A Mild Calcium Carbonate Treatment Improves Moisture Resistance and Mechanical/Interfacial Properties of Jute and Hemp Fibers

Natural fibers are attractive, sustainable reinforcements, but often exhibit high moisture uptake and weak bonding with polymer matrices. In this study, jute and hemp were treated by immersion in aqueous calcium carbonate (CaCO3) suspensions (10–40 wt %, 1.5 h, room temperature) and were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), moisture sorption testing, single-fiber tensile testing, and bundle pull-out testing. SEM showed granular CaCO3 deposition on fiber surfaces, with particulates bridging surface voids and microcracks. At 40 wt % CaCO3, equilibrium moisture uptake decreased to ∼5% (hemp) and ∼3% (jute), while tensile strength increased to ∼904 MPa (hemp) and ∼960 MPa (jute). Apparent interfacial shear strength from pull-out testing increased up to ∼1.35 MPa (hemp) and ∼0.56 MPa (jute). These results indicate that CaCO3 deposition is a mild, scalable surface treatment that improves moisture resistance, fiber tensile strength, and interfacial load transfer, relevant to semistructural composite applications, including interior and secondary automotive components.