Single-walled carbon nanotubes were added to two different grades of polypropylene to produce composites. The composites were then melt-spun into fibers, and the fibers were tested with both a conventional tensile pull tester and dynamic mechanical analysis. The changes in tensile properties were related to the grade of polypropylene used. In addition to fibers being made from the mixes, coarse extrudates (i.e., undrawn, gravity-spun filaments) were also produced. Density measurements on these extrudatesshowed that the addition of nanotubes increased the composite density in a highly nonlinear manner, which suggested interaction between the polypropylene and the carbon nanotubes.

The dual-jet slot die is the most common device used for producing melt-blown fibers. In this die, high-velocity air impinges upon a polymer stream. A comprehensive model was applied to predict the performance of these slot dies. This model involves the simultaneous solution of the momentum, energy, and continuity equations that are applied to the fiber threadline. Predicted parameters include fiber attenuation, vibration frequency, vibration amplitude, temperature, and stress. Experimental measurements were taken during melt blowing with an actual slot die. These measurements compared very well with the simulated results.

Online measurements of fiber temperature and diameter were made for both the melt-spinning and the meltblowing processes. The fiber temperature was determined by infrared thermography, and the fiber diameter was determined by high-speed photography. These measurements were then compared with predictions made with mathematical models for melt spinning and melt blowing. There was good agreement between the models and the experimental results, and the agreement was best when heat-transfer correlations developed specifically for fine fibers (cylinders) were used.

An infrared (IR) camera was used to measure the temperature of polymer filaments held in a stream of hot air. Filament diameters of 0.1−4 mm were tested. The air stream velocity and temperature fields were independently measured with a Pitot tube and a thermocouple. Under certain conditions, the air temperatures determined by the thermocouple closely approximate the temperatures of the polymer filaments. These air-temperature measurements were compared to the temperature readings given by the IR camera. This procedure allowed the development of calibration curves for the infrared camera. The calibration curves were found to depend on (a) the diameter of the filament and (b) the image size of the filament upon the pixel array in the IR camera. These calibration curves can be used with the IR camera to allow online measurement of fiber temperature during melt spinning, melt blowing, and other fiber production processes.

In commercial operation, a melt-blowing die is used to produce fine fibers that are solid, not hollow. In this paper, a model was developed to predict what would happen if hollow fibers were produced with a modified melt-blowing die. The model involved the simultaneous solution of the momentum, energy, and continuity equations. The model equations were solved numerically. Predicted parameters included fiber hollowness, fiber attenuation, vibration frequency, vibration amplitude, temperature, and stress. Hollowness can affect the laydown pattern of the melt-blown fibers.