Synthesis and characterization of waterborne polyurethane dispersion for antifouling paint

The continuous accumulation of marine fouling on the submerged marine structures has caused significant impacts to the maritime industries. This led to the development of more effective anti-fouling paints. To date, toxic to green biocides were still widely used in anti-fouling paints to remove fouling. Recent studies showed that polyurethane coatings can exhibit anti-fouling activity without using biocide. However, they had low anti-fouling efficiency. In this study, the biocide-free, and waterborne polyurethane dispersion (PUD) was synthesised using a prepolymer mixing process. The main ingredients were isophorone diisocyanate (IPDI), polyethylene glycol (PEG), dimethylolpropionic acid (DMPA), 1,4-butanediol (BD), and water. The effects of the molar ratio of diisocyanate to PEG (NCO/OHPEG), and DMPA content were investigated on the particle size and distribution, zeta potential, thermal stability, adhesion strength, and solubility rate of PUD coating in seawater and distilled water. The stable PUD at NCO/OHPEG (9 -11) and DMPA content (7 -11 wt%) exhibited small particle size (around 48 -166 nm), high zeta potential (around -50 to -66 mV), and can form dry PUD coatings. The presence of urethane groups in the PUD was ascertained via Fourier Transform Infra-red (FT-IR) spectroscopy. The PUD coatings exhibited adhesion strength of more than 2 MPa on stainless steel substrates and did not detach in seawater. However, they detached in distilled water. (3-aminopropyl)triethoxysilane (APTES) was added to improve the coating stability in distilled water. APTES-modified (APUD) sample was produced using two methods either APTES addition at either (a) before, or (b) after the reaction with BD in the PUD synthesis. The APTES content of 10 mol% was just sufficient to form stable APUD and APUD coatings. APUD coatings produced from method (a) detached in distilled water but not for the APUD coating from method (b). APUD coating from method (b) exhibited the highest adhesion strength on stainless steel (3.303 MPa), followed by carbon steel (2.537 MPa), and the lowest on aluminium (2.280 MPa). This coating was found not suitable to be coated on carbon steel as heavy blisters, scratches, and white spots formed when immersed in seawater and distilled water. The solubility of this APUD coating on stainless steel and aluminium ranged from 0.161 to 0.237 %/day in seawater and 0.468 to 0.550 %/day in distilled water. In overall, this research showed that APUD coating had the potential to work as an anti-fouling paint in the maritime industries