Abstract
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.
Highlights
Plastic production has been in continuous growth since their discovery
Bioinert low density polyethylene (LDPE) has been efficiently converted to bio-amenable LDPE using an energy favourable, and industrially scalable, fast high throughput reactive extrusion (REX) assisted oxidation process
In comparison to virgin LDPE, ready biofilm formation was demonstrated for REX pretreated LDPE
Summary
The global plastic production has reached 368 million tons giving direct employment to more than 1.56 million people in Europe [1]. Their remarkable properties and high performances at low market prices mean that plastic materials are common-place across the globe. An important example of such consumption is plastic bags which is estimated to be in the range of 500 billion to 1 trillion plastic bags each year worldwide [2] Most of these plastic bags are made from low density polyethylene (LDPE); a polymer widely used in food packaging and agriculture applications. LDPE constitutes a major environmental pollutant with reported threats to wildlife such as blockages in the intestines of different marine animals and birds [3,4]
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