Methods for determining the shear viscosity of polymer melts using the velocity controlled reciprocating screw injection molding process.

摘要

The bulk flow properties of polymer melts are of considerable importance in most polymer processing operations. Imposed rate capillary rheometers are widely used for the purpose of characterizing the rheology of bulk polymer melts, for both quality control and process design purposes. Quantitative measurements of shear viscosity obtained from laboratory capillary rheometers are subject to a large number of experimental errors, and in many cases may not be indicative of the material's flow behavior during actual melt processing conditions.; A number of studies have shown that polymer melt flow properties can be measured using modified, small scale injection molding machines. In this study, a highly instrumented dual capillary nozzle was designed, constructed, and used in partnership with a velocity controlled reciprocating screw injection molding machine, for the purposes of measuring polymer melt shear viscosity. The flow behavior of three high density polyethylenes (Melt Index 4.0, 12 and 30) has been measured as a function of temperature at shear rates ranging from 10{dollar}sp2{dollar}-10{dollar}sp4{dollar} S{dollar}sp{lcub}-1{rcub}{dollar}, using both a standard imposed rate laboratory capillary rheometer, and the reciprocating screw rheometric apparatus developed. The experimental results obtained using the two viscosity measurement techniques were in good agreement. The rheometric apparatus developed for the study was also used in an "in-line" manner, quantitatively measuring melt viscosity during conventional injection molding trials.