Synergistic effects of dune sand-based silica and alkali-treated date palm fiber as efficient fillers for improving the properties of hybrid epoxy composites

Lignocellulosic fiber-reinforced composites exhibit enhanced physical properties and eco-friendliness, which has resulted in extended application of these biocomposite materials in important engineering sectors. In this study, we investigated the synergistic impacts of dune sand (DS)-based silica (SiO₂) and alkali-treated date palm fiber (ADPF) fillers on the thermophysical and viscoelastic characteristics of epoxy (EP) hybrid composites. A hand layup procedure was employed to produce EP hybrid composites reinforced with 20 wt.% ADPF as well as 5, 7, and 10 wt.% DS. Compared to the other composite samples, the EP matrix reinforced with 20 wt.% ADPF and 10 wt.% DS (HC5) exhibited better thermal (T_max = 380°C, T_g = 63.13°C) and dynamic mechanical properties (storage modulus = 2700 MPa). Additionally, Cole–Cole plots revealed the excellent interaction between ADPF, DS, and epoxy matrix. Scanning electron microscopy (SEM) measurements further confirmed that the development of an effective interface between DS particles, ADPF fiber, and epoxy matrix caused a decrease in water absorption (1.5%). The best wetting conditions with the lowest thickness swelling (2.8%) were obtained by increasing the DS content up to 10 wt.%. Based on these findings, it can be concluded that, owing to their superior dynamic mechanical characteristics, hybrid composites containing 10 wt.% DS may be employed in important aircraft and aeronautic applications.