On-line density and crystallinity of polyethylene terephthalate during melt spinning

The density and crystallinity of polyester fiber were measured on the movin g threadline during the melt spinning process. The density was calculated b y applying the continuity equation at points along the length of the thread line. Experimental inputs to the equation included parallel, on-line measur ements of fiber diameter, fiber velocity, polymer mass flowrate, fiber temp erature, and fiber birefringence. When spinning speeds exceeded 4500 m/min, a distinct rise in density occurred along the threadline. This rise corres ponded with the rise in birefringence.