Encapsulating montmorillonite and ammonium polyphosphate in one polyurea microcapsule to improve flame‐retardant and mechanical properties of polypropylene composites

Abstract Ammonium polyphosphate (APP) and montmorillonite (MMT) have been widely used in the flame‐retardant of polypropylene (PP), but the low synergistic flame‐retardant efficiency and their poor compatibility with PP matrix need to be greatly improved. In this work, APP and MMT were encapsulated in the one microcapsule (PU@A‐M) at the determined optimal ratio through the “bridging” reactions of diethylenetriamine (DETA) with APP and MMT. Compared with the PP/A + M composites with the physical mixture of APP and MMT, the limiting oxygen index, peak of heat release rate, total heat release, and total smoke production of PP/PU@A‐M were decreased by 5.7%, 48.8%, 3.1%, and 20%, respectively. The well‐dispersed PU@A‐M with charring‐forming agent (CFA) generated continuous and compact char layers with COP, COSi, and SiOP crosslinking structure. Furthermore, the tensile strength and elongation at break of PP/PU@A‐M were enhanced by 4.8% and 36.9%, respectively, as compared with PP/A + M because of good dispersibility and compatibility of PU@A‐M in PP matrix.