsorbed onto the silica surface through physical action, but cannot be grafted through strong covalent bonds. The binding strength of physical adsorption is insufficient, and they are easily detached during subsequent operations. In addition, the oligomers adsorbed on the surface of nano-silica form an excessively thick coating layer, affecting the full realization of its mechanical reinforcing effect as a nanofiller.

[0048] In some optional instances, the temperature at which the silane coupling agent solution and the silica dispersion are mixed, stirred, and heated is 60-70°C, for example, 60°C, 61°C, 62°C, 63°C, 64°C, 65°C, 66°C, 67°C, 68°C, 69°C, or 70°C, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0049] In some optional instances, the stirring and heating speed for mixing the silane coupling agent solution and the silica dispersion is 200 to 300 rpm, for example, 200 rpm, 210 rpm, 220 rpm, 230 rpm, 240 rpm, 250 rpm, 260 rpm, 270 rpm, 280 rpm, 290 rpm or 300 rpm, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0050] In some optional examples, the mixing, stirring, and heating time of the silane coupling agent solution and the silica dispersion is 8 to 10 hours, for example, 8.0 hours, 8.2 hours, 8.4 hours, 8.6 hours, 8.8 hours, 9.0 hours, 9.2 hours, 9.4 hours, 9.6 hours, 9.8 hours, or 10.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0051] As a preferred technical solution of the present invention, in step (III), the mass ratio of the modified silica powder to anhydrous ethanol is 1:(15~20), for example, it can be 1:15, 1:15.5, 1:16, 1:16.5, 1:17, 1:17.5, 1:18, 1:18.5, 1:19, 1:19.5 or 1:20, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0052] In some optional instances, the mass ratio of the compound emulsifier to deionized water is 1:(5~10), for example, it can be 1:5.0, 1:5.5, 1:6.0, 1:6.5, 1:7.0, 1:7.5, 1:8.0, 1:8.5, 1:9.0, 1:9.5 or 1:10.0, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0053] In some optional examples, the compound emulsifier consists of Span 60 and Tween 60 in a mass ratio of 3:7.

[0054] The compound emulsifier in this invention is composed of Span 60 and Tween 60 in a mass ratio of 3:7. Its main function is to stably disperse the hydrophobic modified silica powder in the aqueous phase, forming a uniform and stable modified silica emulsion. The nano-silica modified with silane coupling agent KH550 has a hydrophobic surface. When it is transferred from anhydrous ethanol to the aqueous phase, it is very easy to aggregate due to excessive interfacial tension. Therefore, this invention emulsifies hydrophobic modified silica powder using a compound emulsifier. The compound emulsifier can be adsorbed at the oil-water interface. The hydrophobic segments of Span 60 can be firmly anchored on the hydrophobic silica surface, while the hydrophilic segments of Tween 60 extend into the aqueous phase. Through steric hindrance, the emulsion droplets are prevented from approaching and agglomerating, thereby forming a stable O / W type emulsion. This allows the modified silica particles to exist stably in the aqueous phase as nanoscale droplets, which is beneficial for the subsequent uniform compounding with the modified nanocellulose solution and ensures the long-term stability of the final reinforcing agent.

[0055] In some optional examples, the compound emulsifier solution is added dropwise to the modified silica dispersion at a stirring speed of 600-800 rpm, for example, 600 rpm, 620 rpm, 640 rpm, 660 rpm, 680 rpm, 700 rpm, 720 rpm, 740 rpm, 760 rpm, 780 rpm, or 800 rpm. After all the solution has been added, the stirring speed is increased to 1500-2000 rpm, for example, 1500 rpm, 1550 rpm, 1600 rpm, 1650 rpm, or 1700 rpm. Continue stirring at 1750 rpm, 1800 rpm, 1850 rpm, 1900 rpm, 1950 rpm, or 2000 rpm for 10 to 20 minutes, for example, 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes, 15 minutes, 16 minutes, 17 minutes, 18 minutes, 19 minutes, or 20 minutes, to obtain a crude emulsion; subsequently, the crude emulsion is sheared and emulsified to obtain the modified silica emulsion, but it is not limited to the values ​​listed, and other unlisted values ​​within this range are also applicable.

[0056] In some optional examples, the mass of the compound emulsifier in the compound emulsifier solution is 5 to 8 wt% of the mass of the modified silica powder in the modified silica dispersion, for example, it can be 5.0 wt%, 5.2 wt%, 5.4 wt%, 5.6 wt%, 5.8 wt%, 6.0 wt%, 6.2 wt%, 6.4 wt%, 6.6 wt%, 6.8 wt%, 7.0 wt%, 7.2 wt%, 7.4 wt%, 7.6 wt%, 7.8 wt%, or 8.0 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0057] This invention specifically limits the mass of the compound emulsifier in the compound emulsifier solution to 5-8 wt% of the mass of the modified silica powder in the modified silica dispersion. After modification with silane coupling agent KH550, the silica surface changes from hydrophilic to hydrophobic. When it is dispersed in anhydrous ethanol and then emulsified with an aqueous phase, the compound emulsifier molecules need to be adsorbed at the oil-water interface to reduce interfacial tension and prevent particle aggregation. When the amount of compound emulsifier is within the range specified in this invention, the compound emulsifier can form a complete and dense adsorption film on the surface of silica particles. Among them, the hydrophobic Span 60 is adsorbed on the hydrophobic silica surface, while the hydrophilic Tween 60 extends into the aqueous phase. Through steric hindrance, the emulsion droplets repel each other, thereby obtaining a modified silica emulsion with uniform particle size distribution and stable dispersion.

[0058] When the amount of compound emulsifier is less than 5wt%, the compound emulsifier molecules are difficult to completely cover the surface of nano silica particles. During shear emulsification, silica particles that are not coated by the emulsifier are prone to agglomeration due to collision, forming large aggregates, which leads to a decrease in the stability of the obtained modified silica emulsion and makes it easy to separate or precipitate during long-term storage.

[0059] When the amount of compound emulsifier exceeds 8 wt%, the excessive compound emulsifier will undergo bilayer adsorption on the surface of silica particles, weakening the stability of the oil-water interface layer, causing emulsion droplet flocculation, and affecting the storage stability of modified silica emulsion.

[0060] In some optional instances, the rotational speed for shear emulsification of the crude emulsion is 5000~10000 rpm, for example, it can be 5000 rpm, 5500 rpm, 6000 rpm, 6500 rpm, 7000 rpm, 7500 rpm, 8000 rpm, 8500 rpm, 9000 rpm, 9500 rpm or 10000 rpm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0061] In some optional instances, the shear emulsification time of the crude emulsion is 5 to 15 minutes, for example, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes or 15 minutes, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0062] As a preferred technical solution of the present invention, in step (III), the compatibilizer solution is added to the modified nanocellulose solution at a stirring speed of 300-500 rpm and a heating temperature of 40-50°C. The stirring speed can be 300 rpm, 320 rpm, 340 rpm, 360 rpm, 380 rpm, 400 rpm, 420 rpm, 440 rpm, 460 rpm, 480 rpm, or 500 rpm, and the heating temperature can be 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C, 49°C, or 50°C. After complete addition, stirring continues for 10-15 minutes, for example, 10 minutes, 10.5 minutes, 11 minutes, 11.5 minutes, 12 minutes, 12.5 minutes, 13 minutes, 13.5 minutes, 14 minutes, 14.5 minutes, or 15 minutes. Then, the stirring speed is adjusted to 600-800 rpm, for example, 600-800 rpm. Continue adding the modified silica emulsion dropwise at 00 rpm, 620 rpm, 640 rpm, 660 rpm, 680 rpm, 700 rpm, 720 rpm, 740 rpm, 760 rpm, 780 rpm, or 800 rpm. After all the emulsion has been added, increase the stirring speed to 1000-1500 rpm, for example, 1000 rpm, 1050 rpm, 1100 rpm, 1150 rpm, 1200 rpm, 1250 rpm, 1300 rpm, 1350 rpm, 1400 rpm, 1450 rpm, or 1500 rpm, and continue stirring for 30-40 minutes. Finally, add deionized water to adjust the viscosity, for example, for 30 minutes, 31 minutes, 32 minutes, 33 minutes, 34 minutes, 35 minutes, 36 minutes, 37 minutes, 38 minutes, 39 minutes, or 40 minutes, but not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0063] This invention involves adding an aqueous solution of polyethylene glycol 6000 at a low stirring speed of 300-500 rpm and a heating temperature of 40-50°C. Polyethylene glycol 6000, as an amphiphilic polymer, has ether oxygen atoms in its molecular chain segments that can form hydrogen bonds with the hydroxyl and silane groups on the surface of nanocellulose, thus achieving strong adsorption. The long-chain hydrophobic portion extends into the solution. Subsequently, the stirring speed is adjusted to 600-800 rpm, and a modified silica emulsion is added dropwise. The surface of the emulsion droplets in the modified silica emulsion is coated with a layer of compound emulsifier. During stirring, the modified silica emulsion droplets coated with the compound emulsifier are uniformly dispersed in the nanocellulose solution. The hydrophobic segments of the polyethylene glycol 6000 extending into the solution are adsorbed onto the compound emulsifier layer on the surface of the emulsion droplets, acting as a bridge connecting the modified nanocellulose and modified silica.

[0064] In some optional examples, the compatibilizer solution is an aqueous solution of polyethylene glycol, wherein the mass fraction of polyethylene glycol in the compatibilizer solution is 30-40 wt%, for example, 30 wt%, 31 wt%, 32 wt%, 33 wt%, 34 wt%, 35 wt%, 36 wt%, 37 wt%, 38 wt%, 39 wt%, or 40 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0065] In some optional instances, the polyethylene glycol is polyethylene glycol 6000.

[0066] Polyethylene glycol 6000 is a long-chain nonionic polymeric surfactant. Its molecular structure consists of repeating ether bonds (-O-) and terminal hydroxyl groups, giving it both hydrophilicity and a certain degree of flexibility. When added to a modified nanocellulose solution, the ether oxygen atoms on the polyethylene glycol 6000 molecular chain can form hydrogen bonds with the abundant hydroxyl groups on the surface of the nanocellulose and the organosilicon segments introduced after modification with silane coupling agents, thereby effectively adsorbing and coating the surface of the nanocellulose fibers.

[0067] When the modified silica emulsion is subsequently added, the surface of the emulsion droplets is coated with a compound emulsifier (Span 60 and Tween 60), and its core is hydrophobic modified silica particles. The hydrophobic long chains of polyethylene glycol 6000 adsorbed on the surface of the modified nanocellulose can further engage in physical entanglement and hydrophobic interactions with the emulsifier molecules on the surface of the modified silica emulsion droplets, thereby forming molecular links between the modified nanocellulose and the modified silica particles. This facilitates a more uniform distribution of the modified silica emulsion droplets and their fixation within the three-dimensional network structure formed by the nanocellulose.

[0068] In some optional examples, the amount of polyethylene glycol added is 3 to 5 wt% of the mass of the modified nanocellulose solution, for example, 3.0 wt%, 3.2 wt%, 3.4 wt%, 3.6 wt%, 3.8 wt%, 4.0 wt%, 4.2 wt%, 4.4 wt%, 4.6 wt%, 4.8 wt%, or 5.0 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0069] In some optional examples, the dripping rate of the modified silica emulsion is 3 to 5 mL / min, for example, 3.0 mL / min, 3.2 mL / min, 3.4 mL / min, 3.6 mL / min, 3.8 mL / min, 4.0 mL / min, 4.2 mL / min, 4.4 mL / min, 4.6 mL / min, 4.8 mL / min or 5.0 mL / min, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0070] In some optional examples, the mass ratio of the modified silica powder to the modified nanocellulose solution is (10~15):100, for example, it can be 10:100, 10.5:100, 11:100, 11.5:100, 12:100, 12.5:100, 13:100, 13.5:100, 14:100, 14.5:100 or 15:100, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0071] This invention specifically defines the mass ratio of modified silica powder to modified nanocellulose solution as (10~15):100. After esterification and silanization treatment, the modified nanocellulose introduces carboxyl groups and organosilicon segments onto its surface, exhibiting good water dispersibility and compatibility with organic polymer matrices. The modified silica is treated with a silane coupling agent, resulting in a surface coating of organosilicon, which enhances its hydrophobicity. Within this ratio range, the modified silica particles can be uniformly dispersed in the three-dimensional network structure formed by the modified nanocellulose. The long fiber network of nanocellulose provides toughness and skeletal support, while the hard particles of the modified silica fill the network voids, improving the hardness and scrub resistance of the paint film.

[0072] When the amount of modified silica powder is below the lower limit defined in this invention, although the modified nanocellulose can form a three-dimensional network structure, the lack of sufficient modified silica powder as supporting points results in limited improvement in the hardness and scrub resistance of the paint film. Furthermore, when the amount of modified silica added is too small, its distribution in the three-dimensional network structure is sparse, failing to effectively hinder crack propagation and withstand external loads. Consequently, the paint film is prone to deformation or damage when subjected to impact or friction, leading to reduced adhesion.

[0073] When the amount of modified silica powder exceeds the upper limit defined in this invention, the excessive modified silica powder is prone to agglomeration during the composite process due to its high surface energy, forming large aggregates that are difficult to disperse uniformly in the nanocellulose network. These aggregates disrupt the continuity of the network structure, leading to defects within the paint film and reducing its hardness and adhesion. Furthermore, large aggregates can cause stress concentration within the paint film, reducing its washability.

[0074] In some optional instances, the viscosity of the added nanocellulose reinforcing agent is 300-500 mPa·s, for example, 300 mPa·s, 320 mPa·s, 340 mPa·s, 360 mPa·s, 380 mPa·s, 400 mPa·s, 420 mPa·s, 440 mPa·s, 460 mPa·s, 480 mPa·s, or 500 mPa·s, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0075] In a second aspect, the present invention provides a post-added nanocellulose reinforcing agent prepared by the preparation method described in the first aspect.

[0076] Thirdly, the present invention provides a method of using the post-added nanocellulose reinforcing agent described in the second aspect, the method comprising:

[0077] Add the nano-cellulose reinforcing agent to the finished latex paint and mix.

[0078] Compared to the "pre-addition" method of adding reinforcing additives during the preparation of latex paint, this invention adopts the "post-addition" method of adding reinforcing additives to the finished latex paint, avoiding the addition of reinforcing additives during the high-temperature, high-pressure, or high-shear polymerization stage of latex paint production. If reinforcing additives are added before or during the emulsion polymerization of latex paint, the nanocellulose and silica in the reinforcing additives are prone to agglomeration in the complex chemical environment, or to uncontrollable interactions with components such as initiators and emulsifiers, even interfering with the smooth progress of emulsion polymerization and affecting the basic properties of the latex paint.

[0079] This invention involves adding reinforcing additives to the finished latex paint and then stirring at high speed. The reinforcing additives in the latex paint mainly undergo physical dispersion. Mechanical stirring ensures that they are evenly dispersed in the latex paint without causing new chemical reactions. This not only simplifies the usage process but also avoids the risk of negatively impacting the basic latex paint formula due to improper addition.

[0080] The "post-addition" method employed in this invention eliminates the need for paint manufacturers to alter existing latex paint synthesis processes and production equipment. The additive is simply mixed in at the final stage, like any other ordinary additive, and a simple mixing process is sufficient to enhance and modify the latex paint, significantly reducing the cost of adjusting production processes and equipment. Simultaneously, this addition method greatly simplifies construction operations, allowing contractors to add the additive directly on-site. This post-addition method makes the reinforcing additive obtained by this invention a more versatile latex paint additive, widely adopted and applied in existing paint production systems.

[0081] As a preferred embodiment of the present invention, the amount of the added nano-cellulose reinforcing agent is 1 to 2 wt% of the mass of the finished latex paint, for example, it can be 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, or 2.0 wt%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0082] In some optional instances, the mixing speed is 1000~1500 rpm, for example, it can be 1000 rpm, 1050 rpm, 1100 rpm, 1200 rpm, 1250 rpm, 1300 rpm, 1350 rpm, 1400 rpm, 1450 rpm or 1500 rpm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0083] In some optional instances, the mixing time is 10 to 20 minutes, for example, 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes, 15 minutes, 16 minutes, 17 minutes, 18 minutes, 19 minutes or 20 minutes, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0084] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0085] This invention first modifies nanocellulose through esterification and silanization, while simultaneously treating nano-silica with silanization for hydrophobicity. Then, it combines the two using a compound emulsifier and compatibilizer to prepare a stable and dispersed water-based reinforcing agent. The reinforcing agent prepared by this invention effectively solves the technical problems of easy agglomeration of nanocellulose and poor compatibility with latex paint. It can be directly added to finished latex paint with simple mixing, ultimately significantly improving the hardness, adhesion, scrub resistance, and coating area of ​​the latex paint film while maintaining a good appearance. Attached Figure Description

[0086] Figure 1 The process flow diagrams for preparing the post-addition of nanocellulose reinforcing agents provided in Examples 1-15 of this invention are shown below.

[0087] Figure 2 Infrared spectra of nanocellulose solution and modified nanocellulose solution prepared in Example 1 of this invention;

[0088] Figure 3 An optical micrograph of the modified silica emulsion prepared in Example 1 of this invention;

[0089] Figure 4 This is a scanning electron microscope image of the surface of the paint film prepared in the comparative example of this invention;

[0090] Figure 5 This is a scanning electron microscope (SEM) image of the surface of the paint film prepared in Example 1 of the present invention;

[0091] Figure 6 This is a magnified scanning electron microscope image of the surface of the paint film prepared in Example 1 of the present invention. Detailed Implementation

[0092] The technical solutions of the present invention will be described in detail below with reference to specific embodiments and accompanying drawings. The embodiments described herein are specific implementations of the present invention, used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary, and should not be construed as limiting the implementation methods or the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can employ other obvious technical solutions based on the content disclosed in the claims and specification of this application. These technical solutions include those that make any obvious substitutions and modifications to the embodiments described herein.

[0093] Example 1

[0094] This embodiment provides a method for preparing a post-added nanocellulose reinforcing agent for latex paint coatings, such as... Figure 1 As shown, the preparation method specifically includes the following steps:

[0095] (1) Butanetetracarboxylic acid, sodium hypophosphite and 0.5wt% nanocellulose solution were mixed, wherein the mass ratio of nanocellulose solution to butanetetracarboxylic acid was 100:10, and the mass of sodium hypophosphite was 20wt% of the mass of butanetetracarboxylic acid. After mixing evenly, the mixture was stirred and heated at 60°C for 10h to induce esterification. After the reaction was completed, the mixture was dialyzed for 48h using a dialysis bag with a molecular weight cutoff of 10000Da to obtain the esterified nanocellulose solution.

[0096] At a heating temperature of 50℃ and a stirring speed of 300 rpm, a silane coupling agent solution was added to the esterified nanocellulose solution. The silane coupling agent solution consisted of silane coupling agent KH550 and an aqueous ethanol solution (the volume ratio of deionized water to anhydrous ethanol was 2:8). The mass fraction of silane coupling agent KH550 in the silane coupling agent solution was 5 wt%, and the mass ratio of silane coupling agent KH550 in the esterified nanocellulose solution to that in the silane coupling agent solution was 100:3. After all the solution was added, the mixture was stirred and heated for 3 hours to allow the reaction to occur. After the reaction was completed, the solution was dialyzed for 48 hours using a dialysis bag with a molecular weight cutoff of 10000 Da to obtain the modified nanocellulose solution.

[0097] (2) Add nano-silica to anhydrous ethanol and ultrasonically disperse it for 40 min at an ultrasonic power of 300 W to obtain a silica dispersion. The mass of silica is 5 wt% of the mass of anhydrous ethanol.

[0098] Add silane coupling agent KH550 to an ethanol aqueous solution (the volume ratio of deionized water to anhydrous ethanol is 2:8), the volume ratio of silane coupling agent KH550 to the ethanol aqueous solution is 1:30, mix and stir for 40 min to hydrolyze to obtain silane coupling agent solution.

[0099] A silane coupling agent solution was added to a silica dispersion. The mass ratio of nano-silica in the silica dispersion to silane coupling agent KH550 in the silane coupling agent solution was 1:0.2. The mixture was stirred and heated at 60°C and 200 rpm for 10 hours to allow the reaction to occur. After the reaction was completed, the modified silica powder was obtained by centrifugation, washing and drying.

[0100] (3) Add the modified silica powder obtained in step (2) to anhydrous ethanol. The mass ratio of modified silica powder to anhydrous ethanol is 1:15. The modified silica powder is ultrasonically dispersed for 40 minutes at an ultrasonic power of 300W to obtain a modified silica dispersion. Mix the compound emulsifier (composed of Span 60 and Tween 60 in a mass ratio of 3:7) with deionized water in a mass ratio of 1:5 to obtain a compound emulsifier solution.

[0101] At a stirring speed of 600 rpm, the compound emulsifier solution was added dropwise to the modified silica dispersion. The mass of the compound emulsifier (Span 60 and Tween 60) in the compound emulsifier solution was 5 wt% of the mass of the modified silica powder in the modified silica dispersion. After all the emulsifier was added, the stirring speed was increased to 1500 rpm and stirring was continued for 20 min to obtain a crude emulsion. The crude emulsion was sheared and emulsified at a stirring speed of 5000 rpm for 15 min to obtain a modified silica emulsion.

[0102] At a stirring speed of 300 rpm and a heating temperature of 40°C, a 30 wt% aqueous solution of polyethylene glycol 6000 was added to the modified nanocellulose solution obtained in step (1). The amount of polyethylene glycol 6000 added was 3 wt% of the mass of the modified nanocellulose solution. After complete addition, stirring was continued for 15 min. Then, the stirring speed was adjusted to 600 rpm and the heating temperature was maintained at 40°C. Modified silica emulsion was added dropwise at a rate of 3 mL / min. The mass ratio of modified silica powder to modified nanocellulose solution was 10:100. After all the emulsion was added, the stirring speed was increased to 1000 rpm and the heating temperature was maintained at 40°C. Stirring was continued for 40 min. Finally, deionized water was added to adjust the viscosity of the solution to 300 mPa·s, and the nanocellulose reinforcing agent was added.

[0103] This embodiment also provides a method for using the post-added nanocellulose reinforcing agent prepared above, the method specifically including the following steps:

[0104] The nano-cellulose reinforcing agent prepared above was added to the finished latex paint (commercially available product, Three Trees BB paint, purchased online). The amount of nano-cellulose reinforcing agent added was 1 wt% of the mass of the finished latex paint. The mixture was stirred at 1000 rpm for 20 min.

[0105] Figure 2 The infrared spectra of the nanocellulose solution and the modified nanocellulose solution prepared in Example 1 of this invention are shown in the figures. As can be seen from the figures, the wavelengths in the 3300~3500 cm⁻¹ range are... -1 The broad and strong absorption peak at 1730 cm⁻¹ is attributed to the OH stretching vibration, originating from hydroxyl groups (-OH) on the nanocellulose molecular chains and adsorbed in water. -1 The absorption peak at this point is attributed to the C=O stretching vibration, originating from the ester group (-COO-) and / or the residual carboxylic acid group (-COOH) generated in the reaction. The absence of this peak in the infrared spectrum of nanocellulose confirms the successful esterification reaction, introducing carbonyl-containing functional groups onto the cellulose backbone. (1000~1100 cm⁻¹) -1 The absorption peaks at this location are attributed to Si-O-Si and Si-OC vibrations. Compared to the infrared curve of nanocellulose, the infrared curve of modified nanocellulose shows increased absorption peak intensity and sharper peak shape in this region. This indicates that new Si-O-Si (siloxane network) and Si-OC (covalent bond between silane and cellulose hydroxyl group) structures have been formed in the modified nanocellulose, proving the effective grafting of KH550.

[0106] Figure 3The image shows an optical micrograph of the modified silica emulsion prepared in Example 1 of this invention. The image reveals a large number of nearly spherical silica particles uniformly dispersed in the continuous phase. The particles have clear outlines and distinct boundaries, exhibiting good overall dispersion. No significant large-scale aggregation or sedimentation was observed. This uniform dispersion is attributed to the stable emulsion formed by the use of a compound emulsifier (Span 60 / Tween 60) combined with high-shear emulsification in this example. The regular spherical morphology and highly dispersed characteristics indicate that the surface of the silica particles has been effectively coated by the compound emulsifier, laying the foundation for its subsequent uniform composite with the modified nanocellulose solution.

[0107] Example 2

[0108] This embodiment provides a method for preparing a post-added nanocellulose reinforcing agent for latex paint coatings, such as... Figure 1 As shown, the preparation method specifically includes the following steps:

[0109] (1) Butanetetracarboxylic acid, sodium hypophosphite and 0.8 wt% nanocellulose solution were mixed, wherein the mass ratio of nanocellulose solution to butanetetracarboxylic acid was 100:11, and the mass of sodium hypophosphite was 22 wt% of the mass of butanetetracarboxylic acid. After mixing evenly, the mixture was stirred and heated at 65°C for 9.5 h to induce esterification. After the reaction was completed, the mixture was dialyzed for 42 h using a dialysis bag with a molecular weight cutoff of 10000 Da to obtain the esterified nanocellulose solution.

[0110] A silane coupling agent solution was added to the esterified nanocellulose solution at a heating temperature of 52℃ and a stirring speed of 350 rpm. The silane coupling agent solution consisted of silane coupling agent KH550 and an aqueous ethanol solution (the volume ratio of deionized water to anhydrous ethanol was 2:8). The mass fraction of silane coupling agent KH550 in the silane coupling agent solution was 6 wt%, and the mass ratio of silane coupling agent KH550 in the esterified nanocellulose solution to that in the silane coupling agent solution was 100:3.5. After all the silane coupling agent was added, the mixture was stirred and heated for 2.8 h to allow the reaction to occur. After the reaction was completed, the mixture was dialyzed for 42 h using a dialysis bag with a molecular weight cutoff of 10000 Da to obtain the modified nanocellulose solution.

[0111] (2) Add nano-silica to anhydrous ethanol and ultrasonically disperse it for 38 min at an ultrasonic power of 350 W to obtain a silica dispersion. The mass of silica is 6 wt% of the mass of anhydrous ethanol.

[0112] Silane coupling agent KH550 was added to an ethanol aqueous solution (the volume ratio of deionized water to anhydrous ethanol was 2:8), and the volume ratio of silane coupling agent KH550 to ethanol aqueous solution was 1:32. After mixing and stirring for 42 minutes, the silane coupling agent solution was obtained.

[0113] A silane coupling agent solution was added to a silica dispersion. The mass ratio of nano-silica in the silica dispersion to silane coupling agent KH550 in the silane coupling agent solution was 1:0.22. The mixture was stirred and heated at 62°C and 220 rpm for 9.5 h to allow the reaction to occur. After the reaction was completed, the modified silica powder was obtained by centrifugation, washing and drying.

[0114] (3) Add the modified silica powder obtained in step (2) to anhydrous ethanol. The mass ratio of modified silica powder to anhydrous ethanol is 1:16. Disperse the modified silica powder under ultrasonic power of 350W for 38 minutes to obtain modified silica dispersion. Mix the compound emulsifier (composed of Span 60 and Tween 60 in a mass ratio of 3:7) with deionized water in a mass ratio of 1:6 to obtain compound emulsifier solution.

[0115] At a stirring speed of 650 rpm, the compound emulsifier solution was added dropwise to the modified silica dispersion. The mass of the compound emulsifier (Span 60 and Tween 60) in the compound emulsifier solution was 6 wt% of the mass of the modified silica powder in the modified silica dispersion. After all the emulsifier was added, the stirring speed was increased to 1600 rpm and stirring was continued for 18 min to obtain a crude emulsion. The crude emulsion was sheared and emulsified at a stirring speed of 6000 rpm for 12 min to obtain a modified silica emulsion.

[0116] At a stirring speed of 350 rpm and a heating temperature of 42°C, a 32 wt% aqueous solution of polyethylene glycol 6000 was added to the modified nanocellulose solution obtained in step (1). The amount of polyethylene glycol 6000 added was 3.5 wt% of the mass of the modified nanocellulose solution. After complete addition, stirring was continued for 13 min. Then, the stirring speed was adjusted to 650 rpm and the heating temperature was maintained at 42°C. Modified silica emulsion was added dropwise at a rate of 3.5 mL / min. The mass ratio of modified silica powder to modified nanocellulose solution was 11:100. After all the emulsion was added, the stirring speed was increased to 1100 rpm and the heating temperature was maintained at 42°C. Stirring was continued for 38 min. Finally, deionized water was added to adjust the viscosity of the solution to 350 mPa·s, and the nanocellulose reinforcing agent was added.

[0117] This embodiment also provides a method for using the post-added nanocellulose reinforcing agent prepared above, the method specifically including the following steps:

[0118] The nano-cellulose reinforcing agent prepared above was added to the finished latex paint (commercially available product, Three Trees BB paint, purchased online). The amount of nano-cellulose reinforcing agent added was 1.2 wt% of the mass of the finished latex paint. The mixture was stirred at 1100 rpm for 18 min.

[0119] Example 3

[0120] This embodiment provides a method for preparing a post-added nanocellulose reinforcing agent for latex paint coatings, such as... Figure 1 As shown, the preparation method specifically includes the following steps:

[0121] (1) Butanetetracarboxylic acid, sodium hypophosphite and a nanocellulose solution with a mass fraction of 1 wt% were mixed, wherein the mass ratio of nanocellulose solution to butanetetracarboxylic acid was 100:12, and the mass of sodium hypophosphite was 25 wt% of the mass of butanetetracarboxylic acid. After mixing evenly, the mixture was stirred and heated at 70°C for 9 h to induce esterification. After the reaction was completed, the mixture was dialyzed for 36 h using a dialysis bag with a molecular weight cutoff of 10000 Da to obtain the esterified nanocellulose solution.

[0122] At a heating temperature of 55℃ and a stirring speed of 400 rpm, a silane coupling agent solution was added to the esterified nanocellulose solution. The silane coupling agent solution consisted of silane coupling agent KH550 and an aqueous ethanol solution (the volume ratio of deionized water to anhydrous ethanol was 2:8). The mass fraction of silane coupling agent KH550 in the silane coupling agent solution was 7 wt%, and the mass ratio of silane coupling agent KH550 in the esterified nanocellulose solution to that in the silane coupling agent solution was 100:4. After all the silane coupling agent was added, the mixture was stirred and heated for 2.5 h to allow the reaction to occur. After the reaction was completed, the mixture was dialyzed for 36 h using a dialysis bag with a molecular weight cutoff of 10000 Da to obtain the modified nanocellulose solution.

[0123] (2) Add nano-silica to anhydrous ethanol and ultrasonically disperse it for 35 min at an ultrasonic power of 400 W to obtain a silica dispersion. The mass of silica is 7 wt% of the mass of anhydrous ethanol.

[0124] Add silane coupling agent KH550 to an ethanol aqueous solution (volume ratio of deionized water to anhydrous ethanol is 2:8), the volume ratio of silane coupling agent KH550 to ethanol aqueous solution is 1:35, mix and stir for 45 min to hydrolyze to obtain silane coupling agent solution.

[0125] The silane coupling agent solution was added to the silica dispersion. The mass ratio of nano-silica in the silica dispersion to silane coupling agent KH550 in the silane coupling agent solution was 1:0.25. The mixture was stirred and heated at 65°C and 250 rpm for 9 hours to allow the reaction to occur. After the reaction was completed, the modified silica powder was obtained by centrifugation, washing and drying.

[0126] (3) Add the modified silica powder obtained in step (2) to anhydrous ethanol. The mass ratio of modified silica powder to anhydrous ethanol is 1:17. Disperse the modified silica powder under ultrasonic power of 400W for 35 minutes to obtain modified silica dispersion. Mix the compound emulsifier (composed of Span 60 and Tween 60 in a mass ratio of 3:7) with deionized water in a mass ratio of 1:7 to obtain compound emulsifier solution.

[0127] At a stirring speed of 700 rpm, the compound emulsifier solution was added dropwise to the modified silica dispersion. The mass of the compound emulsifier (Span 60 and Tween 60) in the compound emulsifier solution was 6 wt% of the mass of the modified silica powder in the modified silica dispersion. After all the emulsifier was added, the stirring speed was increased to 1700 rpm and stirring was continued for 15 min to obtain a crude emulsion. The crude emulsion was sheared and emulsified at a stirring speed of 7000 rpm for 10 min to obtain a modified silica emulsion.

[0128] At a stirring speed of 400 rpm and a heating temperature of 45°C, a 35 wt% aqueous solution of polyethylene glycol 6000 was added to the modified nanocellulose solution obtained in step (1). The amount of polyethylene glycol 6000 added was 4 wt% of the mass of the modified nanocellulose solution. After complete addition, stirring was continued for 12 min. Then, the stirring speed was adjusted to 700 rpm and the heating temperature was maintained at 45°C. Modified silica emulsion was added dropwise at a rate of 4 mL / min. The mass ratio of modified silica powder to modified nanocellulose solution was 12:100. After all the emulsion was added, the stirring speed was increased to 1200 rpm and the heating temperature was maintained at 45°C. Stirring was continued for 35 min. Finally, deionized water was added to adjust the viscosity of the solution to 400 mPa·s, and the nanocellulose reinforcing agent was added.

[0129] This embodiment also provides a method for using the post-added nanocellulose reinforcing agent prepared above, the method specifically including the following steps:

[0130] The nano-cellulose reinforcing agent prepared above was added to the finished latex paint (commercially available product, Three Trees BB paint, purchased online). The amount of nano-cellulose reinforcing agent added was 1.5 wt% of the mass of the finished latex paint. The mixture was stirred at 1200 rpm for 15 min.

[0131] Example 4

[0132] This embodiment provides a method for preparing a post-added nanocellulose reinforcing agent for latex paint coatings, such as... Figure 1 As shown, the preparation method specifically includes the following steps:

[0133] (1) Butanetetracarboxylic acid, sodium hypophosphite and a nanocellulose solution with a mass fraction of 1.2 wt% were mixed, wherein the mass ratio of nanocellulose solution to butanetetracarboxylic acid was 100:13, and the mass of sodium hypophosphite was 28 wt% of the mass of butanetetracarboxylic acid. After mixing evenly, the mixture was stirred and heated at 75°C for 8.5 h to induce esterification. After the reaction was completed, the mixture was dialyzed for 30 h using a dialysis bag with a molecular weight cutoff of 15000 Da to obtain the esterified nanocellulose solution.

[0134] A silane coupling agent solution was added to the esterified nanocellulose solution at a heating temperature of 58℃ and a stirring speed of 450 rpm. The silane coupling agent solution consisted of silane coupling agent KH550 and an aqueous ethanol solution (the volume ratio of deionized water to anhydrous ethanol was 2:8). The mass fraction of silane coupling agent KH550 in the silane coupling agent solution was 8 wt%, and the mass ratio of silane coupling agent KH550 in the esterified nanocellulose solution to that in the silane coupling agent solution was 100:4.5. After all the silane coupling agent was added, the mixture was stirred and heated for 2.2 h to allow the reaction to occur. After the reaction was completed, the mixture was dialyzed for 30 h using a dialysis bag with a molecular weight cutoff of 15000 Da to obtain the modified nanocellulose solution.

[0135] (2) Add nano-silica to anhydrous ethanol and ultrasonically disperse it for 32 min at an ultrasonic power of 450 W to obtain a silica dispersion. The mass of silica is 8 wt% of the mass of anhydrous ethanol.

[0136] Silane coupling agent KH550 was added to an ethanol aqueous solution (the volume ratio of deionized water to anhydrous ethanol was 2:8), and the volume ratio of silane coupling agent KH550 to ethanol aqueous solution was 1:38. After mixing and stirring for 48 minutes, the silane coupling agent solution was obtained.

[0137] A silane coupling agent solution was added to a silica dispersion. The mass ratio of nano-silica in the silica dispersion to silane coupling agent KH550 in the silane coupling agent solution was 1:0.28. The mixture was stirred and heated at 68°C and 280 rpm for 8.5 h to allow the reaction to occur. After the reaction was completed, the modified silica powder was obtained by centrifugation, washing and drying.

[0138] (3) Add the modified silica powder obtained in step (2) to anhydrous ethanol. The mass ratio of modified silica powder to anhydrous ethanol is 1:18. Disperse the modified silica powder under ultrasonic power of 450W for 32 minutes to obtain a modified silica dispersion. Mix the compound emulsifier (composed of Span 60 and Tween 60 in a mass ratio of 3:7) with deionized water in a mass ratio of 1:8 to obtain a compound emulsifier solution.

[0139] At a stirring speed of 750 rpm, the compound emulsifier solution was added dropwise to the modified silica dispersion. The mass of the compound emulsifier (Span 60 and Tween 60) in the compound emulsifier solution was 7 wt% of the mass of the modified silica powder in the modified silica dispersion. After all the emulsifier was added, the stirring speed was increased to 1800 rpm and stirring was continued for 12 min to obtain a crude emulsion. The crude emulsion was sheared and emulsified at a stirring speed of 8000 rpm for 8 min to obtain a modified silica emulsion.

[0140] At a stirring speed of 450 rpm and a heating temperature of 48°C, a 38 wt% aqueous solution of polyethylene glycol 6000 was added to the modified nanocellulose solution obtained in step (1). The amount of polyethylene glycol 6000 added was 4.5 wt% of the mass of the modified nanocellulose solution. After complete addition, stirring was continued for 11 min. Then, the stirring speed was adjusted to 750 rpm and the heating temperature was maintained at 48°C. Modified silica emulsion was added dropwise at a rate of 4.5 mL / min. The mass ratio of modified silica powder to modified nanocellulose solution was 13:100. After all the emulsion was added, the stirring speed was increased to 1300 rpm and the heating temperature was maintained at 48°C. Stirring was continued for 32 min. Finally, deionized water was added to adjust the viscosity of the solution to 450 mPa·s, and the nanocellulose reinforcing agent was added.

[0141] This embodiment also provides a method for using the post-added nanocellulose reinforcing agent prepared above, the method specifically including the following steps:

[0142] The nano-cellulose reinforcing agent prepared above was added to the finished latex paint (commercially available product, Three Trees BB paint, purchased online). The amount of nano-cellulose reinforcing agent added was 1.8 wt% of the mass of the finished latex paint. The mixture was stirred at 1300 rpm for 12 min.

[0143] Example 5

[0144] This embodiment provides a method for preparing a post-added nanocellulose reinforcing agent for latex paint coatings, such as... Figure 1 As shown, the preparation method specifically includes the following steps:

[0145] (1) Butanetetracarboxylic acid, sodium hypophosphite and a nanocellulose solution with a mass fraction of 1.5 wt% were mixed, wherein the mass ratio of nanocellulose solution to butanetetracarboxylic acid was 100:15, and the mass of sodium hypophosphite was 30 wt% of the mass of butanetetracarboxylic acid. After mixing evenly, the mixture was stirred and heated at 80°C for 8 h to induce an esterification reaction. After the reaction was completed, the mixture was dialyzed for 24 h using a dialysis bag with a molecular weight cutoff of 15000 Da to obtain an esterified nanocellulose solution.

[0146] At a heating temperature of 60℃ and a stirring speed of 500 rpm, a silane coupling agent solution was added to the esterified nanocellulose solution. The silane coupling agent solution consisted of silane coupling agent KH550 and an aqueous ethanol solution (the volume ratio of deionized water to anhydrous ethanol was 2:8). The mass fraction of silane coupling agent KH550 in the silane coupling agent solution was 10 wt%, and the mass ratio of silane coupling agent KH550 in the esterified nanocellulose solution to that in the silane coupling agent solution was 100:5. After all the silane coupling agent was added, the mixture was stirred and heated for 2 hours to allow the reaction to occur. After the reaction was completed, the mixture was dialyzed for 24 hours using a dialysis bag with a molecular weight cutoff of 15000 Da to obtain the modified nanocellulose solution.

[0147] (2) Add nano-silica to anhydrous ethanol and ultrasonically disperse it for 30 min at an ultrasonic power of 500 W to obtain a silica dispersion. The mass of silica is 10 wt% of the mass of anhydrous ethanol.

[0148] Add silane coupling agent KH550 to an ethanol aqueous solution (the volume ratio of deionized water to anhydrous ethanol is 2:8), the volume ratio of silane coupling agent KH550 to the ethanol aqueous solution is 1:40, mix and stir for 50 min to hydrolyze to obtain silane coupling agent solution.

[0149] The silane coupling agent solution was added to the silica dispersion. The mass ratio of nano-silica in the silica dispersion to silane coupling agent KH550 in the silane coupling agent solution was 1:0.3. The mixture was stirred and heated at 70°C and 300 rpm for 8 hours to allow the reaction to occur. After the reaction was completed, the modified silica powder was obtained by centrifugation, washing and drying.

[0150] (3) Add the modified silica powder obtained in step (2) to anhydrous ethanol. The mass ratio of modified silica powder to anhydrous ethanol is 1:20. Disperse the modified silica powder under ultrasonic power of 500W for 30 minutes to obtain modified silica dispersion. Mix the compound emulsifier (composed of Span 60 and Tween 60 in a mass ratio of 3:7) with deionized water at a mass ratio of 1:10 to obtain compound emulsifier solution.

[0151] At a stirring speed of 800 rpm, the compound emulsifier solution was added dropwise to the modified silica dispersion. The mass of the compound emulsifier (Span 60 and Tween 60) in the compound emulsifier solution was 8 wt% of the mass of the modified silica powder in the modified silica dispersion. After all the emulsifier was added, the stirring speed was increased to 2000 rpm and stirring was continued for 10 min to obtain a crude emulsion. The crude emulsion was sheared and emulsified at a stirring speed of 10000 rpm for 5 min to obtain a modified silica emulsion.

[0152] At a stirring speed of 500 rpm and a heating temperature of 50°C, a 40 wt% aqueous solution of polyethylene glycol 6000 was added to the modified nanocellulose solution obtained in step (1). The amount of polyethylene glycol 6000 added was 5 wt% of the mass of the modified nanocellulose solution. After complete addition, stirring was continued for 10 min. Then, the stirring speed was adjusted to 800 rpm and the heating temperature was maintained at 50°C. Modified silica emulsion was added dropwise at a rate of 5 mL / min. The mass ratio of modified silica powder to modified nanocellulose solution was 15:100. After all the emulsion was added, the stirring speed was increased to 1500 rpm and the heating temperature was maintained at 50°C. Stirring was continued for 30 min. Finally, deionized water was added to adjust the viscosity of the solution to 500 mPa·s, and the nanocellulose reinforcing agent was added.

[0153] This embodiment also provides a method for using the post-added nanocellulose reinforcing agent prepared above, the method specifically including the following steps:

[0154] The nano-cellulose reinforcing agent prepared above was added to the finished latex paint (commercially available product, Three Trees BB paint, purchased online). The amount of nano-cellulose reinforcing agent added was 2 wt% of the mass of the finished latex paint. The mixture was stirred at 1500 rpm for 10 min.

[0155] Example 6

[0156] This embodiment provides a method for preparing a post-added nanocellulose reinforcing agent for latex paint coatings. The difference from Example 1 is that in step (1), the mass ratio of nanocellulose solution to butanetetracarboxylic acid is adjusted to 100:5. Other operating steps and process parameters are exactly the same as in Example 1.

[0157] Example 7

[0158] This embodiment provides a method for preparing a post-added nanocellulose reinforcing agent for latex paint coatings. The difference from Example 1 is that in step (1), the mass ratio of nanocellulose solution to butanetetracarboxylic acid is adjusted to 100:20. Other operation steps and process parameters are exactly the same as in Example 1.

[0159] Example 8

[0160] This embodiment provides a method for preparing a post-added nanocellulose reinforcing agent for latex paint coatings. The difference from Example 1 is that in step (1), the mass ratio of esterified nanocellulose solution to silane coupling agent KH550 in silane coupling agent solution is adjusted to 100:1. Other operation steps and process parameters are exactly the same as in Example 1.

[0161] Example 9

[0162] This embodiment provides a method for preparing a post-added nanocellulose reinforcing agent for latex paint coatings. The difference from Example 1 is that in step (1), the mass ratio of esterified nanocellulose solution to silane coupling agent KH550 in silane coupling agent solution is adjusted to 100:10. Other operation steps and process parameters are exactly the same as in Example 1.

[0163] Example 10

[0164] This embodiment provides a method for preparing a post-added nanocellulose reinforcing agent for latex paint coatings. The difference from Embodiment 1 is that in step (2), the mass ratio of nanosilica in the silica dispersion to silane coupling agent KH550 in the silane coupling agent solution is adjusted to 1:0.1. Other operating steps and process parameters are exactly the same as in Embodiment 1.

[0165] Example 11

[0166] This embodiment provides a method for preparing a post-added nanocellulose reinforcing agent for latex paint coatings. The difference from Embodiment 1 is that in step (2), the mass ratio of nanosilica in the silica dispersion to silane coupling agent KH550 in the silane coupling agent solution is adjusted to 1:0.5. Other operating steps and process parameters are exactly the same as in Embodiment 1.

[0167] Example 12

[0168] This embodiment provides a method for preparing a post-added nanocellulose reinforcing agent for latex paint coatings. The difference from Embodiment 1 is that in step (3), the mass of the compound emulsifier in the compound emulsifier solution is adjusted to 1 wt% of the mass of the modified silica powder in the modified silica dispersion. Other operation steps and process parameters are exactly the same as in Embodiment 1.

[0169] Example 13

[0170] This embodiment provides a method for preparing a post-added nanocellulose reinforcing agent for latex paint coatings. The difference from Embodiment 1 is that in step (3), the mass of the compound emulsifier in the compound emulsifier solution is adjusted to 10 wt% of the mass of the modified silica powder in the modified silica dispersion. Other operating steps and process parameters are exactly the same as in Embodiment 1.

[0171] Example 14

[0172] This embodiment provides a method for preparing a post-added nanocellulose reinforcing agent for latex paint coatings. The difference from Embodiment 1 is that in step (3), the mass ratio of modified silica powder to modified nanocellulose solution is adjusted to 5:100. Other operation steps and process parameters are exactly the same as in Embodiment 1.

[0173] Example 15

[0174] This embodiment provides a method for preparing a post-added nanocellulose reinforcing agent for latex paint coatings. The difference from Embodiment 1 is that in step (3), the mass ratio of modified silica powder to modified nanocellulose solution is adjusted to 20:100. Other operation steps and process parameters are exactly the same as in Embodiment 1.

[0175] Comparative Example

[0176] This comparison example uses Three Trees BB paint purchased online.

[0177] Application examples

[0178] According to the national standard GB / T 1727-2021 "General Method for Preparing Paint Films", the latex paints provided in Examples 1-15 and the comparative examples were sprayed onto the surface of tinplate using a spraying method. Three coats were applied, and the final paint film thickness was controlled to be between 20 and 30 μm.

[0179] Figure 4 This is a scanning electron microscope (SEM) image of the surface of the paint film prepared in the comparative example of this invention. Figure 5 and Figure 6 The images shown are scanning electron microscope (SEM) images of the surface of the paint film prepared in Example 1 of this invention and a magnified SEM image of the surface. A comparison reveals that the paint film structure of the comparative example (commercially available latex paint without reinforcing additives) has obvious defects, and the paint film surface (…) Figure 4 The surface of the paint film is relatively rough, with an uneven particle distribution. This non-dense structure results in poor hardness, adhesion, and scrub resistance. In contrast, the paint film surface of Example 1 (with the reinforcing additive prepared according to this invention) is... Figure 5 The surface is flat and smooth, with no obvious defects; especially in high-magnification surface images ( Figure 6 In the study, the interwoven fibrous structure formed by the modified nanocellulose can be clearly observed. These fibrous filaments are tightly bonded to the modified silica particles filling them, together forming a robust and dense composite network. This change in microstructure significantly improves the hardness, adhesion, and scrub resistance of the paint film.

[0180] The latex paints provided in Examples 1-15 and the comparative examples were sprayed using the spraying method provided in the application examples to obtain paint film test panels. The hardness, adhesion, scrub resistance, and coating area of ​​the paint film samples were tested. The specific test steps are as follows:

[0181] (1) Hardness

[0182] The hardness of the paint film was tested according to the national standard GB / T 6739-2022 "Determination of Hardness of Paint Film by Pencil Method". The specific test steps are as follows:

[0183] The prepared and cured paint film test panel was fixed on a horizontal platform. Using a set of drawing pencils of known hardness (from the softest 6B to the hardest 9H), the pencils were sharpened to expose the lead and then flattened on 400-grit sandpaper. The pencils were held against the paint film at a 45° angle and advanced approximately 6.5 mm at a speed of about 1 mm / s. The test was started with softer pencils and gradually replaced with harder pencils until a pencil of a certain hardness could scratch the paint film. The pencil hardness of the paint film is defined as the highest pencil hardness grade that could not scratch the paint film.

[0184] (2) Adhesion

[0185] The adhesion of the paint film was tested according to the national standard GB / T 9286-2021 "Paints and Varnishes - Cross-cut Test". The specific test steps are as follows:

[0186] Use a cross-cutting tool to cut a grid of squares at specified intervals into the paint film. Apply pressure-sensitive adhesive tape and quickly peel it off. Assess the adhesion level based on the proportion of paint film that has detached from the grid. A higher level indicates poorer adhesion.

[0187] (3) Washability

[0188] The scrub resistance of the paint film was tested according to the national standard GB / T 9266-2009 "Determination of Scrub Resistance of Architectural Coatings". The specific test steps are as follows:

[0189] The prepared and cured paint film test panel is fixed on the scrub resistance tester with the coated surface facing upwards and subjected to a 1kg brush load. The brush bristles are soaked in a soap solution of a specific concentration to keep them moist. After starting the instrument, the brush will repeatedly scrub the paint film surface at a fixed stroke of 300mm and a frequency of 37 times / minute until the paint film is worn through and the substrate is exposed. The number of scrubs at this point is recorded (one reciprocating motion of the brush is one scrub).

[0190] (4) Coating area

[0191] Prepare a piece of land with a known area (S, m) 2 A smooth wall surface was prepared. Then, the latex paint to be tested (mass denoted as m1, kg) was evenly sprayed onto the entire wall surface, forming a paint film (dry film) with a thickness of 20-30 μm. The remaining latex paint was weighed again and recorded as m2 (kg). The coated area was calculated using the following formula:

[0192] Coating area (m) 2 / kg)=S / [(m2-m1)].

[0193] The test results are shown in Table 1.

[0194] Table 1

[0195] Pencil hardness Adhesion rating Number of washes (times) <![CDATA[Painting area (m 2 / kg)]]> Example 1 H 1 5520 8.5 Example 2 H 0 5630 8.8 Example 3 2H 0 5780 9.2 Example 4 H 0 5590 8.7 Example 5 H 1 5230 8.3 Example 6 HB 3 4020 7.5 Example 7 B 4 3530 6.3 Example 8 HB 3 4240 7.0 Example 9 B 4 3850 6.8 Example 10 HB 3 4160 7.4 Example 11 B 4 3770 6.5 Example 12 HB 3 3980 6.0 Example 13 B 4 3690 6.6 Example 14 HB 2 4510 7.5 Example 15 B 4 3420 6.2 Comparative Example 2B 5 2580 4.7

[0196] The test data from Examples 1, 6, and 7 show that in Example 6, the amount of butanetetracarboxylic acid was too low, resulting in insufficient esterification of nanocellulose, too few carboxyl groups on the surface, weak electrostatic repulsion, and easy aggregation of nanocellulose, which reduced the adhesion and scrub resistance of the paint film. In Example 7, the amount of butanetetracarboxylic acid was too high, causing cross-linking and aggregation between nanocellulose particles, forming aggregates, reducing the specific surface area, weakening the mechanical reinforcement effect, and significantly reducing the hardness and scrub resistance of the paint film.

[0197] The test data from Examples 1, 8, and 9 show that in Example 8, the amount of silane coupling agent KH550 was too low, resulting in insufficient silanization of the nanocellulose surface, low grafting density of organosilicon segments, poor compatibility with the latex paint matrix, and affecting the adhesion and scrub resistance of the paint film. In Example 9, the amount of silane coupling agent KH550 was too high, causing KH550 to self-polymerize and form oligomers, which could only be physically adsorbed on the surface of nanocellulose. The coating layer was too thick, affecting the dispersion and reinforcing effect of nanocellulose, and reducing the hardness and scrub resistance of the paint film.

[0198] The test data from Examples 1, 10, and 11 show that in Example 10, the amount of silane coupling agent KH550 was too low, resulting in insufficient hydrophobicity of the nano-silica surface, making it prone to agglomeration in the aqueous phase, with poor dispersibility, which reduced the hardness and scrub resistance of the paint film. In Example 11, the amount of silane coupling agent KH550 was too high, causing KH550 to self-polymerize and form oligomers, which were not firmly bonded to silica and were easy to fall off during wear, reducing the adhesion and scrub resistance of the paint film.

[0199] The test data from Examples 1, 12, and 13 show that the amount of compound emulsifier used in Example 12 was too low, resulting in insufficient emulsification of modified silica. The modified silica emulsion was unstable, and the particles were prone to agglomeration, which affected the uniform compounding with modified nanocellulose and reduced the scrub resistance and coating area of ​​the paint film. In Example 13, the amount of compound emulsifier used was too high. Excessive emulsifier caused double-layer adsorption on the surface of modified silica particles, weakening the interfacial stability and even causing flocculation, which affected the adhesion and scrub resistance of the paint film.

[0200] The test data from Examples 1, 14, and 15 show that in Example 14, the amount of modified silica powder was too low, resulting in insufficient rigidity reinforcement points in the paint film, a lack of support for the nanocellulose network, and limited improvement in the hardness and scrub resistance of the paint film. In Example 15, the amount of modified silica powder was too high, leading to the agglomeration of silica particles, which destroyed the three-dimensional network structure of the nanocellulose, thereby forming stress concentration points in the paint film and reducing the adhesion, hardness, and scrub resistance of the paint film.

[0201] As can be seen from the test data of Example 1 and the comparative example, the hardness, adhesion, scrub resistance and coating area of ​​the paint film are significantly improved after adding the reinforcing additive prepared in this invention. This is due to the synergistic reinforcing effect of modified nanocellulose and modified silica, as well as the post-addition method to avoid degradation and agglomeration during the production process, thus ensuring the full play of the reinforcing effect.

[0202] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a post-added nanocellulose reinforcing agent for latex paint coatings, characterized in that, The preparation method includes: (I) Butanetetracarboxylic acid, sodium hypophosphite, and nanocellulose solution are mixed, stirred, and heated to induce an esterification reaction. The nanocellulose solution has a mass fraction of 0.5-1.5 wt%, the mass ratio of the nanocellulose solution to the butanetetracarboxylic acid is 100:(10-15), and the mass of the sodium hypophosphite is 20-30 wt% of the mass of the butanetetracarboxylic acid. After the reaction is completed, the mixture is dialyzed to obtain an esterified nanocellulose solution. Under heating and stirring conditions, a silane coupling agent solution is added to the esterified nanocellulose solution to induce a reaction. The mass ratio of the silane coupling agent in the esterified nanocellulose solution to that in the silane coupling agent solution is 100:(3-5). After the reaction is completed, the mixture is dialyzed to obtain a modified nanocellulose solution. (II) Disperse nano-silica in anhydrous ethanol to obtain a silica dispersion; add silane coupling agent to an aqueous ethanol solution, mix and stir to hydrolyze, and obtain a silane coupling agent solution; add the silane coupling agent solution to the silica dispersion, wherein the mass ratio of nano-silica in the silica dispersion to silane coupling agent in the silane coupling agent solution is 1:(0.2~0.3), mix, stir and heat to react, and after the reaction is completed, obtain modified silica powder by centrifugation, washing and drying; (III) The modified silica powder is dispersed in anhydrous ethanol to obtain a modified silica dispersion; a compound emulsifier is mixed evenly with deionized water to obtain a compound emulsifier solution; under stirring conditions, the compound emulsifier solution is added to the modified silica dispersion, wherein the mass of the compound emulsifier in the compound emulsifier solution is 5-8 wt% of the mass of the modified silica powder in the modified silica dispersion; then shear emulsification is performed to obtain a modified silica emulsion; under heating and stirring conditions, a compatibilizer solution is added to the modified nanocellulose solution, followed by the addition of the modified silica emulsion, wherein the mass ratio of the modified silica powder to the modified nanocellulose solution is (10-15):100; finally, deionized water is added to adjust the viscosity to obtain the post-added nanocellulose reinforcing agent.

2. The preparation method according to claim 1, characterized in that, In step (I), the reaction temperature of the esterification reaction is 60~80℃; The esterification reaction takes 8-10 hours. The dialysis bag used in the dialysis has a molecular weight cutoff of 10,000 to 15,000 Da; The dialysis time is 24-48 hours.

3. The preparation method according to claim 1, characterized in that, In step (I), the silane coupling agent solution is added to the esterified nanocellulose solution at a heating temperature of 50~60℃ and a stirring speed of 300~500rpm. After all the solution is added, stirring and heating are continued for 2~3 hours. The silane coupling agent solution is composed of a silane coupling agent and an aqueous ethanol solution; The silane coupling agent is KH550; The mass fraction of the silane coupling agent in the silane coupling agent solution is 5-10 wt%. The dialysis bag used in the dialysis has a molecular weight cutoff of 10,000 to 15,000 Da; The dialysis time is 24-48 hours.

4. The preparation method according to claim 1, characterized in that, In step (II), the nano-silica is added to the anhydrous ethanol and ultrasonically dispersed to obtain the silica dispersion. The mass of the nano-silica is 5-10 wt% of the mass of the anhydrous ethanol. The ultrasonic power of the ultrasonic dispersion is 300~500W; The ultrasonic dispersion time is 30-40 minutes; The volume ratio of the silane coupling agent to the aqueous ethanol solution is 1:(30~40); The silane coupling agent is KH550; The mixing and hydrolysis time is 40-50 minutes.

5. The preparation method according to claim 1, characterized in that, In step (II), the temperature for mixing, stirring, and heating the silane coupling agent solution and the silica dispersion is 60~70℃; The mixing and heating speed of the silane coupling agent solution and the silica dispersion is 200~300 rpm; The mixing, stirring, and heating time for the silane coupling agent solution and the silica dispersion is 8-10 hours.

6. The preparation method according to claim 1, characterized in that, In step (III), the mass ratio of the modified silica powder to anhydrous ethanol is 1:(15~20); The mass ratio of the compound emulsifier to deionized water is 1:(5~10); The compound emulsifier is composed of Span 60 and Tween 60, with a mass ratio of Span 60 to Tween 60 of 3:

7. At a stirring speed of 600-800 rpm, the compound emulsifier solution is added dropwise to the modified silica dispersion. After all the solution is added, the stirring speed is increased to 1500-2000 rpm, and stirring is continued for 10-20 minutes to obtain a crude emulsion. Subsequently, the crude emulsion is sheared and emulsified to obtain the modified silica emulsion. The rotational speed for shear emulsification of the crude emulsion is 5000~10000 rpm; The shear emulsification time of the crude emulsion is 5-15 min.

7. The preparation method according to claim 1, characterized in that, In step (III), the compatibilizer solution is added to the modified nanocellulose solution at a stirring speed of 300-500 rpm and a heating temperature of 40-50°C. After the solution is completely added, stirring is continued for 10-15 minutes. Then, the stirring speed is adjusted to 600-800 rpm, and the modified silica emulsion is added dropwise. After all the solution is added, the stirring speed is increased to 1000-1500 rpm, and stirring is continued for 30-40 minutes. Finally, deionized water is added to adjust the viscosity. The compatibilizer solution is an aqueous solution of polyethylene glycol, and the mass fraction of polyethylene glycol in the compatibilizer solution is 30-40 wt%. The polyethylene glycol is polyethylene glycol 6000; The amount of polyethylene glycol added is 3-5 wt% of the mass of the modified nanocellulose solution; The dripping rate of the modified silica emulsion is 3~5 mL / min; The viscosity of the added nanocellulose reinforcing agent is 300~500 mPa·s.

8. A post-added nanocellulose reinforcing agent prepared by the preparation method according to any one of claims 1 to 7.

9. A method of using the post-added nanocellulose reinforcing agent as described in claim 8, characterized in that, The method of use includes: Add the nano-cellulose reinforcing agent to the finished latex paint and mix. The amount of the added nanocellulose reinforcing agent is 1-2 wt% of the mass of the finished latex paint.

10. The method of use according to claim 9, characterized in that, The mixing speed is 1000~1500 rpm; The mixing and stirring time is 10-20 minutes.

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