Rendering bio-inert low-density polyethylene amenable for biodegradation via fast high throughput reactive extrusion assisted oxidation

An energy efficient high throughput pre-treatment of low density polyethylene (LDPE) using a fast reactive extrusion (REX) assisted oxidation technique followed by bacterial attachment as an indicator for bio-amenability was studied. Silicon dioxide (SiO₂) was selected as a model oxidizing and catalytic reagent with the REX process demonstrated to be effective both in the presence and absence of the catalyst. Optimized 5-minute duration pretreatment conditions were determined using Box-Behnken design (BBD) with respect to screws speed, operating temperature, and concentration of SiO₂. The crystallinity index, carbonyl index and weight loss (%) of LDPE were used as the studied responses for BDD. FTIR and DSC spectra of the residual LDPE obtained after pretreatment with the REX assisted oxidation technique showed a significant increase in residual LDPE carbonyl index from 0 to 1.04 and a decrease of LDPE crystallinity index from 29% to 18%. Up to 5-fold molecular weight reductions were also demonstrated using GPC. Optimum LDPE pretreatment with a duration of 5 minutes was obtained at low screw speed (50 rpm), operating temperature of 380-390⁰C and variable concentration of SiO₂ (0 and 2% (w/w)) indicating that effective pretreatment can occur under noncatalytic and catalysed conditions. Biofilms were successfully formed on pretreated LDPE samples after 14 days of incubation.

Furthermore, the technique proposed in this study is expected to provide a high throughput approach for pretreatment of pervasive recalcitrant PE based plastics to reduce their bio inertness.