Organic-Inorganic Hybrid Fillers for The Controlled Release of Antioxidants

the barrier provided by the inorganic domains of organic-inorganic hybrids towards the absorption of low molecular weight penetrants was used in this study as a basis for the development of systems capable of desorbing antioxidants at a slow rate. Polyethyleneoxide-silica hybrids, compatibilized with glycidoxylpropyltrimethoxysilane, were used as carriers of conventional stabilizers for polymers, respectively two phenolic antioxidants and one hindered aromatic diamine system. Ternary phase diagrams were produced in order to determine the compatibile compositions using DSC to measure changes in melting point and enthalpy of the antioxidant and polyethylene oxide (PEO). A compatible composition of PEO-silica-BHT (tert. butyl hydroxyl toluene) was used to produce a filler, which was pressed on the form of a fine powder between two polyamide-6 films and subsequently sandwiched with further seven layers of fresh films. The multiple-film stack was aged first in an air circulated oven at 60 °C for 360 days and then for further 475 days at ambient atmospheric conditions. The concentration of carbonyl groups in the aged films was monitored by ATR-IR spectroscopy. A sigmoidal increase was found for the amount of new carbonyl groups formed, starting from the inside layer nearest to the source of antioxidant. This confirms that the antioxidant has diffused from the filler into the surrounding polymer matrix and has reduced the rate of evolution of carbonyl groups resulting from oxidative degradation reactions.