Environmental Engineering Reference
In-Depth Information
modiication can promote its biodegradability. The polymer biodegradability is
also inluenced by the functional groups on the surface that impart water solubility.
A substrate that dissolves would induce the production of necessary enzymes for the
biodegradation of the polymer whereas an insoluble substrate would not. Most of the
enzyme catalysed reactions occur in aqueous media, so the hydrophobic-hydrophilic
balance of the material affects its biodegradation. Polymers containing both the
hydrophobic and hydrophilic segments have higher biodegradability than those with
either hydrophobic or hydrophilic structures alone.
High MW polymers such as PE and PP do not support the growth of fungi on the
surface [15].
PE and PP are prone to oxidation, however, they are not susceptible
to microbial attack because of the presence of a methyl group in the
β
position [9].
Oxidation makes the surface more hydrophilic. The surface charge of the material
determines the bacterial adhesion process. Positive surface charge inluences bacterial
surface growth, and Kerr and Cowling [16] suggested that substrates with a surface
energybetween5and25mN/mwouldhaveminimumfouling.
3.2.5 Additives
Some of the plasticisers that are added to polymers to increase their lexibility and
processing are: ethylene glycol, glycerol, polypropylene glycol, sorbitol, triacetin
and so on. Most of them are organic and they completely breakdown in the
environment. The metabolites of this degradation could be toxic to the growth of the
organism. Introduction of pro-oxidants such as chromium, cobalt, iron, manganese,
molybdenum, and nickel on aluminium oxide or silicon dioxide, to a polymer helps
to make it more photo-degradable. One could achieve different rates of degradation
by the balanced combination of both the antioxidant and pro-oxidant additives.
Ferric iron (Fe
3+
) plays a role in photo-oxidation by initiating a radical reaction.
Metals act as good pro-oxidants making polymers susceptible for thermo-oxidative
degradation. Manganese is also responsible for pro-oxidant activity. Upon activation
by heat in the presence of oxygen, pro-oxidants produce free radicals on the polymer
chain leading to oxidation and changes in the physical properties of the material
[17]. PVA derivatives, biodegradable polyesters, cellulose, starch and vegetable oil
(renewable resource) are some of the pro-oxidants added to polyoleins. Muthukumar
and co-workers [5] studied the effect of the marine environment on starch and
pro-oxidant blended polyoleins and observed biodegradation and biodeterioration.
Catalyst blended polymers exposed to sunlight degrade faster when compared to
other environments such as marine or biological and so on.
