Crystallization Morphology and Behavior of Polypropylene Composites Containing Microencapsulated Flame Retardant

With shells of melamine-formaldehyde (MF), urea-melamine-formaldehyde (UMF), or poly(vinyl alcohol)-melamine-formaldehyde (VMF), microencapsulated ammonium polyphosphate (APP) was prepared by in-situ polymerization for use as a flame retardant in polypropylene (PP). Microencapsulated APP showed rougher surface, smaller size, and narrower size distribution compared with APP. The results of polarized optical microscopy (POM) showed that the additives resulted in a decrease of the spherulite size and less perfection in crystal geometry of PP composites. Due to the interaction and alignment of the PP polymer chains at the surface, the surface modification of APP influenced the formation and further development of PP crystals remarkably. The crystallization and melting behaviors of the PP composites were affected by the rough surface of the microencapsulated APP, which was helpful for the formation of beta-crystals and decreased the crystal growth rate compared with APP.