Modulating fiber morphology to achieve tunable optical and mechanical properties in bamboo cellulose film

Transparent cellulose films exhibit tremendous potential for optoelectronic applications due to their exceptional optical/mechanical properties and environmental sustainability. However, the intricate relationship between fiber morphology and film performance remains insufficiently understood, which hampers the precise engineering of film performance for targeted applications. In this study, we present a novel strategy to fabricate transparent cellulose films with tunable optical/mechanical properties by precise morphological manipulation of bamboo fibers. A two-stage modification process was employed: initial structural alteration was achieved using a sulfate/deep eutectic solvent pulping method (choline chloride-lactic acid system), followed by molecular-level modification via carboxymethylation to promote fiber swelling. This approach produced two distinct fiber morphologies: non-uniformly swollen "bulging"/uniformly swollen fibers, each endowing resulting films with unique properties. Films made from "bulging" fibers displayed exceptional light scattering behavior, with an impressive haze exceeding 80 % at a transmittance of 85 %. In contrast, films fabricated from uniformly swollen fibers exhibited remarkable mechanical strength, with tensile strength reaching 137 MPa. These findings elucidate the mechanisms by which fiber morphology governs the optical and mechanical properties of cellulose films, advancing the fundamental understanding of structure-property relationships and providing a foundation for the rational design of transparent cellulose films for applications such as solar cells.