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.

The kinetics of sonochemical oxidation of CS 2 and the effects of process parameters (e.g., concentration, pH, temperature, ultrasonic intensity, irradiation medium, dissolved gas and time, etc.) on the degradation rates and product distributions were studied in a batch reactor at 20 kHz. Sonochemical oxidation was found to decrease with an increase in the solution temperature, and the reaction rate order was dependent on the temperature (T) range studied: zero-order at T g 10 °C [with rate constants of (0.66-3.68) × 10 -5 M min -1 ] and first-order at T e 5 °C (with rate constants of 0.037-0.266 min -1 ). From Arrhenius law, k ) A exp(E A /RT), the activation energy, E A , for the zero-order degradation of CS 2 in the presence of air as the irradiating gas was found to be 7.2 kJ/mol at the higher temperatures compared to 28.7 kJ/mol for the firstorder degradation at the lower temperatures. Sonochemical oxidation pathways leading to sulfate formation are discussed. The results of this study suggest that the ultrasonic degradation of CS 2 might provide an environmentally conscious method for the control of this hazardous pollutant in industrial wastewater.

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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 gellike 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.