Preparation,characterization and antimicrobial application of hybrid cellulose-lignin beads

In the present study, cellulose-lignin beads were prepared using pretreated dissolving grade-pulp and extracted from birch wood hydrotropic lignin as starting materials. The preparation involved dissolution of both polymers in environmentally friendly 7% NaOH/12% urea aqueous solution, shaping the solution into beads and subsequent regeneration. Lignin content in the beads varied from 0 to 40%. The beads were characterized using FTIR, scanning electron and confocal fluorescence microscopy. Porosity, swelling behavior and leaching of lignin from the beads in water were studied as well. The antibacterial properties of the beads and original hydrotropic lignin were tested using Escherichia coli (XL-1 Blue) and Staphylococcus aureus (ATCC 25923). The obtained beads in a never-dried state were highly porous spherical particles with evenly distributed lignin in them. Their shape, structure and properties were influenced by the lignin content. The beads did not show antibacterial activity against gram-negative E. coli. On the other hand, never-dried cellulose-lignin beads inhibited growth of gram-positive S. aureus, and the inhibition efficiency increased with the lignin content. The half inhibitory concentration for never-dried beads with 40% of lignin was 1.06 mg (dry weight) per 1 mL of broth determined after incubation for 24 h at 37 °C and at initial concentration of S. aureus of 6.48 log(CFU/mL). In contrast to cellulose-lignin beads, pure cellulose beads did not inhibit growth of S aureus. The results demonstrated that hydrotropic birch lignin can be used for the preparation of composite cellulose-lignin beads. Such beads show a great potential for antibacterial applications against S. aureus.