Thermodynamic effect on interaction between crystalline phases in size-controlled ACC-bacterial nanocellulose and poly(vinyl alcohol)

The aqueous counter collision (ACC) method can provide single bacterial nanocellulose ribbons (ACC-BNC) in a desired width, from a pellicle produced by Gluconacetobacter xylinus. Kose et al. (Biomacromolecules, 12:716–720, 2011) reported that the ACC process transformed the major I_α crystalline phase of the native fiber to a stable I_β phase, without decreasing the overall crystallinity. The current study investigated the variation of the crystalline phases of ACC-BNC, upon interaction with poly(vinyl alcohol) (PVA). ACC-BNC of desired width was mixed with PVA, without any chemical reaction occurring. This resulted in a homogeneous suspension. The equilibrium melting point of PVA in cast nanocomposite films was investigated, as a probe for evaluating the crystalline surface properties of the ACC-BNC. A decrease in the equilibrium melting point of PVA would have indicated attractive interactions between the PVA and ACC-BNC. However, the nature of the ACC-BNC surface in the presence of PVA depended on the ACC-BNC width. Thicker ACC-BNC acted as a nucleating agent for PVA. Thinner ACC-BNC acted as a diluent of PVA. This tendency was opposite to the case for I_β-dominant ACC-wood nanocellulose. ACC-BNC acting as a nucleating agent was more efficient than ACC-wood nanocellulose. The results suggested that ACC-BNC surfaces, which probably contained I _α phases, had different characteristics to those of I_β-dominant ACC-wood nanocellulose surfaces.