Rheological properties, flow visualization and extrudate swell of NR compound by rotating‐die rheometer

Abstract

An experimental apparatus coupled with a rotating die system was especially designed and manufactured to study the rheological properties, flow patterns and swelling behavior of natural rubber (NR) compound for different shear rates and die rotating speeds at a test temperature of 1108C, the results being compared with those by the static capillary die. It was found that NR compound used exhibited psuedoplastic non-Newtonian behavior. The rotation of the capillary die could reduce the extrusion load. The wall shear stress for any given shear rates increased with increasing die rotating speed. The fluctuation of the entrance pressure drop increased with increasing die rotating speed. The flow pattern development in the rotating-die rheometer was different from that observed in the static die. The flow patterns in the rotating die were clearly unstable and contained two flow components which included axial flow along the barrel and circumferential flow at the die entrance. The size and shape of the axial and circumferential flows were more dependent on the piston displacement. It was found that the swelling ratio of the NR compound decreased with increasing die rotating speed.

Flow visualization & extrudate swell behavior of natural rubber compound in annular die capillary rheometer

“…At the same shear rate, it was found that the difference in shear stress of both types of NR compound was no more than 4.5%. It could be concluded that a mixture with TiO 2 did not affect overall flow property of NR compound [16] . Results from the measurement of flow property indicated that the wall shear stress from divergent annular die was higher than the wall shear stress from convergent annular die by an average of 6.5 % at every shear rate.…”

“…The formulation of the NR compound was shown in Table 1. The materials were compounded in accordance with the experimental procedure by Intawong et al [16] . The compound was divided into two separate parts, one of which was pigmented with titanium oxide (TiO 2 ) to create a white compound.…”

“…The rubber was partially extruded at a temperature below vulcanization point, which in this study was 110°C. In addition, after adding rubber into the barrel to its full extent, the experiment had to wait for 15 minutes for the rubber's temperature to become isothermal before extrusion [16] . The displacements of the piston was limited to stop moving at 30 mm, 60 mm, 90 mm and 120 mm from the barrel's top.…”

“…They found the swell of natural rubber compound changed in accordance with the flow pattern and was influenced by convergent flow angle. Intawong, et al [16] the studied flow pattern of natural rubber compound in circular rotating die capillary rheometer and found that die rotation caused complex flow pattern at the die entrance. The circumferential flow caused repetitious circulation at the die entrance.…”

Influence of flow pattern development at die entrance and inside annular die on extrudate swell behavior of NR compound

“…Figure 1b shows a cross-section of annular die that is assembled to a split barrel of the capillary rheometer, where the annular die is centrally fixed at the bottom of the barrel with a Die holder. In addition, a pressure transducer (Dynisco, Model PT460E-2CB-6, Franklin, MA) [10,11] is also installed on the 5mm top of the die entrance, in order to measure die entrance pressure drop, which will be further used to study the rheological properties.…”