A Study of Fine Structure Development of Poly(ethylene terephthalate) in High Speed Spinning by Using a Pneumatic Drawdown Device

High speed melt spinning of linear, branched, and high molecular weight poly(ethylene terephthalate) (PET) polymers using a pneumatic drawdown device was carried out in this study. Characterization of the structure of final spun fibers of each polymer and the structure development along the spinline for different mass throughputs and take-up velocities were studied. The final spun fibers were characterized with various techniques: birefringence, density, wide angle x-ray scattering (WAXS), differential scanning calorimetry (DSC), shrinkage, and tensile testing. A filament cutting technique was utilized and on-line temperature and birefringence measurements were performed to study the PET structure development along the spinline. A sharp diameter thinning (necking) phenomena was clearly observed on the spinline for linear and high molecular weight samples at high take-up speeds. After necking, the fiber exhibited almost constant diameter and a semi-crystalline structure. Mechanisms for necking formation were considered in this study. A computer simulation was also performed in this research. The computer simulation results agreed qualitatively with the the experimental dataal data but quantitative agreement with the experimental data was not achieved. The changes of fiber structure from fully amorphous to semi-crystalline, however, could be simulated on the spinline