Effects of Different Drying Processes on the Material Properties of Bacterial Cellulose Membranes

Summary: Membranes of bacterial cellulose produced by Gluconacetobacter xylinus show a high water and gas permeability that can be altered by different drying techniques. It could be shown that freeze-drying reduces the swellability of the polymer membranes by a factor of 5 while evaporation drying causes a reduction by a factor of 50. The strong decrease of swellability for an evaporation dried membrane could be correlated with a reduction of the absolute number of polymer strands that form the network structure of the membrane, determined with oscillatory shear rheological experiments. The removal of network meshes by a complete aggregation of polymer strands could be confirmed by IR-spectroscopy with an increased degree of intramolecular hydrogen bonding of cellulose strands. In contrast to this, the freeze-drying process shows a slight increase of the number of network meshes due to partial aggregation of free polymer strands. Freeze-dried membranes show a gas permeability two orders of magnitude higher then evaporation dried membranes. The absolute permeability strongly depends on the bacterial strain used for the polymer membrane synthesis and varies by up to 1.5 orders of magnitude for the same drying process. The Young's modulus of the polymer membranes varies with the bacterial strain used, but does not show the same trends as the permeability. Finally, a comparison of the characterized properties shows that only one of the tested strains shows the capability to synthesize membranes that meets the requirements for an application as a wet wound dressing.