The development of a marine antifouling system using environmentally acceptable and naturally occuring products

Abstract

Due to legislative pressures and the recent ban of trybutyl tin, alternative environmentally acceptable ship hull antifouling systems are required. This thesis uses a multidisciplinary approach to combine two disparate areas of research namely marine biology and surface engineering, to develop a novel natural product (NP) based antifouling system. The overall objective of this thesis is to transfer a natural marine biological defence mechanism into an engineered antifouling coating system. By combining natural product extraction and incorporation into a trial coating an extensive test progranlme was able to investigate the antifouling performance and address the issues of bringing this active area of research to the next technological readiness level. By using a stepwise approach to the development of the engineered solution, a suite of techniques were used to fully characterise a NP based system. The biological and surface engineering techniques adapted and developed are described here and their future use to evaluate a novel NP based anti foul ant system is critically assessed. After an extensive literature review, an ethanol extract from the red seaweed Chondrus crispus was selected as the natural product source. NP specimens were harvested locally and also purchased as industrially processed dried algae. The industrially processed algae showed good antifoulant activity ( ::; 25 flg mL- 1 ) in laboratory bioassays and had a greater efficacy than the locally harvested samples highlighting its potential as an economically viable solution. The direct incorporation of the NP into a commercial control depletion polymer binder, allowed for the rapid development of characterisation techniques to evaluate the effects this had on the performance of the NP-binder matrix. The feasibility of a range of electrochemical techniques to measure corrosion potential, impedance, resistance and water uptake in the NP coating was critically assessed. A combination of open-circuit potential and electrochemical impedance spectroscopy provided a unique and rapid means to non-destructively measure the contribution of incorporated NPs to the degradation and water uptake of the binder film. Studies of biofilm growth were used to successfully measure community viability and structure using fluorescent staining and differential interference contrast microscopy. These techniques were found to be very infonnative on Southampton water marine biofilm community structure and were cross correlated by fourier transform infrared measurements. Resistance to biofouling was deternlined through field trials, an important testing platfornl for an antifouling system, and specifically trials which test the entire coated system including any primers and substrate preparation requirements. An initial NP antifouling perfornlance greater than the booster biocide (Chlorothalonil) control was documented for one field trial over a period of the first 6 weeks. A key aspect was to deternline the potential efficacy of NPs and their viability in a coating system. To achieve this, a range of standard and non-standard teclmiques were used to assess this novel combination of crude NP extract and commercial binder system. This work has shown that a limited antifoulant activity is achievable. By evaluating the effect of a NP on both the fouling community and a binder system this unique approach helps define key teclmiques to assess future NP antifoulants and identifies the optimisation required to increase their functionality.

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