Viscoelastic Behavior of Cellulose Acetate in a Mixed Solvent System

Abstract

The effect of increasing water composition on the rheological and microstructural behavior of a ternary cellulose acetate (CA)/N,N-dimethylacetamide (DMA)/water system is examined. Addition of water to the CA/DMA system results in enhanced steady shear viscosity and dynamic viscoelastic properties and ultimately to phase-separated gel formation. The changes in dynamic rheological behavior of the system during gelation correlate well with the combined solubility parameter (delta) and, in particular, the Hansen hydrogen-bonding solubility parameter index (delta(h)) of the solvent system, suggesting hydrogen-bonding interactions may be the major route initiating the sol-gel process. For all gels studied, the elastic modulus and the critical stress to yield shifts to higher values with increasing CA concentration and/or water content. In addition, the elastic modulus exhibits a power-law behavior with water content, with the same power-law exponent observed for gels containing different CA concentrations. Addition of water leads to formation of a denser gel network, as evidenced from direct visualization of the gel microstructure through confocal microscopy.

Effect of processing conditions on gel formation in ternary cellulose acetate systems

“…The ternary systems exhibited Newtonian behaviour at low shear stress followed by shear thinning as shear stress increased ( Fig. 1), consistent with previously reported results (Appaw et al 2007;Kadla and Korehei 2010).…”

“…The gels prepared using this CA/DMA/water ternary system have been shown to fractal in nature, therefore a power law behaviour should exist between G 0 and non-solvent volume fraction (Appaw et al 2007(Appaw et al , 2010. Figure 12 illustrates that the power law exponents vary between the different preparation temperatures and the different methods of addition (i.e.…”

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

“…We investigate the sequence of component addition, specifically, the addition of CA to various DMA/water solutions. Unlike the previous system (Appaw et al 2007) in which water was added to CA/DMA solutions, the addition of CA to DMA with various water contents resulted in a two-phase system with distinctly different viscoelastic properties.…”

“…Subsequently, the system was purged with nitrogen to ensure an inert atmosphere and heated for 10 min at 70°C to produce clear/homogeneous samples. In this paper, the dissolution process is termed ''dissolution method 2'', as compared to that previously reported (Appaw et al 2007) in which water was added to CA/DMA solutions (dissolution method 1). In both systems the heated samples (at 70°C) are clear homogeneous solutions.…”

“…Recently, we reported the viscoelastic behaviour of cellulose acetate in a mixed solvent system (Appaw et al 2007). The addition of a nonsolvent (water) to a CA/N,N-dimethylacetamide (DMA) solution led to phase-separated gel formation.…”