Bacterial Degradation Of

PlasticByShivam SainiShirin Akhtar

Saksham SaxenaDr. Gajendra B. Singh

Department of Biotechnology

National conference on “Bio resources as a key to value added

products”

What is Plastic ?

Plastic are typically organic polymers of high molecular

mass, but they often contain other substances.

They are usually synthetic, most commonly derived from

petrochemical but many are partially natural.

The first fully synthetic plastic was Bakelite ,invented in New

York in 1907 by Leo Baekeland.

•POLYETHYLENE TEREPTHALATE (PET) : Carbonate drinks, bottles, peanut butter jars, plastic film, microwavable packaging.

•POLYETHYLENE (PE) : Wide range of inexpensive uses including supermarket bags, plastic bottles.

•POLYLVINYL CHLORIDE (PVC) : Plumbing pipes and guttering, shower curtains, window frames, flooring.

•LOW DENSITY POLYETHYLENE (LDPE) : Outdoor furniture, siding, floor tiles, shower curtains, clamshell packaging.

•POLYCARBONATE (PC) : Compact Disk, Eye Glasses, riot shield, security windows, traffic light, lenses.

Types of Plastic

World Plastic Production

Polyethylene terephthalate

Polyethylene terephthalate, commonly abbreviated PET, is the most common thermoplastic polymer resin of the polyester family.

It is used in fibers for clothing, containers for liquids and foods. The majority of the world's PET production is for synthetic fibers (in

excess of 60%), with bottle production accounting for about 30% of global demand in the context of textile applications.

PET is referred to by its common name, polyester, whereas the acronym PET is generally used in relation to packaging.

Polyester makes up about 18% of world polymer production and is the fourth-most produced polymer; polyethylene (PE), polypropylene (PP) and polyvinyl chloride (PVC) are first, second and third, respectively.

PET consists of polymerized units of the monomer ethylene terephthalate, with repeating (C10H8O4) units.

PET was patented in 1941 by John Rex Whinfield, James Tennant Dickson and their employer the Calico Printers' Association of Manchester, England. E. I. DuPont de Nemoursin Delaware, USA, first used the trademark Mylar in June 1951 and received registration of it in 1952. It is still the best-known name used for polyester film. The current owner of the trademark is DuPont Teijin Films US, a partnership with a Japanese companyThe PET bottle was patented in 1973 by Nathaniel Wyeth.

History

Uses of PET Because PET is an excellent water and moisture barrier material,

plastic bottles made from PET are widely used for soft drinks. For certain specialty bottles, such as those designated for beer

containment PET sandwiches an additional polyvinyl alcohol (PVOH) layer to

further reduce its oxygen permeability. PET is also used as a substrate in thin film solar cells. Terylene is also spliced into bell rope tops to help prevent wear

on the ropes as they pass through the ceiling.

Physical Properties

PET in its natural state is a colorless, semi-crystalline resin. Based on how it is processed, PET can be semi-rigid to rigid, and it is very lightweight. It makes a good gas and fair moisture barrier, as well as a good barrier to alcohol and solvents. It is strong and impact-resistant. PET becomes white when exposed to chloroform and also certain other chemicals such as toluene.

Production

Polyethylene terephthalate is produced from ethylene glycol and dimethyl terephthalate (C6H4(CO2CH3)2) or terephthalic acid.The former is a transesterification reaction, whereas the latter is an esterification reaction.

DegradationPET is subjected to various types of degradations during processing. The main degradations that can occur are hydrolytic, and probably most important, thermal oxidation. When PET degrades, several things happen: discoloration, chain scissions resulting in reduced molecular weight, formation of acetaldehyde, and cross-links ("gel" or "fish-eye" formation). Discoloration is due to the formation of various chromophoric systems following prolonged thermal treatment at elevated temperatures. This becomes a problem when the optical requirements of the polymer are very high, such as in packaging applications. The thermal and thermo oxidative degradation results in poor processibility characteristics and performance of the material.

Biodegradation

Ideonella sakaiensis is a bacterium from the genus Ideonella and family Comamonadaceae capable of breaking down PET plastic which was isolated from outside a plastic bottle recycling facility.

Discovery of Bacteria

Ideonella sakaiensis was identified in 2016 by a team of researchers from Kyoto Institute of Technology and Keio University, after collecting samples of PET debris in a search for bacteria which relied on the plastic for carbon growth. The bacterium was observed to utilize two distinct enzymes that reacted with water to break down PET plastics into terephthalic acid and ethylene glycol, substances which on their own pose no threat to the environment.

Mechanism of PETase and MHETase

c =o-o

ocH2-cH2-o-c =

n

c-o=

oo-c =

H+ OH-

H+ OH-

CH2-CH2-O

PETPETase

MHET

MHETase

Ethylene glycol Terephthalic acid

Impact

The discovery of Ideonella sakaiensis has potential importance for the recycling process of PET plastics. Prior to discovery of the bacterium, the only known consumers of PET were a small number of fungi including Pestalotiopsis microspora, and knowledge of the new species has spurred discussion about biodegradation as a method of recycling. The bacterium can currently break down a thin film of PET in a little over six weeks, so it is thought that any prospective applications in mass recycling programs will have to be preceded by enhancement of its abilities through genetic modification.

Conclusion

Compare with chemical Process PET degradation using microorganisms and enzymes consumes less energy and environmentally friendly option. We believe that the present research results bring us closer to achieving an ideal model for PET recycling, so long as we are able to enhance the activity level and stability of these newly discovered microbial enzymes.

Reference Yoshida, S., Hiraga, K., Talehana, T., Taniguchi, I., Yamaji, H., Maeda, Y., Toyohara, K., Miyamoto, K., Kimura, Y., Oda, K. (2016) “A bacterium that degrades and assimilates poly(ethylene terephthalate)”, Science, Vol. 351:6278, 1196-1199.

The new plastic economy : Rethinking the future of plastic (World economic Forum) : January 2016

Tokiwa, Y., Calabia, B.P., Ugwu, C.U., Aiba, S. (2009) “Biodegradability of Plastics”, International Journal of molecular Sciences, Vol. 10, 3722-3742.

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