6
K. Ramani et al.
1.2.4 Mechanochemical Degradation
The degradation of polymers under mechanical stress and by strong ultrasonic irradiations comes under mechanochemical degradation. Breakdown of molecular chains
under shear or mechanical force is often accompanied by a chemical reaction.
1.2.5 Catalytic Degradation
Catalytic transformation of polymeric substances into hydrocarbons with higher
commercial value can be greatly advantageous. Gases and oils can be extracted by
thermally or catalytically degrading polyolefins. A lot of attention has been directed
towards polyolefins (PE, PP, PS) which comprise an important part of industrial and
domestic waste. The addition of a catalyst not only improves the quality of products
obtained from pyrolysis of plastic wastes and lower the temperature of decomposition, but also enables high selectivity for the products to be achieved. Free radical
mechanism can be adopted for the catalytic degradation of the polypropylene using
Fe activated carbon catalyst [10].
1.3 Biodegradation
Biodegradation comprises of the biochemical breakdown of compounds by microorganisms. Under aerobic conditions mineralization of organic compounds yields
carbon dioxide and water whereas methane and carbon dioxide are released under
anaerobic conditions. Biodegradation of polymers can be enhanced by abiotic hydrolysis, photo-oxidation and physical disintegration which in turn would increase their
surface area for microbial colonization [11]. Biodegradation causes a change in
surface properties leading to a loss of mechanical strength, degradation by enzymes
and the final decrease in the average molecular weight of the polymers. Degradation
can occur as a combination of these mechanisms or even individually. Depending
on the mechanism biodegradation can occur at microscopic, macroscopic, molecular
and macromolecular levels.
1.3.1 Solubilization
The hydrophilicity of the polymer plays a huge role in the hydration of polymers. The
secondary and tertiary structures of the polymers stabilized by van der Waals forces
and hydrogen bonds are disturbed on hydration. For polymers having crosslinks the
breakage of either the polymer backbone or crosslinker can reduce its strength [12].
A bio-surfactant that increases the solubility of polyaromatic hydrocarbons can also
be used in the biodegradation of polymers.
K. Ramani et al.
1.2.4 Mechanochemical Degradation
The degradation of polymers under mechanical stress and by strong ultrasonic irradiations comes under mechanochemical degradation. Breakdown of molecular chains
under shear or mechanical force is often accompanied by a chemical reaction.
1.2.5 Catalytic Degradation
Catalytic transformation of polymeric substances into hydrocarbons with higher
commercial value can be greatly advantageous. Gases and oils can be extracted by
thermally or catalytically degrading polyolefins. A lot of attention has been directed
towards polyolefins (PE, PP, PS) which comprise an important part of industrial and
domestic waste. The addition of a catalyst not only improves the quality of products
obtained from pyrolysis of plastic wastes and lower the temperature of decomposition, but also enables high selectivity for the products to be achieved. Free radical
mechanism can be adopted for the catalytic degradation of the polypropylene using
Fe activated carbon catalyst [10].
1.3 Biodegradation
Biodegradation comprises of the biochemical breakdown of compounds by microorganisms. Under aerobic conditions mineralization of organic compounds yields
carbon dioxide and water whereas methane and carbon dioxide are released under
anaerobic conditions. Biodegradation of polymers can be enhanced by abiotic hydrolysis, photo-oxidation and physical disintegration which in turn would increase their
surface area for microbial colonization [11]. Biodegradation causes a change in
surface properties leading to a loss of mechanical strength, degradation by enzymes
and the final decrease in the average molecular weight of the polymers. Degradation
can occur as a combination of these mechanisms or even individually. Depending
on the mechanism biodegradation can occur at microscopic, macroscopic, molecular
and macromolecular levels.
1.3.1 Solubilization
The hydrophilicity of the polymer plays a huge role in the hydration of polymers. The
secondary and tertiary structures of the polymers stabilized by van der Waals forces
and hydrogen bonds are disturbed on hydration. For polymers having crosslinks the
breakage of either the polymer backbone or crosslinker can reduce its strength [12].
A bio-surfactant that increases the solubility of polyaromatic hydrocarbons can also
be used in the biodegradation of polymers.