Comparative effect of metal stearates as pro-oxidant additives on bacterial biodegradation of thermal- and photo-degraded low density polyethylene mulching films

The effect of Iron, Cobalt and Manganese stearates are examined on the post-bacterial photochemical and thermal degradation of polyethylene (LDPE). The activity of stearates has been evaluated by ATR-FTIR, chemiluminescence and GPC of polyethylenes. A significant increase in carbonyl index for PE containing stearates was determined by FTIR together with a marked decrease in molecular weight as measured by GPC. All three metal stearates induced the development of drastic photo- and thermal-degradation processes for polyethylenes containing metal stearates except in the case of LDPE-Fe film which did not exhibit any significant thermocatalytic effect on degradation. In a second post bacterial study step, a mixture of three Bacillus MIX (Bacillus cereus, Bacillus megaterium and Bacillus subtilis) as well as Brevibacillus borstelensis were tested for biodegradation (90 days at 45 °C) of the highly photo- and thermo-degraded polyethylene films. Biodegraded materials were characterized using different techniques and mineralization was evaluated by carbon dioxide measurement using an indirect impedance technique. The biodegradation of degraded LDPE films by B. borstelensis and the mixture of Bacillus MIX was highly effective following the order LDPE-Co > LDPE-Mn > LDPE-Fe and in the range of 9.0–59.2% of mineralization after only 90 days of bacterial bioassay at 45 °C. The approach studied in this work showed much higher degradable efficacy than that already reported in the literature.