CN112479185B

CN112479185B - Polyurethane-tannin-stabilized carbon nanotube aqueous dispersion and preparation method thereof

Info

Publication number: CN112479185B
Application number: CN202011398688.5A
Authority: CN
Inventors: 张建安; 刘玲; 吴明元; 吴庆云; 杨建军; 刘久逸
Original assignee: Anhui University
Current assignee: Anhui University
Priority date: 2020-12-03
Filing date: 2020-12-03
Publication date: 2022-03-29
Anticipated expiration: 2040-12-03
Also published as: CN112479185A

Abstract

The invention discloses a carbon nano tube aqueous dispersion with stable polyurethane tannin and a preparation method thereof, wherein the preparation method comprises the following steps: tannin and aromatic isocyanate monomers are taken as raw materials and gradually polymerized into polyurethane tannin; then adding an alkali aqueous solution to neutralize unreacted phenolic hydroxyl in the polyurethane to obtain the water-soluble polyurethane. The polymer is used as a hyperdispersant to disperse the carbon nano tube, aromatic rings contained in the polyurethane can be anchored on the surface of the carbon nano tube through pi-pi interaction, so that the dispersion of the carbon nano tube is promoted, and meanwhile, the secondary agglomeration of the carbon nano tube is avoided due to the steric hindrance effect brought by the polyurethane with high molecular weight; the water-soluble polyurethane tannin has the structural characteristics and the volume steric effect, realizes the highly uniform dispersion of the carbon nano tube in a water system, and can be applied to the fields of electric conduction, static resistance, electromagnetic shielding and the like. And the method has simple process, is easy to control and is suitable for industrial production.

Description

Polyurethane-tannin-stabilized carbon nanotube aqueous dispersion and preparation method thereof

Technical Field

The invention belongs to the field of preparation of high polymer materials, and particularly relates to a carbon nanotube aqueous dispersion with stable polytannic acid and polyurethane and a preparation method thereof.

Background

In recent years, Carbon Nanotubes (CNTs) have been widely used in the field of electronic components because of their excellent electrical properties, light weight, good mechanical properties, etc., which enable the formation of a conductive network in a polymer matrix at a much lower concentration than spherical particles. However, carbon nanotubes have the characteristics of high aspect ratio and large specific surface area, have extremely strong hydrophobicity, and are easy to aggregate and deposit in water. Therefore, the study of opening and stabilizing the aggregates of carbon nanotubes is of great importance.

The hyper-dispersant is a novel and efficient polymer dispersant, has remarkable space shielding effect and electric repulsion when dispersing solid particles, can quickly and fully wet carbon nanotubes, greatly improves the content of the solid particles in a dispersion system, and ensures that the dispersion system is more uniform and has good stability.

Wang et al (Wang T, Geng H-Z. Tangnic acid modified graphene/CNT thread-dimensional controlled network for preparing high-performance transport flexible coaters [ J ]. Journal of Colloid and Interface Science,2020,577.) the specific steps are: the mass ratio of the single-walled carbon nanotube to the tannin is 1:2 in deionized water, stirring, centrifuging, washing and freeze-drying to obtain the tannin functionalized carbon nanotube dispersion liquid (TCNTs). Then, dispersing the obtained TCNTs powder in deionized water by using Sodium Dodecyl Benzene Sulfonate (SDBS) as a dispersing agent; followed by sonication, centrifugation and careful collection of 80% supernatant. The process is complicated and not easy for industrial production. The tannin functionalized carbon nano tube is freeze-dried and then redispersed, is easy to agglomerate, cannot be rapidly dispersed in water, and finally has a greatly weakened application effect. And the steric hindrance effect brought by the high molecular weight polyurethane avoids the secondary agglomeration of the carbon nano tube.

Tan et al (Tan Kan, Luo J. Organic acid functionalized UV-curable carbon nanotube: Effective re-initiation of acylated epoxidized soybean oil coating [ J ] Progress in Organic Coatings,2019,130: 214. 220.) synthesized photosensitive tannic acid by ring-opening addition reaction using tannic acid and glycidyl methacrylate as raw materials, triphenyl phosphate as catalyst, hydroquinone as inhibitor, and used for dispersing multi-walled carbon nanotubes after precipitation, washing and drying. Then the photosensitization multi-wall carbon nano tube is obtained after ultrasonic treatment, centrifugation and drying. It was sonicated in tetrahydrofuran and highly dispersed for 2h each to achieve uniform dispersion. The whole operation steps are complicated, and the industrial production is not easy to realize.

CN 108192137A discloses a method for preparing a highly dispersed carbon nanotube used as a rubber filler, which comprises the steps of carrying out amination treatment on the surface of the carbon nanotube by using strong oxidizing acid and polyamine, then carrying out in-situ polymerization by using an unsaturated vinyl amide polar monomer and an aryl ethylene monomer, and forming a coating layer with the characteristics of polystyrene molecular structure on the surface of the carbon nanotube to prepare the highly dispersed carbon nanotube. In the process, strong oxidizing acid is used and is difficult to remove, and the polystyrene coating layer is only suitable for dispersing the carbon nanotubes in the oil phase, so the application range is limited.

Disclosure of Invention

In view of the defects of the prior art, the invention aims to provide a stable carbon nanotube aqueous dispersion of polyurethane tannin and a preparation method thereof, wherein after the first step of polymer synthesis, the next step of blending is directly carried out without purification, drying and other steps. The prepared polyurethane tannin can be used as a hyperdispersant and can be used for dispersing carbon nanotubes in different systems to obtain highly dispersed carbon nanotubes. The method has the advantages of simple process, easy operation, mild reaction conditions, easy control, low cost and easy industrialization.

This application patent compares with the report in the past, and the novelty lies in synthesizing high molecular weight's polytannic acid polyurethane, and the aromatic ring that make full use of tannic acid and aromatic diisocyanate promotes its dispersion on the carbon nanotube surface through pi-pi interact anchoring, and the steric hindrance effect that high molecular weight's polytannic acid polyurethane brought has avoided carbon nanotube's secondary reunion simultaneously, and water-soluble polytannic acid polyurethane's structural feature and the volume steric hindrance effect of self have realized the high homodisperse of carbon nanotube in water system.

In order to achieve the purpose, the invention adopts the technical scheme that:

a preparation method of a polyurethane-tannin-stabilized carbon nanotube aqueous dispersion comprises the following steps:

s1, dissolving tannic acid in an organic solvent, and then adding an aromatic diisocyanate monomer into the organic solvent, wherein phenolic hydroxyl groups of tannic acid and isocyanate groups of the aromatic diisocyanate monomer are subjected to polymerization reaction to generate high molecular weight (sampling from the reaction system by using an injector, and testing the molecular weight of the polymer by adopting GPC); then adding an alkali aqueous solution to neutralize unreacted phenolic hydroxyl in the polyurethane to obtain the water-soluble polyurethane. It is worth noting that: the aromatic diisocyanate monomer is required to be slowly added and can be dripped into the reaction system through a syringe or a peristaltic pump. The polymerization temperature and time are not particularly limited and may be adjusted according to the desired molecular weight of the polyurethane tannin, and in some embodiments of the invention, the polymerization temperature is preferably 40 to 80 ℃, such as 40 ℃, 60 ℃, 65 ℃ or 80 ℃, and the reaction time is preferably 2 to 3 hours. The processing parameters are also conventional for the adjustment of the stepwise polymerization and can be adjusted as required by the person skilled in the art, and are not specifically limited here.

S2, uniformly mixing the carbon nano tube with water-soluble polyurethane tannin and deionized water, and dispersing to obtain the stable carbon nano tube water dispersion of the polyurethane tannin.

Further, in step S1, the tannic acid is dried under vacuum before use to remove moisture.

Further, in step S1, the aromatic diisocyanate monomer has a molecular structure containing both a benzene ring and an isocyanate group; the alkali in the aqueous solution of the alkali is one of sodium hydroxide, potassium hydroxide, calcium hydroxide and barium hydroxide. Further, the aromatic diisocyanate-based monomer is preferably at least one of toluene diisocyanate or diphenylmethane diisocyanate.

Furthermore, in step S1, the molar ratio of the tannic acid, the aromatic diisocyanate monomer and the alkali is 1 (0.5-1.0) to (22.5-23).

Further, in the step S2, high speed dispersion is adopted for dispersion, the speed of high speed dispersion is 10000-20000 rpm, and the time is 3-5 min.

Further, the kind of the carbon nanotube is not limited. The carbon nanotube used in step S2 has a diameter of 10-20 nm and a length of 20-100 μm. The mass ratio of the carbon nano tube to the polyurethane is 1: 10-10: 1.

The above range is preferred in the present invention because the reaction is more efficient and rapid and the drug is maximally utilized.

Another object of the present invention is to provide a stable aqueous dispersion of carbon nanotubes of polyurethane polytannate prepared by the above-mentioned preparation method. Aromatic rings of tannic acid and aromatic diisocyanate are anchored on the surface of the carbon nano tube through pi-pi interaction to promote dispersion of the carbon nano tube, secondary agglomeration of the carbon nano tube is avoided due to the steric hindrance effect brought by high-molecular-weight polyurethane, and the high-degree uniform dispersion of the carbon nano tube in a water system is realized by the water-soluble polyurethane structure.

Compared with the prior art, the invention has the following beneficial effects:

(1) according to the invention, after the tannin and the aromatic diisocyanate monomer are polymerized to generate the polymer in the first step, the next step of blending is directly carried out without the steps of settling, drying and the like, the operation is simple, and the method is suitable for industrial production.

(2) The tannin and the aromatic diisocyanate monomer used by the invention are both from natural plants, are low in price, are green and environment-friendly, and have commercial value. In addition, the carbon nano tube aqueous dispersion prepared by the invention has the characteristics of high concentration, high dispersion degree and high stability, and can be applied to the fields of electric conduction, antistatic property, electromagnetic shielding, fluorescent marking and the like.

(3) The carbon nano tube is a tubular object formed by connecting a plurality of benzene ring structures, and the chemical bond is completely sp²Carbon bonds. The monomer tannic acid of the polyurethane of poly tannic acid contains 10 benzene rings, and the aromatic diisocyanate monomer also contains benzene rings. There is structural similarity between carbon nanotubes and polyurethane tannins. Compared with tannic acid, the polyurethane polytannic acid increases molecular weight, enlarges surface area and increases steric hindrance; the aromatic ring is easier to anchor on the carbon nano tube structure through pi-pi interaction, thereby promoting the dispersibility of the carbon nano tube in water and avoiding the agglomeration among the tubes. The structure can not only form a stable conductive network, but also improve the adhesive force to the matrix. When mixed with carbon nanotubes, the hydrophobic portions of the polymer interact with the sidewalls of the carbon nanotubes, extending the hydrophilic portions into the water, and the water-soluble polyurethane promotes the carbon nanotubes in the waterTo obtain a uniformly dispersed dispersion.

(4) Non-covalent functionalization of carbon nanotubes by polymer encapsulation to facilitate their dispersion is preferred over organic functionalization due to the pristine sp²The hybrid state is preserved. The non-covalent interaction constructed by the polyurethane tannin containing hydrophilic and hydrophobic structures can keep the carbon main chain of the carbon nano tube intact without damaging the structure and the electronic property of an inherent electronic tube.

Drawings

FIG. 1 is a transmission electron micrograph of the aqueous dispersion of carbon nanotubes in example 1 at different magnifications;

FIG. 2 is a graph showing a distribution of the particle size of carbon nanotubes before and after adding polyurethane tannin in example 1;

FIG. 3 is an infrared spectrum of tannic acid and polyurethane of example 1;

FIG. 4 is a UV spectrum of an aqueous dispersion of carbon nanotubes in example 1

Detailed Description

In order that the invention may be more fully understood, reference will now be made to the specific embodiments illustrated. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

Example 1

2g of tannic acid after vacuum drying is taken to be put into a three-neck flask, 10g N N-dimethylformamide is added, and the two are stirred by magnetic force to be mixed evenly to form a uniform solution. Introducing nitrogen, condensing, and heating to 40 deg.C in oil bath; toluene diisocyanate was slowly added dropwise into the three-necked flask using a syringe. Phenolic hydroxyl group of tannic acid and isocyanate group of aromatic diisocyanate monomerReact with each other to grow polymer gradually, and when the required polymer molecular weight is reached (7.65X 10)³) When the reaction is terminated, adding an aqueous solution of sodium hydroxide to neutralize unreacted phenolic hydroxyl groups in the polyurethane tannin to obtain the water-soluble polyurethane tannin. Wherein the molar ratio of the tannic acid to the toluene diisocyanate to the sodium hydroxide is 1:0.5: 23.5. Weighing 1g of carbon nano tube, adding 5.7g of polyurethane tannin and 93.3g of deionized water, blending, and then dispersing at 10000rpm for 5min at a high speed to obtain the carbon nano tube aqueous dispersion with the solid content of 1%.

Test example

FIG. 1 is a transmission electron microscope image of the carbon nanotube aqueous dispersion under different magnifications in example 1, from which it can be seen that the carbon nanotubes have a long tubular structure with a diameter of about 10-15 nm.

In FIG. 2, a is a distribution diagram of the particle size of the carbon nanotubes in example 1, and b is a distribution diagram of the particle size of the polyurethane obtained in example 1 after adding the carbon nanotubes, as can be seen from the following figures: the carbon nanotubes have a particle size of about 730.7nm, and the carbon nanotubes have a particle size of about 91.8nm after the polyurethane tannin is added. It can be seen that: the addition of polyurethane tannin leads the particle size of the carbon nano tube to be obviously reduced. This is because the polyurethane tannin can effectively reduce the agglomeration of the carbon nanotubes.

FIG. 3 is an infrared spectrum of tannic acid and polyurethane of example 1, showing that: compared with infrared spectrum of pure tannic acid, polyurethane tannin has infrared spectrum of 3450 and 1656cm^-1New peaks appear at (a) indicating imino groups and ester groups, respectively. It can thus be derived: the tannin and isocyanate groups are gradually polymerized to generate the polyurethane of the poly tannin.

When the polyurethane tannin obtained in example 1 was added to carbon nanotubes as a dispersant to prepare a 25mg/L aqueous dispersion of carbon nanotubes, the ultraviolet spectrum thereof is as shown in FIG. 4, and it is found that the absorbance at 224nm was 1.025. Therefore, the dispersing agent has more stable particles and better dispersing performance.

Adding 0.3g of carbon nano tube (XFQ041) into 30mL of deionized water, and dispersing at high speed of 12000rpm for 3min to obtain solution A; meanwhile, 0.3g of carbon nanotubes (XFQ041) and the polyurethane polytannate (0.06g, 0.18g, 0.3g) prepared in example 1 were added together to 30mL of deionized water, and dispersed at 12000rpm for 3min at high speed to obtain solutions B (20 wt%), C (60 wt%), and D (100 wt%), respectively. The solution A, B, C, D was allowed to stand for 24h and its change was observed (as shown in Table 1 below). Then, 4mL of the solution A, B, C, D was centrifuged at 5000r/min for 10min, and the centrifugation stability was measured by observing the state after centrifugation (see Table 2 below).

TABLE 1

TABLE 2

As can be seen from tables 1 and 2 above, the solution without dispersant is left standing for a while, the carbon nanotubes are deposited on the bottom of the sample bottle in a distinct layered state and cannot be dispersed in water. The tube was centrifuged and the carbon nanotubes were found to be deposited all at the bottom of the tube. And with the increase of the mass of the dispersing agent, the carbon nano tubes can be gradually dispersed in water, when the mass fraction of the dispersing agent reaches 60 wt%, no layering phenomenon occurs, and only a small amount of carbon nano tubes are deposited at the bottom of the centrifugal tube. When the mass fraction of the dispersant reached 100 wt%, it was subjected to a centrifugal stability test, and it was found that the carbon nanotubes were completely dispersed in water. Therefore, the poly tannic acid urethane is further proved to be capable of effectively reducing the agglomeration of the carbon nano tubes, thereby achieving the effect of dispersing the carbon nano tubes.

Example 2

3g of tannic acid after vacuum drying is taken to be put into a three-neck flask, 18g of acetone is added, and the two are stirred by magnetic force to be mixed evenly to form a uniform solution. Introducing nitrogen, condensing, and heating to 50 deg.C in oil bath; and (3) slowly dropwise adding diphenylmethane diisocyanate into the three-neck flask by using a peristaltic pump. Phenolic hydroxyl group of tannic acid and isocyanate group of aromatic diisocyanate monomer react with each otherGradually grow into polymer, and when the required polymer molecular weight (8.5X 10) is reached³) When the reaction is terminated, potassium hydroxide is added to neutralize unreacted phenolic hydroxyl groups in the polyurethane, thereby obtaining the water-soluble polyurethane. Wherein the molar ratio of the tannic acid to the diphenylmethane diisocyanate to the potassium hydroxide is 1:0.6: 23.4. Weighing 1g of carbon nano tube, adding 6.7g of polyurethane tannin and 42.3g of deionized water, blending, and then dispersing at 11000rpm for 5min at a high speed to obtain carbon nano tube dispersion liquid with the solid content of 2%.

Example 3

4g of tannic acid after vacuum drying is taken to be put into a three-neck flask, 28g of dimethyl sulfoxide is added, and the two are stirred by magnetic force to be mixed evenly to form a uniform solution. Introducing nitrogen, condensing, and heating to 60 deg.C in oil bath; toluene diisocyanate was slowly added dropwise into the three-necked flask using a syringe. The phenolic hydroxyl group of the tannic acid and the isocyanate group of the aromatic diisocyanate monomer react with each other to grow into polymer gradually, and when the desired molecular weight of the polymer is reached (1.02X 10)⁴) When the reaction is terminated, barium hydroxide is added to neutralize unreacted phenolic hydroxyl groups in the polyurethane, and the water-soluble polyurethane is obtained. Wherein the molar ratio of the tannic acid to the toluene diisocyanate to the barium hydroxide is 1:0.7: 23.3. Weighing 1g of carbon nano tube, adding 7.5g of polyurethane tannin and 24.8g of deionized water, blending, and then dispersing at high speed of 12000rpm for 4min to obtain carbon nano tube dispersion liquid with solid content of 3%.

Example 4

And (3) putting 5g of the tannic acid subjected to vacuum drying into a three-neck flask, adding 40g of sulfolane, and stirring by magnetic force to uniformly mix the tannic acid and the sulfolane to obtain a uniform solution. Introducing nitrogen, condensing, and heating to 65 ℃ in an oil bath; and (3) slowly dropwise adding diphenylmethane diisocyanate into the three-neck flask by using a peristaltic pump. The phenolic hydroxyl group of the tannic acid and the isocyanate group of the aromatic diisocyanate monomer react with each other to grow into a polymer gradually when the desired molecular weight of the polymer (1.6X 10)⁴) When the reaction is terminated, calcium hydroxide is added to neutralize the unreacted phenolic hydroxyl groups in the polyurethane, and the water-soluble polyurethane is obtained. Wherein the tannic acid and diphenylmethane areThe molar ratio of isocyanate to calcium hydroxide was 1:0.8: 23.2. Weighing 1g of carbon nano tube, adding 8.3g of polyurethane tannin and 90.7g of deionized water, blending, and then dispersing at 13000rpm for 4min at a high speed to obtain a carbon nano tube dispersion liquid with a solid content of 1%.

Example 5

And (3) putting 6g of the tannic acid subjected to vacuum drying into a three-neck flask, adding 54g of anisole, and stirring the two by magnetic force to fully and uniformly mix the tannic acid and the anisole to form a uniform solution. Introducing nitrogen, condensing, and heating to 70 deg.C in oil bath; toluene diisocyanate was slowly added dropwise into the three-necked flask using a syringe. The phenolic hydroxyl group of the tannic acid and the isocyanate group of the aromatic diisocyanate monomer react with each other to grow into a polymer gradually when the desired molecular weight of the polymer (2.1X 10)⁴) When the reaction is terminated, sodium hydroxide is added to neutralize unreacted phenolic hydroxyl groups in the polyurethane, and the water-soluble polyurethane is obtained. Wherein the molar ratio of the tannic acid to the toluene diisocyanate to the sodium hydroxide is 1:0.9: 23.1. Weighing 1g of carbon nano tube, adding 9.1g of polyurethane polytannate and 39.9g of deionized water, blending, and then dispersing at a high speed of 15000rpm for 3min to obtain a carbon nano tube dispersion liquid with the solid content of 2%.

Example 6

And (3) putting 7g of the tannic acid after vacuum drying into a three-neck flask, adding 70g N N-dimethylformamide, and stirring the two by magnetic force to fully and uniformly mix the tannic acid and the N-dimethylformamide into a uniform solution. Introducing nitrogen, condensing, and heating to 80 deg.C in oil bath; and (3) slowly dropwise adding diphenylmethane diisocyanate into the three-neck flask by using a peristaltic pump. The phenolic hydroxyl group of the tannic acid and the aromatic diisocyanate monomer react with each other to grow into polymer gradually, and when the required polymer molecular weight (2.5X 10)⁴) When the reaction is terminated, potassium hydroxide is added to neutralize unreacted phenolic hydroxyl groups in the polyurethane, thereby obtaining the water-soluble polyurethane. Wherein the molar ratio of the tannic acid to the diphenylmethane diisocyanate to the potassium hydroxide is 1:1: 23. Weighing 1g of carbon nano tube, adding 10g of polyurethane tannin and 22.3g of deionized water, blending, and then dispersing at 20000rpm for 3min at high speed to obtain carbon nano tube dispersion liquid with solid content of 3%.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. A preparation method of a polyurethane-tannin-stabilized carbon nanotube aqueous dispersion is characterized by comprising the following steps: the method comprises the following steps:

s1, dissolving tannic acid in an organic solvent, adding an aromatic diisocyanate monomer into the organic solvent, and carrying out polymerization reaction on phenolic hydroxyl of tannic acid and isocyanate groups of the aromatic diisocyanate monomer to generate polyurethane of poly tannic acid; then adding an alkali aqueous solution into the polyurethane to neutralize unreacted phenolic hydroxyl in the polyurethane to obtain water-soluble polyurethane; the molecular structure of the aromatic diisocyanate monomer contains benzene ring and isocyanate group at the same time, and is at least one of toluene diisocyanate or diphenylmethane diisocyanate;

s2, uniformly mixing the carbon nano tube with water-soluble polyurethane tannin and deionized water, and dispersing to obtain the carbon nano tube water dispersion with stable polyurethane tannin.

2. The method of claim 1, wherein: in step S1, the tannic acid is dried in vacuum before use; the molar ratio of the tannic acid, the aromatic diisocyanate monomer and the alkali is 1 (0.5-1.0) to (23-23.5).

3. The method of claim 1, wherein: in step S1, the organic solvent is one of N, N-dimethylformamide, acetone, dimethyl sulfoxide, sulfolane, and anisole; the mass of the organic solvent is 5-10 times of that of the tannic acid; the alkali in the aqueous solution of the alkali is one of sodium hydroxide, potassium hydroxide, calcium hydroxide and barium hydroxide.

4. The method of claim 1, wherein: in the step S1, the temperature of the polymerization reaction is 40-80 ℃; the speed of dispersion is 10000-20000 rpm, and the time is 3-5 min.

5. The method of claim 1, wherein: in the step S2, the mass ratio of the carbon nanotubes to the polyurethane tannin is 1: 10-10: 1.

6. The aqueous dispersion of stable carbon nanotubes of polytannate according to any one of claims 1 to 5.