Investigation of application efficiencies of bio-based organic compounds into polyolefins as antioxidant additives

In this thesis study, compounds with different compositions were prepared by melt blending method using low density polyethylene (LDPE), which contains no antioxidant additives, and various organic extracts obtained from natural sources (milk thistle, coffee, thyme oil and resveratrol). Two different synthetic and commercial polyphenol and phosphite-based antioxidants (Irganox®1010 and Irgafos®168) were also used to prepare control samples. In the experimental studies, the formulation details of milk thistle (Silybum Marianum, SM) extract, which shows high antioxidant activity as a natural and phenolic primary antioxidant, were examined and the amount of this additives varied in the range of 0.1-1.0 wt%. In addition, a systematic formulation study was carried out by changing the primary and secondary antioxidant ratios in the composition. The resistances of prepared compounds against thermal-oxidative degradation were analyzed by oxidation induction time (OIT) test and oxidation onset temperature (OOT) test performed in a differential scanning calorimeter (DSC) device under isothermal and non-isothermal conditions. Isothermal oxidation induction time tests were carried out at 200, 210, 220, and 230 °C, and the oxidation behaviors of PE compounds prepared with milk thistle extract were examined depending on the composition and temperature. In addition, the thermo-oxidative degradation of some prepared samples at high temperatures was determined by tests performed on a thermogravimetric analysis (TGA) device. Some structural and physical properties of the samples, such as transparency, color coordinates, contact angle and degree of crystallinity were also examined by various analytical methods. According to the analysis results, it was determined that milk thistle extract and resveratrol showed high antioxidant activity for polyethylene at low loading amounts (e.g. 0.2 wt%). It was determined that increasing the amount of milk thistle extract and Irgafos®168 significantly improved the oxidation stability of polyethylene under isothermal and non-isothermal conditions. It has been determined that resveratrol, another antioxidant additive that shows antioxidant activity in thermal analyses, also gives successful results. TGA analyzes showed that the type and amount of antioxidants did not affect the decomposition behavior of polyethylene at very high temperatures. Additionally, it has been found that the milk thistle extract did not change the transparency and physical properties of LDPE even in the loading amount of 1.0 wt%. Consequently, it has been observed that milk thistle extract, which shows antioxidant activity even at low concentrations, can be used successfully as a natural antioxidant additive in polyolefins and exhibits a potential to compete with synthetic antioxidants.