bioplastics-130405065027-phpapp01

8/13/2019 bioplastics-130405065027-phpapp01

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Overview

BackgroundImportance and ApplicationsPolyhydroxyalkanoates (PHAs)PHA Biosynthesis

PHA RecoveryPolymer PropertiesBiodegradation


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Background

Degradable polymers that are naturally degradedby the action of microorganisms such as bacteria,

fungi and algae

What are Bioplastics?

Benefits Include:

100 % biodegradableProduced from natural, renewable resources

Able to be recycled, composted or burned withoutproducing toxic byproducts


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Importance2003- North America

107 billion pounds ofsynthetic plasticsproduced frompetroleumTake >50 years to

degradeImproper disposal andfailure to recycle overflowing landfills


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ApplicationsIndustry

Products, films, paper laminates & sheets,bags and containers

AutomobilesMedical

Sutures, ligament replacements, controlleddrug release mechanisms, arterial grafts

HouseholdDisposable razors, utensils, diapers, femininehygiene products, containers


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Polyhydroxyalkanoates (PHAs)

Polyesters accumulated inside microbialcells as carbon & energy source storage

Ojumu et al., 2004


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Polyhydroxyalkanoates (PHAs)

Produced under conditions of:Low limiting nutrients (P, S, N, O)

Excess carbon2 different types:

Short-chain-length 3-5 CarbonsMedium-chain-length 6-14 Carbons

~250 different bacteria have been foundto produce some form of PHAs


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Polyhydroxybutyrate (PHB)

Example of short-chain-length PHA

Produced in activatedsludgeFound in Alcaligeneseutrophus

Accumulatedintracellularly asgranules (>80% cell dry

weight) Lee et al., 1996


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PHA Biosynthesis

Ojumu et al., 2004


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phb C-A-B Operon in A. eutrophus

Structural genes encoded in single operonPHA synthase

b-ketothiolaseNADPH-dependent acetoacetyl-CoA reductase

Lee et al., 1996


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Recovery of PHAs from Cells

PHA producing microorganisms stainedwith Sudan black or Nile blue

Cells separated out by centrifugation orfiltrationPHA is recovered using solvents

(chloroform) to break cell wall & extractpolymerPurification of polymer


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Bioplastic PropertiesSome are stiff and brittle

Crystalline structure rigiditySome are rubbery and moldable

Properties may be manipulated by blendingpolymers or genetic modificationsDegrades at 185C

Moisture resistant, water insoluble, opticallypure, impermeable to oxygenMust maintain stability during manufacture anduse but degrade rapidly when disposed of orrecycled


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BiodegradationFastest in anaerobic sewage and slowest inseawaterDepends on temperature, light, moisture,exposed surface area, pH and microbial activityDegrading microbes colonize polymer surface &secrete PHA depolymerasesPHA CO2 + H 2O (aerobically)PHA CO2 + H 2O + CH 4 (anaerobically)


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Biodegradation by

PHA depolymerases


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Conclusions

Need for bioplastic optimization:Economically feasible to produceCost appealing to consumersGive our landfills a break

Question:Show of hands- How many of you would bewilling to pay 2-3 times more for plasticproducts because they were environmentallyfriendly?


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