2. Plastic is being used wherever you look: in bottles, cell phones,
printers, and cars etc.
Unfortunately, this great discovery gets buried in landfills
everyday and takes up space.
These plastics are not biodegradable and can be a very big
threat to our environment due to their accumulation.
It is true that these plastics can be disposed of by incineration or
recycling, but incineration is very difficult, dangerous and
expensive and recycling is a long process and not very efficient.
Some plastics still cannot be recycled or incinerated due to
pigments, coatings and other additives added to the plastics when
they are made.
If plastics were made biodegradable, plastics would no longer
accumulate as they do and recycling and incineration troubles
would no longer be a problem
3. 2003- North America
◦ 107 billion pounds of synthetic
plastics produced from
petroleum
◦ Take >50 years to degrade
◦ Improper disposal and failure to
recycle overflowing landfills
4. ◦ Degradable polymers that are naturally degraded by the action of
microorganisms such as bacteria, fungi and algae
What are Bioplastics?
Benefits Include:
• 100 % biodegradable
• Produced from natural, renewable resources
• Able to be recycled, composted or burned without producing toxic
byproducts
5. The term “biodegradable plastic” is the one that will
breakdown quickly to natural earthly elements and
compounds.
However, the terms “degradable”, “biodegradable” and
“compostable” have different meanings.
6. Degradable Plastic:
“A plastic designed to undergo significant change in its
chemical structure under specific environmental conditions,
resulting in a loss of some properties that may be measured by
standard methods appropriate to the plastic and the
application.”
There are no requirements that these plastics have to degrade
from natural processes or any other criteria.
A residue is always left behind from degradable plastics.
Degradable plastics are further categorized based on the
method of degradation.
7. Biodegradable Plastic:
“A degradable plastic in which the degradation results
from the action of naturally occurring microorganisms such
as bacteria, fungi, and algae.”
Biodegradable plastics must biodegrade in specific
environments such as soil, compost, or marine
environments.
There is no regulation addressing toxic residue, and no
specific time requirement for degradation.
Numerous factors affect the biodegrading process,
including composition of materials and disposal
environment.
In order for plastics to biodegrade they go through a two-
step process as shown in figures 1 and 2.
8. Figure 1. This figure shows the first step of biodegradation.
Depending on the type of biodegradation taking place, this process is
initiated by heat, moisture, microbial enzymes, or other environmental
factors.
9. Figure 2. This figure shows the second step which takes place when the
short carbon chains pass through the cell walls of the bacteria or
microbes and are used as an energy source. This is biodegradation, when
the carbon chains are used as a food source and are converted into
water, biomass, and carbon dioxide or methane.
10. Compostable Plastic:
“A plastic that undergoes biological degradation during
composting to yield carbon dioxide, water, inorganic compounds
and biomass at a rate consistent with other known compostable
materials and leaves no visually distinguishable or toxic residues.”
Toxic residues important for compost quality include heavy
metal content and ecotoxins.
12. Benefits of such biodegradable products:
1. Biodegradable plastics take less time to break down
Biodegradable packaging and biodegradable bags take much
less time to break down after being discarded, if they haven’t
been recycled, of course. What this means is that it gets
absorbed in the earth, and there will no longer be tons of
plastic dominating our landfills.
2. Biodegradable plastics are renewable
Biodegradable plastics are made from biomass, which is a
completely renewable resource. It is an organic compound,
which breaks down. There is plenty of it around the globe.
Biomass includes trees, plants, grass, and all organic materials
that decompose.
13. 3. Biodegradable plastics are good for the environment
Biodegradable plastics are much better for the environment,
because there is no harm done to the earth when recovering fossil
fuels. Also, in this process there are very few greenhouse gas and
harmful carbon emissions.
4. Biodegradable plastics require less energy to produce
Biodegradable plastics need less than half the energy to produce
than their non-biodegradable counterparts. This means that it is
possible to make twice the amount of biodegradable packaging
and biodegradable bags using the same amount of energy.
5. Biodegradable plastics are easier to recycle
Biodegradable plastics are created from materials that are fully
biodegradable. This means that they can break down much faster
and recycling them takes less energy. Biodegradable plastics can
be reused more efficiently, which gives them a clear advantage.
14. 6. Biodegradable plastics are not toxic
Traditional plastics are full of harmful by-products and
chemicals, which are released during their breakdown process.
Biodegradable plastics are completely safe and do not have any
chemicals or toxins.
This plastic harmlessly breaks down and gets absorbed into the
earth. Such advantages of bioplastics are of extreme importance,
as the toxic plastic load on the earth is growing and at this rate
will cause a whole range of problems for future generations.
7. Biodegradable plastics reduce dependence on oil
The use of biodegradable plastics will decrease the dependence
on other countries for fossil fuels.
15. Some are stiff and brittle
◦ Crystalline structure rigidity
Some are rubbery and moldable
Properties may be manipulated by blending polymers or
genetic modifications
Degrades at 185°C
Moisture resistant, water insoluble, optically pure,
impermeable to oxygen
Must maintain stability during manufacture and use but
degrade rapidly when disposed of or recycled
16. One kind of compound that has been thought to be a potential
replacement compound to the traditional plastic compounds are
polyesters called polyhy-droxyalkanoates (PHAs).
Various kinds of bacteria produce these polyesters as storage
compounds within the cell when a nutrient such as nitrogen or
phosphorous is limited and there is an excess carbon source.
Polyhydroxyalkanoates (PHAs)
17. Polyesters accumulated inside microbial cells as carbon &
energy source storage.
The general formula of PHAs is [-O-CH(R)- -CH2-CO]n,
18. Some common PHAs are polyhydroxyvalerate and
poly(3-hydroxybutyrate) (PHB).
PHB was the first PHA discovered by Maurice Lemoigne in 1923
and is the most commonly studied PHA polymer.
PHAs are seen within the bacteria under the microscope as
inclusions within the cell’s cytoplasm that are approximately
0.2 +/- 0.5 micrometers in diameter.
An advantage is that PHAs are degraded to carbon dioxide
and water in aerobic conditions and methane in anaerobic
conditions by microbes found in soil, water and other various
natural habitat.
PHA CO2 + H2O (aerobically)
PHA CO2 + H2O + CH4 (anaerobically)
19. Fastest in anaerobic sewage and slowest in seawater
Depends on temperature, light, moisture, exposed surface
area, pH and microbial activity
Degrading microbes colonize polymer surface & secrete
PHA depolymerases
PHA CO2 + H2O (aerobically)
PHA CO2 + H2O + CH4 (anaerobically)
20.
21. Produced under conditions of:
◦ Low limiting nutrients (P, S, N, O)
◦ Excess carbon
• 2 different types:
• Short-chain-length 3-5 Carbons
• Medium-chain-length 6-14 Carbons
~250 different bacteria have been found to
produce some form of PHAs
22. Example of short-chain-length
PHA
Produced in activated sludge
Found in Alcaligenes eutrophus
Accumulated intracellular as
granules (>80% cell dry weight)
Lee et al., 1996
23. Naturally occurring polyhydroxyalkanoates (PHAs) are optically
active linear polyesters.
Their physical and mechanical properties are largely determined
by the chemical structure and relative amount of the monomers,
as well as the molecular weight.
To date, more than 150 different monomeric constituents have
been reported in microbially synthesized PHAs.
As a result, properties may vary.
In general, SCL-PHAs are thermoplastics with high melting
temperature and crystallinity.
MCL-PHAs are typically elastomers with low melting temperature
and crystallinity but good elongation properties.
SCL-co-MCL-PHAs are somewhere in between depending on the
exact compositions.
25. PHA producing microorganisms stained with Sudan
black or Nile blue
Cells separated out by centrifugation or filtration
PHA is recovered using solvents (chloroform) to
break cell wall & extract polymer
Purification of polymer
26. Polyhydroxyalkanoates: a family of biodegradable bioplastics
PHA stands for “Polyhydroxyalkanoate”, a family of
biopolyesters synthesized by a variety of microorganisms.
PHAs are bioplastics. Their properties are similar to many
petroleum based thermoplastics and elastomeric materials.
But unlike most petroleum plastics, PHAs are sustainable,
biodegradable and biocompatible.
27. Sustainable: Naturally, many microorganisms can synthesize
PHA from a wide variety of organic matter.
These include sugars, vegetable oils, petroleum
hydrocarbons, wastewater sludge, and even carbon dioxide.
Technological advancements are making the microbial
conversion of sugars and vegetable oils to PHAs more and
more efficient in large scale fermentations.
PHAs are truly sustainable (able to be maintained at a certain
rate or level) and renewable plastics.
28. Biodegradable: PHAs are made by microorganisms but, they
can also be degraded to water and carbon dioxide by
microorganisms found in soil, compost, as well as in rivers,
lakes, and oceans.
The mechanism is microbial enzymatic degradation, not
simple aqueous hydrolysis.
Products made of PHA or containing PHA are actually water
resistant, and with life span similar to conventional plastics.
They only biodegrade when exposed to suitable enzymes.
PHAs can also be recycled with some loss of molecular weight
and mechanical properties.
29. Biocompatible: Numerous studies have shown that PHAs are
generally biocompatible, and can be slowly degraded and
absorbed in the body.
These intracellular polyester granules are accumulated,
possibly as carbon and energy storage materials.
30. PHA granules can be observed by electron microscopy (left photo), or
by phase contrast microscopy using a light microscope (right photo).
31. Polyhydroxyalkanoates are generally classified into short-
chain-length PHA (SCL-PHA) and medium-chain-length PHA
(MCL-PHA) by the different number of carbons in their
repeating units (general structure as below).
SCL-PHAs contain 4 or 5 carbons in their repeating units,
while MCL-PHAs contain 6 or more carbons in the repeating
units.
There are numerous microorganisms capable of synthesizing
PHAs, one form or another. Some of the most-studied ones
are listed in the following table, along with typical PHAs
synthesized and their chemical structures.
32.
33. There are lots of similarities between properties of PHAs and
those of many conventional plastics.
Therefore, PHAs can be processed to many different forms and
shapes using conventional techniques such as injection molding,
extrusion, film blowing, fiber-spray molding, etc.
They may also be provided in the form of colloidal suspensions
in water, or solutions in various solvents.
Combining their unique water resistance, biodegradability and
biocompatibility not found in any other materials, a wide range of
possible commercial applications can be exploited.
34. ● Plastic bags have only been around for about 50 years,
so how do the scientists know how long they take to
degrade?
● To make long-term estimates, scientists often use
respirometry tests. The experimenters place a solid
waste sample – like a newspaper, banana peel or plastic
bag – in a container with microorganisms and soil, and
then they aerate the mixture. Over the course of several
days, microorganisms digest the sample bit by bit and
produce carbon dioxide – the resulting amount of CO2
serves as an indicator of degradation.
35. Item Time to degrade
Paper towel 2-4 weeks
Vegetables 5 days –1 month
Newspaper 6 weeks
Cardboard box 2 months
Waxed milk carton 3 months
Apple core 2 months
Cotton gloves 1-5 months
Wool gloves 1 year
Plywood 1-3 years
Painted wooden sticks 13 years
36. Cotton T-shirt 6 months
Photo-degradable beverage holder 6 months
Plastic beverage holder 400 years
Plastic bags 10-20 years
Plastic bottle 100 years
Glass bottle and jars undetermined
Disposable diapers 50-100 years
Tin can 50 years
Aluminium can 200 years
Monofilament fishing line 600 years
37.
38.
39.
40. How many of you would be
willing to pay 2-3 times more for
plastic products because they
were “environmentally
friendly”?
