In situ tunability of bacteria produced cellulose by additives in the culture media

Bacterial cellulose offers several advantages over other celluloses not only in terms of purity and properties but also because it allows modifications during synthesis (in situ modification). This possibility has been explored in this paper to tune bacterial cellulose in terms of cellulose microfibril dimensions, branching, crystallinity, crystallite size and porosity. It has been shown that modifiers can be added to the bacterial cell culture medium to obtain these variations during the cellulose biosynthesis. The effects of four of the several possible modifiers have been reported, namely calcofluor (dye used for cellulose), carboxy methyl cellulose (cellulose derivative), polyethylene glycol and nalidixic acid (antibiotic). Crystallinity was found to decrease from over 80 % for unmodified cellulose to about 50 % for that modified by calcofluor. The crystallite size also decreases, but to different extents along the different crystal directions, on modifications. The microfibril dimensions were found to decrease from 65 nm in case of unmodified cellulose to about 30 nm in case of carboxy methyl cellulose modification. The cellulose modified with polyethylene glycol does not show much change in crystallinity, crystallite size and microfibril dimension. Porosity was also found to decrease in all cases except that modified by polyethylene glycol where it increased from 79 to over 110 m²/g. All these observations are explained on the basis of the effect of modifier on cellulose polymerization and assembly.