Hydrophobic Electrospun PVB/SiO₂ Nanofiber Membranes Incorporating Rice Husk Ash-Derived Silica

Electrospun polyvinyl butyral (PVB)/SiO₂ nanofiber membranes incorporating rice husk ash (RHA)–derived silica were developed to enhance hydrophobic surface characteristics. Amorphous SiO₂ obtained from RHA via controlled thermal treatment (600 °C, 4h) exhibited a specific surface area of approximately 154 m2/g and was subsequently incorporated into PVB. After silane surface modification, the water contact angle on the nanofiber membranes increased from 89.8 to 111.2°, exceeding the hydrophobicity threshold defined in ASTM D7334. Standardized AATCC 22 spray tests further confirmed improved water repellency, achieving a rating of 90 (equivalent to ISO grade 4). These results are consistent with a Cassie–Baxter-type interfacial state associated with the hierarchical porous structure of the nanofiber network. Such structure-induced wetting characteristics reduce surface water adhesion while preserving the intrinsic porosity of the nanofiber network.