Microcapsules-based multifunctional coatings for anticorrosion and antibacterial applications

• Main Author: Chong, Yong Bing
• Other Authors: Yue Chee Yoon
• Format: Theses and Dissertations
• Language: English
• Published: 2019
• Subjects: DRNTU::Engineering::Materials
• Online Access: https://hdl.handle.net/10356/89652; http://hdl.handle.net/10220/47801
• Institution: Nanyang Technological University

Corrosion and biofouling are among the most challenging issues in the marine industry which has caused huge economic losses annually. The complex marine environment has caused severe corrosion problem due to the damage of paint or coating and biofouling problem due to the accumulation of micro- and macro-organisms on the coatings. One of the most common approaches to treat biofouling is the use of biocides, which was found to pose negative impact to the environment and human health. Additionally, the encapsulation of corrosion inhibitors for anticorrosion properties of the coatings involves the use of toxic organic solvent, which raises concern over environmental and health issues. Hence, a more environmental friendly solution to solve both corrosion and biofouling problems is needed. Clove oil as a natural antimicrobial agent was successfully encapsulated through interfacial and in-situ polymerizations. The release of clove oil from the double layered PU/PUF microcapsules fitted well against the Baker-Lonsdale model, indicating diffusion as the release mechanism. The calculation of Baker-Lonsdale constant (kB) values validates the feasibility to fabricate microcapsules with a wide range of diffusivity up to 8 times difference, indicating the versatility of this microencapsulation technique for a vast range of applications. In particular, the release rate decreases with increasing PU shell thickness and increasing surface roughness. Additionally, the microcapsules possess excellent antibacterial activities against different marine bacterial strains – Escherichia coli, Vibrio coralliilyticus and Exiguobacterium aestuarii. Multifunctional microcapsules containing clove oil and 8-hydroxylquinoline (8-HQ) with good mechanical strength, anticorrosion and antibacterial features were fabricated. Accelerated corrosion test indicates the formation of inhibition layer based on the reaction between the released 8-HQ compound and the steel substrate, which retards corrosion attack. Additionally, these microcapsules possess excellent antibacterial effect against E. coli, V. coralliilyticus and E. aestuarii. These results successfully validate the ideas to encapsulate two different functional agents – 8-HQ as the corrosion inhibitor and clove oil as the natural antimicrobial agent in a single robust microcapsule, eliminating the use of toxic organic solvent to dissolve solid 8-HQ compound and serving both anticorrosion and antibacterial functions simultaneously. To further improve the functionality of the microcapsules, the shell interface was decorated with zinc oxide (ZnO) nanosheets, which render the microcapsules close to superhydrophobic properties, with a contact angle of around 144.2 ± 4.0°. Additionally, epoxy coatings with embedded ZnO-decorated microcapsules indicates improved anticorrosion performance due to the better affinity between the rough surface morphology of ZnO nanosheets decorated microcapsules and the matrix. The microcapsules possess improved antibacterial properties due to the release of zinc ions and the direct contact between the ZnO nanosheet and the bacterial cell membrane. The results successfully validate the hypothesis that microcapsules shell interface can be designed to incorporate additional functionality as well as improving the existing functionalities originated from the encapsulated core materials. Antifouling field test was conducted at the Sebarok Island, Singapore for duration up to 45 days. In general, microcapsules-based epoxy coatings indicate better antifouling performances as compared to the blank epoxy coating and epoxy coatings with clove oil without encapsulation. However, the antifouling effect of the microcapsules-based coatings generally deteriorates as the immersion period in the seawater increases to 45 days. Barnacles, tubeworms, algae and bryozoans were successfully identified as the fouled macro-organisms on the coatings. Overall, microcapsules-based coatings were examined and proven to be a potential environmental friendly solution for corrosion and biofouling problems in the marine industry.