Mechanisms of polymer biodegradation

Ikram and co-workers have shown that in normal soils at 25 C, natural rubber (NR) gloves showed 54% loss of thickness after four weeks and 94% mass loss after 48 weeks. On the other hand, nitrile and neoprene rubbers showed insignificant loss in this time and plasticised PVC showed a smaller mass loss (11.6%) due entirely to biodegradation of the plasticiser. Ikram went on to show (see Table 12.1) that the rate of mass loss is strongly dependent upon the nutritional quality of the soil.  

After 24 weeks NR in the high N (lOOmg/1), P (150mg/l) system had lost 61.5% of its mass whereas in the low N (lOmg/1), P (15mg/l) system, only 23.6% mass was lost. Control (unfertilised) soil produced least mass loss (17.3%). Microbial growth measured on the mbber pieces were in decreasing 

The most biodegradable of the commodity polyolefins is polypropylene (PP). Pandey and Singh have recently shown that polypropylene (PP), after removal of antioxidants by solvent extraction, biodegrades much more rapidly than polyethylene by mass loss in compost. PP lost over 60% mass in six months whereas low density polyethylene (LDPE) lost about 10% in the same time. Ethylene-propylene (EP) co-polymers biodegraded at rates intermediate between PP and PE. As expected, prior UV irradiation (photo-oxidation) increased both the rate and extent of the bioassimilation. This is fiilly in accord with the rates of environmental peroxidation of these molecules and it has been shown that PP acts as a sensitiser for the peroxidation of LDPE.  

4 Arrhenius plots for molar mass change (reproduced from Jakubowicz I, Polym. Deg. Stab., 80, 42 (2003) with permission). 

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