Physical properties of bacterial cellulose composites and cellulose Iα/Iβ ratio of their bacterial cellulose through in situ fabrication involving water-soluble polymers.

Bacterial cellulose (BC) produced by Komagaeibacter xylinum exhibits greater purity, Young's modulus, tensile strength and crystallinity than plant-derived cellulose. In contrast, natural plant cellulose, which is Iβ-rich, BC comprised a predominantly cellulose Iα structure. In this study, we cultivated BC in situ in the presence of water-soluble polymers-poly(vinyl alcohol) (PVA) or poly(ethylene glycol) (PEG)-to obtain BC/water-soluble polymer composites. Their physical properties were systematically examined. We specifically evaluated the effect of increasing the viscosity of the culture media on the crystalline structure of BC. Higher polymer concentrations and lower polymer molecular weights in the culture media resulted in larger polymer fractions in the resulting composites, with PVA and PEG contents reaching approximately 70 % by weight. The incorporation of PVA and PEG into BC brought the mechanical reinforcements of the BC composites. Because BC network suppressed the mobility of the polymers' chains strictly, Tg of PVA and PEG disappeared. In addition, the cellulose Iα ratio increased to 75 % upon the addition of PVA and PEG to the culture media. These findings demonstrate that in situ cultivation with water soluble polymers enables tunable mechanical properties and adjustable cellulose Iα/Iβ ratios in BC composites.