Synthesis of cellulose nanofiber hydrogels from fique tow and Ag nanoparticles

Composite cellulose hydrogels result from physical or chemical crosslinking processes. Unique tridimensional architectures, arising from the hydrogel components’ interactions, make these materials ideal to design function-driven structures. We follow the development of cellulose nanofiber/silver nanoparticle (Ag NP) hydrogels in aqueous media. TEMPO-oxidized cellulose nanofibers (TOCNs), extracted from fique residual biomass, acted as both capping and reducing agents for the in-situ synthesis of Ag NPs. Temperature and COONa:AgNO₃ molar ratios influence hydrogel formation. Increasing temperatures (60 ºC) resulted in shorter reaction times (28 h) compared to the behavior at lower temperatures (25 ºC), which required longer reaction times (192 h). High COONa:AgNO₃ molar ratios (1:3) produced stiffer and darker TOCN/Ag NP hydrogels at the expense of large cubic Ag NP clusters formation (1 µm). Conversely, lower COONa:AgNO₃ molar ratios (1:1) resulted in softer hydrogels with spherical Ag NPs exhibiting diameters between 15 and 80 nm. Ag NP formation and crosslinking processes strongly depend on unreacted aldehydes on the TOCN surfaces after the TEMPO oxidation reaction. IR spectra indicated that there is a bridging bidentate interaction between COO⁻ groups and Ag⁺ ions. These carboxylate-metal complexes might weaken the hydrogen bond system by increasing the distance between cellulose molecules, decreasing the material’s crystallinity index, as observed in XRD analyses. TGA analyses demonstrated that Ag NPs significantly increased the TOCN/Ag NP hydrogels’ thermal stability compared to TOCN hydrogels. Rheological probing of the hydrogels elucidated the role of Ag NP distribution and loading on the elastic response to cyclical deformations, suggesting a myriad of uses for these materials, particularly in medicinal applications.