Study on the Rheological Behaviour of Sisal Fibre/HDPE Composites with Flame Retardant

Abstract

The rheological behaviour of sisal fibre/HDPE composites containing two types of flame retardants as magnesium hydroxide and ammonium polyphosphate was studied using a capillary rheometer. The mass ratio of HDPE to sisal fibre was set as 20 phr. Flame retardants were added at 10, 20 and 30 phr. Results showed that the composites exhibited pseudoplastic behaviour as the shear viscosity decreased with increasing shear rate. Shear stress and real shear viscosity increased with increasing flame retardant, with magnesium hydroxide giving higher values than ammonium polyphosphate. Therefore, magnesium hydroxide had a marked effect on the processing power, while ammonium polyphosphate did not greatly affect the shear viscosity of the composites. An increase in elongation rate reduced the elongation viscosity. The flame retardant contents had no significant effect on the elongation viscosity at high elongation rate. The materials showed increased extrudate swell with increasing apparent shear rate, but this significantly decreased with the addition of flame retardant. The power law index (n) for all composites was less than 1 and the flow consistency index K was higher for composites with flame retardant than those without. Moreover, magnesium hydroxide was more effective than ammonium polyphosphate causing an increase in the K value.