Phase separation and heat-induced gelation characteristics of cellulose acetate in a mixed solvent system

The addition of cellulose acetate (CA) to a mixed solvent of N,N dimethylacetamide (DMA) and water is examined at different CA concentrations and water contents. Unlike the addition of water to a CA/DMA solution, the addition of CA to a DMA/water solution leads to a transition from a homogeneous solution at low water content to a two-phase system at higher water contents. The two-phase system has an upper liquid layer with an almost clear “solution-like” appearance and a lower gel-like layer. Treating the two-phase system at 100 °C for 30 min results in the formation of a uniform gel structure, similar to that produced by directly adding water to a CA/DMA solution. Although the phase behavior of these systems is similar, their viscoelastic properties are not. The moduli of the heat treated gels do not significantly vary from that of the bottom gel-like portion of the original two-phase samples. This may indicate that thermal treatment at 100 °C is not able to disrupt the pre-established CA intra- and intermolecular interactions and form the stronger CA-DMA interactions.