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-min duration pre-treatment 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 pre-treatment 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 fivefold molecular weight reductions were also demonstrated using gel permeation chromatography. Optimum LDPE pre-treatment with a duration of 5 min was obtained at low screw speed (50 rpm), operating temperature of 380–390 °C and variable concentration of SiO₂ (0 and 2% (w/w)) indicating that effective pre-treatment can occur under noncatalytic and catalysed conditions. Biofilms were successfully formed on pre-treated LDPE samples after 14 days of incubation. Furthermore, the technique proposed in this study is expected to provide a high throughput approach for pre-treatment of pervasive recalcitrant PE-based plastics to reduce their bio inertness.