In-situ synthesis and binding of silver nanoparticles to dialdehyde and carboxylated cellulose nanofibrils, and active packaging therewith

Abstract

The present work reveals the potential application of dialdehyde and carboxylated nanocellulose for the in-situ reduction of Ag+ and immobilization as silver nanoparticles (AgNPs) on cellulose surfaces. Tollens’ reagent (Ag(NH3)2OH) at concentrations ranging from 5·10–3 to 10–1 M was incorporated in both dialdehyde cellulose (DAC) and dialdehyde-modified TEMPO-oxidized cellulose nanofibers (DA-TOCNFs). The results showed that DA-TOCNFs facilitated faster reduction of Ag+ and effective immobilization of AgNPs on the nanocellulose surface. The resulting suspensions exhibited stability and demonstrated strong antimicrobial activity against Bacillus subtilis when coated on paper surfaces. Importantly, the coated papers did not show significant silver migration to food simulants B (3 vol% acetic acid) and D1 (ethanol/water mixture, 50 vol%), indicating the potential of these suspensions for active food packaging. The advantages of using DA-TOCNFs over DAC were attributed to their higher cationic demand and ζ-potential, resulting in a higher density of binding sites. Moreover, the charged and entangled network of DA-TOCNFs allowed for the individualization of AgNPs, unlike DAC, where some agglomerations were observed. Overall, this study presents an improved single-step process for the synthesis of AgNPs on nanocellulose surfaces, highlighting their potential for safe and high-performance applications in food packaging. Paper sheets coated with nanocellulose/AgNPs suspensions fully inhibited the growth of B. subtilis, at least for one month after coating, and caused damage to their cell membranes. This research provides a one-pot facile route to fabricating hybrid nanocellulose/AgNPs systems, stable in water, and may be used directly as a coating layer for board and paper active packaging with little or even undetectable release of Ag