Coloration of bacterial cellulose using in situ and ex situ methods

This study aimed to produce colored bacterial cellulose (BC) by adding dye during cultivation (in situ) and by dyeing BC after cultivation (ex situ), respectively. Three different dyestuffs—direct, acid and reactive—were selected for application in the coloring of BC. In the in situ method, the dyestuff is adding into the culture medium. The effects of various dyestuff and carbon sources on the production yield were evaluated. In the ex situ method, the dyestuff, BC gel, was dyed under various dyestuff and dyeing conditions. The production yield of BC cultured by the in situ method in glucose as the carbon source and using a reactive dyestuff was the highest, at about 86%. The ex situ dyeability of BC was improved by setting the dyeing conditions to pH 3 and 135℃. Both methods were evaluated regarding the surface appearance of the BC by scanning electron microscopy (SEM). The SEM showed that the defined cellulose fibril networks retained their inherent nanostructures when the dye penetrated the site through dyeing. The surface roughness of the BC, colored by the two methods, was evaluated by atomic force microscopy. The BC colored by both methods showed smooth surfaces. For BC colored by the in situ method, the surface roughness was 194 nm, indicating that the BC was smoother and finer than that obtained via the ex situ method. In comparing hue and saturation values, the BC colored by the in situ method showed clearer blue colors than that colored by the ex situ method. The in situ method was more effective than the ex situ method for coloring BC.