Characterization of chemically treated bacterial (Acetobacter xylinum) biopolymer: Some thermo-mechanical properties

Bacterial cellulose prepared from pellicles of Acetobacter xylinum (Gluconacetobacter xylinus) is a unique biopolymer in terms of its molecular structure, mechanical strength and chemical stability. The biochemical analysis revealed that various alkali treatment methods were effective in removing proteins and nucleic acids from native membrane resulting in pure cellulose membrane. The effect of various treatment regimens on thermo-mechanical properties of the material was investigated. The cellulose in the form of purified cellulose membranes was characterized by differential scanning calorimetry (DSC), thermo-gravimetric analysis (TGA) and dynamic mechanical thermal analysis (DMTA). The glass transition temperature (Tg) of the native cellulose (untreated, compressed and dried pellicle) was found to be 13.94 °C, in contrast, the chemically treated cellulose membranes has higher Tg values, ranging from 41.41 °C to 48.82 °C. Investigations on isothermal crystallization were carried out to study the bulk crystallization kinetics. Thermal decomposition pattern of the native as well as alkali treated cellulose was determined by obtaining thermo-gravimetric curves. At higher temperatures (>300 °C), the biopolymer was found to degrade. Nevertheless, the alkaline treated cellulose membrane was more stable (between 343.27 °C and 370.05 °C) in comparison to the native cellulose (298.07 °C). Further, the percentage weight loss in case of native cellulose was found to be 26.57%, in comparison to 6.45% for the treated material, at 300 °C. The DMTA revealed complex dynamic modulus of the material, at different temperatures and fixed shear stress, applied at a frequency of 5 Hz. The study delineated the effect of alkali treatment regimens, on the thermo-mechanical properties of bacterial cellulose for its application over a wide range of temperatures.