Biodegradable Plastics Produced by Microorganisms

1. Biodegradable Plastics Produced by Microorganisms Jackie Whitaker December 5, 2005 MB 433

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. 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 Importance

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. CO2 H2O Biodegradation Plants Carbohydrates PHA Polymer Carbon Cycle of Bioplastics Photosynthesis Recycle Plastic Products Fermentation

7. Ojumu et al., 2004 Polyhydroxyalkanoates (PHAs) • Polyesters accumulated inside microbial cells as carbon & energy source storage

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. Lee et al., 1996 Polyhydroxybutyrate (PHB) • Example of short-chain-length PHA • Produced in activated sludge • Found in Alcaligenes eutrophus • Accumulated intracellularly as granules (>80% cell dry weight)

10. Ojumu et al., 2004 PHA Biosynthesis

11. Lee et al., 1996 phbC-A-B Operon in A. eutrophus • Structural genes encoded in single operon • PHA synthase • b-ketothiolase • NADPH-dependent acetoacetyl-CoA reductase

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 by PHA 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. QuestionsorComments?