Thermal, dynamic-mechanical and electrical properties of UV-LED curable coatings containing porcupine-like carbon structures

Abstract

In this work, multi-functional coatings based on a UV-LED curable epoxy-acrylate resin and different loadings (namely, 1, 2.5, 5 and 10 wt%) of carbonaceous structures having a peculiar porcupine (PuP)-like morphology were formulated and thoroughly characterized through thermal, dynamic-mechanical and electrical analyses. More specifically, biochar-based particles derived from cellulose nanocrystals were modified through the growth of carbon nanofibers onto their outer surface, aiming at combining the effects of globular and high aspect ratio structures in a single filler. The preliminary characterization of the carbonaceous structures documented the achievement of a highly carbonized material involving spherical biochar particles having an average diameter ranging from 15 to 20 µm, covered by fibers displaying length up to 100 µm. As assessed by dynamic-mechanical characterization, the UV-LED cured composite films showed a progressive increase of the storage modulus values as a function of the amount of embedded PuP structures, indicating a strong level of interfacial interactions between the polymer network and the particles. Furthermore, the introduction of increasing amounts of PuPs induced a progressive increase of the material thermal conductivity (from 0.109 W/mK for unfilled cured resin, up to 0.161 W/mK, for the composite film containing 10 wt% of filler) and a remarkable enhancement of the electrical conductivity (up to (3.1 ± 0.2)*10−2 S/m, for the composite film containing 10 wt% of filler), thus pointing out the effectiveness of the proposed approach of surface modifying biochar particles in obtaining composite coating films with superior properties.