Dr. Mohamed Abd-Elhakeem Biodegradable Plastics Faculty of
Biotechnology Organic Chemistry Chapter 5
Slide 2
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.
Slide 3
Some plastic products
Slide 4
The plastics industry uses large amounts of energy. The
manufacturing of conventional plastics uses substantial amounts of
toxic chemicals. But
Slide 5
Plastic litter disfigures the oceans and the coastlines.
Ingestion of plastic kills marine creatures and fish. Plastics use
valuable resources of oil.
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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
Slide 7
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
Slide 8
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.
Slide 9
One of the typical groups of materials that one can easily find
in the nature is Polyhydroxyalkanoates (PHA)
Polyhydroxybutyrate
Slide 10
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.
Slide 11
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 Biosynthesis 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
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The yield of PHA obtained from the intracellular inclusions can
be as high as 80% of the organism's dry weight.
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PHA Production
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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
0.5m were observed in Alcaligenes eutrophus. Transmission electron
micrograph of thin sections of recombinant R. eutropha PHB cells
containing large amounts of PHB
Slide 15
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. Extraction
Slide 16
PHA BIODEGRADABILITY
Slide 17
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
Slide 18
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
Slide 19
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.
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Applications
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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.