Properties of filaments spun from poly(ethylene terephthalate) chips containing PET-dust

It is observed that the thick portions in a poly(ethylene terephthalate) (PET) filament differ from the rest in their solution viscosity and birefringence, indicating that they are caused by the inhomogeneity of the polymer melt. To identify the cause of the latter, the PET chips are critically examined. It is found that the waferlike tails on the edge of the PET chips and PET–dust have slightly higher viscosity than the chips. The behavior of the chips and the dust during drying and melt spinning are examined to find whether the dust becomes postpolymerized during drying. Such dried PET–dust exhibits substantially different melting behavior than the chips. The filaments spun from the mixture of chips and PET–dust exhibit significantly higher nonuniformity in properties than the filaments spun from the chips only. It is concluded that the PET–dust entering the extruder with the chips can cause thick portions in the filaments.