Polyethylene microbial degradation

Tansengo, M. L. Tokiwa, Y. (1998). Thermophilic microbial degradation of polyethylene succinate. World Journal of Microbiology and Biotechnology, 14, 133-8. 

Tokiwa, Y. Suzuki, T. (1977). Microbial-degradation of poly esters 3. Purification and some properties of polyethylene adipate-degrading enzyme produced by Penicillium sp strain 14-3. Agricultural and Biological Chemistry, 41, 265-74. 

An example of the first approach was given in Ref. [2]. The AWPA (the American Wood-Preservers Association) Soil Block test method has been employed. Samples were polyethylene-wood composite materials with wood content ranging from 50 to 70% (w/w). Weight losses as a result of microbial degradation were up to 18% when treated for 16 weeks with white-rot organism, Trametes versicolor, and up to 7% when treated for 12 weeks with brown-rot organism, Gloeophyllum trabeum. 

Some synthetic polymers like, polyurethanes, specifically polyether-polyurethanes, are likely to be degraded by microbes but not completely. However, several polymers such as, polyamides, polyfluorocarbons, polyethylene, polypropylene, and polycarbonate are highly resistant to microbial degradation. Natural polymers are generally more biodegradable than synthetic polymers specifically, polymers with ester groups like aliphatic polyesters [1]. Therefore, several natural polymers such as cellulose, starch, blends of those with synthetic polymers, polylactate, polyester-amide, and polyhydroxyalkanoates (PHAs) have been the focus of attention in the recent years [3]. 

Restrepo-Fldrez J, Bassi A, Thompson MR. Microbial degradation and deterioration of polyethylene—a review. Int Biodeterior Biodegrad 2014 88 83-90. 

Haines J R, Alexander M (1975), Microbial degradation of polyethylene glycols , Appl Microbiol, 29, 621-625. 

Anaerobic microbes in the presence of water in the landfill will consume these natural products and produce methane, CO2 and humus. One study reported the average composition of 20 year old refuse to be 33 % paper, 22% ash and 12% wood [18]. Thirty core samples revealed a wide range of degradation and microbial activity that were directly attributed to sample moisture content. Recovered polyethylene degradation was evaluated and determined to be as high as 54 %. 

Polyurethanes in particular appear to be susceptible to microbial attack, though polyether polyurethanes (see Chapter 4) are more resistant to biological degradation than are polyester polyurethanes. The precise mechanisms of these degradations are not fully understood. Polyethylene,... 

Low molecular weight dicarboxylic acids, keto acids and hydroxy acids have been shown to form as photooxidation products of polyethylene and polypropylene. These are almost certainly formed by intramolecular reactions of alkylperoxyl and peracyl radicals shown typically in Scheme 3.7. Back-biting along the aliphatic chain gives rise to unstable hydroperoxides and the elimination of small molecular fragments. It will be seen in Chapter 5 that these low molar mass oxidation products, which are already present in the environment from natural sources, are the first point of microbial attack in the surface of environmentally degraded polymers, leading to oxidation initiated bioerosion (Chapter 5). 

I. Jakubowicz, N. Yarahmadi, V. Arthurson, Kinetics of abiotic and biotic degradability of low-density polyethylene containing prodegradant additives and its effect on the growth of microbial communities. Polym. Degrad. Stab. 96, 919 (2011)... 

Crystalline starch beads can be used as a natural filler in traditional plastics [3]. They have been particularly used in polyolefins. When blended with starch beads, polyethylene films biodeteriorate upon exposure to a soil environment. The microbial consumption of the starch component leads to increased porosity, void formation, and loss of integrity of the plastic matrix. Generally, starch is added at fairly low concentrations (6-15 wt%). The total disintegration of these materials is obtained using transition metal compounds, soluble in the thermoplastic matrix, used as pro-oxidant additives to catalyze the photo and thermo-oxidative processes [4]. These products belong to the first generation of degradable polymers that biodeteriorate more than mineralize to CO2 and H2O in a time... 

In the past, industrial and academic researchers traditionally focused on developing stable and durable polymeric materials that resisted exposure to natural forces such as heat, sunlight, oxygen (O2), water and microbial attack. The most widespread modern plastics such as polyethylene (PE), polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET) and polyvinyl chloride (PVC) are inexpensive, easily processable, resistant and durable. In fact, most man-made polymers on the market cannot be biologically degraded because their carbon components are not broken down by microbial enzymes. The hydrophobic character of plastics, their low surface area and high molecular weights (MW) are all features which inhibit or decrease enzyme activity and enhance resistance to microbial attack [1]. 

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