Marine biomass amphoteric response type polycarboxylate superplasticizer and preparation method thereof

Abstract

The invention discloses a marine biomass amphoteric response type polycarboxylate superplasticizer and a preparation method thereof, and belongs to the technical field of concrete admixtures. The preparation method comprises the following steps: carrying out acid hydrolysis on sodium alginate, and carrying out ultrafiltration purification to obtain alginic acid oligosaccharide; the preparation method comprises the following steps: pre-activating alginic acid oligosaccharide, adding citric anhydride, carrying out esterification reaction under the action of a catalyst, and purifying to obtain an alginic acid grafted product; mixing the alginic acid grafted product with chitosan quaternary ammonium salt, and then carrying out ionic crosslinking reaction to obtain an ionic crosslinked product; and adding a physical cross-linking agent into the ionic cross-linked substance, and purifying after freeze-thaw cycle to obtain the product. The marine biomass amphoteric response type polycarboxylate superplasticizer can solve the problems of non-renewable raw materials and low utilization rate of marine biomass of a traditional superplasticizer, can also overcome the defects of delayed cement setting and increased consistency caused by direct application of natural polysaccharides and derivatives thereof, and has wide application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of concrete admixtures, and particularly relates to a marine biomass amphoteric responsive polycarboxylate water reducer and a preparation method thereof. Background Art

[0002] Polycarboxylate superplasticizers are essential admixtures in modern concrete engineering. They adsorb onto the surface of cement particles, generating electrostatic repulsion and steric hindrance, thereby reducing concrete water consumption and improving its strength and performance. However, traditional polycarboxylate superplasticizers, primarily derived from petrochemicals, face challenges such as non-renewable raw materials, resource depletion, and high carbon emissions during production, making them difficult to meet sustainable development requirements. Marine biomass resources are abundant, such as brown algae and chitosan, which are renewable and environmentally friendly. Among them, natural polysaccharides such as calcium alginate, cellulose and maltodextrin have certain thickening properties, but their direct application in concrete will significantly delay the setting and hardening of cement, resulting in slow development of early strength of concrete, increased concrete consistency, increased cost of admixture use, and failure to meet the construction schedule requirements of actual projects. In addition, the development and utilization rate of marine biomass in the field of water reducers is low, and a large number of potential functionalities have not been fully explored and utilized. At the same time, in the preparation process of water reducers, the presence of small molecular fragments will affect the stability and performance of the product. For example, fragments with too small a molecular weight cannot be effectively adsorbed on the surface of cement particles, and may also interfere with the normal function of the macromolecular structure. Therefore, effective separation and purification methods are urgently needed to improve product quality.

[0003] Therefore, how to efficiently utilize biomass resources such as the ocean, develop water-reducing agent products with excellent performance and green environmental protection, and solve the problem of product purification has become an urgent problem to be solved in the field of concrete admixtures. Summary of the Invention

[0004] In response to the above-mentioned deficiencies in the prior art, the present invention provides a marine biomass amphoteric responsive polycarboxylate water reducer and a preparation method thereof, so as to solve the problems of non-renewable raw materials of traditional water reducers and low utilization rate of marine biomass, while overcoming the defects that direct application of natural polysaccharides and their derivatives will lead to delayed cement setting and increased consistency.

[0005] The technical solution adopted to solve the technical problem is to provide a method for preparing a marine biomass amphoteric responsive polycarboxylate water reducer, comprising the following steps: (1) hydrolyzing sodium alginate with acid and purifying it by ultrafiltration to obtain alginate oligosaccharides; (2) pre-activating alginate oligosaccharides and then adding citric anhydride to carry out esterification reaction under the action of a catalyst, and obtaining an alginate grafted product after purification; (3) mixing the alginate grafted product and chitosan quaternary ammonium salt and performing an ion crosslinking reaction to obtain an ion crosslinked product; (4) Adding a physical crosslinking agent to the ionic crosslinked product, and then purifying it after freeze-thaw cycles to obtain the product.

[0006] The beneficial effects of the above technical solution adopted by the present invention are as follows: the present invention uses acid hydrolysis to prepare alginic acid oligosaccharides in a targeted manner and introduces carboxylic acid groups through an esterification reaction, which significantly enhances the hydrophilicity of the molecular chain and the auxiliary dispersion ability of cement particles. The ionic crosslinking effect of chitosan quaternary ammonium salt forms an amphoteric responsive structure, enabling the water reducer to intelligently adjust its adsorption performance according to environmental conditions, greatly improving the water reduction efficiency and concrete fluidity. Furthermore, the synergistic treatment of freeze-thaw cycles and physical crosslinkers constructs a dense double crosslinked network, which not only enhances structural stability to adapt to complex construction environments, but also has good durability. The water reducer should have excellent dispersibility, good cement adaptability and chloride ion curing function, and the raw materials are completely derived from renewable resources, which can achieve the green and sustainable development of concrete admixtures.

[0007] Preferably, the acid hydrolysis in step (1) comprises the following steps: dissolving sodium alginate in a mixed solution of acid and ethanol, adjusting the pH to 2.5-3, and hydrolyzing at 30-50° C. for 20-24 h; the ultrafiltration pressure is 0.1-0.3 MPa, and the stirring rate is 200-300 r / min; the molecular weight of the alginate oligosaccharide is 3000-8000 Da.

[0008] More preferably, the mass ratio of sodium alginate to the mixed solution of acid and ethanol is 1:(18-22); each 1 L of the mixed solution of acid and ethanol contains 50-100 mL of ethanol and 0.05-0.2 mol of acid, and the acid is at least one of hydrochloric acid, formic acid and acetic acid.

[0009] More preferably, the mass ratio of the mixed solution of sodium alginate and acid and ethanol is 1:20.

[0010] Preferably, the preactivation in step (2) is carried out using a preactivation reagent, the preactivation reagent is at least one of N,N-dicyclohexylcarbodiimide, N,N-dimethylformamide, N,N-dimethylacetamide, N,N-dimethylacrylamide and tetrahydrofuran, and the preactivation time is 0.5 to 1.5 h.

[0011] More preferably, the pre-activation time is 1 h.

[0012] More preferably, the mass ratio of alginate oligosaccharide to pre-activation reagent is 1:10.

[0013] Preferably, in step (2), the molar ratio of alginate oligosaccharides to citric anhydride is 1.5-2:1; the catalyst is at least one of p-toluenesulfonic acid, trifluoromethanesulfonic acid, phosphoric acid and boric acid; the esterification reaction is carried out under ultrasonic vibration at 20-40 kHz, the esterification reaction temperature is 100-120° C., and the reaction time is 3-5 h.

[0014] More preferably, the mass of the catalyst is 0.8-1.2% of the total mass of citric anhydride and alginate oligosaccharides.

[0015] Preferably, in step (3), the molar ratio of the alginate grafted product to the chitosan quaternary ammonium salt is 1:2.5-3.5; the ionic crosslinking reaction conditions are: stirring the reaction for 2-4 h in a water bath at 25-30° C. and a pH of 6.0-6.5, and using intermittent ultrasound assistance at 200-400 W during the reaction, running the ultrasound for 1-2 min and then stopping for 5-7 min, and then recirculating until the reaction is completed.

[0016] More preferably, 300 W intermittent ultrasound is used to assist the ionic crosslinking reaction, and the ultrasound is run for 1 minute and then stopped for 5 minutes, and then recycled until the reaction is completed.

[0017] More preferably, the chitosan quaternary ammonium salt is at least one of N,N,N-trimethyl chitosan, hydroxyethyl trimethyl ammonium chloride chitosan, hydroxypropyl trimethyl ammonium chloride chitosan and carboxymethyl chitosan quaternary ammonium salt.

[0018] Preferably, in step (4), the physical crosslinking agent is a mixture of nanocellulose whiskers and maltodextrin; the mass ratio of the physical crosslinking agent to the ionic crosslinker is 0.5-1:100; and the freeze-thaw cycle conditions are: freezing at -20--18°C for 10-12 h, thawing at 20-25°C for 5-7 h, and repeating 2-3 times.

[0019] More preferably, the diameter of the nanocellulose whiskers is 20-50 nm; the mass ratio of the nanocellulose whiskers to the maltodextrin is 1:1; and the mass concentration of the physical crosslinking agent is 0.8-1 wt%.

[0020] More preferably, the freeze-thaw cycle conditions are: freezing at -20°C for 12 h, thawing at 25°C for 6 h, repeated twice.

[0021] The present invention also provides a marine biomass amphoteric responsive polycarboxylate water reducer prepared by the above preparation method.

[0022] The present invention has the following beneficial effects: (1) The present invention applies the alginate-chitosan system to the preparation of a water reducer. The raw materials are 100% derived from renewable biomass resources. The production process is green and environmentally friendly, reducing the consumption of fossil resources and pollution to the environment, and is in line with the concepts of green chemistry and sustainable development.

[0023] (2) -COO of the alginic acid oligosaccharide of the present invention - With chitosan quaternary ammonium salt -N + (CH3)3 forms a dynamic ionic cross-linked network through electrostatic attraction. This process is reversible and pH responsive, constructing a unique water reducer-COO - With -NH 3+ The zwitterionic structure gives the water-reducing agent a wider pH adaptability range, allowing it to be adsorbed more quickly and stably on the surface of cement particles in concrete systems with different cement types and different mineral compositions. At the same time, after removing the small molecule fragments of sodium alginate, the interference of small molecules on the interaction between the water-reducing agent and cement particles is reduced, further improving the adaptability and working stability of cement.

[0024] (3) The present invention introduces chitosan quaternary ammonium salt, nanocellulose whiskers and maltodextrin, and realizes the synergistic effect of electrostatic self-assembly and low-temperature physical curing to achieve hydrogen bond-strengthened three-dimensional network stability and enhance adsorption stability, thereby exerting stronger electrostatic repulsion and steric hindrance effects, while retaining the chitosan quaternary ammonium salt's ability to solidify chloride ions. By complexing or chemically reacting with chloride ions in concrete, the chloride ions are solidified inside the concrete, effectively reducing the mobility and corrosiveness of chloride ions, improving the durability of concrete structures, and extending the service life of concrete projects.

[0025] (4) The water-reducing agent of the present invention has a high water-reducing rate and good slump-retaining performance. After adding the water-reducing agent to concrete, the fluidity of the concrete can be significantly improved, and the slump loss rate within 3 hours is less than 9%, which meets the requirements of long-distance transportation and complex construction technology for the working performance of concrete. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with Examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. That is, the embodiments described are only part of the present invention, rather than all of the embodiments. In the embodiments, if specific conditions are not specified, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the reagents or instruments are not specified by the manufacturer, they are all conventional products that can be purchased commercially.

[0027] Therefore, the detailed description of the embodiments of the present invention provided below is not intended to limit the scope of the invention as claimed, but is merely intended to represent selected embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0028] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0029] Example 1 A method for preparing a marine biomass amphoteric responsive polycarboxylate water reducer comprises the following steps: (1) 80 mL of ethanol was dissolved in 920 mL of water, and 0.1 mol of hydrochloric acid was added thereto to obtain a mixed solution of acid and ethanol; sodium alginate and the mixed solution of acid and ethanol were mixed at a mass ratio of 1:20, the pH was adjusted to 2.5-3, and the mixture was hydrolyzed at 30°C for 24 h to obtain a hydrolyzate. After the reaction, the hydrolyzate was prepared into an aqueous solution with a mass concentration of 15%, and ultrafiltration was performed at room temperature using an ultrafiltration membrane with a molecular weight cutoff of 1000-10000 Da. During the ultrafiltration process, the operating pressure was controlled at 0.2 MPa and the stirring speed was 240 r / min. After the ultrafiltration was completed, the retentate was neutralized, filtered, washed and dried to obtain alginate oligosaccharides with a molecular weight of 3000-8000 Da; (2) Alginate oligosaccharide was added to N,N-dicyclohexylcarbodiimide solution at a mass ratio of 1:10 for pre-activation for 1 h to obtain oligosaccharide activation solution; then citric anhydride was added to the oligosaccharide activation solution at a molar ratio of citric anhydride to alginate oligosaccharide of 1:1.5, and an esterification reaction was carried out at 120°C for 3 h under the catalysis of p-toluenesulfonic acid with a mass of 1.2% of the total mass of citric anhydride and alginate oligosaccharide. The esterification reaction was carried out under ultrasonic vibration at 40 kHz. After the reaction, the alginate grafted product was purified by anti-solvent precipitation method; the solvent used in the anti-solvent precipitation method was a mixed solvent of ethanol and acetone at a volume ratio of 4:1; (3) Alginic acid grafted product and N,N,N-trimethyl chitosan were prepared in sequence at a mass ratio of 1:10 to prepare an alginate grafted product solution and an N,N,N-trimethyl chitosan solution; the pH of the alginate grafted product solution was adjusted to 6.0-6.5 with NaOH / HCl, and the N,N,N-trimethyl chitosan solution was added dropwise to the alginate grafted product solution at a molar ratio of 1:2.5 of alginate grafted product:N,N,N-trimethyl chitosan in a water bath at 25°C for 4 h. The reaction was stirred continuously during the addition process. Intermittent ultrasonication at 300 W was used to assist the reaction. The ultrasonication was run for 1 min and then stopped for 5 min, and then recycled until the ionic crosslinking reaction was completed to obtain an ionic crosslinked product; (4) Nanocellulose whiskers with a diameter of 20-50 nm were mixed with maltodextrin in a mass ratio of 1:1 to prepare a mixture with a mass concentration of 0.8 wt% as a physical crosslinker; the physical crosslinker was added to the ionic crosslinker in a mass ratio of 0.5:100, and the mixture was frozen at -20°C for 12 h and thawed at 25°C for 6 h, repeated twice, and the product was neutralized, filtered, and washed to obtain the product.

[0030] Example 2 A method for preparing a marine biomass amphoteric responsive polycarboxylate water reducer comprises the following steps: (1) 50 mL of ethanol was dissolved in 950 mL of water, and 0.05 mol of hydrochloric acid and 0.05 mol of formic acid were added thereto to obtain a mixed solution of acid and ethanol; sodium alginate and the mixed solution of acid and ethanol were mixed at a mass ratio of 1:20, the pH was adjusted to 2.5-3, and hydrolysis was carried out at 40°C for 24 h to obtain a hydrolyzate. After the reaction, the hydrolyzate was prepared into an aqueous solution with a mass concentration of 20%, and ultrafiltration was carried out at room temperature using an ultrafiltration membrane with a molecular weight cutoff of 1000-10000 Da. During the ultrafiltration process, the operating pressure was controlled at 0.2 MPa and the stirring speed was 240 r / min. After the ultrafiltration was completed, the retentate was neutralized, filtered, washed and dried to obtain alginate oligosaccharides with a molecular weight of 3000-8000 Da; (2) Alginate oligosaccharide was added to N,N-dimethylformamide solution at a mass ratio of 1:10 for pre-activation for 1 h to obtain oligosaccharide activation solution; then citric anhydride was added to the oligosaccharide activation solution at a molar ratio of citric anhydride to alginate oligosaccharide of 1:2, and an esterification reaction was carried out at 100°C for 5 h under the catalysis of trifluoromethanesulfonic acid with a mass of 0.8% of the total mass of citric anhydride and alginate oligosaccharide. The esterification reaction was carried out under ultrasonic vibration at 40 kHz. After the reaction, the product was purified by anti-solvent precipitation method to obtain an alginate grafted product; the solvent used in the anti-solvent precipitation method was a mixed solvent of ethanol and acetone at a volume ratio of 3:1; (3) Alginic acid grafted product and hydroxypropyl trimethyl ammonium chloride chitosan were prepared in sequence at a mass ratio of 1:10 to prepare an alginate grafted product solution and a hydroxypropyl trimethyl ammonium chloride chitosan solution; the pH of the alginate grafted product solution was adjusted to 6.0-6.5 with NaOH / HCl, and the hydroxypropyl trimethyl ammonium chloride chitosan solution was added dropwise to the alginate grafted product solution at a molar ratio of 1:3 of alginate grafted product: hydroxypropyl trimethyl ammonium chloride chitosan in a water bath at 30°C for 2 h. The reaction was continuously stirred during the addition process. Intermittent ultrasound at 300 W was used to assist the reaction. The ultrasound was run for 1 min and then stopped for 5 min, and then recycled until the ionic crosslinking reaction was completed to obtain an ionic crosslinked product; (4) Nanocellulose whiskers with a diameter of 20-50 nm were mixed with maltodextrin in a mass ratio of 1:1 to prepare a mixture with a mass concentration of 0.8 wt% as a physical crosslinker; the physical crosslinker was added to the ionic crosslinker in a mass ratio of 0.8:100, and the mixture was frozen at -20°C for 12 h and thawed at 25°C for 6 h, repeated twice, and the product was neutralized, filtered, and washed to obtain the product.

[0031] Example 3 A method for preparing a marine biomass amphoteric responsive polycarboxylate water reducer comprises the following steps: (1) 100 mL of ethanol was dissolved in 900 mL of water, and 0.1 mol of acetic acid was added thereto to obtain a mixed solution of acid and ethanol; sodium alginate and the mixed solution of acid and ethanol were mixed at a mass ratio of 1:20, the pH was adjusted to 2.5-3, and the mixture was hydrolyzed at 50°C for 24 h to obtain a hydrolyzate. After the reaction, the hydrolyzate was prepared into an aqueous solution with a mass concentration of 10%, and ultrafiltration was performed at room temperature using an ultrafiltration membrane with a molecular weight cutoff of 1000-10000 Da. During the ultrafiltration process, the operating pressure was controlled at 0.2 MPa and the stirring speed was 240 r / min. After the ultrafiltration was completed, the retentate was neutralized, filtered, washed and dried to obtain alginate oligosaccharides with a molecular weight of 3000-8000 Da; (2) Alginate oligosaccharide was added to a mixed solution of N,N-dimethylacrylamide and tetrahydrofuran in a volume ratio of 1:10 at a mass ratio for 1 h to obtain an oligosaccharide activation solution; citric anhydride was then added to the oligosaccharide activation solution at a molar ratio of citric anhydride to alginate oligosaccharide of 1:1.8, and an esterification reaction was carried out at 110°C for 4 h under the catalysis of phosphoric acid with a mass ratio of 1% of the total mass of citric anhydride and alginate oligosaccharide. The esterification reaction was carried out under ultrasonic vibration at 40 kHz. After the reaction, the alginate grafted product was purified by anti-solvent precipitation method; the solvent used in the anti-solvent precipitation method was a mixed solvent of ethanol and acetone in a volume ratio of 5:1; (3) Alginic acid grafted product and carboxymethyl chitosan quaternary ammonium salt were prepared in a mass ratio of 1:10 to prepare an alginic acid grafted product solution and a carboxymethyl chitosan quaternary ammonium salt solution; the pH of the alginate grafted product solution was adjusted to 6.0-6.5 with NaOH / HCl, and the carboxymethyl chitosan quaternary ammonium salt solution was added dropwise to the alginate grafted product solution in a water bath at 28°C at a molar ratio of 1:3.5 of alginate grafted product:carboxymethyl chitosan quaternary ammonium salt. The addition time was 4 h, and the reaction was continuously stirred during the addition process. During the reaction, intermittent ultrasound at 300 W was used to assist, and the ultrasound was run for 1 min and then stopped for 5 min, and then recycled until the ionic crosslinking reaction was completed to obtain an ionic crosslinked product; (4) Nanocellulose whiskers with a diameter of 20-50 nm were mixed with maltodextrin in a mass ratio of 1:1 to prepare a mixture with a mass concentration of 0.8 wt% as a physical crosslinker; the physical crosslinker was added to the ionic crosslinker in a mass ratio of 1:100, and the mixture was frozen at -20°C for 12 h and thawed at 25°C for 6 h, repeated twice, and the product was neutralized, filtered, and washed to obtain the product.

[0032] Example 4 A method for preparing a marine biomass amphoteric responsive polycarboxylate water reducer comprises the following steps: (1) 80 mL of ethanol was dissolved in 920 mL of water, and 0.1 mol of hydrochloric acid and 0.1 mol of acetic acid were added thereto to obtain a mixed solution of acid and ethanol; sodium alginate and the mixed solution of acid and ethanol were mixed in a mass ratio of 1:20, the pH was adjusted to 2.5-3, and hydrolysis was carried out at 50°C for 24 h to obtain a hydrolyzate. After the reaction, the hydrolyzate was prepared into an aqueous solution with a mass concentration of 15%, and ultrafiltration was carried out at room temperature using an ultrafiltration membrane with a molecular weight cutoff of 1000-10000 Da. During the ultrafiltration process, the operating pressure was controlled at 0.2 MPa and the stirring speed was 240 r / min. After the ultrafiltration was completed, the retentate was neutralized, filtered, washed and dried to obtain alginate oligosaccharides with a molecular weight of 3000-8000 Da; (2) Alginate oligosaccharide was added to a mixed solution of N,N-dimethylacetamide and N,N-dimethylacrylamide in a volume ratio of 1:1 at a mass ratio of 1:10 for pre-activation for 1 h to obtain an oligosaccharide activation solution; citric anhydride was then added to the oligosaccharide activation solution at a molar ratio of citric anhydride to alginate oligosaccharide of 1:2, and an esterification reaction was carried out at 100°C for 5 h under the catalysis of phosphoric acid with a mass ratio of 1% of the total mass of citric anhydride and alginate oligosaccharide. The esterification reaction was carried out under ultrasonic vibration at 40 kHz. After the reaction, the alginate grafted product was purified by anti-solvent precipitation method; the solvent used in the anti-solvent precipitation method was a mixed solvent of ethanol and acetone in a volume ratio of 4:1; (3) ‌Hydroxyethyltrimethylammonium chloride chitosan and N,N,N-trimethyl chitosan were mixed in a mass ratio of 1:1 to prepare chitosan quaternary ammonium salt; alginate grafted product and chitosan quaternary ammonium salt were respectively prepared in a mass ratio of 1:10 to prepare alginate grafted product solution and chitosan quaternary ammonium salt solution; the pH of the alginate grafted product solution was adjusted to 6.0-6.5 with NaOH / HCl, and the chitosan quaternary ammonium salt solution was added dropwise to the alginate grafted product solution in a molar ratio of 1:3 of alginate grafted product:chitosan quaternary ammonium salt in a water bath at 30°C for 3 h. The reaction was stirred continuously during the addition process. Intermittent ultrasonic assistance of 300 W was used during the reaction. The ultrasonic wave was run for 1 min and then stopped for 5 min, and then recycled until the ionic crosslinking reaction was completed to obtain an ionic crosslinked product; (4) Nanocellulose whiskers with a diameter of 20-50 nm were mixed with maltodextrin in a mass ratio of 1:1 to prepare a mixture with a mass concentration of 0.8 wt% as a physical crosslinker; the physical crosslinker was added to the ionic crosslinker in a mass ratio of 1:100, and the mixture was frozen at -20°C for 12 h and thawed at 25°C for 6 h, repeated twice, and the product was neutralized, filtered, and washed to obtain the product.

[0033] Comparative Example 1 A method for preparing a marine biomass amphoteric responsive polycarboxylate water reducer is different from the preparation method in Example 1 in that: after the hydrolyzate is obtained in step (1), it is not subjected to ultrafiltration treatment, but is directly neutralized, filtered, washed and dried to obtain alginate oligosaccharides; the remaining conditions and parameters are the same as those in Example 1.

[0034] Comparative Example 2 A method for preparing a marine biomass amphoteric responsive polycarboxylate water reducer is disclosed, which differs from the preparation method of Example 2 in that: on the basis of Example 2, the physical crosslinking of step (4) is not performed, and the ionic crosslinked product obtained in step (3) is directly neutralized, filtered and washed to obtain the product; the remaining conditions and parameters are the same as those of Example 1.

[0035] Comparative Example 3 A water reducing agent is sodium alginate without any modification treatment.

[0036] Comparative Example 4 A polycarboxylate water reducer is a commercially available polycarboxylate water reducer prepared with acrylic acid and polyether macromonomer as raw materials, and is sourced from China Construction Western Construction New Materials Technology Co., Ltd.

[0037] Experimental example (1) The water reducers in Examples 1 to 4 of the present invention and Comparative Examples 1 to 4 were treated with the same admixture formula (concentration of 14%, only the water reducer samples in the Examples and Comparative Examples were replaced in equal amounts, and the other components and proportions remained unchanged) and applied to C30 and C50 concrete to test the fluidity and mechanical strength of the concrete over time. The cement was Esheng's P·O 42.5 cement, the machine-made sand fineness modulus was 2.6, the crushed stone was a continuously graded crushed stone with a particle size of 5 to 25 mm, the fly ash was Class I fly ash, and the mineral powder was S95 mineral powder. The test method was based on GB / T50080-2016 "Standard for Test Methods of Ordinary Concrete Mixtures", GB / T50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete" and GB / T 50082-2024 "Standard for Test Methods of Long-term Performance and Durability of Concrete". The mix proportions and test results are detailed in Tables 1 and 2.

[0038] Table 1 C30 and C50 concrete mix ratio (kg / m 3 ) Table 2 Test table of C30 and C50 concrete at room temperature (Esheng Cement) From the data in Table 2, it can be seen that under the conditions of consistent admixture dosage and water consumption, the initial concrete fluidity of Examples 1 to 4 is better than that of Comparative Examples 1 to 4, and the slump loss rate after 3 hours is 2.5~4.9% (C30) and 3~9.2% (C50) lower than that of Comparative Example 4. In terms of mechanical properties, except for Comparative Example 2, the overall difference in 7d compressive strength between Examples 1 to 4 and Comparative Examples 1, 2, and 4 is small (±2 MPa). In terms of 28d strength, Examples 1 to 4 are 3~5 MPa (C30) and 3~9 MPa (C50) higher than Comparative Example 4. Compared with Comparative Examples 1 and 2, the concrete fluidity and compressive strength of Examples 1 to 4 are basically equivalent. Comparing Example 2 with Comparative Example 2, it can be found that the 3h loss of concrete in Comparative Example 2 is more obvious, whether in C30 or C50 concrete, and its 3h slump loss is more obvious. The rates of the concrete were increased by 4.2% (C30) and 6% (C50) compared to Example 2, respectively. This indicates that the introduction of nanocellulose whiskers and maltodextrin can reduce the slump loss of concrete. Furthermore, in Comparative Example 3, unmodified sodium alginate was directly used as a water reducer in the admixture. The slump and expansion at 3 hours were smaller than the initial loss, and the concrete setting time was significantly prolonged, not reaching the initial setting state after 24 hours. Furthermore, the concrete strength developed slowly, with the 7-day compressive strength being only 56.7% (C30) and 59% (C50) of that in Comparative Example 3, and the 28-day compressive strength being only 71.5% (C30) and 78.6% (C50) of that in Comparative Example 3.

[0039] Comparing the chloride ion migration coefficient (RCM method) data of each embodiment and comparative example, it can be seen that compared with comparative example 4, the chloride ion migration coefficient D of embodiments 1 to 4 and comparative examples 1 to 2 is RCM The values ​​decreased significantly, among which the chloride ion migration coefficient D RCM The value is from 5.56×10 -12 The maximum value of m² / s dropped to 2.98×10 -12 m² / s, decreased by as much as 46.4%; the chloride ion migration coefficient D in C50 concrete RCM The value is from 3.81×10 -12 The maximum value of m² / s is reduced to 1.88×10 -12 m² / s, a decrease of up to 50.7%. In addition, by comparing Examples 1-2 with Comparative Examples 1-2, it can be seen that the addition of ultrafiltration treatment and physical crosslinking steps in the preparation process can reduce the chloride ion migration coefficient of concrete. This shows that after the introduction of chitosan quaternary ammonium salt, nanocellulose whiskers and maltodextrin, the water reducer molecules strengthen the three-dimensional support network through the synergistic effect of electrostatic self-assembly and physical curing, while retaining the chloride ion curing performance of chitosan quaternary ammonium salt. By complexing or chemically reacting with the chloride ions in the concrete, the chloride ions are solidified inside the concrete, effectively reducing the mobility and corrosiveness of the chloride ions and improving the durability of the concrete structure.

[0040] (2) At the same time, the water reducers in Examples 1 to 4 of the present invention and Comparative Examples 1 to 4 were subjected to the same admixture formulation, C30 concrete mix ratio and test method as in Experimental Example (1) to study the adaptability and working performance of cements from four different manufacturers. The test results are detailed in Table 3.

[0041] Table 3 Test table of different types of cement C30 concrete at room temperature From the data in Table 3, it can be seen that under the conditions of consistent admixture dosage and water consumption, the initial concrete fluidity of cements from different manufacturers in Examples 1 to 4 and Comparative Example 1 is not much different, and the slump loss after 3 hours is controllable, and the slump loss rate basically fluctuates within the range of 4 to 9%, with small discreteness. However, after the cement in Comparative Example 3 was replaced, the initial and 3-hour fluidity loss of the concrete was large, and the slump loss rate basically fluctuated within the range of 8 to 17%, with a more obvious discreteness. This indicates that the -COO - With chitosan quaternary ammonium salt -N + (CH3)3 forms a dynamic ionic cross-linking network through electrostatic attraction, constructing a unique water reducer -COO - With -NH 3+The zwitterionic structure gives the water-reducing agent a wider pH adaptability range, enabling it to be adsorbed more quickly and stably on the surface of cement particles in concrete systems with different cement types and different mineral compositions, demonstrating good cement adaptability and working stability. In terms of mechanical properties, the overall difference in the 7-day and 28-day compressive strength of the examples and comparative examples is 2-6 MPa, both meeting the strength grade requirements. Among them, the compressive strength of comparative example 3 is lower overall due to slow setting.

[0042] Comparing Example 1 with Comparative Example 1, after removing the ultrafiltration treatment, the initial fluidity of the concrete in Comparative Example 1 fluctuated significantly under different manufacturers' cement systems, and the 3-hour fluidity loss was significantly greater than that of Example 1. Its slump loss rate increased from 4.7-6.8% to 9-14%. This indicates that the addition of ultrafiltration during the preparation of alginic acid oligosaccharides, which removed small molecule fragments, reduced the interference of small molecules on the interaction between the water reducer and cement particles, thereby further improving the adaptability and working stability of the cement. Comparing Example 2 with Comparative Example 2, the 3-hour fluidity loss of the concrete in Comparative Example 2 was greater under different manufacturers' cement systems, with the slump loss rate fluctuating between 7-15.6%. The degree of dispersion increased by 2-8.6% compared to Example 2 (5-7%). This indicates that the introduction of nanocellulose whiskers and maltodextrin into the water reducer molecular structure can achieve synergistic effects through low-temperature physical curing, achieve hydrogen bonding to strengthen the three-dimensional network stability, enhance adsorption stability, and further exert stronger electrostatic repulsion and steric hindrance effects, thereby significantly improving the fluidity of the concrete and reducing slump loss.

[0043] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a marine biomass amphoteric responsive polycarboxylate water reducer, characterized in that: The following steps are involved: (1) hydrolyzing sodium alginate with acid and purifying it by ultrafiltration to obtain alginate oligosaccharides; (2) pre-activating alginate oligosaccharides and then adding citric anhydride to carry out esterification reaction under the action of a catalyst, and obtaining an alginate grafted product after purification; (3) mixing the alginate grafted product and chitosan quaternary ammonium salt and performing an ion crosslinking reaction to obtain an ion crosslinked product; (4) Adding a physical crosslinking agent to the ionic crosslinked product, and then purifying it after freeze-thaw cycles to obtain the product.

2. The method for preparing the marine biomass amphoteric responsive polycarboxylate water reducer according to claim 1, wherein: The acid hydrolysis in step (1) comprises the following steps: dissolving sodium alginate in a mixed solution of acid and ethanol, adjusting the pH to 2.5-3, and hydrolyzing at 30-50° C. for 20-24 hours; the ultrafiltration pressure is 0.1-0.3 MPa, and the stirring rate is 200-300 r / min; the molecular weight of the alginate oligosaccharide is 3000-8000 Da.

3. The method for preparing the marine biomass amphoteric responsive polycarboxylate water reducer according to claim 2, wherein: The mass ratio of the sodium alginate and the mixed solution of acid and ethanol is 1:(18-22); each 1 L of the mixed solution of acid and ethanol contains 50-100 mL of ethanol and 0.05-0.2 mol of acid, and the acid is at least one of hydrochloric acid, formic acid and acetic acid.

4. The method for preparing the marine biomass amphoteric responsive polycarboxylate water reducer according to claim 1, wherein: The preactivation in step (2) is carried out using a preactivation reagent, which is at least one of N,N-dicyclohexylcarbodiimide, N,N-dimethylformamide, N,N-dimethylacetamide, N,N-dimethylacrylamide and tetrahydrofuran, and the preactivation time is 0.5 to 1.5 h.

5. The method for preparing the marine biomass amphoteric responsive polycarboxylate water reducer according to claim 1, wherein: In step (2), the molar ratio of alginate oligosaccharides to citric anhydride is 1.5-2:1; the catalyst is at least one of p-toluenesulfonic acid, trifluoromethanesulfonic acid, phosphoric acid and boric acid; the esterification reaction is carried out under ultrasonic vibration of 20-40 kHz, the esterification reaction temperature is 100-120° C., and the time is 3-5 h.

6. The method for preparing the marine biomass amphoteric responsive polycarboxylate water reducer according to claim 5, wherein: The mass of the catalyst is 0.8-1.2% of the total mass of citric anhydride and alginate oligosaccharide.

7. The method for preparing the marine biomass amphoteric responsive polycarboxylate water reducer according to claim 1, wherein: In the step (3), the molar ratio of the alginate grafted product to the chitosan quaternary ammonium salt is 1:2.5-3.5; the ionic crosslinking reaction conditions are: stirring the reaction for 2-4 hours in a water bath at 25-30°C and a pH of 6.0-6.5, using intermittent ultrasound assistance at 200-400W during the reaction, running the ultrasound for 1-2 minutes and then stopping for 5-7 minutes, and then recirculating until the reaction is completed.

8. The method for preparing the marine biomass amphoteric responsive polycarboxylate water reducer according to claim 7, wherein: The chitosan quaternary ammonium salt is at least one of N,N,N-trimethyl chitosan, hydroxyethyl trimethyl ammonium chloride chitosan, hydroxypropyl trimethyl ammonium chloride chitosan and carboxymethyl chitosan quaternary ammonium salt.

9. The method for preparing the marine biomass amphoteric responsive polycarboxylate water reducer according to claim 1, wherein: In the step (4), the physical crosslinking agent is a mixture of nanocellulose whiskers and maltodextrin; the mass ratio of the physical crosslinking agent to the ionic crosslinker is 0.5-1:100; and the freeze-thaw cycle conditions are: freezing at -20--18°C for 10-12 h, thawing at 20-25°C for 5-7 h, and repeating 2-3 times.

10. The marine biomass amphoteric responsive polycarboxylate water reducer prepared by the preparation method according to any one of claims 1 to 9.

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