Investigation of flexible PVA reinforced composite using basalt fiber/nickel microwire and biocarbon particles reinforced EMI shielding applications

This study investigates the mechanical, dielectric, magnetic and electromagnetic interference shielding behaviour of flexible PVA-based hybrid composites reinforced with silane-treated basalt microfibers, silane-treated nickel microwires and silane-treated hazelnut shell biocarbon. The results demonstrate that the incorporation of hybrid reinforcements significantly enhances the multifunctional performance of the composites. Among the investigated specimens, PMB2 exhibits the highest overall mechanical performance, with a tensile strength of 136 MPa, flexural strength of 142 MPa, impact energy of 3.8 J and hardness of 81 Shore-D. These improvements arise from the effective synergy between the fibers, microwires and 3 vol% biocarbon, which promotes optimal dispersion, strong interfacial adhesion and efficient stress transfer. In contrast, PMB3 shows superior functional properties, recording the highest dielectric permittivity (4.56) and dielectric loss (0.68), along with the highest magnetic permeability values across all tested frequencies, and maximum EMI shielding of 9.26 dB (E), 14.99 dB (F), 21.17 dB (I) and 31.31 dB (J). The enhanced electrical and magnetic responses of PMB3 result from the increased availability of polarizable and conductive pathways facilitated by 5 vol% biocarbon, which complements the ferromagnetic behaviour of the nickel microwire. SEM analysis further supports these findings, revealing clear improvements in interfacial bonding and filler embedding in PMB2, while PMB3 displays localized biocarbon agglomeration that promotes electromagnetic loss mechanisms. Therefore, PMB3 is well-suited for functional applications requiring high dielectric, magnetic, or EMI shielding performance, such as flexible electronics, electromagnetic protection devices, sensors, and wearable electronics. Overall, the results demonstrate the tunability of PVA hybrid composites through controlled reinforcement architecture, enabling tailoring of mechanical or functional properties according to specific application requirements.