Bioinspired Nanocomposites of Sodium Carboxymethylcellulose and Polydopamine-Modified Cellulose Nanocrystals for UV-Protective Packaging

Bioinspired nanocomposites have attracted considerable attention as robust, lightweight, and functional materials for various applications. These bioinspired materials contain high fractions of reinforcements and form highly ordered hard/soft nanocomposite structures with balanced molecular interactions. Herein, we fabricate bioinspired ternary nanocomposites of sodium carboxymethylcellulose (CMC) and polydopamine (PDA)-modified cellulose nanocrystals (DCNCs) with bouligand-type architectures via water-borne evaporation-induced self-assembly (EISA). The surfaces of cellulose nanocrystals (CNCs) were coated with PDA polymer to improve the interfacial adhesion between CNCs and CMC. We tune the structure formation and material properties by using different feed ratios of polymer-to-CNCs. Material properties were tailored further in ternary nanocomposites by balancing CMC and PDA amounts within the total polymer content at a given feed ratio. CMC–DCNC ternary nanocomposites with higher CNC content exhibit better-ordered structures, synergistic mechanical performances, and improved functional properties than CMC–CNC binary nanocomposites. CMC–DCNC nanocomposites with 70 wt % CNC loading show excellent mechanical strength (183 ± 36 MPa) and stiffness (15 ± 0.5 GPa) at 20% relative humidity (RH), placing these materials among the top-end of CNC-based bioinspired nanocomposites reported so far. Due to the stable and efficient interfacial interactions between DCNCs and CMC, ternary nanocomposites demonstrate comparatively much higher mechanical properties than CMC–CNC and pristine CMC films, even at higher RH (50 and 80% RH). Crack propagation studies using field-emission scanning electron microscopy display different crack growth and toughening mechanisms like crack deflection, layered delamination, and microcrack generation, resulting in synergistic mechanical improvement in the ternary nanocomposites. Due to the presence of PDA, CMC–DCNC nanocomposites also exhibit higher thermal stability, UV-shielding properties, free-radical scavenging ability, and water vapor barrier properties, which are essential characteristics for packaging materials. Thus, CMC–DCNC nanocomposites prepared from sustainable building blocks using a bioinspired design strategy show potential as robust, green, UV-protective films for food packaging