FLY-ASH–BASED HIERARCHICAL PARTICLES FOR POLYMER COMPOSITES: MECHANISM-ORIENTED MODELING OF CRACK-PATH CONTROL

Fly ash from thermal power plants is an abundant technogenic by-product and a promising low-cost mineral filler for polymer composites. However, its practical use is often limited by property variability, insufficient interfacial adhesion, and the tendency of filled polymers to undergo brittle fracture. This work discusses a route to increase fly-ash efficiency by forming a hierarchical aluminosilicate (zeolite-like) surface shell via hydrothermal treatment, which enhances surface roughness and creates additional interaction sites. A mechanism-oriented micromechanical interpretation is proposed, linking the hierarchical particle morphology to crack-path deflection/branching, stress redistribution, and an increase in the effective fracture energy due to crack shielding by HWFA inclusions. To support the hypothesis, computational modeling of crack propagation in a polymer matrix with embedded particles is performed, and the key parameters governing crack-trajectory deviation are analyzed. The modeling results indicate that hierarchical surface modification of fly-ash particles can enable controlled crack-path tortuosity and improved fracture resistance compared to unmodified fly ash. The study provides a foundation for targeted experimental validation (XRD/FTIR, SEM, mechanical testing) and for developing a practical processing route that converts fly ash into a functional filler for polymer composites.