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  • 1. Biodegradable Plastics Produced by Microorganisms Gunjan Mehta, Virani Science College Rajkot
  • 2. Overview Background Importance and Applications Polyhydroxyalkanoates (PHAs) PHA Biosynthesis PHA Recovery Polymer Properties Biodegradation
  • 3. Background What are Bioplastics?  Degradable polymers that are naturally degraded by the action of microorganisms such as bacteria, fungi and algae Benefits Include:  100 % biodegradable  Produced from natural, renewable resources  Able to be recycled, composted or burned without producing toxic byproducts
  • 4. Importance 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
  • 5. 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…
  • 6. Carbon Cycle of Bioplastics CO2 Photosynthesis H2 O Biodegradation Recycle Plants Plastic ProductsCarbohydrates Fermentation PHA Polymer
  • 7. Polyhydroxyalkanoates (PHAs) Polyesters accumulated inside microbial cells as carbon & energy source storage Ojumu et al., 2004
  • 8. 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
  • 9. Polyhydroxybutyrate (PHB) Example of short-chain- length PHA Produced in activated sludge Found in Alcaligenes eutrophus Accumulated intracellularly as granules (>80% cell dry weight) Lee et al., 1996
  • 10. PHA Biosynthesis Ojumu et al., 2004
  • 11. phbC-A-B Operon in A. eutrophus Structural genes encoded in single operon  PHA synthase  -ketothiolase  NADPH-dependent acetoacetyl-CoA reductase Lee et al., 1996
  • 12. 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
  • 13. 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 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
  • 14. 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)
  • 15. Biodegradation byPHA depolymerases
  • 16. 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”?
  • 17. Questions orComments?