Graphene-based polymer composite, preparation and use thereof

Abstract

A graphene-oxide based polymer composite is prepared by: i) dispersing, under an inert gas atmosphere, a modified silica having amino groups on the surface thereof and 4-dimethylaminopyridine into an

Description

TECHNICAL FIELD

[0001] The present disclosure is related to the field of nano-materials, and in particular to a graphene-based polymer composite and its preparation and use. BACKGROUND ART

[0002] Corrosion is the deterioration of a metal as a result of chemical or electrochemical reactions between it and the surrounding environment, and makes the metal turn into an oxidation (ionization) state from the surface exposed to the environment. Corrosion reduces the original mechanical properties, such as, strength, plasticity, and toughness, of the meal, alters the geometry of the components made of the metal, and increases an amount of wear between the components, thereby deteriorating the optical and electrical properties and shortening a life of the associated equipment, or even leading to a disastrous accident such as a fire or an explosion.

[0003] It is extremely difficult to completely prevent metal corrosion from occurring, but it has been found feasible to provide a metal with corrosion protection which can decelerate the corrosion of the metal and reduce the hazards arising from meal corrosion.

[0004] Epoxy resins of bisphenol A-type are now commonly used as an anticorrosive coating material due to their high chemical resistance, strong adhesion to metals, and good heat resistance and electrical insulating properties. However, the epoxy resins of bisphenol A-type usually exhibit poor weather resistance, and coatings of the epoxy resins, when exposed to weather, tend to chalk and tarnish. These problems limit their use in the open. SUMMARY

[0005] In view of the above problems, among the objectives of the present disclosure are to provide a graphene-based polymer composite and its preparation and use.

[0006] A first objective of the present disclosure is realized by a process for preparing a graphene-based polymer composite, comprising steps of

[0007] i) dispersing graphene oxide (GO) powder having an abundant number of carboxyl groups on the surface thereof into an alcohol solution under an inert gas atmosphere, followed by addition of a modified silica having amino groups on the surface thereof and 4-dimethylaminopyridine, to conduct a condensation reaction so as to obtain a first precursor (the abundant number of carboxyl groups on the surface of the GO powder being any number that is sufficient to enable the GO powder to be uniformly dispersed in the alcohol solution);

[0008] ii) dispersing the first precursor into water by sonication, followed by addition of a curing agent and a binder and then a bisphenol A-type epoxy resin, to obtain a second precursor after drying; and

[0009] iii) extruding the second precursor into pellets using a screw extruder, followed by crushing the pellets, to obtain the graphene-based polymer composite, which can be applied directly onto a target surface by an electrostatic spray method.

[0010] In an embodiment, the condensation reaction in step (i) may be carried out at a stirring rate of 100 to 150 rpm and a temperature of 20 to 30 °C for a time period of 1.5 to 3 h.

[0011] In an embodiment, the GO powder may be prepared by synthesizing GO having an abundant number of carboxyl groups on the surface thereof from graphite by Hummers’ approach followed by mechanical grinding.

[0012] In an embodiment, a mass ratio of the GO powder to the modified silica may be in the range of 1: 1 to 1: 10.

[0013] In an embodiment, a volume to mass ratio of the GO powder to the alcohol solution may be in the range of 0.1 to 10 mg / mL.

[0014] In an embodiment, the alcohol solution may be an aqueous ethanol solution having an ethanol concentration in the range of 75 to 90 % by volume.

[0015] In an embodiment, the curing agent may be one or more of ethylenediamine, diethylenetriamine, and triethylenetetramine.

[0016] In an embodiment, the binder may be methylcellulose, hydroxy cellulose, or carboxyl cellulose.

[0017] In an embodiment, a mass ratio of the bisphenol A-type epoxy resin to the first precursor may be in the range of 0.15 to 0.25.

[0018] In an embodiment, a mass ratio of the binder to the first precursor may be in the range of 0.001 to 0.005.

[0019] In an embodiment, a mass ratio of the curing agent to the first precursor may be in the range of 1: 6 to 1: 12.

[0020] In an embodiment, the modified silica may be prepared by subjecting a mixture formed by mixing tetraethyl orthosilicate, ethanol, and water at a ratio of 1: 15: 15 with stirring at a temperature of 35 to 45 °C and adjusting the pH to about 3.1 to 3.4, to a reaction at a temperature of 50 to 60 °C and a stirring rate of 350 to 450 rpm for a time period of 10 to 30 min; adjusting the pH of the resulting reaction mixture to about 8.5 to 9.5, followed by stirring at a rate of 350 to 450 rpm for a further time period of 10 to 15 min and then addition of (3-aminopropyl)triethoxysilane; and subjecting the resulting mixture to a reaction at a temperature of 60 to 70 °C and a stirring rate of 200 to 300 rpm for a time period of 60 to 120 min, followed by filtration, giving the modified silica as filter cake. It has been found that there is an abundant number of amino groups on the silica surface. In an embodiment, a mass ratio of the (3 -aminopropyljtri ethoxy silane to the tetraethyl orthosilicate may be in the range of 0.1 to 1.5.

[0021] In an embodiment, in step (iii), the second precursor may be extruded into pellets using a screw extruder with an infeed section, an intermediate section, and an outfeed section thereof to be operated at a temperature of 130 to 140 °C, 190 to 210 °C, and 135 to 155 °C, respectively, and then dried, and the dried pellets may be crushed using a crusher to a size of 200 to 500 mesh.

[0022] A second objective of the present disclosure is realized by a graphene-based polymer composite prepared according to the process described above.

[0023] A third objective of the present disclosure is realized by use of the graphene-based polymer composite in preparation of an anticorrosive coating.

[0024] The present disclosure provides several advantages over prior art.

[0025] Nano-silica may be formed from tetraethyl orthosilicate and then treated with (3-aminopropyl)tri ethoxy silane such that an abundant number of amino groups are chemically bound to the surface thereof. The presence of the abundant number of amino groups avoids nano-silica agglomeration and enables its layered structure to be maintained. These amino groups on the surface of the modified silica are coupled with the carboxyl groups on the surface of the GO powder in the presence of 4-dimethylaminopyridine, causing the silica and the GO powder to be closely bound together and avoiding GO agglomeration at a latter stage of the reaction. Modified GO powder doped with silica (that is the first precursor) is thus obtained.

[0026] Uses of sonication and the binder enable the first precursor to uniformly come in contact with the bisphenol A-type epoxy resin. Residual unreacted amino groups present in the first precursor allow the first precursor, together with the curing agent, to be involved in the curing process of the bisphenol A-type epoxy resin. This can improve the problem that needle-like holes tend to be formed during formation of a film of conventional bisphenol A-type epoxy resins. Thus, the graphene-based polymer composite so obtained can exhibit improved film forming properties, and the coating of the composite can exhibit a higher density and greatly improved weather and corrosion resistance. In addition, both GO and silica have a layered structure, which can further improve the corrosion resistance of the coating. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] The present disclosure will now be described in further detail by way of the following examples.

[0028] Example 1

[0029] A graphene-based polymer composite of the disclosure was prepared as follows.

[0030] GO powder having an abundant number of carboxyl groups on the surface thereof was uniformly dispersed into 80 % ethanol to be at a mass to volume ratio of 5 mg / mL under a helium atmosphere (the purity is equal to 99.9999 %). Then, a modified silica having amino groups on the surface thereof and 4-dimethylaminopyridine were added thereto (a mass ratio of the GO powder to the silica: 1: 5) and uniformly mixed. The resulting mixture was stirred at a stirring rate of 130 rpm and 25 °C for 2 h to give a first precursor.

[0031] The first precursor was uniformly dispersed into water as a solvent by sonication. Ethylenediamine and methylcellulose were then added thereto (a mass ratio of the ethylenediamine to the first precursor: 1: 9, and a mass ratio of the methylcellulose to the first precursor: 0.003: 1) and uniformly mixed with stirring. Thereafter, a bisphenol A-type epoxy resin was added thereto (a mass ratio of the bisphenol A-type epoxy resin to the first precursor: 0.2: 1). The mixture was then uniformly mixed with stirring and dried to give a second precursor.

[0032] The second precursor was extruded into pellets using a twin-screw extruder, and then crushed to give the graphene-based polymer composite, which can be applied directly onto a target surface by an electrostatic spray method.

[0033] In this example, the modified silica was prepared as follows.

[0034] Tetraethyl orthosilicate, ethanol, and water were uniformly mixed at a mixing ratio of 1: 20: 20 with stirring at 40 °C. After pH adjustment to 3.2, the mixture was reacted at 55 °C and a stirring rate of 400 rpm for 20 min. At this time, pH adjustment was performed again such that the pH of the resulting reaction mixture was adjusted to 9, and the mixture was further stirred at 400 rpm for 12 min. At this time, (3 -aminopropyljtri ethoxy silane was added thereto (a mass ratio of the (3 -aminopropyljtri ethoxy silane to the tetraethyl orthosilicate: 0.5: 1), and the resulting mixture was stirred at a stirring rate of 250 rpm and 65 °C for 90 min, followed by filtration, giving the modified silica as filter cake.

[0035] Example 2

[0036] A graphene-based polymer composite of the disclosure was prepared as follows.

[0037] GO powder having an abundant number of carboxyl groups on the surface thereof was uniformly dispersed into 75 % ethanol to be at a mass to volume ratio of 0.1 mg / mL under a helium atmosphere (the purity is equal to 99.9999 %). Then, a modified silica having amino groups on the surface thereof and 4-dimethylaminopyridine were added thereto (a mass ratio of the GO powder to the silica: 1: 1) and uniformly mixed. The resulting mixture was stirred at a stirring rate of 100 rpm and 20 °C for 3 h to give a first precursor.

[0038] The first precursor was uniformly dispersed into water as a solvent by sonication. Ethylenediamine and methylcellulose were then added thereto (a mass ratio of the ethylenediamine to the first precursor: 1: 6, and a mass ratio of the methylcellulose to the first precursor: 0.001: 1) and uniformly mixed with stirring. Thereafter, a bisphenol A-type epoxy resin was added thereto (a mass ratio of the bisphenol A-type epoxy resin to the first precursor: 0.15: 1). The mixture was then uniformly mixed with stirring and dried to give a second precursor.

[0039] The second precursor was extruded into pellets using a twin-screw extruder, and then crushed to give the graphene-based polymer composite, which can be applied directly onto a target surface by an electrostatic spray method.

[0040] In this example, the modified silica was prepared as follows.

[0041] Tetraethyl orthosilicate, ethanol, and water were uniformly mixed at a mixing ratio of 1: 20: 20 with stirring at 35 °C. After pH adjustment to 3.1, the mixture was reacted at 50 °C and a stirring rate of 350 rpm for 30 min. At this time, pH adjustment was performed again such that the pH of the resulting reaction mixture was adjusted to 8.5, and the mixture was further stirred at 350 rpm for 15 min. At this time, (3-aminopropyljtri ethoxy silane was added thereto (a mass ratio of the (3-aminopropyljtri ethoxy silane to the tetraethyl orthosilicate: 0.5: 1), and the resulting mixture was stirred at a stirring rate of 200 rpm and 60 °C for 120 min, followed by filtration, giving the modified silica as filter cake.

[0042] Example 3

[0043] A graphene-based polymer composite of the disclosure was prepared as follows.

[0044] GO powder having an abundant number of carboxyl groups on the surface thereof was uniformly dispersed into 90 % ethanol to be at a mass to volume ratio of 10 mg / mL under an argon atmosphere (the purity is equal to 99.9999 %). Then, a modified silica having amino groups on the surface thereof and 4-dimethylaminopyridine were added thereto (a mass ratio of the GO powder to the silica: 1:10) and uniformly mixed. The resulting mixture was stirred at a stirring rate of 150 rpm and 30 °C for 1.5 h to give a first precursor.

[0045] The first precursor was uniformly dispersed into water as a solvent by sonication. Ethylenediamine and methylcellulose were then added thereto (a mass ratio of the ethylenediamine to the first precursor: 1: 12, and a mass ratio of the methylcellulose to the first precursor: 0.005: 1). The resulting mixture was uniformly mixed with stirring. Thereafter, a bisphenol A-type epoxy resin was added thereto (a mass ratio of the bisphenol A-type epoxy resin to the first precursor: 0.25: 1). The mixture was then uniformly mixed with stirring and then dried to give a second precursor.

[0046] The second precursor was extruded into pellets using a twin-screw extruder, and then crushed to give the graphene-based polymer composite, which can be applied directly onto a target surface by an electrostatic spray method.

[0047] In this example, the modified silica was prepared as follows.

[0048] Tetraethyl orthosilicate, ethanol, and water were uniformly mixed at a mixing ratio of 1: 20: 20 with stirring at 45 °C. After pH adjustment to 3.4, the mixture was reacted at 60 °C and a stirring rate of 450 rpm for 10 min. At this time, pH adjustment was performed again such that the pH of the resulting reaction mixture was adjusted to 9.5, and the mixture was further stirred at 450 rpm for 10 min. At this time, (3 -ami nopropyl )tri ethoxy silane was added thereto (a mass ratio of the (3 -aminopropyljtri ethoxy silane to the tetraethyl orthosilicate: 1.5: 1), and the resulting mixture was stirred at a stirring rate of 300 rpm and 70 °C for 60 min, followed by filtration, giving the modified silica as filter cake.

[0049] Comparative Example 1

[0050] A composite was prepared in a similar manner to that of Example 1 except that the modified silica was not used.

[0051] Comparative Example 2

[0052] A composite was prepared in a similar manner to that of Example 1 except that the GO powder having an abundant number of carboxyl groups on the surface thereof was not used.

[0053] Comparative Example 3

[0054] A composite was prepared in a similar manner to that of Example 1 except that neither the GO powder having an abundant number of carboxyl groups on the surface thereof nor the modified silica was used.

[0055] Comparative Example 4

[0056] A composite was prepared in a similar manner to that of Example 1 except that the silica was not modified.

[0057] Performance Tests

[0058] A piece of tinplate (150 mm x 70 mm x 2 mm) was used as a substrate (test plate) to which a test composite was to be applied. First, a target surface to be coated of the tinplate was sanded by using a sand paper (e.g. 120 Grit), and residual iron fines were removed from the surface using absorbent cotton. Then, the surface was wiped clean with absolute ethanol and acetone. The piece of tinplate was placed into a vacuum drying cabinet to remove the residual solvent on the surface thereof and was then ready for use.

[0059] Five pieces of tinplate subjected to the treatment described above were placed into a spray booth. The composite materials prepared in Examples 1 to 3 and in Comparative Examples 1 to 4 were sprayed onto their respective target surfaces of the five pieces of tinplate using a high-voltage electrostatic generator. The thickness of the sprayed coating on each surface was controlled at 80 pm. After spraying, these pieces of tinplate were placed vertically into a drying cabinet for curing at 180 °C for 30 min, and remained vertically oriented during the entire curing process. Thereafter, the pieces of tinplate were then allowed to stand in an environment where the temperature was controlled at (23 ± 2) °C and the relative humidity was controlled at (50 ± 5) %, for 24 h. Test samples of coatings of the composite materials in Examples 1 to 3 and in Comparative Examples 1 to 4 were thus obtained.

[0060] Performance characteristics of the samples were then measured through the following tests.

[0061] (1) Adhesion Test

[0062] Adhesion was evaluated via a circle-drawing test in accordance with GB / T 9286-1998 (Paints and varnishes - Cross cut test for films). A cycloid scratch was drawn, and the upper side of the scratch was observed. The results are shown in Table 1.

[0063] (2) Impact Resistance Test

[0064] Impact resistance test was performed in according with GB / T1732-93 (Determination of Impact Resistance of Film) which specifies that the impact resistance of coating films is expressed by the maximum height (cm) of the heavy hammer when the punch hits the test plate without causing damage to the coating film, by using a heavy hammer of fixed mass to fall on the punch.

[0065] (3) Hardness Test

[0066] Hardness Test was performed in accordance with GB / T6739-1996 (Determination of Film Hardness by Pencil Test). Results are shown in Table 1.

[0067] (4) Chemical Resistance Test

[0068] Chemical resistance test was performed in accordance with GB1763-89 (Methods for Test for Chemical Resistance of Paint Films). The samples were each immersed in an acid solution, an alkali solution, and a salt solution, respectively, to observe the change in appearance of the coatings. Results are shown in Table 2.

[0069] Acid resistance test

[0070] Each sample was immersed in a 4.5 % by weight sulfuric acid solution at 25 °C and one third of the sample was exposed to the atmosphere above the acid solution. Every 24 h, the samples were removed from the acid solutions, rinsed using water, and wiped dry on their coated surfaces using a piece of moisture absorbing paper to observe the change in appearance of the coatings, including, but not limited to: discoloration, tarnishing, blistering, spotting, and flaking.

[0071] Alkali resistance test

[0072] Each sample was immersed in a 4.5 % by weight sodium hydroxide solution at 25 °C and one third of the sample was exposed to the atmosphere above the alkali solution. Every 24 h, the samples were removed from the alkali solutions, rinsed using water, and wiped dry on their coated surfaces using a piece of moisture absorbing paper to observe the change in appearance of the coatings, including, but not limited to: discoloration, tarnishing, blistering, spotting, and flaking.

[0073] Salt resistance test

[0074] Each sample was immersed in a 3 % by weight sodium chloride solution at 25 °C and one third of the sample was exposed to the atmosphere above the alkali solution. Every 24 h, the samples were removed from the solutions, rinsed using water, and wiped dry on their coated surfaces using a piece of moisture absorbing paper to observe the change in appearance of the coatings, including, but not limited to: tarnishing, wrinkling, blistering, rusting, and flaking.

[0075] Table 1 - Test results for hardness, adhesion, and impact resistance Samples Hardness Adhesion Impact Resistance / 50kg .cm Ex. 1 2H Grade 1 No cracks Ex. 2 2H Grade 1 No cracks Ex. 3 2H Grade 1 No cracks Comp. Ex. 1 2H Grade 2 No cracks Comp. Ex. 2 2H Grade 2 No cracks Comp. Ex. 3 3H Grade 2 Cracked Comp. Ex. 4 2H Grade 1 No cracks

[0076] Table 2 - Test results for chemical resistance Samples Acid resistance Alkali resistance Salt resistance Ex. 1 No change after 40 d No change after 40 d No change after 40 d (no chalking and elution) (no chalking and elution) (no chalking and elution) Ex. 2 No change after 40 d No change after 40 d No change after 40 d (no chalking and elution) (no chalking and elution) (no chalking and elution) Ex. 3 No change after 40 d No change after 40 d No change after 40 d (no chalking and elution) (no chalking and elution) (no chalking and elution) Comp. Ex. 1 Eluted after 12 d Discolored and tarnished Wrinkled and blistered after 15 d after 20 d Comp. Ex. 2 Eluted after 6 d Discolored and tarnished Wrinkled and blistered after 8 d after 16 d Comp. Ex. 3 Eluted after 3 d Discolored and tarnished Wrinkled and blistered after 5 d after 7 d Comp. Ex. 4 Eluted after 15 d Discolored and tarnished Wrinkled and blistered after 17 d after 23 d

[0077] It can be seen from the above that the graphene-based polymer composite of the present disclosure exhibited improved corrosion resistance, strength, and toughness over existing epoxy resins.

[0078] The GO powder used in the above examples and comparative examples were prepared by: synthesizing GO having an abundant number of carboxyl groups on the surface thereof from graphite by Hummers’ approach, and mechanically grinding the synthesized GO followed by sieving with a sieve of 50 to 200 mesh.

[0079] The twin-screw extruder used in the above examples and comparative examples was provided with an infeed section, an intermediate section, and an outfeed section. In these examples and comparative examples, the second precursor was extruded into pellets using the screw extruder with the infeed, intermediate, and outfeed sections operated at a temperature of 130 to 140 °C, 190 to 210 °C, and 135 to 155 °C, respectively, and was then dried. The dried pellets were crushed using a crusher to a size of 200 to 500 mesh.

[0080] The process of the present disclosure advantageously utilizes not only shielding performance of GO but also the action of a curing agent which can improve the problem that needle-like holes tend to be formed during formation of a film of conventional bisphenol A-type epoxy resins, thereby providing the prepared graphene-based polymer composite with improved film forming properties and corrosion resistance.

[0081] The described embodiments are exemplary only, and are not exhaustive of the scope of the disclosure. Accordingly, those skilled in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the disclosure.

Claims

1. A process for preparing a graphene-based polymer composite, comprising:i) dispersing, under an inert gas atmosphere, a modified silica having amino groups on the surface thereof and 4-dimethylaminopyridine into an alcohol solution in which graphene oxide (GO) powder having an abundant number of carboxyl groups on the surface thereof is dispersed, to conduct a condensation reaction so as to obtain a first precursor;ii) dispersing the first precursor into water by sonication, followed by addition of a curing agent and a binder and stirring and then addition of a bisphenol A-type epoxy resin and stirring, to obtain a second precursor after drying; andiii) extruding the second precursor into pellets using a screw extruder, followed by crushing the pellets, to obtain the graphene-based polymer composite.

2. The process according to claim 1, wherein, the condensation reaction is carried out at a stirring rate of 100 to 150 rpm and a temperature of 20 to 30 °C for a time period of 1.5 to 3 h.

3. The process according to claim 1, wherein, a mass ratio of the GO powder to the modified silica is in the range of 1: 1 to 1: 10.

4. The process according to claim 1, wherein, a volume to mass ratio of the GO powder to the alcohol solution is in the range of 0.1 to 10 mg / mL.

5. The process according to claim 1, wherein, the alcohol solution is an aqueous ethanol solution having an ethanol concentration in the range of 75 to 90 % by volume.

6. The process according to claim 1, wherein, the curing agent is one or more of ethylenediamine, diethylenetriamine, and triethylenetetramine, and wherein, the binder is methylcellulose, hydroxy cellulose, or carboxyl cellulose.

7. The process according to claim 1, wherein, a mass ratio of the bisphenol A-type epoxy resin to the first precursor is in the range of 0.15 to 0.25,wherein, a mass ratio of the binder to the first precursor is in the range of 0.001 to 0.005,and wherein, a mass ratio of the curing agent to the first precursor is in the range of 1: 6 to 1: 12.

8. The process according to claim 1, wherein, the modified silica is prepared by: forming silica by mixing tetraethyl orthosilicate, ethanol, and water at a mixing ratio of 1: 15: 15 with stirring at a temperature of 35 to 45 °C, and modifying the formed silica by addition thereto of (3-aminopropyl)tri ethoxy silane to obtain the modified silica having an abundant number of amino groups on the surface thereof,wherein, a mass ratio of the (3-aminopropyl)tri ethoxy silane to the tetraethylorthosilicate is in the range of 0.1 to 1.5.

9. A graphene-based polymer composite prepared by the process according to any of claims 1 to 8.

10. Use of the graphene-based polymer composite according to claim 9 in preparation of an anticorrosive coating.