On-line determination of density and crystallinity during melt spinning

The density and crystallinity of polypropylene fiber were measured on the moving threadline during the melt spinning process. Heretofore, threadline densities have never been measured on-line. These density measurements were accomplished by taking parallel, on-line measurements of fiber diameter, fiber velocity, polymer mass flow rate, fiber temperature, and fiber birefringence. Under certain spinning conditions, a distinct rise in density occurs along the threadline. This rise in density corresponds well with the rise in crystallinity as measured by birefringence.