Biomedical Engineering Reference
In-Depth Information
Chapter 5
Poly-
β
-hydroxybutyrate (PhB): a Biodegradable
Polymer of microbial origin
N. S. Gangurde and R. Z. Sayyed
iNtroduCtioN
Plastics have been an integral part of our life. World wide production of plastics is
about 180 million tonnes/year (mt/year) with Asia, Australia, and India accounting
for about 33% of the output, Western Europe 25% and North America 29%. By 2012,
global consumption of plastics is expected to increase from the current 180 mt/year to
258 mt/year (Tuominen et al., 2002). Data released by the United States Environmen-
tal Protection Agency (2003) shows that somewhere between 500 billion and a trillion
plastic bags are consumed worldwide each year. Less than 1% of bags are recycled.
It costs more to recycle a bag than to produce a new one. The annual consumption of
plastics in India is about to reach 4 kg/person/year, which is very small compared to
a world average of 24.5 kg in 2000 and 12.5 kg for South and East Asia. But with a
population of 1.0 billion people, the total demands for plastic in India are still around 4 mt
and are growing fast. The current worldwide demand for plastics is in excess of 100
mt/year. The disposal of petrochemical derived plastics poses a threat to our environ-
ment. Liberal use of large amount of non-biodegradable synthetic polymers has cre-
ated frightening scenario for environment. Further, more conventional petrochemical
plastics are recalcitrant to microbial degradation. These non-degradable petrochemical
plastics accumulate in environment at a rate of 25 mt/year. Therefore, replacement of
non-biodegradable by biodegradable and eco-friendly polymers like Poly-b-hydroxy-
butyrate (PHB) will help to combat environmental problems created due to the use of
synthetic polymers (Kumar et al., 2004). The PHB has been found as eco-friendly and
best alternative biopolymer having variety of saturated or unsaturated and straight or
branched chains containing aliphatic or aromatic side groups (Doi et al., 1992; Smet et al.,
1983). The PHB has been found as eco-friendly substitutes and ideal candidate for
making biodegradable plastics since its physical characteristics are similar to those of
petrochemical polyesters such as polypropylene, in the natural environment.
The PHB as a biodegradable thermoplastic has captured the attention for more
than 30 years, due to their similar properties to various thermoplastics and elastomers,
which have been used in consumer products, and completely degraded to water and
carbon dioxide upon disposal under various environments (Choi and Lee, 1999). How-
ever, the inefficient and expensive production and recovery methods, lack of detailed
knowledge about the cultural conditions regulating PHB production, need of gene
transfer from efficient PHB producer to easily cultivable organisms have hampered
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