Analysis of Recycled PET for Production of Polyester Fiber

This study presents an entirely experimental and mathematical analysis of extrusion and melt spinning to obtain polyethylene terephthalate (PET) fibers. In addition, results concerning the design and construction of a quench system were investigated. PET fibers were obtained from two raw materials: postconsumer PET thermoform packaging (R-PET) and virgin PET (V-PET). The mathematical analysis part for the extruder contemplated a melt flow model based on the Navier–Stokes constitutive equations for a rectangular coordinate in the z-direction to predict the extruded mass flow depending on processing conditions (temperature and extrusion speed) and physical properties of raw material (intrinsic viscosity and density). Concerning the spinning process, a rheological model based on the Phan–Thien and Tanner (PTT) constitutive equations was used for the simulation of the dynamic flow of postconsumer PET thermoform packaging, including the combined effects of material flow, filament cooling, air drag, surface tension, and gravity to determine the necessary quench system length to cooling melt PET fiber down to their glass transition temperature (T_g), as well as axial velocity, filament diameter, and filament temperature profiles along all draw region of the spinning process. For this, it was necessary to fabricate and evaluate three different quench system designs to ensure a uniform air velocity profile along all cooling systems. The experimental analysis contemplated all critical steps for PET fiber fabrication, such as extrusion and spinning processes. This physical and chemical characterization of raw material, extruded PET, and fabricated PET fibers were obtained. Finally, the experimental data were used to validate both mathematical models. Proper sorting of PET thermoforms, removing impurities, and appropriately operating conditions for the extrusion and spinning processes allowed us to obtain elongation at yield, Young’s modulus, and tenacity values of 4.18%, 5568.1 Kg_f/cm², and 0.94 g_f/den for V-PET fibers and 7.11%, 4795 Kg_f/cm², and 0.7 g_f/den for R-PET fibers, respectively.