Phase separation modulation and aggregation prevention: Mechanism of the non-solvent addition method in the presence and absence of polyisobutylene as an additive

The mechanism by which microcapsule aggregation is diminished in the presence of low concentrations of adjunct non-walling polymers such as polyisobutylene PIB in organic solvents is uncertain. It is here investigated by phase separation studies employing the non-solvent addition method cyclohexane in parallel with microencapsulation experiments, using Eudragit wall polymers and tetrahy-drofurane THF as solvent with and without PIB. Polymer incompatibility leads to formation of two dilute liquid phases and emulsification from the outset. Progressive solvent transfer to the PIB phase modulates the rate of wall polymer desolvation and maintains the concentrated wall polymer phase in a fluid state during the critical microencapsulation stages of wall polymer entrapmen and spreading. A three-phase system is formed when gelling ensues L₁+ L₂ + gel In the absence of PIB, phase separation leads immediately to deposition of the wall polymer in gel form L₁+ gel leading to adhesion. Phase diagrams are presented.