Surface-modified nano-calcium carbonate, its preparation methods and applications

Abstract

This invention provides a surface-modified nano-calcium carbonate, its preparation method, and its application. By introducing surface-modified calcium carbonate into the Ca... 2+ An amphiphilic molecular solution is added to the solution, and after ultrasonic mixing, anhydrous sodium carbonate solution is slowly added dropwise. The reaction is carried out with thorough stirring to obtain calcium carbonate precipitate. The pH of the solution is adjusted to neutral, and the calcium carbonate precipitate is washed and dried. It is then reacted with a long-chain alkane compound in an exchanger to obtain surface-modified nano-calcium carbonate. The preparation method of this invention features rapid activation and a simple process. Unlike traditional methods of activating calcium carbonate with coupling agents, this invention prepares surface-modified nano-calcium carbonate by self-assembling two organic layers on the surface of the nano-calcium carbonate. This results in nano-calcium carbonate with advantages such as concentrated size distribution, uniform particle size, and high activation degree. It also exhibits good compatibility with polyolefin materials and can be widely used in the filling modification of polymer materials such as plastics, rubber, and coatings to improve the mechanical properties, thermal stability, and processing performance of these materials.

Description

Technical Field

[0001] This invention relates to the field of nano-calcium carbonate technology, and in particular to a surface-modified nano-calcium carbonate, its preparation method, and its application. Background Technology

[0002] Nano-calcium carbonate is an ultrafine calcium carbonate with a particle size ranging from 1 to 500 nm. Due to its small particle size and altered surface electronic and crystal structures, it possesses physical properties not found in heavy calcium carbonate, such as quantum size effect, surface effect, and small size effect, making it widely used in the plastics processing field. Nano-calcium carbonate materials are widely used as important reinforcing, toughening, volume-increasing, and weight-increasing inorganic fillers in various organic polymer matrices. However, directly applying unmodified nano-calcium carbonate materials to materials such as polyolefin films can lead to problems such as numerous interfacial defects, poor structural density, low strength, low toughness, and reduced water resistance. Therefore, surface modification of nano-calcium carbonate materials is necessary to improve the dispersibility of nano-calcium carbonate particles and their compatibility with polyolefin matrices.

[0003] Currently, the main methods for modifying nano-calcium carbonate include coupling agent modification, surfactant modification, grafting modification, inorganic material encapsulation modification, and iso-stereoscopic modification. Patent CN118165547A discloses a nano-calcium carbonate surface treatment agent and its preparation method, including emulsion A and emulsion B. Emulsion A includes vinyl-terminated polymethylsiloxane, hydrogen-containing polysiloxane, polyether-modified silicone oil, deionized water, etc.; emulsion B includes a platinum metal catalyst emulsion. Although the nano-calcium carbonate treated by this invention has high activation, the preparation process of activated nano-calcium carbonate is complex and time-consuming, and there is still no better method for treating finer nano-calcium carbonate.

[0004] In view of this, it is necessary to design an improved surface-modified nano-calcium carbonate, its preparation method, and its application to solve the above problems. Summary of the Invention

[0005] To address the shortcomings of the prior art, the present invention aims to provide a surface-modified nano-calcium carbonate, its preparation method, and its application. By self-assembling two organic layers on the surface of the nano-calcium carbonate, the prepared surface-modified nano-calcium carbonate has the advantages of concentrated size distribution, uniform particle size, high activation degree, and good compatibility with polyolefin materials.

[0006] To achieve the above objectives, the present invention provides a method for preparing surface-modified nano-calcium carbonate, comprising the following steps:

[0007] S1. Configure Ca respectively 2+ Solutions, amphiphilic molecular solutions, and anhydrous sodium carbonate solutions are available for use.

[0008] S2. To Ca2+ Add an amphiphilic molecular solution to the solution and mix ultrasonically for a predetermined time;

[0009] S3. Slowly add anhydrous sodium carbonate solution to the solution obtained in step S2, stir the reaction thoroughly to obtain calcium carbonate precipitate, and adjust the pH of the solution to neutral.

[0010] S4. The calcium carbonate precipitate obtained in step S3 is washed and dried, and then fully exchanged with long-chain alkane compounds in an exchanger to obtain surface-modified nano-calcium carbonate.

[0011] As a further improvement of the present invention, in step S1, the Ca 2+ The concentration of the solution is 0.1–1 mol / L; the concentration of the anhydrous sodium carbonate solution is 0.1–1 mol / L.

[0012] Furthermore, the amphiphilic molecule is a long-chain sodium benzenesulfonate salt or a long-chain stearic acid, and the Ca... 2+ The solution is one of calcium chloride, calcium sulfate, calcium nitrate, and calcium hydroxide.

[0013] As a further improvement of the present invention, in step S2, the Ca 2+ Ca in solution 2+ The molar ratio of the amphiphilic molecules to the amphiphilic molecules in the solution is 1:(1-10).

[0014] The ultrasonic mixing time is 25–35 minutes.

[0015] As a further improvement of the present invention, in step S4, both the calcium carbonate precipitate and the long-chain alkane compound are transported to the exchanger via high-temperature air at 120–250°C; the long-chain alkane compound is one of n-octane, n-nonane, n-decane, n-undecane to n-docosahexadecane, and low-temperature paraffin. The mass ratio of the calcium carbonate precipitate to the long-chain alkane compound is 1:(0.05–0.5).

[0016] The present invention also provides a surface-modified nano-calcium carbonate, which is prepared by the above-described method for preparing surface-modified nano-calcium carbonate.

[0017] An application of surface-modified nano-calcium carbonate involves melt-blending the prepared surface-modified nano-calcium carbonate with polypropylene to prepare a PP / nano-calcium carbonate composite material, wherein the filler mass of the surface-modified nano-calcium carbonate is 5-8%.

[0018] The beneficial effects of the present invention are:

[0019] This invention provides a surface-modified nano-calcium carbonate, its preparation method, and its application. By introducing surface-modified calcium carbonate into the Ca... 2+An amphiphilic molecular solution is added to the solution, and the mixture is ultrasonically mixed for a predetermined time. Then, anhydrous sodium carbonate solution is slowly added dropwise, and the reaction is stirred thoroughly to obtain calcium carbonate precipitate. The pH of the solution is adjusted to neutral, and the calcium carbonate precipitate is washed and dried. It is then fully exchanged with a long-chain alkane compound in an exchanger to obtain surface-modified nano-calcium carbonate. The preparation method of this invention is characterized by rapid activation and simple process. Unlike traditional methods of activating calcium carbonate with coupling agents, this invention prepares surface-modified nano-calcium carbonate by self-assembling two organic layers on the surface of nano-calcium carbonate. This results in nano-calcium carbonate with advantages such as concentrated size distribution, uniform particle size, and high activation degree. It also exhibits good compatibility with polyolefin materials and can be widely used in the filling modification of polymer materials such as plastics, rubber, and coatings to improve the mechanical properties, thermal stability, and processing performance of the materials.

[0020] This invention utilizes the combined action of amphiphilic molecules and long-chain alkane compounds to impart excellent hydrophilicity and hydrophobicity to the surface of nano-calcium carbonate, facilitating its dispersion in a polymer matrix. The improved interfacial compatibility between the surface-modified nano-calcium carbonate and the polymer matrix enhances the mechanical properties of the composite material. Simultaneously, the addition of surface-modified nano-calcium carbonate helps improve the thermal stability of the composite material, reduces melt flow rate, and facilitates control over processing performance. The preparation method provided by this invention is simple, uses readily available raw materials, and is easy to control in the production process, thus reducing production costs and aligning with the trend of green and environmentally friendly development.

[0021] The surface-modified nano-calcium carbonate of this invention can be applied to the reinforcement, filling, and modification of polymer materials, and has great application prospects. Attached Figure Description

[0022] Figure 1 A schematic diagram of the structure of the surface-modified nano-calcium carbonate provided by the present invention.

[0023] Figure 2 This is a SEM image of the surface-modified nano-calcium carbonate provided in Example 1 of the present invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] It should also be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and / or processing steps closely related to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0026] Additionally, it should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0027] This invention provides a method for preparing surface-modified nano-calcium carbonate, comprising the following steps:

[0028] S1. Configure Ca respectively 2+ Solutions, amphiphilic molecular solutions, and anhydrous sodium carbonate solutions are available for use.

[0029] Specifically, Ca 2+ The concentration of the solution is 0.1–1 mol / L; the concentration of the anhydrous sodium carbonate solution is 0.1–1 mol / L. Ca 2+ The solution is one of calcium chloride, calcium sulfate, calcium nitrate, and calcium hydroxide.

[0030] The amphiphilic molecules are preferably long-chain sodium benzenesulfonate salts or long-chain stearic acids.

[0031] Long-chain sodium benzenesulfonate salts are preferably sodium dodecylbenzenesulfonate; long-chain sodium benzenesulfonate salts have good water solubility and can form stable micelle structures in water. The sulfonic acid groups can provide a negative charge, which helps to disperse and stabilize nanoparticles.

[0032] Long-chain stearic acids are preferably hexadecanoic acid and octadecanoic acid; long-chain stearic acids have strong hydrophobicity, which helps to improve the hydrophobicity of nano-calcium carbonate and its dispersibility in non-polar media.

[0033] S2. To Ca 2+ An amphiphilic molecular solution is added to the solution, and the mixture is ultrasonically mixed for a predetermined time.

[0034] Specifically, Ca 2+ The molar ratio with the amphiphilic molecule is 1:(1-10). The ultrasonic mixing time is 25-35 min.

[0035] Amphiphilic molecules form micelles in water, where their hydrophobic long chains aggregate together. These molecules can stabilize Ca. 2+ Ions, with Ca 2+ The ions form stable complexes, preventing them from reacting directly with anhydrous sodium carbonate to form large precipitates, which helps control the nucleation and growth process of calcium carbonate. Simultaneously, the amphiphilic molecules can also help long-chain alkane compounds adsorb more effectively onto the surface of nano-calcium carbonate during subsequent surface modification.

[0036] S3. Slowly add anhydrous sodium carbonate solution to the solution obtained in step S2, stir the reaction thoroughly to obtain calcium carbonate precipitate, and adjust the pH of the solution to neutral.

[0037] Specifically, the anhydrous sodium carbonate solution and the Ca in step S2 2+ The preferred molar ratio of the solutions is 1:1. Adjusting the pH of the solution to neutral ensures stable precipitation of calcium carbonate and avoids the formation of other forms of calcium carbonate or byproducts.

[0038] S4. The calcium carbonate precipitate obtained in step S3 is washed and dried, and then fully exchanged with long-chain alkane compounds in an exchanger to obtain surface-modified nano-calcium carbonate.

[0039] Specifically, the long-chain alkane compound is preferably one of n-octane, n-nonane, n-decane, n-undecane to n-docosahexanes, and low-temperature paraffin. Both the calcium carbonate precipitate and the long-chain alkane compound are transported to the exchanger via high-temperature air at 120–250°C. This temperature range promotes effective interaction between alkane molecules and the calcium carbonate surface while avoiding excessively high temperatures that could lead to alkane decomposition or calcium carbonate structural damage. The preferred mass ratio of calcium carbonate precipitate to long-chain alkane compound is 1:(0.05–0.5). The long-chain alkane compound adsorbs onto the calcium carbonate surface, forming a hydrophobic layer, thereby endowing the nano-calcium carbonate with specific surface properties.

[0040] An application of surface-modified nano-calcium carbonate involves melt-blending surface-modified nano-calcium carbonate with polypropylene (PP) to prepare a PP / nano-calcium carbonate composite material, wherein the filler mass of surface-modified nano-calcium carbonate is 5-8%.

[0041] The surface-modified nano-calcium carbonate exhibits improved interfacial compatibility with polypropylene, reducing nanoparticle aggregation and enabling uniform dispersion of nanoparticles within the polymer matrix. The modifier forms a bonding layer on the surface of the nano-calcium carbonate, enhancing the interaction between nanoparticles and polymer molecules, thereby improving the mechanical properties of the composite material. The nano-calcium carbonate particles act as a barrier to molecular chain movement within the composite material; when heated, they impede polymer chain segment movement, thus improving thermal stability. Appropriate amounts of nano-calcium carbonate particles can act as stress concentration points, inducing yielding and plastic deformation in the surrounding polymer matrix, thereby absorbing more energy and improving the impact toughness of the composite material. A filler content of 5–8% nano-calcium carbonate ensures improved composite performance without excessively reducing its processing properties and toughness. Excessive filler content may lead to nanoparticle aggregation and processing difficulties, while insufficient filler content may not significantly improve the composite material's performance.

[0042] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0043] Example 1

[0044] Example 1 provides a method for preparing surface-modified nano-calcium carbonate, comprising the following steps:

[0045] S1. Prepare a calcium chloride solution with a concentration of 0.5 mol / L and an anhydrous sodium carbonate solution with a concentration of 0.5 mol / L;

[0046] S2. Measure 500 ml of calcium chloride solution and place it in a beaker, add dodecylbenzenesulfonic acid solution, and sonicate for 30 min;

[0047] S3. Slowly add 500 ml of anhydrous sodium carbonate solution and stir the reaction thoroughly to obtain calcium carbonate precipitate, and adjust the solution to neutral.

[0048] S4. The calcium carbonate precipitate is washed and dried. It is then transported to an exchanger using 180°C hot air. Octane is vaporized using 180°C hot air and transported to the exchanger for complete exchange reaction, yielding surface-modified nano-calcium carbonate material. (Example:) Figure 1 As shown, amphiphilic small molecules are distributed around calcium carbonate, and long-chain alkyl molecules surround the amphiphilic small molecules, forming two organic layers. Surface-treated calcium carbonate particles are more easily dispersed in the polymer matrix, thereby improving the processing properties of the composite material and the physical and mechanical properties of the final product. Figure 2 As shown, the prepared surface-modified nano-calcium carbonate has a concentrated size distribution and uniform particle size, ranging from 50 to 100 nm.

[0049] Examples 2-8

[0050] Examples 2-8 provide a method for preparing surface-modified nano-calcium carbonate. Compared with Example 1, the only difference is the type of amphiphilic molecule, the type of long-chain alkyl group, and the amount added, as shown in Table 1. Other experimental parameters and conditions are basically the same as those in Example 1, and will not be repeated here.

[0051] Table 1 Comparison of experimental parameters

[0052]

[0053] Comparative Example 1

[0054] Comparative Example 1 provides a method for preparing surface-modified nano-calcium carbonate. The only difference from Example 1 is that no long-chain alkane compound is added in step S4. Other experimental parameters and conditions are basically the same as in Example 1, and will not be repeated here.

[0055] Comparative Example 2

[0056] Comparative Example 2 provides a method for preparing surface-modified nano-calcium carbonate, which uses a coupling agent to treat the nano-calcium carbonate, including the following steps: surface treatment of the prepared nano-calcium carbonate with a titanate coupling agent, wherein the mass ratio of nano-calcium carbonate to titanate coupling agent is 1:0.1, and other experimental parameters and conditions are basically the same as those in Example 1, and will not be repeated here.

[0057] The characterization of nano-calcium carbonate includes oil absorption value, water absorption rate, and activation degree. The tests were conducted according to the GB / T 19590-2011 test standard for nano-calcium carbonate. The test results are shown in Table 2. The oil absorption value is the amount of DOP (dioctyl phthalate) absorbed per 100 grams of sample; the water absorption rate is the test result after the sample has been continuously exposed at 85℃ and 95% humidity for 72 hours.

[0058] Table 2. Test results of the examples and comparative examples.

[0059] project Oil absorption value (g) Water absorption rate (%) Activation degree (%) Example 1 10.85 0.25 98.78 Example 2 10.29 0.19 99.01 Example 3 9.87 0.13 99.26 Example 4 9.43 0.08 99.86 Example 5 13.45 0.18 95.69 Example 6 12.78 0.15 96.28 Example 7 11.97 0.11 97.88 Example 8 11.12 0.09 98.45 Comparative Example 1 49.57 0.76 15.78 Comparative Example 2 31.29 0.51 85.89

[0060] As shown in Table 2, under the same conditions, both long-chain stearic acid and long-chain alkylbenzene sulfonic acid amphiphilic small molecules exhibit good surface treatment effects on nano-calcium carbonate. With increasing amphiphilic small molecule content, the oil absorption value and water absorption rate of nano-calcium carbonate gradually decrease, while the activation degree gradually increases. This is because an increase in the content of the modifying molecules leads to a better modification effect on nano-calcium carbonate. Amphiphilic small molecules can adsorb onto the surface of nano-calcium carbonate, forming a modified layer. The hydrophilic and hydrophobic ends of these molecules can interact with water and oily substances, respectively, thereby altering the surface properties of nano-calcium carbonate. With increasing amphiphilic small molecule content, more of the nano-calcium carbonate surface is modified, reducing the direct contact area with oil or water; therefore, the oil absorption value and water absorption rate gradually decrease. As the molecular weight of amphiphilic molecules and long-chain alkane modifiers increases, the oil absorption value and water absorption rate of nano-calcium carbonate gradually decrease, while the activation degree gradually increases. This is because the larger molecular weight amphiphilic molecules and activating molecules have a better coating effect on calcium carbonate, and the molecular coating layer on the surface of nano-calcium carbonate is more complete and dense, which further reduces the oil absorption value and water absorption rate and increases the activation degree.

[0061] Comparative Example 1, without the addition of long-chain alkane compounds, showed a significant increase in oil absorption value and water absorption rate, and a decrease in activation degree. This indicates a synergistic effect between the long-chain alkane compounds and the amphiphilic molecules. The amphiphilic molecules bind to the surface of nano-calcium carbonate through their hydrophilic and hydrophobic ends, while the long-chain alkane compounds enhance the formation of the hydrophobic layer, making the modified layer more complete and dense. The long-chain alkyl groups can reduce the interaction between nanoparticles and oily substances, thereby reducing the oil absorption value. The synergistic effect of the amphiphilic molecules and the long-chain alkane compounds can reduce the hydrophilicity of the nano-calcium carbonate surface, thereby reducing the water absorption rate. At the same time, the long-chain alkane compounds also help the amphiphilic molecules to better anchor on the surface of nano-calcium carbonate, thereby increasing its activation degree. In contrast, Comparative Example 2, which used traditional coupling agents to activate calcium carbonate, showed a high oil absorption value and low activation degree, indicating that the method of this application has a better surface modification effect on nano-calcium carbonate.

[0062] The nano-calcium carbonate prepared in the examples and comparative examples was melt-blended and modified with polypropylene, wherein the nano-calcium carbonate filler mass was 5%. The mixture was then modified and granulated using a twin-screw extruder to prepare standard test specimens, and the mechanical properties of the modified composite material were tested. The testing standard referenced Part 2 of GB / T1040.2, "Determination of Tensile Properties of Plastics: Test Conditions for Molded and Extruded Plastics". The test results are shown in Table 3.

[0063] Table 3 Performance test results of composite materials

[0064]

[0065]

[0066] As shown in Table 3, when the amphiphilic molecule is sodium dodecylbenzenesulfonate, the tensile yield stress and tensile fracture stress of the modified polypropylene increase with the increase of the concentration of the amphiphilic molecule compared with the unmodified polypropylene material. This is because the polypropylene material with added inorganic powder has a better reinforcing effect of activated calcium carbonate, thus increasing the rigidity of the composite material. Similarly, the increase of long-chain alkyl modifiers also enhances the activation effect of calcium carbonate, resulting in a better modification effect on the composite material. As shown in Examples 5-8, both hexadecanoic acid and octadecanoic acid can affect the performance of the composite material, both having a certain reinforcing and toughening effect; the reinforcing and toughening effect on the polypropylene / calcium carbonate composite material becomes more obvious with the increase of the number of carbon atoms in the long-chain alkyl group.

[0067] In summary, this invention provides a surface-modified nano-calcium carbonate, its preparation method, and its applications. Unlike traditional methods of activating calcium carbonate with coupling agents, the surface-modified nano-calcium carbonate prepared by this invention has the advantages of concentrated size distribution, uniform particle size, and high activation. The preparation method of this invention has the advantages of rapid activation and simple process. Unlike traditional modification methods using coupling agents and surfactants, this invention self-assembles two organic layers on the surface of the nano-calcium carbonate, exhibiting advantages of high activity and good compatibility with polyolefin materials. The surface-modified nano-calcium carbonate of this invention can be applied to the reinforcement, filling, and modification of polymer materials, showing great application prospects.

[0068] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing surface-modified nano-calcium carbonate, characterized in that, Includes the following steps: S1. Configure Ca respectively 2+ Solutions, amphiphilic molecular solutions, and anhydrous sodium carbonate solutions are prepared for use; the amphiphilic molecules in the amphiphilic molecular solutions are long-chain sodium benzenesulfonate salts or long-chain stearic acids. S2. To Ca 2+ Add an amphiphilic molecular solution to the solution and mix ultrasonically for a predetermined time; S3. Slowly add anhydrous sodium carbonate solution to the solution obtained in step S2, stir the reaction thoroughly to obtain calcium carbonate precipitate, and adjust the pH of the solution to neutral. S4. The calcium carbonate precipitate obtained in step S3 is washed and dried, and then fully exchanged with the long-chain alkane compound in an exchanger to obtain surface-modified nano-calcium carbonate; both the calcium carbonate precipitate and the long-chain alkane compound are transported to the exchanger through high-temperature air at 120~250℃, and the mass ratio of the calcium carbonate precipitate to the long-chain alkane compound is 1:(0.05~0.5).

2. The method for preparing surface-modified nano-calcium carbonate according to claim 1, characterized in that, In step S1, the Ca 2+ The concentration of the solution is 0.1~1 mol / L; the concentration of the anhydrous sodium carbonate solution is 0.1~1 mol / L.

3. The method for preparing surface-modified nano-calcium carbonate according to claim 2, characterized in that, The Ca 2+ The solution is one of calcium chloride, calcium sulfate, calcium nitrate, and calcium hydroxide.

4. The method for preparing surface-modified nano-calcium carbonate according to claim 1, characterized in that, In step S2, the Ca 2+ Ca in solution 2+ The molar ratio of the amphiphilic molecules to the amphiphilic molecules in the solution is 1:(1~10).

5. The method for preparing surface-modified nano-calcium carbonate according to claim 4, characterized in that, The ultrasonic mixing time is 25-35 minutes.

6. The method for preparing surface-modified nano-calcium carbonate according to claim 1, characterized in that, The long-chain alkane compound is one of n-octane, n-nonane, n-decane, n-undecane to n-docoane, and low-temperature paraffin.

7. A surface-modified nano-calcium carbonate, characterized in that, It is prepared by the method for preparing surface-modified nano-calcium carbonate according to any one of claims 1-6.

8. An application of the surface-modified nano-calcium carbonate as described in claim 7, characterized in that, The surface-modified nano-calcium carbonate was melt-blended with polypropylene to prepare a PP / nano-calcium carbonate composite material, wherein the filler mass of the surface-modified nano-calcium carbonate was 5-8%.

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