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Novel organic luminescent substance (3,12-bis(dibutylamine)-7,8-dicyano-5,6,9,10-tetrahydro[5]helicene; M123) was successfully synthesized and employed to prepare luminescent polypropylene (PP/M123) fibers of different cross-sectional shapes via melt spinning. For all cross-sectional shapes (circular, hollow triangular, flat, star, and W), the PP/M123 fibers were continuously spun without fiber breakage, and possessed smooth surfaces. The designed structure of M123, containing 4 butyl groups, enabled its homogeneous mixing with hydrophobic polypropylene matrix. Addition of M123 did not alter the PP melt flow through complex spinneret orifices during fiber spinning, as evidenced by rheological measurements that melt viscosities of PP and PP/M123 at different shear rates (10–10,000 s−1) were almost identical. Results from differential scanning calorimetry also confirmed homogeneity of M123 and PP matrix as the melting temperatures and crystallinities of PP/M123 fibers were comparable to those of PP fibers. By employing organic luminescent M123, the processes of additive preparation and additive/polymer compounding were simplified, and small amount of luminescent substance as 0.05 % wt. could be used to yield effective luminescence. The PP/M123 fibers exhibited yellowish green color under normal light and emitted bright green light under ultraviolet (UV) light.

Melt spinning of cross-shaped polypropylene (PP) and poly (lactic acid) (PLA) fibers was conducted to investigate influences of polymer properties and processing conditions on cross-sectional shape change in fibers. PP fibers possessed cross-shaped profile, resembling that of the original spinneret orifice, with dull edges due to die swell. Their shape factor (SF) values (1.4–1.6) were close to that of the spinneret orifice (1.7), indicating that the complex shape of the orifice could be maintained. High melt viscosity of PP, as well as its rapid crystallization, helped preventing shape change induced by surface tension. PLA fibers, on the other hand, exhibited shape change from cross to square and to round shape when spinning temperature was increased from 200 to 220 and 240 °C, respectively. Their SF values (1.1–1.2) were close to unity, indicating shape change towards circular shape. Shape deviation towards circular shape in PLA fibers was mainly driven by surface tension. Slow crystallization in PLA allowed great influence of surface tension in determining shape change of the extrudate. Increasing fiber take up speed tended to decrease SF value. Such effect was small compared to that of spinning temperature.