Bio Degradation of Plastics

3/8/20103/8/2010 Dr.Navdeep BhullarDr.Navdeep Bhullar

Biodegradation of PlasticsBiodegradation of Plastics


Plastic?Plastic?Synthetic polymers can be classified as plastics, elastomers and synthetic fibers.

Plastics is the general term for a wide range of synthetic or semi synthetic polymerization products. They are composed of organic condensation or addition polymers and may contain other substances to improve performance or reduce costs.


Plumbing, textiles, paint, floor coverings at Plumbing, textiles, paint, floor coverings at home are mostly made of synthetic home are mostly made of synthetic polymers, some of which are described as polymers, some of which are described as plastics.plastics.

The term The term ‘‘polymerpolymer’’ are derived from Greek are derived from Greek words meaning words meaning ““many partsmany parts””. .

Polymers are macromolecules built up Polymers are macromolecules built up from linked smaller molecules called from linked smaller molecules called monomers.monomers.


Plastics

Benefits of using plastics:

Low costStrength (physically strong): lightweight and do not break like glassDurabilityPrintability


Plastic UsesPlastic UsesPLASTIC USES

Polyethylene Packaging, electrical insulation

Polyvinyl chloride (PVC) Credit cards, floor coverings, rainwear

Polyvinyl acetate (PVA) Latex paints

Polybutadine (BUNA) rubbers Car tires, hoses

Poly (methyl methacrylate) Transport equipment


Some common synthetic polymers chemical structures


http://upload.wikimedia.org/wikipedia/commons/b/b2/Plastic_household_items.jpg


The ProblemPublic concern about the long term effects of plastics technology.

Barry Commoner in late 1960s suggested that the earth surface would be buried ten feet deep in plastic waste because there were no biological organisms capable of destroying it.


Plastics are the most common manPlastics are the most common man--made object made object sighted at sea. During a 1998 survey, 89% of the sighted at sea. During a 1998 survey, 89% of the trash observed floating in the North Pacific Ocean trash observed floating in the North Pacific Ocean was plastic.was plastic.

Plastic sheeting has been documented in the Plastic sheeting has been documented in the stomachs of sperm whales, roundstomachs of sperm whales, round--toothed toothed dolphins and a Curvier beaked whale.dolphins and a Curvier beaked whale.

Many sea turtles frequently swallow plastic bags Many sea turtles frequently swallow plastic bags when they mistake them for jelly fish, which is when they mistake them for jelly fish, which is one of their favorite foods.one of their favorite foods.


The lightweight nature of plastics which can make The lightweight nature of plastics which can make them deadly in the marine environment, as plastic them deadly in the marine environment, as plastic items can float on the surface of the ocean or items can float on the surface of the ocean or within the water column.within the water column.

Plastics are composed of long chains of Plastics are composed of long chains of hydrocarbons, which are hydrogen and carbon hydrocarbons, which are hydrogen and carbon atoms that are bound together very tightly. Microatoms that are bound together very tightly. Micro-- organisms such as plankton do not have the organisms such as plankton do not have the ability to break down these bonds and therefore ability to break down these bonds and therefore plastic does not decompose easily. plastic does not decompose easily.


Biodegradation (Biotic degradation) - Chemical degradation from the action of naturally occurring microorganism such as bacteria, fungi and algae.


Biodegradable Plastic

A degradable plastic in which the degradation results from the action of naturally occurring microorganisms such as bacterial, fungi, and algae.


Biodegradation of PlasticsBiodegradation of polymers involves Biodegradation of polymers involves breakdown by microorganisms or higher breakdown by microorganisms or higher organisms, using enzymeorganisms, using enzyme--catalyzed catalyzed pathways.pathways.

Biological systems tend to degrade natural Biological systems tend to degrade natural polymers e.g. starch by hydrolysis then polymers e.g. starch by hydrolysis then oxidation. oxidation.


Aliphatic e.g. nonaromatic polyesters are among Aliphatic e.g. nonaromatic polyesters are among most biodegradable.most biodegradable.

Example, the degradable and absorbable sutures Example, the degradable and absorbable sutures used in surgical procedures are often made of used in surgical procedures are often made of poly (glycolic acid).poly (glycolic acid).

Thermoplastic materials made from Thermoplastic materials made from polycaprolactone have been shown to almost polycaprolactone have been shown to almost completely degrade on burial in soil for 12 completely degrade on burial in soil for 12 months. Microorganisms used the polymer as a months. Microorganisms used the polymer as a growth substance and converting it into microbial growth substance and converting it into microbial biomass, CObiomass, CO22 and Hand H22 O. O.


Polyethylene, polypropylene, polyvinyl chloride Polyethylene, polypropylene, polyvinyl chloride and polystyrene are most widely used plastics.and polystyrene are most widely used plastics.

These polymers are very bioresistant because it These polymers are very bioresistant because it involves only carbon atoms in their main chain, involves only carbon atoms in their main chain, with no hydrolyzable functional group.with no hydrolyzable functional group.

These compounds are degraded by These compounds are degraded by microorganisms such as fungi up until the alkane microorganisms such as fungi up until the alkane molecular weight reaches 500. For larger alkanes, molecular weight reaches 500. For larger alkanes, biodegradation becomes effectively zero.biodegradation becomes effectively zero.

Chain branching inhibits biodegradation (a Chain branching inhibits biodegradation (a phenomenon observed with surfactants).phenomenon observed with surfactants).


Influence of chain length and extent of branching of Influence of chain length and extent of branching of alkanes on biodegradation by fungi mixturealkanes on biodegradation by fungi mixture

COMPOUNDCOMPOUNDMOLECULAR MOLECULAR

WEIGHTWEIGHT

RELATIVE RELATIVE BIODEGRADABILITY BIODEGRADABILITY

(0=poor, 4=good)(0=poor, 4=good)

Hexadecane (CHexadecane (C1616 HH3434 )) 226226 44

OctadecaneOctadecane (C(C1818 HH3838 )) 255255 44

HexatriacontaneHexatriacontane (C(C3636 HH7474 )) 507507 00

TetracontaneTetracontane (C(C4040 HH8282 )) 563563 00

2,6,112,6,11--Trimethyldocane Trimethyldocane (C(C1515 HH3232 ))aa 212212 00

a Branched chain


Materials with low molecular weights with a Materials with low molecular weights with a higher proportion of chain 535 carbons and higher proportion of chain 535 carbons and less branching would be susceptible to less branching would be susceptible to biodegradation.biodegradation.

Most biodegradable plastics are technically Most biodegradable plastics are technically unsuitable for uses such as packaging and unsuitable for uses such as packaging and thus cannot be readily substituted for the thus cannot be readily substituted for the less biodegradable substances. less biodegradable substances.


Solution?Biodegradation capacity can be improved Biodegradation capacity can be improved by:by:

Mixing with natural biodegradable Mixing with natural biodegradable substances such as starch and proteins substances such as starch and proteins e.g. conversion of cellulose into e.g. conversion of cellulose into cellulose nitrate and cellulose acetate;cellulose nitrate and cellulose acetate;

Cellulose nitrate has been used for movie films Cellulose nitrate has been used for movie films and old films using this material are often in and old films using this material are often in degraded statedegraded state


Incorporating hydrolyzable functional Incorporating hydrolyzable functional groups such as esters, amides and groups such as esters, amides and urethanes;urethanes;

Ensuring that the main chain is flexible Ensuring that the main chain is flexible and thus able to facilitate binding to and thus able to facilitate binding to active sites of enzyme.active sites of enzyme.

Solution?


Compostable Plastic

A plastic that undergoes degradation by biological processes during composting to yield CO2 , H2 O, inorganic compounds and biomass at a rate consistent with other known compostable materials (cellulose) and leaves no visually distinguishable or toxic residues.


Composting is an effort of developing biodegradable plastics for waste management and agricultural application.

Bio Degradation of Plastics

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