Balancing Water Uptake, UV Visible Screening, and Mechanical Strength in Cellulose Alginate Quercetin Hydrogel Films

Combining high water affinity and strong UV–vis shielding while preserving mechanical performance in fully biobased cellulose films remains challenging, as hydrophilic polysaccharide modifiers and polyphenolic additives can disrupt network cohesion, promote phase-enriched domains, and trigger early fracture. Here, renewable hydrogel films were engineered from bleached Eucalyptus cellulose by incorporating sodium alginate (SA) and quercetin (Q) as multifunctional additives to tune structure–property relationships. Composite hydrogels were homogenized under a standardized and scalable protocol and converted into continuous films by doctor blade coating. Film morphology, intermolecular interactions, crystallinity, optical response, wetting and hydration, and tensile behavior were assessed by FE-SEM, ATR-FTIR, XRD, UV–vis spectroscopy, contact-angle kinetics, gravimetric water uptake, and tensile testing. Quercetin governed the visible color shift and enabled strong UV–vis attenuation (>95%), whereas alginate improved film continuity and enhanced hydration. FTIR and XRD supported predominantly noncovalent incorporation, consistent with a physically cross-linked polysaccharide network. An optimum formulation, CEL-2SA-1Q (97/2/1 wt %), delivered the highest mechanical performance (Fmax = 147.85 ± 9.82 N, UTS = 67.20 ± 4.46 MPa, and Young’s modulus = 1411.3 ± 18.3 MPa), corresponding to ∼1.5× higher Fmax and UTS and 2.75× higher modulus than neat cellulose films. The same formulation showed enhanced hydrophilicity, with the contact angle decreasing to ∼35° within 60 s and a 24 h water uptake about 3-fold higher than neat cellulose. These combined attributes suggest the potential of the optimum film as a prospective fully biobased, high-absorbency, UV–vis-opaque liner for sustainable packaging of high-moisture, light-sensitive products, where exudate retention and photoprotection are critical for preserving appearance and delaying oxidation.