Physicomechanical, water absorption and thermal properties and morphology of Paederia foetida fiber–Al2O3 powder hybrid-reinforced epoxy composites

Hybridization of natural fibers with ceramic materials for reinforcing composites allows the optimization of the properties of these materials. For this reason, the present study aims to investigate physical, mechanical, water absorption, swelling and thermal properties as well as morphological characteristics of a hybrid Paederia foetida fibers–alumina powder (PFs–Al₂O₃)-reinforced epoxy composite. Epoxy resin served as the matrix, while PFs and Al₂O₃ were employed as reinforcement. Five types of composites were fabricated using the hot-pressing technique. The corresponding ratios of PFs:Al₂O₃ volume fractions (%) considered here were 0:40 (SFA), 10:30 (SFB), 20:20 (SFC), 30:10 (SFD) and 40:0 (SFE). The results reveal that the density of the hybrid PFs–Al₂O₃ composites decreased for increasing volume fractions of PFs: from 2.173 g cm⁻³ of SFA to 1.042 g cm⁻³ of SFE. The highest values of tensile strength (i.e. 49.085 MPa), tensile elastic modulus (i.e. 1.431 GPa) and impact strength (24 kJ m⁻²) were obtained for the SFD composite material with 30% volume fraction of PFs and 10% volume fraction of Al₂O₃: this happened because interface bonds between PFs, Al₂O₃ and epoxy phases achieved their optimal configuration. Overall, mechanical properties of the hybrid PFs–Al₂O₃-reinforced epoxy composites were superior to those of composites reinforced only by PF fibers or only by Al₂O₃. Water absorption and swellability reached their maximum values at the steady state occurring after tested samples remained immersed in water for 820 h. The SFE composite reinforced only by PFs presented the highest water absorption and swelling (i.e. 6.034% and 5.81%, respectively) while for all other hybrid composites (SFD, SFC and SFB) these two quantities remained below 5%. Density and volume fraction of voids of hybrid PFs–Al₂O₃-reinforced composites were consistent with the corresponding properties of the composites reinforced only by Al₂O₃ or PFs. SFD was also the most thermally stable material. Scanning electron microscopy observations of fractured surfaces indicated that the microstructure of the PFs–Al₂O₃-reinforced epoxy composites presents several voids, fiber pullouts and transverse fibers, which together optimize the mechanical response of the composite material. Remarkably, the SFD composite material was highly competitive with the most recently developed hybrid composites employing natural reinforcements. © 2024 Society of Industrial Chemistry.