ELONGATIONAL RHEOLOGY OF POLYMER MELTS AND SOLUTIONS

Elongational rheological properties of polymer melts and solutions may be measured using nonlubricated flow characteristics through a semihy perbolic converging die. The effects of body forces related to develop ing orientation in the fluid during converging extensional flow are so strong that the shearing contribution become negligible in comparison , eliminating the need for lubrication to achieve an essentially pure elongational flow. The effective elongational viscosities of polypropy lene melts and lyocell solutions correlated with shear-flow determinat ions were used to estimate the enthalpy and entropy changes as functio n of processing conditions. The flow of lyocell solutions through a co nverging die had, as a result, not only phase separation and cellulose crystallization, but also microfibers formation and high orientation. (C) 1998 John Wiley & Sons, Inc.