In Situ and Ex Situ Silver Nanoparticle Modification of Lyocell Fibers: Insights into Nanoparticle Size Control and Physicochemical Properties

Controlling the parameters of nanoparticles within a polymer matrix is a key challenge in advancing modern materials science, particularly in developing functional cellulose-based materials. This study focused on a comprehensive comparison of in situ and ex situ methods for synthesizing silver nanoparticles (AgNPs) to determine the optimal approach for achieving precise control over nanoparticle size and distribution within Lyocell-type fibers. Cellulose fibers were produced via the NMMO (N-methylmorpholine N-oxide) method, using glucose as an eco-friendly reducing agent for silver nitrate in both approaches. The in situ method involved generating AgNPs directly during spinning dope preparation, whereas the ex situ approach utilized chemical reduction under various conditions (12 h and 24 h, 70 °C) prior to incorporating the pre-synthesized nanoparticles into the fibers. UV-Vis, DLS, and TEM measurements were employed to characterize the nanoparticles, while the resulting fibers were evaluated for their degree of cellulose polymerization, as well as their mechanical and hygroscopic properties. The comparative analysis revealed that the ex situ synthesis (24 h, 70 °C) is the optimal method, enabling superior control over the nanoparticle parameters and successfully introducing a high percentage of small-diameter AgNPs (2–8 nm) into the fiber matrix without degrading the fundamental properties of the cellulose.