Microhardness Enhancement in Polymer Composites via BaZrO3-Based Ceramic Reinforcement

Defect-tolerant oxide ceramics offer an alternative reinforcement strategy for high-performance polymer composites beyond conventional silica- and zirconia-based systems. In this work, a novel BaZrO3-Y2O3-SrTiO3 (BZYS) ceramic hybrid was introduced as a reinforcing phase in a polyetherimide (PEI) matrix to evaluate its effect on interphase formation, thermal stability and mechanical performance. BZYS powders were prepared by ball milling and incorporated at 1 and 3 wt% into solution-cast PEI films. X-ray diffraction confirmed the preservation of the BaZrO3 perovskite structure after mechanical activation, with a slight lattice expansion, indicating partial ion incorporation and defect-mediated structural accommodation. SEM analysis revealed predominantly submicron agglomerates with homogeneous dispersion at low loading and controlled agglomeration at higher content. Differential scanning calorimetry demonstrated a systematic increase in glass transition temperature from 202.0 °C for neat PEI to 210.4 °C and 212.0 °C for 1 wt% and 3 wt% composites, respectively, evidencing restricted segmental mobility and interphase formation. Instrumented microindentation showed substantial hardness enhancement of 40% and 83% for 1 wt% and 3 wt% reinforcement, respectively (p < 0.05), with a strong linear dependence on filler content (R2 = 0.9845). The results demonstrate that chemically stable, strain-tolerant BZYS ceramics effectively promote interphase-mediated reinforcement in PEI, establishing a novel oxide-based pathway for mechanically enhanced dental composite materials design.