Biobased diglycidyl ether diphenolates: Effect of the ester moiety on fragrance oil microencapsulation by interfacial polymerization

Health risks are associated with capsule-forming synthetic chemicals such as formaldehyde, isocyanates, and bisphenol A (BPA). This work is focused on using safe biobased molecules to build capsule walls for oil encapsulation. Cellulose-derived diphenolic acid was converted into a series of diglycidyl ether n-alkyl diphenolates (DGEDP-esters). Interfacial polymerization of oil-soluble DGEDP-esters and water-soluble amine hardeners, hexamethylenediamine (HMDA) and chitosan oligosaccharide (COS), were used to build capsule walls. DGEDP-esters with small methyl and polar monomethyl ethylene glycol (DGEDP-ME and DGEDP-MG, respectively) are most reactive forming compact crosslinked capsules with high microencapsulation efficiency (EE of 97% and 94.3%) and good stability (oil leaking was ≤ 15.7% after acidification, and ≤ 64.2% after sonication). With increased hydrophobicity of the DGEDP ester moiety, deformed capsules with low EE (63 – 87%) and poor stability (oil leaking was ≥ 18.4% after acidification, and ≥ 81.8% after sonication) were obtained. Oil encapsulated with DGEDP-esters exhibits oil release of 0.5 – 8% at day 30 (45 °C and 11 kPa). The use of COS as the hardener yields capsules with EE (88.3 – 94%) and higher oil release (9–15% at day 30) compared to HMDA, but the acid stability was remarkably improved (oil leaking ≤ 3.7%). Cytotoxicity tests suggest that capsules formed with DGEDP-ME and HMDA or COS show very low cytotoxicity against human breast cancer cells and human fibroblasts cells (cell viability of 87–102% after 24 h exposure at capsule concentration of 2 mg/mL). These observations demonstrate that the structures of DGEDP epoxy monomers and amine hardeners have significant effects. Preferred DGEDP ester groups were methyl and mono-methoxy, and effective capsule formation was achieved using either HMDA or COS, the latter providing the advantage of being a readily renewable biobased multifunctional amine.