Calcium alginate microspheres coated by bio-based UV-cured resin with high water retention performance

In this work, a bio-based resin of acrylated epoxidized soybean oil (AESO) mixed with three types of active diluents (Isoborneol methacrylates [IBOMA], tripropylene glycol diacrylate [TPGDA], and Ethoxylated trimethylolpropane triacrylate [ETPTA]) is used to form a protective UV-curable coating film on calcium alginate water-carrying microspheres (CA-WCMs). Calcium alginate microspheres (CAMs) have previously been used to encapsulate only ester soluble or oil-in-water core materials, thus limiting their application. After UV-curing with an increased active diluent dose, the pencil hardness, pendulum hardness, and mechanical strength of the CAMs increased. A photopolymerization kinetics study reveals that the maximum double bond (C=C) conversion rates of AESO-IBOMA, AESO-TPGDA, and AESO-ETPTA are 95, 92, and 86%, respectively, and the maximum conversion rate of C=C bond is 87% in their mixed system. Additionally, the water retention rate of the water-carrying microspheres (WCMs) increased with an increasing number of coating layers, plateauing after the number of layers exceeded four. The water retention is favorable, with more than 75% of the water stored for a duration of 50 days. Overall, the cost-effective and environmentally friendly method has shown encouraging results in the acquisition of water-absorbing CAMs, with the potential to overcome existing implementation constraints.