Comparative studies of Tung and linseed oil microcapsule as self-healing coating for corrosion protection of low carbon steel substrates

Zulkifli, Muhammad Hasif (2023) Comparative studies of Tung and linseed oil microcapsule as self-healing coating for corrosion protection of low carbon steel substrates. Project Report. Universiti Teknikal Malaysia Melaka, Melaka, Malaysia. (Submitted)

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Abstract

Corrosion, the gradual breakdown of a substance due to its contact with its environment, can happen at any stage of the refining process for petroleum and natural gas. Polymer coatings have traditionally served as a barrier against corrosion species, shielding the surface of metallic materials from corrosive attack. In fact, this concept is almost always used in reference to metal alloys. However, the corrosion process cannot be avoided if the barrier layer is mechanically broken, and corrosive species can penetrate the metal surface. One of the most significant properties required of the coatings is the ability to self-heal, which means that a chemical component of the coating will naturally restore the damaged surface. Self-healing protective coatings, which can automatically cure damage, have recently been actively explored to lengthen material lifetime, reduce maintenance costs, and improve public safety. In this study, the main objective is to develop a self-healing coating using tung and linseed oil as a healing agent and analyse the corrosion behaviour of uncoated and coated low-carbon steel substrates in 3.5 wt.% sodium chloride (NaCl). The second objective is to investigate the effectiveness between tung oil and linseed oil as self-healing agent coating on a low carbon steel substrate. Mechanical testing, namely a hardness test, has been performed on a low carbon steel substrate of 20 mm in length, 20 mm in width, and 2 mm in thickness. After that, the microstructure study of low carbon steel substrate has been analyse using a microscope. The microcapsule was prepared by in-situ polymerization of urea-formaldehyde (UF) to construct a microcapsules shell containing linseed and tung oil in self-healing coating formulation on 7.5 wt.% of microcapsule which has been added in the coating. The samples have been submerged in a 3.5 wt.% NaCl solution and sorted into four containers namely uncoated, epoxy coated, linseed oil self-healing, and tung oil selfhealing for 7, 14, 21, 28, and 35 days of immersion test. The Attenuated total reflectance - Fourier-transform infrared spectroscopy (ATR-FTIR) process is used to detect structural changes in biomolecules for epoxy, linseed oil, and tung oil. Scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM/EDX) analysis has been performed for surface morphology study after immersion test. The results demonstrated that when comparing uncoating and epoxy coating, linseed oil self-healing coating had the lowest values for weight loss and corrosion rate. By measuring the weight loss and corrosion rate, we were able to determine which healing agent is more efficient. After 35 days of the immersion test, linseed oil shows a 0.018g of weight loss average while tung oil is 0.020g. The EDX analysis after 35 days of immersion reveals that 83.14 wt.% of iron (Fe) exists in the uncoated sample, 53.15 wt.% in the epoxy coating, 18.79 wt.% in the self-healing coating tung oil, and zero occurrence of iron (Fe) in the self-healing coating linseed oil. Based on the value, linseed oil self-healing coating was more effective at repairing the scratched area of the material. After conducting the research, it was revealed that linseed oil is more effective than Tung oil as a self-healing agent, and the corrosion behaviours of uncoated and coated low-carbon steel substrates were identified after immersion in 3.5 wt.% NaCl. The application on this study is suitable in oil and gas industries.

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