Environmental Engineering Reference
In-Depth Information
• Ingredients(dependsonthetypeofadditivesusedsuchasanti-oxidants,UV
stabilisers and so on).
• Environmentalfactors(light,heat,humidity,dissolvedoxygen,temperature,water
quality, salinity, pH, radiation, mechanical force, waves and seasonal variation).
Dissolved oxygen will aid in the oxidation of the polymer.
• Biologicalenvironment(bacteria,fungi,macrofoulersandenzymes).Tropical
regions have a higher number of microorganisms than colder seas.
Table 1.3 Plastics likely to be found in the oceans
Plastic
Speciic gravity
Gear-related plastics
PE
0.92−0.97
PP
0.91
Nylon
1.14
Polyester
1.38
Packaging-related plastics
PE and PP 0.92−0.97 and 0.91
PVC
1.38
Polyester
1.38
PS (Styrofoam)
<0.2
Speciic gravity of sea water at 25 °C, with a salinity of 3.5%, at atmospheric pressure is
around 1.025
PS: Polystyrene
The degradation of plastics in the natural environment is very slow and it is irst
initiated by environmental factors including temperature, pH, humidity and UV
light. This is followed by the biotic degradation (microorganisms) [15]. Most plastics
are reported to be stable in all environments. The plastic materials are capable of
degrading under aerobic and anaerobic conditions. When UV-B radiation between
290−315 nm hits the plastic it tends to weaken the chemical bonds. The continuous
exposure makes the plastics unstable and brittle. Some polymers have benzene rings,
which have the ability to absorb energy from UV photons which makes the plastics
undergo photodegradation. Once the material is broken down by fragmentation then
they will not continue to degrade further, but they will undergo deterioration because
of ocean currents and wind forces. Because of this property the biodegradable plastics
