Controlled Functionalisation of PE in Molten State Using Ozone at the Gas-Fluid Interface

High-value recycling petroleum-based polyethylene (PE) can effectively reduce carbon emissions and promote a circular economy. This study proposed a new method for functionalisation of low density polyethylene (LDPE) matrix at gas-liquid interface. The controlled functionalisation of LDPE at molten state was successfully achieved using ozone by altering reaction parameters. After ozone treatment, functionalised groups such as ketone (C=O), ether (C-O-C) and carboxyl groups (-COOH) were generated in ozonized PE (OPE) confirmed by FTIR and XPS. The contact angle with water dropped from 99 degrees of pristine PE to 85.4 degrees of OPE, which demonstrated that the hydrophilicity of OPE was improved significantly. The degree of ozonation was sensitive to temperature. A slight degradation of PE predominantly occurred under the mild condition (below 220 degrees C within 2 h) while the cross-linking structure was primarily generated after further oxidation (beyond 240 degrees C over 4 h), which revealed that functionalisation of OPE could be controllably achieved. Due to the formation of cross-linking structure, the crystallinity of OPE decreased from 33.8 % to 11.0 %. Meanwhile, the residue weight of OPE had a slight increase while its activation energy of thermal degradation reduced. Therefore, the functionalisation of PE using ozone is a promising technical and environmental-friendly approach to upcycle PE in the future.