Paint formulation comprising a protective additive

Abstract

A paint formulation comprising paint, and an additive comprising graphene oxide functionalised with tannic acid.

Description

PAINT FORMULATION COMPRISING APROTECTIVE ADDITIVE  Field of InventionThe invention relates to paint formulation comprising an additive which forms a protective coating.  BackgroundIn the oil and gas industry, corrosion is the main factor that contributes to the ageing and failures of metallic structures. Polymeric protective coating is a common technology used to protect the metal components from corrosion. However the barrier performance of the coatings may be severely jeopardized because of damage caused by environmental and mechanical attacks during service.  As for critical areas such as a splash zone, the epoxy glass flake paint (GF) is a typical grade of coating used to protect the structure which includes jacket legs, risers, and platform decks. However, due to consistent and long exposure of the coating under harsh environment such as saltwater and ultraviolet (UV) light, the coating may degrade and lose the contact adhesion between the coating and metal substrate. Frequent structure maintenance and repainting is thus needed, but surface preparation by grit blasting or power tools is needed prior to repainting, which increases time and cost. An aim of the invention therefore is to provide a material which overcomes the above issues. Summary of InventionIn an aspect of the invention, there is provided a paint formulation comprising paint, and an additive comprising graphene oxide functionalised with tannic acid.  Advantageously when the paint formulation is applied as a coating to a corroded structure, the tannic acid converts rust (iron oxide) into an inert compound (iron tannate and / or iron phosphate, the graphene improving the dispersion of the tannic acid due to its large surface area and aspect ratio (the two-dimensional structure of graphene oxide improves the coating’s barrier properties). Thus the additive is protective and the need for sand blasting and thorough surface preparation is eliminated, which reduces maintenance time, energy and cost. In one embodiment the graphene oxide comprises particles of less than 100µm. In one embodiment the ratio of tannic acid to graphene oxide is around 3:1. Advantageously this ensures excellent dispersion of the additive in the paint while excess tannic acid in the paint is minimised. In one embodiment the paint formulation comprises an epoxy primer, typically an epoxy glass flake primer or a surface tolerant epoxy. However other types of primer could also be used, such as inorganic zinc silicate, phenolic epoxy, silicone aluminium, polyester glass flake, modified silicone acrylic, zinc rich epoxy primer, and / or the like. In one embodiment a mixture of 0.01g / ml additive / isopropanol is mixed with the paint, typically using a mixer at 1000 to 1400rpm for 3 minutes in a vacuum. In one embodiment the concentration of the additive in the paint formulation is 0.05-0.2 wt%, typically 0.1 wt%. Thus the concentration of the additive in the paint formulation is 10mg / ml.  Isopropanol is usually added in a quantity just enough to disperse the functionalised graphene oxide (f-GO) as after the paint is cured, all the isopropanol used will have evaporated, leaving behind the well dispersed f-GO. Advantageously the epoxy primer with additive can be applied directly to a corroded structure with minimal surface preparation and work as a permanent coating for 5 years or more. In one embodiment, the paint formulation, when applied to a metal substrate and cured, has one or more of the following properties:a. an electrical impedance resistance in the order of 107-109 Ohms;b. an adhesion strength which is 50% or more higher than paint without the additive, after curing has completed;c. a corrosion creepage of less than 7mm;d. no blistering, surface rusting or coating delamination after a 4200 hour cyclic UV test. In a further aspect of the invention there is provided an additive as herein described.  In a further aspect of the invention there is provided a method for making an additive for a paint formulation comprising the steps of:suspending graphene oxide in a solvent;adjusting the pH of the suspension;ultrasonicating the suspension; adding tannic acid to the suspension to form a mixture. In one embodiment the suspension is ultrasonicated for 30 minutes at 80kHz and 70A power. In one embodiment the solvent is water and the pH is adjusted to pH10 by adding ammonia water (NH4OH) In this embodiment the concentration of graphene oxide is 0.1% w / v and the concentration of tannic acid is 0.2% w / v In this embodiment the mixture is heated to 96°C for 1 hour with stirring. In this embodiment the mixture is cooled to room temperature and subsequently frozen overnight. In this embodiment the frozen mixture is freeze dried for 2 days or until fine powder is formed.  In an alternative embodiment the solvent is 0.1M Trizma buffer solution pH 8.5, and the concentration of graphene oxide and tannic acid therein is 50% w / v and 200% w / v respectively. In the alternative embodiment the mixture is stirred at room temperature for 24 hours. In the alternative embodiment the mixture is either then:a. filtered through a 0.2µm anode aluminum oxide (AAO) membrane filter, washed several times with deionised water, purified in DMSO and finally washed with ethanol before being dried in vacuum oven at 35°C overnight; orb. centrifuged at 10krpm for 1 hour, the solution is decanted, and 100ml deionised water is added into the centrifuge bottle before continuing to centrifuge at 10krpm for 30 minutes, and the solution is decanted, after which the same step is repeated for 30 minutes at 10krpm with DMSO (purification) and ethanol, then the filtrate is dried at room temperature.  Brief Description of DrawingsIt will be convenient to further describe the present invention with respect to the accompanying drawings that illustrate possible arrangements of the invention. Other arrangements of the invention are possible, and consequently the particularity of the accompanying drawings is not to be understood as superseding the generality of the preceding description of the invention. Figure 1 is a schematic representation of paint comprising the additive according to an embodiment of the invention applied to a corroded substrate. Figure 2 is a graph illustrating adhesion strength of embodiments of the invention. Figure 3 is a graph illustrating impedance of the coating comprising embodiments of the invention. Figure 4 is a graph illustrating impedance of the coating comprising embodiments of the invention at different frequencies. Figure 5 illustrates the effect of UV on a coating comprising embodiments of the invention. Figure 6 illustrates an FTIR analysis of functionalised graphene oxide prepared using a first method. Figure 7 illustrates an FTIR analysis of functionalised graphene oxide prepared using a second method. Figure 8 is a scanning electron micrograph of a metal substrate to which a coating comprising an embodiment of the invention has been applied. Figure 9 is an XRD spectrum of a metal substrate to which a coating comprising an embodiment of the invention has been applied.  Detailed DescriptionWith regard to Figure 1, there is illustrated a coating 2 of an epoxy primer comprising an additive dispersed therein, applied to a corroded substrate 4. The additive comprises graphene oxide functionalised with tannic acid for converting rust into inert compounds. The graphene oxide is used as a carrier for the tannic acid to enhance dispersion as well as the effectiveness of the epoxy primer.  With respect to Figure 2, the adhesion performance of epoxy glass flake paint with a wt% of additive is illustrated in relation to a rusted surface grade C without surface preparation, and the results are summarised in Table 1 below:.  Table 1SampleType of failureControl100% adhesive failureGO 0.05%100% adhesive failureF-GO 0.05%80% cohesive failure: 20% adhesive failureF-GO 0.1%90% cohesive failure : 10% adhesive failureF-GO 0.2%70% cohesive failure :  Cohesive failure was seen in the functionalised graphene oxide (f-GO) sample, while adhesion failure was observed in the control sample without f-GO. The outcome in a pull-off adhesion test serves as a crucial indicator of the adhesive bond's quality. Ideally, achieving cohesive failure is desirable because it signifies that the coating has excellent bonding between the coating and steel substrate and the failure occurs within the coating material. Adhesion failure, on the other hand, suggests that the bonding may be poor because of inadequate adhesion between the coating and the steel substrate, so low adhesive failure is observed. With regard to Figures 3-4, the graphs show that the additive increases electrolyte impedance by two orders of magnitude, and thus improves water barrier properties.  With respect to Figure 5, coatings comprising the additive were subject to cyclic UV for 4200 hours. The test was in accordance to ASTM D5894. The coated test panels were exposed for one week under UV at 60°C and one week under salt spray chamber at 35°C alternately. The cycle was continued until the test completes for 25 cycles or 4200 hours exposure. Blistering was observed for the control and the coating with 0.05 wt% of F-GO. However, the absence of blistering on the surface of the coating containing 0.1 wt% F-GO indicates that the F-GO is capable of preventing water diffusion and improving adhesion contact between the coating and metal substrate, passing the minimum requirement of corrosion creepage size and coating durability without any surface delamination and blistering. With regard to Figure 6, an FTIR analysis of functionalised graphene oxide prepared using a first method is illustrated. The preparation method comprises the steps of:suspending 0.1% w / v graphene oxide in water;ultrasonicating the suspension for 30 minutes at 80kHz and 70A power; adjusting the pH of the suspension to 10 by adding ammonia water (NH4OH);adding is 0.2% w / v tannic acid to the suspension to form a mixture;heating the mixture to 96°C for 1 hour with stirring;cooling the mixture to room temperature and subsequently freezing overnight; and freeze-drying the mixture for 2 days to form a powder. The functionalised GO were analysed with Fourier Transform Infra-Red (FTIR) in ATR (Attenuated Total Reflection) mode to investigate the spectrum intensity particularly at carbonyl peak C=O (1720 – 1550 cm-1), both before and after functionalisation. These analyses are carried out using a Perkin Elmer FTIR Spectrum 400, in conjunction with a proprietary spectrum software. To conduct FTIR analysis, an initial calibration was performed to ensure the instrument is properly aligned. This typically involves checking the instrument with a reference material. Then, the dried f-GO was prepared by mixing in a kBr pallet. The sample was placed in the sample holder, and carefully inserted into the instrument. The measurement parameters were set in the software, such as the spectral range (wavenumber range: 4000 to 450 cm-1) and the number of scans (3 replicates). In the analysis, the presence of a new functional group for the functionalized graphene oxide (F-GO) spectrum at wavelengths ranging from 870 to 1700 cm-1 indicates the successful functionalization of GO with TA. With respect to Figure 7, an FTIR analysis of functionalised graphene oxide prepared using a second method is illustrated. The preparation method comprises the steps of:suspending 50% w / v graphene oxide in Trizma buffer solution;ultrasonicating the suspension for 30 minutes at 80kHz and 70A power; adding 200% w / v tannic acid to the suspension to form a mixture;stirring the mixture at room temperature for 24 hours;the mixture is then either:a. filtered through a 0.2µm anode aluminum oxide (AAO) membrane filter, washed several times with deionised water, purified in DMSO and finally washed with ethanol before being dried in vacuum oven at 35°C overnight; orb. centrifuged at 10krpm for 1 hour, decanting the solution, and adding 100ml of deionised water into the centrifuge bottle before continuing to centrifuge at 10krpm for 30 minutes, decanting the solution, after which the same step is repeated for 30 minutes at 10krpm with DMSO (purification) and ethanol, then the filtrate is dried at room temperature. The Trizma buffer solution can be made by dissolving Trizma base into deionised water (8.72g / L) and the pH is adjusted to pH 8.5 by adding an equal amount of hydrochloric acid. The FTIR analysis shows GO before and after functionalization together with TA, which acts as a functionalisation agent. As can be seen clearly, functionalized GO exhibits a distinctly different spectrum compared to GO (before functionalization). Notably new functional group peaks appear on functionalized GO, which show almost the same major functional groups from TA , especially peaks at 3397.2 cm-1, 1585 cm-1, 1250.6 cm-1 and 1108 cm-1 which correspond to O-H, C=C stretching, C-O-C and C-O respectively. Hence it can be said that the functionalization of GO with TA was successful. With regard to Figure 8, a scanning electron micrograph of a corroded metal substrate to which a coating comprising an embodiment of the invention has been applied is shown on the right, compared to a control sample on the left. The EDX mapping shows that the active oxides on the metal substrate have been reduced by the activation of the rust converter additive, as less oxygen was detected, the active oxide layer having been converted into inert substances. With respect to Figure 9, an XRD spectrum of a metal substrate to which a coating comprising an embodiment of the invention has been applied is shown at the bottom, compared to a control sample at the top. The identification of less Fe2O3 compound in the XRD spectra after the application of paint containing the rust converter additive shows that the additive manages to reduce the oxides on the metallic substrate. In summary 0.1 wt% additive performs well and successfully improves the adhesion strength of epoxy glass flake paint on rusted surfaces (grade A, B and C) by 55%. In addition there is a 16% cost reduction in overall maintenance costs. For a platform comprising 5000m2 painting area, this represents a saving of some RM520k. It will be appreciated by persons skilled in the art that the present invention may also include further additional modifications made to the system which does not affect the overall functioning of the system.   

Claims

1. A paint formulation comprising paint, and an additive comprising graphene oxide functionalised with tannic acid.

2. The paint formulation according to claim 1 wherein the paint is an epoxy primer.

3. The paint formulation according to claim 1 wherein the concentration of the additive in the paint is 0.05-0.2 wt%.

4. The paint formulation according to claim 1 wherein the graphene oxide comprises particles of less than 100µm.

5. The paint formulation according to claim 1 wherein the ratio of tannic acid to graphene oxide is around 3:

16. The paint formulation according to claim 1 wherein, when applied to a metal substrate and cured, it has one or more of the following properties:a. an electrical impedance resistance in the order of 107-109 Ohms;b. an adhesion strength of which is 50% or more higher than paint without the additive, after curing has completed;c. a corrosion creepage of less than 7mm;d. no blistering, surface rusting or coating delamination after a 4200 hour cyclic UV test.

7. An additive for paint according to claim 1.

8. A method for making an additive for a paint formulation comprising the steps of:suspending graphene oxide in a solvent;adjusting the pH of the suspension;ultrasonicating the suspension; adding tannic acid to the suspension to form a mixture.

9. A method according to claim 8 wherein the solvent is water and the pH is adjusted to pH10 by adding NH4OH.

10. A method according to claim 8 wherein the concentration of graphene oxide is 0.1% w / v and the concentration of tannic acid is 0.2% w / v.

11. A method according to any of claims 8 wherein the mixture is heated to 96°C for 1 hour with stirring.

12. A method according to any of claims 8 wherein the mixture is cooled to room temperature, subsequently frozen overnight then freeze dried until fine powder is formed.

13. A method according to claim 8 wherein the solvent is 0.1M Trizma buffer solution pH 8.5.

14. The method according to claim 13 wherein the concentration of graphene oxide and tannic acid therein is 50% w / v and 200% w / v respectively.

15. The method according to claim 13 wherein the mixture is stirred at room temperature for 24 hours.

16. The method according to any of claims 13 wherein the mixture is filtered through a 0.2µm anode aluminum oxide (AAO) membrane filter, washed several times with deionised water, purified in DMSO and finally washed with ethanol before being dried in vacuum oven at 35°C overnight.

17. The method according to any of claims 13 wherein the mixture is centrifuged at 10krpm for 1 hour, the solution is decanted, and deionised water is added into the centrifuge bottle before continuing to centrifuge at 10krpm for 30 minutes, and the solution is decanted, after which the same step is repeated for 30 minutes at 10krpm with DMSO (purification) and ethanol, then the filtrate is dried at room temperature.

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