A basic study of spunbonding polypropylene

Spunbonded fabrics have been challenging woven fabrics and paper. Almost no technical papers have been published in this field. In this thesis, a fundamental study of the spunbonding process is reported. A model spunbonding apparatus was designed and built based on con-siderations of the patent literature. This involved extruding molten polymer filaments through a spinneret and into an aspirator from which they were blown onto a moving conveyer belt.

The force balance for a filament in the spunbonding process was developed. The air drag coefficient for air flow past a fiber in an aspirator was measured in a specially designed experiment. The values are expressed as a function of the Reynolds number based on relative velocities, fiber diameter and kinematic viscosity of the air. The dependence of the drag coefficient on the Reynolds number is the same as a correlation of air drag in melt but the magnitudes are larger. This could be caused by the vibration of the filament while it is in the aspirator.

Wide-angle X-ray diffraction and birefringence were used to characterize the orientation of spunbonded or better air drag attenuated polypropylene filaments. Hermans-Stein orientation factors were determined for the crystalline phase. Comparing the orientation factors of these filaments with those of melt spun fibers taken-up on a winder, we find that these correspond to the same measured spinline stress. Birefringence measurements confirm that the structure developed in the filament is a unique function of the spinline stress.

A solid filament or a melt spinning filament drawn down by an aspirator was used to investigate the formation of the spunbonded fabric on the surface of the conveyer belt. An empirical equation was developed to predict the number of loops on the surface of the conveyer belt for a spunbonding process.