Bacterial cellulose (BC) produced by Gluconacetobacter Xylinus is rich in cellulose Iα. Structural analysis of BC by Fourier-transform infrared (FTIR) and 13C CP/MAS NMR has confirmed the transformation of cellulose Iα to Iβ by annealing BC at a temperature between 260°C and 280°C. However, there remain uncertainties on the mechanism of allomorphs transformation of native cellulose during hydrothermal treatment. In our project, the allomorph of bacterial cellulose was converted at different temperature and duration (235°C for 5 min; 235°C for 10 min; 235°C for 15 min; 250°C for 15 min; 250°C for 40 min). Two independent techniques - SFG and FTIR - have been used to show the transformation of cellulose Iα to Iβ. Deconvolution of hydrogen bonding vibrations region near the 700~800 cm−1 in IR spectra and OH stretch region (3100-3800 cm-1) in SFG spectra indicate the Iα portion almost disappears completely at 250°C treated for 40 min. The d-spacing data from X-ray diffraction (XRD) are also in accordance with cellulose Iα → Iβ transformation. The alkyl/hydroxyl intensity ratio in SFG spectra (sensitive to meso-scale arrangement of cellulose) decreases with increased annealing temperature and duration. Previous study reported that increased alkyl/hydroxyl intensity ratio indicated more ordered lateral packing. However, XRD shows higher crystallinity and larger crystal size after annealing and Field-emission scanning electron microscopy (FESEM) shows very marginal changes in packing and bundle diameter for control BC and annealed BC. The alkyl/hydroxyl intensity ratios in SFG spectra combined with XRD and FESEM indicate there is unknown structural change during hydrothermal treatment of BC, and alkyl/hydroxyl intensity ratios in SFG are sensitive to this structural change.

Structural characterization of annealed bacterial cellulose by SFG, FTIR and XRD

249th National Meeting (2015)

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