Doctoral Dissertations

Date of Award

5-2004

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemical Engineering

Major Professor

John R. Collier

Committee Members

Billie J. Collier, Duane D. Bruns, Simioan Petrovan, Dong Zhang

Abstract

Polymer rheology plays a significant role in many polymer-processing operations such as polymer extrusion, fiber spinning, and nonwovens processing. To develop real time, online process and quality control system in these operations, knowledge of polymer rheology and how the rheological properties can be determined is crucial.

In this work, rheological properties of two melt blowing grades polypropylene (PP) under different processing conditions were determined by various off line methods, which includes dynamic rheological properties, shear and elongational viscosities. The elongational viscosity was measured at different Hencky strain by using semi-hyperbolic dies developed in this research group. Good master curves were generated for the temperature and Hencky strain shifting, and simultaneous shifting with respect to both temperature and Hencky strain.

Carreau and Cross-rheological models were used to fit the rheological properties to generate different functions that were used to calculate the viscosity at different processing during typical melt blowing process conditions. The correlation between the melt blowing processing condition and the properties of final nonwoven products were achieved by introducing dimensionless numbers, such as air Reynolds number, polymer Reynolds number and Hencky strain.

A high resolution IR camera was used to capture thermographs during the melt blowing process. From these thermographs, a plateau or shoulder was evident in thermographs taken during fiber drawn down by high velocity air. This represented the crystallization of polypropylene during the melt blowing process, assuming that fiber attenuation cease at the point of crystallization, which is a fundamental problem during the melt blowing process.

It was found that the polymer degraded to a small extent during the melt blowing process, the degree being dependent on the processing variables such as melt temperatures, airflow rate and throughput.

The rheological properties of PPs were used to determine the molecular weight and molecular weight distribution based on Mead’s approach. The technique for measuring shear and elongational viscosities in the laboratory was used as the basis for an online rheological sensor to measure the shear and elongational viscosities simultaneously online in a twin-screw extruder by drawing a small amount of polymer melt from the main processing stream. A laptop with software based on Labview and instruments bridged by an OPC server for MODBUS communication protocol through RS485 serial interface were configured for the control and measurement.

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