Investigation of silane-treated Cyperus platystylis stem fiber and nickel oxide reinforced vinyl ester composites for enhanced mechanical and EMI shielding properties

This research examines the multifunctional performance of silane treated natural fiber and unmodified nickel oxide (NiO) filler reinforced vinyl ester composites, emphasizing the best performing hybrid composite, ABS1 (50 vol% fiber and 1.5 vol% filler). The composite exhibited a substantial improvement in mechanical properties compared to the unreinforced and fiber only composites. Specifically, the tensile, flexural, impact and hardness strengths of ABS1 were 82.7 MPa, 107.4 MPa, 7.2 kJ/m² and 83 shore D respectively indicating enhanced load transfer and strong interfacial bonding due to effective silane treatment of the fibers. The thermal conductivity of ABS1 decreased to 0.23 W/mK demonstrating improved phonon scattering and heat dissipation resistance. Moreover, ABS1 showed an increase in relative permittivity to 4.12 and loss of 0.023 attributed to interfacial polarization and dipolar relaxation effects. The magnetic permeability values, µ′ and µ″ reached 1.45 and 0.37 at 20 GHz highlighting strong magnetic dipole alignment and eddy current loss behaviour. Correspondingly, the electromagnetic interference (EMI) shielding effectiveness of ABS1 increased steadily with frequency achieving total shielding of 45 dB at 20 GHz dominated primarily by absorption mechanisms. These results confirm that ABS1 provides the best combination of mechanical strength, dielectric stability and EMI attenuation, suitable for lightweight structural and shielding applications.