Fabrication and performance analysis of titania-polyurea spray coating in marine application

• Main Author: Li, Yuanzhe
• Other Authors: Dong Zhili
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Engineering::Materials
• Online Access: https://hdl.handle.net/10356/145964
• Institution: Nanyang Technological University

Marine structures often suffer from biofouling, which greatly increase the resistance of the ship’s hull and turbine blades. Extensive biofouling can even lead to the failure of the coating structures. From the current trend of antibacterial materials development, the use of hydrophobic texture combined with antibacterial agents is a promising antibacterial means. Besides, Polyurea coatings with extreme physicochemical properties also provide a great solution as well as a platform for the fabrication of new type coatings. However, a study on application of Titania-Polyurea spray coating for marine use against biological fouling as well as abrasion impact is still lacking. This thesis proposes an anti-biofouling Titania-Polyurea spray coating, which uses nano-scale antibacterial agents, titanium dioxide, to construct hydrophobic surface texture on the polyurea coating system. On one hand, this newly fabricated coating can effectively prevent biofilm and fouling from enriching on the surface of the object and reduce the growth of mold on the surface. On the other hand, this coating still keeps the fast reactivity and excellent mechanical performance from its coating systems and extends the maintenance intervals at the same time. Through the formulating analysis of anti-biofouling performance, it is found the causal factors include antibacterial TiO2, surface wettability, and morphology in order of their importance. The most optimized formula group is able to obtain uniform surface textures, high contact angle (91.5 °), low surface energy (32.5 mJ/m2), and strong hardness (74 A). Moreover, this Titania-Polyurea spray coating reaches high strength of tensile over elongation and strong hardness. The results show that the best formulation coating has the highest yield stress of 14.34 MPa. Multiple mechanical performances indicate that this composite Titania-Polyurea spray coating still keeps its original characters, like insensitivity to temperature and humidity, outstanding anti-aging performance, and extreme abrasion resistance, from polyurea itself. Moreover, there are neither toxins nor gas leakage from this Titania-Polyurea spray coating compared to the traditional antifouling paint, which makes it eco-friendly even after long-time exposure. Besides, the drag reduction result of such a coating system also indicates a low flow resistance effect under non-standard designed microchannel at a drag reduction rate of 3.0%. Through the formulating analysis of antibiofouling performance, it is found the causal factors include antibacterial TiO2, it is found that the direct causal factors include: (i) antibacterial TiO2, (ii) surface wettability, and (iii) textures and morphology in order of their importance. Nano-titanium dioxide (TiO2 wt.%) in the coating system may use photocatalytic degradation to inhibit the attachment of biofilm by damaging microbial membrane; hydrophobic wettability might reduce the adhesion of the biofilm more significantly than hydrophilic ones, especially under high shear force; and nano-texture may also potentially reduce the biofouling adhesion. Moreover, the surface hardness is affected by (i) the proportion of Component “B” (long-chain) to P1000 (short-chain) wt.%, (ii) deformer PDMS wt.%, and (iii) nano-titanium dioxide (TiO2 wt.%) in the coating system, which also has an internal relationship. The root cause of such features would be the two main additives, nano-titanium dioxide (TiO2) and low surface energy defoamer (PDMS) inside the coating system. All of these studies would also provide a good reference of formulation design and promising application for further application in marine, as well as biomedical engineering.