Marine Biofouling of Polymers - Polymers in a Marine Environment - page 41

Table 2.3 Microorganisms degrading synthetic polymers PVC and PU and
their mode of action [70]

Synthetic polymer Degrading microorganisms Main mode of action

PVC Fungi (e.g., Aureobasidium pullulans )

and bacteria (e.g., Pseudomonas
aeruginosa )

Increased loss of plasticisers due
to microbial degradation

PU Fungi (e.g., Chaetomium globosum )

and bacteria (e.g., Bacillus subtilis )

Enzymatic activity

In a study carried out on PC, Artham and Doble [61] found that bioilm forming
microorganisms used PC as their sole carbon source and initiated oxidative
type degradation (9% gravimetric weight loss in one year). The most abundant
strain isolated from the polymer immersed in the sea for a year was identiied as
Pseudomonas sp ., BP2. The polymer was degraded into smaller oligomers for
metabolism and growth of the microorganisms. The degradation and deterioration of
PC ilms immersed in ocean may be because of a combination of biofouling and ocean
currents. Muthukumar and co-workers [7] also made similar indings. Gravimetric
weight loss of 7.49 and 4.25% was observed for PET and PU, respectively, after one
year. CFRP was found to be stable in a marine environment with 0.45% gravimetric
weight loss in one year.

Surface oxidation, as measured by Fourier-transform infrared spectroscopy (FTIR), has
been observed in polymers immersed in the ocean. Muthukumar and co-workers [7]
reported that some polymers (PET, GFRP and CFRP) underwent biotic degradation
and polymers such as PU underwent abiotic oxidation. This led to an increase in
the carbonyl and ester indices of PU ilm immersed in the ocean for one year. In all
these four cases unsaturation increases (leading to an increase in the double bond),
indicating that the cleavage of the macromolecules happens from one end of the
chain ( Figure 2.13 ).

Surface roughness of the polymers changes gradually because of biofouling. Artham
and Doble [61] reported that the surface roughness of PC increased from 14 nm for
the control to 23 nm and that the contact angle changed from 78.4 to 70 for polymers
immersed in the sea for three months. Similar indings were reported by Muthukumar
and co-workers [7]. The maximum increase in roughness was seen in syntactic foams
with an increase of 254.13 nm followed by PU (140.52 nm) and polyester (73.80 nm).