Naima Aissi, Said Alem, Djamel Aliouche
In this study, dual-crosslinked calcium alginate-nanocrystalline cellulose (CaAlg-NCC) bio-nanocomposite films were synthesized via a two-step gelation method. NCC, prepared by acid hydrolysis of microcrystalline cellulose (MCC), exhibited 79% crystallinity and a zeta potential of -32.14 mV at pH 5.8, and was incorporated into the CaAlg matrix at 2, 5, and 10 wt% relative to the alginate content. Physicochemical analyses (FTIR, XRD, AFM, SEM, TGA-DSC) revealed improved crystallinity, enhanced thermal stability, and homogeneous NCC dispersion at 2 and 5 wt%, with limited aggregation observed at 10 wt%. Rheological analysis showed that NCC intensified shear-thinning behavior and increased zero-shear viscosity, while shifting the frequency crossover from 156.94 rad/s for neat CaAlg to 75.23 rad/s for CaAlg-NCC10%. This lower crossover frequency suggests a longer relaxation time and a more developed viscoelastic network. Power-law analysis (n' = 1.43 to 2.03, n″ = 0.80 to 1.05) indicated fluid-like entanglement networks without gelation, maintaining reinforced viscoelastic liquid behavior across 20 to 60 °C. The CaAlg-NCC5% sample exhibited the highest tensile strength (83.18 MPa), tensile modulus (5752.67 MPa), and melting enthalpy (ΔHm = 43.04 J/g), together with a zero-shear viscosity of 0.5069 Pa·s and a crossover frequency of 77.91 rad/s, supporting its role as the most likely percolation-related optimum. This dual-gelation approach preserved NCC dispersion through internal gelation and completed ionic crosslinking by external gelation, resulting in enhanced viscoelastic and mechanical properties. These structure-property relationships link suspension rheology to improved film performance, underscoring the interfacial compatibility between the biopolymer matrix and filler and providing a framework for designing cellulose-based nanocomposites for packaging and biomedical applications.