Studies on melt flow properties during capillary extrusion of PP/Al(OH)3/Mg(OH)2 flame retardant composites

The apparent melt shear viscosity of polypropylene (PP) composites filled with aluminium hydroxide (Al(OH)3) and magnesium hydroxide (Mg(OH)2) was measured by means of a melt flow rate instrument under experimental conditions of temperature ranging from 170 to 195 °C and load varying from 2.16 to 12.5 kg, to identify the effects of particle size and content. The results showed that the melt shear flow of the composites obeyed the power law under the experimental conditions, the dependence of the melt apparent shear viscosity (ηa) on temperature was consistent with the Arrhenius equation, and the sensitivity of the ηa for the composite melts to temperature increased with addition of flame retardant. The ηa of the composites decreased with increasing apparent shear rate. The ηa increased with an increase of the content of flame retardant, but this rate of increase decreased with a rise of temperature or load. When the particle size of flame retardant was smaller than 5 μm, the ηa of the composites increased with increase of particle size of flame retardant, and then reduced with a further increase of particle size of flame retardant.