The Effect of the Drying Process on the Properties of Bacterial Cellulose Films from Gluconacetobacter hansenii

Abstract

Bacterial cellulose (BC) is a polymeric material that presents unique structural and mechanical properties, high crystallinity, biocompatibility, and biodegradability. All these excellent properties make BC attractive for various biotechnological applications, ranging from biomedical to electronic devices. However, the cultivation conditions to produce BC as well as the downstream processing steps can affect the properties of BC films by modifying the microstructure of the material. This paper reports on the effect of drying method on BC films produced by Gluconacetobacter hansenii using two different procedures (oven drying at 50°C and freeze- drying). Structural changes in the BC films were evaluated using scanning electron microscopy (SEM), thermogravimetric analyses (TGA), X-ray diffraction (XRD), and Fourier-Transform Infrared (FT-IR). The two samples were visually different, as the oven dried BC was transparent while the freeze-dried BC was whitish. SEM micrographs showed that the samples had similar interweaving, but the freeze-dried material presented a higher porosity while oven dried presented collapsed fibers, leading to a volume reduction of the film. The analysis of the thermal stability showed that the films have a similar degradation profile, starting the process of degradation at 319 °C for the oven and at 325 °C for the freeze-dried samples. The BC films showed also similar crystallinities (85%), although their diffratograms exhibit different peaks suggesting that the drying process changed the percentage of Ia/Is polymorphs of the films, which was corroborated by the FT-IR results. These differences in the BC films characteristics submitted to different drying procedures can have an impact on their mechanical properties and water absorption capability, thus potentially influencing the type of possible applications.