Multi-chambered flame retardant microcapsules containing bisphenol A-bis (diphenyl phosphate) and zinc borate prepared by Pickering emulsions polymerization and their application in water-borne polyacrylic acid coatings

Multi-chambered flame retardant microcapsules (ZB-FRM) containing bisphenol A-bis(diphenyl phosphate) (BDP) and zinc borate (ZB) with calcium alginate (CA) shells were prepared by Pickering emulsions polymerization. The aim was to microencapsulate BDP to form a CA shell with many hydroxyl groups, improve its compatibility with aqueous polyacrylic acid (PAA), and reduce the flammability of PAA by using the flame suppression ability of BDP. Next, the high smoke generation caused by BDP was suppressed and the mechanical properties of the flame retardant coating were improved by introducing ZB in the shell layer. The thermal properties of the microcapsules, the mechanical and flame retardant properties in aqueous substrates, and smoke generation during cone calorimetry tests were tested. It was found that ZB-FRM had good compatibility with PAA. The introduction of ZB-FRM increased PAA's limiting oxygen index (LOI) to 25.5% and vertical combustion level to V-0. ZB improved the thermal stability of the microcapsules, the mechanical properties of the flame retardant coating, and the reduced smoke from BDP by 19.9%. However, ZB inhibited the initial flame retardant mechanism of BDP, resulting in a slight decrease in LOI, but still, a 6.9% improvement compared to pure PAA.