Green hydrothermal extraction of banana cellulosic fibers by seawater-assisted media as an alternative to freshwater: physico-chemical, morphological and mechanical properties

Environmental threats posed by overreliance on synthetic materials have encouraged the valorization of the abundant sustainable agro-residues lignocellulosic biomass. This promotes bio-circularity and lowers the carbon footprint. To convert lignocellulosic biomass to more value-added materials, pretreatments are necessary. In this study, annually abundant banana pseudostem agro-residues were hydrothermally pretreated to obtain long banana cellulosic fibers. Natural seawater without extra chemicals was used as the pretreatment media at temperatures and retention times varied from 120 to 130 °C, and 15–45 min respectively. From the results, seawater and distilled water media pretreated fibers noted 15% and 11% higher optimum crystallinity index at 125 °C and 130 °C for 45 min respectively, compared to untreated fibers. Under severe pretreatment conditions, the cellulosic fibers surfaces were distorted, presented voids, and pseudo-lignin particle-sized deposits. At 130 °C for 15 min under seawater media, optimum cellulose content of 67.04 wt%, a tensile strength of 529 MPa, and Young’s modulus of 21 GPa were recorded. Meanwhile, under distilled water media, the maximum cellulose content of 67.17 wt%, a tensile strength of 458 MPa, and Young’s modulus of 22 GPa were noted at 120 °C for 30 min. Compared to untreated and distilled water media pretreated fibers, seawater media pretreated fibers exhibited higher tensile strength and crystallinity index. Thus, this suggests that seawater hydrothermal pretreatment avails an eco-friendly alternative, reduces freshwater footprint and equipment corrosion compared to acidic or alkaline pretreatments. Graphical abstract