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 ( 0.1 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 ( 0.1 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.

Interaction between 0.05 wt % organoclay and polyethylenes of different short chain branching (SCB) was studied. Linear rheology (van Gurp-Palmen plot) was used to study the effect of organoclay on the rheology of polyethylenes. Organoclay had effect only on the van Gurp-Palmen plot of linear polyethylene. Fourier transform (FT) rheology, extrusion at high-shear rates in a slit rheometer, transient stress growth analysis, and extensional rheology were conducted to examine the potential of organoclay as a processing aid. Organoclay reduced the transient stress overshoot, normal stress difference, go, onset of shear thinning, and extrusion pressure of polyethylene. The reduction was more pronounced in linear poly-ethylene without branching. Such effects gradually decreased as the branch content increased. The trend was independent of the type of flow (shear or extensional). It was interesting to note that FT rheology was not effective in explaining the impact of organoclay on polyethylene. The work concluded with the proposition that organoclay (as low as 0.05 wt %) was a good processing aid for linear polyethylene and polyethylenes with low content of SCB.

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The effect of different processing additives on the extrusion instabilities of high density polyethylene (HDPE) was investigated. The concentration of each processing additive was fixed at 0.05 wt%. Organoclay, boron nitride, and fluoropolymer reduced transient shear and extensional viscosities of HDPE melt. Drop in extrusion pressure occurred during the extrusion experiment. The initial loss of glossiness in HDPE was restored with the addition of these additives. However, the fluoropolymer did not succeed in eliminating the stick-slip fracture. Despite the inclusion of the processing additives, gross-melt fracture in HDPE reappeared at apparent shear rate of 141 s −1 . Both moment and distortion factor methods of analyses were employed and their findings support the observed visual trends of the extrudate surface. The quantifying tools indicated that combined organoclay and fluoropolymer reduced the pressure fluctuations and its performance surpassed that of the individual additives.

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