A modified nano calcium carbonate and its preparation method and application

Abstract

The present invention relates to the field of calcium carbonate technology, and more particularly to a modified nano-calcium carbonate, a preparation method thereof, and an application thereof. The preparation method of the modified nano-calcium carbonate provided by the present invention controls the crystal form and grain morphology of the nano-calcium carbonate by using a crystal form controller and a stabilizer, and then modifies the obtained nano-calcium carbonate using a surface modifier. The obtained modified nano-calcium carbonate has significantly improved dispersibility, hydrophobicity, and compatibility with an organic matrix. When the modified nano-calcium carbonate is filled into a rubber product, it can achieve good compatibility with the rubber matrix. The tensile strength, elongation at break, and tear strength of the obtained rubber product are significantly improved, and the rubber product has a significant reinforcing effect.

Description

Technical Field

[0001] The present invention relates to the technical field of calcium carbonate, and in particular to a modified nano calcium carbonate and a preparation method and application thereof. Background Art

[0002] Nano-calcium carbonate, also known as ultrafine calcium carbonate, is a cubic calcium carbonate nanoparticle with uniformly dispersed surface charges. Due to the ultrafine size of nano-calcium carbonate particles, their crystal structure and surface electronic structure change, resulting in quantum size effects, small size effects, surface effects, and macroscopic quantum effects not found in ordinary calcium carbonate. These effects offer significant advantages over conventional powder materials in terms of reinforcement, transparency, dispersibility, thixotropy, and rheological properties. Consequently, nano-calcium carbonate is often used as a filler in industries such as rubber, plastics, papermaking, coatings, inks, pharmaceuticals, food, and daily necessities.

[0003] However, due to its high specific surface area and surface energy, nano-calcium carbonate is prone to agglomeration during application. Furthermore, the presence of numerous hydroxyl groups on its surface renders it hydrophilic and oleophobic, resulting in poor affinity with non-polar or weakly polar substances, leading to poor compatibility with organic matrices, preventing the full realization of the advantages of nano-materials. Furthermore, the carbonization method often yields nano-calcium carbonate with multiple different crystal forms and morphologies. When nano-calcium carbonate with these different crystal forms and morphologies is used to fill other materials, the desired reinforcement effect is often unattainable due to the coexistence of these various crystal forms and morphologies. Summary of the Invention

[0004] In view of this, the present invention provides a method for preparing modified nano-calcium carbonate. The method modifies nano-calcium carbonate to obtain a modified nano-calcium carbonate with a chain structure, complete grains, uniform particle size, good dispersibility, hydrophobicity and compatibility with organic matrices.

[0005] In order to solve the above technical problems, the present invention provides a method for preparing modified nano-calcium carbonate, comprising the following steps:

[0006] S1, quicklime and water are mixed to form a slurry with a calcium hydroxide content of 15wt% to 20wt%, and a gas containing CO2 is introduced at room temperature for carbonization. When the carbonization rate reaches 20% to 40%, a stabilizer is added and carbonization is continued until the pH of the calcium hydroxide slurry is 7.0 to 7.5. The carbonization is completed to obtain a nano calcium carbonate slurry;

[0007] S2, aging the obtained nano calcium carbonate slurry, then heating it to 60-90° C., adding a surface modifier, and stirring the reaction for 2-4 hours to obtain a modified nano calcium carbonate slurry;

[0008] S3, filtering and drying the obtained modified nano-calcium carbonate slurry to obtain modified nano-calcium carbonate;

[0009] The stabilizer is at least one of aluminum hydroxide, aluminum oxide or aluminum chloride; the surface modifier is obtained by mixing equimolar sodium salts, phosphate compounds and fatty acid salts; and the crystal form controller is obtained by mixing at least one of lysine, arginine or histidine with at least one of sodium hexametaphosphate, ethylenediaminetetraacetic acid or maleic acid.

[0010] The present invention provides a method for preparing modified nano-calcium carbonate. A crystal form controller is added at the beginning of the reaction, and a stabilizer is added when the carbonization rate reaches a certain value. This helps to obtain crystals with complete crystal form and uniform particle size. The use of the crystal form controller allows the amino acid in the crystal form controller to guide the nano-calcium carbonate to form calcite-type crystals. The salt or acid in the crystal form controller can also interfere with the growth and distribution of the crystals, causing the crystals to tend to align along the same axis. When the carbonization rate reaches 20% to 40%, the stabilizer is added. The binding effect of aluminum hydroxide, a hydrolysis product of the stabilizer, is utilized to bond the calcium carbonate crystals, which have been coaxially arranged due to the interference of the salt or acid in the crystal form controller, together, to obtain chain-like nano-calcium carbonate with stable morphology.

[0011] In addition, the inventors unexpectedly discovered in experimental research on the surface modification of nano-calcium carbonate that after modifying the surface of nano-calcium carbonate using a surface modifier obtained by mixing three modifiers: sodium salt, phosphate compound, and fatty acid salt, the dispersibility, hydrophobicity, and compatibility with organic matrices of the resulting nano-calcium carbonate were significantly improved compared to the effects of using any one modifier alone. The inventors speculate that the reason for this is as follows: when the three modifiers are used in combination, the three modifiers can simultaneously undergo physical or chemical reactions with the nano-calcium carbonate. During this simultaneous physical or chemical reaction, their modification effects on the surface of the nano-calcium carbonate promote each other, thereby generating a synergistic effect, which significantly improves the above-mentioned properties of the modified nano-calcium carbonate.

[0012] Specifically: sodium salt is adsorbed on the surface of calcium carbonate as an electrolyte, which can significantly increase the absolute value of the surface potential of nano-calcium carbonate, and then the repulsion of like charges can be used to prevent the agglomeration of nano-calcium carbonate particles; under the action of sodium salt in preventing the agglomeration of nano-calcium carbonate particles, the contact space between phosphate compounds and fatty acid salts and nano-calcium carbonate is relatively increased, making the chemical reaction between phosphate compounds and fatty acid salts and calcium carbonate easier to proceed; and the alkyl chains in phosphate compounds and fatty acid salts can further increase the steric hindrance between nano-calcium carbonate particles, so that the smaller sodium salt can continue to be adsorbed to the surface of unreacted nano-calcium carbonate, realizing the synergistic modification of nano-calcium carbonate by the three modifiers.

[0013] The specific surface area of the modified nano-calcium carbonate is reduced, and the total surface energy is lowered, making agglomeration less likely to occur; and the alkyl ends of the phosphate compounds and fatty acid salts surround the surface of the nano-calcium carbonate, increasing the compatibility of the nano-calcium carbonate with the organic matrix; at the same time, due to the presence of phosphorus in the phosphate compounds, the modified nano-calcium carbonate has a certain flame retardancy.

[0014] In conjunction with the first aspect, the amount of the crystal form control agent added in S1 is 0.2% to 1.0% of the dry weight of the calcium hydroxide in the slurry, and the amount of the stabilizer added is 0.5% to 3.0% of the dry weight of the calcium hydroxide in the slurry. If the amount of the crystal form control agent and stabilizer added is too small, chain-like nano-calcium carbonate cannot be generated, while if it is too large, it is not conducive to obtaining complete grains with uniform particle size.

[0015] In combination with the first aspect, the volume concentration of CO2 in the gas in S1 is 35% to 45%.

[0016] In combination with the first aspect, the mass ratio of at least one of lysine, arginine or histidine to at least one of sodium hexametaphosphate, ethylenediaminetetraacetic acid or maleic acid is 1:0.8-1.2.

[0017] Among them, lysine, arginine or histidine is used to guide and control the formation of calcite-type grains of nano-calcium carbonate, and sodium hexametaphosphate, ethylenediaminetetraacetic acid or maleic acid is used to interfere with the growth and distribution of grains so that the grains tend to be arranged along the same axis.

[0018] In combination with the first aspect, the added amount of the surface modifier in S2 is 3.0% to 8.0% of the dry weight of the nano-calcium carbonate in the nano-calcium carbonate slurry.

[0019] In combination with the first aspect, the drying temperature in S3 is 140-150° C. and the moisture content in the modified nano-calcium carbonate is less than 0.2%. Such drying temperature and moisture content can obtain modified nano-calcium carbonate with satisfactory whiteness.

[0020] In combination with the first aspect, the sodium salt is selected from sodium silicate or sodium aluminate; the phosphate ester compound is selected from lauryl alcohol monophosphate, dilauryl alcohol phosphate, myristyl alcohol monophosphate, myristyl alcohol diester phosphate, octadecyl phosphate or ethylene glycol acrylate phosphate; the fatty acid salt is selected from sodium stearate or sodium palmitate.

[0021] A second aspect of the present invention provides a modified nano-calcium carbonate prepared using the aforementioned method. This modified nano-calcium carbonate can be used to fill rubber. When this modified nano-calcium carbonate is added to a rubber raw material, during the mixing process, the chain-like nano-calcium carbonate "chains" are severed, forming a large number of active sites with highly active surfaces. These active sites can bond with molecules in the rubber, significantly enhancing the reinforcing effect.

[0022] A third aspect of the present invention provides a use of modified nano-calcium carbonate in the preparation of rubber products or plastic products, which can be used as a reinforcing agent for rubber products or plastic products, thereby improving the mechanical strength of the rubber products or plastic products.

[0023] The present invention has the following beneficial effects: the method for preparing modified nano-calcium carbonate provided by the present invention controls the crystal form and grain morphology of the nano-calcium carbonate by sequentially adding a crystal form control agent and a stabilizer to obtain chain-like nano-calcium carbonate; the obtained nano-calcium carbonate is then modified with a surface modifier. Through the synergistic effect between the different substances that make up the surface modifier, the obtained modified nano-calcium carbonate has significantly improved dispersibility, hydrophobicity, and compatibility with organic matrices. When the modified nano-calcium carbonate is filled into a rubber product, it can achieve good compatibility with the rubber matrix, and the resulting rubber product has significantly improved tensile strength, elongation at break, and tear strength, showing a significant reinforcing effect. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0025] Example 1

[0026] This embodiment provides a preparation method of modified nano-calcium carbonate and modified nano-calcium carbonate, and the specific steps include:

[0027] S1, quicklime and water are mixed in proportion to obtain a slurry with a calcium hydroxide content of 18wt%, a crystal form control agent equivalent to 0.6% by weight of calcium hydroxide on dry basis is added, CO is introduced at a flow rate of 18L / h at room temperature The gas with a volume concentration of 40% is bubbling and carbonizing, when the carbonization rate reaches 30%, a stabilizer equivalent to 2.0% by weight of calcium hydroxide on dry basis is added, and bubbling and carbonizing are continued to the pH of the slurry being 7.0, and carbonization terminates to obtain nano calcium carbonate slurry;

[0028] S2, aging the obtained nano-calcium carbonate slurry for 15 hours, then heating to 75° C., adding a surface modifier equivalent to 5.0% of the dry weight of the nano-calcium carbonate, and stirring the reaction for 3 hours to obtain a modified nano-calcium carbonate slurry;

[0029] S3. Filter the obtained modified nano-calcium carbonate slurry, and dry it at 145° C. until the moisture content is less than 0.2% to obtain modified nano-calcium carbonate.

[0030] The stabilizers are aluminum hydroxide and aluminum oxide, the surface modifier is obtained by mixing equimolar amounts of sodium silicate, lauryl alcohol monophosphate and sodium stearate, and the crystal form controller is obtained by mixing lysine and sodium hexametaphosphate in a mass ratio of 1:1.

[0031] Example 2

[0032] This embodiment provides a preparation method of modified nano-calcium carbonate and modified nano-calcium carbonate, and the specific steps include:

[0033] S1, quicklime and water are mixed in proportion to obtain a slurry with a calcium hydroxide content of 20wt%, a crystal form control agent equivalent to 1.0% by weight of calcium hydroxide on dry basis is added, CO is passed through at a flow rate of 20L / h at room temperature The gas with a volume concentration of 45% is bubbling and carbonizing, when the carbonization rate reaches 20%, a stabilizer equivalent to 3.0% by weight of calcium hydroxide on dry basis is added, and bubbling and carbonizing are continued to a pH of 7.5 to the calcium hydroxide slurry, and carbonization terminates to obtain nano calcium carbonate slurry;

[0034] S2, aging the obtained nano-calcium carbonate slurry for 20 hours, then heating it to 90° C., adding a surface modifier equivalent to 8.0% of the dry weight of the nano-calcium carbonate, and stirring the reaction for 4 hours to obtain a modified nano-calcium carbonate slurry;

[0035] S3. Filter the obtained modified nano-calcium carbonate slurry, and dry it at 150° C. until the moisture content is less than 0.2% to obtain modified nano-calcium carbonate.

[0036] Among them, the stabilizer is aluminum hydroxide and aluminum chloride, the surface modifier is obtained by mixing equimolar amounts of sodium aluminate, myristyl alcohol phosphate diester and sodium palmitate, and the crystal form controller is obtained by mixing lysine and arginine with ethylenediaminetetraacetic acid in a mass ratio of 1:1.2.

[0037] Example 3

[0038] This embodiment provides a preparation method of modified nano-calcium carbonate and modified nano-calcium carbonate, and the specific steps include:

[0039] S1, quicklime and water are mixed in proportion to obtain a slurry with a calcium hydroxide content of 15wt%, a crystal form control agent equivalent to 0.2% by weight of calcium hydroxide on dry basis is added, CO is passed through at a flow rate of 15L / h at room temperature The gas with a volume concentration of 35% is bubbling and carbonizing, when the carbonization rate reaches 40%, a stabilizer equivalent to 0.5% by weight of calcium hydroxide on dry basis is added, and bubbling and carbonizing are continued to a pH of 7.5 to the calcium hydroxide slurry, and carbonization terminates to obtain nano calcium carbonate slurry;

[0040] S2, aging the obtained nano-calcium carbonate slurry for 15 hours, then heating to 75° C., adding a surface modifier equivalent to 3.0% of the dry weight of the nano-calcium carbonate, and stirring the reaction for 2 hours to obtain a modified nano-calcium carbonate slurry;

[0041] S3. Filter the obtained modified nano-calcium carbonate slurry, and dry it at 140° C. until the moisture content is less than 0.2% to obtain modified nano-calcium carbonate.

[0042] The stabilizers are aluminum chloride and aluminum oxide, the surface modifier is obtained by mixing equimolar amounts of sodium silicate, ethylene glycol acrylate phosphate and sodium stearate, and the crystal form controller is obtained by mixing histidine and sodium maleate in a mass ratio of 1:0.8.

[0043] Example 4

[0044] This embodiment provides a preparation method of modified nano-calcium carbonate and modified nano-calcium carbonate. The specific steps are similar to those in Example 1, except that the stabilizer used is aluminum hydroxide, the surface modifier is obtained by mixing equimolar amounts of sodium silicate, octadecyl phosphate, and sodium palmitate, and the crystal form control agent is obtained by mixing a mixture of lysine, arginine, and histidine with a mixture of ethylenediaminetetraacetic acid and maleic acid in a mass ratio of 1:1.

[0045] Example 5

[0046] This embodiment provides an application of the modified nano-calcium carbonate prepared in Example 1 in EPDM rubber, and the specific method is as follows:

[0047] Mix 100 parts of EPDM rubber, 20 parts of modified nano-calcium carbonate, 1 part of methyl methacrylate, 0.2 parts of dicumyl peroxide and 1.2 parts of stearic acid and mix them in an open mill at 40°C for 10 minutes. After standing for 12 hours, add 1.5 parts of sulfur and mix them in an internal mixer at 170°C for 6 minutes, and then drain the glue to obtain the product.

[0048] Comparative Example 1

[0049] This embodiment provides a preparation method of modified nano-calcium carbonate and modified nano-calcium carbonate. The specific steps are similar to those in Example 1, except that the stabilizer and crystal form control agent in S1 are added simultaneously, that is, the stabilizer is added before the carbonization reaction begins. The remaining steps are the same as those in Example 1.

[0050] Comparative Example 2

[0051] This embodiment provides a preparation method of modified nano-calcium carbonate and modified nano-calcium carbonate. The specific steps are similar to those in Example 1, except that only a crystal form control agent is added in S1 without adding a stabilizer. The remaining steps are the same as those in Example 1.

[0052] Comparative Example 3

[0053] This embodiment provides a preparation method of modified nano-calcium carbonate and modified nano-calcium carbonate. The specific steps are similar to those in Example 1, except that the crystal form control agent used in S1 is only lysine, arginine, histidine or a mixture thereof, and the remaining steps are the same as those in Example 1.

[0054] Comparative Example 4

[0055] This embodiment provides a preparation method of modified nano-calcium carbonate and modified nano-calcium carbonate. The specific steps are similar to those in Example 1, except that the surface modifier used in S2 is only sodium silicate, and the remaining steps are the same as those in Example 1.

[0056] Comparative Example 5

[0057] This embodiment provides a preparation method of modified nano-calcium carbonate and modified nano-calcium carbonate. The specific steps are similar to those in Example 1, except that the surface modifier used in S2 is only one of the above-mentioned phosphate compounds, and the remaining steps are the same as those in Example 1.

[0058] Comparative Example 6

[0059] This embodiment provides a preparation method of modified nano-calcium carbonate and modified nano-calcium carbonate. The specific steps are similar to those in Example 1, except that the surface modifier used in S2 is only sodium stearate, and the remaining steps are the same as those in Example 1.

[0060] Comparative Example 7

[0061] This embodiment provides a preparation method of modified nano-calcium carbonate and modified nano-calcium carbonate. The specific steps are similar to those in Example 1, except that the amino acid in the crystal form control agent used in S1 is glutamic acid. The remaining steps are the same as those in Example 1.

[0062] Comparative Example 8

[0063] This embodiment provides a preparation method of modified nano-calcium carbonate and modified nano-calcium carbonate. The specific steps are similar to those in Example 1, except that the amino acid in the crystal form control agent used in S1 is alanine. The remaining steps are the same as those in Example 1.

[0064] Test Example 1

[0065] The modified nano-calcium carbonate obtained in Examples 1 to 4 and Comparative Examples 1 to 8 were subjected to static water contact angle tests, and their grain integrity and particle size uniformity were observed using a scanning electron microscope. The results are shown in Table 1.

[0066] Table 1 Test results of modified nano calcium carbonate obtained from Examples 1 to 4 and Comparative Examples 1 to 8

[0067]

[0068] As can be seen from Table 1, when the stabilizer and the crystal form controller are added at the same time or only amino acid is used as the crystal form controller, the particle size of the obtained nano-calcium carbonate particles is not uniform, indicating that the addition of the stabilizer in the early stage of carbonization affects the growth of the grains, while the use of a single type of crystal form controller cannot interfere with the growth and distribution of the grains, allowing the grains to grow freely, resulting in different grain sizes.

[0069] From the water contact angles of the nano-calcium carbonate obtained in Examples 1 to 4 and Comparative Examples 1 to 8, it can be seen that the hydrophobicity of the modified nano-calcium carbonate obtained by using the surface modifier provided by the present invention is significantly better than that of using a single modifier.

[0070] Effect Example 1

[0071] The modified nano-calcium carbonate obtained in Examples 1 to 4 and Comparative Examples 1 to 8 were respectively used as reinforcing agents to be filled into EPDM rubber, and the specific method was as follows:

[0072] Mix 100 parts of EPDM rubber, 20 parts of modified nano-calcium carbonate, 1 part of methyl methacrylate, 0.2 parts of dicumyl peroxide and 1.2 parts of stearic acid and mix them in an open mill at 40°C for 10 minutes. After standing for 12 hours, add 1.5 parts of sulfur and mix them in an internal mixer at 170°C for 6 minutes, and then drain the glue to obtain the product.

[0073] The tensile strength, elongation at break and tear strength of the obtained rubber were tested respectively, and the results are shown in Table 2.

[0074] Table 2 Mechanical properties test results of filled rubber

[0075]

[0076] As can be seen from Table 2, compared with the mechanical properties of the rubber filled with the modified nano-calcium carbonate obtained in Comparative Examples 1 to 8, the tensile strength, elongation at break and tear strength of the rubber filled with the modified nano-calcium carbonate provided by the present invention are significantly improved, indicating that the present invention has successfully prepared modified nano-calcium carbonate with a chain structure and good compatibility with the rubber matrix, and its use in filling rubber can play a significant reinforcing role.

[0077] The above is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with this technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solutions and inventive concepts of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing modified nano calcium carbonate, characterized in that the steps include: S1, quicklime and water are mixed to form a slurry with a calcium hydroxide content of 15wt% to 20wt%, a crystal form control agent is added, and a gas containing CO2 is introduced at room temperature for carbonization. When the carbonization rate reaches 20% to 40%, a stabilizer is added and carbonization is continued until the pH of the slurry is 7.0 to 7.

5. The carbonization is completed to obtain a nano calcium carbonate slurry; S2, aging the obtained nano-calcium carbonate slurry, then heating it to 60-90° C., adding a surface modifier, and stirring the reaction for 2-4 hours to obtain a modified nano-calcium carbonate slurry; S3, filtering and drying the obtained modified nano-calcium carbonate slurry to obtain modified nano-calcium carbonate; The stabilizer is at least one of aluminum hydroxide and aluminum chloride, or a mixture of at least one of aluminum hydroxide and aluminum chloride and aluminum oxide; the surface modifier is obtained by mixing equimolar sodium salts, phosphate compounds and fatty acid salts, the sodium salt is selected from sodium silicate or sodium aluminate, the phosphate compounds are selected from lauryl alcohol monophosphate, dilauryl alcohol phosphate, myristyl alcohol monophosphate, myristyl alcohol diester phosphate, n-octadecyl phosphate or ethylene glycol acrylate phosphate, and the fatty acid salt is selected from sodium stearate or sodium palmitate; the crystal form control agent is obtained by mixing at least one of lysine, arginine or histidine with at least one of sodium hexametaphosphate, ethylenediaminetetraacetic acid or maleic acid.

2. The preparation method of modified nano calcium carbonate as claimed in claim 1, wherein S1: the amount of the crystal form control agent added is 0.2% to 1.0% of the dry weight of calcium hydroxide in the slurry; and / or The amount of the stabilizer added is 0.5% to 3.0% of the dry weight of the calcium hydroxide in the slurry.

3. The preparation method of modified nano calcium carbonate as claimed in claim 1, wherein The volume concentration of CO2 in the gas S1 is 35% to 45%.

4. The preparation method of modified nano calcium carbonate as claimed in claim 1, wherein The mass ratio of at least one of lysine, arginine or histidine to at least one of sodium hexametaphosphate, ethylenediaminetetraacetic acid or maleic acid is 1:0.8-1.

2.

5. The preparation method of modified nano calcium carbonate as claimed in claim 1, wherein The amount of the surface modifier added in S2 is 3.0% to 8.0% of the dry weight of the nano-calcium carbonate in the nano-calcium carbonate slurry.

6. The method for preparing modified nano-calcium carbonate according to any one of claims 1 to 5, characterized in that: The drying temperature in step S3 is 140-150° C.; and / or The moisture content of the modified nano-calcium carbonate is less than 0.2%.

7. A modified nano calcium carbonate, characterized in that, The modified nano calcium carbonate is prepared by the preparation method of any one of claims 1 to 6.

8. The use of the modified nano-calcium carbonate according to claim 7 in the preparation of rubber products or plastic products, characterized in that: The modified nano calcium carbonate is used as a reinforcing agent for rubber products or plastic products.

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