The microencapsulated red phosphorus (MRP) filled polypropylene (PP) composites were prepared using a twin-screw extruder. The effects of load and temperature on the extrudate swell behavior of the PP/MRP composite melts were investigated by means of a melt flow indexer. The test temperatures and loads were varied from 180 to 205 degrees C and from 2.16 to 12.5 kg, respectively. The results showed that the die-swell ratio (B) of the composite melts increased roughly linearly with increasing load while decreased slightly with a rise of test temperature. The sensitivity of the die-swell ratio of the composite melts to load was significant. When the test temperature or load was constant, the values of the B of the composite melts decreased slightly with increasing MRP weight fraction. The findings can provide useful information for processing of these composites. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013