The 'cold-solutioning' phenomenon in cellulose triacetate-acetone mixtures

摘要

Direct mixing of cellulose triacetate (CTA) in acetone at room temperature produces only an opaque swollen gel at all concentrations. However, cycling the mixture between room temperature and -78 +/- 3degreesC results in a stable solution at room temperature, if the concentration is less than 6% (w/w). This process has been called "cold-solutioning." Such a process also produces a clear solution at concentrations between 6% (w/w) and 10%, (w/w); however, in time, the solution separates slowly into at least two phases, a clear liquid and an opaque gel phase. At concentrations above 10% (w/w) and below 20% (w/w), the system exhibits two phases. A completely opaque swollen gel forms at concentrations of 20% (w/w) and above. The above-described cold-solutioning phenomena are shown to be the coupled kinetic and thermodynamic consequences of (1) the large thermal stresses that would result from thawing a swollen mixture of CTA and acetone, arising from the large differences in their thermal expansion coefficients; and (2) the "bimodal" composition of the cellulose derivative. (C) 2003 Wiley Periodicals, Inc. [References: 25]