Rheological properties of feedstocks prepared with steatite powder and polyethylene-based thermoplastic binders

In this study, rheological properties and behaviors of binder formulations and powder injection molding (PIM) feedstocks, used in the ceramic industry, were investigated. For this purpose, various binder formulations and PIM feedstocks were prepared. In these formulations, polyethylene (PE) and three waxes (carnauba, bees wax and paraffin) were used with steatite powder loading. A 50% (v/v) fraction of feedstocks was steatite powder with 8.15 μm average particle size. Steatite powder and binder formulations were mixed as dry in a Turbula shaker/mixer for 30 min. To achieve a good disperse mixing, twin screw extruder was also used. The rheological properties of the resulting binder formulations and feedstocks were characterized by a capillary rheometer. In the rheometer, temperature was varied from 120 to 180 °C and pressure was varied from 12.3 to 124.7 kPa. From the capillary rheometer flow curves, the flow behavior index (n) parameters for the binder formulations and PIM feedstocks were determined to be less than 1. The apparent shear rates (γ̇a) of binder formulations and PIM feedstocks were determined to be in the range of 22.6–1005 s−1. For the above apparent shear rates and shear stresses, the apparent viscosities (ηa) were calculated as in the range of 23.8–1105.2 Pa s. The melt flow indexes (MFI) were determined under various shear stresses (τw=12.3–124.7 kPa) and found to be in the range of 4–231 g per 10 min. Effect of temperature onto apparent viscosities (ηa) of feedstocks were also studied, and flow activation energies under various shear stresses were determined to be within the range of 59–182 and 25–99 kJ/mol, for the binder formulations and feedstocks, respectively. Further, the thermal behavior and removal of binders from the feedstocks were determined by DTA–TG analysis, and the removal the binders from feedstocks by thermal treatments were achieved.