Fabrication and characterization of surface-functionalized pineapple fiber and novel finger millet husk ceramic biosilica vinyl ester biocomposite

The present study aims to investigate the mechanical, water absorption, thermal conductivity, and drilling properties of vinyl ester composites reinforced with natural fiber and biosilica particles. The novelty of this study is the utilization of waste biomass as fiber and filler material, treating those materials under silane for better bonding strength and comparing their strength features with untreated material. The composite is prepared by the manual hand layup method and evaluates its performance as per ASTM standards. According to the results, the silane-treated composite TP-4 (58 vol.% vinyl ester matrix, treated pineapple fiber 40 vol.%, biosilica 2 vol.%) exhibited improved values across all properties. It achieved the highest tensile strength of 153.4 MPa, flexural strength of 163.1 MPa, impact strength of 4.51 J, and hardness of 89 Shore-D, and it is 14.7%, 10.9%, 31.5%, and 4.7% more than the untreated counterpart UPT-4 (58 vol.% vinyl ester matrix, untreated pineapple fiber 40 vol.%, and biosilica 2 vol.%). Additionally, the TP-4 achieved the highest thermal conductivity of 0.31 W/mK, a 6.9% improvement over UPT-4, and showed the lowest water absorption at 2.1%, which is 38.2% reduction compared to UPT-4, highlighting its hydrophobic nature due to silane treatment. According to the drilling study, TP-4 (58 vol.% vinyl ester matrix, treated pineapple fiber 40 vol.%, biosilica 2 vol.%) demonstrated excellent dimensional stability with the smallest top drill diameters, measuring 4.05 mm for 4 mm drills and 8.07 mm for 8 mm drills. Moreover, the SEM analysis revealed a homogeneous dispersion of biosilica particles and enhanced particle–matrix adhesion in silane-treated specimens. These findings underline the critical role of silane treatment in optimizing composite properties and found that TP-4 specimen is the most suitable for high-performance applications.