An environmentally friendly water-reducing agent based on natural materials and its preparation method

Abstract

This invention discloses an environmentally friendly water-reducing agent based on natural materials and its preparation method, belonging to the field of building materials. The invention utilizes lignin laccase to activate the phenolic hydroxyl groups of lignin under mild conditions, and then grafts PEG molecular chains with PEG-acrylate. Subsequently, sulfonic acid groups are introduced under weakly alkaline conditions, followed by mild acylation to introduce phosphate ester groups, forming metal-phosphate coordination bonds with metal ions. The metal-coordinated lignin is encapsulated using polylactic acid microencapsulation technology. After pH adjustment, purification, and drying, the environmentally friendly water-reducing agent based on natural materials is obtained. This water-reducing agent maintains stable high dispersibility and low corrosivity at room temperature. During the high-temperature and high-alkali stage of concrete hydration, the microcapsules rupture, releasing metal ions and breaking coordination bonds, actively exposing a large number of negative charges and hydrophilic sites, thus improving the water reduction and water retention rates during the high-temperature and high-alkali stage. This solves the technical problems of traditional water-reducing agents, such as single function, temperature sensitivity, and heavy metal corrosion.

Description

Technical Field

[0001] This invention relates to the field of building materials, specifically to an environmentally friendly water-reducing agent based on natural materials and its preparation method. Background Technology

[0002] Concrete, as the world's most consumed building material, directly determines the quality and lifespan of a project through its workability, mechanical strength, and durability. High-efficiency water-reducing agents are one of the core technologies for achieving high-performance concrete. With the increasing number of mega-projects such as super high-rise buildings, cross-sea bridges, and deep-water dams, and the increasing frequency of construction under extreme weather conditions, commonly used traditional polycarboxylate superplasticizers have gradually revealed a series of problems. For example, single-function water-reducing agents exhibit severe temperature sensitivity and high-temperature failure. Furthermore, the added polyvalent metal ions can irreversibly and rigidly complex with the carboxyl active sites on the polycarboxylate superplasticizer backbone, forming large and insoluble polymer-metal network flocs, which are detrimental to cement dispersion.

[0003] To address the above issues, some researchers have begun to focus on the modification of lignin and its use as a water-reducing agent. CN120943557A discloses an environmentally friendly concrete water-reducing agent and its preparation method. The method involves compounding modified lignin sulfonate and polycarboxylate mother liquor with other additives and reacting them in a one-pot process. Microwave assistance is also used in the preparation process to calcine and activate industrial waste residue at high temperature and by acid leaching. However, this method of mixing multiple raw materials with different properties lacks focus on the core functional components and does not take into account the interaction mechanism between the components. Different raw materials may undergo chemical reactions that interfere with each other. CN121107741A also discloses an environmentally friendly concrete water-reducing agent and its preparation method. It uses lignin sulfonate after oxidation by peroxide as a retarder and combines it with other additives and polycarboxylate water-reducing agent mother liquor. However, the whole is still a separate preparation of each functional component and then physical mixing. This piecemeal design with functional segmentation ignores the interaction between the components in the cement system and lacks a systematic design of the water-reducing agent molecule itself. Moreover, the modification of lignin is only carried out by oxidation by peroxide, which is just a simple adjustment of the surface groups of the existing lignin sulfonate and fails to redesign the structure of lignin at the molecular skeleton level.

[0004] In summary, there is an urgent need to develop a new type of environmentally friendly water-reducing agent that can not only achieve green and non-destructive activation of biomass lignin, but also utilize the internal heat of hydration of concrete as a trigger signal to realize intelligent thermal response of the water-reducing agent molecular structure, so as to meet the needs of concrete construction under modern extreme working conditions. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes an environmentally friendly water-reducing agent based on natural materials and its preparation method. This invention utilizes lignin laccase to activate the phenolic hydroxyl groups of lignin under mild conditions, and then grafts PEG molecular chains onto PEG-acrylate. Subsequently, sulfonic acid groups are introduced under weakly alkaline conditions, followed by mild acylation to introduce phosphate groups, forming metal-phosphate coordination bonds with metal ions. The metal-coordinated lignin is encapsulated using polylactic acid microencapsulation technology. After pH adjustment, purification, and drying, the environmentally friendly water-reducing agent based on natural materials is obtained. This water-reducing agent maintains stable high dispersibility and low corrosivity at room temperature. During the high-temperature and high-alkali stage of concrete hydration, the microcapsules rupture, releasing metal ions and breaking coordination bonds, actively exposing a large number of negative charges and hydrophilic sites. This improves the water reduction and water retention rates during the high-temperature and high-alkali stage, solving the technical problems of traditional water-reducing agents such as single function, temperature sensitivity, and heavy metal corrosion.

[0006] This invention proposes a method for preparing an environmentally friendly water-reducing agent based on natural materials, the specific technical solution of which is as follows: Step 1: After pre-wetting lignin in a reaction vessel, add lignin laccase for constant temperature reaction, then add chelating agent and stir. Add PEG-acrylate dropwise to the system and adjust the pH value. After continuous stirring, remove unreacted PEG-acrylate by nanofiltration to obtain PEG-grafted lignin reaction solution.

[0007] Step 2: Transfer the reaction solution to a new reactor and adjust the pH with NaOH. Then, under continuous stirring, add hydrogen peroxide dropwise for oxidation and activation. Next, quench the hydrogen peroxide and add sodium sulfite dropwise in batches for sulfonation. After the reaction is complete, let it stand. Then, heat the system and add a phosphorylation reagent for phosphorylation modification. Finally, add a metal ion solution dropwise to obtain a metal ion-phosphorylated lignin system.

[0008] Step 3: Polylactic acid is added to ethyl acetate and stirred until homogeneous. Then, the metal ion-phosphorylated lignin system is added to the polylactic acid / ethyl acetate system under high-speed stirring to emulsify it into a primary emulsion. The primary emulsion is then dropped into a PVA aqueous solution and stirred to form a water / oil / water double emulsion. After purification, centrifugation, and redispersing in deionized water, a metal ion-phosphorylated lignin suspension encapsulated in microcapsules is obtained.

[0009] Step 4: Add sodium bicarbonate to the system to adjust the pH, then pass the treatment liquid through a spray drying tower to obtain a dried powder. After sieving, mix it with an anti-caking agent to obtain a lignin-based environmentally friendly water-reducing agent.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. By designing thermally activated metal-phosphate coordination bonds and utilizing the bond breaking characteristics under alkaline conditions, more negatively charged sites and hydrophilic sites are actively released when the internal temperature and pH of concrete increase. This can greatly enhance the dispersion ability of cement particles, improve the water reduction and water retention rate during the hydration stage, and reduce the risk of cracking in large-volume concrete.

[0011] 2. Using non-heavy metal ions to replace heavy metal ions such as zinc in traditional coordination water-reducing agents, it is completely compatible with the main components of cement, will not react with cement to form harmful compounds, and will not corrode the steel bars inside the concrete, while maintaining the function of metal ions participating in the formation of coordination bonds.

[0012] 3. Through enzymatic PEG grafting and multi-stage sulfonation modification, the hydrophilicity and negative charge density of lignin are greatly increased. This dual effect of high hydrophilicity and high charge density enables the water-reducing agent to maintain excellent dispersion performance in low-temperature environments, rapidly adsorb cement particles and attract water molecules, greatly accelerating the hydration rate of cement. This allows the product to significantly improve the early strength of concrete in low-temperature curing environments and avoid the problem of strength lag caused by low temperatures. Attached Figure Description

[0013] Figure 1 The infrared spectrum of the sample prepared in Example 1 of this invention; Figure 2 This is a scanning electron microscope image of the water-reducing agent powder prepared in Example 1 of the present invention. Detailed Implementation

[0014] This invention proposes a method for preparing an environmentally friendly water-reducing agent based on natural materials, the specific technical solution of which is as follows: 1. Enzyme activation and grafting Pre-wetted lignin was activated with laccase and grafted with PEG-acrylate in the presence of a chelating agent to obtain a PEG-grafted lignin reaction solution. Because the molecular chains of lignin are intertwined in the dry state, active groups such as phenolic and alcoholic hydroxyl groups are embedded within the three-dimensional network structure, making them difficult to contact with reagents. By slowly adding lignin powder to deionized water and continuously stirring for pre-wetting, water molecules gradually penetrate into the lignin particles, breaking intermolecular hydrogen bonds, causing the structure to loosen and expand, and exposing the previously hidden active sites, which helps to improve the efficiency of subsequent enzyme catalysis and chemical grafting.

[0015] Since lignin raw materials or water may contain trace amounts of metal ions, such as Fe, 3+ Mn 2+These ions can inhibit laccase activity or catalyze undesirable side reactions. Therefore, the addition of chelating agents can shield these metal ions through complexation, ensuring that laccase performs its catalytic function in optimal condition, while avoiding the disordered destruction of lignin structure caused by free radical chain reactions initiated by metal ions. Laccase is a copper-containing redox enzyme that can selectively oxidize the phenolic hydroxyl groups of lignin under mild conditions, generating active intermediates such as quinones and phenoxy radicals. Because its catalytic action can act highly selectively on phenolic structural units, it causes less damage to the β-O-4 ether bonds and other linkages of the lignin backbone, thus maintaining the integrity of the lignin macromolecular skeleton. Furthermore, the generated active sites can serve as anchors for subsequent grafting reactions.

[0016] After laccase oxidizes the phenolic structure in lignin molecules to phenoxy radicals, PEG-acrylate can be used for free radical copolymerization grafting with phenoxy radicals under alkaline conditions. This grafts hydrophilic polyethylene glycol long chains onto the lignin backbone, introducing a large number of hydrophilic segments onto the hydrophobic lignin molecules. This significantly improves the product's water solubility and steric hindrance. Simultaneously, the presence of PEG chains can shield the π-π stacking interactions between lignin molecules, preventing product aggregation and providing a good dispersion for subsequent phosphorylation reactions. After the reaction is complete, nanofiltration is used to retain the larger molecular weight PEG-grafted lignin, allowing smaller unreacted PEG molecules, salts, and byproducts to pass through, resulting in a pure and concentrated reaction solution.

[0017] 2. Phosphorylation and metal coordination Under alkaline conditions, the reaction solution was subjected to sequential sulfonation, phosphorylation, and metal ion coordination to obtain a metal ion-phosphorylated lignin system. Adjusting the system pH to alkaline provided a suitable reaction environment for sulfite activation and also kept the phenolic hydroxyl groups on the lignin in a deprotonated state, facilitating subsequent reactions. The purpose of subsequent sulfonation was to introduce strongly hydrophilic sulfonic acid groups, which are the core functional groups for the dispersing effect of water-reducing agents. However, due to the limited reaction sites in lignin, simple sulfonation with sulfite is inefficient. Therefore, a synergistic oxidation-sulfonation system composed of sulfite and hydrogen peroxide is needed to improve reaction efficiency. Since hydrogen peroxide can partially oxidize lignin side chains or aromatic rings to generate active intermediates such as carbonyl or quinone groups, these intermediates are more readily reacted with sulfite. Therefore, the synergistic effect of both systems more easily increases the degree of sulfonation. The introduction of sulfonic acid groups gives the lignin molecules a large number of negative charges, allowing them to adsorb onto the surface of positively charged cement particles in cement paste, achieving dispersion through electrostatic repulsion.

[0018] Phosphorylation involves using sodium trimetaphosphate as the phosphate donor. Under alkaline conditions, the lignin hydroxyl groups are first activated, forming a strongly nucleophilic oxonium. This oxonium acts as a nucleophile, attacking the phosphorus atom in the sodium trimetaphosphate ring structure, initiating a nucleophilic substitution reaction. This causes the sodium trimetaphosphate ring structure to open and covalently attach to the lignin molecular chain, thereby generating a phosphate ester group. Although sodium trimetaphosphate undergoes stepwise hydrolysis under these conditions, generating intermediates such as tripolyphosphate and pyrophosphate, these intermediates also possess phosphorylation capabilities and can react with the lignin hydroxyl groups, rather than being simply consumed by hydrolysis. Therefore, the phosphorylation reaction can still proceed smoothly. Since the phosphate ester group is a multifunctional group with a negative charge, it enhances the anionic nature of lignin and has a strong affinity for calcium ions, enabling it to react with Ca in cement paste. 2+ They form complexes, and the phosphate ester bonds can also be hydrolyzed under specific conditions, providing a chemical basis for the sustained-release properties of the product.

[0019] Adding metal ions to the system under heating conditions induces a coordination reaction between the metal ions and the phosphate groups on the lignin, forming a Metal-OP coordination bond. This is an unstable coordination structure under alkaline conditions. While the coordination bond is stable under normal storage conditions, the phosphate groups are blocked. However, in the highly alkaline environment of cement hydration, the OH groups... - It competitively substitutes for coordination sites, breaks Metal-OP bonds, and releases free phosphate groups. The high temperature generated during hydration further promotes this competition, increasing the negative charge density of lignin molecules and more effectively dispersing cement particles through electrostatic repulsion. At the same time, phosphate groups can also react with Ca produced during cement hydration. 2+ It forms a complex, regulates the crystallization process of hydration products, and delays the peak of hydration exothermic reaction, thereby synergistically improving the dispersion and slump retention properties of the water-reducing agent.

[0020] 3. Microcapsule encapsulation A metal ion-phosphorylated lignin system was added to a PLA / ethyl acetate system and stirred at high speed to obtain an active lignin coordination structure encapsulated in PLA microcapsules. The metal ion-phosphorylated lignin coordination solution containing the complete Metal-OP coordination structure was used as the inner aqueous phase. A small amount of PVA was added as an emulsifier to enhance the stability of the inner aqueous phase during subsequent emulsification and prevent droplet coalescence. The coordination structure maintained dynamic equilibrium in the liquid phase, and its direct use in emulsification effectively encapsulated this equilibrium within the subsequently formed capsules. Polylactic acid (PLA) is a biodegradable polyester that hydrolyzes under alkaline conditions, making it particularly suitable as a slow-release carrier in cement environments. Ethyl acetate, as a good solvent for PLA, has advantages such as low boiling point, high volatility, and relatively low toxicity, making it a commonly used solvent for preparing PLA microcapsules.

[0021] Under high-speed shearing, a metal ion-phosphorylated lignin coordination solution, serving as the inner aqueous phase, is slowly dripped into the PLA / ethyl acetate oil phase. The inner aqueous phase is dispersed into micron-sized droplets, uniformly suspended in the oil phase. At this point, each droplet contains an active lignin coordination structure and is encapsulated by the oil phase, forming a water-in-oil primary emulsion. After the primary emulsion is dripped into the PVA-containing outer aqueous phase, with further high-speed shearing, the primary emulsion is further dispersed into even smaller droplets. Each droplet contains numerous small droplets containing active lignin, surrounded by the PLA / ethyl acetate oil phase, and the outermost layer is a continuous aqueous phase containing PVA, thus forming a water / oil / water complex emulsion.

[0022] At this stage, the complex emulsion still contains ethyl acetate from the oil phase, making its structure unstable. Therefore, it needs to be placed in a vacuum evaporator to slowly evaporate the ethyl acetate. As the ethyl acetate gradually escapes from the oil phase, the concentration of PLA in the oil phase continuously increases, eventually leading to supersaturation and precipitation. This precipitation forms a solid shell on the surface of the water droplets in the inner aqueous phase, resulting in microcapsules. Further processing involves centrifugation to collect the microcapsules, followed by washing with deionized water to remove residual PVA and unencapsulated free substances. The microcapsules are then redispersed in deionized water to create conditions for the subsequent preparation of clean water-reducing agent powder.

[0023] 4. Drying and molding After the suspension is pH-adjusted, it is spray-dried to form a dry water-reducing agent powder. This powder is then sieved and mixed with an anti-caking agent to obtain the finished water-reducing agent. The pH of the microcapsule suspension deviates from the neutral range after a series of chemical reactions and washing. Therefore, the system pH needs to be readjusted back to around 7.0 before spray drying. This ensures that the final product will not impact the alkaline environment of the concrete during use, and also avoids potential corrosion of the spray drying equipment by acidic or alkaline conditions.

[0024] Because microcapsule suspensions contain a large amount of water, direct packaging and storage would not only result in bulky materials and high transportation costs, but the moisture could also lead to hydrolysis of the microcapsule shell or premature release of internal active substances. Spray drying, on the other hand, can remove moisture instantly while preserving the original core-shell structure of the microcapsules. During the rapid dehydration process, the evaporation of water absorbs heat, ensuring that the actual temperature the microcapsules withstand is far lower than the temperature of the drying medium. This prevents the shell from melting or deforming, and the resulting powder form facilitates precise measurement and uniform dispersion, conforming to the usage habits of concrete admixtures, and significantly reducing storage and transportation costs.

[0025] However, during the spray drying process, due to fluctuations in atomization conditions or electrostatic agglomeration of tiny particles, a small number of particles or agglomerates with excessively large sizes may be generated. These large particles cannot dissolve or disperse quickly when the concrete is mixed, which may lead to uneven concentration of water-reducing agent in some areas, affecting the homogeneity of the concrete. In severe cases, they may even leave visible defects in the hardened concrete. Therefore, after spray drying, these abnormal particles need to be removed by sieving to ensure that the particle size distribution of the product is within a controllable range.

[0026] Even after drying, microcapsule powder may still absorb trace amounts of moisture from the environment if exposed to air. Furthermore, particles may stick together during long-term storage or transportation under pressure. Therefore, a small amount of anti-caking agent is added to the microcapsule powder to prevent this adhesion. Because anti-caking agents (such as nano-silica) have a large specific surface area and strong adsorption capacity, they preferentially adsorb moisture and form a physical isolation layer between particles, preventing direct contact and adhesion. However, since the amount of anti-caking agent added is generally very low, thorough mixing is necessary to ensure its uniform distribution on the surface of each powder particle, thereby guaranteeing consistent anti-caking performance across the entire product.

[0027] The following are some specific embodiments of the present invention, and Table 1 shows the raw material information used in the embodiments.

[0028] Table 1 Raw Material Information Table

[0029] Example 1 S1: Slowly add 30g of lignin powder to a reactor containing 1500mL of deionized water, and mechanically stir at 500rpm for 10min to fully pre-wet and swell the lignin. Then add 30mL of lignin laccase, adjust the pH to 7.0 with 0.1mol / L NaOH solution, set the reactor temperature to 30℃, and react at a constant temperature for 12h. During this period, check the pH every 2h to keep the solution pH constant at 7.0. After the reaction is complete, add 2.5g of EDTA-2Na, and continue stirring for 30min. Then add 10g of PEG-acrylate dropwise to the system, and adjust the pH to 8.5 with 0.5mol / L NaOH. Raise the reactor temperature to 40℃ and stir continuously for 6h. Pass the reaction solution through a nanofiltration system with a molecular weight cutoff of 1000Da, and circulate and filter for 2h at a transmembrane pressure of 1.5MPa. Collect the retentate to obtain the PEG-grafted lignin reaction solution.

[0030] S2: Transfer the PEG-grafted lignin reaction solution obtained in S1 to a new reactor, add deionized water to a total volume of 2500 mL, start stirring at 300 rpm, adjust the pH to 9.0 with 0.5 mol / L NaOH, add 100 mL of 30% hydrogen peroxide dropwise, stir at 25℃ for 30 min for oxidation activation, then add 2.5 g of sodium thiosulfate, stir for 10 min to quench residual hydrogen peroxide, then raise the system temperature to 35℃, and add 6.0 g of sodium sulfite dropwise in three portions. After each addition, the mixture was stirred for 10 minutes, with a 15-minute interval between each addition. The sulfonation reaction was carried out at 25°C for 45 minutes. The system temperature was then raised to 30°C and allowed to stand for 30 minutes. The system temperature was then raised to 60°C, and 30 g of sodium trimetaphosphate was added. The reaction was carried out at a constant temperature for 3 hours. Subsequently, 500 mL of an aqueous solution containing 15 g of calcium nitrate tetrahydrate was added dropwise at a rate of 1 mL / min, while stirring at 300 rpm. After the addition was completed, stirring was continued for 40 minutes to obtain a metal particle-phosphorylated lignin liquid phase system.

[0031] S3: Add 1% by volume of PVA to the metal particle-phosphorylated lignin liquid phase system obtained in S2, stir for 15 min until completely dissolved, and use this solution as the inner aqueous phase; take 30 g of polylactic acid and add it to 500 mL of ethyl acetate, heat to 40 °C and stir for 15 min until completely dissolved, use this solution as the oil phase; add the inner aqueous phase dropwise to the oil phase at a rate of 0.5 mL / s in a high-speed disperser, maintaining a speed of 8000 rpm, and continue emulsifying for 5 min after the addition is complete to obtain a water-in-oil primary emulsion; take 200 mL of an aqueous solution containing 1% PVA as the outer aqueous phase, slowly pour the primary emulsion into the outer aqueous phase while stirring, and then stir again at 800 rpm. Shear emulsification was performed at 0 rpm for 5 min to obtain a water / oil / water double emulsion. The double emulsion was then transferred to a vacuum evaporator with a water bath temperature of 40℃ and a vacuum degree of 0.08 MPa. The mixture was stirred at 200 rpm for 2 h to allow ethyl acetate to evaporate, resulting in a solidified microcapsule suspension. The suspension was centrifuged at 3000 rpm for 10 min, and the supernatant was discarded. 500 mL of 4℃ deionized water was added to the precipitate, and the mixture was stirred for 2 min and then centrifuged again for 10 min. This process was repeated 3 times, and the centrifuged precipitate was collected. 2000 mL of deionized water was added to the precipitate, and the mixture was stirred until it was evenly dispersed to obtain a phosphorylated lignin suspension encapsulated in microcapsules.

[0032] S4: Adjust the pH of the suspension obtained in S3 to 7.0 with 1 mol / L sodium bicarbonate, then add 1% (by volume) of maltodextrin and continue stirring for 10 min. The suspension is then passed through a spray drying tower with an inlet temperature of 110℃, an outlet temperature of 40℃, and an atomizing air velocity of 1.8 m / s. 3The feed rate is 45 mL / min. The microcapsule powder at the bottom of the drying tower is collected. The powder is passed through a 100-mesh vibrating screen, and the powder under the screen is collected. 0.2% of nano-silica is added. Then all the powder is put into a V-type mixer, the speed is set to 20 rpm, and the mixture is mixed for 45 min. The mixed powder is put into an aluminum foil composite bag and vacuum sealed to obtain a lignin-based environmentally friendly water-reducing agent.

[0033] Example 2 The preparation method according to Example 1 differs in that: S1: After adding laccase, adjust the pH to 6.0, set the reactor temperature to 20℃, and react at a constant temperature for 8 hours. Replace the chelating agent with EDTA, add PEG-acrylate, adjust the pH to 8.0, raise the reactor temperature to 30℃, and continue the reaction for 3 hours. S2: Adjust the pH to 8.0, the sulfonation reaction temperature to 15℃, the reaction time to 15min, after sulfonation, raise the temperature to 20℃, let it stand for 10min, then raise the temperature of the system to 50℃, replace sodium trimetaphosphate with sodium tripolyphosphate, keep the reaction at a constant temperature for 1.5h, and replace calcium nitrate tetrahydrate with magnesium nitrate hexahydrate. S3: The internal aqueous phase droplet acceleration rate is 0.2 mL / s, the initial emulsification time is 3 min, the PVA concentration in the external aqueous phase is 0.5%, and the re-emulsification shearing time is 3 min; S4: Adjust the pH of the suspension to 6.0, then continue stirring for 5 minutes. The spray drying inlet temperature is 100℃, the outlet temperature is 30℃, and the atomizing air flow rate is 1.5m. 3 The feed rate is 20 mL / min, and the nano-silica is replaced with talc powder. All other steps are the same.

[0034] Example 3 The preparation method according to Example 1 differs in that: S1: After adding laccase, adjust the pH to 8.0, set the reactor temperature to 40℃, and react at a constant temperature for 24 hours. Replace the chelating agent with EDTA-4Na, add PEG-acrylate, adjust the pH to 9.5, raise the reactor temperature to 50℃, and continue the reaction for 12 hours. S2: Adjust the pH to 10.0, the sulfonation reaction temperature to 35℃, the reaction time to 60min, after sulfonation, raise the temperature to 45℃, let stand for 60min, then raise the system to 70℃ and keep the temperature for 6h. S3: The internal aqueous phase droplet acceleration rate is 1.0 mL / s, the initial emulsification time is 10 min, the PVA concentration in the external aqueous phase is 2.0%, and the re-emulsification shearing time is 10 min; S4: Adjust the pH of the suspension to 8.0, then continue stirring for 20 minutes. The spray drying inlet temperature is 120℃, the outlet temperature is 45℃, and the atomizing air velocity is 2.2m / s.3 The feed rate is 60 mL / min, and the nano-silica is replaced with kaolin. All other steps are the same.

[0035] Example 4 The preparation method according to Example 1 differs in that: S1: After adding laccase, adjust the pH to 7.5, set the reactor temperature to 25℃, and react at a constant temperature for 15 hours. After adding PEG-acrylate, adjust the pH to 9.0, raise the reactor temperature to 45℃, and continue the reaction for 9 hours. S2: Adjust the pH to 8.5, the sulfonation reaction temperature to 20℃, the reaction time to 30min, after sulfonation, raise the temperature to 40℃, let stand for 45min, then raise the system to 65℃ and keep it at a constant temperature for 4.5h. S3: The internal aqueous phase droplet acceleration rate is 0.8 mL / s, the initial emulsification time is 8 min, the PVA concentration in the external aqueous phase is 1.5%, and the re-emulsification shearing time is 8 min; S4: Adjust the pH of the suspension to 7.5, then continue stirring for 15 minutes. The spray drying inlet temperature is 105℃, the outlet temperature is 35℃, and the atomizing air flow rate is 2.0 m / s. 3 The feed rate is 30 mL / min, and the rest of the steps are the same.

[0036] Comparative Example 1 The preparation method according to Example 1 differs in that: S2: After phosphorylation of lignin, calcium nitrate solution is not added to the system to directly obtain the phosphorylated lignin liquid phase system. The remaining steps are the same.

[0037] This comparative example prepares a lignin-based water-reducing agent with missing metal ions.

[0038] Comparative Example 2 The preparation method according to Example 1 differs in that: S2: Replace calcium nitrate tetrahydrate with zinc nitrate hexahydrate, and the rest of the steps are the same.

[0039] This comparative example shows the preparation of lignin-based water-reducing agents using heavy metal ion coordination.

[0040] Comparative Example 3 The preparation method according to Example 1 differs in that: S1: After lignin is pre-wetted and swollen, the suspension is used directly as the subsequent reaction solution without adding laccase, chelating agent, PEG grafting, or nanofiltration purification. S2: Add sodium sulfite directly in one drop, without adding hydrogen peroxide, sodium thiosulfate, disodium pyrophosphate, or o-toluenesulfonic acid. All other steps are the same.

[0041] This comparative preparation prepared lignin water-reducing agents lacking enzymatic grafting and sulfonated phosphorylation modification.

[0042] Comparative Example 4 The preparation method according to Example 1 differs in that: Cancel S3; S4: The metal particle-phosphorylated lignin liquid phase system obtained in S2 is adjusted to neutral, maltodextrin is added and stirred evenly, and then spray-dried into powder. The remaining steps are the same.

[0043] This comparative example prepares a water-reducing agent without microcapsule encapsulation.

[0044] Experimental Example 1 According to GB / T 8077-2023 "Test Method for Homogeneity of Concrete Admixtures", a forced concrete mixer (capacity 60L, mixing speed 48r / min) was used to prepare reference concrete and test concrete of the same mass. The mix proportion of the reference concrete was 360kg / m³ of cement. 3 The sand ratio was 40%, and the coarse aggregate was 5mm~25mm continuously graded crushed stone. The reference concrete did not contain any water-reducing agent. The unit water content was adjusted to achieve a slump of 80mm±10mm, and the unit water content W0 was recorded. The tested concrete contained 1.0% water-reducing agent by mass of cement. The water-reducing agent used was the lignin water-reducing agent prepared in Examples 1-4 and Comparative Examples 1-4. The unit water content was adjusted to achieve the same slump of 80mm±10mm, and the unit water content W1 was recorded. The water reduction rate W was calculated according to the formula. R =(W0- W1) / W0×100%.

[0045] According to GB / T 8077-2023 "Test Method for Homogeneity of Concrete Admixtures", 3g of the water-reducing agent prepared in Examples 1-4 and Comparative Examples 1-4 was weighed and added to 300g of reference cement conforming to GB / T 8077. The mixture was poured into a mixing pot, followed by 87g of water. The pot was then placed on a cement paste mixer and slowly stirred for 120s, stopped for 15s, and then quickly stirred for 120s. After stirring, the paste was quickly poured into a truncated conical mold (upper diameter 36mm, lower diameter 60mm, height 60mm). After leveling, the mold was lifted vertically, allowing the paste to flow freely on a glass plate for 30s. The maximum diameter in two perpendicular directions was measured with calipers, and the average value was taken as the fluidity of the cement paste.

[0046] Slump retention tests were conducted according to GB / T 50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures". The concrete mix proportion adopted a cement content of 360 kg / m³. 3The sand ratio was 40%, the water-cement ratio was 0.45, the crushed stone was continuously graded from 5mm to 25mm, and the water-reducing agent dosage was 1.0% of the cement mass. The water-reducing agent used was the lignin water-reducing agent prepared in Examples 1-4 and Comparative Examples 1-4. After the concrete mixture was prepared, the initial slump and spread were measured immediately at a temperature of 20℃ and a relative humidity of 60%. The remaining concrete mixture was covered with plastic film to keep it moist. After stirring for 15 seconds at 30min, 60min, and 90min, the slump and spread were measured again. The slump loss rate over time was calculated as (initial slump - slump at a certain moment) / initial slump × 100%, and the spread loss rate over time was calculated as (initial spread - spread at a certain moment) / initial spread × 100%.

[0047] The test results of the above water-reducing agent's fresh mixing performance are shown in Table 2.

[0048] Table 2. Fresh Mixing Performance Data of Examples and Comparative Samples

[0049] As can be seen from Table 2, the metal ion coordination of the sample obtained by laccase activation, hydrophilic modification and sulfonation phosphorylation treatment in the example samples obtained excellent fresh mixing performance. This indicates that the water-reducing agent molecules prepared in the example achieved rapid adsorption and effective dispersion of cement particles. Moreover, the presence of microcapsules prevents the active ingredients from being released all at once. Instead, the active ingredients are continuously replenished over time and with increasing temperature, thus giving the sample good slump retention performance. Comparative Example 1, lacking metal ion coordination, failed to form Metal-OP coordination bonds, resulting in the complete release of phosphate groups in the initial stage. This led to excessively rapid adsorption and consumption of the water-reducing agent molecules on cement particles, and the inability to replenish fresh negative charge sites through coordination bond breakage in the later stages, thus significantly reducing slump retention performance. Comparative Example 2 replaced calcium ions with zinc ions. Zinc ions formed insoluble precipitates in the alkaline environment of cement, coating the surface of cement particles and consuming water-reducing agent molecules, interfering with the hydration process and further weakening the dispersion efficiency. Comparative Example 3 used unmodified virgin lignin, which has poor hydrophilicity and extremely low water solubility, failing to provide sufficient negative charge density, resulting in extremely low water reduction rate. Its initial fluidity was only slightly higher than the baseline system, and its low loss rate over time was due to poor initial workability rather than excellent slump retention performance. Comparative Example 4 lacked microcapsule coating, causing all active ingredients to be exposed in the initial stage. Although the initial water reduction rate and fluidity did not decrease significantly, the active ingredients were rapidly consumed in the initial stage, resulting in a significantly higher loss rate of slump and spread over time after 60 minutes compared to the example, and a substantial decrease in slump retention capacity.

[0050] Experimental Example 2 According to GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete", the concrete mix proportion adopts a cement content of 360 kg / m³. 3The sand ratio is 40%, the water-cement ratio is 0.45, the crushed stone is continuously graded from 5mm to 25mm, the water-reducing agent dosage is 1.0% of the cement mass, and the water-reducing agent used is the lignin water-reducing agent prepared in Examples 1-4 and Comparative Examples 1-4. The reference concrete does not contain water-reducing agent, and the water content is adjusted to make the slump comparable to that of the tested concrete. Prepare 150mm×150mm×150mm cubic specimens, 3 specimens per group. Cured under standard curing conditions of 20℃ and relative humidity ≥95%. Remove the specimens after 3d, 7d, and 28d of curing, wipe off the surface moisture, and place the specimens in the center of the bearing plate of a pressure testing machine with an accuracy of ±0.5% and a load of 1000kN. Load continuously and uniformly at a loading rate of 0.5MPa / s until the specimen fails. Record the failure load. The compressive strength f=F / A, where F is the failure load and A is the bearing area. The compressive strength ratio R=(compressive strength of tested concrete / compressive strength of reference concrete)×100%.

[0051] According to GB / T 50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures", the concrete mix proportion adopts a cement content of 360 kg / m³. 3 The sand ratio was 40%, the water-cement ratio was 0.45, the crushed stone was continuously graded from 5mm to 25mm, and the water-reducing agent dosage was 1.0% of the cement mass. The water-reducing agent used was the lignin water-reducing agent prepared in Examples 1-4 and Comparative Examples 1-4. Mortar was sieved from the concrete mixture using a 5mm sieve and poured into a mold with a diameter of 160mm and a height of 150mm. After being manually tamped 25 times, it was compacted on a vibrating table, and the surface was leveled. The mold was placed in a 20℃ environment, and the timing started from the time water was added and stirred. Tests were conducted every 30 minutes before initial setting and every 60 minutes after initial setting, depending on the setting condition. A cross-sectional area of ​​1mm² was used. 2 The initial setting probe was inserted into the mortar to a depth of 25mm, and the penetration pressure was recorded. The time corresponding to the penetration resistance reaching 3.5MPa was taken as the initial setting time. A probe with a cross-sectional area of ​​20mm² and an annular attachment was then used. 2 The final setting probe continues to test. The time corresponding to the penetration resistance reaching 28MPa is the final setting time. The initial setting time and the final setting time are recorded. The setting time difference = setting time of the tested concrete - setting time of the reference concrete.

[0052] The results of the hardening performance tests are shown in Table 3.

[0053] Table 3. Hardening performance test data of the examples and comparative samples

[0054] As shown in Table 3, all the sample examples exhibited excellent hardening performance, indicating that the presence of active ingredients and microcapsule encapsulation endowed the samples with excellent and controllable retarding effects. Comparative Example 1, lacking metal ion coordination, could not replenish fresh negative charge sites through coordination bond breakage in the middle and later stages. Its dispersion effect gradually diminished with the hydration process, and the density of hydration products was lower than that of the examples, limiting strength development. Comparative Example 2 replaced calcium ions with zinc ions. Zinc ions formed insoluble precipitates in the alkaline environment of cement, coating the surface of cement particles and consuming water-reducing agent molecules, resulting in a loose internal concrete structure and hindered strength development. Furthermore, zinc ions, acting as a hydration inhibitor, severely delayed setting and hardening, significantly increasing the initial setting time difference. Comparative Example 3 uses unmodified virgin lignin, which has almost no effective water-reducing function. The slight increase in strength mainly comes from physical filling rather than dispersion enhancement. It has no chemical interference with the setting process and its hardening performance is similar to that of blank concrete. Comparative Example 4 lacks microcapsule coating. The retarding component is rapidly consumed in the early stage and cannot continuously delay the hydration process. The initial setting time difference is much smaller than that of the example. At the same time, there is a lack of active ingredient replenishment in the middle and later stages, and the hydration products have insufficient density, resulting in a significantly lower compressive strength ratio than the example.

[0055] Experimental Example 3 The PEG-grafted lignin reaction solution prepared in Example 1 (S1) and the sulfonated lignin intermediate liquid system obtained after quenching hydrogen peroxide in Example 1 (S2) were freeze-dried into powder. Infrared spectroscopy was then performed on the powder and the final lignin water-reducing agent powder obtained in Example 1. The three powders were then mixed with dry KBr powder, ground uniformly, and pressed into tablets at 4000–4000 cm⁻¹. -1 Scan within the range, the scan results are as follows Figure 1 As shown.

[0056] from Figure 1 As can be seen from this, in PEG-grafted lignin, the content is similar to that at 3400 cm⁻¹ -1 The previously strong and broad hydroxyl absorption band was significantly reduced, indicating that a large number of phenolic hydroxyl groups in the lignin molecule were consumed and converted into ether bonds, in the range of 1720~1736 cm⁻¹. -1 The appearance of a sharp ester carbonyl stretching vibration peak within the range indicates the successful introduction of the PEG-acrylate segment, with a peak at 1636 cm⁻¹. -1 and 808cm -1 The absence of a peak representing a carbon-carbon double bond in the acrylate monomer indicates that the introduction of the PEG-acrylate segment is a covalent graft rather than a physical bond. (The peak at 1150 cm⁻¹ is also mentioned.) -1 The presence of extremely strong asymmetric stretching vibration peaks of aliphatic COC in the vicinity, originating from the PEG backbone, indicates successful grafting of the hydrophilic PEG segments; the infrared spectrum of the sulfonated lignin intermediate shows peaks in the 1180–1200 cm⁻¹ range. -1A new asymmetric S=O tensile vibration peak was added at 1040 cm⁻¹. -1 The presence of a symmetrical S=O stretching vibration peak nearby indicates that the sulfonic acid group was successfully introduced; in the final infrared spectrum of the water-reducing agent powder, the peak value is in the range of 1230~1250 cm⁻¹. -1 The appearance of the P=O stretching vibration peak at 715 cm⁻¹ is evidence of successful grafting of sodium trimetaphosphate, and this peak is further evidenced by the presence of the peak at 715 cm⁻¹. -1 990cm -1 1020cm -1 The presence of symmetric / asymmetric stretching vibration peaks of the POC framework nearby indicates that inorganic phosphate and the lignin macromolecular organic framework have formed a stable covalent bond.

[0057] Experiment Example 4 The water-reducing agent powder prepared in Example 1 was placed in a buffer solution with a pH of 7-9 and a temperature of 20-25°C to simulate the behavior of the water-reducing agent during the initial low hydration period. After soaking and suspending for 10 hours, it was freeze-dried to re-form the powder. The powder was then adhered to conductive adhesive, sputtered with gold, and its surface morphology was microscopically scanned using SEM. Additionally, using precise focused ion beam cutting technology, microcapsules were dissected at the nanometer scale in situ to observe the cross-sectional morphology of the samples. Another batch of the water-reducing agent powder prepared in Example 1 was placed in a NaOH aqueous solution with a pH of 14 and heated to 60°C in a water bath to simulate the water-reducing agent under the high-alkali and high-heat environment during cement hydration. Samples after 5 minutes and 3 hours of simulation were rapidly quenched and dried to prepare samples, and their morphology was observed. The results are as follows: Figure 2 As shown.

[0058] from Figure 2 As can be seen from a, in the simulated initial stage of mixing in a weakly alkaline environment at room temperature, the microcapsules in the water-reducing agent exhibit a highly regular near-spherical three-dimensional outline. The overall spherical shell structure is tight and seamless, with a dense surface and no penetrating holes or macroscopic cracks. This high degree of physical integrity establishes a strong physical barrier, effectively preventing premature contact between the highly active complex inside and the external environment. Figure 2 b shows that the cross-section of the microcapsule exhibits a clear core-shell structure. It can be seen that the outer layer is a dense and relatively uniform polylactic acid solid polymer shell. In the huge cavity inside the shell, due to the instantaneous removal of water during the spray drying process, the originally suspended active metal ions - phosphorylated lignin inevitably aggregate and shrink, leaving a sponge-like and porous solid residue skeleton, which proves that the microcapsule contains active modified lignin. Figure 2c shows that in the early stage of dual stimulation at pH=14 and temperature>40℃, the rigid PLA shell begins to soften and the microcapsule volume undergoes significant macroscopic swelling. This is caused by the osmotic pressure difference generated by the extremely high salt concentration in the internal phase, as well as the electrostatic repulsion and solvation effect brought about by the deprotonation of the carboxyl groups at the ends of the polylactic acid chain. With the breaking of macromolecular ester bonds and the stripping of oligomers, the originally smooth shell surface is eroded and the roughness increases sharply, developing a large number of nano- to micron-sized mesopores and irregular macroporous fluid channels. At this time, the overall framework of the microcapsule has not yet completely disintegrated, but the internal active substances have begun to leak early through the pore channels. Figure 2 As can be seen from d, with the continuous deepening of high temperature and strong alkali hydrolysis, the long chain of polylactic acid is completely cut and destroyed, and the material completely loses the physical and mechanical strength to maintain the cavity structure. The micro-morphology starts with deep penetrating microcracks in local areas, leading to the collapse of the entire structure, and finally irreversibly breaking into sheet-like irregular polymer fragments. At this time, the high concentration of metal-phosphorylated lignin encapsulated inside quickly enters the high-alkali slurry, initiating a strong dispersion and water retention effect, while only empty cavities remain in the fragments of the capsule wall. This marks the complete completion of the intelligent trigger release mechanism.

[0059] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An environmentally friendly water-reducing agent based on natural materials, characterized in that: The natural material is modified lignin; the modified lignin is lignin with PEG molecular chains, sulfonic acid groups, and coordination structures on its molecular chain; the PEG molecular chains are connected to the phenolic hydroxyl groups in the lignin molecule activated by laccase via ether bonds; the coordination structure is a reversible coordination structure; the reversible coordination structure is a metal-phosphate coordination bond formed by phosphate groups and metal ions; the coordination bond is a stable complex crystal field network formed by the combined action of electrostatic attraction and coordination bonds; the complex crystal field network is formed by the empty orbitals of metal ions and the lone pair electrons of oxygen atoms on the phosphorus-oxygen bonds in the phosphate groups; the water-reducing agent is a core-shell structured microcapsule powder; the shell of the microcapsule is a polylactic acid shell, and the core encapsulates the modified lignin.

2. The environmentally friendly water-reducing agent based on natural materials according to claim 1, characterized in that: The metal ion is Ca. 2+ or Mg 2+ One or more of them are derived from the corresponding nitrates.

3. The preparation method of an environmentally friendly water-reducing agent based on natural materials as described in claims 1-2, characterized in that, It is prepared by the following method: S1: After pre-wetting lignin in a reaction vessel, lignin laccase is added for constant temperature reaction. Then, a chelating agent is added and stirred. PEG-acrylate is added dropwise to the system and the pH value is adjusted. After continuous stirring, unreacted PEG-acrylate is removed by nanofiltration to obtain PEG-grafted lignin reaction solution. S2: The reaction solution was transferred to a new reaction vessel and the pH was adjusted with NaOH. Then, hydrogen peroxide was added dropwise under continuous stirring for oxidation and activation. The hydrogen peroxide was then quenched and sodium sulfite was added dropwise in batches for sulfonation. After the reaction was completed, the mixture was allowed to stand. Then, the system was heated and a phosphorylation reagent was added for phosphorylation modification. Then, a metal ion solution was added dropwise to obtain a metal ion-phosphorylated lignin system. S3: Polylactic acid was added to ethyl acetate and stirred until homogeneous. Then, the metal ion-phosphorylated lignin system was added dropwise to the polylactic acid / ethyl acetate system under high-speed stirring to emulsify it into a primary emulsion. The primary emulsion was then added dropwise to PVA aqueous solution and stirred to form a water / oil / water type double emulsion. After purification, centrifugation and redispersion in deionized water, a metal ion-phosphorylated lignin suspension encapsulated in microcapsules was obtained. S4: Add sodium bicarbonate to the system to adjust the pH and continue stirring. Then add maltodextrin to the treatment liquid and let it pass through a spray drying tower to obtain a dry powder. After sieving, mix it with an anti-caking agent to obtain a lignin-based environmentally friendly water-reducing agent.

4. The preparation method of an environmentally friendly water-reducing agent based on natural materials according to claim 3, characterized in that: The chelating agent mentioned in S1 is one or more of EDTA, EDTA-2Na, and EDTA-4Na.

5. The preparation method of an environmentally friendly water-reducing agent based on natural materials according to claim 3, characterized in that: The pH of the isothermal reaction described in S1 is 6.0~8.0, the reaction temperature is 20~40℃, and the reaction time is 8~24h; the pH is adjusted to 8.0~9.5; the temperature for continuous stirring is 30~50℃, and the stirring time is 3~12h.

6. The preparation method of an environmentally friendly water-reducing agent based on natural materials according to claim 3, characterized in that: The phosphorylation reagent mentioned in S2 is one or more of sodium trimetaphosphate and sodium tripolyphosphate.

7. The preparation method of an environmentally friendly water-reducing agent based on natural materials according to claim 3, characterized in that: S2 The pH is adjusted to 8.0~10.0; the temperature of the oxidation-sulfonation reaction is 15~35℃ and the reaction time is 15~60min; the temperature during the standing period is 20~45℃ and the standing time is 10~60min; the temperature of the phosphorylation modification is 50~70℃ and the reaction time is 1.5~6h.

8. The preparation method of an environmentally friendly water-reducing agent based on natural materials according to claim 3, characterized in that: The dripping rate of S3 is 0.2~1.0 mL / s; the emulsification time is 3~10 min; the degree of PVA polymerization is 1750±50, the degree of alcoholysis is 87.0%~89.0%, and the mass fraction of the aqueous solution is 0.5%~2.0%; the stirring reaction time is 3~10 min.

9. The preparation method of an environmentally friendly water-reducing agent based on natural materials according to claim 3, characterized in that: The anti-caking agent mentioned in S4 is one or more of nano-silica, talc, and kaolin.

10. The method for preparing an environmentally friendly water-reducing agent based on natural materials according to claim 3, characterized in that: S4 describes adjusting the pH to 6.0-8.0; the continued stirring time is 5-20 minutes; the inlet temperature of the spray drying tower is 100-120℃, the outlet temperature is 30-45℃, and the atomizing air velocity is 1.5-2.2 m / s. 3 The feed rate is 20~60 mL / min.

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