Polycaprolactone diol-mediated interfacial energy modulation for enhancing processability and thermal conductivity of highly filled epoxy/alumina composites

The application of highly filled ceramic–epoxy composites is often limited by the rapid increase in viscosity at high filler loadings. Here, polycaprolactone diol (PCLD) is shown to function as a combined viscosity and interfacial modifier in alumina-filled epoxy composite systems, enabling effective flow control under high solid loading. PCLD content (0–15 wt%) and molecular weight (Mn = 530 and 2000 g·mol −1 ) were varied to evaluate rheological behavior and thermal transport. At 30 vol% alumina, 15 wt% PCLD (Mn 530) reduced viscosity from 57.8 to 5.3 Pa·s at 10 s −1 , nearly one order of magnitude compared with the composite without PCLD. Under the same condition, thermal conductivity increased by 36%, from 0.60 to 0.82 W·m −1 ·K −1 . PCLD altered the surface free energy of the epoxy matrix and reduced the estimated epoxy–alumina interfacial energy, consistent with improved filler wetting and changes in filler organization. These results indicate that the combined effects of bulk viscosity reduction and interfacial-energy modification can improve processability and heat transport in highly filled epoxy composites. However, the accompanying decreases in glass-transition temperature and tensile strength represent important trade-offs for application at elevated temperatures or under higher mechanical requirements.