Process for the preparation of a stable suspension of mixed-hollow attapulgite clay for water-based paints

Abstract

This invention discloses a method for preparing a water-based coating material containing mixed-fiber attapulgite clay that is stable in water. This method uses natural plant extracts as modifiers to prepare a water-stable mixed-fiber attapulgite clay suspension, effectively solving practical application problems such as poor dispersibility, easy sedimentation, and unstable storage of the whitened mixed-fiber attapulgite clay product in water. This invention, using a highly efficient, green, and economical semi-dry modification method to construct a mineral functional composite material with high suspension stability, has promising application prospects in the field of water-based coatings.

Description

Technical Field

[0001] This invention relates to a stable high-suspension rheology modifier for water-based coatings, specifically to a method for preparing a mixed-fiber attapulgite clay stable suspension for water-based coatings, belonging to the technical field of high-value application of clay minerals. Background Technology

[0002] Attapulgite is a natural 2:1 type layered chain hydrous magnesium-aluminate clay mineral with a unique rod-like morphology. When dispersed in water, under the influence of electrostatic forces, van der Waals forces, and hydration forces, the rod-like crystals entangle and overlap to form a chaotic three-dimensional network structure, simultaneously binding water molecules within the network, forming a colloidal material with excellent thickening, thixotropic, and suspending properties. Its use in water-based coatings can improve the coatings' anti-sagging, anti-settling, anti-dehydration shrinkage, and anti-splashing properties. However, the aspect ratio of attapulgite rod-like crystals significantly affects its colloidal properties; the smaller the aspect ratio, the weaker the cross-entanglement ability, resulting in a weaker network structure and poorer colloidal properties. Therefore, the application of mixed-layer attapulgite clay with a small aspect ratio and abundant associated minerals (Science Bulletin, 2022, 67, 28-29, 3411-3424) in the coating industry is greatly limited.

[0003] my country possesses extremely rich reserves of mixed-layer attapulgite clay, with the prospective reserves in Linze County, Gansu Province alone reaching 3.4 billion tons, far exceeding the reserves of high-viscosity attapulgite clay with large rod-like aspect ratios. With a deeper understanding of the nanomineralogical properties of attapulgite, the technology for whitening dark-colored mixed-layer attapulgite clay has been developed (ZL201910672767.1) and is becoming increasingly mature. Furthermore, mixed-layer attapulgite clay with different whiteness levels is already in large-scale production. However, how to achieve long-term stable suspension of the whitened mixed-layer attapulgite clay in water remains a pressing issue.

[0004] Natural plant extracts contain numerous active groups such as -COOH, -OH, and -NH2, and extracts containing saponins also possess surfactant properties. Introducing these extracts into attapulgite clay can regulate the surface charge of attapulgite, endowing it with various active groups, thereby improving the suspension stability of the attapulgite clay. Therefore, this invention, based on the whitening process of attapulgite clay, uses plant extracts as modifiers and, through the synergistic effect of other one-dimensional or two-dimensional clays, optimizes conditions to prepare a highly suspended attapulgite clay with long-term stability in water, suitable for use in water-based coatings. To date, there are no related research reports or application precedents for this technology. Summary of the Invention

[0005] To address the issues of poor suspension and rapid sedimentation in water caused by the whitening of brick-red mixed attapulgite clay, this invention uses plant extracts as modifiers, in conjunction with other one-dimensional or two-dimensional clays, to prepare mixed attapulgite clay that can be stably suspended in water for a long time. This expands the application of whitening mixed attapulgite clay with small rod-crystal aspect ratio in the field of water-based coatings.

[0006] This invention relates to a method for preparing stable, highly suspended mixed-dimensional attapulgite clay for water-based coatings using plant extracts in conjunction with other one-dimensional or two-dimensional clays, comprising the following steps:

[0007] (1) Extraction of plant active ingredients: After drying and grinding the natural plant, disperse it in an ethanol aqueous solution, sonicate for 0.5-1 h, stir at room temperature to 70℃ and 500 rpm for 4 h, cool and filter, and make up the volume of the filtrate to obtain a plant extract solution, wherein the mass fraction of the plant extract in the plant extract solution is 0.25-10.0%.

[0008] The natural plant is at least one of the following: gallnut, soapberry, sea buckthorn, bupleurum, licorice, and platycodon. The natural plant drying and grinding process involves drying the natural plant at 105℃ for 2 hours and then grinding it to a mesh size of 300. The ethanol aqueous solution is a 30% (v / v) ethanol aqueous solution.

[0009] (2) Semi-dry modification: Add other one-dimensional or two-dimensional clays with excellent colloidal properties to white mixed attapulgite clay, mix well, spray with plant extract solution, stir again to form uniform wet particles, place at room temperature for 24 hours under sealed conditions, and then dry at 105℃ to obtain modified white mixed attapulgite clay; disperse the modified white mixed attapulgite clay in water to obtain a water-based coating mixed attapulgite clay stable suspension.

[0010] The whiteness of the white mixed-fiber attapulgite clay is R. 457 =20~80. The other one-dimensional or two-dimensional clay with excellent colloidal properties is at least one of sepiolite, montmorillonite, and lithium saponite. The amount of the other one-dimensional or two-dimensional clay with excellent colloidal properties added is 20~45% of the mass of the white mixed-dimensional attapulgite clay. The spraying volume of the plant extract solution is 20%~35% of the total mass of the white mixed-dimensional attapulgite clay and the other one-dimensional or two-dimensional clay with excellent colloidal properties. The preparation method of white mixed-dimensional attapulgite clay is described in ZL201910672767.1.

[0011] The semi-dry method used in this invention can effectively control the product preparation cost, improve production efficiency, and reduce environmental pollution.

[0012] Figure 1 Photos showing the before and after of the brick-red mixed attapulgite clay turning white. Figure 2Infrared spectra of plant extract (a), white mixed attapulgite clay (b), and modified white mixed attapulgite clay (c). Figure 2 a is 1730 cm -1 and 1452 cm -1 The presence of an infrared absorption peak at 3390 cm⁻¹ indicates the presence of -COOH groups in the extract. -1 A broad peak (-OH) and 2933 cm⁻¹ -1 The appearance of the peak (-CH2) indicates the presence of -OH and -CH2 groups in the extract. Figure 2 b, 400~600 cm -1 and 1000~1200 cm -1 The absorption bands in the wavenumber range are attributed to the SiO4 tetrahedral framework and silica of the mixed-dimensional attapulgite, with the 521 cm⁻¹ band being the most prominent. -1 and 471cm -1 The absorption bands at 1669 cm⁻¹ represent the bending vibrations of the Si–O–Si and O–Si–O tetrahedra of SiO₄, respectively. -1 1618 cm -1 1318 cm -1 and 667 cm -1 The absorption peak can be attributed to the C2O4 after the mixed-dimensional attapulgite turns white. 2- . Figure 2 c is at 2932 cm -1 1739 cm -1 1451 cm -1 and 1667 cm -1 1618 cm -1 1318 cm -1 521 cm -1 471 cm -1 Characteristic absorption peaks of the extract and white mixed attapulgite clay were observed respectively, and no new absorption peaks appeared, indicating that the extract had been compounded with the white mixed attapulgite clay.

[0013] Figure 3 The suspension curves (A) and viscosity changes (B) of white mixed attapulgite clay before and after modification are shown. Figure 3A shows that the white mixed attapulgite clay before modification had a fast settling speed, with a settling volume of 60 mL in 15 min (initial suspension volume of 100 mL), and the suspension volume decreased to 17 mL within 1 hour and reached stability. The settling speed of the white mixed attapulgite clay after modification was significantly reduced, and the suspension volume of the sample only reached stability after 5 days. In the following 20 days, the suspension volume remained basically unchanged at 93 mL, which was 83% higher than that before modification (suspension volume of 10 mL after 30 days). The significant improvement in the suspension of the white mixed attapulgite clay after modification can be attributed to the following aspects: (1) The introduction of the extract can increase the viscosity of the mixed attapulgite clay (see Figure 3 (B) thus reducing the sedimentation rate of the sample; (2) the infrared spectrum shows (see Figure 2 (3) The extract contains -COOH, -OH and other groups, which can form hydrogen bonds with the -OH groups in the mixed attapulgite clay in the aqueous solution. The network structure formed under this action can make the mixed attapulgite clay dispersed more evenly in the water, thereby improving the suspension stability; (4) The micelles formed by the saponins with surfactant properties in the extract are evenly distributed in the water, which also prevents the aggregation of mixed attapulgite clay particles, further improving the suspension of mixed attapulgite clay.

[0014] Table 1 shows the evaluation of the application of modified mixed-fiber attapulgite clay in waterborne acrylic resin damping coatings. As can be seen from Table 1, the unmodified white mixed-fiber attapulgite clay (comparative example) meets the requirements in all aspects except for storage stability. The modified white mixed-fiber attapulgite clay (Examples 1 and 2) meets all requirements. Therefore, the modified white mixed-fiber attapulgite clay prepared in this invention can be used as a stable, high-suspension rheology modifier for waterborne coatings.

[0015]

[0016] In summary, the present invention has the following advantages compared with the prior art:

[0017] 1. This invention utilizes abundant plant extracts to replace chemically synthesized surfactants. Through semi-dry modification and optimization of preparation conditions (such as modifier dosage and reaction time), a stable and highly dispersed mixed-fiber attapulgite clay in water was successfully prepared. This effectively solves the practical application problems of brick-red mixed-fiber attapulgite clay turning white in water, such as rapid settling and poor dispersion, thereby expanding the application of mixed-fiber attapulgite clay in water-based coatings.

[0018] 2. This invention reduces the use of synthetic surfactants and lowers the environmental pollution caused by the use of chemical reagents during the production process. The entire preparation process of this invention is rationally designed, with mild reaction conditions and easy process control, facilitating large-scale industrial production. Attached Figure Description

[0019] Figure 1 Photos showing the before and after of the brick-red mixed attapulgite clay turning white.

[0020] Figure 2 Infrared spectra of plant extract (a), white mixed attapulgite clay (b), and modified white mixed attapulgite clay (c).

[0021] Figure 3 The suspension curves (A) and viscosity changes (B) of white mixed attapulgite clay before and after modification are shown.

[0022] Figure 4 The following are suspension photographs of the sample at different time points for the examples (1# - comparative example, 2# - example 1, 3# - example 2, 4# - example 3, 5# - example 4). Detailed Implementation

[0023] The following specific embodiments further illustrate the preparation method of the long-lasting and stable high-suspension whitening mixed attapulgite clay of the present invention.

[0024] Comparative Example

[0025] 100 kg of red attapulgite clay ore was crushed into powder and mixed evenly with 150 kg of whitening agent (composition: 75% sulfuric acid, 5% hydroxylamine hydrochloride, and 20% ammonium citrate, all by mass fraction). The mixture was then pressed into a 4 mm thick sheet using a roller mill and microwaved at 2.5 kW for 30 min. The mixture was then placed in a reaction vessel and heated to 160 °C for 2 h. Finally, the reaction product was thoroughly washed with water, centrifuged, dried, and pulverized to obtain white mixed attapulgite clay mineral (see ZL201910672767.1). Figure 1 Photos of brick-red mixed attapulgite clay before and after turning white (raw ore before turning white) R 457 =15.62, product after turning white R 457 =72.45).

[0026] Example 1

[0027] (1) Dry and grind Sapindus mukorossi at 105℃ to 300 mesh. Weigh 20g of Sapindus mukorossi powder and disperse it in 100 mL of 30% ethanol aqueous solution. Sonicate for 0.5~1h, then stir at room temperature and 500 rpm for 4h. Filter and dilute the filtrate to 100 mL to obtain Sapindus mukorossi extract solution for later use.

[0028] (2) Weigh 75 g of white mixed attapulgite clay (R 457=41) and 25g sepiolite, sprayed with 35 mL of the above Sapindus mukorossi extract solution, mixed well, and placed at room temperature for 24 hours under sealed conditions. Then, dried at 105℃ and pulverized to 300 mesh to obtain modified white mixed attapulgite clay. Its suspension stability in water within 30 days is shown in the figure. Figure 4 .

[0029] Example 2

[0030] (1) Dry and grind Sapindus mukorossi at 105℃ to 300 mesh, weigh 20g of powder and disperse it in 100 mL of 30% ethanol aqueous solution, sonicate for 0.5~1h, then stir at 40℃ and 500 rpm for 4h, cool and filter, and make up to 100 mL of the filtrate to obtain Sapindus mukorossi extract solution for later use.

[0031] (2) Weigh 65g of white mixed attapulgite clay (R 457 =49) and 35g sepiolite, sprayed with 30 mL of the above Sapindus mukorossi extract solution, mixed well, and placed at room temperature for 24 hours under sealed conditions. Then, dried at 105℃ and pulverized to 300 mesh to obtain modified white mixed attapulgite clay. Its suspension stability in water within 30 days is shown in the figure. Figure 4 The evaluation of its application in water-based damping coatings is shown in Table 1.

[0032] Example 3

[0033] (1) Dry and grind Sapindus mukorossi at 105℃ to 300 mesh, weigh 5g of powder and disperse it in 100 mL of 30% ethanol aqueous solution, sonicate for 0.5~1h, then stir at 60℃ and 500 rpm for 4h, cool and filter, and make up to 100 mL of filtrate to obtain Sapindus mukorossi extract solution for later use.

[0034] (2) Weigh 55g of white mixed attapulgite clay (R 457 =57) and 45g sepiolite, mix well, spray with 25 mL of the above Sapindus mukorossi extract solution and mix again, place at room temperature for 24 hours under sealed conditions, then dry at 105℃ and pulverize to 300 mesh to obtain modified white mixed attapulgite clay. Its suspension stability in water within 30 days is shown in the figure. Figure 4 The evaluation of its application in water-based damping coatings is shown in Table 1.

[0035] Example 4

[0036] (1) Dry and grind Sapindus mukorossi at 105℃ to 300 mesh, weigh 15g of powder and disperse it in 100 mL of 30% ethanol aqueous solution, sonicate for 0.5~1h, then stir at 70℃ and 500 rpm for 4h, cool and filter, and make up to 100mL of the filtrate to obtain Sapindus mukorossi extract solution for later use.

[0037] (2) Weigh 60g of white mixed attapulgite clay (R 457 =76) and 40g lithium soapstone were mixed well, and 20 mL of the above Sapindus mukorossi extract solution was sprayed on top and mixed again. The mixture was then left to stand at room temperature for 24 hours under sealed conditions. It was then dried at 105℃ and pulverized to 300 mesh to obtain modified white mixed attapulgite clay. Its suspension stability in water within 30 days is shown in the figure. Figure 4 .

Claims

1. A method for preparing a water-based coating stabilized suspension of attapulgite clay with mixed fiber, comprising the following steps: (1) Extraction of plant active ingredients: After drying and grinding the natural plant, disperse it in an ethanol aqueous solution, sonicate it for 0.5-1h, stir it at room temperature to 70℃ and 500 rpm for 4h, cool it and filter it. The filtrate is diluted to obtain a plant extract solution, wherein the mass fraction of the plant extract in the plant extract solution is 0.25-10.0%; the natural plant is at least one of gallnut, soapberry, sea buckthorn, bupleurum, licorice and platycodon. (2) Semi-dry modification: Add other one-dimensional or two-dimensional clays with excellent colloidal properties to white mixed attapulgite clay, mix well, spray with plant extract solution, stir again to form uniform wet particles, place at room temperature for 24 h under sealed conditions, and then dry at 105℃ to obtain modified white mixed attapulgite clay; disperse the modified white mixed attapulgite clay in water to obtain a water-based coating mixed attapulgite clay stable suspension. The plant extract contains -COOH and -OH groups, which undergo hydrogen bonding with the -OH groups in the mixed attapulgite clay in aqueous solution. The network structure formed under this interaction improves suspension stability.

2. The preparation method of the water-based coating stabilized suspension of attapulgite clay with mixed fiber as described in claim 1, characterized in that: In step (1), the natural plant drying and grinding involves drying the natural plant at 105°C for 2 hours and then grinding it to 300 mesh.

3. The preparation method of the water-based coating stabilized suspension of attapulgite clay with mixed fiber as described in claim 1, characterized in that: In step (1), the ethanol aqueous solution is an ethanol aqueous solution with a volume concentration of 30%.

4. The preparation method of the water-based coating stabilized suspension of attapulgite clay with mixed fiber as described in claim 1, characterized in that: In step (2), the whiteness of the white mixed attapulgite clay is 20~80.

5. The preparation method of the water-based coating stabilized suspension of attapulgite clay with mixed fiber as described in claim 1, characterized in that: In step (2), the other one-dimensional or two-dimensional clay with excellent colloidal properties is at least one of sepiolite, montmorillonite, and lithium saponite.

6. The preparation method of the water-based coating stabilized suspension of mixed attapulgite clay as described in claim 1, characterized in that: In step (2), the amount of other one-dimensional or two-dimensional clays with excellent colloidal properties added is 20-45% of the mass of white mixed attapulgite clay.

7. The preparation method of a water-based coating stabilized suspension of attapulgite clay with mixed fiber as described in claim 1, characterized in that: In step (2), the spraying volume of the plant extract solution is 20% to 35% of the total mass of white mixed attapulgite clay and other one-dimensional or two-dimensional clays with excellent colloidal properties.

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