Process for preparing a high adhesion carboxylated styrene-butadiene latex for sealing

Abstract

This invention relates to the field of polymer materials technology and discloses a method for preparing a high-adhesion carboxylated styrene-butadiene latex for sealing. After pre-alkalization of the base latex, a citric acid-modified solution is pumped in at a constant rate while dynamically adjusting the pH value to construct a dynamic hydrogen bond network. After thermodynamic infiltration, a crosslinking aid is added to induce multi-level self-assembly, and the growth of citric acid crystals is controlled by gradient temperature-controlled drying. Through the above scheme, this invention achieves a synergistic improvement in material strength, self-healing properties, and shape memory function. It exhibits high peel strength and excellent high-temperature creep resistance, and can automatically repair microscopic damage and achieve spontaneous compensation of sealing morphology.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a method for preparing a high-adhesion carboxylated styrene-butadiene latex for sealing. Background Technology

[0002] Carboxylated styrene-butadiene latex possesses excellent film-forming properties, chemical stability, and high polar adhesive strength imparted by the carboxyl groups, making it widely used in building expansion joints, steel drum packaging, automotive component sealing, and bonding of various composite materials. To improve the mechanical properties and weather resistance of carboxylated styrene-butadiene latex, mainstream improvement methods often involve introducing inorganic fillers such as nano-silica, kaolin, or calcium carbonate, utilizing the physical filling effect to enhance the rigidity and deformation resistance of the film; or adding inert tackifying resins, emulsified oils, and other chemical additives to improve the wettability and initial bond strength of the latex during film formation.

[0003] To achieve extremely high adhesion and shear strength, this is often achieved by increasing the crosslinking density or the content of rigid fillers. This inevitably leads to excessive rigidity and a lack of flexibility in the polymer network structure. When the sealing area is subjected to high temperature or continuous cyclic mechanical stress for a long time, micro-stress easily accumulates inside the latex film, inducing microcracks. Because traditional crosslinking networks (especially covalent crosslinking or simple physical entanglement) are irreversible, once microcracks occur, the material lacks an effective energy dissipation mechanism and structural recombination ability, causing the microcracks to rapidly evolve into macroscopic fractures under stress, ultimately leading to seal failure.

[0004] In real-world applications, sealing materials often face drastic cycles of thermal expansion and contraction. For example, during the storage and transportation of building expansion joints or metal packaging containers, environmental temperature differences can cause significant dimensional changes in the substrate. Existing carboxylated styrene-butadiene latexes, lacking an effective shape recovery mechanism, often exhibit creep when subjected to such periodic deformation. This means that under long-term stress or periodic temperature changes, polymer chain segments undergo non-recoverable slippage, causing the sealant film to gradually lose its initial designed geometry, leading to detachment of the sealing interface or the formation of gaps. While existing techniques using inorganic fillers can alleviate creep, they simultaneously sacrifice the material's self-adaptive capabilities, preventing it from recovering to its initial sealing state through its own memory function when faced with irregular deformation. Summary of the Invention

[0005] This invention provides a method for preparing a high-adhesion carboxylated styrene-butadiene latex for sealing, aiming to solve the technical problems of ordinary carboxylated styrene-butadiene latex in the prior art, such as easy creep failure under high temperature or long-term stress environment, lack of self-healing ability of microcracks, and poor shape stability under complex deformation conditions. This invention introduces a high content of bio-based citric acid to construct a programmable dynamic hydrogen bond network in the polymer network of the carboxylated styrene-butadiene latex, and utilizes the multi-level self-assembly precipitation behavior of citric acid during film formation to achieve a synergistic improvement in the material's mechanical strength, self-healing properties, and shape memory function.

[0006] The present invention provides a method for preparing a high-adhesion carboxylated styrene-butadiene latex for sealing, the technical solution of which is achieved through the following steps: The first step is the pretreatment and parameter selection of the base latex. The raw material selected for this invention is a high-polarity carboxylated styrene-butadiene latex, with a solid content set at 48% to 52%, a styrene content set at 45% to 55%, and a carboxyl content controlled between 2.0% and 5.0% by the monomer feeding ratio. The Mooney viscosity (ML(1+4)) of this base latex at 100°C is controlled within the range of 80 to 120 to ensure sufficient molecular weight for constructing a physical cross-linking network. The carboxylated styrene-butadiene latex is added to a reactor equipped with a double-layer anchor stirrer, a reflux condenser, and a precise temperature control jacket. The stirring device is started, and the speed is set between 150 rpm and 200 rpm for continuous physical homogenization for more than 30 minutes. Simultaneously, the jacket circulating water is turned on to stabilize the system temperature at 25°C to 30°C.

[0007] The second step is the preparation of the bio-based modified solution. Bio-based citric acid granules are selected and slowly added to deionized water to prepare a citric acid aqueous solution with a mass percentage concentration of 40% to 60%. During the preparation process, a magnetic stirrer is used to stir at 400 rpm at room temperature until the solution becomes completely transparent and free of visible suspended matter. Subsequently, a nonionic surfactant, selected from fatty alcohol polyoxyethylene ether, is added to the solution at an amount of 0.5% to 1.2% of the citric acid mass. This surfactant is used to reduce the surface tension of citric acid molecules in the latex system and prevent demulsification caused by excessively high local concentrations.

[0008] The third step is pH balancing of the modified system. Since citric acid is a strong acid, to avoid gelation caused by a local pH drop below the isoelectric point due to direct addition to the latex, the base latex needs to be pre-alkalized. A 10% to 15% sodium hydroxide solution or ammonia solution is added dropwise to the reactor using a precision feed pump, with the system pH monitored in real time until it reaches 9.0 to 10.5. Under these conditions, the carboxyl groups on the surface of the carboxylated styrene-butadiene latex particles are completely deprotonated, forming a negatively charged electrostatically stable layer, providing a stable physicochemical environment for the subsequent introduction of acidic components.

[0009] The fourth step is the induced construction of a programmable hydrogen bond network. The precision metering system is activated, and the citric acid aqueous solution prepared in the second step is pumped into the reactor at a constant rate of 3 ml / min to 8 ml / min. The pumping point is set in the turbulent mixing zone generated by the stirrer to ensure that the citric acid molecules are diluted instantly upon contact with the latex particles. During the dropwise addition, a 5% (w / w) sodium hydroxide solution is automatically added to dynamically maintain the pH of the reaction system between 7.5 and 8.5. Within this pH range, the citric acid molecules retain some undissociated carboxyl groups, which lays the foundation for subsequent hydrogen bond interactions with the carboxyl groups on the styrene-butadiene latex segments.

[0010] The fifth step involves thermodynamically controlled infiltration and assembly. After the citric acid solution is added, the reflux condenser is shut off, and the temperature inside the reactor is increased to 50°C to 70°C at a rate of 1.5°C / min, and maintained at this temperature for 2 to 4 hours under isothermal shearing. The significance of this stage is to promote the penetration of small citric acid molecules into the swollen layer of carboxyl-based styrene-butadiene latex particles through thermal motion. Under heated conditions, the free volume of the styrene-butadiene latex chain segments increases, and citric acid molecules diffuse into the polymer chains, forming preliminary physical entanglement with the carboxyl groups on the latex chains.

[0011] The sixth step is the induction of multi-level structure self-assembly. The temperature of the reaction system is lowered to 40°C to 45°C, and then a crosslinking aid is added. The crosslinking aid is a multifunctional polyol or polyethylene glycol with a molecular weight distribution between 400 and 1000, and the amount added is 1% to 3% of the dry weight of the latex. The introduction of this component is to establish a molecular bridge between citric acid molecules and styrene-butadiene latex segments, forming a more complex hydrogen-bonded complex through the hydroxyl groups of the polyol and the carboxyl groups of both. A micro / nano-scale dispersing aid, such as modified sodium lignosulfonate, is added at an amount of 0.2% to 0.5% to control the growth rate and morphology of citric acid crystals during the subsequent film formation process.

[0012] The seventh step involves phase separation and crystal growth control during film formation. The latex obtained by the preparation method is coated onto the substrate surface during use, with the film thickness controlled between 0.5 mm and 2.0 mm. During water evaporation, as the solid content of the system increases, the solubility of citric acid in the styrene-butadiene rubber matrix reaches supersaturation. Due to the strong hydrogen bonding between citric acid and styrene-butadiene segments, citric acid molecules do not aggregate randomly but instead precipitate through self-assembly along the spatial orientation of the polymer chains. By controlling the ambient humidity at 50% to 60% and the ambient temperature at 25°C to 35°C, citric acid is induced to form a multi-level crystal structure ranging from nanoscale (20 nm to 100 nm) to microscale (1 m to 5 m). These crystal particles are uniformly embedded in the rubber matrix, constituting the hard segment support phase of this invention.

[0013] In the technical solution described in this invention, the amount of citric acid introduced is strictly limited. When the amount of citric acid added accounts for 10wt% to 25wt% of the dry weight of the carboxylated styrene-butadiene latex, a high-density dynamic hydrogen bond network is mainly formed inside the system. In this network structure, each citric acid molecule forms multiple hydrogen bond nodes with the adjacent styrene-butadiene polymer chain through its three carboxyl groups and one hydroxyl group. This hydrogen bond network is thermally reversible. When the material is subjected to external force and microcracks are generated, the stress at the crack tip first causes the lower-energy hydrogen bonds to break rather than the carbon-carbon backbone to break, and this process dissipates a large amount of mechanical energy. In the subsequent heating or resting process, the carboxyl groups and hydroxyl groups at the broken point approach each other again under the drive of thermal motion, and the crack interface is able to heal again based on the spontaneous recombination characteristics of hydrogen bonds.

[0014] In a preferred embodiment of the present invention, when the citric acid content is further increased to a threshold range of 30wt% to 45wt%, the internal physical structure of the system undergoes a fundamental transformation. Excess citric acid precipitates at the nanoscale and arranges itself into a regular crystalline lattice, which acts as highly functional physical cross-linking points. These crystalline lattices are tightly bonded to the surrounding styrene-butadiene rubber segments through a hydrogen-bonded interface layer, forming a micro-reinforced structure similar to reinforced concrete.

[0015] The composite network supported by nanocrystals constructed in this invention endows the material with unique shape memory capabilities. Under conditions above the material's glass transition temperature, the polymer segments exhibit high mobility. When an external force is applied to the material, it deforms, and is subsequently cooled to room temperature under load. Due to the extremely high rigidity of citric acid crystals at room temperature, they can lock the styrene-butadiene segments in their deformed state, thus fixing the shape. When the ambient temperature rises again to the set recovery temperature (typically 60°C to 80°C), the hydrogen bond network partially softens, releasing the entropic elastic stress stored in the polymer segments and driving the material to return to its initial sealed state. This characteristic allows the latex to spontaneously compensate for interfacial gaps in situations involving severe thermal expansion and contraction, such as steel drum packaging or building expansion joints, ensuring a durable sealing effect.

[0016] In the preparation method described in this invention, carboxyl styrene-butadiene latex provides the basic film-forming and elastic matrix, and the carboxyl groups on its chain segments are the anchoring points for constructing the hydrogen bond network; bio-based citric acid, as the core modifier, provides dynamic crosslinking through hydrogen bonds and provides rigid support and shape memory sites through the self-assembled crystal phase; pH adjusters and surfactants ensure the colloidal stability of the latex system throughout the preparation process and prevent acid-induced aggregation; crosslinking aids and dispersing aids finely control the density of the hydrogen bond network and the growth morphology of the crystals, ensuring the synergistic output of the multi-level structure in macroscopic performance.

[0017] As a crucial process detail of this invention, during the fifth step of the isothermal shearing process, the edge linear velocity of the stirring paddle must be strictly controlled between 1.5 m / s and 2.5 m / s. A lower linear velocity cannot provide sufficient shear stress for citric acid molecules to overcome the electric double-layer repulsion on the latex particle surface, while an excessively high linear velocity may cause mechanical demulsification of the latex in a high-temperature sensitive state. Through this precise flow field control, a deep and uniform distribution of modified molecules within the colloidal particles is achieved.

[0018] The self-healing efficiency of this invention was evaluated using the residual strength method. After the cured adhesive film was completely cut and pressed together at 65°C for 24 hours, its tensile strength recovery rate reached 70% to 90% of the original strength, fully demonstrating the high efficiency of the programmable hydrogen bond network in the interface reconstruction process. This self-healing capability has extremely high engineering value in sealing applications, automatically repairing microscopic physical damage caused by vibration, stress concentration, or environmental erosion, preventing leakage accidents.

[0019] Within the technical system of this invention, the tricarboxylic acid molecule's tricarboxylic acid structure is the core for achieving the aforementioned functions. Compared to dicarboxylic acids, the tricarboxylic acid structure of citric acid can form a more complex network crosslinking in space, rather than a simple linear chain extension. The establishment of this three-dimensional network is the structural basis for achieving high shape fixation and shape recovery rates. Simultaneously, intramolecular hydrogen bonds can form between the hydroxyl and carboxyl groups in the citric acid molecule. The competition and balance between these intramolecular and intermolecular hydrogen bonds, through precise adjustment of pH and temperature during the process, is transformed into a controllable program, i.e., the programmable characteristic described in this invention.

[0020] As a supplementary embodiment of the present invention, in order to further improve the performance of latex in extremely low temperature environments, a very small amount of antifreeze additive can be introduced during the preparation process. The antifreeze additive is selected from propylene glycol or glycerin, and the amount added is 0.5% to 1.0% of the total mass of the latex. Since these polyol components can also participate in the construction of hydrogen bond networks, they can act like internal plasticizers at low temperatures, preventing excessive embrittlement of the hydrogen bond network and ensuring that the sealing layer maintains good flexibility and adhesion even at extreme low temperatures of -40°C.

[0021] In the seventh step of film formation control, the control of the drying rate is crucial to the spatial distribution of citric acid crystals. This invention employs a gradient temperature-controlled drying process. In the initial stage, constant-rate drying is performed at 35°C to remove 70% of the free water in the system, at which point citric acid begins to accumulate in the gaps between latex particles. In the second stage, the temperature is raised to 55°C for decreasing-rate drying, during which citric acid undergoes molecular arrangement and crystal nucleation. Finally, a short-term post-heat treatment at 80°C induces crystal growth and maturation, forming stable hydrogen-bonded interfaces with the polymer chains. This segmented drying process ensures that no macroscopic pores are generated within the material, and that the crystalline phase is uniformly distributed, avoiding stress concentration points.

[0022] In specific industrial implementations, the reactor material is limited to 316L stainless steel to resist the weak acid corrosion of citric acid during the intermediate reaction process. The agitator blades are tilted at 45 degrees to generate a strong circulating flow field in the vertical direction, ensuring that citric acid molecules can quickly penetrate the electrostatic repulsion layer between latex particles. The feeding system is equipped with a high-precision mass flow meter with an error controlled within 0.01 kg / h, ensuring the uniformity of hydrogen bond network density in each batch of product, thereby guaranteeing consistent performance of self-healing and shape memory functions at the macroscopic level.

[0023] The method described in this invention constructs a smart polymer composite system with stress dissipation and shape memory functions through precise molecular-level modification of carboxylated styrene-butadiene latex. When unexcited, this system exhibits high modulus and high adhesion, providing a robust physical barrier for the sealing interface. Under conditions of damage or environmental temperature fluctuations, it achieves self-repair and structural recovery through dynamic hydrogen bond exchange and the morphological memory function of the crystalline phase. This perfect combination of dynamic and static properties essentially solves the reliability bottleneck of traditional sealing materials under complex operating conditions.

[0024] Furthermore, the preparation method described in this invention also includes a crucial defoaming step. Before heating in the fifth step, an organosilicon polyether defoamer is added to the reaction system at a concentration of 0.05% to 0.1% of the total mass. Because this system contains a high concentration of carboxyl groups and surfactants, it is highly susceptible to generating microbubbles under high-speed stirring. If these bubbles are embedded during film formation, they will become structural defects in the hydrogen bond network, severely reducing the material's creep resistance and self-healing efficiency. Using the specific type of defoamer described above effectively eliminates microbubbles, ensuring that the resulting film has extremely high density, thereby guaranteeing the continuity of the hydrogen bond network at the molecular level.

[0025] In the physical property testing after film formation, dynamic thermomechanical analysis revealed a significant modulus transition region in the latex film prepared by this invention within the temperature range of 50°C to 80°C. This corresponds to the dynamic dissociation and recombination of the hydrogen bond network. The span and depth of this region can be fine-tuned by adjusting the citric acid content and pH value. This programmability allows engineers to customize the self-healing trigger point of the material according to the specific sealing service temperature, ensuring that the material maintains sufficient rigidity at the service temperature while exhibiting dynamic repair properties when necessary.

[0026] The high adhesion described in this invention is not only reflected in the adhesion to common polar substrates, but also in the formation of a high-density hydrogen bond acceptor layer due to the migration and enrichment of citric acid molecules to the interface during film formation, which enhances the van der Waals forces and dipole interactions between the interfaces.

[0027] During use, the latex prepared by this invention can be mixed with appropriate amounts of inorganic pigments or functional fillers, such as carbon black, titanium dioxide, or conductive graphite, as needed. Because the hydrogen bond network constructed by this invention has extremely strong coating ability and affinity for the filler surface, the addition of these fillers will not damage the system's self-healing and shape memory functions; on the contrary, it can further improve the material's UV aging resistance and flame retardant properties through physical barrier effects.

[0028] As an important implementation detail of this invention, during the isothermal stage after the addition of citric acid, the pressure inside the reactor needs to be maintained at a slightly positive pressure of 0.05 MPa to 0.1 MPa. This pressure control helps to suppress the trace volatilization of low-boiling-point components, maintain the stability of the system's chemical potential, and thus ensure that the partition coefficient of citric acid molecules in the polymer matrix remains constant.

[0029] In applications requiring high-vacuum sealing, the latex film prepared according to this invention exhibits extremely low outgassing rates. This is attributed to the strict control of small molecule residues during the preparation process and the strong locking effect of the hydrogen bond network on free molecules. At 10 -5 At a vacuum level of Pa, its leakage rate per unit area is reduced by an order of magnitude compared to traditional sealing latex, which expands the application prospects of this invention in sealing aerospace and semiconductor manufacturing equipment.

[0030] Compared with the prior art, the beneficial effects of the present invention are: 1. By constructing a dynamic hydrogen bond network and a multi-level crystal reinforcement structure, the bonding strength of the latex is improved, and it has good compatibility with a variety of substrates. At the same time, the thermal stability is optimized, and it can maintain a stable bonding effect in high-temperature environments, without easy strength decay, thus meeting long-term sealing requirements. 2. The dynamic hydrogen bond network has thermally reversible properties, which can automatically repair micro-damage generated during use, avoid sealing failure caused by the expansion of micro-cracks, extend the service life of materials, and improve sealing reliability. 3. The multi-level crystal structure forms a stable composite system with the polymer matrix, which effectively suppresses creep deformation under high temperature or long-term stress; at the same time, it endows the material with shape memory function, which can spontaneously restore the initial sealing shape and compensate for the interface gap when the temperature changes cause the substrate to deform. 4. Utilizing bio-based citric acid as the core modifier, the entire reaction process is carried out in an aqueous phase, producing no volatile organic compounds, aligning with green development trends. The proportions of key components can be adjusted to suit different sealing scenarios, and it exhibits excellent film-forming properties, maintaining stable performance under various operating conditions. 5. The system has strong colloidal stability and is not prone to delamination or clumping when stored at room temperature; after film formation, the film has high density and is resistant to high and low temperature, humid heat and other environmental tests, and is not prone to abnormal volume changes, making it suitable for diverse high-end sealing scenarios. Detailed Implementation

[0031] This invention provides a method for preparing a high-adhesion carboxylated styrene-butadiene latex for sealing. By precisely controlling the interaction between macromolecular chain segments and small-molecule functional modifiers, a composite network with dynamic response characteristics is constructed. The technical solution of this invention first focuses on the screening and pretreatment of the base latex. A highly polar carboxylated styrene-butadiene latex is selected as the film-forming matrix, and a specific proportion of carboxyl monomers are introduced into its molecular chain, giving the latex a good polar adhesive foundation after film formation.

[0032] The technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples, so as to ensure that those skilled in the art can fully understand and implement the present invention.

[0033] Example 1: Basic carboxylated styrene-butadiene latex (solid content 50%, bound styrene content 50%, carboxyl content 3.5%, Mooney viscosity ML(1+4) 100°C is 100); Bio-based citric acid (added at 25% of the dry weight of the latex); Nonionic surfactant (fatty alcohol polyoxyethylene ether, 0.8% of citric acid by mass); Alkaline adjustment solution (12% sodium hydroxide solution); Crosslinking aid (polyethylene glycol, number average molecular weight 600, 2% dry weight of latex); Dispersing agent (modified sodium lignosulfonate, 0.3%); Defoamer (organosilicone polyether, 0.08%) Antifreeze agent (propylene glycol, 0.8%); Preparation steps: S1: Basic latex pretreatment, put the basic latex into a 316L stainless steel reactor and physically homogenize it at 180rpm for 35 minutes at 28℃; S2: Preparation of modified solution: Citric acid is dissolved in deionized water to prepare a 50% aqueous solution, stirred at 400 rpm at room temperature until transparent, and fatty alcohol polyoxyethylene ether is added. S3: pH balance adjustment, add 12% sodium hydroxide solution to adjust the pH of the system to 9.8; S4: Hydrogen bond network construction, a precision metering system pumps citric acid aqueous solution into the turbulent mixing zone at a rate of 5 ml / min, dynamically replenishes 5% sodium hydroxide solution, and maintains pH 8.0; S5: Thermodynamic infiltration assembly, adding defoamer, heating to 60℃ at 1.5℃ / min, isothermal shearing for 3 hours, stirring edge linear velocity 2.0m / s, pressure inside the vessel 0.08MPa; S6: Multi-level self-assembly induction, cooling to 42℃, adding crosslinking aid, dispersing aid and antifreeze aid, stirring for 60 minutes; S7: Film structure control, latex coating substrate film thickness 1.2mm, gradient temperature controlled drying (35℃ constant rate drying, 55℃ rate drying, 80℃ post-heat treatment).

[0034] Example 2: Citric acid was added at 10% of the dry weight of the latex, and the remaining components and proportions were the same as in Example 1; Preparation steps: Same as in Example 1.

[0035] Example 3: Citric acid was added at 45% of the dry weight of the latex, and the remaining components and proportions were the same as in Example 1; Preparation steps: Same as in Example 1.

[0036] Example 4: Citric acid aqueous solution concentration 40%, other components and proportions are the same as in Example 1; Preparation steps: Same as in Example 1.

[0037] Example 5: Citric acid aqueous solution concentration 60%, other components and proportions are the same as in Example 1; Preparation steps: Same as in Example 1.

[0038] Example 6: Same as Example 1; Preparation steps: The isothermal shearing stage temperature is 50℃, and the temperature is maintained for 4 hours. The remaining steps are the same as in Example 1.

[0039] Example 7: Same as Example 1; Preparation steps: The isothermal shearing stage temperature is 70℃, and the temperature is maintained for 2 hours. The remaining steps are the same as in Example 1.

[0040] Example 8: The crosslinking aid was replaced with a multifunctional polyol (number average molecular weight 800), and the other components and proportions were the same as in Example 1; Preparation steps: Same as in Example 1.

[0041] Comparative Example 1: Citric acid was omitted, and the remaining ingredients were the same as in Example 1; Preparation steps: The steps related to the preparation of modified solution and construction of hydrogen bond network are omitted, and the remaining process parameters and steps are the same as in Example 1.

[0042] Comparative Example 2: Same as Example 1; Preparation steps: Without dynamically adjusting the pH value, the citric acid aqueous solution is directly added to the pre-alkalized latex, and the remaining process parameters and steps are the same as in Example 1.

[0043] Test method: Adhesion test: Determine the 180 peel strength of stainless steel substrate and evaluate the strength retention rate after aging at 100°C for 72 hours; Self-healing performance test: After the adhesive film is completely cut, it is pressed at 65°C for 24 hours, and the tensile strength recovery rate is measured. Creep resistance test: The creep deformation was measured at 100℃ and under constant load for 72 hours; Physicochemical property testing: latex solid content, pH value, and Brookfield viscosity at 25°C were determined; Film-forming performance testing: Determine the tensile strength and elongation at break of the film; Environmental adaptability test: The volume expansion rate was measured after 168 hours of high temperature and high humidity treatment (60℃, 90% relative humidity).

[0044] The test data comparisons are shown in Table 1 and Table 2.

[0045] Table 1. Comparison of 180° peel strength, 100°C aging strength retention rate, and self-healing tensile strength recovery rate. Table 2 Comparison of creep deformation at 100℃ for 72 hours, Brinell viscosity at 25℃, tensile strength, and volumetric expansion rate under high temperature and high humidity Examples 1 to 8 utilize the thermally reversible hydrogen bond network formed by citric acid and latex carboxyl groups. During film formation, this network self-assembles into a multi-level crystalline structure, providing both high adhesion and self-healing and creep-resistant properties. Comparative Example 1, lacking citric acid, could not construct a hydrogen bond network and crystalline reinforcing phase, resulting in a significant decrease in adhesion and self-healing properties. Comparative Example 2, lacking dynamic pH adjustment, suffered from insufficient hydrogen bond formation, leading to performance degradation.

[0046] When the amount of citric acid added is 25% to 45%, the concentration is 50% to 60%, and the temperature is 60℃ to 70℃, the adhesion and creep resistance are better. Among them, the amount of citric acid added directly affects the hydrogen bond density and crystal content, the concentration determines the penetration efficiency, and the temperature controls the chain segment movement and crystal growth. The three factors work together to ensure the overall performance of the latex.

[0047] Compared to Comparative Example 1 without citric acid, the peel strength of the example is increased by more than 118%, the aging strength retention rate is increased by more than 42%, and the self-repair recovery rate is increased by more than 240%. Compared to Comparative Example 2 without dynamic pH adjustment, the peel strength is increased by more than 76%, the creep deformation is reduced by more than 80%, and the high temperature and high humidity volume expansion rate is reduced by more than 45%, meeting the long-term stability requirements of high-end sealing scenarios.

[0048] In summary, this invention achieves simultaneous improvement in adhesion, self-healing, and creep resistance through citric acid-induced dynamic hydrogen bond network and multi-level self-assembly coupling, solving the core pain points of traditional carboxylated styrene-butadiene latex. It is suitable for high-end sealing applications and has good potential for industrialization.

[0049] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-adhesion carboxylated styrene-butadiene latex for sealing, characterized in that, Includes the following steps: (1) Basic latex pretreatment: Using high polarity carboxylated styrene-butadiene latex as a matrix, the carboxylated styrene-butadiene latex is put into a reaction vessel equipped with a double-layer anchor stirrer, a condenser reflux pipe and a temperature control jacket for physical homogenization; (2) Preparation of bio-based modified solution: Dissolve bio-based citric acid particles in deionized water to prepare citric acid aqueous solution, and add nonionic surfactant during the preparation process; (3) pH balance adjustment: Add an alkaline adjustment solution to the base latex in the reaction vessel to adjust the pH; (4) Induced construction of programmable hydrogen bond network: Start the precision metering feeding system and pump the citric acid aqueous solution prepared in step (2) into the stirring turbulent mixing zone of the reactor; During the dripping process, the pH is maintained by automatically replenishing sodium hydroxide solution; (5) Thermodynamically controlled permeation and assembly: After the feeding is completed, the condensation reflux device is turned off, and the temperature inside the reactor is raised and then sheared at a constant temperature; (6) Multilevel structure self-assembly induction: After cooling the reaction system, crosslinking aids and micro-nano-scale dispersing aids are added in sequence to form a multi-hydrogen bonded complex.

2. The method for preparing a high-adhesion carboxylated styrene-butadiene latex for sealing according to claim 1, characterized in that, The amount of the nonionic surfactant added is 0.5% to 1.2% of the mass of citric acid.

3. The method for preparing a high-adhesion carboxylated styrene-butadiene latex for sealing according to claim 1, characterized in that, The amount of the crosslinking aid added is 1% to 3% of the dry weight of the latex; the amount of the micro-nano-scale dispersing aid added is 0.2% to 0.5% of the dry weight of the latex.

4. The method for preparing a high-adhesion carboxylated styrene-butadiene latex for sealing according to claim 1, characterized in that, The reactor in step (1) is made of 316L stainless steel; the blade angle of the double-layer anchor stirrer is set to 45 degrees.

5. The method for preparing a high-adhesion carboxylated styrene-butadiene latex for sealing according to claim 1, characterized in that, The nonionic surfactant in step (2) is selected from fatty alcohol polyoxyethylene ether; when preparing the citric acid aqueous solution, a magnetic stirrer is used to stir at room temperature at a speed of 400 rpm until the solution is completely transparent and free of suspended matter.

6. The method for preparing a high-adhesion carboxylated styrene-butadiene latex for sealing according to claim 1, characterized in that, The alkaline adjustment solution in step (3) is selected from a sodium hydroxide solution or an ammonia solution with a mass fraction of 10% to 15%.

7. The method for preparing a high-adhesion carboxylated styrene-butadiene latex for sealing according to claim 1, characterized in that, In step (4), the precision metering feeding system is equipped with a mass flow meter; the pH is dynamically maintained between 7.5 and 8.

5.

8. The method for preparing a high-adhesion carboxylated styrene-butadiene latex for sealing according to claim 1, characterized in that, In step (5), during the isothermal shearing process, the edge linear velocity of the stirrer is strictly controlled between 1.5 m / s and 2.5 m / s; and the pressure inside the vessel is maintained at a slightly positive pressure state of 0.05 MPa to 0.1 MPa.

9. The method for preparing a high-adhesion carboxylated styrene-butadiene latex for sealing according to claim 1, characterized in that, The crosslinking aid mentioned in step (6) is selected from polyfunctional polyols or polyethylene glycol; the micro-nano-scale dispersing aid is selected from modified sodium lignosulfonate.

10. The method for preparing a high-adhesion carboxylated styrene-butadiene latex for sealing according to claim 1, characterized in that, Before heating in step (5), the process also includes adding an organosilicon polyether defoamer into the reactor, wherein the amount of defoamer added is 0.05% to 0.1% of the total mass of the system.

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