A preparation method of nano calcium carbonate for gas-phase rust preventive masterbatch

Abstract

The present invention relates to the technical field of nano calcium carbonate, and specifically to a preparation method of nano calcium carbonate for gas-phase rust-proof masterbatch, which includes the following steps: Mix corn starch with deionized water and gelatinize to obtain a semi-transparent gel; Add a crystal form control agent to the CaCl 2 solution to obtain a loaded mixture; Immerse the semi-transparent gel in the loaded mixture and freeze-dry to obtain a starch template; Transfer the starch template to a fixed-bed reactor and introduce C0 2 to obtain a carbonization product; Perform enzymatic hydrolysis treatment on the carbonization product, centrifuge and wash, and vacuum-dry to obtain nano calcium carbonate; Immerse the nano calcium carbonate in an inhibitor solution, centrifuge to remove the excess solution, and vacuum-dry to obtain nano calcium carbonate loaded with an inhibitor; Coating a pH-sensitive film layer on the outer surface of the nano calcium carbonate loaded with an inhibitor to obtain a nano calcium carbonate product. The pH-sensitive film layer coated on the nano calcium carbonate dissolves and releases the inhibitor in an acidic environment to achieve dynamic rust prevention on the metal surface.

Description

Technical Field

[0001] The present invention relates to the technical field of nano calcium carbonate, and specifically to a preparation method of nano calcium carbonate for gas-phase rust preventive masterbatch. Background Art

[0002] As an important filler, nano calcium carbonate is widely used in industries such as plastics, papermaking, sealants, and coatings. The particle size of nano calcium carbonate is relatively small, which can better penetrate into gaps and form a strong adhesion force with the surfaces of various materials.

[0003] Chinese invention patent with the publication number CN106277011B discloses a nano calcium carbonate concentrated slurry and its preparation method. The concentrated slurry is composed of 100 parts of nano calcium carbonate, 5 - 10 parts of organic corrosion inhibitor, 0.1 - 0.3 parts of rust preventive pigment, 0.3 - 0.6 parts of auxiliary agent, and 15 - 20 parts of organic solvent; weigh each component according to the proportion, mix the organic corrosion inhibitor, rust preventive pigment, and auxiliary agent with the organic solvent evenly; gradually add nano calcium carbonate powder during the continuous rotation of a high-speed disperser. After all the required nano calcium carbonate powder is added, continue to disperse for 5 - 30 minutes, and the rotation speed of the disperser is 1500 - 2500 rpm; grind the obtained nano calcium carbonate slurry in a ball mill or a sand mill for 1 - 10 hours to make its average particle size below 100 nanometers, and obtain the nano calcium carbonate concentrated slurry.

[0004] In the above scheme, components such as organic corrosion inhibitor are dispersed in the nano calcium carbonate concentrated slurry, and the corrosion inhibitor is directly exposed to the solvent environment, with an excessively fast initial release rate and unable to achieve long-term protection. Summary of the Invention

[0005] Aiming at the problems existing in the prior art, the present invention provides a preparation method of nano calcium carbonate for gas-phase rust preventive masterbatch, aiming to achieve staged controlled release of the corrosion inhibitor. Specifically, it is realized through the following technical solutions:

[0006] A preparation method of nano calcium carbonate for gas-phase rust preventive masterbatch includes the following steps:

[0007] S1. Mix corn starch and deionized water according to a mass ratio of (3 - 8)∶40, disperse evenly to form a suspension, heat up to 70 - 80 °C for gelatinization treatment to obtain a semi-transparent gel;

[0008] S2. Add a crystal form control agent accounting for 0.5% - 1% of its mass to a CaCl 2 solution with a mass concentration of 20% - 45% to obtain a loaded mixture;

[0009] S3. Immerse the semi-transparent gel in the loaded mixture, take it out and perform freeze-drying to obtain a starch template with oriented pores;

[0010] S4. Spread the starch template flat on the bed of the fixed-bed reactor, maintain the temperature at 25 ± 1 °C, and introduce CO from the bottom at a flow rate of 0.5 - 0.8 L / min. 2 Carry out the carbonization reaction. When the pH of the system measured at the pH monitoring site drops to 8.2, stop introducing CO. 2 , and obtain the carbonized product;

[0011] S5. Subject the carbonized product to enzymatic hydrolysis to degrade the starch template, use the washing solution to centrifuge and wash the enzymatic hydrolysis product, collect the solid matter, and dry it under vacuum to obtain needle-shaped nano calcium carbonate;

[0012] S6. Dissolve the corrosion inhibitor in ethanol to prepare a corrosion inhibitor solution with a mass concentration of 1% - 5%. Immerse the nano calcium carbonate in the corrosion inhibitor solution according to the mass ratio of (1 - 4):10, evacuate to 0.01 - 0.05 MPa, maintain for 1 - 1.5 h, centrifuge to remove the excess solution, and dry it under vacuum to obtain nano calcium carbonate loaded with the corrosion inhibitor;

[0013] S7. Coating the outer surface of the nano calcium carbonate loaded with the corrosion inhibitor with a pH-sensitive film layer to obtain the nano calcium carbonate product.

[0014] Preferably, in step S7, first dissolve chitosan in an acetic acid solution with a mass concentration of 1% to prepare a chitosan solution with a mass concentration of 1% - 5%. Then, immerse the nano calcium carbonate loaded with the corrosion inhibitor in the chitosan solution according to the mass ratio of (1 - 3):1, add a cross-linking agent accounting for 0.1% - 0.5% of the total mass of the chitosan solution, stir for 6 - 8 h, take it out, centrifuge to remove the excess solution, and dry it under vacuum to obtain the nano calcium carbonate product.

[0015] Preferably, the cross-linking agent is glutaraldehyde.

[0016] Preferably, in step S3, first rapidly freeze the surface layer of the starch template with liquid nitrogen to form macropores, and then slowly freeze the interior of the starch template at -40 °C to form mesopores, constructing a gradient pore structure of the starch template.

[0017] Preferably, in step S5, first immerse the carbonized product in an α-amylase solution for enzymatic hydrolysis for 3.5 - 5 h, maintain the temperature at 50 - 60 °C, and then use an ethanol solution with a mass concentration of 75% as the washing solution for centrifugal washing to remove residual enzymes and sugars.

[0018] Preferably, the mass ratio of the α-amylase solution to the carbonized product is 1:(3 - 5), and the mass concentration of the α-amylase solution is 1% - 5%.

[0019] Preferably, the corrosion inhibitor is compounded from benzotriazole and capric acid according to the mass ratio of 3:1.

[0020] Preferably, the crystal form control agent is polyacrylic acid.

[0021] After adopting the above technical solution, the beneficial effects of the present invention are as follows:

[0022] The present invention uses a bio-template method to synthesize a carrier with a mesoporous-macroporous structure, guides the directional growth of nano-calcium carbonate, and the pH-sensitive film layer coated with nano-calcium carbonate releases corrosion inhibitors in an acidic environment to achieve dynamic rust prevention on the metal surface. Specific Embodiments

[0023] The features and exemplary embodiments of various aspects of the present invention will be described in detail below. In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in combination with specific embodiments. It should be understood that the specific embodiments described herein are only configured to explain the present invention and are not configured to limit the present invention. For those skilled in the art, the present invention can be implemented without some of these specific details. The following description of the embodiments is only to provide a better understanding of the present invention by showing examples of the present invention.

[0024] Example 1

[0025] In this specific embodiment, the present invention provides a preparation method of nano-calcium carbonate for a vapor-phase rust preventive masterbatch, achieving the high-efficiency and long-lasting performance of the nano-calcium carbonate-based vapor-phase rust preventive masterbatch.

[0026] S1: Preparation of semi-transparent gel

[0027] Mix corn starch and deionized water at a mass ratio of 3:40, stir well to prepare a uniform suspension. Heat up to 70 °C for gelatinization treatment, keep the temperature for 15 min and continue stirring to obtain a semi-transparent gel. Stirring can ensure the uniform dispersion of starch granules and prevent agglomeration, and the stirring shear force promotes the full expansion and rupture of starch granules. The three-dimensional gel network and pore structure formed after the gelatinization of corn starch provide spatial constraints and directional channels for the nucleation and growth of calcium carbonate. Naturally cool to room temperature to form a uniform pore substrate.

[0028] S2: Preparation of loaded mixture

[0029] Add polyacrylic acid accounting for 0.5% of its mass to a CaCl 2 solution with a mass concentration of 20%, ultrasonically treat the mixture for 10 min to ensure the full dispersion of polyacrylic acid, and prepare a uniform loaded mixture.

[0030] The three-dimensional gel network formed after the gelatinization of corn starch adsorbs calcium ions through hydrogen bonding and electrostatic interactions. Due to the coordination between the hydroxyl groups on the starch molecular chain and calcium ions, calcium ions are preferentially enriched in the pores of the starch template, forming a locally high-concentration region, which restricts the free growth of calcium carbonate crystals and guides them to grow into needles along the pore axis.

[0031] As a crystal form control agent, polyacrylic acid inhibits the growth rate of specific crystal planes of calcium carbonate through chemical adsorption and chelation, promoting the formation of needle-like nano calcium carbonate.

[0032] S3: Gradient pore construction

[0033] Under the condition of 20 °C, immerse the translucent gel in the loading mixture, with the liquid level 1 cm higher than the top of the translucent gel to ensure complete immersion. Maintain a negative pressure of -0.08 MPa, and use a peristaltic pump to circulate the loading mixture for 20 min. After impregnation, take out the translucent gel to obtain the loaded gel.

[0034] Use a liquid nitrogen spray gun to evenly spray the surface of the loaded gel for 15 - 30 s. This process will rapidly reduce the temperature of the loaded gel, causing water molecules to freeze rapidly inside the gel to form ice crystals. The rapid growth of ice crystals constructs macropores on the loaded gel.

[0035] Then transfer the loaded gel to a freeze dryer, pre-freeze it at a low temperature of -40 °C for 3 h to ensure that all water molecules inside the loaded gel form ice crystals, constructing mesopores on the loaded gel. After pre-freezing, adjust the vacuum degree ≤ 10 Pa, first raise the temperature to 0 °C to directly sublimate the ice crystals, and then raise the temperature to 20 °C for desorption drying, finally obtaining a starch template with a gradient pore structure.

[0036] S4. Carbonization reaction

[0037] Immerse the starch template in a 0.2 mol / L NH 3 ·H 2 O solution, with the liquid level 1 cm higher than the top of the starch template to ensure complete immersion. Maintain a negative pressure of -0.08 MPa and impregnate for 5 min. Take out the starch template and lay it flat on the porous bed layer of a fixed-bed reactor. Maintain the temperature at 25 °C and introduce C0 2 from the bottom at a flow rate of 0.5 L / min for carbonization reaction. When the pH of the system measured at the pH monitoring site drops to 8.2, stop introducing C0 2 and terminate the reaction to obtain the carbonized product.

[0038] The gradient distribution of macropores - mesopores in the starch template optimizes the mass transfer path and improves the diffusion efficiency of C0 2 NH 3 ·H 2 O provides an alkaline environment, C02 The generated carbonate reacts with calcium ions to form calcium carbonate precipitate. The hydroxyl groups of the starch template coordinate with calcium ions, enriching calcium ions within the pores. The diffusion of carbonate is restricted, prompting the growth of calcium carbonate along the pore axis. Polyacrylic acid directionally regulates the crystal growth direction, ultimately forming needle-shaped nano-calcium carbonate.

[0039] When this needle-shaped nano-calcium carbonate is made into a vapor-phase rust inhibitor masterbatch with other raw materials and applied to metal packaging, its unique needle-shaped structure can form a fiber-like stress transfer network in the composite material. This network structure not only enhances the overall strength of the composite material, improves its pressure-bearing capacity (such as the stacking pressure of metals, reduces creep deformation under long-term stress, and extends the service life of metal packaging), but also significantly enhances the impact resistance of the composite material, enabling it to better protect metal packaging from damage during transportation and storage.

[0040] S5: Enzymatic hydrolysis and washing

[0041] Immerse the carbonization product in an α-amylase solution with a mass concentration of 1%. The mass ratio of the α-amylase solution to the carbonization product is 1:3. Maintain the temperature at 50°C and carry out enzymatic hydrolysis for 5 h. α-Amylase hydrolyzes starch, releasing nano-calcium carbonate. Use an ethanol solution with a mass concentration of 75% as the washing solution to centrifuge and wash the enzymatic hydrolysis product to remove residual enzymes and sugars. Collect the solid material and vacuum dry it to obtain needle-shaped nano-calcium carbonate.

[0042] S6: Loading of corrosion inhibitor

[0043] Benzotriazole and capric acid are compounded into a corrosion inhibitor according to a mass ratio of 3:1. Dissolve the corrosion inhibitor in ethanol to prepare a corrosion inhibitor solution with a mass concentration of 1%. According to a mass ratio of 1:10, immerse the nano-calcium carbonate obtained in step 5 in the corrosion inhibitor solution, evacuate to 0.01 MPa, and hold for 1 h to ensure that the corrosion inhibitor is fully adsorbed onto the nano-calcium carbonate. Then centrifuge to remove the excess solution and vacuum dry it to obtain nano-calcium carbonate loaded with a corrosion inhibitor.

[0044] S7: Coating with a pH-sensitive film layer

[0045] Dissolve chitosan in an acetic acid solution with a mass concentration of 1% to prepare a chitosan solution with a mass concentration of 1%. According to a mass ratio of 1:1, immerse the nano-calcium carbonate loaded with a corrosion inhibitor in the chitosan solution, add 0.1% glutaraldehyde based on the total mass of the chitosan solution, and stir for 6 h. After taking it out, centrifuge and wash it with a 0.2% sodium cyanoborohydride solution, and then centrifuge and wash it twice with deionized water, and vacuum dry it to obtain a nano-calcium carbonate product.

[0046] Chitosan is adsorbed on the surface of nano-calcium carbonate through electrostatic interaction to form a uniform film layer. Glutaraldehyde reacts with the amino groups in the chitosan molecule to form a Schiff base reaction, forming a three-dimensional cross-linked structure to enhance the mechanical strength of the film layer. Sodium cyanoborohydride reduces the unreacted aldehyde groups of glutaraldehyde and the unstable Schiff base intermediate to stable amino groups, eliminating toxicity and improving the stability of the film layer. The cross-linking reaction of glutaraldehyde will consume some of its hydrophilic amino groups. The introduction of hydrophobic segments can reduce the hydration ability of the film layer and inhibit swelling. When the local environmental pH decreases (such as the acidic environment caused by metal corrosion), the amino groups in the chitosan film are further protonated, the film layer swells and ruptures, and the corrosion inhibitor is released from the nano-calcium carbonate.

[0047] Example 2

[0048] S1 adjustment: Corn starch and deionized water are mixed at a mass ratio of 5:40, and heated to 72 °C for gelatinization treatment to obtain a translucent gel.

[0049] S2 adjustment: Add polyacrylic acid accounting for 0.8% of its mass to a 25% mass concentration CaCl 2 solution to prepare a uniform loading mixture.

[0050] S4 adjustment: Carbonization reaction is carried out by introducing C0 2 at a flow rate of 0.55 L / min. After the reaction ends, a carbonized product is obtained.

[0051] S5 adjustment: The carbonized product is immersed in a 3% mass concentration α-amylase solution. The mass ratio of the α-amylase solution to the carbonized product is 1:3.5. The temperature is maintained at 55 °C and enzymolysis is carried out for 3.5 h to release nano-calcium carbonate. A 75% mass concentration ethanol solution is used as the washing liquid to carry out centrifugal washing on the enzymolysis product to obtain needle-shaped nano-calcium carbonate.

[0052] S6 adjustment: The corrosion inhibitor is dissolved in ethanol to prepare a corrosion inhibitor solution with a mass concentration of 3.5%. According to a mass ratio of 3:10, the nano-calcium carbonate is immersed in the corrosion inhibitor solution, evacuated to 0.02 MPa, maintained for 1.2 h, centrifuged to remove the excess solution, and vacuum dried to obtain nano-calcium carbonate loaded with the corrosion inhibitor.

[0053] S7 adjustment: Chitosan is dissolved in a 1% mass acetic acid solution to prepare a chitosan solution with a mass concentration of 3%. According to a mass ratio of 2:1, the nano-calcium carbonate loaded with the corrosion inhibitor is immersed in the chitosan solution, add 0.3% of glutaraldehyde accounting for the total mass of the chitosan solution, stir for 6.5 h, take it out, and carry out centrifugal washing with a 0.25% mass concentration sodium cyanoborohydride solution, and then carry out centrifugal washing with deionized water twice, and vacuum dry to obtain a nano-calcium carbonate product.

[0054] Example 3

[0055] S1 Adjustment: Corn starch and deionized water are mixed at a mass ratio of 1:5, and the temperature is raised to 80 °C for gelatinization treatment to obtain a translucent gel.

[0056] S2 Adjustment: 1% of polyacrylic acid by mass is added to a CaCl solution with a mass concentration of 45% to prepare a uniform loading mixture. 2 Solution to prepare a uniform loading mixture.

[0057] S4 Adjustment: Carbonization reaction is carried out by introducing CO at a flow rate of 0.8 L / min. After the reaction ends, a carbonized product is obtained. 2 to obtain a carbonized product.

[0058] S5 Adjustment: The carbonized product is immersed in an α-amylase solution with a mass concentration of 5%. The mass ratio of the α-amylase solution to the carbonized product is 1:5. The temperature is maintained at 60 °C and enzymatic hydrolysis is carried out for 5 h to release nano-calcium carbonate. An ethanol solution with a mass concentration of 80% is used as the washing liquid to centrifugally wash the enzymatically hydrolyzed product to obtain needle-shaped nano-calcium carbonate.

[0059] S6 Adjustment: The corrosion inhibitor is dissolved in ethanol to prepare a corrosion inhibitor solution with a mass concentration of 5%. According to a mass ratio of 2:5, the nano-calcium carbonate is immersed in the corrosion inhibitor solution, the vacuum is pumped to 0.05 MPa, and it is maintained for 1.5 h. The excess solution is removed by centrifugation and vacuum dried to obtain nano-calcium carbonate loaded with the corrosion inhibitor.

[0060] S7 Adjustment: Chitosan is dissolved in a 1% acetic acid solution to prepare a chitosan solution with a mass concentration of 5%. According to a mass ratio of 3:1, the nano-calcium carbonate loaded with the corrosion inhibitor is immersed in the chitosan solution, 0.5% of glutaraldehyde based on the total mass of the chitosan solution is added, and it is stirred for 8 h. After taking it out, it is centrifugally washed with a 0.5% sodium cyanoborohydride solution, and then centrifugally washed twice with deionized water and vacuum dried to obtain a nano-calcium carbonate product.

[0061] Preparation of VCI gas-phase rust inhibitor masterbatch

[0062] Benzotriazole, sodium benzoate, hexamine, and phytic acid are mixed evenly according to a mass ratio of 3:5:1:1 to prepare a compound rust inhibitor. The compound rust inhibitor, nano-calcium carbonate (from Examples 1-3), and polyethylene are mixed according to a mass ratio of 2.5:1.5:6, and the mixed raw materials are made into a rust inhibitor masterbatch by a high-speed granulator. According to the raw material selection of Examples 1-3, the rust inhibitor masterbatches are respectively denoted as VCI-1, VCI-2, and VCI-3. In addition, the compound rust inhibitor and polyethylene are mixed according to a mass ratio of 2.5:6, and the mixed raw materials are made into a rust inhibitor masterbatch, denoted as VCI-4, as a control group.

[0063] Preparation of rust-proof film

[0064] Add the prepared 4 kinds of antirust masterbatches to polyethylene at a mass fraction of 15%, and make polyethylene through blown film treatment after mixing. In addition, prepare pure polyethylene and make it into an antirust film.

[0065] According to GB / T 1040.3-2006, make specimens for testing the tensile and tear strengths of the above 5 kinds of antirust films to analyze the mechanical properties of the antirust films. The results are shown in Table 1.

[0066] Table 1. Mechanical properties of antirust films

[0067]

[0068] Due to the strengthening effect and stress dispersion of nano calcium carbonate in VCI-1 to 3, the tensile strength and tear strength of the antirust film are significantly higher than those of pure polyethylene and VCI-4, and it can better withstand external forces and maintain the integrity of the packaging, enhancing the antirust effect to a certain extent.

[0069] Prepare 10 copper sheets of 15mm×40mm×1mm, wrap 8 of them with antirust films respectively, and leave the remaining 2 without coating. Conduct acid salt spray (GB / T 24195-2009; acid salt spray for 2h + drying for 4h + wetting for 2h; cycle 30 times) and neutral salt spray tests (GB / T 10125-2012; spraying for 8h, stopping for 16h; for 10 days). The results are shown in Table 2 (the proportion of the corroded area of the copper sheet).

[0070] Table 2. Corrosion resistance of antirust films

[0071]

[0072] Under acidic conditions, the polysaccharide film rapidly protonates and swells, and the corrosion inhibitor is rapidly released to form a passivation film to inhibit copper corrosion. Under neutral conditions, the polysaccharide film is stable, and the corrosion inhibitor is slowly released to inhibit alkaline corrosion for a long time.

[0073] In accordance with the embodiments of the present invention as described above, these embodiments do not describe all the details in detail, nor limit the invention to only the specific embodiments. Obviously, according to the above description, many modifications and variations can be made. These embodiments are selected and specifically described in this specification to better explain the principle and practical application of the present invention, so that those skilled in the art can make good use of the present invention and its modifications based on the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing nano calcium carbonate for gas phase antirust masterbatch, characterized in that: The steps include: S1, corn starch and deionized water are mixed in a mass ratio of (3-8):40, dispersed evenly to form a suspension, heated to 70-80°C for gelatinization to obtain a translucent gel; S2, adding 0.5% to 1% by weight of polyacrylic acid to a CaCl2 solution having a mass concentration of 20% to 45% to obtain a loaded mixed solution; S3, immersing the translucent gel in the loading mixed solution, taking it out and freeze-drying it to obtain a starch template with directional pores; S4, completely immersing the starch template in NH3·H2O solution, taking it out and spreading it on the bed of the fixed bed reactor, maintaining the temperature at 25±1°C, introducing CO2 from the bottom at a flow rate of 0.5-0.8L / min for carbonization reaction, and stopping the introduction when the pH of the system measured at the pH monitoring point drops to 8.2 to obtain a carbonized product; S5, enzymatically treating the carbonized product to degrade the starch template, centrifugally washing the enzymatic product with a washing liquid, collecting the solid matter, and vacuum drying to obtain needle-shaped nano-calcium carbonate; S6. Dissolve the corrosion inhibitor in ethanol to prepare a corrosion inhibitor solution with a mass concentration of 1% to 5%, wherein the corrosion inhibitor is prepared by compounding benzotriazole and capric acid at a mass ratio of 3:1, immerse the nano-calcium carbonate in the corrosion inhibitor solution at a mass ratio of (1-4):10, evacuate to 0.01-0.05MPa, maintain for 1-1.5h, centrifuge to remove excess solution, and vacuum dry to obtain nano-calcium carbonate loaded with corrosion inhibitor; S7. Coating a pH sensitive film layer on the outer surface of the nano calcium carbonate loaded with corrosion inhibitor to obtain a nano calcium carbonate product.

2. The method for preparing nano calcium carbonate for gas phase antirust masterbatch according to claim 1, characterized in that: In the step S7, chitosan is first dissolved in an acetic acid solution with a mass concentration of 1% to prepare a chitosan solution with a mass concentration of 1% to 5%, and then the nano-calcium carbonate loaded with a corrosion inhibitor is immersed in the chitosan solution at a mass ratio of (1 to 3):1, and a cross-linking agent accounting for 0.1% to 0.5% of the total mass of the chitosan solution is added, stirred for 6 to 8 hours, taken out and centrifuged to remove excess solution, and vacuum dried to obtain a nano-calcium carbonate product.

3. The method for preparing nano calcium carbonate for gas phase antirust masterbatch according to claim 2, characterized in that: The cross-linking agent is glutaraldehyde.

4. The method for preparing nano calcium carbonate for gas phase antirust masterbatch according to claim 1, characterized in that: In step S3, the surface of the starch template is firstly rapidly frozen by liquid nitrogen to form macropores, and then the interior of the starch template is slowly frozen at -40°C to form mesopores, thereby constructing a gradient pore structure of the starch template.

5. The method for preparing nano calcium carbonate for gas phase antirust masterbatch according to claim 1, characterized in that: In step S5, the carbonized product is first immersed in an α-amylase solution for enzymolysis for 3.5 to 5 hours, and the temperature is maintained at 50 to 60° C., and then centrifuged and washed using an ethanol solution with a mass concentration of 75% as a washing liquid to remove residual enzymes and sugars.

6. The method for preparing nano calcium carbonate for gas phase antirust masterbatch according to claim 5, characterized in that: The mass ratio of the α-amylase solution to the carbonized product is 1:(3-5), and the mass concentration of the α-amylase solution is 1%-5%.

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