Modified amorphous calcium carbonate, method for producing the same, and cellulose composite paper

Abstract

The application provides a modified amorphous calcium carbonate, a preparation method of the modified amorphous calcium carbonate and a cellulose composite paper, and the preparation method of the modified amorphous calcium carbonate comprises the following steps: (1) mixing magnesium chloride and calcium chloride in water, adding sodium carbonate, and performing reaction under stirring to generate amorphous calcium carbonate; (2) adding cationic chitosan to the reaction system obtained in the step (1) and performing reaction under stirring; and (3) washing and drying the product obtained in the step (2) to obtain the modified amorphous calcium carbonate. The modified amorphous calcium carbonate prepared by the application exhibits high affinity to protein and high stability in a dry environment, and the cellulose composite paper prepared by compounding cellulose and the modified amorphous calcium carbonate exhibits high protein affinity capacity, so that the application of the cellulose composite paper in the detection field is widened.

Description

Technical Field

[0001] This invention belongs to the field of functional paper preparation technology, specifically a modified amorphous calcium carbonate, its preparation method, and cellulose composite paper. Background Technology

[0002] Paper-based materials have long been used as solid matrices for immobilizing biomolecules in various bioassays. Due to their reliable results and ease of operation, they are commonly used in lateral chromatography (LFA). LFA primarily relies on ligand-receptor interactions to detect the presence or absence of a target. In a typical LFA, trapped molecules are usually passively adsorbed and immobilized on the paper matrix to form a test zone. When the target molecule and detector particles flow through the paper matrix, they form a complex with the trapped molecule in the test zone. Subsequently, the detector particles generate a signal, producing a visually distinguishable line or dot. Furthermore, the analyte passing through the LFA test strip can be self-driven by the capillary force of the paper matrix, eliminating the need for an external fluid control system. One of the most commonly used paper-based materials in LFA is nitrocellulose membrane. Nitrocellulose membranes exhibit high affinity for proteins, but their relatively high price limits their application.

[0003] On the other hand, cellulose paper has become a research hotspot due to its low cost and wide availability, but its protein binding capacity is relatively low. To improve the performance of cellulose paper, researchers have adopted various strategies, such as surface modification to introduce different functional groups, regulating pore structure, and controlling surface charge. These chemical activation techniques can greatly improve protein immobilization. However, their application in LFA (Liquid Acid Fabrication) is very limited because many chemical reagents need to be prepared fresh, which does not meet practical application requirements.

[0004] Currently, most calcium carbonate fillers commonly used in paper bases are calcite-type calcium carbonate, which has relatively large particles that may aggregate on the paper surface, thus affecting the paper's physical properties. Amorphous calcium carbonate, on the other hand, has smaller particles and a larger specific surface area. This type of calcium carbonate is beneficial for improving paper gloss, smoothness, and printability. It can also fill the micropores in the paper, increasing its density and uniformity, thereby enhancing its mechanical properties. However, amorphous calcium carbonate has poor stability and easily crystallizes upon contact with water. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a modified amorphous calcium carbonate, its preparation method, and cellulose composite paper. The modified filler prepared by this invention exhibits high affinity for proteins and high stability in a dry environment. The cellulose composite paper obtained by combining cellulose and modified amorphous calcium carbonate exhibits high protein affinity, thus broadening the application of cellulose composite paper in the field of detection.

[0006] This invention is achieved through the following technical solution:

[0007] A method for preparing modified amorphous calcium carbonate includes the following steps:

[0008] (1) Mix magnesium chloride and calcium chloride in water, add sodium carbonate, and react under stirring to produce amorphous calcium carbonate.

[0009] (2) Add cationic chitosan to the reaction system obtained in step (1) and carry out the reaction under stirring conditions;

[0010] (3) Wash and dry the product obtained in step (2) to obtain modified amorphous calcium carbonate.

[0011] Preferably, in step (1), the molar ratio of magnesium chloride to calcium chloride is (0.1-2):1, and the number of moles of sodium carbonate is the same as the total number of moles of calcium chloride and magnesium chloride.

[0012] Preferably, in step (1), the reaction temperature is 20-40°C and the reaction time is 10-60s.

[0013] Preferably, in step (2), the mass ratio of cationic chitosan to sodium carbonate is (0.3-3):1.

[0014] Preferably, in step (2), the reaction temperature is 20-40°C and the reaction time is 60-120 min.

[0015] Preferably, in step (3), the drying process specifically involves vacuum drying at 50–100°C.

[0016] Modified amorphous calcium carbonate obtained by the preparation method described above.

[0017] A modified amorphous calcium carbonate / cellulose composite paper is obtained by combining the modified amorphous calcium carbonate and cellulose.

[0018] Preferably, the modified amorphous calcium carbonate accounts for 10% to 50% of the cellulose composite paper.

[0019] The method for preparing the modified amorphous calcium carbonate / cellulose composite paper involves dissolving modified amorphous calcium carbonate and cellulose, forming the paper, and obtaining the modified amorphous calcium carbonate / cellulose composite paper.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] This invention uses magnesium chloride and cationic chitosan as crystal stabilizers for amorphous calcium carbonate. In solution, because Mg... 2+ Its smaller ionic radius, when it replaces Ca in calcium carbonate2+ The placement of the material triggers a distortion of the crystal structure, complicating the crystallization process and hindering the transformation of amorphous calcium carbonate into crystalline calcium carbonate. This solves the problem of poor stability and rapid crystallization of amorphous calcium carbonate in solution. Simultaneously, the encapsulation of cationic chitosan on the surface of amorphous calcium carbonate not only further enhances its stability but also increases its surface potential, mitigating the low affinity of pure cellulose paper for proteins. The method of this invention utilizes widely available pharmaceutical materials, is environmentally friendly, and involves a simple process. Attached Figure Description

[0022] Figure 1 These are the XRD patterns of pure calcium carbonate (a) prepared without any stabilizer, magnesium chloride-stabilized amorphous calcium carbonate (b), and cationic chitosan-modified amorphous calcium carbonate (c) prepared according to Comparative Examples 1, 3, and 5 of this invention.

[0023] Figure 2 These are the FT-IR spectra of pure calcium carbonate (a) prepared without any stabilizer, magnesium chloride-stabilized amorphous calcium carbonate (b), and cationic chitosan-modified amorphous calcium carbonate (c) prepared according to Comparative Examples 1, 3, and 5 of this invention.

[0024] Figure 3 These are SEM images of pure calcium carbonate (a) prepared without any stabilizer, magnesium chloride-stabilized amorphous calcium carbonate (b), and cationic chitosan-modified amorphous calcium carbonate (c) prepared according to Comparative Examples 1, 3, and 5 of this invention.

[0025] Figure 4 This study investigates the stability of calcium carbonate obtained in Comparative Example 3 and Example 5 of this invention under humid and dry conditions.

[0026] Figure 5 This is an EDS elemental distribution map of the cationic chitosan-modified amorphous calcium carbonate prepared in Example 5.

[0027] Figure 6 This is an analysis of the protein adsorption performance of calcium carbonate obtained in Comparative Examples 1, 3, and 5.

[0028] Figure 7 The surface potential analysis of calcium carbonate obtained in Comparative Example 1, Comparative Example 3, and Example 5 is presented.

[0029] Figure 8 This is a three-dimensional perspective view of the fiber base paper prepared in Comparative Example 5 and the cellulose composite paper made by adding modified fillers in Example 5.

[0030] Figure 9 These are paper images of protein adsorption samples from Comparative Example 5 and Examples 2, 4, 5, and 6. Detailed Implementation

[0031] To further understand the present invention, the present invention will be described below with reference to embodiments. These descriptions are only for further explaining the features and advantages of the present invention and are not intended to limit the claims of the present invention.

[0032] The method for preparing modified amorphous calcium carbonate according to the present invention includes the following steps:

[0033] (1) Mix magnesium chloride and calcium chloride in deionized water, add sodium carbonate solution, and react under stirring to produce amorphous calcium carbonate.

[0034] (2) After the amorphous calcium carbonate is formed, cationic chitosan is added and the reaction is carried out under stirring to generate a cationic chitosan-modified amorphous calcium carbonate nanosphere structure.

[0035] (3) The cationic chitosan-modified amorphous calcium carbonate nanospheres were washed with deionized water and vacuum dried to obtain cationic chitosan-modified amorphous calcium carbonate nanospheres (i.e. modified amorphous calcium carbonate).

[0036] In this invention, in step (1), the molar ratio of magnesium chloride to calcium chloride is (0.1-2):1, and the total number of moles of sodium carbonate and calcium chloride and magnesium chloride in the solution is the same.

[0037] In this invention, in step (1), the reaction temperature is 20-40°C, the stirring speed is 200-1200 rpm, and the reaction time is 10-60 s.

[0038] In this invention, in step (2), after the amorphous calcium carbonate has formed for 10 seconds, cationic chitosan is added, wherein the mass ratio of cationic chitosan to sodium carbonate is (0.3-3):1. The reaction temperature is 20-40℃, the stirring speed is 200-1200 rpm, and the reaction time is 60-120 min.

[0039] In this invention, in step (3), the product is washed with deionized water 1 to 3 times, centrifuged at 8000 rpm for 5 to 15 minutes, and vacuum dried at 50 to 100°C and -70 to 100 kPa.

[0040] The method of the present invention further includes: adding the prepared cationic chitosan-modified amorphous calcium carbonate nanospheres and cellulose into a fiber delamination machine for delamination, forming paper on a paper forming machine to obtain amorphous calcium carbonate / cellulose composite paper.

[0041] The disintegration time is 10–60 min, and the proportion of cationic chitosan-modified amorphous calcium carbonate in the cellulose composite paper is 10%–50%.

[0042] Comparative Example 1

[0043] (1) Weigh 0.111 g of calcium chloride and dissolve it in 10 mL of deionized water to prepare solution A; weigh 0.106 g of sodium carbonate and dissolve it in 10 mL of deionized water to prepare solution B. At room temperature, mix equal volumes of solution A and solution B, and calcium carbonate precipitate will be formed.

[0044] (2) The calcium carbonate precipitate was washed three times with deionized water and dried under vacuum at 60°C for 48 hours to obtain calcium carbonate.

[0045] (3) The obtained calcium carbonate is added to the fiber dissolving solution, wherein the mass ratio of the dry fiber to the calcium carbonate is 2:1. The fiber is dissolved for 30 minutes on the fiber dissolving machine, and then paper is formed on the paper forming machine.

[0046] The cellulose composite paper prepared in Comparative Example 1 exhibited an adsorption capacity of 3.21 g / m³ for protein. 2 .

[0047] Comparative Example 2

[0048] (1) Weigh 0.111 g of calcium chloride and dissolve it in 10 mL of deionized water to prepare solution A; weigh 0.095 g of magnesium chloride and dissolve it in 10 mL of deionized water to prepare solution B; weigh 0.106 g of sodium carbonate and dissolve it in 10 mL of deionized water to prepare solution C. At room temperature, mix solution B and solution A at a volume ratio of 0.1:1 and stir at 1000 rpm until fully mixed. Then add an equal volume of solution C, and the reaction will produce an amorphous calcium carbonate precipitate.

[0049] (2) The amorphous calcium carbonate precipitate was washed three times with deionized water and dried under vacuum at 60°C for 48 hours to obtain amorphous calcium carbonate powder.

[0050] (3) The prepared amorphous calcium carbonate powder is added to the fiber dissolving liquid, wherein the mass ratio of the dry fiber to the amorphous calcium carbonate is 2:1. The fiber is dissolved for 30 minutes on the fiber dissolving machine and then formed into paper on the paper forming machine.

[0051] The cellulose composite paper prepared in Comparative Example 2 exhibited an adsorption capacity of 4.47 g / m³ for protein. 2 .

[0052] Comparative Example 3

[0053] (1) Weigh 0.111 g of calcium chloride and dissolve it in 10 mL of deionized water to prepare solution A; weigh 0.095 g of magnesium chloride and dissolve it in 10 mL of deionized water to prepare solution B; weigh 0.106 g of sodium carbonate and dissolve it in 10 mL of deionized water to prepare solution C. At room temperature, mix solution B and solution A at a volume ratio of 1.5:1 and stir at 1000 rpm until fully mixed. Then add an equal volume of solution C, and the reaction will produce an amorphous calcium carbonate precipitate.

[0054] (2) The amorphous calcium carbonate precipitate was washed three times with deionized water and dried under vacuum at 60°C for 48 hours to obtain amorphous calcium carbonate powder.

[0055] (3) The prepared amorphous calcium carbonate powder is added to the fiber dissolving liquid, wherein the mass ratio of the dry fiber to the amorphous calcium carbonate is 2:1. The fiber is dissolved for 30 minutes on the fiber dissolving machine and then formed into paper on the paper forming machine.

[0056] The cellulose composite paper prepared in Comparative Example 3 exhibited an adsorption capacity of 8.33 g / m³ for protein. 2 .

[0057] Comparative Example 4

[0058] (1) Weigh 0.111 g of calcium chloride and dissolve it in 10 mL of deionized water to prepare solution A; weigh 0.095 g of magnesium chloride and dissolve it in 10 mL of deionized water to prepare solution B; weigh 0.106 g of sodium carbonate and dissolve it in 10 mL of deionized water to prepare solution C. At room temperature, mix solution B and solution A at a volume ratio of 1.5:1 and stir at 1000 rpm until fully mixed. Then add an equal volume of solution C, and the reaction will produce an amorphous calcium carbonate precipitate.

[0059] (2) The amorphous calcium carbonate precipitate was washed three times with deionized water and dried under vacuum at 100°C for 48 hours to obtain amorphous calcium carbonate powder.

[0060] (3) The prepared amorphous calcium carbonate powder is added to the fiber dissolving liquid, wherein the mass ratio of the dry fiber to the amorphous calcium carbonate is 2:1. The fiber is dissolved for 30 minutes on the fiber dissolving machine and then formed into paper on the paper forming machine.

[0061] The cellulose composite paper prepared in Comparative Example 4 exhibited an adsorption capacity of 8.34 g / m³ for protein. 2 .

[0062] Comparative Example 5

[0063] Cellulose is decomposed on a fiber decomposition machine for 30 minutes, and then formed into paper on a paper forming machine to obtain fiber base paper.

[0064] The fiber base paper prepared in Comparative Example 5 exhibited an adsorption capacity of 7.01 g / m³ for protein. 2 .

[0065] Example 1

[0066] (1) Weigh 0.111 g of calcium chloride and dissolve it in 10 mL of deionized water to prepare solution A; weigh 0.095 g of magnesium chloride and dissolve it in 10 mL of deionized water to prepare solution B; weigh 0.106 g of sodium carbonate and dissolve it in 10 mL of deionized water to prepare solution C. At room temperature, mix solution B and solution A at a volume ratio of 1.5:1 and stir at 1000 rpm until fully mixed. Then add an equal volume of solution C, and the reaction will produce an amorphous calcium carbonate precipitate.

[0067] (2) After calcium carbonate precipitates for 10 seconds, cationic chitosan is added to the solution, and the concentration of cationic chitosan in the final solution is controlled to be 1 mg / mL. The reaction continues for 1 hour, and then the product is centrifuged at 8000 rpm for 8 minutes. The product is washed three times with deionized water and dried under vacuum at 60°C for 48 hours to obtain cationic chitosan modified calcium carbonate powder.

[0068] (3) The prepared cationic chitosan-modified calcium carbonate is added to the fiber dissolving solution, wherein the mass ratio of the dry fiber to the cationic chitosan-modified calcium carbonate is 8:1. The fiber is dissolved for 30 minutes on the fiber dissolving machine and then formed into paper on the paper forming machine.

[0069] The cellulose composite paper prepared in Example 1 exhibits a protein adsorption capacity of 8.99 g / m³. 2 .

[0070] Example 2

[0071] (1) Weigh 0.111 g of calcium chloride and dissolve it in 10 mL of deionized water to prepare solution A; weigh 0.095 g of magnesium chloride and dissolve it in 10 mL of deionized water to prepare solution B; weigh 0.106 g of sodium carbonate and dissolve it in 10 mL of deionized water to prepare solution C. At room temperature, mix solution B and solution A at a volume ratio of 1.5:1 and stir at 1000 rpm until fully mixed. Then add an equal volume of solution C, and the reaction will produce an amorphous calcium carbonate precipitate.

[0072] (2) After calcium carbonate precipitates for 10 seconds, cationic chitosan is added to the solution, and the concentration of cationic chitosan in the final solution is controlled to be 2 mg / mL. The reaction continues for 1 hour, and then the product is centrifuged at 8000 rpm for 8 minutes. The product is washed three times with deionized water and dried under vacuum at 60°C for 48 hours to obtain cationic chitosan modified calcium carbonate powder.

[0073] (3) The prepared cationic chitosan-modified calcium carbonate is added to the fiber dissolving solution, wherein the mass ratio of the dry fiber to the cationic chitosan-modified calcium carbonate is 8:1. The fiber is dissolved for 30 minutes on the fiber dissolving machine and then formed into paper on the paper forming machine.

[0074] The cellulose composite paper prepared in Example 2 exhibits a protein adsorption capacity of 9.87 g / m³. 2 .

[0075] Example 3

[0076] (1) Weigh 0.111 g of calcium chloride and dissolve it in 10 mL of deionized water to prepare solution A; weigh 0.095 g of magnesium chloride and dissolve it in 10 mL of deionized water to prepare solution B; weigh 0.106 g of sodium carbonate and dissolve it in 10 mL of deionized water to prepare solution C. At room temperature, mix solution B and solution A at a volume ratio of 1.5:1 and stir at 1000 rpm until fully mixed. Then add an equal volume of solution C, and the reaction will produce an amorphous calcium carbonate precipitate.

[0077] (2) After calcium carbonate precipitates for 10 seconds, cationic chitosan is added to the solution, and the concentration of cationic chitosan in the final solution is controlled to be 8 mg / mL. The reaction continues for 1 hour, and then the product is centrifuged at 8000 rpm for 8 minutes. The product is washed three times with deionized water and dried under vacuum at 60°C for 48 hours to obtain cationic chitosan modified calcium carbonate powder.

[0078] (3) The prepared cationic chitosan-modified calcium carbonate is added to the fiber dissolving solution, wherein the mass ratio of the dry fiber to the cationic chitosan-modified calcium carbonate is 8:1. The fiber is dissolved for 30 minutes on the fiber dissolving machine and then formed into paper on the paper forming machine.

[0079] The cellulose composite paper prepared in Example 3 exhibits an adsorption capacity of 8.97 g / m³ for protein. 2 .

[0080] Example 4

[0081] (1) Weigh 0.111 g of calcium chloride and dissolve it in 10 mL of deionized water to prepare solution A; weigh 0.095 g of magnesium chloride and dissolve it in 10 mL of deionized water to prepare solution B; weigh 0.106 g of sodium carbonate and dissolve it in 10 mL of deionized water to prepare solution C. At room temperature, mix solution B and solution A at a volume ratio of 1.5:1 and stir at 1000 rpm until fully mixed. Then add an equal volume of solution C, and the reaction will produce an amorphous calcium carbonate precipitate.

[0082] (2) After calcium carbonate precipitates for 10 seconds, cationic chitosan is added to the solution, and the concentration of cationic chitosan in the final solution is controlled to be 2 mg / mL. The reaction continues for 1 hour, and then the product is centrifuged at 8000 rpm for 8 minutes. The product is washed three times with deionized water and dried under vacuum at 60°C for 48 hours to obtain cationic chitosan modified calcium carbonate powder.

[0083] (3) The prepared cationic chitosan-modified calcium carbonate is added to the fiber dissolving solution, wherein the mass ratio of the dry fiber to the cationic chitosan-modified calcium carbonate is 4:1. The fiber is dissolved for 30 minutes on the fiber dissolving machine and then formed into paper on the paper forming machine.

[0084] The cellulose composite paper prepared in Example 4 exhibits a protein adsorption capacity of 11.93 g / m³. 2 .

[0085] Example 5

[0086] (1) Weigh 0.111 g of calcium chloride and dissolve it in 10 mL of deionized water to prepare solution A; weigh 0.095 g of magnesium chloride and dissolve it in 10 mL of deionized water to prepare solution B; weigh 0.106 g of sodium carbonate and dissolve it in 10 mL of deionized water to prepare solution C. At room temperature, mix solution B and solution A at a volume ratio of 1.5:1 and stir at 1000 rpm until fully mixed. Then add an equal volume of solution C, and the reaction will produce an amorphous calcium carbonate precipitate.

[0087] (2) After calcium carbonate precipitates for 10 seconds, cationic chitosan is added to the solution, and the concentration of cationic chitosan in the final solution is controlled to be 2 mg / mL. The reaction continues for 1 hour, and then the product is centrifuged at 8000 rpm for 8 minutes. The product is washed three times with deionized water and dried under vacuum at 60°C for 48 hours to obtain cationic chitosan modified calcium carbonate powder.

[0088] (3) The prepared cationic chitosan-modified calcium carbonate is added to the fiber dissolving solution, wherein the mass ratio of the dry fiber to the cationic chitosan-modified calcium carbonate is 2:1. The fiber is dissolved for 30 minutes on the fiber dissolving machine and then formed into paper on the paper forming machine.

[0089] The cellulose composite paper prepared in Example 5 exhibits a protein adsorption capacity of 14.11 g / m³. 2 .

[0090] Example 6

[0091] (1) Weigh 0.111 g of calcium chloride and dissolve it in 10 mL of deionized water to prepare solution A; weigh 0.095 g of magnesium chloride and dissolve it in 10 mL of deionized water to prepare solution B; weigh 0.106 g of sodium carbonate and dissolve it in 10 mL of deionized water to prepare solution C. At room temperature, mix solution B and solution A at a volume ratio of 1.5:1 and stir at 1000 rpm until fully mixed. Then add an equal volume of solution C, and the reaction will produce an amorphous calcium carbonate precipitate.

[0092] (2) After calcium carbonate precipitates for 10 seconds, cationic chitosan is added to the solution, and the concentration of cationic chitosan in the final solution is controlled to be 2 mg / mL. The reaction continues for 1 hour, and then the product is centrifuged at 8000 rpm for 8 minutes. The product is washed three times with deionized water and dried under vacuum at 60°C for 48 hours to obtain cationic chitosan modified calcium carbonate powder.

[0093] (3) The prepared cationic chitosan-modified calcium carbonate is added to the fiber dissolving solution, wherein the mass ratio of the dry fiber to the cationic chitosan-modified calcium carbonate is 1:1. The fiber is dissolved for 30 minutes on the fiber dissolving machine and then formed into paper on the paper forming machine.

[0094] The cellulose composite paper prepared in Example 6 exhibits a protein adsorption capacity of 14.72 g / m³. 2 .

[0095] The calcium carbonate powders prepared in Comparative Examples 1, 3, and 5 were subjected to XRD analysis. Figure 1 As shown, the control sample prepared without the addition of magnesium chloride consisted entirely of calcite (JCPDS 47-1743). Figure 1 (a) When magnesium chloride is added to the solution, the sharp peak in the XRD pattern disappears, and is replaced by broad peaks resembling two steamed buns. Figure 1 (b) This is a typical spectrum of amorphous calcium carbonate. After the amorphous calcium carbonate is formed, further addition of cationic chitosan to the solution results in a spectrum that still exhibits a typical "bun" double peak. Figure 1 c) indicates that the addition of cationic chitosan did not disrupt the amorphous state of amorphous calcium carbonate.

[0096] The calcium carbonate powders prepared in Comparative Examples 1, 3, and 5 were subjected to FT-IR detection, such as... Figure 2 As shown, the FT-IR spectrum obtained in Comparative Example 1 is ( Figure 2 a) is shown at 1430cm -1 There is a relatively narrow ν3 absorption band at 875 cm⁻¹. -1 CO3 2- (Out-of-plane bending) has a strong ν2 absorption band at 713 cm⁻¹.-1 CO3 2- The in-plane bending of the calcite exhibits a strong ν4 absorption band, a characteristic peak typical of calcite-type calcium carbonate. In Comparative Example 3, after the addition of magnesium chloride, the infrared spectrum ( Figure 2 (b) 1487cm -1 and 1423cm -1 The peak splits into two peaks at 875 cm⁻¹, with the ν₂ absorption peak decreasing from 875 cm⁻¹. -1 Moved to 868cm -1 700cm -1 A faint, broad peak appears at 1608 cm⁻¹, which is characteristic of amorphous calcium carbonate and corresponds to the XRD pattern, confirming the formation of amorphous calcium carbonate. -1 The absorption peaks appearing nearby are attributed to the asymmetric stretching vibrations of OH groups in water, indicating that Mg... 2+ Doping can increase the water content in amorphous calcium carbonate. Example 5 ( Figure 2 The spectrum in (c) shows that after the addition of cationic chitosan, the chromatogram at 1608 cm⁻¹... -1 The increased relative intensity of the peak at this point indicates that cationic chitosan further increases the water content in amorphous calcium carbonate. Previous studies have shown that an appropriate amount of water helps to improve the stability of amorphous calcium carbonate.

[0097] Scanning electron microscopy was used to examine the calcium carbonate powders from Comparative Examples 1, 3, and 5. Figure 3 As shown, pure calcium carbonate (a1, a2) prepared without any stabilizers exhibits a rhombic structure, which is typical of calcite-type calcium carbonate, with a particle size of approximately 3 μm. Magnesium chloride-stabilized amorphous calcium carbonate (b1, b2) and cationic chitosan-modified amorphous calcium carbonate (c1, c2) clearly show, under high magnification, a regular spherical shape with a size of approximately 50 nm.

[0098] XRD characterization was performed on calcium carbonate samples from Comparative Example 3 and Example 5 at different reaction times. Figure 4As shown in Figure a, when only magnesium chloride was added to stabilize amorphous calcium carbonate, the XRD pattern after 6 hours of reaction in aqueous solution exhibited a sharp calcite peak (crystal plane 104), indicating that the crystal structure had begun to transform. However, it is noteworthy that when cationic chitosan was added, the XRD pattern remained amorphous within the same reaction time, without showing the sharp calcite peak. This confirms that the introduction of cationic chitosan further improved the stability of amorphous calcium carbonate. This may be because cationic chitosan forms a protective film or coating on the surface of the amorphous calcium carbonate particles. This coating may affect ion diffusion in solution, hindering the growth of calcium carbonate particles and thus slowing down the crystallization process. To further evaluate the stability of the samples during long-term storage, the powders obtained from Comparative Example 3 and Example 5 were sealed in airtight bags and placed in a desiccator. Subsequent observations revealed that the amorphous calcium carbonate powder stabilized only with magnesium chloride showed a sharp calcite peak in its XRD pattern after 100 days, indicating that the crystal structure gradually became more ordered. Conversely, amorphous calcium carbonate powder coated with cationic chitosan remained amorphous under the same conditions, without exhibiting the sharp peaks of calcite. This observation indicates that the introduction of cationic chitosan effectively prolonged the amorphous state of the calcium carbonate powder. This is likely because the cationic chitosan forms a protective film on the surface of the amorphous calcium carbonate, preventing direct contact between water vapor and the amorphous calcium carbonate, thereby slowing down crystallization and prolonging the amorphous state.

[0099] EDS elemental distribution map of the cationic chitosan-modified amorphous calcium carbonate prepared in Example 5, as shown in the figure. Figure 5 As shown, abundant nitrogen elements can be seen distributed on its surface, indicating that cationic chitosan has been successfully modified onto the surface of amorphous calcium carbonate.

[0100] The calcium carbonate prepared in Comparative Examples 1, 3, and 5 adsorbs proteins in solution, such as... Figure 6 As shown, the calcium carbonate prepared in Example 5 exhibits significantly higher adsorption capacity and adsorption rate for proteins than Comparative Examples 1 and 3. Figure 7 The potential changes show that the addition of magnesium chloride and cationic chitosan plays a positive role in improving the particle size and surface charge of calcium carbonate. This may be because the addition of magnesium chloride optimizes the structure of calcium carbonate, while the introduction of cationic chitosan increases the affinity of calcium carbonate for proteins and increases the active sites for protein adsorption.

[0101] 3D images of Example 5 cellulose composite paper and Comparative Example 5 fiber base paper are shown below. Figure 8 As shown, the surface of the paper after adding filler has no obvious undulations and tends to be flat.

[0102] The adsorption of proteins in solution by fiber base paper and cellulose composite paper with filler is shown in Table 1.

[0103] Table 1

[0104]

[0105] As can be seen from Table 1, the cellulose composite paper in Comparative Example 1 had a worse adsorption effect on protein in solution compared to the cellulose base paper in Comparative Example 5. This is because the calcium carbonate added in Comparative Example 1 did not contain any crystal stabilizer and was the most common calcite type calcium carbonate, which has a low affinity for protein. In addition, the added calcium carbonate also blocked the porous structure of the cellulose composite paper, resulting in a decrease in adsorption effect.

[0106] Compared to Comparative Example 1, Comparative Example 2 showed a slightly enhanced adsorption effect on proteins in solution. This is because the addition of magnesium chloride improved the surface structure of calcium carbonate.

[0107] The adsorption effect of comparative example 4 on protein was basically the same as that of comparative example 3, indicating that high temperature did not destroy the amorphous calcium carbonate stable by magnesium chloride, indicating that it has good thermal stability.

[0108] Paper images of protein adsorption in Comparative Example 5 and Examples 2, 4, 5, and 6 are shown below. Figure 9 As shown, 50 μL of a 1 mg / mL bovine serum albumin solution was loaded onto one end of the paper. Due to the capillary action of the paper, the protein distribution on the paper was observed after it was fully wetted. The pure cellulose paper shows a uniform protein distribution, indicating that cellulose has a low affinity for proteins. However, as the proportion of modified fillers in the cellulose composite paper increases, the protein remains at the front end of the paper base due to the higher affinity of amorphous calcium carbonate for proteins and the electrostatic attraction of ammonium ions in cationic chitosan. This achieves the purpose of enriching or retaining proteins, indicating that the paper base material has a high affinity for proteins at this stage.

Claims

1. A method for preparing modified amorphous calcium carbonate, characterized in that, Includes the following steps: (1) Mix magnesium chloride and calcium chloride in water, add sodium carbonate, and react under stirring to produce amorphous calcium carbonate; the reaction time is 10-60 s. (2) Add cationic chitosan to the reaction system obtained in step (1) and carry out the reaction under stirring conditions; the mass ratio of cationic chitosan to sodium carbonate is (0.3~3):1; the reaction time is 60~120 min; (3) Wash and dry the product obtained in step (2) to obtain modified amorphous calcium carbonate.

2. The method for preparing modified amorphous calcium carbonate according to claim 1, characterized in that, In step (1), the molar ratio of magnesium chloride to calcium chloride is (0.1-2):1, and the number of moles of sodium carbonate is the same as the total number of moles of calcium chloride and magnesium chloride.

3. The method for preparing modified amorphous calcium carbonate according to claim 1, characterized in that, In step (1), the reaction temperature is 20–40°C.

4. The method for preparing modified amorphous calcium carbonate according to claim 1, characterized in that, In step (2), the reaction temperature is 20–40°C.

5. The method for preparing modified amorphous calcium carbonate according to claim 1, characterized in that, In step (3), the drying process specifically involves vacuum drying at 50–100°C.

6. Modified amorphous calcium carbonate obtained by the preparation method according to any one of claims 1 to 5.

7. A modified amorphous calcium carbonate / cellulose composite paper, characterized in that, It is obtained by combining the modified amorphous calcium carbonate and cellulose as described in claim 6.

8. The modified amorphous calcium carbonate / cellulose composite paper according to claim 7, characterized in that, The modified amorphous calcium carbonate accounts for 10% to 50% of the cellulose composite paper.

9. The method for preparing the modified amorphous calcium carbonate / cellulose composite paper according to claim 7, characterized in that, Modified amorphous calcium carbonate and cellulose are decomposed and paper-made to obtain modified amorphous calcium carbonate / cellulose composite paper.

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