Melt shear viscosity of PP/Al(OH)3/Mg(OH)2 flame retardant composites at high extrusion rates

The melt apparent shear viscosity (ηa) of 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 10 to 2 × 103 s−1, to identify the effects of the filler particle content and size on the melt viscosity. The results showed that the melt shear flow of the composites obeyed the power law and presented pseudoplastic behavior. The dependence of ηa on temperature was consistent with the Arrhenius equation. The sensitivity of ηa for the composite melts to temperature was greater than that of the unfilled PP, and weakened with increasing apparent shear rate. The ηa increased linearly with an increase of the weigh fraction of the flame retardant, especially in the low apparent shear rate region. The ηa of the composites decreased slightly with an increase of particle size of flame retardant. Moreover, the variation for the ηa with particle size of flame retardant was much less than with apparent shear rate under these test conditions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011