Microbial Cellulosic Fibers (Bacterial Cellulose) from Legen Sap: Sugar-Dependent Fiber Diameter, Crystallinity, and Thermal Behavior

Microbial cellulosic fibers, commonly known as bacterial cellulose (BC), form highly pure nanoscale fibrillar networks and are increasingly explored as sustainable fiber materials. This study evaluated lontar sap (legen), a traditional Indonesian sugar-rich bioresource, as a fermentation feedstock for BC production by Komagataeibacter intermedius SB110. Legen-based media were supplemented with glucose (LWG), fructose (LWF), or sucrose (LWS), and BC production was assessed after 14, 21, and 28 days of static cultivation. The resulting cellulose was characterized by ATR-FTIR, FE-SEM, XRD, and TGA to confirm functional groups, examine fiber morphology, determine crystallinity, and evaluate thermal behavior. Sugar supplementation influenced BC formation and structural characteristics, yielding average fiber diameters of 147.09 nm (LWG), 191.92 nm (LWF), and 148.64 nm (LWS). XRD analysis showed that LWF exhibited the highest crystallinity index among the tested conditions. Thermal analysis revealed distinct decomposition profiles, indicating that sugar type affected not only fiber morphology and crystallinity but also thermal stability. These findings demonstrate that legen sap is a promising renewable feedstock for BC production and that sugar supplementation provides a practical approach to modulating fiber structure and thermal properties.