Biodegradation of Polymers in Marine Environment - Polymers in a Marine Environment - page 74

low-density polyethylene (LDPE) with a marine organism, Bacillus cereus , showed
a 25% weight loss in a period of 12 months [4]. Sudhakar and co-workers [5] have
studied the biodegradation of different polymeric substrates widely used by the marine
and ishery industries for a period of one year by immersing them in the marine
environment and found the maximum gravimetric weight loss was seen in polyester,
polyethylene terephthalate (PET), (7.49%) followed by polyurethane (PU) (4.25%)
and the minimum weight loss was in carbon ibre reinforced plastic (CFRP) (0.45%).
The maximum thermogravimetric weight loss was observed in PET (73.5% at
400 °C) followed by PU (71.1%) and the least loss was in silicone rubber (SR) (2.4%).
3.2 Factors Affecting Polymer Biodegradation
The biodegradability of the polymeric material depends on their physical and chemical
properties and the mechanism of biodegradation depends on the pretreatment of the
polymer. All polymers are biodegradable to some extent because they are organic in
nature. Polymer biodegradation is a heterogeneous process because it is a mixture
of many components, including low molecular weight additives (plasticisers),
colorants and different polymers (blends) which can all serve as a good nutrient
source for microorganisms that grow on the polymer surfaces [6]. Surface properties
of the polymer (including surface area, hydrophobic and hydrophilic properties),
the low order structure (including molecular weight (MW), chemical structure and
molecular weight distribution (MWD)) and the high order-structure (including melting
temperature (T m ), glass transition temperature (T g ), crystallinity, crystal structure and
modulus of elasticity) of the polymers affect their degradation. There are many types
of biodegradable polymers available today and they include naturally biodegradable
polymers and blends prepared by the addition of biodegradable materials.
These biodegradable polymers include:
• Starch-basedproductsincludingthermoplasticstarch,starchandsynthetic
aliphatic polyester blends, and starch and polyvinyl alcohol (PVA) blends.
• Naturallyproducedpolyestersincludingpolyvinylbutyral,polyhydroxybutyrate
(PHB) and poly(3-hydroxybutyrate- co -3-hydroxyhexanoate).
• Renewableresourcepolyesters,suchaspolylacticacid(PLA)whichhastwo
racemic forms L and D.
• Photo-biodegradableplastics.
• Controlleddegradationadditivemasterbatches.
• Syntheticaliphaticpolyestersincludingpoly(e-caprolactone) (PCL) and
polybutylene succinate.