**7. Effect of microbial activities on FRP properties**

Microorganisms in sea water can settle on structures, such as on metals, FRPs, and on almost all materials. The microbes form a very thin layer of viscoelastic nature as micro-fouling, quite adherent, and this layer is commonly termed as a slime. The slime formation on a substrate can take place within few days of immersion, as there are enormous amounts and varieties of microbes in the sea.

The slime facilitates the settlement of macro-organisms, which is termed as macro-fouling, and most common fouling macro-organisms are bryozoans, barnacles, mollusks, polychaete and other tube worms, zebra mussels, etc. The size of macro foulants is quite large, could be few centimeters even. The slime formation and macro-fouling are highly undesirable for marine vessels and structures, because of many reasons such as evolution of corrosive gases such as hydrogen sulfide, hydrogen, etc., due to metabolism of the organisms, surface roughness of vessels due to macro-fouling, thereby increasing the drag on movement substantially. FRPs are equally vulnerable to such settlements and degradation due to microbial settlement. There are many microbiological studies on the effect of microbes on various materials immersed in sea water. A brief discussion and most important findings are given here for FRP composites.

#### *FRP for Marine Application DOI: http://dx.doi.org/10.5772/intechopen.101332*

Little et al. [58] studied the adhesion of the slime on substrates. Gu et al. [59, 60] reported microbial growth and degradation of glass and carbon fibers upon penetration of fungi into the resin matrix. Organic additives to fibers, such as plasticizers and surfactants, may provide nutrients for microbial growth and ultimate degradation as reported by Upsher [61]. Glass fibers are more vulnerable.

Wagner et al. [62] examined carbon fiber-reinforced epoxy (T-300) and a glass (S-2) and carbon fiber (T-300) vinyl ester exposed to microbial culture for 161 days, to study the possible microbiologically influenced degradation. Composites, resins, and fibers were exposed to various microbes including hydrogen producing and sulfate-reducing bacteria (SRB). All types of bacteria colonized surfaces, preferentially on irregularities such as scratches and fiber disruptions. SRB degraded the organic surfactant on glass fibers. Tensile strength of a CFRP of epoxy was reduced on exposure to SRB. The SRB mixed culture did not degrade neat vinyl ester. Degradation of the organic surfactant on glass fibers due to the microbes was observed. Hydrogen-producing bacteria appear to have disrupted fiber-vinyl ester resin bonding with gas production. The study indicated that it is essential for marine application to screen the FRPs against various microbes of sea water before designing the structure.
