Ethyl Cellulose-Solvent Phase Relationships Relevant to Coacervation Microencapsulation Processes

Qualitative and quantitative solubility studies of ethyl cellulose, Type N-10, in 112 and 36 solvents respectively are reported. The relative contribution of dispersive, polar and hydrogen bonding intermolecular forces are depicted on two-dimensional and triangular solubility graphs. Phase separation phenomena may be explained in terms of the differences in both the solubility parameter (δ) and the polymer-solvent interaction parameter (χc) values between ethyl cellulose and each solvent. Coacervation occurs in very poor solvents with δ values just outside the solubility spectrum of ethyl celluloseA mean value for the solubility parameter and critical interaction parameter (χc) for ethyl cellulose obtained from turbidity titration measurements were 9.39 ± 0.17 (cal/cm3)½ and 0.38 ± 0.04 respectively. Gelation occurs with nonsolvents with δ values significantly outside the solubility spectrum and with correspondingly larger χc values. Flocculation was observed only in polar solvents in which large χc values occurTheoretical values for the ethyl cellulose-solvent interaction parameters were calculated for 112 solvents. It is proposed these parameters can identify potentially useful solvents or solvent-nonsolvent systems for the preparation of microcapsules using coacervation