Faculty of Biotechnology
Organic Chemistry
Chapter 5
Biodegradable Plastics
Dr. Mohamed Abd-Elhakeem
A plastic material is any of a wide range of
synthetic or semi-synthetic organic polymer
Plastics important to a range of
industries,
including
aerospace,
building and construction, electronics,
packaging, and transportation.
Some plastic products
But
The plastics industry uses large amounts of energy.
The manufacturing of conventional plastics uses
substantial amounts of toxic chemicals.
Plastic litter disfigures the oceans and the coastlines.
Ingestion of plastic kills marine creatures and fish.
Plastics use valuable resources of oil.
one common property is the
high resistance to natural
degradation processes.
The fact that the plastics are
mostly non-degradable is the
primary cause of still
increasing amount of solid
waste
1- Prepare materials of such resistance and quality that
could be used for a very long time and therefore they will
not create waste in high amount.
2- Prepare plastics that are recyclable, i.e. usable
repeatedly.
3- Prepare plastics that are easily degradable, i.e.
biodegradable
the third strategy embodies the right choice e.g. for
the one-use daily-used things.
Many of the living systems (mainly plants and
microorganisms) are producing materials with
a great potential of replacing the synthetic polymers
prepared mainly from oil.
One of the typical groups of materials that
one can easily find in the nature is
Polyhydroxyalkanoates (PHA)
Polyhydroxybutyrate
Polyhydroxyalkanoates or PHAs are linear
polyesters produced in nature by bacterial
fermentation of sugar or lipids. They are
produced by the bacteria to store carbon and
energy.
Biosynthesis
PHA are synthesized and intracellular accumulated in
most bacteria a under unfavorable growth condition
such as limitation of nitrogen, phosphorus, oxygen or
magnesium in the presence of excess supply of carbon
source
The stored PHA can be degraded by intracellular
depolymerases and metabolized as carbon and
energy source as soon as the supply of the limiting
nutrient is restored
The yield of PHA obtained from the intracellular
inclusions can be as high as 80% of the organism's
dry weight.
PHA Production
PHAs are accumulated in the cells as discrete granules,
the size and number per cell varies depending on the
different species. about 8 to 13 granules per cell having
diameter range of 0.2 to 0.5μm were observed in
Alcaligenes eutrophus.
Transmission electron micrograph of
thin sections of recombinant R.
eutropha PHB cells containing large
amounts of PHB
Extraction
• The dry cells were blended with chloroform
using the high speed homogenizer.
• The supernatant was then filtered through the
filter paper.
•
The remaining solution was concentrated by
rotary evaporator.
• PHB was then precipitated by dropping the
viscous solution into 10 volume of 95% ethanol.
PHA BIODEGRADABILITY
• Microorganisms colonize on the surface of the
polymer and secrete enzymes which degrade
P(HB-HV) into HB and HV units. These units are
then used up by the cell as a carbon source for
biomass growth.
• The rate of polymer biodegradation depends on a
variety of factors, including
• 1- microbial activity of the disposal environment
• 2-pH, temperature, moisture and the pressure
of other nutrient materials. P(HB-HV) is water
insoluble and is not affected by moisture, does not
degrade under normal conditions of storage,
in air The end products of PHA degradation in
aerobic environments are carbon dioxide and water,
while methane is also produced in anaerobic
conditions
The effect of different environments on the
degradation rate of PHB and P(HB-HV) has been
studied by several worker Degradation occurs
most rapidly in anaerobic sewage and slowest in
seawater.
P(HBHV) completely degraded after 6, 75 and
350 weeks in anaerobic sewage, soil and sea
water, respectively.
Applications
1. Packaging : P(HB-HV) could be used for films,
and bottles.
2. Medical : P(HB-HV) biocompatibility coupled
with its slow hydrolytic degradation lead to
potential in reconstructive surgery.
END of the
Course
Best wishes