Plastic Degradation and Microbial Degradation of Polyethylene Terephthalate (PET)

Law, Jing Jhi (2021) Plastic Degradation and Microbial Degradation of Polyethylene Terephthalate (PET). Final Year Project (Bachelor), Tunku Abdul Rahman University College.

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Abstract

Globally, plastics are produced in hundreds of million tonnes yearly, many are single-use items. Plastic pollution has become one of the most pressing environmental and ecosystem crises. Plastic products are high molecular weight macromolecules with repeating units mainly made of hydrocarbon and various elements. Currently, plastics are classified into seven resin types. They are durable and resistant yet the polymer diversity and versatility of properties create the tremendous waste management challenges. Polyethylene Terephthalate (PET) is a general-purpose thermoplastic polymer which belongs to the polyester family of polymers widely used in packaging, textile, electrical and electronic industries because of the thermal, chemical, and mechanical strength. PET is known to be recalcitrant because of the inertness, there is still continual effort to screen for PET-degrading bacteria to reduce its impact. Broadly, there are two main mechanisms of plastic degradation: physical and biological. The abiotic methods have higher degradation rates compared with the biotic method because commonly abiotic processes are easier to manipulate to achieve optimal conditions to degrade plastic polymers. UV radiation, chemical, hydrolytic, mechanical, thermal degradation considered as abiotic degradation. On the other hand, biotic mechanisms include microbial and enzymatic degradation. Microbial degradation studies usually involve survey and isolation of potential microbes with conventional, culture-dependent procedures. This project aims to give a brief overview of the biotic and abiotic degradability of plastics with emphasis of PET as well as the current literature on PET- degrading microorganisms and enzymes. Although many reports are available, significant degradation of plastics (and PET in particular) water has yet to achieve in real scales due to limitations in the complete understanding of the degradation mechanisms and the complex interactions of various factors. The rate of plastic biodegradation process is influenced by the chemical structure, structural phase, molecular weight, environment factors, and chemical compounds which trigger microorganisms to carry out degradation toward the plastic polymers. The preliminary results of simulated soil burial experiments did not show detectable weight loss in the PET pieces and no observable appearance changes were found. However, PET pieces immersed in lake water showed cloudy surfaces and approximately 2% weight reduction which would be useful subjects to pursue if physical and/chemical analysis can be done with SEM or FTIR.