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Environmental Degradation of Polyolefin's
Ambika Arkatkar and Mukesh Doble, Department of Biotechnology,
Indian Institute of Technology Madras,
Chennai-600036, India
Email: mukeshd@iitm.ac.in

In India according to future flow analysis the total virgin plastics consumption is expected to reach 20,000 KT by the year of 2030 and over 18, 800 KT of waste can be generated. The consumption of thermoplastics was 40 million tones in European countries (Plastemart.com website, 2004 & 2006). Polyolefins like Polypropylene (PP), Low density polyethylene (LDPE) & High density polyethylene (HDPE) account for about 60% of the total plastics consumption in India. Dumping of plastic in the environment at such a large amount is causing already serious problems to the flora and fauna. The conventional method like incineration is a source of secondary hazardous product. This plastic waste degrades the environmental conditions at a very slow rate. The low rate of biodegradation of plastics is usually due to properties of the polymeric material like lack of water solubility (Hydrophobicity) and size of the polymer molecules (long chains and high molecular weight which prevents the breakdown of the polymeric bond) that microbial cell are unable to transport directly in their cells.

Literature review

Biodegradation ultimately results in the consumption of polymer by the microorganism. The growth activity study of the microbes like fungi (Aspergillus niger, A.flavus, A.oryzae, Chaetomium globusum, Penicillium funiculosum, Pullularia pullulan), bacteria (Pseudomonas aeruginosa,Pseudomonas sp., Bacillus cereus,Bacillus sp., Coryneformes bacterium, Mycobacterium, Nocardia, Corynebacterium and Candida) and Actinomycetales (Streptomycetaceae) on the agar plate for a definitetime period revealed the capability of these microbes to degrade. Polyethylene (PE). There are scare reports on PP biodegradation. Fungal species (A. niger) and microbial communities such as Pseudomonas and Vibrio species have been reported to biodegrade PP. Isotactic PP exposed to a bacterial consortium for 175 days had 40% methylene chloride extractable compounds, which was mixture of hydrocarbons (between C10H22 to C31H64). 30-60 % growth of A. niger was observed on gamma irradiated PP films in six weeks, indicating that the fungus is able to grow taking this polymer as its sole carbon source. The continuous chain of repetitive methylene units makes PP resistant to degradation.

How to address the problem?

For achieving the task of biodegradation it is a prerequisite that the polymer surface is modified to some extent. Pretreatment and blending PE with natural polymer can modify the surface.


Under environmental conditions natural weathering, which includes solar radiation, UV and thermal, is a process that affects polymeric properties to some extent but at a slower rate. It is reported that there is a synergistic effect between photo oxidation and the biodegradation of polyethylene. Treatments such as UV, thermal and chemical leading to oxidation of the polymer surface
can be effectively used as a pretreatment strategy before subjecting it to biodegradation. These pretreatments lead to oxidation of the polymer surface that decreases the hydrophobicity and helps in the attachment of microorganism. The attachment of organism to the polymeric surface further enhances the biofilms formation. Microbes utilize the functional groups like carbonyl, carboxyl and ester produced on the polymer surface during oxidation. Such studies are done with polyethylene and have shown positive results in the form of increase in the biodegradation with increase in the irradiation time of UV.


Natural polymers like Poly lactic acid (PLA), Poly -caprolactone (PCL) and Polysaccharides can be blended to some extent with the synthetic polymer. In these blends the natural polymer being biodegradable will help in the formation of biofilm on the surface.

Current research in our laboratory

We are studying the effect of various physical and chemical pretreatment on the biodegradation of LDPE, HDPE, starch blended PE and PP. Soil and marine microorganisms have been isolated and are being tested for their efficacy in carrying out the biodegradation of these polymers. Several different pretreatment strategies such as UV, thermal, chemical are being tested to enhance the process. The pretreated PP is then exposed to mixed soil culture. The mixed soil culture is a suspension of soil sample from a local dumping site. The experiments are carried out in a minimal media. From our one year experiments with thermally pretreated PP and mixed soil culture we found good results. As already reported pretreatment of the polymer surface works in synergy with microbial attachment to enhance biodegradation. After one year microorganism isolated from the mixed culture are found to be Bacillus and Pseudomonas sp.

The polymer samples are monitored by techniques like Baclight staining, Fourier transform infrared (FTIR) spectroscopy, Differential scanning calorimetry (DSC), Scanning electron microscopy (SEM), Contact angle and Tensile strength etc. Baclight staining helps us to observe live and dead microorganisms on the polymer surface. SEM and Contact angle measurements helps in studying surface changes on the polymer whereas FTIR and DSC techniques analyse the chemical and structural changes in the polymer.

1.The SEM analysis of the PP surface after 12 months

2.The Baclight staining of PP surface after 12 months (Live organism- green and dead organism- red in colour)

Further reading:

Arutchelvi, J., Sudhakar, M., Ambika Arkatkar, Mukesh Doble, Sumit Bhaduri and Parasu Veera Uppara (2008). Biodegradation of polyethylene and polypropylene. Indian Journal of Biotechnology. 7, 9-22.

Trishul Artham and Mukesh Doble. (2007). Biodegradation of Aliphatic and Aromatic Polycarbonates. Macromolecular Bioscience. doi 10.1002/mabi.200700106 (Press).

Sudhakar, M., Mukesh Doble, Sriyutha Murthy, P., and Venkatesan, R. (2007). Marine Microbe Mediated Biodegradation of Low and High Density Polyethylene . International Biodegardat ion and Biodeterioration. doi:10.1016/j.ibiod.2007.07.011 (in press).

Sudhakar, M., Trishul, A., Mukesh Doble, Suresh Kumar, K., Syed Jahan, S., Inbakandan, Viduthalai, R., Umadevi, P., Sriyutha Murthy, P. and Venkatesan, R. (2007). Biofouling and biodegradation of polyolefins in ocean waters. Polymer Degradation and Stability. 92, 1743-1752.

Sudhakar, M., Priyadarshini, Mukesh Doble, Sriyutha Murthy, P., and Venkatesan, R. (2007). Marine Bacteria Mediated Degradation of nylon 66 and 6. International Biodeterioration and Biodegradation. 60, 144-151.

For more details contact:

Dr. Mukesh Doble, Ph. D.
Lab : Bioengineering & Drug Design
Professor, Department of Biotechnology
IIT Madras, Chennai - 600036, INDIA
(Tel:044-2257 4107; Fax:044-2257 4102)
Email: mukeshd@iitm.ac.in,
Website: http://www.biotech.iitm.ac.in/faculty/md.htm

ENVIS CENTRE Newsletter Vol.6, No 2 June 2008 Back 
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