Comparison of biodegradability of various polypropylene films containing pro-oxidant additives based on Mn, Mn/Fe or Co

The biodegradability of two polypropylene films with low content of ethylene (a statistical copolymer (PPs) and a block copolymer (PPb) with balanced additions of phenolic antioxidant and pro-oxidants based on Mn, Mn/Fe or Co was studied. Abiotic pre-treatments by accelerated artificial photooxidation and thermooxidation representing about 3-4 years of outdoor weathering, including 3-4 months of exposure to daylight and 3 years in soil were followed by FTIR and SEC measurements. When a controlled oxidation was reached in the films, they were inoculated, in a second step, with the strain Rhodococcus rhodochrous in mineral medium and incubated up to 180 days. The metabolic activity of bacteria was evaluated by measuring ATP content, ADP/ATP ratio and cell viability. Complementary 1H NMR experiments were conducted on the incubation media, with and without cells, in order to monitor the consumption of soluble compounds excreted from the oxidized polymers by R. rhodochrous cells. The main conclusions are that the Co derivatives (with Co content ≥ 150 ppm) must be considered toxic for R. rhodochrous. PP films containing pro-oxidants based on Mn and Mn + Fe give positive results for the biotest (low ADP/ATP ratio, post-development in Petri dishes). However the biodegradability of oxidized PP films is less efficient in comparison to oxidized PE films (see paper published in this journal). This observation may be correlated with the accumulation in the incubation media of oxidized oligomers that cannot be metabolized rapidly by the bacterial cells and/or by the residual crystallinity of PP derivatives.