Interfacial optimisation and micro-mechanics driven performance analysis of hybrid sheep wool/GGBFS composites

Hybrid composites combining protein-based natural fibres and chemically reactive micro-particulates offer excellent performance, yet their interphase load transfer mechanisms remain under-characterised. Four laminates were fabricated by vacuum-assisted resin transfer moulding (VARTM) using coarse sheep wool (CSW) fibre and ground granulated blast-furnace slag (GGBFS) filler in epoxy at 0, 4, 8 and 12 wt. % (CSWG-0 to CSWG-12). The lysine-rich α-keratin CSW surface and silanol-bearing amorphous calcium-alumino-silicate (CAS) GGBFS surface were examined for their potential to form a tri-phase bridging interphase. X-ray diffraction (XRD) resolved a broad amorphous CAS halo at 2θ ∼ 21.9°. Fourier-transform infrared (FTIR) spectroscopy validated the silanol-epoxy pathway via a + 21 cm ⁻¹ epoxide ring blue-shift (914 cm ⁻¹ ) and a distinct Si-O-C band (1072 cm ⁻¹ , +190% area), operating alongside partial cross-linking, hydrogen bonding, and physical interlocking. Mechanically, CSWG-8 was optimal, achieving a tensile strength of 52.0 MPa (+30%), interlaminar shear strength (ILSS) 9.81 MPa (+36%) and impact energy 15.8 kJ/m ² (+52%) at 0.82% void content, with flexural and compressive strengths improving by +28%. The tensile modulus exceeded the Halpin-Tsai prediction by 10.1%, signifying active interphase stiffening, whereas CSWG-12 inverted to −4.6%. Fuzzy multi-criteria decision-making (MCDM), which weighs these agglomeration trade-offs, recommends CSWG-8 for designs requiring strict interfacial integrity.