Utilization of Silybum marianum extract as a high-performance natural antioxidant for polyethylene

Abstract In this study, Silybum marianum extract powder was introduced into low density polyethylene (LDPE) as a primary polyphenolic antioxidant via melt blending method. Two synthetic and commercial polyphenol- and phosphite-based antioxidants (Irganox® 1010 and Irgafos® 168) were also used for comparing the antioxidant efficiency and performance of Silybum marianum extract with commercial ones. A systematic formulation study was achieved by varying the amount of Silybum marianum extract in the range of 0.1–1.0 wt% and the primary:secondary antioxidant ratio. Antioxidant efficiency of Silybum marianum extract was quantified with the oxygen induction time (OIT) and oxidation onset temperature values determined by thermal analysis in a differential scanning calorimeter depending on the compositional variations. Some physical properties of specimens such as transparency, color coordinates, contact angle, and degree of crystallinity values were also examined. It was found that 0.2 wt% of Silybum marianum extract and 0.2 wt% of Irgafos® 168 loaded sample showed an OIT value of 22 min. at 210 °C that could be regarded as a very successful commercial potential. Increasing amount of Silybum marianum extract and Irgafos® 168 significantly improved the oxidation stability of polyethylene under isothermal and non-isothermal conditions. It was also found that introducing Silybum marianum extract, even the loading content of 1.0 wt%, did not alter the transparency and physical properties of LDPE. It has been concluded that Silybum marianum extract can be successfully used as a natural antioxidant in polyolefins and these samples could be used in packaging film applications. Graphical Abstract