Effect of Waste MDF-Derived Carbonisate Morphology on the Dielectric Stability of Epoxy-Based Composites

This paper presents the next stage of research on epoxy-glass composites modified with carbonisate obtained from the pyrolysis of waste MDF boards. Previous studies focused on assessing the mechanical properties of the developed material, while the aim of this work was to expand its characterization to include assessment of electrical properties and to determine the potential use of carbonisate as a functional filler in electrically insulating composites. The effect of carbonisate particle size (<500, <1000, and <1500 µm), carbonisate content (5% and 7.5% by weight), and resin-to-reinforcement ratio on the surface and volume resistivity of epoxy-glass composites was analysed. The microstructure of the materials was assessed using optical microscopy and scanning electron microscopy (SEM). To quantitatively assess changes in electrical insulating properties, we used logarithmic resistivity analysis and our own dielectric destabilization index (D), which serves as a comparative engineering index. The obtained results showed that increasing the carbonisate particle size leads to a gradual decrease in the electrical insulating properties of the composites and an increase in their structural heterogeneity. The highest dielectric destabilization index value was obtained for the composite containing 7.5% carbonisate with a fraction <1500 µm (D = 0.403). Microstructural observations confirmed the presence of agglomerates, micropores, and local structural discontinuities, which can reduce the electrical resistivity of the tested materials. The conducted studies confirmed the possibility of using carbonisate obtained from waste MDF (Medium-Density Fibreboard) boards as a functional filler in epoxy-glass composites. The obtained results constitute the next stage of comprehensive characterization of the developed material and indicate that the appropriate selection of the carbonisate morphology and the composition of the composite may enable shaping its electrical insulating properties depending on the planned application.