Evaluations of corrections in rheometric measurements of polyethylene.
Part I. Slippage at channel wall
An evaluation of the phenomenon of polymer slippage at die wall and its effects on the courses of flow and viscosity curves has been done as a result of rheological investigations carried out in extruding rheometer i.e. in the actual processing conditions. The evaluation of slippage velocity (Vs) by Mooney method required the use of additional measurement and calculation procedures resulted from the method of operation of single-screw extruder plastifying system. Two types of low-density polyethylene (PE-LD FABS 23-D 022 and PE-LD 402L) were investigated. Comparative analysis for shear stress in the range 212-300kPa showed significant differences in slippage velocity (Vs) of both polyethylenes tested, what resulted from viscosity differentiation. An introduction of the correction of capillary rheometry side effect, in this case wall slippage effect, causes significant shifts of viscosity curves positions. The differences in polymer viscosity, allowing for wall slip effect, reached 70% in the measurements carried out.
Key words: rheological measurements, capillary rheometry side effects, wall slippage, corrections in rheological measurements, viscosity curve, polyethylene
A. Kloziński, T. Sterzyński
Evaluations of corrections in rheometric measurements of polyethylene. Part I. Slippage at channel wall