Doctoral Dissertations

Nejib Hajji

Date of Award

5-1992

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Polymer Engineering

Major Professor

Joseph E. Spruiell

Committee Members

D. C. Bouge, R. S. Benson, M. G. Hansen

Abstract

In this research, experimental and analytical studies were carried out on the melt spinning and spunbonding processes. Experimental studies consisted mainly of developing and using an improved technique to measure the temperature of the running fiber during single filament melt spinning. This technique is based on the measurement of thermal radiation coming from the fiber and requires prior knowledge of the emissivity of the polymer. For this reason, the emissivities of polypropylene and nylon 6 fibers of different diameters were measured in the temperature range usually covered by melt spinning. It was found that the emissivity is a strong function of diameter but does not depend much on temperature. It was also found that nylon 6 has a higher emissivity than polypropylene due to differences in chemical structure. When these emissivity values were applied to online temperature measurements, the resulting temperature profiles showed considerable scattering. This scattering was greatly reduced by smoothing diameter and raw temperature measurements data.

The temperature profiles measured in this manner were used along with diameter and tension measurements to calculate the apparent elongational viscosity and the heat transfer coefficient of various polypropylene and nylon 6 resins using the inversion procedure. The apparent elongational viscosity of each of the resins studied was found to follow approximately an Arrhenius type of temperature dependence in the range of temperatures studied. The heat transfer coefficient correlation developed for nylon 6 was found to be closer to the Kase-Matsuo correlation with vibrations than to the same correlation without vibrations. The correlation obtained for polypropylene was in good agreement with the nylon 6 correlation in the upper part of the spinline but fell below it further from the spinneret due probably to the effect of crystallization or to larger errors in temperature measurements warranted by a lower polypropylene emissivity.

Two different subjects were treated in the analytical studies. The first subject dealt with the effect of radial temperature variations inside the fiber on temperature measurements. Since the surface and center temperatures of the fiber are usually different, it was attempted to find out where the measured temperature stands with respect to these two values. Based on an analysis for non-isothermal sheets, it was found that the apparent temperature measured in these experiments is more likely to be far from the surface temperature. As a result of this finding, the error made by assuming uniform temperature in the heat transfer calculations was estimated to be on the order of 5% which is reasonable in heat transfer related measurements.

The second subject of analytical studies consisted of extending the existing single filament model for melt spinning to the spunbonding process. The Reicofil spunbonding process, which is based on multifilament melt spinning, was modeled using the single filament model with some modifications that take into account differences between these processes. First, the model was applied to the standard Reifenhauser conditions of the Reicofil process as an example of model predictions. Then, the predictions of the model for a set of experimental conditions were compared to experimental measurements on final fibers. It was found that the model gave relatively good prediction of final diameter and crystallinity. Birefringence predictions were roughly in the same range as experiment but the trends were not in good agreement with it. It is not clear at present whether the explanation of the differences lie in problems in the model or in the experimental data used for comparison.

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