Bio-based alternative for encapsulating fragrance oils in epoxy resin microcapsules

There is increased pressure on microcapsule manufacturers to develop microcapsules following green chemistry principles and using safe biobased materials. Diphenolic acid, prepared from cellulose-derived levulinic acid and phenol, was used as a replacement for bisphenol-A. The resulting diepoxy resin diglycidyl ether diphenolate methyl ester (DGEDP-methyl ester) was incorporated in the fragrance oil and reacts with hexamethylenediamine (HMDA) to build capsule walls by interfacial polymerization. The biobased emulsifier gum arabic at 2.5 wt% was found to provide good capsule formation. The effect of DGEDP-methyl ester/HMDA ratios on various capsule properties was studied. A low HMDA concentration at 0.75 wt% yields deformed capsules with lower microencapsulation efficiency (EE< 90%) and lower stability (oil leaking > 26.3% after acid treatment, and > 87.2% after sonication). A medium HMDA concentration (1 wt%) with 2 - 4 wt% DGEDP-methyl ester generates spherical capsules with higher EE (91.2 - 96.5%) and improved stability (oil leaking was < 20.3% after acid treatment, and < 76% after sonication). Increasing the content of HMDA to 1.25 wt% along with ≥ 2 wt% DGEDP-methyl ester led to extensive aggregation with a slight increase in EE at the expense of capsule stability. These observations demonstrate that DGEDP-methyl ester/HMDA interfacial polymerization is a promising biobased alternative for isocyanate and formaldehyde approaches for oil encapsulation.