Cation adsorption strategy to increase the impregnation limit of thermally conductive alumina filler in adhesives: mass-producible and eco-friendly scheme for direct industrial application

Increasing the concentration of crystalline fillers in a polymer matrix is one of the most straightforward and effective strategies to enhance the thermal conductivity and mechanical performance of thermally conductive adhesive composites. Alumina (Al₂O₃) is particularly compatible with epoxy resins, and various surface modification techniques have been explored to maximize its loading within such composites. This study presents a highly effective surface modification method for Al₂O₃ using simple agitation in an aqueous solution containing iron salt at parts-per-million (ppm) concentrations. This treatment shifts the zeta potential of the alumina fillers to a more positive value, improving their electrostatic stability and interactions with polar moieties in the uncured resin. Introducing iron-modified alumina increased the filler loading to 82.5 wt%, compared to a maximum of 80 wt% with unmodified alumina while preserving solution processability. This enhancement led to a 1.46-fold increase in thermal conductivity at 25 °C. Industrial applicability was demonstrated by producing 2 kg of modified alumina powder without generating manufacturing waste. The composite's heat dissipation performance was evaluated using a high-power LED chip array mounted on a printed circuit board (PCB), with the adhesive applied between the PCB and a heat sink. The heat sink using the modified Al₂O₃-based composite (82.5 wt%) reached a temperature 7.37 °C higher than that of the composite filled with unmodified Al₂O₃ (80 wt%), indicating significantly improved heat transfer efficiency.