Dyeing of PET/co-PP composite fibers using supercritical carbon dioxide

Abstract

Polypropylene (PP) is a widely used synthetic fiber. Due to its advantages, PP has been used for numerous applications. However, the utilization of PP is limited by poor dye-ability. To improve this, the fiber is typically composited with polyester (PET), which is dyed with a disperse dye using either the conventional method or with a high technology such as Supercritical carbon dioxide (scCO2). In this investigation, the sheath-core polyester/co-polypropylene composite fibers (PET/co-PP fibers) were annealed at 150 °C for 1 h and dyed with three types of disperse dyes using scCO2 at the various dyeing temperatures and pressures. Optical and scanning electron microscopes (SEM) were used to examine the cross section of the fibers. Extraction of disperse dye in the fibers was carried out followed by quantification of the dye contents. SEM images showed the order distribution of core-PET which was affected due to molecular re-orientation after annealing. Dye content in the fibers varied with the type of fiber, dyeing temperatures and pressures. Remarkably increased dye contents were found from 100 to 120 °C. The dye-ability of the fibers was found to be more profound for pressure variation than for the variation of temperature. No dye content was found in the fibers dyed at 50 MPa, but significant increases in the dye content were observed at higher pressures. Images from optical microscope confirmed that high color depth was found in fibers dyed at higher pressure than obviously seen in PET core. However, uniformly dyed PET/co-PP fibers were, typically observed.