Preparation and Performance of Caster Oil Polyurethane Marine Antifouling Coatings with Acrylamide Quaternary Ammonium Salts as Antimicrobial Agents

The surfaces of underwater ship hulls and aquaculture equipment, such as fish cages, are highly susceptible to damage from fouling organisms. Although traditional marine antifouling coatings exhibit effective antifouling properties, the leaching of antifouling agents into the marine environment can lead to pollution and ecological disruption. In this study, we prepared castor oil polyurethane (CO-PU) by reacting castor oil with isocyanate. We then incorporated self-synthesized acrylamide-based quaternary ammonium salts (QASs), specifically dimethyloctylaminopropyl methacrylamide-ammonium QD-BC and its polymer PQDBCAM, into the CO-PU resin to develop CO-PU marine antifouling coatings. By optimizing the formulation to enhance the cross-linking degree of the coating, we obtained coatings with improved mechanical properties and antifouling performance. The results indicate that, in comparison to the pure CO-PU coating, the hydrophilicity of the coating is enhanced, the flexibility is superior, the pencil hardness increases from 5H to 6H, and the adhesion of the PQDBCAM antifouling coating reaches a maximum of 4.79 MPa. All of the coatings demonstrated effectiveness in inhibiting the growth of Pseudomonas aeruginosa, diatoms, and protein attachment, and the increase of QASs leads to enhanced effects. This suggests that acrylamide QAS marine antifouling coatings have a certain degree of antifouling performance, and polymer-based quaternary ammonium PQDBCAM antifouling coatings show superior efficacy. After the 3.6% PQDBCAM coating was statically placed in diatoms for 7 days, the coverage area of diatoms was merely approximately 22.3% and the protein adsorption amount on the surface of the antifouling coating was 31.72 μg/cm². The coating could maintain its integrity after 3 months and still exhibit excellent antibacterial effects. The antifouling effect was more durable, effectively reducing the maintenance times of ships and the cleaning frequency of aquaculture equipment.