Covalently introducing amino-functionalized nanodiamond into waterborne polyurethane via in situ polymerization: Enhanced thermal conductivity and excellent electrical insulation

Abstract

Polymer-based thermal management nanocomposites with favorable electrical insulation have received increasing attention in the microelectronics industry. How to effectively disperse nanofillers and improve interfacial compatibility with polymer matrix is crucial to enhance comprehensive performance of nanocomposites. In this work, nanodiamond (ND) was first oxidized by hydrogen peroxide and then amino groups generated on its surface via hydrothermal reaction in the presence of ethylenediamine. Amino-functionalized ND particles (ND-NH2) were covalently incorporated into isocyanate-terminated polyurethane prepolymer chains via in situ polymerization, and a series of waterborne polyurethane (WPU)/ND-NH2 (WPN) nanocomposites with low loading levels (0.5, 1 and 2 wt%) were successfully prepared. ND functionalized with amino groups achieved excellent compatibility with the WPU matrix, improving the interfacial interactions between filler and matrix, and reducing the interface thermal resistances and phonon scatterings, further favoring the formation of thermal conductive paths. The highest thermal conductivity of the WPN nanocomposite with a lower ND-NH2 loading of 2 wt% was 0.369 W m−1 K−1, which is about 82% higher than that of the pure WPU film (0.203 W m−1 K−1). The excellent electrical insulation was also found at 2 wt% nanofiller content and the volume electrical resistivity reaches 2.525 × 1015 Ω·cm. Moreover, the incorporating and good dispersion state of ND particles in the WPU-based nanocomposites could increase the thermal stability and mechanical performance of the nanocomposite films. This method provides an effective and promising way to prepare environmentally friendly polyurethane nanocomposites reinforced with reactive surface of functionalized ND.