Calculation of alcohol‐acetone‐cellulose acetate ternary phase diagram and their relevance to membrane formation

Abstract

Alcohol-acetone-cellulose acetate phase diagrams incorporated with methanol, ethanol, and isopropanol as nonsolvents are calculated according to a new form of the Flory-Huggins equation. Nonsolvent-cellulose acetate interaction parameters are measured by swelling experiments. Concentration-dependent nonsolvent-solvent interaction parameters are obtained by vapor-liquid equilibrium and the Wilson equation. It is shown that alcohol is a week coagulant compared with water, and water Ͼ methanol Ͼ ethanol Ͼ isopropanol for cellulose acetate. The phase diagrams characteristic of acetone-cellulose acetate combined with water, methanol, ethanol, and isopropanol as nonsolvents is different, which leads to the different morphological structure of a cellulose acetate membrane. The structure of a water coagulated membrane has large macrovoids from liquid-liquid phase separation. A methanol coagulated membrane has a honeycomb-like structure from spinodal microphase separation. An ethanol or isopropanol coagulated membrane has a thicker, dense top layer from the delay time phase separation.

Influence of water on phase transition and rheological behavior of cellulose/ionic liquid/water ternary systems

“…The change depends on the nature of forces such as hydrogen bonds, hydrophobic interaction, and Coulombic interaction . Also, in polymeric systems phase separation can be induced by solvent evaporation, changes in temperature, or the addition of a nonsolvent . In the MCC/EmimAc/water system, although all systems have the same concentration of MCC, changes in phase are observed as the amount of water increases.…”

“…Consequently, gelation of cellulose occurs owing to the formation of cellulose chain aggregates through cellulose–cellulose interactions and self‐associated interactions. This results in intensification of hydrogen‐bond interactions in the solution, resulting in an increase in G ′ . The following are several types of hydrogen bonds that can occur between cellulose and solvent and between cellulose molecules: intra‐ and intermolecular hydrogen bonding between the hydroxyl groups of cellulose; hydrogen bonding between the hydroxyl groups of cellulose and solvent molecules; and hydrogen bonding and electrostatic interaction between solvent molecules .…”

“…To identify the phase transition as a function of water content, a multifrequency plot of tan (δ) as a function of water content for systems was illustrated in Figure . Determination of the gel point using this method was developed by Winter and Chambon and is as the Winter–Chambon criterion . The point of intersection of the various curves at different frequencies is indicative of the gel point .…”

“…Gelation occurs because of nonsolvent‐induced polymer aggregation and formation of large macromolecular associates and clusters . For example, Appaw et al . investigated the viscoelastic behavior of cellulose acetate (CA) in a mixed solvent system and found that the addition of a nonsolvent (water) to a CA/DMAc solution led to phase‐separated gel formation.…”

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

“…In nonsolventinduced phase separation, the concentration of polymer, solvent, and nonsolvent are critical (Kunst and Sourirajan 1970;Matsuyama et al 2000). Depending on the system phase separation can lead to physical gel formation (Vaessen et al 2002), which occurs as a result of nonsolvent-induced polymer aggregation and the formation of large macromolecular associates and clusters (Reuvers et al 1986;Hao and Wang 2001).…”