Short communicationDegradation of unpretreated and thermally pretreated polypropylene by soil consortia
Introduction
The consumption of plastics in the year 2006 in India was around 4545 KT, and out of this polypropylene (PP) accounted for 1200 KT. The consumption of thermoplastics was 40 million tonnes in European countries (Plastemart.com website, 2004). These figures give the scenario of the alarming rate at which plastic will be dumped in the environment after its useful life. Natural weathering, which includes solar radiation, UV rays and ambient temperature, affect the properties of the polymer to some extent, but generally these changes take place at a slow rate (Suits and Hsuan, 2003). Biodegradation is the result of the utilisation of the polymer as a carbon source by the microorganism. This process is facilitated if the microorganism initially forms a biofilm over the polymer surface (Hadad et al., 2005). In the case of polymers such as PP, a continuous chain of repetitive methylene units makes it resistant to degradation. The hydrophobic nature of PP hinders the attachment of microorganism on its surface.
Physical treatments which include UV, thermal and chemical lead to oxidation of the polymer surface. This in turn leads to the formation of carbonyl, carboxyl and ester functional groups (Iring and Tudos, 1990, Graeme and Mathew, 2000) and also decreases the hydrophobicity of the surface (Sudhakar et al., 2008) that ultimately helps in the formation of microbial biofilm on its surface (Gilan et al., 2004). Thus treatments leading to oxidation of the polymer can be effectively used as a pretreatment strategy before subjecting it to biodegradation. It is reported that there is a synergistic effect between photo-oxidation and biodegradation of polyethylene (Albertsson et al., 1987). An increase in the biodegradation of polyethylene was observed with increase in the time of exposure to UV (Hadad et al., 2005). Reports on biodegradation of PP are very scarce, although considerable literature addresses the biodegradation of low and high density polyethylenes (Arutchelvi et al., 2008). Fungal species (Aspergillus niger) and microbial communities such as Pseudomonas and Vibrio species have been reported to biodegrade PP (Cacciari et al., 1993). Isotactic polypropylene exposed to bacterial consortia for 175 days had 40% methylene chloride extractable compounds, and this extract was identified to be a mixture of hydrocarbons (between C10H22 and C31H64) (Cacciari et al., 1993). Thirty to sixty percent growth of A. niger was observed on gamma irradiated PP films at the end of 6 weeks, which indicated that the fungus was able to utilise this polymer as its sole carbon source (Alariqi et al., 2006).
In this paper, the in vitro biodegradation of unpretreated (PP-UT) and thermally pretreated polypropylene (PP-TT) films by mixed soil culture from a local plastic dumping site is reported. Here the polymer is supplied to the organism as the sole carbon source. The changes in its physical, chemical and mechanical properties at different time intervals were monitored. A pure culture, isolated at the end of 12-months of experiment was characterised using biochemical tests and the nucleotide sequence of the conserved region was determined from 16S rRNA.
Section snippets
Polypropylene
Commercial PP films (Reliance Industries Ltd., Mumbai, India) of size 8 × 2.5 cm and 0.05 mm thickness were used for the present experiments. The films were thermally pretreated at 80 °C for 10 days in a hot air oven (Sigma instruments, Chennai, India) (Achimsky et al., 1997). Unpretreated films of the same size and thickness were subjected to similar study to determine the effect of thermal pretreatment on the process. These polypropylene films had additives such as Irganox 1010, Irgafos 126,
Biodegradation of PP subjected to mixed culture
The formation of a biofilm on the polymer surface is the first crucial step prior to the onset of biodegradation. Since the biodegradation proceeds at a slow rate, the biofilm on the surface should remain active having live microorganisms for a long period of time. After 12 months of treatment with mixed culture, both live and dead organisms were observed on the PP surface as shown in Fig. 1. More live organisms were observed on PP-TT surface when compared to that on the PP-UT surface.
The
Acknowledgements
The author thanks Mr. Tej Pandit (Polymer Research Center, Reliance Industry, Mumbai) for DSC analysis and Miss. Shridevi (Sophisticated Analytical Instruments Facility, IIT Madras, Chennai) for FTIR analysis.
References (34)
- et al.
On a trasition at 80 °C in polypropylene oxidation kinetics
Polymer Degradation and Stability
(1997) - et al.
Biodegradation of γ-sterilised biomedical polyolefins under composting and fungal culture environments
Polymer Degradation and Stability
(2006) - et al.
The mechanism of biodegradation of polyethylene
Polymer Degradation and Stability
(1987) - et al.
Degradation product pattern and morphology changes as means to differentiate abiotically and biotically aged degradable polyethylene
Polymer
(1995) - et al.
The influence of biotic and abiotic environments on degradation of polyethylene
Progress in Polymer Science
(1990) - et al.
LIVE/DEAD BacLight: application of a new rapid staining method for direct enumeration of viable and total bacteria in drinking water
Journal of Microbiological Methods
(1999) - et al.
Biodegradation of thermally oxidized, fragmented low density polyethylene
Polymer Degradation and Stability
(2003) - et al.
The mechanism of the low-temperature oxidation of polypropylene
Polymer Degradation and Stability
(1993) - et al.
Weight loss mechanism in the photooxidation of polypropylene
Polymer Degradation and Stability
(1996) Microbial colonization of polymeric materials for space applications and mechanism of biodeterioration: a review
International Biodeterioration & Biodegradation
(2007)
Effect of imaging technique on the observed surface morphology of oxygen plasma etched polyethylene fibres
Polymer Degradation and Stability
Thermal oxidation of polyethylene and polypropylene: effects of chemical structure and reaction condition on oxidation process
Progress in Polymer Science
Fourier transform infra-red study of polypropylene
Polymer
Thermal behaviour of polypropylene fractions: 1
Influence of tacticity and molecular weight on crystallization and melting behaviour Polymer
Marine microbe mediated biodegradation of low and high density polyethylenes
International Biodeterioration & Biodegradation
Biofouling and biodegradation of polyolefins in ocean waters
Polymer Degradation and Stability
Assessing the photo-degradation of geosynthetics by outdoor exposure and laboratory weatherometer
Geotextiles and Geomembranes
Cited by (162)
Bacterial screening in Indian coastal regions for efficient polypropylene microplastics biodegradation
2024, Science of the Total EnvironmentEffect of landfilling time on physico-chemical properties of combustible fractions in excavated waste
2024, Science of the Total EnvironmentPlastic pollution from takeaway food industry in China
2023, Science of the Total EnvironmentFacemasks: An insight into their abundance in wetlands, degradation, and potential ecotoxicity
2023, Science of the Total EnvironmentImpacts and mechanism of biodegradable microplastics on lake sediment properties, bacterial dynamics, and greenhouse gasses emissions
2023, Science of the Total Environment