Synthesis of two TiO2-based prodegradant additives and their efficiency in inducing the accelerated photo-oxidation of low-density polyethylene

Abstract

In this study, two prodegradant additives derived from TiO2 nanoparticles were synthesized and comprehensively characterized through a range of analytic techniques, such as X-ray diffraction (DRX), Fourier Transform Infrared Spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The hydroxyl groups adsorbed on the surface of TiO2 were esterified with biobased arachidonic acid (AA) and cervonic acid (DHA), resulting in levels of functionalization at 13 % and 16 % w/w, respectively. These additives were incorporated into low-density polyethylene (LDPE) films, at concentrations of 1 % and 3 % w/w. The prodegradant efficiency of the additives was subsequently assessed through accelerated UV aging. Following 200 h of exposure, the aged films experienced a loss in molecular weight (Mw) by approximately 95 %, accompanied by carbonyl indexes (CI) measuring 1.8 and 2.0. This high level of degradation observed in the LDPE films denotes an effective degradation mechanism, reliant on the generation of hydroxyl radicals by the TiO2 moiety, upon UV light exposure, and the subsequent abstraction of labile hydrogens within the polyunsaturated sidechain of the additives, resulting in the formation of peroxyl radicals, thereby initiating the swift auto-oxidation of the polyethylene films.