Download - Bioplastics
BIOPLASTICSBiodegradable Plastics
Produced by Microorganisms
Gunjan Mehta,Virani Science College
Rajkot
Overview
Background Importance and Applications Polyhydroxyalkanoates (PHAs) PHA Biosynthesis PHA Recovery Polymer Properties Biodegradation
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
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
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…
Carbon Cycle of BioplasticsCO2
H2O Biodegradation
CarbohydratesPlastic
Products
Plants
Fermentation PHA Polymer
Photosynthesis
Recycle
Polyhydroxyalkanoates (PHAs)
Polyesters accumulated inside microbial cells as carbon & energy source storage
Ojumu et al., 2004
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
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
PHA Biosynthesis
Ojumu et al., 2004
phbC-A-B Operon in A. eutrophus
Structural genes encoded in single operon PHA synthase b-ketothiolase NADPH-dependent acetoacetyl-CoA
reductase
Lee et al., 1996
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
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
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)
Biodegradation by PHA depolymerases
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”?
Questionsor
Comments?