Antifouling with Biocides vs. PDMS-Based Antifouling: Sustainability and Energy Savings in the Maritime Sector
In the maritime sector, combating biofouling, the accumulation of marine organisms such as algae, barnacles, and bacteria on ship surfaces, poses a critical challenge. The presence of fouling not only worsens the hydrodynamic efficiency of ships but also increases fuel consumption, significantly impacting both economic and environmental aspects.
Traditionally, antifouling solutions have relied on coatings containing biocides, such as cuprous oxide and zinc compounds, designed to prevent the growth of marine organisms by releasing toxic substances. However, these coatings present significant drawbacks, including toxicity to the marine environment and human health, contributing to water pollution and the degradation of ecosystems.
An innovative approach gaining increasing attention is the use of PDMS (polydimethylsiloxane)-based antifouling coatings, a biocide-free solution operating on a completely different principle. These coatings, also known as “fouling release” systems, do not kill marine organisms but create a smooth, non-adhesive surface that prevents organisms from attaching to the ship’s hull. When the ship is in motion, the combination of the slippery surface and water flow naturally facilitates the detachment of fouling.
The Integration of Amphiphilic Additives
Incorporating amphiphilic additives into silicone-based antifouling coatings can further enhance their fouling release performance. Amphiphilic additives are molecules that possess both hydrophilic (water-attracting) and hydrophobic (water-repelling) parts. When incorporated into a silicone (PDMS) coating, these additives can modify the surface characteristics to further reduce the adhesion of marine biofoulers.
These enhanced coatings combine the benefits of an extremely smooth surface with the ability to inhibit or release marine organisms, improving fouling resistance and, consequently, the ship’s hydrodynamic performance. The combination of silicone and amphiphilic additives reduces the coefficient of friction even more compared to pure silicone coatings, further enhancing fuel efficiency.
HYDROVEST® 2000
Maflon’s new additive, HYDROVEST® 2000, is designed as an amphiphilic polymer capable of phase segregation and self-assembly at the interface with the environment. These properties allow the coating to modify the surface characteristics, creating a barrier that confounds the recognition and adhesion mechanisms of biofouling. Adding HYDROVEST® 2000 to antifouling coatings reduces the number of adhering biofouling organisms and facilitates their removal from treated surfaces. This is achieved through the polymer structure, which interferes with the settlement of biofouling and enhances their detachment under shear stress generated by the vessel’s movement. As seen earlier, PDMS-based coatings exploit their low coefficient of friction to remove deposited organisms.
How Surface Tension Affects Performance
Let’s delve into how the hull’s surface tension affects external factors:
- Surface tension and wettability: The surface tension of water affects the wettability of the hull surface. A surface with low surface tension is less wetted by water, reducing the resistance opposing the ship’s movement. This phenomenon can lead to a decrease in viscous drag (one of the components of total resistance), contributing to reducing the load on the engine.
- Superhydrophobic surfaces: Coatings that create superhydrophobic surfaces (which strongly repel water) can further reduce wettability, thus reducing friction. While surface tension is not the primary factor, coatings that lower surface tension can enhance the effectiveness of hydrophobic surfaces, contributing to lower drag.
Friction Coefficients and Antifouling Performance
The friction coefficient of biocide-based antifouling coatings can vary significantly depending on the specific biocide used and environmental conditions. However, studies indicate that these coatings typically exhibit a friction coefficient between 0.2 and 0.4 under laminar flow conditions in water, although this value may increase in the presence of biofilms or other forms of marine fouling.
In contrast, the friction coefficient of a PDMS (polydimethylsiloxane) surface in water can vary depending on factors such as the exact composition of the PDMS, surface roughness, and experimental conditions. However, the static friction coefficient of PDMS in water is generally found to be in the range of 0.01 to 0.1, significantly lower than that of biocide-based coatings.
Environmental Benefits and Fuel Savings
The primary advantage of PDMS-based coatings over traditional biocides is their reduced environmental impact. While biocides release toxic substances into the water, silicone-based fouling release coatings do not release harmful substances, making them a more ecological and sustainable choice.
In addition to environmental benefits, these coatings offer significant advantages in terms of energy efficiency. Thanks to their smooth, low-energy surface, PDMS-based coatings reduce the friction between the hull and water, decreasing fluid resistance. This results in a reduction of the power required by the ship’s engine to maintain a given speed, which in turn leads to substantial fuel savings.
- Drag reduction: Even a small reduction in hydrodynamic drag can lead to significant fuel savings, especially for ships traveling long distances. This effect, combined with other drag reduction technologies such as antifouling coatings, can result in a notable decrease in fuel consumption.
- Overall effects: While surface tension reduction can contribute to fuel savings, its impact is generally less significant than that achieved through reducing the coefficient of friction or hull shape resistance.
Conclusion
In summary, PDMS-based antifouling coatings offer a sustainable alternative to traditional biocide-based solutions, addressing both environmental and energy efficiency concerns. Their ability to significantly reduce drag and fouling adhesion, combined with the environmental benefits of being biocide-free, positions them as a forward-thinking solution in the maritime industry. With continuous improvements, such as the integration of amphiphilic additives, these coatings can further enhance ship performance and contribute to the industry’s move toward greener, more energy-efficient
