Maximizing filler content and manufacturing highly thermal conductive composite materials through eutectic liquefaction of epoxy resin

Abstract

We report novel research results demonstrating the production of polymer nanocomposites with high thermal conductivity. The use of diluents, a conventionally used method to reduce viscosity and increase processability, had clear limitations that could not be used for solid epoxy, but in this study, the melting point of the epoxy itself was reduced through the introduction of the eutectic system, allowing the solid epoxy to be converted into a liquid phase. By utilizing eutectic liquid (EL) derived from ketone-containing epoxy resin (DBPE) and diphenylamine (DPA), we achieved maximal filler content. Unlike DBPE’s solid form at 135 °C, EL displayed liquidity with a viscosity of 50 Pa·s at 50 °C, enabling curing with isophorone diamine (IPDA) below DBPE’s melting point. While DBPE/IPDA yielded a tensile strength of 7.2 MPa due to uneven mixing, EL/IPDA reached 44.3 MPa, marking a 520 % improvement. EL’s viscosity dropped dramatically, reaching 0.06 Pa·s at 98 °C. The EL/IPDA mixture’s viscosity at 98 °C was 150 Pa·s, allowing up to 80 wt% hexagonal boron nitride (h-BN) filler. This led to a thermal conductivity of 16 W/m·K, 20 wt% higher than DGEBA’s 60 wt% filling rate. Notably, EL/h-BN composites achieved 16 times the thermal conductivity of DGEBA/h-BN composites, which is 1 W/m·K. Lowering the melting point and viscosity expanded curing agent choices, enhanced tensile strength, increased filler content, and heightened thermal conductivity, showcasing EL’s remarkable potential.