Abstract
In the melt spinning process of poly(ethylene terephthalate) (PET), extrusion conditions such as shear-flow history and thermal history influence the characteristics of resultant as-spun fibers. For the detailed analysis on the mechanism of thermal degradation of PET in fiber extrusion, an extrusion system consisting of a twin-screw extruder and a melt line equipped with three gear pumps and a draining channel was constructed to control the shear-flow history and residence time independently. Through the analysis of the effect of residence time, rate constants for the reduction of the degree of polymerization in the extruder and that in the melt line were estimated. The analyzed rate constant for the extruder was about three times higher than that for the melt line. It was also found that a certain degree of degradation occurring during the extrusion is independent of residence time. Estimated activation energies for the molecular weight reduction in the extruder and that in the melt line were similar. It was also confirmed that there was an acceleration of molecular weight reduction with an increase in the rotation frequency of the screw in the extruder. Heat and stress caused by the shear-flow are attributable for this result.
