Abstract: The effect of composition of black masterbatches on tensile strength of weld line of halogeflame retardant polypropylene was studied. When added as an individual component, the carrier, dispersant, and carbon black had small effect on the tensile strength of weld line, and was not the primary reason for the screw column burst. However, in the black masterbatches, the high viscosity caused by increasing carbon black content and decreasing particle size resulted in low tensile strength of weld line and higher possibility of screws column burst. When PP was used as a carrier, the low resultant low viscosity may improve the tensile strength of weld line and lower the possibility of screw column burst.

Key words: black masterbatch, polypropylene, weld line, viscosity, tensile strength, flame retardant