Occurrence and morphology of bead-on-string structures in centrifugal forcespun PA6 fibers

Abstract

This research aimed at investigating the morphology and frequency of bead-on-string occurrences on forcespun nano- and sub-micron fibers. The formation of bead-on-string structures was observed on a range of fiber samples forcespun in varied conditions from PA6 solutions of different concentrations. Bead-on-string structures were characterized for morphology using SEM micrographs, and were counted on all samples. Two major factors appeared to affect both the morphology and the bead count, namely spinning solution concentration, i.e. viscosity, and spinning needle gage or diameter. Low viscosity solutions resulted in large numbers of mostly spherical beads. Solutions with higher viscosity appeared to suppress the fluid jet instability thus resulting in significantly fewer beads with exclusively elongated spindle-like shapes. Spinning needle diameter also had a significant impact on beading behavior, with the larger diameter exhibiting higher bead counts. A significant interaction between the two factors was detected and its impact on the competition between the fluid jet visco-elastic relaxation and the Rayleigh instability is discussed.