Effect of Melt-Mixing Duration on the Thermal Degradation and Apparent Activation Energy of Low-Loading PS/NiFe2O4 Nanocomposites: A Sensitivity-Assessed Kinetic Analysis

PS/NiFe2O4 nanocomposites containing 2.5 wt.% NiFe2O4 were melt-blended in a twin-screw micro-compounder for 6 and 12 min (PS-NF-6 and PS-NF-12) and compared with neat PS processed for 6 min to examine whether mixing duration at a fixed low loading affects thermal degradation and apparent kinetics. XRD confirmed that the NiFe2O4 spinel structure was retained; surface SEM observations were treated as preliminary. TG data were normalized to the principal degradation step to minimize low-temperature mass-loss and balance-drift effects. PS-NF-12 degraded at higher temperatures than neat PS at all heating rates (5–20 K min−1), with mean shifts of 5–8 K over α = 0.05–0.80, whereas the effect of PS-NF-6 was limited to the early stage. Kissinger apparent activation energies (Ea) were 194 ± 18, 201 ± 14, and 252 ± 12 kJ mol−1 for PS, PS-NF-6, and PS-NF-12, respectively, and PS-NF-12 remained the highest when any single heating rate was omitted. The KAS conversion-dependent activation energy (Eα) of PS-NF-12 increased with conversion only when the 5 K min−1 run was included; without it, Eα remained at 206–212 kJ mol−1. At constant low loading, longer mixing was thus associated with delayed mass loss and a higher peak-region Ea.