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

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