Kinetics of migration of antioxidants from polyolefins in natural environments as a basis for bioconversion studies

Plastics ending up in soil or landfill environment will eventually be degraded. At the same time a slow migration of additives from the plastics will occur. The additives and the degradation products of these and the polymer are potential compounds for bioconversion. To predict the rate of the migration of antioxidants from polyolefins, a medium-density polyethylene film MDPE containing two commercial antioxidants, Irganox 1010 and Irgafos 168, was exposed to simulated landfill environments, viz. aqueous media at pH 5 and 7, with temperatures of 25, 50, 80, and 105 degrees C and solid-to-liquid ratios of 1:5. The migration process of the antioxidants was studied by an ultrasonic extraction technique using chloroform as extraction solvent to recover the nonmigrated antioxidants from the polymeric matrix, followed by quantitative analysis of the extracted antioxidants by high performance liquid chromatography (HPLC) with acetonitrile as the mobile phase and a wavelength of 280 nm. It was found that the release of both Irganox 1010 and Irgafos 168 increases at higher temperature, longer time, and lower pH. Moreover, the migration of Irgafos 168 proceeds faster than that of Irganox 1010 at lower temperatures while at higher temperatures the opposite behavior was observed. No degradation of the polymeric matrix was detected under the testing time. Migration processes included diffusion of the antioxidants within the polymer and their desorption from the surface of the polymer into the boundary layers of leachate. In general, the kinetic of the migration process was well described by first-order equations while an Arrhenius-type relationship was applicable for the temperature dependence of the constants. The general constants calculated for the migration processes were applied to the prediction of the time required for complete release of the antioxidants under different landfill conditions.