Effect of solid-state polymerization on fiber structure development in melt spinning of mechanical recycled PET

This study assessed the feasibility of producing industrial PET filament fibers from mechanically recycled PET (mr-PET) and aimed to establish the optimal solid-state polymerization (SSP) and melt-spinning conditions required for their manufacture. Virgin PET (v-PET) and mr-PET with the same intrinsic viscosity (IV) were selected and subjected to SSP at temperatures of 220, 230, and 240 °C for 6, 12, and 18 h. Among the samples with similar IV (~ 1.1 dL/g), the 230 °C–6 h sample was selected for melt spinning due to its comparable molecular weight(MW) and IV, as well as process efficiency. Melt spinning was performed at 285 °C, and the PET filament fibers were obtained at specified take-up velocities. WAXD analysis showed that crystalline structures formed at a take-up velocity of 4000 m/min in samples before SSP, whereas in samples after SSP, crystallization occurred at 3000 m/min. As the take-up velocity increased, the tenacity of both pre- and post-SSP samples tended to increase. When mr-PET that underwent SSP was spun at 3000 m/min, its tenacity was comparable to that of v-PET under the same conditions. Therefore, industrial PET filament fibers with properties comparable to v-PET can be produced from mr-PET under optimized SSP and melt-spinning conditions.