Interfacial/free radical polymerization microencapsulation: kinetics of particle formation

Area of Science:

• Polymer Chemistry
• Materials Science
• Colloid Science

Background:

• Microcapsules are essential for encapsulating active ingredients like pigments.
• Controlling microcapsule size and stability is critical for their application performance.
• Interfacial polycondensation and free radical polymerization are common microencapsulation techniques.

Purpose of the Study:

• To investigate the effects of key variables on pigment-containing microcapsule formation.
• To elucidate the mechanism of particle size evolution during microencapsulation.
• To identify methods for preventing microcapsule suspension failure.

Main Methods:

• Preparation of pigment-loaded microcapsules via interfacial polycondensation and free radical polymerization.
• Systematic variation of shearing time, surfactant concentration, and monomer addition.
• Kinetic analysis of particle formation and size changes.

Main Results:

• Polyvinyl alcohol (PVOH) depletion due to reaction with oil-soluble shell monomers was identified as a primary cause of instability.
• Low PVOH concentrations exacerbated particle growth and led to suspension failure.
• A two-stage particle formation mechanism involving equilibrium breakage/coalescence and PVOH depletion-induced coalescence was revealed.
• An optimal shearing time exists for minimizing microcapsule size, dependent on process variables.

Conclusions:

• PVOH plays a critical role as a stabilizer, and its depletion compromises microcapsule integrity.
• Understanding the interplay between mechanical forces and chemical reactions is key to controlling microencapsulation.
• Strategies to prevent PVOH depletion are proposed to enhance microcapsule stability and performance.