Preparation and Characterization of Zinc Phosphinate Flame Retardant Masterbatch on Polyester Fibers' Thermal, Rheological, Physical and Mechanical Properties

ABSTRACT A novel, industry‐oriented strategy was developed to enhance flame retardancy in polyester fibers through a zinc phosphinate‐based masterbatch. The masterbatch was prepared via twin‐screw extrusion using 20 wt% Exolit OP950 and high‐viscosity bottle‐grade PET granules, selected to mitigate molecular degradation and preserve rheological integrity during melt‐spinning. It was subsequently incorporated into virgin fiber‐grade PET at 3%, 5%, and 7 wt% concentrations to produce flame‐retardant fibers. Rheological evaluations revealed pronounced shear‐thinning behavior and increased elasticity with higher flame retardant (FR) loading, indicating improved melt strength and viscoelastic stability. Thermal analyses demonstrated enhanced char formation and reduced heat release, with residual carbon content rising from 5.7% in neat PET to 10.7% in the 7% FR sample. The limiting oxygen index (LOI) increased from 20.5% to 24.5%, and vertical burning tests confirmed a UL‐94 V‐2 rating with significantly reduced melt dripping. Mechanical testing showed that fibers maintained appropriate tenacity (2.98 g/den), although accompanied by reduced elongation at break, highlighting the trade‐off between strength and ductility. SEM/EDX analysis confirmed uniform dispersion of FR particles and the presence of phosphorus and zinc. This approach provides a scalable solution for producing flame‐retardant PET fibers without compromising industrial processability, while balancing mechanical performance and fire safety.