biostudies-literatureUnknown16(11)Horathal Pedige MPCellulose nanofibers (CNFs) are increasingly recognized as sustainable alternatives to petroleum-derived plastics. However, their intrinsic hydrophilicity results in poor water resistance, which severely restricts applications in humid or aqueous environments. Therefore, improving water durability while maintaining mechanical performance remains a key challenge. In this study, we fabricated water-resistant composite films by combining oxidized CNFs (OCNFs), obtained <i>via</i> a simple sodium hypochlorite (NaClO) oxidation introducing carboxyl groups, with chitosan (CS). The OCNF/CS films exhibited markedly enhanced tensile strength (∼50 MPa <i>vs.</i> ≤20 MPa for pristine OCNF) and retained their integrity in water for 24 h, with a swelling ratio of ∼200% compared to ≥900% for OCNF alone.RSC advances9621-9630https://www.ebi.ac.uk/biostudies/studies/S-EPMC12911662biostudies-literatureNaClO-oxidized cellulose nanofiber/chitosan composite films with improved water resistance and high mechanical strength.PMC12911662Onishi RHatanaka YHorathal Pedige MPUyama HSugawara AfalseNaClO-oxidized cellulose nanofiber/chitosan composite films with improved water resistance and high mechanical strength.Cellulose nanofibers (CNFs) are increasingly recognized as sustainable alternatives to petroleum-derived plastics. However, their intrinsic hydrophilicity results in poor water resistance, which severely restricts applications in humid or aqueous environments. Therefore, improving water durability while maintaining mechanical performance remains a key challenge. In this study, we fabricated water-resistant composite films by combining oxidized CNFs (OCNFs), obtained <i>via</i> a simple sodium hypochlorite (NaClO) oxidation introducing carboxyl groups, with chitosan (CS). The OCNF/CS films exhibited markedly enhanced tensile strength (∼50 MPa <i>vs.</i> ≤20 MPa for pristine OCNF) and retained their integrity in water for 24 h, with a swelling ratio of ∼200% compared to ≥900% for OCNF alone.2026-01-01T00:00:00Z2026 Feb2026-07-16T11:55:43.235Z2026-07-09T10:52:15.077ZS-EPMC129116624171049710.1039/d6ra00188b