New approaches for the development of cellulose acetate/tetraethyl orthosilicate composite membranes: Rheological and microstructural analysis

Abstract

The rheological behavior of cellulose acetate (CA)/tetraethyl ortosilicate (TEOS) blends in tetrahydrofuran (THF), microstructural properties and thermal stability of the corresponding films were investigated in this work. The studied blends exhibit different behaviors depending on the amount of tetraethyl orthosilicate contained. Cellulose acetate pure solution present a Newtonian behavior on the entire shear rate domain, while by addition of TEOS a decrease in viscosity with increasing of shear rate is observed, as result of the polymer backbone disentanglement and orientation of the polymer chain in the flow direction during the rheological tests. On the other hand, for the CA/TEOS blends increasing of viscosity with increasing of TEOS content is a consequence of the two components possibility to form hydrogen and covalent bonds. Also, for a high content of TEOS a gel behavior, with storage modulus higher than loss modulus, was identified. Studies of infrared spectroscopy, atomic force microscopy and thermal stability confirm that, as TEOS content increases the number of interactions is supplemented, so that for a TEOS content that exceeds 2 wt% the process of film casting will be difficult. Thus, this study represents a first stage to identify the optimal compositions of the CA/TEOS mixtures that would favor the obtaining of uniform and homogeneous porous films with improved properties and suitable for use as membranes both in industrial and biomedical applications.