Ozone-based in-situ reactive extrusion for rapid functionalisation and degradation of low density polyethylene

Improving the hydrophilicity of low density polyethylene (LDPE) expends its use in blends. LDPE melt was rapidly functionalised and degraded by ozone in twin-screw extruder by varying extrusion times from one to seven and temperatures from 160 degrees C to 240 degrees C. Abundant oxygen-containing groups, such as carbonyl group (C--O) at 1718 cm-1, hydroxyl group (-OH) at 3400 cm-1 and aldehyde group (-CHO) at 1740 cm-1, were generated into ozone treated PE, resulting in improved hydrophilicity. At 200 degrees C, ozone treated PE exhibited a high melt flow index (21.5 g/10 min) and low complex viscosity modulus due to molecular degradation. Nevertheless, cross-linking occurred at a higher temperature of 240 degrees C. A higher crystal peak temperature of ozone treated PE at 200 degrees C was attributed to the introduction of oxygen atoms. The poor thermal stability of ozone treated PE was evidenced by a lower initial decomposition temperature. The oxidation induction time of ozone treated PE at 200 degrees C declined from 32 min for one extrusion to 12 min for seven extrusions demonstrating a vulnerability of ageing. Increasing the extrusion times gradually enhanced the tensile modulus of the ozone treated PE at 200 degrees C, while raising the treatment temperature had no effect on the tensile properties. Rapid functionalisation and degradation of LDPE were successfully achieved using ozone in reactive extrusion, thus broadening the applications of ozone treated PE in composites.