Biodegradable Plastics Produced by Microorganisms

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Biodegradable Plastics Produced by Microorganisms

• Jackie Whitaker
• December 5, 2005
• MB 433

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Overview

• Background
• Importance and Applications
• Polyhydroxyalkanoates (PHAs)
• PHA Biosynthesis
• PHA Recovery
• Polymer Properties
• Biodegradation

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Background

• 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

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Importance

• 2003- North America
• 107 billion pounds of synthetic plastics produced
  from petroleum
• Take gt50 years to degrade
• Improper disposal and failure to recycle ?
  overflowing landfills

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Applications

• Industry
• Products, films, paper laminates sheets, bags
  and containers
• Automobiles

• Medical
• Sutures, ligament replacements, controlled drug
  release mechanisms, arterial grafts

• Household
• Disposable razors, utensils, diapers, feminine
  hygiene products, containers

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Carbon Cycle of Bioplastics
Photosynthesis
Recycle
Plastic Products
Fermentation
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Polyhydroxyalkanoates (PHAs)

• Polyesters accumulated inside microbial cells as
  carbon energy source storage

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Polyhydroxyalkanoates (PHAs)

• 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

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Polyhydroxybutyrate (PHB)

• Example of short-chain-length PHA
• Produced in activated sludge
• Found in Alcaligenes eutrophus
• Accumulated intracellularly as granules (gt80
  cell dry weight)

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PHA Biosynthesis
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phbC-A-B Operon in A. eutrophus

• Structural genes encoded in single operon
• PHA synthase
• b-ketothiolase
• NADPH-dependent acetoacetyl-CoA reductase

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Recovery of PHAs from Cells

• 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

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Bioplastic Properties

• 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 185C
• Moisture resistant, water insoluble, optically
  pure, impermeable to oxygen
• Must maintain stability during manufacture and
  use but degrade rapidly when disposed of or
  recycled

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Biodegradation

• 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)

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Biodegradation by PHA depolymerases
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Conclusions

• Need for bioplastic optimization
• Economically feasible to produce
• Cost appealing to consumers
• Give our landfills a break

• Question
• Show of hands- How many of you would be willing
  to pay 2-3 times more for plastic products
  because they were environmentally friendly?

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QuestionsorComments?