Shear and effective elongational rheology and polymer molecular characteristics

Author

Xiaoling Wei

Date of Award

8-2003

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Polymer Engineering

Major Professor

John R. Collier

Abstract

Extensional deformations play a significant role in many processing operations which involve a rapid change of shape such as fiber spinning, film blowing, blow molding, and nonwoven melt processing. To develop real time, online process and quality control analysis in these operations, know ledge of the molecular weight (MW) and molecular weight distribution (MWD}, effects of molecular characteristics and processing con9itions on the elongational rheology, and orientation of polymeric materials in these operations is essential. In this work, shear rheology of six polyethylenes (PE}, one polyisobutylene (PIB}, and _five cellulose solutions was measured at different temperatures using a rotational rheometer. Effective elongational viscosity of polyethylenes and polyisobutylene was also measured at different Hencky strains and temperatures using a capillary rheometer by replacing the capillary cylindrical die with a hyperbolic converging die. The hyperbolic shape of the dies establishes a purely elongational flow field at a constant elongational strain rate throughout the die. The effect of molecular characteristics such as MW, MWD, and long chain branches and the processing conditions such as temperature and Hencky strain on the elongational rheology of PE and PIB samples was studied. The results from the hyperbolic dies were compared with results from other techniques, namely Rheometrics Extensional Rheometer (RER) and Elongational Rheometer for Melts (RMB). Good master curves were generated for the temperature and Hencky strain shifting, and simultaneous shifting with respect to both temperature and Hencky strain. The enthalpy and entropy changes were calculated from the effective elongational and shear viscosities to investigate flow induced orientation of the polymer melts in hyperbolic dies. The enthalpy and entropy changes increase in magnitude with higher elongational strain rate and higher Hencky strain. The storage and loss moduli were used to determine and test the three parameters needed to predict the MW and MWD.

Recommended Citation

Wei, Xiaoling, "Shear and effective elongational rheology and polymer molecular characteristics. " PhD diss., University of Tennessee, 2003.
https://trace.tennessee.edu/utk_graddiss/5204