Sepiolite fiber with high length-diameter ratio and high dispersity as well as preparation method and application of sepiolite fiber

Abstract

The invention discloses a sepiolite fiber with high length-diameter ratio and high dispersity and a preparation method and application thereof, and the sepiolite fiber is prepared according to the following steps: (1) mixing sepiolite raw ore with water to prepare slurry with the solid content of 5-20wt%; (2) adding the slurry into a high-shear homogenizing emulsifying machine, and performing shearing treatment at the rotating speed of 6000-15000rpm to realize protective physical stripping of sepiolite fiber bundles; (3) carrying out centrifugal separation on the slurry subjected to shearing treatment to obtain a sepiolite fiber suspension with good dispersion; and (4) the sepiolite fiber suspension is subjected to pre-freezing treatment and then subjected to programmed temperature control freeze drying under the vacuum condition, and the freeze drying process comprises at least one low-temperature sublimation platform stage at the temperature ranging from-30 DEG C to-10 DEG C. The sepiolite-based thickening material with excellent thickening performance and stability is successfully prepared by innovatively optimizing high-speed shearing and emulsifying process parameters and combining a rheological property regulation and control technology.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of mineral nanomaterials, in particular to a sepiolite fiber with high aspect ratio and high dispersibility, a preparation method and application thereof. BACKGROUND

[0002] Sepiolite is a natural one-dimensional nanofibrous silicate mineral. Its huge specific surface area and abundant surface hydroxyl groups make it an excellent thickening, adsorption and carrier material. However, the fibers in sepiolite ore usually exist in bundle form. How to efficiently dissociate them into single fibers while maximizing the inherent high aspect ratio is the key to improving their application performance.

[0003] The preparation of traditional sepiolite thickening materials mainly faces the following technical problems: on the one hand, although the conventional mechanical grinding method can improve the dispersibility of the fibers, it will damage the aspect ratio of the fibers, resulting in a decrease in the thickening efficiency (viscosity loss up to 60%); on the other hand, although the chemical modification method can improve the dispersion stability, it will change the surface properties of the fibers, affect their interaction with the water phase, and there are environmental hazards. Studies have shown that the thickening mechanism of sepiolite fibers mainly comes from three aspects: (1) the three-dimensional network structure formed by sepiolite fibers; (2) the hydrogen bond interaction between the fiber surface hydroxyl groups and water molecules; (3) the steric hindrance formed by the electrostatic repulsion between the fibers. Therefore, how to achieve full dissociation while maintaining the integrity of the fibers is the key to improving the thickening performance.

[0004] High-speed shear emulsification technology, as a kind of efficient physical treatment method, has unique advantages in the field of nanomaterial dispersion. Compared with traditional methods, this technology has controllable shear force, small temperature rise (<50℃), low energy consumption, etc. However, the existing technology has obvious deficiencies in the preparation of sepiolite thickening materials: first of all, it does not consider the special requirements of fiber aspect ratio for thickening applications; secondly, it ignores the correlation between slurry rheological properties (such as viscosity, thixotropy) and shear parameters; in addition, improper post-processing process can easily lead to fiber re-entanglement, affecting the thickening stability of the final product.

[0005] A preparation method of sepiolite thickening agent adopts ball milling-surface modification two-step method, but the product has problems such as low thickening efficiency (Brookfield viscosity <5000 cP), poor suspension stability (delamination rate >30% after 24 hours standing), etc. Patent CN201920456789.Y proposes a chemical grafting modification process, which improves the thickening performance, but the process is complex and the cost is high. These methods have not effectively solved the balance between thickening efficiency and fiber structure protection.

[0006] Therefore, it is of great significance to develop a sepiolite thickening material preparation technology that can simultaneously maintain fiber integrity and good dispersibility to meet the growing market demand for high-performance thickening agents. SUMMARY

[0007] To solve the above technical problems, the first object of the present application is to provide a high aspect ratio, high dispersibility sepiolite fiber and its preparation method, and the second object is to provide its application. The present application successfully prepares a sepiolite-based thickening material with excellent thickening performance and stability by innovatively optimizing the high-speed shear emulsification process parameters and combining rheological property regulation technology.

[0008] To achieve the above first object, the present application is implemented by the following technical scheme: a preparation method of a high aspect ratio, high dispersibility sepiolite fiber, characterized by being prepared according to the following steps:

[0009] (1) mixing sepiolite raw ore with water to prepare a slurry with a solid content of 5-20wt%;

[0010] (2) adding the slurry into a high-shear homogenization emulsifier and performing shear treatment at a rotation speed of 6000-15000rpm to achieve protective physical peeling of sepiolite fiber bundles;

[0011] (3) performing centrifugal separation on the slurry after shear treatment to obtain a well-dispersed sepiolite fiber suspension;

[0012] (4) performing pre-freezing treatment on the sepiolite fiber suspension, and then performing program-controlled temperature freeze-drying under vacuum conditions, wherein the freeze-drying process includes at least one low-temperature sublimation plateau at -30℃--10℃, and the plateau maintenance time is not less than 5 hours to prevent the fibers from re-agglomerating during the drying process.

[0013] In the above scheme: the high-shear homogenization emulsifier has a double-layer stator-rotor structure, the inner lining stator has a pore size of 1-3mm, and the outer layer stator has a pore size of 0.5-1.5mm round hole. To achieve step-by-step refinement and uniform shear of high-viscosity slurry.

[0014] In the above scheme: in step (2), the shear treatment time is 10-30 minutes. By controlling the shear rate and time, the protective physical peeling of sepiolite fiber bundles is achieved.

[0015] In the above scheme: before the pre-freezing treatment in step (4), 0.05-0.2wt% of sodium hexametaphosphate is added to the fiber suspension as a dispersant.

[0016] In the above scheme: the freeze-drying is divided into four stages:

[0017] First stage: cooling from room temperature to -50℃ and maintaining at -50℃ for 14-24 hours;

[0018] Second stage: -50℃ to -30℃, and maintain at -30℃ for 10-24 hours;

[0019] Third stage: -30℃ to 0℃, and maintain at 0℃ for 20-24 hours;

[0020] Fourth stage: 0℃ to 30℃, and maintain at 30℃ for 4-24 hours.

[0021] A preparation method of the high aspect ratio and high dispersibility sepiolite fiber.

[0022] In the above scheme, the average length of the high aspect ratio and high dispersibility sepiolite fiber is greater than 5 μm, the average diameter is less than 100 nm, and the aspect ratio is greater than 50.

[0023] The high aspect ratio and high dispersibility sepiolite fiber is applied to preparation of a thickening agent, an adsorbent or a composite material.

[0024] The present application realizes the "carding" but not "cutting" type peeling of the sepiolite fiber bundle by precisely controlling the slurry rheological state (viscosity) in the high shear homogenization process; further, the dispersed fiber network is "in-situ fixed" through the ice crystal template effect by using the program temperature control freeze drying technology, and the moisture is removed under vacuum sublimation, so that the high aspect ratio sepiolite fiber product which is fluffy, porous and easy to be dispersed again is finally obtained.

[0025] Compared with the prior art, the present application has the beneficial effects that:

[0026] 1. The synergistic effect is prominent: the high shear process and the freeze drying process are not simply connected in series, but the "1+1>2" effect is generated through parameter coupling. The shear process provides sufficient dispersed "precursor" for the freeze drying, and the freeze drying process "locks" the dispersed results of the shear, avoiding performance retrogression.

[0027] 2. The product performance is excellent: the sepiolite fiber prepared by the present application has high aspect ratio and good dispersibility, and can quickly recover the nanofiber morphology after rehydration, form a stable three-dimensional network structure, and the thickening efficiency is improved by more than 50% compared with the traditional method product.

[0028] 3. The process is green and efficient: the whole process is a physical method, water is used as a medium, and there is no three wastes emission; the shear treatment time is short, and the energy consumption is low; the freeze drying avoids the potential damage of high temperature to the fiber structure. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The scanning electron microscope image of the 15% solid content sepiolite ball-milled and dispersed.

[0030] Figure 2Scanning electron micrograph of 15% solids sepiolite after high shear.

[0031] Figure 3 Scanning electron micrograph of sepiolite after direct drying.

[0032] Figure 4 Viscosity of sepiolite after shear for (a) 5%, (b) 10%, (c) 15%, (d) 20%. DETAILED DESCRIPTION

[0033] The application is further described below in conjunction with the accompanying drawings and examples.

[0034] The high shear homogenizer emulsifier is a laboratory emulsifier produced by Shanghai Ouhai Machinery Equipment Co., Ltd. with a double-layer stator-rotor structure.

[0035] Example 1

[0036] A sample of sedimentary sepiolite ore was weighed and prepared into a slurry with a solid content of 5 wt%. The high shear homogenizer emulsifier (equipped with a double-layer stator, inner stator hole diameter 2 mm round hole, outer stator hole diameter 1 mm round hole) was used to shear at a speed of 15000 rpm for 15 minutes. During this process, the viscosity of the slurry was monitored in real time. The fiber suspension was collected by centrifugation, and after adding 0.1% sodium hexametaphosphate, it was quickly frozen in liquid nitrogen and then transferred to a freeze dryer. The drying program was set as follows: -50°C (14h) > rise to -30°C and maintain for 10 hours (low temperature sublimation plateau) > rise to 0°C (20h) > rise to 30°C (4h) to complete drying. The resulting product has an average length greater than 5 μm, an average diameter less than 100 nm, and an aspect ratio greater than 50.

[0037] Example 2

[0038] A sample of sedimentary sepiolite ore was weighed and prepared into a slurry with a solid content of 10 wt%. The high shear homogenizer emulsifier (equipped with a double-layer stator, inner stator hole diameter 2 mm round hole, outer stator hole diameter 1 mm round hole) was used to shear at a speed of 15000 rpm for 15 minutes. During this process, the viscosity of the slurry was monitored in real time. The fiber suspension was collected by centrifugation, and after adding 0.1% sodium hexametaphosphate, it was quickly frozen in liquid nitrogen and then transferred to a freeze dryer. The drying program was set as follows: -50°C (14h) > rise to -30°C and maintain for 10 hours (low temperature sublimation plateau) > rise to 0°C (20h) > rise to 30°C (4h) to complete drying. The resulting product has an average length greater than 5 μm, an average diameter less than 100 nm, and an aspect ratio greater than 50.

[0039] Example 3

[0040] Sedimentary sepiolite ore was weighed and mixed with water to form a slurry with a solid content of 15 wt%. A high-shear homogenizer (equipped with a double-layer stator, inner stator with 2 mm orifice and outer stator with 1 mm orifice) was used for shearing at 15,000 rpm for 15 minutes. The slurry viscosity was monitored in real time during this process. The fiber suspension was collected by centrifugation, and after adding 0.1% sodium hexametaphosphate, it was rapidly frozen in liquid nitrogen and then transferred to a freeze dryer. The drying program was set as follows: -50℃ (14 h) > rise to -30℃ and maintain for 10 hours (low-temperature sublimation plateau period) > rise to 0℃ (20 h) > rise to 30℃ (4 h). The resulting product had an average length greater than 5 μm, an average diameter less than 100 nm, and an aspect ratio greater than 50.

[0041] Until completely dry.

[0042] Example 4

[0043] Sedimentary sepiolite ore was weighed and mixed with water to form a slurry with a solid content of 20 wt%. A high-shear homogenizer (equipped with a double-layer stator, inner stator with 2 mm orifice and outer stator with 1 mm orifice) was used for shearing at 15,000 rpm for 15 minutes. The slurry viscosity was monitored in real time during this process. The fiber suspension was collected by centrifugation, and after adding 0.1% sodium hexametaphosphate, it was rapidly frozen in liquid nitrogen and then transferred to a freeze dryer. The drying program was set as follows: -50℃ (14 h) > rise to -30℃ and maintain for 10 hours (low-temperature sublimation plateau period) > rise to 0℃ (20 h) > rise to 30℃ (4 h). The resulting product had an average length greater than 5 μm, an average diameter less than 100 nm, and an aspect ratio greater than 50.

[0044] Comparative Example 1

[0045] With other conditions remaining unchanged, the 15wt% aqueous solution was dispersed by ball milling instead of high-speed shearing.

[0046] Performance comparison: The products obtained in Examples 1-4 of this invention are fibrous and easily redispersible in water. They do not separate after standing for 24 hours. The Brookfield viscosities of 5wt%, 10wt%, 15wt%, and 20% aqueous solutions are 551 cP, 1526 cP, 6527 cP, and 7134 cP, respectively.

[0047] In contrast, the product of Comparative Example 1 was a hard lump that was difficult to redisperse. Its 15wt% aqueous solution had a viscosity of only 800 cP and rapidly separated into layers.

[0048] Comparative Example 2

[0049] With other conditions remaining unchanged, the freeze-drying of the 15wt% aqueous solution was changed to drying.

[0050] Performance Comparison: The product obtained in the embodiments of this invention is fibrous, and its 15wt% aqueous solution has a Brookfield viscosity of 6527 cP. In contrast, the product of Comparative Example 2 is a hard lump with poor dispersibility in water; its 15wt% aqueous solution has a viscosity of only 1000 cP and rapidly separates into layers.

[0051] Comparative Example 3

[0052] Other conditions remain unchanged, 15 wt% aqueous solution, without the addition of sodium hexametaphosphate.

[0053] Performance Comparison: In Example 1, the 15 wt% aqueous solution with added dispersant achieved a Brookfield viscosity of 6527 cP. In Comparative Example 3, the viscosity of sepiolite without added dispersant decreased slightly, with a Brookfield viscosity of 6023 cP.

[0054] Example 5

[0055] Sedimentary sepiolite ore was weighed and mixed with water to form a slurry with a solid content of 15 wt%. The slurry was divided into two portions and sheared for 10 minutes at 15000 rpm using a high-shear homogenizer (equipped with a double-layer stator, inner stator with 2 mm orifice and outer stator with 1 mm orifice). The slurry viscosity was monitored in real time during this process. The fiber suspension was collected by centrifugation, and after adding 0.1% sodium hexametaphosphate, it was rapidly frozen in liquid nitrogen and then transferred to a freeze dryer. The drying program was set as follows: -50℃ (14 h) > rise to -30℃ and maintain for 10 hours (low-temperature sublimation plateau period) > rise to 0℃ (20 h) > rise to 30℃ (4 h). The resulting product had an average length greater than 5 μm, an average diameter less than 100 nm, and an aspect ratio greater than 50.

[0056] The product obtained in this embodiment of the invention is fibrous, readily redispersible in water, and shows no stratification after standing for 24 hours. Its Brinell viscosity reaches 5242 cP.

[0057] Example 6

[0058] Sedimentary sepiolite ore was weighed and mixed with water to form a slurry with a solid content of 15 wt%. A high-shear homogenizer (equipped with a double-layer stator, inner stator with 2 mm orifice and outer stator with 1 mm orifice) was used for shearing at 6000 rpm for 30 minutes. The slurry viscosity was monitored in real time during this process. The fiber suspension was collected by centrifugation, and after adding 0.1% sodium hexametaphosphate, it was rapidly frozen in liquid nitrogen and then transferred to a freeze dryer. The drying program was set as follows: -50℃ (14 h) > rise to -30℃ and maintain for 10 hours (low-temperature sublimation plateau period) > rise to 0℃ (20 h) > rise to 30℃ (4 h). The resulting product had an average length greater than 5 μm, an average diameter less than 100 nm, and an aspect ratio greater than 50.

[0059] The product obtained in this embodiment of the invention is fibrous, readily redispersible in water, and shows no stratification after standing for 24 hours. Its Brinell viscosity reaches 3562 cP.

[0060] Example 7

[0061] Sedimentary sepiolite ore was weighed and mixed with water to form a slurry with a solid content of 15 wt%. A high-shear homogenizer (equipped with a double-layer stator, inner stator with 2 mm orifice and outer stator with 1 mm orifice) was used for shearing at 15,000 rpm for 15 minutes. The slurry viscosity was monitored in real time during this process. The fiber suspension was collected by centrifugation, and 0.1% sodium hexametaphosphate was added. The suspension was then rapidly frozen in liquid nitrogen and transferred to a freeze dryer. The drying program was set as follows: -50℃ (24 h) > to -10℃ and maintain for 24 hours (low-temperature sublimation plateau) > to 0℃ (24 h) > to 30℃ (24 h). The resulting product had an average length greater than 5 μm, an average diameter less than 100 nm, and an aspect ratio greater than 50.

[0062] The product obtained in this embodiment of the invention is fibrous, readily redispersible in water, and shows no stratification after standing for 24 hours. Its Brinell viscosity reaches 6498 cP.

[0063] Example 8

[0064] Sedimentary sepiolite ore was weighed and mixed with water to form a slurry with a solid content of 15 wt%. A high-shear homogenizer (equipped with a double-layer stator, inner stator with 2 mm orifice and outer stator with 1 mm orifice) was used for shearing at 15,000 rpm for 15 minutes. The slurry viscosity was monitored in real time during this process. The fiber suspension was collected by centrifugation, and after adding 0.05% sodium hexametaphosphate, it was rapidly frozen in liquid nitrogen and then transferred to a freeze dryer. The drying program was set as follows: -50℃ (14 h) > rise to -30℃ and maintain for 10 hours (low-temperature sublimation plateau period) > rise to 0℃ (20 h) > rise to 30℃ (4 h). The resulting product had an average length greater than 5 μm, an average diameter less than 100 nm, and an aspect ratio greater than 50.

[0065] The product obtained in this embodiment of the invention is fibrous, readily redispersible in water, and shows no stratification after standing for 24 hours. Its Brinell viscosity reaches 6410 cP.

[0066] Example 9

[0067] Sedimentary sepiolite ore was weighed and mixed with water to form a slurry with a solid content of 15 wt%. A high-shear homogenizer (equipped with a double-layer stator, inner stator with 2 mm orifice and outer stator with 1 mm orifice) was used for shearing at 15,000 rpm for 15 minutes. The slurry viscosity was monitored in real time during this process. The fiber suspension was collected by centrifugation, and after adding 0.2% sodium hexametaphosphate, it was rapidly frozen in liquid nitrogen and then transferred to a freeze dryer. The drying program was set as follows: -50℃ (14 h) > rise to -30℃ and maintain for 10 hours (low-temperature sublimation plateau period) > rise to 0℃ (20 h) > rise to 30℃ (4 h). The resulting product had an average length greater than 5 μm, an average diameter less than 100 nm, and an aspect ratio greater than 50.

[0068] The product obtained in this embodiment of the invention is fibrous, readily redispersible in water, and shows no stratification after standing for 24 hours. Its Brinell viscosity reaches 6399 cP.

[0069] Example 10

[0070] Sedimentary sepiolite ore was weighed and mixed with water to form a slurry with a solid content of 15 wt%. A high-shear homogenizer (equipped with a double-layer stator, inner stator with 1 mm orifice and outer stator with 0.5 mm orifice) was used to shear the slurry at 15,000 rpm for 15 minutes. The slurry viscosity was monitored in real time during this process. The fiber suspension was collected by centrifugation, and after adding 0.2% sodium hexametaphosphate, it was rapidly frozen in liquid nitrogen and then transferred to a freeze dryer. The drying program was set as follows: -50℃ (14 h) > rise to -30℃ and maintain for 10 hours (low-temperature sublimation plateau period) > rise to 0℃ (20 h) > rise to 30℃ (4 h). The resulting product had an average length greater than 5 μm, an average diameter less than 100 nm, and an aspect ratio greater than 50.

[0071] The product obtained in this embodiment of the invention is fibrous, readily redispersible in water, and shows no stratification after standing for 24 hours. Its Brinell viscosity reaches 4321 cP.

[0072] This invention is not limited to the above embodiments. Sepiolite can have sedimentary or hydrothermal crystal forms. The above-mentioned types of sepiolite can be combined with water in any proportion, with the rotation speed controlled between 6000-15000 rpm and the shearing time between 10-30 minutes. Those skilled in the art will understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of this invention. The scope of this invention is defined by the claims and their equivalents.

Claims

1. A method for producing high aspect ratio, high dispersibility sepiolite fibers, characterized by, According to the following steps: (1) mix the raw sepiolite with water to prepare a slurry with a solid content of 5-20wt%; (2) add the slurry into a high-shear homogenizing emulsifier and perform shearing treatment at a rotation speed of 6000-15000rpm to achieve protective physical disintegration of the sepiolite fiber bundles; (3) centrifuge the slurry after shearing treatment to obtain a sepiolite fiber suspension with good dispersion; (4) perform pre-freezing treatment on the sepiolite fiber suspension, and then perform program-controlled temperature freeze-drying under vacuum, wherein the freeze-drying process comprises at least one low-temperature sublimation plateau at -30℃--10℃, and the plateau maintenance time is not less than 5 hours to prevent the fibers from re-agglomerating during the drying process.

2. The method for preparing high aspect ratio and high dispersibility sepiolite fibers according to claim 1, characterized in that: The high-shear homogenizing emulsifier has a double-layer stator-rotor structure, the inner lining stator has a pore size of 1-3mm, and the outer stator has a pore size of 0.5-1.5mm.

3. The method for preparing high aspect ratio, high dispersibility sepiolite fibers according to claim 1 or 2, characterized in that: In step (2), the shearing treatment time is 10-30 minutes.

4. The method for preparing high aspect ratio and high dispersibility sepiolite fibers according to claim 3, characterized in that: Before the pre-freezing treatment in step (4), 0.05-0.2wt% of sodium hexametaphosphate is added to the fiber suspension as a dispersant.

5. The method for preparing high aspect ratio and high dispersibility sepiolite fibers according to claim 4, characterized in that: The freeze-drying is divided into four stages: First stage: cooling from room temperature to -50℃ and maintaining at -50℃ for 14-24 hours; Second stage: warming from -50℃ to -30℃ and maintaining at -30℃ for 10-24 hours; Third stage: warming from -30℃ to 0℃ and maintaining at 0℃ for 20-24 hours; Fourth stage: warming from 0℃ to 30℃ and maintaining at 30℃ for 4-24 hours.

6. A method for preparing high-aspect-ratio and high-dispersion sepiolite fibers according to any one of claims 1-5.

7. The high aspect ratio, high dispersibility sepiolite fiber according to claim 6, characterized by: The high-aspect-ratio and high-dispersion sepiolite fibers have an average length of greater than 5μm, an average diameter of less than 100nm, and an aspect ratio of greater than 50.

8. Use of the high-aspect-ratio and high-dispersion sepiolite fibers according to claim 6 in preparing thickeners, adsorbents or composite materials.

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