Impact of organoclay and maleated polyethylene on the rheology and instabilities in the extrusion of high density polyethylene

The impact of organoclay on the rheology and extrusion of high density polyethylene (HDPE) was studied. Organoclay effect was studied at very low clay loading (≤0.1 wt %) while serving as a processing aid. A special design slit die with three transducers was used in the study of the extrusion melt instabilities. The rheological results showed that normal stress difference of HDPE was reduced during steady shear rate and stress growth tests when organoclay (a;circ0.1 wt %) was added. The extensional strain and stress growth of HDPE reduced with the addition of organoclay. So, organoclay (≤0.1 wt %) has an effect on the shear and extensional rheology of HDPE. The intensity of the melt instability was characterized with both a moment analysis and distortion factor (DF) from an advanced Fourier transform analysis. Both showed the same trends in the characterization of the pressure fluctuations in the die. Generally, addition of organoclay (a;circ0.1 wt %) to HDPE led to the reduction in DF. The ratio of first and second moment analyses became reduced as well. The results quantified the extent of elimination of gross melt fracture in HDPE by organoclay. Also, the extrusion pressure was reduced with organoclay (≤0.1 wt %) inclusion hence more throughput. There was a good correlation between rheology and extrusion. Both showed that the platy-like organoclay streamlined the melt flow. However, the maleated polyethylene added as a compatibilizer did not give substantial synergistic effect.