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

Abstract

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.