Sodium alginate solutions: correlation between rheological properties and spinnability

In the present work, different sodium alginates were used to prepare nanofibrous mats by means of electrospinning technique. Firstly, a molecular characterization of each sample was carried out: the molecular mass and the composition, i.e. mannuronic/guluronic acid ratio, were determined using the Mark-Houwink-Sakurada relation and FTIR spectroscopy, respectively. Afterwards, the polyelectrolyte nature and the characteristic concentration regimes of each alginate were studied through rheological tests. The results indicated that both the molecular mass and the composition strongly influence the properties of the polymer in solution; in particular, long chains and the predominance of guluronic moiety lead to a marked polyelectrolyte behaviour. Subsequently, in order to obtain a good spinnability, polyethylene oxide and Triton X-100 were added to alginate-based solutions. The resulting solutions were carefully characterized by a rheological point of view; the viscosity, viscoelasticity, thixotropy and thermal stability were investigated and correlated with their capability of being electrospun. Two different set-ups were used for electrospinning: one consisted in a dry collector and the other one in a wet collector (immersed in a collecting solution). The morphology of the membranes was characterized through scanning electron microscopy; moreover, thermogravimetric analysis was performed in order to study the final composition and the thermal degradation. The preliminary results indicated that the membrane obtained using guluronic-rich alginate and the wet-collector system is composed of only sodium alginate and characterized by thin fibres and a high porosity, which could make it suitable for pharmaceutical and biomedical applications.