CN115058183A

CN115058183A - Preparation method of short fluoroalkyl compound modified hydrophobic/super-hydrophobic aqueous polyurethane coating

Info

Publication number: CN115058183A
Application number: CN202210614982.8A
Authority: CN
Inventors: 潘明旺; 靳尧; 袁金凤; 张广林; 潘志成
Original assignee: Hebei University of Technology
Current assignee: Hebei University of Technology
Priority date: 2022-05-31
Filing date: 2022-05-31
Publication date: 2022-09-16
Anticipated expiration: 2042-05-31
Also published as: CN115058183B

Abstract

The invention relates to a preparation method of a short fluoroalkyl compound modified hydrophobic/super-hydrophobic aqueous polyurethane coating. The method comprises the following steps: adding diisocyanate and a catalyst dibutyltin dilaurate into dihydric alcohol, adding 2, 2-dimethylolpropionic acid after reaction, adding an amine compound for neutralization after continuous reaction, and then adding perfluorohexylpropanol for reaction to obtain a polyurethane prepolymer; dropwise adding deionized water into the obtained waterborne polyurethane prepolymer, and dispersing at a high speed for 1-3 hours to obtain a waterborne polyurethane emulsion; and (3) dripping the aqueous polyurethane emulsion on a substrate, and drying at 40-60 ℃ to obtain the short fluoroalkyl compound modified aqueous polyurethane coating. The hydrophobicity of the coating obtained by the invention is greatly improved, the contact angle is up to 157.5 degrees, and the coating shows excellent super-hydrophobicity on different base materials such as glass, fabrics and leather.

Description

Preparation method of short fluoroalkyl compound modified hydrophobic/super-hydrophobic aqueous polyurethane coating

Technical Field

The invention belongs to the field of manufacturing of super-hydrophobic materials, and particularly relates to a preparation method of a short fluoroalkyl compound modified hydrophobic/super-hydrophobic aqueous polyurethane coating.

Background

The waterborne polyurethane takes water as a dispersion medium, and the volatilization of organic compounds is reduced on the premise of keeping the original excellent performance of the polyurethane. However, in order to ensure that the prepolymer can be stably dispersed in water, hydrophilic groups are introduced into the main chain of the polymer molecule, which leads to poor hydrophobicity of the waterborne polyurethane and limits further development of the waterborne polyurethane. The fluorine-containing chain segment or compound is introduced into the polyurethane molecular chain to prepare the fluorine-containing waterborne polyurethane, which is one of effective ways for improving the hydrophobicity of the waterborne polyurethane. The element with the strongest electronegativity in nature is fluorine element, the electronegativity of which can reach 4.0 at most, so that the atomic nucleus of the fluorine atom has strong electron attracting and bonding capabilities. And the bond energy of the carbon-fluorine bond is 485kJ/mol which is much higher than that of the carbon-carbon bond. The adjacent fluorine atoms are spirally distributed along the carbon chain, so that the macromolecular chain is strongly shielded, and the fluorine-containing compound is endowed with outstanding chemical stability. The fluorine compound has the lowest surface energy of only 15mJ/m due to the strong electronegativity and the small atomic radius ² . Thus containing fluorineThe compound has a tendency to migrate to the surface during drying, which results in a fluorine-containing aqueous polyurethane coating having excellent hydrophobic properties.

Long fluorine or perfluoroalkyl compounds (C.gtoreq.8) have proven to be effective compounds for achieving superhydrophobicity due to their inherently low surface energy. Perfluorocarboxylates and sulfonates containing six or fewer perfluorocarbon atom chains are reported to not accumulate in the human body, to be biologically persistent, to be excreted with the metabolism within a short period of time, and to be nontoxic as degradation products. The substitution of linear long fluorocarbon alkyl chains with environmentally friendly short fluoroalkyl compounds is very important for the construction of strongly hydrophobic surfaces. However, the short-fluoroalkane-based compound tends to have a short molecular chain, and fluorine element is not efficiently oriented on the surface, and the short-fluorine compound tends to be immobilized on the molecular main chain, and the behavior of migration to the surface is limited. Therefore, the introduction of short fluoroalkyl compounds into aqueous polyurethanes to construct superhydrophobic surfaces still faces great challenges.

Disclosure of Invention

The invention aims to provide a preparation method of a short fluoroalkyl compound modified hydrophobic/super-hydrophobic aqueous polyurethane coating, aiming at the defects in the prior art. The waterborne polyurethane coating with excellent hydrophobic property is prepared by modifying the short fluoroalkyl compound. The method adopts perfluorohexylpropanol (C6) as a fluorine-containing end-capping agent, introduces short fluoroalkyl compounds into two ends of a polyurethane molecular chain, reduces the constraint of molecular chain rigidity on migration motion of fluorine elements, and improves the migration efficiency of the fluorine elements. In the film forming process, fluorine element is migrated and concentrated on the surface of the coating, so that the surface energy of the coating is reduced, and the hydrophobicity of the coating is improved. On the basis, hexamethylene diisocyanate or a mixture of hexamethylene diisocyanate and isophorone diisocyanate, toluene-2, 4-diisocyanate and 4, 4' -diisocyanate dicyclohexylmethane is used as a hard segment, the structure of the isocyanate hard segment connected with a fluorine-containing blocking agent is changed, and the migration of fluorine elements is further promoted by virtue of the movement of a flexible isocyanate segment. The content of fluorine elements on the surface of the coating is increased, so that the hydrophobicity of the coating is improved, and the coating is changed from hydrophobicity to super-hydrophobicity.

The technical scheme of the invention is as follows:

a preparation method of a short fluoroalkyl compound modified hydrophobic/super-hydrophobic aqueous polyurethane coating comprises the following steps:

(1) preparation of polyurethane prepolymer

Adding dihydric alcohol into a reactor, heating to 75-80 ℃ under the nitrogen atmosphere, adding diisocyanate and a catalyst dibutyltin dilaurate, reacting for 1-1.5 hours, adding a hydrophilic chain extender 2, 2-dimethylolpropionic acid dissolved in N, N-dimethylformamide, reacting for 1-1.5 hours, cooling to 40-60 ℃, adding an amine compound for neutralization, reacting for 0.5-1.5 hours, and then adding perfluorohexylpropanol for reacting for 1-2 hours to obtain a polyurethane prepolymer;

wherein the molar ratio of the dihydric alcohol to the diisocyanate is 1/2-4; the mass of the dibutyltin dilaurate is 0.5-1.5% of the total mass of the dihydric alcohol and the diisocyanate; the dosage of the 2, 2-dimethylolpropionic acid and the amine compound is 3-10% of the total mass of the dihydric alcohol and the diisocyanate; the perfluorohexyl propanol accounts for 5-30% of the total mass of the dihydric alcohol and the diisocyanate;

(2) preparation of aqueous polyurethane emulsion

Dropwise adding deionized water into the obtained waterborne polyurethane prepolymer, and simultaneously dispersing at high speed (1200-1500 rpm) for 1-3 hours to obtain a waterborne polyurethane emulsion;

wherein the addition amount of the deionized water is 2-4 times of the total mass of the dihydric alcohol and the diisocyanate;

(3) preparation of aqueous polyurethane coating

Dripping the aqueous polyurethane emulsion on a substrate, and drying at 40-60 ℃ to obtain a short fluoroalkyl compound modified aqueous polyurethane coating;

wherein 0.5-10 ml of aqueous polyurethane emulsion is dripped on each 10-20 square cm of base material;

in the step (1), the dihydric alcohol is any one or more of polyoxypropylene dihydric alcohol, polyoxyethylene dihydric alcohol, polycaprolactone dihydric alcohol, polyethylene glycol adipate dihydric alcohol, polyester dihydric alcohol and polytetrahydrofuran ether dihydric alcohol; the molecular weight of the dihydric alcohol is 500-2500;

in the step (1), the diisocyanate is one of isophorone diisocyanate and hexamethylene diisocyanate, or a mixture of a substance A and a substance B; wherein the substance A is isophorone diisocyanate; the substance B is toluene-2, 4-diisocyanate, 4-diisocyanate dicyclohexylmethane or hexamethylene diisocyanate;

in the step (1), the amine compound is any one or more of triethylamine, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate and ethylenediamine tetraacetic acid;

the substrate is glass, fabric and leather.

The invention has the substantive characteristics that:

the chemical methods reported at present for introducing fluorine-containing compounds into aqueous polyurethane are mainly as follows: introducing fluorinated polyethylene glycol as a soft segment, introducing fluorinated diisocyanate as a hard segment, introducing a fluorine-containing chain extender, and introducing fluorine-containing acrylate through copolymerization to prepare the core-shell composite emulsion. However, the fluorine-containing compound introduced by the first three ways is fixed in the middle of the main chain of polyurethane, and due to the limitation of the rigidity of the main chain, fluorine generally shows poor migration capability and hydrophobic modification effect is poor. The rigidity of the polyurethane backbone and the interaction between the fluorochemical and the backbone directly determine the migration efficiency of elemental fluorine, and therefore careful design of the introduction position of the fluorochemical is required.

According to the invention, the short-chain fluoroalcohol, the introduction position of the fluoroalcohol and the flexible isocyanate are selected as the hard segment, so that the waterborne polyurethane modified by the short-chain fluoroalkyl compound has a super-hydrophobic characteristic. The method has the advantages that perfluorohexylpropanol is used as a blocking agent, and a short fluoroalkyl compound is introduced to two ends of a molecular chain, so that the limitation of the rigidity of the main chain on the migration of fluorine elements is reduced, and the migration efficiency of the fluorine elements is improved. On the basis, the structure of the isocyanate hard segment connected with the fluorine-containing blocking agent is changed, and the migration efficiency of fluorine element is further improved by virtue of the movement of the flexible isocyanate chain. Fluorine element migrates and is enriched on the surface of the coating in the emulsion drying film forming process, so that the surface energy of the coating is reduced, and the roughness of the coating is increased. Under the combined action of low surface energy and high roughness, the short fluoroalkyl compound modified water-thinned polyurethane coating is changed from original hydrophobicity to super hydrophobicity.

The invention has the beneficial effects that:

the preparation method of the (super) hydrophobic polyurethane coating provided by the invention adopts the environment-friendly short fluoroalkyl compound as the hydrophobic modifier, and introduces the perfluorohexylpropanol as the end-capping agent into the polyurethane molecular chain. Compared with the traditional main chain fluorine-containing polyurethane, fluorine elements of the polyurethane chain are positioned at two ends of a molecular chain, the limitation of the rigidity of the main chain is small, and the migration capacity in the film forming process is improved. With the increase of the introduction amount of the fluorine-containing end-capping agent, the hydrophobicity of the coating is continuously enhanced, and the contact angle is as high as 128.2 degrees. On the basis, the introduction amount of the fluorine-containing blocking agent is fixed, the structure of an isocyanate hard segment connected with the fluorine-containing blocking agent is changed, the movement of a flexible isocyanate chain further drives fluorine elements to migrate to the surface, and the fluorine elements enriched on the surface of the coating reduce the surface energy of the coating and improve the roughness of the coating. Under the combined action of low surface energy and high roughness, the hydrophobicity of the coating is greatly improved, the contact angle is as high as 157.3 degrees, and the conversion from hydrophobicity to super-hydrophobicity is realized. The prepared super-hydrophobic coating has good adhesive force, and shows excellent super-hydrophobicity on different base materials such as glass, fabric, leather and the like.

Drawings

FIG. 1 is a photograph of the water contact angle of the coating prepared in example 1;

FIG. 2 is a photograph of the water contact angle of the coating prepared in example 2;

FIG. 3 is a photograph of the water contact angle of the coating prepared in example 3;

FIG. 4 is a photograph of the water contact angle of the coating prepared in example 4;

FIG. 5 is a photograph of the water contact angle of the coating prepared in example 5;

FIG. 6 is a photograph of the water contact angle of the coating prepared in example 6;

FIG. 7 is a photograph of the water contact angle of the coating prepared in example 7;

FIG. 8 is a photograph of the water contact angle of the superhydrophobic coating prepared in example 8;

FIG. 9 is a photograph of the water contact angle of the superhydrophobic coating prepared in example 9;

FIG. 10 is a photograph of the water contact angle of the superhydrophobic coating prepared in example 10;

FIG. 11 is a photograph of water contact angle of the superhydrophobic coating on the fabric substrate in example 11;

FIG. 12 is a photograph of water contact angle of the superhydrophobic coating on leather as a substrate in example 11;

FIG. 13 is a surface roughness of the coating prepared in example 5;

FIG. 14 is a surface roughness of the coating prepared in example 6;

FIG. 15 is a surface roughness of the coating prepared in example 7;

FIG. 16 is the surface roughness of the coating prepared in example 9;

Detailed Description

Example 1.

(1) Preparation of polyurethane prepolymer

10.40g (i.e.5.20 mmol) of polytetrahydrofuran ether having a molecular weight of 2000 are introduced into a four-necked flask and dried under vacuum at 120 ℃ for 2 hours. The temperature was reduced to 80 ℃ and 3.47g (i.e., 15.6mmol) of isophorone diisocyanate and 0.1g of dibutyltin dilaurate were added and the reaction was allowed to proceed for 1 hour with incubation. 0.67g of 2, 2-dimethylolpropionic acid dissolved in 3.00g N N-dimethylformamide was added to a four-necked round-bottomed flask and the mixture was allowed to stand for 1.5 hours. And cooling to 40 ℃, adding 0.50g of neutralizing agent triethylamine, and keeping the temperature for 1 hour to obtain the polyurethane prepolymer.

(2) Preparation of aqueous polyurethane emulsion

And transferring the prepolymer into a 500mL plastic beaker while the prepolymer is hot, dripping 40g of deionized water into the beaker, and dispersing for 1.5 hours under high-speed stirring at 1500rpm to obtain the waterborne polyurethane emulsion.

(3) Preparation of aqueous polyurethane coatings

2mL of aqueous polyurethane emulsion is measured by a measuring cylinder, the emulsion is uniformly dripped on a glass plate by a dropper, and the glass plate is dried for 24 hours at 40 ℃ to obtain a flat coating.

The coating was subjected to a static water contact angle test by the sitting drop method using an optical contact angle measuring instrument of model DSA30S, and as can be seen from fig. 1, the static water contact angle of the coating was 86.9 °, and the coating exhibited hydrophilicity.

Example 2.

(1) Preparation of fluorine-containing polyurethane prepolymer

10.40g of polytetrahydrofuran ether diol having a molecular weight of 2000 were introduced into a four-necked round-bottomed flask and dried under vacuum at 120 ℃ for 2 hours. The temperature is reduced to 80 ℃, 3.47g of isophorone diisocyanate and 0.1g of dibutyltin dilaurate are added, and the reaction is carried out for 1 hour under the condition of heat preservation. 0.67g of 2, 2-dimethylolpropionic acid dissolved in 3.00g N N-dimethylformamide was charged into a four-necked round-bottomed flask and the reaction was allowed to proceed for 1.5 hours while maintaining the temperature. The temperature is reduced to 40 ℃, 0.50g of neutralizing agent triethylamine is added, and the temperature is kept for 1 hour. And finally, adding 1.00g of perfluorohexylpropanol, and preserving the heat for 1 hour to obtain the fluorine-containing polyurethane prepolymer.

(2) Preparation of aqueous fluorinated polyurethane emulsions

And transferring the prepolymer into a 500mL plastic beaker while the prepolymer is hot, dropwise adding 40g of deionized water into the beaker, and dispersing for 1.5h under the high-speed stirring of 1500rpm to obtain the aqueous polyurethane emulsion.

(3) Preparation of aqueous fluorinated polyurethane coatings

Measuring 2mL of aqueous polyurethane emulsion by using a measuring cylinder, and uniformly dripping the emulsion on 18.8cm by using a dropper ² Dried at 40 ℃ for 24h to give a smooth coating.

When the coating is subjected to a static water contact angle test, as can be seen from fig. 2, the static water contact angle of the coating is 105.7 degrees, the coating shows hydrophobicity, and the introduction of the fluorine-containing compound enables the coating to realize the transition from hydrophilicity to hydrophobicity.

Example 3.

This example is substantially the same as example 2 except that perfluorohexylpropanol was added in an amount of 2g in the preparation of the fluorinated polyurethane prepolymer. As can be seen from fig. 3, the static water contact angle of the coating was 118.5 °.

Example 4.

This example is substantially the same as example 2 except that perfluorohexylpropanol was added in an amount of 3g in the preparation of the fluorinated polyurethane prepolymer. As can be seen from fig. 4, the static water contact angle of the coating was 123.6 °.

Example 5.

This example is substantially the same as example 2, except that the amount of perfluorohexylpropanol added in the preparation of the fluorinated polyurethane prepolymer was 4g, and the amount of the fluorinated end-capping agent added was maximized. As can be seen from fig. 5, the static water contact angle of the coating reached 128.2 °. The roughness of the coating surface was observed by means of an optical microscope, and the result is shown in FIG. 13, from which it can be seen that the coating surface was relatively smooth.

Example 6.

(1) Preparation of fluorine-containing polyurethane prepolymer with hard segment of isophorone diisocyanate and toluene-2, 4-diisocyanate

10.40g of polytetrahydrofuran ether diol having a molecular weight of 2000 were introduced into a four-necked round-bottomed flask and dried under vacuum at 120 ℃ for 2 hours. The temperature was reduced to 80 ℃ and 1.16g of isophorone diisocyanate, 1.81g of toluene-2, 4-diisocyanate and 0.1g of dibutyltin dilaurate were added and the mixture was allowed to stand for 1 hour. 0.77g of 2, 2-dimethylolpropionic acid dissolved in 3.00g N, N-dimethylformamide was added to a four-necked flask and the flask was kept warm for 1.5 hours. The temperature is reduced to 40 ℃, 0.58g of neutralizing agent triethylamine is added, and the reaction is carried out for 1 hour under the condition of heat preservation. And finally, adding 4.00g of perfluorohexylpropanol, and reacting for 1 hour under the condition of heat preservation to obtain the fluorine-containing polyurethane prepolymer with the hard segment of toluene-2, 4-diisocyanate.

(2) Preparation of fluorine-containing aqueous polyurethane emulsion with hard segment of isophorone diisocyanate and toluene-2, 4-diisocyanate

(3) Preparing fluorine-containing aqueous polyurethane coating with hard segment of isophorone diisocyanate and toluene-2, 4-diisocyanate

The coating was tested for static water contact angle, and as can be seen from fig. 6, the static water contact angle of the coating was 131.1 °. The roughness of the coating surface was observed by means of an optical microscope, and the result is shown in FIG. 14, from which it can be seen that the coating surface was relatively smooth.

Example 7.

This example is substantially the same as example 6, except that isophorone diisocyanate and 4, 4-diisocyanate dicyclohexylmethane were selected as the hard segment, isophorone diisocyanate was added in an amount of 1.38 g, and 4, 4-diisocyanate dicyclohexylmethane was added in an amount of 2.47g in the preparation of the fluorinated polyurethane prepolymer. As can be seen from fig. 7, the static water contact angle of the coating was 146.2 °. The roughness of the coating surface was observed by means of an optical microscope, and as a result, as shown in FIG. 15, it was seen that the coating surface had a slightly rough structure.

Example 8.

This example is substantially the same as example 6, except that isophorone diisocyanate and hexamethylene diisocyanate were selected as the hard segments in the preparation of the fluorinated polyurethane prepolymer, the amount of isophorone diisocyanate added was 0.71g, the amount of hexamethylene diisocyanate added was 2.08g, and the static water contact angle of the coating was 153.2 ° as seen in fig. 8.

Example 9.

This example is substantially the same as example 8 except that, in the preparation of the fluorinated polyurethane prepolymer, the content of hexamethylene diisocyanate in the hard segment was increased, the amount of isophorone diisocyanate added was 0.28g, and the amount of hexamethylene diisocyanate added was 2.41 g. As can be seen from fig. 9, the static water contact angle of the coating was 157.3 °. The roughness of the coating surface was observed by means of an optical microscope, and the result is shown in FIG. 16. As can be seen from the figure, the rough structure of the coating surface is obvious, the migration of the fluorine-containing blocking agent is further promoted by the hexamethylene diisocyanate chain which is easy to move, a large amount of fluorine is enriched on the coating surface, the roughness of the coating is increased while the surface energy of the coating is reduced, and the super-hydrophobic characteristic of the coating is realized under the combined action of low surface energy and high roughness.

Example 10.

This example is substantially the same as example 8, except that hexamethylene diisocyanate was used as a hard segment in the preparation of the fluorinated polyurethane prepolymer in an amount of 2.62g, and the static water contact angle of the coating layer was 157.5 ° as shown in FIG. 10.

Example 11.

This example is essentially the same as example 9, except that in the preparation of the fluorine-containing aqueous polyurethane coating, a fabric and leather were selected as the substrate. As can be seen from fig. 11 and 12, the static water contact angles of the coatings were 154.3 ° and 163.0 °, respectively.

It can be seen from the above examples that the water-borne polyurethane is less hydrophobic due to the presence of the hydrophilic component and the contact angle is only 86.9 ° (example 1). Perfluorohexylpropanol is introduced as a capping agent by molecular design, and as the amount of introduction increases, the coating contact angle increases. When the incorporation amount reached a maximum of 4g, the contact angle reached 128.2 ° (example 5), and the hydrophobicity of the coating was greatly increased. After that, the amount of perfluorohexylpropanol added was fixed, and the structure of isocyanate was changed to further increase the contact angle. When a blend of isophorone diisocyanate and hexamethylene diisocyanate was chosen as the hard segment, the coating gradually changed from hydrophobic to superhydrophobic with a contact angle of up to 153.2 ° (example 8). And increases with increasing hexamethylene diisocyanate content.

The invention is not the best known technology.

Claims

1. A preparation method of a short fluoroalkyl compound modified hydrophobic/super-hydrophobic aqueous polyurethane coating is characterized by comprising the following steps:

(1) preparation of polyurethane prepolymer

Adding dihydric alcohol into a reactor, heating to 75-80 ℃ under the atmosphere of nitrogen, adding diisocyanate and a catalyst dibutyltin dilaurate, reacting for 1-1.5 hours, adding a hydrophilic chain extender 2, 2-dimethylolpropionic acid dissolved in N, N-dimethylformamide, reacting for 1-1.5 hours, cooling to 40-60 ℃, adding an amine compound for neutralization, reacting for 0.5-1.5 hours, and then adding perfluorohexylpropanol for reacting for 1-2 hours to obtain a polyurethane prepolymer;

wherein, the molar ratio of the dihydric alcohol: 1/2-4% of diisocyanate; the mass of the dibutyltin dilaurate is 0.5-1.5% of the total mass of the dihydric alcohol and the diisocyanate; the dosage of the 2, 2-dimethylolpropionic acid and the amine compound is 3-10% of the total mass of the dihydric alcohol and the diisocyanate; the perfluorohexyl propanol accounts for 5-30% of the total mass of the dihydric alcohol and the diisocyanate;

(2) preparation of aqueous polyurethane emulsion

Dropwise adding deionized water into the obtained waterborne polyurethane prepolymer, and simultaneously dispersing at a high speed to obtain a waterborne polyurethane emulsion after 1-3 hours;

(3) preparation of aqueous polyurethane coating

in the step (1), the dihydric alcohol is any one or more of polyoxypropylene dihydric alcohol, polyoxyethylene dihydric alcohol, polycaprolactone dihydric alcohol, polyethylene glycol adipate dihydric alcohol, polyester dihydric alcohol and polytetrahydrofuran ether dihydric alcohol;

in the step (1), the diisocyanate is one of isophorone diisocyanate and hexamethylene diisocyanate, or a mixture of a substance A and a substance B; wherein the substance A is isophorone diisocyanate; the substance B is toluene-2, 4-diisocyanate, 4-diisocyanate dicyclohexylmethane or hexamethylene diisocyanate.

2. The method for preparing the hydrophobic/superhydrophobic aqueous polyurethane coating modified by the fluoroalkyl compound according to claim 1, wherein in the step (1), the amine compound is one or more selected from triethylamine, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate and ethylenediamine tetraacetic acid.

3. The method for preparing the fluoroalkyl compound modified hydrophobic/superhydrophobic aqueous polyurethane coating according to claim 1, wherein the substrate is glass, fabric or leather.

4. The method for preparing the short fluoroalkyl compound modified hydrophobic/super hydrophobic aqueous polyurethane coating according to claim 1, wherein the high speed dispersion in step (2) is 1200 to 1500 rpm.

5. The method for preparing the short fluoroalkyl compound modified hydrophobic/super hydrophobic aqueous polyurethane coating according to claim 1, wherein the molecular weight of the diol in step (1) is 500-2500.