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

Abstract

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.

Rheology of organoclay assisted extrusion of HDPE using Particle Image Velocimetry

“…The figure shows that C15A was present and dispersed. A similar SEM result was obtained for HDPE-1000, as discussed in a previous publication by Adesina and Hussein (Adesina and Hussein, 2012). …”

“…Such behavior is common to HDPE that shows strain hardening behavior (Hyun et al, 2007). Extensional rheology of the HDPE used in this work was reported earlier, and the results showed that it exhibited strain hardening behavior (Adesina and Hussein, 2012). However, the reported slope in the work of Hyun et al was 1.56 (Hyun et al, 2007).…”

“…Clay is said to be intercalated if polymer movement into the gallery spacing causes less than 20-30 A o separation between the clay while clay exfoliation occurs if the separation of the clay platelets is more than 80-100 A o or complete disappearance of the WAXD signal (Wagener and Reisinger, 2003). In this present work, the disappearance of the peaks might be the result of the exfoliation of the organoclay in HDPE or due to dilution effect during sample preparation, as previously discussed in our work (Adesina and Hussein, 2012). The SEM image of HDPE-500 shown in Fig.…”

“…The final concentrations of C15A in HDPE were 0.1 wt% (HDPE-1000) and 0.05 wt% (HDPE-500). Such concentrations were shown to ease the processing of HDPE (Hatzikiriakos and Dealy, 1991;Adesina and Hussein, 2012). Oleamide was added to HDPE (HDPE-Oleamide) at a concentration of 0.5 wt%.…”

“…However, apparent slip may be possible (Rosenbaum et al, 1998). Addition of organoclay to polyolefins generally resulted in a decrease in extrusion pressure (low viscosity or high throughput) during capillary (Hatzikiriakos et al, 2005) and recently, in slit die extrusion (Adesina and Hussein, 2012;Adesina et al, 2015). Addition of organoclay also resulted in stress decay in high density polyethylene during (LAOS).…”