Cellulose Nanocrystals Influence Polyamide 6 Crystal Structure, Spherulite Uniformity, and Mechanical Performance of Nanocomposite Films

Cellulose nanocrystals (CNCs) are an ideal reinforcing agent for polymer nanocomposites. CNCs can form hydrogen bonds with polyamide 6 (PA6); however, the direct effects of unmodified CNCs on PA6 morphology and crystal structure have not been fully elucidated. This work investigated the influence of CNCs on the mechanical performance and physicochemical properties of spin-coated CNC–PA6 films through quantitative analysis using techniques that probe multiple length scales. CNCs interacted with PA6 to induce the γ (chiral) allomorph over the α allomorph at low CNC loadings (≤1 wt %) and nucleated a high density of small uniform spherulites, leading to stiffer nanocomposites. Higher loadings caused CNC aggregation and crystalline, non-spherulitic features. Overall, we hypothesize that the reinforcement mechanism of CNCs in PA6 is dominated by morphological changes in the matrix, not percolation. Understanding CNC–polymer interactions and morphology (on films prepared without thermal processing or surface modification of CNCs) offers “design rules” for how to incorporate CNCs into nanocomposites for optimized material performance in various applications, for example, membranes, coatings, and packaging.