Die-swell behavior of PP/Al(OH)₃/Mg(OH)₂flame retardant composite melts

Die-swell is an important parameter related to the melt elasticity during extrusion of polymeric melts, and the degree of swell is usually expressed by die-swell ratio (B). The die-swell ratio for polypropylene (PP) composites filled with aluminum hydroxide (Al(OH)3) and magnesium hydroxide (Mg(OH)2) was measured by means of a capillary rheometer under experimental conditions of temperature ranging from 180 to 200 °C and apparent shear rate varying from 101to 103s-1, to identify the effects of the extrusion conditions as well as the filler particle content and size on the melt die-swell ratio. The results of the experiments indicated that B of the composite melts increased linearly with increase of shear stress and apparent shear rate, and this rate of increase reduced gradually with further increase of the apparent shear rate. However, the B of the composite melts decreased with a rise of the test temperature when the apparent shear rate was fixed. When the apparent shear rate and temperature were constant, the B of the composite melts decreased linearly with an increase of the filler concentration, and increased approximately linearly with increase of the particle size of the flame retardant.