Description:
The extrusion (single-screw) characteristics of four high molecular weight, broad molecular weight distribution (MWD) polyethylene resins are discussed with an emphasis on the output rate. Despite the high molecular weights of the subject polyethylenes, their broad MWD (Mw/Mn range: 10 to 50) does not limit the pressure and torque developed during extrusion. However, the specific output of the four polymers was quite varied. First, the dynamics of the solids conveying section were examined with the highest molecular weight polyethylene exhibiting lower solids conveying rate compared to the other three. Further, a simple and quick method to evaluate the relative solids conveying efficiencies for various polyethylenes will be presented. Finally, the dependence of the specific output on the melt rheology of the polymers is also addressed; specifically, the shear-thinning extent of the melt in the metering section was found to influence output rate. The unique and counter-intuitive temperature-dependence of the shear-thinning character for one of the four polymers will also be addressed in relation to its extrusion characteristics.