Concentration-Dependent Thermo-Oxidative Degradation Behavior and Filler Loading Effects in Talc- and...

This study examines the concentration-dependent thermo-oxidative behavior of polypropylene/ethylene-octene rubber (PP/EOR, 80/20) composites reinforced with talc, whisker, and hybrid talc/whisker fillers (5-15 phr) for automotive interior applications. Accelerated thermal aging was conducted at 140 °C for 300 h to evaluate mechanical retention, oxidation behavior, crystallinity evolution, and residual thermal stability. Low talc loadings (≤10 phr) provided the most favorable aging response: T5 and T10 exhibited impact retention values of 165.46% and 139.37%, respectively, together with crystallinity retention values of 142.86% and 124.49%. These improvements were associated with crystallinity enhancement, limited carbonyl formation, and the barrier-related effect of platelet-like talc fillers. In contrast, high-whisker-loading and hybrid systems showed severe deterioration after aging, with W15 and TW7.5 retaining only 33.56% and 25.50% of their initial impact strength, respectively. These samples also showed pronounced early stage thermal instability, as indicated by reductions in the 5% weight-loss temperature (T _5%) from 364.57 to 289.65 °C for W15 and from 374.78 to 305.32 °C for TW7.5. FT-IR, DSC, TGA/DTG, SEM, and ANOVA results indicate that excessive filler loading, particularly in whisker-rich and hybrid systems, promotes filler-matrix interfacial defects, stress concentration, oxidation, and impact embrittlement. These findings provide a quantitative structure-property-degradation framework linking filler morphology, crystallinity evolution, oxidation behavior, thermal stability, and long-term mechanical durability of PP/EOR composites under high-temperature aging conditions.