Functionalised graphene and coatings comprising the same

Abstract

A method of preparing functionalised graphene is disclosed. The method includes the step of functionalising graphene with a chemical linker when the graphene is in a substantially dry condition.

Claims

1. A method of preparing functionalised graphene, the method comprising the step of functionalising an oxide-free graphene powder with a chemical linker for reacting with a resin and/or a hardener without dispersing the oxide-free graphene powder in a solvent, wherein the oxide-free graphene powder is sprayed with the chemical linker.

2. The method according to claim 1, wherein the method comprises the step of adding a wetting and/or dispersing agent to the functionalised oxide-free graphene powder.

3. The method according to claim 1, wherein the functionalisation of the oxide-free graphene powder is carried out under an inert atmosphere or in air.

4. The method according to claim 1, wherein the functionalised oxide-free graphene powder is dried.

5. The method according to claim 1, wherein the oxide-free graphene powder is functionalised in a fluidised bed, a dry/wet mill or in a mechanical mixer.

6. The method according to claim 1, wherein the chemical linker comprises an organosilane.

7. The method according to claim 1, wherein the method comprises the step of adding a wetting and/or dispersing agent to the functionalised oxide-free graphene powder by spraying.

8. The method according to claim 1, wherein the chemical linker comprises an unhydrolysed organosilane.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) In order that the invention may be more clearly understood, one or more embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, in which:

(2) FIG. 1 shows a reaction scheme for producing a zinc epoxy coating according to the prior art;

(3) FIG. 2 shows a reaction scheme in accordance with the present invention for producing an epoxy coating with functionalised graphene and reduced quantities of zinc;

(4) FIG. 3 shows salt spray test results after 1500 hours for zinc-containing epoxy coatings with and without functionalised graphene; and

(5) FIG. 4 shows further salt spray test results after 1500 hours for zinc-containing epoxy coatings with and without functionalised graphene.

REACTION SCHEME FOR REDUCED ZINC CONTENT COATING

(6) A reaction scheme for producing a zinc epoxy coating according to the prior art is shown in FIG. 1. As alluded to hereinbefore, while coatings with a high zinc content typically exhibit good corrosion protection, they can often suffer from a reduced service life, particularly in respect of epoxy/zinc coatings where the service life is limited by the zinc content in the coating. FIG. 2 depicts an improved reaction scheme to that depicted in FIG. 1. The reaction scheme shown in FIG. 2 involves mixing functionalised graphene with zinc, an epoxy resin and a polyamine hardener to produce a zinc epoxy coating with functionalised graphene. The incorporation of graphene into the epoxy coating network enables the content of zinc pigments in the epoxy coating to be reduced without any detrimental effect on corrosion protection (see FIGS. 1 and 2). FIG. 2 additionally shows that the functionalised graphene is chemically linked with the resin/hardener cross-linked structure. This not only increases the barrier protection properties of the zinc epoxy coatings, it also results in a denser coating network being formed with improved mechanical properties, all of which serve to minimise the service life issues experienced by the prior art zinc epoxy coating systems (FIG. 1) whilst offering other benefits such as reduced manufacturing costs and coating weight due to the reduced zinc content.

(7) One embodiment of such an improved reaction scheme which includes functionalised graphene preparation and subsequent coating composition preparation components is described in further detail below.

(8) Functionalised Graphene Preparation

(9) Pristine, oxide-free graphene nanoplatelets (GNP) are functionalised by introducing GNP (94 wt %) into a LDIGE Ploughshare Mixer in the form of a powder. The GNP powder is in a substantially dry condition and free from moisture. The mixer is then activated and as the GNP powder starts to atomise or deagglomerate it is sprayed with BYK 333 wetting agent, then (2 wt %), BYK 9076 dispersing agent (2 wt %) and then with APTES (4 wt %) to produce functionalised GNP powder. Following functionalisation of the GNP powder, it is subjected to a heat treatment of 50-100 C. in order to ensure complete functionalisation and to drive off any residual liquid that may be present. The heat treatment is carried out within the mixer in air or under a nitrogen atmosphere to minimise the risk of the functionalised pristine GNPs becoming oxidised.

(10) Coating Composition Preparation

(11) The functionalised GNP powder is mixed with the other powder components of the coating composition, namely zinc and CaCO.sub.3. These powder components are then mixed with a bisphenol A diglycidyl ether (DGEBA) epoxy resin and polyamide hardener in the presence of xylene and this mixture is stirred for 5 minutes at 2000 RPM. The mixture is then spray-coated onto a steel substrate. The coated steel substrate is then cured at room temperature (i.e. 1.5 hours for through-drying and 7 days for complete curing) to form a coating having a dry film thickness of 60 microns. Exemplary compositions E1-E2 are shown in Table 1 below together with comparative examples C1 and C2.

(12) The E1-E2 coatings were prepared in accordance with the above described methods. Comparative examples C1 and C2 are commercially available zinc based epoxy coating compositions, namely Hempadur Avanguard 750 by Hempel (C1) and Barrier ZEP by Jotun (C2).

(13) TABLE-US-00001 TABLE 1 Coating Functionalized Thickness Zinc Graphene Binder (Microns) C1 30% 0 38% 90 microns C2 40% 0 38% 60 microns E1 15% 1% 38% 60 microns E2 20% 1.2% 38% 60 microns

(14) The coated substrates C1 and E1 were subjected to a salt spray test (ASTM B117) for 1500 hours to determine the corrosion resistant properties of the respective coatings. The results of the salt spray test (shown in FIG. 3) show that the E1 coating exhibits superior corrosion resistance relative to the C1 coating despite the E1 coating containing 50% less zinc and having a reduced layer thickness.

(15) The coated substrates C2 and E2 were also subjected to a salt spray test (ASTM B117) for 1500 hours to determine the corrosion resistant properties of the respective coatings. The results of this salt spray test (shown in FIG. 4) show that the E2 coating also exhibits superior corrosion resistance relative to the C2 coating despite the E2 coating containing 50% less zinc.

(16) By way of the improved reaction scheme as depicted in FIG. 2, the present invention serves to reduce the metallic content in a coating composition (particularly of zinc) while providing enhanced corrosion resistance/protection and mechanical performance. Furthermore, reducing the metallic content can also facilitate a number of additional benefits including improved environmental sustainability (i.e. metallic pigments sacrificially result in corrosion products which can be toxic to marine environments, one reason why zinc rich epoxies are less preferred on underwater parts of vessels), enhanced lifetime (i.e. since metal pigments would eventually corrode while graphene would remain inert) and potential realisation of coating thickness/weight/cost reductions. Still further, other potential benefits of a coating composition produced by way of the improved reaction scheme may include enhancement of coating adhesion due to graphene reinforcement and denser crosslinking and improvements in impact and abrasion resistance.

(17) The one or more embodiments of the present invention are described above by way of example only. Many variations are possible without departing from the scope of protection afforded by the appended claims.

(18) For example, the present invention is also applicable to a range of other commercially available two-component products, including for example, those from Sherwin Williams (i.e. Macropoxy L524, Macropoxy C123, Spec M155), PPG (i.e. SigmaZinc 19, SigmaCover 522 MIO, SigmaCover 522), Jotun (i.e. Barrier 77, 90 & ZEP9), International Paints (i.e. Intergard 263, Interzinc 75V, Interzinc 52, Intergard 343HS, Interseal 670HS, Interzon 5140, Intershield 300) and Hempel (i.e. Hempadur Zinc 17360, Hempadur 1555 E, Zinc Rich Epoxy Primer 178US).