Influence of date-palm-fibers (DPFs) content and nanocrystallite FeCrCuMnTi high-entropy alloy fillers in polypropylene matrix on mechanical and structural performance of thermoplastic composite materials

Date palm fibers (DPFs) are natural, bio-degradable, green, and eco-friendly materials possessing broad applications. In this study, polypropylene (PP) thermoplastic matrix granules were reinforced with different weight percentages of DPFs (0, 2.5, 5.0, and 7.5 wt%). Two different sizes of DPFs, 75 μm (aspect ratio: ∼4.7) and 150 μm (aspect ratio: ∼2.7), were also taken for investigation. The optimal combination of PP-5DPFs was further reinforced with 2.5 wt% of nanocrystallite FeCrCuMnTi high-entropy alloy (HEA) fillers. These composites were produced in a twin screw extruder at a temperature of 200°C, chopped into granules, and consolidated into bulk samples using a vertical injection moulding machine. The composite samples were characterized using field emission gun scanning electron microscopy (FEG-SEM), differential thermal analysis/thermogravimetric analysis (DTA/TGA), X-ray Diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The effect of DPF size, content, and filler integration with PP matrix on the mechanical, flexural, and impact properties was evaluated and reported. The results revealed that the PP-5DPFs (75 µm)-2.5HEA (FeCrCuMnTi) nanocrystallite composite exhibited significantly enhanced mechanical and impact resistance properties due to improved dispersion, interfacial bonding, and load transfer capability enabled by the HEA fillers. Quantitatively, PP-5DPFs (75 mm)-2.5HEA filler composite exhibited the best performance with improvements in tensile strength (41.9%), flexural modulus (28%), and energy absorption (33.5%) compared to neat PP. Smaller fibers (75 µm) showed superior dispersion, interfacial bonding, and stress transfer, while larger fibers (150 µm) exhibited aggregation and reduced efficiency, especially at higher loadings. HEA fillers enhanced matrix crystallinity, reduced fiber pullout, and distributed stress effectively, mitigating the adverse effects of fiber aggregation. SEM fracture analysis confirmed ductile failure in neat PP and fiber pullout and matrix cracking in composites, with the optimized composition showing strong fiber-matrix adhesion and minimal voids. These findings highlight the potential of hybrid PP-DPF-HEA composites for sustainable, lightweight, and high-performance applications in the automotive, packaging, structural, and advanced manufacturing sectors.