Plastic waste is a major environmental challenge that the world has failed to address so far. The extensive reliance on non-biodegradable polymers in packaging contributes to pollution, carbon emissions, and the accumulation of microplastics. These challenges have intensified global efforts to develop biodegradable materials that can replicate the functional performance of conventional plastics. [1]. Among available candidates, biopolymer-based films have garnered increasing attention due to their renewability and potential to mitigate environmental impact [2,3]. However, their limited mechanical strength and barrier performance continue to hinder large-scale industrial adoption. Lignocellulosic derivatives such as carboxymethyl cellulose (CMC), are widely used in the production of biodegradable films due to their excellent film-forming properties [4]. However, most CMC-based films have low mechanical strength and high water vapor permeability and cannot be used in packaging applications [5]. To overcome these limitations, the reinforcement of CMC films with various additives has been investigated. For example, studies by Sadi et al. [6] and Helmiyati et al. [7] have demonstrated that the inclusion of specific reinforcing polymers/agents, such as organoclay, montmorillonite, and polyvinyl alcohol, significantly enhanced the tensile strength and moisture barrier properties of CMC films. Non-isocyanate polyurethanes (NIPUs) represent a safer and more environmentally benign alternative to conventional isocyanate-based PUs. These polymers are synthesized through cyclic‑carbonate-amine reactions without using toxic precursors [3,8]. Recent studies have demonstrated the versatility of NIPU derivatives in coatings and packaging films due to their tunable mechanical, chemical resistance and thermal properties [3,9]. Within this category, non-isocyanate hydroxyurethanes (NIHUs) have emerged as a new subclass of NIPU with a high density of hydroxyl groups, which can promote strong intermolecular hydrogen bonding and compatibility with polysaccharides (e.g., starch and CMC) [10]. We have recently explored the green synthesis of NIHUs through a catalyst-free and solvent-free reaction and their combination with CMC to develop novel composite films [11]. Our results showed that blending NIHU with CMC produced flexible and thermally stable hybrid films; however, the hybrid CMC/NIHU materials lacked sufficient stiffness and active functional properties for advanced packaging applications.

To address these deficiencies, the incorporation of lignin-based additives has gained attention because of their aromatic structure, antioxidant functionality, and UV-shielding capacity [[12], [13], [14]]. Sodium lignosulfonate (LS) is a sulfonated lignin derivative and by-product of the paper industry. It contains phenolic hydroxyl and sulfonate groups that can participate in hydrogen bonding and π–π interactions with polymer matrices [15,16]. These interactions can improve film cohesion while imparting additional bioactivity. Petkovska et al. [17] and Nunez et al. [18] have demonstrated that LS can significantly enhance the UV-blocking capabilities and antioxidant properties of polymer matrices, thereby extending their functional lifespan. Despite these promising merits, LS has not yet been investigated as a multifunctional filler within NIHU/CMC hybrid films, where its phenolic and sulfonate functionalities could simultaneously reinforce mechanical integrity and confer active protection.

To bridge this gap of knowledge, the present study aimed to develop and characterize multifunctional CMC/NIHU films reinforced with LS. NIHU was synthesized through a catalyst-free, solvent-free reaction and subsequently incorporated into CMC with varying LS loadings using a solution-casting approach. The films were systematically evaluated for their structural, thermal, mechanical, barrier, UV-blocking, and antioxidant properties to elucidate the effects of LS concentration and interfacial interactions. This work provides new insights into the synergistic role of lignosulfonate within polysaccharide–polyurethane matrices, demonstrating a scalable route toward bio-based packaging films that combine mechanical robustness, improved barrier performance, and active functionality. By addressing both environmental sustainability and functional performance, these LS-reinforced NIHU/CMC films offer a promising step toward next-generation eco-friendly packaging materials.