Environmental Engineering Reference
In-Depth Information
2.4 Polymers in Marine Fouling
Polymers and composites are used in a wide variety of applications in the marine
industry. These include PU, GFRP, polyester resins (PET), PP, synthetic foam and
so on. PU are extensively used in the fabrication of selectivity grids, oceanographic
appliances including fenders in underwater antenna protection gear and tubing on
underwater vehicles [6]. GFRP are used as a lightweight material in ships, boats,
underwater sea pipes and ishing. Polyester resins are mostly used with glass ibres
and in reinforced composite structures. The surface characteristics of these polymers
help in the formation of bioilms and biofouling. Table 1.1 shows the polymers
and composites that are predominantly used in the marine environment and their
applications. Typical surface energy, contact angle and roughness of these materials
are also listed.
2.4.1 Effect of Polymer Properties on Biofouling
There are several types of interactions, which could affect the settlement of cells on
wet surfaces. The balance between dispersion and electrostatic forces was hypothesised
in the theory of 'lyophobic colloid stability'. This theory states that this balance leads
to a weak secondary minimum of repulsion forces between a cell and a substratum.
This allows for an association at a slight distance from the surface. This theory
was recommended as the basis for an initial reversible bacterial attachment [16].
Electrostatic and dispersion forces are the most important factors in cell adhesion.
Additional interactions, which might also affect attachment include hydrophobic
bonding, polar group interactions, coordination with metals, steric interferences and
irreversible reactions between the functional groups on the surface [40]. A number
of studies have shown that there is a greater tendency for marine bacteria and other
aquatic organisms to attach to hydrophobic surfaces.
In marine environments with a high ionic strength, wettability or critical surface
tension, γ c (surface energy) of the substratum is the most important property in
initiation of microbial settlement [41].
2.4.1.1 The Correlation of Critical Surface Tension and Bioadhesion
Surface free energy has been believed to be the most important polymer property that
inluences biofouling. Surface free energy of a material is a measure of the capacity
of a surface to interact spontaneously with other materials by forming new bonds
c is a related parameter and is a measure of surface wettability) [42]. Baier [43]
and Dexter and co-workers [44] were among the irst researchers to explain how the
 
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