Bio-Based Gum Arabic-Reinforced Epoxy Overlay System: Mechanical, Thermal, and Tribological Performance with Wear...

This study investigates the tribological performance of gum arabic (GA)-reinforced epoxy (EP) overlays on EN8 steel. Four GA concentrations (0.25, 0.5, 1, and 3 wt.%) were incorporated into the epoxy matrix to prepare overlays designated as EPGA1-EPGA4. Tribological performance was evaluated using a reciprocating tribometer under varying loads (5-20 N), sliding frequencies (1-2.5 Hz), and temperatures (40-70 °C). An L16 orthogonal array based on the Taguchi method was used to design the experimental matrix, and multi-criteria decision-making using the TOPSIS technique was employed to identify the optimum tribological condition based on minimum coefficient of friction (COF) and specific wear rate (SPWR). The optimum condition was obtained for the EPGA3 overlay (1 wt.% GA) at 5 N, 2 Hz, and 60 °C, which exhibited the lowest COF of 0.0567 ± 0.0021 and negligible wear. In contrast, the pure epoxy overlay showed severe adhesive wear, catastrophic delamination, a high COF of 1.15 ± 0.0023, and a wear rate of 163 × 10^-8 mm³/Nm. Thermal characterization showed that GA improved the thermal stability and thermal transition behaviour of the epoxy matrix. Thermogravimetric analysis revealed an increase in onset degradation temperature from 320 °C for pure EP to 342 °C for EPGA4, while differential scanning calorimetry showed that EPGA3 exhibited the highest glass transition temperature (~118 °C), indicating improved interfacial interactions and restricted polymer-chain mobility. Nanoindentation and pull-off adhesion tests further confirmed the improved mechanical integrity and interfacial adhesion of the GA-reinforced overlays, demonstrating its potential as a sustainable reinforcement for tribological coating applications.