Controlled functionalisation of PE in molten state using ozone at the gas-fluid interface.

• Controlling functionalisation of molten low density polyethylene (LDPE) using ozone was achieved. • Oxygen-containing groups were generated into ozonized PE (OPE) to improve hydrophilicity of OPE. • A slight degradation of OPE occurred at mild condition (below 220 within 2 h). • Cross-linking structure was formed after further ozonation (beyond 240 ℃ over 4 h). • The crystallinity of OPE decreased while thermal stability of OPE enhanced due to cross-linking structure. 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 ° of pristine PE to 85.4 ° 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 ℃ within 2 h) while the cross-linking structure was primarily generated after further oxidation (beyond 240 ℃ 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. [Display omitted] [ABSTRACT FROM AUTHOR]