Relationship Between Hardness and Impact Strength of Epoxy–Glass Composites Modified with Carbonisate from MDF Pyrolysis

The study analysed epoxy-glass laminates containing carbonisate produced during medium-density fibreboard (MDF) waste pyrolysis were evaluated with respect to their hardness and their ability to withstand impact loads. All composite samples were prepared manually using a hand-laying method, using two resin-reinforcement ratios (60/40 and 65/35) and carbonisate additives in amounts of 5% and 7.5% by weight (with particle sizes < 500 µm). The mechanical properties were assessed on the basis of hardness tests using the Barcol method and impact tests using the Charpy method. To analyse the results, a normality assessment (Shapiro-Wilk) was performed, followed by a non-parametric analysis of variance based on ranks (Kruskal-Wallis). It was found that an increase in carbonisate content increases the surface hardness of composites while reducing their impact resistance, which confirms the existence of a typical trade-off between stiffness and energy absorption capacity. The most favourable mechanical properties were obtained for a composite containing 7.5% carbonisate material and a resin-reinforcement ratio of 60/40, which was characterised by the highest hardness (35.19 HBa), a moderate impact strength (43.56 kJ/m²) and the lowest variability of results. The statistical analysis confirmed significant differences between the tested samples and a quantitative relationship between hardness and impact strength. The results of the study indicate that carbonisate (MDF) using waste material as a filler provides a sustainable means of improving the stiffness and consistency of epoxy-glass composites, with only a negligible effect on their ability to resist fracture.