Doctoral Dissertations

Date of Award

12-1991

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Mechanical Engineering

Major Professor

Mancil W. Milligan

Committee Members

H. Wilkerson, L. Wadsworth, D. Prang

Abstract

An extensive experimental investigation was undertaken to study the influence of the processing variables on the production of microfibers using a single hole melt blowing process. included: The processing variables that were investigated air jet exit velocity, polymer throughput, die air gap, die setback, polymer and air temperatures, polymer melt viscosity as expressed by ASTM Melt Flow Rate (MFR), and collection distance. Polypropylene was used for the investigation. In addition to the experimental investigation, a one dimensional single hole melt blowing analytical model was developed.

The air jet exit velocity and polymer throughput had the most influence on the average final fiber diameter. Increasing the air jet exit velocity or decreasing the polymer throughput decreased the average final fiber diameter. The processing geometry influenced the diameter by changing the air jet momentum for a fixed air jet exit velocity. In general, increasing the air jet momentum resulted in smaller average fiber diameters. Increasing the processing temperature decreased the average final fiber diameter. This was due to changes in the viscosity of the polymer. Higher polymer melt flow rate (MFR) materials resulted in smaller diameter fibers. The average final fiber diameter was found to be insensitive to the collection distance. Several empirical models were developed for the majority of the experimental data which was for an 800 MFR polypropylene resin.

Stop motion photography indicated that the fiber was continuous and experienced various degrees of flapping depending on the air jet exit velocity. The photographs also provided attenuation profiles for comparison with the one dimensional single hole melt blowing analytical model. It was also discovered that most of the attenuation occurred within 1.5 cm from the die.

The development of the one dimensional single hole melt blowing analytical model was similar to existing melt spinning models. The analytical model predicted general trends for varying processing conditions but consistently predicted a larger fiber diameter. However, the analytical model did accurately predict changes in the diameter ratio.

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