Synergistic effects of pretreatment and blending on fungi mediated biodegradation of polypropylenes

Highlights

• Phanerochaete chrysosporium NCIM 1170 (F1) and Engyodontium album MTP091 (F2) were tested.

• Starch blended (ST-PP) and metal ions blended polypropylene (MI-PP) are used.

• About 18.8% and 9.42% gravimetric weight loss were observed.

• About 79% and 57% TGA weight loss (at 400 °C) were observed.

• Extractable low-molecular weight hydrocarbons are high in UV treated MI-PP.

Abstract

Environmental issues raise concern on restrict the use of nondegradable polymers and encourage the development of degradable once. This study is carried out was to understand the rate of biodegradation of untreated and pretreated (100 °C or UV for 10 days) polypropylene (PP), pro-oxidant blended (MI-PP) and starch blended polypropylenes (ST-PP) with two different fungal strains, Phanerochaete chrysosporium NCIM 1170 (F1) and Engyodontium album MTP091 (F2). About 18.8% and 9.42% gravimetric weight loss and 79% and 57% TGA weight loss (at 400 °C) were observed with UV pretreated MI-PP in 1 year with F2 and F1 strains respectively. The amount of lacasse produced by the organism and biomass attached on the polymer surface are correlated with TGA weight loss (0.6–0.93). The formation of extractable oxygenated compounds and unoxidized low-molecular weight hydrocarbons are high in pretreated and blended samples. These results indicate blending and pretreatment strategy leads to an optimal waste-disposal strategy.

Introduction

Polyolefins have found widespread applications due to their physico-chemical properties and their recalcitrant nature. They represent 20–30% of the total polymer sales in United States and Canada in the year 2004 (Trishul and Doble, 2010). So it could be concluded that more than 50% of plastic waste in the environment could be polyolefins (Sivan et al., 2006). Degradation of polyolefins in nature is a very slow process leading to their accumulation in the environment at the rate of 25 million tons per year (Orhan and Buyukgungor, 2000). Formation of biofilm or attachment of microorganism on polypropylene is very poor because of its this hydrophobic nature (Singhania et al., 2012).

Several approaches for solving the pollution problem caused by polyolefins are developed in the past 20 years. These included blending with biopolymers, biodegradable polymers, or additives including starch and metal ions etc. (Jeyakumar et al., 2012, Arutchelvi et al., 2008, Williams and Bagri, 2003, Sebaa et al., 1993). There is a great interest in incorporating starch into conventional plastics because it is environmentally friendly (Lima and Estudo, 2005). Polyolefins that has been oxidized by metal ions are more susceptible to microbial degradation than the virgin ones since the former are more hydrophilic than the latter and also due to the formation presence of low-molecular weight degraded fragments (Sebaa et al., 1993). The rate of degradation of polyolefin can also be enhanced by pre-treatment which includes thermal treatment (TT) or ultraviolet radiation (UV) (Jeyakumar et al., 2012). These pre-treatments generate free radicals, which can oxidize the polymer resulting in the breakage of the chain. Oxidation leads to the formation of carbonyl, carboxyl and ester functional groups (Graeme and Mathew, 2000) and also decreases the hydrophobicity of the surface (Sudhakar et al., 2008) which helps in the formation of microbial biofilm. In earlier study synergistic interaction of pre-treatment strategy and blending such as starch and metal ions on the stability of High-Density Polyethylene has been reported (Jeyakumar et al., 2012). This study reports the synergistic interaction of blending with pretreatment on the biodegradation of PP by two fungi.

Fungi are potential organisms for biodegradation since they have a rich source of degrading enzymes and have the ability to survive in harsh environments under low nutrient and moisture conditions. They have the ability to extend and penetrate into cracks and crevices through the distribution of hyphae (Trishul and Doble, 2010). Use of Aspergillus niger for the degradation of PP has been reported (Cacciari et al., 1993). Biodegrdation of pretreated polycarbonate using two fungi namely, Engyodontium album and Penicillium spp. isolated from a plastic dump site along with a commercial white rot fungus, Phanerochaete chrysosporium NCIM 1170 has been reported (Trishul and Doble, 2010). The biodegradation of bisphenol A, a monomer of PC, by fungi has also been reported (Kang et al., 2006). In the earlier studies the synergistic effects UV and TT on the degradation of pretreated polypropylene has been reported with soil consortia (Ambika et al., 2009). The effects of environments such as soil, ocean and direct sunlight on the biodegradation of starch and catalyst blended HDPE and PP have been reported (Muthukumar et al., 2011). The biodegradation of starch and metal ions blended polypropylene by fugal sp is reported here. UV and thermally pretreated and unpretreated samples were exposed to P. chrysosporium (F1) NCIM 1170 and E. album (F2) MTP09 for one year.