Environment-friendly water-based cutting fluid and preparation method thereof

Abstract

This invention relates to the field of metalworking fluid technology, specifically to an environmentally friendly water-based cutting fluid and its preparation method; it is composed of the following components in parts by weight: 100 parts deionized water; 1.5-3.5 parts carboxymethyl chitosan; 0.3-1.0 parts lauroyl arginine ethyl ester; 0.5-1.5 parts silver-loaded nano-hydroxyapatite; 3-6 parts triethanolamine borate; 1-3 parts sebacic acid; 15-25 parts polyethylene glycol 400; and 0.05-0.2 parts silicone defoamer; the silver loading in the silver-loaded nano-hydroxyapatite is 1-3 wt%; and the degree of substitution of the carboxymethyl chitosan is 0.6-0.9. This invention kills bacteria by electrostatically adsorbing onto the negatively charged bacterial cell membrane surface, altering cell membrane permeability, and causing leakage of intracellular substances. Carboxymethyl chitosan and LAE have complementary antibacterial mechanisms; the former mainly destroys the cell wall, while the latter mainly acts on the cell membrane, resulting in a synergistic antibacterial effect.

Description

Technical Field

[0001] This invention relates to the field of metalworking fluid technology, specifically to an environmentally friendly water-based cutting fluid and its preparation method. Background Technology

[0002] Water-based cutting fluids are widely used in machining processes such as cutting, milling, and drilling due to their excellent cooling performance, low operating costs, and low fire safety risks. With increasingly stringent environmental regulations, sulfur-free, phosphorus-free, and chlorine-free environmentally friendly water-based cutting fluids are becoming the industry trend. However, existing technologies still have the following common shortcomings: First, water-based cutting fluids are prone to the growth of large amounts of bacteria or fungi during use. Bacterial proliferation leads to a series of problems: it decomposes additives in the cutting fluid, disrupting their stability; it consumes emulsifiers, causing the oil phase to separate and reducing its concentration; and it releases aerobic bacteria. This causes the pH value to drop, which in turn reduces the rust-preventive properties and further promotes bacterial growth. Microbial growth is the main cause of cutting fluid deterioration and foul odor, seriously affecting the service life of the cutting fluid.

[0003] Second, existing technologies typically employ the addition of bactericides to inhibit microbial growth. However, traditional bactericides have the following shortcomings: Firstly, some bactericides (such as phenols and formaldehyde-releasing bactericides) are toxic to humans, causing health damage to the skin and respiratory tract of operators; secondly, there is a lack of synergistic effect between bactericides and rust inhibitors, with bactericides often only focusing on killing microorganisms and contributing nothing to rust prevention, and may even weaken the rust prevention effect by altering the pH of the system; furthermore, the antibacterial components in existing technologies are mostly consumable—as the usage time increases, the bactericide is continuously consumed, and the antibacterial ability gradually declines, making it difficult to achieve long-lasting antibacterial effects; in view of this, we propose an environmentally friendly water-based cutting fluid and its preparation method. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings mentioned in the background art and provide an environmentally friendly water-based cutting fluid and its preparation method.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: An environmentally friendly water-based cutting fluid, comprising the following components in parts by weight: 100 parts deionized water; 1.5–3.5 parts of carboxymethyl chitosan; 0.3–1.0 parts of lauroyl arginine ethyl ester; 0.5–1.5 parts of silver-loaded nano-hydroxyapatite; 3-6 parts of triethanolamine borate ester; Sebacic acid 1-3 parts; 15-25 parts of polyethylene glycol 400; 0.05–0.2 parts of silicone defoamer; The silver loading in the silver-loaded nano-hydroxyapatite is 1–3 wt%. The degree of substitution of the carboxymethyl chitosan is 0.6 to 0.9; The cutting fluid has a Zeta potential of -15 to -30 mV at 25°C, and the average particle size measured by dynamic light scattering is ≤200 nm, indicating that the system is in a uniform and stable colloidal dispersion state, without obvious microphase separation or precipitation caused by anion and cation complexation.

[0006] Preferably, the silver-loaded nano-hydroxyapatite has a particle size of 50–100 nm and is prepared by the following method: (1) and Dissolved in deionized water at a Ca / P molar ratio of 1.67:1, and then in a 40°C water bath... The solution was slowly dripped in. In the solution, ammonia water was added dropwise to maintain the pH at 10-11. The mixture was stirred for 2 hours, aged for 24 hours, and then centrifuged and washed to obtain nano-hydroxyapatite. (2) Disperse the nano-hydroxyapatite in In solution, Ag + The concentration was 0.01–0.05 mol / L. Ion exchange reaction was carried out for 4 hours under light-protected conditions, followed by centrifugation and washing until no Ag was found. + The silver-loaded nano-hydroxyapatite was obtained by drying at 60℃ for 12 hours.

[0007] Preferably, the lauroyl arginine ethyl ester is lauroyl arginine ethyl ester hydrochloride with a purity ≥98%.

[0008] Preferably, the carboxymethyl chitosan has a weight-average molecular weight of 3000-5000 Da and a degree of substitution of 0.7-0.85.

[0009] Preferably, the weight-average molecular weight of the polyethylene glycol 400 is 380–420 Da.

[0010] Preferably, the organosilicon defoamer is a polydimethylsiloxane emulsion with a solid content of 30-40%.

[0011] Preferably, the cutting fluid has a pH value of 8.5 to 9.5.

[0012] A method for preparing an environmentally friendly water-based cutting fluid includes the following steps: Step 1: Add deionized water to the reaction vessel and heat to 45-55℃; Step 2: Add carboxymethyl chitosan and stir until completely dissolved; Step 3: Add polyethylene glycol 400 and triethanolamine borate, and stir until completely dissolved; Step 4: Add sebacic acid and stir until completely dissolved; Step 5: Add silver-loaded nano-hydroxyapatite and ultrasonically disperse for 20-30 minutes. The ultrasonic power is 200-400W and the frequency is 40-60kHz. Step 6: After cooling the system to room temperature, add ethyl lauroyl arginine and silicone defoamer under stirring. Add ethyl lauroyl arginine slowly at a rate of 1-3 mL / min while stirring rapidly at 400-600 rpm. After the addition is complete, continue stirring for 10-15 minutes to obtain the environmentally friendly water-based cutting fluid.

[0013] Preferably, in step six, lauroyl arginine ethyl ester is added slowly dropwise at a rate of 2 mL / min, with a stirring speed of 500 rpm.

[0014] An application of an environmentally friendly water-based cutting fluid in metal cutting processes, wherein the cutting fluid is diluted with deionized water to a working fluid concentration of 3-8% by mass, and is suitable for light to medium load cutting, milling and drilling of cast iron, carbon steel and aluminum alloys.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. In this invention, the amino groups on the carboxymethyl chitosan molecular chain can interact with bacterial cell membranes, disrupting the integrity of the bacterial cell wall and exerting antibacterial activity. Lauroyl arginine ethyl ester (LAE) is a cationic surfactant with broad-spectrum inhibitory effects on Gram-positive bacteria, Gram-negative bacteria, yeast, and molds. Its mechanism of action is to electrostatically adsorb onto the negatively charged bacterial cell membrane surface, altering cell membrane permeability and causing leakage of intracellular substances, thereby killing bacteria. Carboxymethyl chitosan and LAE are complementary in their antibacterial mechanisms; the former mainly disrupts the cell wall, while the latter mainly acts on the cell membrane, resulting in a synergistic antibacterial effect. This invention optimizes the feeding sequence—slowly adding LAE dropwise after carboxymethyl chitosan at a high dilution ratio while simultaneously engaging in rapid stirring—and utilizes a kinetic control strategy to suppress aggregation and precipitation caused by electrostatic complexation. This allows anionic carboxymethyl chitosan and cationic LAE to coexist stably in the same system, imparting immediate antibacterial properties to the cutting fluid while maintaining the system's homogeneity and transparency. DLS and Zeta potential data confirm the absence of microphase separation within the system.

[0016] 2. Hydroxyapatite (HAp) belongs to the hexagonal crystal system and has relatively large channels parallel to the c-axis in its crystal structure. Ag + It can replace part of Ca through ion exchange 2+ Silver-loaded nano-hydroxyapatite enters the lattice of hydroxyapatite and slowly releases Ag into the cutting fluid.+ Ag + It binds to the thiol group (-SH) of enzyme proteins in bacterial cells, inactivating the enzyme and continuously inhibiting microbial growth. This mechanism solves the problem of "one-time consumption" of traditional bactericides and achieves long-lasting antibacterial effect.

[0017] 3. Silver-loaded nano-hydroxyapatite exhibits a significant synergistic enhancing effect on rust prevention, and its mechanism may involve Ca... 2+ / 3- Multiple factors, including corrosion-inhibiting release and the physical deposition and coverage of nanoparticles on the metal surface, contribute to the release of Ag from hydroxyapatite. + At the same time, slowly release Ca 2+ and 3- Ca 2+ It can form complexes with rust-inhibiting anions in cutting fluid (such as borate ester anions and sebacic acid ions), deposit on the micro-anodic region of the metal surface, and inhibit electrochemical corrosion; 3- It can participate in the formation of phosphate conversion film on the metal surface, enhancing the rust prevention effect. Thus, silver-loaded nano-hydroxyapatite achieves "one agent, two effects", providing both slow-release antibacterial function and rust prevention by releasing calcium and phosphate ions, overcoming the shortcomings of traditional bactericides that only kill bacteria and do not prevent rust, or even kill bacteria and damage rust prevention.

[0018] 4. Triethanolamine borate and sebacic acid form a dense passivation film on the metal surface. Carboxymethyl chitosan, as a polymeric film-forming agent, is adsorbed on the metal surface to form a basic protective layer. Silver-loaded nano-hydroxyapatite particles are dispersed in the system and continuously release antibacterial and anti-rust ions, forming a "self-replenishing" long-term protective system. Triethanolamine borate also acts as a pH buffer, maintaining the cutting fluid pH in the weakly alkaline range of 8.5 to 9.5, which is beneficial for rust prevention and unfavorable for the growth and reproduction of most bacteria. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Unless otherwise specified, the raw materials used in the embodiments of this invention can all be obtained commercially: Carboxymethyl chitosan (degree of substitution 0.6-0.9, weight average molecular weight 3000-5000 Da): purchased from Hubei Shiteng Chemical Technology Co., Ltd., industrial grade, purity ≥99%; Lauroyl arginine ethyl ester hydrochloride (purity ≥98%): purchased from Chengdu Aofei Biochemicals Co., Ltd.; Triethanolamine borate ester (effective content ≥99%): purchased from Shandong Yukang Chemical Co., Ltd., industrial grade; Sebacic acid (content ≥99.5%): purchased from Hebei Kaide Biomaterials Co., Ltd. (a wholly-owned subsidiary of Arkema Group), industrial grade; Polyethylene glycol 400 (weight average molecular weight 380-420 Da): purchased from Jiangsu Haian Petrochemical Plant, industrial grade; Organosilicon defoamer (polydimethylsiloxane emulsion, solid content 30-40%): purchased from Dow Corning (Shanghai) Co., Ltd., DC-544 type; Silver nitrate (AgNO3, analytical grade): purchased from Sinopharm Chemical Reagent Co., Ltd.; Calcium nitrate ( (Analytical grade): purchased from Sinopharm Chemical Reagent Co., Ltd.; diammonium hydrogen phosphate ( (Analytical grade): purchased from Sinopharm Chemical Reagent Co., Ltd.; Ammonia water (NH3·H2O, analytical grade): purchased from Sinopharm Chemical Reagent Co., Ltd.

[0021] Preparation of silver-loaded nano-hydroxyapatite (general method): (1) and Dissolved in deionized water at a Ca / P molar ratio of 1.67:1, and then in a 40°C water bath... The solution was slowly added dropwise at a rate of 5 mL / min. Ammonia was added dropwise to the solution to maintain pH 10.5. The mixture was stirred for 2 hours, aged for 24 hours, and then centrifuged and washed until neutral to obtain nano-hydroxyapatite (particle size approximately 80 nm). (2) Disperse the nano-hydroxyapatite in AgNO3 solution (Ag + In a solution of 0.03 mol / L, an ion exchange reaction was carried out for 4 hours under light-protected conditions, followed by centrifugation and washing until no Ag was found. + The silver was detected (using NaCl solution), and dried at 60°C for 12 hours to obtain silver-loaded nano-hydroxyapatite (silver loading of approximately 2 wt%).

[0022] XRD characterization of silver-loaded nano-hydroxyapatite confirmed a change in lattice parameters (Ag). + Radius greater than Ca 2+ The cell volume expansion is approximately 1.2–1.8%, and there is no Ag₂O impurity phase, indicating that Ag… +The silver has entered the hydroxyapatite lattice and is not merely a surface physical adsorption. The Ca / P molar ratio of the product, as determined by ICP-AES, is 1.65–1.67, which is consistent with the stoichiometric composition range of hydroxyapatite. The total silver content, as determined by ICP-MS digestion, is 1.9–2.1 wt%, consistent with the expected feed composition.

[0023] The silver-loaded nano-hydroxyapatite used in the following examples was prepared according to the above method.

[0024] The present invention will describe the above technical solution in detail through the following embodiments: Example 1

[0025] An environmentally friendly water-based cutting fluid, comprising the following components in parts by weight: 100 parts deionized water; 2.5 parts carboxymethyl chitosan (degree of substitution 0.75, weight average molecular weight 4000 Da); 0.6 parts lauroyl arginine ethyl ester hydrochloride (purity 99%); 1.0 part silver-loaded nano-hydroxyapatite (silver loading 2wt%); 4.5 parts triethanolamine borate; 2.0 parts sebacic acid; 20 parts polyethylene glycol 400 (weight average molecular weight 400 Da); 0.1 parts organosilicon defoamer (polydimethylsiloxane emulsion, solid content 35%).

[0026] The preparation method includes the following steps: Step 1: Add deionized water to the reaction vessel and heat to 50°C; Step 2: Add carboxymethyl chitosan and stir at 300 rpm until completely dissolved (about 20 minutes). Step 3: Add polyethylene glycol 400 and triethanolamine borate, and stir at 300 rpm until completely dissolved (about 10 minutes). Step 4: Add sebacic acid and stir at 300 rpm until completely dissolved (about 10 minutes). Step 5: Add silver-loaded nano-hydroxyapatite and ultrasonically disperse for 25 minutes (ultrasonic power 300W, frequency 50kHz). Step 6: After cooling the system to room temperature, add lauroyl arginine ethyl hydrochloride and silicone defoamer under stirring. Add lauroyl arginine ethyl hydrochloride slowly at a rate of 2 mL / min while stirring rapidly at 500 rpm. After the addition is complete, continue stirring for 10 minutes to obtain the environmentally friendly water-based cutting fluid.

[0027] The resulting cutting fluid was a uniform, transparent, pale yellow liquid with a pH of 9.0. Dynamic light scattering (DLS) analysis showed an average particle size of 85 nm and a zeta potential of -22 mV, confirming that the system was a homogeneous and stable colloidal dispersion.

[0028] Example 2

[0029] An environmentally friendly water-based cutting fluid, comprising the following components in parts by weight: 100 parts deionized water; 1.5 parts carboxymethyl chitosan (degree of substitution 0.70, weight average molecular weight 3500 Da); 0.3 parts lauroyl arginine ethyl ester hydrochloride (purity 98%); 0.5 parts silver-loaded nano-hydroxyapatite (silver loading 1 wt%); 3.0 parts triethanolamine borate; 1.0 part sebacic acid; 15 parts polyethylene glycol 400 (weight average molecular weight 400 Da); 0.05 parts silicone defoamer (polydimethylsiloxane emulsion, solid content 30%).

[0030] The preparation method is the same as in Example 1. The resulting cutting fluid is a uniform, transparent, pale yellow liquid with a pH of 8.7, an average DLS particle size of 92 nm, and a Zeta potential of -18 mV.

[0031] Example 3

[0032] An environmentally friendly water-based cutting fluid, comprising the following components in parts by weight: 100 parts deionized water; 3.5 parts carboxymethyl chitosan (degree of substitution 0.85, weight average molecular weight 4500 Da); 1.0 part lauroyl arginine ethyl ester hydrochloride (purity 99%); 1.5 parts silver-loaded nano-hydroxyapatite (silver loading 3wt%); 6.0 parts triethanolamine borate; 3.0 parts sebacic acid; 25 parts polyethylene glycol 400 (weight average molecular weight 400 Da); 0.2 parts silicone defoamer (polydimethylsiloxane emulsion, solid content 40%).

[0033] The preparation method is the same as in Example 1. The resulting cutting fluid is a uniform, transparent, pale yellow liquid with a pH of 9.3, an average DLS particle size of 78 nm, and a Zeta potential of -25 mV.

[0034] Example 4

[0035] An environmentally friendly water-based cutting fluid, comprising the following components in parts by weight: 100 parts deionized water; 3.0 parts carboxymethyl chitosan (degree of substitution 0.80, weight average molecular weight 4200 Da); 0.8 parts lauroyl arginine ethyl ester hydrochloride (purity 98%); 1.2 parts silver-loaded nano-hydroxyapatite (silver loading 2.5 wt%); 5.0 parts triethanolamine borate; 2.5 parts sebacic acid; 22 parts polyethylene glycol 400 (weight average molecular weight 400 Da); 0.15 parts silicone defoamer (polydimethylsiloxane emulsion, solid content 35%).

[0036] The preparation method is the same as in Example 1. The resulting cutting fluid is a uniform, transparent, pale yellow liquid with a pH of 9.1, an average DLS particle size of 82 nm, and a Zeta potential of -23 mV.

[0037] Comparative Example 1 The difference from Example 1 is that silver-loaded nano-hydroxyapatite is not added, while the remaining components and amounts are exactly the same as in Example 1, and the preparation method is the same as in Example 1.

[0038] Comparative Example 2 The difference from Example 1 is that carboxymethyl chitosan and lauroyl arginine ethyl ester are not added, while the remaining components and amounts are exactly the same as in Example 1, and the preparation method is the same as in Example 1.

[0039] Comparative Example 3 The difference from Example 1 is that an equal amount of nano-hydroxyapatite (without silver loading, prepared in the same way as step (1) of the preparation method of silver-loaded nano-hydroxyapatite) is used to replace silver-loaded nano-hydroxyapatite. The remaining components and amounts are exactly the same as in Example 1, and the preparation method is the same as in Example 1.

[0040] Comparative Example 4 The difference from Example 1 is that an equal amount of silver nitrate (AgNO3, added directly) was used instead of silver-loaded nano-hydroxyapatite. The remaining components and amounts were exactly the same as in Example 1, and the preparation method was the same. In Comparative Example 4, a slight brown turbidity was observed during preparation. After standing for 12 hours, a trace amount of brown precipitate appeared at the bottom. After filtration, the supernatant was used for subsequent testing. This phenomenon is similar to that observed with Ag... + The chemical rules for the formation of Ag2O under alkaline conditions are consistent, and the direct addition of AgNO3 has poor compatibility with the system.

[0041] Test case The cutting fluids of Examples 1-4 and Comparative Examples 1-4 were diluted with deionized water to a working fluid concentration of 5% by mass, and the following performance tests were performed: I. pH value measurement The pH values ​​of each working fluid were determined according to the method specified in GB / T 6144-2010 "Synthetic Cutting Fluids". A pH meter with an accuracy of 0.01 was used to measure the pH value at 25°C. The results are shown in Table 1.

[0042] II. Rust prevention performance test The tests were conducted according to the single-piece rust prevention test and stacked-piece rust prevention test methods for cast iron specified in GB / T 6144-2010 "Synthetic Cutting Fluids".

[0043] (a) Rust prevention test of single piece of cast iron Experimental steps: (1) Grind the cast iron test piece (HT200, diameter 50mm, thickness 3-5mm) with 200# sandpaper until the surface roughness Ra≤0.8μm, clean it with distilled water and anhydrous ethanol in sequence, and blow it dry for later use; (2) Add the working solution to be tested to the surface of the test piece, so that the surface of the test piece is completely wetted, and place it in a constant temperature and humidity chamber at 35℃±2℃ and relative humidity≥95%; (3) Observe the rust on the surface of the test piece every 8 hours and record the time when the first rust spot appears, which is the rust prevention time of a single piece.

[0044] (ii) Rust prevention test of cast iron laminations Experimental steps: (1) Treat the two cast iron test pieces as described above; (2) Apply the working solution to be tested evenly to the working surface of the test piece, put the working surfaces of the two test pieces together, and clamp them with a clamp; (3) Place it in a constant temperature and humidity chamber at 35℃±2℃ and relative humidity ≥95%; (4) Observe the corrosion of the bonding surface of the test piece every 8 hours and record the time when corrosion occurs. This is the rust prevention time of the stacked pieces. The results are shown in Table 1.

[0045] Table 1

[0046] Table 1 shows that the single-piece rust prevention time of Examples 1-4 is ≥60 hours, and the stacked rust prevention time is ≥36 hours. Among them, the single-piece rust prevention time of Examples 1, 3, and 4 is ≥72 hours, and the stacked rust prevention time is ≥48 hours. The rust prevention performance of Comparative Example 1 (without silver-loaded nano-hydroxyapatite) is significantly reduced (single-piece rust prevention time is only ≥48 hours), indicating that silver-loaded nano-hydroxyapatite has a significant synergistic enhancing effect on rust prevention performance. Its mechanism may involve Ca 2+ / PO4 3- The corrosion inhibition performance of Comparative Example 3 (using un-silver-loaded nano-hydroxyapatite instead of silver-loaded nano-hydroxyapatite) decreased compared to the examples, but its corrosion inhibition performance was still better than Comparative Example 1. This indicates that un-silver-loaded nano-hydroxyapatite itself has a certain auxiliary corrosion inhibition effect (possibly due to the physical deposition coverage of nanoparticles), and the silver loading process did not weaken its auxiliary corrosion inhibition function. The corrosion inhibition performance of Comparative Example 4 (direct addition of AgNO3) was comparable to that of the examples, but the system's appearance stability was poor (see appearance observation results).

[0047] III. Four-ball friction test Tribological properties were tested in accordance with GB / T 3142-2019 "Determination of Lubricant Carrying Capacity - Four-Ball Method".

[0048] Test conditions: MRS-10A testing machine; GCr15 steel ball material, 12.7mm diameter; rotation speed 1450r / min; room temperature; loading time 10s; test time 60s.

[0049] The maximum non-seize load (PB value) and wear scar diameter (WSD, under a load of 392 N for 60 s) were measured. The results are shown in Table 2.

[0050] Table 2 Results of the four-ball friction test

[0051] As shown in Table 2, the PB values ​​of Examples 1 to 4 are all ≥588N, with Examples 1, 3, and 4 reaching 686N and wear scar diameter ≤0.58mm. This indicates that the cutting fluid of the present invention has good extreme pressure lubrication performance and is suitable for light to medium load cutting of cast iron, carbon steel, and aluminum alloys. Comparative Example 1 (without silver-loaded nano-hydroxyapatite) has the lowest PB value (549N) and the largest wear scar diameter (0.62mm), indicating that silver-loaded nano-hydroxyapatite also has a certain synergistic enhancing effect on lubrication performance.

[0052] IV. Antibacterial Performance Test The antimicrobial performance was tested according to the film application method recommended in ASTM E2275-14, "Standard Practice for Evaluating the Efficacy of Antimicrobial Agents in Aqueous Metalworking Fluids".

[0053] Test bacteria: Escherichia coli (ATCC 25922) and Staphylococcus aureus (ATCC 6538).

[0054] Experimental steps: (1) Each working solution sample was coated onto the surface of a sterile glass slide (approximately 0.5 mL / slide) and allowed to dry naturally under sterile conditions to form a film. (2) The test strain was activated and cultured on nutrient agar medium at 37℃±1℃ for 24 hours. A bacterial suspension was prepared using sterile physiological saline and the concentration was adjusted to 10. 5 ~10 6 CFU / mL; (3) Add 0.2 mL of bacterial suspension evenly to the surface of the coated test piece, and cover it with a sterile polyethylene film (40 mm × 40 mm) to spread the bacterial suspension evenly. (4) Place in a constant temperature incubator at 37℃±1℃ and relative humidity≥90% for 24 hours; (5) After the culture is completed, the test strip and the covering film are placed in an Erlenmeyer flask containing 20 mL of sterile physiological saline, shake thoroughly to elute, take the eluent for serial dilution, and use the plate counting method to determine the number of viable bacteria; (6) Use sterile glass slides without cutting fluid as blank controls and operate in the same way; (7) The antibacterial rate is calculated using the following formula: Antibacterial rate (R) = (C0-C1) / C0×100%.

[0055] Wherein, C0 is the average colony count (CFU) of the blank control sample after 24 hours, and C1 is the average colony count (CFU) of the sample. The results are shown in Table 3.

[0056] Table 3

[0057] As shown in Table 3, the antibacterial rates of Examples 1-4 against *Escherichia coli* and *Staphylococcus aureus* were all ≥99.0%, with Examples 1, 3, and 4 showing antibacterial rates ≥99.2%. The antibacterial rate of Comparative Example 2 (without carboxymethyl chitosan and LAE) was ≤10%, indicating that carboxymethyl chitosan and LAE are the core contributing components to the immediate antibacterial performance of this invention. The antibacterial rate of Comparative Example 3 (using unloaded nano-hydroxyapatite instead of silver-loaded nano-hydroxyapatite) was ≥90%, indicating that nano-hydroxyapatite itself has certain physical antibacterial activity (possibly related to the surface effect of nanoparticles), but the antibacterial performance was significantly improved to ≥99.2% after silver loading. The immediate antibacterial performance of Comparative Examples 1 and 4 was comparable to that of the Examples, indicating that silver-loaded nano-hydroxyapatite showed no significant difference in immediate antibacterial effect compared to traditional silver ion antibacterial methods, but its sustained-release characteristics offered an advantage in terms of service life.

[0058] V. Silver Ion Sustained-Release Performance Test Ag in the working solution was determined by inductively coupled plasma mass spectrometry (ICP-MS, according to US EPA Method 6020B). + Concentration. Sample pretreatment: Take 5 mL of working solution sample from each time point, add 2 mL of concentrated nitric acid (HNO3) and 1 mL of 30% hydrogen peroxide (H2O2), digest on a 120℃ hot plate until nearly dry, and then dilute to 25 mL with 2% dilute nitric acid to completely convert particulate silver into dissolved Ag. + Further measurements were then taken. The cutting fluid working fluids (5% diluted solution) of Example 1 and Comparative Example 4 were placed in open containers and placed at room temperature (25℃±2℃). Samples were taken periodically for measurement, and the results are shown in Table 4.

[0059] Table 4. Test results of silver ion sustained-release performance (Ag) + Concentration, mg / L

[0060] Note: Ag in Table 4 + The concentration refers to the total silver content measured after acid digestion of the sample, reflecting the dissolved Ag in the working solution.+ The total silver concentration is the sum of the silver that can be released from the silver-loaded nanoparticles. The theoretical total silver concentration in Example 1 is approximately 10 mg / L (the concentration of silver-loaded particles in 5% working solution is approximately 500 mg / L × 2% silver loading), but the Ag in Table 4 within 180 days... + The concentration was only 1.5–2.0 mg / L, indicating that most of the silver remained in the nano-hydroxyapatite lattice and had not yet been released, confirming the sustained-release characteristics of the material.

[0061] As shown in Table 4, the Ag in the silver-loaded nano-hydroxyapatite in Example 1 + Ag exhibits a continuous and slow release trend in cutting fluids, with Ag being released within 30 days. + The concentration was gradually increased from 0.5 mg / L to 1.8 mg / L, and Ag was observed within 60 to 180 days. + The concentration fluctuated within the range of 1.5–2.0 mg / L, and 1.5 mg / L was still detectable after 180 days. In contrast, Comparative Example 4 (direct addition of AgNO3) showed a significantly lower concentration of Ag. + The concentration dropped to 0.1 mg / L within 7 days and was undetectable after 14 days. This indicates that silver-loaded nano-hydroxyapatite has good silver ion sustained-release properties, which can achieve long-term antibacterial effect; while the silver ions added directly with AgNO3 are rapidly consumed and cannot provide long-term antibacterial protection.

[0062] VI. Service life test Based on the principles of ASTM D3946-13 "Standard Practice for Evaluating the Antimicrobial Efficacy of Metalworking Fluids", the following specific parameters were used for testing, taking into account laboratory conditions.

[0063] Experimental steps: (1) Place each working solution (5% dilution) into a sterile Erlenmeyer flask, 500 mL per flask; (2) Ventilate for 8 hours a day (ventilation rate 0.5L / min) to simulate the circulating use of cutting fluid; (3) Inoculate weekly with a mixed bacterial solution (containing Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa, with an initial concentration of approximately 10). 5 (CFU / mL) (4) Take samples once a week to determine the pH value, total bacterial count (plate counting method) and rust prevention performance (single-piece rust prevention test) of the working solution. (5) Stop the test when the working solution shows any of the following failure criteria: ① Total bacterial count > 10 6 CFU / mL; ② The working solution shows obvious odor, discoloration, or stratification; ③ The rust prevention time of a single piece is <24 hours; (6) Record the time from the start of the test to the failure, which is the service life. The results are shown in Table 5.

[0064] Table 5

[0065] As shown in Table 5, Examples 1 to 4 performed excellently in the service life test. Examples 1, 3, and 4 did not fail within the 8-month test period (the test was terminated rather than failed). Example 2 did not fail within the 6-month test period, which was significantly longer than Comparative Example 1 (2.5 months), Comparative Example 2 (1.0 month), Comparative Example 3 (3.0 months), and Comparative Example 4 (1.5 months).

[0066] Comparative Example 2, lacking the antibacterial protection of carboxymethyl chitosan and LAE, experienced rapid bacterial proliferation leading to a foul odor and failure of the working solution (within only 1 month); Comparative Example 1, lacking the calcium-supplementing and rust-preventing function of silver-loaded nano-hydroxyapatite, saw its rust-preventing performance fail before its antibacterial performance (2.5 months); Comparative Example 3, lacking the continuous release of silver ions, had insufficient physical antibacterial activity of the nano-hydroxyapatite itself, and its antibacterial performance was insufficient to inhibit bacterial growth after 3 months; Comparative Example 4, although initially containing Ag... + The concentration is the same as in Example 1, but Ag + It was quickly depleted (undetectable after 14 days), and then bacteria multiplied rapidly, causing the working solution to become ineffective after 1.5 months.

[0067] Example 1 utilizes the dual protection of immediate antibacterial properties of "carboxymethyl chitosan + LAE" and sustained-release antibacterial properties of "silver-loaded nano-hydroxyapatite," as well as the release of Ca from hydroxyapatite. 2+ and PO4 3- The continuous replenishment of rust-preventive properties achieves a synergistic and long-lasting effect of antibacterial and rust-preventive properties.

[0068] VII. Observation of the appearance and stability of the working fluid This observation used newly prepared independent samples (not samples that had failed in the service life test), which were placed in transparent glass bottles and observed at room temperature (25℃±2℃). The changes in appearance were recorded, and the results are shown in Table 6.

[0069] Table 6

[0070] As shown in Table 6, Examples 1-4 maintained a uniform, transparent, pale yellow liquid state throughout the 90-day standing observation period, without stratification, precipitation, or discoloration, indicating that the cutting fluid of the present invention has excellent storage stability. Comparative Example 4 showed a trace amount of brown precipitate immediately after preparation. After filtration, its initial appearance was transparent pale yellow, but after 90 days, slight turbidity and brown precipitate appeared at the bottom, which is related to Ag... +The chemical pattern of Ag2O formation under alkaline conditions is consistent with that of silver, further indicating that loading silver onto a hydroxyapatite support has better system compatibility and stability than directly adding silver salts.

[0071] The data in the table above shows that the environmentally friendly water-based cutting fluids prepared in Examples 1-4 of this invention exhibit superior performance in rust prevention (single-piece rust prevention ≥ 60 hours, stacked-piece rust prevention ≥ 36 hours), tribological properties (PB value ≥ 588 N, wear scar diameter ≤ 0.58 mm), antibacterial properties (antibacterial rate against Escherichia coli and Staphylococcus aureus ≥ 99.0%), and silver ion sustained-release properties (Ag within 180 days). + The solution exhibits excellent performance in terms of concentration fluctuation within the range of 1.5–2.0 mg / L, service life (≥6 months), and working fluid stability (uniformly transparent and non-stratifying within 90 days). Comparative data show that the dual functions of "slow-release antibacterial and calcium-supplementing rust prevention" of silver-loaded nano-hydroxyapatite, the synergistic antibacterial effect of carboxymethyl chitosan and LAE, and the synergistic cooperation among the components together constitute the long-lasting antibacterial and long-lasting rust prevention properties of the cutting fluid of this invention. This invention effectively solves the technical problems of existing water-based cutting fluids, such as the difficulty in synergistic antibacterial and rust prevention, rapid consumption of antibacterial components, and short service life.

[0072] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. An environmentally friendly water-based cutting fluid, characterized in that: It consists of the following components in parts by weight: 100 parts deionized water; 1.5–3.5 parts of carboxymethyl chitosan; 0.3–1.0 parts of lauroyl arginine ethyl ester; 0.5–1.5 parts of silver-loaded nano-hydroxyapatite; 3-6 parts of triethanolamine borate ester; Sebacic acid 1-3 parts; 15-25 parts of polyethylene glycol 400; 0.05–0.2 parts of silicone defoamer; The silver loading in the silver-loaded nano-hydroxyapatite is 1–3 wt%. The degree of substitution of the carboxymethyl chitosan is 0.6 to 0.9; The cutting fluid has a Zeta potential of -15 to -30 mV at 25°C, and the average particle size measured by dynamic light scattering is ≤200 nm.

2. The environmentally friendly water-based cutting fluid as described in claim 1, characterized in that: The silver-loaded nano-hydroxyapatite has a particle size of 50–100 nm and is prepared by the following method: (1) and Dissolved in deionized water at a Ca / P molar ratio of 1.67:1, and then in a 40°C water bath... The solution was slowly dripped in. In the solution, ammonia water was added dropwise to maintain the pH at 10-11. The mixture was stirred for 2 hours, aged for 24 hours, and then centrifuged and washed to obtain nano-hydroxyapatite. (2) Disperse the nano-hydroxyapatite in In solution, Ag + The concentration was 0.01–0.05 mol / L. Ion exchange reaction was carried out for 4 hours under light-protected conditions, followed by centrifugation and washing until no Ag was found. + The silver-loaded nano-hydroxyapatite was obtained by drying at 60℃ for 12 hours.

3. The environmentally friendly water-based cutting fluid as described in claim 1, characterized in that: The lauroyl arginine ethyl ester is lauroyl arginine ethyl ester hydrochloride with a purity ≥98%.

4. The environmentally friendly water-based cutting fluid as described in claim 1, characterized in that: The carboxymethyl chitosan has a weight-average molecular weight of 3000–5000 Da and a degree of substitution of 0.7–0.

85.

5. The environmentally friendly water-based cutting fluid as described in claim 1, characterized in that: The weight-average molecular weight of the polyethylene glycol 400 is 380–420 Da.

6. The environmentally friendly water-based cutting fluid as described in claim 1, characterized in that: The organosilicon defoamer is a polydimethylsiloxane emulsion with a solid content of 30-40%.

7. The environmentally friendly water-based cutting fluid as described in claim 1, characterized in that: The cutting fluid has a pH value of 8.5 to 9.

5.

8. A method for preparing an environmentally friendly water-based cutting fluid, applicable to the environmentally friendly water-based cutting fluid according to any one of claims 1-7, characterized in that, Includes the following steps: Step 1: Add deionized water to the reaction vessel and heat to 45-55℃; Step 2: Add carboxymethyl chitosan and stir until completely dissolved; Step 3: Add polyethylene glycol 400 and triethanolamine borate, and stir until completely dissolved; Step 4: Add sebacic acid and stir until completely dissolved; Step 5: Add silver-loaded nano-hydroxyapatite and ultrasonically disperse for 20-30 minutes. The ultrasonic power is 200-400W and the frequency is 40-60kHz. Step 6: After cooling the system to room temperature, add ethyl lauroyl arginine and silicone defoamer under stirring. Add ethyl lauroyl arginine slowly at a rate of 1-3 mL / min while stirring rapidly at 400-600 rpm. After the addition is complete, continue stirring for 10-15 minutes to obtain the environmentally friendly water-based cutting fluid.

9. The method for preparing the environmentally friendly water-based cutting fluid as described in claim 8, characterized in that: In step six, lauroyl arginine ethyl ester is added slowly at a rate of 2 mL / min, with a stirring speed of 500 rpm.

10. The application of the environmentally friendly water-based cutting fluid as described in any one of claims 1 to 7 in metal cutting, characterized in that, The cutting fluid is diluted with deionized water to a working concentration of 3-8% by mass and is suitable for light to medium load cutting, milling and drilling of cast iron, carbon steel and aluminum alloys.

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